Abstract: A rolled round steel material contains C: 0.38 to 0.55%, Si: 1.0% or less, Mn: 0.20 to 2.0%, S: 0.005 to 0.10%, Cr: 0.01 to 2.0%, Al: 0.003 to 0.10%, B: 0.0005 to 0.0030%, Ti: 0.047% or less, Cu: 0 to 1.0%, Ni: 0 to 3.0%, Mo: 0 to 0.50%, Nb: 0 to 0.10%, V: 0 to 0.30%, Ca: 0 to 0.005%, and Pb: 0 to 0.30%, a remaining portion being constituted by Fe and an impurities, the impurities containing P in an amount of 0.030% or less and N in an amount of 0.008% or less, and has a chemical composition satisfying [3.4N?Ti?3.4N+0.02]. The microstructure is constituted by ferrite (F), lamellar pearlite (LP), and cementite (C) and microstructural features vary in terms of the lateral, longitudinal and central portions of the steel. This steel material has a high base material toughness and good machinability without performing thermal refining.

Abstract: A rolled round steel material for a steering rack bar, having a chemical composition consisting of C: 0.38 to 0.55%, Si: not more than 1.0%, Mn: 0.20 to 2.0%, S: 0.005 to 0.10%, Cr: 0.01 to 2.0%, Al: 0.003 to 0.10%, and N: 0.003 to 0.03%, with the balance being Fe and impurities, and P being not more than 0.030% in the impurities, and a microstructure consisting of ferrite (F), lamellar pearlite (LP), and cementite (C). The average grain diameter of (F), an area fraction of (LP), and the number of particles of spheroidal cementite (SC) among C are controlled in a region from the surface to a position at ½ radius and in a central part of the material. An average aspect ratio of F is controlled in a region from a surface to a position at ½ radius.

Abstract: A rolled round steel material for a steering rack bar contains C in an amount of 0.38 to 0.55%, Si in an amount of 1.0% or less, Mn in an amount of 0.20 to 2.0%, S in an amount of 0.005 to 0.10%, Cr in an amount of 0.01 to 2.0%, Al in an amount of 0.003 to 0.10%, B in an amount of 0.0005 to 0.0030%, Ti in an amount of 0.047% or less, Cu in an amount of 0 to 1.0%, Ni in an amount of 0 to 3.0%, Mo in an amount of 0 to 0.50%, Nb in an amount of 0 to 0.10%, V in an amount of 0 to 0.30%, Ca in an amount of 0 to 0.005%, and Pb in an amount of 0 to 0.30%, a remaining portion being constituted by Fe and an impurities, the impurities containing P in an amount of 0.030% or less and N in an amount of 0.008% or less, and has a chemical composition satisfying [3.4N?Ti?3.4N+0.02].

Abstract: A rolled round steel material for a steering rack bar, having a chemical composition consisting of C: 0.38 to 0.55%, Si: not more than 1.0%, Mn: 0.20 to 2.0%, S: 0.005 to 0.10%, Cr: 0.01 to 2.0%, Al: 0.003 to 0.10%, and N: 0.003 to 0.03%, with the balance being Fe and impurities, and P being not more than 0.030% in the impurities, and a microstructure consisting of ferrite (F), lamellar pearlite (LP), and cementite (C), wherein in a cross-section perpendicular to the rolling direction: an average grain diameter of F?10 ?m, an area fraction of LP is less than 20%, and the number of particles of spheroidal cementite (SC) among C?4×105/mm2, in a region from the surface to a position at ½ radius; and an area fraction of LP?20% and the number of particles of SC<4×105/mm2, in a central part, and wherein in a cross-section including a center line of the round steel material and parallel to the rolling direction: an average aspect ratio of F is ?3 in a region from a surface to a position at ½ radius.