Corrosion behavior and mechanism of the high‐strength low‐alloy steel joined by multilayer and multipass welding method

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. With the increase of the number of welding layers, the uniformity of the microstructure gradually deteriorates, the voltaic potential gradually becomes negative, and the corrosion resistance comes to be worse. The heat‐affected zone (HAZ) became the weak link for corrosion of welded joint, on account of the nonequilibrium organization and galvanic coupling among base metal, weld metal, and HAZ.