上海科技大学知识管理系统

The effect of post-weld heat treatment (PWHT) on the microstructures and tensile properties of Ni-12Mo-7Cr-2Nb weld metal has been investigated systematically. Three kinds of PWHT (as-welded, PWHT at 871 degrees C and PWHT at 1177 degrees C) were carried out, and then the accelerated aging treatment at 750 degrees C was carried out to simulate the long-term service state. The results show that PWHT can mitigate the elemental segregation and increase the grain size in the as-welded metal, especially at 1177 degrees C. After the accelerated aging treatment, many nanoscale MC carbides form within the matrix of all three samples, and dense MC carbides form on the grain boundaries (GBs) of the 1177 degrees C PWHT samples. The tensile tests of three aged samples were carried out at 700 degrees C with the as-welded one as a control. The yield strength of the as-welded and 871 degrees C PWHT samples after aging increases by similar to 14 % due to precipitation strengthening. The yield strength of the 1177 degrees C PWHT samples does not change significantly after aging, which is attributed to grain coarsening and reduced dislocation density. The high elongation of the 1177 degrees C PWHT samples is mainly attributed to the dense MC carbides at the GBs and dislocation annihilation, which can relieve strain concentration along GBs and thus restrain intergranular cracking.