Last class - Ceramic tools Cast irons Last class - Ceramic tools Cast irons Today - Case hardening Hardenability test Quenching design 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 Carbonitriding - add C & N from CO & NH 3 Case must be Q & T, except for nitrided

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 Mn YS = 49 ksi, TS = 90 ksi, EL = 15% (hot-rolled) YS = 80 ksi, TS = 120 ksi (Q+T) depends on heat treat conditions Ford uses SAE 1050 steel with manganese content modified from 0.80 to 1.10% in rear axle shafts. Normally 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

Example quench design problems What is max bar size for 4140 which will full harden with quench severity of 0.35? Jominy curve

Example quench design problems What quench should be used for 2" diam bar to full harden 1/2" deep? 6 6 Quench severity ≈ 1.25 Water quench w/some agitation Quench severity ≈ 1.25 Water quench w/some agitation

Example quench design problems Quench severity ≈ What is hardness at center? 7 7

Jominy curve Example quench design problems Quench severity ≈ What is hardness at center? 2" bar quenched at 1.25 corresponds to 7/16" on Jominy bar Hardness ≈ 54 2" bar quenched at 1.25 corresponds to 7/16" on Jominy bar Hardness ≈

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) 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 Most corrosion is electrochemical Galvanic cell is necessary No corrosion if one of these is missing: anode cathode electrolyte electrical connection No corrosion if one of these is missing: anode cathode electrolyte electrical connection anode cathode electrolyte electrical connection

Corrosion Most corrosion is electrochemical Galvanic cell is necessary Corrosion at anode Me = Me +n + ne – (metal dissolves) Corrosion at anode Me = Me +n + ne – (metal dissolves) anode cathode electrolyte electrical connection No dissolution at cathode

Corrosion What constitutes an anode/cathode pair? Zn Cu electrolyte electrical connection Dissimilar metals Ex: Cu & Zn (Zn corrodes) Ex: Cu & Zn (Zn corrodes) How do we know? Many combos tried experimentally How do we know? Many combos tried experimentally