Mechanical properties of heat-treated medium carbon steel in renewable and biodegradable oil

The heat treatment of steels under controlled conditions alters their physical and mechanical properties, enabling them to meet the desired engineering applications. In this study, the suitability of a Namibian local oil (marula oil) as an alternative quenchant to SAE40 engine oil (Standard quenchant - a synthetic oil derived from natural or crude oil) for industrial heat treatment of medium carbon steels was investigated. SAE40 engine oil served as the control. The mechanical properties (tensile strength, yield strength, percentage elongation and hardness) of the treated and untreated samples were investigated at the temperatures of 850^oC, 900^oC, 950^oC and 1000^oC. The untreated sample had the highest amount of elongation (40%), while the sample quenched in marula oil had the highest hardness (24.33HRD) and tensile strength (530.32 N/mm²) values compared with both the untreated and the SAE40 engine oil quenched samples. Hence, marula oil showed high potential as an alternative quenchant to petroleum based SAE40 engine oil for quenching medium carbon steels, without cracking or distortion.