X-RAY-DIFFRACTION STUDY OF PRECIPITATION IN MELT-SPUN HIGH-SPEED STEELS

The high speed steels ASP30 and ASP60 were rapidly quenched from the m elt using the melt spinning method. Their structure was investigated i n the as-quenched state as well as in-situ during annealing at 560-deg rees-C and 700-degrees-C, respectively. The carbide precipitates were identified by wide angle X-ray diffraction. For the small angle X-ray scattering measurements (down to Q(min) = 2 x 10(-3) angstrom-1) a lab oratory-built pin-hole instrument, equipped with a furnace and a 2-dim ensional detector, was used. Slowly growing M6C-carbides are the domin ant precipitates. Rapidly growing MC-carbides are present in ASP60 wit h a smaller fraction, but no M2C-carbides develop. The coarsening of t he precipitates saturates at long annealing times. The Johnson-Mehl-Av rami analysis of the evolution of the volume fraction of M6C in ASP60 indicates a transition in the precipitation kinetics.