Recrystallization Annealing of Copper

You anneal copper to make it soft again after cold forming and to relieve stresses. The material forms new, undeformed grains. When welding, you have to be careful that the heat doesn't spread too much into the surrounding material, otherwise the zone becomes coarse-grained and brittle. Done right, you get a workable and tough structure again. Simply bring it to annealing temperature in the furnace and let it cool slowly, then it's fine.