Question

Specify a quency rate neccessary to ensure a hardness of at least rockwell C X in a Y Steel. Express the critical rate.

Answer 1

Critical Rate:-

The minimum rate of continuous cooling which is, just enough to avoid unwanted phase-conversions of the metal. For example, in case of steel, the slowest cooling rate at which it can be cooled form above the upper critical temperature to prevent the formation of Martensite at any temperature from unstable austenite.

The hardness in order of Rockwell C is done for high carbon steels, enough hard as like as cutting tools. The quenching rate necessary for the formation of these kinds of steels are 400-500 deg C/sec. The quenching would be Oils, Brine or may be water.