Nippon Steel Corporation

Nippon Steel & Sumitomo Metal Corporation

Hideaki Gotohda

Shingo Yamasaki

Makoto Okonogi

Akifumi Kawana

A predetermined composition is had, when a C content is represented by (C %), in a case of (C %) being not less than 0.35% nor more than 0.65%, a volume fraction of pearlite is 64&#xd7;(C %)+52% or more, and in a case of (C %) being greater than 0.65% and 0.85% or less, the volume fraction of pearlite is not less than 94% nor more than 100%, and a structure of the other portion is composed of one or two of proeutectoid ferrite and bainite. Further, in a region to a depth of 1.0 mm from a surface, a volume fraction of pearlite block having an aspect ratio of 2.0 or more is not less than 70% nor more than 95%, and a volume fraction of pearlite having an angle between an axial direction and a lamellar direction on a cross section parallel to the axial direction of 40&#xb0; or less is 60% or more with respect to all pearlite.

Steel wire and wire rod

A wire material used for manufacturing a non-heat treated component whose tensile strength is 900 MPa to 1300 MPa, containing, in mass %: C: 0.20% to 0.50%, Si: 0.05% to 2.0%, Mn: 0.20% to 1.0%, being limited to contain P: 0.030% or less, S: 0.030% or less, N: 0.005% or less, F1 defined by the following expression (1) is less than 0.60, with the balance made up of Fe and inevitable impurities, wherein a metal structure contains a pearlite structure of 64&#xd7;(C %)+52% or more in a volume fraction, with the balance made up of one kind or two kinds of a pro-eutectoid ferrite structure and a bainite structure, an average block grain diameter of the pearlite structure at a region from a surface layer to 0.1 D is 15 &#x3bc;m or less when a diameter of the wire material is set to be D, and (the average block grain diameter of the pearlite structure at the region from the surface layer to 0.1 D)/(an average block grain diameter of the pearlite structure at a range from 0.25 D to a center) is less than 1.0.F1=C (%)+Si (%)/24+Mn (%)/6&#x2003;&#x2003;(1)

Wire material for non-heat treated component, steel wire for non-heat treated component, and non-heat treated component and manufacturing method thereof

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Tokyo, Japan

Hideaki Gotohda