Density measurements of CaO-MnO-SiO2 slags were carried out using the Archimedean method. The density decreased with increasing temperature, and the negative temperature coefficient (-dρ/dT) was in the range of 1.46-3.10 × 10 -1 kg/m 3 K. At a fixed CaO content (25 wt%) and at a fixed SiO2 content (30 wt%), the density of CaO-MnO-SiO2 slag increased with increasing MnO content. The molar volumes of CaO, MnO and SiO2 at 1 773 K were estimated 21.0, 17.2, and 28.0 × 10 -6 m 3 /mol, respectively. The molar excess volume was expressed by , where Ω = -8.97 × 10 -6 m 3 /mol at 1 773 K. The thermal expansion coefficient decreased with increasing XSiO 2 because of the enhanced silicate network structure.KEY WORDS: Archimedean method; CaO-MnO-SiO2 slag; density; molar volume; silicate network structure; thermal expansion coefficient.
The surface tension of 430 stainless steel was measured using an electromagnetic levitation (EML) method at temperatures of 1 707-2 000 K, under a 5 vol% H2-He atmosphere. For comparison, the surface tension was also measured using a constrained drop method; specifically the advanced sessile drop method. At 1 823 K, the surface tension of the 430 stainless steel was estimated from the electromagnetic levitation and the constrained drop methods to be 1.802 and 1.614 N/m, respectively. A subsequent analysis of oxygen content showed that the former contained ~7 ppm oxygen, whereas the latter had 60 ppm. It was therefore considered that the observed difference in measurements was the result of a contamination by oxygen. Furthermore, the EML experimental results were found to be close to the theoretically calculated values for the Fe-Cr-Si system. Consequently, for complex multi-component commercial steels such as the 430 stainless steel, the levitation method is recommended for the measurement of surface tension.
As global regulations of CO<sub>2</sub> emissions and fuel consumption efficiency become more strict, the automotive powertrain system has become more compact with lower lubrication viscosity. With the current trends in powertrain system improvement, the operating conditions of powertrain components such as gears are becoming more severe. As a result, it is increasingly important to improve the strength and durability of the materials used for the powertrain system by optimizing alloy design and heat treatment. Much research and development has focused on improving components by heat treatment, and especially carburization. Also, many different alloy concepts, such as Fe-Cr-Mo or Fe-Cr-Ni systems have been proposed for automotive components. Among various approaches, Cr and Si , and solid solution hardening, are known to effectively increase hardenability. However, it has been reported in many works that the carburized case depth can also be reduced by increasing the Cr/Si content, due to oxide film formation. The mechanism of Cr/Si oxide film formation during carburization has not yet been clearly determined. In the present work, therefore, the mechanism of surface oxide film formation during carburization was examined. Also, the microstructure, composition and crystal structure of different oxides were examined and compared in detail.
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