Seven autogenous tungsten inert gas (TIG) welds were produced in each of 2 plates of AISI(1) 308 stainless steel (SS). The chromium-to-nickel equivalency ratios [(Cr/Ni)eq] of the plates were 2.07 and 2.22. Each weld was formed with a different combination of heat input and torch speed. In spite of variations in the 2 latter parameters, all 7 welds for each plate possessed the same aswelded microstructure. Because of the high values of (Cr/Ni)eq, each weld solidified as 100% ferrite, which partially transformed to Widmanstatten austenite during cooling. Because of the Widmanstatten transformation, a large fraction of the austenite-ferrite boundaries were low-energy interfaces. The susceptibility of the low-energy α-γ interfaces to localized boundary corrosion as a result of isothermal sensitizing treatments was slight. However, the susceptibility of high-energy incoherent α-γ interfaces to localized corrosion was strong and reached a maximum in ≈4 h at 550 C. The results are qualitatively consistent with a previously developed model of the sensitization behavior of duplex SSs.

Subject
Water, Microstructure, Chromium, Corrosion cracking, Intergranular cracking, Interfaces, Heat, Sensitization, Carbon, Localized corrosion, Ferrite, Heat treatment, Austenite
National Association of Corrosion Engineers
1989
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