Study of uniform quenching technology of NM450 wear-resistant steel

State Key Lab of Rolling and Automation, Northeastern University, Shenyang City, Liaoning Province, P.R. China
e-mail: ral_wangchao@163.com

Received: 21 June 2013
Accepted: 10 October 2013

Abstract

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.