“…Grain refinement is an effective procedure to improve the fatigue strength of metallic materials. Various technologies, such as cold rolling, 1,2) warm rolling, 3) equal channel angular pressing, 4) and high-pressure torsion 5,6) are applied to obtain fine grains, and their effects on the mechanical properties of metals have been investigated. However, grain refinement generally leads to a reduction of ductility, and compatibility between ductility and fatigue strength is necessary.…”