Abstract
In the present work, microwave energy is used for the surface treatment of the low-carbon steel (AISI 1018) using the Microwave Hybrid Heating (MHH) approach. The steel samples were heat-treated using microwaves at 2.45 GHz for 4–10 min using charcoal powder and charcoal + graphite powder as susceptor materials. Heated samples were quenched using water at room temperature. The parent steel and heat-treated samples were characterized for microstructure analysis using Scanning Electron Microscope (SEM), carbon content using Optical Emission Spectroscopy (OES), and a Rockwell hardness tester. The characterization results revealed that the microwave heating was intense enough to reach the austenization temperatures of steels at the surfaces. The Microwave Hybrid Heating (MHH) approach allowed successful heating to desired temperatures, and surface heat treatment with quenching resulted in the fine martensitic structure within 8 minutes of microwave exposure. The OES results revealed that the carbon intake during the microwave heating process and the carbon percentage at the surface increased from 0.16% to 0.21% due to the diffusion of graphite (carbon atoms) during phase change from austenite to martensitic structures. The formation of martensite at the surface increased the hardness by more than 3 times (58 ± 9 HRC) to the parent steel hardness (18–22 HRC) but reduced the impact strength from 26.75 to 15.28 J. Overall analysis revealed that microwave heating was successfully used for surface heat treatment of steels with significantly lower energy and time consumption making it sustainable process.
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