Determining on welding methods and parameters for the 3%Ni steel welded joints-insights into the corrosion resistance of the fusion zone

Abstract

Through exposing the 3%Ni (wt. %) steel welded joints in a tropical marine environment, the effects of welding methods and the corresponding parameters on the corrosion resistance of fusion zone (FZ) were investigated in detail. Results indicated that the microstructures of FZ were mainly composed of more finer primary austenite grains for welded joint made by CO2 gas metal arc welding (GMAW), compared with shielded metal arc welding (SMAW) and automatic submerged arc welding (SAW), which resulted in more uniform Volta potential distribution on FZ (0.02–0.21 V for GMAW, 0.37–0.64 V for SMAW, −1.21–1.2 V for SAW). The uniform corrosion morphology facilitated by the fine primary austenite grains on GMAW FZ improved the combination of the rust layer on matrix, presenting highest corrosion potentials after exposure tests (Ecorr = −577 mV for one year and −408 mV for two years). The rust layer formed on GMAW FZ contained more amorphous substance and presented better corrosion protectiveness (α/γ = 1.36) compared with other two welding processes (0.86 for SMAW and 0.75 for SAW), which was attributed to the electrode welding materials with fine diameter (1.2 mm) and the moderate welding heat input (14.5–15 kJ/cm) for GMAW.