Effect of austempering time on microstructure and properties of a low-carbon bainite steel

The effect of austempering time after the bainitic transformation on the microstructure and property in a low-carbon bainite steel was investigated by metallography and dilatometry. The results showed that by prolonging the austempering time after the bainite transformation, the amount of large-size martensite/austenite islands decreased, but no significant change of the amount and morphology of bainite were observed. In addition, more austenite with a high carbon content was retained by prolonging the holding time at the bainite transformation temperature. Moreover, with a longer holding time, the elongation was improved at the expense of a small decrease in tensile strength. Finally, the Avrami equation B_RF = 1− exp(−0.0499 × t^0.7616) for bainite reaction at 350°C was obtained for the tested steel. The work provided a reference for tailoring the properties of low-carbon steels.