Transformation behavior of primary MCand MC2carbides in Cr4Mo4V steel

The transformation of primary MCand MC2carbides, during high-temperature treatment, was investigated by quasi in-situ observation of Cr4Mo4V steel. It was found that the V-rich rod-like MC carbides have great thermal stability, and disintegrating and coarsening are their dominant transformation mechanisms. The MC2carbides mainly possess rod-like (MC-R2) and lamellar (MC-L2) morphologies. The MC-R2carbides are Mo-enriched, and their transformation follows the paths: the separate precipitation of MC and MC-R2+ MC + MC6. The V- and Fe-rich MC carbides nucleates randomly in the interior of MC-R2before the nucleation of Mo- and Fe-rich MC6carbides, which is controlled by the diffusion of V. Soaking for longer durations can cause spheroidization and coarsening of the MC carbides, along with the dissolution of MC6carbides. The evolution of Fe- and Mo-rich MC-L2carbides consists of two stages: the partial dissolution of MC-L2into the matrix and the transformation of MC-L2MC + . These novel findings contribute towards the understanding of how primary carbides evolve during heat treatment and provide a potential method for carbides refinement in Cr4Mo4V steel.