1987 Volume 27 Issue 1 Pages 51-59
Microstructures of hot work tool steels, AISI H13, HIO, and H19 tempered after quenching at various cooling rates are studied for improvements of the toughness of these steels. It is found that the development of upper bainite with decreasing rate of quenching is accompanied by the following microstructural changes.
1) Increase in the width and length of bainite grains and the effective grain size
2) Preferential precipitation of carbides along prior austenitegrain boundaries
3) Dispersion of fine carbides in matrix
These microstructural changes lead to reduction of the toughness in all the steels; deterioration occurs in H10 and H19 at a higher cooling rate than in H13. The toughness value reduces in the order of H13, H10, and H19, in good correlation with increasing order of the density of frne carbides in matrix and the fraction of retained carbides.
