Theoretical Insight into the Cooperative Strengthening of Interstitial Atoms(C/N/O) and Cr in Dilute Fe-Cr System

Solution strengthening is an effective strategy to improve the properties of martensitic steels (MSs). However, the microscopic mechanism of solution strengthening between Cr and interstitial atoms (IAs; C/N/O) remains elusive in dilute Fe-Cr system. Herein, this research aimed to ascertain the stability of Cr and IAs, and the interaction mechanisms between Cr and IAs by energy analysis and four-level electronic structure analysis (projected density of states, Electron Localization Function, crystal orbital Hamiltonian population, and charge density difference) in Fe-Cr alloys based on the first-principles calculations. First, studies on the thermostability of Cr and IAs show that Cr tends to occupy a central substitution site, IAs prefer to occupy octahedral interstitial sites (O-sites), whereas Fe53Cr1N/O is the most stable structure in the Cr-rich region. Therefore, the Fe53Cr1X (X=C/N/O) is selected to investigate the interaction between Cr and IAs. Moreover, the formation energy of IAs in the Fe-Cr system is significantly lower than the solid solution of IAs in the pure Fe system, indicating that there is a cooperative effect between Cr and IAs. Then, the four-level electronic structure analyses of Fe53Cr1X reveal the strong bonding between IAs and Cr, implying that the system has high stability. Furthermore, compared to the pure iron system, the increase in the dissociation temperature of IAs in the Fe-Cr system again verifies the enhancement of stability by cooperative strengthening. The results provide a theoretical basis for understanding the solid solution strengthening of IAs and Cr in martensitic steels.