| 摘要 |
PROBLEM TO BE SOLVED: To provide a micro-screw which has high surface hardness, shows high toughness, and does not cause " head crack" when fastened for use, and to provide a useful method for manufacturing such a micro-screw. SOLUTION: This micro-screw has Vickers hardness HV higher than 700 in the outer surface, and the Vickers hardness HV lower than 320 in the center of the screw; a tensile strength of 800 to 1,200 MPa; and a chemical composition of a used steel material, as needed, comprising 0.03-0.08% C, 0.2% or less (including 0%) Si, 0.8-1.8% Mn, 0.005-0.07% Ti, 0.020% or less (including 0%) P, 0.020% or less (including 0%) S, 0.01-0.06% Al, 0.0008-0.003% B, 0.01% or less (including 0%) N and the balance Fe with unavoidable impurities. COPYRIGHT: (C)2005,JPO&NCIPI
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