Prominent work hardening and ultrahigh yield strength both realized in 3Mn steel multiply alloyed with Cu/Ni/Al/V

In this paper, we developed a 3 wt% Mn contained, and Cu–Ni–Al–V alloyed steel, in which several types of precipitations and metastable austenite phase were both formed via the intercritical annealing (IA) at 670–750 °C and the ageing at 500 °C. It was found that the choice of IA temperature had the critical influence on the resultant tensile properties. An intermediate IA temperature of 700 °C produced the best mechanical combination, i.e. yielding at the ultrahigh stress of 1320 MPa followed by a prominent work hardening increment of 334 MPa over 26% tensile strain, which is superior to the tensile properties of similarly alloyed medium Mn steels. This is because the multiple precipitations contribute to ultrahigh yield strength; and the formed bimodally-sized retained austenite (RA) grains, resulting from a remarkable reverse transformation occurring during the ageing, provide the sustainable transformation-induced-plasticity (TRIP) effect for enhanced work hardening. Therefore, we propose that the multiple precipitations and bimodally sized RA grains could be a new microstructural design strategy for the simultaneous improvement of both yield strength and work hardening capacity.