Ulvi ŞEKER, Özgür TEKASLAN, Nedim GERGER

AISI 304 östenitik paslanmaz çeliklerin farklı kesme parametreleri ile tornalama işleminden sonra oluşan kalıcı gerilmelerin araştırılması

Kullanım alanlarına göre istenen mekanik ve kimyasal özelliklerin sağlanması için paslanmaz çeliklerin bileşimlerinde yapılan değişiklikler, paslanmaz çeliklerin işlenebilirliğini etkilemektedir. Bütün üretim işlemleri (ısıl işlem, talaşlı ve talaşsız imalat, kimyasal işlemler gibi) makine parçaları üzerinde kalıcı gerilmeler oluşturur. Özellikle talaş kaldırma yöntemlerine bağlı olarak malzeme üzerinde gerilmeler oluşmaktadır. Bu gerilmeler, makine elamanları üzerinde yorulma dayanımını azaltacak ve boyutsal değişikliklere yol açabilecek zararlı etkilere de neden olabilir. Bu nedenle makine elamanlarındaki kalıcı gerilme değerlerinin bilinmesi gerekmektedir. Bu araştırmada, AISI 304 östenitik paslanmaz çelik malzeme değişik kesme parametreleri ile işlendikten sonra, işlemeye bağlı olarak bünyesinde nasıl bir kalıcı gerilme oluştuğunu belirlemek hedeflenmiştir. AISI 304 çeliğinden 61 mm çapında, 250 mm boyunda 31 adet deney numunesi hazırlanmış ve değişik kesme parametrelerinde CNC torna tezgâhında işlenmiştir. Daha sonra deney numuneleri üzerinde oluşan kalıcı gerilme, katman kaldırma yöntemi kullanılarak tespit edilmiş ve en uygun işleme parametreleri belirlenmiştir. Deney numunelerinin tornalama işlemi sonunda yüzeylerde maksimum -1876.69 MPa ile -136.71 MPa’lık basma kalıcı gerilmelerinin oluştuğu tespit edilmiştir. Yüzeydeki basma kalıcı gerilmelerinin, katman kaldırılması ile 0.0465 mm derinlikten sonra çekme kalıcı gerilmelerine yöneldiği tespit edilmiştir.

A study on residual stresses formed on AISI 304 austenitic stainless steels when machined with different cutting parameters

Changes made in the composition of stainless steels so as to provide the mechanical and chemical properties desired according to the fields of application affect also their machining. All production processes such as heat treatment, production with or without machining, and chemical processes create residual stresses on the machine parts. Stress on materials occurs due to especially the methods of machining. These stresses may as well render harmful effects that may cause a decrease in the fatigue strength of the machine elements, and eventually dimensional changes. Therefore, it is necessary to know the residual stress values on machine elements. This study aims to determine the residual stress, depending on the process, occurring on the AISI 304 austenitic stainless steel material after it is processed under various cutting conditions. Thirty-one test specimens, of AISI 304 steel, with a diameter of 61 mm and 250 mm length were prepared and machined in CNC lathes with different cutting conditions. Later on, using “layer removal” method residual stresses on the specimens were found out, and the best processing conditions determined. A maximum of -1876.69 MPa and -136.71 MPa compressive residual stresses on the surfaces have been found after the turning process of the test specimens. The compressive residual stresses on the surface, upon layer removal, turn to be tensile residual stresses 0.0465mm beneath the surface.

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