Flow curves up to peak strength of hot deformed D2 and W1 tool steels

Abstract

A high carbon, high chromium cold work die steel (D2) and a water hardenable carbon tool steel (W1) were hot deformed in torsion between 900 and 1150°C for the alloy steel and 900 and 1200°C for the carbon steel, at strain rates from 0·1 to 4 s^-1. The slope of the stress–strain curves, which represents strain hardening, decreased linearly then changed gradually to a slower linear decline before decreasing quickly to zero at the peak stress. On further strain, stress decreased to a steady state regime, indicative of dynamic recrystallisation. Kocks–Mecking analysis provided an activation enthalpy with an average comparable to the activation energy derived from a sinh modified Arrhenius analysis of peak stress. The alloy carbides of the D2 steel have the effect of raising its strength to over twice that of the carbon steel, accelerating the onset of dynamic recrystallisation but drastically lowering its ductility.