Chemically Induced Solidification: A New Way to Produce Thin Solid-Near-Net Shapes
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12, Park et al.[1] suggested the feasibility of decarburizing 4 wt pct C cast iron in solid state during the continuous strip casting process using oxidizing gases (such as CO2 and H2O), called the S3 process. The advantage of such a process would be that aspects of the steelmaking process, such as the basic oxygen furnace (BOF), can be circumvented, therefore avoiding large amounts of oxygen and unwanted oxide inclusion products. Although the results showed promise, decarburization rates to 0.5 wt pct were in excess of 30 minutes for a 1-mm strip. Later the S3-II[2] process was proposed where some decarburization occurs in the tundish (down to 1.2–1.9 wt pct) by bubbling O2 before further solid state decarburization. Decarburizing to this point in the liquid ensures no excess oxygen to form oxides and, thus, still achieves ‘‘clean’’ steel production. This reduced solid state decarburization decreases the time to around 10 minutes for 1-mm strips held at 1473 K (1200 °C). Belt casting (particularly horizontal single belt casting (HSBC)) offers the unique possibility of introducing gases during the solidification of steel and affects the steel chemistry through the strip thickness thanks to the CARL SLATER, Research Fellow, STEPHEN SPOONER, Ph.D. Student, CLAIRE DAVIS, Professor, and SEETHARAMAN SRIDHAR, Professor, are with WMG, University of Warwick, Coventry, U.K. Contact e-mail: [email protected]. Manuscript submitted June 27, 2016. Article published online September 26, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
thin cross section. This opens up the possibility of expanding on the premise of the S3-II process and of decarburizing to a lower carbon fraction in the liquid to the point of solidification (a limit not desirable to attain in the tundish). Therefore, the aim of this work is to understand and observe the isothermal solidification of liquid iron similar in composition to pig iron by means of decarburization in both air and N2 atmospheres. This therefore explores the feasibility of an inline continuous decarburizing and non-CO2 forming (in the case of N2) method of producing steel while allowing for a different solidification structure. The limit of decarburization in this case may be the balance between the desirable removal of carbon and the undesirable dissolution of interstitials (oxygen and nitrogen) and the formation of oxides (and other such undesirably products of interaction with these gases). A high-temperature confocal scanning laser microscope (CSLM) was used to observe the in situ solidification of the molten steel (an outline of the CSLM technique has been covered in a previous paper[3]). A Fe-4C-0.2P steel was used for this study, and samples were machined to cubes of around 0.25 g. The purpose of phosphorous addition was to enable the solidification structure to be revealed. The samples were heated at 10 K/s to a set peak temperature under argon (with and O2 concentration
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