JP7095071B2 - Plants and methods for multimode manufacturing of metal strips and plates - Google Patents

Description

The present invention relates to plants and methods for continuous or batch production of hot rolled strips and plates with high plant productivity and cost effectiveness, high product quality and large dimensional range.

The steel industry has low investment and production costs and high production flexibility, especially high quality, given rising raw material and energy costs used, intensifying competition in the global market, and increasingly stringent regulations on pollution. It is known that there is a strong demand for methods for manufacturing hot-rolled steel strips and plates. As a result, the competitiveness of the manufacturing industry of final products with low energy consumption may be increased, and thus the adverse effect on the environment can be minimized.

The prior art is substantially described in the inventor's previous patents, in particular European Patent No. 15584088 and European Patent No. 1868748, which will be detailed later. European Patent No. 15584088 uses the so-called "casting and rolling" technique. This combines continuous casting of thin slabs under unsolidified reduction (LCR) and is the first rough rolling step with a high pressure lower mill (HRM) or coarse reduction mill, thereby producing intermediate products. The intermediate product is further processed in the second stage of finish rolling after a heating step in an induction heater and subsequent scale removal.

Also, in European Patent No. 1558408, if there is a problem in the plant portion downstream of the rough rolling mill, after the first rough rolling step, in order to prevent the continuous casting process and the resulting interruption of line production. It is predicted that the rough rolled plate may be extracted as an emergency system. Due to the lack of a controlled cooling system required for the production of high quality boards, these boards cannot be sold and will inevitably need to be scrapped and reintroduced into the production cycle.

In both European Patent No. 15584088 and other plants of the prior art, the intermediate product undergoes a temperature drop of approximately 230 ° C between the rough rolling mill outlet and the finish rolling mill inlet, thus inducing that temperature drop. Compensated by a heater, the temperature at the outlet of the rough rolling mill must exceed about 820-850 ° C., which corresponds to the lower limit of the austenite temperature range of the product.

European Patent No. 1868748 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 reality, it is a single rolling process rather than two independent rolling processes of rough rolling and finish rolling, and the distance between the outlet of continuous casting and the first stand of the rolling mill limits the temperature drop of the slab. In order to do so, it is not allowed to exceed 50 m. European Patent No. 1868748 also manufactures plates using the cooling system used for the coils in "endless" mode only. This method is well suited for coil production in the "endless" mode, which has been found to be less suitable for plate production, and the cooling conditions of the plate are very different from those of the coil.

Other prior art casting and rolling plants are described in International Publication No. 2007/045988 and German Patent Application Publication No. 102011100424 (DE10201112445). In the case of WO 2007/045988, the cast slab has a maximum thickness of 50 mm before unsolidification reduction and is reduced to 40 mm by unsolidification reduction. A pinch roll just downstream of the foundry provides a thickness reduction of up to 3 mm. In German Patent Application Publication No. 102011004245, the rough rolling mill is located just downstream of the casting machine, reducing the thickness of the slab by up to 70%. However, if there is a problem with the subsequent rolling line, this reduction in thickness can be temporarily reduced to zero.

European Patent No. 15584088 European Patent No. 1868748 International Publication No. 2007/045988 German Patent Application Publication No. 102011004245

The results obtained so far with the teachings of the above patent show that while the quality of the product, especially 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 improvement are shown below.

1. 1. Introduces the possibility of production in "batch" mode or "composite" mode with interruption of the casting slab between the mill and the rolling mill. In other words, the slab entering the rolling mill has a different speed than that of a continuous casting machine. This possibility provides significant plant and production flexibility for the following reasons:
-In the manufacture of coils with a thickness of more than 3 mm, by using the "batch" mode instead of the "endless" mode, the tolerance between two consecutive coils with different thicknesses, depending on the production plan. A considerable amount of steel strips on the outside are eliminated.
-In the manufacture of coils with a thickness greater than 1.5-2.0 mm, the mass flow rate in the casting machine may be smaller than the mass flow rate in the rolling mill, and the "batch" mode can reduce energy consumption. Especially in an induction heater, heat loss is reduced due to the high rolling speed.
-In the production of high quality plates, the mass flow rate in the casting machine must be lower than the mass flow rate in the rolling mill because the casting speed required for the type of steel to be cast must be kept low.
-In the manufacture of coils with significantly different thicknesses of two consecutive coils, it is necessary to change the setting of the gap of the rolling stand when there is no material to pass through. In "composite" mode, the first coil is manufactured in near endless mode, the last part of which is made by cutting the slab in "batch" mode. This accelerates and rolls faster, emptying the mill and creating the time required to reset the second coil of different thickness.

2. 2. Improve slab surface quality before rolling process.

3. 3. A "mechanical filter" will be introduced between the continuous casting machine and the pendulum type shear used in plants that employ "batch" technology. This avoids the problems that occur when cutting the slab with a pendulum die shear causes perturbations in the meniscus of the casting die.

4. If the rolling mill is not available due to repairs, the profitability of the plant is increased by producing slabs that can be heated and rolled, instead of discarding the plate material as in conventional plants.

5. Improving plant profitability by introducing the following rolling possibilities for slabs.
Rolling slabs produced in the same operation and introduced into the production line when melting plants, especially the slabs mentioned in 4 above, and / or rolled slabs purchased at a favorable price on the market in a particular scenario.

6. By installing a dedicated cooling system and a dedicated plate processing line following it, the quality of the produced plate will be improved.

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

8. Further improve the width crossing of steel strips.

9. The width of the strip is reduced without changing the position of the side surface in the continuous casting mold. As a result, the mold width and, by extension, the mass flow rate do not change, so that productivity is improved.

10. Further improve the end face quality of both strips and boards.

Therefore, an object of the present invention is to provide a solution for continuous production of a hot-rolled strip or plate, with the strip having a thickness of 0.6 mm to 12 mm and a plate having a thickness of 12 mm to 12 mm. Half the thickness of the slab at the outlet of a continuous casting machine using 50 mm or in any case under unsolidified rolling, the slab thickness is a minimum of 80 mm, the maximum width is at least 2100 mm, or the expected maximum mold width. Is. This solution has the same or better quality of strip or plate, less energy consumption, less environmental impact, higher productivity and flexibility as compared to the prior art described above.

The result is an uninterrupted "endless" production technology for casting slabs and casting and rolling mills to achieve production flexibility not found in plants built according to the teachings of prior art. Obtained using both "batch" or "composite" production techniques that interrupt the casting slab between.

Advantageous means adopted in the present invention for improving plants and methods include:
a) Introduce a minimum rolling stand (so-called "kiss pass" stand) that can achieve the following between the continuous casting machine and the induction heater.
-Optimization of the crystal structure of the slab. At the outlet of the continuous casting machine, the coarse crystal grains constituting the slab surface are recrystallized to obtain fine crystal grains that are difficult to separate easily in the subsequent rolling steps.
• Form a "mechanical filter" between the foundry and subsequent shear cutting machines to avoid the above problems that occur in prior art plants that use "batch" techniques.

b) Introduce a narrow surface vertical rolling stand (edger). It is preferably located upstream of the first rolling stand (ie, the "kiss pass" stand) for the following purposes:
-Recrystallize the edges of the slab, which is the coldest part and the most sensitive part to crack formation.
• Form slab edges to minimize tensile stress in subsequent rolling steps.
· Improve the ever-tightening tolerances required by end customers.
-Reduce the slab width by up to 50 mm on each side without reducing the productivity of the plant.

c) Introduce a connecting roller or walking beam furnace between the "Kiss Pass" stand and the induction heater to enable:
・ If the rolling mill cannot be used, retract the slab. The slab may be reintroduced for production rather than being made into a plate that can be discarded.
-Choose from three production operating modes: "endless" (ideal for thin strip production) or "composite" and "batch" (best for thicker strip and plate production).
-Start the production cycle from the slab introduced into the furnace at ambient temperature.-The high temperature slab produced in the furnace, which is used as a buffer for repairing the rolling mill, is stored and supplied when the rolling mill becomes usable again.

d) A specific cooling device will be introduced for the plate material downstream of the rolling mill, and in some cases, a dedicated plate material processing line will be introduced thereafter.

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 embodiments with reference to the sole drawings attached as FIG.

Schematic of the plant, which is the most complete embodiment.

Referring to FIG. 1, the plant according to the present invention, as in the past, includes a continuous casting machine 1, followed by an induction heater 2 at a constant distance, in which a "mechanical filter" is introduced between the pendulum type shear 3 and the pendulum type shear 3. .. This results in a pendulum type shear 3, followed by a rolling mill 4, a rotary shear 5, a runout table with a cooling device 6, a pusher or pusher / piler 7 for planks, and finally a high speed in front of the downcoiler 9. There is a shear 8.

More specifically, the casting machine 1 includes a mold, is followed by a curved unsolidified area, and produces a slab having a minimum thickness of 80 mm, for example, 100 mm × 2100 mm, at a maximum casting speed of 9 m / min. The slab is then heated by an induction heater 2 containing four coils in the illustrated example before entering the finish rolling mill 4. The finish rolling mill 4 includes up to 7 stands in the illustrated example, the slabs are sequentially reduced in thickness, and the rolling ratios are, for example, 58%, 52%, 47%, 43%, 40%, 35%. , Is gradually reduced to 30%. The work roll diameter of the first stand (the first two in the illustrated example) is large.

The finish rolling mill 4 includes a cooling device and / or a heating device (eg, a gas heater or an induction heater) arranged between the rolling stands at any position after the first two stands, and has specific characteristics and characteristics. Rolling conditions can be better controlled by adapting to the temperature of the rolling material according to the needs.

The resulting strip is then cooled by the cooling device 6 and finally wound up by the downcoiler 9 and cut by the high speed shear 8 when the coil reaches the intended weight. Alternatively, if the slab is compressed to the thickness of the plate, it is cut into plates by the rotary shear 5 and the plate is moved from the line by the pusher or pusher / piler 7. The movement may 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 "kiss pass" stand 10 between the continuous casting machine 1 and the pendulum type shear 3. The "kiss pass" stand 10 performs a reduction of about 10% and is in any case less than 20%. Therefore, it starts with a thickness reduction of about 8 mm. It has a metallic purpose rather than a mechanical purpose. In fact, as described above, this minimum rolling ratio recrystallizes the coarse crystal grains on the slab surface from the casting machine 1 and is unlikely to separate during the rolling process performed by the rolling mill 4. The purpose is to optimize the slab surface crystal structure as crystal grains. Preferably, the plant also comprises an additional induction heater 11 and a descaler 12 having two coils in the illustrated example between the casting machine 1 and the stand 10 a) avoiding a ductile draft temperature range, b). Maintaining the solid solution of the segregation element and c) improving the results under "kiss pass" rolling (similarly, it is preferable to further install the descaler 13 in front of the rolling mill 4).

In addition, the cast alloy contains low melting point elements that tend to collect at the edges of the crystal grains (eg copper and tin in the case of steel made from EAF scrap), making the edges of the crystal grains even weaker. It is clear that the problem increases with the concentration of the above low melting point elements. The grain reconstitution and refinement achieved by the "light" reduction path provides the following dual benefits: a) A larger reduction factor can be applied in the subsequent first actual rolling step without breaking the surface material. b) The same high quality strip / plate can be obtained by using cheap and low quality scrap, that is, scrap containing high concentrations of impurities such as copper and tin.

It should be noted that the "kiss pass" stand 10 preferably has a work cylinder having a smaller diameter than the first stand of the rolling mill 4. This is because the minimum reduction must be applied while cooling the slab as little as possible, the contact arc length is small and sufficient, and the tensile stress on the surface of the rolled material is minimized. Is.

Another advantage gained by placing the so-called "kiss pass" stand 10 between the continuous casting machine 1 and the pendulum shear 3 is, as mentioned above, by forming a "mechanical filter" between the two configurations. be. That is, it is possible to avoid disturbance to the casting machine 1 when the slab is cut by the shear 3 when repairing the plant portion downstream of the shear 3 in an emergency.

According to the second novel aspect of the present invention, there is an edger 14, that is, a narrow surface vertical rolling stand. The edger 14 is preferably located just upstream of the "kisspass" stand 10, preferably an inductive edge heater 15, i.e. a heater with a C-coil that heats only the edges of the slab first. However, the edger 14 may be placed immediately upstream of the rolling mill 4 along with the corresponding induction heater 15 and may be placed adjacent to any side of the induction heater 2.

As mentioned above, with the addition of the edger 14, the slab edges, which are the most sensitive to crack formation because they are the most cooled part, are recrystallized and formed to minimize the tensile stress in the subsequent rolling process. , Width tolerance can be improved. In addition, the paint edger 14 can reduce the slab width on each side up to 50 mm, thereby providing a narrower strip / plate without the intervention of molds and thus without reduced plant productivity. Obtainable.

According to a third novel aspect of the invention, a connecting furnace 16 suitable for allowing the introduction / removal and controlled advancement of the slab S between the "kisspass" stand 10 and the induction heater 2. Exists. A typical example is a gas-heated roller hearth or walking beam furnace, typically about 30 m long, but it is clear that other equivalent types of furnaces can also be used.

Immediately in front of the connecting furnace 16 is an additional pendulum type shear 17, which, as mentioned above, not only allows the reusable slab 18 to be retracted if the mill 4 is unavailable, but also. Select either the "endless" operating mode or the "batch / combined" operating mode and charge the market-purchased slabs into the connecting furnace 16 (via the loading station 19) at ambient temperature. The connecting furnace 16 also functions as a buffer, and in the case of repairing the rolling mill 4, the manufactured high temperature slab is held in the furnace, and when it becomes available again, the stored slab is sent to the rolling line.

Since the "kiss pass" stand 10 is located between the continuous casting machine 1 and the additional pendulum type shear 17, it functions as a "mechanical filter" as described above, and the "batch / composite" mode is selected and the slab is selected. The disturbance in the casting machine 1 when the shear 17 is cut is avoided.

Since the width of the slab does not change, as the thickness of the slab decreases at a predetermined rate, the length increases correspondingly. With this in mind, it should be noted that the "kiss pass" stand 10 can be used just as the first rolling pass upstream of the furnace 16. This is because the "kiss pass" stand 10 reduces the thickness by about 10%, and in each case reduces the thickness by 20% or less. This rolling reduction is much smaller than the rolling reduction of 50-70% in the first stand of prior art rough or finish rolling mills. Prior art reductions require an unacceptably long furnace 16. In fact, the furnace must be sized to hold a slab of weight corresponding to the weight of the coil of strip or the laminate of lumber produced in the batch production cycle, which would be unacceptably long if the slab was thin. I can't get enough weight.

This is the rationale for the 20% reduction rate limit described above. It is clear that significant rolling on the "Kiss Pass" stand 10 will help the mill 4 more easily achieve the desired final thickness and will require fewer stands. However, there are also "metallurgical limits" that depend on the alloy composition, so the "Kiss Pass" stand 10 only provides the maximum reduction suitable for obtaining the required grain recrystallization without causing fracture of the slab surface. 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 subsequent work processes provides higher quality planks than those produced in prior art plants. This is because in a prior art plant, the cooling area is optimized for strips only.

Alternatively, the cooling device 20 dedicated to the plate material can be arranged offline. Multi-stage high pressure cooling is performed on the plate material removed by the pusher or the pusher / piler 7. That is, after each cooling, subsequent cooling is performed after a time during which the plate material becomes substantially uniform. In this way, the desired cooling pattern for each steel grade can be obtained and the plate material (cooled by the ultrafast cooling section of the particular cooling device 20 or the cooling device 6 above) to complete the processing of the plate material. The processing cooling device 20 is followed by a tempering furnace 21, 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 the plate material specific settings. In that case, it is clear that a pusher / piler 7 or an additional pusher / piler 7'can be placed between the cooling devices. In this way, the cooling device 6 can be adequately used for cooling both high quality strips and high quality plates.

Therefore, the plant according to the invention described above is in an "endless" mode without a solution for the continuity of the slab between the foundry 1 and the rolling mill 4 (ie, the inlet speed of the rolling mill 4 is at the kiss pass stand. In both "batch / composite" modes where the slab entering the rolling mill 4 is separated from the slab of the rolling mill 1), high quality strips and high quality plates. Suitable for manufacturing both.

In addition, the plant can also use slabs flowing from the connecting furnace 16 as a starting material. The slab is either charged at ambient temperature through the loading station 19 or the furnace 16 is used as a buffer and kept at a high temperature in the furnace 16.

Claims (25)

A plant for endless, batch or composite production of hot rolled steel strips and plates with a thickness of 0.6 mm to 50 mm or half the maximum thickness of cast slabs.
A continuous casting machine (1), which is a continuous casting machine (1) and uses an unsolidified compaction to make a thin slab having a minimum slab thickness of 80 mm at the outlet of the continuous casting machine (1).
Subsequently, the induction heater (2), via the first shear (3),
Next, the rolling mill (4),
Next, the second Shah (5),
Run-out table with cooling device (6) and pusher / piler (7) for plate material,
Next, a third shear (8) and a plurality of coilers (9).
In the plant equipped with
The plant further comprises a minimum reduction rolling stand (10) disposed between the continuous casting machine (1) and the first shear (3), wherein the minimum reduction rolling stand (10) is 8 mm. A plant designed to perform rolling with a rolling reduction of 10% to 20%, starting with thickness reduction. 1 according to claim 1, further comprising an additional induction heater (11) and a descaler (12) disposed between the continuous casting machine (1) and the minimum reduction rolling stand (10). Plant. The plant according to claim 1 or 2, wherein the minimum rolling rolling stand (10) has a work roll having a diameter smaller than that of the first stand of the rolling mill (4). The plant according to any one of claims 1 to 3, further comprising an edger (14) designed to reduce the slab width by up to 50 mm on each side. The plant according to claim 4, wherein the edger (14) is arranged immediately upstream of the minimum rolling roll stand (10) or the rolling mill (4). The plant according to claim 4 or 5, further comprising an inductive edge heater (15) disposed in front of the edger (14). A connecting furnace (16) is further provided between the minimum reduction rolling stand (10) and the induction heater (2), in which the connecting furnace (16) introduces / removes and controls forward movement of the slab (S). The connection furnace (16) is designed to allow for the weight of the slab (S) corresponding to the weight of the coil of the strip of the final product or the laminate of the plate material produced in the batch production cycle. The plant according to any one of claims 1 to 6, characterized in that it has a sufficient length. The plant according to claim 7, wherein the connecting furnace (16) is a gas-heated roller hearth furnace or a walking beam furnace. A fourth shear (17) is provided immediately in front of the connecting furnace (16), and the connecting furnace (16) is a piler (18) and a slab (S) for taking out a slab (S) from the connecting furnace (16). The plant according to claim 7 or 8, wherein the plant is provided with a loading station (19) for introducing the) into the connecting furnace (16). The plant according to any one of claims 1 to 9, wherein the cooling device (6) has a first cooling region capable of quenching the plate material. One of claims 1 to 10, further comprising an offline cooling device (20) dedicated to the plate material that performs multi-stage high-pressure cooling of the plate material taken out by the pusher or the pusher / piler (7). The plant described in. Further, a plate material processing line for receiving the plate material from the first cooling region of the cooling device (6) or the offline cooling device (20) dedicated to the plate material is further provided, and the plate material processing line is sequentially provided with a tempering furnace (21) and controlled cooling. (22) The plant according to claim 11, citing claim 10, comprising a skin pass stand (23) and a roller leveler (24). The cooling device (6) is adjustable to a setting dedicated to the plate material, and an additional pusher / pile (7') is arranged between the cooling device (6) and the coiler (9). The plant according to any one of claims 1 to 12. Any of claims 1 to 13, further comprising a cooling or heating device located between the rolling stands of the rolling mill (4) at any position after the first two rolling stands. The plant described in item 1. According to the plant according to any one of claims 1 to 14, hot-rolled steel strips and plates having a thickness of 0.6 mm to 50 mm or half the maximum thickness of a cast slab. Endless or batch manufacturing method
Continuous casting (1) of a thin slab (S) having a minimum slab thickness of 80 mm under unsolidified pressure was performed.
After that, heating with an induction heater (2), finish rolling (4), and
After that, in the above-mentioned manufacturing method including final shearing (5) in the case of manufacturing a plate material, controlled cooling (6), final shearing (8) in the case of manufacturing a strip material, and winding.
Prior to heating in the induction heater (2), starting with a thickness reduction of 8 mm, further including initial rolling (10) with a reduction rate of 10% to 20% in the slab (S). A manufacturing method characterized by. The production method according to claim 15, wherein the initial rolling (10) is preceded by heating by an additional induction heater (11) and descaling (12). Further including vertical rolling (14) of the narrow side of the slab capable of reducing the width by up to 50 mm on each side, said vertical rolling (14) immediately prior to the initial rolling (10) or the finish rolling (4). The manufacturing method according to claim 15 or 16, wherein the method is performed. The manufacturing method according to claim 17, wherein the slab edge is heated by the induction edge heater (15) before the vertical rolling (14). 13. Manufacturing method. The fifteenth aspect of the present invention further comprises taking out the plate material (7) after the final shearing (5) and multi-stage high-pressure cooling of the plate material by an offline cooling device (20) dedicated to the plate material. The manufacturing method according to any one of claims 18. 19. The production method according to claim 19, further comprising tempering (21), controlled cooling (22), skin path (23) and leveling (24) of the plate material after the quenching. The production method according to claim 20, further comprising tempering (21), controlled cooling (22), skin path (23) and leveling (24) of the plate material in order after the multi-stage high-pressure cooling. In the case of manufacturing a plate material, after the final shearing (5), the controlled cooling (6) adjusted to the setting dedicated to the plate material is performed, and after the controlled cooling (6), the plate material is taken out. The manufacturing method according to any one of claims 15 to 18. The manufacturing method is carried out by the plant according to claim 9.
Using the connecting furnace (16) provided between the minimum rolling stand (10) and the induction heater (2), the slab (S) from the connecting furnace (16) is used as a starting material. The slab is characterized by being introduced by the loading station (19) at ambient temperature or kept at a high temperature in the connecting furnace (16) when used as a buffer. The manufacturing method according to any one of claims 15 to 23. The manufacturing method is carried out by the plant according to claim 9.
When a connection furnace (16) provided between the minimum reduction rolling stand (10) and the induction heater (2) is used and a problem occurs in a plant portion downstream of the connection furnace (16). 1 The manufacturing method described in the section.

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