Martensitic Shear Mechanism

Martensite forms when you cool steel too quickly. The structure becomes extremely hard and brittle, which quickly leads to cracks in the weld. The problem is that the transformation happens suddenly and the material gets stressed. To prevent this, you have to slow down the cooling after welding, for example by preheating or letting it cool slowly. The higher the carbon content, the more sensitive the material is – you have to be especially careful not to get a hard, crack-prone zone.