The corrosion behavior and mechanism of the high-strength low-alloy steelwelded 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.

In this paper, Cr2O3-25TiO2 composite coatings were prepared on the surface of steel structure samples by atmospheric plasma spraying. The phase composition, microstructure, microhardness and long-term immersion corrosion behavior in 3.5 wt.% NaCl solution of Cr2O3-25TiO2 composite coatings were studied. The corrosion behavior of Cr2O3-25TiO2 composite coating was analyzed by potentiodynamic polarization and electrochemical impedance spectroscopy. The impedance data were fitted into an appropriate equivalent circuit to explain the electrochemical corrosion behavior of the coating at different stages. The results of scanning electron microscopy showed that the Cr2O3-25TiO2 composite coating was agglomerated, and the rhombohedral Cr2O3 powder was wrapped around the rhombohedral TiO2 powder. The coating melted completely without obvious defected. The XRD results showed that no phase transformation occurred in the Cr2O3-25TiO2 composite coating. The Cr2O3-25TiO2 coatings showed high corrosion resistance and good passivation behavior in the initial stage of corrosion. The coating itself did not corrode. With the extension of corrosion time, the corrosive medium had passed through the pores between the coatings, resulting in the contact between the corrosive medium and the matrix interface, resulting in the matrix corrosion damage. Corrosion products would deposit on the surface of the coating, blocking the pores between the coatings, and the corrosion rate would be reduced.