Lecture 4 Chapter 5 Austenite, Ferrite and Cementite 1
Austenite, Ferrite, Martensite and Cementite Austenite FCC Structure of Fe/steel at elevated temperatures (~ >727 o C) Ferrite BCC Relatively soft and ductile Steel structure at lower temperatures than Austenite Martensite non-equilibrium structure BCT Hard and brittle Cementite Fe 3 C Iron carbide Orthorhombic Hard and brittle Austenite Transformation Isothermal Transformation TTT curve Pearlite Bainite Martensite 2
Mechanical Property Differences Between Ferrites and Spheroidite Mechanical Property Differences Between Ferrite and Martensite (b) 3
Tempering of Martensite Heat Treatments of Plain Carbon Steel 4
Cooling Effects on Hardness of Plain Carbon Steels Effect of Tempering on Plain Carbon Steels 5
Electric Furnaces Carbon steels are the least expensive of all structural metals Electric furnaces Direct Arc Indirect Arc Induction Electric Furnaces 6
Electric Furnaces Electric Furnaces 7
Blast Furnace Design Selection of Carbon and Alloy Steels TABLE 5.1 Product Steel Product Steel Aircraft forgings, tubing, fittings Automobile bodies Axles Ball bearings and races Bolts Camshafts Chains (transmission) Coil springs Connecting rods Crankshafts (forged) 4140, 8740 1010 1040, 4140 52100 1035, 4042, 4815 1020, 1040 3135, 3140 4063 1040, 3141, 4340 1045, 1145, 3135, 3140 Differential gears Gears (car and truck) Landing gear Lock washers Nuts Railroad rails and wheels Springs (coil) Springs (leaf) Tubing Wire Wire (music) 4023 4027, 4032 4140, 4340, 8740 1060 3130 1080 1095, 4063, 6150 1085, 4063, 9260, 6150 1040 1045, 1055 1085 Designation for steels AISI First two digits indicate the alloying elements Last two digits are for amount of C by weight 1040 Steel No alloying elements outside of C 0.40% C 8
Mechanical Properties of Selected Steels TABLE 5.2 Typical Mechanical Properties of Selected Carbon and Alloy Steels in the Hot-Rolled, Normalized, and Annealed Condition AISI Condition Ultimate tensile strength (MPa) Yield Strength (MPa) Elongation in 50 mm (%) Reduction of area (%) Hardness (HB) 1020 1080 3140 4340 8620 As-rolled Normalized Annealed As-rolled Normalized Annealed Normalized Annealed Normalized Annealed Normalized Annealed 448 441 393 1010 965 615 891 689 1279 744 632 536 346 330 294 586 524 375 599 422 861 472 385 357 36 35 36 12 11 24 19 24 12 22 26 31 59 67 66 17 20 45 57 50 36 49 59 62 143 131 111 293 293 174 262 197 363 217 183 149 Stainless Steel Stainless steels Stainless refers to its corrosion resistance (due to layer of Chromium Oxide) Used where corrosion is an issue Kitchenware Knives Pots Pans Aircraft fittings High vacuum components 9
AISI (UNS) 303 (S30300) Stainless Steel TABLE 5.4 Room-Temperature Mechanical Properties and Typical Applications of Selected Annealed Stainless Steels Ultimate tensile Yield Elongation strength strength in 50 mm (MPa) (MPa) (%) Characteristics and typical applications 304 (S30400) 316 (S31600) 550 620 240 260 53 50 Screw machine products, shafts, valves, bolts, bushings, and nuts; aircraft fittings; bolts; nuts; rivets; screws; studs. 565 620 240 290 60 55 Chemical and food processing equipment, brewing equipment, cryogenic vessels, gutters, downspouts, and flashings. 550 590 210 290 60 55 High corrosion resistance and high creep strength. Chemical and pulp handling equipment, photographic equipment, brandy vats, fertilizer parts, ketchup cooking kettles, and yeast tubs. 410 (S41000) 416 (S41600) 480 520 240 310 35 25 Machine parts, pump shafts, bolts, bushings, coal chutes, cutlery, tackle, hardware, jet engine parts, mining machinery, rifle barrels, screws, and valves. 480 520 275 30 20 Aircraft fittings, bolts, nuts, fire extinguisher inserts, rivets, and screws. Tool and Die Steels TABLE 5.6 Processing and Service Characteristics of Common Tool and Die Steels AISI designation Resistance to decarburization Resistance to cracking Approximate hardness (HRC) Machinability Toughness Resistance to softening Resistance to wear M2 Medium Medium 60 65 Medium Low Very high Very high T1 High High 60 65 Medium Low Very high Very high T5 Low Medium 60 65 Medium Low Highest Very high H11, 12, 13 Medium Highest 38 55 Medium to high Very high High Medium A2 Medium Highest 57 62 Medium Medium High High A9 Medium Highest 35 56 Medium High High Medium to high D2 Medium Highest 54 61 Low Low High High to very high D3 Medium High 54 61 Low Low High Very high H21 Medium High 36 54 Medium High High Medium to high H26 Medium High 43 58 Medium Medium Very high High P20 High High 28 37 Medium to high High Low Low to medium P21 High Highest 30 40 Medium Medium Medium Medium W1, W2 Highest Medium 50 64 Highest High Low Low to medium Source: Adapted from Tool Steels, American Iron and Steel Institute, 1978. Tool and Die Steels High strength Impact toughness Wear resistance 10