LAUSR

In this study, the correlation between reversed austenite formed at different tempering temperatures and mechanical properties in a low Ni steel treated by ultra-fast cooling, intercritical quenching and tempering was investigated in detail. It was found that reversed austenite was formed at fresh martensite and retained austenite during tempering. As tempering temperature increased, volume fraction and size of reversed austenite increased, alloy concentration in reversed austenite decreased, and reversed austenite stability was thus deteriorated. When tempering temperature is not higher than 590 °C, reversed austenite that remains completely stable at − 196 °C greatly improves cryogenic toughness. When tempering temperature reaches 610 °C and above, partial reversed austenite transforms into hard secondary fresh martensite at − 196 °C or even room temperature, which is harmful to cryogenic toughness. By tempering at 590 °C, an optimum combination of mechanical properties was achieved, which is comparable to that of 9% Ni steels.