Activity of titanium in Fe-Cr melts
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In an attempt to reduce the use of expensive alloying elements such as nickel, specialty steel makers have developed less expensive ferritic grades of stainless steel, which are suitable for automotive exhaust applications, in particular, catalytic converter applications. Dual-stabilized titaniumniobium ferritic stainless steel can meet most of the application requirements for catalytic converters with its properties of low thermal expansion, improved surface quality, and good oxidation and corrosion resistance. One key issue with stabilized titanium stainless steel is that the titanium oxide and titanium nitride are one of the main causes of nozzle clogging in continuous casting, which greatly affects productivity. The Ti and TiN also react with mold fluxes and can result in casting instability (floater formation) and surface defects on the slab. In addition, the titanium reacts with carbon and nitrogen and can cause surface defects in hotrolled, annealed, and pickled stainless strip.[1] Many research articles have been published regarding the deoxidation equilibria of titanium in liquid iron. Because of experimental difficulties, significant disagreements exist in the literature concerning the relationship between titanium content in the melt and the equilibrium oxide phase. However, it has been recently shown that Ti3O5 is the equilibrium oxide phase at titanium contents ranging from 0.01 to 0.25 pct, which is the range commonly used for deoxidation. Ti2O3 and Ti3O5 are the equilibrium oxide phases below and above 4.5 wt pct titanium, respectively, as indicated in Table I. Some values for the activity coefficient of titanium at infio nite dilution, g Ti , reported in the literature vary by more than an order of magnitude, as shown in Table II. H.Y. CHOI, formerly Graduate Student, Materials Science and Engineering Department, Carnegie Mellon University, is Research Engineer, Pohang Iron & Steel Co., Ltd., Pohang-shi, Kyungbuk, South Korea. W.E. SLYE, formerly Graduate Student, Materials Science and Engineering Department, Carnegie Mellon University, is Manager, Industrial Applications R&D–Primary Metals and Metals Fabrication, Praxair Inc., Tonawanda, NY 14150. R.J. FRUEHAN, Professor, is with the Materials Science and Engineering Department, Carnegie Mellon University, Pittsburgh, PA 15213. Contact e-mail: [email protected] R.C. NUNNINGTON, Research Engineer, is with LWB Refractories, York, PA 17405. Manuscript submitted March 23, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS B
The measurements in this study were made using an oxygen electromotive force (EMF) cell with a cermet contacting the liquid metal. The cermet was constructed of Mo and Al2O3 and does not significantly dissolve into the melt. To produce the ceramics, a die cylinder and piston were swabbed with a stearic acid ethanol solution that served as the die lubricant. Then a small piston was inserted into the bottom of the cylinder. The premixed ceramic powder packed into the cylinder, and then, the upper piston was placed into the cylinder on top
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