Thermal fatigue resistance of the salt quenched AISI H11 hot work tool steel

In the present work the thermal fatigue resistance of a typical hot work tool steel was studied. The material was subjected to salt quenching, by cooling the specimens in two different ways (520oC and then to room temperature, 220oC and then room temperature). The first cooling cycle produces a coarser microstructure than the second one, and induces the formation of upper bainite. While the thermal fatigue crack density is the same in the two materials, a clear difference in their propagation was found. The coarser microstructure and the presence of upper tend to reduce the thermal fatigue resistance. (author)