INVESTIGATION OF THE MICROSTRUCTURAL AND MECHANICAL PROPERTIES OF EQUAL CHANNEL ANGULAR PRESSED (ECAPED) SHIP BUILDING STEEL

Öz

Low-medium strength steels are used by increasing their thickness in parts where high strength is required on ships due to the low weldability and formability of high-strength steels. The use of thicker plates brings about a significant increase in the ship’s weight and their fuel consumption as expected. So, it is very important to improve the strength of low-medium strength shipbuilding steels by applying severe plastic deformation methods or heat treatments. Grain refinement via severe plastic deformation (SPD) seems to be an essential strengthening mechanism without changing the chemical composition of metallic materials. Among SPD methods, equal channel angular pressing (ECAP) is one of the most commonly used one due to its high grain refinement capacity. When the literature is examined, it is clearly seen that ECAP is not applied to any shipbuilding steel before. Therefore, in this study, one pass ECAP at 300 0C to low-medium strength shipbuilding steel (Grade A) which has intensively used in the shipbuilding industry and the changes in the microstructural and mechanical properties of steel after ECAP were investigated. After investigations, it was determined that the average grain size after ECAP decreased from 25 μm (base material) to 7 μm and as a result of this, hardness and strength values increased significantly compared to the base material. On the other hand, wear and formability tests were applied after and before ECAP and it was determined that while a slight improvement was obtained in wear behavior, formability behavior deteriorated after ECAP.

Anahtar Kelimeler

• Equal Channel Angular,Pressing,Shipbuilding,Low Carbon Steel,Microstructure,Mechanical Properties

EŞ KANALLI AÇISAL PRESLEME (EKAP) UYGULANAN GEMİ İNŞA ÇELİĞİNİN İÇYAPI VE MEKANİK ÖZELLİKLERİNİN İNCELENMESİ

Öz

Yüksek mukavemetli çeliklerin düşük kaynak edilebilirlik ve şekillendirilebilmeleri nedeniyle, gemilerde yüksek dayanım istenen kısımlarda düşük-orta mukavemetli çelikler kalınlıkları arttırılarak kullanılmaktadır. Daha kalın sacların kullanılması beraberinde ağırlığın ve yakıt tüketiminin önemli ölçüde artmasını getirmektedir. Bu bağlamda düşük-orta mukavemetli gemi imalat çeliklerinin aşırı plastik deformasyon yöntemleri veya ısıl işlemler uygulanarak dayanımlarının geliştirilmesi oldukça önemlidir. Aşırı plastik deformasyon (APD) yöntemleri ile malzemenin kimyasal bileşiminde herhangi bir değişiklik yapmadan tane boyutunu küçülterek malzemenin mukavemetini arttırmak son dönemlerde sıklıkla kullanılmaktadır. APD yöntemleri arasında eş kanallı açısal presleme (EKAP) yöntemi yüksek oranda tane inceltme ve mukavemet arttırma özelliği bakımından öne çıkmaktadır. Literatür incelendiğinde EKAP yönteminin herhangi bir gemi inşa çeliğine uygulamasının olmadığı açıkca görülmektedir. Bu yüzden yapılan çalışmada gemi inşaatından yoğun bir kullanıma sahip düşük-orta mukavemetli Grade A gemi inşa çeliğine 300 0C’de tek paso EKAP uygulanmış ve EKAP sonrası çelikteki içyapısal ve mekanik özelliklerinin değişimleri incelenmiştir. İncelemeler sonucunda EKAP sonrası ortalama tane boyutunun 25 μm seviyesinden 7 μm seviyesine indiği ve tane boyutunda meydana gelen bu azalmanın sonucu olarak sertlik ve mukavemet değerlerinin ana yapıya göre önemli oranda arttığı belirlenmiştir. Öte yandan EKAP sonrası numunelere aşınma ve şekil verilebilirlik deneyleri de uygulanmış ve aşınma davranışının bir miktar iyileştiği şekil verilebilirliğin ise EKAP sonrası kötüleştiği belirlenmiştir.

Anahtar Kelimeler

• Eş Kanallı Açısal Presleme,Gemi İnşaatı,Düşük Karbonlu Çelik,İçyapı,Mekanik Özellik

Teşekkür

Çalışma kapsamında laboratuvar imkânlarının kullanılması noktasındaki katkılarından ötürü Karadeniz Teknik Üniversitesi Makine Mühendisliği Bölümü Öğretim Üyesi Prof. Dr. Gençağa PÜRÇEK’e teşekkürü bir borç bilirim.

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