Microstructural and mechanical properties of mild steel pipes joined using selective microwave hybrid heating

Abstract

Microwave joining is an eco-friendly non-conventional technique resulting in fine grain structure, overall improvement in quality, and performance of the processed materials with up to 90 % less energy consumption than conventional processes. Due to problems including difficulty in positioning the susceptor material in the joint region and reduced solid cross-section area of hollow pipes, an efficient and precise process for microwave joining metallic pipes is yet to be developed. The present work is an attempt to join mild steel (MS) pipes placed horizontally in a conventional microwave oven. COMSOL Multiphysics software has been used to simulate the microwave joined MS pipes, wherein the temperature distribution in the specimen inside the microwave cavity was analyzed. The MS pipe was successfully joined at an exposure time of 900 s with nickel powder as an interfacial material. Characterization of the welded joint has been carried out using microstructural and mechanical properties. A fully dense and homogeneous microstructure with good metallurgical bonding was revealed through scanning electron microscopy (SEM). The Vicker's microhardness of joined specimen was 262 ± 10 HV at the joint zone, while the heat affected zone (HAZ) was 240 ± 10 HV. The joined specimen exhibited an ultimate tensile strength of 217 ± 8 MPa with an elongation of 4.4 ± 0.7 %.