In this study, we investigate the effects of shear and compressive deformation on microstructural evolution during hot working of low carbon micro-alloyed steel containing 0.03 mass% Nb. By systematically introducing shear and compressive strains under controlled conditions, we clarified the role of shear strain in phase transformation and grain refinement. Results show that when the equivalent strain exceeds 2 with shear strain (γ ≈ 2.2) at 800 °C, effective nucleation sites are generated, promoting the formation of ultrafine ferrite grains (<1 µm). These findings highlight the importance of the deformation mode and strain path in controlling final microstructures, offering insights for optimizing the thermomechanical processing of steels and alloys.

This study addresses the challenge of nonuniform deformation in noncircular wire drawing by introducing a profiled die with uniform contact length, designed to achieve simultaneous contact initiation across the wire perimeter. The die geometry was realized by circumferentially varying the approach angle and evaluated by experiments and finite element analysis (FEA) during the single-pass drawing of an elliptic wire from a round wire. This design concept aims to improve deformation uniformity and reduce frictional effects, which are critical for die life and product quality. Results showed that the profiled die with uniform contact length achieved uniform contact initiation, unlike conventional dies, where contact starts at the minor axis. Dies with contact lengths of 3.3 and 5.0 mm showed reduced drawing force and wire temperature rise, compared with a conventional die. FEA confirmed a significant reduction in maximum contact pressure. These findings indicate that using a profiled die with uniform contact length can reduce localized pressure and frictional heating, minimizing seizure risk and extending die life in noncircular wire drawing.

High-strength sheet steel has been applied to automobiles to improve crash safety and reduce greenhouse gas emissions. However, high-strength sheet steel is susceptible to cracking induced by fatigue and hydrogen embrittlement especially on a sheared edge. It is known that cracks are formed by tensile residual stress. Therefore, a shearing method to reduce tensile residual stress cost-effectively is required. To develop this type of method, it is important to investigate the relationship between residual stress and basic shearing conditions, and understand the underlying mechanism. In this study, it is revealed that the residual stress in the thickness direction on the sheared edge of the product part markedly decreases with an increase in the radius of the cutting edge of the die. Numerical analysis showed that, during shearing, the increase in the radius of the cutting edge of the die reduces the strain inside the blank near the cutting edge of the die and delays the crack propagation consisting mainly of Mode II from the die side. It is considered that the residual stress on the sheared edge was reduced by the increase in the rate of Mode II crack propagation from the punch side. This method can be easily used as the shearing method to reduce the tensile residual stress on a sheared edge.

In this research, the effect of steel grade on the solid-phase forge welding (SPFW) of steel/Al was investigated. In a previous study, a new test method for evaluating SPFW was developed. Using this method, we prepared test pieces bonded with SUS304/A1070 by varying the surface enlarging ratio（Π _Steel）and surface pressure （P） at the interface. After bonding, tension tests were performed to measure bonding strength. In this research, the same experiments were performed using S10C/A1070. It was found that strong bonding was obtained above Π _Steel = 3.5 and P = 990 MPa in S10C/A1070. However, the bonding strength measured using the test pieces bonded with S10C/A1070 showed a larger scatter than in the case of using SUS304/A1070 ones. After the tensile tests, the fracture surfaces（for SUS304/A1070 and S10C/A1070） were observed by electron microscope. It was confirmed that the oxide films were broken following with the surface enlarging in both metal combinations. After the surface enlargement, intact virgin areas were allowed to come into contact with each other and bonded. In addition, it was confirmed that the areas of the oxide film and aluminum lump adhesion in S10C/A1070 were clearly smaller than those SUS304/A1070.

In magnetic pulse welding to the fixed copper sheet of the moving aluminum sheet, collision velocity is important to affect the impact pressure applied to the fixed sheet, which varies by gap length. When the moving sheet collided with the fixed sheet, the impact pressure is estimated with a compression stress generated on the moving sheet, and the maximum is approximately 4 GPa at a discharge energy of 2.0 kJ. When the discharge energy is constant, the maximum impact pressure is proportional to the collision velocity. During the continuous collision process, the two sheets repeatedly come into contact and separate, in other words, vibrate. A collision angle and a velocity of a collision point are a joining parameter in the process, and are affected by the vibration. The analysis were compared with the interface observations of a welded sheet. In the joining region of the welded sheet, the range of collision angles was from 3.0° to 32.9° and the range of the velocities of the collision point was from 5.6 km∙s ^-1 to 0.72 km∙s ^-1 . The vibration of the two sheets during the process and numerical values of the joining parameter in the joining region were clarified.

The application of ultrahigh-strength steel plates in automobile bodies is aimed at reducing weight and enhancing collision safety, with hot stamping (HS) technology being increasingly used for components with a tensile strength of 1.5 GPa or higher. HS simulations that consider phase transformation are conducted to predict formability, hardenability, and shape accuracy. However, the hardness of hot-stamped components obtained via die quenching is lower than that of martensitic structures obtained via water quenching owing to self-tempering beyond the martensite-transformation temperature (Ms point). Few HS simulations consider self-tempering. We developed a material model to accurately reproduce self-tempering behavior. By measuring the hardness of water-quenched martensite after tempering and calculating the activation energy of the tempering reaction, we determined the tempering parameter. The hardness of the self-tempering martensite is predicted by accumulating the tempering parameter during continuous cooling. An HS test and numerical analysis were conducted using a die with partially clearance sections, and the results were compared to verify the accuracy of the hardness prediction. The model developed improves the accuracy of hardness prediction in HS simulations.

This study investigated the effect of rolling on tensile and stretch deformation behavior, with the aim of applying high-purity electrolytic iron and their rolled sheets to press forming. Electrolytic iron exhibited a columnar structure along the normal direction (ND) and a strong γ-fiber structure characterized by a <111>//ND orientation. Rolling caused the crystals to rotate and the columnar structure to refine owing to the formation of shear bands. Additionally, rolling increased the {001}<110> texture, corresponding to the α-fiber component. In tensile tests, the electrolytic iron showed substantial necking owing to preferential deformation in the width direction. The deformation was accompanied by crystal rotation toward the {111}<110> orientation. During stretch forming (Erichsen tests), the electrolytic iron exhibited early necking due to poor strain uniformity, leading to poor stretchability. However, in the rolled sheets with a thickness reduction of 33 %, the rolling process refined the microstructure and promoted thickness reduction, thereby improving stretchability. These results indicate that the refinement of the structure and the change in texture due to rolling have significant effects on the formability of electrolytic iron.

The purpose of this study was to form a porous material made of titanium fibers that has an elastic modulus similar to that of biological bone and a uniform internal structure. Titanium fibers were wound in a spiral shape at regular intervals, placed in a cylindrical container, and then compressed at various compression stresses while applying shear stress due to rotation to create a compact material. Furthermore, compression tests, porosity measurements, pore size measurements, and bonding rate measurements were performed on the samples produced to clarify the effect of molding stress on the mechanical properties of the porous material made of titanium fibers. The internal structure was also compared with that of a molded body produced by randomly filling it with fibers, and the uniformity of porosity was evaluated. As a result, the compressive modulus of the compacts produced by spiral winding was higher than that of the compacts produced by random filling. The compressive modulus increased with forming stress and was equal to that of living bone at all forming stresses. The porosity was found to be uniform, with pore sizes distributed in the range of 10-20%. Furthermore, the pore size distribution showed two peaks at 12-16 μm and 24-28 μm.