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dc.contributor.authorDeshpande, Makarand-
dc.guideGhosh, P. K.-
dc.guideKrishanan, K. N.-
dc.description.abstractWelding of austenitic stainless steel involves problems like microfissuring and carbide precipitation. Microfissuring can be controlled by presence of a controlled amount of delta ferrite in the weld by proper choice of filler metal. Carbide precipitation occurs when the austenitic stainless steel is heated in the range of 500° to 800°C. In this work, formation of delta ferrite, carbide precipitation and quality of flash butt welded austenitic steel was assessed by varying the welding parameters. During this investigation, austenitic stainless steel-(3 mm thick plates) of AISI type 316 was used. The material was welded by changing the welding parameters like effective current, flashing way, flashing acceleration, current way, upsetting way (with and without current), upsetting pressure. Microstructural studies were carried out by using suitable etchant to find out the presence of delta ferrite and carbides. The quality of weld was assessed by notch tensile and C impact tests as well as bend test of the weld metals. The fracture surfaces of the specimens failed during bend, notch tensile and impact tests were observed under SEM. It was found that quality of flash butt welds of austenitic stainless steels was affected by welding parameters. The increase in effective current increased peak temperature which enhanced the amount of delta ferrite and its dendritic iii iv growth at weld centre. The notch tensile strength increased with the increase in current upto 13 KA followed by decrease in it with further increase in effective current upto 15 KA caused by oxidation at weld region. The longer 'flashing way' of the order of 8.5 mm produced a microstructure having relatively more dendrites. A moderate change was observed in notch tensile strength with variation in flashing way from 6.5 mm to 7.5 & 8.5 mm.. Increase in 'flashing acceleration' also controlled the peak temperature reached during welding. Higher flashing acceleration of the order of 0.2 mm/sect minimised delta ferrite transformation and enhanced carbide precipitation. The notch tensile properties increased with the increase in flashing acceleration. A high 'upsetting way with current' of the order of 2.0 mm increased the peak temperature which formed coarse dendritic delta ferrite. This reduced the notch tensile strength. The forging action during flash butt welding was controlled by 'upsetting without current' and 'upsetting pressure'. With higher 'upsetting way without current' of the order of 3.-0 mm and 4.0 mm the specimens with overlap were observed, but interestingly very high notch tensile strength was observed for these specimens. With very low upsetting pressure, the high amount of delta ferrite of V dendritic nature was observed. The notch tensile strength increased with reduction in upsetting pressure. The effect of water quenching and oil quenching of the weldments immediately after welding was studied during this work. It was found that the quenching of welds in water and oil reduces the carbide precipitation along the grain boundary. The weld zone microstructure containing high amount of delta ferrite of dendritic nature was observed. In general, all specimens were found to have good bend properties except for those prepared at a high effective current of the order of 15.8 EAen_US
dc.typeM.Tech Dessertationen_US
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