Characterization on Microstructure and Carbides in an Austenitic Hot-work Die Steel during ESR Solidification Process

Abstract

The current work was undertaken to systematically examine the as-cast microstructure and carbides in a developed austenitic hot work die steel produced by conventional electroslag remelting (ESR) and continuous directional solidification of electroslag remelting (ESR-CDS). In addition, the growth pattern of carbides was also discussed. A combination of optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize microstructure and carbides. The segregation was analyzed using an original position analyzer (OPA) and electron probe microanalysis (EPMA). The electrolytically extracted carbides were analyzed by SEM and x-ray diffraction (XRD) to identify their three-dimensional microstructure and compositions. The microstructure of electroslag remelted austenitic die steel was composed of austenite matrix and primary carbides V₈C₇-type and Mo₂C-type. Compared with conventional ESR, ESR-CDS contributed to a finer as-cast microstructure, a smaller amount and smaller size of carbides in remelted steel. Meanwhile, the alloying elements segregation was reduced through ESR-CDS. The enrichment of carbide-forming elements was reduced through directional solidification of ESR, resulting in the change in the morphology of V-rich carbides from rod-like to lamellar-shaped. The hardness and V-notched impact energies of remelted ingot (produced by ESR-CDS) after heat treatment (solution temperature 1180°C for 2 hours, aging temperature 720°C for 2 hours) was increased by 3 to 5HRC and 4 to 6 J/cm2 respectively, in comparison with that produced by conventional ESR.