Bu çalışmada Inconel 625 nikel bazlı süper alaşım ile AISI 304L paslanmaz çelik malzeme çifti, TIG (tungsten arc welding) yöntemi ile, ER 310 ve ERNiCrMo3 ilave metalleri kullanılarak birleştirilmiştir. Kullanılan ilave metallerin kimyasal özellikleri sonucu oluşan kaynak metalinin mikroyapı, tokluk ve mikrosertlik dağılımı incelenmiştir. Kaynaklı bağlantının genel mikroyapısı optik mikroskop ile çentik darbe deneyinden sonra kırılma yüzeylerinin incelenmesi taramalı elektron mikroskobu kullanılarak incelenmiştir. Özellikle benzer olmayan birleştirmenin, ergime sınırında meydana gelen geçiş bölgesinin mikroyapısal karakterizasyonu yapılarak, bu bölgede meydana gelen değişimler açıklanmıştır. İlave metallerin Nikel içeriği nedeni ile tüm çentik darbe testi numunelerinde sünek kırılma meydana gelmiştir. Ayrıca ERNiCrMo3 kırılma tokluğu açısından diğerlerine göre çok daha iyi sonuçlar ortaya koymuştur.

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In this study, the microstructural features and mechanical properties of dissimilar joints between Hastelloy C276 and AISI 316L by gas tungsten arc welding were characterized. ERNiCrMo-4, a Ni-Cr-Mo based filler metal, was used and the welding was performed by multi-pass. Both macro and microstructural features of joints were examined using microscopic techniques. Macrostructural characterization revealed no defects like cracking, pores and undercuts within the joints. The microstructure of weld metal had several forms of solidified austenitic matrix and P phases embedded in dendritic structure. Partially melted zones were observed at the fusion line between the weld metal and AISI 316L and grain growth was determined within the fusion line between the weld metal and Hastelloy C276. In mechanical characterization, not only the variation of hardness but also mechanical properties under tensile and impact loadings were investigated as a function of microstructural features of the joint. The hardness profile throughout the dissimilar joint had a gradual increase from AISI 316L to Hastelloy C276, both having polygonal grains and hardness values of the weld metal strongly affected its solidified form. Due to the superior mechanical properties of Hastelloy C276, failure under tensile loading occurred within AISI 316L. Under impact loading, heat affected zone of Hastelloy C276 showed the highest impact strength.

At moderate and high temperature applications, nickel-based superalloys are widely preferred as suitable candidate materials due to their high mechanical properties and corrosion/oxidation resistance, however, difficulties in mass production of these alloys and their cost cause the use of these alloys as a part of dissimilar weld joints with any structural material. In this study, a dissimilar weld joint between a nickel-based superalloy (UNS 10276) and unalloyed steel (SA 516 GR 70) was successfully performed by gas tungsten arc welding method by using ErNiCrMo-3 filler metal. Initially, the microstructural features of base materials, heat affected zone and weld metal were characterized and cellular, coarser cellular and epitaxial growth dendrites as matrix phases and several Mo-rich and Nb-rich precipitates embedded in the solidified structure were observed in weld metal. In heat affected zones and fusion lines of the dissimilar joints, some metallurgical phenomena like partially melted zone, solidification at grain boundary, migrated grain boundary and decarburization were also examined. All these microstructural features affected the mechanical properties.

Abstract. In this study, a dissimilar weld joint between SAF 2205 and Hastelloy C-276 was manufactured by using gas tungsten arc welding and its notched impact fracture behaviour was investigated. Initially, V-type welding mouth was opened and the welding was performed by multi-pass. In welding procedure, ERNiCrMo-3 material used as a filler metal and the heat input was varied between 0.48-1.10 kJ/mm depending on welding parameters. Both welding pool and root zone were protected by an argon atmosphere. Multi notched impact tests were performed at room temperature. Weld metal had an impact toughness value as 92 J and its fracture surface exhibited several oriented cracking paths due to its solidified structure. The impact toughness value was measured as 82 J for heat affected zone of SAF 2205 and its fractograph reflected the coarser and deeper dimples. Heat affected zone of nickel based alloy had the highest impact toughness value as 116 J among the studied joints due to the more plastic deformation capability of nickel having face centered cubic structure, however, its fracture surface under impact loading exhibited several cracks propagating throughout the fusion line having equiaxed dendrites.