Tempering and secondary hardening of M 42 high-speed steel

Abstract

A detailed experimental study of the tempering and associated secondary hardening of M 42 high–speed steel is described. Analytical electron microscopy has been used to study the carbide reactions occurring over the temperature range 380 to 800°C after tempering for 2+2 h. The secondary hardening carbide was found to be face–centred cubic M2C containing an approximately constant 55 at.–%Mo over the entire temperature range of its stability. The vanadium content of this carbide decreased from about 30 to below 20 at.–% in the temperature range 380 to 600°C,while the chromium content increased from about 10 to 20 at.–%. It has been found that the secondary vanadium carbide V4C3 (MC type), containing 67 at.–%V and 18 at.–%Mo, precipitated after tempering for 24 h at 700°C, which is well beyond the secondary hardening range.MST/234