Phase transformation refinement of coarse primary carbides in M2 high speed steel

The decomposition of the coarse primary M2C carbide in M2 high speed steel was investigated by using optical microscope, scanning electron microscope, energy dispersive spectrometer and X-ray diffraction analysis. It is indicated that the SEM observation using deeply etched samples can clearly reveal the details of the decomposition products of primary M2C eutectic carbides. The MC is granular and M6C is peanut-shaped in the decomposition products, and the decomposition products are found to be very small in the size. With the increase of annealing temperature and duration, part of the peanut-shaped M6C carbides change to simple skeleton-shaped ones. The phase transformation refinement of primary M2C carbides in M2 steel by the decomposition of metastable M2C carbides at high temperature can be obtained if suitable annealing parameters are applied. The complete decomposition of M2C to M6C and MC will occur when (1 100 °C, 4 h) or (1 150 °C, 2 h) annealing treatment is employed in M2 high speed steel.