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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.

 

Means of preventing sensitization:

  • Solution heat treatment: heating to a temperature above 1900°F (1040°C) followed by quenching (rapid cooling) in water or quenching oils. During the heating stage the carbides dissolve and their formation is suppressed by fast cooling.
  • Lowering concentration of carbon. Sensitization is depressed in low carbon (max. 0.03%) stainless steels, designated with the suffix L (304L, 316L).
  • Stabilization by carbide forming elements. Formation of chromium carbides is avoided in stabilized austenitic stainless steels (321, 347) containing carbide forming elements like titanium, niobium, tantalum, zirconium. Stabilization heat treatment of such steels results in preferred formation of carbides of the stabilizing elements instead of chromium carbides.

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