The minimum rate of continuous cooling just enough to prevent undesired transformations.
The slowest rate of cooling required to suppress phase changes. The term is most usually applied to the rate of quenching various products that are heated or “worked.” For example, the rate required to produce a martensic structure in the hardening of steel. The critical cooling rate in patenting is selected to provide minimum pearlitic spacing.
The minimum rate of cooling which will produce a fully martensitic microstructure in a steel when it is cooled from austenitic condition to room temperature. As the alloy content and carbon content of steel is increased the critical cooling rate of the steel decreases.