Patent ID: 8491732
Filing Date: 2013-07-23
Classification: C21D,C22C,C23C

Abstract:
1. A hot-rolled steel bar or wire rod having a chemical composition consisting of, by mass percent, C: 0.1 to 0.3%, Si: 0.05 to 1.5%, Mn: 0.4 to 2.0%, S: 0.003 to 0.05%, Cr: 0.5 to 3.0%, Al: 0.02 to 0.05%, and N: 0.010 to 0.025%, the balance being Fe and impurities, and the contents of P, Ti and O in the impurities being P: 0.025% or less, Ti: 0.003% or less, and O: 0.002% or less, wherein the structure of the hot-rolled steel bar or wire rod is composed of a ferrite-pearlite structure, ferrite-pearlite-bainite structure, or ferrite-bainite structure; the standard deviation of ferrite fractions at the time when randomly selected 15 viewing fields of a transverse cross section are observed and measured with the area per one viewing field being 62,500 μm when a region from the surface to one-fifth of the radius and a region from the center to one-fifth of the radius in the transverse cross section are observed, in each of the regions, the amount of Al precipitating as AlN is 0.005% or less, and the density in terms of the number of AlN having a diameter of 100 nm or larger is 5/100 μm