Evolution of Metallurgical Phases and Its Co-relation with Mechanical Properties and Corrosion Resistance of 22Cr-5Ni-3Mo and 16Cr-10Ni-2Mo Dissimilar Weldments

摘要

22Cr-5Ni-3Mo is highly sustainable in aggressive environments and also better substitute of 16Cr-10Ni-2Mo austenitic grade, which illustrates the unavoidability of dissimilar joint in many corrosive environments for cost effectiveness. The information about welding parameters, microstructure, mechanical properties, texture, and corrosion resistance behavior in highly harsh environment of dissimilar weld by common fusion welding is limited. The present study addresses dissimilar welds between 22Cr-5Ni-3Mo and 16Cr-10Ni-2Mo stainless steels, employing SMAW process by using two different weld parameters (based on current) and investigates the microstructural evolution and correlated with mechanical and corrosion resistance of the weldment. The microstructural studies were done by using an optical microscope and scanning electron microscopy. Mechanical properties are studied in terms of tensile strength and hardness. The electrochemical assessments were carried out including modified double-loop electrochemical potentiodynamic reactivation test and modified tensile test. EBSD analysis was carried out to know the grain size variation quantitatively in the weld metal and/or heat affected zone. Analyzed results showed the well-balanced ferrite/austenite amount for both high and low heat input. 16Cr-10Ni-2Mo base metal showed twin boundaries, whereas 22Cr-5Ni-3Mo base metal showed banded structure of ferrite and austenite. EBSD analysis revealed that the low heat input weld showed less grain growth as compared to high heat input with <111> austenite orientation, because oflower misorientation. With increasing heat input, ferrite content of the weld region decreases resulting in lower hardness and tensile strength. Modified tensile test in chloride environment affected the plasticity of the materials. High heat input helps to increase the intergranular corrosion resistance by increasing austenite phase formation.