Browsing by Author "Saklakoğlu N."

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    Characterization of hot forged P285NH steel by metallurgical investigation and reliability analysis; [Charakterisierung von warmgeschmiedetem P285NH-Stahl durch metallurgische Untersuchungen und Zuverlässigkeitsanalyse]
    (Wiley-VCH Verlag, 2020) Saklakoğlu N.; Çivi C.; Hocalar Ç.; Demirok S.
    An extensive study was carried out to investigate the effect of cooling rate after hot forging process and normalization step on the hardness, strength and impact toughness and microstructure of P285NH steel. Understanding of the combined effect of cooling rate and normalization on the mechanical and microstructural properties of the steel would help to select conditions required to achieve optimum mechanical properties. The results indicated that the microstructures of all forging and cooling conditions were dominated by ferrite and pearlite phases with different morphologies and grain sizes according to various cooling rates. Conveyor cooling led to a formation of relatively fine acicular ferrite and pearlite grains in comparison to batch cooling which presented coarse polygonal ferrite with pearlite. Based on the data fluctuation of Charpy tests, the normal distribution provided a statistical analysis method for assessing the reliability. Through the statistical analysis of the distribution function, it can be concluded that normalization step is necessary for higher reliability. Both batch cooling and conveyor cooling did not give the required reliability level for safety components due to heterogeneities in the microstructure. © 2020 Wiley-VCH GmbH
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    The effect of thermomechanical process on metallurgical and mechanical properties of 38MnVS6 micro alloyed steel; [Einfluss des thermomechanischen Prozesses auf die metallurgischen und mechanischen Eigenschaften von mikrolegiertem 38MnVS6-Stahl]
    (John Wiley and Sons Inc, 2021) Erçayhan Y.; Saklakoğlu N.
    This study aims to have the proper mechanical properties without applying any heat treatment process after hot forging by using 38MnVS6 micro alloyed steel in tow hook manufacturing which is used in automobiles. The effect of forging temperature and cooling rate on metallurgical and mechanical properties of micro alloyed steel is investigated. The samples of micro alloyed steel are forged at 800 °C, 850 °C, 900 °C, 1050 °C and cooled down at the rates of 0.75 °C/s and 1.5 °C/s. The forging temperature and the cooling rate have a significant effect on toughness by the experimental and numerical studies. The amount of ferrite increases with a decreasing forging temperature, and the toughness is improved by increasing the amount of ferrite. Also, by increasing the cooling rate after forging at 1050 °C, the acicular ferrite is observed which has a positive effect on both the toughness and strength of the micro alloyed steel. © 2021 Wiley-VCH GmbH
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    Selective laser melting of Ti6Al4V alloy: Effect of post-processing on fatigue life, residual stress, microstructure, microhardness and surface roughness
    (Elsevier Inc., 2023) Önder S.; Saklakoğlu N.; Sever A.
    In this study; turning, milling, heat treatment and shot peening (SP) post-process operations alone or in different combinations were performed on Ti6Al4V specimens which were produced by selective laser melting (SLM); then the effects of these operations on the fatigue life, residual stress, microstructure, microhardness and surface roughness were investigated. SP processes were carried out in two different types, traditional and multiple, and it was observed that the multiple SP process, which was carried out with the same almen intensity as traditional, with a smaller ball diameter, was effective in reducing the surface roughness. As a result of the heat treatment, α + β transformation was observed in the microstructure. α phase was seen in both lamellar and globular forms. Traditional SP and multiple SP processes provided a significant increase in microhardness values in the 0–250 μm depth range. A significant decrease in the microhardness values of the heat-treated specimens was observed due to the α + β transformation in the microstructure. Traditional SP and multiple SP processes enabled the residual stress type to become compressive type in both the x-axis and the y-axis in the 0–150 μm depth which is a very critical region for fatigue cracks despite the x-axis direction surface unmachined. Fatigue test were performed on machined, multiple shot-peened and machined after heat-treated specimens. The best results in terms of fatigue strength were obtained in the specimens that were heat-treated. It was observed that the most important cause of fatigue crack initiation in multiple shot-peened specimens was an internal defect located deeper than 250 μm. Fisheye formation was observed on fracture surfaces of some multiple shot-peened fatigue specimens. © 2022 Elsevier Inc.