JP2002028702A - Method for rolling bar and wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for rolling a bar and wire for obtaining the bar and wire having a fine grain size by efficiently cooling the center temperature of the bar and wire at hot rolling. SOLUTION: In the method for rolling the bar and wire for hot-rolling with a rolling train in which rolling stands, F1, F3, F5, F7 for forming an oval cross section and rolling stands F2, F4, F6, F8 for forming a round cross section are alternately arranged and which consists of an even number of the rolling stands as the whole, the bar and wire are cooled at least at points D1, D2, D3, D4 of time when the bar and wire are induced from the rolling stands F1, F3, F5, F7 for forming the oval cross section and, in particular, the cross section of the bar and wire at cooling is an oval cross section having an aspect ratio of 1 < the major axis/the minor axis < 2.5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling method for a rod and a wire, and more particularly, to a method for efficiently lowering the center temperature of a hot rolled rod and a wire. The present invention relates to a method for rolling a rod or wire capable of suppressing growth.

[0002]

2. Description of the Related Art A rolling train for hot-rolling a steel slab extracted from a heating furnace into a rod having a round cross-section having a predetermined diameter usually has an even number of rolling stands arranged in series at equal intervals. Line. Then, the steel slab bitten by the first rolling stand is sequentially moved to the downstream rolling stand, and is continuously rolled at each rolling stand.

[0003] As such a rolling train, there is a rolling train in which rolling stands composed of roll holes for forming an oval cross section and rolling stands composed of roll holes for forming a round cross section are alternately arranged. Such a rolling train with eight rolling stands is shown in FIG. In this rolling row, rolling stands F ₁ , F ₃ , F ₅ , F ₇ for forming oval sections and rolling stands F ₂ , F ₄ , F ₆ , F ₈ for forming round sections are alternately arranged at equal intervals. Line. Then, the rod wire introduced into the roll stand F _1, in the process of flowing through each rolling stand, oval cross-section in the rolling stand F ₁ → rolling stand F ₂
In a round cross-section → sequentially rolled to oval cross-section with a round cross-section → rolling stand F ₇ with oval section → rolling stand F ₄ with a round cross-section → rolling stand F ₅ rolling stand F ₃ in oval section → rolling stands F _6, finally It is formed into a round cross-section of the desired diameter roll stand F _8.

[0004] The temperature of the rod or wire passing through the rolling train rises due to the heat generated during the rolling by each rolling stand. And this temperature rise promotes the coarsening of the austenite grain size in the rolled bar and wire, so that the obtained bar and wire has high hardness and its workability is greatly reduced. for that reason,
Although measures have been taken to cool the rod or rod after rolling, conventionally, a line C ₁ between the round section forming stand F ₂ and the oval section forming stand F ₃ , a round section forming stand F ₄ and the oval section forming stand F between ₅ line C _2, and a total of three places in the line of a round cross-section forming stand F ₆ and oval cross-section forming stand F between ₇ line C ₃ by providing the water-cooled zone, the round cross-sectional form Stand F ₂ ,
The rod or wire that is derived from F ₄ and F ₆ and generates heat is cooled.

Conventionally, the reason why the rods are cooled in the lines C ₁ , C ₂ , and C _{3 is} that the rods to be cooled have a round cross section, so that the rods are moved from the surface layer to the center. This was because it was considered that the cooling could be performed uniformly.

[0006]

However, in order to increase the productivity of the rods, the rolling speed of the rods in the rolling train may be at most 70 m / sec. And
If the distance between the rolling stands is too long, the rolling yard becomes large, so that the distance may be relatively short, several tens of cm. That is, the lines C ₁ , C ₂ , and C ₃ , which are the water cooling zones, may be set to have a length of about several tens of cm.

In such a case, the rod wire passes through these lines in less than 0.1 second, so that the cooling time for the rod wire becomes very short. Therefore, although the surface portion of the rod is cooled, the central portion is hardly cooled, and the temperature of the central portion hardly decreases. When such a situation occurs, the temperature rise in the central part of the rod becomes remarkable, and the structure and crystal grain size in the central part and the surface part of the rod differ, so that their dispersion is large in the radial direction of the rod. Problem occurs.

In order to suppress the occurrence of such a problem, it is considered effective to lower the center temperature by strongly cooling the rod or wire rod. The temperature has dropped too much,
When rolling is performed on the next rolling stand for forming an oval section, a crack may occur in the rod or wire due to a decrease in deformability.

The present invention relates to a rolling train provided with a water-cooling zone at lines C ₁ , C ₂ and C ₃ immediately after the rolling stand for forming a round section and immediately before the rolling stand for forming an oval section. To solve the above-mentioned problem in hot rolling using a steel wire, without causing an excessive temperature difference between the central portion and the surface layer portion of the rod and wire, and efficiently lowering the temperature at the central portion, thereby comparing with the conventional case. It is another object of the present invention to provide a method of rolling a rod and a wire having a fine crystal grain size and a small variation, so that a high-quality rod can be manufactured.

[0010]

In order to achieve the above-mentioned object, in the present invention, rolling stands for forming an oval section are alternately arranged with rolling stands for forming a round section, and an even number of rolling stands are formed as a whole. In a method of hot rolling a bar and a wire in a rolling train comprising a rolling stand,
At the time when the bar wire is drawn out from at least the rolling stand for forming the oval cross section, a method of rolling the bar wire characterized by cooling the bar wire, particularly, the cross section of the bar wire at the time of cooling is 1 Provided is a method for rolling a rod or wire having an oval cross-section having an aspect ratio of <major axis / minor axis <2.5.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is characterized in that a rod or wire drawn from a rolling stand for forming an oval cross section, that is, a rod having an oval cross section is cooled. Hereinafter, the configuration and effects of the present invention will be described in detail for the case of the rolling train shown in FIG. 1 in which eight rolling stands are arranged at equal intervals.

(1) First, in carrying out the present invention, a line D ₁ between a rolling stand F ₁ for forming an oval section and a rolling stand F ₂ for forming a round section, and a rolling stand F for forming an oval section. ₃ and line D ₂ between the rolling stands F ₄ for a round cross-section form, oval cross rolling for forming stand F ₅ and line D ₃ between the rolling stands F ₆ for a round cross-section form, and for oval cross-section formed total line D ₄ between the rolling stand F ₇ and the rolling stand F ₈ for a round cross-section form 4
Water cooling zones are arranged in each of the lines.

On the other hand, in the conventional rolling train, water cooling zones are arranged at a total of three places of the line C ₁ to the line C ₃ to cool the rod-shaped rod having a round cross section. Therefore, in the rolling of the present invention, the number of water cooling zones arranged is always one more than in the case of the conventional rolling, so that the number of times of cooling the rod or wire is increased by one. Therefore, in the rolling of the present invention, the temperature at the center of the rod or wire is lower than that in the conventional rolling.

[0014] (2), the rolling stand is arranged on all regular intervals, for example, transit time of the line D ₁ of the rod wire is longer than the transit time of the line C _1. this is,
Relationship between the line D ₂ and the line C _2, line D ₃ and the line C ₃
The same applies to the relationship. The reason is that the rolling speed of the rod or wire derived from the rolling stands F ₁ (F ₃ , F ₅ , F ₇ ) for forming the oval section is reduced by the rolling stands F ₂ (F ₄ , F ₆ ) for forming the round section. This is because the rolling speed is always lower than the rolling speed of the rod or wire derived from the above.

Therefore, in the rolling of the present invention, the cooling time is longer than that in the conventional rolling, and as a result, the central portion of the rod or wire is more effectively cooled. (3) Considering a rod wire having an oval cross-sectional shape and a rod wire having a round cross-sectional shape having the same cross-sectional area, in the case of the former rod wire,
Since its short axis is always smaller than the diameter of the latter, the distance to the surface layer is short. And the former rod and wire is
The surface area is larger than that of the latter.

Therefore, comparing the two cooling modes, in the case of the rod wire having the oval cross-sectional shape, the cooling to the center thereof proceeds more quickly than in the case of the rod wire having the round cross-sectional shape. That is, in the case of a rod wire having an oval cross section,
The temperature at the center will be reduced efficiently. As described above, cooling a rod having an oval cross-sectional shape is useful in that the center temperature thereof can be efficiently reduced. However, in this case, the aspect ratio (hereinafter A) represented by the ratio of the major axis to the minor axis (major axis / minor axis) in the oval section is within the range of 1 <A <2.5. Is preferred.

When A is 2.5 or more, not only does the cooling effect on the center of the rod or wire begin to show a tendency to saturate, but also supercooling occurs at both ends in the longitudinal direction, so that the next rolling stand ( This is because cracks and the like are likely to occur at the rolling stand for forming a round section. Further, as a practical problem, it is difficult to perform rolling when A is 2.5 or more, and it is difficult to bite into the next rolling stand.

As described above, according to the rolling of the present invention, it is possible to cool the center portion of the rod or wire more efficiently than before. Therefore, the rod or wire obtained by the rolling of the present invention has a fine crystal grain size and a small variation in the radial direction, and is soft and easily workable.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Relationship between cross-sectional shape of rod and rod and cooling effect Steel type is JIS SCM435 and cross-sectional area is 143mm
² was prepared. Assuming that hot rolling and cooling in the following manner were performed on the bar and wire, the temperature distribution in the cross section in that case was simulated.

In the simulation, the center temperature of the rod and wire immediately after rolling was set to 933 ° C., and the temperature of the surface layer was set to 721 ° C. Aspect 1: An aspect in which the rod or wire is cooled through a water cooling zone for 0.16 seconds immediately after being hot-rolled by a rolling stand for forming an oval cross section at a reduction of area of 16%. Aspect 2: An aspect in which the rod or wire is cooled through a water-cooling zone for 0.08 seconds immediately after being hot-rolled with a reduction ratio of 16% by a rolling stand for forming a round section.

FIG. 2 shows the results of the simulation. In FIG. 2,-●-marks indicate the case of an oval cross section,
○ -marks indicate round sections. Here, x on the horizontal axis
The value represents the distance from the center of the rod to the center of the cross-sectional portion located on the surface layer side, and the d value represents the overall distance d (constant) from the center of the rod to the surface. Therefore, the x / d value is an index indicating the relative position in the cross section of the rod. For example, x / d = 0 represents the center of the rod, and x / d = 1 represents the surface of the rod.
Note that the x value in the case of the oval cross section is a value in the short axis direction.

As is apparent from FIG.
All show the same tendency in the temperature distribution in the cross section from the central part (point x / d = 0) to the surface layer part (point x / d = 1). However, in the case of the first embodiment, which is a conventional example, the center temperature hardly decreases even after cooling. On the contrary, in the case of the embodiment 1 which is an example of the present invention, the center temperature is lowered by about 35 ° C. due to the cooling, and the temperature of the surface portion is also lower than that of the embodiment 2.

As described above, it can be seen that cooling to the rod or wire drawn out from the rolling stand for forming the oval cross section is effective in that the temperature at the center is efficiently reduced. 2. In the rolling train the D ₄ line shown aspect ratio oval cross section and in relation Figure 1 and the cooling effect, changing the aspect ratio of the oval cross section of the rod wire is rolled at rolling stand F ₇ a (long axis / short axis) , then passed through a water cooling zone of 0.06 seconds to simulate the temperature of the center portion and surface layer portion in the immediately preceding roll stand F _8. The result is shown in FIG.

As is apparent from FIG. 3, the temperature drop at the center of the rod material increases as the aspect ratio increases. However, when the aspect ratio becomes 2.5 or more, the temperature at the center does not change much, and the state of temperature decrease starts to show a saturation tendency. Also, the temperature drop of the surface layer shows the same tendency as the case of the center part. For example, when the aspect ratio is 3.0, the temperature of the surface layer becomes 45%.
It is 7 ° C., and there is a concern that cracking or the like may occur if the roll is stuck in the rolling stand F ₈ in this state.

In addition, when the aspect ratio becomes 2.5 or more, it becomes difficult to bite into the rolling stand F ₆ as a practical problem. Therefore, considering the efficient cooling of the center and the safety of rolling, the aspect ratio A of the oval cross section is set to 1 <A <2.
It is preferable to set it within the range of 5.

3. In the rolling train shown in actual machine test Figure 1, a rolling train of the present invention of arranging the water-cooled zone in four positions of the D ₁ line to D ₄ line, C ₁
It was designed a conventional rolling column of arranging the water-cooling zone in three locations of line ~C ₃ line. In each of the lines, the length of the water-cooled zone of the rod or wire was 500 mm. Then, both, by setting the surface temperature of the rod wire is introduced into the roll stand F ₁ to 747 ° C. assumes when performing hot rolling of the rolling stand at that time before and bars material immediately after The temperature of the central part and the surface part was simulated.

FIG. 4 shows the result. In the figure,-●-mark and-■-mark respectively show the simulation results of the temperature at the center and the temperature at the surface layer by the rolling train adopting the method of the present invention. The simulation results of the temperature of the central part and the temperature of the surface part by the conventional rolling train are shown. In any of the rolling train, after the rolling stand F _4, and then measuring the surface temperature of the bar wire immediately after the rolling stands F _8, the value, if the rolling train adopting the method of the present invention - ◆ -, And the conventional rolling train is indicated by-◇-. In any rolling train, by actually measuring the surface temperature of the bar wire in the immediately preceding roll stand F _1, the value - shown as a sign - ◇.

The following is clear from FIG. (1) are in good agreement and the actual measurement value and simulation results of surface temperature immediately after rolling stands F ₄ with rolling stands F _8. This is a result of verifying the validity of the simulation used in the examples. (2) The rolling train adopting the method of the present invention and the conventional rolling train are:
Both with the progress of rolling, although the center temperature of the rod wire material rises, at the time derived from the final roll stand F _8, when the rolling train adopting the present method, conventional rolling train The center temperature of the rod and wire is about 18
It is possible to lower the temperature by about 0 ° C. This is the same for the temperature of the surface layer.

Therefore, the steel type is JIS SCM435, J
The IS SUS304 rod or wire is hot-rolled in a rolling row employing the method of the present invention and a conventional rolling row, and a rolling stand F ₈
After the rear end of the rolled material from which was extracted was cut with a flying shear, it was immediately cooled with water and the austenite grain size near the center was measured. As a result, in the case of the rolling train adopting the method of the present invention, the grain size is about 12 μm (in the case of SCM435), 2
It was about 9 μm (for SUS304). But,
In the case of the conventional rolling train, each is about 38 μm (SCM4
35) and about 68 μm (for SUS304).

Further, the rolled rod or wire was wound at a temperature of 750 ° C., then cooled to a temperature of 640 ° C. at a cooling rate of 0.4 ° C./sec, and Vickers hardness (Hv) was measured. In the case of a rolling train employing the method of the present invention, the Hv value is 223,
In the case of the conventional rolling train, it was Hv324.

[0031]

As is apparent from the above description, when the rod or wire is hot-rolled by the method of the present invention, it is possible to efficiently suppress an increase in the temperature of the central portion due to the heat generated during processing. as a result,
The crystal grain size of the obtained rod wire is fine and the dispersion is small, and the rod wire becomes soft. In addition, when a steel wire rod that undergoes phase transformation is hot-rolled by the method of the present invention, the austenite grain size of the obtained rod wire becomes fine, so that phase transformation is promoted in the subsequent cooling process, and as a result, wire drawing is performed. It becomes a rod wire that can be drawn without performing the previous heat softening treatment.

[Brief description of the drawings]

FIG. 1 is a rolling line diagram showing a rolling train in which oval section rolling and round section rolling are alternately performed.

FIG. 2 is a graph showing a simulation result of a relationship between a cross-sectional position and a temperature there.

[FIG. 3] Aspect ratio of oval section and rolling stand F
₈ is a graph showing the relationship with the temperature of the rod material immediately before ₈ .

FIG. 4 is a graph showing a simulation result of the temperature of a rod material immediately before and immediately after each rolling stand in a rolling row.

[EXPLANATION OF SYMBOLS] _{F 1, F 3, F 5} , F 7 rolling stand F ₂ for oval cross-section _{forming, F 4, F 6, F} 8 rolling stands C ₁ for round cross-section forming, C _2, C ₃ conventional arrangement line of the water-cooled zone in the rolling sequence employing the arrangement line _{D 1, D 2, D 3} , D 4 present invention a method of water cooling zones in the rolling train the

Claims (2)

[Claims] 1. Rolling of a rod or wire in which rolling stands for forming an oval cross section and rolling stands for forming a round cross section are alternately arranged, and the rod or wire is hot-rolled in a rolling row including an even number of rolling stands as a whole. A method of rolling a rod or wire, wherein the rod or wire is cooled at least at a time when the rod or wire is led out of the rolling stand for forming the oval cross section. 2. The cross section of the rod or wire during cooling is 1
2. The method according to claim 1, wherein the oval cross section has an aspect ratio of <major axis / minor axis <2.5.