Determination of Alloying Elements Ti, Nb, Mn, Ni, and Cr in Double-Stabilized Ferritic Stainless Steel Process Sample U
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INTRODUCTION
STAINLESS steel is in increasing demand. The trend is that there is also increasing demand for its quality and properties. New steel grades are being manufactured to achieve new quality standards. One of the main criteria for quality is steel cleanness which means that the steel should have a minimal amount of harmful inclusions that originate from different process stages and which may form during solidification. All steels contain inclusions as impurities. Zhang and Thomas reviewed several methods for the analysis of inclusions in steel.[1,2] These techniques face many challenges when it comes to simultaneous analysis of steel and inclusion compositions. So far, only optical emission spectrometry with pulse discrimination analysis (OES-PDA) has been tested for the simultaneous analysis of steel and oxide inclusions, but the results have not been consistent with other techniques.[3] Sometimes the surface analysis can be misleading, especially when large amounts of small inclusions are present. Another challenge is the analysis of microalloying elements due to their small quantities compared to the main components.
TEIJA SIPOLA and TUOMAS ALATARVAS, Doctoral Students, EETU-PEKKA HEIKKINEN, University Lecturer, and TIMO FABRITIUS, Professor, are with the Laboratory of Process Metallurgy, University of Oulu, P.O Box 4300, 90014 Oulu, Finland. Contact e-mail: teija.sipola@oulu.fi Manuscript submitted January 12, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
Only recent studies have combined inclusion studies with steel matrix chemical analysis. Depending on the composition and temperature of steel, alloying elements can occur either in the steel lattice or as a separate phase in the steel matrix. An electrolytic extraction method is used in 3D inclusion studies and also in the study of soluble and insoluble alloying elements from deoxidized ferrous materials and stainless steel.[4–8] The alkali fusion method has been used in the elemental analysis of inclusions.[5,9] The determination of alloying elements from the steel lattice and insoluble particles with acid digestion after sample dissolution using electrolytic extraction is fairly a new method of analysis for steel purity.[4] Precise information about steel’s chemical composition is required when new, more intricate steels are manufactured. Steel composition studies are particularly interesting when rare and expensive alloying elements such as Nb and Hf are used. Detailed analysis of steel composition is also necessary for many industrial problems that are caused or aggravated by inclusions, such as clogging.[10] Ti and Nb are used in stainless steel to stabilize the ferritic structure of steel as well as to remove nitrogen and oxygen. The influence of carbide-forming elements on the microstructure and mechanical properties as well as wear resistance of ferritic stainless steel has been studied.[11,12] Titanium and niobium precipitate in ferritic stainless steel as TiN, NbC, and Fe2Nb.[13] Ti- and Nb-containing particles have been studied from Nbmo
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