Steel wire and non-corrugated machine parts for non-corrugated machine parts

摘要

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.20 to 0.40% of C, 0.05 to 0.50% of Si, 0.50 to 2.00% of Mn and 0.005 to 0.050% of Al, the balance being Fe and impurities, The average aspect ratio of the bainite particles at a depth of 50 μm at the cross section of the D and L is defined as AR at a position of 50 μm in depth at the cross section of C, (AR) / (average aspect ratio of bainite particles at a depth of 0.25D in the L section) of 1.1 or more and GD is ( 15 / AR) 탆 or less, and (GD) / (average particle diameter of bainite particles at the depth 0.25D position on the cross section of C) is less than 1.0.