What Does Weld Decay Mean?
Weld decay is a corrosion process that mainly occurs as a result of sensitization (regions susceptible to corrosion) in the heat affected Zones (HAZ) of metal during welding operations.
This process mostly occurs in stainless steels or certain nickel-based alloys. It is a form of intergranular corrosion.
Corrosionpedia Explains Weld Decay
During the welding process in nickel alloys and austenitic stainless steels, where chromium is added for corrosion resistance, local sensitized zones often develop. Sensitization is due to the formation of chromium carbide along grain boundaries, resulting in depletion of chromium in the region adjacent to the grain boundary. This chromium depletion produces localized galvanic cells. If this depletion drops the chromium content below the necessary 12 wt% that is required to maintain a protective passive film, the region will become sensitized to corrosion, resulting in intergranular attack.
This condition occurs when the material is heated to temperatures around 700°C (1290°F) for too long, and often happens during welding or an improper heat treatment. When such localized galvanic cells form due to welding, the resulting corrosion is known as weld decay.
Methods for preventing weld decay include:
- Using low carbon grade stainless steels alloyed with stabilized grades of titanium or niobium, which are strong carbide formers. They react with the carbon to form the corresponding carbides, thereby preventing chromium depletion.
- Using post-weld heat treatment
- Using laser beam surfacing