JPH10330847A - Method for directly softening hot rolled wire rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method directly softening a hot rolled steel wire rod, capable of uniformly softening a wire rod from the head part to the tail part to <=75 kgf/mm tensile strength and also uniformizing scale characteristic. SOLUTION: In this method for directly softening the wire rod which is unrolled into ring shape after hot rolling, a wire bar of 700-1000 deg.C to be rolled is finish-rolled and the temp. of the resultant wire rod directly after rolling is regulated to <=1100 deg.C and then the distribution of the temp. of the wire rod in the longitudinal direction is regulated so that the temp. is higher by >=50 deg.C in the head part and the tail part. Subsequently, the wire rod is coiled by means of a laying reel, unrolled on a conveyer while regulating ring density to (150 to 500) pieces/m, air-cooled until the temp. T1 in the region of 550-850 deg.C is reached, cooled down to the temp. T2 in the region of 500-640 deg.C at (0.05 to 2) deg.C/sec cooling rate, and then air-cooled, where T1>T2 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for directly softening a hot-rolled wire. More specifically, it is a direct softening method of a wire rod developed in a ring shape after hot rolling, and a temperature condition before and after finish rolling for finishing to a predetermined shape in continuous hot rolling of a steel wire, a laying type winder after finish rolling. By adjusting the conditions before (hereinafter referred to as a laying head) to develop into a ring shape (hereinafter, "development into a ring shape" in the present invention is also simply referred to as "winding") and cooling conditions thereafter. The present invention relates to a method for directly softening a hot-rolled wire, which uniformly softens the wire from the head to the tail.

[0002]

[Prior Art] JIS G 3502 piano wire manufactured by hot rolling, JIS G 3507 carbon steel wire for cold heading, and JI
SG 4051, carbon steel and alloy steel for machine structures described in JIS G 4104, JIS G 4105, etc., bearing steel described in JIS G 4805, JIS
Wire rods based on spring steel described in G 4801 and tool steels described in JIS G 4401 and JIS G 4401 are used as secondary processing, drawing, drawing, cutting, forging, cutting, etc. The required product can be obtained through the cold working process.

[0003] However, many of the above-mentioned wires, which are usually hot-rolled, have a hard phase such as pearlite, bainite or martensite in their structure.
Therefore, in order to perform the secondary working and the tertiary working in the cold, generally, a hot-rolled wire is subjected to a softening heat treatment such as annealing or spheroidization to reduce strength and increase ductility. .

However, the above softening heat treatment requires 10 to 2 times.
It often requires as long as 0 hours. For this reason,
From the viewpoint of productivity improvement or energy saving, there has been an increasing demand for a so-called "direct softening" technique capable of obtaining a soft structure equivalent to that obtained by performing a softening heat treatment while rolling.

[0005] Therefore, various techniques for obtaining a softened structure by adjusting the cooling rate of the wire by variously adjusting rolling conditions and cooling conditions in continuous hot rolling of the wire have been studied.

For example, Japanese Patent Publication No. Sho 60-56208,
JP-A-62-180023, JP-A-62-199
No. 718, JP-A-63-293122, JP-A-3-64420 and JP-A-4-268028 disclose a soft structure as hot-rolled by omitting a softening heat treatment such as annealing or spheroidization. Have been proposed.

[0007] However, a "method for slowly cooling a hot-rolled wire" proposed in Japanese Patent Publication No. 60-56208 and a "heat treatment method for a hot-rolled wire" proposed in Japanese Patent Application Laid-Open No. 62-180023. ", JP-A-63-2931
No. 22, "Method for producing a softened medium carbon steel wire or low alloy tough steel wire" proposed in Japanese Patent Application Laid-Open No. Hei.
The “slow cooling method of a wire” proposed in Japanese Patent Publication No. 8028 is a technique of slow cooling after winding all of them in a coil shape. For this reason, the surface property, especially the scale property, of the treated wire is extremely high in the area where the wire is in very close contact with the outer or inner periphery of the coiled wire (that is, the wire density is high). It is difficult to avoid unevenness,
For this reason, there is a problem that the descaling process becomes complicated.

[0008] Japanese Patent Application Laid-Open No. 62-199718 proposes a "method for directly softening a rolled material of steel for machine structural use" in which the temperature range from hot rolling to completion of pearlite transformation is 15 minutes.
Cool slowly at a cooling rate of not more than ℃ / min.
This is a technique of obtaining a soft tissue by maintaining the temperature at a temperature in the range of 80 to 730 ° C until the pearlite transformation is completed and then allowing it to cool. According to this method, it is possible to soften the hot-rolled steel. However, even with the above method, it is not possible to perform uniform softening over the entire length in the longitudinal direction of the rolled steel material. That is, in the longitudinal direction of the rolled steel material, the so-called “unsteady portion” of the first rolled steel material and the last rolled steel material in the longitudinal direction is hard, and extends over the entire length in the longitudinal direction from the leading portion to the tail. May not be able to be softened uniformly.

Japanese Patent Application Laid-Open No. 3-64420 proposes "a method and an apparatus for manufacturing a softened wire" in which "a wire discharged from a laying head is cooled while being conveyed by a stermore type conveyor. Is 650 ±
Cooling under conditions maintained at a temperature of 10 ° C. for at least 3 minutes to provide substantially bainite-free ferrite +
This is a technique for softening the wire rod by using a “pearlite structure”. According to this method, the wire can certainly be softened. However, especially in an alloy steel having high hardenability containing a large amount of Cr, Mo, Ni, Mn, etc., even if SCM4
Even if it is 30 or SCM440, if it is kept in the temperature range of 650 ± 10 ° C. for at least 3 minutes or more, austenite enriched with carbon remains untransformed and transforms into bainite in the subsequent cooling, so that the wire rod In this case, a uniform soft structure cannot be obtained over the entire length of the steel sheet, and the mechanical properties vary greatly.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a hot-rolling method that can uniformly soften the wire from the head to the tail to a tensile strength of 75 kgf / mm ² or less and can make the scale properties uniform. An object of the present invention is to provide a method for directly softening a wire.

[0011]

The gist of the present invention resides in the following method (1) for directly softening a hot-rolled wire.

(1) This is a method for directly softening a wire developed in a ring shape after hot rolling, in which a wire to be rolled having a temperature of 700 to 1000 ° C. is finish-rolled, and the temperature immediately after rolling is set to 110.
After the temperature is reduced to 0 ° C. or less, the temperature distribution in the longitudinal direction of the wire is adjusted so as to be 50 ° C. or more at the leading and trailing ends, and then wound with a laying winder to reduce the ring density to 15 ° C.
0 to 500 lines / m and spread on conveyor
After allowing to cool to a temperature T1 in a temperature range of 850 ° C.,
A method for directly softening a hot-rolled wire, comprising cooling to a temperature T2 in a temperature range of 500 to 640 ° C. at a cooling rate of 0.05 to 2 ° C./sec, and then allowing it to cool. However, T1> T2
It is.

Here, "finish rolling" means rolling in a so-called "finish rolling mill train". However, when rolling using a rolling mill such as a three-roll or four-roll is performed after performing rolling using a finishing rolling mill row using a normal two-roll rolling mill, the three-roll or four-roll is used. Rolling using a rolling machine such as a roll.

"Temperature" refers to the temperature of the surface of the wire, and "cooling rate" refers to the average cooling rate of the wire surface in a predetermined temperature range. “Cooling” refers to natural cooling in the atmosphere.

"After cooling to a temperature T1 in a temperature range of 550 to 850 ° C., a cooling rate of 0.05 to 2 ° C./sec is followed by cooling to a temperature T2 in a temperature range of 500 to 640 ° C. “Cooling” refers to the temperature and cooling conditions of a specific portion of a specific portion of a wire rod developed in a ring on a conveyor. The whole wire material developed in a ring shape on the conveyor is the sum of the specific portions. For this reason, 550-850 ° C.
The temperature T1 in the temperature range and the temperature T2 in the temperature range of 500 to 640 ° C. do not indicate specific ones.

The "leading portion" of the wire refers to a portion of the wire from the most distal position to at least 4% by weight. Further, the “tail portion” of the wire refers to a portion from the rearmost position of the wire to at least 4% by weight.

The term "ring density" refers to a "ring that crosses a 1-m long line parallel to the conveyor moving direction through the center of the ring on a wire rod developed on a conveyor by a laying head after finish rolling. Number. "

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have developed a method for directly softening a hot-rolled wire which can uniformly soften the wire from the beginning to the tail using various types of steel and can also make the scale properties uniform. As a result of conducting an experiment, the following findings were obtained.

In order to prevent the scale properties of the wire from becoming non-uniform and to facilitate the descaling process, it is necessary to optimize the ring density of the wire. For this purpose, the winding method may be a so-called “loading type” in which the laying head develops (takes up) a ring shape on the conveyor after the finish rolling.

The temperature conditions before and after finish rolling to finish to a predetermined shape, the temperature condition of the wire rod after the finish rolling and before winding into a ring by a laying head, the ring density of the wound wire rod, and the cooling condition after winding are as follows. If adjusted, it is possible to uniformly soften the wire from the head to the tail by the above-described winding method.

The tensile strength of the softened wire is 75 kgf /
If it is not more than mm ² , problems such as disconnection and cracking do not occur during the second and third workings as a post-process.

The present invention has been completed based on the above findings.

It should be noted that there is no need to impose any particular restrictions on the chemical composition of the wire that is targeted by the method of the present invention. What is necessary is just a component composition that can secure the characteristics (for example, strength and toughness) required for the final product.

Specifically, for example, in terms of% by weight, C: 0.0
1-1.2%, Si: 0.01-2.0%, Mn: 0.
01 to 2.0%, Cr: 0 to 2.0%, Mo: 0 to 0.
6%, Cu: 0 to 2.0%, Ni: 0 to 4.0%, T
i: 0 to 0.10%, Al: 0.001 to 0.10%,
N: 0 to 0.03%, V: 0 to 0.40%, Nb: 0 to 0
0.15%, B: 0 to 0.005%, S: 0 to 0.10
%, Pb: 0 to 0.35%, and Ca: 0 to 0.01%, the balance being Fe and unavoidable impurities, and P as an impurity may be 0.05% or less.

Hereinafter, each requirement of the present invention will be described in detail.

(A) Temperature of Wire to be Rolled Before and After Finish Rolling If the temperature of the wire to be rolled before finish rolling is less than 700 ° C.,
The load on the rolling mill increases and cracks may occur during rolling. In addition, a hard low-temperature transformation product (supercooled structure) such as martensite or bainite may be formed on the surface layer of the rolled wire. On the other hand, when the above temperature exceeds 1000 ° C., the crystal grains during or after finish rolling are coarsened to increase the quenchability, and after cooling, a hard phase such as bainite may be formed. The scale formed during the subsequent cooling becomes thicker, complicating the process of scale removal. Therefore, the temperature of the wire to be rolled before the finish rolling is set to 7
The temperature was set to 00 to 1000 ° C.

The temperature of the wire to be rolled immediately after the finish rolling is 11
When the temperature exceeds 00 ° C., the crystal grains become coarse and the hardenability increases, and a hard phase such as bainite may be formed after cooling. Further, the scale generated during cooling after rolling becomes thicker, and the process of removing the scale becomes complicated. Therefore, the temperature of the wire rod immediately after rolling was set to 1100 ° C. or less. The lower limit of the temperature immediately after this finish rolling is 70
The temperature is preferably set to 0 ° C. A more preferred lower limit of the temperature is 750 ° C.

The temperature before finish rolling is 700 to 10
In order to finish-roll a wire to be rolled at 00 ° C. and reduce the temperature immediately after rolling to 1100 ° C. or lower, for example, adjust the rolling reduction in rough rolling and intermediate rolling, and reduce the rolling reduction in finish rolling to finish. The rolling pass schedule may be such that the heat generated during the rolling process is kept low. Further, simultaneously with the finish rolling, the surface of the wire to be rolled may be cooled by heat removal by roll contact, cooling by roll cooling water, water cooling, or the like.

(B) Temperature distribution in the longitudinal direction of the wire before winding When the wire to be rolled is finish-rolled by an ordinary method, the temperature of the wire at the time of winding by the laying head is substantially the same in the longitudinal direction. When such a wire is spread in a ring shape on a conveyor with a laying head, the cooling rate at the leading and trailing ends of the wire increases, so that the slow cooling start temperature is not constant in the longitudinal direction of the wire. For this reason, it is difficult to uniformly soften the wire from the head to the tail.

Therefore, in order to reduce the cooling rate of the leading and trailing portions of the wound wire so that the slow cooling start temperature is constant in the longitudinal direction of the wire, after the finish rolling, the leading and trailing portions of the wire are finished. Adjust so that the tail is hot at 50 ° C or higher,
A temperature distribution is provided in the longitudinal direction of the wire.

As described above, in the present invention, the leading portion of the wire as a so-called "unsteady portion" is a portion having a weight ratio of at least 4% from the foremost position of the wire, and the trailing portion is a portion of the wire which is at least 4%. Since it refers to a portion of at least 4% by weight from the rear end position, it is sufficient to raise the temperature of the head portion and the tail portion by about 50 to 300 ° C.

By taking at least 5% by weight of the leading and trailing ends of the wire from the leading and trailing ends of the wire, the wire can be directly softened more uniformly. is there. Furthermore, if the leading and trailing portions of the wire are taken to be at least 10% by weight from the leading edge of the wire and the end of the wire, respectively, the wire can be directly softened more uniformly.

As long as the slow cooling start temperature is substantially constant in the longitudinal direction of the wire, a uniform structure can be obtained after the softening treatment irrespective of the method of giving a temperature distribution in the longitudinal direction of the wire. It becomes possible to soften uniformly. Therefore, in order to impart the above temperature distribution in the longitudinal direction of the wire before winding, for example, by inclining the furnace temperature of the heating furnace at the time of wire rolling, it corresponds to the leading and trailing portions after wire rolling. Method of heating the material part to high temperature, keeping the temperature of the head part and tail part high by cooling control at the time of wire rod rolling, reheating the head part and tail part after finish rolling and keeping the temperature at high temperature, etc. May be performed alone or in combination.

(C) Ring density of wire rod spread on conveyer After finishing rolling by a so-called "loading type", it is spread on a conveyer by a laying head in a ring shape (wound).
The ring density of the wire is usually 100 wires / m or less. Moreover, the wires spread on the conveyor are densely overlapped at the end on the conveyor side, but are sparsely overlapped at the center of the conveyor. For this reason, the cooling rate differs depending on the portion, and uniform softening cannot be performed, and the scale properties are also non-uniform.

If the ring density of the wire exceeds 500 strands / m, the scale properties become non-uniform, making descaling difficult. On the other hand, the ring density of the wire is 150 wires / m.
If the temperature is lower than the above range, uniform softening may not be performed due to a difference in cooling rate between the above-described portions. Therefore, the ring density of the wire was set to 150 to 500 wires / m. In this case, by satisfying the cooling condition after winding described in the following (D), the wire from the head to the tail can be softened uniformly.

As described above, the ring density of the wire rod that is developed (taken up) in a ring shape on the conveyor by the laying head after the finish rolling is, as described above, “in the moving direction of the conveyor through the center of the ring. Number of rings that traverse a parallel 1-meter long line ". Therefore, this ring density is uniquely determined by the finish rolling speed and the conveyor speed, and is 1 / ｛(conveyor speed / finishing rolling speed) × π ×
(Ring diameter)｝

Since the ring diameter is determined for each wire rolling equipment, the ring density of the wire rod of 150 to 500 wires / m can be easily adjusted by adjusting the conveyor speed and the finish rolling speed. it can.

(D) Wire Rolled on Conveyor In order to uniformly soften the wire from the head to the tail by the so-called "direct softening treatment", the wire is spread on the conveyor at the ring density described in (C) above. First, 550-
It is necessary to cool down to a temperature T1 in a temperature range of 850 ° C. When T1 is a temperature of less than 550 ° C., when left to cool,
A hard structure such as bainite is generated in the surface layer, and desired softening cannot be performed. On the other hand, when the cooling end temperature T1 is higher than 850 ° C., the temperature is then 0.05 to 2 ° C. to soften.
Temperature T2 in the temperature range of 500 to 640 ° C. at a cooling rate of
Since it takes a long time to cool down, the productivity is lowered.

In order to uniformly soften the wire from the head to the tail by the "direct softening treatment", the above-mentioned 550 to 8
The ring-shaped wire rod cooled to a temperature T1 in a temperature range of 50 ° C. is further cooled at a cooling rate of 0.05 to 2 ° C./sec.
It is necessary to cool to a temperature T2 in a temperature range of 00 to 640 ° C. Note that T2 is a temperature lower than the above T1.

When the cooling rate exceeds 2 ° C./sec, C
In the case of a highly hardenable alloy steel containing a large amount of r, Mo, Ni, Mn, or the like, a hard structure such as bainite may be formed and uniform softening may not be performed. On the other hand, when the cooling rate is 0.0
When the temperature is lower than 5 ° C./second, a long-time treatment is required, and the productivity is lowered. For this reason, 500-640 ° C
The cooling rate for cooling to the temperature T2 in the temperature range of 0.05 to
2 ° C./sec. In order to further enhance the productivity, the above cooling rate is preferably set to 0.1 to 2 ° C./sec.

The temperature T2 for cooling at the above cooling rate is 64
When the temperature exceeds 0 ° C., particularly in the case of a highly hardenable alloy steel containing a large amount of Cr, Mo, Ni, Mn, etc., austenite remains untransformed and transforms to bainite by subsequent cooling. In addition, a uniform soft structure cannot be obtained over the entire length of the wire rod, and the mechanical properties vary greatly, which may cause problems such as disconnection or cracking during the subsequent second or third working. On the other hand, when the temperature T2 is lower than 500 ° C., a long-time treatment is required, and the productivity is reduced.

The ring-shaped wire rod cooled to a temperature T1 in a temperature range of 550 to 850 ° C.
In order to cool to a temperature T2 in a temperature range of 500 to 640 ° C. at a cooling rate of 2 ° C./sec, as a temperature compensation, for example,
A method of installing a heat insulating cover on a conveyor, blowing hot or hot air, heating, and the like may be used alone or in combination.

It is preferable that the wire to be subjected to the direct softening method of the present invention has a diameter of 20 mm or less.

Now, the present invention will be described in further detail with reference to Examples.

[0045]

EXAMPLES Steels A to C having the chemical compositions shown in Table 1 were continuously cast and slab-rolled by ordinary methods to produce 1-ton billets. In addition, steel A in Table 1 is SCM435 equivalent steel,
Steel B is S45C equivalent steel, and steel C is SCr430 equivalent steel. This billet was rolled and cooled under the conditions shown in Table 2 to obtain a wire having a diameter of 10 mm. It should be noted that the rolling reduction in the rough rolling and the intermediate rolling was adjusted so that the heat generated during the finishing rolling did not exceed 1100 ° C. immediately after the finish rolling. The cooling control was performed. After allowing to cool to the temperature T1, the heat insulating cover was placed on the conveyor and cooled to the temperature T2. Therefore, the temperatures T1 and T2 described in Table 2 are “temperature at the heat retaining cover entrance” and “temperature at the heat retaining cover exit”, respectively.

50k from the tip of the wire thus obtained
g ("head"), center 50kg and rear 50k
g ("rear tail"), a test piece was sampled and subjected to a tensile test to investigate the tensile strength. In addition, a scale property survey was conducted as the surface property at the “leading portion”, “center portion”, and “tail portion” of the wire. The scale properties were evaluated based on the scale thickness. Table 3 shows the test results.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

[Table 3]

From Table 3, it can be seen that if the treatment is carried out under the conditions specified in the present invention, the tensile strength from the leading end to the trailing end of the wire is evenly increased.
It is clear that the material can be softened to 5 kgf / mm ² or less, and the scale can be uniform and the thickness can be reduced.

[0051]

According to the method for directly softening a hot-rolled wire of the present invention, the wire can be softened uniformly as it is while being rolled, and the scale properties can be made uniform. Therefore, softening heat treatment such as annealing or spheroidization is not required, and descaling can be easily performed.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenichi Kawazoe 1 Konomi-cho, Kokurakita-ku, Kitakyushu-shi, Fukuoka Sumitomo Metal Industries Co., Ltd. Street address Sumitomo Metal Industries Co., Ltd.

Claims (1)

[Claims] 1. A method for directly softening a wire rod developed in a ring shape after hot rolling, wherein the wire rod having a temperature of 700 to 1000 ° C. is finish-rolled so that the temperature immediately after rolling is reduced to 1100 ° C. or lower. , The temperature distribution in the longitudinal direction of the wire is adjusted so as to be 50 ° C. or more at the head and tail,
Winding with a laying type winder to increase the ring density to 150 to 5
Developed on a conveyor at a rate of 00 pieces / m, 550-850
After cooling to a temperature T1 in the temperature range of
A method for directly softening a hot-rolled wire, comprising cooling to a temperature T2 in a temperature range of 500 to 640 ° C. at a cooling rate of ２2 ° C./sec, and then allowing it to cool. However, T1> T2.