In the lower part of the blast furnace, molten slag and iron accumulate in the coke packed bed and is drained from the tapping hole. However, if tapping rate is reduced, these melts accumulate and an increase in the gas pressure drop occurs. This leads to the furnace troubles such as raw materials hanging.

In this paper, the cause of the increase in gas pressure drop by the accumulation of melt was clarified phenomenologically using experiments of cold model and numerical simulation.

As the result, it was proven that the gas flow region shrinks due to the accumulation of the melt, and the gas flow velocity near the tuyere increases. In addition, a numerical simulation of an actual blast furnace showed that gas pressure drop increased rapidly when average liquid level was within 1 m from the tuyere. If average liquid level increases to the vicinity of the tuyere, the shape of molten slag surface changes by gas pressure gradient, and liquid level on the tuyere side descends. In other words, when gas pressure drop due to the accumulation of molten slag is rapidly increased in the actual blast furnace, it is preferable to reduce the blast volume and increase the amount of tapping rate as soon as possible.

Molten steel flow in the submerged entry nozzle (SEN) largely affects the cast steel quality. However, it wasn’t clarified how non-metallic inclusions behave at the front of nozzle wall in the SEN. One of the reasons is that the contact angle of inclusions with molten steel is bigger than 90 degree and the effect of wettability of the inclusions and nozzle wall on the multi-phase flow behavior in SEN has not been fully clarified. In this study, water model to simulate the multi-phase flow in the SEN has been constructed to investigate the effect of wettability of particles and the nozzle wall on the fluid flow by changing the contact angle of the surface of particles and the nozzle wall. Additionally, an endoscope has been installed into the stopper in order to directly observe the behavior of particles in the SEN. As a result, it was found that particles coated with hydrophobic agent are swept away as if they hit on the nozzle wall and changed the flow direction in the air. This is why the air film was surrounded around the particle by the hydrophobic treatment and cavity bridge was formed between the hydrophobic treated particles in the water. The adhesion force acting between the hydrophobic treated particles was calculated by theoretical analysis and the aforementioned adhesion force could not be ignored compared to the buoyancy force and the drag force in the water.

The warm V-bendabilities and hydrogen embrittlement properties of ultrahigh-strength Quenching and Partitioning (QP)-Transformation-Induced Plasticity (TRIP) steel sheets were investigated to apply the QP-TRIP steel sheets for automotive structural parts manufactured by cold or warm press forming. V-bending tests were carried out at a crosshead speed of 1 mm/min at V-bending temperatures of 25, 100 and 150°C using a hydraulic servo testing machine with a 88-degree V-punch (punch tip radius R = 2 mm, R/t₀ = 1.7) and a V-dice (dice groove size l = 12 mm, dice shoulder diameter 0.8 mm) using V-bend specimens with dimensions of 5 mm width, 50 mm length and 1.2 mm thickness without and with hydrogen charging. Hydrogen charging was conducted by means of cathodic charging using a 3 wt% NaCl + 3 g/L NH₄SCN solution at a current density of 10 A/m² for 48 h before V-bending. The main results were obtained as follows.

(1) QP-A steel enabled to conduct V-bending at a V-bending temperature T = 25°C although the bending angle after unloading (θ₂) was less than 90-degree.

(2) When V-bending tests were carried out at T = 100°C, QP-B, C, and E steels without hydrogen and QP-B steel with hydrogen charging enabled to conduct V-bending. In addition, QP-B steel was also possible to carry out the V-bending at T = 150°C. These results implied that the V-bending at warm temperatures can improve the V-bendabilities of the QP-TRIP steels.

Effect of combined addition of boron (B) and molybdenum (Mo) on recrystallization behavior in austenite was investigated using low-carbon steels. The B-Mo combined added steel remarkably retarded recrystallization after hot deformation, compared to the steels added individually. Three-dimensional atom probe analysis revealed that the addition of B significantly increases the amount of Mo segregation in the austenite grain boundaries. Thermodynamic calculations based on the grain boundary phase model suggested that the interaction between B and Mo atoms increases the grain boundary segregation energy of Mo. The solute drag force was estimated by Cahn's model using the increased segregation energy of Mo, which quantitatively explained the remarkable retardation in recrystallization in the B-Mo combined steel.

Primary recrystallization texture strongly influences the magnetic properties of grain-oriented electrical steel through secondary recrystallization. In this study, the effect of applied tensile stress during annealing on grain growth and primary recrystallization texture formation in Fe-3%Si alloy was investigated. It was revealed that grain growth is promoted under the condition of applied tension, and the intensity of {411}<148> orientation increases, while the intensity of {111}<112> orientation decreases. The changes in grain diameters and textures are explained by the normal grain growth with the size advantage of larger {411}<148> grains and disadvantage of smaller {111}<112> grains than the average sized grains. Moreover, KAM value of {111}<112> grains was confirmed to be larger than that of {411}<148> grains after tension annealing. This suggests that the stored energy in {111}<112> grains is larger than that in {411}<148> grains, which would promote the selective growth of {411}<148> grains with SIBM mechanism by consuming {111}<112> grains with relatively higher stored energy.

Nitrogen-added austenitic stainless steels exhibit excellent work-hardenability due to planar slips of dislocations. Two mechanisms of the planar slip have been proposed so far: glide plane softening mechanism and stacking-fault energy (SFE) reduction mechanism, which are thought to be dependent on nitrogen content and deformation temperature. In this study, conventional TEM, STEM-EDS and HR-STEM characterizations were carried out to clarify the influences of deformation temperature and nitrogen content on the dislocation characteristics of austenitic stainless steels. In the case of the nitrogen-added steel, the dislocation configurations became planar at a high temperature, 973 K. HR-STEM analysis revealed that SFE decreased with N addition and increased with temperature increase. Weak-beam TEM and HR-STEM analyses revealed that the planar dislocations were composed of 60° mixed-dislocations and SFs at room temperature, and edge-dislocation and SFs at 973 K. These results suggested that the edge components of defects interacted elastically with N and N-Cr pairs and contributed to the origin of the planar slips.

Fe-Si sheet, which has {110}<001> crystal orientation (Goss-FeSi), consists of Basic domain and Lancet-comb domain. Although the geometric structures of the Lancet-comb domain have been predicted by theoretical aspects, they have not been proved by experimental studies.

In this paper, we study the Lancet-comb domain structures of a Fe-Si steel by a volume sensitive method, i.e., transparent X-ray topography (XRT). From the XRT results, we found the parallelogram structures, which is bulk structure of the Lancet-comb domain. The long side of the parallelogram forms about 55° angle to the rolling direction and the short side forms about 35° angle to the rolling direction. We assigned the long side of the parallelogram to {110} domain wall and the short side to {111} domain wall based on the geometric analysis. This Lancet-comb domain model well explains the behavior of the magnetic moments of Goss-FeSi.