Steel wire

A steel wire composed of a steel containing:

• not less than 1.0 mass % and not more than 1.1 mass % C,
• not less than 0.15 mass % and not more than 0.25 mass % Si,
• not less than 0.25 mass % and not more than 0.35 mass % Mn, and
• not less than 0.15 mass % and not more than 0.25 mass % Cr,
• with the balance being Fe and unavoidable impurities;
• the steel wire having a wire diameter of not less than 0.15 mm and not more than 0.42 mm,
• the steel having a pearlitic microstructure formed by patenting, wherein the patenting includes austenitizing at a temperature Acm or higher and then isothermal transformation to obtain a fine pearlite structure;
• the steel having a dislocation density of not less than 2.4×1016 m−2 and not more than 5.0×1016 m−2, the dislocation density being determined from X-ray diffraction line-profile analysis of Fe (110), (200), (211), (220), and (310) reflections using a synchrotron radiation source and calculated by the modified Williamson-Hall method and the modified Warren-Averbach method;
• and
• the steel having a full width at half maximum in a circumferential direction of not less than 42° at a peak of a maximum intensity of a Debye ring for Fe (211) plane, the full width at half maximum being measured using an X-ray residual-stress analyzer with a Cr tube while aligning the wire axis with the incident direction and setting an incident angle of 35°, and determined as the angular distance between half-maximum points on a circle concentric with the Debye ring that passes through the maximum-intensity peak.