Effect of post-weld heat treatment on fatigue reliability of super-duplex-stainless-steel weldments

Abstract

To assess the reliability of weldments of a super duplex stainless-steel (UNS S32750), we have studied how the microstructure and fatigue strength of a welded joint is affected by post-weld heat treatment, focusing on the formation of the intermetallic phase during cooling. The microstructure of the welded zone of arc-welded single-V joints was examined by optical microscopy and SEM-EBSD. It revealed that the phase appears as the tertiary constituent when cooled from the solution-treatment temperature of 1 323 K at rates below 101 K s-1, with its fraction reaching 20% at rates as low as 10-1 K s-1. Fatigue properties were evaluated by plane-bending tests, and were found to be deteriorated correspondingly to the amount of the phase. Specimens without heat treatment performed better than any of those subjected to the solution treatment and cooled at a rate in the range between 0.1 to 50 K s -1. To secure fatigue reliability it is advisable that weldments of the material should not be subjected to post-weld heat treatment. If the treatment is necessary for some reasons, the condition should be carefully selected.