A method for improving surface color difference of thin gauge non-oriented silicon steel after secondary rolling

Abstract

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

Description

Technical Field

[0001] This invention belongs to the field of surface quality control technology for non-oriented silicon steel, and specifically relates to a method for improving the surface color difference of thin-gauge non-oriented silicon steel during secondary rolling. Background Technology

[0002] Thin-gauge non-oriented silicon steel, due to its thinness, generally requires at least two cold rolling processes to achieve the specified thickness. However, if the processing control of thin-gauge non-oriented silicon steel is inadequate, rolling color difference will occur after cold rolling. Rolling color difference is caused by uneven distribution of rolling force and metal elongation on the surface of the workpiece, resulting in uneven surface roughness of the strip or rolls and thus differences in reflectivity. Figure 1 As shown.

[0003] Chinese Patent CN113088636 A discloses a method for improving surface color difference defects in high-grade non-oriented silicon steel. The method involves sequentially subjecting a continuously cast billet to hot rolling, normalizing, pickling, single-stand rolling, and continuous annealing processes. The continuously cast billet, by weight percentage, contains the following composition: C < 0.003%, Si 1.6–2.0%, Mn 0.35–0.65%, Al 0.35–0.65%, P < 0.02%, S < 0.0025%, with the balance being Fe and other unavoidable impurities, totaling 100%. The coiling temperature during the hot rolling process is 620–640°C. This method can reduce the thickness of iron oxide on the strip surface and alter the iron oxide structure, thereby improving surface color difference defects in high-grade non-oriented silicon steel. The patent focuses on improving the surface color difference defects of high-grade non-oriented silicon steel by selecting an appropriate hot rolling temperature. Although this method can improve the surface color difference defects of high-grade non-oriented silicon steel, the surface color difference rejection rate of high-grade non-oriented silicon steel is still as high as 1.2%. Moreover, this method is for high-grade non-oriented silicon steel products that have been cold rolled once, and it is not applicable to thin-gauge non-oriented silicon steel that has been cold rolled twice.

[0004] In existing technologies, no method has been disclosed for improving the surface color difference of thin-gauge non-oriented silicon steel produced by secondary cold rolling. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for improving surface color difference in thin-gauge non-oriented silicon steel after secondary rolling. This method effectively eliminates surface color difference defects in thin-gauge non-oriented silicon steel after secondary rolling, with a surface color difference rejection rate below 0.2%.

[0006] To achieve the above objectives, 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, wherein the production method of the thin-gauge non-oriented silicon steel includes the following steps: hot rolling → normalizing → first cold rolling → first annealing → second cold rolling → second annealing.

[0008] In the hot rolling step, the billet is in the furnace for 150-190 minutes; high-pressure water descaling is performed during rough rolling and finish rolling.

[0009] In the aforementioned cold rolling step, the roll roughness is 1.8-2.1 μm;

[0010] In the first annealing step, the temperature of the SF section of the continuous annealing furnace is 880-920℃; the atmosphere inside 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 per pass is 23-30%; the mass percentage concentration of the emulsion is 4.5-6%; and the roughness of the mirror roll during the final rolling pass is 0.4-0.6μm.

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

[0013] In the hot rolling step, the billet exits the heating furnace at a rate of 95-110 seconds.

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

[0015] During the hot rolling process, in the finishing rolling, the spacing between the descaling manifold nozzles is 50-53 cm, and the distance between the manifold support height and the surface of the intermediate billet is 98-105 mm.

[0016] In the normalization step, the normalization temperature is 830-910℃ and the normalization time is 4-6 minutes.

[0017] In the secondary cold rolling step, the thickness of the steel strip at the secondary cold rolling inlet 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℃; the annealing time is 1.8-2.5min; and the atmosphere inside the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 10-25%.

[0019] The thin-gauge non-oriented silicon steel continuous casting billet contains the following composition by 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%, with the balance being Fe and other unavoidable impurity elements.

[0020] Several aspects of the production process of thin-gauge non-oriented silicon steel can affect the surface color difference of the thin-gauge non-oriented silicon steel after secondary rolling. For example, a slow heating and tapping rhythm and descaling process issues can make it difficult to completely and effectively remove the dense oxide layer during shot blasting and pickling. This results in the iron oxide scale and substrate interface morphology in the color difference area of ​​the pickled substrate differing from that in the normal area. The difference in surface roughness of the strip after pickling causes a difference in visual reflectivity, which macroscopically manifests as a patchy color difference defect on the substrate. Improper use of rolling rolls can lead to excessively small surface roughness and large differences in surface roughness of the strip, which easily produce color differences. When the lubricity of the rolling emulsion is poor, the color difference becomes more obvious when rolling the lower surface of the strip. In addition, if a weak oxidizing atmosphere is used in continuous annealing, an oxide layer is easily formed on the surface during the first annealing. During the second rolling, the friction coefficient between the local surface and the roll increases, leading to abnormal wear of the roll and easily producing color differences on the steel strip surface.

[0021] If the heating and tapping rhythm of hot-rolled slabs is slow, the slabs will spend a long time in the furnace, which promotes the solid solution of AlN inclusions, thickens the oxide layer, and makes it more difficult to descaling and pickling during hot rolling. Therefore, this invention controls the time of the slabs in the furnace to 150-190 minutes and controls the tapping rhythm to 95-110 seconds to reduce the thickness of the surface oxide layer.

[0022] If the descaling pressure is too low during rough rolling, the iron oxide scale on the slab surface will not be effectively removed and will be pressed into the strip. Similarly, if the positions of the descaling manifold nozzles are not properly distributed or the manifold support height is too low, resulting in a small coverage area on the slab surface, the iron oxide scale generated during finish rolling will not be effectively removed. This invention controls the descaling water pressure to 20-30 MPa during rough rolling, and during finish rolling, the spacing between the descaling manifold nozzles is 50-53 cm, and the distance between the manifold support height and the intermediate slab surface is 98-105 mm. This increases the coverage area of ​​the descaling water impacting the slab surface, thereby enhancing the surface iron oxide scale removal capacity during both rough and finish rolling.

[0023] If the roll roughness is too low during the first cold rolling process, the transfer effect on the substrate surface after normalization will be poor, and the surface roughness difference of the strip cannot be effectively reduced. This invention controls the roll roughness Ra of 1.8-2.1 μm during the first cold rolling process, which can improve the transfer effect on the substrate surface after normalization and reduce the surface roughness difference of the strip.

[0024] If annealing is performed at a high primary annealing temperature and in an atmosphere with low hydrogen content in the furnace, the residual organic matter on the surface after primary annealing and cleaning, under the conditions of high-temperature heating and a weak oxidizing atmosphere, can easily lead to the formation of a composite oxide layer mainly composed of SiO2 and MnO2 on the steel plate surface. This invention controls the temperature of the SF section of the continuous annealing furnace at 880-920℃ during primary annealing, while using a mixture of hydrogen and nitrogen in the furnace atmosphere, controlling the hydrogen volume percentage to 25-30%. This enhances the reduction effect on residual organic matter on the surface after cleaning and reduces the thickness of the composite oxide layer mainly composed of SiO2 and MnO2 on the steel plate surface.

[0025] During rolling, the rolling mill and the workpiece are in a mixed lubrication state, where hydrodynamic lubrication and boundary lubrication are intertwined. As the relative reduction rate increases, the rolling force also increases, leading to a decrease in the oil film thickness between the rolls and the workpiece. Furthermore, as the emulsion concentration decreases, the surface adsorption of the rolling oil decreases, further reducing the oil film thickness between the rolls and the workpiece. Consequently, the fluid lubrication components in the mixed lubrication state between the rolls and the workpiece are relatively reduced, resulting in a deterioration of the friction state, specifically an increase in the coefficient of friction between the rolls and the workpiece. If the entry thickness is too thick during secondary cold rolling, the reduction rate in the first pass will be too high. If the emulsion concentration used is too low, it will lead to an increase in the coefficient of friction between the rolls and the workpiece, poor lubrication, and a tendency to produce color differences. This invention controls the entry thickness during secondary cold rolling to be 0.57-0.64 mm, the reduction rate per pass during secondary cold rolling to be 23-30%, and the emulsion concentration to be 4.5-6%. This increases the oil film thickness between the rolls and the workpiece, reduces the friction coefficient between the rolls and the workpiece, and improves the lubricity of the emulsion. Furthermore, the roughness Ra of the mirror rolls during the final pass of secondary cold rolling is controlled to be 0.4-0.6 μm, matching the surface roughness of the strip after primary annealing. In the final pass, the extrusion effect of the emulsion on the roll roughness dominates, resulting in a gradual decrease in oil film thickness as the roll roughness increases. This enhances the rolling effect of the rolls on the strip surface, significantly improving the surface roughness of the strip from the previous passes.

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

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

[0028] 1. By controlling the time the billet spends in the heating furnace to 150-190 minutes, production efficiency is improved, while the thickness of the oxide layer on the surface of the hot-rolled coil is reduced.

[0029] 2. By increasing the coarse descaling pressure and optimizing the fine descaling manifold, the thickness of the oxide layer on the surface of the hot-rolled coil and the iron oxide scale being pressed into the plate surface are effectively improved.

[0030] 3. By increasing the roll roughness during a single rolling process, the surface roughness difference of the strip is reduced, resulting in a more uniform surface roughness distribution.

[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 rolls and the workpiece is increased, the friction coefficient between the rolls and the workpiece is reduced, and the lubricity of the emulsion is improved.

[0033] 6. Improved the surface roughness of the mirror roll in the final pass of secondary rolling, matching 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 after secondary rolling was reduced from 14% before implementation to 0.2%. The improved surface is shown in the figure. Figure 2 With a monthly output of approximately 6,000 tons and an average downgrade loss of 3,400 yuan per ton, the monthly reduction in quality loss is at least 6,000 × (14% - 0.2%) × 3,400 = 2.815 million yuan. Attached Figure Description

[0035] Figure 1 A schematic diagram illustrating the surface color difference in thin-gauge non-oriented silicon steel after secondary rolling;

[0036] Figure 2 This is a schematic diagram of the secondary rolled surface of thin-gauge non-oriented silicon steel produced using the method of this invention. Detailed Implementation

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

[0038] In the hot rolling process, the billet is in the furnace for 150-190 minutes, and the billet exits the furnace at a rate of 95-110 seconds. High-pressure water descaling is performed during roughing and finishing rolling. The pressure of the descaling water during roughing is 20-30 MPa. During finishing rolling, the spacing between the descaling manifold nozzles is 50-53 cm, and the distance between the manifold support and the surface of the intermediate billet is 98-105 mm.

[0039] In the normalization step, the normalization temperature is 830-910℃ and the normalization time is 4-6 minutes.

[0040] In the aforementioned cold rolling step, the roll roughness is 1.8-2.1 μm;

[0041] In the first annealing step, the temperature of the SF section of the continuous annealing furnace is 880-920℃; the atmosphere inside 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 entry point of the secondary cold rolling is 0.57-0.64 mm, the reduction rate per pass is 23-30%, the mass percentage concentration of the emulsion is 4.5-6%, and the roughness of the mirror roll during the final rolling pass 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℃; the annealing time is 1.8-2.5min; and the atmosphere inside the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 10-25%.

[0044] The thin-gauge non-oriented silicon steel continuous casting billet contains the following composition: C≤0.003%, Si 2.8~3.3%, Mn0.20~0.40%, Al 0.75~1.00%, P≤0.02%, S≤0.0025%, with the balance being Fe and other unavoidable impurity elements.

[0045] The present invention will now be described in detail with reference to the embodiments.

[0046] Example 1

[0047] A method for producing thin-gauge non-oriented silicon steel with a thickness of 0.3 mm and a grade of 30W1500 includes the following steps: converter smelting → RH vacuum treatment → continuous casting → hot rolling → normalizing → first cold rolling → first annealing → second cold rolling → second annealing.

[0048] In the hot rolling process, the billet is in the furnace for 150 minutes and exits the furnace at a rate of 95 seconds. High-pressure water descaling is performed during roughing and finishing rolling. The pressure of the descaling water during roughing is 22 MPa. During finishing rolling, the spacing between the descaling manifold nozzles is 53 cm and the distance between the manifold support and the surface of the intermediate billet is 100 mm.

[0049] In the normalization step, the normalization temperature is 900℃ and the normalization time is 4.5min.

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

[0051] In the first annealing step, the temperature of the SF section of the continuous annealing furnace is 880°C; the atmosphere inside 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 secondary cold rolling inlet is 0.57 mm, the reduction rate per pass is 23%, the mass percentage concentration of the emulsion is 4.5%, and the roughness of the mirror roll during the final 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℃; the annealing time is 1.9 min; and the atmosphere inside the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 15%.

[0054] Example 2

[0055] A method for producing thin-gauge non-oriented silicon steel with a thickness of 0.27 mm and a grade of 27W1400 includes the following steps: converter smelting → RH vacuum treatment → continuous casting → hot rolling → normalizing → first cold rolling → first annealing → second cold rolling → second annealing.

[0056] In the hot rolling process, the billet is in the furnace for 160 minutes and exits the furnace at a rate of 100 seconds. High-pressure water descaling is performed during roughing and finishing rolling. The pressure of the descaling water during roughing is 25 MPa. During finishing rolling, the spacing between the descaling manifold nozzles is 50 cm, and the distance between the manifold support and the surface of the intermediate billet is 100 mm.

[0057] In the normalization step, the normalization temperature is 890℃ and the normalization time is 4.5min.

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

[0059] In the first annealing step, the temperature of the SF section of the continuous annealing furnace is 890°C; the atmosphere inside 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 entry point of the secondary cold rolling is 0.60 mm, the reduction rate per pass is 25%, the mass percentage concentration of the emulsion is 4.8%, and the roughness of the mirror roll during the final 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℃; the annealing time is 2.1 min; and the atmosphere inside the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 15%.

[0062] Example 3

[0063] A method for producing thin-gauge non-oriented silicon steel with a thickness of 0.25 mm and a grade of 25W1300 includes the following steps: converter smelting → RH vacuum treatment → continuous casting → hot rolling → normalizing → first cold rolling → first annealing → second cold rolling → second annealing.

[0064] In the hot rolling process, the billet is in the furnace for 170 minutes and exits the furnace at a rate of 105 seconds. High-pressure water descaling is performed during roughing and finishing rolling. The pressure of the descaling water during roughing is 25 MPa. During finishing rolling, the spacing between the descaling manifold nozzles is 53 cm and the distance between the manifold support and the surface of the intermediate billet is 100 mm.

[0065] In the normalization step, the normalization temperature is 880℃ and the normalization time is 4.5min.

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

[0067] In the first annealing step, the temperature of the SF section of the continuous annealing furnace is 900°C; the atmosphere inside 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 entry point of the secondary cold rolling is 0.62 mm, the reduction rate per pass is 27%, the mass percentage concentration of the emulsion is 5.5%, and the roughness of the mirror roll during the final rolling pass is 0.5 μm.

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

[0070] Example 4

[0071] A method for producing thin-gauge non-oriented silicon steel with a thickness of 0.20 mm and a grade of 20W1300 includes the following steps: converter smelting → RH vacuum treatment → continuous casting → hot rolling → normalizing → first cold rolling → first annealing → second cold rolling → second annealing.

[0072] In the hot rolling process, the billet is in the furnace for 185 minutes and exits the furnace at a rate of 108 seconds. High-pressure water descaling is performed during roughing and finishing rolling. The pressure of the descaling water during roughing is 30 MPa. During finishing rolling, the spacing between the descaling manifold nozzles is 50 cm, and the distance between the manifold support and the surface of the intermediate billet is 100 mm.

[0073] In the normalization step, the normalization temperature is 870℃ and the normalization time is 4.5min.

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

[0075] In the first annealing step, the temperature of the SF section of the continuous annealing furnace is 910°C; the atmosphere inside 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 secondary cold rolling inlet is 0.64 mm, the reduction rate per pass is 30%, the mass percentage concentration of the emulsion is 6.0%, and the roughness of the mirror roll during the final 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℃; the annealing time is 2.5min; and the atmosphere inside the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 15%.

[0078] Comparative Example 1

[0079] A method for producing thin-gauge non-oriented silicon steel with a thickness of 0.25 mm and a grade of 25W1300 includes the following steps: converter smelting → RH vacuum treatment → continuous casting → hot rolling → normalizing → first cold rolling → first annealing → second cold rolling → second annealing.

[0080] In the hot rolling process, the billet is in the furnace for 190 minutes and exits the furnace at a rate of 120 seconds. High-pressure water descaling is performed during roughing and finishing rolling. The pressure of the descaling water during roughing is 15 MPa. During finishing rolling, the spacing between the descaling manifold nozzles is 54 cm, and the distance between the manifold support and the surface of the intermediate billet is 95 mm.

[0081] In the normalization step, the normalization temperature is 880℃ and the normalization time is 4.5min.

[0082] In the aforementioned cold rolling step, the roll roughness is 1.5 μm;

[0083] In the first annealing step, the temperature of the SF section of the continuous annealing furnace is 925°C; the atmosphere inside 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 secondary cold rolling inlet is 0.65 mm, the reduction rate per pass is 31%, the mass percentage concentration of the emulsion is 3.0%, and the roughness of the mirror roll during the final 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℃; the annealing time is 2.3min; and the atmosphere inside the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 15%.

[0086] Comparative Example 2

[0087] A method for producing thin-gauge non-oriented silicon steel with a thickness of 0.27 mm and a grade of 27W1400 includes the following steps: converter smelting → RH vacuum treatment → continuous casting → hot rolling → normalizing → first cold rolling → first annealing → second cold rolling → second annealing.

[0088] In the hot rolling process, the billet is in the furnace for 200 minutes and exits the furnace at a rate of 125 seconds. High-pressure water descaling is performed during roughing and finishing rolling. The pressure of the descaling water during roughing is 15 MPa. During finishing rolling, the spacing between the descaling manifold nozzles is 54 cm, and the distance between the height of the manifold support and the surface of the intermediate billet is 95 mm.

[0089] In the normalization step, the normalization temperature is 890℃ and the normalization time is 4.5min.

[0090] In the aforementioned cold rolling step, the roll roughness is 1.5 μm;

[0091] In the first annealing step, the temperature of the SF section of the continuous annealing furnace is 920°C; the atmosphere inside 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 secondary cold rolling inlet is 0.68 mm, the reduction rate per pass is 34%, the mass percentage concentration of the emulsion is 4.3%, and the roughness of the mirror roll during the final 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℃; the annealing time is 2.1 min; and the atmosphere inside 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 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] As can be seen from the above, the method provided by the present invention can effectively eliminate surface color difference defects in thin-gauge non-oriented silicon steel after secondary rolling, with a surface color difference rejection rate of less than 0.2%.

[0098] The above detailed description of a method for improving surface color difference in secondary rolling of thin-gauge non-oriented silicon steel with reference to the embodiments is illustrative rather than limiting. Several embodiments can be listed within the defined scope. Therefore, variations and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A method for improving surface color difference in thin-gauge non-oriented silicon steel after secondary rolling, characterized in that, The production method of the thin-gauge non-oriented silicon steel includes the following steps: hot rolling → normalizing → first cold rolling → first annealing → second cold rolling → second annealing. In the hot rolling step, the billet stays in the heating furnace for 150-190 minutes, and exits the heating furnace at a rate of 95-110 seconds; high-pressure water descaling is performed during roughing and finishing rolling. In the hot rolling step, during finish rolling, the distance between the height of the descaling manifold support and the surface of the intermediate billet is 98-105 mm. In the aforementioned cold rolling step, the roll roughness 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℃; the atmosphere inside 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 per pass is 23-30%; the mass percentage concentration of the emulsion is 4.5-6%; and the roughness of the mirror rolls in the final rolling pass is 0.4-0.6 μm. In the secondary cold rolling step, the thickness of the steel strip at the secondary cold rolling inlet is 0.57-0.64 mm; The thin-gauge non-oriented silicon steel billet contains the following composition by 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%, with the balance being Fe and other unavoidable impurity elements.

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 pressure of the descaling water during rough rolling is 20-30 MPa.

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

5. 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℃; the annealing time is 1.8-2.5min; and the atmosphere inside the furnace is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 10-25%.

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