JP2768152B2 - Method for producing hot-rolled carbon steel wire with high strength and high ductility - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a hot-rolled carbon steel wire.

[0002]

2. Description of the Related Art As a typical method of adjusting and cooling a hot-rolled carbon steel wire, there is a method of immersing the wire in hot water of 80 ° C. to boiling. . In this method, the hot-rolled wire is wound in a ring shape at 850 to 800 ° C., dropped on a conveyor, immersed in warm water in the process of being transported in a non-concentric ring state, and subjected to pearlite transformation by conditioning and cooling. The purpose is to increase the strength of the steel wire.

However, in this method, there is a limit in controlling the metallographic structure. At present, carbon steel is considerably inferior in both strength and ductility as compared with an off-line lead patenting wire.

By the way, when comparing the metal structures of an off-line lead patenting material excellent in both strength and ductility with the hot-rolled carbon steel wire rod, the former crystal grains (former austenite grains) are large, and the pearlite lamellar spacing is large. It turns out that it is considerably fine.

[0005] Further, comparing the two manufacturing conditions, the wire temperature of the carbon steel wire before the heat treatment is remarkably different. That is, while hot rolling is 800 to 850 ° C., lead patenting is a high temperature of 940 to 960 ° C., suggesting that this temperature difference results in a difference in metal structure.

[0006] Therefore, simply hot-rolled carbon steel wire rod 98
It is wound in a ring shape at a high temperature of 0 to 1100 ° C, dropped on a conveyor, and transported in a non-concentric ring state.
It was allowed to cool for ２０20 seconds, and then immersed in warm water boiling from 80 ° C. to perform adjustment cooling. As a result, several sites did not undergo pearlite transformation locally within the one-ton coil ring, but some sites had martensitic transformation.

In such a cooling method, the wire is 850
Since the wire is immersed in warm water at a high temperature exceeding ℃, the surface properties of the wire deteriorate, and a needle-like scale called a whisker is generated. This caused the martensitic structure to be induced by the controlled cooling of the hot water. As a result, the pearlite-transformed part in the 1-ton coil has the same strength and ductility as the off-line lead-patented wire, but the part where martensitic transformation occurs locally causes disconnection in the drawing process. , Productivity and the like. In other words, unless the pearlite transformation is performed over the entire length of the 1-ton coil, there is a serious drawback that the wire rod has no value.

For this reason, in order to prevent the generation of whiskers, it is necessary to immerse in warm water at a linear temperature of 850 to 750 ° C. However, it takes 25 to 88 seconds for a 5.5 mmφ wire to cool the wire finished and wound at a high temperature of 980 to 1100 ° C. on a conveyor to a temperature of 850 to 750 ° C. That is, a conveyor of 15 to 45 m is required between the winder and the hot water tank, and the equipment becomes enormous.

Further, when the cooling time in the atmosphere is prolonged, the temperature difference between the central portion and the end portion of the non-concentric ring-shaped wire increases, that is, the central portion has a low temperature and the both end portions have a high temperature. There is a problem that the strength and scale properties of the wire become non-uniform.

The present invention has been made under such a technical background, and an object of the present invention is to provide a method for producing a wire having the same strength and ductility as an off-line lead patenting wire. is there.

[0011]

In order to achieve the above object, a method of the present invention is to roll a hot-rolled carbon steel wire into a ring shape and convey it on a conveyor in a non-concentric ring state.
In the process of immersion in hot water at 0 ° C to boiling and cooling, the wire is finished at a high temperature of 980 to 1100 ° C, wound up at the same temperature, transferred to a conveyor, and kept at a high temperature for 3 to 15 seconds. After growing, it is cooled by air-water mist spray for 5 to 17 seconds, the wire temperature is set to 850 to 750 ° C, and the pearlite transformation is performed over the entire length by adjusting cooling with 80 ° C to boiling hot water. And

Further, when the wire in a non-concentric ring state is cooled by steam-water mist spraying in this manufacturing method, it is required to convey the wire while keeping the temperature difference between the center and both ends of the ring within 0 to 40 ° C. Features.

Further, it is preferable that the air-water mist spray is disposed on the upper surface or upper and lower surfaces of the conveyor to perform cooling. In addition, when the wire is transferred to the conveyor and held at a high temperature, a heat insulating cover is provided. It is preferred to do this.

A specific example of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing the steps of the method of the present invention. As shown in the drawing, a hot-rolled carbon steel wire rod 1 rolled at 980 to 1100 ° C. by a finish rolling mill 2 passes through a winder 3. At the same temperature, it is wound in a ring shape and dropped on the roller conveyor 4. The temperature of the wire is measured with a radiation thermometer or the like.

The wire dropped on the conveyor 4 is conveyed in a non-concentric ring state.
Hold for 2 seconds at high temperature. To maintain this high temperature, a protective cover 5
Etc. may be used. The crystal of the metal structure grows by this holding, and the crystal grain of the metal structure grows remarkably as the rolling finishing temperature and the winding temperature are higher. This holding time is required to be at least about 3 seconds, and is set to about 20 seconds at most, and preferably up to about 15 seconds, from the relationship between the equipment space or the temperature difference between the center and both ends of the non-concentric ring-shaped wire.

Next, cooling is performed on the conveyor 4 by the steam-water mist spray 6. FIG. 2A shows the arrangement of the air-water mist spray from the front in the wire rod traveling direction. As shown,
The air / water mist spray 6 is disposed on the upper and lower surfaces of the conveyor, and jets the air / water mist 10 to the wire through a nozzle 9 connected to an air supply pipe 7 and a water supply pipe 8. Further, an open / close electric valve (not shown) is attached to the nozzle 9 so that the cooling distance (time) can be adjusted.

As shown in the plan view of FIG. 2B, the nozzles 9 are arranged coarsely (small) at the center of the conveyor and densely (many) at both ends in the traveling direction of the wire. I have. This is because if you look at the wire on the conveyor as a plan view,
In the overlapping state as shown in FIG. 3A, when the overlapping state is viewed as a density ratio from the wire rod traveling direction, as shown in the graph of FIG. 3B, both ends of the ring are dense. Based on That is, since the center of the ring has a low temperature and the ends thereof have a high temperature, the center and both ends of the wire can be uniformly cooled.

The cooling by the air-water mist is performed for about 5 to 17 seconds. The air / water ratio is, for example, 50 to 100 Nm ³ /
At m ³ , the cooling capacity is 20-40 ° C./sec. By such air-water mist cooling, the line temperature becomes 850 to 750.
℃.

Then, the adjustment cooling with the hot water 11 is performed. The temperature of the hot water was boiling from 80 ° C.
Into the hot water tank 12, the pearlite transformation is performed over the entire length of the wire, and a wire having the same strength and ductility as the off-line lead patenting wire can be obtained.

[0020]

As described above, the method of the present invention lies in the pre-cooling of the controlled cooling with hot water. In the method described in the prior art, 9
The hot carbon steel wire wound at a high temperature of 80 to 1100 ° has a wire temperature exceeding 850 ° C when immersed in warm water,
Whiskers are formed 1 to 20 seconds after immersion in warm water. As mentioned earlier, this whisker is a needle-like scale, and when produced in conditioned cooling with warm water,
Induces a martensitic structure.

In the present invention, as described above, the ring-shaped hot-rolled wire rod is dropped onto the conveyor, kept at a high temperature to grow crystal grains, cooled with steam-water mist spray, and then adjusted and cooled with hot water. ing. By such pre-cooling, the line temperature is set to 850 to 750 ° C., and the generation of whisker scale is prevented, and the induction of the martensite structure due to the supercooling phenomenon can be prevented by performing stable adjustment cooling.

[0022]

[Test example]

(Tensile Test) Hereinafter, test examples of the present invention will be described. SWRH62A, SWRH72A, SWRH80A by the method described in FIG.
With each of the above materials, the wire rod having a finished wire rod diameter of 5.5 or 7.0 mmφ was cooled (Example). Then, a tensile test was performed on the obtained wire. The test method is 1 ton of wire rod, 1 /
One ring was divided into eight equal parts for each of 10 rings at 4 sites, the center, 3/4 site, and 5 sites at the end.

In addition, the same wire rod is used in the prior art,
After finishing at a low temperature of 850 ° C. and winding, it was immersed in hot water and cooled, and then subjected to an off-line lead patenting wire (lead: 550 ° C.) and a high temperature finishing at 980 to 1100 ° C. as a comparative example. Those immersed in warm water without water mist cooling (immersed at 850 ° C. or higher) were similarly tested. Tables 1 and 2 show the results together with the presence or absence of martensite.

[0024]

[Table 1]

[0025]

[Table 2]

As shown in the table, the higher the finishing temperature and the higher the winding temperature, the higher the wire strength shifts to the higher strength side. Even though it is a hot-rolled wire, the strength equivalent to that of an off-line lead patenting wire is obtained. It was confirmed that it would be able to be. In addition, it can be seen that the wire obtained by the method of the present invention has high homogeneity.

(Bending test) Next, each of the above-mentioned wires was drawn with a reduction in area of 82.5%, and was subjected to 150, 200, 250, 3
Tempering (tempering) was performed at each temperature of 00, 350 and 400 ° C. for 20 minutes. The obtained wire was bent at 90 ° using the punch 13 and the die 14 shown in FIG. 4, and the breakage rate was evaluated as ductility. The radius of the tip of the punch 13 is 0.
8 mm, groove shape of die 14 → V shape, groove width 10 mm. 5.5mmφ → 2.3mmφ wire drawn SW
The test results for RH80A are shown in the graph of FIG. 5, and the evaluation of all the wires is shown in Tables 1 and 2.

As is evident from the test results, in the examples, there was no breakage at each tempering temperature as compared with the conventional material, and it was confirmed that the example had ductility equal to or higher than that of the off-line lead patenting wire.

[0029]

As described above, according to the method of the present invention, it is possible to obtain a wire having the same strength and ductility as an off-line lead patenting wire, while being a hot-rolled wire. In addition, by controlling the temperature difference in the width direction on the conveyor, a uniform wire can be obtained,
This contributes to the improvement of the yield and can omit the off-line lead patenting step. In addition, high strength,
Since it has high ductility, it is possible to satisfy product specifications with light processing.

[Brief description of the drawings]

FIG. 1 is a schematic view showing the steps of the method of the present invention.

FIG. 2A is an explanatory view showing a cooling state by air-water mist spray viewed from a wire rod traveling direction, and FIG. 2B is a plan view showing an arrangement of spray nozzles.

FIG. 3A is a plan view showing an overlapping state of wires being conveyed in a non-concentric ring state, and FIG. 3B is a graph showing the overlapping state as a density ratio when viewed from a wire rod traveling direction.

FIG. 4 is an explanatory view showing a punch and a die used for a bending test.

FIG. 5 is a graph showing a breakage rate in a bending test performed on wires having different tempering temperatures.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wire rod 2 Finishing rolling mill 3 Winding machine 4 Roller conveyor 5 Protective cover 6 Air mist spray 7 Air supply pipe 8 Water supply pipe 9 Nozzle 10 Air mist 11 Hot water 12 Hot water tank 13 Punch 14 Die 15 Wire drawing and tempering wire 16 Cooling trough 17 Finish rolling thermometer 18 Winding thermometer

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C21D 9/52 C21D 8/06

Claims (4)

(57) [Claims] 1. A hot-rolled carbon steel wire rod is wound in a ring shape and conveyed on a conveyor in a non-concentric ring state.
In the process of being immersed in boiling hot water and adjusted and cooled, the wire is finished at a high temperature of 980 to 1100 ° C, wound up at the same temperature, transferred to a conveyor, and kept at a high temperature for 3 to 15 seconds to grow crystal grains. After that, use air-water mist spray
High-strength, high-ductility hot-rolled carbon characterized by cooling the wire for 17 seconds to bring the wire temperature to 850 to 750 ° C, and then performing pearlite transformation over the entire length by adjusting cooling with hot water at 80 ° C to boiling. Manufacturing method of steel wire rod. 2. The method according to claim 1, wherein when the wire in a non-concentric ring state is cooled by air-water mist spray, the temperature difference between the center and both ends of the ring is conveyed within a range of 0 to 40 ° C. Item 4. The method for producing a hot-rolled carbon steel wire having high strength and high ductility according to Item 1. 3. The hot-rolled carbon steel wire rod having high strength and high ductility according to claim 1, wherein the steam-water mist spray is disposed on the upper surface or upper and lower surfaces of the conveyor and is cooled. Production method. 4. A hot-rolled carbon steel wire having high strength and high ductility according to claim 1, wherein a heat insulating cover is provided when the wire is held at a high temperature after being transferred to the conveyor. Production method.