Method for improving the surface quality of cold-rolled sheet

Abstract

The application belongs to the technical field of steel smelting, and particularly relates to a production method for improving the surface quality of a cold-rolled plate. The production method of the cold-rolled plate comprises the following steps: the residual amount of emulsified working fluid on the surface of the cold-rolled strip steel after pickling is greater than or equal to 300 mg / m 3 The roughness of the surface of the cold-rolled strip steel after pickling is greater than or equal to 0.6 microns. The production method of the cold-rolled plate provided by the application can effectively avoid the shape defects of the strip steel by precisely controlling the shape of the plate, the concentration of the emulsified working fluid and the coiling tension in the pickling and rolling process, significantly reduces the sticking problem of the cold-rolled plate in the production process, and improves the qualified rate and the yield of the product.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, and specifically relates to a production method for improving the surface quality of cold-rolled steel sheets. Background Technology

[0002] Cold-rolled steel sheet, as an important metallic material, is widely used in the following fields: automotive manufacturing, home appliance industry, construction and building materials, industrial equipment and packaging. However, during the production process of cold-rolled steel sheet, improper control of pickling, rolling, annealing and leveling processes can easily lead to surface quality problems, such as adhesion and scratches, resulting in a decrease in product qualification rate and yield. Existing technologies for addressing adhesion and scratches in cold-rolled steel sheets mostly focus on improving single processes, lacking systematic optimization and failing to fundamentally solve the problem.

[0003] The reasons why adhesion problems easily occur in existing processes are as follows: 1) The strip shape after pickling and rolling, especially the presence of rib defects in the middle, is prone to adhesion after annealing; 2) Surface roughness of the strip after pickling and rolling. The larger the roughness Ra value, the better it is to avoid adhesion. 3) Pickling and rolling tension: the higher the tension, the tighter the strip layers, which makes it easier for them to bond after annealing; 4) If the concentration of the emulsion working fluid is too low during pickling and rolling, less rolling oil will remain on the surface of the strip, making it easier for it to stick after annealing. 5) When stacking, the bottom coil is subjected to pressure from the top coil, making it more prone to adhesion defects.

[0004] 6) In the annealing process, problems such as excessive speed in the high-temperature section and abnormal flameout can increase the temperature difference between the inside and outside of the steel coil and the middle part, making it easy for sticking to occur.

[0005] 7) During the annealing process, if a large amount of hydrogen is blown at temperatures above 600°C, carbon precipitation will occur, the steel coil will soften, and it will be prone to sticking. Summary of the Invention

[0006] To address the aforementioned problems, the present invention provides a cold-rolled sheet, its production method, and its application, thereby resolving at least one of the above-mentioned technical problems.

[0007] This invention is achieved through the following technical solution: This invention provides a method for producing cold-rolled steel sheet, comprising the following steps: The residual emulsion working fluid on the surface of the pickled and cold-rolled strip is ≥300mg / m². 3 .

[0008] In some possible implementations, the surface roughness of the pickled and cold-rolled strip is greater than 0.6 μm.

[0009] In some possible implementations, the surface roughness of the pickled and cold-rolled strip is 0.6 μm to 1.0 μm.

[0010] In some possible implementations, the residual amount of the emulsifying working fluid on the surface of the pickled and cold-rolled strip is 300 mg / m³. 2 ~500mg / m 2 .

[0011] In some possible implementations, during the cold rolling process, the concentration of the emulsion concentrate in the emulsion working fluid is 1.8 wt% to 2.5 wt%.

[0012] In some possible implementations, the emulsion concentrate is a DPD ionic emulsifier (S-enhanced) product manufactured by Quaker.

[0013] In some possible implementations, the acid solution in the pickling and cold rolling process includes: acid solution concentration of 45g / L to 75g / L in acid tank #1; acid solution concentration of 95g / L to 135g / L in acid tank #2; and acid solution concentration of 135g / L to 175g / L in acid tank #3.

[0014] In some possible implementations, the pickling temperature in the pickling and cold rolling process is 80°C to 85°C.

[0015] In some possible implementations, the acid solution used in the pickling and cold rolling process is hydrochloric acid reduced acid produced by acid regeneration in a cold rolling mill.

[0016] In some possible implementations, the concentration of the acid solution in the pickling and cold rolling process includes: The acid concentration in acid tank #1 is 45g / L~75g / L; The acid concentration in acid tank #2 is 95 g / L to 135 g / L; The acid concentration in acid tank #3 is 135g / L~175g / L.

[0017] In some possible implementations, the production method further includes the following steps: Annealing includes: the rolled strip undergoes a first heating and holding period followed by a second heating and holding period, and then cooling.

[0018] In some possible implementations, the first heating and heat preservation temperature is 410℃~430℃.

[0019] In some possible implementations, the holding time for the first heating and holding is 2h to 4h.

[0020] In some possible implementations, the second heating and heat preservation includes the following steps: The first stage involves heating up, followed by a second stage involving heating up and maintaining the temperature.

[0021] In some possible implementations, the heating rate of the first stage of heating is 40℃ / h to 45℃ / h.

[0022] In some possible implementations, the final temperature of the first stage of heating is 700℃~710℃.

[0023] In some possible implementations, the heating rate of the second stage is 15℃ / h to 25℃ / h.

[0024] In some possible implementations, the final temperature of the second stage of heating is 730℃~750℃.

[0025] In some possible implementations, the second heating and heat preservation process involves a heat preservation temperature of 730℃~750℃.

[0026] In some possible implementations, the second heating and heat preservation process involves a heat preservation time of 10 to 12 hours.

[0027] In some possible implementations, the cooling includes shrouded cooling.

[0028] In some possible implementations, the cooling time of the shroud is 6 to 8 hours.

[0029] In some possible implementations, during the annealing step, the heating time is controlled to be ≥4h, and there is no abnormal flameout during the heating and holding process. If an abnormal flameout occurs, an additional ≥2h is required. When the temperature is ≥600℃, large-scale hydrogen blowing is prohibited.

[0030] In some possible implementations, the production method further includes the following steps: During winding, the winding tension is 2.4 kN / m. 2 ~2.6kN / m 2 .

[0031] In some possible implementations, the production method further includes the following steps: During the unwinding process, the unwinding speed is less than 30 mpm.

[0032] In some possible implementations, the elongation of the flat unwinding is 0.4% to 0.5%.

[0033] In some possible implementations, the tension of the flattened unwinding is 1200kN~1400kN.

[0034] In some possible implementations, the steel grade of the cold-rolled sheet includes one of stamping steels, DC04 and DC05.

[0035] The method for producing cold-rolled steel sheets provided by this invention has at least the following beneficial technical effects compared with the prior art: (1) The cold-rolled sheet production method provided by the present invention effectively avoids strip shape defects by precisely controlling the sheet shape, emulsion working fluid concentration and coiling tension during the pickling and rolling process, significantly reduces the adhesion problem of cold-rolled sheet in the production process, and improves the product qualification rate and yield.

[0036] (2) The cold-rolled sheet production method provided by the present invention ensures that there is sufficient residual oil on the surface of the strip after rolling by controlling the concentration of the emulsifying working fluid.

[0037] (3) The cold-rolled sheet production method provided by the present invention ensures the strip roughness by improving the roll roughness.

[0038] (4) The cold-rolled sheet production method provided by the present invention avoids the increase of temperature difference between the inside and outside of the steel coil and the middle by controlling the three-stage heating rate and two-stage holding time during the annealing process. The outer layer of the steel coil forms a tight state with the inner layer that has not yet cooled down due to cold shrinkage. Because the yield strength of the strip steel is greatly reduced after crystallization, plastic deformation occurs between the strip steel layers under compressive stress during the process of the core temperature decreasing from the peak value. The middle part of the steel coil is under high temperature and high pressure, which easily causes adhesion.

[0039] (5) The cold-rolled sheet production method provided by the present invention controls the hydrogen reduction process (introducing a mixed gas of reducing atmosphere H2 and N2, where H2 reacts with FeO and Fe3O4 at high temperature to convert them into Fe), so that an oxide film forms on the strip at the end of the heat preservation period. When the core temperature drops below 600°C, the oxide film is then removed by hydrogen reduction. If a large amount of hydrogen is blown above 600°C, carbon precipitation will occur, the steel coil will soften, and adhesion will easily occur.

[0040] (6) The cold-rolled sheet production method provided by the present invention produces a cold-rolled sheet with an adhesion rate of less than 1.25%. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described and illustrated below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments provided by this invention without inventive effort are within the scope of protection of this invention.

[0042] Obviously, the following description is merely some examples or embodiments of the present invention. Those skilled in the art can apply the present invention to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this invention, modifications to design, manufacturing, or production based on the technical content disclosed in this invention are merely conventional technical means and should not be construed as insufficient disclosure of the present invention.

[0043] However, there may be instances where unnecessary detailed descriptions are omitted. For example, detailed descriptions of well-known matters or repetitive descriptions of essentially the same structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand the invention and is not intended to limit the subject matter of the claims.

[0044] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions, and all technical features and optional technical features of the present invention can be combined with each other to form new technical solutions.

[0045] The following description, in conjunction with specific embodiments, provides further details. For ease of explanation, the following embodiments and comparative examples involve: (1) The steel grade of the cold-rolled sheet is DC04.

[0046] (2) The emulsion concentrate is a DPD ionic emulsifier (S-enhanced) product manufactured by Quaker.

[0047] (3) The cold rolling process is as follows: the strip is rolled to the target thickness through a 5-stand continuous rolling mill, and the surface roughness of the strip is changed by the change of the surface roughness of the rolls in the last stand. In each embodiment, the roughness distribution of the cold rolling rolls in the last stand is 0.5μm~1.2μm.

[0048] Example 1 Example 1 provides a method for producing cold-rolled steel sheet, wherein the steps of pickling, cold rolling, annealing, coiling, leveling, and uncoiling the continuously cast steel sheet are as follows: E1. During pickling, the pickling temperature is 83℃; acid concentration: 60g / L for acid tank #1, 100g / L for acid tank #2, and 160g / L for acid tank #3.

[0049] E2. In cold rolling, the concentration of the emulsion working fluid is 2.0 wt%, and the surface roughness of the strip obtained by cold rolling is controlled to be 0.6 μm, with the residual amount of emulsion working fluid being 310 mg / m³. 2 ±10mg / m2 .

[0050] E3. Annealing: E3-1. First heating and holding: Freely heat to 420℃ and hold for 2 hours.

[0051] E3-2. Second heating and heat preservation: E3-2-1. First stage of heating: Heating from 420℃ to 700℃ at a heating rate of 43.1℃ / h.

[0052] E3-2-2. Second stage of heating: Heating from 700℃ to 730℃ at a heating rate of 20℃ / h.

[0053] E3-2-3. Insulation: Insulate at 730℃ for 10 hours.

[0054] E3-3. Cooling: After heat preservation, cool with a cover for 7 hours.

[0055] E4. Winding: The winding tension is 2.5 kN / m 2 .

[0056] E5. Flat unwinding: unwinding speed is 20mpm, elongation is 0.4%, and tension is 1200kN.

[0057] Example 2 Example 2 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 1, except that: E2. In cold rolling, the concentration of the emulsion working fluid is 2.2 wt%, and the surface roughness of the cold-rolled strip is controlled to be 0.8 μm, with a residual emulsion working fluid content of 340 mg / m². 2 ±10mg / m 2 .

[0058] Example 3 Example 3 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 1, except that: E2. In cold rolling, the concentration of the emulsion working fluid is 2.5 wt%, and the surface roughness of the cold-rolled strip is controlled to be 1.0 μm, with a residual emulsion working fluid content of 390 mg / m². 2 ±10mg / m 2 .

[0059] Example 4 Example 4 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 1, except that: E3. Annealing: E3-1. First heating and holding: Freely heat to 410℃ and hold for 4 hours.

[0060] E3-2. Second heating and heat preservation: E3-2-1. First stage of heating: Heating from 410℃ to 700℃ at a heating rate of 40℃ / h.

[0061] E3-2-2. Second stage of heating: Heating from 700℃ to 740℃ at a heating rate of 15℃ / h.

[0062] E3-2-3. Insulation: Insulate at 740℃ for 12 hours. Example 5 Example 5 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 1, except that: E3. Annealing: E3-1. First heating and heat preservation: Freely heat up to 430℃ and keep warm for 4 hours.

[0063] E3-2. Second heating and heat preservation: E3-2-1. First stage of heating: Heating from 430℃ to 710℃ at a heating rate of 45℃ / h.

[0064] E3-2-2. Second stage of heating: Heating from 710℃ to 750℃ at a heating rate of 25℃ / h.

[0065] E3-2-3. Insulation: Insulate at 750℃ for 10 hours.

[0066] Example 6 Example 6 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 1, except that: E4. Winding: The winding tension is 3.0 kN / m 2 .

[0067] E5. Flat unwinding: unwinding speed is 25mpm, elongation is 0.5%, and tension is 1400kN.

[0068] Example 7 Example 7 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 1, except that: E4. Winding: The winding tension is 2.2 kN / m 2 .

[0069] E5. Flat unwinding: unwinding speed is 15mpm, elongation is 0.4%, and tension is 1300kN.

[0070] Example 8 Example 8 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 2, except that: E3. Annealing: E3-1. First heating and holding: Freely heat to 410℃ and hold for 4 hours.

[0071] E3-2. Second heating and heat preservation: E3-2-1. First stage of heating: Heating from 410℃ to 700℃ at a heating rate of 40℃ / h.

[0072] E3-2-2. Second stage of heating: Heating from 700℃ to 740℃ at a heating rate of 15℃ / h.

[0073] E3-2-3. Insulation: Insulate at 740℃ for 12 hours.

[0074] E4. Winding: The winding tension is 2.0 kN / m 2 .

[0075] Example 9 Example 9 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 2, except that: E3. Annealing: E3-1. First heating and heat preservation: Freely heat up to 430℃ and keep warm for 4 hours.

[0076] E3-2. Second heating and heat preservation: E3-2-1. First stage of heating: Heating from 430℃ to 710℃ at a heating rate of 45℃ / h.

[0077] E3-2-2. Second stage of heating: Heating from 710℃ to 750℃ at a heating rate of 25℃ / h.

[0078] E3-2-3. Insulation: Insulate at 750℃ for 10 hours.

[0079] Example 10 Example 10 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 3, except that: E3. Annealing: E3-1. First heating and heat preservation: Freely heat up to 430℃ and keep warm for 4 hours.

[0080] E3-2. Second heating and heat preservation: E3-2-1. First stage of heating: Heating from 430℃ to 710℃ at a heating rate of 45℃ / h.

[0081] E3-2-2. Second stage of heating: Heating from 710℃ to 750℃ at a heating rate of 25℃ / h.

[0082] E3-2-3. Insulation: Insulate at 750℃ for 10 hours.

[0083] Comparative Example 1 Comparative Example 1 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 1, except that: E2. In cold rolling, the concentration of the emulsion working fluid is 2.0 wt%, and the surface roughness of the cold-rolled strip is controlled to be 0.5 μm, with a residual emulsion working fluid content of 280 mg / m³. 2 ±10mg / m 2 .

[0084] Comparative Example 2 Comparative Example 2 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 1, except that: E3. Annealing: Heat from room temperature (25℃~30℃) to 730℃ at a heating rate of 20℃ / h, and hold at 730℃ for 12h.

[0085] Comparative Example 3 Comparative Example 3 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 1, except that: E3. Annealing: Heat from room temperature (25℃~30℃) to 730℃ at a heating rate of 50℃ / h, and hold at 730℃ for 12h.

[0086] Comparative Example 4 Comparative Example 4 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 1, except that: E4. Winding: The winding tension is 3 kN / m 2 .

[0087] E5. Flat unwinding: Unwinding speed is 40mpm, tension is 1500kN.

[0088] Comparative Example 5 Comparative Example 5 provides a method for producing cold-rolled steel sheets, the steps of which are basically the same as those in Example 3, except that: E3. Annealing: Heat from room temperature (25℃~30℃) to 730℃ at a heating rate of 50℃ / h, and hold at 730℃ for 12h.

[0089] To verify the advancement of the cold-rolled sheet production method provided in this embodiment of the invention, samples of the cold-rolled sheets obtained in the embodiments and comparative examples were taken for roughness and adhesion rate testing, and the results are shown in Table 1 below.

[0090]

[0091] From the table above, at least the following conclusions can be drawn: (1) In Examples 1 to 10, under the same annealing process conditions, the residual amount of emulsion working fluid on the strip surface gradually increases, which can gradually reduce the adhesion rate of the strip after leveling. Therefore, it can be seen that the greater the surface roughness of the strip, the more residual emulsion working fluid there is, and the lower the adhesion rate under the same annealing process conditions. It can be seen that the cold-rolled sheet production method provided by the embodiments of the present invention can significantly reduce the adhesion rate of the strip by controlling the surface roughness of the strip and the residual emulsion working fluid.

[0092] (2) As can be seen from Examples 1 and Comparative Examples 1 to 3, and Examples 3 and 5, under the same (or similar) strip surface roughness and residual emulsion working fluid conditions, problems such as excessively fast speed and abnormal quenching in the high-temperature section of the annealing process increase the temperature difference between the inside and outside of the steel coil and the middle, making it prone to adhesion. Therefore, the cold-rolled sheet production method provided in the embodiments of the present invention can reduce the temperature difference between the inside and outside of the steel coil by controlling the heating rate during annealing, thereby significantly reducing the adhesion rate of the strip.

[0093] (3) As can be seen from Example 1 and Comparative Example 4, the higher the rolling tension, the tighter the strip layers are, and the easier it is to form adhesion after annealing. It can be seen that the cold-rolled sheet production method provided by the embodiments of the present invention controls the strip coiling tension and the tension during flattening and uncoiling, which can keep a certain space between the strip layers and prevent adhesion after annealing, thereby reducing the adhesion rate of the strip.

[0094] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for producing cold-rolled steel sheet, characterized in that, Includes the following steps: The continuous casting plate is pickled, cold rolled, annealed, coiled, leveled, and uncoiled. The residual emulsion working fluid on the surface of the pickled and cold-rolled strip is ≥300mg / m². 2 ; The surface roughness of the pickled and cold-rolled strip is above 0.6 μm; The residual amount of the emulsified working fluid on the surface of the pickled and cold-rolled strip is 300 mg / m³. 2 ~500mg / m 2 ; In the pickling and cold rolling process, the pickling temperature is 80℃~85℃; In the pickling and cold rolling process, the concentration of the acid solution includes: 45g / L~75g / L for acid tank #1, 95g / L~135g / L for acid tank #2, and 135g / L~175g / L for acid tank #3. In the cold rolling process, the concentration of the emulsion concentrate in the emulsion working fluid is 1.8wt%~2.5wt%. The annealing process includes: cooling the rolled strip after a first heating and holding period and a second heating and holding period; The first heating and heat preservation temperature is 410℃~430℃; the first heating and heat preservation time is 2h~4h; the second heating and heat preservation includes the following steps: first stage heating, second stage heating and heat preservation; the cooling includes cooling with a cover; During the winding process, the winding tension is 2.4 kN / m. 2 ~2.6kN / m 2 .

2. The method for producing cold-rolled sheet according to claim 1, characterized in that, The surface roughness of the pickled and cold-rolled strip is 0.6μm~1.0μm.

3. The method for producing cold-rolled sheet according to claim 1, characterized in that, It satisfies at least one of the following characteristics (1) to (7): (1) The heating rate of the first stage of heating is 40℃ / h~45℃ / h; (2) The final temperature of the first stage of heating is 700℃~710℃; (3) The heating rate of the second stage is 15℃ / h~25℃ / h; (4) The final temperature of the second stage of heating is 730℃~750℃; (5) In the second heating and heat preservation process, the heat preservation temperature is 730℃~750℃; (6) In the second heating and heat preservation process, the heat preservation time is 10h~12h; (7) The cooling time of the cover is 6h~8h.

4. The method for producing cold-rolled sheet according to any one of claims 1 to 3, characterized in that, The production method further includes the following steps: During the unwinding process, the unwinding speed is less than 30 mpm.

5. The method for producing cold-rolled sheet according to claim 4, characterized in that, The elongation rate of the flattened unwinding is 0.4%~0.5%.

6. The method for producing cold-rolled sheet according to claim 4, characterized in that, The tension of the flattening unwinding is 1200kN~1400kN.

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