Austenitising temperature and quenchant viscosity influence on mechanical properties of normalised green oil quenched 42CrMo4 steel

Green oils are plant extract oils such as Karanja, Pinnay, Coconut oil, which are non-corrosive, non-toxic and environmentally friendly, and are capable of replacing petrol oil quenchants. In this study, Pinnay oil, Karanja seed oil and their blends (equal volume in proportion) were used as quenchants. Before quenching for hardening, austenitising was performed at three different temperatures ranging from 890 °C to 950 °C. The effects of austenitising temperature and vegetable oil quenchants on the hardness, room-temperature impact toughness and microstructure of normalised 42CrMo4 steel were determined. Prior to the hardening treatment, the as-received 42CrMo4 steel was subjected to normalising treatment, which enhanced the hardness and toughness properties due to grain refinement of the as-received steel. As the oil viscosity decreases, the hardness increases with marginal alteration in the impact resistance. In all the quenching condition, with an increase in austenitising temperature up to 920 °C, there was an increase in hardness around 7% and decrease in toughness around 37%, whereas at 950 °C there was a decrease in hardness around 24% and an increase in the toughness of the steel around 47% as compared to that of 920 °C. Also, blend oil quenched specimens showed balanced hardness and impact toughness compared to Pinnay oil and Karanja oil quenched specimens.