Intergranular Corrosion Resistance and Microstructure of Laser-Metal Active Gas Hybrid Welded Type 301L-MT Stainless Steel Joint

The microstructure and intergranular corrosion resistance of 6 mm thick Type 301L-MT stainless steel joints welded by laser-MAG (metal active gas) hybrid welding were investigated. Double loop electrochemical potentiokinetic reactivation measurement (DL-EPR) and electrochemical impedance spectroscopy (EIS) were conducted to study the corrosion behavior of laser-MAG hybrid welded (LMHW) joints in a slightly oxidative medium (a solution of 0.5 mol/L H2SO4 + 0.01 mol/L KSCN). The results show that the weld metal mainly consists of austenite and delta-ferrite, while the base metal (BM) and heat affected zone are the rolled structure including the original austenite and lath martensite. The different parts of LMHW joints present diverse intergranular attack resistance as a result of the microstructural difference. BM shows the best corrosion resistance with average I-r/I-a ratio (I-r is the reactivation peak current density, and I-a is the activation peak current density) of not more than 1%. The results indicate that there is no intergranular corrosion sensitivity because of Cr segregation according to ISO 12732: 2006. The EIS tests indicate that the passive film and substrate should be responsible for the corrosion process of LMHW joints.