Martensitic phase transformation

A diffusionless shear transformation of the crystal lattice upon rapid cooling, resulting in a highly dislocation-dense distorted structure and high hardness.

Martensite forms when steel cools quickly. The structure becomes hard and brittle. During welding, this can happen when heat is removed too fast, e.g., with thick plates or cold base material. The result is hard, crack-prone zones in the heat-affected zone. To avoid this, you have to slow down cooling, e.g., by preheating or slow cooling. If the steel is martensitic, tempering after welding often helps to relieve stresses and restore toughness.

MetallurgieSchweißtechnik