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

Abstract

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 ℃. 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 decreases 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.