Microstructure And Mechanical Properties Of High-carbon Bearing Steels After Q&P

In this paper, we studied the microstructure and mechanical properties of martensite andretained austenite obtained after the quenching and partitioning in the high-carbon bearingsteels. The microstructure of samples after Q&P was examined by optical microscopy,scanning electron microscopy, transmission electron microscopy and X-ray diffractionand the hardness, impact toughness and tensile strength were tested in the roomtemperature. Based on the above results, we selected an optimum heat-treatment as thepotential use of bearing.The Ac1s、Ac1fand Mswere determined by DIL and Gleeble-3500. The quenching andpartitioning heat-treatment were determined by the formula ofMagee-Koistinen-Marburger. The microstructure consisted of martensite, retainedaustenite and undissolved carbides. The mean thickness of martensite was on a range of80nm-137nm. The volume fraction of retained austenite on a range of12%-25%due todifferent heat-treatments. The undissolved carbides were and5%-7%.The results of high-carbon bearing steels indicated that: The hardness decreasesdwith the increasing of partioning temperature and time and the impact toughness energy、ultimate tensile strength and yield strength increased with the increasing of partioningtemperature and time. Based on the analysis of microstructure and mechanical properties,the optimum mechanical properties of hardness、impact toughness energy、ultimate tensilestrength and yield strength were61.9±0.8HRC、96J、2291MPa and1820MParespectively in the steel of1.2Si after austenitizing at880℃for1h followed by waterquenched to60℃austempered for1min and then partitioning at400℃in salt bath for60s and finally water quenched to room temperature. The optimum mechanical propertiesof hardness、impact toughness energy、ultimate tensile strength and yield strength were61.9±1HRC、85J、2123MPa and1702MPa respectively in the steel of A afteraustenitizing at890℃for1h followed by water quenched to60℃austempered for1min and then partitioning at400℃in salt bath for60s and finally water quenched toroom temperature.