Dramatically enhanced creep rupture performance and failure analysis of 9Cr–CrMoV dissimilar welded joint

Abstract

The relationship between the microstructure evolution and the corresponding creep rupture performance are systematically investigated. Dramatically enhanced creep rupture performance is achieved for the 9Cr–CrMoV dissimilar welded joint by adjusting the heat treatment process (HTP) of CrMoV steels before welding. The crystallographic structure illustrates that the longer normalizing process could lead to the larger grain size, and the shorter tempering time devotes to the residual lath structure and finer second phase particles. The creep rupture test results show that the welded joint using CrMoV steel with original HTP ruptures in the soft zone with an obvious necking. After adjusting the HTP of CrMoV steel, the creep rupture life increases from 9634 h to 16,108 h accompanied with the rupture location transferred to the weld metal (WM), together with the fracture morphology from dimples to cleavage planes under the same creep rupture parameters. The fracture transition and enhancement of rupture life is resulted from the simultaneous strengthening effect of the lath structure and the precipitated fine particles in the matrix.