Hardenability

Question 1

Hardenability effects

Answer 1

> 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

Question 2

Fe-C alloys have ____ hardenability

Answer 2

low

Question 3

Increase in the carbon content of steel increases

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

Answer 3

does not

Question 4

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

Answer 4

decrease

Question 5

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

Answer 5

low solubility

>

Question 6

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

Answer 6

decreases

Question 7

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

Answer 7

not

Question 8

Boron hardenability factor _____ with increase in carbon wt%

Answer 8

decreases

Question 9

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

Answer 9

increases; no effect; decreases

Question 10

B can compensate for loss of hardenability due

to fine austenite grain size because

Answer 10

with finer austenite grains, boron multiplier factor increases

Question 11

Quenching medium: rate of cooling depends on

Answer 11

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.

Question 12

Stages of quenching

Answer 12

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.

Question 13

Brine yields the ____ cooling rate and oil gives the

____ cooling rate.

Answer 13

highest; lowest

Question 14

If hardenability is low, a ____ cooling is needed to

producemartensite

Answer 14

faster

Question 15

_____ coolingleadsto

higher residual stresses, distortion and cracking

Answer 15

faster

Question 16

Why isn’t hardenability always wanted?

Answer 16

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