Abstract
Abstracts
This study examined the suitability of bamboo shoots for case-hardening of mild steel with a view to creating a sustainable ecofriendly means of carbonitriding, thereby eliminating the use of toxic cyanide salts in carbonitriding heat treatment process. Fresh bamboo shoots were harvested, oven dried, pulverized and mixed with powder eggshell in the ratio 4:1 and poured into metallic crucible. Suitably dimensioned 8620 steel samples were completely embedded in this case-hardening mixture and covered with kaolin luting to prevent the escape of the nascent carbon and nitrogen. The crucible and its content were loaded into the muffle furnace at ambient temperature and heated into 870oC, soaked for 4 hours and then air cooled to room temperature. This procedure was repeated for another 8620 steel samples but at a temperature of 550oC. The heat-treated samples were then ground, polished, etched with Nital and viewed under optical and scanning electron microscope for microstructural examination. The etched samples were used to obtain hardness using microhardness tester. The case depth of the case-hardened steel samples was determined with macrostructure method. X-ray diffraction (XRD) was carried out to determine the phases that constituted the case-hardened steel samples both at low and high temperatures. The results showed an increased in hardness value for the case-hardened samples when compared with the as-received. The microstructures of the case-hardened samples indicate substantial case formation for the two temperatures adopted with high temperature samples having the highest case depth and hardness. The XRD results indicate the presence of nitride and carbide phases for the case-hardened samples. The microstructure of the case-hardened sample at 550oC indicated thinner case typical of nitrided case. The study concluded that bamboo shoot can be used for carbonitriding of low carbon steel, with waste eggshell as energizer.