Surface hardening characteristics of microalloyed steel during ex-situ and in-situ Al₂O₃ reinforcement under TIG arcing

This work presents a comparative study of the influence of producing ex-situ and in-situ surface composite (by Tungsten Inert Gas (TIG) arcing process) on the hardenability of microalloyed steel, hereafter mentioned as steel. The ex-situ surface composite was prepared by adding hard Al₂O₃ particles into the fused surface matrix, while for in-situ surface composite, Al₂O₃ particles were made to grow in the fused surface matrix through the addition of Al. In the latter process, Al as deoxidizer reacts with the oxygen present in the steel to form the in-situ growth of Al₂O₃. The modified surface matrix exhibited the presence of martensite phase and the particle reinforcements when studied under optical microscopy, field emission scanning electron microscopy (FESEM) supported by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Vickers’ microhardness testing of the modified surface affirmed a noteworthy improvement in hardness (2.13 times) with respect to the base metal (BM) for both the cases (ex-situ and in-situ) of Al₂O₃ reinforcement. Although, the hardness improvement was found to be similar in both the cases of reinforcement, but the depth of peak hardening was observed to be greater in case of matrix reinforcement by in-situ grown Al₂O₃ (∼1.25 mm) than the ex-situ added Al₂O₃ (∼0.9 mm), which is more useful for tribological requirements of industries.