JPH11300410A - Manufacture of thin hot rolled steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin hot rolled steel sheet excellent in shape and homogeneity of material by advantageously suppressing deterioration in shape such as the so-called edge wave and middle waviness which are generated caused by irregularity of cooling and variation of the material in cooling from a finishing mill later in a hot rolling process. SOLUTION: At the time of cooling the hot rolled steel sheet 10 after completing finish rolling, a high polymer solution which consists of the copolymer containing ethylene oxide and propylene oxide as monomer components, and is separated into a high polymer liquid and water at >=100 deg.C and is mixed with water at <100 deg.C is applied on the high temp. steel sheet 10 after finish rolling and, after forming the uniform coating film of the high polymer on the surface of a heat transfer surface, the thin hot rolled steel sheet 19 is manufactured by executing water cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin hot-rolled steel sheet, and more particularly, to deterioration of a sheet shape such as so-called edge elongation and medium elongation caused by uneven cooling in cooling after a finish rolling mill in a hot rolling process. Another object of the present invention is to obtain a thin hot-rolled steel sheet having excellent uniformity in shape and material by advantageously suppressing variation in material.

[0002]

2. Description of the Related Art Generally, when a thin hot-rolled steel sheet is manufactured, a cooling medium such as water is sprayed on the steel sheet after finishing rolling to cool the steel sheet. In cooling such a steel sheet, film boiling, based on the physical and chemical properties of the heat transfer surface,
The shape of the cooling curve that follows the transition boiling, nucleate boiling, etc. changes, and the cooling curve does not align over the entire heat transfer surface, causing a variation in cooling stop temperature, resulting in shape defects and material variations due to residual stress. I was

Therefore, various techniques for solving the above-mentioned inconvenience have been conventionally disclosed. For example,
Japanese Patent Application Laid-Open No. 61-117211 discloses that the wetting between the refrigerant and the heat transfer interface is made uniform to stabilize and uniform the cooling.
As a technology to prevent material variations due to non-uniform cooling and deterioration of shape and dimensional accuracy, at least at the cooling stop temperature or higher, use a refrigerant in which a substance that forms a dirt layer or film on the heat transfer surface is added to water. Thus, there is disclosed a method of uniformly forming a dirt layer or coating on a heat transfer interface of a metal surface due to a decomposition product of an additive substance.

[0004]

However, in the technology described in Japanese Patent Application Laid-Open No. 61-117211, uniform cooling is possible, but no measures are taken against scales and the like generated on the steel sheet surface. Did not. That is, forming a dirt layer or a film on the surface of the steel sheet is nothing but generating scale or the like on the surface of the steel sheet. The scale generated on the surface of the steel material is partly exfoliated and pressed into the product when performing press working, etc. is there. In addition, when the amount of scale increases, there is a problem in that the processing time of the pickling step becomes longer.

[0005] Further, cooling of the steel sheet is generally performed by spraying a refrigerant from both the upper and lower surfaces of the steel sheet. However, if the refrigerant sprayed on the upper surface of the steel sheet stays, there is a possibility that uneven cooling may occur. . The present invention has been proposed in view of the above-described circumstances, and in cooling after a finish rolling mill in a hot rolling step, so-called edge elongation caused by uneven cooling, deterioration in plate shape such as middle elongation, and variation in material are advantageous. It is an object of the present invention to provide a method for manufacturing a thin hot-rolled steel sheet that can obtain a thin hot-rolled steel sheet having excellent uniformity in shape and material.

[0006]

<Features> The present invention has the following features in order to achieve the above-mentioned object. The method for producing a thin hot-rolled steel sheet according to the invention according to claim 1 is characterized in that a polymer comprising a copolymer containing ethylene oxide and propylene oxide as monomer components upon cooling after finish rolling of the hot-rolled steel sheet. A solution with a liquid temperature of 1
At a temperature of 00 ° C. or higher, a polymer solution and water are separated, and at a temperature lower than 100 ° C., a polymer solution mixed with water is applied to a high-temperature steel plate after finish rolling, and the polymer film is coated on the heat transfer surface. It is characterized in that after being uniformly formed, it is cooled with water.

A method of manufacturing a thin hot-rolled steel sheet according to a second aspect of the present invention is characterized in that, in addition to the features of the first aspect, the polymer solution is used as the water-cooled refrigerant. Is what you do.

According to a third aspect of the present invention, there is provided a method for producing a thin hot-rolled steel sheet, wherein the hot-rolled steel sheet is cooled after finish rolling.
A polymer solution comprising a copolymer containing ethylene oxide and propylene oxide as monomer components. At a solution temperature of 100 ° C. or higher, a polymer solution is separated into water and 1
When the temperature is lower than 00 ° C., a polymer solution mixed with water is used as a cooling medium, and water cooling is performed while uniformly forming the polymer film on the heat transfer surface.

A method of manufacturing a thin hot-rolled steel sheet according to a fourth aspect of the present invention is characterized in that, in addition to the features of the first to third aspects of the present invention, water cooling after the finish rolling is completed. Is performed only from the lower surface side of the steel plate.

<Operation> The present invention has the above-mentioned features, and thus has the following operation. According to the first aspect of the present invention, the polymer solution is applied to the high-temperature steel sheet after the rolling of the steel sheet, so that the polymer film is uniformly formed on the surface of the heat transfer surface. This polymer film can prevent scale from being generated on the surface of the steel sheet.

[0011] In the subsequent water cooling, the cooling state uniformly shifts from film boiling cooling to nucleate boiling cooling starting from the core of the polymer film. In addition, the polymer solution is separated from water at 100 ° C. or higher, and a polymer solution other than water adheres to the surface of the steel sheet. In the subsequent cooling, ordinary cooling equipment is used without performing a special oxidation suppression treatment. Can be cooled. Furthermore, since the polymer solution is water-soluble, when it is necessary to remove the polymer solution, it can be easily removed by washing with water.

According to the second aspect of the present invention, since the polymer solution is used as the refrigerant, the polymer film generated on the surface of the steel sheet can be reliably maintained until the cooling is completed.
According to the third aspect of the present invention, the steel sheet is cooled using the polymer solution as a coolant without previously applying the polymer solution to the steel sheet. Therefore, the cooling step can be simplified, and the oxidation suppressing process can be performed in the cooling step.

According to the fourth aspect of the present invention, as described above, the polymer film is formed uniformly on the surface of the heat transfer surface, and in the subsequent water cooling, the film is cooled from the nucleus of the polymer film as a starting point. Since the cooling is uniformly shifted to the nucleate boiling cooling, it has an extremely high cooling capacity as compared with the film boiling cooling. Therefore, the steel sheet can be sufficiently cooled only by cooling from the lower surface of the steel sheet. Further, since a coolant such as water does not stay on the upper surface of the steel sheet, uneven cooling does not occur, and the shape of the steel sheet is improved, and a thin hot-rolled steel sheet having excellent uniformity can be manufactured.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a thin hot-rolled steel sheet according to the present invention will be described below with reference to the drawings. First, a polymer solution comprising a copolymer containing ethylene oxide and propylene oxide as a monomer component used in the method for producing a thin hot-rolled steel sheet according to the present invention will be described. This polymer solution is used as an oxidation inhibitor,
It consists of the following chemical formula (1).

HO— (CH ₂ CH ₂ O) _x — (CH ₂ CHO) _y —OCH ₃ (1) This polymer solution is a uniform polymer solution at a temperature lower than 100 ° C. At 100 ° C. or higher, there is a property of causing heat separation and separating into two layers of water and a 100% polymer liquid. Therefore, when the temperature of the steel material is 100 ° C. or higher, a film of the polymer liquid (oxidation inhibitor) is formed on the surface of the steel material, and the steel material exhibits an oxidation inhibiting action.
As described above, since the film of the polymer liquid (oxidation inhibitor) exists on the surface of the steel material, even at 500 ° C. or more, the film boiling phenomenon that generates a water vapor film hardly occurs.

Further, as is apparent from the above chemical formula (1), the oxidation inhibitor composed of a polymer solution has a hydroxyl group in the monomer. Therefore, the hydroxyl group in the polymer solution (oxidation inhibitor) present as a film on the surface of the steel material causes a reduction reaction with iron, thereby increasing the generation ratio of Fe ₃ O ₄ and further increasing the oxidation suppression effect. Can be done.
Next, an apparatus for attaching a polymer solution to the steel plate 10 will be described. FIG. 1 is an explanatory diagram showing the configuration of an apparatus for attaching a polymer solution to a steel plate 10. As shown in FIG.

As shown in FIG. 1, after the finishing mill in the hot rolling process, the steel sheet 10 passing between the pair of upper and lower pinch rolls 20, 20 is supported by a plurality of rollers 30 from the lower surface side. While passing, cooling is performed. On the exit side of the pinch rolls 20, 20, a pair of upper and lower application nozzles 40, 40 for spraying the polymer solution toward the upper and lower surfaces of the steel plate 10 are provided. By spraying the above-described polymer solution from the application nozzles 40 onto the upper and lower surfaces of the steel sheet 10, a polymer film is uniformly formed on the surface of the heat transfer surface.

In a line subsequent to the pinch rolls 20, 20, an upper cooling nozzle 50 is provided above the steel plate 10, and a lower cooling nozzle 60 is provided below the steel plate 10. Refrigerant is blown from the upper cooling nozzle 50 and the lower cooling nozzle 60 toward the upper surface or the lower surface of the steel plate 10, respectively. The refrigerant blown from the upper cooling nozzle 50 and the lower cooling nozzle 60 may be water alone, but it is preferable to use the above-described polymer solution as the refrigerant. That is, by using a polymer solution as a refrigerant,
The polymer film generated on the surface of the steel sheet 10 can be reliably maintained until the end of cooling.

When a polymer solution is used as the refrigerant, the above-described coating nozzles 40, 40 can be omitted. In this case, a cooling water treatment system and the like are separately provided in a closed circuit. In addition, since the concentration of the polymer solution gradually decreases, the polymer solution is replenished at appropriate times, and the concentration of the polymer solution is controlled so as to be within a predetermined range. When the steel plate 10 can be sufficiently cooled only by the lower cooling nozzle 60, the upper cooling nozzle 50 is preferably omitted. That is, by omitting the upper cooling nozzle 50, a coolant such as water does not stay on the upper surface of the steel sheet 10, so that uneven cooling does not occur, and the shape of the steel sheet 10 is further improved, and a material having excellent uniformity is obtained. Thin hot-rolled steel sheet can be manufactured.

The specific effect when the upper cooling nozzle 50 is omitted and the steel sheet 10 is cooled only by the lower cooling nozzle 60 will be described.
A description will be given based on FIG. FIG. 2 shows the case where both-side cooling is performed using the lower cooling nozzle 60 and the upper cooling nozzle 50,
6 is a graph comparing the cooling bending amounts of the steel sheet 10 when single-side cooling is performed only by the lower cooling nozzle 60. In addition,
In the experiment results shown in FIG. 2, water alone, a 0.5% polymer solution, a 1% polymer solution, and a 5
% Polymer solution and a 10% concentration polymer solution.

As is apparent from FIG. 2, when only water is used as the refrigerant, the amount of bending in the single-sided cooling is significantly larger than that in the double-sided cooling, indicating that the single-sided cooling is inappropriate. However, when the above-described polymer solution was used as the refrigerant, the amount of cooling bend in the double-sided cooling and the single-sided cooling was slight, and it was found that even single-sided cooling did not adversely affect the product quality. .

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is a description of experimental results regarding the effects obtained when the method for manufacturing a thin hot-rolled steel sheet according to the present invention is used. Under the conditions described below, a controlled cooling experiment was performed using the above-described apparatus at a cooling target temperature of 500 ° C.

<Experimental Conditions> (1) Test material: 1.5 mm (thickness) × 200 mm (length) × 1200 mm (width) (2) Heating setting: 900 ° C. (10 min) (3) Concentration of added polymer solution : 0.5%, 1%, 5%, 10% (4) Cooling start temperature: 850 ° C Under the above-mentioned experimental conditions, cooling was performed by blowing a refrigerant from the outer periphery of the steel plate 10 using a multi-hole nozzle.

[0024] As is clear from the above-described experimental results, the use of the above-described polymer solution as the refrigerant significantly stabilized the cooling end temperature and drastically reduced the bending caused by residual stress caused by uneven cooling due to film boiling.

[0025]

Since the present invention has the above-described configuration,
The following effects are obtained. According to the first aspect of the invention, it is possible to perform uniform film boiling cooling by applying the polymer solution to the surface of the steel sheet. Therefore, it is possible to advantageously suppress plate shape deterioration such as so-called ear elongation and medium elongation caused by uneven cooling, and to suppress variation in materials, and to manufacture a thin hot-rolled steel sheet excellent in uniformity in shape and material. it can.

In particular, in the production of high-strength steel sheets, quenching does not occur in a supercooled state due to uneven cooling,
It is possible to eliminate a large change in the material caused by the hardening caused by the quenching. In addition, the polymer solution is separated from water at 100 ° C. or higher, and a polymer solution other than water adheres to the surface of the steel sheet. In the subsequent cooling, ordinary cooling equipment is used without performing a special oxidation suppression treatment. Can be cooled. Furthermore, since the polymer solution is water-soluble, when it is necessary to remove the polymer solution, it can be easily removed by washing with water.

According to the second aspect of the present invention, the polymer solution is used as the refrigerant. Therefore, the polymer film generated on the surface of the steel sheet can be reliably maintained until the end of cooling, and more uniform cooling can be performed, and oxidation of the steel sheet surface can be more reliably suppressed. According to the third aspect of the present invention, the steel sheet is cooled using the polymer solution as a coolant without previously applying the polymer solution to the steel sheet. Therefore, the cooling step can be simplified, and the oxidation suppressing treatment can be performed in the cooling step.

According to the invention described in claim 4, cooling is performed only from the lower surface side of the steel sheet. Therefore, since coolant such as water does not stay on the upper surface of the steel sheet, uneven cooling does not occur,
Further, the shape of the steel sheet is improved, and a thin hot-rolled steel sheet made of a material having excellent uniformity can be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an apparatus configuration for attaching a polymer solution to a steel sheet.

FIG. 2 is a graph comparing the cooling bending amount of a steel sheet in both-side cooling and one-side cooling.

[Explanation of symbols]

 10 Steel plate 20 Pinch roll 30 Roller 40 Application nozzle 50 Upper cooling nozzle 60 Lower cooling nozzle

Continued on the front page (72) Inventor Katsuhiro Aso 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division

Claims (4)

[Claims] 1. A polymer solution comprising a copolymer containing ethylene oxide and propylene oxide as monomer components when cooled after finishing rolling of a hot-rolled steel sheet, and is a high-temperature solution at a liquid temperature of 100 ° C. or higher. Separated into molecular liquid and water,
When the temperature is lower than 100 ° C., a polymer solution mixed with water is applied to a high-temperature steel sheet after finish rolling to form a uniform polymer film on the heat transfer surface, and then cooled with water. A method for producing a thin hot-rolled steel sheet. 2. The method for producing a thin hot-rolled steel sheet according to claim 1, wherein the polymer solution is used as the water-cooled refrigerant. 3. A polymer solution comprising a copolymer containing ethylene oxide and propylene oxide as monomer components when cooled after finishing rolling of a hot-rolled steel sheet, and is a high temperature solution at a liquid temperature of 100 ° C. or higher. Separated into molecular liquid and water,
A method for producing a thin hot-rolled steel sheet, comprising using a polymer solution mixed with water at a temperature of less than 100 ° C. as a coolant, and water cooling while uniformly forming the polymer film on the heat transfer surface. 4. The method for producing a thin hot-rolled steel sheet according to claim 1, wherein the water cooling after the finish rolling is performed only from the lower surface side of the steel sheet.