The Effect of Bainite Type on the Evolution of Carbide Constituent During an Accelerated Aging in Cr-Mo-V Steel

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.