Microstructure and Phase Analysis of Multilayer Ni–Cr–Mo Clad for Corrosion Protection

Abstract

Ni–Cr–Mo clads are commonly used on carbon steels in the oil and gas industry due to the high resistant corrosion. In this study, a three-layer Ni–Cr–Mo clad was deposited using the GMAW process. The welding current of 200 A, the welding speed of 35 cm/min, and the electrode extension of 20 mm, as well as the torch angle of 25°, are utilized to obtain a low dilution. The results showed that Fe content in the second and third layers of the clad was below 2 wt%. The segregation of Nb and Mo to interdendritic regions contributed to the formation of secondary phases, such as Laves and MC carbide precipitates. The results of chemical analysis across some dendrites and interdendritic regions confirmed that the contents and distribution of secondary phases were insignificant. Also, the transition region where the chemical composition significantly changes to reach the composition of the first layer of the clad is apparent. The microstructure of this region changes from the planar to cellular. The corrosion behavior of the clad was investigated, and it was found that corrosion resistance is not affected when the Fe content is restricted to below 2%. A passive layer consisting of Mo, Nb, Ni and Cr with O is formed on the corroded surface.