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Last class - Ceramic tools Cast irons. Today - Case hardening Hardenability test Quenching design. Case hardening. Gear tooth. Carburizing - pack & gas - add C from CO gas. Nitriding - add N from NH 3. Case must be Q & T, except for nitrided. Carbonitriding - add C & N from CO & NH 3.
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Last class - Ceramic tools Cast irons Today - Case hardening Hardenability test Quenching design
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
Example quench design problems Jominy curve 6 6 What is max bar size for 4140 which will full harden with quench severity of 0.35?
Example quench design problems 6 What quench should be used for 2" diam. 4140 bar to full harden 1/2" deep? Quench severity ≈ 1.25 Water quench w/some agitation
Example quench design problems 7 Quench severity ≈ 1.25. What is hardness at center?
Example quench design problems Jominy curve 7 Quench severity ≈ 1.25. What is hardness at center? 2" bar quenched at 1.25 corresponds to 7/16" on Jominy bar Hardness ≈ 54
Corrosion Hint for exams (and life): A substance which is corrosive will corrode other substances SS is thus certainly non-corrosive But it is also non-corrodable (in most instances)
Corrosion Galvanic cell is necessary electrical connection anode cathode electrolyte Most corrosion is electrochemical No corrosion if one of these is missing: anode cathode electrolyte electrical connection
Corrosion Galvanic cell is necessary electrical connection anode cathode electrolyte Most corrosion is electrochemical Corrosion at anode Me = Me+n + ne– (metal dissolves) No dissolution at cathode
Corrosion electrical connection Zn Cu electrolyte What constitutes an anode/cathode pair? Dissimilar metals Ex: Cu & Zn (Zn corrodes) How do we know? Many combos tried experimentally