Last class -

Ceramic toolsCast irons

Last class -

Ceramic toolsCast irons

Today -

Case hardeningHardenability testQuenching design

Today -

Case hardeningHardenability testQuenching design

Case hardeningCase hardening

Gear toothGear tooth

Carburizing - pack & gas - add C from CO gasCarburizing - pack & gas - add C from CO gas

Nitriding - add N from NH3

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

Carbonitriding - add C & N from CO & NH3

Case must be Q & T, except for nitrided

Case must be Q & T, except for nitrided

Case hardeningCase hardening

Alternate case hardening methodAlternate case hardening method

Induction hardening - surface heating by high-frequency AC, then Q & T

Induction hardening - surface heating by high-frequency AC, then Q & T

Truck rear axle shaftTruck 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

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 testJominy test

Specimen & water quenchSpecimen & water quench Hardness measurementHardness measurement

Jominy testJominy test

Quench severitiesQuench severities

Example quench design problemsExample quench design problems

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

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

Jominy curve

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Example quench design problemsExample quench design problems

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

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Quench severity ≈ 1.25 Water quench w/some agitation

Quench severity ≈ 1.25 Water quench w/some agitation

Example quench design problemsExample quench design problems

Quench severity ≈ 1.25. What is hardness at center?Quench severity ≈ 1.25. What is hardness at center?

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Jominy curveJominy curve

Example quench design problemsExample quench design problems

Quench severity ≈ 1.25. What is hardness at center?Quench severity ≈ 1.25. 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 ≈ 54

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Corrosion 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 Corrosion

Most corrosion is electrochemicalMost corrosion is electrochemical

Galvanic cell is necessaryGalvanic 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 Corrosion

Most corrosion is electrochemicalMost corrosion is electrochemical

Galvanic cell is necessaryGalvanic 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

No dissolution at cathode

Corrosion Corrosion

What constitutes an anode/cathode pair?What constitutes an anode/cathode pair?

Zn Cu

electrolyte

electrical connection

Dissimilar metalsDissimilar 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