Thermodynamic Stability and Strengthening Mechanisms of MX and M 23 C 6 Precipitates in 9–12Cr Martensitic Heat‐Resistant Steels: A Combined First‐Principles and Experimental Study

This study systematically investigated the precipitation behavior and strengthening mechanisms of MX and M 23 C 6 in 9–12Cr martensitic heat‐resistant steels by combining first‐principles calculations with experiments. The results show that the primary precipitates in 9–12Cr martensitic heat‐resistant steels are (Cr,V)N and (Fe, Cr) 23 C 6 phases, which are dispersed along the prior austenite grain boundaries and martensite lath boundaries, forming rigid obstacles that impede dislocation motion. This microstructural feature yields a yield strength of 636 MPa and an elongation of 21% at room temperature. First‐principles calculations reveal that, except for Fe 23 C 6 , the formation enthalpies of all other precipitates are negative, with NbN and Cr 22 FeC 6 being thermodynamically the most stable among the MX and M 23 C 6 . NbC exhibits brittle characteristics, while the other precipitates exhibit ductile behavior. This study clarifies the stability rules of precipitates and their strengthening mechanisms, providing theoretical guidance and experimental support for the composition design of 9–12Cr martensitic heat‐resistant steels.