Hardenability Flashcards
Hardenability effects
> 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
Fe-C alloys have ____ hardenability
low
Increase in the carbon content of steel increases
hardness of martensite significantly, but it ____ ___ increase hardenability proportionally.
does not
Higher amounts of B lead to precipitation of brittle Fe2B phase, which ______ in toughness of steel
decrease
Due to its ___ _____, B is segregates on the austenite grain boundaries and reduces grain boundary energy
low solubility
>
B ____ heterogeneous nucleation rate of pro-eutectoid ferrite, which shifts the C-curves for austenite to ferrite transformation to right and increases hardenability.
decreases
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
not
Boron hardenability factor _____ with increase in carbon wt%
decreases
Boron \_\_\_\_\_\_ hardenability of a hypo-eutectoid steel, it has \_\_\_\_\_\_ on the hardenability of eutectoid steel, and it \_\_\_\_\_\_ hardenability of hyper- eutectoid steels
increases; no effect; decreases
B can compensate for loss of hardenability due
to fine austenite grain size because
with finer austenite grains, boron multiplier factor increases
Quenching medium: rate of cooling depends on
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.
Stages of quenching
- formation of insulating barrier around surface, decreases cooling rate
- water comes into contact with steel, increases cooling rate
- specimen temperature decreases below boiling point of oil, the heat is, extracted only by convection, and cooling rate is low.
Brine yields the ____ cooling rate and oil gives the
____ cooling rate.
highest; lowest
If hardenability is low, a ____ cooling is needed to
producemartensite
faster
_____ coolingleadsto
higher residual stresses, distortion and cracking
faster