Control Of Microstructure And Property For Gear Steel 16MnCr5

In recent years, the development of China's automobile industry is so rapid that China has become the world's third largest vehicle-producing country following the United States and Japan and become the world's second largest auto consumer over Japan. Gear is an important vehicle part, whose consumption rapidly increases. Therefore, the prospect of gear steel is bright. Major gear manufacturers lay emphasis on the development and research of steel gear in order to improve the market competitiveness. In this paper, based on Baosteel Special Steel Branch wire rod production line, the production processes of the gear steel 16MnCr5 was optimized by the thermal simulation experiments.Investigations were conducted upon transformation and microstructure change of austenite during controlled cooling processes with different prior states. CCT diagrams were determined for austenite without deformation and with true strain 0.5 compressive deformation at 860℃, respectively, after reheating 1200℃. Optical micrographs were obtained. The compressive deformation at 860℃promotes polygonal ferrite transformation during continuous cooling. Pearlite and polygonal ferrite are formed in the un-deformed and un-recrystallized austenite when cooled at a cooling rate no more than 0.025℃/s and 0.2℃/s, respectively. Pearlite and polygonal ferrite are formed when the steel is continuously cooled at rate no more than 0.05℃/s and held isothermally between 620℃and 700℃,after deformation at 1100℃at which austenite is recrystallized dynamically.Implementing the single-pass and multi-pass deformation in thermal simulation machine, single-pass, multi-pass deformation stress-strain curves and microstructure of the multi-pass deformation were analysed. Single-pass, multi-pass deformation stress-strain curves show that as the temperature drops, roll force significantly increasesm,, so that rolling at the scene should be accomplished in the high-temperature. Multi-pass deformation also shows that in high-temperature rolling process, the material will be softened as a result of the recovery and recrystallization, so the rolling force is reduced and the time interval of the passes of rough rolling should be longer. Through the combination of multi-pass deformation analysis and the actual production at the scene, all-pass deformation has been educed and the end of the rolling deformation temperature should be 900℃. The research topic optimizes the gear steel 16MnCr5 production process and provides thetheoretical foundation for other types of gear steel for further study.