Nippon Steel Corporation

Kiichiro Tsuchida

Koji Tanabe

Manabu Kubota

Tatsuro Ochi

Hideo Kanisawa

Koji Adachi

Ryuichi Seki

Seiji Ito

A steel wire rods and bars for machine structural use having, in the as-hot-rolled state, the same cold workability as a conventional steel wire rods and bars subjected to softening annealing after hot rolling, and a production method thereof are provided. This hot-rolled wire rods and bars usable for machine structural use without annealing comprises, in terms of mass %, C: 0.1 to 0.5%, Si: 0.01 to 0.5%, Mn: 0.3 to 1.5% and the balance of Fe and unavoidable impurities and if desired, comprises strengthening elements, wherein the microstructure of steel is composed of ferrite and pearlite, the ferrite grain size is No. 11 or more as defined in JIS G 0552, a granular carbide having an equivalent-circle diameter of 2 &#x3bc;m or less and an aspect ratio of 3 or less is contained in an area ratio of 5 to 40%, and the steel wire rods and bars has a tensile strength TS (MPa)&#x2266;573&#xd7;Ceq+257 and a reduction of area RA (%)&#x2267;&#x2212;23&#xd7;Ceq+75 (wherein Ceq=C+Si/7+Mn/5+Cr/9+Mo/2).

Hot-rolled steel wire rods and bars usable for machine structural use without annealing and method for producing the same

The present invention relates a train of in-line continuous manufacturing equipment for producing steel wire, considered difficult with a block mill up to now, capable of efficiently carrying out controlled-rolling and slow-cooling by an effective in-line combination of controlled rolling apparatuses and slow cooling apparatuses, having a hot rolling mill for steel wire, a winder to wind the rolled steel wire into rings, bundling apparatuses to pack the wound steel wire into bundled coils and an in-line heat treatment furnace to slow-cool the steel wire bundled into coils, which are sequentially connected, and using, preferably, a block mill with an area reduction rate of 25 to 60% having at most 4 roll stands as a final finish rolling mill of the hot rolling mill.

Continuous production facilities for wire

The present invention provides a hot rolled steel wire rod or bar for machine structural use having, in the as-hot-rolled condition, cold workability equal to that of the conventional wire rods or bars softened through annealing after hot rolling, and a method to produce the same: and relates to a hot rolled steel wire rod or bar for machine structural use, characterized in that; the wire rod or bar is made from a steel consisting of, in weight, 0.1 to 0.5% of C, 0.01 to 0.5% of Si, 0.3 to 1.5% of Mn, and the balance comprising Fe and unavoidable impurities and containing strengthening elements as required; its microstructure consists of ferrite and pearlite; its ferrite crystal grain size number defined under Japanese Industrial Standard (JIS) G 0552 is 11 or higher; and a granular carbide 2 &mgr;m or less in circle-equivalent diameter and having an aspect ratio of 3 or less accounts for a percentage area of 3 to 15%.

Hot-rolled steel wire and rod for machine structural use and a method for producing the same

The present invention provides a steel wire rod for cold forging which can be spheroidizing-annealed in an as hot-rolled state without requiring preliminary drawing and can have high ductility after the spheroidizing annealing, and a method to produce the same: and is characterized in that; the steel contains, by weight, 0.1 to 0.5% of C, 0.01 to 0.5% of Si and 0.3 to 1.5% of Mn, with the balance consisting of Fe and unavoidable impurities, and further contains hardening elements as required; and the steel has a prior austenite grain size number, defined under Japanese Industrial Standard (JIS) G 0551, of 11 or higher, the amount of diffusible hydrogen in the steel measured by the programmed temperature gas chromatography being 0.2 ppm or less, and the hardness being Hv 250 to 700. The production method is characterized by: hot rolling the steel at a low temperature; rapidly cooling and tempering the wire rod thus rolled by holding it in a furnace atmosphere controlled in the temperature range of 300 to 600&deg; C. for 15 min. or longer but shorter than 1 h.; and then applying spheroidizing annealing as required.

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Muroran, Japan

Kiichiro Tsuchida