LAUSR

This paper aims to understand the effect of the type of bainite (i.e., the lower, the upper and the granular, developed by bainitic hardening at 550, 650 and 750 °C, respectively) on the evolution of carbide constituent due to a subsequent aging (at 700 °C for up to 500 h). The secondary carbides were identified by x-ray diffraction in the configurations of M3C, M7C3, M23C6, M2C, M6C and MC (M=Fe, Cr, Mo, Mn and V), which varied with the time of aging. Despite that the three types of bainites shared similar constituent of carbides after the aging for 2-100 h, the constituent of the upper bainite (M7C3 + M23C6 + MC) was different from that of granular bainite and lower bainite (M7C3 + M23C6 + MC + M6C) after the aging for 500 h. The concentration of the enrichment of alloying elements in ferrite matrix plays a dominant role in governing the precipitation of carbides in the aged steel.