Tozaltı Ark Kaynağı ile Kaynaklanmış X70M Çeliklerinin Mikro Yapı ve Mekanik Özelliklerinin İncelenmesi

Öz

Bu çalışmada, petrol boru hatlarında kullanılan X70M PSL 2 (API 5L) çeliği, tozaltı ark kaynağı yöntemiyle kaynatılmıştır. Kaynak dikişi ve ITAB, optik mikroskop, taramalı elektron mikroskobu (SEM), çekme deneyi, sertlik deneyi ve Charpy darbe deneyi yöntemleri ile karakterize edilmiştir. Optik inceleme sonucunda yapı içerisinde herhangi bir kaynak hatasının oluşmadığı görülmüştür. Kaynak bölgesi, ana metal ve ITAB olarak belirgindir ve kaynak metalinde sütunsal tane büyümesi gerçekleşmiştir. SEM çalışmasında ana malzemenin ferrit (açısal ferrit, poligonal ferrit) tanelerinden, ITAB bölgesinin daha iri tanelerden ve kaynak metalinin ise sütunsal ince ferrit plakalarından oluştuğu görülmüştür. Çekme deneyi sonucunda, ana malzemenin çekme dayanımının yaklaşık 648 MPa, kaynaklı birleştirmenin çekme dayanımının ise yaklaşık 695 MPa olduğu tespit edilmiştir. Elde edilen sonuçlar kaynaklı birleştirmede kopmanın ana malzemede gerçekleştiğini göstermektedir. En yüksek ortalama sertlik değeri 229 HV olarak kaynak metalinde ölçülmüştür. Buna karşın ana malzeme ve ITAB’daki ortalama sertlik değerleri ise sırası ile 218 HV ve 221 HV’dir. Ana malzemede elde edilen ortalama darbe enerjisi değeri 428 J’dür. En düşük darbe enerjisi ise kaynak metalinde elde edilmiştir. Kaynak metalinde elde edilen ortalama darbe enerjisi değeri yaklaşık 94 J’dür. Kaynak metalinden ana malzemeye doğru gidildikçe darbe enerjisindeki artış dikkat çekicidir.

Anahtar Kelimeler

• Boru Hattı Çelikleri
• X70M
• Kaynak

Investigation of Microstructure and Mechanical Properties of X70M Steels Welded by Submerged Arc Welding

Öz

In this study, X70M PSL 2 (API 5L) steel used in oil pipelines was welded by submerged arc welding method. Weld seam and HAZ were characterized by optical microscopy, scanning electron microscopy (SEM), tensile test, hardness test and Charpy impact test methods. As a result of the optical inspection, it was observed that no welding defects had occurred within the structure. The weld zone, base metal, and HAZ are distinct, and columnar grain growth has occurred in the weld metal. In the SEM study, it was observed that the base material consists of ferrite grains (angular ferrite, polygonal ferrite), the HAZ consists of coarser grains, and the weld metal consists of fine columnar ferrite. As a result of the tensile test, it was determined that the tensile strength of the base material is approximately 648 MPa, while the tensile strength of the welded joint is approximately 695 MPa. The obtained results indicate that the fracture in the welded joint occurred in the base material. The highest average hardness value was measured as 229 HV in the weld metal. In contrast, the average hardness values in the base material and HAZ are 218 HV and 221 HV, respectively. The average impact energy value obtained in the base material is 428 J. The lowest impact energy was obtained in the weld metal. The average impact energy value obtained in the weld metal is approximately 94 J. As one moves from the weld metal towards the base material, the increase in impact energy is remarkable.

Anahtar Kelimeler

• Pipeline Steels
• X70M
• Welding

Kaynakça

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