When ferrous metals are induction hardened, quenching is just as important as the proper heating of the metal. Inadequate or improper quenching of the heated part results in low hardness values as well as spotty hardness and may cause quench cracking.
The intent of the quench is to cool the already austenitized material at a rate that converts most of the austenite to martensite. Grain size of the material is a major factor in conversion of the metal into austenite and then martensite. The smaller the grain, the faster the material will go into solution. Smaller grain sizes reduce the time required at temperature as well as the temperature necessary to go into solution. Accordingly, rolled, forged, annealed or previously quench-and-tempered materials will all be affected differently by the heat and quench cycles.