Peak Aging

The aging peak is the point where the weld reaches its maximum strength and hardness after heat treatment. This directly depends on the cooling rate: if you cool too fast, the structure becomes too soft and the weld won't hold. If you cool too slowly or incorrectly, the structure can overharden and you'll get cracks. So you have to hit the temperature window where the structure transforms optimally. This varies depending on the steel and filler material; only the data sheet or experience helps. If you cool the weld in a controlled way, you get a uniform, tough structure that withstands the load.