Effect of preheating temperature and filler metal type on the microstructure, fracture toughness and fatigue crack growth of stainless steel welded joints

It is known that the main problem related with the welding of low carbon 12% Cr stainless steels is its hydrogen induced cracking susceptibility. Thus, it is common practice to perform welding with two alternative ways, preheating the welded parts and using similar filler material or using an austenitic stainless steel filler metal without preheating. This research work consists in identifying and comparing, for these two alternatives, the effect on microstructure, fracture toughness and fatigue crack growth rate of the welded joint. On the first alternative, using a GMAW welding process and similar filler metal, the variable is preheating temperature, with the purpose of minimizing internal residual stresses and the level of diffusible hydrogen. On the second alternative, also using a GMAW welding process and austenitic stainless steel filler metal (greater hydrogen solubility), the variable is hydrogen concentration in the argon shielding gas with the purpose of diffusing hydrogen to the heat affected zone. The results indicate how the thermal cycle, different hydrogen levels and hydrogen trapping sites affect the mechanical properties.