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The corrosion behavior and mechanism of the high‐strength low‐alloy steel‐welded joint fabricated by the multilayer and multipass welding method were investigated using a scanning Kelvin probe, electrochemical measurements, and so forth. The results revealed that the microstructure of the first layer welding zone was dominated by granular bainite and acicular ferrite and was fine and uniform, which exhibited the best corrosion resistance. Whereas, since the average cooling rate decreased with the increase of welding pass, the grain size of the second and third layer weldings gradually grew, and the voltaic potential gradually decreased. In addition, the microstructure of the heat‐affected zone (HAZ) changed from the tempered sorbite structure of the equilibrium phase to the granular bainite or bainite structure of the nonequilibrium phase under the action of heat transfer. The HAZ became the weakest link for corrosion of welded joint, on account of the nonequilibrium organization and galvanic coupling among base metal, weld metal and HAZ. [ABSTRACT FROM AUTHOR]

In this paper, the passive behavior of 304 stainless steel (SS) in NaCl solution is studied by electrochemical methods and surface analysis. The polarization measurement results show that the pitting potential (Ep) has a simple linear relationship with the temperature increase. Scanning Kelvin probe results show that the surface potential difference on the surface of 304 SS is well correlated with the temperature. Scanning electron microscope results show that the rupture of the passive film accelerates with the increase of temperature. The X‐ray photoelectron spectroscopy analysis shows that the high temperature causes more oxidation on the surface of 304 SS, leading more Cr3+ oxidized to Cr6+ at high temperature. [ABSTRACT FROM AUTHOR]

In this work, the corrosion behavior of high‐strength low alloy (HSLA) steel welded joints in natural seawater solution was investigated by electrochemical and immersion tests. The experimental results prove that the corrosion resistance of the weld metal (WM) was higher than that of the base metal (BM). The scanning Kelvin probe results show that the potential distribution of the BM zone is lower than the heat‐affected zone (HAZ) and WM zone. The scanning vibrating electrode technique results demonstrate that the initial attack for the HSLA welded joint majorly took place in the BM zone after immersion in natural seawater. The corrosion morphology of the HSLA welded joint after immersion was observed by scanning electron microscope. The corrosion morphology of BM and HAZ regions tends to be uniform corrosion, whereas it is mainly pitting corrosion for the WM zone. [ABSTRACT FROM AUTHOR]