Influence Of Process Parameters On Phase Stability In Powder Metallurgical High-Speed Steel During Integrated Hardening

The properties of tool steels are optimized through heat treatments tailored to the specific chemical composition and processing history. Understanding the kinetics of carbide dissolution, precipitation, growth, coarsening and their effect on the austenitic matrix, is essential. Modern hot isostatic presses allow the integration of the hardening process in powder-metallurgy, with isostatic pressure also influencing the transformation kinetics.This study investigates the stability of austenite with respect to a transformation into martensite in the powder-metallurgically produced high-speed steel PM HS 3-3-4, subjected to pressure-assisted heat treatments in a hot isostatic press. Based on experimental Ms and As temperatures, the T0 temperature was determined and compared with Calphad calculations and precipitate simulations. The key result is the identification of a pressure-dependent offset in the Gibbs-free-energy difference ?Giso, which quantifies the stabilizing effect of isostatic pressure on the austenite phase and enables the integration of isostatic pressure effects into existing simulation models.