Microstructure and properties of borided layer on medium-carbon high-strength bainitic steel treated by boro-austempering treatment

The integration of boronizing and austempering termed boro-austempering treatment is a new processing route for preparing high strength bainitic steel with high surface hardness and high corrosion resistance. The microstructure and properties of a medium-carbon bainitic steel prepared by boro-austempering treatment were characterized and analyzed. The results show that a single Fe₂B layer on bainite substrate was obtained with surface hardness of ~ 1400 HV, and the critical load for adhesive failure of borided layer reached 73.6 N. The silicon-rich α-Fe phase in transition zone was clarified as ferrite, which was formed at the beginning stage of cooling process from boronizing to low-temperature bainite transformation. Moreover, the relative potential differences between Fe₂B and bainite matrix, and ferrite and bainite matrix were 75 and 92 mV, respectively, with bainite matrix acting as active anode, indicating that the corrosion resistances of Fe₂B and ferrite were better than that of bainite.