Abstract
In this study, the microstructure and mechanical properties of laser welds before and after post-weld heat treatment processes were studied. The results show that the tensile strength of the joints can be increased by 90MPa by a post-weld heat treatment process at 871°C for 6h, exceeding the strength of the original state of the base metal. Besides, elongation of the joints are also increased to 43% by the process, whereas the elongation of as-welded joints are only 22%. In addition, the Charpy impact properties of laser welds almost do not change. Second phase precipitates, which were identified as Mo–Si rich M6C-type carbides by transmission electron diffraction and scanning electron microscope, were observed at solidification grain boundaries and solidification subgrain boundaries. These carbides can pin dislocations during the following tensile deformation, hence are responsible for the strengthening of tensile properties of the joints.
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