Study on corrosion behavior of high-nitrogen steel laser-arc hybrid welding joints in different heat source action area

This paper investigates the effects on corrosion mechanism and pitting resistance in high-nitrogen austenite steel laser-arc hybrid weld. Electrochemical corrosion technology was used to study the corrosion behavior in 3.5% NaCl solution. The conclusions as follow: Both from microcosmic and macroscopical analysis, the delta-ferrite precipitated from dendrites is preferentially be corroded and exfoliated. The growth pattern and dense degree of dendrites is found to be the most significant factors that affect the corrosion tendency. Compared to the arc acting area, the laser acting area at the weld bottom prefer better corrosion mechanism because of the enhancement of Laser keyhole action. Pitting corrosion mainly concentrated in the center of the small fir-tree crystals and leave regular special secondary pitting hole. This phenomenon only exists in the austenite welds with dendritic distribution. The coarse dendrites with large structure is the starting layer of exfoliation corrosion which promote the further erosion of Cl-. Through the study of the weld hardness, it is further proved that the laser acting area does have more uniform structure distribution and thus has excellent corrosion resistance. Research reveals that the hybrid weld has unique corrosion behavior which is different from the conventional Austenite stainless steel.