JPH08300003A - Hot rolling method - Google Patents

Abstract

PURPOSE: To provide a hot rolling method for preventing surface roughening of a work roll and for reducing defects in the surface quality of a rolled product caused by the fitting in of rolling mill scales. CONSTITUTION: Cooling spray devices 5 which consist of a header 5a and a nozzle 5b are arranged on the biting side of a material 3 to be rolled at the respective rolling mills 1a, 1b, 1c of a rolling mill group 1 on the front stage side on the heavy load side in a continuous hot rolling mill. Just before the material 3 to be rolled is bitten and rolled with the work rolls 4, 4, when cooling water of a volume determined based on the temp. on the outlet side of the material 3 to be rolled on the outlet side of the rolling mill 1c of the last stage of the rolling mill group 1 on the front stage side is jetted, temp. rising in the outer layer part of the respective work rolls 4, 4 of the rolling mills 1a, 1b, 1c on the heavy load side is suppressed and the amount of the mill scales which are peeled off from the surface of these work rolls 4, 4 are reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a hot rolling method, and more specifically, it can effectively prevent roughening of work rolls when rolling a material to be rolled by a continuous hot rolling mill. Hot rolling method.

[0002]

2. Description of the Related Art As is well known, a continuous hot rolling mill is a series of rolling mills consisting of a plurality of rolling mills arranged in series, and a series of rolling mills arranged downstream of the rolling mill group. The rear-stage rolling mill group includes a plurality of rolling mills arranged in an array. The material to be rolled is gradually thinned as it moves to the downstream side, and is finally rolled by the final rolling mill of the post-rolling mill group to a target plate thickness to be a hot rolled product.

In such a group of continuous-stage hot rolling mills on the upstream side, since the work rolls come into contact with the hot-rolled material, an oxide film called black scale is formed on the surface of the work rolls. This black skin not only prevents metal-to-metal contact between the material to be rolled and the base material of the work roll, but also smoothes the surface of the material to be rolled on the exit side of the work roll. In, since the material to be rolled is rolled under high load, the black scale is partially peeled from the surface of the work roll due to the continuous rolling of the material to be rolled, and crater-like rough skin is generated on the surface of the work roll. There is.

[0004] A convex projection is formed on the surface of the material to be rolled which is rolled by the work roll having the roughened surface, and it is flattened by being rolled by the rolling mill in the next rolling step. However, at that time, since the secondary scale generated on the protruding portion on the surface of the material to be rolled is bitten into the material to be rolled, a surface quality defect called biting scale flaw occurs in the hot rolled product. The surface of the work roll is roughened by peeling the black skin from the surface, thermal stress fatigue of the surface layer portion of the work roll due to heating and cooling during rolling, rolling fatigue of the surface of the work roll due to rolling load, It is considered to be caused by a composite action such as shearing force at the interface between the work roll and the material to be rolled.

Therefore, in order to prevent the work roll from being roughened, a method of strongly cooling the work roll to lower the surface temperature of the work roll and a method of reducing the shearing force at the interface of the work roll by lubrication have been tried. There is. Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. 4-200903, immediately before the material to be rolled is caught in the work rolls of the rolling mill, cooling water is sprayed to cool the surface of the material to be rolled and rolled. There is also a way to do it.

[0006]

However, both the method of strongly cooling the work roll to lower the surface temperature of the work roll and the method of reducing the shearing force at the interface of the work roll by lubrication peels the black skin. One of the factors
Since this is only one solution, it is not always possible to reliably prevent the work roll from becoming rough. As a result, the surface quality of the hot-rolled product is deteriorated due to the scale flaw due to the black skin being caught, and the yield of the hot-rolled product (the portion with the scale flaw is discarded before shipment) is improved. In addition to blocking, the work rolls must be replaced, which increases the running cost of the continuous hot rolling mill.

Further, in the method disclosed in Japanese Patent Application Laid-Open No. 4-200303 in which the surface is cooled and the material to be rolled is rolled, for example, when the amount of the refrigerant is too much, the temperature of the material to be rolled further decreases, and the final stage The temperature of the material to be rolled on the exit side of the rolling mill becomes too low, and as a result of the rolling load of the rolling mill on the final stage side becoming excessive, it will induce peeling of the surface layer portion of the work roll of the rolling mill, On the other hand, when the amount of the refrigerant is too small, the effect of suppressing the temperature rise of the work roll by the roll bite is small, so that it is not possible to reliably prevent the work roll from being roughened.

Therefore, an object of the present invention is to provide a hot rolling system capable of surely preventing the roughening of the work rolls of the rolling mills of the series arrangement constituting the continuous hot rolling mill. There is a way to provide.

[0009]

Means for Solving the Problems As a result of intensive studies, the inventors have found that the work rolls of some of the rolling mills of the preceding rolling mill group of the continuous hot rolling mill are roughened. The present invention has solved the above-mentioned problems by finding that the surface quality defects of hot-rolled products can be reduced by only preventing the roughening of the work rolls of these rolling mills.

Therefore, the feature of the means adopted by the hot rolling method according to claim 1 of the present invention is that a group of a plurality of rolling mills arranged in series and a group of preceding rolling mills and this rolling mill When rolling the material to be rolled by a continuous hot rolling mill that is provided on the downstream side of the group and is composed of a rear-stage rolling mill group in which a plurality of rolling mills are arranged in series, the material to be rolled is the former-stage rolling mill. Immediately before being bitten by the work rolls of each rolling mill of the group, the amount of cooling liquid that is determined based on the outgoing temperature of the material to be rolled at the outgoing side of the final rolling mill of the preceding rolling mill group is injected It is in.

Further, the feature of the means adopted by the hot rolling method according to claim 2 is that in the hot rolling method according to claim 1, the material to be rolled is the entry side of the former rolling mill group. The amount of the cooling liquid sprayed on the material to be rolled is gradually reduced as it moves to the outlet side.

[0012]

According to the hot rolling method of the first aspect of the present invention, immediately before the material to be rolled is caught by the work rolls of the rolling mills of the preceding rolling mill group, the final rolling of the preceding rolling mill group is performed. The surface of the material to be rolled is cooled by injecting a specified amount of cooling liquid based on the temperature of the material to be rolled on the outlet side of the multi-stage rolling mill, but the surface of the material to be rolled is cooled. The cooling liquid is injected in an amount such that the temperature of the outgoing side of the material to be rolled on the outgoing side becomes a temperature required for rolling by each rolling mill of the subsequent rolling mill.

According to the hot rolling method of the second aspect of the present invention, as the material to be rolled moves from the inlet side to the outlet side of the preceding rolling mill group, the amount of the cooling liquid injected to the material to be rolled. Is gradually reduced.

[0014]

EXAMPLES A continuous hot rolling mill for realizing the hot rolling method of the present invention will be described below with reference to FIG. 1 which is a schematic explanatory view thereof, and cooling water which is a cooling liquid injected per 1 m ^{2 of a} material to be rolled. as the amount and rough conditions of FIG. 2 (hot rolled product to the longitudinal axis of the relationship diagram of rough conditions of the work rolls, taking visual observation of the work roll surface and injected into the material to be rolled 1 m ² per horizontal axis The amount of cooling water to be used is shown in FIG. The results of visual observation of the surface of the work roll are indicated by points, and the concrete evaluation criteria for the rough surface of the work roll are as described later.

The continuous hot rolling mill, as shown in FIG.
A front-stage rolling mill group 1 in which three rolling mills 1a, 1b, 1c are arranged in series, and four rolling mills 2a, 2b, 2c, 2d provided downstream of the front-stage rolling mill group 1 And a rear-stage rolling mill group 2 which are arranged in series. It should be noted that the former rolling mill group 1 and the latter rolling mill group 2
In each of the rolling mills constituting the above, the pair of upper and lower small diameter rolls rolling on the material to be rolled 3 are work rolls 4, 4, and the large diameter rolls rolling on the outside of these work rolls 4, 4 are Backup rolls 4 ', 4'.

Further, each rolling mill 1 of the preceding rolling mill group 1
a, 1b, and 1c, the header 5a is arranged on the entry side of the rolled material 3 on each of the upper side and the lower side of the rolled material 3 in the direction orthogonal to the moving direction of the rolled material 3. There are provided spraying devices 5 and 5 which are arranged at a predetermined interval in the longitudinal direction of the header 5a and include nozzles 5b which spray cooling water on the surface of the material 3 to be rolled. In addition, what is indicated by reference numeral 6 on the leftmost side is a scale breaker.

As is well known, the work rolls 4, 4 of the rolling mills 1a, 1b, 1c constituting the preceding rolling mill group 1 roll the material 3 to be rolled under a high load, so that high chromium is used. Rolling mills 2a, 2b, 2c, 2 which are made of steel or high-speed tool steel, etc., and which constitute the rear-stage rolling mill group 2
The work rolls 4 and 4 of d are made of nickel grain or high speed tool steel.

It is possible to prevent the work rolls 4, 4 of each rolling mill of the preceding rolling mill group 1 from being roughened, and is necessary for finish rolling of the material 3 to be rolled by each rolling mill of the succeeding rolling mill group 2. In order to grasp the amount of cooling water that can ensure a sufficient outlet temperature, first, the rolling mill 1c at the final stage of the upstream rolling mill group 1
By changing the amount of cooling water sprayed from the spraying devices 5, 5 on the inlet side of the rolled material 3 to the rolled material 3 (per 1 m ² ), the amount of cooling water and the rough surface condition of the work rolls 4, 4 can be changed. Was investigated and the results shown in FIG. 2 were obtained. That is,
According to FIG. 2, as the amount of cooling water sprayed on the material to be rolled 3 (per 1 m ² ) decreases, the work rolls 4, 4
The rough skin condition of No. 4 gradually deteriorates, and when the amount is less than 100 l / min, the rough skin condition of the work rolls 4 and 4 tends to deteriorate sharply.

In other words, this means that 100
This suggests that the surface roughness of the work rolls 4 and 4 can be reduced and the surface quality defects of the hot-rolled product can be reduced by cooling by spraying cooling water in an amount of 1 / min or more. The rough surface condition of the work rolls 5 and 5 is visually observed. After rolling under all conditions for a certain period, the work rolls 4 and 4 are pulled out to display the rough surface condition of the work rolls, and an average value of these points is calculated. It was determined by The rough skin condition has a score of 10 to 50, where 50 is a state where the work rolls 4, 4 are entirely covered with black skin, and 10 is black over almost the entire work rolls 4, 4. The skin is peeled off.

Then, by injecting cooling water to the rolled material 3 from the spraying devices 5, 5 on the inlet side of the rolled material 3 of all the rolling mills 1a, 1b, 1c of the preceding rolling mill group 1,
The rough skin condition of the work rolls 4 and 4 could be significantly improved. In this case, it is preferable to reduce the amount of the cooling water injected from the spray devices 5 and 5 as the material to be rolled 3 moves from the front stage side to the rear stage side of the front stage rolling mill group 1. That is, since the rolled material 3 becomes thinner and the heat capacity per unit area becomes smaller toward the subsequent stage, even if the amount of the cooling water injected is small, the temperature of the rolled material 3 becomes equal. This is because it becomes possible to roll while maintaining it.

Further, the material 3 to be rolled rolled by the former rolling mill group 1 is processed by the rolling mills 2a, 2a of the latter rolling mill group 2, respectively.
Further rolled by 2b, 2c, 2d to obtain hot rolled products. By the way, the exit temperature of the material 3 to be rolled when it comes out of the final rolling mill of the continuous rolling mill has a great influence on the material of the material 3 to be rolled, and therefore it is necessary to set it to a predetermined target temperature. If the amount of cooling water is too large, the temperature becomes lower than the target temperature, so it is necessary to set the upper limit of the amount of cooling water. Incidentally, Table 1 shows an example of the amount of the cooling water sprayed from the spray devices 5, 5, and 5.

[0022]

[Table 1]

According to the rolling test result of the rolled material 3, the maximum amount of cooling water is 30 mm × 1259 mm, and when the rolled material 3 is rolled to produce a hot rolled product having a plate thickness of 1.2 mm, It is 640 l / min per 1 m ² . However, the amount of cooling water sprayed from the spray device is 100 to 1000 l / min according to the outlet temperature and strip thickness of the material 3 to be rolled on the outlet side of the last stage rolling mill 1c of the preceding stage rolling mill group 1. It will be changed in the range of. The exit temperature of the material 3 to be rolled was measured by a radiation thermometer.

When the material 3 to be rolled was rolled by injecting the cooling water in the amount as described above, the surface quality of the hot rolled product was deteriorated due to the black skin being caught due to the roughening of the work rolls 4 and 4. The rate can be reduced from the conventional 0.3% to 0.1% or less, which can greatly contribute to the improvement of the yield of hot rolled products. Furthermore, work rolls 4, 4
Since the replacement time interval of is also longer than that of the conventional one, the running cost of the continuous hot rolling mill can be reduced, and at the same time, the continuous hot rolling mill based on the reduction of the replacement work time of the work rolls 4, 4 can be achieved. As a result of the improvement in the operating rate of, the productivity of hot rolled products can be significantly improved.

Next, a hot rolling method according to another embodiment of the present invention will be described. Although not shown in the drawings, the hot rolling method is applied to the bite side of the material to be rolled of the frontmost rolling mill of the rear rolling mill group. A spray device having the same configuration as the spray device provided on the bite side of the material to be rolled of each rolling mill constituting the preceding rolling mill group was provided. Then, in order to manufacture a hot rolled product having a plate thickness of 2.5 mm by rolling the material 3 to be rolled of 30 mm x 1259 mm, a spray provided on the biting side of the frontmost rolling mill of the front rolling mill group. From device to 960 l / m per 1 m ^{2 of} rolled material
Injecting cooling water at a maximum of 240 l / min per 1 m ^{2 of} rolled material from the spray device on the bite side of the rolled material of the frontmost rolling mill of the latter rolling mill group. It has been sprayed on. As a result, the occurrence rate of the surface quality defect of the hot rolled product due to the biting of the black skin caused by the rough surface of the work roll was 0.
It could be reduced to 1% or less. Specific examples of the amount of cooling water sprayed from each spray device are as shown in Table 2.

[0026]

[Table 2]

In the above, when rolling the material to be rolled by the continuous hot rolling mill, immediately before the material to be rolled 3 is caught in the work rolls of the rolling mill, the cooling water is jetted and the material to be rolled 3 is rolled. Although the case where the temperature is decreased has been described as an example, the material 3 to be rolled may be cooled by laminar cooling or mist cooling.

[0028]

As described above, according to the hot rolling method of the first or second aspect of the present invention, the work roll is caught at the entrance side of the rolling mill for rolling the material to be rolled under high load. The material to be rolled immediately before being cooled is cooled with a cooling liquid. Therefore, the temperature rise of the surface layer part of the work roll is suppressed, and the thermal stress fatigue due to the temperature rise of the surface layer part is reduced, so that the rough surface of the work roll is prevented, and as a result, the hot rolled product due to the biting of the black leather There is a great effect that the surface quality defect of 1) is reduced, and it can contribute to the improvement of the yield of the hot rolled product and the reduction of the running cost of the continuous hot rolling mill.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a continuous hot rolling mill that realizes the hot rolling method of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between an amount of cooling water sprayed per 1 m ^{2 of a} material to be rolled and a rough surface condition of a work roll.

[Explanation of symbols]

 1 ... Front rolling mill group, 1a, 1b, 1c ... Rolling mill 2 ... Rear rolling mill group, 2a, 2b, 2c, 2d ... Rolling mill 3 ... Rolled material 4 ... Work roll, 4 '... Backup roll 5 ... Spray device, 5a ... Header, 5b ... Nozzle 6 ... Scale breaker

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Ishimaru 1 Kanazawa-machi, Kakogawa-shi, Hyogo Kamido Steel Works Co., Ltd. Kakogawa Works

Claims (2)

[Claims] 1. A front-stage rolling mill group in which a plurality of rolling mills are arranged in series, and a rear-stage rolling mill group provided downstream of the front-stage rolling mill group and in which a plurality of rolling mills are arranged in series. When rolling the material to be rolled by the continuous hot rolling mill consisting of, immediately before the material to be rolled is bitten by the work rolls of the rolling mills of the preceding rolling mill group, the final rolling of the preceding rolling mill group is performed. A hot rolling method characterized by injecting a cooling liquid in an amount determined based on an outlet temperature of a material to be rolled on an outlet side of a multi-stage rolling mill. 2. The amount of cooling liquid injected to the material to be rolled is gradually reduced as the material to be rolled moves from the inlet side to the outlet side of the preceding rolling mill group. Hot rolling method.