SEARCH RESULT

In the diesel common rail systems, it is necessary to increase the fuel pressure up to 2500 bar to make engines more efficient and economical as well as to correspond more strict environmental standards. Bainitic forging steels were recently developed for the common rail systems and also becoming increasingly attractive for many forged parts such as crankshafts, injection rails, axle pivots in the automotive industry. A controlled cooling route comprising of hot forging without any quenching and tempering has been established for developing ductile high strength steels with tensile strengths up to 1250 MPa. In this study, the austenite grain growth of a microalloyed bainitic forging steel was investigated using light microscopy. It is well known that the precipitation of microalloying elements can prevent the austenite grain growth. Therefore, phase transformation temperatures were calculated using Thermo-Calc software to obtain an overview about the possible austenitization temperatures. In order to investigate the austenite grain growth, annealing experiments were performed at temperatures between 1000 ºC and 1300 ºC for 5 minutes. The mean intercept length of the grains has been determined according to ASTM E112 intercept method. The results showed that prior austenite grain size and distribution depend on austenitization temperature.

International Iron & Steel Symposium
UDCS

Sibel Ün Emre Alan Nurten Başak Dürger Caner Güney Ersoy Erişir

Influence of different austenitization conditions on retained austenite quantity and composition investigated on SAE 52100 steel. SAE 52100 steels are being widely used as bearing component regarding to their hardness and wear resistance. Traditional production cycle includes hot rolling, spheroidization, cold rolling, quenching from two phase region and tempering steps. This cycle results with martensitic matrix and undissolved course carbides. Course carbides maintain adequate wear performance but due to course carbides providing appropriate nucleation sites for crack propagation and growth this structure shows poor fatigue behavior. Previous studies showed better carbide size and distribution with experimental two step hardening cycle. This cycle results with considerable increase at retained austenite fraction. It’s well known that mechanically unstable retained austenite improves fatigue resistance in this type of steel. Transformation retained austenite to martensite caused by deformation eliminates local stresses and retards crack propagation and growth. XRD studies are carried on to determining retained austenite quantity with various austenitizing conditions. Computational simulations with Thermo-Calc and Dictra are used for predicting carbon concentration gradient of austenite during austenitization which determines retained austenite fraction at the end. A good correlation between XRD data and simulation results was obtained.

International Iron & Steel Symposium
UDCS

Ersoy Erişir Oğuz Gürkan Bilir Ahmet Efe Gezmişoğlu

Co-Cr and 316L are the commonly used alloys in biomedical industry. However, both 316L and mostly used Co-Cr alloys as F-562, L-605 contain large portions of Ni as alloying element. Ni may cause allergic and toxic impacts on human health. In recent years, N-alloyed Ni free stainless steels seemed as good candidate for replacing Ni contained metals. However, liquid steel has a limited N solubility at atmospheric pressure. Thus, high pressured melting techniques are required. In this study, N alloying of ferritic 430 stainless steel sheet was performed in solid state. Nitrogen absorption of stainless steel was performed in a furnace filled with nitrogen gas with atmospheric pressure at 1200°C. Solid state N absorption was applied in four different time periods as 4, 8, 12, 24 hours. Microstructure after absorption process was investigated by Scanning Electron Microscope and Light Microscope. Fully austenitic structure was observed in surface of specimens. However, duplex microstructure of ferrite and austenite was seen in the center of specimen. Vickers hardness was carried out to evaluate of phases. It was concluded that optimum microstructure is achieved by 4 hours of N absorption.

International Iron & Steel Symposium
UDCS

Oğuz Gürkan Bilir İsmail GÜVENİR Ersoy Erişir

Finer martensitic and ferritic microstructures are demanded to obtain high strength and toughness for dual phase steels. In this study, reducing of prior austenite grain size selected as an effective method to reduce the size of dual phase microstructure. The effect of prior austenite grain size on microstructure of medium carbon dual phase steel produced by intercritical annealing were investigated for different austenitizing conditions. Annealing experiments were performed to fully austenitizate the steel at different austenitizing temperatures (900, 950, 1000ᵒC) and times (5, 10, 15 min) and followed by quenching. Finally, as-quenched martensitic microstructures were intercritical annealed at 760ᵒC for 15 min to attain martensitic and ferritic dual phase steel. The microstructures were analyzed using light microscopy and image analysis methods. It is concluded that grain size of dual phase steel is reducing by decreasing of the austenitizing temperature and the holding time.

International Iron & Steel Symposium
UDCS

Ersoy Erişir Özge Ararat Oğuz Gürkan Bilir

Islah çelikleri sahip olduğu düşük maliyet ve iyi mekanik özellik kombinasyonu nedeniyle otomotiv sektöründe yaygın bir kullanım alanına sahiptir [1,2]. 100Cr6 (AISI 52100) çeliği, yüksek karbon ve krom oranına sahip olup, yüksek sertlik ve aşınma direnci istenen rulmanlar, rulman yatakları, zımbalar ve kalıplarda kullanılmaktadır [3] . Sıcak basma testi, bir dizi silindirik veya kare numunenin çeşitli kalınlıklara veya aynı kalınlığa, çeşitli numune uzunluk/çap (uzunluk-genişlik) oranlarına kadar sıkıştırılmasından oluşur. Bu testler dövme endüstrisinde yaygın olarak kullanılmaktadır [4]. Sıcak presleme işlemi plastik deformasyon, sürünme ve difüzyon içerdiğinden, presleme süreleri birkaç dakika veya hatta saatlere kadar uzatılabilmektedir [5]. Kompozit malzeme üretiminde amaç tek başına mevcut olmayan bazı özelliklerin (hafiflik, dayanım esneklik, vb.) geliştirilmesi ve bir araya getirilmesidir. Çalışma kapsamında uygun akma koşulları ve değişim sıcaklığı tespit edilerek ıslah çeliği ve takım çeliği kompozit malzemesini üreterek ağırlık tasarrufu ve maliyetten kazanç sağlanması hedeflenmiştir. Bu çalışmada düşük maliyet ve yüksek tokluk özelliklerine sahip C45 imalat çeliği (çekirdek) ile sert, aşınmaya ve yorulmaya dayanıklı 100Cr6 (dış silindir); sıcak basma test düzeneği kullanılarak Şekil 1’de şematik olarak verilen proses akış şemasına göre birleştirilerek iç kısmı tok, dış kısmı ise aşınmaya karşı dayanıklı kompozit numuneler elde edilmiştir. Elde edilen numuneleri karakterize etmek amacıyla mikroyapı incelemeleri ve sertlik ölçümleri yapılmıştır.

International Symposium on Light Alloys and Composite Materials
UHAKS

Gülben Karayel Mustafa Çöl Funda Gül Koç Taner Makas Ersoy Erişir