Reversion of strain induced martensite to achieve high strength and ductility in AISI 304 L

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This work presents an optimized thermo-mechanical processing route to produce ultrafine grained AISI 304 L stainless steel with enhanced strength. Here AISI 304 L was rolled to 93% thickness reduction at room temperature to form 70% strain induced martensite with the remaining phase being untransformed deformed austenite. Subsequently, this was subjected to a thermal treatment in the range of 650–750 °C with time ranging from 10 to 1440 min so as to revert the strain induced martensite to ultrafine grained austenite. The median grain size obtained after different reversion treatments varied from 0.42 to 1.2 μm. The major texture components observed after reversion at 650 and 700 °C were {110}〈112〉 Brass and {123}〈634〉 S, whereas those observed after reversion at 750 °C were {110}〈112〉 Brass, {123}〈634〉 S and {113}〈112〉 R. Tensile tests showed a higher strength (but lower ductility) along the transverse direction as compared to that along the rolling direction. The yield strengths obtained after reversions at different temperatures and times were correlated with grain size, dislocation density and texture. A combination of high tensile strength and good ductility was obtained in the rolling direction after reversion at 700 °C for 60 min (900 MPa and 45% ductility) and at 750 °C for 10 min (900 MPa and 55% ductility).