Structural Transformation

Change in crystalline structure or phase arrangement resulting from temperature or pressure variations. This fundamentally alters the physical and mechanical properties of the metal.

When you weld steel and heat it up, then cool it down again, the structure changes. The steel becomes hard and brittle if you cool it too quickly – that's called martensite formation. You don't want that because the material becomes cracky. So you have to slow down the cooling, for example by preheating or letting it cool slowly. Then you get a softer, tougher structure that is easier to work with and doesn't break as easily.

MetallurgieSchweißtechnik