JPH11129016A - Method of manufacturing hot-steel plate with good tight-scale properties - Google Patents

Abstract

PROBLEM TO BE SOLVED: To offer a method of manufacturing a hot rolled steel plate with good tight-scale properties by controlling the generation of blister during finishing, and thus preventing the generation of abnormal scale such as double scale. SOLUTION: In the hot-rolled steel plate manufacturing method in which hot finishing is done immediately after descaling, the steel plate carrying time from a descalig equipment to the first stand of a hot finishing mill is set to 5 seconds or less, or controlled by the formula shown below in accordance with the steel plate temperature, and thus blister generation is controlled and tight scale is achieved. If the steel plate temperature is assumed to be T ( deg.C) and carrying time t (sec): Formula (I) T>(16t<2> +1760t-9200)<1/2> +1020, when T>1020 deg.C or Formula (II) T<-(16t<2> +1760t-9200)<1/2> +1020, when T<=1020 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-rolled steel sheet having good tight-scale properties, that is, adhesiveness of scale at the time of surface processing, and more particularly, to oxidizing conditions after descaling immediately before hot finish rolling. The present invention relates to a method for producing a hot-rolled steel sheet having good tight-scale properties by suppressing the formation of blisters by controlling.

[0002]

2. Description of the Related Art Hot-rolled steel sheets are subjected to rough rolling of a slab heated in a heating furnace, and then to final rolling by descaling with high-pressure water, cooling to a predetermined material on a run-out table, and then coiling. It is manufactured by winding up. Since all of these steps are performed in the atmosphere, a scale (secondary scale) is generated again on the hot steel sheet surface even if the descaling is performed immediately before the finish rolling.

FIG. 1 is a diagram showing the steps from descaling to winding before finish rolling of a hot rolling line. Generally, the scale generated on the surface of the steel sheet 1 as a material to be rolled is removed (descaled) by high-pressure water by the descaling device 2 before entering the finishing mill 3. The descaled steel sheet enters the finishing mill 3, is rolled to a predetermined thickness, is water-cooled by a cooling device 4 on a run-out table, and is cooled to a predetermined winding temperature.
And sent to the next process. The steel sheet manufactured in this manner has a scale of about 5 to 15 μ thickness usually formed on the surface of the steel sheet.

[0004] The hot-rolled steel sheet with the scale adhered not only has a poor appearance, but also undergoes processing such as bending and pressing, so that the scale peels off from the steel sheet surface. Can not do it. In addition, when subjected to cold rolling, there is a problem in that the scale is pressed or bitten on the surface of the steel sheet to generate surface flaws and deteriorate the surface quality. Under such circumstances, various techniques for producing a tight-scale hot-rolled steel sheet having excellent adhesion have been proposed.

[0005] As a conventional method for producing a tight-scale hot-rolled steel sheet, there is a method in which the residence time in a high-temperature region after finish rolling is shortened by quenching. For example, in Japanese Patent Application Laid-Open No. 58-122105, 800-9
After finishing rolling in the temperature range of 00 ° C, 40 ° C / s
A method of manufacturing a steel strip which is rapidly cooled to 600 ° C. or lower at a cooling rate of ec or higher has been proposed. As another method, an oxidation inhibitor is applied to the surface of the steel sheet, or a steel sheet is formed. There is a method of suppressing oxidation of the steel sheet surface by bringing the steel sheet into contact with an active gas.
In Japanese Patent No. 23, when a steel strip after hot rolling is wound around a coil at a temperature of 550 ° C. or more, a heat radiation preventing plate is arranged close to the edge of the coil, and the coil and the heat radiation preventing plate are arranged. A method for producing a tight-scale steel sheet which is wound with a non-oxidizing gas filled between them is proposed. The former has a drawback that a large amount of water is required for rapid cooling, the cooling equipment becomes large, and the equipment cost increases. The latter uses an oxidation inhibitor or an inert gas, and thus has the disadvantage that running costs and the like increase.

Moreover, all of the proposed methods for producing a tight-scale steel sheet are related to suppressing the formation of scale after finish rolling, and the scale generated during finish rolling is taken into consideration. Absent.
That is, there is a problem that the conventional method cannot suppress the blister-like scale generated in the finishing mill, and cannot secure tight scale properties when an abnormal scale such as a double scale occurs.

[0007]

SUMMARY OF THE INVENTION The present inventor has found that when a blister-like scale is generated during hot finish rolling, it becomes an abnormal scale such as a double scale and cannot produce a good tight-scale steel sheet. I learned. This will be described with reference to the drawings. FIG. 2A is a schematic diagram illustrating a state in which blisters are generated, and FIG. 2B is a schematic diagram illustrating a state in which an abnormal scale such as a double scale is generated during finish rolling. is there. That is, as shown in FIG. 2A, the scale formed on the surface of the steel sheet during the finish rolling is peeled to form a blister 6 having a blister-like scale. If the blister is rolled while being generated, the blister is bent and overlaps to form a double scale 7 and is pushed into the steel sheet 1.
The scale in such a state does not become a tight scale because the scale peels off from the steel sheet surface.

Accordingly, an object of the present invention is to provide a method for producing a hot-rolled steel sheet having good tight-scale properties by suppressing the occurrence of blisters during finish rolling and preventing the occurrence of abnormal scale such as double scale. It is assumed that.

[0009]

SUMMARY OF THE INVENTION The inventor of the present invention has proposed a method in which a blister generated during hot finish rolling transfers a steel sheet from a descaling device (descaling end position) to a finishing mill (first stand). And control the temperature of the steel sheet, the time of exposure to the atmosphere (passing speed) and the atmosphere until it is transported from the descaling device to the first stand of the finishing mill. Thus, the occurrence of blisters (scale swelling) is suppressed, and the occurrence of abnormal scale such as double scale is prevented, thereby producing a hot-rolled steel sheet having good tight scale properties.

The specific gist of the present invention is as follows.

(1) In the method for manufacturing a hot-rolled steel sheet in which hot finish rolling is performed immediately after descaling, the time required for transporting the steel sheet from the descaling device to the first stand of the hot finish rolling mill and the temperature of the steel sheet are defined as follows. A method for producing a hot-rolled steel sheet having good tight-scale properties, characterized in that blister formation is suppressed and tight-scaling is achieved by controlling based on the following equation.

The temperature of the steel sheet is T (° C.), and the transport time is t (se).
c) If T> 1020 ° C. T> (16t ² + 1760t-9200) ^1/2 +1020 If T ≦ 1020 ° C. T <− (16t ² + 1760t-9200) ^1/2 +102
0 (2) In the method for producing a hot-rolled steel sheet in which hot finish rolling is performed immediately after descaling, the transfer time from the descaling device to the first stand of the hot finish rolling mill is controlled to 5 seconds or less, so that the blister is reduced. A method for producing a hot-rolled steel sheet having good tight-scale properties, characterized in that formation is suppressed and tight-scaling is performed.

(3) The above (1) or (2), wherein the distance from the descaling device to the first stand of the hot finishing mill is 4 m or less, and the passing speed is 800 mm / sec or more. A method for producing a hot-rolled steel sheet having good tight-scale properties as described in the above.

(4) The steel plate between the descaling device and the first stand of the hot finishing mill is protected in a non-oxidizing gas atmosphere. The method for producing a hot-rolled steel sheet having good tight-scale properties according to any one of the first to third aspects.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The inventor of the present invention has investigated the effect of blistering on the carbon steel sheet maintained at various temperatures due to the time of exposure to the atmosphere during the transfer to the first stand (F1) of the finishing mill after descaling. Was investigated.

FIG. 3 shows the result. That is, FIG. 3 is a diagram showing a situation in which blisters are generated in relation to the exposure time (sec) of the steel sheet and the entrance temperature (° C.) of the finishing mill. In FIG. 3, the mark ○ indicates the condition where no blister was generated, and the mark を indicates the condition where the blister was generated.

As is evident from FIG. 3, the steel sheet entrance temperature is 1
At 020 ° C or lower, there is a tendency that blisters do not occur even if the exposure time is prolonged in a specific region. However, if the exposure time is 5 seconds or less, the generation of blisters can be suppressed, and if the exposure time is less than 3 seconds, the generation of blisters can be completely suppressed.

The exposure time at which this blister does not occur is 5
The region exceeding seconds can be defined by the following empirical formula.

That is, assuming that the temperature of the steel sheet is T (° C.) and the transfer time is t (sec), T> 1020 ° C. T> (16t ² + 1760t-9200) ^1/2 +1020 T ≦ 1020 ° C. T <− ^{(16t 2 + 1760t-9200)} 1/2 +102
0 That is, the blister generation region and the blister non-generation region are separated by a curve, and the right side of the curve is the blister generation region and the left side is the non-generation region. Therefore, it can be understood that blisters can be suppressed by controlling the sheet passing speed (transport time) corresponding to the atmospheric exposure time based on the steel sheet temperature based on the empirical formula in FIG.

Further, the steel sheet conveying time is determined by the descaling device (descaling end position) from the first hot rolling mill.
It is determined by the distance to the stand and the passing speed. The distance is preferably set to 4 m or less in consideration of the shortening of the transfer time and the arrangement of the rolling line equipment. In this case, the passing speed is set to 800 mm / sec or more to satisfy the transfer time of 5 seconds or less. There is a need to.
However, in the present invention, the distance is not limited to only 4 m or less. In order to shorten the transport time, it is only necessary to shorten the distance as much as possible and to increase the transport speed, but there is naturally a limit due to the arrangement of the rolling line equipment. In addition, it is desirable that the transfer time be less than 3 seconds in consideration of variations such as steam oxidation in an actual machine.

Further, in order to effectively prevent oxidation of the steel sheet during transportation, a non-oxidizing gas such as nitrogen gas or argon gas is sprayed on the surface of the steel sheet after descaling to cause the steel sheet to be exposed to a non-oxidizing gas atmosphere. Protection is more effective in suppressing blister generation. A cover may be provided to effectively protect the steel sheet in a non-oxidizing gas atmosphere.

[0023]

The embodiments will be described below in detail.

Using a carbon steel sheet, the entry temperature (° C.) and entry speed (mm / sec) of the steel sheet during finish rolling were changed. The scale formed on the surface of the steel sheet obtained by finish rolling was subjected to a peel test and a tight scale test.

The test conditions were such that the inlet temperature was in the range of 900 to 950 ° C., and the transfer time from the descaling device to the first stand of the rolling mill was 5 seconds or less in the present invention examples (Nos. 1 to 5). However, in Comparative Examples (Nos. 6 to 8), the test was performed under the condition outside the control range of the present invention exceeding 5 seconds. Table 1 shows the test conditions.

[0026]

[Table 1] In addition, the thickness and width of the steel sheet as the test material were almost the same in all tests. The rolling temperature after rolling was 550 to 600 ° C.

With respect to the steel sheet obtained under the above test conditions, a test for a peel test of a scale formed on the surface of the steel sheet was performed.

(Peeling Test) After a tape was attached to the obtained steel sheet, a tape peeling test was performed to peel off and test the scale peeling state.

When the present invention example and the comparative example are compared, No. Nos. 1 to 5 are Nos. Of Comparative Examples. Scale peeling was smaller than in Examples 6 to 8, and excellent test results were obtained. Particularly excellent results were obtained at the plate TOP center portion and the edge portion.

Next, the tightness of the scale formed on the steel sheet was tested by changing the inlet speed in the range of 40 to 115 mpm and the inlet temperature in the range of 902 to 958 ° C. Was obtained in five stages. The higher the rating, the better the tightness. The results are shown in FIGS.

(Tight Scale Property) FIG. 4 shows the relationship between the entry speed and the tight scale property. As shown in FIG. 4, the higher the entry speed (mpm), the higher the tight scale property.

FIG. 5 shows the relationship between the inlet temperature and the tight scale property. As shown in FIG. 5, the lower the entry temperature (° C.), the higher the tight scale property. Especially about 930 ℃
When it exceeds, the tight scale property rapidly deteriorates.

As is apparent from these results, it was confirmed that the steel sheet of the present invention, in which the sheet passing speed was increased and the inlet temperature was lowered, had a better tight-scale property than the comparative example. .

FIG. 7 shows the entrance speed (mpm) of the finishing mill.
FIG. 4 is a diagram illustrating conditions for preventing blisters from being generated in relation to the distance (m) between a descaling device and a first stand of a finishing mill. The test conditions are as follows, using ordinary steel plates.
A lab experiment with a transfer time of 5 seconds and a test on an actual machine with a transfer time of 3 seconds were performed. Inlet speed 30-100 mpm
The occurrence of blisters was observed in the range of, but no blisters were observed under any of the test conditions.

That is, it was confirmed that blisters did not occur in any case within the control condition range of the present invention.

[0036]

According to the present invention, it has become possible to produce a hot-rolled steel sheet having good tight-scale properties without occurrence of press flaws due to scale peeling.

[Brief description of the drawings]

FIG. 1 is a view showing a process from descaling to winding up before finish rolling of a hot rolling line.

FIG. 2 is a diagram showing a state of a scale, wherein (a)
FIG. 4B is a schematic diagram illustrating a state in which blisters are generated, and FIG. 4B is a state in which an abnormal scale such as a double scale is generated during finish rolling.

FIG. 3 is a diagram showing a situation in which blisters are generated according to a relationship between an exposure time (sec) of a steel sheet and an entrance temperature (° C.) of a finishing mill.

FIG. 4 is a diagram showing the relationship between the entry speed and tight scale properties.

FIG. 5 is a diagram showing the relationship between the inlet temperature and tight scale properties.

FIG. 6 shows the entrance speed (mpm) of the finishing mill and the distance (m) between the descaling device and the first stand of the finishing mill.
FIG. 6 is a diagram showing conditions for preventing blisters from being generated in relation to the above.

[Explanation of symbols]

 Reference Signs List 1 steel sheet 2 descaling device 3 hot finishing rolling mill 4 cooling device 5 coiler 6 blister 7 double scale

Claims (4)

[Claims] In a method for producing a hot-rolled steel sheet in which hot finish rolling is performed immediately after descaling, a steel sheet transport time from a descaling device to a first stand of a hot finish rolling mill and a steel sheet temperature are defined as follows. A method for producing a hot-rolled steel sheet having good tight-scale properties, characterized in that blister formation is suppressed and tight-scaled by controlling based on the formula. The temperature of the steel sheet is T (° C), and the transport time is t (se).
c) If T> 1020 ° C. T> (16t ² + 1760t-9200) ^1/2 +1020 If T ≦ 1020 ° C. T <− (16t ² + 1760t-9200) ^1/2 +102
0 2. A method for producing a hot-rolled steel sheet in which hot finish rolling is performed immediately after descaling, by controlling a transfer time from a descaling device to a first stand of a hot finish rolling mill to 5 seconds or less. Suppress blister formation,
A method for producing a hot-rolled steel sheet having good tight-scale properties, characterized in that the hot-rolled steel sheet is formed into a tight scale. 3. The tight scale according to claim 1, wherein the distance from the descaling device to the first stand of the hot finishing mill is 4 m or less, and the passing speed is 800 mm / sec or more. Method for producing hot-rolled steel sheet with good heat resistance. 4. The steel sheet between a descaling device and a first stand of a hot finishing mill is protected in a non-oxidizing gas atmosphere. A method for producing a hot-rolled steel sheet having good tight-scale properties as described in the above.