X-ray diffraction study of precipitation in melt-spun high speed steels

The high speed steels ASP30 and ASP60 were rapidly quenched from the melt using the melt spinning method. Their structure was investigated in the as-quenched state as well as in-situ during annealing at 560 °C and 700 °C, respectively. The carbide precipitates were identified by wide angle X-ray diffraction. For the small angle X-ray scattering measurements (down to Qmin= 2 x 10-3Å-1) a laboratory-built pin hole instrument, equipped with a furnace and a 2-dimensional detector, was used. Slowly growing M6C-carbides are the dominant precipitates. Rapidly growing MC-carbides are present in ASP60 with a smaller fraction, but no M2C-carbides develop. The coarsening of the precipitates saturates at long annealing times. The Johnson-Mehl-Avrami analysis of the evolution of the volume fraction of M6C in ASP60 indicates a transition in the precipitation kinetics.