Investigation on the Interrelationship between the Chemical Composition, Heat Treatment Parameters and the Phase Transformation Process, Microstructure Evolution and the Mechanical Properties of Austempered Steel (Published)
The interrelationship between chemical composition, heat treatment parameters, and phase transformation, microstructural evolution and the mechanical properties of austempered steel was studied. Two samples of steel with different percentage composition of carbon of 0.56 and 0.76 were used for the study. They were austentized at the respective temperatures of 8000C, 8400C, 9000C and 9600C for 30 minutes. They were thereafter quenched using bitumen-palm kernel oil, and subjected to austempering isothermal heat treatment at 4200Cfor different time durations of 5, 15, 30, 45 and 60 minutes. The samples were tested for tensile strength, elongation, hardness and impact strength. They were also subjected to microstructural characterization to determine the phases in the microstructures and their effects on the properties of the developed materials. Results obtained revealed that the dominant phases in the microstructure were bainite, matensite and traces of retained austenite. It was found that decreasing austenitizing temperature yields finer grain structures with increase in tensile strength and elongation with decrease in hardness and relatively little effect on the impact strength. At any given austenitizing temperature, shorter austempering holding time yielded optimum properties in tensile strength and elongation while higher hardness values were associated with shorter holding time. These results proved that the process conditions have strong correlation with both the microstructures and the mechanical properties. It was concluded that the most promising microstructures with respect to excellent strength-ductility property are those obtained at the ausenitizing temperature range of 800 -8400C for the austempering time range of 5 – 30 minutes. These materials have potential for load bearing application while those austenitized within the range of 900 – 9600C using austempering time range of 5 – 15 minutes are candidate material for wear resistant application.
According to Van Dijk, all phenomena have macro and Microstructures. This paper examines the interaction of these structures, leading to an innovative one: the structure termed Macrofiction. It is a layer of patchy structures, joined together to build an untold story. Separate stories are connected through the cohesive elements they share. Moreover, the cognitive mechanism and information structure of a story on the level of the Microstructure is in harmony with the plot and the general idea of the fiction. This idea is inspired by specimens from classical Persian literature such as “The Conference of the Birds” (1177) and continues well into contemporary literature. This paper demonstrates the nature of macrofiction and the process by which it may be formed in a fictional discourse such as that found in Ebrahim Golestan’s story cycle, “Hunting the Shadow”.