Low-temperature sensitisation behaviour in weld metal in austenitic stainless steel: Low-temperature sensitisation of austenitic stainless steel welds and its improvement by laser surface melting treatment (1st Report)

Abstract

This paper describes an investigation of low-temperature sensitisation (LTS) behaviour in the weld metal of type 308 stainless steel. Three type 308 stainless steels with carbon contents of 0.04, 0.06, and 0.08% were used. TIG welding was employed to prepare the corresponding weld metals, which were subjected to sensitising heat treatment in the 773–1073 K temperature range. The degree of sensitisation was examined by the EPR method and Strauss test. Chromium carbide was precipitated at the δ/γ grain boundaries in the as-welded weld metals. Corrosion test results show that a higher carbon content leads to earlier sensitisation. Sensitisation of weld metals is found to occur faster in those solution heat-treated at 1273 K before sensitising heat treatment. This suggests that the prior chromium carbides have the effect of accelerating sensitisation, clarifying the fact that the LTS phenomenon also occurs in the weld metal. Sensitisation of the weld metal occurs in a much shorter time than in the HAZ. This is attributable to preferential precipitation of chromium carbide at the δ/γ grain boundaries in the weld metal.