ORIGINAL ARTICLE Characterization of microstructure, chemical composition, and toughness of a multipass welded joint of austenitic stainless steel AISI316L Mustafa Tümer 1 & Ramazan Yılmaz 2 Received: 24 March 2015 /Accepted: 7 March 2016 # Springer-Verlag London 2016 Abstract In this study, AISI 316 types of austenitic stainless steels were welded by FCAW (flux-cored arc welding) using E316LT1-1/4 flux-cored wire under various shielding gas mixtures containing CO 2 at different ratios. Effects of mixed ratio of Ar and CO 2 in the in the shielding gas on the micro- structure, impact toughness, and microhardness of welded materials were studied. Stereo optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), and TEM/ mapping analysis techniques were used for microstructural characterizations. The impact toughness values of the weld- ments were decreased as a result of the formation and growth of inclusions in the microstructure due to the increases amount of CO 2 in the shielding gas. The hardness values and δ-ferrite amount in the weld metal were affected by depending on of the shielding gas mixtures. Keywords Flux cored arc welding . Stainless steel . δ-ferrite . Shielding gas . Inclusion 1 Introduction AISI 316 L austenitic stainless steel materials have a wide range of usage area for their superior mechanical and corro- sion properties. They are commonly preferred in energy in- dustries such as ship building, chemistry, defense, nuclear energy, and cryogenic applications. Compared to other stain- less steels, austenitic stainless steel is distinguished with its excellent corrosion resistance and high toughness characteris- tics. Due to the internal structure being austenitic, embrittle- ment, which is a significant problem encountered in ferritic stainless steels and seen under transition temperature, is not observed in this type of steels. Furthermore, their resistance to intergranular corrosion is high due to low carbon content. Their toughness properties are significantly good, and no mar- tensite transformation is observed during cooling. Therefore, cold cracking problems are not observed in joining austenitic stainless steels as in ferritic martensitic stainless steels, and no pre-heating during joining and post-welding heat treatment are required [1–5]. Flux-cored arc welding (FCAW) method is used in joining thick section stainless steels in today’s industry, which leads to a considerable increase in production speed of welding treat- ments. Welding performed by using flux-cored arc is a more economical and efficient method compared to other welding methods due to its high melting power, suitability for automa- tion for continuous welding process, its usability in every position, ease of performance, and smooth weld nuggets with high mechanical properties. Slag formation in welding and protection of weld metal by shielding gas ensure less oxida- tion of nugget surfaces in welds performed with flux cored wires and minimization of foreign matters in weld bath [5–9]. * Mustafa Tümer mustafa.tumer@kocaeli.edu.tr Ramazan Yılmaz ryilmaz@sakarya.edu.tr 1 Department of Welding Technology, Uzunçiftlik Nuh Çimento Vocational High School, Kocaeli University, Kocaeli, Türkiye 2 Department of Metallurgical and Materials Engineering, Technology Faculty, Sakarya University, Esentepe, Sakarya, Türkiye Int J Adv Manuf Technol DOI 10.1007/s00170-016-8614-4