Tempering Response of Direct-Quenched and Reheat-and-Quenched Low-Carbon Martensitic Steels

摘要

The microstructure and mechanical properties of a 0.12 wt-pct carbon, low-alloy, martensitic steel produced by direct quenching after hot rolling to various finishing temperatures were compared to those of the steel processed by reaustenitizing, quenching and tempering. Tempering time and temperature varied between 1 and 64 h and 350 to 650℃, and mechanical property results were plotted as a function of a Hollomon-Jaffe time-temperature parameter. Although all steels exhibited secondary hardening behavior, the direct-quenched steels consistently showed higher tempered strength than the reaustenitized-and-quenched steel, with the steels finished at the lower temperatures showing the highest strengths. A difference of up to 150 Mpa was found between the direct-quenched steel with the lowest finishing temperature and the reaustenitized-and-quenched steel. Severe tempering led to recrystallization in all steels, resulting in sharp drops in strength and rapid increases in ductility. Strength-ductility relationships reveal distinct ranges of property combinations that rank according to thermomechani-cal processing treatment.