Structure, nucleation, growth and morphology of secondary carbides in high chromium and Cr-Ni white cast irons

Abstract

Heat-treated high chromium and Cr-Ni white cast irons are widely used by the mining and mineral industries for impact and abrasion resistance. With certain heat treatments, Fe-Cr carbides are precipitated within the chromium- and carbon-rich austenitic matrix, thereby destabilizing the austenite which transforms substantially to martensite on subsequent cooling. The crystal structures of these carbides were determined indirectly by referring electron microprobe analyses of the austenitic matrix to the appropriate isothermal solid-state sections of the Fe-Cr-C phase diagram and directly by microprobe analyses of exposed secondary carbides. The nucleation, growth and morphology of these carbides were studied by a combination of selective removal of the austenitic matrix and subsequent scanning electron microscopy of the exposed carbides.