| 摘要 |
<p>A steel wire rod or bar steel, the chemical composition of which comprises, in terms of mass%, 0.1-0.6% of C, 0.01-1.5% of Si, 0.05-2.5% of Mn, 0.015-0.3% of Al, and 0.004-0.015% of N, optionally together with definite arbitrary element(s), with the balance consisting of iron and impurities, wherein the impurities contain not more than 0.035% of P and not more than 0.025% of S. In the steel wire rod or bar steel: a surface layer area to a depth equivalent to 15% of the section radius from the surface is a steel tissue that is configured from ferrite having an average particle diameter of 1-15 mum and spherical cementite having an average aspect ratio of 2 or less and an average particle diameter of 0.1-2 mum; an inner area ranging from the point of a depth equivalent to 25% of the section radius from the surface to the core is a steel tissue that is configured from ferrite having an average particle diameter of 15-40 mum and pearlite and/or spherical cementite; after removing surface scale, the surface roughness (Ra) of the surface in the circumferential direction is not more than 4 mum; and the depth of a grain boundary oxidation layer on the surface is not more than 30 mum.</p> |
