Dissolution kinetics of alumina into mold fluxes for the continuous steel casting was investigated by employing the rotating cylinder method. The dissolution rate of Al 2 O 3 was determined by measuring weight loss of Al 2 O 3 rod, initial dipping area and immersion time. It is concluded that the alumina dissolution is controlled not only by the mass transfer in the molten flux but also by the formation of intermediate compounds such as CaO · 6Al 2 O 3 , CaO · 2Al 2 O 3 , and 2CaO · Al 2 O 3 · SiO 2 on the rod/flux interface. Concentration driving force, rod rotation speed, temperature of molten flux and chemical composition are also important factors which affect the alumina dissolution. The dissolution rate increased with addition of MgO or CaF 2 , or up to 5%mass of Na 2 O, and then decreased with further increase in the amount of Na 2 O content. The physical erosion of the rod surface by the solid 2CaO · SiO 2 dispersed in the liquid was attributed to fast alumina dissolution.

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Dissolution behavior of ZrO2-graphite refractories used in a submerged entry nozzle (SEN) during continuous casting of steel was investigated using the rotating cylinder method. In the present work, the dissolution rate of the zirconia-graphite rod was determined by measuring the corrosion depth of the rod after a given immersion time. It was found that the dissolution rate was slow at the surface where molten flux alone is contacted, but much higher at the region that contacts the interface of the molten flux and liquid metal. The dissolution rate was influenced by the rotation speed of the rod, ZrO2 content in the refractories, and the presence of Na2O and fluoride (F ) in the mold flux. It is speculated that a cyclic process wherein zirconia dissolves into the molten flux and graphite dissolves into the liquid metal accelerates the dissolution at the flux-metal interface.

Nitrogen oxides (NO x ) and carbon monoxide (CO) are among the most dangerous chemical species to human health present in the atmosphere. Acute CO toxicity leading to unconsciousness, respiratory failure or death can occur after 1 hr of exposure when ambient CO levels reach 1000 ppm, whilst increase of NOx emissions can contribute to acid deposition, pollution of groundwater, eutrophication of surface waters, and tropospheric ozone and ecosystem damage. In this work, pure SnO 2 sensors for CO and NO x were prepared by spin coating solutions derived from a washed Gel-precipitate followed by a calcining step. SnO2 sensors of nanometer grain size prepared by this process showed good sensitivity to CO and NOx gases. The increase of calcining temperature not only affected grain size and surface morphology, but also caused a decrease in sensitivity of the SnO 2 sensors.

With the emerge of vacuum technology, it is possible to produce ultra low carbon (ULC) steels with carbon content of less than 0.005 %mass which is called interstitial free (IF) steels. In this study, strength and microstructure of IF steel after cold-rolling have been determined. The initial steel plates were cold-rolled using two different cold reductions (CR) as 80 and 90% in total, thereafter the steel sheets were cut into specimens for tensile test and optical microscopy. Ultimate tensile strength (UTS) of the cold-rolled steel was high (650807 MPa), but the elongation (EL) was low (3.55.3%). Meanwhile, UTS of the annealed steels was decreased to 290 MPa when soaking temperature was 800 o C because of stress relief and recrystallization. It was concluded that higher CR (more severe deformation) increased the strength but decreased the ductility of the IF steels. In consistence with micrograph of the steels, X-ray diffraction (XRD) results showed that microstructure of the cold-rolled and annealed IF steels was only ferrite. Textures, one of the most important factors affecting the recrystallization, were found in cold-rolled steels. Keywords:Cold reduction, Cold-rolling, IF steel, Residual stress, Texture IntroductionThe demands for the steel with excellence formability from automotive industry have accelerated the progress in the steelmaking process, leading to the development of the ultra low carbon (ULC) steels containing carbon less than 0.01 %mass [1,2]. With the emerge of vacuum technology, it is possible to produce ULC steels with carbon content of less than 0.005 %mass which is called interstitial free (IF) steels [3][4][5][6]. It is well known that the interstitial elements such as carbon (C) and nitrogen (N) in the steel are lower owing to vacuum treatment, thereafter one of the most important properties of ULC steel (formability) is improved to apply for automotive body. In general, two important objectives being pursued by the automobile industry are a decrease in car weight and improvements in safety [7]. To realize these requirements, several researches have been implemented to reduce thickness of the steel sheet, increase strength and improve press formability of the steel. For example, J. Galan et al. studied on improving strength and dent resistant capacities with bake hardenable ULC steels in order to fulfill the requirements of thinner sheet steel for automotive applications [2]. M. Wang et al. analyzed the source and disadvantages of macro-inclusions in titanium stabilized ULC steel and reported that the total

This paper presents experimental process of ultra-low carbon (ULC) steel using vacuum heat treatment. After adjusting the chemical compositions as desired, the ULC steel was casted into plate, hot-forged and cold-rolled to sheet of 1 mm thickness, finally annealed at 800^oC. Microstructure, crystalline phase, non-metallic inclusions and mechanical properties of the ULC steels were characterized by optical microscopy, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and tensile test. Under argon vacuum atmosphere, decarburization occurred and C contents of the treated steels were reduced to 36 and 40 ppm corresponding to the decarburizing rate of 84.2 and 82.4%, respectively. The vacuum induction melting is thought to accelerate the rate of carbon removal from liquid steel. Electromagnetic force was attributed to promote the decarburization due to increasing the mass transfer coefficient during vacuum treatment. The annealed steels obtained a good combination of the strength and ductility; the total elongations were 45.2 and 42.9 %, while the yield strengths were 199 and 285 MPa, respectively. The results indicated that the ULC steels have only ferrite phase, of which grains size were 30 µm in average. The relative volume of non-metallic inclusions in the ULC steels was calculated as 0.23 vol. %, resulting positive contribution in the mechanical properties.

The behaviour of iron ore pellets in a blast furnace must be considered to improve ironmaking operations, especially when a large amount of the pellets is used. This study presents the reduction degree, mineralogical composition, and morphology of the pellet reduced in a gas mixture of 60% CO and 40% Ar at temperatures between 900 and 1,100oC. The pellet was prepared from iron ore from the Cao Bang province, Vietnam, by rotary drum. The obtained results showed that the reduction degree of the pellet increased with increasing reduction time and temperature. The activation energy of the reducing reaction was calculated to be 63.2 kJ/mol, which indicated that reduction occurred more easily in the present condition. X-ray diffraction (XRD) results revealed mineralogical phases such as hematite (Fe2O3), magnetite (Fe3O4), wüstite (FeO), metallic iron (Fe), and fayalite (Fe2SiO4) existing in the pellets when reduced for different times and temperatures. Fe and Fe2SiO4 were found to be the majority in the pellet that was reduced for 90 min at 1,100oC. Scanning electron microscopy (SEM) observations suggested the formation of a liquid phase, e.g., Fe2SiO4, which retarded the reducing reaction because it hindered the diffusion of gas flow inside the pellet. This phenomenon is essential to blast furnace ironmaking because pellets must be completely reduced before they move down to the liquid zone.