Question

The cooling rate must be _________ the critical cooling rate for hardening of steel by quenching.

(a) Higher than

(b) Lower than

(c) Equal to

(d) Half of

The question was asked during an interview.

This interesting question is from Hardening and Hardenability topic in portion Heat Treatment of Engineering Material & Metallurgy

Answer 1

Right option is (a) Higher than

The explanation is: Post heating and soaking, the steels must be cooled. The cooling rate must be higher than the critical cooling rate to get the completely martensitic structure. The steel is quenched to room temperature with the help of a water bath or oil bath.