A novel route for joining of austenitic stainless steel (SS-316) using microwave energy

Material processing through microwaves is a challenging area of research. The present work illustrates an application of the developing technology of joining bulk metallic materials through microwave heating. Stainless steel (SS-316) in bulk form was used as candidate material to be joined. Joining of bulk SS-316 was carried out using a multimode microwave applicator at the frequency of 2.45 GHz and power of 900 W. Joining was effected through fusing and metallurgical bonding of a sandwich layer between the bulk pieces. Heating in the sandwich layer was selectively induced by exposing it to controlled microwave radiation for a predetermined period. The joints were characterized through field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and measurement of Vickers microhardness, porosity, and tensile strength. The FE-SEM study showed that the faying surfaces are well fused and get bonded with base material. Examination of the joint microstructure showed cellular-like growth in the entire joint region. The average Vickers microhardness of the core of the joint area was observed to be 290 +/- 14 Hv; however, that in the interface zone was found to be significantly higher (similar to 420 +/- 15 Hv). Precipitation of metallic carbides occurred predominantly in the joint interface region. Porosity measurement in the joint area revealed negligible porosity (0.78 per cent). Evaluation of the tensile properties of the joints showed an ultimate tensile strength of the order of 309 MPa with an elongation of 11.50 per cent.