Hydrogen Assisted Cracking in Welding of 13% Cr Supermartensitic Stainless Steels

Supermartensitic stainless steels are known to be prone to hydrogen induced cold cracking. Therefore, the objective of this work was to assess the susceptibility to hydrogen cracking in Gas Metal Arc Welding (GMAW) with use of matching base and filler materials (supermartensitic stainless steel), using the Instrumented Restraint Cracking (IRC) test. Root welding in the IRC test did not result in hydrogen induced cracking, neither for low nor high weld metal hydrogen content. Because of the martensitic transformation, the global residual stresses are very low after welding (below 100 MPa). Since the yield strength (R_p0.2%) of the material is about 600–720 MPa, it implies that the IRC test method is not very suitable for supermartensitic stainless steels. However, by performing IRC test multi-layer welding, micro-cracks were found in the last pass. An increase in the weld metal hydrogen content resulted in reduced fracture stress and ductility, as observed in tensile testing of IRC test specimens directly after welding. Investigation of the fracture surfaces of the specimens with high hydrogen contents showed fish eyes, which are strong indications of hydrogen embrittlement. By performing heat treatment (225°C for 24 hours) of specimens with high hydrogen contents and subsequent tensile testing, the fracture stress and ductility were restored to the initial base metal level. Slow Strain Rate Testing (SSRT) with and without Cathodic Protection (CP) was performed on test specimens sampled transverse to the welding direction. CP has detrimental effect on the fracture stress and ductility due to the high weld metal hydrogen pick up.