Unexpected strengthening of the Mo-containing low-density steel achieved through a novel nano-ordered phase

Abstract

Mo element has been considered as an effective element to regulate the nano-precipitation behavior in low-density steel. In this work, a novel nano-ordered phase was found in austenite of the Fe–28Mn–10Al-1.2C (wt.%) low-density steels with 3 wt% and 5 wt% Mo addition. HRTEM characterization indicated that this nano-ordered phase had a chemical composition similar to austenite matrix and a L′12 structure similar to κ-carbides. Although the Mo addition suppressed the precipitation and growth of κ-carbides in austenite, the nano-hardness testing showed that the formation of the novel nano-ordered phase caused by Mo addition resulted in a higher hardness of austenite. Based on the tensile property analysis of the Mo-containing steels, although the Mo addition decreased the precipitation strengthening of intragranular κ-carbides, the novel nano-ordered phase resulted in an additional strength contribution of 309 MPa. In addition, the formation of this novel nano-ordered phase had significant improvement on the strain hardening rate. Consequently, the Mo addition simultaneously increased the strength and plasticity of the low-density steels. The novel nano-ordered phase caused by Mo has rarely been reported in literatures, its contribution on the strength and strain hardening ability indicated its potential application in the regulation of mechanical properties.