Excellent workability steel wire rod and method for production of same
The present invention provides a steel wire rod with stable workability. The steel wire rod has steel components containing, by mass %, C: 0.20 to 0.60%, Si: 0.15 to 0.30%, Mn: 0.25 to 0.60%, P: ≤0.020%, S: ≤0.010%, and a balance of Fe and unavoidable impurities, and an internal microstructure including cementite, in which by number ratio, 80% or more of the cementite in a cross-section vertical to a longitudinal direction of the wire rod has a short axis of 0.1 μm or less and a ratio of a long axis to the short axis, defined as an aspect ratio, of 2.0 or less.
1. A steel wire rod comprising steel components including, by mass %, C: 0.20 to 0.60%, Si: 0.15 to 0.30%, Mn: 0.25 to 0.60%, P: ≤0.020%, S: ≤0.010%, and a balance of Fe and unavoidable impurities, and having an inside microstructure including cementite,
wherein by number ratio, 80% or more of the cementite in a cross-section vertical to a longitudinal direction of the wire rod has a short axis of 0.1 μm or less and a ratio of a long axis to the short axis, defined as an aspect ratio, of 2.0 or less,
wherein the inside microstructure comprises ferrite and bainite structures, and
wherein a ratio of lamellar-type structures contained in the inside microstructure is less than 5%.
2. The steel wire rod according to claim 1 further containing, in addition to said steel components, by mass %, one or more of Al: 0.06% or less, Cr: 1.5% or less, Mo: 0.50% or less, Ni: 1.00% or less, V: 0.50% or less, B: 0.005% or less, and Ti: 0.05% or less.
3. A method for production of a steel wire rod comprising heating a billet of a chemical composition according to claim 1 to 950° C. to 1080° C., supplying the billet to a wire rod rolling process to obtain a wire rod, coiling the wire rod in a temperature region of 750° C. to 900° C., then subjecting the wire rod to in-line heat treatment by a molten salt of 400° C. to 430° C., and ejecting the molten salt to the wire rod being dipped in the molten salt at a stirring flow rate of 0.5 m/s to 2.0 m/s in range.
4. A method for production of a steel wire rod comprising heating a billet of a chemical composition according to claims 2 to 950° C. to 1080° C., supplying the billet to a wire rod rolling process to obtain a wire rod, coiling the wire rod in a temperature region of 750° C. to 900° C., then subjecting the wire rod to in-line heat treatment by a molten salt of 400° C. to 430° C., and ejecting the molten salt to the wire rod being dipped in the molten salt at a stirring flow rate of 0.5 m/s to 2.0 m/s in range.