Tempering stability of retained austenite in nanostructured dual phase steels

Abstract

The tempering resistance and stability of retained austenite in superbainitic and quenching–partitioning martensitic steels were investigated over the temperature range of 400 to 700°C. The X-ray diffraction analysis and hardness tests showed that the quenching–partitioning martensitic steel contained a considerable amount of retained austenite (26·6 vol.-) and had a relatively high hardness up to 556 HV1 after tempering at ∼600°C. In contrast, the fraction of retained austenite and hardness of superbainitic steel were considerably lower (24·5 vol.- and 385 HV1) after the same tempering cycle. The present work also showed that the quenching–partitioning steel had a higher tempering stability, probably due to the higher fraction of carbon rich retained austenite.