Abstract
In this paper, the scientific challenges associated with obtaining high impact toughness in the medium-Mn TRIP steel, Fe-0.2C-6Mn-1.5Al, have been explored. This was enabled by a novel and effective heat treatment involving the combination of intercritical hardening and tempering to obtain high impact toughness. Electron microscopy and x-ray diffraction studies clearly underscored absence of TRIP effect in Fe-0.2C-6Mn-1.5Al medium manganese steel during impact and the volume fraction of austenite played a determining role in governing impact toughness. The highest impact toughness of 180.17 J/cm2 was obtained when the steel was subjected to intercritical hardening temperature of 630 °C and low tempering temperature of 200 °C. The presence of martensite in the microstructure reduced the impact toughness on quenching from 670 to 700 °C. When the quenching temperature was increased to 750 °C, the impact toughness of steel was slightly increased, which is ascribed to the supersaturated carbon in martensite that precipitated as carbides. The fracture mode was ductile after intercritical hardening in the temperature range of 600-700 °C.
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