JP3369021B2 - Steel sheet cooling method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of cooling a steel sheet, and more particularly to a method of cooling a steel sheet with water or a water-soluble medium following hot rolling. And a method for uniformly cooling the temperature distribution. [0002] A steel sheet manufactured by hot rolling is usually forcibly cooled after hot rolling in order to obtain predetermined material properties. Water is often used as a medium for forced cooling. Water is used because of its high cooling capacity and relatively low equipment and operating costs of the cooling device. However, when water is used as the cooling medium, cooling fluctuations due to the boiling heat transfer characteristics of water occur, which leads to variations in materials, poor shape, and increased residual stress. [0003] The reason why the variation in cooling is likely to occur due to the boiling heat transfer characteristics of water is that the boiling heat transfer phenomenon
This is because the change of the heat transfer characteristic is relatively sensitive to the change of the fluid side factor and the change of the heat transfer surface side factor such as roughness. Among them, for the roughness, cooling medium not related to boiling,
For example, when cooling with a molten metal or a molten salt, the heat transfer characteristics are usually hardly affected, but a problem occurs only in the case of boiling heat transfer such as water. Therefore, in cooling a steel sheet in which boiling heat transfer is dominant, such as water or an aqueous medium in which an organic solvent is dissolved in water, factors on the heat transfer surface side such as roughness are adjusted before cooling. Conventionally, several cooling methods have been proposed. For example, in Japanese Unexamined Patent Publication No. 62-54507, before cooling, a steel sheet surface is coated with Rz roughness by 20%.
It has been proposed to provide a roughness having a protrusion height of at least μm. Further, Japanese Patent Application Laid-Open No. 63-149315 proposes a method of cooling the steel sheet after rolling, by adjusting the surface roughness of the steel sheet to 8 μm or more and 15 μm or less in terms of Ra roughness. Further, Japanese Patent Application Laid-Open No. 02-70017 proposes that the surface is provided with a roughness composed of a large number of linear grooves of 25 μm or less in terms of Rz roughness. [0006] All of these conventional proposed methods limit the degree of roughness (level) of the roughness provided to the steel sheet surface. However, the degree of the roughness is still the target value of the effective adjustment of the heat transfer surface side factor before cooling so that it can be inferred that even in the three methods of the conventional proposal, the limited ranges are different from each other. The fact is that is not fixed. The present inventors have studied in detail the conventional techniques including the three examples of the conventional method described above, and attempted a reproduction experiment, but could not obtain the expected results. Therefore, the present inventors, in any of the conventional proposed methods, because the reason for limiting the roughness of the steel sheet surface does not necessarily clearly show a direct relationship with the variation in cooling characteristics,
In the end, he recognized that the problem was that it was not clear what kind of roughness adjustment should be made. The present invention clarifies this problem through experiments and the like, and provides a method of uniformly cooling the temperature distribution in the width direction of the steel sheet when the steel sheet is cooled with water or a water-soluble medium following hot rolling. Is what you do. According to the present invention, the surface of a rolling roll is polished and roughened prior to cooling the steel sheet with water or a water-soluble medium, following hot rolling. In controlling the cooling by transferring the roughness to the steel sheet during hot rolling and adjusting the roughness of the steel sheet, the surface roughness of the rolling roll is expressed by Rz roughness, and the steel sheet is rolled by the rolling roll. The method for cooling a steel sheet is characterized in that the convergence value of the change in the roughness of the rolling roll when rolling is continued is adjusted to the range of the convergence value +5 μm. Hereinafter, the present invention will be described in detail. First, the results of experiments performed by the present inventors before reaching the proposal of the present invention will be described. The experiment was performed in two stages. First
The stage is a reproduction experiment of the effect of the conventional method, and the second stage is
This is an experiment for examining in detail the relationship between roughness, which is a heat transfer surface side factor, and cooling characteristics. The first stage reproduction experiment of the conventional method was conducted in order to clarify the question "whether the degree (level) of the roughness of the steel sheet surface itself has a remarkable effect on the variation in cooling". The experiment was carried out on a rolling mill line at a factory, and a steel plate rolled for a certain period of time after exchanging a roll for which the roughness was adjusted to an experimental level beforehand was replaced offline, and the experiment was repeated. Table 1 shows the main conditions of the experiment, and Table 2 shows the experimental results. The target set value of the roughness of the steel sheet surface is, as a conventional method, proposed in JP-A-62-54507, "Before cooling, the steel sheet surface has a projection height of 20 μm or more in terms of Rz roughness. In order to examine the effect of “giving roughness”, the average roughness Rz within the plate width was 15
μm and 30 μm. In making these settings, the relationship between the adjusted surface roughness of the roll itself and the roughness of the steel sheet surface transferred during rolling was previously examined. The variation in cooling characteristics within the width of the sheet is the maximum temperature deviation (° C) of the surface temperature of the steel sheet immediately after the stop of water cooling.
Was used as an index and compared. [Table 1] [Table 2] As shown in Table 2, according to the experimental results at the factory A, when the average roughness Rz of the steel sheet is 30 μm than that of 15 μm, the maximum temperature deviation in the width of the steel sheet surface temperature is clearly smaller. It seemed to reproduce the effect,
According to the experimental result at the factory B, the average roughness Rz of the steel sheet was 15 μm.
No difference in the maximum temperature deviation in the width of the steel sheet surface temperature was observed between m and 30 μm, and the effect of the conventional method could not be reproduced. Then, when the set value of the roughness Rz of the steel sheet within the sheet width was examined in detail, it was found that the range of the variation was the value shown in Table 2. From these values, the experimental results at Factory A:
The reason why the maximum temperature deviation within the width of the steel sheet surface temperature is smaller when the average roughness Rz of the steel sheet is 30 μm than when it is 15 μm is not because the average roughness Rz is 30 μm but the roughness Rz of the steel sheet at that time. Was questioned because the variation in the sheet width was as small as 6 μm. That is,
The degree (level) of the roughness of the steel plate surface itself is
It is also conceivable that cooling variations would not be significantly affected. Therefore, as a second stage, the result of an experiment for examining in detail the relationship between roughness, which is a factor on the heat transfer surface side, and cooling characteristics will be described. Table 3 shows the experimental conditions, and FIG. 2 shows the experimental results. In FIG. 2, the horizontal axis is the roughness Rz of the steel sheet surface, and the vertical axis is a representative of the cooling characteristics.
The average cooling rate from 870 ° C. to 500 ° C. immediately after cooling is taken. The reason why the average cooling rate is used as a representative of the cooling characteristics is that the temperature deviation at the end of cooling by the steel plate portion can be almost expressed when the cooling conditions such as the cooling time are the same. According to the results of FIG. 2, the surface roughness Rz of the steel sheet was 60 μm.
m, the roughness Rz (μm)
With the increase, the average cooling rate (° C./s) increases almost linearly. That is, the surface roughness Rz of the steel sheet is 60 μm.
When the roughness Rz changes within a certain range within the range of m or less, the corresponding change in the average cooling rate is substantially constant regardless of the degree of the roughness Rz. [Table 3] From the experimental results of the first and second stages, the inventors of the present invention have proposed a method of limiting the degree of roughness (level) of the roughness to be applied to the steel sheet surface, which has been conventionally proposed. The concern of whether or not the uniform cooling of the steel sheet cannot always be achieved led to the proposal of the present invention. In other words, rather than adjusting the roughness of the surface imparted to the steel sheet to a specific level from the above experimental results, a level of roughness that can reduce the range of the variation in roughness is found, and the target is the roughness level. Adjusting the degree was considered to be effective. Based on this idea, after the rolling roll was ground to several roughness levels with a rotating grinding wheel, the range of variation in the roughness transferred to the rolled steel sheet was investigated. From the convergence value of the change in the roughness of the rolling roll when the steel sheet is continuously rolled at
It has been found that, when the roughness of the rolling roll is adjusted by grinding in the range of m, the range of the variation in the roughness transferred to the steel sheet is minimized, and the temperature variation of the steel sheet is also minimized. here,
The convergence value of the change in the roughness of the rolling roll means that when a certain rolling roll is continuously used and the rolling amount is increased, the surface roughness of the rolling roll tends to converge to a certain value. Therefore, it is defined as the value of this converging roughness. FIG. 3 shows an example of the relationship between the roll roughness and the rolling amount when a certain rolling roll is continuously used to increase the rolling amount and the roughness is not adjusted during that time. In FIG.
Rolls showing the history of roll roughness with the curve marked with
Initially, it was ground with a high roughness,
Also, the rolls showing the history of the roll roughness with the curve attached are those that were initially ground and given a lower roughness, but the properties other than the initial roughness, such as the material of the rolls, are the same. Roll. As shown in FIG. 3, even when the initial roughness differs, the roll roughness tends to converge to a certain value as the rolling amount increases. It is considered that this convergence value is determined by the interrelationship between the rolling roll and the material to be rolled, such as mechanical properties at the operating temperature. Usually 100
The convergence value becomes clear when rolling is performed for about 300 tons from the above. Note that this convergence value is sufficiently effective in a single investigation unless there is a significant change in roll material, rolling equipment, rolling conditions, and the like. According to the investigations conducted by the present inventors, the range of the in-plate variation in the roughness of the steel sheet surface after the transfer has been determined.
As shown in FIG. 4, it changes depending on the roughness adjustment value of the rolling roll 3. That is, the range of the in-plate variation in the roughness of the steel sheet surface is such that the roll roughness adjustment value is minimized between the convergence value of the roll roughness and the convergence value +5 μm, and the roughness given to the steel sheet surface described above. Instead of adjusting the roughness to a specific level, the present invention proposes a method of realizing the idea of adjusting the roll roughness with the aim of finding a roughness level that can reduce the range of roughness variation and aiming at it. Reached. Hereinafter, the present invention will be described in detail together with its operation with reference to the drawings. FIG. 1 is a schematic side sectional view of a facility for explaining an embodiment of the method of the present invention. In FIG. 1, 1 is a transport roll, 2 is a steel plate, 3 is a roll, 4 is a roll roll roughness adjusting device,
Is a cooling device. The rolling roll roughness adjusting device 4 is a device capable of online grinding adjustment of the roll surface with a rotating grinding wheel. In FIG. 1, a steel sheet 2 is rolled by a rolling roll 3 while being conveyed by a conveying roll 1. At this time, the surface of the rolling roll 3 is adjusted by a rolling roll roughness adjusting device 4.
The roughness is adjusted in advance. Roller roughness adjusting device 4
The roughness of the polishing grindstone is selected so that it is polished from the convergence value of the roll roughness to the range of the convergence value + 5 μm. The surface roughness of the rolling roll 3 is transferred to the steel plate 2 and changes the surface roughness of the steel plate 2. At this time, the variation in the roughness of the surface of the steel plate 2 has the minimum value as described above. The steel plate 2 with the surface roughness thus formed is carried into the cooling device 5 and cooled with water or a water-soluble medium. At this time, the average cooling rate of each part in the plate on the surface of the steel plate 2 has a different value in the plate according to the roughness of each part. As described in FIG. 2, the relationship between the average cooling rate and the variation in the roughness (range of change) in the range of 60 μm or less, which is the range of the roughness of the steel sheet in practical use, is explained in FIG. Since the roughness is constant irrespective of the degree of roughness, the degree of roughness was adjusted by setting the degree of roughness to a level at which variation in roughness was most easily reduced. Since the variation can be minimized, extremely uniform cooling is performed. Examples of the present invention will be described below. FIG.
Table 4 shows the results of the examples performed using the apparatus shown in Table 4 in comparison with the results obtained by setting the roughness Rz of the conventional method to 10 μm and adjusting the roughness. In Table 4, according to the method of the present invention, the convergence value of the roll roughness of the rolling roll 3 was investigated and tested in advance.
0 μm, the surface roughness of the roll 3 was reduced from 20 μm to 25 μm.
After adjusting the roughness of the steel sheet 2, the steel sheet 2 was rolled by the rolling roll 3 and subsequently cooled by the cooling device 5. It is apparent from Table 4 that the method of the present invention achieves uniform cooling as compared with the conventional method. From this result, it is understood that the purpose of uniformly cooling the temperature distribution in the width direction of the steel sheet is achieved. [Table 4] As described above, according to the present invention,
When cooling a steel sheet with water or a water-soluble medium, it is possible to provide a method for uniformly cooling the temperature distribution in the steel sheet, and a great contribution can be expected in the industrial field.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side sectional view illustrating an apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing an experimental result of a relationship between an average cooling rate and roughness. FIG. 3 is an explanatory diagram showing a relationship between a roll roughness and a rolling amount. FIG. 4 is an explanatory diagram showing a relationship between a variation in roughness of a transfer steel sheet and a target value for adjusting roll roughness. [Description of Signs] 1 Transport roll 2 Steel plate 3 Roll roll 4 Roll roll roughness adjusting device 5 Cooling device

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-54507 (JP, A) JP-A-6-79305 (JP, A) JP-A-7-290129 (JP, A) JP-A-1- 181902 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B21B 1/22 B21B 45/00-45/02

Claims (1)

(57) [Claims 1] Following hot rolling, prior to cooling the steel sheet with water or a water-soluble medium, the surface of a rolling roll is polished to impart roughness. When controlling the cooling by transferring the roughness to the steel sheet during hot rolling and adjusting the roughness of the steel sheet, the surface roughness of the rolling roll is displayed as Rz roughness, and the steel sheet is continued with the rolling roll. A method for cooling a steel sheet, comprising adjusting a convergence value of a change in roughness of a rolling roll when rolling is performed to a range of the convergence value +5 μm.