Recently, demands for reduction of CO₂ gas emission in iron making process are increasing. For further reduction of CO₂ gas emission, a method of capturing carbon dioxide from blast furnace exhaust gas has been studied. The oxygen blast furnace using pure oxygen for blast does not contain nitrogen in the exhaust gas and that is more advantageous than conventional blast furnace in the point of view of CO₂ separation energy. Although the oxygen blast furnace has been studied with the experimental furnace, the experimental furnace was not sufficiently investigated on the properties of cohesive layer because of the small load of burden materials. Therefore, in this study, the properties of cohesive layer of the oxygen blast furnace were studied.

The properties of the cohesive layer were evaluated under blast furnace conditions and nitrogen-less conditions in a load-softening test. As a result, the properties of cohesive layer were remarkably improved in nitrogen-less conditions. As a result of discussion, improvement of the properties of cohesive layer was quantitatively explained due to suppression of contraction of the sintered ore and the decrease of slag liquid because the nitrogen-less atmosphere promoted reduction reaction.

Coal compatibility in coke strength is known as the effect that good combination of coals gives high strength coke and bad one gives the opposite in comparison with the strength expected from their average properties. To understand the phenomena of compatibility, we studied a correlation between adhesive strength and surface properties of semi-cokes obtained by heat treatment of coals at 500 °C. As a result, we found that when the difference in surface tension between two semi-cokes was large, the strength of coke produced from the mixture of the two raw coals became low. The same tendency was also observed in laboratory scale carbonization tests and this effect was rationalized by high interfacial tension between two semi-cokes in the case that the difference in the surface tension was large, and accordingly, adhesive strength of the interface became low. To apply these findings to a multi-component coal blending technique used for commercial coke production, we proposed a new blending factor, the interfacial tension of a heat-treated coal blend which was derived from surface tensions of semi-cokes from coals in a coal blend, so that deterioration of coke strength was confirmed in commercial oven operation by increasing interfacial tension while other average properties of the blend were kept constant. This new technology enables us to evaluate more precisely the coal compatibility and to select the good combination of coals, which can contribute to the production of high strength coke and effective usage of coking coal resources.

Predeformation treatment is known to be one of effective methods for preventing slab surface cracks in continuous casting.

In order to clarify mechanism of improvement in hot ductility by predeformation, the influence of the amount of predeformation and the number of repeated predeformation operations on the hot ductility of carbon steel was investigated in laboratory-scale experiments.

Small predeformation was given several times using a tensile machine, and reduction of area (RA) was evaluated. Metallographic observation was also carried out on these test pieces by optical microscopy and scanning electron microscopy (SEM).

The metallographic examination revealed that the grain size of the test piece was refined from 195 micrometers to 160 micrometers, and RA improved from 45.6% to 76.1% by predeformation. One reason for improvement of hot ductility by predeformation is recrystallization of austenite grains by dislocation nucleation.

In continuous casting of steel, prevention of surface cracks on the slab is an important issue. For quantitative evaluation of cracks that occur in the continuous casting machine, the critical strain for crack generation was analyzed by a high-temperature tensile test and FEM simulation. Based on obtained material property values, a model for crack generation by tensile strain was constructed. The local strain at the notch relative to the strain in the whole specimen was determined by a simulation of the tensile test, and the critical strain for crack generation ε_c was calculated. The results of a crack simulation by FEM using ε_c showed that the average strain until crack initiation was small under deep notch conditions. The average strain at crack generation calculated by the simulation model was in good agreement with the value measured in the tensile test. As a result of the simulation applying temperature distribution to the slab, the depth change of the oscillation mark was more influential to crack formation than the change of the width. The effect of the shape of the oscillation mark on the crack cannot be organized only by the stress concentration factor. Simulation analysis that includes the shape of the oscillation mark is considered to be effective. Using this simulation model, it is possible to predict the generation of cracking when the temperature distribution or the oscillation mark shape in actual operation changes.

In the Hot-Rolling process, when a thin strip runs on the Run-Out-Table (ROT) at high speed in the state of non-tension (at the head or the tail of the strip), the defects resulting from the running instability pose a chronic problem. Moreover, because of unstable running phenomenon, the maximum line speed has been restrained, and has also become an aggravation factor of productivity. In order to solve this problem and improve this process, various methods have been proposed in the past, but it has not been eradicated completely.

In this paper, we proposed using the numerical simulation method based on multi-body dynamics (MBD) to simulate the ROT strip running phenomenon. The proposed strip model is a sub-class of the large deflection plate model. This model prevents the numerical instabilities, which come from the buckling phenomenon and the finite rotation with the strip large deflection. It was clarified that the numerical results corresponded with the theoretical result and the experimental results. By utilizing the proposed method, the cost and term which are necessary to improve the unstable strip running phenomena become cheaper and shorter.

Because of the increasing demand for automobile outer panels with sharper streamlines, it is important to improve the surface qualities of outer panel products. In the present study, the effects of microstructural properties – particularly the deformation-mode dependence of heterogeneous deformation at the grain scale and the fraction of {001} oriented grains – on surface roughening during deformation were investigated experimentally. The results showed that surface roughening decreased as the average grain size and the fraction of {001} oriented grains decreased. These trends were more pronounced under equibiaxial tension than under plane-strain tension. Surface roughening decreased with the fraction of {001} oriented grains, presumably because the heterogeneity of deformation resistance decreased at the grain scale. Moreover, if the texture and average grain size were similar, the development of surface roughening in the low-strain range (equivalent plastic strain of less than 0.3) was independent of the work-hardening coefficient n. On the basis of the abovementioned results, the optimum annealing conditions were examined to realize crystal grain refinement and reduction of {001} orientation. As a result, we obtained a high-strength steel with excellent surface roughening resistance.

The Influence of the Si content of Mn-added steel sheets on the reduction of Fe-oxide was investigated. 5.2 mass%Mn with 0, 0.2 and 0.5 mass%Si steel was oxidized and annealed in 10% H₂ atmosphere. Reduction speed of Fe oxide was faster in 0.2%, 0.5%massSi steel than that in 0%Si steel. It is considered the difference of reduction speed of Fe oxide depends on the composition of Fe oxide. Si addition increased Fe₂O₃ and decreased wustite (FeO) in Fe oxide. Reduction from hematite (Fe₂O₃) to magnetite (Fe₃O₄) would introduce larger lattice defects into Fe oxide and it lead to the higher diffusion rate of O.

Ferritic stainless steels are used for automobile exhaust parts because of their high heat and corrosion resistances. Among them, parts located upstream near engine, so-called hot-end parts, for example, exhaust manifolds, are required to show excellent heat resistance. Since thermal fatigue is induced by repeating heating and cooling with strain restriction, thermal fatigue resistance is one of the most important properties for upstream exhaust-parts materials.

In this study, the effect of plastic strain and recovery rate on thermal fatigue behavior was investigated for high heat-resistant ferritic stainless steel SUS444 which has been used for automobile exhaust parts. In the case of a maximum temperature at 973 K, cracking occurred without necking. On the other hand, in the case of a maximum temperature at and above 1073 K, failure with necking was predominant.

To improve the thermal fatigue resistance of SUS444 in a higher-temperature exhaust gas atmosphere, high-temperature strengthening would be more favorable.