JPH0830218B2 - Cooling method for rolled steel sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlled cooling of a rolled steel sheet after completion of rolling in a rolling manufacturing facility for rolled steel sheets, and more specifically, after controlled cooling. The purpose is to maintain the flatness of the rolled steel sheet of No. 1 at a higher value.

[Conventional technology]

In the recent rolling manufacturing process of thick steel plate, from the aspects of component saving and energy saving, heating temperature control, controlled rolling,
Research on each process of controlled cooling has become popular.

Of the above processes, the controlled cooling process is
It is a technique to improve the tensile strength of the rolled steel sheet produced by quenching from the unrecrystallized austenite region or the ferrite-austenite two-phase region to 400 to 500 ° C, and the metallurgical clarification has progressed considerably, There are still many problems regarding cooling technology, especially shape control technology,
As for the straightening rate (the straightening rate after cooling in the cooling bed), when comparing the rolled steel sheet controlled by cooling with other rolled steel sheets, the rolled steel sheet under controlled cooling has a very high value. Is.

The main reason why the straightening rate in this controlled cooled rolled steel sheet becomes a very high value is that during controlled cooling of the rolled steel sheet, among the cooling water sprayed on the upper and lower surfaces of the rolled steel sheet,
The cooling water to the upper surface of the rolled steel sheet does not flow down from the rolled steel sheet immediately and stays on the rolled steel sheet for a certain period of time as it is, so the cooling action of this accumulated water causes uneven cooling of the rolled steel sheet. It was thought to be because. That is, this accumulated water flows in the width direction or the longitudinal direction of the rolled steel sheet according to the conveying operation of the rolled steel sheet, and makes both side edges of the rolled steel sheet or both front and rear ends supercooled, thereby unevenly cooling the rolled steel sheet. To

As a conventional technique for uniforming the temperature distribution in the rolled steel sheet without uneven cooling of the rolled steel sheet, according to the temperature distribution along the measured width direction of the rolled steel sheet during controlled cooling, along the width direction of the rolled steel sheet, , The amount of cooling water jetted out is controlled to be large for the central portion of the rolled steel sheet and small for both edges of the rolled steel sheet (JP-A-61-219412). For example, the masking of the rolled steel sheet edge portion in which the jetting of the cooling water to both edge portions of the rolled steel sheet is blocked by the shield plates at a desired timing (JP-A-61-086022).
No. gazette) was adopted.

Although the above-mentioned conventional technique exhibits a certain degree of uniform cooling effect, the degree is not sufficient, and uniform cooling of higher rolled steel sheets is desired.

As a result of research on the cause of non-uniform cooling of rolled steel sheets, recently, in addition to the above-described retention of cooling water on the rolled steel sheet,
It was revealed that the scale layer on the surface of the rolled steel sheet has a great influence on the cooling of the rolled steel sheet. That is, the surface scale with good adhesion of the rolled steel plate surface is less likely to peel off from the surface of the rolled steel plate during cooling, so the heat transfer coefficient of the surface of the rolled steel plate is lowered, and conversely the surface scale with poor adhesion is cooled, Since it easily separates from the surface of the rolled steel sheet, it improves the heat transfer coefficient of the surface of the rolled steel sheet. Uniformity will occur, and distortion will occur in the rolled steel sheet after cooling.

The present invention was devised in order to solve the problems in the above-mentioned conventional example, and the properties of the surface scale generated on the surface of the rolled steel sheet just subjected to the hot rolling and the cooling action of the cooling water on the rolled steel sheet. It is a technical subject to achieve good controlled cooling of a rolled steel sheet by utilizing the relationship with.

[Means for solving problems]

Hereinafter, the present invention will be described with reference to the drawings showing an embodiment of the present invention.

The means of the present invention is a discharge water amount in a cooling device 1 for controlling and cooling a rolled steel plate H discharged from a hot rolling mill by controlling a discharge water amount density distribution of cooling water along the plate width direction of the rolled steel plate H. The present invention relates to a density distribution setting method, in which the cooling water discharge water amount density distribution of the cooling device 1 is made to correspond exactly to the adhesion and production amount of the surface scale of the rolled steel sheet H in the axial direction of the rolling roll 5 of the rolling mill. It is set so as to correspond almost exactly to the surface roughness distribution along the line.

[Action]

As described above, since the surface scale having good adhesion generated on the surface of the rolled steel sheet H is difficult to be peeled from the surface of the rolled steel sheet H during cooling, the heat transfer coefficient of the surface of the rolled steel sheet H is lowered, and conversely the adhesion is reduced. Since the surface scale having poor property easily peels off during cooling, it improves the heat transfer coefficient of the surface of the rolled steel sheet H, but from many experiments, the rolled steel sheet H of the surface scale produced on the surface of the rolled steel sheet H is found. It was confirmed that the adhesion to the surface directly corresponds to the roughness of the surface of the rolled steel sheet H after roll forming. That is, the rolled and formed steel sheet H
If the surface roughness is large, the amount of the generated surface scale is large and the adhesion is large, and conversely, if the surface roughness of the rolled steel sheet H formed by rolling is small, the amount of the generated surface scale is generated. It is also small and its adhesion is small.

It has been confirmed that the surface roughness of the roll-formed rolled steel sheet H is accurately determined in accordance with the roll surface roughness of the rolling roll 5 that roll-forms the rolled steel sheet H.

Then, associating the relationship between the roll surface roughness distribution of the rolling roll 5 and the width direction temperature distribution of the cooled rolled steel sheet H, the roll surface roughness distribution curve A and the width direction temperature distribution curve of the rolled steel sheet H are shown. As shown in (a) and (b) of FIG. 4, T means that the temperature of the central portion of the rolled steel sheet H corresponding to the portion having a high roughness is high and that of the rolled steel sheet H corresponding to the portion having a low roughness is high. The temperature of the ears is low.

Therefore, a roll surface roughness distribution along the axial direction of the rolling rolls 5 of the hot rolling mill is obtained, and the roll surface roughness distribution is directly corresponded to the cooling of the rolled steel plate H surface with cooling water along the plate width direction. The degree distribution is set. That is, the central portion of the rolled steel sheet H corresponding to the central portion of the rolling roll 5 having a large roll surface roughness is sufficiently cooled, and conversely it corresponds to both end portions of the rolling roll 5 having a small roll surface roughness. Cooling is limited to both ears of the rolled steel plate H.

As described above, the method of the present invention does not control the cooling of the rolled steel sheet H according to the temperature distribution generated in the rolled steel sheet H that is the cooling target, but causes the non-uniform cooling of the rolled steel sheet H to occur. Since the cooling of the rolled steel sheet H is controlled according to the surface roughness distribution of the roll 5, it is possible to achieve the basic uniform cooling of the rolled steel sheet H. Moreover, since the initial surface roughness distribution of the rolling roll 5 can be obtained by measuring the surface structure itself of the rolling roll 5, it can be directly or indirectly known accurately, and its change can also be obtained. Since it can be accurately known based on abundant data from the past and can be actually measured during rolling, the controlled cooling of the rolled steel sheet H can be achieved more accurately.

〔Example〕

As a means for directly measuring the roll surface roughness along the axial direction of the rolling roll 5, a means for assembling a conventional roughness meter to the on-line roll, or irradiating the surface of the rolling roll 5 with light and reflecting the reflected light Therefore, various means such as an optical means for indirectly measuring the surface roughness can be considered, and any means can be used.

The surface roughness distribution of the rolling roll 5 is, as shown in FIG. 2, a roughness distribution curve A1 immediately after roll change in FIG. 2 (a),
Roughness distribution curve A2 of the 100th roll after roll change in FIG. 2 (b) (rolling of 100 rolled steel plates H after roll change), 200th roll after roll change in FIG. 2 (c) The roughness distribution curve A3 of Fig. 2 and the roughness distribution curve A4 of the 300th roll after roll change of Fig. 2 (d), and the degree and distribution thereof change. That is, since the rolled steel sheet H is usually formed through three steps of forming, tentering and finish rolling, even if the coffin schedule of rolling from a wide material is followed, a recent roll chance Even if free rolling is performed, the surface roughness of the rolling roll 5 becomes higher than that of the central portion 5a due to heat cracks due to thermal stress and roll wear. Then, as the number of rolled steel sheets H increases, the increased surface roughness gradually spreads to the end portion 5b, and as a result, the surface roughness distribution tends to be uniform along the axial direction of the rolling roll 5. Becomes

As described above, the degree and distribution of the surface roughness of the rolling roll 5 increases and expands as the number of rolling increases, so that the controlled cooling of the rolled steel sheet H is performed by the surface roughness of the rolling roll 5 as the number of rolling increases. The cooling of the central portion of the rolled steel sheet H is gradually strengthened in accordance with the degree and distribution of the degree, and the portion where the cooling is strengthened is expanded from the central portion of the rolled steel sheet H to the ear side. .

FIG. 1 shows a structural example of a cooling device 1 configured to be capable of controlling the width of the rolled steel plate H in a width direction. In this example, a cooling header for ejecting cooling water onto the surface of the rolled steel plate H is shown. The two nozzles 3 are divided into 7 along the width direction, the supply of cooling water to the 7 divided nozzles 3 is set by the flow rate control valve 4, and the rolled steel sheet H traveling and conveyed on the table roller 6 is cooled. Can be set for each of the seven divisions in the width direction.

FIG. 3 shows an example of the flow of determining the amount of cooling water along the width direction of the rolled steel sheet H using the method of the present invention, in which the degree and distribution of the surface roughness of the rolling roll 5 is preliminarily online in the preliminary step Sy. Obtained with a measurement or prediction model,
Step S1 of determining the degree and distribution of the surface roughness of the rolling roll 5 is performed according to the conditions of this preliminary step Sy, and step S2 of predicting and setting the degree of roughness and distribution of the surface of the rolled steel sheet H is performed according to the setting conditions of this step S1. To do. Step of determining the water amount density distribution of the cooling water injected from the vertical direction onto the rolled steel plate H according to the set value of step S2
Do S3.

Based on the determination condition of step S3, step S4 of predicting and determining the heat transfer coefficient change characteristic of the rolled steel sheet H in the width direction is performed, and the determination model for determining the width direction cooling water amount density distribution in the cooling device 1 is stepped according to this step S4. Determined in S5.

The water density distribution of the cooling water along the width direction for the controlled cooling of the rolled steel sheet H is basically determined according to the surface roughness degree and distribution of the rolled steel sheet H. In actual cooling with cooling water,
There is a non-uniform distribution of the cooling power due to external factors other than the heat transfer coefficient distribution on the surface of the rolled steel sheet H due to the retention of cooling water on the upper surface of the rolled steel sheet H and the form of its flow. Is extremely small, but if it cannot be ignored, more accurate cooling control can be performed by learning-based correction from the change in the temperature distribution of the rolled steel sheet H after cooling during the rolling operation. it can.

If it is difficult to continuously measure the change in the surface roughness distribution of the rolling roll 5 online, it is convenient to create a prediction model and use this prediction model.

The method of the present invention, plate thickness 12mm ~ 32mm, plate width 2200mm ~ 4500m
It was applied to the controlled cooling of a total of 200 rolled steel plates H having m and a plate length of 25400 mm to 35000 mm. As a result, the number of sheets requiring re-straightening was 24 (12%), and the re-straightening rate for the rolled steel sheet H could be significantly reduced as compared with the conventional re-straightening rate of 18%.

〔The invention's effect〕

As is clear from the above description, the present invention, since it is possible to cool the rolled steel sheet more uniformly, it is possible to significantly reduce the re-rectification rate of the controlled cooled rolled steel sheet,
This makes it possible to dramatically improve the productivity of rolled steel sheets using controlled cooling as an example, and since the basis of the controlled cooling model is obtained from the degree and distribution of the surface roughness of the rolling roll, The basics can be patterned accurately and easily, and thus controlled cooling of the rolled steel sheet can be achieved without causing large cooling unevenness, and the existing cooling device can be used as it is. Therefore, many excellent effects are exhibited, such as no new cost is required for implementing the method of the present invention.

[Brief description of drawings]

FIG. 1 is a front view showing a configuration example of a cooling device suitable for carrying out the method of the present invention. FIG. 2 is a roughness distribution characteristic diagram according to the number of times of rolling showing the characteristics of the degree and distribution of the surface roughness along the axial direction of the surface of the rolling roll. FIG. 3 is an explanatory view showing an example of a flow for carrying out the method of the present invention. FIG. 4 shows the surface roughness distribution along the width direction of the rolled steel sheet,
It is a diagram which shows the corresponding characteristic example with the temperature distribution along the width direction of the cooled rolled steel plate. DESCRIPTION OF SYMBOLS 1; Cooling device, 2; Cooling header, 3; Nozzle, 4; Flow control valve,
5; rolling roll, 6; table roller, H; rolled steel plate.

Claims (1)

[Claims] 1. A rolled steel sheet (H) discharged from a hot rolling mill.
In the cooling device (1) for controlling and cooling by adjusting the discharge water amount density distribution of the cooling water along the plate width direction of the rolled steel plate (H), the cooling water discharge water amount density distribution of the cooling device (1) is The surface scale adhesion of the rolled steel plate (H) and the amount of formation are formed in a direct correspondence, and are set so as to correspond approximately to the surface roughness distribution along the axial direction of the rolling roll (5) of the rolling mill. Cooling method for rolled steel sheet.