Primary Recrystallization
The formation of a new, strain-free grain structure with altered grain boundaries from deformed starting material via thermal activation.
Primary recrystallization happens when you heat a cold-worked metal strongly enough. The strained crystals rearrange, forming fresh, undeformed grains, and the hardness from deformation goes down. In welding, this is important because the heat-affected zone next to the weld is deformed by shrinkage. If the structure doesn't recrystallize there, the material stays hard and brittle, and you risk cracks. But caution: if you get too hot or stay on it too long, the grains grow excessively and the part becomes soft and tough like chewing gum. In practice, this means: after welding, don't let the critical spots cool down, but deliberately post-heat them so the structure can relax. The right temperature and holding time depend on the material – you have to follow the data sheet, not gut feeling.