EFFECT OF HEAT TREATMENT ON HARDNESS AND WEAR RESISTANCE OF A FAILED AUTOMOBILE BRAKE DISC
In an attempt to improve the wear resistance of a failed automobile brake disc, different type of heat treatment operation was carried out on the samples of the disc. The samples were heated to 840°C 860°C and 880°C in a muffle furnace, and quenched in water, palm oil and air, separately. Water and oil quenched samples were later tempered at 200°C. The chemical composition of the failed brake disc was obtained by an optical emission spectrometer (OES), while the hardness value was measured using Brinell hardness testing machine. The highest Brinell hardness value of 331 BHN was obtained from the water-quenched sample heated to 880°C. The hardness values of the oil-quenched samples surpass that of air-quenched samples. The tempered samples displayed lower hardness values compared with the hardened samples, although the sample heat treated at 880°C, water-quenched and tempered still possesses high hardness value. The reduction in hardness of most of the samples after tempering suggests possible increase in ductility and toughness. As a result of the heat treatment and subsequent quenching, the retained austenite in the samples transforms to martensite, while the ferrite, flakes of graphite, and cementite were restructured. This shows that the brake disc could be hardened and tempered to obtain optimum hardness with improved ductility and toughness. This will result in better wear resistance, increase service life, and thus reduce brake failure and other related transportation hazard.
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