1,721,011 research outputs found
Production of Api X60 Ve X70 Grade Steel Plates by Thermomechanical Controlled Rolling
Get PDFBu çalışma, API PSL2 X60M ve X70M sınıflarında çelik levha üretimi için haddeleme ve soğutma koşullarını belirlemek üzere bir ön çalışma olarak gerçekleştirilmiştir. Kimyasal kompozisyonları ilgili API spesifikasyonuna uygun 200 mm kalınlığında iki adet tam boy Nb-Ti-V mikroalaşımlı çelik slab, 14 adet küçük slaba dilimlenmiş ve bu slab dilimlerine 20 mm kalınlığında levha üretmek üzere farklı koşullarda termomekanik haddeleme ve hızlandırılmış soğutma işlemleri uygulanmıştır. Özel olarak; i) bitirme haddelemesi sıcaklığı, ii) toplam ezmenin kaba ve bitime haddelemesi arasındaki dağılımı ve iii) duşlu masa kullanarak hızlandırılmış soğutma uygulamanın etkileri çalışılmıştır. Deneme üretimi levhalardan alınan numunelerin mekanik testleri (çekme, darbe ve düşürme ağırlıklı yırtma deneyi-DWTT) ve metalografik incelemeleri gerçekleştirilmiştir. API PSL 2 kapsamında X60 sınıfı çelik levhalar için istenen mekanik özellikleri karşılayan ince taneli ferritik içyapıların tek başına denetimli haddeleme ile üretilebildiği koşullar belirlenmiştir. Öte yandan, API X70 sınıfı çelik levha üretimi için denetimli haddelemeye ek olarak hızlandırılmış soğutmanın da uygulanması gerekmiştir.This study was undertaken as an initial work to determine the rolling and cooling conditions for the production of API PSL2 X60M and X70M grade steels plates. Two full size Nb-Ti-V microalloyed steel slabs of 200 mm thickness with compositions compliant to the API specification were sliced into 14 small size slabs and these small slabs were subjected to different thermomechanical controlled rolling and accelerated cooling operations to produce 20 mm thick plates. Specifically, the effects of i) finish rolling temperature, ii) partitioning of the total reduction between the rough and finish rolling phases, and iii) accelerated cooling using water shower were studied. Mechanical tests (tensile, impact and drop weight tear test-DWTT) and metallographic examinations of the samples taken from the trial production plates were done. The conditions that could produce fine grained ferritic microstructures with mechanical properties satisfying the API PSL 2 requirements for API X60 steel plates solely by controlled rolling were determined. On the other hand, the use of accelerated cooling in addition to controlled rolling was required for the production of API X70 grade steel plates
Investigation of the High Temperature Oxidation Behaviour of Cvd Aluminized Inconel 718 and Inconel 738lc Superalloys
No full textBu çalışma alüminize edilmiş Inconel 718 ve Inconel 738LC nikel bazlı süper alaşımların yüksek sıcaklık oksitlenme davranışlarını araştırmak ve karşılaştırmak amacıyla gerçekleştirilmiştir. Kaplamasız ve yüksek aktivite kimyasal buhar biriktirim (KBB) yöntemiyle alüminize edilmiş Inconel 718 ve Inconel 738LC numuneler 200 saat boyunca 925, 1000 ve 1050°C sıcaklıklarda havada oksitlenmeye maruz bırakılmıştır. Numunelerin oksidasyon mekanizmalarını araştırmak ve değerlendirebilmek amacıyla detaylı kesit incelemeleri, elementel analizler, ağırlık değişimi ölçümleri ve x-ışını kırınım çalışmaları yapılmıştır. Alüminizasyon sırasında numunelerin yüzeyinde oluşan NiAl fazının üstünde koruyucu Al2O3 tabakası oluşumu sayesinde hem 718 hem de 738LC alaşımında oksidasyon direncinin önemli ölçüde iyileştiği gözlemlenmiştir. Alüminizasyonun faydalı etkisinin tüm test sıcaklıklarında daha düşük oksidasyon hızı gösteren 738LC alaşımı numunelerde daha belirgin olduğu bulunmuştur. 738LC alaşımı altlığın daha yüksek alüminyum içeriğine sahip olmasının alüminyumun NiAl fazından difüzyon yoluyla uzaklaşmasını yavaşlattığı ve böylece bu alaşımın daha üstün oksidasyon direnci göstermesindeki ana neden olduğu öne sürülmüştür.This study was undertaken to investigate and compare the high temperature oxidation behavior of aluminized Inconel 718 and Inconel 738LC nickel based superalloys. Bare and high activity chemical vapor deposition (CVD) aluminized Inconel 718 and Inconel 738LC samples were oxidized in air at 925, 1000 and 1050°C for 200 hours. Detailed cross-sectional examinations, elemental analyses, weight change measurements, and x-ray diffraction studies were performed in order to investigate and evaluate the oxidation mechanisms of the samples. It was observed that the oxidation resistances of both 718 and 738LC alloys were significantly improved by the protective Al2O3 layer formed on the NiAl phase that was created on the surfaces of the samples during aluminizing. The beneficial effect of aluminizing was found to be more evident in the case of 738LC alloy samples which showed lower oxidation rates at all test temperatures. It is suggested that the higher aluminum content of the 738LC alloy substrate slows down the diffusion flux of Al away from the NiAl phase and hence this is the main reason for its superior oxidation resistance
A Comparison of the Ballistic Performances of Various Microstructures in Mil-A Armor Steel
No full textKonca, Erkan/0000-0001-8943-091XDue to their advantageous properties, there is a growing interest in developing armor steels containing fully or partially bainitic microstructures. In this study, bainitic and martensitic microstructures were obtained in rolled homogeneous armor (RHA) steel samples and their ballistic protection performances were investigated. RHA (MIL-A-12560) steel samples were subjected to isothermal heat treatments at three different temperatures, where one temperature (360 degrees C) was above the martensite formation start (Ms) temperature of 336 degrees C while the other two (320 degrees C and 270 degrees C) were below. For the assessment of the ballistic protection performance, the kinetic energy losses of the 12.7 mm bullets fired at the test samples were determined. The promising nature of the bainite microstructure was confirmed as the sample isothermally treated at 360 degrees C provided approximately 10% higher ballistic protection as compared to the regular RHA sample of tempered martensite microstructure. However, the ballistic performances of the isothermally treated samples decreased as the treatment temperature went below the Ms temperature. Following the ballistic tests, hardness measurements, impact tests at -40 degrees C, and macro- and microstructural examinations of the samples were performed. No correlation was found between the hardness and impact energies of the samples and their ballistic performances.ROKETSAN Missile Industries Inc. (Ankara, Turkey)This research was funded by ROKETSAN Missile Industries Inc. (Ankara, Turkey). The APC was paid for by the author
Effect of Aluminizing on the Oxidation of Inconel 718 and Inconel 738LC Superalloys at 925-1050 °C
No full textKonca, Erkan/0000-0001-8943-091XThis study was undertaken to investigate the effect of aluminizing on the oxidation of Inconel 718 and Inconel 738LC superalloys. Bare and high-activity chemical vapor deposition (CVD) aluminized Inconel 718 and Inconel 738LC samples were oxidized in air at 925, 1000, and 1050 degrees C for 200 h. Detailed cross-sectional examinations, elemental analyses, mass change measurements, and X-ray diffraction studies were performed. It was observed that the oxidation resistances of both alloys were significantly improved by the Al2O3 scale formed on the NiAl layer that was created on the surfaces of the samples during aluminizing. The beneficial effect of aluminizing was found to be more evident in the case of Inconel 738LC alloy samples which showed lower oxidation rates at all test temperatures. The results have been discussed on the basis of the differences in aluminum contents of the alloys and their effects on diffusion
Effects of Current Density, Coating Thickness, Temperature, Ph and Particle Concentration on Internal Stress During Ni-mos<sub>2</Sub> Electrocodeposition
No full textGüler, Ebru Saraloğlu/0000-0002-3732-1268; Konca, Erkan/0000-0001-8943-091X; Karakaya, ishak/0000-0002-4646-6207Internal stress in plated deposits has been a common problem that may affect the functionality of coatings. Electrodeposition parameters and insoluble particles modify the characteristics and the level of internal stress of coatings. The influence of the electrocodeposition parameters and their interaction effects on the internal stress during the electrodeposition of Ni and Ni-MoS2 composite coatings were studied by fractional factorial design. The parameters studied and their ranges were: MoS2 particle concentration (0-10 g L-1), temperature (30-50 degrees C), pH (2-4), current density (1.2-4.8 A dm(-2)), and coating thickness (25-50 mu m). MoS2 addition into Watts bath resulted in the decrease in the tensile internal stress values or even changed the stress character from tensile to compressive. Moreover, low stress values were obtained when pH was 2 and coating thickness was 50 mu m.Scientific Research Projects (BAP) of Middle East Technical UniversityThe authors acknowledge the partial support provided by the Scientific Research Projects (BAP) of Middle East Technical University
Effect of Electroplating Parameters on "her" Current Density in Ni-mos<sub>2</Sub> Composite Plating
No full textKonca, Erkan/0000-0001-8943-091XNickel composites with co-deposited insoluble, solid lubricant particles such as MoS2 have been reported to reduce friction. It is known that hydrogen evolution reaction (HER), competes with nickel deposition. The influence of the electroplating parameters and their interaction effects on the peak current density for HER were studied by fractional factorial design. The parameters and their ranges were; MoS2 concentration (0-30 g/l), temperature (30-50 degrees C), pH (2-4) and surfactants (0-1 g/l). Electrodeposition processes were carried out from a typical Watts bath containing leveler, wetting agent and brightener by using a potentiostat. The peak currents (I-p) were extended to higher values and the peaks on linear sweep voltammograms became noticeable by increasing the scan rate from 20 mV/s to 100 mV/s over the range 0 to 2.5 V. The peak current densities (i(p)) for each experimental route were determined by fractional factorial design for three types of mineral processing surfactants; sodiumlignosulfonate (SLS), depramin-C (DC) and ammoniumlignosulfonate (ALS) using Minitab program [1]. Adding MoS2, decreasing temperature and increasing pH has decreasing effect on peak current density for all surfactants. ALS and DC have increasing effect whereas SLS has descending effect on peak current.Conference Proceedings Citation Index - Scienc
Investigation of the Tribological Behaviour of Electrocodeposited Ni-mos<sub>2</Sub> Composite Coatings
No full textGüler, Ebru Saraloğlu/0000-0002-3732-1268; Konca, Erkan/0000-0001-8943-091X; Karakaya, ishak/0000-0002-4646-6207Composite electroplating of solid lubricants in a metal matrix is an effective way to lower coefficient of friction (COF) and improve wear resistance of surfaces in sliding contact. In this work, Ni-MoS2 composite coatings were deposited on AISI 304 stainless steel substrates by electroplating from Watts bath containing suspended MoS2 particles and their tribological behaviour was studied. The effects of MoS2 particle concentration (5, 10 and 30 g/l), MoS2 particle size (1.440 and 5.156 mu m), pH (2, 3 and 4), current density (3.8, 4.8 and 5.8 A/dm(2)) and the surfactant (sodium lignosulfonate, SLS) concentration (0.3 and 1 g/l) on the tribological behaviour were investigated using a ball-on-disc tribometer at ambient conditions. Lower current density, smaller particle size and higher concentration of MoS2 decreased COF. While increasing the surfactant concentration decreased the COF, its friction lowering effect was much more pronounced at relatively lower concentrations of MoS2 in the electrolyte
Mechanical Behavior of Anodic Alumina Coatings Reinforced With Carbon Nanofibers
No full textXia, Zhenhai/0000-0002-0881-2906; Konca, Erkan/0000-0001-8943-091XAnodic alumina was reinforced with three types of carbon nanofibers differing in the orientation of their graphene structure-perpendicular to the fiber axis, and parallel to the fiber axis both with dense core and hollow core (i.e., nanotubes). This study was designed to identify potential toughening and damage tolerant mechanisms in these nanoscale fiber-reinforced composite coatings. The dense carbon fibers improved contact damage resistance and reduced frictional resistance in sliding contacts. The hollow core reinforcements were much more promising for improving the fracture toughness of the composite coatings.NSF-NIRT [CMS-03034246]Financial support from NSF-NIRT Grant No. CMS-03034246 is highly appreciated
Effects of Alloying Elements (Mo, Ni, and Cu) on the Austemperability of GGG-60 Ductile Cast Iron
No full textKonca, Erkan/0000-0001-8943-091X; TUR, KAZIM/0000-0002-8017-8209The interest in austempered ductile irons (ADI) is continuously increasing due to their various advantageous properties over conventional ductile irons and some steels. This study aimed to determine the roles of alloying elements Ni, Cu, and Mo, on the austemperability of GGG-60 ductile cast iron. Two different sets of GGG-60 (EN-GJS-600-3) samples, one set alloyed with Ni and Cu and the other set alloyed with Mo, Ni, and Cu, were subjected to austempering treatments at 290 degrees C, 320 degrees C, and 350 degrees C. A custom design heat treatment setup, consisting of two units with the top unit (furnace) serving for austenitizing and the 200 L capacity bottom unit (stirred NaNO2-KNO3 salt bath) serving for isothermal treatment, was used for the experiments. It was found that austempering treatment at 290 degrees C increased the hardness of the Ni-Cu alloyed GGG-60 sample by about 44% without causing a loss in its ductility. In the case of the Mo-Ni-Cu alloyed sample, the increase in hardness due to austempering reached to almost 80% at the same temperature while some ductility was lost. Here, the microstructural investigation and mechanical testing results of the austempered samples are presented and the role of alloying elements (Mo, Ni, and Cu) on the austemperability of GGG-60 is discussed
Effects of Solutionizing and Aging Conditions on the Hardness, Microstructure and Wear Resistance of Cast Fe-Mn-Al-C-Si Lightweight Steel
Get PDFBu çalışma, çözündürme ve yaşlandırma ısıl işlemlerinin östenit matrisli deneysel döküm Fe-Mn-Al-C-Si hafif çeliğinin mekanik özellikleri ve içyapısı üzerine etkilerini incelemeyi amaçlamıştır. Hedeflenen kompozisyonda ve 6,60 g/cm³ yoğunluğunda dökümler yapılmıştır. Çözündürme işlemleri 950°C-1150°C arasında 2, 4 ve 16 saat uygulanmış, ardından 400°C ile 700°C arasında 4, 16 ve 64 saat yaşlandırma işlemleri gerçekleştirilmiştir. Isıl işlemlerin etkilerini değerlendirmek amacıyla makro/nano sertlik ölçümleri, optik mikroskopi, enerji saçılım spektroskopisi ve elektron geri saçılma kırınımı ile donatılmış elektron mikroskobu, x-ışını kırınım analizleri ve aşınma testleri yapılmıştır. Elde edilen verilere göre, yaşlandırma öncesinde 1000°C'de 4 saat süreyle uygulanan çözündürme ısıl işleminin iç yapısal kararlılık ve mekanik özellikler açısından en uygun sonucu verdiği görülmüştür. 400°C–700°C sıcaklık aralığında 16 saat süreyle uygulanan yaşlandırmanın özellikle sertlik artışı açısından en uygun koşul olduğu söylenebilir. Yaşlandırma işlemleri içyapı içerisinde sertlik artışına katkıda bulunan κ-karbürlerin oluşumuyla sonuçlanmıştır. Ancak, yaşlandırmanın çok uzun süreyle yapılması mekanik özellikleri olumsuz etkilemesi nedeniyle istenmeyen tane sınırı çökeltilerinin oluşumuna yol açmıştır.This study aimed to investigate the effects of solutionizing and aging treatments on the mechanical properties and microstructure of an experimentally cast Fe-Mn-Al-C-Si lightweight steel of austenite matrix. Castings of target composition were made with a density of 6.60 g/cm³. Solutionizing treatments were applied at 950°C-1150°C for 2, 4, and 16 hours, followed by aging at temperatures ranging from 400°C to 700°C for 4, 16, and 64 hours. Macro/nano hardness measurements, optical microscopy, electron microscopy with energy-dispersive spectroscopy, electron backscatter diffraction, x-ray diffraction analyses, and wear tests were performed to evaluate the effects of heat treatments. Based on the obtained data, it was found that solution treatment at 1000°C for 4 hours prior to aging provided the optimum results in terms of microstructural stability and mechanical properties. Aging for 16 hours within the 400°C–700°C temperature range was suggested as the most promising condition, particularly for hardness improvement. Notably, aging treatments resulted in the formation of κ-carbides within the microstructure, contributing to hardness enhancement. However, aging for even longer times induced undesirable grain boundary precipitations, which adversely affected the mechanical properties
- …
