Due to the complexity of controlling parameters in carburization, there has been relatively little work on process variables during the surface hardening process. This work focuses on the effects of the carburizing temperature and time on the mechanical properties of mild steel carburized with activated carbon, at 850, 900 and 950 °C, soaked at the carburizing temperature for 15 and 30 minutes, quenched in oil, tempered at 550 °C and held for 60 minutes. Prior carburization process, standard test samples were prepared from the as received specimen for tensile and impact tests. After carburization process, the test samples were subjected to the standard test and from the data obtained, ultimate tensile strength, engineering strain, impact strength, Youngs' moduli were calculated. The case and core hardness of the carburized tempered samples were measured. It was observed that the mechanical properties of mild steels were found to be strongly influenced by the process of carburization, carburizing temperature and soaking time at carburizing temperature. It was concluded that the optimum combination of mechanical properties is achieved at the carburizing temperature of 900 °C followed by oil quenching and tempering at 550 °C.
This paper reports investigations made on the annealing heat treatment effects on steel welds. The properties of the weld investigated were hardness value and toughness. Micro examination of the samples was also done with optical microscopy. Four (4) different grades of steel rods (10mm) in diameter were obtained. The range of the carbon contents of the steel rods was from 0.16 wt pct C to 0.33 wt pct C. From each grade of the steel materials, grooved specimen of about 150mm were prepared. The groves were then filled to create welds using arc welding. The resulting welds were then subjected to annealing heat treatment. The hardness values and toughness of the welds were determined. The microstructural analyses of the welds were carried out as well. The results show that hardness and toughness were dependent on the carbon content. There was also significant microstructural modification due to heat treatment.
This study focussed on the work hardening behaviour and microstructure of austenitic manganese steel relative to premature failure of crusher jaws. Samples of sound and failed crusher jaws were taken, the change with depth from the working surface to the sample core was measured and their microstructures observed. The study revealed a sharp hardness gradient in the failed crusher jaws, and presence of large carbides at both the austenite grain boundaries and in the austenite matrix. The failure of crusher jaws was attributed to brittle fracture as a result of precipitates of carbides from the inability of precipitated carbides to absorb shock during impact working. Finally, we conclude that the failure occurred as a result of inadequate quenching operations during the manufacturing process that resulted in the formation of carbide precipitates which embrittle the austenitic manganese steel, reduce its ability to withstand shock and create a non uniform plastic flow as it is work hardening.
This study focuses on the characterization of cold briquetted iron (CBI) using powder diffraction techniques. CBI is under-sized metallic fines produced during the direct reduction process (DR-process), which are made into briquettes when they are cold using sodium silicate and lime as binder and flux respectively. Powder sample of CBI was prepared by crushing and grinding some of the briquettes and sieved through 30-microns aperture. Thereafter, the constituent phases in the sample were identified using X-Ray Powder Diffraction (XRD) techniques and scanning electron microscopy. It was observed that CBI includes among others, 67% metallic iron, 23% cementite, 5% silica and 5% wustite. It was also noted that the concentrations of the constituent phases were not uniformly distributed. The spherical quartz particles were found to be concentrated along the crack lines, which were suspected to be initiator of these cracks and crevices that characterize CBI.
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