Method for reducing occurrence rate of edge cracks of double-roller continuous casting hot rolling strip steel

Abstract

The invention belongs to the field of thin-strip continuous casting, and relates to a method for reducing the occurrence rate of edge cracks of double-roller continuous casting hot-rolled strip steel. The method comprises the steps of optimizing the angle of a flow guide hole in the end of a molten pool flow distribution water opening, increasing the flow speed of molten steel in the flow guide hole, and solving the problem that temperature distribution in the width direction of molten steel in the molten pool is remarkably uneven, especially the problem that the temperature of molten steel near a side sealing plate in the molten pool is low. According to the method disclosed by the invention, by adopting the control means, the occurrence rate of edge cracks of the hot-rolled strip steel can be effectively reduced when the strip steel is produced by adopting a double-roller cast-rolling process. According to the method, under the condition that the production cost is not increased, the surface quality of the strip steel produced through the double-roller thin-strip cast-rolling technology is effectively improved, and the edge cracks of the strip steel account for more than 50% of the plate surface cracks and are reduced to less than 10% of the plate surface cracks.

Description

Technical Field

[0001] The present invention belongs to the field of thin slab continuous casting, and relates to a method for reducing the incidence rate of edge cracks in hot-rolled strip steel by twin-roll continuous casting. Background Art

[0002] The thin slab continuous casting technology is a new type of thin strip steel production process. In the molten steel casting process, the molten steel is distributed by a cloth-flow nozzle into a molten pool composed of a pair of reversely rotating casting rolls and a pair of side seal plates. Circulating cooling water is introduced into the casting rolls, and the molten steel is directly cooled and solidified into a strip on the surface of the casting rolls. Compared with the traditional continuous casting and hot rolling processes, it has the advantages of short production process, low energy consumption, and low product cost. However, there are still certain bottlenecks in this technology at present. The main problem is that the incidence rate of surface cracks in the hot-rolled strip steel produced is relatively high, especially the incidence rate of edge cracks in the surface cracks of the strip steel, which affects the product quality.

[0003] Starting from the purpose of reducing the incidence rate of edge cracks in hot-rolled strip steel by twin-roll continuous casting, the present invention improves the temperature distribution uniformity in the width direction of the molten pool by increasing the molten steel renewal speed near the side seal plates in the molten pool, thereby improving the consistency of the solidification process of the molten steel in the molten pool and solving the problem of high incidence rate of edge cracks caused by the relatively low temperature of the molten steel near the side seal plates. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technologies at present, the purpose of the present invention is to provide an advantageous technical solution. By increasing the flow velocity of the molten steel flow at the end of the cloth-flow nozzle, increasing the molten steel renewal speed near the side seal plates in the molten pool, and optimizing the inclination angle of the diversion holes at the end of the cloth-flow nozzle to change the flow direction, the temperature distribution and uniformity of the molten steel near the side seal plates in the molten pool are optimized, and then the solidification consistency and uniformity of the molten steel in the width direction of the molten pool are improved, thereby reducing the incidence rate of edge cracks in hot-rolled strip steel by twin-roll continuous casting.

[0005] To achieve the above technical purpose, the present invention adopts the following technical solutions and methods:

[0006] The present invention discloses a method for reducing the incidence rate of edge cracks in hot-rolled strip steel by twin-roll continuous casting. The method includes the following steps:

[0007] (1) Qualified molten steel is produced by the primary melting furnace and the refining furnace. The molten steel in the ladle flows into the cloth-flow nozzle through the long nozzle, the tundish, and the transition tundish. It flows into the molten pool formed by a pair of reversely rotating casting rolls and a pair of side seal plates through the diversion holes on both sides and at the end of the cloth-flow nozzle.

[0008] (2) The molten steel in the cloth-flow nozzle flows through the diversion holes at its end to the vicinity of the end of the molten pool.

[0009] (3) Circulating cooling water is introduced into the casting rolls, and the flow rate and temperature of the circulating cooling water are controlled.

[0010] (4) The molten steel in the molten pool is cooled and solidified by the casting rolls to form a steel strip with a thickness of 1.5 to 2.5 mm.

[0011] (5) The strip steel is hot-rolled in one pass to a certain thickness.

[0012] Preferably, the molten steel composition can be medium carbon steel, high carbon steel, weathering steel, stainless steel composition, etc.

[0013] Preferably, the diversion hole at the end of the cloth flow nozzle forms an angle of 40° with the vertical direction.

[0014] Preferably, the flow velocity of the molten steel flow in the diversion hole at the end of the cloth flow nozzle increases to 4 - 5 m / s.

[0015] Preferably, the width of the molten pool is 1500 mm.

[0016] Preferably, the flow rate of the circulating cooling water of the casting rolls is controlled at 2400 - 3000 m 3 / h.

[0017] Preferably, the temperature of the circulating cooling water of the casting rolls is controlled at 20 - 40 °C.

[0018] Preferably, the drawing speed of the strip steel is controlled at 40 - 80 m / min.

[0019] The present invention specifically adopts the following technical solutions:

[0020] According to the first aspect of the present invention, a method for reducing the incidence of edge cracks in hot-rolled strip steel by twin-roll continuous casting is proposed, and the method includes the following steps:

[0021] (1) Qualified molten steel is made in the primary melting furnace and the refining furnace, and flows into the cloth flow nozzle through the long nozzle, tundish, and transition tundish;

[0022] It flows into the molten pool formed by a pair of reversely rotating casting rolls and a pair of side sealing plates through the two sides of the cloth flow nozzle and the diversion holes at its end;

[0023] (2) The molten steel in the cloth flow nozzle flows towards the vicinity of the end of the molten pool through the diversion hole at its end, and the flow direction of the flow is controlled by controlling the angle of the diversion hole;

[0024] (3) Increasing the flow velocity of the molten steel in the end diversion hole to accelerate the renewal speed of the molten steel near the side sealing plate of the molten pool;

[0025] (4) Circulating cooling water is introduced into the casting rolls, and the flow rate and temperature of the circulating cooling water are controlled;

[0026] (5) The molten steel is cooled and solidified by the casting rolls to form a cast strip with a thickness of 1.5 - 2.5 mm;

[0027] (6) The strip steel is hot-rolled in one pass to form hot-rolled thin strip steel.

[0028] The method for reducing the incidence of edge cracks in hot-rolled strip by twin-roll continuous casting according to the present invention, preferably, the molten steel composition is carbon steel, weathering steel or stainless steel composition.

[0029] The method for reducing the incidence of edge cracks in hot-rolled strip by twin-roll continuous casting according to the present invention, preferably, diversion holes are opened on both sides and at the ends of the cloth-flow nozzle.

[0030] The method for reducing the incidence of edge cracks in hot-rolled strip by twin-roll continuous casting according to the present invention, preferably, the diversion holes on both sides of the cloth-flow nozzle are horizontally distributed.

[0031] The method for reducing the incidence of edge cracks in hot-rolled strip by twin-roll continuous casting according to the present invention, preferably, the diversion holes at the ends of the cloth-flow nozzle form an angle of 30-50° with the vertical direction.

[0032] The method for reducing the incidence of edge cracks in hot-rolled strip by twin-roll continuous casting according to the present invention, preferably, the diversion holes at the ends of the cloth-flow nozzle form an angle of 40° with the vertical direction.

[0033] The method for reducing the incidence of edge cracks in hot-rolled strip by twin-roll continuous casting according to the present invention, preferably, in step (3), the flow velocity of the flow stream of the end diversion holes is controlled at 4-5 m / s.

[0034] The method for reducing the incidence of edge cracks in hot-rolled strip by twin-roll continuous casting according to the present invention, preferably, in step (3), the flow velocity of the flow stream of the end diversion holes is controlled at 4.8 m / s.

[0035] The method for reducing the incidence of edge cracks in hot-rolled strip by twin-roll continuous casting according to the present invention, preferably, the length of the casting roll is 1200-2000 mm.

[0036] The method for reducing the incidence of edge cracks in hot-rolled strip by twin-roll continuous casting according to the present invention, preferably, the length of the casting roll is 1500 mm or 1800 mm.

[0037] The method for reducing the incidence of edge cracks in hot-rolled strip by twin-roll continuous casting according to the present invention, preferably, in step (4), the flow rate of the circulating cooling water of the casting roll is controlled at 2400-3000 m 3 / h.

[0038] The method for reducing the incidence of edge cracks in hot-rolled strip by twin-roll continuous casting according to the present invention, preferably, in step (4), the flow rate of the circulating cooling water of the casting roll is controlled at 2600 m 3 / h.

[0039] The method for reducing the incidence of edge cracks in hot-rolled strip by twin-roll continuous casting according to the present invention, preferably, in step (4), the temperature of the circulating cooling water of the casting roll is controlled at 20-40 °C.

[0040] According to the method for reducing the incidence of edge cracks in hot-rolled strip produced by twin-roll continuous casting of the present invention, preferably, in step (4), the temperature of the circulating cooling water for the casting rolls is controlled at 30°C.

[0041] According to the method for reducing the incidence of edge cracks in hot-rolled strip produced by twin-roll continuous casting of the present invention, preferably, in step (5), the thickness of the cast strip is controlled to be 1.5 - 2.5 mm.

[0042] According to the method for reducing the incidence of edge cracks in hot-rolled strip produced by twin-roll continuous casting of the present invention, preferably, in step (5), the thickness of the cast strip is controlled to be 1.8 - 2.2 mm.

[0043] According to the method for reducing the incidence of edge cracks in hot-rolled strip produced by twin-roll continuous casting of the present invention, preferably, in step (6), the thickness of the rolled strip is controlled to be 0.6 - 1.65 mm.

[0044] According to the second aspect of the present invention, a hot-rolled thin strip steel is provided. The edge crack control in the production process of the hot-rolled thin strip steel is carried out by the aforementioned method, wherein the incidence of the edge cracks accounts for less than 10% of the incidence of surface cracks on the plate surface.

[0045] Beneficial technical effects

[0046] Compared with the prior art, the technical concept and corresponding technical solution of the present invention can at least obtain the following beneficial technical effects:

[0047] By the method of the present invention, the renewal speed of the molten steel near the side sealing plate of the molten pool can be accelerated, the low-temperature area of the molten steel near the side sealing plate can be reduced, the temperature distribution in the width direction of the molten steel in the molten pool can be improved, so that the cooling and solidification of the molten steel in the width direction are more uniform, greatly avoiding the problem of non-uniform solidification in the width direction of the hot-rolled strip, strong cooling near the edge, resulting in strong stress near the edge and high crack sensitivity, thereby solving the problem of high incidence of edge cracks in hot-rolled strip produced by twin-roll continuous casting, improving the product quality and reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of the present invention and do not limit the present invention.

[0049] Figure 1 is a schematic diagram of a twin-roll continuous casting hot-rolled strip production line.

[0050] Figure 2 is a schematic diagram of the molten pool structure of a twin-roll continuous casting hot-rolled strip production line.

[0051] Figure 3It is a curve graph of the outlet temperature distribution in the width direction of the molten pool under different side hole angles.

[0052] Figure 4 It is a curve graph of the outlet temperature distribution in the width direction of the molten pool under different side hole flow rates. Specific implementation mode

[0053] In order to make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0054] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention pertains.

[0055] The following are embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention. All other embodiments that those of ordinary skill in the art can obtain based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0056] Now refer to Figure 1 and Figure 2 to show the production steps of twin-roll continuous casting hot-rolled strip steel and the molten pool of the twin-roll continuous caster. And the beneficial effects of the present implementation mode are further illustrated through 3 comparative examples and 3 embodiments. The described embodiments are only part of the embodiments of the present invention, rather than all of them. All other embodiments that those of ordinary skill in the art can obtain based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0057] The qualified molten steel refined by the primary melting furnace and the refining furnace flows from the ladle 5 through the tundish 6 and the transition ladle 7 into the distribution nozzle 4. It flows into the molten pool 3 formed by a pair of reversely rotating casting rolls 1 and a pair of side seals 2 through the diversion holes 4B on both sides and at the ends of the distribution nozzle 4.

[0058] The casting roll 1 is internally cooled (for example, water-cooled inside), so that as the casting roll 1 rotates relatively, the molten steel in the molten pool comes into rotational contact with the surface of the casting roll 1 and cools and solidifies on the surface of the casting roll 1. During continuous casting, the metal shell solidified on the surface of the casting roll 1 is brought together at the roll gap 8 between the casting rolls 1 to form a thin cast strip 9 with a thickness of 1.5 - 2.5 mm conveyed downward from the roll gap 8. The cast strip 9 is rolled into hot-rolled strip steel 11 by a one-pass rolling mill 10.

[0059] Due to the uneven temperature distribution of the molten steel in the width direction of the molten pool 3, particularly, the temperature fluctuates greatly near the side seal plate 2 (refer to Figure 3 and Figure 4 ), to ensure the uniformity of the cooling and solidification of the molten steel in the molten pool on the surface of the casting roll 1 during the twin-roll strip casting process, it is necessary to control the angle of the diversion holes 4B at the end of the distribution nozzle 4 and the flow rate of the molten steel in the distribution holes to accelerate the renewal rate of the molten steel near the side seal plate 2 of the molten pool, improve the temperature distribution in the width direction of the molten steel in the molten pool 3, and make the cooling and solidification in the width direction of the cast strip 9 more uniform.

[0060] Three comparative examples and three examples respectively provide a hot-rolled strip steel, and their production situations are specifically as shown in Table 1 below:

[0061] Table 1 Production situations of comparative examples and examples

[0062]

[0063] It can be seen from the data in Table 1 that:

[0064] (1) Compared with Comparative Example 1, the distribution nozzle 4 in Example 1 is provided with end diversion holes 4B (side holes), which improves the temperature difference in the width direction of the cast strip 9 formed at the roll gap 8 at the outlet of the molten pool 3, and the temperature distribution in the width direction is more uniform (refer to Figure 3 ), and no cracks are found on the edges of the hot-rolled strip steel 11.

[0065] (2) Compared with Comparative Example 2 and Comparative Example 3, too large (50°) or too small (30°) inclination angles of the diversion holes are not conducive to the improvement of the molten pool flow field and the improvement of the temperature distribution in the width direction. Preferably, an inclination angle of 40° of the diversion holes can reduce the temperature difference in the width direction of the cast strip 9 formed at the roll gap 8 at the outlet of the molten pool 3 (refer to Figure 3 ), and no cracks are found on the edges of the hot-rolled strip steel 11 under this process parameter.

[0066] (3) Compared with Example 1 and Example 2, increasing the flow rate of the molten steel in the end diversion holes 4B (side holes) of Example 3 can significantly improve the temperature distribution in the width direction of the cast strip 9 formed at the roll gap 8 at the outlet of the molten pool 3 (refer to Figure 4 ), the temperature distribution in the width direction is more uniform, and no cracks are found on the edges of the hot-rolled strip steel 11.

[0067] Generally speaking, it can be seen from the above comparative examples and examples that by adopting the implementation mode of the present invention to produce twin-roll hot-rolled strip steel, without increasing the production cost, the incidence of edge cracks of the strip steel is reduced, and the incidence of the edge cracks is reduced from 50% of the surface cracks of the plate to less than 10%, improving the product quality.

[0068] The above are only specific embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip steel, characterized in that: The method comprises the following steps: (1) Qualified molten steel is smelted in the primary refining furnace and the refining furnace, and flows into the distribution outlet through the long nozzle, the tundish and the transition ladle; The water flows into the molten pool formed by a pair of counter-rotating casting rolls and a pair of side sealing plates through the guide holes on both sides of the cloth flow outlet and its end; (2) The molten steel in the water distribution nozzle flows to the vicinity of the end of the molten pool through the guide hole at the end thereof, and the direction of the flow stream is controlled by controlling the angle of the guide hole; (3) Increasing the flow rate of molten steel in the end guide hole accelerates the renewal speed of molten steel near the side sealing plate of the molten pool; (4) circulating cooling water is introduced into the casting rolls, and the flow rate and temperature of the circulating cooling water are controlled; (5) The molten steel is cooled and solidified by the casting rollers to form a cast strip with a thickness of 1.5 to 2.5 mm; (6) The strip steel undergoes a single hot rolling process to become a hot-rolled thin strip steel.

2. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip according to claim 1, characterized in that: The composition of the molten steel is carbon steel, weathering steel or stainless steel.

3. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip according to claim 1, characterized in that: Both sides and ends of the water outlet are provided with flow guide holes.

4. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip according to claim 1, characterized in that: The guide holes on both sides of the water distribution outlet are horizontally distributed.

5. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip according to claim 1, characterized in that: The guide hole at the end of the water distribution outlet forms an angle of 30 to 50 degrees with the vertical direction.

6. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip according to claim 5, characterized in that: The guide hole at the end of the water distribution outlet forms an angle of 40° with the vertical direction.

7. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip according to claim 1, characterized in that: In the step (3), the flow velocity of the end guide hole is controlled at 4 to 5 m / s.

8. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip according to claim 7, characterized in that: In the step (3), the flow velocity of the end guide hole flow stream is controlled at 4.8 m / s.

9. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip steel according to claim 1, characterized in that: The length of the casting roll is 1200-2000 mm.

10. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip steel according to claim 9, characterized in that: The length of the casting roll is 1500 mm or 1800 mm.

11. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip steel according to claim 1, characterized in that: In step (4), the flow rate of circulating cooling water for the casting rolls is controlled at 2400-3000 m 3 / h.

12. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled steel strip according to claim 11, characterized in that: In step (4), the flow rate of circulating cooling water for the casting rolls is controlled to be 2600m 3 / h.

13. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip steel according to claim 1, characterized in that: In the step (4), the temperature of the circulating cooling water of the casting rolls is controlled at 20-40°C.

14. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip steel according to claim 13, characterized in that: In the step (4), the temperature of the circulating cooling water of the casting rolls is controlled at 30°C.

15. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled strip steel according to claim 1, characterized in that: In the step (5), the thickness of the cast strip is controlled to be 1.5 to 2.5 mm.

16. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled steel strip according to claim 15, characterized in that: In the step (5), the thickness of the cast strip is controlled to be 1.8 to 2.2 mm.

17. The method for reducing the incidence of edge cracks in twin-roll continuous casting hot-rolled steel strip according to claim 1, characterized in that: In the step (6), the thickness of the rolled strip is controlled to be 0.6 to 1.65 mm.

18. A hot rolled thin strip steel, characterized in that: The production process of the hot-rolled thin strip steel adopts the method according to any one of claims 1 to 17 to control edge cracks, wherein the occurrence rate of the edge cracks accounts for less than 10% of the occurrence rate of the plate surface cracks.

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