The Effect of Matrix Component on the Precipitation Strengthening of Austenitic Hot Work Die Steels

Abstract

An attempt has been made to survey the effect of Ni, Cr and Mn in the matrix on the precipitation strengthening of austenitic hot work die steels containing 0.5%C and 2%V. The materials tested are a Fe-Cr-Ni austenitic steel with 15%Cr and 15%Ni and two kinds of Fe-Cr-Ni-Mn austenitic steels in which some of Ni is replased by 13% and 25% Mn respectively. Cr is decreased with the increase of Mn in order to suppress the precipitation of σ-phase.
The maximum hardness of Fe-Cr-Ni-Mn steels are much higher than that of Fe-Cr-Ni steel, while the maximum hardness decreases slightly when Mn increases from 13% to 25%.
The hardness in the early aging stage rises more rapidly with the increase of Mn content. This is probably attributed to the difference of the amount of C and V in matrix when solution treated and the difference of the coherency between the matrix and VC carbide which precipitates during aging. The elongation and reduction in area of aged steels decrease markedly with the increase of Mn content, because the fracture occurs on the grain boundary. But, it is possible to improve them by hot rolling at about 1 200°C before aging without the decrease of the strength.