Round steel bars for quenching and tempering

Abstract

This invention provides a quenching and tempering steel that reduces manufacturing costs and exhibits excellent corrosion resistance, wear resistance, hot workability, and toughness. The quenching and tempering round bar steel of this invention is characterized by having a prescribed composition, wherein in a cross-section perpendicular to the long side direction of the round bar steel, the concentration distribution of C, Si, Mn, and Mo in the region from the surface of the round bar steel to a depth corresponding to 10% of the diameter of the cross-section in the direction from the surface toward the center satisfies a prescribed relationship.

Claims

1. A round bar steel for quenching and tempering, comprising the following composition, in mass %: C: 0.10% or more and 0.50% or less, Si: 0.002% or more and 1.200% or less, Mn: 2.38% or more and 5.00% or less, P: 0.050% or less, S: 0.050% or less, Cu: 0.005% or more and 2.000% or less, Ni: 0.002% or more and 5.000% or less, Cr: 0.10% or more and 3.00% or less, Al: 0.0010% or more and 1.0000% or less, Mo: 0.20% or more and 2.00% or less, V: 0.0010% or more and 1.0000% or less, and N: 0.0010% or more and 0.0250% or less. The remaining portion contains Fe and unavoidable impurities. The quenched and tempered round bar steel is characterized in that, in a cross section perpendicular to the long side direction of the round bar steel, the concentration distribution of C, Si, Mn and Mo in the region from the surface of the round bar steel to a depth equivalent to 10% of the diameter of the cross section in the direction from the surface toward the center satisfies the following equation (1) [number 1] … (1) Here, [X] is the content of element X in the composition, and [X]atCmin and [X]atCmax are the concentrations of element X at the positions where the C concentration is minimum and maximum in the concentration distribution, respectively.

2. The round bar steel for quenching and tempering as described in claim 1, wherein, The composition further contains, by mass%, selected from Mg: The group consisting of at least one element: less than 0.0100%, Ti: less than 0.100%, Nb: less than 0.100%, Ta: less than 0.1000%, Pb: less than 0.500%, Bi: less than 0.100%, O: less than 0.0100%, As: less than 0.0100%, Ca: less than 0.0100%, B: less than 0.0100%, Zr: less than 0.0500%, Hf: less than 0.0500%, W: less than 1.0000%, Co: less than 0.5000%, Zn: less than 0.0100%, Te: less than 0.100%, Sn: less than 0.100%, Sb: less than 0.100%, and rare earth metals: less than 0.1000%.

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