8Austenite 727 degrees Celsius Quenching to a slightly lower temperature lowers the driving force of ferrite and cementite nucleation.Consequently, the time span for ferrite and cementite nucleation is longer.
9Pearlite Pearlite start time (Ps) Austentite transforms into Ferrite and Cementite platelets.Pearlite finish time (Pf)High temperature means that the diffusion is fast.The pearlite will be coarse and the hardness will be low.
10Pearlite ContinuedIf quenched to a lower temperature than the nucleation time is shorter.The diffusion distances are also smaller.Pearlite will then be finer and the hardness will be higher.
11Bainite If quenching is lowered even further… Bainite Start time (Bs) Bainite Finish time (Bf)Quenched higher= Coarser, Softer, More DuctileQuenched lower= Finer, Harder, Less Ductile
12Martensite Quenched below 220 degrees Celsius. Skips Bainite and Pearlite.Hardest of the 4.Most brittle.Transforms structure.Tempering must be applied.
13TemperingCauses precipitation of equilibrium ferrite in which very fine cementite particles are dispersed.Results in increased ductility at the expense of hardness.For Martensitic steel tempering between 450 and 600 degrees Celsius is typically used.
14Quenching Medium Influences the martensitic transformation. Changes the rate at which the piece is cooled.Rate is doubled by stirring.
15Size and Shape Do Matter They effect the rate of transformation as well as the hardness.If a thick part is quenched from austenite then…May result in quench cracks.
16Alloyed SteelsAlloying elements such as Mn, Si, Ni, Cu, Mo, and V into steel favorably alter the properties.Usually under 1 percent.1st hardenability.2nd shift in eutectoid composition.3rd decrease in eutectoid temperature.4th martensitic start and finish temperatures are reduced.5th tempering time is reduced.Stainless steel is steel that contains an addition of at least 12 percent chromium.Keeps the steel from corroding or rusting.
17Cast Irons Chinese began manufacturing cast iron 3000 years ago. Enabled the melting temperature to be reduced to around 1150 degrees Celsius.Which gave us a liquid metal that could be effectively cast.Raw Cast Iron is called Pig iron.(the material that flows out of a blast furnace)Contains carbon above 2.11 percent. For practical uses 2.5 to 4.5 percent carbon is used.
18Gray Cast Irons advantages disadvantages Very brittle, though hard. Used more because it is the least expensive metallic material of all.Also, has the ability to dampen mechanical vibrations.Frequently used in the bodies of heavy machines that require vibration reduction.Flows easily when molten. Allowing the casting intricate shapes.Barely shrinks after casting.Very brittle, though hard.Very weak in tension.Should never be used in the creation of tools. Especially hammers.Will shatter when exposed to a blow.
19More on Gray Cast Irons Contains 1 to 3 mass percent silicon. If the Si concentration is lowered or the cooling rate is increased, the decomposition of the cementite into graphite and ferrite is incomplete and the graphite is then surrounded by cementite.
20Nodular Cast IronGraphite precipitates in spherical particles that are imbedded in PearliteWhen heated it will increase ductility
21White Cast Iron Another type of cast iron which is hard and brittle The surface contains the hard phase whereas the interior transforms into gray cast iron
22Malleable Cast IronDuctility increases by heating in an inert atmosphereThis results in a high strength and fair ductility
2310 Question Exercise What is a microconstituent? What is the Af temperature?What is the hardest of the four phases?Which is more brittle? Hypoeutectoid steel or Hypereutectoid steel.Name two of the most common elements for alloying steel?What is the temperature range for tempering martensitic steel?What percent carbon does cast iron have?What is one advantage and one disadvantage of a gray cast iron?Name one of the Iron-Carbon Phases.In a white cast iron the interior transforms into what?
24Answers Questions 1-7, 9, 10 Question 8 A phase or a mixture of phases which has certain characteristics in a microstructure.727 degrees Celsius.Martensite.Hypereutectoid.Manganese, Silicon, Nickel, Copper, Molybdenum, and Vanadium.450C - 600C.percent.Austenite, Ferrite, Delta-Ferrite, and Liquid phase.Gray Cast IronDisadvantages:Very brittle, though hard.Very weak in tension.Should never be used in the creation of tools. Especially hammers.Will shatter when exposed to a blow.Advantages:Used more because it is the least expensive metallic material of all.Also, has the ability to dampen mechanical vibrations.Frequently used in the bodies of heavy machines that require vibration reduction.Flows easily when molten. Allowing the casting intricate shapes.Barely shrinks after casting
25Steel alloys Carbon Steels High Strength Low Alloy Steels Quenched and Tempered SteelsHeat Treatable Low Alloy SteelsChromium-Molybdenum Steels
26Carbon SteelLow-carbon steels: Steel alloys that contain up to 0.30 weight percent C.Medium-carbon steels: Contain carbon ranges from 0.30 to 0.60 weight percent and the manganese from 0.60 to 1.65 weight percent.High-carbon steels: 0.60 to 1.00 weight percent C with 0.30 to 0.90 weight percent Mn.High-Strength Low-Alloy steels (microalloyed steels): are designed to provide better mechanical properties than conventional carbons.
27Low Carbon SteelsGood Weldabillity, Formability, Machinability (rated 55-60%)0.1%-0.2%: chain, stampings, rivets, nails, wire, pipe, and where very soft,%: structural steels, machine parts, soft and tough steels.Low costs most common
28Medium Carbon More Machinable (60-70%) : lead screws, gears, worms, spindles, shafts, and machine parts.: crankshafts, gears, axles, mandrels, tool shanks, and heat-treated machine parts.: called “low carbon tool steel” and is used where a keen edge is not necessary, but where shock strength is wanted. Drop hammers dies, set screws, screwdrivers, and arbors.: tough and hard steel. Anvil faces, band saws,hammers, wrenches, cable wire, etc.Good toughness and ductility. Balanced
29High CarbonToughness, Formabillity, Hardenability, and Weldability are Low: rock drills, shear blades, cold chisels, rivet sets, and many hand tools.: used for hardness and high tensile strength, springs, cutting tools, press tools, and striking dies.: drills, taps, milling cutters, knives, cold cutting dies, wood working toolsused where a keen cutting edge is necessary, razors, saws, and where wear resistance is importantHardness is high and wear resistant
30High Strength Low-Alloy HSLA Greater Strength-to-weight Ratio than low carbon steelsDeveloped primarily for automotive industryLow carbon ( %) with Manganese up to 2% and small quantities chromium, nickel, molybdenum, copper, nitrogen, vanadium, niobium, titanium and zirconium are used in various combinations
31Elements Used to Alloy Steel CarbonManganesePhosphorusSulfurSiliconCopperLeadBoronChromiumNickelMolybdenumAluminumZirconiumNiobiumTitaniumVanadium
32Stainless SteelStainless steel is defined as a steel alloy with a minimum of 10% Chromium.However resistance in air is usually achieved at 13%.Chromium in stainless steel forms a layer of chromium oxide. ( very thin )Impervious to water and airPassivation
33Stainless Steel contd. There are over 150 grades of stainless steel. Classified by crystal structure:Austenitic: over 70% of stainless steel production.Ferritic: highly corrosion resistant but less durable than austeniticMartenistic: not as corrosion resistant, but much tougher
34Stainless Steel contd.Stainless steel is 100% recyclable and has antibacterial properties.Stainless steel is not “invulnerable”
35Stainless steel uses St.Louis Gateway Arch (left) Art Work and building Facades due to high sheenSt.Louis Gateway Arch (left)Walt Disney Concert Hall
36Modern Bridges Suspension bridges have been around since antiquity Modern suspension bridges made up of concrete slabs on top of steel plates with steel reinforced towers and held up by steel cables
37Silver Bridge Built 1928 spanning the Ohio River Steel body frame with and steel eyebars and cable
38Silver bridge Cont.Fatigue failure in eyebar causes collapse
39Tacoma Narrows Bridge Built between 1938 and July 1940 Nicknamed “Galloping GertieCollapsed November 1940
41The TitanicWeak rivets in part to blame for the sinking of the titanic.Roughly 3 million rivets used to keep the titanic together.Iron used to rivets were No.3 bar (known as best), the standard was No.4.
42The Titanic Contd.Rivets used on the titanic contained 3 times the accepted amount of slag in iron.Rivet head’s broke, letting in ice water
43The Titanic Contd.If quality iron had been used for the rivets the section of the titanic might not have sunk.If the Quality of the iron used for the rivets had not contained excess slag the rivets might have held the sections of the titanic together and prevented other areas of the ship from becoming flooded.
44Questions Which element is the primary hardening element? What is fully-killed steels?What is a solid solution of carbon in alpha-iron?What weight percent chromium is needed for oxidation-resistance in room temperature? In harsh environments?What is the key element in stainless steel?What is the layer that protects stainless steel from corrosion called?What is the name of the process that makes stainless steel so durable?Which elements kill steels?Austenitic stainless steel makes up ____% of total steel alloy production.Stainless steel is ____% recyclable.CarbonFully-deoxidized steelMartensite13%, 26%ChromiumChromium-oxidePassivationSilicon, and Aluminum70100