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Öğe Effect of grain size and deformation temperature on mechanical properties and failure Behaviour of 316l austenitic stainless steel(G.V. Kurdyumov Institute for Metal Physics of N.A.S. of Ukraine, 2021) Katiksiz, H.; Gündüz, S.In this work, the effects of grain size and deformation temperature on me-chanical properties and failure behaviour of 316L austenitic stainless steel (ASS) are investigated. The cold, warm and hot deformation are carried out at temperatures of 25, 500, and 800°C for the strain rate of 1?10?3 s?1. The results show that strength and workhardening index of all samples decrease with increasing test temperature; however, decrement in strength and work-hardening index is more less in coarse grained samples compared to the finer grained samples. This is due to dynamic strain ageing (DSA) occurred in the coarse grained samples which showed more pronounced serrated behaviour after testing at 500 or 800°C due to interaction of mobile dislocations and solute atoms. © 2021 G. V. Kurdyumov Institute for Metal Physics, National Academy of Sciences of Ukraine.Öğe The effect of martensite morphology on static strain ageing(2013) Türkmen, M.; Gündüz, S.In this study, strain ageing behaviour of dual phase steel with different martensite morphology was investigated. Three different types (Intercritical annealing, intermediate quenching and step quenching) of heat treatment was applied in the critical temperature (775 °C). Ageing experiments after 4 % prestrain were carried out at 180 °C for different times ranging from 10 to 160 min. The microstructure after different heat treatments applied to the work pieces with the network, fiber, and the bulky martesite morphologies have been identified. It was found that the martensite morphology has no effect on the trend of ?Y (an increase in strength due to strain ageing), YS and UTS at different ageing times for 180 °C. However, at a given ageing time for 180 °C ?Y, YS, UTS and hardness values of fibrous martensite are higher than network or bulky martensite.Öğe Examining the machinability of 38MnVS6 microalloyed steel, cooled in different mediums after hot forging with the coated carbide and ceramic tool(SAGE Publications Ltd, 2021) Özlü, B.; Demir, H.; Türkmen, M.; Gündüz, S.In this study, the effect of the microstructure, hardness, and cutting speed on main cutting force and surface roughness in medium carbon microalloyed steel cooled in different mediums after hot forging, was investigated. As-received sample, which was not hot forged, and the samples cooled in the sand, air, oil, and polymerized water after hot forging were used for the experimental studies. The machinability tests were performed via turning method by using coated carbide and coated ceramic cutting tools with five cutting speed (120, 150, 180, 210, and 240 m/min), constant feed rate (0.04 mm/rev), and constant depth of cut (0.6 mm). The microstructure examinations of the samples were carried out and their hardness values were determined. Also, the wear of cutting tools were examined with scanning electron microscope. In the experimental study, it was revealed that the microstructure, hardness and cutting speed had a significant effect on the surface roughness values of the samples cooled in dissimilar environments following forging. Moreover, the samples cooled in air and polymerized water, whose hardness increased depending on the increase in the cooling rate, had the highest cutting force after machining by using the coated carbide and ceramic tool. © IMechE 2021.Öğe Friction stir spot weldability of Al-Cu-Al material couple(2011) Kaçar, R.; Emre, H.E.; Demir, H.; Gündüz, S.Recently joining of metallic materials has gained a big importance. The problem can arise joining of advanced and new materials especially in industry. Thus, the solid state bonding methods have become much more popular effective in joining such materials. One of them is friction stir spot welding. In this study, 5754 quality aluminum couple using interlayer copper were joined by friction stir spot welding method using 1000 and 1600 rpm pin rotation for 3 and 5 second time intervals. The mechanical and metallurgical properties of weldment determined. The finding from this study compared with result that was obtained from FSSW Al-Al couple. The mechanical properties of FSSW welded Al-Cu-Al couple found better than Al-Al weldment.Öğe Increasing the strength of AISI 430 ferritic stainless steel by static strain ageing(2009) Kaçar, R.; Gündüz, S.In this study, the strain ageing behaviour of AISI 430 ferritic stainless steel is investigated. A certain part of the as-received ferritic stainless steel test pieces was pre-strained for 5 % in tension, then aged at 100, 200, 300, and 400 °C for 30 min in a furnace. The other part was solution heat-treated at 950 °C for 15 minutes, water quenched and pre-strained for 2 or 5 % in tension, then aged at 100, 200, 300, and 400 CC for 30 min. UTS (ultimate tensile strength), ? Y(increase in yield strength due to strain ageing), percentage elongation and yield point elongation measurements were employed to investigate the effect of strain ageing on the mechanical properties. The experimental work has revealed that different ageing temperatures significantly affect the mechanical properties of the AISI 430 ferritic stainless steel.Öğe An internal friction study of a vanadium microalloyed steel by a dynamic mechanical thermal analyser(2002) Gündüz, S.The internal friction of a C-Mn-Al-V-N steel was investigated using a dynamic mechanical thermal analyser (DMTA) under different austenitisation time, cooling and tempering conditions. Internal friction measurements using a DMTA instrument showed energy loss peaks at different temperatures for a frequency of 1 Hz. For example, as well as the normal nitrogen peak, other broader loss peaks were observed centred on 100°C in the case of air-cooled samples austenitised at 900°C for 1 h. This is most probably due to carbon or nitrogen atom jumps associated with Fe-N-V sites, since the energy barrier which must be overcome for a carbon or nitrogen atom to break away from the foreign atom such as vanadium will be larger than that in a normal interstice. In addition, this abnormal damping peak disappeared after tempering at 450°C for 72 h. This indicates the precipitation of carbon and/or nitrogen.Öğe Strengthening of 6063 aluminium alloy by strain ageing(2008) Gündüz, S.; Kaçar, R.In this study, the artificial ageing behaviour of 6063 Al-alloy is investigated. A certain part of the aluminium test pieces was solution heat treated (SHT) at 520°C for 2 h, water quenched, then aged at 180°C for 1, 3, 5, 7, 9 and 15 h and the other part was pre-strained for 2 % in tension shortly after the solution heat treatment (SHTP), then aged at 180°C for 1, 3, 5, 7, 9, 15 h in a furnace. Tensile strength, flow stress at 3 %, microhardness and electrical conductivity measurements were employed to investigate the effect of artificial ageing on the mechanical properties of Al-alloy. The variations in ageing time have improved the mechanical properties of the 6063 Al-alloy, whereas the ductility has decreased. The experimental work has revealed that different ageing times at 180°C play a very important role in the precipitation hardening process of the 6063 Al-alloy.
