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Quench severities. 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?.

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Quench severities

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Quench severities


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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?


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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


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Example quench design problems

7

Quench severity ≈ 1.25. What is hardness at center?


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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 ≈ 53


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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)


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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


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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


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Corrosion

Ex: Cu & Zn

(Zn corrodes)

electrical connection

Zn

Cu

electrolyte

What constitutes an anode/cathode pair?

Dissimilar metals

How do we know?

Many combos tried experimentally


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Corrosion

more cathodic

electrical connection

electrical connection

Zn

anode

Cu

cathode

electrolyte

electrolyte

more anodic

Result: the galvanic series


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Corrosion

Ex:

1 contains little dissolved oxygen

2 contains much dissolved oxygen

1

2

What constitutes an anode/cathode pair?

Dissimilar metals

Different electrolytes


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Corrosion

Practical example:

crevice corrosion

1

2

What constitutes an anode/cathode pair?

Dissimilar metals

Different electrolytes


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Corrosion

Deformation ––>

non-homogeneous

residual stress

1

2

What constitutes an anode/cathode pair?

Dissimilar metals

Different electrolytes


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Corrosion

Deformation ––>

non-homogeneous

residual stress

1

2

What constitutes an anode/cathode pair?

Dissimilar metals

Different electrolytes

Non-passivated vs. passivated metal or alloy


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Corrosion

What constitutes an anode/cathode pair?

In summary–

Anything that makes two half-cells different gives anode & cathode

––> corrosion

We can call these types macro cells


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Corrosion

Then what about micro cells?

anode & cathode within single material

operating on a micro scale

Grain boundary - high energy region…anodic wrt bulk of grain

Differently oriented grains - some planes of atoms dissolve faster than others

Segregation (coring)


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Corrosion

Then what about micro cells?

anode & cathode within single material

operating on a micro scale

Segregation (coring)


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