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.
Keywords: Austempering, Austenitize, Composition, Heat treatment, Microstructure, Properties
Exploring the Potentials of Using Palm Kernel Oil Esters (Palm Kernel Oil+Bitumen) For Austempering Process of Medium Carbon and High Carbon Steel (Published)
Exploring the potentials of using palm kernel oil esters as quenching media on medium and high carbon steel was investigated for a more efficient production of engineering and industrial materials that requires steel as its major raw material since steel and steel industry is one of the catalysts for a number of industries such as the automobile, shipbuilding, containers, railroads, constructions and a lot of domestic appliances which will complement each other in economic growth. The samples were austenitized at various temperatures (8500C to 9500C). Tensile strength, impact strength and hardness test were used to measure the quenching strength of the media. The microstructures and mechanical properties were used to determine the severity of the palm kernel ester. From the results obtained, it shows that the hardness values for both 0.56%C and 0.76%C-Steel were higher (502 and 513 HV) than the as received values (321 and 406 HV) which shows better improvement as a result of formation of bainite structure and diffusion of carbon precipitates in the steel samples. The research carried out showed that palm kernel oil+bitumen can be used as quenching media in austempering process.
Keywords: Austempering, Austenitizing Temperature., High Carbon Steel, Holding Time, Medium Carbon Steel, Palm Kern Oil+Bitumen