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.

Optimization of GMAW Process Parameters for Weld Overlay of Inconel 686 Superalloy on Low-Carbon Steel

“…More dilution and microsegregation of Mo and Cr can reduce the welding quality and corrosion resistance of the overlay [8,11,16,31,32]. Hence, the present study confirms that the process parameters employed to fabricate overlay IN686 alloy on low-carbon steel plates can be optimized by selecting parameters that reduce heat input, dilution, and, therefore, microsegregation.…”

“…The presence of elongated chains of precipitates in the intercellular regions (Fig. 15 c) can significantly impair the mechanical properties of the weld overlay not only because they are brittle phases, but also due to their orientation, providing a preferential path for crack propagation which has been also reported by [5,8,10,16,29]. As for the columnar dendritic growth in the middle of the weld metal, the volumes for the formation of secondary phases became narrower due to the growth of secondary arms, which help to break the continuity of the secondary phases, making smaller particles and a more tortuous crack propagation path.…”

“…GMAW reduces the amount of the dilution (by increasing arc efficiency and inducing lower heat input [13]) and increases the surface quality of the overlay, which consequently enhances the weld overlay corrosion resistance. Najafi et al [16] reported a maximum of 13% dilution in the fusion zone by using the GMAW for IN625 overlay, as measured by Fe content in the weld overlay, which was less than the minimum dilution observed for GTAW overlays as noted above. Petrzak et.…”

“…Conversely, the GMAW technique results in greater filler metal deposition, due to a continuous wire feeding process, and is attracting more attention for weld overlays in industrial applications [13][14][15][16]. GMAW reduces the amount of the dilution (by increasing arc efficiency and inducing lower heat input [13]) and increases the surface quality of the overlay, which consequently enhances the weld overlay corrosion resistance.…”

Microstructure and electrochemical evaluation of ER-308L weld overlays on AISI 321 stainless steel for repair applications

“…14,15 According to the existing literature, various studies have been made on the CR of Ni-Cr-Mo coatings and the various steel welds in salt environments. [16][17][18] Based on the mentioned literature, the research attempts emphasized the multilayer deposition of stainless steels, Ni-based superalloys as a coating material, and the influence of alloying elements on the microstructure and mechanical properties. However, few research attempts on the microstructural and corrosion behaviour of multilayer coatings deposited by the gas metal arc welding (GMAW) process have been published so far.…”