(1.School of Materials Science and Engineering, Tianjin University, Tianjin 300350, China) (2.China Special Equipment Inspection and Research Institute, Beijing 100029, China) (3.Tianjin Key Laboratory of Advanced Joining Technology, Tianjin 300350, China)
In this paper, the effects of high temperature service process on the microstructure and mechanical properties of welded joints were studied in a section of HP40Nb hydrogen reformer tubes that have been in service for about 7 years. The characteristics of microstructure and the morphology and distribution of precipitated phases in different regions were observed and analyzed. The properties such as hardness, strength and impact toughness of each region were determined. The results showed that only a small amount of carbides were precipitated out from the deposited metal, lots of carbides were precipitated in the base metal and aggregated on the austenite grain boundary to form a network chain; the tensile strength of the joints only declined a little, but its elongation and impact toughness had been seriously reduced.