Nickel hardening mechanism

Nickel-based alloys can be precipitation-hardened during welding. This means fine phases form in the weld pool that make the structure stronger. That's good for high temperatures, but you have to be careful: if cooling is too fast or heat input is not right, you build up stresses and risk hot cracking. So let the weld cool slowly and evenly so the phases can form properly. Too fast cooling prevents hardening and makes the material susceptible. Keep the interpass temperature in check and give the weld time to cool down after welding before further processing.