A novel strengthening and toughening strategy for T250 maraging steel: Cluster-orientation governed higher strength-ductility combination induced by electropulsing

T250 steel is promising maraging steel for the development of ultrahigh strength structural materials due to the reduced cost of losing Co element. Whereas, the ductility of this steel is unsatisfactory owing to its high content of Ti. In this research, high-energy and instantaneous electropulsing is devised to improve the ductility of T250 steel. What's more, the substructure evolution and aging behavior of T250 steel after S (solution) + TA (traditional aging) and S + EPA (electropulsing treated followed with air cooling) treatment are systematically investigated by Transmission Electron Microscope (TEM) characterization, Atom Probe Technology (APT), Finite Element Modelling (FEM) simulation and Electron Back-Scattered Diffraction (EBSD) technology. It is found that unlike S + TA sample, the S + EPA sample consists of Ni3(Ti,Al) clusters, Ni2.67Ti1.33 phase and NiTi phase, respectively, which have different morphologies and sizes caused by their diverse enthalpies of formation and the thermal effect induced by the different conductivity. Furthermore, a great quantity of sub-grain boundaries, relatively considerable α variants and higher schmid factors are detected in S + EPA sample. Consequently, the higher ultimate strength (1855 MPa, 4.4% higher than S + TA sample) with better ductility (15.1%, 23.7% higher than S + TA sample) is obtained.