An Experimental Study of Microstructure and Mechanical Behavior of Alloy 625 Weld Overlay Deposited On ASTM A516 Grade 70

Background/Objectives: Surface modification for protection against corrosion is a critical field of research in the oil and gas industry. Alloy 625 is a superalloy with excellent resistance to pitting and corrosion. Methods/Statistical Analysis: Alloy 625 weld overlays were cladded through GTAW process on A516 carbon steel. The welding current ranging from 230 - 240 A the welding voltage 11 - 13 V; welding polarity EN (-). After welding, optical and SEM observations were conducted to determine the changes in the microstructure of base metal and clad. For examination of mechanical strength of claddings shear test was performed in accordance with ASTM A265 standard. Results: After Optical microscopy examinations, two different microstructures were observed in the HAZ zone. In the base metal, the grain size was reduced during the manufacturing process. The microstructure of weld metal was austenitic with dendritic structure. EDX observation showed that precipitates were mainly Niobium carbide (NbC). In the HAZ near the clad, microstructure included acicular ferrite, widmanstatten pattern, bainite, and pearlite. The tensile strength of a clad interface can be an important Consideration. For examination of mechanical strength of claddings shear test was performed in accordance with ASTM A265 standard. The minimum shear strength of different samples was 210 and 255 Mpa, which is higher than what it is stated in ASTM A265 standard. Conclusion/Application: The results showed that the manufacturing parameters in welding result in an appropriate mixing between base metal and clad material. The shear strength is higher than base metal and acceptable.