Hardenability Flashcards

1
Q

Hardenability effects

A

> increase in cc, increase in hardenability and Di
fine austenite grains, lower hardenability as lower Di
cobalt decreases hardenability
effect of boron depends on CC
Mn, Cr, Mo, and V substantially increase hardenability of steel

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2
Q

Fe-C alloys have ____ hardenability

A

low

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3
Q

Increase in the carbon content of steel increases

hardness of martensite significantly, but it ____ ___ increase hardenability proportionally.

A

does not

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4
Q

Higher amounts of B lead to precipitation of brittle Fe2B phase, which ______ in toughness of steel

A

decrease

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5
Q

Due to its ___ _____, B is segregates on the austenite grain boundaries and reduces grain boundary energy

A

low solubility

>

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6
Q

B ____ heterogeneous nucleation rate of pro-eutectoid ferrite, which shifts the C-curves for austenite to ferrite transformation to right and increases hardenability.

A

decreases

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7
Q

Gibbs free energies, Gv, and Ms of austenite, ferrite, pearlite, and martensite, diffusion coefficient, hardenability of eutectoid steel and nuc and growth are ___ affected by B

A

not

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8
Q

Boron hardenability factor _____ with increase in carbon wt%

A

decreases

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9
Q
Boron \_\_\_\_\_\_ hardenability of a 
hypo-eutectoid steel, it has \_\_\_\_\_\_ on 
the hardenability of eutectoid steel, and 
it \_\_\_\_\_\_ hardenability of hyper-
eutectoid steels
A

increases; no effect; decreases

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10
Q

B can compensate for loss of hardenability due

to fine austenite grain size because

A

with finer austenite grains, boron multiplier factor increases

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11
Q

Quenching medium: rate of cooling depends on

A

on the rate at which quenching medium can remove the heat from the surface and the rate at which the heat is transferred from interior to the surface of steel.

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12
Q

Stages of quenching

A
  1. formation of insulating barrier around surface, decreases cooling rate
  2. water comes into contact with steel, increases cooling rate
  3. specimen temperature decreases below boiling point of oil, the heat is, extracted only by convection, and cooling rate is low.
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13
Q

Brine yields the ____ cooling rate and oil gives the

____ cooling rate.

A

highest; lowest

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14
Q

If hardenability is low, a ____ cooling is needed to

producemartensite

A

faster

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15
Q

_____ coolingleadsto

higher residual stresses, distortion and cracking

A

faster

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16
Q

Why isn’t hardenability always wanted?

A

High hardenability steels are difficult to weld
successfully; high hardenability leads to formation of
martensite in the heat affected zone, which may lead to
cracking