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1 PowerPoint to accompany Welding Principles and Practices 4th edition Edward R. Bohnart © 2012 The McGraw-Hill Companies, Inc. All rights reserved. Chapter 3 Steel and Other Metals

2 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 2 Objectives 1.Describe steelmaking process. 2.List metalworking processes used to shape and improve steel. 3.State proper use of each heat-treating process for steel. 4.Describe internal structures of metals. 5.Name various alloying elements and their effects.

3 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 3 Objectives 6.List various types of ferrous metals and their applications. 7.List various types of nonferrous metals and their applications. 8.Describe various systems used to designate metals. 9.Explain heating and cooling effects on weldment and how they can be controlled.

4 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 4 Metal Major Groupings FerrousFerrous –High iron content –Includes: Many types of steel and its alloysMany types of steel and its alloys Cast ironCast iron Wrought ironWrought iron NonferrousNonferrous –Almost free of iron

5 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 5 Nonferrous Metals CommonCommon –Copper, lead, zinc, titanium, aluminum, nickel, tungsten, manganese, brass, bronze PreciousPrecious –Gold, platinum, silver RadioactiveRadioactive –Uranium, radium

6 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 6 Steel Combination of iron and carbonCombination of iron and carbon –Percentage of carbon determines how strong and hard the steel WeldmentsWeldments –80% fabricated from steel 85% welded is in mild (low carbon) steel classification85% welded is in mild (low carbon) steel classification

7 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 7 History of Steel Assyrians (3700 B.C.) first recorded use of ironAssyrians (3700 B.C.) first recorded use of iron –Low carbon iron first produced in low flat hearth furnaces 1350 B.C. to 1300 A.D. all iron tools and weapons produced directly from iron ore1350 B.C. to 1300 A.D. all iron tools and weapons produced directly from iron ore –Furnaces increased in height and charge introduced through top (shaft furnaces) Modern blast furnaceModern blast furnace

8 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 8 History of Steel Little known of first process for making steelLittle known of first process for making steel –Tools found dating back to 1000 to 500 B.C. Prior to Bessemer process two methods usedPrior to Bessemer process two methods used –Cementation process Increased carbon content by heating iron in contact with hot carbon in absence of airIncreased carbon content by heating iron in contact with hot carbon in absence of air Still used to limited extentStill used to limited extent –Crucible process Melting wrought iron in crucibles in which carbon already addedMelting wrought iron in crucibles in which carbon already added Replaced by various electric furnace processesReplaced by various electric furnace processes

9 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 9 Steelmaking in the US Extends back over 300 yearsExtends back over 300 years –Ironworks in Saugus, Massachusetts (1646–1670) First patent for steel issued in 1728First patent for steel issued in 1728 Succession of events spurred growthSuccession of events spurred growth –New uses for iron –Discovery of large iron ore deposits –Development of Bessemer and open hearth processes –Civil War and Americas industrial growth –Expansion of railroads –World Wars I and II

10 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 10 Annual Steel Production

11 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 11 Changes in U.S. Steel Production Reduction in number of blast furnacesReduction in number of blast furnaces –250 down to 36 No open hearth furnacesNo open hearth furnaces Increased use of recycled steelIncreased use of recycled steel Perfection of welding process to join metals speeded up and expanded use of steelPerfection of welding process to join metals speeded up and expanded use of steel

12 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 12 Raw Materials United States well supplied with basic resourcesUnited States well supplied with basic resources –Iron ore, limestone and coal Other countries provide other necessary materialsOther countries provide other necessary materials –Manganese, tin, nickel and chromium

13 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 13 Iron Ore 5% of Earths crust5% of Earths crust Large depositsLarge deposits –Northern Minnesota near Lake Superior in U.S. Principally taconitePrincipally taconite –Brazil Largest and best sourceLargest and best source –Sweden Purest iron orePurest iron ore

14 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 14 Iron Ores Magnetite (Fe 3 O 4 )Magnetite (Fe 3 O 4 ) –Brownish, richest, least common, 65–70% iron Hematite (Fe 2 O 3 )Hematite (Fe 2 O 3 ) –Red, mined in US, 70% iron Limonite (2Fe 2 O 3 H 2 O)Limonite (2Fe 2 O 3 H 2 O) –52–66% iron Siderite (FeCO 3 )Siderite (FeCO 3 ) –48% iron TaconiteTaconite –Green, 22–40% iron JasperJasper –Iron-bearing rock –Predominately magnetite or hematite

15 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 15 Iron Ore Mining UndergroundUnderground –Vertical shaft sunk in rock next to ore body –Tunnels drilled from shaft and blasted horizontally into ore body at number of levels Open pitOpen pit –Mineral lying relatively near surface –Earth and rock first removed –Blast holes drilled, explosives shatter ore and hauled out of pit by truck, train or conveyor belt

16 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 16 Oxygen Most abundant element on earthMost abundant element on earth –One half weight of land, 21% by weight of air and 90% by weight of sea Steel industry major consumerSteel industry major consumer –Used to purify the material Oxidizes the carbon, silicon, manganese and other elementsOxidizes the carbon, silicon, manganese and other elements –Speeds up process by supporting combustion of other fuels

17 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 17 Fuels Three major natural fuelsThree major natural fuels –Coal Most importantMost important –Oil –Natural gas Used to provide heat essential in making steel mill productsUsed to provide heat essential in making steel mill products

18 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 18 Coal Supplies more than 80% of total heat and energy requirementsSupplies more than 80% of total heat and energy requirements Large part used in making coke for blast furnaceLarge part used in making coke for blast furnace –About 1,300 pounds of coke per each ton of pig iron –Coking quality coal mined in 24 states 90% comes from West Virginia, Pennsylvania, Kentucky and Alabama90% comes from West Virginia, Pennsylvania, Kentucky and Alabama

19 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 19 Oil Used as both fuel and lubricantUsed as both fuel and lubricant Heaviest grade of oil most commonly usedHeaviest grade of oil most commonly used Percentage of usePercentage of use –70% consumed in melting iron –20% burned in heating and annealing furnaces for special heat treatments –10% used in all other applications

20 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 20 Natural Gas Burned in furnaces and places where clean burn necessaryBurned in furnaces and places where clean burn necessary More heating value than all other gases employedMore heating value than all other gases employed –1,000 BTU per cubic foot –Steel industry consumes over 400 billion cubic feet per year 50% used in heat-treating and annealing furnaces50% used in heat-treating and annealing furnaces

21 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 21 Coke Supplies heat for smelting iron in blast furnacesSupplies heat for smelting iron in blast furnaces Solid residue obtained when coal heated to high temperature in absence of airSolid residue obtained when coal heated to high temperature in absence of air –Causes gases and other impurities to be released Hard, brittle substance consisting chiefly of carbonHard, brittle substance consisting chiefly of carbon 1919 – coal chemical process of producing coke developed1919 – coal chemical process of producing coke developed

22 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 22 Coke Leading fuel of steel industryLeading fuel of steel industry Volatile products which pass out of ovens piped to chemical plantVolatile products which pass out of ovens piped to chemical plant –Yields gas, tar, ammonia liquor, ammonium sulfate, and light oil –Further refinement of light oil produces benzene, toulene, and other chemicals Production in United States exceeds 64 million tons per year (92% consumed as blast furnace fuel)Production in United States exceeds 64 million tons per year (92% consumed as blast furnace fuel)

23 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 23 Coke Oven Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

24 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 24 Steel Scrap Oxygen furnaces (BOFs) capable of using scrapOxygen furnaces (BOFs) capable of using scrap –66% of steel used is recycled Integrated producerIntegrated producer –80% liquid metal (from blast furnace) –20% scrap Best source is old automobilesBest source is old automobiles

25 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 25 Limestone Used as flux in blast furnace to separate impurities from iron oreUsed as flux in blast furnace to separate impurities from iron ore Sedimentary rockSedimentary rock –Consists largely of calcium carbonate –Color changes with presence of impurities Silica makes it harderSilica makes it harder Clay makes it softerClay makes it softer

26 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 26 Refractory Materials Nonmetallic materials which can tolerate severe or destructive service conditions at high temperaturesNonmetallic materials which can tolerate severe or destructive service conditions at high temperatures –2,600ºF for light duty fireclay –5,000ºF for magnesia brick ApplicationsApplications –Linings for blast furnaces, steelmaking furnaces, soaking pits, reheating furnaces, ladles, submarine cars

27 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 27 Producing Refractory Materials Produced from quartzite, fireclay, alumina, magnesia, iron oxide, graphites, coal, coke and tarProduced from quartzite, fireclay, alumina, magnesia, iron oxide, graphites, coal, coke and tar Materials crushed, combined with binder and fed to forming machinesMaterials crushed, combined with binder and fed to forming machines Methods for forming refractory bricksMethods for forming refractory bricks –Power pressing –Extrusion –Hand molding

28 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 28 Iron Blast Furnace Slag Residue produced from interaction of molten limestone and impurities of ironResidue produced from interaction of molten limestone and impurities of iron Contains oxides of calcium, silicon, aluminum and magnesium (also iron oxide and sulfur)Contains oxides of calcium, silicon, aluminum and magnesium (also iron oxide and sulfur) Processed for use in cement, road materials, insulating roofing material and soil conditionerProcessed for use in cement, road materials, insulating roofing material and soil conditioner

29 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 29 Carbon Nonmetallic element that can form compound with other elementsNonmetallic element that can form compound with other elements –Organic compounds Three pure carbon formsThree pure carbon forms –Diamond (hard crystalline form) –Graphite (soft form) –Carbon black (amorphous form)

30 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 30 Blast Furnace First step in converting iron ore into steelFirst step in converting iron ore into steel Iron freed from most impuritiesIron freed from most impurities Furnace charged with iron ore, limestone and cokeFurnace charged with iron ore, limestone and coke –Heat melts iron, limestone form slag and two liquids separate (remove and repeat: 5–8 hrs) –Liquid iron poured into molds (pigs of iron) Hard and brittleHard and brittle

31 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 31 Blast Furnace Schematic Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. American Iron & Steel Inst.

32 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 32 Steelmaking Processes CementationCementation CrucibleCrucible Bessemer furnaceBessemer furnace –Invented in both Europe and United States in 1856 Open hearth furnaceOpen hearth furnace –Invented in 1868 in the United States

33 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 33 Cementation Process Oldest method of steelmakingOldest method of steelmaking Consists of heating wrought iron with carbon in a vacuumConsists of heating wrought iron with carbon in a vacuum –Increases carbon content of surfaces and edges Edges hardened by heating and quenchingEdges hardened by heating and quenching –Impurities not removed –Only surface is affected Later process layered soft and hard metal for strengthLater process layered soft and hard metal for strength

34 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 34 Crucible Process Revived in England during early 1740sRevived in England during early 1740s Process involved melting wrought iron in clay crucible to remove impuritiesProcess involved melting wrought iron in clay crucible to remove impurities –When fluid, slag skimmed off top –Metal then poured into mold to solidify into a workable mass United States used graphite crucibles (100 lb. capacity) in gas-fired furnaceUnited States used graphite crucibles (100 lb. capacity) in gas-fired furnace

35 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 35 Electric Furnace Processes: Electric Arc French metallurgist Paul Heroult in 1899French metallurgist Paul Heroult in 1899 Introduced into U.S. in 1904Introduced into U.S. in 1904 Produce more than 800 tons of steel in 24 hrs.Produce more than 800 tons of steel in 24 hrs. Electricity used solely for production of heatElectricity used solely for production of heat Uses three carbon electrodes (4–24 inches) for direct arcUses three carbon electrodes (4–24 inches) for direct arc Circular furnace shape which can be titled to pour molten steel into ladleCircular furnace shape which can be titled to pour molten steel into ladle

36 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 36 Electric Arc Furnace Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

37 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 37 Electric Furnace Processes: Electric Induction Furnace Transformer with molten metal acting as coreTransformer with molten metal acting as core Consists of magnesia crucibleConsists of magnesia crucible –Surrounded by layer of tamped-in magnesia refractory –Copper tubing coil around this connected to current source; encased in heavy box with silica brick bottom lining Charge melted down in 45 minutesCharge melted down in 45 minutes –Further heated for 15 minutes to tapping temperatures –Alloys and deoxidizers added Furnace tilted and liquid metal runs outFurnace tilted and liquid metal runs out

38 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 38 Electric Induction Furnace Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

39 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 39 Oxygen Process Also known as Linz-Donawitz processAlso known as Linz-Donawitz process First established in Linz, Austria (1952)First established in Linz, Austria (1952) First used in United States in 1954First used in United States in 1954 Method of pig iron and scrap conversion whereby oxygen is injected downward over bath of metalMethod of pig iron and scrap conversion whereby oxygen is injected downward over bath of metal –Chemical reaction of oxygen and fluxes refines pig iron and scrap into steel –Temperature reaches 3,000ºF –Refining continues for 20 to 25 minutes

40 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 40 Oxygen Process After scrap and hot metal are charged into furnace, dust cap is put on, and oxygen blown through the lance to the surface of the molten metal in order to burn out impurities. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

41 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 41 Vacuum Furnaces and Degassing Melting of steel and other alloys in vacuum reduces gases in metal and produces metal with minimum of impuritiesMelting of steel and other alloys in vacuum reduces gases in metal and produces metal with minimum of impurities –Gases formed in vacuum furnace pulled out by vacuum pumps Two general types of furnacesTwo general types of furnaces –Vacuum induction melting –Consumable electrode vacuum arc melting

42 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 42 Vacuum Induction Melting First used in 1940sFirst used in 1940s Charge melted in furnace within airtight, water-cooled steel chamberCharge melted in furnace within airtight, water-cooled steel chamber Advantages include:Advantages include: –Freedom form air contamination –Close control of heat –Fewer air inclusions

43 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 43 Vacuum Induction Melting Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

44 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 44 Consumable Electrode Vacuum Arc Melting Refining process for steel prepared by other methodsRefining process for steel prepared by other methods Steel electrodes of predetermined composition are remelted by an electric arc in airtight, water-cooled crucibleSteel electrodes of predetermined composition are remelted by an electric arc in airtight, water-cooled crucible –Principle similar to arc welding Furnace consists of water-cooled copper crucible, vacuum system for removing air from crucible during melting, and a d.c. power source for producing arcFurnace consists of water-cooled copper crucible, vacuum system for removing air from crucible during melting, and a d.c. power source for producing arc

45 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 45 Consumable Electrode Vacuum Arc Melting Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

46 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 46 Vacuum Furnaces and Degassing Produce high quality steel and steel alloysProduce high quality steel and steel alloys Advantages:Advantages: –Production of alloys too expensive to manufacture by air-melt processes –Use of reactive elements –Decreased amounts of hydrogen, oxygen, and nitrogen in finished product –Improved mechanical properties –Close heat control –Better hot and cold workability

47 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 47 Vacuum Degassing Refining operationRefining operation Purpose to reduce amounts of hydrogen, oxygen and nitrogen in steelPurpose to reduce amounts of hydrogen, oxygen and nitrogen in steel Process carried out after molten metal removed from furnace and before poured into ingotsProcess carried out after molten metal removed from furnace and before poured into ingots Three processes todayThree processes today –Steam degassing –Ladle degassing –Vacuum lifter degassing

48 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 48 Steam Degassing Steel is poured into a tank from which air has been removed. Collected in ingot mold or ladle. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

49 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 49 Ladle Degassing Process A ladle of molten steel placed in tank and then air removed from tank, exposing it to vacuum. Can process smaller amounts of steel than steam degassing. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

50 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 50 Vacuum Lifter Degassing Metal forced upward into vacuum chamber through nozzles by means of atmospheric pressure. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A vacuum is created in a chamber suspended above a ladle of steel.

51 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 51 Benefits From Degassing Reduction of hydrogen eliminates flaking of steelReduction of hydrogen eliminates flaking of steel Reduction of oxygen promotes internal cleanlinessReduction of oxygen promotes internal cleanliness –Oxygen reduction not as low as achieved in vacuum-melted steels Nitrogen content reduced slightlyNitrogen content reduced slightly Transverse ductility of most degassed forced products nearly double that of air- cast steelTransverse ductility of most degassed forced products nearly double that of air- cast steel

52 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 52 Continuous Casting of Steel Process by which molten steel solidified into semifinished billet, bloom, or slab for subsequent finishingProcess by which molten steel solidified into semifinished billet, bloom, or slab for subsequent finishing –Prior method was forming ingots Improved yield, quality, productivity and cost efficiencyImproved yield, quality, productivity and cost efficiency Various shapes castVarious shapes cast Complete operation can be achieved in 2 hoursComplete operation can be achieved in 2 hours

53 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 53 Example of Continuous Casters American Iron & Steel Inst. into tundish

54 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 54 Casting Process Sections Tundish to feed liquid steel to moldTundish to feed liquid steel to mold Primary cooling zone to generate solidified outer shellPrimary cooling zone to generate solidified outer shell Secondary cooling zone to further solidified the strandSecondary cooling zone to further solidified the strand Unbending and straightening sectionUnbending and straightening section Severing unit to cut solidified strandSevering unit to cut solidified strand

55 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 55 Liquid Steel Transfer Two steps involved in transferring liquid steel from ladle to moldsTwo steps involved in transferring liquid steel from ladle to molds –From ladle to tundish –From tundish to molds Regulated by orifice control devices of various designsRegulated by orifice control devices of various designs Designs: slide gates, stopper rods, or metering nozzlesDesigns: slide gates, stopper rods, or metering nozzles

56 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 56 Tundish overview Enhances oxide inclusion separationEnhances oxide inclusion separation Provides continuous flow of liquid steel to mold during ladle exchangesProvides continuous flow of liquid steel to mold during ladle exchanges Maintains steady metal height above nozzles to moldsMaintains steady metal height above nozzles to molds Provides more stable stream patterns to moldsProvides more stable stream patterns to molds

57 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 57 Mold Purpose to allow establishment of solid shell sufficient in strength to contain liquid corePurpose to allow establishment of solid shell sufficient in strength to contain liquid core Open-ended box structure containing water-cooled inner copper liningOpen-ended box structure containing water-cooled inner copper lining Oscillation necessary to minimize friction and sticking of solidifying shellOscillation necessary to minimize friction and sticking of solidifying shell –Achieved either hydraulically or via motor- driven cams or levers

58 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 58 Secondary Cooling Series of zonesSeries of zones Sprayed medium either water of air and waterSprayed medium either water of air and water Three basic forms of heat transferThree basic forms of heat transfer –Radiation: to atmosphere –Conduction: by direct contact –Convection: by moving airflow Purpose of spray chamberPurpose of spray chamber –Enhance and control rate of solidification –Regulate strand temperature –Control machine containment cooling

59 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 59 Casting and Soaking Ingots Molten steel cast into molds directly gives us cast steelMolten steel cast into molds directly gives us cast steel –Cast steel inferior to wrought steel Molten steel poured into ingot molds or continuous casting gives inside chance to become solid while outside kept from cooling off too muchMolten steel poured into ingot molds or continuous casting gives inside chance to become solid while outside kept from cooling off too much –Lowered into soaking pit –Heat steel for rolling

60 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 60 Deoxidation Type of steel determined by control of amount of gas evolved during solidificationType of steel determined by control of amount of gas evolved during solidification Increasing degrees of gas evolutionIncreasing degrees of gas evolution –Killed steels –Semikilled steels –Capped steels –Rimmed steels

61 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 61 Killed Steel Strongly deoxidizedStrongly deoxidized Relatively high degree of uniformity in composition and propertiesRelatively high degree of uniformity in composition and properties Suitable for applications involvingSuitable for applications involving –Forging –Piercing –Carburizing –Heat treatment

62 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 62 Semikilled Steels Intermediate in deoxidation between killed and rimmed gradesIntermediate in deoxidation between killed and rimmed grades Composition more uniform than rimmed steelsComposition more uniform than rimmed steels Used where neither cold-forming and surface characteristics of rimmed steel nor uniformity of killed steels essential requirementsUsed where neither cold-forming and surface characteristics of rimmed steel nor uniformity of killed steels essential requirements

63 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 63 Capped Steels Have thin low-carbon rimHave thin low-carbon rim Remainder of cross section approaches degree of semikilled steelsRemainder of cross section approaches degree of semikilled steels Great increase in use of capped steels over rimmed steels in recent yearsGreat increase in use of capped steels over rimmed steels in recent years

64 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 64 Rimmed Steels Surface and cold-forming characteristics of capped steelsSurface and cold-forming characteristics of capped steels Only slightly deoxidizedOnly slightly deoxidized Low-carbon surface layer very ductileLow-carbon surface layer very ductile Rolling produces sound surfaceRolling produces sound surface Used when surface is of prime importanceUsed when surface is of prime importance

65 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 65 Environmental Progress in the Steel Industry Each year, 15% of steel industrys capital spent for environmental facilitiesEach year, 15% of steel industrys capital spent for environmental facilities –$10 to $20 per ton of steel produced Amount of energy to produce ton of steel decreased by 45% from 1975 to 1998Amount of energy to produce ton of steel decreased by 45% from 1975 to 1998 –Accurate and efficient microprocessor controls –Two-thirds less labor producing more steel From 12 labor hours to 45 labor minutesFrom 12 labor hours to 45 labor minutes

66 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 66 Environmental Progress in the Steel Industry Air quality greatly improved since 1970Air quality greatly improved since 1970 –Discharge of air and water pollutants reduced by over 90% Made great strides in terms of recyclingMade great strides in terms of recycling –Over 95% of water Has worked cooperatively with federal environmental agenciesHas worked cooperatively with federal environmental agencies

67 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 67 Metalworking Processes Shape it and improve its characteristicsShape it and improve its characteristics –Forging –Rolling Destroy the cast structureDestroy the cast structure –Orienting the grain Steel strongerSteel stronger More ductileMore ductile Greater shock resistanceGreater shock resistance

68 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 68 Forging Method of reducing metal to desired shapeMethod of reducing metal to desired shape Usually done with steam hammerUsually done with steam hammer –Today most done with hydraulic presses Can take cooler ingots and work to closer dimensionsCan take cooler ingots and work to closer dimensions Drop forgingDrop forging –Piece of roughly shaped metal placed between die-shaped faces of exact form of finished piece Metal forced to take form by drawing dies togetherMetal forced to take form by drawing dies together Many automobile parts made this wayMany automobile parts made this way

69 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 69 Rolling Steel rolled hot except for finishing passesSteel rolled hot except for finishing passes After rolling, ingots known by size and shapeAfter rolling, ingots known by size and shape –Bloom Square or oblong with minimum cross-sectional area of 36 inchesSquare or oblong with minimum cross-sectional area of 36 inches –Billet Square or oblong, but smaller than bloomSquare or oblong, but smaller than bloom –Slab Oblong and varies in thickness from 2 to 6 inches and in width from 5 to 6 feetOblong and varies in thickness from 2 to 6 inches and in width from 5 to 6 feet

70 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 70 Samples of Various Shapes Produced by Hot Rolling Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

71 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 71 Processes for Rolling Steel One-half rolled steel products in U.S. are flat rolledOne-half rolled steel products in U.S. are flat rolled –Includes plates, sheet and strip Flat-rolled steel divided into two categoriesFlat-rolled steel divided into two categories –Hot rolled Finished at temperatures between 900 and 2,400ºFFinished at temperatures between 900 and 2,400ºF Black ironBlack iron –Cold rolled Finished at room temperatureFinished at room temperature Coated with zinc (galvanized), tin (tin plate), tin and lead (Terne plate)Coated with zinc (galvanized), tin (tin plate), tin and lead (Terne plate)

72 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 72 Tubular Steel Products Classified according to method of manufactureClassified according to method of manufacture –Welded (flash welding steel strip) Metal pieces heated until contacting surfaces plastic state, then forced together quickly under pressureMetal pieces heated until contacting surfaces plastic state, then forced together quickly under pressure –Seamless Piercing: Heated steel bar pierced by mandrel and rolled to desired diameter and wall thicknessPiercing: Heated steel bar pierced by mandrel and rolled to desired diameter and wall thickness Cupping: Heated plate formed around cup-shaped diesCupping: Heated plate formed around cup-shaped dies

73 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 73 Piercing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

74 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 74 Structural Steel Shapes Steel may also be shaped into wire, bars, forging, extrusions, rails and structured shapes. These are just a few of the basic steel shapes with which welder fabricator works. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

75 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 75 Rolling Directions X Direction: Best strength and ductility Y Direction: 30% reduction in strength 30% reduction in ductility Z Direction: Lower strength; virtually no ductility In rolling operations, grains are oriented in direction of rolling.

76 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 76 Drawing Operation of reducing cross section and increasing length of metal bar or wireOperation of reducing cross section and increasing length of metal bar or wire –Draw through series of conical, tapering holes in die plate Each hole smaller than preceding oneEach hole smaller than preceding one Shapes varying in size from finest wire to very large are drawnShapes varying in size from finest wire to very large are drawn

77 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 77 Extrusion Forming by pressing through an openingForming by pressing through an opening Can obtain perfectly round rodsCan obtain perfectly round rods Metal placed in closed chamber fitted with opening at one end and piston at other endMetal placed in closed chamber fitted with opening at one end and piston at other end –Forced out through opening by hydraulic pressure Used to form brass rodUsed to form brass rod

78 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 78 Cold Working Shaping of metals by working at ordinary temperaturesShaping of metals by working at ordinary temperatures MethodsMethods –Hammered –Rolled –Drawn

79 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 79 Heat Treatment Process of heating and cooling metal for purpose of improving its structural or physical propertiesProcess of heating and cooling metal for purpose of improving its structural or physical properties Done to remove stresses caused by welding, casting, or heavy machiningDone to remove stresses caused by welding, casting, or heavy machining Can make it easier to work with or increase hardness for wear resistanceCan make it easier to work with or increase hardness for wear resistance

80 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 80 Important Variables in Any Heat Treatment Process 1.Carbon content 2.Temperature of heating 3.Time allowed for cooling 4.Cooling medium –Water, oil, or air

81 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 81 Hardening Process in which steel heated above its critical point and cooled rapidlyProcess in which steel heated above its critical point and cooled rapidly –Critical point is point at which carbon changes structure of steel Produces hardness superior to that of steel before heating and coolingProduces hardness superior to that of steel before heating and cooling Only medium, high, and very high carbon steel can be treatedOnly medium, high, and very high carbon steel can be treated

82 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 82 Case Hardening Process that gives steel hard, wear- resistant surface while leaving interior soft and toughProcess that gives steel hard, wear- resistant surface while leaving interior soft and tough ProcessesProcesses –Cyaniding –Carburizing –Nitriding –Flame hardening –Hard surfacing by welding –Metal spraying Plain carbon steels and alloy steels are often case hardened.

83 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 83 Cyaniding Method of surface-hardening low-carbon steelsMethod of surface-hardening low-carbon steels Carbon and nitrogen absorbed in outer layer of steel to depth of to inchCarbon and nitrogen absorbed in outer layer of steel to depth of to inch Done in liquid or gas formDone in liquid or gas form –For hard, but very thin, surface over steel

84 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 84 Carburizing Process whereby low carbon steel made to absorb carbon in its outer surfaceProcess whereby low carbon steel made to absorb carbon in its outer surface Depth to which carbon will penetrateDepth to which carbon will penetrate –Time heat held –Temperature reached –Carburizing compound used Can use carbonaceous solids, cyanidizing liquids, or hydrocarbon gasesCan use carbonaceous solids, cyanidizing liquids, or hydrocarbon gases

85 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 85 Nitriding Process used only with group of low alloy steelsProcess used only with group of low alloy steels –Contain elements such as vanadium, chromium or aluminum Will combine with nitrogen to form nitridesWill combine with nitrogen to form nitrides Nitrides act as super hard skin on surface of steelNitrides act as super hard skin on surface of steel Parts heated in nitrogenous atmosphere to temperature of 900 to 1,000ºFParts heated in nitrogenous atmosphere to temperature of 900 to 1,000ºF Quenching unnecessary with little distortion or warpageQuenching unnecessary with little distortion or warpage

86 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 86 Flame Hardening Most recent of hardening processesMost recent of hardening processes Permits localized treatment with complete controlPermits localized treatment with complete control Steel must contain enough carbon for hardening to take placeSteel must contain enough carbon for hardening to take place –Article heat treated and drawn –Surface exposed to oxyacetylene flame that heats to high temperature quickly –Cooled quickly by water (depth of hardness controlled by temperature of water) Can be used on parts too bulky to put into furnaceCan be used on parts too bulky to put into furnace

87 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 87 Annealing Includes several different treatmentsIncludes several different treatments Effects of annealingEffects of annealing –To remove stresses –To induce softness for better machining properties –To alter ductility, toughness, or electrical, magnetic, or other physical properties –To refine crystalline structure –To produce definite microstructure Changes depend on annealing temperature, rate of cooling and carbon contentChanges depend on annealing temperature, rate of cooling and carbon content

88 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 88 Difference Between Hardening and Softening of Steels Due to rate of coolingDue to rate of cooling –Fast cooling hardens –Slow cooling softens Both tempering and annealing reduce hardness of materialBoth tempering and annealing reduce hardness of material

89 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 89 Tempering Process wherein hardness of steel reduced after heat treatment and relieve stressProcess wherein hardness of steel reduced after heat treatment and relieve stress –Heat hardened steel to predetermined temperature between room temperature and critical temperature –Hold temperature for length of time –Cooling in air or water Reduction of hardness depends on 3 factorsReduction of hardness depends on 3 factors –Tempering temperature –Amount of time steel is held at temperature –Carbon content of steel

90 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 90 Normalizing Improves grain structure of metal and returns it to normal by removing stressesImproves grain structure of metal and returns it to normal by removing stresses –Stresses caused by uneven cooling following welding, casting, or forging Requires faster rate of cooling than used for annealingRequires faster rate of cooling than used for annealing –Results in harder, stronger metal than annealing

91 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 91 Metal Internal Structures MetallurgyMetallurgy –Science that deals with internal structure of metals Four states of matterFour states of matter –Solids, liquids, gases, and plasmas Subatomic particlesSubatomic particles –Electrons – carry negative charge –Protons – carry positive charge –Attraction and repelling forces effect properties of metals

92 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 92 Metal Internal Structures Atoms are in constant state of vibrationAtoms are in constant state of vibration Heat energy increases atomic movementHeat energy increases atomic movement –Temperature rises, atomic structure expands –Rises high enough, atoms move freely and solid becomes liquid –Continues to rise, vaporization occurs Liquid to gasLiquid to gas –Superheated, it ionizes and becomes plasma Gas that has become electrical conductorGas that has become electrical conductor

93 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 93 Solid Metals Take on three-dimensional crystalline structureTake on three-dimensional crystalline structure –Atoms align themselves into orderly layers, lines and rows Common phases of metalsCommon phases of metals –Body-centered cubic (BCC) –Face-centered cubic (FCC) –Body-centered tetragonal (BCT) –Hexagonal close-paced (HCP)

94 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 94 Metals Crystalline Structures Iron Carbon steels Chromium Molybdenum Tungsten Aluminum Copper Nickel Silver Austenitic Stainless Steels Martensite Zinc Cadmium Magnesium Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

95 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 95 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

96 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 96 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

97 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 97 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

98 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 98 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

99 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 99 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

100 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 100 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

101 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 101 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

102 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 102 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

103 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 103 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

104 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 104 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

105 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 105 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

106 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 106 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

107 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 107 Cooling rate critical above 1333 Not so critical below 1333 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cannot go between Matensite, Bainite, or Pearlite without going through Austenite first.

108 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 108 Solidification Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Starts at interface between molten weld metal and cooler unmelted heat-affected zone. Clusters of atoms form grains and grain boundaries.

109 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 109 Grain Size Effects on Metals Fine-grained metalsFine-grained metals –Good tensile strength –Good ductility –Good low temperature properties Coarse-grained metalsCoarse-grained metals –Slightly lower strength –Slightly less ductility –Good high temperature properties

110 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 110 Welding Effect on Grain Size Heat inputHeat input Cooling rate (preheat)Cooling rate (preheat) Long or short arcLong or short arc Slow or fast travel speedSlow or fast travel speed Welding on high or low end of parameter rangesWelding on high or low end of parameter ranges Process selectedProcess selected

111 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 111 Alloying Another method of affecting mechanical properties of metalsAnother method of affecting mechanical properties of metals Changes the orderly rows, lines, and layers of the three-dimensional crystalline structureChanges the orderly rows, lines, and layers of the three-dimensional crystalline structure Interstitial alloyingInterstitial alloying –Small atoms such as carbon, nitrogen and hydrogen can occupy spaces between larger atoms Substitutional alloyingSubstitutional alloying –Additional elements create irregularities in crystal

112 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 112 Alloying Schematic Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

113 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 113 Physical Properties of Metals Common properties divided into three general classificationsCommon properties divided into three general classifications –Those related to the absorption and transmission of energy –Internal structure of the metal –Resistance to stress

114 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 114 Properties Related to Energy Melting pointMelting point –Temperature at which substance passes from solid to liquid condition –Higher carbon content, lower melting point WeldabilityWeldability –Capacity of metal substance to form strong bond of adherence while under pressure or during solidification from liquid state

115 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 115 Properties Related to Energy FusibilityFusibility –Ease with which metal may be melted VolatilityVolatility –Ease with which substance may be vaporized –Measured by degree of temperature at which metal boils under atmospheric pressure Electrical conductivityElectrical conductivity –Ability of substance to conduct electrical current

116 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 116 Properties Related to Energy Electrical resistanceElectrical resistance –Opposition to electric current as it flow through wire –Measured by unit called ohm Thermal conductivityThermal conductivity –Ability of substance to carry heat Hot shortnessHot shortness –Brittleness in metal when hot

117 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 117 Properties Related to Energy Coefficient of thermal expansionCoefficient of thermal expansion –Amount of expansion metal undergoes when it is heated and amount of contraction that occurs when cooled –Linear coefficient of thermal expansion Increase in length of bar 1 inch long when its temperature raised 1ºCIncrease in length of bar 1 inch long when its temperature raised 1ºC OverheatingOverheating –When temperature exceeds its critical range Heated to such a degree that properties impairedHeated to such a degree that properties impaired

118 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 118 Properties Related to Internal Structure Specific gravitySpecific gravity –Unit of measurement based on weight of volume of material compared with equal volume of water DensityDensity –Expressed as quantity per unit volume –Dense metal is compact and does not contain discontinuities PorosityPorosity –Internal structure that lacks compactness of have discontinuities that leave voids in metal

119 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 119 Typical Stresses of Metals Compression: squeezingCompression: squeezing Shear: strain on lap joint pulled in opposite directionsShear: strain on lap joint pulled in opposite directions Bending: deflection as result of compressive forceBending: deflection as result of compressive force Tension: pulling in opposite directionsTension: pulling in opposite directions Fatigue: result of repeated cycles of forces applied and released in all directionsFatigue: result of repeated cycles of forces applied and released in all directions Torsion: twisting force in opposite directionTorsion: twisting force in opposite direction

120 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 120 Typical Stresses Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Compression – The application of pressure Tension – A pulling action

121 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 121 Typical Stresses Bending – Pressure applied to force away from a straight line Shear – A pulling action causing two bodies to slide on each other, parallel to their plane of contact Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

122 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 122 Typical Stresses Torsion – A turning or twisting action Fatigue – Condition caused by repeated stretching, twisting, compression, while in service Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

123 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 123 Properties Related to Stress Resistance PlasticityPlasticity –Ability of material to deform without breaking –Combined with strength is most important combination of properties metal can have StrengthStrength –Ability of material to resist deformation –Express ultimate tensile strength in pounds per square inch Ultimate tensile strength of material is its resistance to breakingUltimate tensile strength of material is its resistance to breaking

124 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 124 Properties Related to Stress Resistance ToughnessToughness –Has high tensile strength and ability to deform permanently without breaking –Opposite of brittleness –No direct method of measuring accurately Impact resistanceImpact resistance –Ability of material to withstand maximum load applied suddenly –Often taken as indication of its toughness

125 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 125 Properties Related to Stress Resistance BrittlenessBrittleness –Fail without any warning as deformation, elongation, or change of shape –Lacks plasticity and toughness MalleabilityMalleability –Ability to deform permanently under compression without breaking or fracturing –Must have to be forged

126 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 126 Properties Related to Stress Resistance HardnessHardness –Ability of one material to penetrate another material without fracture –Greater the hardness, greater resistance to marking –Measured by pressing hardened steel ball into material Brinell hardness test – diameter of impression measuredBrinell hardness test – diameter of impression measured Rockwell hardness test – depth of impression measuredRockwell hardness test – depth of impression measured

127 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 127 Properties Related to Stress Resistance ElasticityElasticity –Ability of material to return to original shape after load been removed Elastic limitElastic limit –Greatest load that may be applied after which material will return to its original condition –Once reached, no longer behaves elastically Permanent deformationPermanent deformation

128 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 128 Properties Related to Stress Resistance Modulus of elasticityModulus of elasticity –Ratio of stress to strain –Measure of relative stiffness –High modulus, material resist movement or distortion; low modulus, material stretches easily ResilienceResilience –Energy stored in material under strain within its elastic limit that causes it to resume its original shape when load removed

129 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 129 Properties Related to Stress Resistance Yield pointYield point –Point at which definite increase in length of specimen occurs with no increase in load –Expressed as pounds per square inch DuctilityDuctility –Ability of material to be permanently deformed by loading and yet resist fracture –Amount of stretching expressed as percent of elongation

130 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 130 Properties Related to Stress Resistance Fatigue failureFatigue failure –Failure under repeated or alternating stress –Fatigue limit: load which may be applied for indefinite number of cycles without causing failure Expressed in pounds per square inchExpressed in pounds per square inch –Level of loading called endurance limit of the material Maximum load that can be applied at which no failure will occur, no matter how many cycles load is appliedMaximum load that can be applied at which no failure will occur, no matter how many cycles load is applied

131 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 131 Properties Related to Stress Resistance CorrosionCorrosion –Gradual wearing away or disintegration of material by chemical process –Measured by Determining loss in strength of tensile samplesDetermining loss in strength of tensile samples Determining loss in weight of materials that dissolve in corroding mediumDetermining loss in weight of materials that dissolve in corroding medium Determining gain in weight when heavy coating of rust is formedDetermining gain in weight when heavy coating of rust is formed Resistance to corrosionResistance to corrosion –Ability of metals to resist atmospheric corrosion and corrosion by liquids or gases

132 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 132 Effect of Common Elements on Steel: Nonmetals CarbonCarbon –Native state both as diamond (very hard) and as graphite (very soft) –Part coal, petroleum, asphalt, and limestone –Increased carbon content increases tensile strength of steel but decreases ductility and weldability PhosphorusPhosphorus –Small amounts improve machinability of low and high carbon steel –Considered impurity in welding

133 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 133 Effect of Common Elements on Steel: Nonmetals BoronBoron –Occurs in nature in combination with other elements –Gray, extremely hard solid with melting point in excess of 400ºF –Increases hardenability of steel SiliconSilicon –Main substance in sand and sandstone –Added mainly as deoxidizing agent to produce soundness during steelmaking

134 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 134 Effect of Common Elements on Steel: Nonmetals SulfurSulfur –Considered a harmful impurity in steel Makes steel brittle and causes cracking at high tempsMakes steel brittle and causes cracking at high temps –Should be kept below 0.05% –Improves machinability of steel SeleniumSelenium –Used interchangeably with sulfur in some stainless steels to promote machinability

135 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 135 Effect of Common Elements on Steel: Metals ManganeseManganese –Very hard, grayish-white metal with reddish luster –Pure state can scratch glass –Addition to steel increases both tensile strength and hardness –High manganese steels Very resistant to abrasionVery resistant to abrasion Used in equipment such as rock crushers, grinding mills, and power shovel scoopsUsed in equipment such as rock crushers, grinding mills, and power shovel scoops

136 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 136 Effect of Common Elements on Steel: Metals MolybdenumMolybdenum –Silvery white metal that increases toughness of steel –Increases corrosion resistance of stainless steels ChromiumChromium –Hard, brittle, grayish-white metal –Highly resistant to corrosion –Addition to low alloy steels increases tensile strength, hardness, and resistance to corrosion and oxidation –Ductility is increased

137 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 137 Effect of Common Elements on Steel: Metals NickelNickel –Hard, silvery white element –Used extensively for plating purposes and as alloying element in steel Increases strength, toughness, and corrosion resistance of steelIncreases strength, toughness, and corrosion resistance of steel NiobiumNiobium –Combines with carbon and improves corrosion resistance in stainless steels

138 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 138 Effect of Common Elements on Steel: Metals CobaltCobalt –Tough, lustrous, silvery white metal –Used as alloying metal in high speed steel and special alloys when high strength and hardness must be maintained at high temperatures Titanium and ZirconiumTitanium and Zirconium –Added in small amounts to certain high strength, low alloy steels to deoxidize metal, control fine grain size, and improve physical properties

139 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 139 Effect of Common Elements on Steel: Metals CopperCopper –Soft, ductile, malleable metal that melts at 1,984ºF –Has expansion rate 1-1/2 times greater than steel –Thermal conductivity 10 times greater than steel –Very good conductor of heat and electricity –Highly corrosion resistant –Added to steel to improve its resistance to corrosion –Brass most common class of copper alloy (zinc) –Bronzes other alloys (zinc, tin, silicon, aluminum)

140 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 140 Effect of Common Elements on Steel: Metals AluminumAluminum –Never found in nature in pure state Derived from bauxiteDerived from bauxite –One of the lightest metals –Good conductor of heat and electricity –Highly resistant to atmospheric corrosion –Ductile and malleable –Used in both carbon and alloy steels Produces fine austenitic grain sizeProduces fine austenitic grain size

141 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 141 Effect of Common Elements on Steel: Metals LeadLead –Soft malleable, heavy metal –Very low melting point: 620ºF –Highly resistant to corrosion –Additions to carbon and alloy steels improve machinability –Leaded carbon steels have been used mainly for stock which is to be free machined –Used extensively in plumbing industry

142 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 142 Effect of Common Elements on Steel: Metals TungstenTungsten –Steel-gray metal more than twice as heavy as iron –Melting point above 6,000ºF –Improves hardness, wear resistance, and tensile strength of steel VanadiumVanadium –Increases toughness of steel and gives it ability to take heavy shocks without breaking –High resistance to metal fatigue and high impact resistance

143 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 143 Carbon Steels Carbon most important alloying ingredient in steelCarbon most important alloying ingredient in steel –Has direct effect on physical properties Divided into four typesDivided into four types –Low carbon –Medium carbon –High carbon –Tool

144 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 144 Low Carbon Steels Carbon content does not exceed 0.30% and may be as low as 0.03%Carbon content does not exceed 0.30% and may be as low as 0.03% Referred to as mild steels and plain steelsReferred to as mild steels and plain steels –General purpose steel: 0.08–0.25% –Machine steel and cold-rolled steel: 0.08–0.30% Excellent weldabilityExcellent weldability May be quenched very rapidly in water or brine and do not harden to any great extentMay be quenched very rapidly in water or brine and do not harden to any great extent Most structures fabricated: bridges, ships, tanks, pipesMost structures fabricated: bridges, ships, tanks, pipes

145 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 145 Medium Carbon Steels Have carbon content ranging from 0.30 to 0.60%Have carbon content ranging from 0.30 to 0.60% Stronger than low carbon steels and have higher heat-treat qualitiesStronger than low carbon steels and have higher heat-treat qualities Should be welded with shielded metal arc low hydrogen electrodes and other low hydrogen processesShould be welded with shielded metal arc low hydrogen electrodes and other low hydrogen processes –Best results obtained if preheated before welding and normalized after welding

146 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 146 High Carbon Steels Have carbon content ranges from 0.60 to 1.7%Have carbon content ranges from 0.60 to 1.7% More difficult to weld than low or medium carbon steelsMore difficult to weld than low or medium carbon steels Can be heat treated for maximum hardness and wear resistanceCan be heat treated for maximum hardness and wear resistance Used in springs, punches, dies, tools, military tanks, and structural steelUsed in springs, punches, dies, tools, military tanks, and structural steel

147 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 147 Alloy Steels Content of alloying elements exceed certain limitsContent of alloying elements exceed certain limits Amounts of alloying elements lie within specified range for commercial alloy steelsAmounts of alloying elements lie within specified range for commercial alloy steels Elements added to obtain desired effect in finished productElements added to obtain desired effect in finished product Readily welded by welding processes such as MIG/MAG, and TIGReadily welded by welding processes such as MIG/MAG, and TIG

148 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 148 High Strength, Low Alloy Steels Group of steels with chemical compositions specially developedGroup of steels with chemical compositions specially developed –To give higher physical property values –For materially greater corrosion resistance Generally used when need savings in weightGenerally used when need savings in weight Includes oil-hardening steel, air-hardening steel and high speed steelIncludes oil-hardening steel, air-hardening steel and high speed steel Readily adaptable to fabrication by shearing, plasma cutting, laser cutting, welding, rivetingReadily adaptable to fabrication by shearing, plasma cutting, laser cutting, welding, riveting

149 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 149 Stainless and Heat- Resisting Steels Possess unusual resistance to corrosion at both normal and elevated temperaturesPossess unusual resistance to corrosion at both normal and elevated temperatures –Accomplished by addition of chromium to iron Corrosion resistance increases with increasing chromiumCorrosion resistance increases with increasing chromium Thin layer of chromium oxide bonded to surfaceThin layer of chromium oxide bonded to surface 11.5% chromium dividing line between low alloy steel and stainless steel11.5% chromium dividing line between low alloy steel and stainless steel Practically indefinite lifePractically indefinite life –Some difficulty with pitting

150 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 150 Advantages of Stainless Steels Resist corrosion and effects of high temperaturesResist corrosion and effects of high temperatures Maintain purity of materials in contact with themMaintain purity of materials in contact with them Permit greater cleanliness than other steelsPermit greater cleanliness than other steels Stainless-steel fabrications usually cost little to maintainStainless-steel fabrications usually cost little to maintain

151 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 151 Advantages of Stainless Steels Low strength-to-weight ratios are possible both at room and elevated temperaturesLow strength-to-weight ratios are possible both at room and elevated temperatures Tough at low temperaturesTough at low temperatures Have high weldabilityHave high weldability Highly pleasing in appearance and require minimum of finishingHighly pleasing in appearance and require minimum of finishing

152 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 152 Five Classifications of Steels 5% chromium, hardenable 500 series5% chromium, hardenable 500 series –Martensitic 12% chromium, hardenable 400 series12% chromium, hardenable 400 series –Martensitic 17% chromium, non-hardenable 400 series17% chromium, non-hardenable 400 series –Ferritic Chromium-nickel 300 seriesChromium-nickel 300 series –Austenitic Chromium-nickel-manganese 200 seriesChromium-nickel-manganese 200 series –Austenitic

153 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 153 Series 400 and 500 (Martensitic) Primarily heat resisting and retain large part of their properties at temperatures up to 1,100ºFPrimarily heat resisting and retain large part of their properties at temperatures up to 1,100ºF More resistant to corrosion than alloy steelsMore resistant to corrosion than alloy steels Not considered true stainless steelsNot considered true stainless steels Satisfactory for mildly corrosive conditionsSatisfactory for mildly corrosive conditions Satisfactory for both hot and cold workingSatisfactory for both hot and cold working Air hardening and must be cooled slowly or annealed after forging or welding to prevent crackingAir hardening and must be cooled slowly or annealed after forging or welding to prevent cracking

154 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 154 Series 400 (Ferritic) Chromium content ranges from 11.5 to 27%Chromium content ranges from 11.5 to 27% Carbon content low (under 0.20%)Carbon content low (under 0.20%) No nickelNo nickel Cannot be hardened by heat treatmentCannot be hardened by heat treatment Hardness may be increased by cold workingHardness may be increased by cold working Low coefficient of thermal expansionLow coefficient of thermal expansion Good resistance to corrosionGood resistance to corrosion Ductility fairDuctility fair Difficult to weldDifficult to weld

155 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 155 Series 200 and 300 (Austenitic) Chromium content ranges from 16 to 26%Chromium content ranges from 16 to 26% Nickel from 3.5 to 22%Nickel from 3.5 to 22% Carbon from 0.15 to 0.08%Carbon from 0.15 to 0.08% More numerous, more often used than 400 seriesMore numerous, more often used than 400 series Stable structure at low temperaturesStable structure at low temperatures Low yield point with high ultimate tensile strength at room temperaturesLow yield point with high ultimate tensile strength at room temperatures

156 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 156 Series 200 and 300 (Austenitic) Provide maximum resistance to corrosionProvide maximum resistance to corrosion Well-suited to standard fabricationWell-suited to standard fabrication –ductility required for severe deep drawing and forming High rupture and creep-strength values at high temperaturesHigh rupture and creep-strength values at high temperatures –Also good oxidation resistance

157 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 157 Duplex Stainless-Steel (DSS) Alloys Chromium content ranges from 18.0 to 29.0%Chromium content ranges from 18.0 to 29.0% Nickel from 2.5 to 8.5%Nickel from 2.5 to 8.5% Carbon from 0.03 to 0.08%Carbon from 0.03 to 0.08% Interest due to resistance to stress corrosion cracking, crevice corrosion, general corrosion and pittingInterest due to resistance to stress corrosion cracking, crevice corrosion, general corrosion and pitting Have yield strengths twice that of 300 seriesHave yield strengths twice that of 300 series Used where thinner sections and weight reduction desirableUsed where thinner sections and weight reduction desirable

158 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 158 Tool Steels Carbon or alloy steels capable of being hardened and temperedCarbon or alloy steels capable of being hardened and tempered Produced primarily for machine tools which cut and shape articles used in manufacturingProduced primarily for machine tools which cut and shape articles used in manufacturing Vary in chemical composition depending upon end useVary in chemical composition depending upon end use Many different types: carbon range from 0.80 to 1.50%Many different types: carbon range from 0.80 to 1.50%

159 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 159 Tool Steels Usually melted in electric furnaces in small batchesUsually melted in electric furnaces in small batches Used in other applications when wear resistance is importantUsed in other applications when wear resistance is important Rarely welded and must be preheated to do soRarely welded and must be preheated to do so –After-treatment also necessary Special hard-surfacing electrodes required for this workSpecial hard-surfacing electrodes required for this work

160 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 160 Carbon Equivalency Variety of formulas for calculationVariety of formulas for calculation One example:One example: –Intended for use with carbon and alloy steels that contain more than 0.5% carbon, 1.5% manganese, 3.5% nickel, 1% chromium, 1% copper and 0.5% molybdenum

161 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 161 SAE/AISI Steel Numbering System Based on chemical analysis of steelBased on chemical analysis of steel Number designations indicating percentage of predominant alloying elementNumber designations indicating percentage of predominant alloying element Table 3-7 shows classification system

162 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 162 Types of Cast Iron Iron-based material containing 91 to 94% ironIron-based material containing 91 to 94% iron –Carbon: 2.0 to 4.0% Cannot be formed by forging, rolling, drawing, bending or spinningCannot be formed by forging, rolling, drawing, bending or spinning –Low ductility and lack of malleability Castings have low ductility and low tensile strengthCastings have low ductility and low tensile strength Has excellent compressive strengthHas excellent compressive strength Four classes: gray, white, nodular, malleableFour classes: gray, white, nodular, malleable

163 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 163 Gray Iron May be fusion welded or braze welded if preheating before welding cooling after are controlledMay be fusion welded or braze welded if preheating before welding cooling after are controlled Low in ductilityLow in ductility Moderate tensile strengthModerate tensile strength High compression strengthHigh compression strength High machinabilityHigh machinability

164 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 164 White Iron Produced through process of rapid cooling which causes carbon to combine with ironProduced through process of rapid cooling which causes carbon to combine with iron Hard, brittle, very difficult to machineHard, brittle, very difficult to machine Considered unweldableConsidered unweldable First step in making of malleable ironFirst step in making of malleable iron Has fine grain structureHas fine grain structure Silvery white appearance when fracturedSilvery white appearance when fractured

165 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 165 Malleable Iron Forms when white cast iron has been heat treated by long annealing processForms when white cast iron has been heat treated by long annealing process Higher tensile strength, impact strength, ductility, and toughness than gray or white ironHigher tensile strength, impact strength, ductility, and toughness than gray or white iron Fusion welding destroys properties in weld areaFusion welding destroys properties in weld area Braze welding recommendedBraze welding recommended If broken, fracture shows white rim with dark centerIf broken, fracture shows white rim with dark center

166 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 166 Nodular Iron Referred to as ductile ironReferred to as ductile iron Amounts of magnesium and/or cerium added to iron when producedAmounts of magnesium and/or cerium added to iron when produced –Change shape of graphite particles from flakes to spheroids Silicon contents higher than other ironsSilicon contents higher than other irons Excellent machinability, shock resistance, thermal shock resistance, wear resistance, and rigidityExcellent machinability, shock resistance, thermal shock resistance, wear resistance, and rigidity

167 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 167 Aluminum-making in the U.S. Worlds largest producers of aluminumWorlds largest producers of aluminum –More than 22 million pounds of metal processed annually Refining of bauxite oreRefining of bauxite ore –Fundamental production process of reducing alumina to aluminum by means of electricity Production done across four-fifths of countryProduction done across four-fifths of country

168 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 168 Primary Products and Their Industrial Applications Sheet: Cans, construction materials, and automobile partsSheet: Cans, construction materials, and automobile parts Plate: Aircraft and space fuel tanksPlate: Aircraft and space fuel tanks Foil: Household aluminum foil, building insulation, automotive partsFoil: Household aluminum foil, building insulation, automotive parts Rod, bar, and wire: Electrical transmission lines and nonrust staplesRod, bar, and wire: Electrical transmission lines and nonrust staples Extrusions: Storm windows, bridge structuresExtrusions: Storm windows, bridge structures

169 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 169 Environmental Progress in Aluminum Industry Focus on reducing air emissions, water discharges, and solid wasteFocus on reducing air emissions, water discharges, and solid waste Recycling very importantRecycling very important –Amount doubled in last decade –Saves almost 95% of energy needed to extract aluminum for original ore –Nearly two-thirds of aluminum beverage cans produced

170 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 170 Types of Aluminum Four-digit numbering systemFour-digit numbering system (see Table 3-23) First digit indicates major alloying groupFirst digit indicates major alloying group Three categories of aluminum find most welding applicationsThree categories of aluminum find most welding applications –Commercially pure aluminum –Wrought aluminum alloys –Aluminum casting alloys

171 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 171 Types of Aluminum Commercially pure wrought aluminum (1100)Commercially pure wrought aluminum (1100) –99% pure (little iron and silicon) –Easily welded (weld strength equal to base metal) Wrought aluminum-manganese alloyWrought aluminum-manganese alloy –1.2% manganese, 97% aluminum –Stronger than 1100 type and less ductile –Welded without difficulty –Welds strong

172 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 172 Types of Aluminum Aluminum-silicon-magnesium-chromium alloyAluminum-silicon-magnesium-chromium alloy –Classification number of 6151 –Silicon and magnesium main alloys –Welds not as strong as base metal Can be improved by heat treatmentCan be improved by heat treatment Aluminum-magnesium-chromium alloy (5052)Aluminum-magnesium-chromium alloy (5052) –Strong, highly resistant to corrosion –Good ductility Aluminum-magnesium-silicon alloy (6053)Aluminum-magnesium-silicon alloy (6053) –Readily welded and can be heat treated

173 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 173 Titanium-making in the U.S. Versatile metalVersatile metal –Light weight, physical properties and mechanical properties Produced from heavy-mineral sands containing ilmenite and/or rutileProduced from heavy-mineral sands containing ilmenite and/or rutile –Also titaniferous slags made by smelting of ilmenite with carbon Typically associated with ironTypically associated with iron One-third of world supply found in U.S.One-third of world supply found in U.S.

174 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 174 Titanium Titanium sponge produced by Kroll processTitanium sponge produced by Kroll process –Produced in a retort by vapor phase reduction of titanium tetrachloride with magnesium Ingot produced by melting sponge, scrap or combination of bothIngot produced by melting sponge, scrap or combination of both –Russia and U.S. produce bulk of world supply Vacuum arc remelt (VAR) process used to refine materialVacuum arc remelt (VAR) process used to refine material –Titanium electrode would be used

175 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 175 Titanium Mill products formed by rolling, forging, drawing, or extruding slabs and ingotsMill products formed by rolling, forging, drawing, or extruding slabs and ingots Can be cast into variety of productsCan be cast into variety of products Scrap and waste produced at each step of production processScrap and waste produced at each step of production process –Large source of feedstock material with growth in cold hearth melting capacity

176 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 176 Titanium Properties Great impact propertiesGreat impact properties Durability with excellent mechanical strengthDurability with excellent mechanical strength Modulus of elasticity half that of stainless steelModulus of elasticity half that of stainless steel Very lightweightVery lightweight Coefficient of thermal expansion half that of stainless steel and copper, one third of aluminumCoefficient of thermal expansion half that of stainless steel and copper, one third of aluminum Very corrosion resistantVery corrosion resistant

177 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 177 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Relative Corrosion Rates

178 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 178 Titanium Implants Inert to human body fluidsInert to human body fluids Natural material to use for implantsNatural material to use for implants Allows bone growth to adhere to implantAllows bone growth to adhere to implant Commonly used for reconstructive surgery applicationsCommonly used for reconstructive surgery applications Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Scott Camazine

179 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 179 Titanium Applications Largest single demand is commercial aerospace industryLargest single demand is commercial aerospace industry Chemical processing, oil and gas exploration and processingChemical processing, oil and gas exploration and processing Heat exchangersHeat exchangers Pollution control equipmentPollution control equipment Bicycles, wheelchairs, motorcycle componentsBicycles, wheelchairs, motorcycle components Eyeglass frames, writing pens, jewelryEyeglass frames, writing pens, jewelry

180 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 180 Titanium NontoxicNontoxic PyrophoricPyrophoric –Produces its own heat when in presence of oxidizing elements such as oxygen Small pieces with lot of surface contact area to air can ignite and burn at extremely high temperaturesSmall pieces with lot of surface contact area to air can ignite and burn at extremely high temperatures Form of machining or grinding chipsForm of machining or grinding chips –Store in nonflammable containers submersed in water with thin layer of oil on top Extinguish with dry sand, powdered graphite, Metal-X *Extinguish with dry sand, powdered graphite, Metal-X *

181 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 181 Expansion and Contraction All materials when loaded or stressed will deform shrink or stretchAll materials when loaded or stressed will deform shrink or stretch Metal expands when heated during weldingMetal expands when heated during welding –Not free to move due to other welds, tackings, etc. Metal contracts when coolsMetal contracts when cools Combination of heating and cooling with restraint causes stresses to build up in weldmentCombination of heating and cooling with restraint causes stresses to build up in weldment

182 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 182 Two Major Aspects of Contraction Distortion (shrinkage)Distortion (shrinkage) –Overall motion of parts being welded from position occupied before welding to that after welding StressStress –Force that will cause distortion later unless relieved Residual stressResidual stress –Temporary distortion and stress occur while welding –Remains after welded members cool

183 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 183 Physical Properties of Metal and Distortion DistortionDistortion –Result of heating and cooling and involves stiffness and yielding Heat changes physical properties of metalsHeat changes physical properties of metals –Yield point lowers –Modulus of elasticity decreases –Coefficient of thermal expansion increases –Thermal conductivity decreases –Specific heat increases

184 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 184 Yield Point Point at which it will stretch and elongate under load even though load is not increasedPoint at which it will stretch and elongate under load even though load is not increased Higher the yield point of weld and base metal, the greater amount of residual stressHigher the yield point of weld and base metal, the greater amount of residual stress Lower the yield point, less severe residual stressLower the yield point, less severe residual stress

185 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 185 Coefficient of Thermal Expansion Amount of expansion a metal undergoes when heated and the amount of contraction that occurs when it is cooledAmount of expansion a metal undergoes when heated and the amount of contraction that occurs when it is cooled High coefficient tends to increase shrinkage of weld metal and base metal next to weldHigh coefficient tends to increase shrinkage of weld metal and base metal next to weld –Increases possibility of distortion in weldment

186 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 186 Other Physical Properties Thermal conductivityThermal conductivity –Measure of flow of heat through metal –Low thermal conductivity retards flow of heat from weld Increases shrinkage of weld and plate next to itIncreases shrinkage of weld and plate next to it Modulus of elasticityModulus of elasticity –Measure of relative stiffness of metal –Modulus high, the material more likely to resist movement and distortion

187 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 187 Types of Distortion: Lengthwise Shrinkage Occurs when weld is lengthwise on unclamped strip of steelOccurs when weld is lengthwise on unclamped strip of steel Bow upwards at both ends when coolsBow upwards at both ends when cools –Due to contraction of weld above plate surface Minimize by small weld beads, flat deep penetrating beads or even heat on both sides of plateMinimize by small weld beads, flat deep penetrating beads or even heat on both sides of plate Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

188 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 188 Neutral Axis of Joint Center of gravity of jointCenter of gravity of joint Welds kept close to neutral axis or balancing weld sequences about neutral axis minimizes lengthwise shrinkageWelds kept close to neutral axis or balancing weld sequences about neutral axis minimizes lengthwise shrinkage Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

189 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 189 Types of Distortion: Crosswise Shrinkage Also called transverse contractionAlso called transverse contraction Butt joint with free movement during welding allows opposite end from weld to be drawn together by contraction of weld metalButt joint with free movement during welding allows opposite end from weld to be drawn together by contraction of weld metal Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

190 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 190 Controlling Transverse Contraction Tack-weld at opposite ends on short seamsTack-weld at opposite ends on short seams Tack-weld at several equidistant positions on long seamsTack-weld at several equidistant positions on long seams –Thickness of plate –Type of material –type of edge preparation –Usually twice as long as thickness of plate and spaced 8–12 inches Clamping devices and wedgesClamping devices and wedges PrespacingPrespacing

191 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 191 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Controlling Transverse Contraction

192 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 192 Types of Distortion: Warping Contraction of weld depositContraction of weld deposit –Uneven deposit in V-groove and U-groove butt joints Places most of weld above neutral axisPlaces most of weld above neutral axis Greater warping on multiple passes on jointGreater warping on multiple passes on joint Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

193 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 193 Counteracting Warping Setting plates before welding so bow in opposite directionSetting plates before welding so bow in opposite direction Clamping platesClamping plates –High internal stress Deforming occurs when residual stress exceed yield strength of metalDeforming occurs when residual stress exceed yield strength of metal Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

194 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 194 Types of Distortion: Angular Distortion Fillet welds contain both longitudinal and transverse stressesFillet welds contain both longitudinal and transverse stresses Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

195 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 195 Types of Distortion: Angular Distortion Fillet weld in T-joint will pull vertical member toward side that is weldedFillet weld in T-joint will pull vertical member toward side that is welded Dotted lines indicate original position. Position after welding is indicated by solid lines. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

196 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 196 Effect on Butt Joint-Groove Welds Factors Affecting Perpendicular Shrinkage Cross-sectional area of weld for given thickness of plateCross-sectional area of weld for given thickness of plate –Larger cross section yields greater shrinkage Free distance spacing between roots and type of grooveFree distance spacing between roots and type of groove Total heat input: greater heat yields greater distortionTotal heat input: greater heat yields greater distortion Rate of heating: greater rate of heat inputRate of heating: greater rate of heat input Weld searching like backstep proceduresWeld searching like backstep procedures PeeningPeening

197 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 197 Factors that Affect Angular Distortion Increases with number of layersIncreases with number of layers Greatest in butt joints with V-grooves welds, next in U-grooves, less in double-V and double-U grooves, and least in square groovesGreatest in butt joints with V-grooves welds, next in U-grooves, less in double-V and double-U grooves, and least in square grooves May be controlled by peening every fill pass layer to suitable extentMay be controlled by peening every fill pass layer to suitable extent Practically eliminated by welding alternately on both side in multilayer welding about neutral axis in double-V and double-U groove weldsPractically eliminated by welding alternately on both side in multilayer welding about neutral axis in double-V and double-U groove welds Time of welding and size of electrodeTime of welding and size of electrode Rate of heatingRate of heating

198 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 198 Distortion Affects on Fillet Welds Shrinkage increases with size of weld and decreases as rate of heat input increasesShrinkage increases with size of weld and decreases as rate of heat input increases Shrinkage proportional to length of weld, if weld intermittentShrinkage proportional to length of weld, if weld intermittent Shrinkage may be decreased materially by choosing suitable sequences and procedures of welding and peeningShrinkage may be decreased materially by choosing suitable sequences and procedures of welding and peening Transverse shrinkage less for lap joint than for V groove-butt jointTransverse shrinkage less for lap joint than for V groove-butt joint

199 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 199 Prevention of Distortion Before Welding DesignDesign –Joints should require minimum amount of filler metal –Joints arranged to balance each other Selection of process and equipmentSelection of process and equipment –Higher welding speeds through use of powdered iron manual electrodes Reduces amount of base metal affected by heat of arcReduces amount of base metal affected by heat of arc

200 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 200 Prevention of Distortion Before Welding PrebendingPrebending –Plates bent in direction opposite to side being welded –Shrinkage restrained curing welding by clamps More effective when welded members are allowed to cool in clampsMore effective when welded members are allowed to cool in clamps –When clamps removed, plates spring back so pulled into alignment Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

201 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 201 Spacing of partsSpacing of parts –Space parts out of position before welding –Arms pulled back to proper spacing by shrinkage forces of welding Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Prevention of Distortion Before Welding

202 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 202 Prevention of Distortion Before Welding Jigs and fixturesJigs and fixtures –Prevent warping by holding weldment in fixed position to reduce movement –Widely used in production welding –Strong backs Temporary stiffeners for purpose of increasing resistance to distortionTemporary stiffeners for purpose of increasing resistance to distortion Removed after welding completed and cooledRemoved after welding completed and cooled

203 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 203 Distortion Control During Welding Reduced by using sequence of welding known asReduced by using sequence of welding known aswandering –Making welds at different points of weldment Shrinkage set up by on weldShrinkage set up by on weld counteracted by shrinkage set up by another –Two methods Chain intermittent fillet weldsChain intermittent fillet welds Staggered intermittent filletStaggered intermittent filletwelds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chain Staggered

204 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 204 Distortion Control During Welding Backstep method of weldingBackstep method of welding –Breaking up welds in short sections and depends upon welding in proper direction –General progression of welding is left to right, but each bead is deposited from right to left –Reduces locked-up stresses and warping Skip-stop, backstep methodSkip-stop, backstep method –Direction same as backstep except short welds not made in continuous sequence

205 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 205 Backstep Method Example Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

206 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 206 Skip-stop, Backstep Method Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

207 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 207 Distortion Control During Welding Balanced welding sequenceBalanced welding sequence –Equal number of welders weld on opposite sides of structure at same time Balanced stressesBalanced stresses Both wandering techniques and balanced welding contribute to completion of welded connections in large fabricationsBoth wandering techniques and balanced welding contribute to completion of welded connections in large fabrications

208 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 208 Correction of Distortion After Welding ShrinkageShrinkage –Alternate heating and cooling, frequently accompanied by hammering or mechanical working Shrink weldingShrink welding –Variation of shrinkage in which heat applied by running beads of weld metal on convex side of buckled area (after correction, ground off) Added stiffeningAdded stiffening –Pulling plate into line with strong backs and welding additional stiffeners to plate to make it retain its plane –Can by used only on plate

209 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 209 Summary of Distortion Control Metal expansionMetal expansion –Metal with high coefficient of expansion distorts more than one with lower coefficient Distortion effectsDistortion effects –Kind of welding process has influence on distortion Use of welding positionersUse of welding positioners –Allows use of larger diameter electrodes or welding procedures with higher deposition rates and faster welding speeds

210 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 210 Summary of Distortion Control Balanced forcesBalanced forces –By prebending and presetting in direction opposite to movement caused by weld shrinkage –Shrinkage pull material back into alignment Forcible restraintsForcible restraints –Restraining parts forcibly through use of clamps, fixtures, and tack welds –Welder must be careful not to overrestrain parts

211 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 211 Summary of Distortion Control Clamping parts during fabricationClamping parts during fabrication –Clamped or welded to heavy fixture which can be stress relieved with weldment Heat distributionHeat distribution –Distribute welding heat evenly though planned welding sequence and planned weld positions Increase speed with heatIncrease speed with heat General rule about warpingGeneral rule about warping –Decrease in speed and increase in number of passes increases warping

212 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 212 Summary of Distortion Control Welding from both sidesWelding from both sides –Distortion reduced by welding from both sides –Welding from both sides at same time all but eliminates distortion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

213 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 213 Summary of Distortion Control Welding directionWelding direction –Away from point of restraint –Toward point of maximum freedom Wandering sequencesWandering sequences –Skip welding and backstep welding prevents local buildup of heat thus reduces shrinkage End fixingEnd fixing –Boxing: when fillet weld wrapped around corner of member as continuation of principal weld

214 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 214 Summary of Distortion Control Avoid overweldingAvoid overwelding –Too much welding increases distortion –Too many weld passes cause additional heat input Single pass better than several passesSingle pass better than several passes –Stringer bead produces less distortion than weave bead –Use smallest leg size permissible when fillet welding Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Use Minimum number of passes

215 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 215 Summary of Distortion Control Reduce weld metalReduce weld metal –Excessive widths of groove weld increase weld shrinkage and cost Add nothing to strengthAdd nothing to strength –Root opening, including angle should be kept to a minimum –Select joints that require little weld metal –Weld joints that cause most contraction first

216 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 216 Correct Edge Preparation and Good Fitup Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

217 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 217 Summary of Distortion Control Fix tack welds firstFix tack welds first –Weak welds or cracked tack welds should be chipped or melted out before proceeding with weld PeeningPeening –Effective –Too much, causes loss of ductility and impact properties

218 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 218 Control of Residual Stress: Preheating Necessary to control or reduce rate of expansion and contraction during weldingNecessary to control or reduce rate of expansion and contraction during welding –Preheat entire structure before welding and maintaining heat during welding Care taken to make sure preheat uniform throughout structureCare taken to make sure preheat uniform throughout structure After weld completed, structure must be allowed to cool slowlyAfter weld completed, structure must be allowed to cool slowly

219 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 219 Control of Residual Stress: Postheating Most common method of stress relievingMost common method of stress relieving Must be done in furnace capable of uniform heating under temperature controlMust be done in furnace capable of uniform heating under temperature control Work must be supportedWork must be supported When weldment reaches maximum temperature, permitted to soakWhen weldment reaches maximum temperature, permitted to soak –One hour per one inch of thickness Reduction of temperature must be gradual and uniformReduction of temperature must be gradual and uniform

220 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 220 Control of Residual Stress: Postheating Suggested Preheat Temperatures Carbon Equivalent (%)Temperature (Fº) Up to 0.45 Optional 0.45– –400ºF Above –700ºF

221 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 221 Control of Residual Stress: Full Annealing Superior to all other methodsSuperior to all other methods Very difficult to handleVery difficult to handle Must be heated to 1,600 to 1,650ºFMust be heated to 1,600 to 1,650ºF –Causes formation of very heavy scale –Danger of collapse on some types of weldments

222 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 222 Control of Residual Stress: Cold Peening Bead hammered to stretch it and counteract shrinkage due to coolingBead hammered to stretch it and counteract shrinkage due to cooling Causes plastic flowCauses plastic flow Identical to cold working steelIdentical to cold working steel OverpeeningOverpeening –Cracks, loss of ductility, work hardened, new stress Root and face layers of well should not be peenedRoot and face layers of well should not be peened

223 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 223 Control of Residual Stress: Vibratory Stress Relieving Uses low frequency, high amplitude vibration to reduce stress levels to point where they cannot cause distortionUses low frequency, high amplitude vibration to reduce stress levels to point where they cannot cause distortion Vibration generator clamped to workpieceVibration generator clamped to workpiece –Vibration level adjusted to create desired amplitude –Sine waves pass through parts, relaxing microstructure –Takes between 15 and 30 minutes depending on size

224 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 224 Control of Residual Stress: Cryogenic Stress Relieving Takes various structures at very slow rate down from room temperature to 300º below 0ºF by exposing them to liquid nitrogen vaporsTakes various structures at very slow rate down from room temperature to 300º below 0ºF by exposing them to liquid nitrogen vapors –Done at 1ºF per minute Allowed to soak at holding temperature for 24 to 36 hoursAllowed to soak at holding temperature for 24 to 36 hours –Molecules in structure get closer together At end of holding period structure slowly warmed back up to room temperatureAt end of holding period structure slowly warmed back up to room temperature –Rate of 1ºF per minute

225 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 225 Control of Residual Stress: Mechanical Loading Base metal stressed just at point of yielding by application of internal pressure to pressure vesselBase metal stressed just at point of yielding by application of internal pressure to pressure vessel Works well with simple weldmentWorks well with simple weldment Important only very small yielding takes placeImportant only very small yielding takes place Hydraulic pressure used rather than air pressureHydraulic pressure used rather than air pressure –Danger with air pressure of vessel rupturing

226 © 2012 The McGraw-Hill Companies, Inc. All rights reserved. WELDING: Principles and Practices, 4e 226 Control of Residual Stress: Welding Technique Product designed to incorporate types of joints having lowest residual stressProduct designed to incorporate types of joints having lowest residual stress Degree of residual stress considered when choosing processDegree of residual stress considered when choosing process Plan assembly welding sequences that permit movement of component parts during weldingPlan assembly welding sequences that permit movement of component parts during welding Avoid highly localized and intersecting weldsAvoid highly localized and intersecting welds Use electrodes that have an elongation of at least 20% in 2 inchesUse electrodes that have an elongation of at least 20% in 2 inches Peening effective method of reducing stressesPeening effective method of reducing stresses –Root and face layer and layers more than 1/8 inch should not be peened


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