ABSTRACT
The effect of cane molasses as quenching medium for high carbon steel was investigated. Samples of high carbon steel were spheroidized annealed and then machined prior to the hardening process. Molasses of eleven different viscosities were prepared by adding varying amounts of water; such that the ratios of molasses to water were 1:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1 and 1:0. The samples were normalized and then austenitised at 800oC. They were then soaked for 40 minutes and then quenched in water, engine oil, raw molasses and molasses solutions (in the ratio mentioned above). Half of quenched samples (ninety one) were further tempered at 350oC, held for 40 minutes and then air-cooled. Cooling curves of all the quenching media used were developed. Specific heat capacities of the various media used were determined. Mechanical properties (tensile strength, percent elongation, hardness and impact energy) of the test samples were evaluated. The test results obtained showed that for the quenched specimens, the highest value of tensile strength (1360 N/mm2) and hardness (679 HVN) was obtained in 1:1 molasses to water solution. Minimum impact strength was also obtained from sample quenched in 1:1 molasses to water solution. Microstructures of the various samples were analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). In all the tests samples martensite structure was observed. Quench cracks were observed in specimen quenched in water and 1:1 molasses to water solution. It was also observed that molasses solutions with mixture ratio 1:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, and 5:1 had quenching severity higher than that of engine oil but lower than that of water while molasses solution (5.5:1) gives cooling rate close to that of engine oil. The research showed that molasses solution with mixture ratio 3:1 gave good combination of mechanical properties (4.2% percent elongation, 905N/mm2 tensile strength, 602HVN hardness and 158KJ/mm2 impact strength); and is hereby recommended to be used as quenching medium for high carbon steels.
