Recrystallization

Recrystallization is what happens when you deliberately heat a cold-worked metal. New, low-stress grains form in the structure, and the material becomes softer and more formable again. This is important if you want a proper structure after welding or bending, otherwise the part stays hard and brittle. In practice, you need to bring the workpiece to the right temperature and hold it there for a while. The exact temperature depends on the material, but you can recognize the effect by the structure becoming uniform again. If you skip it, you risk cracks, especially on heavily cold-formed sheets.