Heat Treatment Response of GCr15 Bearing Steel under Annealing, Quenching and Low-Temperature Tempering Conditions

Abstract

GCr15 high-carbon chromium bearing steel is a key material for rolling bearing components, and its heat treatment process directly affects microstructure and hardness. In response to the requirements of bearing-steel processing and final hardening, this study investigated the effects of annealing temperature, quenching temperature and low-temperature tempering holding time on the optical microstructure and hardness of industrial GCr15 steel. Five replicate hardness measurements were conducted for each condition. The experimental results show that annealing at 780 °C for 3 h followed by furnace cooling produced relatively uniform spheroidized carbides and the highest annealed hardness of 214 ± 2.0 HBW among the tested conditions. For the subsequent quenching trials, the same annealing condition of 780 °C for 3 h with furnace cooling was used as the pre-treatment. Austenitization at 840 °C for 0.5 h followed by oil quenching gave the maximum hardness of 61.4 ± 2.6 HRC, while lower temperatures showed insufficient hardening and higher temperatures showed evidence of coarser martensitic morphology. For specimens annealed at 780 °C for 3 h and austenitized at 840 °C for 0.5 h, tempering at 150 °C for 5 h provided a hardness of 58.2 ± 1.1 HRC and a more stable tempered martensitic appearance under optical microscopy. Because the study was limited to optical microscopy and hardness testing, wear resistance, fatigue performance, retained austenite fraction and carbide morphology require further verification by SEM, XRD/EBSD and bearing-related mechanical tests.