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]. The microstructure is constituted by ferrite (F), lamellar pearlite (LP), and cementite (C), and in the latitudinal cross-section, in a region extending from a surface to a position located a distance of ½ the radius therefrom, the average particle diameter of F is 10 μm or less, the area percentage of LP is less than 20%, and the number of pieces of spheroidal cementite (SC) in C is 4×105 pieces/mm2 or more, and, in a central portion, the area percentage of LP is 20% or more and the number of pieces of SC is less than 4×105 pieces/mm2, and in the longitudinal cross-section, the average aspect ratio of F in a region extending from a surface to a position located a distance of ½ the radius therefrom is 3 or more. This steel material has a high base material toughness and good machinability without performing thermal refining.


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    Title :

    ROLLED ROUND STEEL MATERIAL FOR STEERING RACK BAR, AND STEERING RACK BAR


    Contributors:

    Publication date :

    2016-06-30


    Type of media :

    Patent


    Type of material :

    Electronic Resource


    Language :

    English


    Classification :

    IPC:    C22C Legierungen , ALLOYS / B21B Walzen von Metall , ROLLING OF METAL / B62D MOTOR VEHICLES , Motorfahrzeuge



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