Hydrogen utilization in a direct reduction shaft furnace is a promising technology for carbon neutrality. On the other hand, some kind of heat compensation appears to be necessary, because the temperature in the furnace decreases and the reduction degree stagnates due to hydrogen enrichment. Therefore, a tool which can quantitatively evaluate the efficiency of heat compensation from a kinetic viewpoint considering detailed heat and mass transfer is useful for operational design. Based on the above, a numerical simulation model based on DEM-CFD was developed for the direct reduction process, and the following findings were obtained.

(1) A numerical analysis simulating a model plant confirmed that the calculation accuracy of the developed model is sufficiently high. The gas composition varies greatly depending on the degree of achievement of shift equilibrium.

(2) A numerical analysis of a commercial plant revealed the distribution with low temperature and low reduction degree in the radial center of the furnace. Hydrogen enrichment lowers the temperature and expands the region with a low reduction degree.

(3) As a technique for thermal compensation for hydrogen enrichment, it was found that increasing the inlet gas temperature increases the reduction degree exponentially.

(4) DEM-CFD can be a useful approach, since operational design considering powder phenomena, as represented by reduction degradation and clustering, appears to be necessary.

Clarification of nonmetallic inclusions behavior in molten steel is a critical challenge for achieving high-quality steel materials. In particular, the inclusion behavior in dendritic regions during solidification plays a significant role in inclusion retention, yet its physical understanding remains insufficient. In this study, a low-temperature model experimental system was developed to investigate the inclusion behavior in the dendritic region. Simulated dendrites with horizontal direction were aligned in a transparent viscous liquid, and the motion of a spherical simulated inclusion with relatively high density was directly observed using a high-speed camera. The particle Reynolds number in this experimental system was 0.0178. This corresponds to an alumina inclusion with a diameter of 37.7 µm in molten steel. Furthermore, numerical calculations were introduced to predict the inclusion behavior. The main results obtained in this research are as follows. When the simulated inclusion fell through inter-dendritic spaces, its velocity decreased to approximately 0.851 of the falling velocity in the liquid while it was about 0.597 when the simulated inclusion fell above the simulated dendrite. The velocity of the simulated inclusion was slower when passing beside the simulated dendrite than moving between the vertically aligned simulated dendrites. The velocity decrease of the simulated inclusion was intensified as decrease of the horizontal distance to the simulated dendrite. Furthermore, the rotation of the simulated inclusion affects its trajectory and velocity.

An inclined-tip burnishing method with active rotary tool was applied to control the surface microstructure of non-oriented electrical steel sheets in order to improve their magnetic properties. The burnishing tools used were made of zirconia and DLC-coated cemented tungsten carbide, which have significantly different thermal conductivities, and the effect of differences in the temperature of the burnished area due to frictional heat on the controllability of the surface microstructure was examined. The tool path of the burnishing process clearly influenced the flow behavior of the surface material. For zirconia tool, the temperature rise at the burnishing point was higher than for DLC-coated tool. Additionally, the width and depth of the burnishing scar were larger, and the burnishing-affected zone was deeper. When zirconia tool was applied at high sliding speed and low thrust force, crystalline grains were clearly observed extending to the outermost surface layer compared to before burnishing. Analysis of the crystalline structure of the outermost layer using X-ray diffraction revealed that applying a burnishing process reduced the intensity of diffraction peaks and increased the full width at half maximum compared to the untreated state. The crystal orientation control was also possible through the burnishing conditions. Evaluation tests of motor cores revealed that magnetic properties varied with burnishing conditions. Analysis of the electromotive force waveform when varying the input rotational speed suggested that burnishing process could potentially reduce eddy current losses in the non-oriented electrical steel.

For manufacturers, rapid and reliable hardness testing of metallic components in the field is essential for ensuring quality and competitiveness. Rebound hardness testing using a hammer with a Vickers indenter has been proposed as a method that minimizes dependency on impact velocity. However, the reliability of this method can be affected by specimen fixation conditions. In this study, the influence of hammer mass and impact velocity on the coefficient of restitution was investigated using two types of hammers with different masses. Experiments were conducted on specimens with varying surface roughness under both fixed and non-fixed conditions. The motions of the hammer and the specimen were measured simultaneously using two laser Doppler vibrometers. Results showed that when the specimen is not bolted, part of the hammer’s kinetic energy is transferred to the specimen’s rigid body motion, leading to a decrease in the coefficient of restitution. This effect was more pronounced with heavier hammers and increased impact distance from the specimen center. Conversely, lighter hammers reduced the specimen’s motion energy more effectively, thereby suppressing the decrease in restitution. Additionally, changes in impact velocity did not significantly affect the restitution coefficient for a given hammer mass. These findings suggest that hammer mass plays a more critical role than impact velocity in determining the required specimen mass under insufficient fixation conditions, and validate the applicability of a predictive model for estimating apparent restitution coefficients.