Effect of Quenching and Tempering Temperatures on Microstructure and Properties of Nb and N Microalloyed GCr15 High Carbon Chromium Bearing Steel

The annealed Nb and N microalloyed GCr15 high carbon chromium bearing steel was quenched at 810–900 ℃ for 1 h and tempered at 170–230 ℃ for 4 h. The effect of quenching and tempering temperatures on the microstructure and wear resistance of the test steel were studied, and the optimal heat treatment process was obtained. The results show that after quenching, the microstructure of the test steel was composed of martensite, undissolved carbides and retained austenite. With the increase of quenching temperature, the martensite changed from fine cryptocrystalline state to coarse needle-like plates, and the prior austenite grain size and carbide size decreased and then increased, reaching the minimum at the quenching temperature of 840 ℃. With the increase of tempering temperature, the content of martensite in the tempered steel increased, the content of retained austenite decreased, the carbides were coarsened, the hardness decreased first and then increased slightly, and the wear rate increased. After tempering at 170 ℃, the wear surface of test steel was smooth, the number of furrows was small, plastic deformation and oxidation traces appeared on the wear surface, and the wear resistance was better. The reasonable quenching temperature of the test steel was 840 ℃, and the tempering temperature was 170 ℃.