Influence of surface microstructure and chemical compositions on grooving corrosion of carbon steel welded joints

Abstract Corrosion behavior of a welded joint is complicated and can be strongly dependent on its local chemical composition and microstructure of the surface. To gain a thorough insight into the grooving corrosion behavior of welded joint, it is necessary to understand the corrosion mechanism of different regions of the welded joint. In this study, the influence of the lattice constant on the electron work function (EWF) and corrosion rate of base metal and two weld metals was investigated using a constant potential polarization approach and a scanning Kelvin probe (SKP). Experimental results showed that surface EWF decreased with increasing lattice constant, whereas the corrosion rate increased with an increase in lattice constant. At the same time, it was theoretically demonstrated that the lattice constant can affect the local EWF fluctuation of a welded joint. The fluctuation further leads to the corrosion rate difference of the different regions of the welded joint. So, the lattice constant change in the surface structure is a possible reason for the average grooving susceptibility coefficient difference of two kinds of welded joint. Besides, the alloying elements distribution of two kinds of welded joint zones should be a main reason for the average grooving susceptibility coefficient difference of joints verified by the EPMA measurements and the quantitative calculatinon of the contents of Cu, Ni and Si in the joints.