Patent ID: 8070888

Claim:
A screw component comprising a hyperfine grain structure steel, the screw component having a shaft part and a head part, the head part having a recess formed therein, wherein a structure of a surface layer part of a bottom part of the recess is an equiaxed structure whose mean grain diameter is 200 nm or smaller, wherein a structure of the shaft part is a bamboo structure whose mean grain diameter in a section structure perpendicular to a longitudinal direction is 200 nm or smaller, wherein a hardness of a region in which the equiaxed structure is formed is 300 or higher in a Vickers hardness, wherein a hardness of a region in which the bamboo structure is formed is 230 or higher in a Vickers hardness, and wherein the screw component is 1.4 mm or smaller in a nominal diameter.