2 Four Types of Engineering Materials MetalsCeramicsPolymersComposites
3 METALS Alloys and Phase Diagrams Ferrous Metals Nonferrous Metals SuperalloysGuide to the Processing of Metals
4 Why Metals Are Important High stiffness and strength ‑ can be alloyed for high rigidity, strength, and hardnessToughness ‑ capacity to absorb energy better than other classes of materialsGood electrical conductivity ‑ Metals are conductorsGood thermal conductivity ‑ conduct heat better than ceramics or polymersCost – the price of steel is very competitive with other engineering materials
5 Starting Forms of Metals used in Manufacturing Processes Cast metal - starting form is a castingWrought metal - the metal has been worked or can be worked after castingPowdered metal - starting form is very small powders for conversion into parts using powder metallurgy techniques
6 Classification of Metals Ferrous ‑ those based on ironSteelsCast ironsNonferrous ‑ all other metalsAluminum, magnesium, copper, nickel, titanium, zinc, lead, tin, molybdenum, tungsten, gold, silver, platinum, and othersSuperalloys
7 Metals and Alloys An Alloy = A metal composed of two or more elements At least one element is metallicEnhanced properties versus pure metalsStrengthHardnessCorrosion resistanceTwo main categoriesSolid SolutionsIntermediate Phases
9 What is a phase (in a material structure)? Solid SolutionsAn alloy in which one element is dissolved in another to form a single‑phase structureBase element is metallic (Solvent)Dissolved element, metallic or non-metalWhat is a phase (in a material structure)?A phase = any homogeneous mass of material, such as a metal, in which the grains all have the same crystal lattice structure!
10 Two Forms of Solid Solutions Atomic radii must be similarLower valence metal is usually solventMust be small atoms:Hydrogen, Carbon, Nitrogen, BoronFigure 6.1Interstitial solid solution - atoms of dissolving element fit into vacant spaces between base metal atoms in the lattice structureSubstitutional solid solution - atoms of solvent element are replaced in its unit cell by dissolved elementIn both forms, the alloy structure is generally stronger and harder than either of the component elements
11 Two Forms of Solid Solutions Figure 6.1Interstitial solid solutionCarbon dissolved in Iron = ??Substitutional solid solutionZinc dissolved in Copper = ??BrassSteel
13 Intermediate PhasesThere are usually limits to the solubility of one element in anotherWhen the amount of the dissolving element in the alloy exceeds the solid solubility limit of the base metal, a second phase forms in the alloyThe term intermediate phase is used to describe it because its chemical composition is intermediate between the two pure elementsIts crystalline structure is also different from those of the pure metals
14 Types of Intermediate Phases Metallic compounds – consist of a metal and nonmetal, such as Fe3CIntermetallic compounds ‑ two metals that form a compound, such as Mg2PbIn some alloy compositions, the intermediate phase is mixed with the primary solid solution to form a two‑phase structureSome two‑phase alloys are important because they can be heat treated for much higher strength than solid solutions
16 Phase DiagramsA graphical picture showing the phases of a metal alloy system as a function of composition and temperatureA phase diagram for an alloy system consisting of two elements at atmospheric pressure is called a binary phase diagramComposition is plotted on the horizontal axis and temperature on the vertical axisAny point in the diagram indicates the overall composition and the phase or phases present at the given temperature under equilibrium conditions
17 Copper-Nickel (Cu- Ni) Phase Diagram Consider point A:Composition: 60% Ni, 40% CuAt C (or 2000o F) the alloy is still at solid stage.Consider point B:About 35% Ni and 65% Cu,At 1250oC, it is a mixture of liquid and solid.solid + liquidFigure 6.2 Phase diagram for the copper‑nickel alloy system.
18 Chemical Compositions of Phases The overall composition of the alloy is given by its position along the horizontal axisHowever, the compositions of liquid and solid phases are not the sameThese compositions can be found by drawing a horizontal line at the temperature of interestWhere the line intersects the solidus and liquidus indicates the compositions of solid and liquid phases, respectively. We use the Inverse Lever Rule to find the compositions:
19 ExampleDetermine compositions of liquid and solid phases in the Cu-Ni system at an aggregate composition of 50% nickel and a temperature of 1260oC (2300oF)The proportion of solid phase present is given byS phase proportion == (50-36)/(14+12)=54%And the proportion of liquid phase present is given byL phase proportion == 100% - 54%= 46%*100*
20 Tin-Lead Phase Diagram Molten Tin and leadSolid Tin and leadSolid Tin and molten mixtureSoli lead and molten mixtureSolid solution of Tin in LeadSolid solution of Lead in TinWidely used in soldering for making electrical connectionsFigure 6.3 Phase diagram for the tin‑lead alloy system.Pure tin melts at 232C (449F)Pure lead melts at 327C (621F)
22 Ferrous Metals Based on iron, one of the oldest metals known to man Ferrous metals of engineering importance are alloys of iron and carbonThese alloys divide into two major groups:SteelCast ironTogether, they constitute approximately 85% of the metal tonnage in the United States
23 What is the difference between steel and cast iron?!
24 Steel and Cast Iron Defined Steel = an iron‑carbon alloy containing from 0.02% to 2.1% carbonCast iron = an iron‑carbon alloy containing from 2.1% to about 4% or 5% carbonSteels and cast irons can also contain other alloying elements besides carbon
25 Iron-Carbon Phase Diagram Figure 6.4 Phase diagram for iron‑carbon system, up to about 6% carbon.
27 SteelAn alloy of iron containing from 0.02% and 2.11% carbon by weightOften includes other alloying elements: nickel, manganese, chromium, and molybdenumSteel alloys can be grouped into four categories:Plain carbon steelsLow alloy steelsStainless steelsTool steels
28 Carbon Strength Carbon Ductility Plain Carbon Steels1Carbon is the principal alloying element, with only small amounts of other elements (about 0.5% manganese is normal)Strength of plain carbon steels increases with carbon content, but ductility is reducedHigh carbon steels can be heat treated to form martensite, making the steel very hard and strongCarbon Strength Carbon Ductility
29 1Figure Tensile strength and hardness as a function of carbon content in plain carbon steel (hot rolled).Hardness is the characteristic of a solid material expressing its resistance to permanent deformation. It is expressed as Brinell hardness number or BHN or HB:P = applied force (kgf)D = diameter of indenter (mm)d = diameter of indentation (mm)
30 AISI-SAE Designation Scheme 1AISI-SAE Designation SchemeSpecified by a 4‑digit number system: 10XX, where 10 indicates plain carbon steel, and XX indicates carbon % in hundredths of percentage pointsFor example, 1020 steel contains 0.20% CDeveloped by American Iron and Steel Institute (AISI) and Society of Automotive Engineers (SAE), so designation often expressed as AISI 1020 or SAE 1020
31 1 Plain Carbon Steels Low carbon steels - contain less than 0.20% C Applications: automobile sheetmetal parts, plate steel for fabrication, railroad railsMedium carbon steels - range between 0.20% and 0.50% CApplications: machinery components and engine parts such as crankshafts and connecting rodsHigh carbon steels - contain carbon in amounts greater than 0.50%Applications: springs, cutting tools and blades, wear-resistant parts
32 Low Alloy Steels2Iron‑carbon alloys that contain additional alloying elements in amounts totaling less than 5% by weightMechanical properties superior to plain carbon steels for given applicationsHigher strength, hardness, wear resistance, toughness, and more desirable combinations of these propertiesHeat treatment is often required to achieve these improved propertiesLarge diameter pipeline
33 AISI-SAE Designation Scheme 2AISI‑SAE designation uses a 4‑digit number system: YYXX, where YY indicates alloying elements, and XX indicates carbon % in hundredths of % pointsExamples:13XX - Manganese steel20XX - Nickel steel31XX - Nickel‑chrome steel40XX - Molybdenum steel41XX - Chrome‑molybdenum steel
34 Carbon Strength Carbon Corrosion protection Stainless Steel (SS)3Highly alloyed steels designed for corrosion resistancePrincipal alloying element is Chromium, usually greater than 15%Cr forms a thin oxide film that protects surface from corrosionNickel (Ni) is another alloying ingredient in certain SS to increase corrosion protectionCarbon is used to strengthen and harden SS, but high C content reduces corrosion protection since chromium carbide forms to reduce available free CrCarbon Strength Carbon Corrosion protection
35 Properties of Stainless Steels 3In addition to corrosion resistance, stainless steels are noted for their combination of strength and ductilityWhile desirable in many applications, these properties generally make stainless steel difficult to work in manufacturingSignificantly more expensive than plain C or low alloy steels
36 Types of Stainless Steel 3Classified according to the predominant phase present at ambient temperature:Austenitic stainless ‑ typical composition 18% Cr and 8% NiFerritic stainless ‑ about 15% to 20% Cr, low C, and no NiMartensitic stainless ‑ as much as 18% Cr but no Ni, higher C content than ferritic stainless
37 Designation Scheme for Stainless Steels 3Three‑digit AISI numbering schemeFirst digit indicates general type, and last two digits give specific grade within typeExamples:Type 302 – Austenitic SS18% Cr, 8% Ni, 2% Mn, 0.15% CType 430 – Ferritic SS17% Cr, 0% Ni, 1% Mn, 0.12% CType 440 – Martensitic SS17% Cr, 0% Ni, 1% Mn, 0.65% C
38 Additional Stainless Steels 3Stainless steels developed in early 1900sSeveral additional high alloy steels have been developed and are also classified as stainless steels:Precipitation hardening stainless ‑ typical composition = 17% Cr and 7%Ni, with additional small amounts of alloying elements such as Al, Cu, Ti, and Mo (Aerospace applications)Duplex stainless ‑ mixture of austenite and ferrite in roughly equal amounts (heat exchangers, pumps)
39 Tool Steels4A class of (usually) highly alloyed steels designed for use as industrial cutting tools, dies, and moldsTo perform in these applications, they must possess high strength, hardness, wear resistance, and toughness under impactTool steels are heat treated
40 AISI Classification of Tools Steels 4T, M High‑speed tool steels ‑ cutting tools in machiningH Hot‑working tool steels ‑ hot‑working dies for forging, extrusion, and die‑castingD Cold‑work tool steels ‑ cold working dies for sheetmetal pressworking, cold extrusion, and forgingW Water‑hardening tool steels ‑ high carbon but little elseS Shock‑resistant tool steels ‑ tools needing high toughness, as in sheetmetal punching and bendingP Mold steels ‑ molds for molding plastics and rubber
42 Cast IronsIron alloys containing from 2.1% to about 4% carbon and from 1% to 3% siliconThis composition makes them highly suitable as casting metalsTonnage of cast iron castings is several times that of all other cast metal parts combined, excluding cast ingots in steel-making that are subsequently rolled into bars, plates, and similar stockOverall tonnage of cast iron is second only to steel among metals
43 What do you think this is? QuestionWhat do you think this is?Cross-section of a gray cast iron using an optical microscopy (up to 1000 times magnification)
44 Types of Cast Irons Most important is gray cast iron Other types include ductile iron, white cast iron, malleable iron, and various alloy cast ironsDuctile and malleable irons possess chemistries similar to the gray and white cast irons, respectively, but result from special processing treatmentsGray cast Iron Special melting and pouring treatment (Chemical treatment) Ductile IronWhite cast Iron Heat treatment Malleable Iron
45 Cast Iron ChemistriesFigure Carbon and silicon % for cast irons, compared to steels (most steels have relatively low Si % ‑ cast steels have higher Si %).Ductile iron is formed by special melting and pouring treatment of gray cast iron.Malleable iron is formed by heat treatment of white cast iron.