Nickel Carbide Precipitation

Nickel carbide precipitation happens when you weld nickel alloys at high temperature and carbon gets into the weld pool. That stuff then settles at the grain boundaries and makes the structure hard and brittle. The weld can crack as a result, especially if it's later subjected to hot loads. Make sure the workpieces are clean and no oil, grease, or other carbon sources come near the weld area. If you keep the heat input under control and don't get too hot, the problem stays manageable. For critical components, letting the weld cool slowly after welding helps.