Simulation of precipitation of secondary carbides in hot work tool steels

Abstract

Precipitation of secondary carbides in hot work tool steels during tempering heat treatments has been investigated using simulations based on a thermodynamic description coupled with kinetic parameters through multicomponent nucleation and growth models. The simulations reproduce the measured effects of steel composition on the precipitation of secondary carbides. Both Si and V increase the volume fraction of fine secondary carbides precipitated during tempering provided that the austenitising temperature is adjusted to give the same fraction of retained primary carbides. The most important effect of Si in 5%Cr steels is its influence on the primary carbide stability at austenitisation temperatures, but increasing the V contents has a strong effect on the fraction of secondary carbides, without increasing the size, and can thus improve the yield strength. The most critical input to the calculations is the thermodynamic description of the individual phases.

Keywords:

• Precipitation
• Hot work tool steel
• Modelling
• Secondary carbides

Discussions with Dr H.-J. Jou, Ques Tek Innovations, on PrecipiCalc calculations and the influence of different calculation parameters are gratefully acknowledged. The present work was financed by competence development funds from RISE (Research Institutes of Sweden).