Hastelloy intergranular corrosion
A selective corrosive attack along grain boundaries triggered by carbide precipitations and local chromium depletion due to insufficient thermal post-treatment.
Intercrystalline corrosion in Hastelloy occurs when carbides form at grain boundaries during welding and the material becomes depleted of chromium there. This happens especially when the heat input is too high or cooling is too slow. The result is fine cracks and brittle fracture in the weld area, especially if the component later comes into contact with acids. To prevent this, keep the heat low and watch the interpass temperature. Weld briskly and let the part cool in air, not with a hammer or water. If the joint geometry allows, help dissipate heat well, for example with a copper backing. And importantly, the filler metal must match the base metal, then the weld remains stable.