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 1/2 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 4×10 5 pieces/mm 2 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 4×10 5 pieces/mm 2 , 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 1/2 the radius therefrom is 3 or more. This steel material has a high base material toughness and good machinability without performing thermal refining.
ROLLED ROUND STEEL MATERIAL FOR STEERING RACK BAR, AND STEERING RACK BAR
RUNDES GEWALZTES STAHLMATERIAL FÜR LENKZAHNSTANGE UND LENKZAHNSTANGE
MATÉRIAU EN ACIER ROND LAMINÉ POUR UNE BARRE DE CRÉMAILLÈRE DE DIRECTION ET BARRE DE CRÉMAILLÈRE DE DIRECTION
2016-07-06
Patent
Electronic Resource
English
ROLLED ROUND STEEL MATERIAL FOR STEERING RACK BAR, AND STEERING RACK BAR
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