Effect of deformation and grain size on austenite decomposition during quenching and partitioning of (high) silicon‑aluminum steels

The effect of austenite deformation on carbon partitioning and transformation to athermal and isothermal martensite, and bainite during quenching and partitioning (QP) is described for three steel compositions: Fe-0.3C-0.6Si-1.1Al, Fe-0.3C-1.0Si and Fe-0.3C-0.5Si-0.5Al. Microstructures were characterized using SEM-EBSD, TEM and XRD. Austenite decomposition kinetics was investigated using dilatometry. Deformation close to the no-recrystallization temperature refines the grain size, lowers the martensite start temperature and affects the stability of austenite during QP processing. The results in respect of dilatation measurements and retained austenite contents at room temperature corroborate the QP microstructures and their hardness and can help in designing optimal QP treatments for these novel steels. •Influence of partially recrystallized structure on Q&P behavior of Si-Al steels•Dilatation curves unraveling a host of austenite decomposition mechanisms•Austenite decomposition rate unaffected during partitioning in strained matrix•Systematic increase in retained austenite fraction with partitioning time