Coupling effect of thermal aging and pre-strain on fracture behavior of SMAW welded joints

A repairing process is commonly needed to correct installation slope and geometrical deviation of nuclear power piping, but the resulting pre-strain has obvious degradation impacts on the long-term operation of surge pipeline, especially for the shielded metal arc welding (SMAW) joints. In this paper, to investigate the embrittlement induced by thermal aging and pre-strain, the SMAW welded joints with the base metal Z2CND18-12N2 and welded metal ER316L were subjected to different pre-strain (0%, 8%, 12% and 15%) and the accelerated thermal aging from 0 h to 13000 h at 400 celcius. Then, the Charpy impact test and compact tension fracture test were conducted to determine fracture properties of the SMAW welded joints. Results showed that both thermal aging and pre-strain can significantly reduce the fracture properties of SMAW welded joints. The impact absorbed energy reached stable after thermal aging 500 h, but it has been decreasing with the pre-strain varying from 0% to 15%. Moreover, it is shown that for pre-strained SMAW welded joints, with the increase of thermal aging duration, the absorbed energy first recovers, and then de-creases until stable. Compared with pre-strain, the influence of thermal aging is dominant. Finally, combined with microscopic analysis, the comprehensive effects of thermal aging and pre-strain on the embrittlement mechanism of SMAW welded joints were discussed.