The finite difference method of the low-alloy wear-resistant steel quenching process was
studied. The temperature field and cooling rate variation of thickness of 45-mm
wear-resistant steel (NM450) were calculated for different quenching practices. The
microstructure and hardness of quenched plates were examined. The results indicate that
when quenching started, the cooling rate was highest on the subsurface and decreased
gradually until the center of the plate. However, as the quenching progressed, the cooling
rate distribution along the plate thickness was reversed. The cooling rate increased
linearly when the heat transfer coefficient (HTC) increased from 0–10 000
W/m2 K, and then the speed gradually slowed down until achieving the maximum
cooling rate. Close to the plate mid-thickness, the maximum cooling rate was easily
reached. Compared with high-pressure (HP) quenching and low-pressure (LP) quenching, under
the HP + LP continuous quenching mode, it is possible to obtain a high critical cooling
rate in the temperature range of 900 °C–400 °C and small temperature difference between
the surface and center below 400 °C. The microstructure and hardness distribution on the
plate surface for the HP + LP quenching mode indicated 100% martensite on the surface and
martensite with a little granular bainite in the plate center, while the hardness
difference in the entire steel plate was less than 7%. This study provided guidance for
the formulation and optimization of wear-resistant steel.