Faculty Publications
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Item Weldments of AISI grade 316 stainless steel, having a ferrite content of 4-6% and a variety of nitrogen concentrations were prepared using a modified element implant technique. Charpy impact specimens prepared from these weldments were subjected to a variety of aging treatments. Impact toughness decreases with aging time at all aging temperatures. Nitrogen is found to be beneficial to toughness. An empirical relation connecting the aging temperature, aging time and nitrogen content with toughness has been developed which can be used to estimate the time for embrittlement.(Indian Academy of Sciences, Estimation of embrittlement during aging of AISI 316 stainless steel TIG welds) Nayak, J.; Udupa, K.R.; Hebbar, K.R.; Nayak, H.V.S.2004Item Improvement in fracture toughness of austempered ductile iron by two-step austempering process(2010) Ravishankar, K.S.; Prasad Rao, P.P.; Udupa, K.R.Ductile cast iron samples were austenitised at 900°C and subjected to two types of austempering called as conventional austempering and two-step austempering. Five different temperatures, 280, 300, 320, 350, 380 and 400°C, with an austempering time of 2 h, were chosen for conventional austempering. For two-step austempering process, the first step temperatures were 280, 300 and 320°C. The samples were austempered at each of these temperatures for different times, i.e. 10, 20, 30, 45 and 60 min, and then upquenched to higher temperature of 400°C for 2 h. Fracture toughness and tensile studies were carried out under all these austempering conditions. During conventional austempering, the fracture toughness initially increased with increasing austempering temperature, reached a peak value of 63 MPa m 1/2 and dropped with further increase in temperature. During the two-step austempering, fracture toughness was found to increase with increasing first step time. The curve shifted to higher values of fracture toughness as the first step temperature was decreased and the maximum value of 78 MPa m 1/2 was obtained. The results of the fracture toughness study and the fractographic examination were correlated with microstructural features such as bainitic morphology, the volume fraction of retained austenite, and its carbon content. Ferrite lath size and stability of the retained austenite were found to influence the fracture toughness. © 2010 W. S. Maney & Son Ltd.Item Corrosion behavior of high and low temperature austempered ductile iron (ADI) in iron ore slurry(ASTM International, 2017) Aithal, P.M.; Vijayan, V.; Surendranathan, A.O.; Udupa, K.R.; Samuel, K.G.Corrosion behavior of austempered ductile iron (ADI) and forged EN31 steel balls in a ground iron ore slurry was studied as a function of time in the slurry, while the microstructure of ADI developed due to different tempering temperature and tempering time. The corrosion rates of the grinding balls immersed in the iron ore slurry were determined using electrochemical analysis and weight loss methods. It was found that the pH of the iron ore slurry increased with time and the corrosion behavior was influenced by the pH of the slurry. The corrosion rate of forged EN31 steel balls increased with the increase in time and pH of the slurry, whereas the corrosion rate of ADI balls depended on the austempering treatment. In general, the forged EN31 steel ball offered better corrosion resistance than ADIs during the early stages of exposure in the slurry (low pH values of the slurry), but at higher pH values of the slurry, the ADIs yielded better corrosion resistance than forged EN31 steel balls. The ADI austempered at higher temperatures showed better corrosion resistance than the ones austempered at lower temperatures. © © 2017 by ASTM International.