Method for improving secondary rolling surface color difference of thin-gauge non-oriented silicon steel

Abstract

The invention discloses a method for improving secondary rolling surface color difference of thin-gauge non-oriented silicon steel. The method comprises the following steps of hot rolling, normalizing, primary cold rolling, primary annealing, secondary cold rolling and secondary annealing. In the hot rolling step, the in-furnace time of a casting blank in a heating furnace is 150-190 minutes; high-pressure water descaling is carried out in the rough rolling and finish rolling processes; in the primary cold rolling step, the roughness of a roller is 1.8-2.1 [mu] m; in the primary annealing step, the SF section temperature of a continuous annealing furnace is 880-920 DEG C; the atmosphere in the furnace is mixed gas of hydrogen and nitrogen, and the volume percentage of the hydrogen is 25-30%; in the secondary cold rolling step, the reduction rate of one pass is 23-30%; the mass percentage concentration of the emulsion is 4.5-6%; the roughness of the mirror roller is 0.4-0.6 [mu] m during rolling of the last pass; by means of the method, the surface color difference defect of the thin-gauge non-oriented silicon steel after secondary rolling can be effectively eliminated, and the surface color difference judgment rate is 0.2% or below.

Description

Technical Field

[0001] The invention belongs to the technical field of non-oriented silicon steel surface quality control, and in particular relates to a method for improving the color difference of the secondary rolled surface of thin-gauge non-oriented silicon steel. Background Art

[0002] Thin gauge non-oriented silicon steel generally needs at least two cold rollings to reach the specified thickness due to its thin thickness. If the process control of thin gauge non-oriented silicon steel is not appropriate, rolling color difference will occur after cold rolling. Rolling color difference is due to the uneven distribution of rolling force and metal extension on the surface of the rolled piece, resulting in uneven surface roughness of the strip or roller, causing differences in reflectivity, such as Figure 1 shown.

[0003] Chinese patent CN113088636 A discloses a method for improving the color difference defect on the surface of high-grade non-oriented silicon steel, which comprises: hot rolling, normalizing, pickling, single-stand rolling and continuous annealing of the continuous casting billet in sequence, wherein the continuous casting billet contains the following components by weight percentage: C < 0.003%, Si 1.6-2.0%, Mn 0.35-0.65%, Al 0.35-0.65%, P < 0.02%, S < 0.0025%, the balance is Fe and other inevitable impurity elements, and all components add up to 100%; wherein the coiling temperature of the hot rolling process is 620-640°C. The method of the present invention can reduce the iron oxide thickness on the strip surface and change the iron oxide structure on the strip surface, thereby improving the color difference defect on the surface of high-grade non-oriented silicon steel. The focus of this patent is to improve the surface color difference defects of high-grade non-oriented silicon steel by selecting the appropriate hot rolling curling temperature. Although this method can improve the surface color difference defects of high-grade non-oriented silicon steel, the surface color difference judgment rate of high-grade non-oriented silicon steel is still as high as 1.2%, and this method is aimed at high-grade non-oriented silicon steel products that have been cold rolled once, and is not applicable to thin-gauge non-oriented silicon steel that has been cold rolled twice.

[0004] However, the prior art does not disclose how to improve the surface color difference of the secondary cold-rolled thin-gauge non-oriented silicon steel. Summary of the invention

[0005] To solve the above technical problems, the present invention provides a method for improving the surface color difference of thin non-oriented silicon steel after secondary rolling. The method can effectively eliminate the surface color difference defect of thin non-oriented silicon steel after secondary rolling, and the surface color difference judgment rate is below 0.2%.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A method for improving the surface color difference of thin-gauge non-oriented silicon steel after secondary rolling, the production method of thin-gauge non-oriented silicon steel comprising the following steps: hot rolling→normalization→one cold rolling→one annealing→secondary cold rolling→secondary annealing;

[0008] In the hot rolling step, the ingot is kept in the heating furnace for 150-190 minutes; high-pressure water descaling is performed during the rough rolling and finishing rolling;

[0009] In the first cold rolling step, the roughness of the roller is 1.8-2.1 μm;

[0010] In the primary annealing step, the temperature of the SF section of the continuous annealing furnace is 880-920°C; the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 25-30%;

[0011] In the secondary cold rolling step, the reduction rate of one pass is 23-30%; the mass percentage concentration of the emulsion is 4.5-6%; and the roughness of the mirror roller in the last rolling pass is 0.4-0.6 μm.

[0012] The thickness of the thin-gauge non-oriented silicon steel is 0.20-0.30 mm.

[0013] In the hot rolling step, the rhythm of the cast billet leaving the heating furnace is 95-110s.

[0014] In the hot rolling step, the pressure of the descaling water during rough rolling is 20-30 MPa.

[0015] In the hot rolling step, during the finish rolling, the spacing between the nozzles of the descaling manifold is 50-53 cm, and the height of the manifold support is 98-105 mm from the surface of the intermediate billet.

[0016] In the normalization step, the normalization temperature is 830-910° C. and the normalization time is 4-6 min.

[0017] In the secondary cold rolling step, the thickness of the steel strip at the secondary cold rolling entrance is 0.57-0.64 mm.

[0018] In the secondary annealing step, the temperature of the SF section of the continuous annealing furnace is 930-990° C.; the annealing time is 1.8-2.5 min, and the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 10-25%.

[0019] The thin non-oriented silicon steel continuous casting billet contains the following components in weight percentage: C≤0.003%, Si 2.8-3.3%, Mn 0.20-0.40%, Al 0.75-1.00%, P≤0.02%, S≤0.0025%, and the balance is Fe and other inevitable impurity elements.

[0020] Multiple links in the production process of thin-gauge non-oriented silicon steel will affect the surface color difference of thin-gauge non-oriented silicon steel after secondary rolling. For example, the slow heating and steel-making rhythm and the descaling process problems will make it difficult to completely and effectively remove the hot-rolled dense oxide layer during shot blasting and pickling, resulting in the combination morphology of the oxide scale and the substrate interface in the color difference area of ​​the pickled substrate being different from that in the normal area. The difference in surface roughness of the strip after pickling causes the difference in visual reflectivity, which is manifested macroscopically as a spotted color difference defect of the substrate; unreasonable use of rolling rollers will cause the plate surface roughness to be too small and the surface roughness of the strip to differ greatly, which is easy to cause color difference; when the lubricity of the rolling emulsion is poor, the color difference becomes more obvious when the lower surface of the strip is rolled; in addition, if a weak oxidizing atmosphere is used for continuous annealing, an oxide layer is easily formed on the surface during the first annealing, and the friction coefficient of the local surface in contact with the roller increases during the second rolling, resulting in abnormal wear of the roller, which is easy to cause color difference on the surface of the steel strip.

[0021] If the heating and steel-out rhythm of the hot-rolled slab is slow, the slab stays in the heating furnace for a long time, which promotes the solid solution of AlN inclusions, thickens the oxide layer, and brings difficulties to hot rolling dephosphorization and pickling. Therefore, the present invention controls the furnace time of the cast slab in the heating furnace to 150-190 minutes and controls the rhythm of leaving the heating furnace to 95-110 seconds, thereby reducing the thickness of the surface oxide layer.

[0022] If the dephosphorization pressure is too low during rough rolling, the oxidized iron scale on the surface of the slab will not be effectively removed and will be pressed into the strip steel; if the positions of the nozzles of the descaling manifolds during finishing rolling are not reasonably distributed and the height of the manifold support is too low, the coverage area of ​​the plate surface will be too small, which will result in the oxidized iron scale generated on the surface during finishing rolling not being effectively removed. The present invention controls the pressure of descaling water during rough rolling to be 20-30MPa, and during finishing rolling, the spacing of the nozzles of the descaling manifolds is 50-53cm, and the height of the manifold support is 98mm-105mm from the surface of the intermediate slab, thereby increasing the coverage area of ​​the dephosphorization water hitting the plate surface, thereby enhancing the ability to remove surface oxidized iron scale during rough rolling and finishing rolling.

[0023] If the roughness of the roller during the first cold rolling is small, the transfer effect to the surface of the substrate after normalization is poor, and the difference in surface roughness of the strip cannot be effectively reduced. The present invention controls the roughness Ra of the roller during the first cold rolling to be 1.8-2.1 μm, which can improve the transfer effect of the surface of the substrate after normalization and reduce the difference in surface roughness of the strip.

[0024] If annealing is performed under a high primary annealing soaking temperature and a low furnace hydrogen content atmosphere, the organic matter remaining on the surface after primary annealing cleaning in the high temperature zone soaking and weak oxidizing atmosphere is likely to form a composite oxide layer mainly composed of SiO2 and MnO2 on the steel plate surface. In the present invention, during the primary annealing, the temperature of the SF section of the continuous annealing furnace is controlled at 880-920°C, and the furnace atmosphere uses a mixed gas of hydrogen and nitrogen, and the volume percentage of hydrogen is controlled to be 25-30%, so as to enhance the reduction effect of the surface organic matter remaining after cleaning and reduce the thickness of the composite oxide layer mainly composed of SiO2 and MnO2 on the steel plate surface.

[0025] During the rolling process, the rollers and the workpiece are in a mixed lubrication state of fluid dynamic lubrication and boundary lubrication. As the relative reduction rate increases, the rolling force increases, which reduces the thickness of the oil film between the rollers and the workpiece; as the emulsion concentration decreases, the adsorption of the rolling oil on the surface decreases, which reduces the thickness of the oil film between the rollers and the workpiece, thereby reducing the flow lubrication component of the mixed lubrication state between the rollers and the workpiece, and the friction state deteriorates, which is specifically manifested as an increase in the friction coefficient between the rollers and the workpiece. If the entrance thickness is too thick during the secondary cold rolling, the reduction rate of the secondary cold rolling will be too high. If the emulsion concentration used is too low, the friction coefficient between the rollers and the workpiece will increase, the lubricity will be poor, and color difference will easily occur. The present invention controls the entrance thickness to 0.57-0.64mm during secondary cold rolling, controls the reduction rate of one pass during secondary cold rolling to 23-30%, and the concentration of emulsion to 4.5-6%, thereby increasing the thickness of the oil film between the roller and the rolled piece, reducing the friction coefficient between the roller and the rolled piece, and improving the lubricity of the emulsion. The roughness Ra of the mirror roller during the final pass of secondary cold rolling is controlled to be 0.4-0.6μm, matching the surface roughness of the strip steel after primary annealing. The roughness of the roller in the final pass has a dominant effect on the extrusion of the emulsion, which is manifested as the thickness of the oil film gradually decreases as the roughness of the roller increases, thereby enhancing the roller polishing effect of the roller on the surface of the strip steel, and significantly improving the surface of the strip steel with higher roughness in the previous pass.

[0026] Through the coordination of the above process sections, the surface color difference defects of thin-gauge non-oriented silicon steel after secondary rolling can be effectively eliminated, and the surface color difference defect rate is below 0.2%.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The ingot time in the heating furnace is controlled to be 150-190 minutes, which improves the production efficiency and reduces the thickness of the oxide layer on the surface of the hot-rolled coil.

[0029] 2. By increasing the rough dephosphorization pressure and optimizing the fine descaling header, the thickness of the oxide layer on the surface of the hot-rolled coil and the pressure of the oxide scale into the plate surface are effectively improved.

[0030] 3. By increasing the roll roughness during one rolling process, the surface roughness difference of the strip is reduced, making the surface roughness distribution more uniform.

[0031] 4. Reduce the annealing heating temperature and increase the hydrogen content in the furnace to reduce the thickness of the composite oxide layer on the surface of the annealed steel strip.

[0032] 5. By reducing the rolling reduction rate and increasing the emulsion concentration, the oil film thickness between the roll and the rolled product is increased, the friction coefficient between the roll and the rolled product is reduced, and the lubricity of the emulsion is improved.

[0033] 6. The roughness of the mirror roller in the last pass of secondary rolling is improved to match the surface roughness of the strip after primary annealing.

[0034] 7. Through the implementation of this technical solution, the surface color difference degradation rate of thin-gauge non-oriented silicon steel secondary rolling has been reduced from 14% before implementation to 0.2%. Figure 2 The monthly output is about 6,000 tons, and the average loss of downgrading is 3,400 yuan / ton. Therefore, the monthly quality loss can be reduced by at least 6,000 × (14% - 0.2%) × 3,400 = 2.815 million yuan. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of the surface color difference of thin-gauge non-oriented silicon steel after secondary rolling;

[0036] Figure 2 It is a schematic diagram of the secondary rolling surface of thin-gauge non-oriented silicon steel produced by the method of the present invention. DETAILED DESCRIPTION

[0037] The present invention provides a method for improving the secondary rolling surface color difference of thin-gauge non-oriented silicon steel with a thickness of 0.20-0.30 mm. The production method of the thin-gauge non-oriented silicon steel comprises the following steps: hot rolling → normalizing → primary cold rolling → primary annealing → secondary cold rolling → secondary annealing;

[0038] In the hot rolling step, the ingot stays in the heating furnace for 150-190 minutes, and the ingot leaves the heating furnace for 95-110 seconds. High-pressure water descaling is performed during rough rolling and finishing rolling. The pressure of the descaling water during rough rolling is 20-30 MPa. During finishing rolling, the spacing between the descaling manifold nozzles is 50-53 cm, and the height of the manifold support is 98 mm-105 mm from the surface of the intermediate billet.

[0039] In the normalization step, the normalization temperature is 830-910° C. and the normalization time is 4-6 min.

[0040] In the first cold rolling step, the roughness of the roller is 1.8-2.1 μm;

[0041] In the primary annealing step, the temperature of the SF section of the continuous annealing furnace is 880-920°C; the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 25-30%;

[0042] In the secondary cold rolling step, the thickness of the steel strip at the entrance of the secondary cold rolling is 0.57-0.64 mm, the reduction rate of one pass is 23-30%, the mass percentage concentration of the emulsion is 4.5-6%, and the roughness of the mirror roller during the last rolling is 0.4-0.6 μm.

[0043] In the secondary annealing step, the temperature of the SF section of the continuous annealing furnace is 930-990° C.; the annealing time is 1.8-2.5 min, and the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 10-25%.

[0044] The thin non-oriented silicon steel continuous casting billet contains the following components: C≤0.003%, Si 2.8-3.3%, Mn0.20-0.40%, Al 0.75-1.00%, P≤0.02%, S≤0.0025%, and the remainder is Fe and other inevitable impurity elements.

[0045] The present invention is described in detail below with reference to the embodiments.

[0046] Example 1

[0047] A production method of thin-gauge non-oriented silicon steel with a thickness of 0.3 mm and a grade of 30W1500, comprising the following steps: converter smelting → RH vacuum treatment → continuous casting → hot rolling → normalizing → primary cold rolling → primary annealing → secondary cold rolling → secondary annealing;

[0048] In the hot rolling step, the ingot stays in the heating furnace for 150 minutes, and the ingot leaves the heating furnace for 95 seconds. High-pressure water descaling is performed during rough rolling and finishing rolling. The pressure of the descaling water during rough rolling is 22 MPa. During finishing rolling, the spacing between the descaling manifold nozzles is 53 cm, and the height of the manifold support is 100 mm from the surface of the intermediate billet.

[0049] In the normalizing step, the normalizing temperature is 900° C. and the normalizing time is 4.5 min.

[0050] In the first cold rolling step, the roller roughness is 2.0 μm;

[0051] In the primary annealing step, the temperature of the SF section of the continuous annealing furnace is 880° C.; the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 25%;

[0052] In the secondary cold rolling step, the thickness of the steel strip at the entrance of the secondary cold rolling is 0.57 mm, the reduction rate of one pass is 23%, the mass percentage concentration of the emulsion is 4.5%, and the roughness of the mirror roller during the last rolling pass is 0.5 μm.

[0053] In the secondary annealing step, the temperature of the SF section of the continuous annealing furnace is 960° C.; the annealing time is 1.9 min, and the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 15%.

[0054] Example 2

[0055] A production method of thin-gauge non-oriented silicon steel with a thickness of 0.27 mm and a grade of 27W1400, comprising the following steps: converter smelting → RH vacuum treatment → continuous casting → hot rolling → normalizing → primary cold rolling → primary annealing → secondary cold rolling → secondary annealing;

[0056] In the hot rolling step, the ingot stays in the heating furnace for 160 minutes, and the ingot leaves the heating furnace at a rate of 100 seconds; high-pressure water descaling is performed during rough rolling and finishing rolling; the pressure of the descaling water during rough rolling is 25 MPa; during finishing rolling, the spacing between the descaling manifold nozzles is 50 cm, and the height of the manifold support is 100 mm from the surface of the intermediate billet.

[0057] In the normalizing step, the normalizing temperature is 890° C. and the normalizing time is 4.5 min.

[0058] In the first cold rolling step, the roller roughness is 2.0 μm;

[0059] In the primary annealing step, the temperature of the SF section of the continuous annealing furnace is 890° C.; the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 27%;

[0060] In the secondary cold rolling step, the thickness of the steel strip at the entrance of the secondary cold rolling is 0.60 mm, the reduction rate of one pass is 25%, the mass percentage concentration of the emulsion is 4.8%, and the roughness of the mirror roller during the last rolling pass is 0.5 μm.

[0061] In the secondary annealing step, the temperature of the SF section of the continuous annealing furnace is 970° C.; the annealing time is 2.1 min, and the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 15%.

[0062] Example 3

[0063] A production method of thin-gauge non-oriented silicon steel with a thickness of 0.25 mm and a grade of 25W1300, comprising the following steps: converter smelting → RH vacuum treatment → continuous casting → hot rolling → normalizing → primary cold rolling → primary annealing → secondary cold rolling → secondary annealing;

[0064] In the hot rolling step, the ingot stays in the heating furnace for 170 minutes, and the ingot leaves the heating furnace at a rate of 105 seconds; high-pressure water descaling is performed during rough rolling and finishing rolling; the pressure of the descaling water during rough rolling is 25 MPa; during finishing rolling, the spacing between the descaling manifold nozzles is 53 cm, and the height of the manifold support is 100 mm from the surface of the intermediate billet.

[0065] In the normalizing step, the normalizing temperature is 880° C. and the normalizing time is 4.5 min.

[0066] In the first cold rolling step, the roller roughness is 2.0 μm;

[0067] In the primary annealing step, the temperature of the SF section of the continuous annealing furnace is 900° C.; the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 30%;

[0068] In the secondary cold rolling step, the thickness of the steel strip at the entrance of the secondary cold rolling is 0.62 mm, the reduction rate of one pass is 27%, the mass percentage concentration of the emulsion is 5.5%, and the roughness of the mirror roller during the last rolling is 0.5 μm.

[0069] In the secondary annealing step, the temperature of the SF section of the continuous annealing furnace is 980° C.; the annealing time is 2.3 min, and the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 15%.

[0070] Example 4

[0071] A production method of thin-gauge non-oriented silicon steel with a thickness of 0.20 mm and a grade of 20W1300, comprising the following steps: converter smelting → RH vacuum treatment → continuous casting → hot rolling → normalizing → primary cold rolling → primary annealing → secondary cold rolling → secondary annealing;

[0072] In the hot rolling step, the ingot stays in the heating furnace for 185 minutes, and the ingot leaves the heating furnace at a rate of 108 seconds. High-pressure water descaling is performed during rough rolling and finishing rolling. The pressure of the descaling water during rough rolling is 30 MPa. During finishing rolling, the spacing between the descaling manifold nozzles is 50 cm, and the height of the manifold support is 100 mm from the surface of the intermediate billet.

[0073] In the normalizing step, the normalizing temperature is 870° C. and the normalizing time is 4.5 min.

[0074] In the first cold rolling step, the roller roughness is 2.0 μm;

[0075] In the primary annealing step, the temperature of the SF section of the continuous annealing furnace is 910° C.; the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 25%;

[0076] In the secondary cold rolling step, the thickness of the steel strip at the entrance of the secondary cold rolling is 0.64 mm, the reduction rate of one pass is 30%, the mass percentage concentration of the emulsion is 6.0%, and the roughness of the mirror roller during the last rolling pass is 0.5 μm.

[0077] In the secondary annealing step, the temperature of the SF section of the continuous annealing furnace is 990° C.; the annealing time is 2.5 min, and the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 15%.

[0078] Comparative Example 1

[0079] A production method of thin-gauge non-oriented silicon steel with a thickness of 0.25 mm and a grade of 25W1300, comprising the following steps: converter smelting → RH vacuum treatment → continuous casting → hot rolling → normalizing → primary cold rolling → primary annealing → secondary cold rolling → secondary annealing;

[0080] In the hot rolling step, the ingot stays in the heating furnace for 190 minutes, and the ingot leaves the heating furnace for 120 seconds. High-pressure water descaling is performed during rough rolling and finishing rolling. The pressure of the descaling water during rough rolling is 15 MPa. During finishing rolling, the spacing between the descaling manifold nozzles is 54 cm, and the height of the manifold support is 95 mm from the surface of the intermediate billet.

[0081] In the normalizing step, the normalizing temperature is 880° C. and the normalizing time is 4.5 min.

[0082] In the first cold rolling step, the roller roughness is 1.5 μm;

[0083] In the primary annealing step, the temperature of the SF section of the continuous annealing furnace is 925° C.; the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 20%;

[0084] In the secondary cold rolling step, the thickness of the steel strip at the entrance of the secondary cold rolling is 0.65 mm, the reduction rate of one pass is 31%, the mass percentage concentration of the emulsion is 3.0%, and the roughness of the mirror roller during the last rolling pass is 0.3 μm.

[0085] In the secondary annealing step, the temperature of the SF section of the continuous annealing furnace is 980° C.; the annealing time is 2.3 min, and the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 15%.

[0086] Comparative Example 2

[0087] A production method of thin-gauge non-oriented silicon steel with a thickness of 0.27 mm and a grade of 27W1400, comprising the following steps: converter smelting → RH vacuum treatment → continuous casting → hot rolling → normalizing → primary cold rolling → primary annealing → secondary cold rolling → secondary annealing;

[0088] In the hot rolling step, the ingot stays in the heating furnace for 200 minutes, and the ingot leaves the heating furnace at a rate of 125 seconds; high-pressure water descaling is performed during rough rolling and finishing rolling; the pressure of the descaling water during rough rolling is 15 MPa; during finishing rolling, the spacing between the descaling manifold nozzles is 54 cm, and the height of the manifold support is 95 mm from the surface of the intermediate billet.

[0089] In the normalizing step, the normalizing temperature is 890° C. and the normalizing time is 4.5 min.

[0090] In the first cold rolling step, the roller roughness is 1.5 μm;

[0091] In the primary annealing step, the temperature of the SF section of the continuous annealing furnace is 920° C.; the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 25%;

[0092] In the secondary cold rolling step, the thickness of the steel strip at the entrance of the secondary cold rolling is 0.68 mm, the reduction rate of one pass is 34%, the mass percentage concentration of the emulsion is 4.3%, and the roughness of the mirror roller during the last rolling pass is 0.3 μm.

[0093] In the secondary annealing step, the temperature of the SF section of the continuous annealing furnace is 970° C.; the annealing time is 2.1 min, and the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 15%.

[0094] The surface conditions of the thin-gauge non-oriented silicon steel produced in the above-mentioned embodiments and comparative examples are shown in Table 1.

[0095] Table 1

[0096] Surface quality Surface color difference degradation rate / % Example 1 good 0.20 Example 2 good 0.18 Example 3 good 0.17 Example 4 good 0.19 Comparative Example 1 Poor 12 Comparative Example 2 Poor 13

[0097] It can be seen from the above that the method provided by the present invention can effectively eliminate the surface color difference defects of thin-gauge non-oriented silicon steel after secondary rolling, and the surface color difference defect rate is below 0.2%.

[0098] The above-mentioned detailed description of a method for improving the surface color difference of thin-gauge non-oriented silicon steel after secondary rolling with reference to the embodiment is illustrative rather than restrictive, and several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for improving the surface color difference of thin-gauge non-oriented silicon steel after secondary rolling, characterized in that: The production method of thin gauge non-oriented silicon steel comprises the following steps: hot rolling → normalizing → primary cold rolling → primary annealing → secondary cold rolling → secondary annealing; In the hot rolling step, the ingot is kept in the heating furnace for 150-190 minutes; high-pressure water descaling is performed during the rough rolling and finishing rolling; In the first cold rolling step, the roughness of the roller is 1.8-2.1 μm; In the primary annealing step, the temperature of the SF section of the continuous annealing furnace is 880-920°C; the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 25-30%; In the secondary cold rolling step, the reduction rate of one pass is 23-30%; the mass percentage concentration of the emulsion is 4.5-6%; and the roughness of the mirror roller in the last rolling pass is 0.4-0.6 μm.

2. The method according to claim 1, characterized in that The thickness of the thin-gauge non-oriented silicon steel is 0.20-0.30 mm.

3. The method according to claim 1 or 2, characterized in that: In the hot rolling step, the rhythm of the cast billet leaving the heating furnace is 95-110s.

4. The method according to claim 1 or 2, characterized in that: In the hot rolling step, the pressure of the descaling water during rough rolling is 20-30 MPa.

5. The method according to claim 1 or 2, characterized in that: In the hot rolling step, during the finish rolling, the spacing between the nozzles of the descaling manifold is 50-53 cm, and the height of the manifold support is 98-105 mm from the surface of the intermediate billet.

6. The method according to claim 1 or 2, characterized in that: In the normalization step, the normalization temperature is 830-910° C. and the normalization time is 4-6 min.

7. The method according to claim 1 or 2, characterized in that: In the secondary cold rolling step, the thickness of the steel strip at the secondary cold rolling entrance is 0.57-0.64 mm.

8. The method according to claim 1 or 2, characterized in that: In the secondary annealing step, the temperature of the SF section of the continuous annealing furnace is 930-990° C.; the annealing time is 1.8-2.5 min, and the atmosphere in the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 10-25%.

9. The method according to claim 1 or 2, characterized in that: The thin non-oriented silicon steel continuous casting billet contains the following components in weight percentage: C≤0.003%, Si 2.8-3.3%, Mn 0.20-0.40%, Al 0.75-1.00%, P≤0.02%, S≤0.0025%, and the balance is Fe and other inevitable impurity elements.

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