Abstract
A novel high-strength steel has been made through thermo-mechanical controlled processing with the finish rolling temperature of 750°C followed by air cooling. Subsequently, both partial austenitisation at 800°C and fully austenitisation at 930°C have been attempted for equal duration of 30min prior to one step quenching and partitioning (Q&P) at 345°C below MS temperature (365°C). As-rolled steel reveals ferrite-bainite-martensite microstructures with a good combination of strength and ductility. After Q&P, all the specimens have exhibited the multiphase microstructures comprising ferrite, lath microstructure (martensite and bainite), and retained austenite with the volume fractions of up to 10.50wt%. It is evident that partitioning for 30min leads to good carbon enrichment (>1wt%) of the austenite phase from the neighbouring martensite or bainite which might be due to fast partitioning kinetics and possible suppression of carbides through a combination of Si and Al additions. The attractive combination of tensile strength (921–922MPa) and ductility (25–26% total elongation) along with low yield ratio (0.63–0.69) are attributed to ferrite and lath microstructures along with the thin film like carbon enriched retained austenite obtained after Q&P process.
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