Correlation between welding structure and corrosion behavior of high strength low alloy (HSLA) ship steel in Cl--containing solutions

Abstract

The high-strength low-alloy (HSLA) steel industry is in great demand due to the continued growth of the ship and marine sectors. The microstructure of HSLA steel is greatly influenced by both the heat input during welding and the variations in salinity resulting from changes in climate. This paper presents the development of HSLA ship steel using a vacuum electric arc furnace and heat treatment techniques. Electrochemical corrosion tests were conducted on the substrate, heat-affected zone, and fused zone of HSLA ship steel. The results showed that the heat treatment process can improve the microstructure homogeneity of the HSLA ship steel, eliminate chemical composition segregation, refine the grain, and promote the formation of the microstructure of pearlite and ferrite. The welded interface structure was uniform and free from defects or inclusions. The metallographic microstructure of the fused zone showed a massive distribution of grain boundary ferrite, martensite, and granular bainite, and that of the heat-affected zone displayed superheated characteristics consisting of pearlite and acicular ferrite. The interlocking microstructure of the base material enhanced performance in a 4.2 % NaCl solution. The corrosion resistance of the heat-affected zone and fused zones of HSLA ship steel deteriorated. Grain boundary ferrite may be related to the inferior corrosion resistance of the heat-affected zone, while the coarse microstructure of granular bainite led to the serious corrosion resistance in the fused zone of HSLA ship steel.