Characteristics of inclusions in rutile-type FCAW weld metal
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RESEARCH PAPER
Characteristics of inclusions in rutile-type FCAW weld metal Jun Seok Seo & Ka Hee Kim & Hee Jin Kim & Changhee Lee
Received: 24 August 2011 / Accepted: 22 March 2012 / Published online: 7 December 2012 # International Institute of Welding 2012
Abstract The morphological and chemical nature of the inclusions in flux cored arc welding (FCAW) weld metal of E71T-1 grade were analyzed in SEM/TEM/scanning transmission electron microscope (STEM) equipped with energydispersive X-ray (EDX) to understand the sequence of inclusion formation and to verify the absence of the Mn-depleted region in close proximity to the inclusion surface. Basically, all the inclusions were nearly spherical in shape and chemically a mixture of Ti-rich oxide and (Si,Mn)-rich oxide partly covered with MnS phase. From the morphological features of each phase, the formation sequence of the inclusion can be predicted in the order of Ti-rich solid oxide, (Si,Mn)-rich liquid oxide, and MnS phase. The MnS phase always presented on the surface of the (Si,Mn)-rich liquid oxide and was fully confined within the outer circle of the inclusion implying that it was formed from (Si,Mn)-rich oxide. STEM/EDX analysis performed on the MnS phase and its neighbor did not show any Mn depletion over a distance of about 70 nm from the outer surface of the MnS phase.Based on these results, it could be concluded that as the MnS phase was formed from the liquid (Si,Mn)-rich oxide, the manganese concentration in the steel matrix cannot be varied. Doc. IIW-2295 recommended for publication by Commission IX “Behaviour of Metals Subjected to Welding”. J. S. Seo Department of Advanced Materials & Chemical Engineering, Hanyang University, Seoul 133-791, South Korea K. H. Kim Korea Advanced Nano Fab Center, Suwon 443-270, South Korea H. J. Kim (*) KITECH, Chonan 331-825, South Korea e-mail: [email protected] C. Lee Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, South Korea
Keywords (IIW Thesaurus) FCA welding . Oxide . Inclusions . Manganese . Ferrite
1 Introduction The nonmetallic inclusions found in the weld metal are the result of deoxidation and/or desulphurization reactions taking place within the weld pool. Therefore, most of these inclusions are well known to be oxides accompanying with small amount of sulfide. The formation of such inclusions comprises various stages such as nucleation, growth, coalescence, and elimination from the weld into the slag. Considering these stages, Kluken and Grong [1] proposed the model of sequential oxidation, and this model was employed to predict the average inclusion composition. This sequential oxidation was adopted by Babu and others [2] and was reported to be in the following order: Al2O3, Ti3O5, SiO2, MnO; eventually, a layered morphology of inclusions is formed. In rutile-type flux cored arc welding (FCAW), however, the slag system contains a high proportion of TiO2 so that the oxidation sequence would be different from that reported previously. It is also well known that the incl
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