Martensitic Dislocation Density

The extreme accumulation of lattice dislocations within the rapidly transformed microstructure. It is primarily responsible for the high hardness and low ductility of this structural type.

If you cool steel too quickly after welding, martensite can form. That makes the structure hard and brittle, the weld becomes prone to cracking, especially cold cracks. So you have to control the cooling. For critical steels, that means: don't cool down too fast, but manage the heat so the structure can transform without hardening. If you can't let the weld cool controlled after welding, preheating or post-heating often helps to defuse the situation.

MetallurgieSchweißtechnik