Koshiro Aoki

Properties of ultrafine-grained steel by repeated shear deformation of side extrusion process

The development of an ultrafine grain size during repeated shear deformation of side extrusion of ultra-low-carbon steel with an initial grain size of approximately 150 μm and a tensile strength of 200 MPa was investigated. Experiments were carried out at room temperature and at a low extrusion speed of 2 mm min−1. Repeated side extrusions with lateral pressure were carried out for up to ten passes for the specimen extruded without rotation (route A). Uniform shear deformation was obtained by the side extrusion with the lateral pressure and an equivalent strain after a single side extrusion was 1.15. After ten passes of the side extrusions, an ultrafine-grained steel with a grain size of 0.5 μm×0.2 μm was realized and the tensile strength was over 1000 MPa.

Formation of texture during high temperature deformation of Ti-50·3 mol.% Al

Abstract Ti-50·3 mol.% Al was deformed in compression under various conditions. Texture as well as microstructure in the dynamically recrystallized state were investigated. One-to-one correspondence existed between the size of dynamically recrystallized grains and the peak stresses appearing in stress-strain curves. Formation of a fiber texture was confirmed. The texture developed with a decrease in peak stress. Extensive occurrence of strain-induced grain boundary migration was observed in the initial stage of dynamic recrystallization at the deformation conditions where sharp textures were formed after large deformation. Measurement of {021) pole figure suggested that the main component of the fibre texture was located between {011) and {021) (compression plane).

Mechanical Properties of Ultrafine Grained Steel Produced by Repetitive Cold Side Extrusion

Abstract Ultrafine grained microstructure was produced by repetitive deformation using the cold side-extrusion method from carbon steels. The side-extrusions with lateral pressure were repeated up to 10 passes without rotation. Each sample was uniformly deformed by the side-extrusion, and the equivalent strain was 1.15 after a single pass of the side-extrusion. After 10 passes of side-extrusion an ultrafine grained steel with a tensile strength of over 1000MPa a grain size of 0.5μm × 0.2 μm was developed for the ultra low carbon steel. The uniform elongation in tensile test for the steels after repetitive side extrusions was very small, but the cold formability was very good. By the heat treatment, the uniform elongation became larger.

Fatigue Property of High-Strength Carbon Steel Deformed by Repetitive Side Extrusion Process

The development of an ultrafine grained carbon steel during repetitive shear deformation of side extrusion and the properties after heat treatment were investigated. Side extrusions were carried out at room temperature and the used material was 0.50% carbon steel. The repetitive side extrusions with a constant lateral pressure were carried out up to 3 passes without rotation. The specimens of these steels after 3 passes were annealed at a constant temperature of 600°C changing the treatment time. After side extrusion and heat treatment, the fatigue property was better than that of the as-received material.