HEAT INPUT EFFECT OF THE FCAW PROCESS ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF STRUCTURAL STEEL JOINTS

Year 2022, Volume: 27 Issue: 3, 1207 - 1220, 31.12.2022

Uğur Gürol

https://doi.org/10.17482/uumfd.1157841

Abstract

Flux-cored wires are commonly used in structural and pipeline welding, shipbuilding, offshore constructions, and petrochemical and power generation industries. The higher heat inputs in the multipass welding result in shorter production time while considerably changing the properties of the welded joint. In this study, robotic flux cored arc welding with varying heat inputs (between 0.56-2.52 kJ/mm) was performed to determine the effect of heat input on weld microstructure, hardness, tensile properties, and impact toughness in the structural steel joints. Results exhibited that decrease in heat input from 2.52 to 0.56 kJ/mm changed the majority of the microstructure from polygonal ferrite to acicular ferrite. Furthermore, this increased by 56%, 37%, and 47% in yield strength, tensile strength, and hardness values, respectively, while decreasing by 30% and 15% in elongation and Charpy impact test results, respectively. Moreover, all welded joints displayed a satisfying toughness value higher than the requested value of 47 J, even at the test temperature of -50 °C. Finally, it can be concluded that the optimum results were obtained with a heat input of 1.26 kJ/mm, considering the minimum requirements of the AWS A5.20 standard and the expectations in applications.

Keywords

Robotic MAG welding, Flux-cored welding wire, Stuctural steel joints, Microstructural characterization, Mechanical properties, Heat input

Thanks

The author wishes to acknowledge the valuable contributions of Ms. Nurten Güleçyüz for assisting the robotic welding operations.

FCAW Prosesi ile Yapısal Çeliklerin Birleştirilmesinde Isı Girdisinin Mikro Yapı ve Mekanik Özelliklere Etkisi

Abstract

Özlü kaynak telleri, yapısal ve boru hattı kaynağı, gemi yapımı, açık deniz inşaatları, petrokimya ve enerji üretim endüstrilerinde oldukça yaygın bir şekilde kullanılmaktadır. Çok pasolu kaynaklarda yüksek ısı girdileri, daha kısa üretim sürelerine neden olurken, kaynaklı birleştirmenin özelliklerini de önemli ölçüde değiştirmektedir. Bu çalışmada, yapısal çeliklerin kaynaklı birleştirmelerde ısı girdisinin kaynak mikroyapısı, sertlik, çekme özellikleri ve darbe tokluğu üzerindeki etkisini belirlemek için değişen ısı girdileriyle (0,56-2,52 kJ/mm arasında) robotik özlü özlü ark kaynağı yapılmıştır. Sonuçlar, ısı girdisinin 2.52’den 0.56 kJ/mm’e düşmesi ile mikro yapının genelinin poligonal ferritten asiküler ferrite dönüştüğünü göstermiştir. Bu da akma mukavemeti, çekme mukavemeti ve sertlik değerlerinde sırasıyla %56, %37 ve %47'lik bir artışa neden olurken, uzama ve Charpy darbe testi sonuçlarında sırasıyla %30 ve %15'lik bir düşüşe neden olmuştur. Ayrıca, kaynaklı birleştirmelerin tümünde -50 °C'lik test sıcaklığında bile istenen 47 J değerinden oldukça yüksek tokluk değerleri elde edilmiştir. Son olarak, AWS A5.20 standardının minimum gereksinimleri ve uygulamalardaki beklentiler dikkate alındığında optimum sonuçların 1,26 kJ/mm ısı girdisi ile elde edildiği sonucuna varılmıştır.

Keywords

Robotik MAG kaynağı, Özlü kaynak teli, Yapısal çelik birleştirmeleri, Mikro yapı karakterizasyonu, Mekanik özellikler, Isı girdisi

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