SSRT properties of austenitic stainless steel weld metals in hydrogen gas at －45 °C and 106 MPa

Abstract

In order to study the hydrogen embrittlement behavior of austenitic stainless steel weld metals, slow strain rate tensile (SSRT) tests were performed in 106 MPa hydrogen gas at −45 ºC. Tensile 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 bars was SUS316 (hi-Ni), and the filler metals were 317L, 316 and 316L. The nickel equivalent values of SUS316 (hi-Ni) base metal, and 317L, 316 and 316L weld metals were 29.69, 29.99, 28.87 and 28.27 mass %, respectively. Two series of weld metals were tested; one was as-welded metal, and the other was post-welded solution-treated weld 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, 316 and 316L post-welded solution-treated weld metals. The result indicated that the resistance against hydrogen embrittlement was recovered by the post-welded solution-treatment. The fracture surface of SUS316 (hi-Ni) base metal and 317L post-welded solution-treated weld metal was entirely covered with dimples, whereas the fracture surface of 316 and 316L post-welded solution-treated weld metals was covered with dimples and quasi-cleavages. Accordingly, it was concluded that 317L post-welded solution-treated weld metal with the highest nickel equivalent had excellent resistance against hydrogen embrittlement, which was recommended for use in high-pressure hydrogen components.