MICROSTRUCTURAL CHARACTERIZATION AND MECHANICAL PROPERTIES OF ST37/ST52 PLATES JOINED BY FRICTION STIR WELDING

Öz

Friction stir welding (FSW) has been applied successfully to aluminum alloys in several industries over the past three decades. However, it is not widely used in joining of steels due to the limitations of the tool materials which can withstand the temperatures experienced. The aim of this study is to investigate the change in the mechanical properties and the microstructures of FSW’ed St37/St52 Microstructure, Mechanical Performancedissimilar low carbon steels joints. The results obtained indicate that the weld region is comprised of complex microstructures such as Widmanstatten ferrite, ferrite with or without carbide aggregates and grain boundary ferrite. The maximum hardness in the stir zone reached up to about 347 HV due to the solid state transformations and grain refinement. The welded plates displayed an ultimate tensile strength of about 389 MPa, which lies between the ultimate tensile strength of St37 and St52 steels, 373 and 526 MPa, respectively. The yield strength of the joint was found to be about 272 MPa. This value is also a value between those of the base plates

SÜRTÜNME KARIŞTIRMA KAYNAĞIYLA BİRLEŞTİRİLEN ST37/ST52 LEVHALARIN MİKROYAPI KARAKTERİZASYONU VE MEKANİK ÖZELLİKLERİ

Öz

Sürtünme Karıştırma Kaynağı (SKK), geçtiğimiz otuz yılda çeşitli endüstrilerde alüminyum alaşımlarına başarı ile uygulanmaktadır. Fakat çeliklerin kaynağında, bu işlemlerde açığa çıkan sıcaklıklara dayanabilecek karıştırıcı takımlardaki kısıtlamalarından ötürü, geniş çaplı olarak kullanılamamaktadır. Bu çalışmada, SKK ile birleştirilen St37/St52 farklı düşük karbonlu çeliklerin mekanik özellikleri ve içyapısındaki değişimlerin araştırılması amaçlanmıştır. Elde edilen sonuçlara göre, kaynak bölgesi, Widmanstatten ferrit, sementit kümesi içeren veya içermeyen ferrit ve tane sınırı ferriti gibi karmaşık içyapılardan oluşmaktadır. Karıştırma bölgesindeki en yüksek sertlik, katı hal dönüşümleri ve tane incelmesinden dolayı yaklaşık 347 HV’ye ulaşmaktadır. Birleştirilen levhalar, 389 MPa’lık bir çekme mukavemeti değeri sergilemiş olup, bu değer sırasıyla St37 ve St52 çeliklerinin çekme mukavemet değerleri olan 373 ve 526 MPa’ın arasında bir değerdir. Bağlantının akma dayanımı 272 MPa olarak bulunmuştur. Bu değer de, her iki ana malzemenin akma dayanımlarının arasında bir değerdir

Anahtar Kelimeler

• Sürtünme Karıştırma Kaynağı, St37, St52

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