Effect of austenitizing temperature on grain size, carbides and toughness of low C-Cr-Mo-Ni bearing steel

Abstract

In order to investigate the microstructure and toughness of low carbon chromium molybdenum nickel bearing steel under different heat treatment processes, an austenitic isothermal insulation test is performed. The effects of heating temperature and holding time on the austenite grain size, carbides and impact energy of low-carbon chromium-molybdenum-nickel bearing steel are studied. The results show that when the austenitizing temperature is not higher than 1 070 ℃, the carbides in the steel do not dissolve significantly, the area percentage of carbides is 1.93%, the austenite grain growth is not obvious, the average grain size is 49 μm, and the impact energy absorption is greater than 50 J. When the austenitizing temperature is 1 080 ℃ or higher, the carbide area percentage is 1.23%, while the carbide area percentage is 0.16% at 1 090 ℃, and the carbides dissolve in large quantities, resulting in a nailing effect and bigger austenite grains, and the impact energy absorption drops sharply to less than 30 J. When the holding time is longer than 45 min, the grain size tends to be stable. According to the test results, a grain growth model of the test steel heated at 1 050~1 090 ℃ for 15~60 min is provided, which can provide theoretical basis for the design of the heat treatment process for the steel.

Keywords

• non-ferrous metal and its alloys; bearing steel; austenitizing temperature; grain; carbide