Partially Diluted Zones in Dissimilar Cladding with AWS ER NiCrMo-3 Alloy Deposited by the MIG Process on ASTM A36 Steel: Analysis and Characterization by EBSD

Abstract

The demand for oil and its derivatives has driven the oil and gas sector to explore deep waters. Nickel-based alloys, like Inconel, are used due to their corrosion resistance properties. Cladding structural steels with these alloys is a cost-effective solution. However, dissimilar metal welding poses challenges, including the formation of Partially Diluted Zones (PDZ). This work highlights the use of Electron Backscatter Diffraction (EBSD) as a very adequate technique for the microstructural characterization of dissimilar anticorrosive materials. The MIG process was utilized to perform cladding of Inconel 625 onto the A36 steel substrate. The samples were prepared for analysis using techniques such as EDS, FEG-SEM, EBSD, and Vickers microhardness testing. The results demonstrate the effectiveness of the EBSD technique in characterizing dissimilar metal cladding. The combination of EBSD with EDS analysis and microhardness testing provided comprehensive insights into the microstructure and mechanical properties of the material. EDS mapping analysis confirmed the formation of PDZ with a distinct beach-like morphology, indicating localized compositional variations. The uniform thickness of the PDZ, approximately 20 µm, highlights the convective motion and solidification behavior of the partially diluted zone. Phase map EBSD analysis revealed different crystal structures in the cladding zone, including a FCC structure for the nickel cladding layer and a BCC structure for the ferritic steel base metal. The PDZ exhibited the same crystal structure as the base metal, indicating chemical element diffusion without altering the ferritic steel structure. Contrast band EBSD analysis provided detailed microstructural information, revealing solidification structures and potential hardness variations. The observed martensite formation in the PDZ highlights its susceptibility to cracking and detachment of the coated layer. The hardness results support the microstructural findings, demonstrating significant variations in hardness across the cladding structure, particularly in the PDZ and at the interface between the Inconel alloy and the base metal. These findings contribute valuable insights into the microstructural and compositional gradients within the joint region, reinforcing their implications for material performance.