Effects of deformation and heating temperature on the austenite transformation to pearlite in high alloy tool steels

Abstract

Two tool steels designated M2 (based on Fe-0.8C-4Cr-5Mo-7W-2V) and A2 (based on Fe-1.0C-5Cr-1Mo-V, all wt-%) were preheated and rolled in three passes to a total reduction of 50% in the range 880 to 1150°C in which alloy carbides are dissolved to varying degree. The rate of isothermal transformation was determined by dilatometry for undeformed or deformed austenite related to annealing at 880°C or rolling from 1150°C preheat for steel M2 and thermomechanical processing (TMP) at 980°C for steel A2. The deformation accelerates the transformation to pearlite, but the high solution temperature retards it so that the net effect in hot rolled M2 (1150°C) is retardation relative to annealed (880°C). In A2, TMP at 980°C results in acceleration compared to simply heat-treated and thus a reduction in hardenability. Carbide precipitation prior to the pearlite transformation is also enhanced by the deformation. The final hardness of the deformed steels is much greater than that of heat-treated steels.