Retained Austenite Decomposition and Carbide Precipitation during Isothermal Tempering of a Medium- Carbon Low-Alloy Bainitic Steel

The effect of isothermal tempering on retained austenite decomposition and carbide precipitation were investigated in a medium-carbon low-alloy bainitic steel. High-resolution dilatometry was used to perform isothermal tempering at 350 degrees C, 550 degrees C and 600 degrees C for different holding times up to 16 h. The decomposition of retained austenite, morphology and composition of carbides were investigated by analyzing the dilatometric curves and were confirmed through scanning and transmission electron microscopy observations. The decomposition behavior of retained austenite varied significantly as a function of the tempering temperature with a full decomposition observed at 600 degrees C. It was also found that by increasing the tempering temperature from 550 degrees C to 600 degrees C, carbides precipitate approximately twice as fast, and evolve from M3C type to Cr7C3 and Cr23C6 after 16 h of tempering at 600 degrees C.