Effect of temperature on corrosion of weld structures for X80 steel in artificial seawater

Abstract

The effect of temperature on the corrosion behavior of weld structures of X80 steel in artificial seawater was studied via polarization curve measurement, AC impedance spectra measurement, SEM, EDS and chemical analysis. The result shows that the heat affected zone presents the greatest corrosion tendency, while the weld seam has better corrosion resistance than the base material. With the increasing temperature, the diffusion, discharge process and thus the corrosion were accelerated due to the depolarization of the anode. The weld seam shows better corrosion resistance rather than the base material and the heat affected zone as well, which may be ascribed to that the compactness and adhesion of the corrosion products on the weld seam are much better than that on the base material and the heat affected zone. In comparison to the base metal, the weld seam presents coarser grains with less grain boundaries as well as lower content of C, Mo and Nb, while, richer in Ni, Cr and Al, which all are responsible to the better corrosion resistance of the weld seam. On the other hand, the heat affected zone presents a complex microstructure of rather nonuniform distribution with very high activation energy, which then results in great tendency of corrosion.