Eutectoid decomposition

Eutectoid decomposition means in plain terms: If you cool steel too quickly after welding, the structure transforms and becomes hard and brittle. This happens especially with higher carbon steel when cooling is too abrupt. Then you get a coarse, hard structure that cracks quickly – especially in the heat-affected zone. The solution is simple: Let the weld cool slowly and controlled, for example with a cover layer or by preheating. This way you get a calm, tough structure and no nasty surprises.