DÜŞÜK KARBONLU GRADE A ÇELİĞİNİN EŞ KANALLI AÇISAL EKSTRÜZYON YÖNTEMİ İLE PROSES EDİLMESİ

Bu çalışmada eş kanallı açısal ekstrüzyon (EKAE) işleminin düşük karbonlu çeliğin mikroyapısal ve mekanik özellikleri ile darbe enerjisi üzerine etkilerinin incelenmesi amaçlanmıştır. Bu amaçla düşük karbonlu Grade A çeliği, (EKAE) işlemine tabi tutulmuştur. 1 pasoluk EKAE işlemi çeliğin tane yapısında önemli bir incelmeye neden olmazken, EKAE numunesinin akma ve dik kesit düzlemlerinde iki farklı mikroyapı oluşumunu beraberinde getirmiştir. Akış düzleminde ekstrüzyon doğrultusu ile 45° açı yapacak şekilde yönlenmiş ferrit ve perlit tanelerinden oluşan mikroyapının, dik kesit düzlemi üzerinde neredeyse eş eksenli tanelerden oluştuğu belirlenmiştir. EKAE numunesinin iki farklı düzleminin mikroyapıları arasındaki bu farklılık, EKAE işlemi sırasında aktif olan kayma düzlemleri ile açıklanmıştır. EKAE işlemi sırasında mikroyapıdaki dislokasyon yoğunluğundaki artıştan dolayı çeliğin sertlik ve dayanım değerlerinin önemli ölçüde arttığı görülmüştür. Ancak, EKAE işlemi kopma uzaması değerinin önemli ölçüde azaltmasına neden olmuştur. EKAE işlemine tabi tutulan numunenin darbe enerjisinin, Charpy darbe testi numunesinin çentik pozisyonuna bağlı olduğu belirlenmiştir.

PROCESSING OF GRADE A LOW CARBON STEEL BY EQUAL CHANNEL ANGULAR PRESSING

The present study aims to analyze the effect of equal channel angular pressing (ECAP) on the microstructural and mechanical properties as well as the impact energy of low carbon steel. Grade A steel was processed using ECAP. One pass of ECAP did not cause a considerable decrease in the grain size of the steel. It brought about two different microstructures on the flow andtransverse planes of an ECAP billet, instead. The microstructure consists of elongated ferrite and perlite grains aligned in a direction having mainly 45° angle with the extrusion direction on the flow plane while nearly equiaxed grains were formed on the transverse plane. These differences between the microstructures of two different planes of the ECAP sample are attributedto the share planes that are operative during ECAP. ECAP increased the hardness and strength values of the steel significantly due to the increase in the dislocation density during the process. However, it decreased the elongation to failure considerably. It was found that the impact energy of the ECAP-processed sample is dependent on the notch position of the Charpy impact test sample.

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