Effect of heat treatment on wear resistance of a grinding plate
The effects of heat treatment on the hardness and by extension the wear resistance of locally produced grinding plate of known composition were investigated. Specimens were prepared from the grinding plate and were heat treated at 840°C, 860°C and 880°C and quenched at different rate. Some of the specimens were quenched in water and palm oil, while some of the quenched specimens were tempered at 200°C. The results obtained were corroborated with the microstructure of the specimens examined under an optical microscope. The hardness values of the grinding plate specimens quenched in various media increased with increased heat treatment temperatures, and are higher than that of the as-cast specimen. Water quenched tempered specimens (WT) displayed higher hardness values than the as-cast, whereas oil quenched tempered specimens (OT) possessed lower hardness values. The presence of carbide was evident on the micrographs of the water quenched specimens at all the exposure temperatures, which corroborated the observed increased in the hardness values with increased heat treatment temperatures. However, there was significant reduction in the hardness value of the water quenched tempered specimens compared with the quenched specimens, which indicates a significant improvement in toughness. Thus, water quenched and tempered specimen with relatively high hardness value and improved toughness, will be suitable for use as grinding plate because of its relatively better wear resistance. The hardness of the specimens was found to depend on the formation of carbide precipitates within the matrix structure. There is also possibility of production of structure consisting of graphite embedded in a martensitic matrix through the heat treatment.
Keyword: carbide, heat treatment, hardness, microstructure, wear resistance