First principles study on the effects of N, Mn, Co, Ni, and Cu on the electronic structure and mechanical properties of austenitic steel

Revealing the microscopic mechanism of N, Mn, Co, Ni, and Cu elements stabilizing austenitic phases in steels can help to solve the problem of austenitic steel instability in extreme service environments. In this work, the preferential occupancy, stability, geometric, electronic structure, and mechanical properties of γ-Fe(C)-M (M=N, Mn, Co, Ni, and Cu) doping systems were calculated by first-principles calculation. The calculation results show that N is preferentially solidified in octahedral interstitial positions, Mn is preferentially solidified in face-center positions, and Co, Ni, and Cu are preferentially solidified in top-angle positions. The solution energy and enthalpy formation of γ-Fe(C)-M are smaller than that of γ-Fe(C), which promotes the stability of the system. The geometric structure shows that the doping of M atoms can make the austenite stable mainly because the doping of N, Co, Ni, and Cu makes the bond length becomes shorter between C and Fe, the Fe-C bond energy is enhanced. And the doping of Mn makes the formation of stable chemical bond between Mn and C, further reducing the activity of C. According to B/G and σ values, it can be concluded that the toughness of γ-Fe(C)-M systems has different degrees of improvement compared with the γ-Fe system.