In physics the truth is rarely perfectly clear, and that is certainly the case with human affairs. Hence, what is not surrounded by uncertainty cannot be the truth – Richard Feynman
Speaking of tools… OK, then, what about "ceramic" tools? Most from Al2O3 - pressed to near-net shape & sintered at 1600-1700° C - ground on diamond wheels At high temps, high hardness, wear resistance Can use for mat'ls w/ up to RC66 Very brittle Cost ≈ 2X that of carbide tools
Grey - C as graphite flakes Ductile (nodular) - C as graphite nodules Cast irons Types White - C is all in CM Grey - C as graphite flakes Ductile (nodular) - C as graphite nodules
Cast irons
very brittle, wear resistant, not machinable, limited use Cast irons White - C is all in CM very brittle, wear resistant, not machinable, limited use Grey - C as graphite ("corn") flakes Si added to graphitize, brittle cuz of flake stress raisers - cheap, widely used, vibration damping Ductile (nodular) - C as graphite nodules "inoculated" w/ Mg or Ce to get nodules - up to 40% EL
Case hardening Gear tooth Carburizing - pack & gas - add C from CO gas Nitriding - add N from NH3 Case must be Q & T, except for nitrided Carbonitriding - add C & N from CO & NH3
Case hardening Alternate case hardening method Induction hardening - surface heating by high-frequency AC, then Q & T
Truck rear axle shaft Ford uses SAE 1050 steel with manganese content modified from 0.80 to 1.10% in rear axle shafts. Normally 0.60-0.90 Mn YS = 49 ksi, TS = 90 ksi, EL = 15% (hot-rolled) YS = 80 ksi, TS = 120 ksi (Q+T) depends on heat treat conditions
Jominy test Specimen & water quench Hardness measurement
Jominy test
Quench severities
Assignment: Review today's classnotes a. cast irons b. case hardening c. Jominy test d. Jominy curves e. quench severities Read in text: pp. 339-345, 219-220, 531-532 see photos on pp. 91, 446