JPH06277706A - Production of hot rolled thick steel plate having tight scale - Google Patents

Abstract

PURPOSE:To uniformly stick a thin high-adhesion scale to the surface of a thick steel plate by rolling the steel plate after descaling at a specified pressure in the vicinity of biting side, cooling it with a specified cooling capacity in the vicinity of delivering side and specifying the temp. for finish rolling. CONSTITUTION:Just before the steel plate to be rolled is bitten between work rolls 2, 3, oxides on the upper and lower surfaces are removed with the high- pressure injection water of the collision pressure of 1.2kg/cm<2> from descaling nozzles 14, 20. The upper and lower surfaces of the steel plate delivered to the back side B after rolling are cooled by jetting the cooling water of the cooling capacity of >=500kcal/m<2>hr deg.C from cooling-water injecting nozzles 12-1, 17-1. Next, just before the steel plate on the back side of a rolling mill 1 is bitten between the work rolls 2, 3 as a 2nd pass, scale is removed with the high-pressure injection water from the descaling nozzles 14-1, 20-1 and the steel plate delivered to the front side A of the rolling mill is cooled with cooling water from the nozzles 12, 17. Ten and several passes of such rolling are reciprocated and simultaneously the steel plate is cooled to <=840 deg.C in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for rolling hot-rolled thick steel plate with a reversible hot rolling mill.

[0002]

2. Description of the Related Art In the manufacture of thick steel plates, a slab is usually placed in a heating furnace, heated in a temperature range of 1200 to 1250 ° C., and then sent to a descaling device to remove the scale generated during heating, and then one Alternatively, ten-sided rolling or finish rolling for rolling to a predetermined product thickness is performed by two reversible rolling mills. The thick steel plate after finish rolling is sent to a hot leveler, hot-corrected, and then water-cooled so that the surface temperature of the steel plate becomes 800 ° C. or lower.

In such a conventional method, since the slab rolled by the reversible rolling mill is at a high temperature and the rolling time is relatively long, a thick scale and non-uniformity occur at the end of finish rolling. When this is passed through the next hot leveler or formed by pressing, the scale peels off and is pushed into the steel plate to form a flaw on the steel plate surface, or such thick steel plate is formed into a bent member. In that case, the scale produced on the surface of the thick steel plate caused many problems in various aspects, such as uneven coating due to non-uniformity of the scale. In order to solve these problems, it has been demanded to make the thickness of the scale formed on the surface of the thick steel plate as thin as possible and to improve the adhesion (tightness).

As a method of improving the adhesion of scale,
In the field of hot-rolled wire, for example, "iron and steel"
65 (1979), S390, a method of reducing the scale thickness has been proposed. In the field of hot-rolled steel strips, as an example of reducing the scale thickness, for example, as described in JP-A-58-157517, a method of covering a finishing rolling mill and a water-cooling device with a laminar water-cooling to shut off from the atmosphere, JP-A-60-24320, JP-A-60-
As described in Japanese Patent No. 77922, a method of cooling low carbon aluminum killed steel after rolling to a low temperature in a non-acidic atmosphere,
A method of cooling to a low temperature in an inert gas or reducing gas atmosphere immediately after finish rolling as described in JP-A-61-123403, or a low carbon containing Cr as described in JP-A-61-195702. Methods such as cooling aluminum killed steel immediately after rolling have been proposed.

However, all of these methods require equipment for cutting off steel strips or wire rods that are passed at high speed from the atmosphere, or equipment for rapidly cooling these steel strips to a low temperature immediately after rolling. Therefore, there is a drawback that a great equipment cost is brought about. The hot-rolled steel strip manufactured in the continuous rolling step described above is extremely advantageous in reducing the scale because the high-temperature residence time is significantly shorter than that of the thick steel sheet. Since the internal heat capacity is large and the rolling time in reverse rolling is relatively long as described above, almost no useful method has been disclosed regarding the scale control method for thick steel plates.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems of thick steel plate and form a thin scale uniformly and with good adhesion on the surface of the thick steel plate.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is to perform descaling at a position closest to the rolling mill in the vicinity of the biting side and the biting side of a rolled steel sheet of a reversible hot rolling mill. Nozzles are arranged vertically, and a plurality of cooling water jet nozzles are sequentially arranged adjacent to the descaling nozzle in the steel plate feed direction and vertically, so that the descaling nozzle is formed on the steel plate surface near the biting. From the surface to remove the scale generated on the surface by spraying pressure water with a collision pressure of 1.2 kg / cm ² or more, and then the rolled steel sheet is rolled into a rolling mill, and then the rolled steel sheet is rolled. The cooling capacity from the cooling water injection nozzle is 50 at the biting side of the
Cooling water of 0 kcal / m ² · hr ℃ or more is sprayed to cover the surface of the rolled steel sheet, and the atmosphere is shut off for cooling.

Then, rolling accompanied by such descaling and cooling is carried out by reciprocally transporting a steel sheet having ten or more passes.
Thus, the rolled steel sheet is rolled to a desired thickness and rapidly cooled to 840 ° C or lower. In this way, descaling and cooling are performed at the same time for each rolling, and by cooling to 840 ° C. or less in a short time, an extremely thin and uniform scale with good adhesion is formed on the surface of the thick steel plate.

That is, according to the above rolling, the scale generated during the transportation and the scale generated after the reduction in the previous pass are removed by the descaling before the rolling, and the surface is cooled by the cooling after the rolling to reduce the scale. The tight scale is realized by suppressing the generation of. Although the thick steel sheet is air-cooled during the waiting time during rolling, thermal scale is generated in the scale layer due to cooling and multiple heat, and the scale is easily peeled off.

[0010]

First, an example of equipment for carrying out the present invention will be described with reference to FIG. In the housing 8 of the reversible hot rolling mill 1,
An upper work roll 2 and an upper rolling reinforcement roll 4 in contact with the roll, and a lower work roll 3 and a lower rolling reinforcement roll 5 in contact with the roll are arranged. Top guides 9 and 9-1 are provided on the biting side (or biting side) and the biting side (or biting side) of the rolling mill, and the top guides 9 and 9-1 are looked into the hole portions of the top guide, and are placed on the steel plate surface. Desuke nozzle 14, 14 which injects water
-1 and cooling water injection nozzles 12 and 12-1 are provided. The Desuke nozzles 14 and 14-1 are provided closest to the upper work roll 2 and are connected to the hydraulic Desuke headers 13 and 13-1 so as to have an attack angle to the moving steel plate surface.

The cooling water injection nozzles 12 and 12-1 are installed adjacent to the Desuke nozzles 14 and 14-1, and are cooled headers 11 and 11 so as to inject water onto the surface of the steel sheet at a substantially right angle.
-1. The injection direction of the nozzles 12 and 12-1 may be directed to the rolling direction in order to improve drainage.

Further, the roller tables 10 and 10-1 having the same feed surface as the feed surface of the lower work roll 3 are provided on the bite side (or bite side) and the bite side (or bite side) of the rolling mill. It is provided, and the Desuke nozzle 20, 20-1 is provided between the lower work roll 3 and the roller of the roller table.
, Through the nozzle holders 19 and 19-1 so as to have an attack angle with respect to the steel plate surface.
1, and cooling headers 15 and 15-1 through nozzle holders 16 and 16-1 so that cooling water jet nozzles 17 and 17-1 spray between the rollers of the roller table at substantially right angles to the steel plate surface. It is provided in.

In the figure, reference numerals 6 and 6-1 designate guides on the rolling mill, and 7, 7
-1 is a rolling mill lower guide. In the above apparatus, when rolling the high-temperature thick steel plate S, the rolling mill 1 is used as the first pass.
Just before the rolled steel sheet on the front surface A of the above is bitten into the work rolls 2 and 3, the upper and lower surface oxides are removed by the high-pressure jet water from the Desuke nozzles 14 and 20, and the rolled steel sheet is rolled to the rear surface B. Cooling water jet nozzle 12-
Cool with cooling water from 1, 17-1.

Next, in the second pass, immediately before the rolled steel sheet on the rear surface B of the rolling mill 1 is engaged with the work rolls 2 and 3, high pressure jet water from the Desuke nozzles 14-1 and 20-1 moves the steel sheet up and down. The scale produced on the surface is removed, and the upper and lower surfaces of the rolled steel sheet rolled and bitten by the front surface A of the rolling mill are cooled with cooling water from the cooling water jet nozzles 12 and 17.
Then, the reciprocal rolling is repeated a plurality of times until the desired plate thickness is obtained.

The state of the scale when rolled by the method of the present invention is shown in FIGS. 2, 3 and 4 together with a comparative example. The descaling and cooling conditions for obtaining the results of these figures are as shown in Table 1. In addition, case 1
4 is an example of the present invention, and cases 5 and 6 are comparative examples. Case 5 is a case where descaling was only performed in passes No. 2 and No. 3, cooling water was not injected in all remaining passes, and case 6 was an example in which the collision pressure of the hydraulic pressure header was less than 1.2 kg / cm ^2. . The expressions (1) and (2) in Table 1 are the values obtained by the following.

Equation (1) Colliding pressure p = 68 × (P ^0.5 × Q
× (90−θ2) / (h ² × θ1) P: Injection pressure kg / cm ² Q: Injection water amount L / min h: Nozzle height mm θ1: Nozzle injection angle θ2: Nozzle attack angle formula (2) Cooling capacity LoGh ＝ 2.358 + 0.663 × LogW-0.00147 ×
Ts W: Water amount density L / m ² · min Ts: Steel plate surface temperature ℃ (using 800 ℃) Source: Special Report No. 29 “Forcible cooling of steel” issued by Japan Iron and Steel Institute, page 16

[0017]

[Table 1]

FIG. 2 shows the scale thickness of a thick steel plate having a finishing temperature of 760 ° C. obtained after rolling 15 passes of a 1160 ° C. ordinary steel slab under the conditions shown in Table 1 for each case. In the case of the present invention (cases 1 to 4), the scale was 4 to 5 μm, but in the comparative example (conventional method (cases 5 and 6)), the thickness was 11 μm, and the scale scores were all 1.

The scale rating is a bending radius r = 1.5 ×
After the 90-degree bending test of t, visual judgment was performed, and the judgment criteria are as shown in the table below. In Cases 2 and 5, the relationship between the rolling finish temperature and the scale thickness was investigated, and the results are shown in FIG. Further, FIG. 4 shows the results of FIG. 3 in the relationship between the scale rating and the scale thickness. In the figure, the mark ● indicates the case 2, and the mark ○ indicates the case 5.

As a result, if the Desuke collision pressure of 1.2 kg / cm ² or more, cooling of 500 kcal / m ² · hr · ° C or more, and rolling finishing temperature of 840 ° C or less, thick steel plate with a scale thickness of 10 μm or less is surely obtained. You can see that As described above, the conditions of the present invention, namely, the descaling with a collision pressure of 1.2 kg / cm ² or more and the cooling capacity of 500 kcal / m ² · hr. It was found that a scale having a thickness of 10 μm or less was formed uniformly and with good adhesion on the surface.

[0021]

EXAMPLES In a thick steel plate production line, the reversible hot rolling mill shown in FIG. 1 was used to measure C: 0.172% by weight% and Si:
0.392%, Mn: 1.46%, P: 0.018%,
A slab consisting of S: 0.007%, Al: 0.28%, and the balance Fe was heated in a heating furnace and then extracted at a temperature of 1160 ° C. Based on the pass schedule shown in Table 2, under the conditions of Table 1 and Case 2. A steel plate having a product thickness of 25 mm was manufactured from a slab having a thickness of 150 mm. The rolling end temperature was 760 ° C.

In the comparative example (conventional method), descaling was performed immediately before rolling in the second and third passes under the conditions shown in Table 1 and Case 5, and the plate was allowed to cool until the surface temperature fell below 800 ° C (waiting for temperature). ), And the subsequent passes were all rolled by non-injection (air cooling). The 14th pass and the 15th pass were shape finish rolling. FIG. 5 shows the relationship between the rolling time and the steel plate surface temperature in the rolling pass. As shown in this figure, in the case of the method of the present invention, the surface temperature of the steel plate is 800 within 300 seconds after the start of rolling.
Although it is cooled to ℃ or less, in the case of the comparative example, it becomes 800 ℃ or less after 700 seconds or more.

Table 3 shows the state of the scale in the above rolling.
Shown in. As can be seen from Table 3, the comparative example has a scale thickness of 11 μm and a scale rating of 4, whereas the scale of the invention example is 5 μm thick and has a scale rating of 1.
However, the surface properties were significantly improved as compared with the comparative example.

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

As described above, according to the method of the present invention, an extremely thin scale having a thickness of 4 to 5 μm and having good adhesion can be applied to the surface of a thick steel plate almost uniformly without exposing the base metal. As a result, a thick steel plate having a smooth surface can be obtained, which makes the subsequent working process extremely easy, and has a great effect on expanding the demand for thick steel plates.

[Brief description of drawings]

FIG. 1 is a schematic front view showing a rolling method of the present invention.

FIG. 2 is a diagram showing a relationship between a case number and a scale thickness.

FIG. 3 is a diagram showing a relationship between a thickness of a thick steel plate surface scale and a rolling finishing temperature.

FIG. 4 is a diagram showing a relationship between a surface thickness of a thick steel plate scale and a scale rating.

FIG. 5 is a diagram showing the relationship between rolling time and steel plate surface temperature in the example of the present invention and the comparative example.

[Explanation of symbols]

 1 ... Reversible hot rolling mill 2, 3 ... Upper and lower work rolls 4, 5 ... Upper and lower rolling reinforcing rolls 6,6-1 ... Rolling mill upper guide 7, 7-1 ... Rolling mill lower guide 8 ... Housing 9, 9-1 ... Top guide 10, 10-1 ... Roller table 11, 11-1 ... Upper cooling header 12, 12-1 ... Upper cooling water injection nozzle 13, 13-1 ... Upper Desuke header 14, 14-1 ... Upper Desuke nozzle 15, 15-1 ... Lower cooling header 16, 16-1, 19, 19-1 ... Nozzle holder 17, 17-1 ... Lower cooling water injection nozzle 18, 18-1 ... Lower Desuke header 20, 20-1 ... Lower deck nozzle

Claims (1)

[Claims] 1. When producing a thick steel sheet by a reversible hot rolling mill, the steel sheet to be rolled is subjected to descaling with a collision pressure of 1.2 kg / cm ² or more in the vicinity of the biting side of the hot rolling mill, and thereafter. Immediately after rolling with the hot rolling mill, the rolled steel sheet is cooled near the biting side of the hot rolling mill immediately after rolling with a cooling capacity of 5
A method for producing a tight-scale hot-rolled thick steel sheet, characterized in that cooling is performed at 00 kcal / m ² · hr · ° C or higher, and such rolling is performed in multiple passes in a reciprocating manner to finish rolling at a finishing rolling temperature of 840 ° C or lower. .