ABSTRACT
The suitability of three types of locally produced fatty oils, as quenchants was investigated in this research work. Palm oil, shea butter oil and ground nut oils were used in quenching ST 60-2 plain carbon steel produced by Delta Steel Company, Aladja. The quench characteristics of the steel as determined by the Jominy End Quench Test compare favourably with the established data for similar grade of steel. Based on the Grossmann test procedure, hardenability of the steel was estimated by measuring the centre hardness of bars with various diameters quenched in these investigated oils. The quench severity of each oil under investigation was determined using the technique developed by Detroit Diesel Engine division of the General Motors Company (U.S.A.) Experimental results indicate a strong dependence of the cooling properties of the oils on their chemical compositions. The presence of reactive (Polar) carboxylic group in addition to the fatty acid content of the oils, contribute to strong molecular adhesion of the oils to metal. This adhesion affects the heat extraction properties of the oil. The iodine content which reflects the degree of saturation is plausibly the most influential chemical constituent which determines quench severity of the oils under investigation. Palm oil which is rated as the best with a quench severity (H) value of 0.12 - 0.15 is capable of generating a hardness value equal to that of 50% martensite at the centre of a bar of 10.2mm maximum diameter as revealed by the Grossmann test. Shea butter and groundnut oils gave similar result with quench severity values of 0.08 - 0.10 and a hardenable bar diameter of 9mm. Microstructural examination of the quenched bars were further used to corroborate hardness measurements. Microstructural examination revealed, principally, ferrite - pearlite structure in all the quenched steel rounds. The observed increase in hardenability in quenched steel rounds in various media can be attributed to the formation of finer and, therefore, stronger ferrite pearlite structure. Definitely, the steel will respond favourably to alloying elements for martensite formation.