| X80 pipeline steel welded joints were chosen as the research objects in this paper.To study the hydrogen embrittlement(HE)susceptibility of X80 welded joints,slow strain rate test(SSRT),hydrogen bubbling,hydrogen penetration and electrochemical experiments were performed on BM,WM and thermal simulated HAZs.To establish the relationship between microstructures and HE susceptibility,the microstructure,microhardness and residual stress were characterized by electron microscopy,nanoindentation and XRD,respectively,and the failure mechanisms were analyzed.Finally,the impact of annealing on HE of X80 welded joints was investigated.SSRT and hydrogen bubbling tests showed that the HE susceptibility of X80 welded joints are as follows: FGHAZ > WM > CGHAZ > ICHAZ > BM,HE can be affected by microstructure,stress,hardness and hydrogen diffusion rate,etc.BM with the lowest HE susceptibility is attributed to the fine acicular ferrite with high density dislocations,the higher susceptibility of WM and HAZs are attributed to their own sensitive structures,more inclusions and high local stress distribution.Compared with CGHAZ and ICHAZ,the higher susceptibility of FGHAZ is due to its softer structure and higher hydrogen diffusion rate,the effect of hardness is mainly reflected in the fact that: the lower hardness contributes to promote the diffusion of hydrogen and the initiation & propagation of micro-cracks under external force.The HE susceptibility of X80 annealed welded joints are as follows: BM-T < CGHAZ-T < WM-T < FGHAZ-T < ICHAZ-T.Tests showed that annealing can improve the mechanical properties,corrosion resistance and anti-HE performance of X80 welded joins,and the improving efficiency of anti-HE from large to small is: BM-T > FGHAZ-T > CGHAZ-T > WM-T > ICHAZ-T.The mechanism of annealing improving the anti-HE performance is that annealing can improve the plasticity and toughness of the structure itself and reduce the hydrogen diffusion rate by optimizing the microstructure. |
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