The effect of M23C6 on the high-temperature tensile strength of two austenitic heat-resistant steels: 22Cr–25Ni–Mo–Nb–N and 25Cr–20Ni–Nb–N

The tensile strength of 25Cr–20Ni–Nb–N and 22Cr–25Ni–Mo–Nb–N during creep testing at 700 °C has been studied. The high temperature tensile tests of two steels after aging revealed that the tensile strength of 22Cr–25Ni–Mo–Nb–N is higher than that of 25Cr–20Ni–Nb–N. Because the tensile fractures of two steels are intergranular, it can be inferred that the interfacial strength of 25Cr–20Ni–Nb–N is weaker than that of 22Cr–25Ni–Mo–Nb–N. The main precipitation on grain boundaries in two steels is M23C6, which generally grows in a cube orientation relationship with the matrix. So XRD is used to define the lattice constants of the matrix and M23C6, with the specific interfacial energy between the matrix and M23C6 calculated correspondingly. The results reveal that the different specific interfacial energies between the M23C6 and the matrix in two steel are the main reason for the different interface strengths and prove that the interface strength of the matrix and M23C6 in 25Cr–20Ni–Nb–N is weaker than that in 22Cr–25Ni–Mo–Nb–N. The difference between the specific interfacial energy of two steels was caused by the difference of the lattice constants of M23C6 in two steels. Combined with EDS analysis result, it can be considered that the main reason for the difference of M23C6 lattice constant is the solution of Mo in M23C6.