Enhancement of the strength and ductility of martensitic steels by carbon

For most engineering materials, the properties of strength and ductility are mutually exclusive, and no process has been reported to enhance the strength and ductility of steels by carbon. Nevertheless, the quenching and partitioning (Q&P) process, which was originally proposed in 2003, is a promising method for the fabrication of carbon-alloyed steels with high strength and ductility. In this work, we show that the development of a composite-like microstructure in steels during Q&P process can enhance the strength and ductility of Fe-Mn-Si-Nb-C steels containing 0.2-0.4 wt% C. In contrast to the traditional quenching and tempering process, the novel Q&P (or Quenching-Partitioning-Tempering) process can link strength enhancement, which is conferred by the hard martensite phase, with ductility enhancement, which is conferred by the retained soft austenite fraction. The origin of such different effects of carbon is revealed by the microstructural characterization.