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    Effect of Deep Cryogenic Treatment on Microstructure, Mechanical Properties, and Residual Stress of AISI 52100 Bearing Steel
    (Engineered Science Publisher, 2023) Kara, F.; Çiçek, A.; Demir, H.
    This study covers tensile, fatigue, and material characterization tests on AISI 52100 material. In this study, the effects of deep cryogenic treatment (DCT) applied to the material at different holding hours on the mechanical properties (macro-hardness, micro-hardness, yield and tensile strength), microstructure, change in residual austenite volume ratio and residual stress values were examined. Five different holding times (12, 24, 36, 48 and 60h) were employed to the bearing steel to compare the effect of holding time in the deep cryogenic temperature. The metallographic findings showed that the deep cryogenic treatment (DCT) decreased the retained austenite and hence improved the micro-hardness, due to more homogenized carbide distribution and the elimination of the retained austenite, compared with the conventional heat treatment (CHT). The improvements in the maximum tensile strength of DCT specimens were 5.2%, 3.6%, 3.35%, 2.9% and 1.7% for DCT-36, DCT-48, DCT-60, DCT-24 and DCT-12, respectively. The highest value in macro and micro-hardness was obtained with the DCT-36 sample. It was observed that the best fatigue performance was obtained with the DCT-12 sample. In addition, the fatigue life of DCT-12, DCT-36, DCT-24, DCT-48 and DCT-60 samples increased by 122%, 108%, 100%, 40% and 12%, respectively, compared to the CHT sample. The lowest stress values for both axial and circumferential tensile residual stresses were obtained in the DCT-12 sample. © Engineered Science Publisher LLC 2023.
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    Multi-Objective Optimization of Process Parameters in Milling of 17-4 PH Stainless Steel using Taguchi-based Gray Relational Analysis
    (Engineered Science Publisher, 2023) Kara, F.; Bulan, N.; Akgün, M.; Köklü, U.
    The present study investigates the effects of cutting parameters and the variation of nose radius on cutting force, surface roughness, cutting temperature, and tool wear in the milling 17-4 PH stainless steel. The milling experiments were carried out using the Taguchi L18 experimental design with two different types of cutting nose radius (0.4 and 0.8), three different cutting speeds (70, 140 and 210 m/min), three different feed rates (0.06, 0.09 and 0.12 mm/tooth), and a constant cutting depth (1 mm). The outcomes of this study show that the cutting force, cutting temperature, and tool wear values are average 2.35, 28.89 and 1.18% lower when 17-4 PH stainless steel is machined with a 0.4 mm cutting nose radius compared to those in a 0.8 mm cutting nose radius. The surface quality is also improved by average 47.48% with an increase in the cutting tool nose radius. According to the multi response optimization results, the optimal levels of milling parameters for multiple output parameters are determined as 0.8 mm cutting nose radius, 70 m/min cutting speed and 0.06 mm/tooth, respectively. © National Research University Higher School of Economics. All rights reserved.