Steel wire or bar

Abstract

Steel wire rod or bar steel, its chemical composition is calculated by mass % as C: 0.1-0.6%, Si: 0.01-1.5%, Mn: 0.05-2.5%, Al: 0.015-0.3%, N: 0.004-0.015%, and It can contain any specified element, and the balance is iron and impurities. Among the above impurities, P and S are P: 0.035% or less, S: 0.025% or less, and the surface layer area from the surface to a depth of 15% of the cross-sectional radius is the average The steel structure of ferrite with a particle size of 1 to 15 μm and spheroidized cementite with an average aspect ratio of 2 or less and an average particle size of 0.1 to 2 μm, from the depth from the surface to the center of 25% of the section radius The inner region of the steel structure is a steel structure composed of ferrite with an average particle size of 15-40 μm, pearlite and / or spheroidized cementite, and the surface roughness Ra in the circumferential direction of the surface after removing the surface scale is 4 μm Below, the depth of the grain boundary oxide layer on the surface is 30 μm or less.

Description

technical field [0001] The present invention relates to steel wire rods or steel bars (including bar in coils; the same applies hereinafter) suitable for cold forging and the like. This application claims the priority based on Japanese Patent Application No. 2012-131316 for which it applied to Japan on June 8, 2012, The content is used here. Background technique [0002] In recent years, in order to increase productivity, it is required to reduce or omit mechanical processing represented by cutting, so the demand for cold forging for medium carbon steel is increasing. However, the deformation resistance of medium carbon steel is higher than that of low carbon steel and low alloy steel, and lacks deformation ability (ductility), so there is a problem that mold cracking and steel material cracking are prone to occur. Therefore, in order to reduce deformation resistance and improve deformability of steel materials for cold forging, spheroidizing annealing for spheroidizing cem...

AI Technical Summary

Problems solved by technology

However, it is limited to steel structures that only specify ferrite and cementite, and there is no regulation on the surface roughness and surface grain boundary oxidation depth that have a great influence on cracking in cold forging.

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