The effect of Nb on the strain rate and temperature dependent behaviour of quenching & partitioning steels

Abstract

In present study, the potential of Niobium (Nb) to improve the mechanical properties of Quenched and Partitioning (Q&P) steels is investigated. To this purpose, the effect of the addition of Nb on the microstructure and mechanical properties of a Q&P steel was thoroughly analysed with special attention on the thermal stability of the retained austenite. The mechanical properties of the Nb Q&P steel were determined using static and dynamic tensile tests and compared to the properties of a Nb free Q&P steel. Additionally, the effect of test temperature was quantified by static and dynamic tests in the temperature range from −40 °C to +80 °C. It was found that the Nb induced grain refinement together with the stabilising effect of Nb on the retained austenite, resulted in an excellent low temperature behaviour of the Nb Q&P steel. Additionally, the high temperature, dynamic behaviour of the Nb micro-alloyed steel was improved with respect to the Nb free steel due to the presence of a large fraction of retained austenite with low thermal stability.