Patent ID: 10072317

Abstract:
A filament according to an aspect of the present invention includes a predetermined chemical composition, in which a diameter r of the filament is 0.15 mm to 0.35 mm, a soft portion is formed along an outer circumference of the filament, the Vickers hardness of the soft portion is lower than that of a position of the filament at a depth of ¼ of the diameter r by Hv 50 or higher, the thickness of the soft portion is 1 μm to 0.1×r mm, the metallographic structure of a center portion of the filament contains 95% to 100% of pearlite by area %, the average lamellar spacing of pearlite in a portion from a surface of the filament to a depth of 1 μm is less than that of pearlite at the center of the filament, the difference between the average lamellar spacing of pearlite in the portion from the surface of the filament to the depth of 1 μm and the average lamellar spacing of pearlite at the center of the filament is 2.0 nm or less, and the tensile strength is 3200 MPa or higher.