JP2003181522A - Method and device for manufacturing steel plate having excellent surface property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel plate manufacturing method which requires no complicated operation from an operating aspect and a steel plate manufacturing device which enables the method to be carried out in preferred conditions and whose equipment is simple and brings about a cost advantage capable of obtaining a steel plate with no relative roughness unevenness and with excellent appearances after pickling by substantially perfectly removing scales on the surface of the steel plate before finish-rolling. <P>SOLUTION: When the steel plate is manufactured by heating and hot-rolling, high-pressured water is sprayed to the surface of the steel plate at a discharge pressure of 45 MPa or more before finish-rolling as a first step descaling and then, for a period of time 0.1-4 seconds, a second step descaling of 0.1 J/mm<SP>2</SP>or more of input energy density onto the steel plate is performed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a steel sheet having excellent surface properties and an apparatus thereof, and more particularly to a method of manufacturing a steel sheet having an excellent appearance without roughness unevenness and an apparatus thereof.

[0002]

2. Description of the Related Art Generally, in the production of a steel sheet, a steel material (steel slab) is charged into a heating furnace prior to hot rolling, and 1100
Heat to a high temperature of ~ 1400 ° C. Since the inside of the heating furnace is in an oxidizing atmosphere, high-temperature oxides called scales are produced and adhered to the steel surface during heating. If this scale adheres to the surface of the steel material and is sent to the rolling process, it will bite on the surface of the rolled material and remain as scale flaws.
This scale layer is removed by jetting high-pressure water of about 15 MPa to the surface of the steel material. However, the ease of scale peeling depends on the steel composition, especially when the Si content is 0.5
In steels with high Si content such as mass% or more, scale containing a large amount of Fe ₂ SiO ₄ (firelite) is generated during heating before rolling, and this creates a complex morphology that penetrates into the base metal in contact with the scale layer. Since it cannot be peeled off, the scale cannot be sufficiently removed by the above high-pressure water jetting means, and the generation of surface defects cannot be prevented.

In order to solve such a problem, in the prior art, as disclosed in Japanese Patent Laid-Open No. 2000-254724, water is discharged from a nozzle to collide with the surface of a steel sheet to remove the scale, and hot rolling is performed. , Si content is 0.5
During hot rolling of high-Si steel of mass% or more, the billet is first heated in a heating furnace so that the surface temperature is less than 1173 ° C. (the melting point of Fe ₂ SiO ₄ ) and then the billet surface is heated. Technology for obtaining good quality steel plate with no surface flaw by removing Si scale by descaling by defining the collision flow velocity perpendicular component, collision energy and jet liquid phase conversion rate at the time of collision respectively Is proposed.

[0004]

In the above-mentioned prior art, the discharge pressure of the descaling water is considered to be 40 MPa or more in order to effectively destroy the scale. When the jet flow from such a nozzle is high, the degree of scale removal differs at the overlap between adjacent nozzle jets and other steel sheet locations, and the surface roughness of the pickled steel sheet after scale removal has a slight roughness. There was an inconvenience that spots were generated and the appearance of the steel sheet was impaired. In addition, the angle of the discharge nozzle with respect to the steel plate, which is effective for destroying and removing the scale, is almost vertical, but when the scale is removed at this angle, part of the scale once removed and scattered on the steel plate surface. It may remain, which is also a big problem for improving the surface quality.

The present invention has been made in order to solve such a problem, and is advantageous in terms of equipment and cost without requiring complicated setting of descaling conditions, and finally. It is an object of the present invention to obtain a method for manufacturing a steel sheet having excellent surface properties without roughness unevenness and a manufacturing apparatus suitable for carrying out the method.

[0006]

The gist of the present invention for solving the above problems is as follows. (1) When manufacturing a steel sheet by heating and hot rolling, before finishing rolling, the first stage descaling is 45 MPa.
High-pressure water was jetted onto the surface of the steel sheet at the above discharge pressure, and then,
The input energy density on the steel sheet was 0.
A method for producing a steel sheet having excellent surface properties, which comprises performing a second stage descaling of 1 J / mm ² or more. (2) The method for producing a steel sheet having excellent surface properties according to (1), characterized in that the high-pressure water jet angle with respect to the steel sheet in the first-stage descaling is made substantially vertical. (3) Manufacturing of a steel sheet having excellent surface properties as described in (1) or (2), wherein the heating temperature is such that the steel surface temperature is less than 1173 ° C., and the time at 1100 ° C. or higher is within 2 hours. Method. (4) In a hot-rolled steel sheet manufacturing apparatus including a rough rolling mill and a finish rolling mill following a heating furnace, high pressure water is jetted onto the surface of the steel sheet at a discharge pressure of 45 MPa or more before the finish rolling mill. An apparatus for producing a steel sheet with excellent surface properties, which is equipped with a second-stage descaling apparatus and a second-stage descaling apparatus with an input energy density on the steel sheet of 0.1 J / mm ² or more. (5) The apparatus for producing a steel sheet having excellent surface properties according to (4), characterized in that the angle of the high-pressure water jet nozzle in the first stage descaling device with respect to the steel sheet is substantially vertical. (6) The angle of the spray nozzle in the second stage descaling device with respect to the steel plate is 5 ° in the direction opposite to the steel plate transport direction.
The apparatus for manufacturing a steel sheet having excellent surface properties according to (4) or (5), which is inclined as described above.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 shows an example of an apparatus comprising a steel plate heating / rolling line for carrying out the manufacturing method of the present invention.
Is the steel (slab) required temperature (1200-1300 ° C)
A heating furnace for heating to 2 to a rough rolling stand for roughly rolling the steel material after heating, 3 to a finish rolling stand for hot rolling the roughly rolled steel material (rough bar) to a target plate thickness,
Reference numeral 4 denotes a runout table for cooling (water cooling) the finished rolled steel sheet while conveying the steel sheet, and 5 denotes a coiler for winding the cooled hot rolled steel sheet. It should be noted that the inlet side of the rough rolling stand 2 is a high-pressure water jet method for removing the scale layer formed on the surface of the steel material when the steel material is heated to a high temperature. A descaling device 6 (for removing scale) is installed.

In the apparatus of the present invention, a first-stage descaling device 7 for injecting high-pressure water onto the surface of the steel sheet at a discharge pressure of 45 MPa or more is installed in front of the finish rolling stand 3 and is followed by this. As the second stage descaling device 8, the input energy density on the steel plate is 0.1 J /
A descaling device with a capacity of mm ² or more is installed. In addition, these descaling devices 7 and 8
Are arranged so as to correspond to the upper and lower surfaces of the steel plate, respectively.

FIG. 2 shows an enlarged schematic view of the first-stage and second-stage descaling devices 7 and 8. As shown in the drawing, it is preferable that the angle α of the high-pressure water jet nozzles 7a, 7b in the first stage descaling device 7 with respect to the steel plate S be substantially vertical (0 °) in terms of effective scale destruction / removal. . Making the angle α substantially perpendicular to the steel plate S includes a range where the incident angle α is 0 ° ± 4 °, and the function does not change if the angle in this range is maintained. Increasing the incident angle is not preferable because high-pressure water jet streams of adjacent nozzles interfere with each other to generate different roughness unevenness.

On the other hand, the angle β of the spray nozzles 8a, 8b in the second stage descaling device 8 with respect to the steel plate S is preferably inclined by 5 ° or more in the direction opposite to the steel plate conveying direction. If the nozzle is tilted in the same direction as the steel plate conveyance direction, the scale that may flow down may be fed to the finish rolling mill 3 side. If the nozzle angle β is less than 5 °, the scale may be sufficiently moved to the upper surface edge portion of the steel plate S. It may not be possible to drain it. Although the nozzle arrangement in the width direction of the steel plate is not shown in the drawing, the first stage and the second stage
Both the stage descaling devices are provided with a number of nozzles that cover the width of the steel plate sufficiently and that the jet flows from the adjacent nozzles collide with the surface of the steel plate without a gap. In this case, it is necessary to adjust the pressure of the nozzle header so that the discharge pressure from each nozzle is almost equal.

In the present invention, as shown in FIG. 2, the surface of the steel sheet S is sprayed by the first-stage descaling device 7 by vertically injecting high-pressure water toward the steel sheet surface at a discharge pressure of 45 MPa or more. The scale layer 9 that has been generated on the steel plate is crushed and removed, and then the steel plate is sprayed by the descaling water that is jetted at an angle of 5 ° or more in the direction opposite to the steel plate transport direction by the second stage descaling device 8. Flush or scatter the remaining crushed scale on the surface. Due to the action of the auxiliary descaling water by the second-stage descaling device 8, a part of the crushed scale 9'which may remain on the steel plate surface only by the first-stage descaling device 7 is transferred to the steel plate surface. It will be completely removed before burning. That is, as shown in FIG. 2, the crushed scale 9 ′ flows down from the edge portion on the upper surface of the steel sheet, and peels off / falls on the lower surface of the steel sheet.

The reason why the discharge pressure in the first stage descaling device 7 is set to 45 MPa or more is to exert the function of crushing the scale layer firmly adhering to the surface of the steel sheet. If it is less than 45 MPa, This is because it is insufficient to sufficiently destroy and crush the layer. Moreover,
When the discharge pressure in the first stage is weak, the above-described subtle roughness unevenness may not be clearly seen even if some unevenness due to descaling occurs. Although the upper limit of the discharge pressure is not specified in particular, there are restrictions on equipment, so it is about 10
It is about 0MPa.

The descaling condition in the second stage descaling device 8 is defined by the input energy density on the steel sheet, because the descaling device 8 has an auxiliary role of the first stage, that is, the scale. It does not require a discharge pressure to crush the layer, it simply cleans (cleans) the remaining scale.
Since it suffices to have such a function, it is defined by the energy density. The lower limit of this input energy density requires at least 0.1 J / mm ² or more of energy in order to achieve cleaning of the crushed scale (flowing off from the steel plate surface or scattering in some cases), and the upper limit. However, if the temperature is too high, the steel plate will be cooled more than necessary, and in order not to impair the descaling effect of the first step, it should be kept to about 0.5 J / mm ^2. Is desirable.

Further, the time constraint of 0.1 to 4 seconds is provided between the descaling by the first stage descaling device 7 and the auxiliary descaling by the second stage descaling device 8. If the descaling work of the 1st and 2nd steps is continued within a time within this range, the descaling of the 2nd step is performed before the crushed scale remaining in the 1st descaling is burned onto the steel plate surface. This is because it can be drained off by scaling. The lower limit of 0.1 seconds is the minimum technically possible time, and if the upper limit of 4 seconds is exceeded, the risk of scale burn-in increases. Note that this time constraint is also related to the distance between the first-stage descaling device and the second-stage descaling device and the steel plate conveyance speed during descaling. Also,
It is desirable that the first-stage and second-stage descaling nozzles are arranged so that the interference portions of the water films do not overlap, as shown in FIG. 3, for example.

As described above, in a high Si-containing steel having a Si content of 0.5% by mass or more, a scale having a high adhesiveness containing a large amount of Fe ₂ SiO ₄ (firelite) is produced during heating before rolling. Therefore, in the practice of the present invention, it is necessary to prevent Fe ₂ SiO ₄ from being generated as much as possible in order to improve the descaling property.
Therefore, it is desirable that the high Si-containing steel sheet is heated at a steel surface temperature below 1173 ° C., which is the melting point of Fe ₂ SiO ₄ . Further, the heating temperature is required to be 1100 ° C. or higher for 2 hours or less. If the temperature is lower than 1100 ° C, the temperature for hot rolling on the subsequent stage cannot be secured, and it is considered that rolling is substantially impossible. Further, the temperature is too low and a uniform scale layer is formed on the surface of the steel sheet. There is a possibility that the scale is not generated and the scale is not crushed in a good state even by the high-pressure water injection by the first stage descaling device. Further, when the time of 1100 ° C. or higher exceeds 2 hours, the heating time is too long and the Fe ₂ SiO in the scale is too long.
_{The four} layers become thicker and difficult to remove, which causes a problem of descaling failure.

[0016]

EXAMPLES Descaling of hot-rolled steel sheets was performed under the various conditions shown in Table 2 using the steel types having the components shown in Table 1. The results are also shown in Table 2 as a descaling effect.
In Table 2, No. 1-5, No. 10-14, N
o. 16, No. 17, No. No. 19 is an example of implementation within the range of the descaling conditions specified in the present invention. Other than that, the heating temperature, the time over 1100 ° C., the first-stage discharge pressure, the descaling time, the first-stage discharge angle, the second stage As a comparative example, one of the eye energy density and the second-stage discharge angle is out of the range defined by the present invention or the second-stage descaling is not performed (No. 7, 15, 18). Listed. As can be seen from Table 2, no descaling spots were found in any of the examples according to the present invention, whereas descaling spots were found throughout the comparative examples.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

As described above, according to the method for manufacturing a steel sheet of the present invention, the scale on the surface of the steel sheet can be removed almost completely before finish rolling, and the roughness unevenness can be obtained by pickling after finish rolling. It is possible to obtain a steel sheet having an excellent appearance without any appearance. Further, the method of the present invention does not require a complicated operation in descaling from the viewpoint of operation. On the other hand, according to the manufacturing apparatus of the present invention, the method can be carried out in a suitable state, and the descaling equipment is simple and cost effective.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a hot-rolled steel sheet production line for carrying out the production method of the present invention.

FIG. 2 is a first-stage and second-stage escapement which is an essential part of the present invention.
It is an expansion schematic diagram of a ring part.

FIG. 3 is a schematic plan view showing a state in which the water film discharged from the first and second stage descaling nozzles of the present invention collides with the steel plate.

[Explanation of symbols]

1 heating furnace 2 Rough rolling stand 3 finish rolling stand 4 Run-out table 5 coilers 6 Descaling device (Rough rolling stand entry side) 7 First stage descaling device 8 Second stage descaling device 9 scale layer S steel plate

Claims (6)

[Claims] 1. When manufacturing a steel sheet by heating / hot rolling, high-pressure water is jetted onto the surface of the steel sheet at a discharge pressure of 45 MPa or more as a first stage descaling before finish rolling, and then 0.1-4. A method for producing a steel sheet having excellent surface properties, which comprises performing second-stage descaling with an input energy density on the steel sheet of 0.1 J / mm ² or more per ^second . 2. The method for producing a steel sheet having excellent surface properties according to claim 1, wherein the high-pressure water jet angle with respect to the steel sheet in the first-stage descaling is made substantially vertical. 3. The production of a steel sheet having excellent surface properties according to claim 1, wherein the heating temperature is such that the steel surface temperature is lower than 1173 ° C., and the time of 1100 ° C. or higher is within 2 hours. Method. 4. A hot-rolled steel sheet manufacturing apparatus comprising a rough rolling mill and a finish rolling mill following a heating furnace, and high-pressure water is jetted onto the surface of the steel sheet at a discharge pressure of 45 MPa or more before the finish rolling mill. 1st stage descaling device and ^2nd with energy density on the steel plate of 0.1 J / mm ² or more
An apparatus for manufacturing steel plates with excellent surface properties, which is equipped with a stage descaling device. 5. The apparatus for producing a steel sheet having excellent surface properties according to claim 4, wherein the angle of the high-pressure water jet nozzle in the first stage descaling device is substantially perpendicular to the steel sheet. 6. The excellent surface texture according to claim 4, wherein the angle of the spray nozzle in the second stage descaling device with respect to the steel plate is inclined by 5 ° or more in the direction opposite to the steel plate conveying direction. Steel plate manufacturing equipment.