Phase transformation study of a high speed steel powder by high temperature X-ray diffraction

The combined utilization of an X-ray diffractometer and a high temperature chamber is used for the direct observation of phase transformations, changes in lattice imperfections, chemistry and the structure of the phases of a high speed steel powder. M6C-carbides are at first suppressed for the high cooling rates during atomization and only MC-carbides are detected at room temperature. The high amount of retained austenite of the origin powder is associated with interstitially dissolved carbon. During heating-up above 710 °C the formation of M6C-carbides occurs simultaneously with the transformation of austenite to a body centered cubic structure. Above 800 °C a significant decrease of the MC-carbides occurs; a direct transformation of the MC to M6C-carbides was not found. The formation and dissolving of carbides occurs only in an interaction with the austenite, martensite and bainite. Therefore the carbon content of the matrix influences the nature and course of transformations. After the whole heat treatment the mixture of phases gets nearer to an equilibrium.