Effect of matrix microhardness on thermal fatigue behaviour of spincast high speed steels for hot rolls

The effect of the matrix hardness on thermal fatigue resistance of some high speed steels (HSS) with different amounts and types of eutectic carbides was studied. The increase in matrix hardness increases thermal fatigue crack density, while the effect on mean length cannot be generalised. The effect on crack density was explained by considering the mechanism responsible for crack nucleation, which involves propagation of small cracks through the metallic matrix. The effect of the interconnection of carbides was confirmed: the less their interconnection, the lower the crack density. The interdendritic MC and M7C3 carbides have an opposite effect, due to the large differences in hardness and brittleness.