Osamu Furukimi

Development of ferritic stainless steel sheets with excellent deep drawability by {1 1 1} recrystallization texture control

Abstract In order to develop ferritic stainless steel sheets with high formability, control of the {1xa01xa01} recrystallization texture has been investigated with the aim of increasing the Lankford values. Based on the results, development of ferrite stainless steel with deep drawability which has an r-value of the highest level in the world has been achieved. The newly developed ferritic stainless steel is expected to be applied in a wide range of automotive parts, and applications requiring corrosion resistance and deep drawability, in which SUS304 or high strength steel with corrosion protection treatment has been used.

Thermoelectric Properties of Ga-Doped Ba8AlxSi46−x Clathrate

Single-crystalline Ba8AlxGaySi46−x−y clathrates were synthesized by the arc melting method and Czochralski method without subsequent treatment, and their thermoelectric properties were compared with those of Ba8AlxGaySi46−x−y and Ba8AlxSi46−x clathrates with almost the same carrier concentration as estimated from the similar Seebeck coefficient and the Zintl concept. The resistivity of Ba7.8Al5.3Ga7.4Si33.3 was lower than that of Ba7.9Al12.6Si33.4. The specific electrical resistance of Ba7.9Al12.6Si33.4 and Ba7.8Al5.3Ga7.4Si33.3 was 0.573xa0mΩxa0cm and 0.282xa0mΩxa0cm at 750xa0K, respectively. The band structure of Ba8Al8Ga8Si30 and Ba8Al16Si30 was estimated by first-principle calculations using density functional theory with the local density approximation. Based on these calculations, it was found that the shape of the bottom of the conduction band for Ba8AlxSi46−x clathrate changed slightly on Ga doping and the radius of curvature of the bottom of the conduction band for Ba8Al8Ga8Si30 clathrate was lower than that for Ba8Al16Si30 clathrate. These results indicate that the mobility was enhanced by Ga doping of Ba8AlxSi46−x clathrate. We also synthesized single-crystalline Ga-doped Ba8AlxSi46−x clathrate. The electrical resistivity decreased dramatically due to the single-crystallization because of reduced electron scattering on grain boundaries. These results suggest that Ga doping and single-crystallization are effective for improvement of the thermoelectric properties of Ba8AlxSi46−x clathrate.

Reinvestigation of Thermoelectric Properties of n- and p-Type Ba8−dAuxSi46−x−y Clathrate

We have synthesized n- and p-type clathrates Ba8−dAuxSi46−x−y with various Au contents (4.6xa0<xa0xxa0<xa06.0) by arc-melting, annealing at 1173xa0K, and spark plasma sintering at 1073xa0K. The Au compositions found by wavelength-dispersive x-ray spectrometry for the synthesized samples were slightly lower than the nominal compositions. Ba7.8Au4.6Si41.4 and Ba7.7Au4.9Si41.1 samples showed n- and p-type conduction, respectively. According to the electron count (Ba2+)8Au(3−)5.33Si40.67, the clathrate composition with xxa0=xa05.33 is expected to be an intrinsic semiconductor. Our experimental results show that increase of the Au composition causes a transition from n-type to p-type conduction between xxa0=xa04.6 and 4.9. We have also calculated the band structures of the Ba8AuxSi46−x clathrate including a vacancy by abxa0initio calculation based on density functional theory with structure optimization. It was found that the vacancy behaves like an electron acceptor and the numbers of vacancies at 24k sites for the synthesized Ba8AuxSi46−x−y clathrates can be estimated as ∼0.4 in a unit cell.

Improvement of die life with surface texture control and solid lubricant

Abstract The methodology of controlling the surface texture of dies by means of Hybrid-shot peening was examined for the improvement of the die life cycle applied to high strength steel sheets. Hybrid-shot is double-shot peening, where the first treatment is performed using large particles, and the second one is performed with finer shot particles. The specimens of tool steels for dies treated by Hybrid-shot showed a high resistance against galling which was evaluated by the galling generation load of the draw bead test by using an oil lubricant, compared with the single shot specimens. This result suggested that the surface texture influenced the galling property. For a quantitative analysis of surface texture of die material, Fast Fourier Transformation (FFT) was used. Findings revealed that the ratio of the spectrum amplitude between high and low frequencies calculated by FFT corresponded to the galling generation load of draw bead tests. On the other hand, the conventional index of surface roughness, Rz, had no relationship to the galling generation load. Furthermore, the effect of solid lubricant, that is, the powder produced by scallop shell, on the galling property was studied. The addition of fine scallop shell powder in the oil lubricant increased the galling generation load.

Annealing time dependence on the phase equilibria and thermoelectric property of type-I Ba8Cu6Ag2Si38 clathrate

Poly-crystalline Ba8Cu6Ag2Si38 clathrates were synthesized by the arc-melting method and a subsequent annealing treatment. The main phase of all the samples was type-I clathrate. However, there were some precipitates which rich in Cu, Ag or Si in the grain boundary of the as-synthesized sample and the precipitates gradually reduced with the increase of annealing time. The transition metal content in the clathrate increased with the annealing time because of the diffusion of the Cu and Ag atoms from precipitates phase into clathrates phase. The as-synthesized sample was n-type material. For the 576 hours annealed sample, the carrier type changed from n-type to p-type because of the increase of Cu and Ag content in the clathrate.

Retardation of 20%Cr Steel Oxidation with Laves Phase Precipitation

A new method to improve oxidation resistance of ferritic stainless steel was studied. Increase in oxidation resistance of ferritic stainless steel with laves phase precipitation was succeeded in addition to the conventional method such as addition of rare-earth element. Ultra low carbon 20%Cr steels with various niobium content continuously oxidized at 1073-1173K in air. A mass gain with exposure at 1073K decreased with increasing niobium content and saturated more than 0.1% in niobium content. In steels contained niobium less than 0.1%, mass gain were also decreased with increase in initial ferritic grain diameter. In steels contained niobium more than 0.1%, laves phase was observed at the ferritic grain boundary by using transmission electron microscope. But then a mass gain with exposure at 1173K did not decreased with niobium content and laves phase was not observed. On the assumption that oxidation behaviors of steels contained niobium more than 0.1% obey the parabolic law, the parabolic rate constant obtained at 1173K is similar to that controlled by grain boundary diffusion, and parabolic rate constant obtained at 1073K is similar to that controlled by lattice diffusion. These results suggest that precipitation of laves phase retard growth of oxide film effectively with suppressing grain boundary diffusion of cation forming oxide film.

Heat–Electric Power Conversion Without Temperature Difference Using Only n-Type Ba8AuxSi46−x Clathrate with Au Compositional Gradient

Thermoelectric power generation is typically based on the Seebeck effect under a temperature gradient. However, the heat flux generated by the temperature difference results in low conversion efficiency. Recently, we developed a heat–electric power conversion mechanism using a material consisting of a wide-bandgap n-type semiconductor, a narrow-bandgap intrinsic semiconductor, and a wide-bandgap p-type semiconductor. In this paper, we propose a heat–electric power conversion mechanism in the absence of a temperature difference using only n-type Ba8AuxSi46−x clathrate. Single-crystal Ba8AuxSi46−x clathrate with a Au compositional gradient was synthesized by Czochralski method. Based on the results of wavelength-dispersive x-ray spectroscopy and Seebeck coefficient measurements, the presence of a Au compositional gradient in the sample was confirmed. It also observed that the electrical properties changed gradually from wide-bandgap n-type to narrow-bandgap n-type. When the sample was heated in the absence of a temperature difference, the voltage generated was approximately 0.28xa0mV at 500°C. These results suggest that only an n-type semiconductor with a controlled bandgap can generate electric power in the absence of a temperature difference.

Effects of Nitriding-Quenching and Carburizing-Quenching on Wear Properties of Industrial Pure Iron

Abstract The wear properties of industrial pure iron treated by nitriding-quenching and carburizing-quenching were investigated. Both the nitrogen martensite and carbon martensite produced by each treatment exhibited the same high degree of wear resistance. The results of sliding tests showed that the nano-indentation hardness near the surfaces of both samples had increased. The surface hardening of the nitrogen martensite was more noticeable than that of the carbon martensite. EBSD analysis revealed that plastic strain had been induced on a relatively large scale (around 20 μm) after sliding in the case of the nitrogen martensite. It was found that the high wear resistance of the nitrogen martensite led to strain hardening through the effect of the load applied in the sliding test.

FEM analysis of friction for pressing dies controlled by shot treatment

Abstract The finite element method (FEM) analysis of elastic-plastic deformation was applied to examine the effect of surface texture controlling of dies by means of hybrid-shot (double shot by two different kinds of particles) treatment on the galling property applied to high tensile strength steel sheets. The FEM analysis results showed that the apparent friction coefficient, which was calculated from pressing load and the drawing force, increased with each increase in the pressing load. The experimental results from the drawing tests with lubricant oil showed that the friction coefficient of the die after hybrid-shot treatment decreased slightly with the increase of the pressing load. On the other hand, the friction coefficient of the die without shot treatment, (i.e. nearly flat surface), slightly increased with the increase of the pressing load due to the digging effect. These findings reveal that the effect of surface texture of dies was caused not only by the elastic-plastic deformation but also by the oil lubrication condition. The FEM analysis was therefore performed by taking into account the digging effect as well as the micro-oil pool effect. The experimental result in the case of hybrid-shot dies corresponds well to the FEM result by adopting the virtual oil model where the oil segment was defined as an elastic solid body.

The effect of Si on the precipitates for Nb bearing high purity ferritic stainless steel

The effect of Si on the precipitation of the Laves phase in high purity 17Cr–0.5Nb ferritic stainless steel was investigated. Precipitation was observed using a scanning electron microscope and transmission electron microscope. Quantitative analysis of the amount of precipitates as Laves phase was performed. The precipitation rate of the Laves phase and the equilibrium amount of precipitates of the Laves phase increased with the amount of Si. A Si peak was detected in the Laves phase in 0.5Si steel by energy dispersive X-ray spectrometer analysis. It was revealed that precipitation of the Laves phase was promoted and the chemical composition of the Laves phase was changed by the addition of Si.