Joining and Characterization of Austenitic Stainless Steel (SS-316) and Hastelloy through Conventional and Microwave Processing Route

Abstract

The application of microwave energy in heating of materials is not new; however, newer applications are emerging in the field of material processing, which allowed microwave processing as novel processing methods. The earlier reported work was based on sintering of many ceramic materials, which are better absorbers of microwaves. The applications were further extended to metallic powders. In recent years, researchers have developed methods to process bulk metallic materials. The developments reported were in the field of joining of bulk metals and claddings on various steels. The present work is based on the comparative evaluation of properties of microwave processed joining and TIG welded joints of SS-316 and Hastelloy steels. The joints were characterized by available techniques such as XRD, EDS and SEM. Mechanical characterizations were carried in the terms of Vickers microhardness and tensile testing of joints. Results revealed that the joining of steels was successfully attempted by using nickel based powder. The characterizations of joints revealed that microwave processed joint showed cellular structure with lower defects. Joints mechanical characterizations showed that microwave processing enhanced the mechanical strength due to better metallurgical bonding and diffusion, with lower processed defects. Ultimate tensile strength was 20.7% more than TIG welded SS-316 joint and 23.25% more than TIG welded Hastelloy steel. Higher hardness was obtained in microwave processed joints due to the presence of carbon which was absorbed from graphite sheet, which led to the formation of carbides in the microstructures. Fractographic analysis showed mixed mode fracture for microwave processed joint and ductile behavior for TIG joint. The brittle behavior was due to the presence of unmelted nickel particles in the joint region.