Assessment of Coconut and Ghee Oils as Quenchants in Hardening of Plain Carbon Steel Process

Certain engineering parts require high hardness values, high tensile strength and impact values so that they can be used successfully for substantial duty processes. Hardening as a form of heat treatment has been used to achieve these requirements in both metal and alloys parts using different quenching media such as water, SAE 40 engine oil and other vegetable oils. The effectiveness of using coconut and ghee oils as quenchants for hardening and tempering processes of plain carbon steel with composition of 0.35% C were investigated. The plain carbon steel samples were austenitized by heating to 850 °C, soaked and quenched in the various selected quenching media. Some of the samples were tempered at 350 °C. The mechanical properties and microstructures of the samples were studied. The mechanical properties and microstructure were compared as-received, annealed quenched in water, coconut and ghee oils respectively. The results showed that tensile strength increased from 754 N/mm² in the as-received conditions to 918, 976, and 998 N/mm² for water, coconut oil and ghee oil respectively. The hardness values of the plain carbon steel also increased from 30HRC in the as-received conditions to 73HRC in water, 59HRC in coconut oil and 55HRC in ghee oil. The as-received conditions plain carbon steel samples gave the highest impact energy value and water quenched sample gave the least impact energy. The impact energies of the plain carbon steel samples of as-received conditions, water, coconut oil and ghee oil were 49, 4.3, 12 and 14 Joules respectively. The microstructures of the plain carbon steel samples quenched in both coconut oil and ghee oil revealed the formation of martensite, little bainite and retained austenite. The high hardness values obtained in these results can be attributed to the various microstructures obtained in the as-received, quenched and hardened in water, coconut and ghee oils respectively. From the investigation carried out, the coconut and ghee oils are suitable as an alternative quenchants to that of water and petroleum based SAE 40 engine oil for carbon steels without cracking or distortion, the most suitable among them being coconut oil. Hence, the oils can be used where cooling severity less than that of water is required for engineering components. The oils are cost effective and environmental friendly.