Effect of microstructure on wear resistance during high temperature carburization heat treatment of heavy-duty gear steel

Abstract

To shorten the production cycle of heavy-duty gear steel and ensure its wear resistance, high temperature carburization, two high-temperature tempering, quenching, subzero treatment, and low-temperature tempering treatments were performed on 18Cr2Ni4WA steel in this work. The effect of surface precipitation phases and retained austenite on wear resistance after different heat treatments was studied throughout the process. The results show that an increase in the volume fraction (Vcar) and size (Dcar) of undissolved carbides and a decrease in the volume fraction of retained austenite (Vr) are beneficial to wear resistance. The Vcar increases from 3.4 % to 6.3 %, and the Dcar increases from 152 nm to 161 nm. The undissolved carbides are mainly cementite. The carbon content of retained austenite decreases from 1.02 % to 0.79 %, and Vr decreases from 40.6 % to 4.8 %. In addition, the microstrain increases from 0.386 % to 0.458 %, and the wear rate decreases from 0.49 × 10−8 mm3·N−1·mm−1 to 0.46 × 10−8 mm3·N−1·mm−1. The improvement in wear resistance is mainly attributed to solid solution strengthening of carbon atoms and precipitation strengthening of undissolved carbides.