SSRT and fatigue life properties of austenitic stainless steel weld metal 317L in high-pressure hydrogen gas

Abstract

In order to study the hydrogen embrittlement behavior of austenitic stainless steel weld metal, slow strain rate tensile (SSRT) tests and fatigue life tests were performed in high-pressure hydrogen gas. Tensile and fatigue life specimens, in which whole of the gauge section consists of weld metals, were machined out from a TIG welded round bar. The base metal of multi-pass welded bar was SUS316 (hi-Ni), and the filler metal was 317L. Two series of weld metals were tested; one was an as-welded metal having coarse columnar gain with dendrite and δ-ferrite, and the other was a post-welded solution-treated metal. The relative reduction of area, RRA, was 0.55 for 317L as-welded metal, and approximately 0.9 for SUS316 (hi-Ni) base metal and 317L post-welded solution-treated metal. The fracture surface of 317L as-welded metal included lamellar weld (LW) fracture surface, whereas those of SUS316 (hi-Ni) base metal and 317L post-welded solution-treated metal were entirely covered with dimples. Fractographic observation in combination with EDS manifested that δ-ferrite was responsible for the hydrogen-enhanced crack growth leading to the formation of LW, and therefore the post-welded solution-treated metal without δ-ferrite exhibited excellent resistance to hydrogen. Regardless of the heat treatment, the fatigue limit of 317L weld metal was not degraded in hydrogen gas as well as the austenitic stainless steel base metal.

Keywords

• austenitic stainless steel weld metal
• hydrogen embrittlement
• δ-ferrite
• post-welded solution-treatment
• realative reduction of area
• fatigue limit
• lamellar weld fracture surface