A method and production line for continuously casting and rolling ultra-low carbon steel coils without a head

Abstract

The present invention relates to a method and a production line for continuously casting and rolling ultra-low carbon steel coils without a head, belonging to the technical field of strip continuous casting and rolling. The production line includes a continuous caster, a rough rolling mill set, an intermediate billet reheating device, a shearing and waste pushing device, a heating device, a finish rolling mill set, a laminar cooling device, a high-speed flying shear, and a coiling mill set arranged sequentially along the rolling direction. Among them, the intermediate billet reheating device is used for reheating the intermediate billet to compensate for the temperature drop caused by the increase in the upstream rough rolling stands and rough descaling, so that the surface temperature of the intermediate billet entering the downstream heating device is higher than the starting temperature Ar3 of the transformation from austenite to ferrite, thereby suppressing the generation of mixed crystal structure in the strip steel, reducing the performance risk, and creating process conditions for the thinner intermediate billets required for rolling thinner strip steel and the rough descaling required for strip steel with higher surface quality.

Description

Technical Field

[0001] The present invention belongs to the technical field of strip continuous casting and rolling, and relates to a method and a production line for continuously casting and rolling ultra-low carbon steel coils without a head. Background Art

[0002] In recent years, the headless continuous casting and rolling process represented by ESP has achieved great success in industrial applications. Compared with conventional hot continuous rolling, its process is compact, energy consumption is low, and the cost per ton of steel is significantly reduced; the continuous casting drawing speed is high, and the production efficiency is relatively high; the headless rolling eliminates the process of threading and tailing of the strip during single-piece rolling, and the accuracy and stability of the strip size and performance are significantly improved. It can stably produce thin strip steel with a thickness of less than 1.2 mm, realizing partial substitution of hot rolling for cold rolling and reducing the production cost of strip steel.

[0003] Currently, in industrial practice, a slab of 105 mm, a drawing speed of 5.2 m / min, and an intermediate slab of 8.5 mm - 9 mm are used. The thinnest low-carbon strip steel that can be stably rolled is 0.8 mm. Among them, the surface temperature of the slab at the continuous casting outlet is about 980°C - 1000°C, and it directly enters the rough rolling without rough descaling. The surface temperature of the intermediate slab at the outlet of the rough rolling mill is about 960°C - 980°C, and the surface temperature at the induction heating inlet is about 910°C - 930°C. If producing thinner, such as 0.6 mm, according to the configuration of the existing ESP production line, it will increase the rolling load of the finishing mill, resulting in inability to stably produce for a long time. Therefore, it is necessary to reduce the thickness of the intermediate slab to reduce the finishing mill load. However, with the configuration of 3 rough rolling mills of the existing ESP, thinning the intermediate slab means that the rolling deformation amount of each rough rolling stand exceeds 60%. Although it is theoretically feasible, it is not practical because it is easy to cause exceeding the design limit of the rolling mill capacity and deterioration of the intermediate slab shape.

[0004] One of the effective means to reduce the thickness of the intermediate slab is to increase the number of rough rolling mills, making the intermediate slab thinner to 6 mm. However, problems then arise. That is, increasing the rough rolling mills will cause an increase in the surface temperature drop of the intermediate slab at the outlet of the rough rolling. At the same time, as the downstream users' requirements for the surface quality of the strip steel are continuously increasing, the use of rough descaling is an effective solution, but rough descaling will also increase the temperature drop. Cumulatively, compared with the existing ESP, the induction heating inlet temperature downstream of the rotary shear will be lower than the phase transformation start temperature Ar3 of low-carbon steel grades, and then rapidly heated to the austenitizing temperature, which is likely to cause mixed crystal structure and pose risks to the performance of low-carbon strip steel.

[0005] Therefore, it is necessary to consider measures to prevent the induction heating inlet temperature of the low-carbon steel intermediate slab from dropping below the phase transformation point after increasing the rough rolling mills and rough descaling in the headless continuous casting and rolling process, resulting in risks to the strip steel tissue performance, and configure the corresponding production line to facilitate thinning of the intermediate slab, and further facilitate the stable production of thinner gauge strip steel. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a method and a production line for continuously casting and rolling ultra-low carbon steel coils without a head, so as to suppress the generation of mixed crystal structures in the strip steel, reduce the performance risks of the strip steel, and create process conditions for thinner intermediate billets required for rolling thinner strip steels and rough descaling required for strip steels with higher surface quality.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A production line for continuously casting and rolling ultra-low carbon steel coils without a head includes the following steps: continuous casting, rough rolling, head cutting, heating, finish rolling, laminar cooling, slitting, and coiling into coils; intermediate billet reheat is performed after rough rolling so that the surface temperature of the intermediate billet when entering the downstream heating device is higher than the starting temperature Ar3 of the transformation from austenite to ferrite.

[0009] Optionally, the reheat temperature T of the intermediate billet is determined according to the number n of roughing mills in the upstream roughing mill set, T≥k(n - 3)+t, where k is the temperature drop of a single roughing mill and t∈[0, 40°C].

[0010] Optionally, when rough descaling is performed before rough rolling, t∈[30°C, 40°C].

[0011] Optionally, at least 4 roughing mills are used for rough rolling.

[0012] Optionally, high-pressure water with a pressure of 10 MPa to 20 MPa is used for rough descaling before rough rolling.

[0013] Optionally, the intermediate billet after rough rolling is reheated to not less than 40°C before entering the downstream flying shear.

[0014] Optionally, the temperature of the surface of the continuous casting billet at the outlet of the continuous caster is 980°C to 1000°C; the temperature of the surface of the intermediate billet at the outlet of the last roughing mill stand is 900°C to 920°C, and the temperature at the inlet of the heating device located after the flying shear is greater than 890°C.

[0015] Optionally, the thickness of the continuous casting billet is 95 mm to 115 mm, the width is 900 mm to 1600 mm, the thickness of the intermediate billet after rough rolling is 6 mm to 20 mm, and the thickness of the strip steel after finish rolling is 0.6 mm to 4 mm.

[0016] Optionally, the continuous casting casting speed is 4.0 m / min to 6.0 m / min.

[0017] Optionally, the chemical composition of the ultra-low carbon steel is C≤0.02%, Si≤0.05%, Mn≤0.1%, P≤0.02%, S≤0.003%, Alt≤0.04%.

[0018] A production line for continuously casting and rolling ultra-low carbon steel coils without a head, comprising a continuous caster, a rough rolling mill set, a shearing and scrap pushing device, a heating device, a finish rolling mill set, a laminar cooling device, a high-speed flying shear and a coiling mill set arranged in sequence along the rolling direction. An intermediate billet temperature compensation device is provided between the rough rolling mill set and the shearing and scrap pushing device to compensate the temperature of the intermediate billet, so that the surface temperature of the intermediate billet when entering the downstream heating device is higher than the starting temperature Ar3 of the transformation from austenite to ferrite.

[0019] Optionally, the rough rolling mill set includes at least 4 rough rolling mills.

[0020] Optionally, a rough descaling device is provided between the continuous caster and the rough rolling mill set.

[0021] Optionally, a finish descaling device is provided between the heating device and the finish rolling mill set.

[0022] Optionally, the rough descaling device and / or the finish descaling device is a high-pressure water descaling device.

[0023] Optionally, the intermediate billet temperature compensation device and the heating device are induction heating devices or flue gas heating devices.

[0024] Optionally, the shearing and scrap pushing device includes a swing shear, a scrap pushing device, a rotary drum shear and a stacker removal device arranged in sequence along the rolling direction.

[0025] Optionally, along the rolling direction, the length of the scrap pushing device is 10m - 12m.

[0026] Optionally, along the rolling direction, the length of the stacker removal device is 2.5m - 4m.

[0027] Optionally, the finish rolling mill set includes 5 finish rolling mills.

[0028] The beneficial effects of the present invention are as follows:

[0029] Through the intermediate billet temperature compensation device located between the last rough rolling stand and the swing shear, the temperature drop of the intermediate billet caused by the increase in the number of rough rolling stands and the use of rough descaling can be effectively compensated. After the ultra-low carbon steel intermediate billet undergoes rough rolling deformation and is transported to the induction heating device after the rotary drum shear, it always remains in the austenite region above Ar3 and does not undergo ferrite transformation. Therefore, the risk of mixed crystal structure formation caused by the premature phase transformation of some tissues and the rapid heating and reverse phase transformation of the non-transformed tissues is effectively reduced. At the same time, increasing the number of rough rolling mills can effectively reduce the thickness of the intermediate billet, creating favorable conditions for rolling thinner specifications in finish rolling; increasing the use of rough descaling effectively solves the problem that the scale formed in the continuous casting billet stage enters the rough rolling, causing the scale to be pressed into the surface of the intermediate billet and being difficult to remove subsequently.

[0030] Other advantages, objects and features of the present invention will be set forth in part in the following description, and in part will be obvious to those skilled in the art upon examination of the following, or may be learned from the practice of the present invention. The objects and other advantages of the present invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter. Brief Description of the Drawings

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, wherein:

[0032] Figure 1 It is a schematic layout diagram of the production line for continuously casting and rolling ultra-low carbon steel coils without a head according to the present invention.

[0033] Reference numerals in the drawings: continuous caster 1, rough descaling device 2, rough rolling mill unit 3, intermediate billet reheating device 4, flying shear 5, waste pushing device 6, rotary drum shear 7, stacker removal device 8, heating device 9, finish descaling device 10, finish rolling mill unit 11, laminar cooling device 12, high-speed flying shear 13, coiling unit 14, casting billet 101, intermediate billet 102, strip steel 103. Detailed Embodiments

[0034] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention schematically, and the following embodiments and the features in the embodiments can be combined with each other without conflict.

[0035] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and should not be construed as limiting the present invention; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, and do not represent the dimensions of actual products; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0036] In the drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only used for exemplary illustration and cannot be understood as a limitation of the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0037] Please refer to Figure 1 , a method for producing ultra-low carbon steel coils by endless casting and rolling, comprising the following steps: continuous casting, rough rolling, head cutting, heating, finish rolling, laminar cooling, slitting, and coiling into coils; intermediate slab supplementary heating is carried out after rough rolling so that the surface temperature of the intermediate slab when entering the downstream heating device is higher than the starting temperature Ar3 of the transformation from austenite to ferrite.

[0038] Since adding one roughing mill will cause the surface temperature drop of the intermediate slab at the roughing exit to increase by approximately 25°C to 35°C, the supplementary heating temperature T of the intermediate slab can be determined according to the number n of roughing mills in the upstream roughing mill unit. At the same time, since rough descaling will also increase the temperature drop by about 30°C to 40°C, when rough descaling is carried out before rough rolling, the supplementary heating temperature T of the intermediate slab should also consider the temperature drop caused by rough descaling. Therefore, when rough descaling is not carried out before rough rolling, T≥k(n - 3), where k is the temperature drop of a single roughing mill; conversely, T≥k(n - 3)+t, t∈[30°C, 40°C]. The two can also be unified as: T≥k(n - 3)+t, t∈[0, 40°C].

[0039] When rough rolling is carried out using 4 roughing mills, the temperature of the slab surface at the continuous caster exit is 980°C to 1000°C; the temperature of the intermediate slab surface at the exit of the last roughing stand is 900°C to 920°C. The intermediate slab is supplemented with heat by 40°C to 80°C through an intermediate slab supplementary heating device located between the last roughing stand and the entry of the flying shear, so that the intermediate slab that is subsequently air-cooled through the flying shear and the emergency shear area has a temperature greater than 890°C at the entry of the heating device downstream of the flying shear. The continuous casting casting speed can be 4.0 m / min to 6.0 m / min.

[0040] When 4 rough rolling mills and 5 finishing mills are used to roll continuous casting billets with a thickness of 95mm to 115mm and a width of 900mm to 1600mm, the thickness of the intermediate billet after rough rolling can reach 6mm to 20mm, and the thickness of the strip after finishing rolling can reach 0.6mm to 4mm. Before rough rolling, 10MPa to 20MPa high-pressure water can be used for rough descaling to remove the oxide scale and prevent the iron oxide scale formed in the continuous casting stage from entering the rough rolling and affecting the surface quality of the strip.

[0041] A production line for producing ultra-low carbon steel coils by headless continuous casting and rolling, comprising a continuous casting machine 1, a roughing mill group 3, a shearing and scrap pushing device, a heating device 9, a finishing mill group 11, a laminar cooling device 12, a high-speed flying shear 13 and a coiling unit 14 arranged in sequence along the rolling direction, an intermediate billet temperature supplement device 4 is provided between the roughing mill group 3 and the shearing and scrap pushing device 6 to supplement the temperature of the intermediate billet so that the surface temperature of the intermediate billet when entering the downstream heating device is higher than the starting temperature Ar3 of the transformation from austenite to ferrite.

[0042] Theoretically, more than 4 roughing mills can be selected for the roughing mill group 3. From the perspective of economy, 4 roughing mills are preferably selected for the roughing mill group 3, and 5 finishing mills are preferably selected for the finishing mill group 11.

[0043] A rough descaling device 2 may be provided between the continuous casting machine 1 and the rough rolling mill 3, and a fine descaling device 10 may be provided between the heating device and the finishing rolling mill 11 to improve the surface quality of the steel strip 103. The rough descaling device 2 and the fine descaling device 10 are preferably high-pressure water descaling devices.

[0044] The intermediate billet temperature supplement device 4 and the heating device 9 can be an induction heating device or a flue gas heating device, and an induction heating device is preferred. The induction heating device is easy to arrange and the temperature can be flexibly controlled.

[0045] The shearing and scrap pushing device can be composed of a swing shear 5 and a scrap pushing device 6 arranged in sequence along the rolling direction, or can be composed of a swing shear 5, a scrap pushing device 6, a drum shear 7 and a stack plate removing device 8 arranged in sequence along the rolling direction, the latter being convenient for accident handling. Along the rolling direction, the length of the scrap pushing device 6 is 10m to 12m, and the length of the stack plate removing device 8 is 2.5m to 4m.

[0046] Example 1

[0047] A production line for continuously casting and rolling ultra-low carbon steel coils without a head includes a continuous caster 1, a high-pressure water rough descaling device 2, a rough rolling mill group 3, an intermediate billet reheating device 4, a flying shear 5, a waste pushing device 6, a rotary drum shear 7, a stacker removal device 8, an induction heating device 9, a high-pressure water fine descaling device 10, a finishing mill group 11, a laminar cooling device 12, a high-speed flying shear 13, and a coiling mill group 14, which are connected in sequence. Among them, the rough descaling pressure is 10 MPa to 20 MPa, the rough rolling mill group uses 4 rolling mills, the intermediate billet reheating device 4 preferably has 2 to 3 induction heating devices, the length of the waste pushing device 6 along the rolling direction is about 11 m, and the length of the stacker removal device 8 along the rolling direction is about 3 m.

[0048] The typical production process based on this production line is as follows:

[0049] Composition of ultra-low carbon strip steel:

[0050] By mass percentage: C ≤ 0.02%, Mn ≤ 0.1%, Si ≤ 0.05%, P ≤ 0.02%, S ≤ 0.003%, Alt ≤ 0.04%, and the balance is Fe.

[0051] It is experimentally measured that the austenite-to-ferrite transformation temperature Ar3 under this composition is 880 °C to 890 °C at a cooling rate of 1 °C / s to 5 °C / s.

[0052] Continuously cast into a continuous slab 101 with a width of 1250 mm and a thickness of 105 mm, the continuous casting speed is 5.5 m / min, and then through rough descaling and a 4-stand rough rolling mill group, it becomes an intermediate billet 102 with a thickness of 6 mm, and then runs to the finishing mill group, rolled into a strip steel 103 with a thickness of 0.7 mm, and then cut by a high-speed flying shear, and finally coiled by a coiling machine.

[0053] According to the above process, the strip steel temperature at each position of the production line is shown in Table 1. To illustrate the characteristics of the present invention, the temperature without intermediate billet reheating under the same equipment parameters and production line layout spacing is also listed for comparison.

[0054] Table 1 Process temperature comparison

[0055]

[0056]

[0057] As can be seen from Table 1, without intermediate billet reheating, when the rough descaling is put into use and after passing through 4 rough rolling mills, the temperature of the intermediate billet with a thickness of 6 mm at the entrance of the induction heating device 9 has dropped below the ultra-low carbon steel phase transformation temperature Ar3, and the austenite-to-ferrite phase transformation will occur.

[0058] Since an intermediate billet reheating device 4 is added between the last roughing stand R4 and the flying shear 5, the additional temperature drop of the intermediate billet caused by the application of the rough descaling device 2 and the addition of one roughing mill can be effectively compensated. As a result, the intermediate billet remains above the Ar3 phase transformation point of the ultra-low carbon steel, that is, in the fully austenite region, from the outlet of the last roughing stand R4 to the inlet of the induction heating device 9. This suppresses the risk of mixed crystal structure and properties caused by prior phase transformation and subsequent reverse phase transformation, which is more reasonable from the perspective of process temperature control. At the same time, it also creates process conditions for rolling thinner intermediate billets required for thinner strip steel and rough descaling required for strip steel with higher surface quality. In addition, due to the local optimization of the existing technology, the feasibility of implementing the present invention is relatively high.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for producing ultra-low carbon steel coils by endless casting and rolling, comprising the following steps: Continuous casting, rough rolling, crop shearing, heating, finish rolling, laminar cooling, slitting, and coiling into coils; characterized in that: intermediate billet supplementary heating is carried out after rough rolling so that the surface temperature of the intermediate billet when entering the downstream heating device is higher than the starting temperature Ar3 of the transformation of austenite to ferrite; The supplementary heating temperature T of the intermediate billet supplementary heating is determined according to the number n of roughing mills in the upstream roughing mill train, T≥k(n - 3)+t, where k is the temperature drop of a single roughing mill and t∈[0, 40°C]; when rough descaling is carried out before rough rolling, t∈[30°C, 40°C]; The continuous casting billet has a thickness of 95mm - 115mm and a width of 900mm - 1600mm. After rough rolling, the intermediate billet has a thickness of 6mm - 20mm, and after finish rolling, the strip has a thickness of 0.6mm - 4mm; the continuous casting casting speed is 4.0m / min - 6.0m / min; the composition of the extra-low carbon steel is C≤0.02%, Si≤0.05%, Mn≤0.1%, P≤0.02%, S≤0.003%, Alt≤0.04%.

2. A method for producing ultra-low carbon steel coils by endless casting and rolling according to claim 1, characterized in that: Rough rolling is carried out using at least 4 roughing mills.

3. A method for producing ultra-low carbon steel coils by endless casting and rolling without a head, characterized in that: High-pressure water of 10MPa - 20MPa is used for rough descaling before rough rolling.

4. A method for producing ultra-low carbon steel coils by endless casting and rolling according to claim 1, characterized in that: The intermediate billet after rough rolling is supplementary heated to not less than 40°C before entering the downstream flying shear.

5. A method for producing ultra-low carbon steel coils by endless casting and rolling without a head, characterized in that: The temperature of the casting billet surface at the outlet of the continuous caster is 980°C - 1000°C; the temperature of the intermediate billet surface at the outlet of the last roughing mill stand is 900°C - 920°C, and the temperature at the inlet of the heating device located after the flying shear is greater than 890°C.

6. A production line for continuously casting and rolling ultra-low carbon steel coils without a head, comprising a continuous caster, a rough rolling mill set, a shearing and waste pushing device, a heating device, a finish rolling mill set, a laminar cooling device, a high-speed flying shear and a coiling mill set that are sequentially arranged along the rolling direction, characterized in that: An intermediate billet supplementary heating device is provided between the roughing mill train and the shearing and pusher device to supplementary heat the intermediate billet so that the surface temperature of the intermediate billet when entering the downstream heating device is higher than the starting temperature Ar3 of the transformation of austenite to ferrite; The supplementary heating temperature T of the intermediate billet supplementary heating is determined according to the number n of roughing mills in the upstream roughing mill train, T≥k(n - 3)+t, where k is the temperature drop of a single roughing mill and t∈[0, 40°C]; when rough descaling is carried out before rough rolling, t∈[30°C, 40°C]; The continuous casting billet has a thickness of 95mm - 115mm and a width of 900mm - 1600mm. After rough rolling, the intermediate billet has a thickness of 6mm - 20mm, and after finish rolling, the strip has a thickness of 0.6mm - 4mm; the continuous casting casting speed is 4.0m / min - 6.0m / min; the composition of the extra-low carbon steel is C≤0.02%, Si≤0.05%, Mn≤0.1%, P≤0.02%, S≤0.003%, Alt≤0.04%.

7. A production line for continuously casting and rolling ultra-low carbon steel coils without a head, characterized in that: The roughing mill train includes at least 4 roughing mills.

8. A production line for continuously casting and rolling ultra-low carbon steel coils without a head, characterized in that: A rough descaling device is provided between the continuous caster and the roughing mill train.

9. A production line for continuously casting and rolling ultra-low carbon steel coils without a head, characterized in that: A finish descaling device is provided between the heating device and the finish rolling mill train.

10. A production line for continuously casting and rolling ultra-low carbon steel coils without a head, characterized in that: The rough descaling device and / or the finish descaling device is a high-pressure water descaling device.

11. A production line for continuously casting and rolling ultra-low carbon steel coils without a head, characterized in that: The intermediate billet supplementary heating device and the heating device are induction heating devices or flue gas heating devices.

12. A production line for continuously casting and rolling ultra-low carbon steel coils without a head, characterized in that: The shearing and pusher device includes a flying shear, a pusher device, a rotary drum shear, and a stacker removal device arranged in sequence along the rolling direction.

13. A production line for continuously casting and rolling ultra-low carbon steel coils without a head, characterized in that: Along the rolling direction, the length of the pusher device is 10m - 12m.

14. A production line for continuously casting and rolling ultra-low carbon steel coils without a head, characterized in that: Along the rolling direction, the length of the stacker removal device is 2.5m - 4m.

15. A production line for continuously casting and rolling ultra-low carbon steel coils without a head, characterized in that: The finish rolling mill train includes 5 finish rolling mills.

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