JP2022107666A - Plant and method for multimode manufacturing metal band material and plate material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means for continuously manufacturing a hot-rolling band material or plate material.

SOLUTION: There is provided a plant for endlessly manufacturing and batch manufacturing a hot-rolling band material or plate material having a thickness of 0.6-50 mm or a thickness that is a half of the maximum thickness of a cast slab. The plant includes a continuous casting machine (1) using an unsolidified state where a thin slab is produced, an induction heater (2) through a first shear (3), a roller (4), a second shear (5), a run-out table having a cooler (6) and a pusher/piler (7) for a plate material, a third shear (8) and a plurality of coilers (9). The plant further includes a rolling stand (10) under a minimum pressure arranged between the continuous casting machine (1) and the first shear (3), and the rolling stand (10) under the minimum pressure is designed so that a rolling reduction ratio is approximately 10%, and 20% or less in any case.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to a plant and method for the continuous or batch production of hot-rolled strip and plate with high plant productivity and cost-effective product quality and large size range.

In the steel industry, given the rising cost of raw materials and energy used, the increasing competition required in the global market, and the increasingly stringent regulations on pollution, particularly high-quality steel with low investment and production costs and high production flexibility is required. It is known that there is a strong demand for hot rolled steel strip and plate manufacturing methods. As a result, the industry may become more competitive in producing end products with lower energy consumption, thus minimizing the negative impact on the environment.

The prior art is substantially described in the inventor's previous patents, in particular EP 1558408 and EP 1868748, which are detailed below. In EP 1 558 408 the so-called "cast rolling" technique is used. It combines continuous casting of thin slabs with green reduction (LCR) as a first rough rolling step by a high pressure mill (HRM) or rough reduction mill, thereby producing an intermediate product. After a heating stage in an induction heater and subsequent descaling, the intermediate product is further processed in a second stage of finish rolling.

Also, in EP 1 558 408 mentioned above, after the first rough rolling step, in order to prevent the interruption of the continuous casting process and thus the line production in the event of a problem in the part of the plant downstream of the roughing mill, The possibility of extracting the rough rolled plate as an emergency system is foreseen. Lacking the controlled cooling system required to produce high quality boards, these boards cannot be sold and must necessarily be returned to scrap and reintroduced into the production cycle.

In both EP 1 558 408 and other plants of the prior art, between the exit of the roughing mill and the entrance of the finishing mill, the intermediate product experiences a temperature drop of about 230° C., thus inducing that temperature drop. It must be compensated by a heater to bring the temperature above about 820-850° C. at the exit of the roughing mill, which corresponds to the lower end of the austenitic temperature range of the product.

EP 1 868 748 teaches some improvements in terms of plant miniaturization and energy saving, connecting continuous casting directly to the rolling process into a single manufacturing process without resolving continuity. there is In fact it is a single rolling step instead of two independent rolling steps of rough rolling and finishing rolling, and the distance between the exit of the continuous casting and the first stand of the rolling mill limits the temperature drop of the slab. not exceed 50m to ensure EP 1 868 748 also performs the production of sheet stock using the cooling system used for the coils only in "endless" mode. This method has been found not to be optimal for plate manufacturing, since the "endless" mode is well suited for coil manufacturing, and the cooling conditions for the plate are very different from those for coils.

Other prior art casting and rolling plants are described in WO 2007/045988 and DE 102011004245 (DE 102011004245). In the case of WO2007/045988, the cast slab has a maximum thickness of 50 mm before green reduction and is brought to 40 mm by green reduction. A thickness reduction of up to 3 mm is achieved by pinch rolls immediately downstream of the caster. In DE 102011004245 A1 a roughing mill is placed immediately downstream of the caster to reduce the slab thickness by up to 70%. However, this reduction in thickness can be temporarily reduced to zero if there is a problem with the subsequent rolling line.

European Patent No. 1558408 European Patent No. 1868748 WO2007/045988 DE 102011004245 A1

The results obtained so far with the teachings of the above patents show that although the quality of the products, in particular the steel strip, is optimal, there is still room for improvement in terms of technology, plant, productivity and production flexibility. ing. The items that need to be improved are shown below.

1. Introducing the possibility of production in "batch" or "combined" mode with interruption of cast slabs between casting and rolling mills. In other words, the slab entering the rolling mill has a different speed than in the continuous caster. This possibility offers important plant and production flexibility for the following reasons.
- In the production of coils with a thickness greater than 3 mm, the tolerance between two consecutive coils having different thicknesses can be adjusted according to the production plan by using the "batch" mode instead of the "endless" mode. A significant weight of steel strip outside is eliminated.
• For the production of coils with a thickness greater than 1.5-2.0 mm, the mass flow rate in the caster can be less than the mass flow rate in the rolling mill, and the "batch" mode can reduce energy consumption. Especially with induction heaters, the heat loss is reduced due to the high rolling speed.
- In the production of high quality plate, the casting speed required for the type of steel being cast must be kept low, so the mass flow rate in the caster must be lower than the mass flow rate in the rolling mill.
• In the production of coils where two successive coils have very different thicknesses, it is necessary to change the roll stand gap setting when there is no material to pass through. In the "composite" mode, the first coil is manufactured in a nearly endless mode, but the last part is manufactured in a "batch" mode by cutting slabs. This accelerates and rolls faster, creating the time required to empty the mill and reset a second coil of different thickness.

2. Improve slab surface quality before rolling process.

3. A "mechanical filter" is introduced between the continuous casting machine and the pendulum type shear used in plants employing "batch" technology. This avoids the problems that arise when cutting a slab with a pendulum shear causes perturbations in the meniscus of the mold of the caster.

4. When the rolling mill is unavailable due to repairs, the profitability of the plant is increased by producing slabs that can be heated and rolled instead of scrapping plate as in prior art plants.

5. Increased plant profitability by introducing the possibility of rolling the following slabs.
Melting plants, especially rolled slabs produced in the same operation and introduced into the production line if the slabs mentioned in 4 above are not available, and/or rolled slabs purchased at favorable market prices in certain scenarios.

6. By installing a dedicated cooling system followed by a dedicated board processing line, the quality of the board produced is improved.

7. By increasing the casting speed to 9m/min and consequently the relative mass flow rate to 8ton/min, the production is increased to 4,000,000 tons per year.

8. To further improve the width crossing of the steel strip.

9. To reduce the width of a strip material without changing the position of the side surface in a mold for continuous casting. As a result, the mold width and thus the mass flow rate remain unchanged, thereby improving productivity.

10. It further improves the end face quality of both strip and plate.

It is therefore an object of the present invention to provide a solution for the continuous production of hot rolled strips or plates, with strip thicknesses between 0.6 mm and 12 mm and plate thicknesses between 12 mm and 12 mm. 50 mm or in any case half the thickness of the slab at the exit of the continuous casting machine with unsolid reduction, the slab thickness being a minimum of 80 mm and a maximum width of at least 2100 mm, or the maximum expected mold width is. This solution has the same or better strip or plate quality, less energy consumption, less environmental impact, higher productivity and flexibility compared to the above prior art.

The result is an "endless" production technique with no interruption of the cast slabs and a combination of casting and rolling mills to achieve production flexibility not found in plants built according to the teachings of the prior art. Obtained using both "batch" or "composite" production techniques that interrupt the cast slabs in between.

Advantageous measures taken in the present invention to improve the plant and process include the following.
a) Introduce a minimum rolling stand (a so-called “kispass” stand) between the continuous caster and the induction heater, which can achieve:
・Optimization of the crystal structure of the slab. At the exit of the continuous casting machine, the coarse grains that make up the slab surface are recrystallized to obtain fine grains that are difficult to separate easily in subsequent rolling steps.
• Form a "mechanical filter" between the caster and the subsequent shear cutting machine to avoid the above problems occurring in prior art plants using "batch" technology.

b) Introduce a narrow-sided vertical rolling stand (edger). It is preferably placed upstream of the first rolling stand (ie the "kispass" stand) for the following purposes.
• Recrystallize the edge of the slab, which is the coldest part and most sensitive to crack formation.
• Shaping the slab edge to minimize tensile stress in subsequent rolling steps.
• Improve the increasingly tight tolerances in width required by end customers.
• Slab width reduction of up to 50mm on each side without reducing plant productivity.

c) Between the "kispass" stand and the induction heater, introduce a connecting roller furnace or walking beam furnace that allows:
・If the rolling mill cannot be used, evacuate the slab. The slabs may be reintroduced for production rather than being turned into board stock which may be scrapped.
• Choose from three modes of production operation: "Endless" (best for thin strip production) or "Combined" and "Batch" (best for thicker strip production and plate production).
• Start the production cycle with slabs introduced into the furnace at ambient temperature • Store the hot slabs produced in the furnace to be used as a buffer for mill repair and supply when the mill is available again.

d) Introduce specific cooling equipment for the plate downstream of the rolling mill, possibly followed by a dedicated plate processing line.

Further advantages and features of the plant and method according to the invention will be apparent to those skilled in the art from the following detailed and non-limiting description of an embodiment with reference to the sole drawing attached as FIG.

Schematic diagram of the plant, the most complete embodiment.

With reference to FIG. 1, the plant according to the invention conventionally comprises a continuous casting machine 1, followed at a distance by an induction heater 2, between which a "mechanical filter" is introduced with a pendulum shear 3. . Hereby there is a pendulum type shear 3, followed by a rolling mill 4, a rotary shear 5, a runout table with cooling device 6, a pusher or pusher/piler for plate material 7 and finally a high speed before a downcoiler 9. There is Shah 8.

More specifically, the casting machine 1 comprises a die, followed by a curved green reduction zone, producing slabs with a minimum thickness of 80 mm, for example 100 mm x 2100 mm, at a casting speed of up to 9 m/min. The slab is then heated before entering the finishing mill 4 by an induction heater 2 which in the example shown comprises four coils. The finishing mill 4 includes up to 7 stands in the example shown, and the slabs are successively reduced in thickness with reductions of, for example, 58%, 52%, 47%, 43%, 40%, 35%. , 30% and so on. The first stand (the first two in the example shown) has a large work roll diameter.

The finishing mill 4 includes cooling and/or heating devices (e.g. gas heaters or induction heaters) located between the rolling stands at any position after the first two stands and has specific characteristics and By adapting the temperature of the rolled material according to needs, the rolling conditions can be better controlled.

The resulting strip is then cooled by a cooling device 6 and finally wound by a downcoiler 9 and cut by a high speed shear 8 when the coil reaches its intended weight. Alternatively, if the slab is rolled down to the thickness of the board stock, it is cut into boards by a rotary shear 5 and the boards are removed from the line by a pusher or pusher/piler 7 . The movement can be after cooling in the first region of the cooling device 6 .

A first novel aspect of the present invention is the presence of a so-called "kispass" stand 10 between the continuous casting machine 1 and the pendulum shear 3 . The "kispass" stand 10 performs a reduction of approximately 10% and in any case no more than 20%. So we start with a thickness reduction of about 8 mm. It has a metallurgical purpose rather than a mechanical one. In fact, as noted above, this minimal reduction recrystallizes the coarse grains on the surface of the slab exiting the caster 1 into small grains that are less likely to separate during the rolling process carried out in the mill 4. The purpose is to optimize the slab surface crystal structure as grains. Preferably, the plant also comprises an additional induction heater 11 with two coils in the example shown and a descaler 12 between the caster 1 and the stand 10 to a) avoid the ductile draft temperature range, b) keeping the segregating elements in solid solution and c) improving the results of the "kispass" reduction (also preferably further descaler 13 is installed before the mill 4).

In addition, the presence of low-melting elements in cast alloys (e.g., copper and tin in the case of steels made from EAF scrap) that tend to collect at the grain edges further weakens the grain edges. It is clear that the problem increases with the concentration of the low melting point element. The grain reorganization and refinement achieved by the "light" reduction pass provides a dual advantage. a) Larger reductions can be applied in the subsequent first actual rolling step without destroying the surface material. b) Cheaper, lower quality scrap, i.e. scrap with high levels of impurities such as copper and tin, can be used to yield the same high quality strip/plate.

Note that the "kispass" stand 10 preferably has smaller diameter work cylinders than the first stand of the mill 4 . This is because the minimum reduction must be provided with as little cooling of the slab as possible, the contact arc length is sufficiently small, and has the advantage of minimizing tensile stresses on the surface of the rolled material. is.

Another advantage obtained by arranging a so-called "kispass" stand 10 between the continuous casting machine 1 and the pendulum shear 3 is, as mentioned above, the formation of a "mechanical filter" between the two configurations. be. That is, it avoids disturbance to the caster 1 when a slab is cut by the shear 3 during emergency repairs in the part of the plant downstream of the shear 3 .

According to a second novel aspect of the invention, there is an edger 14, a narrow-faced vertical rolling stand. An edger 14 is preferably placed immediately upstream of the "kispass" stand 10, preferably preceded by an induction edge heater 15, ie a heater with a C-shaped coil that heats only the edges of the slab. However, edgers 14 may be positioned immediately upstream of mill 4 with corresponding induction edge heaters 15 and may be positioned adjacent to any side of induction heaters 2 .

As noted above, the addition of the edger 14 recrystallizes the slab edge, which is the most cooled and therefore most susceptible to crack formation, and forms to minimize tensile stresses during subsequent rolling steps. , the width tolerance can be improved. In addition, the edger 14 can reduce the slab width up to 50mm on each side, thereby allowing narrower strips/plates to be cut without die intervention and thus reducing plant productivity. Obtainable.

According to a third novel aspect of the present invention, between the "kispass" stand 10 and the induction heater 2, a connecting furnace 16 suitable for allowing introduction/removal and controlled advancement of the slab S. exists. Typical examples thereof are gas-heated roller hearth furnaces or walking beam furnaces, usually about 30 m long, but it is clear that other comparable types of furnaces can also be used.

Immediately before the connecting furnace 16 there is an additional pendulum shear 17 which, as mentioned above, not only allows the reusable slabs 18 to be evacuated if the rolling mill 4 is not available, Either the "endless" mode of operation or the "batch/combined" mode of operation is selected and the slabs purchased from the market are charged (via loading station 19) into the connected furnace 16 at ambient temperature. The connecting furnace 16 also functions as a buffer, holding the produced hot slabs in the furnace in the event of repair of the mill 4 and allowing the stored slabs to flow to the rolling line when available again.

The "kispass" stand 10 is located between the continuous caster 1 and the additional pendulum shear 17 and thus functions as a "mechanical filter", as described above, to allow the "batch/combined" mode to be selected to Disturbance in the casting machine 1 when the is cut by the shear 17 is avoided.

Since the width of the slab does not change, a given percentage decrease in slab thickness results in a corresponding increase in length. With this in mind, it should be noted that the "kispass" stand 10 can be used just as the first rolling pass upstream of the furnace 16 . This is because the "kispass" stand 10 has a thickness reduction of about 10% and in any case less than 20% thickness reduction. This reduction is much less than the 50-70% reduction in the first stand of the prior art roughing or finishing mills. Prior art reduction ratios would require an unacceptably long furnace 16 . In fact, the furnace must be dimensioned to hold a slab with a weight corresponding to the weight of the coil of strip or the stack of plates produced in the batch production cycle, and the thin slabs require unacceptable lengths. can't gain weight.

This is the rationale for the 20% reduction limit mentioned above. A large reduction in the "kispass" stand 10 would obviously help achieve the desired final thickness more easily in the mill 4, and would require fewer stands. However, there are also "metallurgical limits" dependent on the alloy composition, so the "kispass" stand 10 can only apply the maximum reduction suitable to obtain the required grain recrystallization without causing slab surface failure. conduct.

According to the fourth novel aspect of the present invention, the cooling device 6 can be provided with a first cooling region capable of performing high-speed cooling of the plate material corresponding to rapid cooling. Tempering in a subsequent operating step provides a higher quality board than that produced in prior art plants. This is because in prior art plants the cooling area is optimized for strip only.

Alternatively, a cooling device 20 dedicated to plate materials can be placed off-line. A multi-stage high-pressure cooling is applied to the strip removed by the pusher or pusher/piler 7 . That is, each cooling is followed by a subsequent cooling with time for the plate to become substantially uniform. In this way, the desired cooling pattern for each steel grade can be obtained, and to complete the processing of the plate (cooled in the specific cooling device 20 or the ultra-fast cooling section of the cooling device 6 above), the is followed by a tempering furnace 21, followed by a controlled cooling 22, a skin pass stand 23 and a roller leveler 24.

Another possibility is to provide a cooling device 6 that can be easily adjusted to board-specific settings. In that case it is clear that the pusher/piler 7 or the additional pusher/piler 7' can be arranged between the cooling devices. In this way the cooling device 6 can be suitably used for cooling both high quality strips and high quality plates.

Thus, the plant according to the invention described above operates in an "endless" mode without a slab continuity solution between the casting mill 1 and the rolling mill 4 (i.e. the inlet speed of the mill 4 is high quality strip and plate in both "batch/combined" mode where the slab entering mill 4 is separated from the slab in caster 1 suitable for manufacturing both

Furthermore, the plant can also use slabs flowing from the connected furnace 16 as starting material. The slabs were either loaded at ambient temperature through the loading station 19 or held at an elevated temperature in the furnace 16 using the furnace 16 as a buffer.

Claims (22)

A plant for the endless, batch or composite production of hot-rolled steel strips and plates with a thickness between 0.6 mm and 50 mm or half the maximum thickness of the cast slab, comprising:
A continuous caster (1) using green reduction to produce a thin slab with a minimum slab thickness of 80 mm at the exit of the continuous caster (1);
followed by an induction heater (2) through a first shear (3),
Next, the rolling mill (4),
followed by a second shah (5),
Runout table with cooling device (6) and pushers/pilers (7) for board material,
Then a third shear (8) and multiple coilers (9)
In the plant comprising
Said plant further comprises a minimum reduction roll stand (10) arranged between said continuous caster (1) and said first shear (3), said minimum reduction roll stand (10) having a thickness of about 8 mm. starting from a thickness reduction of about 10% and in any case no more than 20% reduction. 2. The method of claim 1 further comprising an additional induction heater (11) and descaler (12) arranged between the continuous casting machine (1) and the minimum reduction stand (10). plant. 3. A plant according to claim 1 or 2, characterized in that the minimum reduction rolling stand (10) has work cylinders of smaller diameter than the first stand of the rolling mill (4). further comprising an edger (14) designed to reduce the slab width by up to 50 mm on each side, preferably said edger (14) immediately upstream of said minimum reduction rolling stand (10) or said rolling mill (4) 4. A plant according to any one of claims 1 to 3, characterized in that it is arranged. A plant according to claim 4, characterized in that it further comprises an induction edge heater (15) arranged in front of said edger (14). further comprising a connecting furnace (16), preferably a gas-heated roller hearth furnace or a walking beam furnace, between said minimum reduction rolling stand (10) and said induction heater (2), said connecting furnace (16) comprising: Designed to allow introduction/removal and controlled advancement of slabs (S), said splicing furnace (16) is used for coils of finished product strip or stacks of plate material produced in a batch production cycle. 6. Plant according to any one of claims 1 to 5, characterized in that it has dimensions to hold slabs (S) of corresponding weight. A fourth shear (17) is provided immediately before said connecting furnace (16), said connecting furnace (16) having a piler (18) for removing slabs (S) from said connecting furnace (16) and a slab (S ) into the connecting furnace (16). 8. The method according to any one of claims 1 to 7, characterized in that the cooling device (6) has a first cooling zone capable of ultra-rapid cooling of the plate corresponding to rapid cooling of the plate. Plants listed. 9. Any one of claims 1 to 8, characterized in that it further comprises an off-line cooling device (20) dedicated to plate material for multi-stage high-pressure cooling of the plate material unloaded by said pusher or pusher/piler (7). The plant described in . It further comprises a sheet material processing line that receives sheet material from the ultra-rapid cooling region of the cooling device (6) or the off-line cooling device (20) dedicated to the sheet material, the sheet material processing line being sequentially composed of a tempering furnace (21) and a controlled cooling (22). ), a skin pass stand (23) and a roller leveler (24). Claim characterized in that said cooling device (6) is adjustable to a plate-specific setting and a pusher/pile (7') is arranged between said cooling device (6) and said coiler (9). A plant as claimed in any one of claims 1 to 10. 12. Any of the preceding claims, further comprising a cooling or heating device located between the roll stands of said mill (4) at any position after the first two roll stands. or the plant described in paragraph 1. Hot-rolled steel strips and plates with a thickness between 0.6 mm and 50 mm or half the maximum thickness of the cast slabs by a plant according to any one of claims 1 to 12. An endless or batch manufacturing method of
Continuous casting (1) of a thin slab (S) with a minimum slab thickness of 80 mm by unsolidification reduction;
In said manufacturing process followed by heating in an induction heater (2), finish rolling (4), controlled cooling (6) and final shearing (5; 8),
Initial rolling with a reduction of the slab (S) of about 10%, in any case not more than 20%, starting from a thickness reduction of about 8 mm, prior to heating in said induction heater (2) A manufacturing method, further comprising (10). 14. Process according to claim 13, characterized in that the initial rolling (10) is preceded by heating with an additional induction heater (11) and descaling (12). further comprising vertical rolling (14) of the narrow side of the slab allowing a width reduction of up to 50 mm on each side, said vertical rolling (14) immediately prior to said initial rolling (10) or said finishing rolling (4). 15. A manufacturing method according to claim 13 or 14, characterized in that 16. A method according to claim 15, characterized in that the vertical rolling (14) is preceded by slab edge heating by an induction edge heater (15). 17. A manufacturing method according to any one of claims 13 to 16, characterized in that, in the case of the manufacture of sheets, said controlled cooling (6) comprises ultra-rapid cooling of the sheets, corresponding to rapid cooling. . 14. from claim 13, characterized in that in the case of the production of the strip, it further comprises removing (7) the strip after said finish rolling (4) and multi-stage high-pressure cooling of the strip by means of an off-line cooling device (20) dedicated to the strip. A manufacturing method according to any one of claims 16 to 16. Claim 17 or claim 17, further comprising tempering (21), controlled cooling (22), skin pass (23) and leveling (24) of the plate material in sequence after said ultra-rapid cooling or said multi-stage high-pressure cooling. 19. The manufacturing method according to Item 18. 17. Any one of claims 13 to 16, characterized in that, in the case of the production of plates, the controlled cooling (6) is adjusted to a plate-specific setting, and that removal of the plates takes place after the controlled cooling (6). 1. The manufacturing method according to item 1. Further comprising the step of using a slab (S) from said splicing furnace (16) as starting material, said slab being introduced by said loading station (19) at ambient temperature or, if used as a buffer, said 21. Manufacturing method according to any one of claims 13 to 20, characterized in that the slab is held at high temperature in a joint furnace (16). Further step of cutting the slab (S) by a fourth shear (17) and removing it from said connecting furnace (16) by a piler (18) if a problem occurs in the part of the plant downstream of said connecting furnace (16). 22. A method as claimed in any one of claims 13 to 21, comprising:

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