摘要 |
PROBLEM TO BE SOLVED: To provide a steel wire for bolt excellent in cold headability and delayed fracture resistance after quenching and tempering.SOLUTION: A steel wire for bolt includes, by mass, 0.3-0.6% C, 1.0-3.0% Si, 0.10-1.5% Mn, over 0% to 0.020% or less P, over 0% to 0.020% or less S, 0.3-1.5% Cr, 0.02-0.10% Al, 0.001-0.02% N, and the balance iron with inevitable impurities. The ferrite grain size number is No. 6-12 at a position of steel wire diameter d×1/4, a proportion of carbide with an aspect ratio of 2.0 or less in an entire carbide is 70% or more, and a C content at a position 0.1 mm deep from a surface is 60-120% C content of a base material. The steel wire for bolt is excellent in cold headability and delayed fracture resistance after quenching and tempering.SELECTED DRAWING: None |