Method for efficiently eliminating color difference defect on surface of hot-rolled low-carbon thin strip steel at low cost

Abstract

The invention provides a method for eliminating the color difference defect on the surface of hot-rolled low-carbon thin strip steel with high efficiency and low cost. According to the method, the chemical components and the strip casting temperature of the hot-rolled low-carbon thin strip steel and the introduction amount of N2 protective atmosphere in the first hot box, the second hot box and the third hot box are optimized, meanwhile, the air flow of the upper surface and the lower surface in the third hot box is controlled, the low oxidation environment is kept, it is guaranteed that rolling lubrication of the hot-rolled low-carbon thin strip steel is guaranteed, and thin oxide skin is generated before rolling; and then the layer cooling outlet temperature and the coiling temperature are controlled, and the uniformity of the strip steel transverse cooling outlet temperature and the coiling temperature is guaranteed. By applying the method, the thickness and the structure of the hot-rolled low-carbon thin strip steel oxide skin can be uniform and consistent, and the defect of color difference on the surface of the thin-strip cast-rolled low-carbon thin strip steel is efficiently eliminated at low cost.

Description

Technical Field

[0001] This invention relates to the field of steel production, and to a method for efficiently and cost-effectively eliminating surface color difference defects in hot-rolled low-carbon thin strip steel. Background Technology

[0002] Low-carbon steel, due to its excellent tensile and bending properties and good stamping formability, can be cold-formed using methods such as cold bending and deep drawing, and is widely used in industries such as automobiles, home appliances, and construction, resulting in significant market demand. In recent years, the demand for thin-gauge hot-rolled sheets with good surface quality to replace cold-rolled sheets has been increasing, and "hot-rolling over cold-rolling" is a development trend.

[0003] Twin-roll cast low-carbon thin strip steel is the mainstream product of thin strip casting and rolling production lines. Due to its thin specifications, it is mainly used in agricultural machinery cover parts, shelf panels, pipe making, or plate cutting for the production of stamped door panels and other thin-gauge hot-rolled plates to replace cold-rolled plates. Poor control of the casting zone and rolling cooling temperature and oxidizing atmosphere during the production of twin-roll cast strip steel can lead to variations in the thickness and structure of the iron oxide scale on the strip surface, resulting in color differences. Uneven pickling during the pickling process can also occur. These defects not only cannot be eliminated during subsequent surface treatments such as electrophoresis and spraying by downstream customers but can also be amplified, affecting downstream customer use, causing significant steel losses, and increasing production costs.

[0004] Therefore, solving the surface color difference defect of hot-rolled low-carbon thin strip steel is of vital importance for improving the grade of thin strip casting and rolling products. Summary of the Invention

[0005] Based on the above background technology, the purpose of this invention is to provide a method for improving the surface indentation of high-strength thin strip steel produced by twin-roll casting and rolling process. The method of this invention, by optimizing the rolling lubrication process and the work roll cooling process, slows down the thermal fatigue rate of the work roll surface, ensures the surface quality of the strip steel, and reduces the rejection rate of indentation in high-strength thin strip steel.

[0006] More specifically, the present invention adopts the following technical solution.

[0007] According to one aspect of the present invention, a method for efficiently and cost-effectively eliminating surface color difference defects in hot-rolled low-carbon thin strip steel is provided, the production method comprising the following steps:

[0008] (1) Smelting: The initial molten steel is smelted in an electric furnace or converter, vacuum degassed in a VD furnace, and refined in an LF furnace to obtain molten steel with qualified composition;

[0009] (2) Thin strip casting and rolling: The molten steel is cast and rolled using a twin-roll thin strip casting and rolling equipment to form a cast strip; the cast strip passes through the No. 1 hot box, the No. 2 hot box and the No. 3 hot box with N2 protection in sequence; air is introduced into the No. 3 hot box; after the cast strip comes out of the hot box, it is hot rolled in one pass to obtain hot rolled strip steel;

[0010] (3) Air mist cooling: The hot-rolled strip steel is cooled by multiple sets of air mist cooling nozzles;

[0011] (4) Temperature-controlled coiling: The hot-rolled strip steel is coiled by a coiling machine under controlled temperature to obtain a hot coil.

[0012] According to the method of the present invention, preferably, in step (1), the molten steel is smelted by batching the following chemical composition and mass ratio: C: ≤0.04%; Si: 0.070~0.2%; Mn: 0.20~0.60%; P: ≤0.020%; S: ≤0.004%; Al: ≤0.003%; N: ≤0.005%; Cr: ≤0.40%; the balance being iron and unavoidable impurity elements.

[0013] According to the method of the present invention, preferably, in step (2), the thickness of the cast strip formed after the molten steel is cast and rolled is 1.4-2.2 mm.

[0014] According to the method of the present invention, preferably, in step (2), the total amount of N2 in the No. 1 heat box, the No. 2 heat box, and the No. 3 heat box is controlled to be 1000~5000m³. 3 / h.

[0015] According to the method of the present invention, preferably, in step (2), the temperature of the casting strip passing through the No. 3 hot box is 1150±50℃.

[0016] According to the method of the present invention, preferably, in step (2), 100±20m is introduced into the upper surface of the casting strip in the No. 3 hot box. 3 An air flow rate of / h is introduced into the lower surface of the casting strip at a rate of 100±20m. 3 / h of air.

[0017] According to the method of the present invention, preferably, in step (2), the thickness of the hot-rolled strip is 0.6-1.8 mm.

[0018] According to the method of the present invention, preferably, in step (3), the hot-rolled strip is cooled to 550-650°C by multiple sets of air mist cooling nozzles, and the temperature uniformity of the hot-rolled strip is controlled within ±10°C.

[0019] According to the method of the present invention, preferably, in step (3), in order to ensure the transverse temperature uniformity of the hot-rolled strip, the water pressure of the manifold is controlled at 5.0-9.0 Bar, the air pressure is controlled at 1.5-4.0 Bar, and the total water flow rate is 50-2000 lpm.

[0020] According to the method of the present invention, preferably, in step (4), in order to ensure the transverse temperature uniformity of the hot-rolled strip, the coiling tension is controlled at 5-50KN.

[0021] According to the method of the present invention, preferably, in step (4), the coiling temperature of the hot-rolled strip is 450-550°C.

[0022] According to the method of the present invention, preferably, after step (4), the hot roll is finished by a tension straightening and leveling process to obtain a finished roll.

[0023] According to a second aspect of the invention, a hot-rolled low-carbon thin strip steel is provided, said hot-rolled low-carbon thin strip steel being produced by a method having one or more of the aforementioned characteristics, wherein the thickness of the iron oxide scale in the middle and at the edges of said hot-rolled low-carbon thin strip steel is uniform and is 4~6μm.

[0024] According to the hot-rolled low-carbon thin strip steel of the present invention, preferably, the oxide scale structure of the edge and the middle surface of the hot-rolled low-carbon thin strip steel is the same and there is no color difference.

[0025] Beneficial technical effects

[0026] (1) This invention addresses the conditions for the formation of iron oxide scale by optimizing the pre-rolling temperature and the amount of N2 introduced into the hot box, thereby reducing the growth rate of oxide scale on the strip surface and controlling the thickness of the oxide scale.

[0027] (2) This invention avoids the problem of uneven oxide scale growth by optimizing the air intake of No. 3 hot box, and by using reasonable rolling temperature and hot rolling lubrication system.

[0028] (3) In terms of cooling, the present invention reasonably controls the amount of air and water for cooling mist according to the thickness and speed of the strip, effectively ensuring the uniformity of the strip cooling temperature and transverse temperature.

[0029] (4) In order to ensure rolling stability during the hot-rolled strip production process, the strip has a certain convexity, which results in a larger gap between the layers of the strip at the edge. Therefore, the cooling rate of the strip edge is different from that of the middle and the coiling cooling rate. In addition, due to the large gap between the layers at the edge, the iron oxide scale at the edge of the strip is in the oxygen-rich zone, while the iron oxide scale in the middle of the strip is in the oxygen-deficient zone. This will greatly improve the thickness and transverse uniformity of the iron oxide scale at the edge and the middle of the strip.

[0030] (5) Through the implementation of the process of the present invention, the thickness of the iron oxide scale on the edge and middle surface of the hot-rolled low carbon thin strip steel is controlled at 4-6 μm. The iron oxide scale composition on the edge and middle surface of the hot-rolled low carbon thin strip steel is mainly Fe3O4 and Fe2O3. The iron oxide scale thickness and structure on the edge and middle surface of the hot-rolled low carbon thin strip steel are the same, and there is no color difference defect on the surface of the hot-rolled low carbon thin strip steel.

[0031] (6) This invention is applicable to thin strip casting and rolling production lines. Under existing production conditions, it analyzes and studies the specific causes of color difference in ultra-hot rolled low carbon thin strip steel. Without increasing existing equipment, it completely eliminates the surface color difference defect of hot rolled low carbon thin strip steel by optimizing the chemical composition and casting, rolling and cooling coiling processes, thereby improving the surface quality of hot rolled low carbon thin strip steel. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0033] Fig. 1 Photographs showing color difference defects on the surface of hot-rolled low-carbon thin strip steel.

[0034] Fig. 2 This is a photograph of the surface of the hot-rolled low-carbon thin strip steel produced in Example 1 of the present invention.

[0035] Fig. 3 A photograph of the surface of hot-rolled low-carbon thin strip steel produced according to Embodiment 2 of the present invention. Detailed Implementation

[0036] 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 clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0038] The following are embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention. All other embodiments that can be obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0040] Example 1

[0041] (1) Smelting: Electric furnace steelmaking, VD furnace degassing, LF refining to obtain molten steel with qualified composition, by weight percentage:

[0042] C: 0.035%; Si: 0.1830%; Mn: 0.380%; P: 0.011%; S: 0.0026%; Al: 0.0017%; N: 0.00032%; Cr: 0.04%; balance is iron and unavoidable impurity elements.

[0043] (2) Thin strip casting and rolling: Molten steel with qualified composition is continuously cast into thin strip using a twin-roll casting machine under inert gas protection to obtain a strip with a thickness of 1.80 mm. The strip passes through three hot boxes protected by N2, and the total amount of N2 in the three hot boxes is controlled to be 4300 mg / L. 3 / h, the temperature of the cast strip in the hot box is 1150℃ to ensure a low-temperature and low-oxidation environment to prevent the growth of iron oxide scale. For strip rolling lubrication, air is also introduced into the No. 3 hot box to form a thin oxide film on the surface of the cast strip. 90m³ of air is introduced into the upper surface of the cast strip. 3 / h of air, 90m is introduced into the lower surface 3 / h of air, high temperature cast strip is hot rolled once to obtain hot rolled thin strip steel with a thickness of 1.2mm.

[0044] (3) Air mist cooling: The strip is cooled by multiple sets of air mist cooling nozzles. The air mist cooling outlet temperature is 600℃, the water pressure in the manifold is controlled at 5.8 Bar, the air pressure is controlled at 3.3 Bar, and the total water flow rate is 800 lpm;

[0045] (5) Temperature-controlled winding: The thin strip is wound in a temperature-controlled manner to obtain a hot roll. The winding temperature is 500℃ and the winding tension is 45KN.

[0046] Example 2

[0047] (1) Smelting: Steelmaking in a converter, degassing in a VD furnace, and refining in an LF furnace to obtain molten steel with qualified composition, by weight percentage:

[0048] C: 0.033%; Si: 0.1850%; Mn: 0.470%; P: 0.013%; S: 0.0020%; Al: 0.0013%; N: 0.00026%; Cr: 0.026%; balance is iron and unavoidable impurity elements.

[0049] (2) Thin strip casting and rolling: Molten steel with qualified composition is continuously cast into thin strip using a twin-roll casting machine under inert gas protection to obtain a cast strip with a thickness of 1.70 mm. The cast strip passes through three hot boxes protected by N2, and the total amount of N2 in the three hot boxes is controlled to be 4100 mg / m³. 3 / h, the temperature of the cast strip in the hot box is 1120℃ to ensure a low-temperature and low-oxidation environment to prevent the growth of iron oxide scale. For strip rolling lubrication, air is also introduced into the No. 3 hot box to form a thin oxide film on the surface of the cast strip. 100m³ of air is introduced into the upper surface of the cast strip. 3 / h of air, 100m is introduced into the lower surface 3 / h of air, high temperature cast strip is hot rolled once to obtain hot rolled thin strip steel with a thickness of 0.8mm.

[0050] (3) Air mist cooling: The strip is cooled by multiple sets of air mist cooling nozzles. The air mist cooling outlet temperature is 550℃, the water pressure in the manifold is controlled at 6.2 Bar, the air pressure is controlled at 3.6 Bar, and the total water flow rate is 1200 lpm;

[0051] (4) Temperature-controlled winding: The thin strip is temperature-controlled and wound to obtain a hot roll. The winding temperature is 450℃ and the winding tension is 36KN.

[0052] from Figs. 1 to 3 As can be seen, after the implementation of the process of the present invention, the surface of hot-rolled low-carbon thin strip steel is free of color difference defects, the oxide scale on the transverse surface of the strip steel is more uniform, and the color difference defects on the surface of hot-rolled low-carbon thin strip steel are completely eliminated.

[0053] The above description is only a specific embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for efficiently and at low cost eliminating surface color difference defects of hot-rolled low-carbon thin strip steel, characterized in that, The production method comprises the following steps: (1) smelting: the initial molten steel is smelted by an electric furnace or a converter, vacuum degassed by a VD furnace, and refined by an LF furnace to obtain molten steel with qualified composition; (2) thin strip casting and rolling: the molten steel is cast and rolled by a double-roller thin strip casting and rolling device to form a cast strip; the cast strip sequentially passes through a No. 1 hot box, a No. 2 hot box and a No. 3 hot box with N2 protection; air is introduced into the No. 3 hot box; the cast strip is hot-rolled by one pass after coming out of the hot box to obtain a hot-rolled strip; (3) gas mist cooling: the hot-rolled strip is cooled by a plurality of gas mist cooling nozzles; (4) temperature-controlled coiling: the hot-rolled strip is temperature-controlled coiled by a coiling machine to obtain a hot coil.

2. The method according to claim 1, wherein: in step (1), the molten steel is smelted by ingredients with the following chemical composition and mass ratio: C: ≤0.04%; Si: 0.070-0.2%; Mn: 0.20-0.60%; S: ≤0.004%; Al: ≤0.003%; N: ≤0.005%; Cr: ≤0.40%; and the balance is iron and inevitable impurity elements.

3. The method according to claim 1, wherein: in step (2), the thickness of the cast strip formed after the molten steel is cast and rolled is 1.4-2.2 mm.

4. The method according to claim 1, wherein: P：≤0.020%； 5. The method according to claim 1, wherein: in step (2), the temperature of the cast strip passing through the No. 3 hot box is 1150±50℃.

6. The method according to claim 1, wherein:

7. The method according to claim 1, wherein: in step (2), the thickness of the hot-rolled strip is 0.6-1.8 mm.

8. The method according to claim 1, wherein: in step (3), the hot-rolled strip is cooled to 550-650℃ by the plurality of gas mist cooling nozzles, and the temperature uniformity of the hot-rolled strip is controlled within ±10℃. In step (2), the total amount of N2 of the No. 1 hot box, the No. 2 hot box and the No. 3 hot box is controlled to be 1000-5000 m3 / h. 3 / h.

9. The method according to claim 1, wherein: in step (3), to ensure the transverse temperature uniformity of the hot-rolled strip, the manifold water pressure is controlled to be 5.0-9.0 Bar, the air pressure is controlled to be 1.5-4.0 Bar, and the total water flow is 50-2000 lpm.

10. The method according to claim 1, wherein: in step (4), to ensure the transverse temperature uniformity of the hot-rolled strip, the coiling tension is controlled to be 5-50 KN.

11. The method according to claim 1, wherein: in step (4), the coiling temperature of the hot-rolled strip is 450-550℃. In step (2), in the No. 3 hot box, 100 ± 20 m 3 / h of air is passed through the upper surface of the cast strip, and 100 ± 20 m 3 / h of air is passed through the lower surface of the cast strip.

12. The method according to claim 1, wherein: after step (4), the hot coil is finished by a stretch leveling and tempering process to obtain a finished coil.

13. A hot-rolled low-carbon thin strip steel produced by the method according to any one of claims 1 to 12, wherein the intermediate and edge scale thicknesses of the hot-rolled low-carbon thin strip steel are uniform and are both 4-6 μm. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 14. The hot-rolled low carbon thin strip according to claim 13, characterized in that: the scale structure of the edge portion and the intermediate surface of the hot-rolled low carbon thin strip is the same and free of color difference.

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