ABSTRACT
The effect of hot-sesame oil bath as an austempering medium for ductile cast iron was investigated. Samples of ductile cast iron were machined to standard dimensions for tensile, impact and hardness/microstructural analysis test specimens prior to the austempering process. Sesame oil was used as hot quenching bath for the austempering process. The samples were normalized and thereafter, austempered in hot Sesame oil bath at 250oC and 300oC for 1-5hrs from austenitizing temperatures of 850oC and 900oC. Mechanical properties of the test samples were evaluated. The test results obtained showed that samples austempered at 250oC and 300oC for 3hrs exhibited superior mechanical properties than those at 1, 2, 4 and 5hrs. The tensile strength increased from 523N/mm2 for the as-received samples to the maximum value of 1029N/mm2 for the austempered samples with percent elongation of 14.6. Impact strength increased from 61kJ/m2 (as-received) to 161kJ/m2 (austempered). It was also observed that the hardness value increased from 324 HVN (as-received) to 418 HVN after austempering. Microstructures of the samples were analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). In all the test samples, ausferrite (bainite) structures which consist of acicular ferrite and carbon enriched austenite was observed. The FTIR analysis of the oil after austempering heat treatment showedthat some peaks (functional groups/radicals) were re-configured.The research showed that, sesame oil produced ausferrite (bainite) structures, hence could be recommended for use as an austempering quenching medium for ductile cast iron