Controlled undercooling of liquid iron in contact with Al 2 O 3 substrates under varying oxygen partial pressures
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NTRODUCTION
THE presence of nonmetallic inclusions in steel is associated with low productivity and the generation of defects in the downstream process and, as a result, low-quality products. The field that studies the minimization of the effect of inclusions on the steelmaking process and on the final product properties is usual called ‘‘clean steel.’’ By the end of the last century, several researchers proposed methods to make use of inclusions in a beneficial way. This new concept was called ‘‘oxide metallurgy,’’[1] and it highlights the possibility of a beneficial use of existing inclusions to control metallurgical changes. In the continuous casting process, since the structure of a solid depends strongly upon the initial solidification condition, and this initial solidification condition in turn depends upon the type and density of nucleants, the inclusions in the steel can be designed to maximize their effect as inoculants. The general objective of the use of oxide metallurgy in casting is to address the importance of nonmetallic inclusions in the definition of the solidification structure and to determine the conditions for its application in the production of bulk steel. The objective of this work is to determine the fundamental conditions under which the inclusions present in liquid steel can act as heterogeneous nucleants for solidification. MARTIN E. VALDEZ, Graduate Student and Postdoctoral Fellow, formerly with the Department of Materials Science and Engineering, Carnegie Mellon University, is with Tenaris/CINI, Campana, Argentina B2804MHA. Contact e-mail: [email protected] PELLO URANGA, Researcher, is with CEIT and TECNUN (University of Navarra), E-20018 Donostia-San Sebastian, Basque Country, Spain. KATSUHIRO FUCHIGAMI, Researcher, is with the Research and Development Lab., Nippon Steel Corporation at Oita, Oita, Japan 870-0992. H. SHIBATA, Lecturer, is with the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan 980-8577. ALAN W. CRAMB, formerly with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, is Dean of Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180. Manuscript submitted February 11, 2006. METALLURGICAL AND MATERIALS TRANSACTIONS B
There are a limited number of articles in the literature that discuss the importance of inclusions on the determination of the solidification structure of metals. Most of these articles came from the field of welding[2,3,4] but there are some references to the production of steel with 100 pct equiaxed structure in Posco[5] and Sumitomo.[6] There are also some interesting insights into the mechanisms of heterogeneous nucleation from the external inoculation process that has been long used in the production of aluminum.[7,8] By reviewing the effect of inclusions on the solidification of the welding process, aluminum production, and the attempts of the steel industry, it is possible to list some factors that are important for solidification control through the
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