Investigation on microstructure and mechanical properties of the dissimilar weld between mild steel and stainless steel-316 formed using microwave energy

Abstract

Dissimilar weld between a mild steel and a stainless steel-316 was formed by exposing the candidate materials to electromagnetic radiation in the microwave band. Characterisations of the joints were carried out with respect to some aspects of microstructural and mechanical properties of the fusion joints. The joining trials were carried out in an industrial microwave applicator at a fixed frequency of 2.45 GHz and 1.2 kW power while exposed for a duration of 600 s in atmospheric condition. Stainless steel-316 powder was used as the filler material for joining. Principles of microwave hybrid heating were utilised for heating and subsequently melting the metal-based materials in the joint zone. Characterisation of the microwave hybrid heating–induced dissimilar welds were carried out using X-ray diffraction, field emission scanning electron microscopy, microhardness tester and universal testing machine. The presence of carbides and intermetallic in the joint zone were evidenced in the X-ray diffraction results. The microstructures observed through scanning electron microscope show the metallurgical bonding between the substrates to be joined through complete melting of the powder particles and fusion of the base materials. The Vicker’s microhardness in the core of the joint was observed to be 380 HV, which was significantly higher as compared to the base materials due to the formation of dendritic structure and various carbides in the joint zone during microwave hybrid heating process. The average ultimate tensile strength of the joints was measured to be 420 MPa with an elongation of 6.67%. The average flexural strength of the joints was observed to be 787.5 MPa with an elongation of 5.14%. The optimum temperature required for joining was measured using an in-built non-contact infrared pyrometer and was found to be 1360 °C.