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Öğe AISI 304 ve AISI 316 Östenitik Paslanmaz Çeliklerin İşlenebilirliğinin Değerlendirilmesi(2017) Özbek, Nursel Altan; Çiçek, Adem; Gülesin, Mahmut; Özbek, OnurBu çalışmada AISI 304 ve AISI 316 östenitik paslanmaz çeliklerin işlenebilirliğini değerlendirmek amacıyla kaplamasız tungsten karbür kesici takımlar kullanılarak tornalama deneyleri yapılmıştır. Deneyler, kuru kesme şartlarında sabit kesme derinliği (2,4 mm), dört kesme hızı (100, 120, 140 ve 160 m/dak) ve üç ilerleme hızında (0,15, 0,3 ve 0,45 mm/dev) gerçekleştirilmiştir. AISI 304 ve AISI 316 çeliklerin işlenebilirliği takım aşınması, esas kesme kuvveti ve yüzey pürüzlülüğü açısından değerlendirilmiştir. Deney sonuçları AISI 316 çeliğinin işlenmesinde kesici takımın daha fazla aşındığını göstermiştir. Ayrıca AISI 316 çeliğinde daha yüksek kesme kuvveti ve yüzey pürüzlülüğü değerleri ölçülmüştür. Deneysel çalışma sonunda, AISI 316 çeliğinin AISI 304 çeliğine kıyasla işlenebilirliğinin zor olduğu ortaya konulmuşturÖğe AISI 304 ve AISI 316 Östenitik Paslanmaz Çeliklerin İşlenebilirliğinin Değerlendirilmesi(Gazi Univ, 2017) Özbek, Nursel Altan; Çiçek, Adem; Gülesin, Mahmut; Özbek, OnurIn this study, turning tests were performed to assess machinability of AISI 304 and AISI 316 austenitic stainless steels using uncoated tungsten carbide tools. The tests were conducted at four cutting speeds (100, 120, 140 and 160 m/min), three feed rates (0.15, 0.3 and 0.45 mm/rev), and a fixed depth of cut (2.4 mm) under dry cutting conditions. Machinability of AISI 304 and AISI 316 steels was evaluated in terms of tool wear, main cutting force and surface roughness. Experimental results showed that larger wear damages formed on the cutting inserts used for machining of AISI 316 steel. In addition, higher values of cutting forces and surface roughness were measured in machining of AISI 316 steel. In consequence of experimental study, it was found that AISI 316 steel had harder machinability characteristics than AISI 304 steel.Öğe EFFECT OF CRYOGENIC TREATMENT AND TEMPERING TEMPERATURE ON MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF AISI 431 STEEL(2022) Özbek, Nursel Altan; Yıldız, EmreThis study investigated the effects of cryogenic treatment and tempering temperature applied after cryogenic treatment on the mechanical and microstructural properties of AISI 431 martensitic stainless steel. After conventional heat treatment (CHT), the steel samples were cryogenically treated at -180 °C for 6 hours and then tempered at 200 °C (CT200) and 300 °C (CT300) for 2 hours. After these processes, hardness measurement, tensile test, and abrasion test were carried out to determine the mechanical properties of the steel samples. In addition, microstructure photographs were taken to determine the microstructural properties. As a result of the study, it was observed that the cryogenic treatment applied after the conventional heat treatment was effective on the mechanical properties of AISI 431 martensitic stainless steel. Cryogenic treatment and tempering temperature showed the greatest effect on wear resistance. CT200 and CT300 samples were 62% and 56% less worn than the CHT sample. Compared to the CHT sample, the yield strength of CT200 and CT300 samples increased by 6.95% and 7.03%, while the hardness increased by 3.89% and 3.52%.Öğe Effect of cryogenic treatment holding time on mechanical and microstructural properties of Sverker 21 steel(Walter De Gruyter Gmbh, 2022) Özbek, Nursel Altan; Özbek, OnurThis study investigated the effects of shallow and deep cryogenic treatment on the microstructural and mechanical properties of Sverker 21 tool steel. After conventional heat treatment, shallow cryogenic treatment at -80 C for 2, 12, and 24 h and deep cryogenic treatment at -180 C for 2, 18, and 36 h were applied on the steel samples. After that, the samples were tempered at 200 C for 2 h. As a result of these treatments, the steel samples' hardness, toughness, and wear rate changes were determined, and their microstructural properties were investigated. As a result of the study, it was observed that the cryogenic treatment had positive effects on the mechanical and microstructural properties of Sverker 21 steel. Mechanical properties also improved with increasing holding time for both cryogenic treatment types. It has been found that the deep cryogenic treatment provides better mechanical properties compared to the shallow cryogenic treatment. The maximum hardness and wear resistance were obtained in the deep cryogenically treated sample for 36 h. Compared to the CHT sample, the hardness and impact energy of the DCT(36) sample increased by approximately 11.75% and 17.36%. An improvement of approximately 64% was observed in the wear rate.Öğe Effect of cryogenic treatment on wear behavior of Sleipner cold work tool steel(Elsevier Ltd, 2023) Kara, Fuat; Küçük, Yılmaz; Özbek, Onur; Özbek, Nursel Altan; Gök, Mustafa Sabri; Altaş, Emre; Uygur, İlyasCryogenic treatment, also known as subzero heat treatment, is a cooling process that complements conventional heat treatment to improve the properties of metals. Unlike coatings, it is a one-time, inexpensive, permanent operation that affects the entire part. This method is mainly applied to tool steels used in mold making. In this study, the changes caused by the effects of shallow and deep cryogenic treatment on Sleipner cold work tool steel were investigated in terms of microhardness, microstructure, coefficient of friction (COF), and wear rate (WR). For this purpose, the test specimens were subjected to the cryogenic treatments performed at two different temperatures (?80 ºC for the shallow cryogenic treatment (SCT) and ? 180 ºC for the deep cryogenic treatment (DCT)) and various retention times (12 h, 24 h for SCT and 12 h, 24 h, 36 h for DCT). Dry sliding wear tests were carried out under different loads (10 N and 20 N) and varying test durations (60, 120, and 240 min) at a constant sliding speed of 0.075 m/s. According to the microhardness results, it was determined that the cryogenic treatment increased the hardness by 6.53 %. According to the microstructure investigations, a more homogeneous structure was observed with the cryogenic treatment, and secondary carbide precipitations were detected. It was observed that the conventional heat-treated (CHT) sample gave the highest COF value with an average coefficient of friction of 0.63. The lowest COF value of 0.58 was observed in the DCT-12 sample. After the wear tests, the lowest wear rate value for both load values was obtained from the DCT-36 specimen. © 2023 Elsevier LtdÖğe Effect of tempering temperature on mechanical properties and microstructure of AISI 4140 and AISI 4340 tempered steels(Walter De Gruyter Gmbh, 2022) Saraç, Erdem; Özbek, Nursel AltanThe AISI 4140 and AISI 4340 tempered steels are widely used in industry. This study investigated the effects of the tempering temperature on the mechanical properties of these steels. The steels were kept at 850 degrees C for 30 min, left in an oil environment, and then subjected to hardening. The samples were then tempered for 1 h at four different temperatures (300, 450, 550, and 650 degrees C). Hardness measurements were performed to determine the mechanical properties of the materials. In addition, the samples were subjected to tensile, notch impact, and wear tests. The samples were also examined microstructurally. The results revealed that the hardness, impact energy, and wear rates of samples of both steels decreased when tempering was applied after quenching. As the tempering temperature was increased, these values tended to decrease. However, the impact value increased in parallel with the tempering heat treatment and tempering temperature.Öğe Effects of Shallow and Deep Cryogenic Treatment on Tool Flank Wear and Surface Roughness in Machining 41Cr4 Steel(Springer, 2023) Özbek, Nursel AltanThis study presents the affects of cryogenic treatment on flank wear (Vb) and surface roughness (Ra) in machining 41Cr4 steel with shallow (SCT (15 h at -80 degrees C)) and deep (DCT (15 h at -196 degrees C)) cryogenically treated carbide tools. The study revealed that the cryogenic treatment increases the hardness and wear resistance of coated carbide tools and improves the surface roughness, thanks to the changes in the microstructure. The eta-phase is approximately 17.5 and 24.64% higher in the shallow and deep cryogenically treated tool's microstructure than in the untreated tool (U). The best machining performance was founded with the deep cryogenically treated cutting tool. Compared to the untreated tool, shallow and deep cryogenic treatment increased the hardness of the cutting tools by approximately 8.66 and 10.17%. Compared to the untreated cutting tool, the deep cryogenically treated tool was less worn at rates ranging from 13.04 to 18.60% and provided a lower average surface roughness between 2.49 and 20.15%. With increasing feed rate and cutting speed, the amount of cutting tool flank wear also increased. While the surface roughness values decreased slightly with increasing cutting speed, the increasing feed rate caused the surface roughness to increase significantly. The analysis of variance results showed that the most significant parameter on the cutting tool flank wear was heat treatment with a rate of 67.34%, and the most influential parameter on the surface roughness was the feed rate with a rate of 96.33%.Öğe Effects of Tempering Heat Treatment Temperatures on Mechanical Properties of Carbon Steels(2021) Saraç, Erdem; Özbek, Nursel AltanIn the present study, the effects of tempering heat treatment temperatures on the mechanical properties of AISI 1020 and 1040 carbon steel types, which have a wide range of use in industry, were investigated. The samples were quenched at 850 °C, and then they were tempered at three different temperatures; 450, 550, and 650 °C, for 1 hour. Hardness measurements of the samples were performed to determine their mechanical properties. Besides, the samples were subjected to tensile and charpy impact tests. The samples were examined microstructurally, as well. The results reveal that the hardness, tensile strength, and yield strength values of both samples decreased when tempering heat treatment was applied after quenching. As the tempering temperature increased, these values tended to decrease. However, the impact value increased with the tempering heat treatment and increasing tempering temperatureÖğe Investigation of the Effect of Deep Cryogenic Process on Residual Stress and Residual Austenite(2021) Kara, Fuat; Uygur, İlyas; Özbek, Onur; Özbek, Nursel AltanThe cryogenic treatment, known as holding materials at sub-zero temperatures, is a method usedto improve the properties of metal and non-metallic materials in recent years. This method ismainly applied to tool steels used in mold making. In our country, the use of cryogenic processescontinues to be widespread by many private sector organizations, primarily in mold materials.The benefits of this process have been recognized in many sectors, from the defense industry tothe automotive industry. In this study, the macro hardness, micro hardness and microstructureproperties of Sleipner cold work tool steel, which was applied traditional heat treatment and deepcryogenic process for 24 hours, were examined and the changes in the mechanical properties andmicrostructure of the material were determined. However, by measuring the residual stress andresidual austenite amounts in the materials with the X-Ray Diffraction (XRD) Method, thedifference between the samples was determined. The macro hardness of the CHT and DCT-24samples was measured as 60.96 HRC and 61.46 HRC, respectively. Micro hardness values were also measured as 734.26 HV and 761.83 HV, respectively. Deep cryogenic treatment increasedmacro and microhardness by 0.5 HRC and 27.57 HV, respectively. The amount of residualaustenite decreased by 36% after deep cryogenic treatment. Axial and circumferential residualstress values also decreased by 48.84% and 36.52%, respectively. As a result, deep cryogenictreatment increased the hardness of Sleipner cold work tool steel, homogenized themicrostructure, reduced residual austenite and residual stress values and provided positiveimprovements.Öğe Investigation of The Effects of Shallow Cryogenic Treatment on The Mechanical and Microstructural Properties of 1.2436 Tool Steel(2022) Özbek, Onur; Özbek, Nursel AltanThis study investigates the effects of shallow cryogenic treatment on the microstructure, hardness and wear resistance of 1.2436 steel. For this purpose, quenched (QT) 1.2436 steel samples were subjected to shallow cryogenic treatment at -80 °C for 12 hours (SCT12) and 18 hours (SCT18). Hardness measurement and wear test were carried out on the samples and the samples were examined microstructurally. As a result of the study, it was observed that the cryogenic treatment provided a denser and homogeneous carbide distribution in the microstructure of 1.2436 steel. The amount of carbide in the microstructure increased by 18.80% with shallow cryogenic treatment for 18 hours. As a result of the hardness and wear tests, it was determined that the cryogenic treatment positively affected the hardness and wear resistance of 1.2436 steel. Compared to the quenched sample alone, the sample cryogenically treated for 18 hours exhibited 9.28% higher hardness and 34.37% less wear.Öğe Kaplamalı Tungsten Karbür Takımlar Üzerine Uygulanan Kriyojenik İşlemin AISI H11 Çeliğinin İşlenebilirliği Üzerine Etkilerinin Araştırılması(2020) Özbek, Nursel AltanBu çalışmada, AISI H11 sıcak iş takım çeliğinin tornalanmasında kriyojenik işlemin kesici takım performansıüzerine etkileri araştırılmıştır. Deneylerde TiAlN+TiN kaplı tungsten karbür takımlar kullanılmıştır. Kesicitakımlar üzerine 6 saat süre ile -80 °C’de sığ kriyojenik işlem (SCT6), 6 saat süre ile -196 °C’de derin kriyojenikişlem (DCT6) ve 24 saat süre ile -196 °C’de derin kriyojenik işlem (DCT24) uygulanmıştır. Tornalama deneyleri0,6 mm kesme derinliği, 0,18 mm/dev ilerleme hızı ve 320, 360, 400 ve 440 m/dak olmak üzere dört farklı kesmehızında gerçekleştirilmiştir. Deneysel sonuçlar kriyojenik işlemin kesici takımın aşınma direncini artırdığınıgöstermiştir. En düşük kesici takım aşınması ve yüzey pürüzlülüğü değerleri DCT24 takımla elde edilmiştir. Yanakaşınmasında %13-28 oranlarda, yüzey pürüzlülüğünde ise %7-14 oranlarda iyileşmeler gözlenmiştir. Diğer yandankriyojenik işlemin kesici takımların sertliğinde %4,4-8,7 oranlarda artış sağladığı tespit edilmiştir. En yükseksertlik artışı da DCT24 takımda meydana gelmiştir.Öğe Machinability of AISI 316 Austenitic Stainless Steel With Cryogenically Treated M35 High-Speed Steel Twist Drills(Asme, 2012) Çiçek, Adem; Uygur, İlyas; Kıvak, Turgay; Özbek, Nursel AltanIn this paper, machinability of AISI 316 austenitic stainless steel was investigated using cryogenically treated and untreated high-speed steel (HSS) twist drills. Machinability of AISI 316 austenitic stainless steel was evaluated in terms of thrust force, tool life, surface roughness, and hole quality of the drilled holes. Experimental results showed from 14% to 218% improvements for treated tool lives. Thrust force, surface roughness, and hole quality are better with treated drills when compared with untreated drills. These improvements were mainly attributed to formation of fine and homogeneous carbide particles and transformation of retained austenite to martensite. Microhardness and microstructure observations verified these formations. [DOI: 10.1115/1.4007620]Öğe OPTIMIZATION of the MACHINING PARAMETERS in TURNING of HARDENED HOT WORK TOOL STEEL USING CRYOGENICALLY TREATED TOOLS(World Scientific Publishing Co. Pte Ltd, 2019) Nas, Engin; Özbek, Nursel AltanThis paper addresses an approach based on the Taguchi method with gray relational analysis for optimizing the turning parameters of hardened DIN 1.2344 hot work tool steel (54 HRC) with multiple performance characteristics. A gray relational grade obtained from the gray relational analysis was used for the performance characteristic in the Taguchi method L18 (21×32). The optimal turning parameters for surface roughness and tool wear were determined using the parameter design proposed by the Taguchi method. Dry turning tests were carried out using cryogenically treated and untreated uncoated carbide cutting tools. The cutting tool (Untreated and Deep Cryogenic Treated), cutting speed (200, 250 and 300m/min) and feed rate (0.09, 0.12 and 0.15mm/rev) were selected as experiment parameters. The analysis results revealed that the feed rate (72.84%) was the dominant factor affecting surface roughness and the cutting speed (93.93%) was the dominant factor affecting flank wear. The optimum turning parameters for the lowest Ra values were A2B1C2 and for the lowest Vb values were A1B3C2. According to the results of gray relational analysis, the optimum parameters for minimum average surface roughness and minimum flank wear were A1B2C2. © 2019 World Scientific Publishing Company.Öğe Temperleme Isıl İşlem Sıcaklıklarının AISI 4140 Çeliğinin Mekanik Özellikleri Üzerine Etkilerinin Araştırılması(2019) Saraç, Erdem; Özbek, Nursel AltanIslah çelikleri, kimyasal bileşimleri özellikle karbon miktarı bakımından, sertleştirilmeye elverişli olan ve ıslahişlemi sonunda belirli bir çekme dayanımında yüksek tokluk özelliği gösteren, alaşımlı ve alaşımız makineimalat çelikleridir. Sunulan bu çalışmada, sanayide geniş kullanım alanına sahip olan AISI 4140 ıslah çeliğininsu verme işleminden sonra uygulanan temperleme ısıl işlemi sıcaklığının çeliğin mekanik özellikleri üzerineetkileri araştırılmıştır. Numunelere 850 °C sıcaklıkta su verme işlemi uygulanmış ve ardından numuneler 300,450, 550 ve 650 °C olmak üzere dört farklı sıcaklıkta 1 saat süre ile temperleme işlemine tabi tutulmuştur.Mekanik özelliklerinin belirlenmesi için; numunelerin sertlik ölçümleri yapılmıştır. Ayrıca numuneler çekme vedarbe deneylerine tabi tutulmuştur. En düşük temperleme sıcaklığı olan 300 °C?de sertlik değeri maksimumaulaşmıştır. En yüksek çekme ve akma dayanımı değeri de yine bu sıcaklıkta elde edilmiştir. Artan temperlemesıcaklığı ile birlikte numunelerin çekme ve akma dayanımı değerlerinde azalma görülmüştür.