Mechanism of Strength-Toughness of High Manganese Austenitic Hot-Work Die Steel Refined by Electroslag Remelting Continuous Directional Solidification Technology

摘要

The working temperatures for molding cavities served as copper extrusion die range from 700 °C to 900 °C. The service conditions of extruding dies for copper alloys are very rigorous. In fact, hot-work die steels with martensite matrix, including 3Cr2W8V, H13, THG2000 and QRO90, are widely used in industrial applications . In many cases, the temperature at the surface of dies may reaches up to 600 °C or exceeds the tempering temperature of steel, inevitably leading to the cumulative effect of tempering and certainly affect properties of dies such as hot hardness, temper resistance and high-temperature fatigue strength. In recent years, austenitic hot-work die steels have attracted researchers' attentions in order to improve the strength of die steels at the temperatures higher than 600 °C The stable austenitic structure is composited by Fe-Cr-Ni, Fe-Cr-Mn and Fe-Mn-C alloy system. Grabovskii et al. reported that austenitic hot-work die steels EK39 and EK40 provided by Fe-Cr-Ni matrix have good hot-hardness, good impact toughness and good thermal stability, and these steels can preferably meet requirements of extrusion for copper at service temperature above 700°C. Austentic hot-work steel with low thermal conductivity, tends to produce solidification mushy zone in the casting process, which will lead to the center segregation, porosity and the shrinkage cavity. Fu et al. demonstrates that the combination of directional solidification technology with electroslag remelting technology (ESR) effectively eliminates macro-segregation in as-cast ingot through the shallow molten metal pool controlled by directional solidification. In this work, the effect of electroslag remelting continuous directional solidification (ESR-CDS) on the microstructure in as-cast ingot and primary carbides evolution during heat treatment process was studied. Moreover, the mechanism of strength-toughness of high manganese austenitic hot-work die steel was discussed.