Microstructure and Performance of High Performance Bainitic Steel Prepared by Boronizing-austempering Process

The integrated process of 950 ℃ insulation for 2 h boron infiltration +350℃ insulation for 1h isothermal quenching was carried out for the medium carbon bainite steel, and it was compared with the sample without boron infiltration under the same process parameters. The microstructure and service performances of the ultra-fine grained bainitic steel prepared by boronizing-austempering process were studied through microstructure characterization, corrosion resistance and wear resistance tests. The results show that the ultra-fine bainite matrix structure is obtained after boronizing-austempering process, and a boronizing layer of about 29 μ m thickness is formed on the surface. There is an obvious dividing line between the boronizing layer and substrate, and the boronizing layer shows comb or needle shape, which is evenly distributed. The boron content in the boronizing layer is high, the carbon content and the silicon content in boronizing layer near the surface are low. During the corrosion in NaCl solution, the bainite matrix exhibits a higher current density than the boronizing layer, and with the increase of the corrosion time, the strong current region does not expand along the surface, but along the bainite matrix. Under the same wear condition, the total wear weight loss of non-boronizing samples is 2.2 times theas that of samples treated by boronizing-austempering process. The corrosion performance and wear resistance of the ultra-fine grained bainitic steel are enhanced significantly by boronizing-austempering process.