JP2003094101A - Continuous hot rolling method and machine thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous hot rolling method and a continuous hot rolling machine suitable for the cost effective manufacturing of a hot-rolled steel plate of fine grained steel. SOLUTION: As a heated plate P is rolled so as to be pressed at the cumulative contortion of 0.6 or more with multiple stands of mills F1-F6 arranged on a tandem, the heated plate is cooled with a curtain wall cooler 7 at the outlet side of the mills F4-F6 of the three rearside stands.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The claimed invention relates to a continuous hot rolling method and a continuous hot rolling equipment suitable for producing a fine grain steel hot rolled steel sheet having a fine structure mainly composed of fine grain ferrite. is there.

[0002]

2. Description of the Related Art As a method for producing a so-called fine grain steel sheet having a fine ferrite structure inside and excellent in mechanical properties, a large reduction rolling method, a controlled rolling method and the like are known. Regarding the large reduction rolling method,
JP-A-58-123823 and JP-B-5-6556.
It is described in Japanese Patent No. This method promotes the strain-induced transformation from the austenite (γ) phase to the ferrite (α) phase by applying a large reduction to the austenite grains, thereby making the structure fine. on the other hand,
In the controlled rolling method of No. 3, not only can Nb (Niobium) or Ti (Titanium) be contained as a component to increase the tensile strength easily by the precipitation strengthening action of Nb and Ti, but also the recrystallization of austenite grains of Nb and Ti can be suppressed. This is a method in which the strain-induced transformation from the γ phase to the α phase is promoted when low-temperature rolling (ferrite region rolling) is performed by the action, and the ferrite grains are miniaturized. In order to industrially and commercially produce fine-grained steel by carrying out such a rolling method, a) a general type of rolling mill cannot be used because of the large load, and There is a problem that it is difficult to maintain an appropriate temperature of the rolled material (steel plate), and c) the rolling load is high and the temperature rises remarkably, so that the rolling roll or the rolled material is deformed and a good sheet profile cannot be obtained.

As means for solving such problems and enabling smooth production of hot-rolled fine-grain steel, the inventors have already developed a new type of rolling in which a multi-stand mill is arranged in tandem. The machine was developed and at the same time an appropriate rolling method was established (patent application for Japanese Patent Application No. 2001-77293). The rolling method is such that the steel sheet is strongly rolled down (i.e., is subjected to high rolling down to a cumulative strain of 0.9 or more) centering on the mill near the rear stage, and the steel sheet is kept at an appropriate temperature so that the ferrite grain size is 4 μm. It is intended to manufacture high-quality fine-grained steel plate of less than or equal to the grade. In order to realize such a method, the rolling mill adopts a configuration capable of achieving required reduction by a relatively low rolling load and capable of strongly cooling the steel sheet.

[0004]

According to the above rolling method, if the steel sheet is sufficiently cooled under high pressure and strongly cooled (temperature control), an extremely high-quality hot-rolled steel sheet of fine-grained steel can be obtained by an ordinary tandem rolling mill. Although it has the significance of clarifying that it can be industrially produced, it is not the one to clarify the technique for reducing the burden on the facility or operation and manufacturing the similar steel sheet most effectively. In other words, it was not known how much each reduction / cooling requirement has an effect on the metallurgical structure of the steel sheet. Therefore, while suppressing the deterioration of quality (ferrite grain size, etc.) as much as possible, It has not been possible to establish a method for producing fine-grained steel sheet at a low cost by alleviating the above.

If the rolling method is not improved in view of such cost-effectiveness, commercial production of fine-grained steel sheet having a practically good quality (grain size etc.) is rather low. Is difficult If the above-mentioned level of high pressure is indispensable regardless of the quality of the steel sheet, the production cost will increase due to the configuration of the rolling mill and the consumption of the rolling rolls. This is because the equipment for cooling also needs a high equipment cost and operation cost due to the above.

An object of the claimed invention is to provide a continuous hot rolling method and a continuous hot rolling equipment suitable for producing a fine grain steel hot rolled steel sheet, which are preferable in terms of cost efficiency. Is.

[0007]

The method of continuous hot rolling according to claim 1 uses a mill having a plurality of stands arranged in tandem so that a heated steel sheet has a cumulative strain of 0.6 or more. It is characterized in that it is cooled on the outlet side of the two or more mills in the latter stage while rolling. In this specification, “strain” means ε = (the difference between the thickness h ₀ of the steel plate on the entrance side of each stand and the thickness h ₁ on the exit side of the stand divided by the average thickness of the two. h ₀ -h ₁₎ / refers to _{{(h 0 + h 1)} / 2}. In addition, "cumulative strain" means the strain at each stage of the latter three stands of the mill used (disregard the stand on the upstream side because they have less influence), considering the strength of influence on the metal structure. Weighted integration, and the strains at the final stage and the preceding and previous stages are respectively ε _n , ε _n-1 , and ε.
_{When n-2} , ε _c is expressed by ε _c = ε _n + ε _n-1 / 2 + ε _n-2 / 4.

According to the method of this claim, it is possible to smoothly manufacture a fine-grain steel hot-rolled steel sheet having an average ferrite grain size that is sufficiently fine and excellent in mechanical properties and is highly practical at low cost. it can. a) Using a mill with multiple stands, applying a high reduction of cumulative strain of 0.6 or more, and b) cooling the steel sheet strongly at the exit side of multiple mills near the rear stage, so that the final stage and until then With the treatment of effectively removing the heat generated during processing with the mill to stop the grain growth of the fine structure by maintaining an appropriate temperature, the fine grain steel hot rolled steel sheet with an average ferrite grain size of about 10 μm or less is obtained. Can be manufactured.

The fact that the fine grain steel sheet can be obtained by such treatment has been clarified by the present inventors through a recent research study. In other words, even if the former of the conditions of high pressure / strong cooling for steel sheets is relaxed to some extent (that is, even if the cumulative strain is not increased to 0.9), high-quality fine-grain steel steel sheets with a ferrite grain size that is not so coarse are obtained. It turned out that it can be manufactured. In the investigation, a thin plate having a carbon content of 0.5% or less and an alloying element content of 5% or less has an average ferrite grain size of 3 to 7 μm due to the above-described cumulative strain and cooling.
It was possible to make it to the extent.

When the accumulated distortion is 0.6 or more,
The reduction rate required for each mill, especially for the mills closer to the rear stage, is considerably reduced (to about 30%), and the cost required for equipment and operation is significantly reduced. It is unlikely that the tip of the steel plate slips without being bitten by one of the mills. On the other hand, if the average ferrite grain size is 10 μm or less, the fine-grain steel plate has significantly higher mechanical properties and is wider than the general (non-fine-grain steel) hot-rolled steel sheet having the same grain size of more than 10 μm. It can be expected to have uses. That is,
According to the continuous hot rolling method of this claim, it becomes possible to manufacture a fine-grain steel hot-rolled steel sheet having sufficiently high practical quality at extremely low cost according to relaxed manufacturing conditions.

The continuous hot rolling method according to a second aspect of the present invention is further characterized in that the rolling end temperature is set within the range of not less than Ar ₃ transformation point −50 ° C. and not more than Ar ₃ transformation point + 50 ° C. . The "rolling end temperature" is the surface temperature of the steel sheet measured by a thermometer installed on the downstream side of the rolling equipment (several meters downstream from the arranged final stage mill).

By controlling the cooling strength and setting the rolling end temperature as in the method of this claim, the ferrite structure is fine (for example, the grain size is 10 μm) and the mechanical strength including elongation is set. It is possible to manufacture a fine-grained hot-rolled steel sheet having a high heat resistance (for example, a steel sheet having a carbon content of 0.5% or less and an alloying element content of 5% or less). According to the investigation by the inventors, when the rolling end temperature exceeds the Ar ₃ transformation point + 50 ° C., the ferrite grain size becomes coarse, and the temperature is the Ar ₃ transformation point −
When the temperature is lower than 50 ° C., the elongation becomes small, and the merit of being a fine-grain steel plate is diminished. However, if the rolling end temperature is kept within a range of ± 50 ° C across the Ar ₃ transformation point, the elongation is high, and the ferrite grain size is small, which is excellent in other mechanical properties. Can be obtained.

The continuous hot rolling method according to claim 3 is characterized in that the steel sheet is cooled by a curtain wall type cooling means. The "curtain wall type cooling means" is a cooling means of a type in which a large amount of cooling water is made to flow in a laminar flow from above and below like a curtain, and is applied to the upper and lower surfaces of the rolled material over the entire width.

Since the curtain wall type cooling means strongly cools the steel sheet with a large amount of cooling water flowing as described above, it enables smooth production of the fine grain steel sheet according to claims 1 and 2. That is, if the cooling means, it is possible to maintain the rolled material in a temperature range suitable for performing under high pressure, including the case where the rolled material is accelerated, the action of stopping the grain growth of the fine structure immediately after rolling Is also secured. Further, since the means applies cooling water over the entire width of the rolled material, the rolled material can be cooled uniformly without being biased in the width direction.

In the rolling method according to claim 4, in particular, the carbon content is 0.5% or less and the alloying element content is 5%.
The following steel sheets are rolled to obtain fine grain steel steel sheets having an internal average ferrite grain size of about 3 to 7 μm.

The fine grain steel sheet having such a chemical composition and a ferrite grain size has a high balance of mechanical properties (it has versatility in terms of tensile strength, elongation, ductility, etc.) and also has good weldability. It is excellent. Therefore, it is considered to be in high demand because it has a wide range of uses, is relatively low in price, is easily available, and has recyclability. Therefore, the rolling method for manufacturing such a steel sheet has a high social contribution and is accompanied by sufficient economic rationality for its production.

The continuous hot rolling equipment according to claim 5 is:
In a continuous hot rolling facility in which multiple-stand mills are arranged in tandem, a curtain wall type cooling means for rolled material is arranged on the exit side of two or more mills in the latter stage, and the rolling end temperature is measured to obtain the temperature. It is characterized in that means for changing the amount of water (cooling water amount) of the cooling means is additionally provided.

According to this continuous hot rolling equipment,
According to the method described in (1), the rolling method according to each of the above claims can be realized. It is easy to give a cumulative strain of 0.6 or more to the heated steel sheet (rolled material) by using the mill arranged as described above,
This is because the steel plate can be cooled sufficiently strongly by using the curtain wall type cooling means arranged on the outlet side of the mill above the stand. If a means for changing the amount of water of the cooling means according to the rolling end temperature is used together with the cooling means, the cooling strength can be appropriately controlled to determine the rolling end temperature as in claim 2, for example. Easy to do.

The continuous hot rolling equipment according to claim 6 is characterized in that a fluid jet spray for removing cooling water on the rolled material is arranged downstream of the cooling means at the exit side of the stand at the final stage. And

As described above, the curtain wall type cooling means enables the production of fine-grained steel sheet due to its strong cooling capacity. However, since a large amount of cooling water is used, a large amount of cooling water is applied to the upper surface of the sheet leaving the rolling equipment. Cooling water will be loaded. There are various measuring instruments on the downstream side of the rolling equipment to measure the shape, dimensions, temperature, etc. of the steel plate, but if there is a large amount of water on the steel plate, accurate measurement becomes impossible, and the result In some cases, the rolling equipment may not operate smoothly. The fluid jet spray described above removes such water. When this spray is used, the jetted fluid can remove the cooling water on the steel sheet by the action of the cooling means, so that the necessary measurement can be appropriately performed on the steel sheet that has left the final stand, and the cooling strength and It becomes possible to accurately control the temperature of the steel sheet, which in turn makes it possible to smoothly continue the operation of the rolling equipment.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION One mode for carrying out the invention is shown in FIGS. FIG. 1 is a side view conceptually showing the overall arrangement of the continuous hot rolling facility A. 2 is a schematic diagram for explaining the CVC function with respect to the mill F1 and the like in the front stage of the rolling equipment A of FIG. 1, and FIG. 3 is a rear stage mills F4 to F6 of the rolling equipment A and the vicinity thereof. It is a side view which shows in detail about.

The continuous hot rolling facility A shown in FIG. 1 is a so-called finish rolling machine for steel plates P, which has a heating furnace and a rough rolling machine upstream (not shown) and a runout on the downstream side (not shown). A table and a winder are arranged. This hot rolling facility A has a total of 6 rolls equipped with rolling rolls.
The stand mills F1 to F6 are arranged in tandem, and by continuously rolling a steel plate (rolled material) roughly rolled on the upstream side, various hot rolled steel plates P having a thickness of about 2 to 16 mm are usually provided. To manufacture. Normal rolling for producing a steel sheet P having a general internal structure (having an average ferrite grain size of 10 μm or more) can be smoothly performed, and fine-grained steel rolling, that is, a fine ferrite structure, can be performed by appropriately setting the operating conditions. The rolling facility A is configured as described below so that the hot-rolled fine-grain steel P having the above can be manufactured.

First, the so-called C is used as the front three stands.
The VC mills F1, F2 and F3 are arranged in tandem.
The frontmost CVC mill F1 is configured as a quadruple rolling mill including work rolls 1a and 1b and backup rolls 1c and 1d as shown in FIG.
Has a crown (CVC, that is, a continuous change in diameter) as shown in FIG. Work roll 1
As shown in FIGS. 2 (b) and 2 (c), a and 1b can be simultaneously moved (shifted) in opposite axial length directions, thereby adjusting the positional relationship between rolls, that is, the roll gap. Is possible. Work roll 1a ・ 1
The diameter of b was 700 mm, and the maximum shift amount was 100 mm in both forward and reverse directions. Other 2-stage CVC mill F2 ・ F3
Also the CVC at the forefront of such a configuration and function.
No difference from Mill F1.

The CVC mills F1, F2, and F3 are arranged in the preceding stage in order to keep the crown (shape) of the steel plate P suitable. Later different diameter roll mill F4.
In F5 and F6, during rolling of fine-grained steel, thermal crowns and the like due to heat generation during processing are likely to occur, so the sheet crown is preliminarily corrected by these CVC mills F1, F2, and F3 placed in the previous stage. It is possible to reduce the aperture. In addition, each CVC mill F1, F2, F
An AC motor (not shown) equipped with variable speed control means is connected to each of the three work rolls (1a, 1b, etc.) via a speed reducer and a universal joint (neither is shown).

As the subsequent three stands, so-called different diameter roll mills F4, F5 and F6 are also arranged in tandem. The stand spacing of all 6 stands including the aforementioned CVC mills F1, F2 and F3 is equal to 5.5 m. The different diameter roll mill F4, which is the fourth stand counting from the CVC mill F1, has a work roll 4a.
4b and backup rolls 4c and 4d, which are configured as a quadruple rolling mill. In this example, work rolls 4a and 4a
4b having different diameters are used. Large-diameter roll 4 on the lower side of the work rolls 4a and 4b
Only b is rotationally driven by a motor (not shown. AC motor with variable speed control means) connected through a speed reducer (not shown) and a universal joint, and the upper small-diameter roll 4a is allowed to rotate freely. I decided not to apply the driving force. The work rolls 4a and 4b are provided with a vendor (not shown)
Since it is attached, it is possible to bend the work rolls 4a and 4b. Further, the work rolls 4a and 4b are also provided with a CVC function, and both can be moved in the axial direction within the range of 100 mm in each of the forward and reverse directions. Since the diameter of the work roll 4a is 480 mm and the diameter of the work roll 4b is 600 mm, the equivalent roll diameter which is the average of the two is as small as 540 mm. With respect to the above-described structure and function, the other two different-diameter roll mills F5 and F6 at the rear side are not different from the different-diameter roll mill F4.

Three-stand roll mills with different diameters F4 / F5 /
F6 has a small equivalent roll diameter and drives only one work roll 4b to apply a shearing force to the steel sheet P, so that F6 has a high reduction rate even with a relatively low rolling load (for example, a reduction rate of 50%). Rolling) can be carried out. for that reason,
With a small rolling load, large reduction rolling for fine grain steel rolling can be performed to an extreme degree, and at that time,
Since the rolling load is small, it is possible to avoid inconveniences due to roll flatness and edge drops even when rolling a thin plate having a thickness of about 2 mm.

In order to continuously perform rolling of fine grain steel, it is necessary to sufficiently cool the steel sheet P and maintain it in an appropriate temperature range. Therefore, the stands F4 and F5 at the subsequent stage in the hot rolling equipment A are required.
The curtain wall cooling device 7 (reference numerals 7A to 7H shown in FIG. 3) is arranged at each rear or front of F6 as shown in FIG. Each of the cooling devices 7 applies a large amount of room-temperature cooling water (laminar flow, for example, symbol f in FIG. 3) in a curtain shape (curtain wall shape) from the header provided above or below toward the entire width surface of the steel plate P. It is a cooling means to be cast. The thickness of the cooling water (curtain thickness) flowing in a curtain shape is 10 mm
The above is necessary, and about 16 mm is desirable in terms of cooling effect. The amount of cooling water in each cooling device 7 is the steel plate P.
Is adjustable within a range of 100 to 500 m ³ / h per unit width (1 m), and the temperature drop of the steel sheet P due to cooling is 20
℃ / sec or more. When a strong reduction is applied, cooling water of 350 m ³ / h per unit width is used, and the temperature drop of the steel plate P in that case is 60 to 60 when the product of the plate thickness and the speed is 1200 mm · mpm. 80 ° C /
sec (40 ° C / se including temperature rise due to processing heat)
reach around c).

A plurality of cooling devices 7 are arranged above and below the steel plate P as shown in FIG.
Rear and front and rear of stand F5, stand F6
Cooling devices 7A, 7B, 7D at the front and rear of the
・ 7E and 7G are placed, and the lower part is the stand F4
・ Cooling devices 7C, 7F, 7 at the rear of F5, F6 respectively
H is arranged. Of these, the cooling device 7H is attached to the frame of the roller table T at the rear part of the sixth stage stand F6, and the other cooling devices 7A to 7G are attached to the housing of each stand.

By using such a cooling device 7 on the outlet side of each of the mills F4, F5, F6 of the latter three stands, even when performing a large reduction rolling method or a controlled rolling method accompanied by remarkable working heat. It is possible to suppress the temperature rise in each of the mills F4, F5, and F6 to keep the steel plate P in an appropriate temperature range, and to suppress the grain growth of the fine structure after rolling. In addition, also in the run-out table (the above-mentioned, not shown) on the downstream side of the hot rolling facility A, the steel sheet P is cooled with cooling water in order to prevent grain growth.

Further, in the hot finish rolling facility A as shown in FIG. 1, several hundred mm from the exit of the mill F6 which is the last stage stand and from the curtain wall cooling device 7 (7G · 7H).
The water spray 8 is arranged at a position on the downstream side by about 1 m. This is for removing the cooling water placed on the surface of the steel plate P by the cooling devices 7G and 7H, and the nozzles (not shown) arranged in a plurality are arranged diagonally forward of the rolled material toward the surface of the steel plate P. The pressurized water is blown out so as to spread in the width direction. If such a water jet spray 8 is used, the cooling water placed on the steel plate P can be smoothly removed by the action of the cooling device 7, so that various measuring devices (thermometer, etc., not shown) located on the downstream side thereof. Thus, various values (rolling end temperature, etc.) regarding the rolled steel plate P can be appropriately measured. If the measurement accuracy is high, it becomes possible to accurately control the rolling conditions such as the rolling end temperature by controlling the amount of cooling water.
The mill F at the final stage downstream of the water jet spray 8
The temperature at the end of rolling of the steel sheet P is measured by a thermometer installed about 2 m downstream from 6, and each curtain wall cooling device 7 (especially at the final stage) is calculated by a calculation / operation means (not shown) that receives the measurement result. Device for sandwiching mill F6 7E ・ 7
Increase / decrease the amount of cooling water for G.7H). The feedback control controls the rolling end temperature and keeps it within an appropriate range.

Continuous hot rolling facility A constructed as described above
Then, sufficient speed with productivity (for example, 7-9m
/ Sec), a good fine-grain steel hot-rolled steel sheet P having a thickness of about 2 to 6 mm can be produced. Specifically, while rolling so that the accumulated strain (the above-mentioned weighted integrated value ε _c ) becomes 0.6 or more, the curtain wall type cooling device 7 is used at each rear part of the mills F4, F5, F6 in the subsequent stage. By performing strong cooling, it was possible to produce a preferable fine-grained steel sheet P having an average ferrite grain size of about 3 to 7 μm while using a steel having a low carbon content and a low alloying element content as a rolled material.
Even fine-grained steel may have low elongation, but it has become possible to eliminate such disadvantages. Example a shown later is an example thereof.

Such production is possible because the temperature of the steel sheet P is kept in an appropriate range by using the curtain wall cooling device 7 having a high cooling ability in the latter stand having a strong influence on the metal structure. , Small diameter different diameter roll mill F
This is because the rolling at the high pressure reduction rate that causes the above-mentioned cumulative strain can be performed by 4.F5.F6. Mill F4 / F5 /
In F6, roll flatness and edge drop can be avoided, and crown control can be performed by the CVC function of each of the mills F1 to F6. Therefore, meandering and deterioration of the shape of the steel plate P can be suppressed even in the subsequent stage where the plate thickness becomes thin. Therefore, this equipment A
Then, it is possible to smoothly roll the fine-grained steel and allow the steel sheet P to have high shape accuracy.

The fact that the preferable fine grain steel plate P can be produced under the above-mentioned conditions is that the steel plate P is produced by using the rolling equipment A.
The present inventors have made clear through a number of tests and investigations conducted by variously changing the cooling strength (rolling end temperature) and the degree of reduction (cumulative strain). The results of such tests and investigations and the data relating to Example a in which the preferred fine-grain steel plate P was obtained are shown below.

[0034]

Example Using the continuous hot rolling equipment A described above,
With respect to the steel types shown in Table 1 (which do not contain any significant amount of other components), the pass schedule and the rolling end temperature were variously changed, and the test rolling was performed. However, in any case, the plate thickness on the exit side of the mill F6 at the final stage is 2 to 3 mm, and the rolling speed is 8 to
It is 9 m / sec.

[Table 1]

For many steel plates P obtained by test rolling, the ferrite grain size was measured at the central portion of the thickness, and the relationship between the cumulative strain during rolling and the finishing temperature (rolling end temperature) was investigated. FIG. 4 shows the relationship between the cumulative strain and the ferrite grain size (vertical axis) on the horizontal axis. In the figure, the symbol ● indicates data in which the finishing temperature is within the range of Ar ₃ transformation point ± 10 ° C, ▲ indicates that the temperature is below the Ar ₃ transformation point −10 ° C, and ■ indicates that the temperature is Ar ₃ transformation. The data above the point + 10 ° C. are shown (same in FIGS. 4 to 8).
According to FIG. 4, when the finishing temperature exceeds the Ar ₃ transformation point + 10 ° C., there is a tendency that the ferrite grain size becomes smaller as the cumulative strain increases, but when the finishing temperature is other than that, the cumulative Even if the strain is increased, the ferrite grain size is hardly reduced.

On the other hand, FIG. 5 shows the relationship with the ferrite grain size (vertical axis) with the finishing temperature on the horizontal axis. According to FIG. 5, it can be seen that the ferrite grain size is obviously smaller as the finishing temperature is lower.

Further, the mechanical properties of each manufactured steel sheet P were investigated, and the results were summarized in FIGS. 6 to 8 in relation to the ferrite grain size and the like. In each figure, the horizontal axis represents the value obtained by multiplying the particle diameter (μm) by −1/2. FIG. 6 shows the relationship between the ferrite particle size and the tensile strength (MPa), and FIG. 7 shows the relationship between the ferrite particle size and the elongation (%). According to these, although the tensile strength tends to be higher as the ferrite grain size is smaller (to the right of the horizontal axis), when the finishing temperature is lower than the Ar ₃ transformation point −10 ° C. (▲ in the figure),
It can be seen that the elongation decreases as the ferrite grains become finer. According to FIG. 8, the product of the tensile strength and the elongation (MPa ×%) also decreases with the refinement when the Ar ₃ transformation point is lower than −10 ° C.

From these, the following facts can be grasped. That is, a) In order to obtain the fine-grained steel hot-rolled steel sheet P having a small ferrite grain size by the above-described rolling facility A, it is more effective to set the finishing temperature lower than to increase the cumulative strain. b) However, if the finishing temperature is too low as compared with the Ar ₃ transformation point, the elongation will be reduced even if grain refinement proceeds, and the strength advantage will be reduced. c) Considering that the high pressure to increase the cumulative strain increases the cost in relation to the rolling mill configuration and roll wear, etc. Is more than 0.65) and less than 0.9, and it is preferable in terms of cost efficiency to obtain the fine-grained steel sheet P by accurately controlling the finishing temperature. If the finishing temperature is kept within the range of Ar ₃ transformation point ± 50 ° C., it is possible to produce a fine-grained steel sheet P having a ferrite grain size of 4 to 6 μm and a good balance of mechanical strength. In order to obtain a steel plate P having particularly high tensile strength, the finishing temperature is set to, for example, Ar.
₃ transformation point −50 ° C. to the same transformation point + 20 ° C. In order to obtain a steel sheet P excellent in elongation, for example, Ar
₃ Transformation point −20 ° C. to same transformation point + 50 ° C. However, it is most preferable to keep the finishing temperature within the range of Ar ₃ transformation point ± 10 ° C. from the viewpoint of high strength and balance between them.

An example a in which a good fine grain steel sheet P is manufactured based on the knowledge obtained in this way is introduced in Tables 2 to 4 and FIG. Table 2 shows the plate thickness of each of the mills F1 to F6 (outgoing side) (“rough bar thickness” refers to the plate thickness on the outflow side of the rough rolling mill), reduction rate (%), strain, cumulative strain, and plate. The width is shown in Table 3, and Table 3 shows the usage status and finishing temperature (rolling end temperature) of each curtain wall type cooling device 7 at the rear of the mills F4 to F6. Table 4 shows the ferrite grain size and mechanical properties at the center of the plate thickness of the steel plate P of Example a obtained under the conditions of Tables 1 to 3. And in FIG.
(A), (b), and (c) are crystallized in the vicinity of the upper surface of the steel sheet P of Example a, at positions inside ¼ of the thickness and at the central position of the thickness. It is the microscope picture which image | photographed the structure. A fine structure having an average ferrite grain size of about 4 to 6 μm is formed in each portion. The rolling for obtaining the data of FIGS. 4 to 8 and the rolling of Example a were performed by the rolling facility A (see FIGS. 1 to 3) as described above, but the cumulative strain was 0.6 to
In the case of rolling to about 0.9, it is not necessary to use the different diameter roll mills F4 to F6 as a stand in the subsequent stage (that is, those mills have work rolls having the same diameter in the upper and lower sides of about 600 to 700 mm). It is supposed to be enough). Further, since it is expected that the thermal crown associated with heat generation during processing will not be significant if such a degree of accumulated strain is sufficient, it is considered that it is not necessary to impart the CVC function and the bending function to the mills F1 to F6.

[Table 2]

[Table 3]

[Table 4]

[0040]

According to the continuous hot rolling method described in claim 1, a fine-grain steel hot-rolled steel sheet having sufficiently high practical quality is obtained.
It can be manufactured at very low cost according to relaxed manufacturing conditions.

According to the continuous hot rolling method of the second aspect, it is possible to manufacture a preferable fine grain steel sheet having a particularly high elongation and a small ferrite grain size and excellent mechanical properties.

In the rolling method according to the third aspect, since the steel sheet can be strongly cooled by the curtain wall type cooling means, it is possible to smoothly manufacture a preferable fine grain steel sheet by accurately controlling the rolling end temperature. To do. Since uniform cooling can be realized, there is also an advantage that the structure can be made uniform over the entire width of the steel sheet.

The rolling method according to claim 4 is a method for producing a fine-grained steel sheet having a high balance of mechanical properties, excellent weldability, and a wide range of applications and a relatively low price. It is preferable in terms of contribution and economic rationality of production.

According to the continuous hot rolling equipment described in claim 5, the rolling method of each of the above claims can be realized while appropriately controlling the cooling strength for the steel sheet, which is advantageous in terms of cost efficiency. It becomes possible to manufacture a fine-grained steel plate.

According to the rolling equipment of the sixth aspect, the cooling strength and the steel sheet temperature can be controlled particularly accurately, and the operation of the rolling equipment can be smoothly continued.

[Brief description of drawings]

FIG. 1 is a continuous hot rolling facility A which is an embodiment of the invention.
FIG. 3 is a side view conceptually showing the overall arrangement of the above.

2 (a), (b), and (c) are CVs of the mill F1 and the like in the preceding stage of the rolling equipment A of FIG.
It is a schematic diagram for demonstrating C function.

FIG. 3 is a side view showing details of the subsequent mills F4 to F6 and their vicinity in the rolling facility A.

FIG. 4 is a diagram showing a relationship between cumulative strain, ferrite grain size and the like for various steel plates P obtained by test rolling.

FIG. 5 is a diagram showing a relationship between a finishing temperature (rolling end temperature), a ferrite grain size, and the like for various steel plates P obtained by test rolling.

FIG. 6 is a diagram showing the relationship between ferrite grain size and tensile strength, etc., for various steel plates P obtained by test rolling.

FIG. 7 is a diagram showing the relationship between the ferrite grain size and elongation etc. for various steel sheets P obtained by test rolling.

FIG. 8 is a diagram showing the relationship between ferrite grain size and tensile strength × elongation of various steel plates P obtained by test rolling.

9 (a), (b), and (c) show the steel plate P obtained by the example, in the vicinity of the upper surface, in the vicinity of one fourth of the thickness, and in the thickness. It is a microscope picture which image | photographed the crystal structure in each place of the center vicinity.

[Explanation of symbols]

A hot rolling mill F1-F6 mill 7 (7A-7H) Curtain wall cooling device 8 water spray

[Procedure amendment]

[Submission date] December 27, 2002 (2002.12.
27)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

[0007]

The method of continuous hot rolling according to claim 1 uses a mill having a plurality of stands arranged in tandem so that a heated steel sheet has a cumulative strain of 0.6 or more. While rolling, cool by curtain wall type cooling means on the exit side of the mill of two or more stands in the latter stage.
The tensile strength and
Finding the rolling end temperature where the product of elongation and the maximum area
It is characterized in that the rolling end temperature is controlled based on
In this specification, “strain” means ε = (the difference between the thickness h ₀ of the steel plate on the entrance side of each stand and the thickness h ₁ on the exit side of the stand divided by the average thickness of the two. h ₀ -h ₁₎ / refers to _{{(h 0 + h 1)} / 2}. In addition, "cumulative strain" means the strain at each stage of the latter three stands of the mill used (disregard the stand on the upstream side because they have less influence), considering the strength of influence on the metal structure. Weighted integration, and the strains at the final stage and the preceding and previous stages are respectively ε _n , ε _n-1 , and ε.
_{When n-2} , ε _c is expressed by ε _c = ε _n + ε _n-1 / 2 + ε _n-2 / 4. "curtain wall
Mold cooling means "are connected from above and below like a curtain.
Flow a large amount of cooling water in a laminar flow,
It refers to a cooling means of the type that is applied over the entire width. Also
The "rolling end temperature" means the downstream side of the rolling equipment (located
A thermometer installed a few meters downstream from the mill at the final stage
It is the surface temperature of the steel sheet measured by

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

According to the method of this claim, it is possible to smoothly manufacture a fine-grain steel hot-rolled steel sheet having an average ferrite grain size that is sufficiently fine and excellent in mechanical properties and is highly practical at low cost. it can. a) Applying a high reduction of cumulative strain of 0.6 or more using a mill with multiple stands, and b) Curtain wall type cooling hand on the outlet side of multiple mills near the rear stage.
By strongly cooling the steel sheet in the stage, effectively removing the heat generated during rolling in the final stage and the mill up to that stage to maintain an appropriate temperature and stop the grain growth of the fine structure- Average ferrite grain size is 10μ
It is possible to manufacture a fine-grain steel hot-rolled steel sheet of about m or less. According to the curtain wall type cooling means,
Suitable temperature for high pressure, including accelerated rolling.
It is possible to maintain the rolled material within the temperature range and immediately after rolling
The effect of stopping the grain growth of the fine structure is also secured. Well
The same method applies cooling water to the entire width of the rolled material.
Therefore, the rolled material can be made uniform without being biased in the width direction.
Can be cooled.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

When the accumulated distortion is 0.6 or more,
The reduction rate required for each mill, especially for the mills closer to the rear stage, is considerably reduced (to about 30%), and the cost required for equipment and operation is significantly reduced. It is unlikely that the tip of the steel plate slips without being bitten by one of the mills. On the other hand, if the average ferrite grain size is 10 μm or less, the fine-grain steel plate has significantly higher mechanical properties and is wider than the general (non-fine-grain steel) hot-rolled steel sheet having the same grain size of more than 10 μm. It can be expected to have uses. That is,
According to the continuous hot rolling method of this claim, it becomes possible to manufacture a fine-grain steel hot-rolled steel sheet having sufficiently high practical quality at extremely low cost according to relaxed manufacturing conditions. Also, should the rolling end temperature be controlled as described above?
, Fine-grained steel with an excellent balance of mechanical strength including elongation
Can produce hot rolled steel sheet.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

[0011] hot rolling process continuously according to claim 2 further rolling end temperature, there is Ar ₃ transformation point -20 ° C. or higher, characterized in that in the range of Ar ₃ transformation point + 50 ℃ or less .

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

By controlling the cooling strength and setting the rolling end temperature as in the method of this claim, the ferrite structure is fine (for example, the grain size is 10 μm) and the mechanical strength including elongation is set. It is possible to manufacture a fine-grained hot-rolled steel sheet having a high heat resistance (for example, a steel sheet having a carbon content of 0.5% or less and an alloying element content of 5% or less). According to the investigation by the inventors, when the rolling end temperature exceeds the Ar ₃ transformation point + 50 ° C., the ferrite grain size becomes coarse, and the temperature is the Ar ₃ transformation point −
When the temperature is lower than 20 ° C , the elongation becomes small, and the merit of being a fine-grain steel plate is diminished. However, if the rolling end temperature is kept within the range of −20 ° C. to + 50 ° C. across the Ar ₃ transformation point, the elongation is high and the ferrite grain size is small, which is excellent in other mechanical properties, which is preferable. A fine-grain steel plate can be obtained.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Delete

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Delete

[Procedure Amendment 9]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

In the rolling method according to claim 3 , in particular, the carbon content is 0.5% or less and the alloying element content is 5%.
The following steel sheets are rolled to obtain fine grain steel steel sheets having an internal average ferrite grain size of about 3 to 7 μm.

[Procedure Amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

The fine grain steel sheet having such a chemical composition and a ferrite grain size has a high balance of mechanical properties (it has versatility in terms of tensile strength, elongation, ductility, etc.) and also has good weldability. It is excellent. Therefore, it is considered to be in high demand because it has a wide range of uses, is relatively low in price, is easily available, and has recyclability. Therefore, the rolling method for manufacturing such a steel sheet has a high social contribution and is accompanied by sufficient economic rationality for its production. The continuous hot rolling method according to claim 4 is the final
At the exit side of the corrugated stand, the action of the cooling means causes the steel
Removes the cooling water on the board by spraying pressurized water
And measure the rolling end temperature, and based on the measurement results
To change the amount of water in the curtain wall type cooling means
Further, the rolling end temperature is controlled. This
According to this method, the rolling end temperature is properly measured and accurately
It becomes possible to manage.

[Procedure Amendment 11]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

The continuous hot rolling equipment according to claim 5 is:
The continuous hot rolling method according to claim 1 is carried out.
A continuous hot rolling equipment for Hodokosuru, after placing the mill multiple stand tandem arranged curtain wall type cooling means for the rolled material outlet side of the 2 stands or more mills in the subsequent stage, further, the Change the amount of water in the cooling means
By adding a means to control the rolling end temperature
Is characterized by.

[Procedure Amendment 12]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

According to this continuous hot rolling facility, the rolling method according to each of the above-mentioned claims can be realized. It is easy to give a cumulative strain of 0.6 or more to the heated steel plate (rolled material) using the mill arranged as described above, and to the exit side of the mill with two or more stands in the latter stage. This is because the steel plate can be cooled sufficiently strongly by using the arranged curtain wall type cooling means. If a means for changing the amount of water of the cooling means according to the rolling end temperature is used together with the cooling means, the cooling strength can be appropriately controlled to determine the rolling end temperature as in claim 2, for example. Easy to do.

[Procedure Amendment 13]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction content]

In the continuous hot rolling equipment according to claim 6 , a plurality of nozzles are provided downstream of the cooling means at the exit side of the stand at the final stage to remove the cooling water on the rolled material.
To spread diagonally forward toward the surface of the steel sheet and in the width direction
It is characterized by arranging a fluid jet spray that blows out pressurized water .

[Procedure Amendment 14]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

As described above, the curtain wall type cooling means enables the production of fine-grained steel sheet due to its strong cooling capacity. However, since a large amount of cooling water is used, a large amount of cooling water is applied to the upper surface of the sheet leaving the rolling equipment. Cooling water will be loaded. There are various measuring instruments on the downstream side of the rolling equipment to measure the shape, dimensions, temperature, etc. of the steel plate, but if there is a large amount of water on the steel plate, accurate measurement becomes impossible, and the result In some cases, the rolling equipment may not operate smoothly. The fluid jet spray described above removes such water. When this spray is used, the sprayed pressurized water can remove the cooling water placed on the steel plate by the action of the cooling means, so that the necessary measurement can be appropriately performed on the steel plate that has left the final stand, and the cooling strength and It becomes possible to accurately control the temperature of the steel sheet, which in turn makes it possible to smoothly continue the operation of the rolling equipment.

[Procedure Amendment 15]

[Document name to be amended] Statement

[Correction target item name] 0040

[Correction method] Change

[Correction content]

[0040]

According to the continuous hot rolling method described in claim 1, a fine-grain steel hot-rolled steel sheet having sufficiently high practical quality is obtained.
It can be manufactured at very low cost according to relaxed manufacturing conditions. By curtain wall type cooling means
Because the steel sheet can be cooled strongly, the rolling end temperature can
It is possible to smoothly manufacture the preferred fine-grain steel plate
Become Noh. Since uniform cooling can be achieved, the width of the steel sheet
There is also an advantage that the structure can be made uniform.

[Procedure Amendment 16]

[Document name to be amended] Statement

[Correction target item name] 0042

[Correction method] Delete

[Procedure Amendment 17]

[Document name to be amended] Statement

[Correction target item name] 0043

[Correction method] Change

[Correction content]

The rolling method according to claim 3 is a method for producing a fine-grained steel sheet having a high balance of mechanical properties, excellent weldability, and a wide range of applications and a relatively low price. It is preferable in terms of contribution and economic rationality of production. Contract
According to the continuous hot rolling method described in claim 4, the rolling is completed.
It is possible to measure the temperature properly and manage it accurately.
With the above, it is possible to produce the preferred fine-grain steel hot-rolled steel sheet as described above.
It

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ichiro Takeshi             1-66, Funamachi, Taisho-ku, Osaka City Stock Association             Inside Nakayama Steel Works (72) Inventor Keiji Morimoto             1-66, Funamachi, Taisho-ku, Osaka City Stock Association             Inside Nakayama Steel Works (72) Inventor Masanori Takahashi             3-1-1 Higashikawasaki-cho, Chuo-ku, Kobe-shi, Hyogo             No. Kawasaki Heavy Industries, Ltd.Kobe factory (72) Inventor Akio Adachi             3-1-1 Higashikawasaki-cho, Chuo-ku, Kobe-shi, Hyogo             No. Kawasaki Heavy Industries, Ltd.Kobe factory (72) Inventor Shinji Takaoka             3-1-1 Higashikawasaki-cho, Chuo-ku, Kobe-shi, Hyogo             No. Kawasaki Heavy Industries, Ltd.Kobe factory F-term (reference) 4E002 AD04 BA01 BD07 CB01                 4K037 EA04 EA05 EA06 EA15 EA27                       FB00 FC02 FC03 FD06 HA00

Claims (6)

[Claims] 1. A multi-stand mill arranged in tandem is used to cool a heated steel sheet so that the cumulative strain is 0.6 or more, and is cooled on the outlet side of the two or more mills in the latter stage. A continuous hot rolling method characterized by the above. 2. The rolling end temperature is Ar ₃ transformation point −50 ° C.
The continuous hot rolling method according to claim 1, wherein the Ar ₃ transformation point is within the range of + 50 ° C. or less. 3. The continuous hot rolling method according to claim 1, wherein the steel plate is cooled by a curtain wall type cooling means. 4. A steel sheet having a carbon content of 0.5% or less and an alloying element content of 5% or less is rolled to obtain a steel sheet having an internal average ferrite grain size of about 3 to 7 μm. The continuous hot rolling method according to any one of claims 1 to 3, which is characterized. 5. A continuous hot rolling facility in which mills with a plurality of stands are arranged in tandem, and a curtain wall type cooling means for the rolled material is arranged on the outlet side of the mills of two or more stands in the subsequent stage, and further rolling is performed. A continuous hot rolling facility, characterized by being equipped with means for measuring the end temperature and changing the amount of water in the cooling means according to the temperature. 6. A fluid jet spray for removing cooling water on the rolled material is arranged downstream of the cooling means on the outlet side of the last stand.
Continuous hot rolling equipment described in.