| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel wire or bar that has excellent cold workability as is hot rolled without performing any heat treatment such as softening, and has superior strength stability after heat treatment without generating variation on in hardness even when it is quenched after forming. SOLUTION: This steel is composed mainly of a ferrite and pearlite structure which contains, by mass, C: 0.1-0.6%, Si: 0.15% or less (0% is not included), Mn: 0.1-0.6%, P: 0.02% or less (0% is included), S: 0.03% or less (0% is included), B: 0.0005-0.005%, Al: 0.01-0.1%, N: 0.010% or less (0% is not included) and Zr: 0.025-0.08% and/or Hf: 0.05-0.16%, and satisfies the formula: 1.2<= (Zr/91.2+ Hf/178.5)/(N/14.0) <=4.0.
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