Being hardenable, martensitic stainless steels are more difficult to weld than most other types of stainless steel. Regardless of prior condition, welding produces a hard martensitic zone adjacent to the weld that is prone to cracking. The hardness increases with the carbon content in the steel and adds to the complexity in welding. The presence of hydrogen increases the risk of hydrogen-induced cold cracking. Nevertheless, martensitic steels can be successfully welded provided the right precautions are taken to avoid cracking in the weldment. Preheat and post-weld heat treatments (PWHT) are normally required to obtain reliable weldments. To get full strength of the welded joint, matching fillers should be used. If PWHT is not possible, austenitic or duplex fillers can be used for improved ductility.

Modified martensitic steels with additions of nickel e.g. 1.4313 that contains some austenite and ferrite show better weldability compared to e.g. 1.4006. The tempered structure, with low carbon martensite and finely dispersed austenite, gives good ductility. Supermartensitic steels with low carbon and nitrogen levels have good weldability with good resistance to cold cracking.

Martensitic weldment. Weld metal (right), HAZ (left).