Step Cooling in Alloy Steel

Temper embrittlement is the characteristics of various alloy steel (especially the ones having impurities especially Sb, Sn, S, As etc) to have a significant drop in toughness and the impact properties.

For many steels this happen in two temperature ranges

Irreversible- formation of carbide films on grain boundaries. the brittleness does not return if re-heated.

Reversible Temper embrittlement - Due to precipitation of impurities on the grain boundaries rather than these being spread across the matrix. This is usually at a higher temperature.

The method to avoid is usually simple. Do not let the steel to stand on this range, quickly quench across this range (this quenching is done even if you are normalising or annealing the steel) - do the usual HT till the upper temp range is reached, quench to the lower range - restart the cycle from here- till the second embrittlement temperature (if exist) is reached then quench through it.

Hope it clarifies all the questions.