The effect of M_(23)C_6 on the high-temperature tensile strength of two austenitic heat-resistant steels: 22Cr-25Ni-Mo-Nb-N and 25Cr-20Ni-Nb-N

摘要

The tensile strength of 25Cr-20Ni-Nb-N and 22Cr-25Ni-Mo-Nb-N during creep testing at 700 ℃ 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 M_(23)C_6, which generally grows in a cube orientation relationship with the matrix. So XRD is used to define the lattice constants of the matrix and M_(23)C_6, with the specific interfacial energy between the matrix and M_(23)C_6 calculated correspondingly. The results reveal that the different specific interfacial energies between the M_(23)C_6 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 M_(23)C_6 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 M_(23)C_6 in two steels. Combined with EDS analysis result, it can be considered that the main reason for the difference of M_(23)C_6 lattice constant is the solution of Mo in M_(23)C_6.