Weld Decay In Austenitic Stainless Steel

Fractures

Weld decay, also known as knife-line attack, occurs in unstabilised austenitic stainless steels, e.g. 18-8 type, within the 600-850°C range in the HAZ. At this temperature range carbon is absorbed by the chromium and chromium carbide is precipitated at the grain boundaries as the metal cools down. This causes a local reduction in chromium content which has the effect of lowering the resistance to corrosive attack allowing rusting to occur. Weld decay is prevented in stabilised stainless steels by the addition of niobium or titanium, but the most common method now used to prevent weld decay is to decarburize the molten steel to below 0.03% C.