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76 巻, 3 号
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解説論文
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武田 全康, 鈴木 淳市, 秋屋 貴博, 加藤 宏朗2012 年 76 巻 3 号 p. 165-176
発行日: 2012年
公開日: 2012/03/01
ジャーナル フリーSmall-angle neutron scattering (SANS) method is applied for the investigation of average internal structures of Neodymium-Iron-Boron (Nd-Fe-B) sintered magnets. The information obtained using SANS is average structure of the magnet and sometimes complementary to the microstructural information using the scanning electron microscopy. The SANS patterns were sensitive to internal structural changes introduced by the sintering process and the formation of magnetic domains, and we found a correlation between the SANS intensity and the coercivity. These observations indicate that SANS is a promising tool to investigate the origin of the coercivity of Nd-Fe-B sintered magnets. This article is a brief introduction to SANS and gives several examples of its application to investigation of Nd-Fe-B sintered magnets in the viewpoint of the correlation between the average structure and the coercivity.
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論文
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中野 多郎2012 年 76 巻 3 号 p. 177-181
発行日: 2012年
公開日: 2012/03/01
ジャーナル フリーRecently, multilayer piping has been used widely. Multilayer piping has excellent durability and corrosion resistance. An effective means for quality maintenance of multilayer piping is the laser ultrasonic technique for checking the state of adhesion of the vinyl chloride layer and the steel layer of multilayer piping. The wave is refracted at the interface between the steel layer and the vinyl chloride layer based on the wave motion principle. The arrival time of the reflection wave was calculated and confirmed by measurements. If measurement of piping under high temperature becomes possible, the effectiveness of the non-destructive testing technology by the laser ultrasonic technique can be expected, enabling the production of higher reliability and quality of multilayer piping.
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吉田 卓, 奥村 晃央, 北 裕史, 潮田 浩作, 阿部 義男2012 年 76 巻 3 号 p. 182-188
発行日: 2012年
公開日: 2012/03/01
ジャーナル フリーFor the purpose of understanding the mechanism of high temperature embrittlement, especially in the heat affected zone of B bearing low-carbon alloy steel, the role of B addition is studied in terms of grain boundary segregation and nitride precipitation of B. BN precipitates at prior austenite grain boundary are supposed to be a dominant cause to the embrittlement of the steels when tensile stress is applied at 600℃ followed by heat cycle of welding, where the environment of fire is simulated. Nitride formation is changed from intragranular TiN after hot rolling followed by reheating to 600℃ for tensile test to intergranular BN at prior austenite grain boundary after reheating to 600℃ following heat cycle of welding. Consequently, the grain boundary fracture takes place for the specimens subjected to the heat cycle of welding when tensile stress is applied after reheating to 600℃, because the intergranular BN leads to the formation of cavity along prior austenite grain boundary. This mechanism is experimentally verified by the fact that high temperature embrittlement is able to be prevented by either the addition of Zr or the more addition of Ti which may fix nitrogen as more stable nitride and inhibit the dissolution of nitride during welding heat cycle.
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朴 相漢, 江阪 久雄, 篠塚 計2012 年 76 巻 3 号 p. 189-196
発行日: 2012年
公開日: 2012/03/01
ジャーナル フリーAt the beginning of solidification in the mold, both temperature gradient (G) and growth velocity (V) are large. But, as solidification proceeds, G and V become small. It is known that solidification structure varies with solidification condition. However, the mechanism of change in solidification structure is still uncertain. Therefore, the present study has been performed to understand the effect of change in growth rate on the primary arm spacing (λ1). Unidirectional solidification using succinonitrile-1 mass% water was made. During solidification the growth velocity was abruptly changed and the change in λ1 was measured. When the amount of change in growth velocity was small, no change in λ1 was observed, though the dendrite tip radius and the secondary dendrite arms quickly changed. When the amount of change of growth velocity was large, λ1 changed to some extent. The time necessary to reach the steady state increased with increasing the amount of change in growth velocity.
In the case of increase in growth velocity, a new primary arm formed due to branching and the average primary arm spacing decreased. In the case of decrease in growth velocity, some primary arms stopped growing and the average primary arm spacing increased.
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朴 相漢, 江阪 久雄, 篠塚 計2012 年 76 巻 3 号 p. 197-202
発行日: 2012年
公開日: 2012/03/01
ジャーナル フリーIn this study, the mechanism of equalization for λ1 has been investigated using succinonitrile-1.0 mass% water alloy. Approximately 15 columnar dendrites have been observed and the maximum and the minimum value of λ1 (λ1Max and λ1Min, respectively) have been characterized. It is found that λ1Max decreased and λ1Min increased with time, i.e., the tip of primary arm grow to the region of wide from region of narrow of dendrite arm spacing. And also, Local primary arm spacings are gradually equalized due to propagation of position of primary trunk. The time necessary for the equalization for λ1 is found to be longer than that of the process for adjusting dendrite tip radius and the change in λ1 due to branching or over growth. This may suggest that solutal filed in the interdendritic region plays and important role for equalization for λ1.
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牛 立斌, 中根 孝浩, 髙久 啓2012 年 76 巻 3 号 p. 203-209
発行日: 2012年
公開日: 2012/03/01
ジャーナル フリーConcerning boiler tube materials of carbon-steel STB410, low-alloy steel STBA24 and stainless-steel SUS304, cyclic voltammetry measurements and immersion tests are conducted in simulated AVT (All Volatile Treatment) waters with the mixed formic acid (HCOOH) and chloride ions (Cl−) at pH9.5, pH8.0 and pH7.0. Characteristics of the oxide films formed on the specimens in immersion tests are evaluated by X-ray photoelectron spectroscopy (XPS). It is confirmed that the corrosions of STB410 and STBA24 steels are accelerated with the decreasing pH in the waters, and that SUS304 steel has the better corrosion resistance in all the waters tested. It is clarified that oxide films formed on STB410 steel in the simulated AVT waters are composed of Fe-oxides and become unstable with the decreasing pH. On the other hand, the films formed on STBA24 steel, even in the waters with lower pH values, show the oxide films with the concentrated Cr in them. Furthermore, the pH decrease in the water results in no influences on the corrosion behaviors of SUS304 steel due to the formation of oxide films with Cr.
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越智 達朗, 間曽 利治, 吉田 卓, 渡邊 忠雄2012 年 76 巻 3 号 p. 210-215
発行日: 2012年
公開日: 2012/03/01
ジャーナル フリーAn increase in the torsional strength of automotive shafts has been a subject of particular interest. The purpose of this study is to establish a method of increasing strength of shaft steels to mode fracture. The effect of austenite grain size on torsional strength in mode fracture is investigated. The torsional strength in mode fracture improves according to the grain refining of the austenite grain. A ductility fracture is observed partially in the fine grained steel though the initiation site of fracture presents the intergranular fracture in all aspects in the coarse grained steel. The amount of P of the grain boundary segregation decreases by the grain refining as a result of investigating the grain boundary properties by AES. The improvement of strength by the grain refining is possibly guessed that the following effect superimposed it above. The amount of the grain boundary segregation must decrease along with an increase of the area of the grain boundary. The ratio of the low energy grain boundary must increase. It must accompany an increase of the ratio of the low energy grain boundary and the amount of the grain boundary segregation must decrease.
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寺澤 佑一, 三上 祐史, 伊藤 孝至, 竹内 恒博2012 年 76 巻 3 号 p. 216-221
発行日: 2012年
公開日: 2012/03/01
ジャーナル フリーBy using first principles cluster calculations, we identified that Ta or W substitution for V is useful for decreasing the lattice thermal conductivity of the Fe2VAl Heusler alloy without greatly affecting the electron transport properties. It was clearly confirmed that the Fe2(V1−xTax)Al0.95Si0.05 (x=0, 0.025, 0.05), Fe2(V0.9−xTaxTi0.1)Al (x=0, 0.10, 0.20), and Fe2(V0.9−2xWxTi0.1+x)Al (x=0, 0.05, 0.10) alloys indeed possessed large Seebeck coefficient regardless of the amounts of substituted elements, while their lattice thermal conductivity was effectively reduced. As a result of partial substitution of Ta for V, we succeeded in increasing the magnitude of the dimensionless figure of merit of the Heusler phase up to 0.18, which is five times as large as the Ta-free compound.
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