| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel plate excellent in screw driving property by providing a recess having specified depth, minor diameter and an area ratio in a surface at an assumed screw driving position to prevent the side slip. SOLUTION: Recesses of 5-50μm in maximum depth and 20μm to 3 mm in minor diameter are provided in a steel plate in an area ratio of >=0.03%. The kind of plating preferably is galvanizing, zinc alloy plating, aluminum plating, aluminum alloy plating or the like from the viewpoint of corrosion resistance and machinability. The plane shape of the recesses is not limited except the minor diameter (r) and a circular, elliptical, rectangular, polygonal shape or the like may be acceptable and a slender shape of straight or curved one may be acceptable. The sectional shape of the recesses may be arc-shaped, rectangular, triangular or the like. The temper-rolling is performed using a rolling roll having raised parts which are inverted the unevenness of the recesses to be applied on the surface of the steel plate after rolling. To stabilize the position of a cutting blade tip of a screw, it is preferable to provide at least one recess per 1 mm<2> and the whole surface may be covered with the recesses.
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