Last class -

Ceramic toolsCast irons

Today -

Case hardeningHardenability testQuenching design

Case hardening

Gear toothCarburizing - pack & gas - add C from CO gas

Nitriding - add N from NH3Carbonitriding - add C & N from CO & NH3

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 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

Example quench design problems

What is max bar size for 4140 which will full harden with quench severity of 0.35?

Jominy curve

6

6

Example quench design problems

What quench should be used for 2" diam. 4140 bar to full harden 1/2" deep?

6

Quench severity ≈ 1.25 Water quench w/some agitation

Example quench design problems

Quench severity ≈ 1.25. What is hardness at center?

7

Jominy curve

Example quench design problems

Quench severity ≈ 1.25. What is hardness at center?

2" bar quenched at 1.25 corresponds to 7/16" on Jominy bar Hardness ≈ 54

7

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

Most corrosion is electrochemical

Galvanic cell is necessary

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)

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)

How do we know?

Many combos tried experimentally