The nitriding behavior of titanium sponges with nitrogen gas and the dissolution behavior of titanium nitride titanium sponges in titanium alloy melt were examined.

A titanium nitride sponge was produced using nitrogen gas. A high nitriding temperature corresponded to a longer nitriding time, and thus to a higher nitrogen concentration in the sponge. Both the titanium sponge and titanium nitride sponge featured a porous structure. Porous structures at both the surface layer and inside were formed at intervals of about 5.0×10^–5 m. When the titanium nitride sponge was immersed into a titanium alloy melt, the melt permeated into the pores. The nominal dissolution rate of the titanium nitride sponge in the titanium alloy melt depends on the temperature of the melt. Higher melt temperatures corresponded to higher nominal dissolution rates. However, the concentration of nitrogen in the titanium nitride sponge had no influence on the nominal dissolution rate. Nitriding models of the titanium sponge with nitrogen gas, and the dissolution model of the titanium nitride sponge into the titanium alloy melt were proposed. These models considered the structure of the sponge; thus, the behavior of both the nitriding and dissolution sponges was predicted and confirmed.

To achieve low RAR operation by coke mixed charging, it is important to control coke segregation behavior in mixed layer at blast furnace top. In this study, a numerical simulator based on screening layer model was developed to estimate the distribution of mixed coke ratio in mixed layer. The results are summarized as follows:

(1) The parameters required for the screening layer model to estimate the segregation behavior of the burden materials were determined by PIV test and numerical fitting.

(2) The screening layer model containing parameters obtained by experiments and fittings was taken into the blast furnace burden distribution simulator. The simulation results showed that the distribution of mixed coke ratio of the small coke in the ore can be accurately estimated under the charging conditions of the actual furnace.

(3) The influence of the difference in tilting direction of the rotating chute on the distribution of mixed coke ratio was evaluated. In the reverse tilting, the radial distribution of the mixed coke ratio became more uniform as compared with the forward tilting charging. Therefore, it is considered that reverse tilting is more effective for carrying out coke mixed charging.

Fundamental experiments were conducted with the aim of crude separation of the phosphorus contained in high-P iron ore prior to the ironmaking process. By reducing high-P iron ore with lime and graphite at an appropriate blending ratio and temperature, a reduction product was obtained consisting of a P-concentrated phase, metallic Fe with low P, and an Fe oxide-containing phase. The reduction product was pulverized by electrical pulse disintegration, and a magnetic separation experiment was performed for each particle group. As a result, 57.5% of the P contained in the reduction product was removed by removing particles of 250 μm or less. Samples simulating the constituent phases of the reduction products were synthesized and subjected to magnetization measurement. It was assumed that the Fe oxide-containing phase was paramagnetic and the P-concentrated phase was diamagnetic. We calculated the magnetic and drag forces acting on the paramagnetic particles in wet magnetic separation. When the magnetic field gradient was low, the magnetic forces acting on the fine particles were low, and attraction was difficult due to the drag force of water.

In our earlier study, the authors revealed that the fatigue limit of ductile cast iron (DCI) specimens whose shapes are similar to the welded joint shapes is about three times larger than that of the welded joint specimens. However, since many defects are usually included in the DCI specimens, the fatigue limit of DCI joints decreases with increasing the maximum defect size. In this paper, therefore, the maximum defect size is estimated by using statistics of extremes. Then, the lowest fatigue limit corresponding to the maximum defect size is estimated from the 4 parameter model and compared with the lowest fatigue limit of the welded joint. As a result, it was confirmed that the lowest fatigue limit of the DCI specimens is about twice as large as the welded joint.

It is well known that Si, Mn and B, the alloying elements for high strength steel sheets, easily form oxides on the steel surface during annealing in a reducing atmosphere, and those oxides have a large influence on the surface performance of steel sheets, such as phosphatability. In this work, we discovered that the oxidation behavior of Mn-added high strength cold-rolled steel sheets could be simulated on mild steel sheets by using an ion plating method and investigated the relationship between the morphology of Mn oxides and phosphatability under the condition that both the amount and kind of Mn oxides were fixed. In a simulated Mn-O layer, fine surface oxides, which covered most of the steel surface, were observed after annealing. On the other hand, in a Mn-B-O layer, large globular surface oxides were observed on the steel surface, and the Fe surface was partially bare. The B-Mn compound oxide is considered to be in a molten phase during annealing because the melting point of the compound oxide is lower than the annealing temperature, and as a result, it is thought that large B-Mn compound oxides coagulate and grow during annealing. In addition, it was found that the large B-Mn compound oxides (about 500 nm) interfere with steel dissolution in the phosphate solution. These results demonstrate the importance of controlling the morphology as well as the amount and kind of surface oxides for obtaining good phosphatability of Mn-added high strength cold-rolled steel sheets.

Skeletal Ni catalysts were prepared by the combined process of thermal treatment, mechanical milling, and dealloying using Ni₄₀Ti₆₀ amorphous alloy as a starting material. The influence of processing sequence on the catalytic activity of the prepared catalyst was investigated. The skeletal Ni catalyst prepared via i) thermal treatment at around the crystallization temperature (ca. 743 K), ii) mechanical milling, iii) dealloying by immersion in 1.0 mol/L HF aqueous solution showed the highest catalytic activity in the dehydrogenation reaction from ammonia borane compared with other skeletal Ni analogues prepared via different processing sequences. Thermal treatment around the crystallization temperature caused atomic rearrangement, which lead to a formation of electron-deficient Ni species on the surface of skeletal Ni alloy after dealloying treatment. SEM morphological observation and surface-area measurement indicated that thermal treatment decreased mechanical strength of the Ni-Ti alloy and that mechanical milling allowed the formation of finer Ni-Ti particles, which facilitated the formation of high-surface-area skeletal Ni after dealloying treatment. We found that processing sequence on Ni-Ti amorphous alloy made drastic impacts on surface area and electronic state of the resulting skeletal Ni, which consequently affected the catalytic performance in the dehydrogenation reaction.

Formation behaviors of aluminides at 450ºC in the interfacial region between M sheets (M=Au, Cu, Fe, Mn, and Ni) and molten 0.2 wt.%Al-Zn were investigated by simple dipping method of M sheets into molten Al-Zn bath. In the Fe and Ni sheets dipped for 60 s, aluminides were formed in the diffusion zone, while not observed in the Au, Cu and Mn sheets. These results were discussed in the view points of the chemical interactions between M and Al, the up-hill diffusion of Al induced by concentration gradient of M element in liquid Zn, and the relative stability of M-Al intermetallic compounds to M-Zn based intermetallic compounds.

Recrystallization and grain growth are important phenomena for controlling the mechanical and magnetic properties of steels through texture. Only a limited number of studies have been carried out on texture evolution during recrystallization and grain growth in heavily cold-rolled Si steel. The present study first focuses on clarifying the texture evolution during normal grain growth, followed by an investigation into the development of the {411}<148> component during recrystallization. The {411}<148> component is remarkably developed during normal grain growth after the completion of recrystallization. At just fully recrystallized stage, the diameters of the {411}<148> grains were larger than that of the grains with other orientations. Therefore, the {411}<148> grains significantly grew owing to the size advantage.

Just at the commencement of recrystallization, differences in grain diameter of recrystallized grains in terms of crystal orientation were not detected. However, it is worthwhile to mention that the nucleation of {411}<148> recrystallized grains is unexpectedly fast in heavily cold-rolled Si steel. Recrystallized {411}<148> grains were observed to nucleate in the deformed α-fiber grains, especially near the grain boundaries. Nuclei with {411}<148> orientation grow easily due to the high mobility of the interface between the recrystallized/non-recrystallized grains and the high driving force. Consequently, the diameter of a {411}<148> recrystallized grain becomes relatively large upon the completion of recrystallization. This contributes to the selective grain growth during the normal grain growth stage because of the size effect.

The better uniform elongation of the 1 GPa-grade TRIP-aided multi-phase steel with retained austenite (γ_R) shape of needle-like was discussed by in situ neutron diffraction experiments during tensile test. The better uniform elongation can be ascribed by not only the deformation-induced martensitic transformation of γ_R but also the deformation behavior of γ_R and ferrite phase. Especially, the tensile deformation behavior of γ_R is found to be closely associated with both of the stress-strain curve and the deformation-induced martensitic transformation of γ_R. The tensile deformation behavior of γ_R should be considered as one of the conditions to obtain better TRIP effect.

An evaluate method for hydrogen embrittlement property of high strength steel sheet has been proposed in this study. To take into consideration of the effect of plastic strain in addition to the effects of applied/residual stress and diffusible hydrogen, U-bend specimens have been adopted because steel sheets for automobiles are usually used after press forming into various parts. After U-shape bending, the specimen was loaded using a bolt. The proposed evaluation method is based on the measurement of critical hydrogen content or critical hydrogen charging condition for hydrogen embrittlement fracture at given stress and strain conditions. The hydrogen charging current density was increased in step-wise manner until cracking was observed, and cracking was detected by optical observation and by monitoring voltage between the sample and a counter electrode. The critical hydrogen contents for specimens with varied applied stress were obtained by means of thermal desorption spectroscopy. For the critical hydrogen content, both the hydrogen contents in strained portion of the specimen and no-strained portion were measured. The former is affected by introduced dislocations caused by straining and the latter is thought to be proportional to the hydrogen fugacity. Both critical hydrogen contents tended to be decreased slightly when the applied stress was relatively high.

In the dislocation characterization by the modified Williamson-Hall method, elastic stiffness ratio c₁₂/c₄₄ and anisotropy parameter A_i (=2c₄₄/(c₁₁–c₁₂)) are important parameters to determine the contrast factor. In order to determine the values of elastic stiffness c_ij, we need the information of Young’s modulus E*, shear modulus G* in poly crystal, and Young’s modulus of single crystal; E₁₀₀, E₁₁₀, E₁₁₁. The values of E* and G* are experimentally obtained by the resonance method. However, it is not so easy to fabricate single crystal, especially for practically used metals in which many alloying elements are contained. Therefore, we need to estimate the values of E₁₀₀, E₁₁₀, E₁₁₁ in some way. In this paper, the following equations were proposed to estimate these values for the steels with bcc structure.

E₁₀₀ = 0.647 × E*　E₁₁₀ = 1.079 × E*　E₁₁₁ = 1.387 × E*

The coefficient in each equation was determined by the average value of E_hkl/E* in pure iron. In the steels with bcc structure (E*=206 GPa), it was confirmed that c₁₂/c₄₄ and A_i are given by the following equations as a function of Poisson’s ratio ν.

c₁₂/c₄₄ = –1.466 + 8.887 × ν　A_i = 2.885 – 1.602 × ν

As a result, c₁₂/c₄₄≒1.11 and A_i≒2.42 are applicable for the modified Williamson-Hall method under the condition; ν=0.29.