Investigation of the Effect of Quenching Media on the Hardness and Microstructure of Low Carbon Steel Produced in Ajaokuta Steel Complex

Heat treatment processes significantly influence the mechanical properties of steel, and the selection of appropriate quenching media is critical in determining the final hardness and microstructural characteristics of treated components. This study investigates the effect of three quenching media, specifically water, brine solution, and palm oil, on the hardness and microstructure of low carbon steel samples obtained from the Ajaokuta Steel Complex in Kogi State. Specimens were austenitised at 900 degrees Celsius for 30 minutes in a muffle furnace and subsequently quenched in each of the three media. Vickers hardness tests were conducted at five points on each specimen, and the mean hardness values were compared. Optical microscopy was performed after standard metallographic preparation to reveal phase transformations and grain structure changes resulting from each quenching treatment. Results showed that brine-quenched specimens attained the highest mean hardness of 312 HV, followed by water-quenched specimens at 287 HV and palm oil-quenched specimens at 241 HV. Microstructural examination revealed predominantly martensitic structures in the brine and water-quenched specimens, while palm oil quenching produced a mixed martensite and bainite structure indicative of a lower cooling rate. All quenched specimens exhibited higher hardness than the as-received normalised condition. The study provides practical guidance for local heat treatment workshops seeking to optimise hardness using accessible quenching media. Keywords: quenching media, low carbon steel, Vickers hardness, microstructure, heat treatment.