Taxonomy of Metals Metal Alloys Ferrous Steels Steels 1 4wt C 1 4 wt C Nonferrous Cast Irons Cast Irons 3 4 5 wt C 3 4 5 wt C Cu Al 1600 d 1200 L g austenite g L a800 ferrite 600 400 0 Fe L Fe3C 1148 C 4 30 1000 727 C Eutectoid 0 76 1 2 Eutectic g Fe3C Fe3C cementite a Fe3C 3 Ti microstructure ferrite graphite cementite T C 1400 Mg 4 5 6 Co wt C 6 7 1 Steels High Alloy Low Alloy low carbon Med carbon 0 25 wt C 0 25 0 6wt C high carbon 0 6 1 4wt C heat plain treatable Cr V Cr Ni Additions none none none Ni Mo Mo Example 1010 4310 1040 4340 1095 Hardenability 0 TS 0 EL 0 Name plain Uses auto struc sheet HSLA bridges towers press vessels plain crank shafts bolts hammers blades pistons gears wear applic wear applic tool Cr V Mo W 4190 drills saws dies increasing strength cost decreasing ductility austenitic stainless Cr Ni Mo 304 0 0 high T applic turbines furnaces V corros resistant 2 Ferrous Alloys Iron containing Steels cast irons Nomenclature AISI SAE 10xxPlain Carbon Steels 11xxPlain Carbon Steels resulfurized for machinability 15xxMn 10 20 40xxMo 0 20 0 30 43xxNi 1 65 2 00 Cr 0 4 0 90 Mo 0 2 0 3 44xxMo 0 5 where xx is wt C x 100 example 1060 steel plain carbon steel with 0 60 wt C Stainless Steel 11 Cr 3 Cast Iron Ferrous alloys with 2 1 wt C more commonly 3 4 5 wt C low melting also brittle so easiest to cast Cementite decomposes to ferrite graphite Fe3C 3 Fe a C graphite generally a slow process 4 Fe C True Equilibrium Diagram T C 1600 Graphite formation promoted by 1400 Si 1 wt 1200 slow cooling L g Austenite Liquid Graphite g L 1153 C 4 2 wt C 1000 g Graphite a g 800 0 65 740 C 600 400 Fe a Graphite 0 1 2 3 4 90 100 Co wt C 5 Types of Cast Iron Gray iron Ductile iron 6 Types of Cast Iron White iron Malleable iron 7 Production of Cast Iron Adapted from Fig 11 5 Callister 7e 8 Limitations of Ferrous Alloys 9 Nonferrous Alloys Cu Alloys Al Alloys Brass Bronze Cu Be NonFerrous Alloys Ti Alloys Mg Alloys Refractory metals Noble metals 10 Metal Fabrication How do we fabricate metals Blacksmith hammer forged Molding cast Forming Operations Rough stock formed to final shape Hot working vs Cold working 11 Metal Fabrication Methods I FORMING CASTING JOINING Forging Hammering Stamping Rolling Hot or Cold Rolling wrenches crankshafts force I beams rails sheet plate roll die A o blank A d often at elev T Drawing force Ao Ad roll Adapted from Fig 11 8 Callister 7e Extrusion rods wire tubing die Ao Ad rods tubing Ao tensile force die die must be well lubricated clean force container ram billet die holder extrusion Ad die ductile metals e g Cu Al hot 12 container Metal Fabrication Methods II FORMING CASTING JOINING Casting mold is filled with metal metal melted in furnace perhaps alloying elements added Then cast in a mold most common cheapest method gives good production of shapes weaker products internal defects good option for brittle materials 13 Metal Fabrication Methods II FORMING CASTING JOINING Sand Casting large parts e g auto engine blocks trying to hold something that is hot what will withstand 1600 C Sand Sand molten metal 14 Metal Fabrication Methods II FORMING CASTING JOINING Investment Casting pattern is made from paraffin mold made by encasing in plaster of paris melt the wax the hollow mold is left pour in metal low volume complex shapes e g jewelry turbine blades plaster die formed around wax prototype wax 15 Metal Fabrication Methods II FORMING CASTING JOINING Die Casting high volume low T alloys Continuous Casting simple slab shapes molten solidified 16 Metal Fabrication Methods III FORMING CASTING Powder Metallurgy materials w low ductility Welding when one large part is impractical pressure filler metal melted base metal melted fused base metal heat area contact JOINING unaffected piece 1 heat affected zone unaffected piece 2 densify Heat affected zone point contact at low T densification by diffusion at higher T region in which the microstructure has been changed 17 Thermal Processing of Metals Annealing Heat to Tanneal then cool slowly Stress Relief Reduce stress caused by plastic deformation nonuniform cooling phase transform Spheroidize steels Make very soft steels for good machining Heat just below TE hold for 15 25 h Types of Annealing Process Anneal Negate effect of cold working by recovery recrystallization Full Anneal steels Make soft steels for good forming by heating to get g then cool in furnace to get coarse P Normalize steels Deform steel with large grains then normalize to make grains small 18 Heat Treatments 800 Austenite stable T C A a Annealing b Quenching c Tempered Martensite TE P 600 B A 400 0 M A 200 50 M A 90 a b 10 1 10 10 time s 3 10 5 c 19 Hardenability Steels Ability to form martensite Jominy end quench test to measure hardenability specimen heated to g phase field 24 C water flat ground Rockwell C hardness tests Hardness HRC Hardness versus distance from the quenched end Distance from quenched end 20 Why Hardness Changes W Position Hardness HRC The cooling rate varies with position 60 40 20 0 1 2 3 distance from quenched end in T C 0 100 600 400 200 M start A M 0 M finish 0 1 1 10 100 1000 Time s 21 Hardenability vs Alloy Composition Jominy end quench results C 0 4 wt C Hardness HRC 100 4140 4340 5140 8640 contain Ni Cr Mo 0 2 to 2wt these elements shift the nose martensite is easier to form 3 60 2 Cooling rate C s 100 4340 80 M 50 40 4140 8640 20 Alloy Steels 10 5140 0 10 20 30 40 50 Distance from quenched end mm 800 T C 600 A 400 200 0 1 10 10 B TE shift from A to B due to alloying M start M 90 103 105 Time s 22 Quenching Medium Geometry Effect of quenching medium Medium air oil water Severity of Quench low moderate high Hardness low moderate high Effect of geometry When surface to volume ratio increases cooling rate increases hardness increases Position center surface Cooling rate low high Hardness low high 23 Precipitation Hardening Particles impede dislocations 700 Ex Al Cu system T C Procedure 600 Pt A solution heat treat get a solid solution Pt B quench to room temp Pt C reheat to nucleate small q crystals within a crystals Other precipitation systems Cu Be Cu Sn Mg Al 500 400 a a L q L A q a q C 300 0 B 10 Al CuAl2 L 20 30 40 50 wt Cu composition range needed for precipitation hardening Temp Pt A sol n heat treat Pt C precipitate q Pt B Time 24 …
View Full Document
Unlocking...