We have developed a micro-macro coupling model for simulating rolling load, rolling temperature and microstructure evolution in tandem wire rod rolling. Because temperature analysis was performed by finite difference method, deformation analysis by rectangular conversion and microstructure analysis by incremental formulation for recrystalization and transformation, it was possible to predict rolling load, rolling temperature and microstructure with good accuracy. Next, thermomechanical rolling was applied to the actual wire rod rolling of plain carbon steel, which was reheated at a low temperature, cooled using cooling troughs, continuously rolled in Ar₃ and cooled using an interstand cooler in finishing mills. As fine as-rolled microstructures, particularly near the surface of the wire rod, not only wire rods but also cold heading and cold form rolling bolts had a high fatigue limit.

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The C-cross-sectional shape of a rolled plate and the distribution of equivalent strain introduced by cross roll rolling with cross angles of 0 to 10 degrees and texture formation are studied through a combination of numerical simulation and experimental observation. Strain distributions are predicted by 3-D elastic-plastic finite element method, and the texture is evaluated by examining an ODF figure obtained from X-ray diffraction measurement method. The rolling conditions, in which the C-cross-sectional shape of a 2-pass cross-roll-rolled plate with a cross angle of 10 degrees becomes the same as that of a conventionally rolled plate, are detected by numerical analysis, and then strain distributions through the plate thickness are shown. The 2-pass rolling with cross angles of 0 and 10 degrees is conducted using a shear-added rolling simulator, and the C-cross-sectional shape of the rolled plates is compared with the numerically predicted plate shape. Even if the shapes of the C-cross sections in the rolled plates are the same, the strong texture in the conventionally rolled plate such as {001}<110> does not develop in the cross-roll-rolled plate; furthermore, the orientation density of the γ-fiber texture becomes weak by cross roll rolling.

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The formability of steels subjected to different cold forming processes was investigated. In this study, the workability of ECAE(Equal channel angular extrusion) processed carbon steel was studied by cold upsetting tests. Three kinds of workpiece were prepared by ECAE process, rolling and combined (ECAE and post rolling) processes. All processes were carried out under the condition at room temperature. Experimental results are evaluated using cumulative equivalent strain. It was observed that the workability of the ECAE processed material was higher than that of the rolled one at the same equivalent strain. The higher workability was due to a continuous dynamic recrystallization which was identified by electron backscatter pattern (EBSP) analysis. The combined process enhanced mechanical properties and maintained good workability even with increasing applied strain, however its mechanism was not clarified.

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To obtain magnesium alloys with a high strength and a good formability, AZ31 magnesium alloys were deformed by ECAE (Equal channel angular extrusion) process. Experiments on the ECAE process were carried out at a constant speed of 2 mm/min at 20, 100, 150, 200 and 250°C with MoS₂ as lubricant. The ECAE process at constant back pressure of 150 MPa was carried out up to 4 passes without rotation (route A). After each ECAE pass, the mechanical properties and grain size of specimens were measured. For the specimen after 4 passes at 200°C, a high tensile strength and the smallest grain size were obtained. Then, the combination of the ECAE process up to 4 passes was investigated. From the experimental results, AZ31 magnesium alloys with a high tensile strength and a high formability were developed.

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In this study, an optimum asymmetric rolling process design system was developed by combining multiscale finite element (FE) analysis with the use of discretized optimization algorithm. This computer-simulation-based process design system is capable of reducing time consumption and cost in industries. However, a numerical scheme for predicting the deformation-induced texture evolution of an asymmetrically rolled sheet metal has not yet been developed. In this study, our crystallographic homogenized elasto/viscoplastic finite element (FE) code is employed in the design system to predict the texture evolution and formability with high accuracy. The response surface algorithm methodology, which can be categorized as a discretized optimization algorithm, is employed. It is confirmed through comparing with experimental results that this optimum asymmetric rolling design system is a powerful tool for finding an optimum rolling process to generate a high formability sheet metal.

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The effects of cross rolling on the microstructure, crystallographic orientation and mechanical properties of α′ martensite (Ti-8mass%V)-4mass%Sn and (Ti-12mass%V)-2mass%Al alloys were examined. After cold rolling, the microstructure of acicular martensite evolved into a refined cell dislocation structure. On crystallographic orientation after cold rolling, the directional cold-rolled plate showed the preferred orientation with the basal plane inclined in the transverse direction (TD). In contrast, the cross cold-rolled plate at reductions of 30-31% for the first rolling direction (RD1) followed by cross rolling (RD2) at reductions greater than 40% showed a rolling texture, having the basal pole scattered within 30° around the normal direction (ND), by increasing cross rolling reduction. Accompanying such texture formation by cross rolling, the anisotropy of Young′s modulus in the rolling plane decreased with increasing cross rolling reduction.

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A trial on an artificial hip joint stem made of Ni-free Co-29Cr-6Mo alloy was conducted by an isothermal hot semiclosed die forging method. The hot forging conditions (i.e., sample dimensions, forging temperature and stroke-speed) were determined by process simulation using “DEFORM-3D” based on FEM. A prototype stem with a shape designed using a FEM simulator was successfully obtained without surface defects or flaws under the predetermined forging conditions. The microstructure of the obtained stem consisted of mainly the ε (H.C.P.) phase as well as the minor γ (F.C.C.) and σ(CoCr:P42/mnm) phases. In addition, inhomogeneous distributions of the σ phase and grain size could be observed in the microstructure of the stem, resulting from the inhomogeneous distributions of effective strain rate, effective strain and effective stress induced in the stem during the forging process. Thus, Vickers hardness exhibited marked scattering, depending on the position of the stem.

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