Tool Steels. On the High Impact Value Heat Treatment, AHIT.

When heat treating hot working dies, it is important to harden with high cooling rate to obtain high toughness without distortion. These two, high toughness and small distortion, are competing each other and difficult to be obtained at the same time. The heat treatment process has been newly developed under the name of AHIT process: Amister High Impact Value Treatment. This process is based on three fundamental concepts: to prevent carbides precipitation along grain boundaries at high temperature, to make die internal temperature distribution uniform in the middle temperature region and to suppress Bainitic transformation. The distortion of the dies processed by AHIT is almost one half the one of blow quenched ones. And the toughness is 1.7to 2 times higher than conventionally heat treated ones, which results in improved heat check resistance. AHIT process has established 40% reduction in finish machining time after heat treatment due to small distortion.