FeO compact which coexists with liquid FeO-SiO2 slag was reduced with H2 at 1500K, the texture of the sample was observed by a laser-microscope and an optical microscope and the influence of the pore blockade by liquid slag on reducibility was investigated. As pores are closed by liquid slag, the reduction rate is decreased by the prevention of the diffusion of the reducing gas due to the dense Fe layer which is formed by reducing the liquid slag in the pore and near FeO/liquid slag interface. The variation of porosity with the pore blockade by liquid slag affects the reducibility and this effect is largely dependent on the pore structure. Liquid slag tend to close a smaller pore preferentially. Then the reduciblity becomes a little worse, but the reducibility is maintained to some extent because of the existence of large pores. The reducibility rapidly deteriorates when large pores are closed with the increase of liquid slag.
Lotus-type porous stainless steel (SUS304L) rods were fabricated by continuous zone melting technique under pressurised gases of hydrogen and inert gas such as argon or helium. The pores with cylindrical shape, whose growth direction is parallel to the solidification direction, were observed in the rods. The dependence of the porosity and pore diameter on the partial pressure of hydrogen or the total pressure and on the transference velocity of rods was investigated. It was found that the porosity increases with increasing partial pressure of hydrogen under the constant total pressure and the pore diameter decreases with increasing transference velocity. The maximum porosity was about 60% under the experimental conditions in the present work. The observation of the microstructure and the measurement of the tensile strength were also carried out.
A combination of laser ablation and ICP-MS offers a powerful and rapid analytical method for steel samples. The determinations of some elements (e. g., C, Si, P and S), however, are seriously disturbed by spectral interferences, mainly caused by the ambient air. In the present work, low-pressure helium-ICP-MS was applied to overcome these problems. The polished and ultrasonically cleaned steel sample was placed in an evacuated ablation cell and irradiated by a pulsed Nd/YAG laser beam (15 Hz, 150 mJ) for 30 s. The resulting sample aerosol was transported to the ICP with a stream of helium for the analysis by MS. The intensities of the analyte signals were corrected by using 57Fe+ as internal standard. The analytical results obtained for C, Si, P, S, Cr, Mn, Ni and Cu were well agreed with the certified values with RSDs of 4-10% (except Si).
Thin Mg-Al alloy, AZ91D sheets annealed around the temperature between 0% and 100% recrystallization have been prepared and tensed at high temperatures and with several strain-rates. Both the total elongation and strain-rate sensitivity m have been obtained and discussed. The values of total elongation have exceeded over 110% at all testing temperatures and with all strain-rates except high strain-rate at testing temperature of 573K, and the maximum total elongation of 270% has been obtained. The m values have indicated 0.5 in range of 1.0×10-4s1 to 2.5×10-4s-1 and maintained about 0.3 up to the neighborhood of 1.0 × 10-2s-1. The activation energy required for superplastic deformation has been calculated to be about 70 kJ·mol-1, which is almost same of the activation energy for self-diffusional grain boundary coefficient in Mg. Therefore, the superplastic deformation of AZ91D annealed around the temperature between 0% and 100% recrystallization has been accommodated by grain boundary diffusion.
Observation of electropolished surface by FE-SEM revealed a multiscale structure composed of prior austenitic grains, packets, blocks and precipitates for ferritic heat-resisting steels. After the creep-fatigue tests the microstructure showed little change except for the precipitate's size and density. Drastic changes of dislocation subgrains within the block were observed by TEM. Occupancy of the precipitates on prior austenitic grain boundaries was newly proposed as an index of creep-fatigue damage.
We investigated the fatigue properties at high temperatures of fine grain and coarse grain nickel-base Alloy718. In the fine grain material, the fatigue strength normalized by the tensile strength was 0.51 at 107 cycles. In contrast, the fatigue strength of the coarse grain material was 0.32 at the same cycles, although the fatigue strengths in the range from 103 to 105 cycles are the same for both materials. The fracture appearances fatigued at around 106 cycles showed internal fractures originating from the flat facets of austenite grains for both materials. The difference in fatigue strength at 107 cycles between the fine and coarse grain materials could be explained in terms of the sizes of the facets from which the fractures originated.
Advanced 700°C class steam turbines require austenitic alloys to replace conventional ferritic 12Cr steels poor at creep strength and oxidation resistance above 650°C. The austenitic alloys, however, possess a higher thermal expansion coefficient than ferritic 12Cr steels. Therefore, Ni-based superalloys were tailored to reduce their coefficients to the level of 12Cr steels. A regression analysis of commercial superalloys proves that Ti, Mo and Al decrease the coefficient quantitatively in this order, while Cr increases it so significantly that Cr should be limited to 12 mass% to secure oxidation resistance. The newly designed Ni-18Mo-12Cr-1.1Ti-0.9Al alloy is strengthened by γ' [Ni3(Al, Ti)] and also A2B [Ni2(Mo, Cr)] phase precipitates. It bears a RT/700°C mean expansion coefficient equivalent to that of 12Cr steels and far lower than that of low-alloyed heat resistant steels. It surpasses a current turbine alloy, Refractaloy 26, in tensile strength at RT to 700°C and SCC life in 330°C deaerated pure water. Its creep rupture life at 700°C is equivalent to that of Refractaloy 26.
Nanban-tetsu is a steel which was imported into Japan by Portuguese or Spanish merchant ships in the end of Muromachi period (1392-1573). The steel was produced in India and called "Wootz steel". Nanban-tetsu steel was shaped in some forms of a gourd called "Hyotan", a oval called "Koban", a square timber called "Saijo", a semi-cylinder called "Tajo" and others. In 1613, one of the Japanese sword smith, Echizen Yasutsugu 1, first produced a sword using Nanban-tetsu steel. Since then, many sword smiths who lived in Echizen area (Fukui Prefecture) had used Nanban-tetsu steel as a material of Japanese swords. The steels produced using the "Nittoho-Tatara" furnace in Shimane prefecture has been examined by forge-welding as a function of phosphor content in the steels. It is concluded that "Hyotan" shaped Nanban-tetsu steel is not good for forging, "Saijo" shaped Nanban-tetsu steel is good for forging, "Koban"-shaped one is difficult to forgeweld and "Tajo"-shaped one is intermediate.
We have examined matrix-masking method for analyzing iron and steels by ICP-OES with ion exchange separation. In the ion exchange separation of impurity elements from iron matrix, it is vital to separate only those elements that are targeted. Therefore, the matrix element was masked with ethylenediamine tetra-acetic acid (EDTA) to prevent the interference with the procedure of ion exchange separation of impurities. Specimen was decomposed by heating with nitric acid, and added 4.0 g of EDTA. Only impurities were adsorbed by cation-exchange resin, whereas iron combined with EDTA was not absorbed. The impurities adsorbed by resin were eluted by nitric acid, and those were measured by ICP-OES. This method enabled to separate matrix Fe by over 99.9%. We found, therefore, the recoveries of aluminum, calcium and magnesium were over 98%. The analytical result of manganese impurities of the Japanese iron and steel CRMs of a JSS003-4 and JSS168-7 were in good agreement with those of the certified values.