A method for reducing color difference defects on the surface of electro-galvanized sheet

Abstract

The present application relates to a method for reducing the color difference defect on the surface of an electro-galvanized sheet, which belongs to the technical field of iron and steel metallurgy. The method comprises: smelting molten steel to obtain a continuous casting billet; heating the continuous casting billet before rolling, rough rolling, finishing rolling, cooling after rolling and coiling to obtain a hot-rolled coil; pickling, cold rolling, annealing, leveling and electro-galvanizing the hot-rolled coil to obtain an electro-galvanized sheet; in the pre-rolling heating process, the heating temperature is controlled to be a set temperature, and the furnace heating time is controlled to be a set time. The method significantly reduces the thickness of the furnace-generated iron oxide scale, avoids the difference in light diffuse reflection caused by the directional growth of the zinc layer and the disordered growth of the surrounding zinc layer, thereby effectively improving the color difference defect on the surface of the electro-galvanized product.

Description

Technical Field

[0001] The present application relates to the technical field of iron and steel metallurgy, and in particular to a method for reducing color difference defects on the surface of an electro-galvanized sheet. Background Art

[0002] Electro-galvanized sheet has good corrosion resistance, processability, weldability and paintability, and is widely used in the automotive and home appliance industries. It is generally used for high-end automotive hood panels, and home appliance companies manufacture washing machine shells, LCD TV back panels and other products. Electro-galvanized products have strict requirements on surface quality, and color difference defects after electroplating have always been a problem that plagues the industry. Summary of the invention

[0003] The present application provides a method for reducing the color difference defects on the surface of an electro-galvanized sheet, so as to solve the technical problem that the existing electro-galvanized sheet has the color difference defects on the surface.

[0004] In a first aspect, the present application provides a method for reducing the color difference defects on the surface of an electro-galvanized sheet, the method comprising:

[0005] Smelting the molten steel to obtain continuous casting billets;

[0006] The continuous casting slab is subjected to pre-rolling heating, rough rolling, finish rolling, post-rolling cooling and coiling to obtain a hot-rolled coil;

[0007] The hot-rolled coil is pickled, cold-rolled, annealed, flattened and electro-galvanized to obtain an electro-galvanized sheet;

[0008] During the pre-rolling heating process, the heating temperature is controlled to be a set temperature, and the heating time in the furnace is controlled to be a set time.

[0009] Furthermore, during the pre-rolling heating process, the temperature is set at 950°C to 1150°C.

[0010] Furthermore, during the pre-rolling heating process, the set time is greater than 120 minutes.

[0011] Furthermore, the thickness of the iron oxide layer in the electro-galvanized sheet is 3 to 8 μm.

[0012] Furthermore, the process parameters of the rough rolling include: the outlet temperature of the rough rolling is 800°C to 950°C.

[0013] Furthermore, during the rough rolling process, full-pass descaling is used for descaling.

[0014] Furthermore, the process parameters of the finishing rolling include: the final rolling temperature of the finishing rolling is 700°C to 850°C.

[0015] Furthermore, the coiling process parameters include: the coiling temperature is 580-650°C.

[0016] Furthermore, the process parameters of the post-rolling cooling include: the terminal temperature of the post-rolling cooling is 550-680°C.

[0017] Furthermore, the chemical composition system of the molten steel is a low-carbon steel composition system or an IF steel plate composition system.

[0018] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0019] The embodiment of the present application provides a method for reducing the color difference defects on the surface of electro-galvanized sheet. The method combines the hot rolling production line process with the electro-galvanizing process. By controlling the heating temperature to a set temperature and the heating time in the furnace to a set time during the pre-rolling heating process, the thickness of the furnace-born iron oxide scale is significantly reduced (the thickness of the furnace-born iron oxide scale is reduced by up to 33%), and the difference in light diffuse reflection caused by the directional growth of the zinc layer and the disordered growth of the surrounding zinc layer is avoided, thereby effectively improving the color difference defects on the surface of the electro-galvanized product. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0022] Figure 1 A schematic flow chart of a method for reducing color difference defects on the surface of an electro-galvanized sheet provided in an embodiment of the present application;

[0023] Figure 2 A morphology of the iron oxide layer on the surface of an electro-galvanized sheet product provided in Example 1 of the present application;

[0024] Figure 3 A morphology of the iron oxide layer on the surface of an electrogalvanized sheet product provided in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0026] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0027] Electro-galvanized sheet has good corrosion resistance, processability, weldability and paintability, and is widely used in the automotive and home appliance industries. It is generally used for high-end automotive hood panels, and home appliance companies manufacture washing machine shells, LCD TV back panels and other products. Electro-galvanized products have strict requirements on surface quality, and color difference defects after electroplating have always been a problem that plagues the industry.

[0028] At present, in order to improve the surface quality of electrogalvanized substrates, the existing technologies include:

[0029] "A method for reducing the defects of filamentous spots on the surface of electro-galvanized sheet" (Chinese Patent, 202010919627.2), proposes to increase the outlet descaling water and descaling between the F1 rear racks. "A production method for controlling the surface filamentous spots defects of electro-galvanized IF steel products" (Chinese Patent, 201911169842.9), proposes to reduce the coiling temperature by controlling the heating temperature and the time in the furnace. "A kind of electro-galvanized ultra-deep drawing sheet for automobile outer panel with high-grade surface morphology and its production method" (Chinese Patent, 201811052483.4), proposes to adopt full-pass descaling. The above inventions have a certain effect on the color difference defects on the surface of electro-galvanized sheet, but the qualified rate still fluctuates.

[0030] The technical solution provided by the embodiment of the present invention is to solve the above technical problems, and the overall idea is as follows:

[0031] like Figure 1 As shown, the embodiment of the present application provides a method for reducing the color difference defect on the surface of an electro-galvanized sheet, comprising:

[0032] Smelting the molten steel to obtain continuous casting billets;

[0033] The continuous casting slab is subjected to pre-rolling heating, rough rolling, finish rolling, post-rolling cooling and coiling to obtain a hot-rolled coil;

[0034] The hot-rolled coil is pickled, cold-rolled, annealed, flattened and electro-galvanized to obtain an electro-galvanized sheet;

[0035] During the pre-rolling heating process, the heating temperature is controlled to be a set temperature, and the heating time in the furnace is controlled to be a set time.

[0036] The embodiment of the present application provides a method for reducing the color difference defects on the surface of electro-galvanized sheet. The method combines the hot rolling production line process with the electro-galvanizing process. By controlling the heating temperature to a set temperature and the heating time in the furnace to a set time during the pre-rolling heating process, the thickness of the furnace-born iron oxide scale is significantly reduced (the thickness of the furnace-born iron oxide scale is reduced by up to 33%), and the difference in light diffuse reflection caused by the directional growth of the zinc layer and the disordered growth of the surrounding zinc layer is avoided, thereby effectively improving the color difference defects on the surface of the electro-galvanized product.

[0037] As an implementation method of the embodiment of the present application, during the pre-rolling heating process, the set temperature is 950°C to 1150°C.

[0038] In the present application, during the heating process before rolling, the heating temperature of the continuous casting billet is controlled at 950-1150°C, and the thickness of the iron oxide skin layer in the heating furnace is reduced under the premise of ensuring heating uniformity. In some specific embodiments, during the heating process before rolling, the set temperature can be 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, 1100°C, 1150°C, etc.

[0039] As an implementation method of the embodiment of the present application, during the pre-rolling heating process, the set time is greater than 120 minutes.

[0040] In the present application, by further controlling the pre-rolling heating process, the setting time is set to > 120 min, so as to further ensure the heating uniformity and reduce the thickness of the iron oxide layer in the heating furnace. In some specific embodiments, the setting time can be 130 min, 150 min, 200 min, etc.

[0041] As an implementation method of the embodiment of the present application, the thickness of the iron oxide layer in the electro-galvanized sheet is 3 to 8 μm.

[0042] In the present application, the thickness of the iron oxide layer in the electro-galvanized sheet is 3 to 8 μm. Compared with the prior art, the thickness of the iron oxide layer is significantly reduced, avoiding the difference in diffuse reflection of light caused by the directional growth of the zinc layer and the disordered growth of the surrounding zinc layer, thereby effectively improving the surface color difference defects of the electro-galvanized product.

[0043] As an implementation method of the embodiment of the present application, the process parameters of the rough rolling include: the outlet temperature of the rough rolling is 800°C to 950°C.

[0044] In the present application, the function of controlling the rough rolling outlet temperature to 800-950°C is to reduce the secondary iron oxide scale pressure during the rough rolling process and avoid the increase of the thickness of the iron oxide scale layer. In some specific embodiments, the rough rolling outlet temperature can be 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, etc.

[0045] As an implementation of the embodiment of the present application, during the rough rolling process, full-pass descaling is used for descaling.

[0046] In the present application, full-pass descaling is used during the rough rolling process to further prevent the intrusion of secondary iron oxide scale during the rough rolling process and avoid the increase in the thickness of the iron oxide scale layer.

[0047] As an implementation method of the embodiment of the present application, the process parameters of the finishing rolling include: the final rolling temperature of the finishing rolling is 700°C to 850°C.

[0048] In the present application, the role of controlling the final rolling temperature at 700-850°C is to control the surface temperature of the strip and reduce the thickness of the oxide scale. In some specific embodiments, cooling water is added between at least two stands during the finishing rolling, and the final rolling temperature is controlled at 700-850°C. At the same time, the strip is rolled in the ferrite zone in the downstream stand of the finishing mill, and the finishing rolling F1-F7 stands are put into rolling lubrication, which is to reduce the shear stress between the strip and the working rolls and reduce the damage to the oxide film of the working rolls.

[0049] As an implementation of an embodiment of the present application, the coiling process parameters include: the coiling temperature is 580-650°C.

[0050] In the present application, in some specific embodiments, the coiling temperature can be selected according to the type of specific steel. For example, if the type of steel is a low-carbon steel component system steel, the coiling temperature can be 580°C, etc.

[0051] As an implementation method of an embodiment of the present application, the process parameters of the post-rolling cooling include: the terminal temperature of the post-rolling cooling is 550-680°C.

[0052] In this application, the strip is subjected to front-end centralized cooling after coiling, and the temperature is rapidly reduced to the range of 550-680°C, so that the thickness of the strip oxide skin layer is 3-8 μm, so that the surface temperature of the strip is rapidly reduced to the target temperature, and the thickness of the tertiary oxide skin is reduced. In this application, "front-end centralized cooling" specifically refers to the cooling water being added to reduce the temperature of the strip after the strip leaves the finishing mill.

[0053] As an implementation of an embodiment of the present application, the chemical composition system of the molten steel is a low-carbon steel composition system or an IF steel plate composition system.

[0054] In the present application, in some specific embodiments, the composition system of low carbon steel may be: C: 0.03%, Si: 0.003%, Mn: 0.20%, S: 0.009%, P: 0.08%, Al: 0.03%, and the rest is iron and residues. The composition system of IF steel plate may be: C: 0.002%, Si: 0.003%, Mn: 0.11%, S: 0.009%, P: 0.08%, Ti: 0.04%, and the rest is iron and residues. The above-mentioned "residues" are also called unavoidable impurities.

[0055] In summary, the embodiment of the present application provides a production method for controlling the color difference defects on the surface of electrogalvanized products. Molten steel is smelted to obtain continuous casting billets; the continuous casting billets are heated, rough rolled, finished rolled and coiled in a hot rolling production line to obtain hot rolled coils; and then pickling, cold rolling, annealing, leveling and electrogalvanizing are performed to obtain finished products.

[0056] The tapping temperature of the continuous casting billet is controlled at 950-1150°C, the furnace time is controlled at more than 120 minutes, and the thickness of the furnace-generated iron oxide scale is reduced by 33%. The rough rolling is carried out in the austenite zone, and full-pass descaling is adopted to reduce the generation of secondary iron oxide scale during high-temperature rolling. The rough rolling outlet temperature is controlled in the range of 800-950°C, and cooling water is put into at least two inter-frames for finishing rolling. The final rolling temperature is controlled at 700-850°C, and the strip is rolled in the ferrite zone in the downstream frame of finishing rolling. The strip is put into rolling lubrication in the finishing rolling F1-F7 frames to reduce the damage of the oxide film to the shear stress between the rollers and the strip. The strip after coiling adopts front-stage centralized cooling, which is quickly reduced to the range of 550-680°C, and the thickness of the strip iron oxide scale layer is obtained to be 3-8μm.

[0057] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0058] Example 1

[0059] This example provides a method for reducing the color difference defect on the surface of an electro-galvanized sheet, the method comprising: smelting molten steel to obtain a continuous casting billet; heating the continuous casting billet before rolling, rough rolling, finishing rolling, cooling after rolling and coiling to obtain a hot-rolled coil; pickling, cold rolling, annealing, leveling and electro-galvanizing the hot-rolled coil to obtain an electro-galvanized sheet. Specifically comprising the following steps:

[0060] Low carbon steel composition system is selected for production. The composition of typical steel grades is: C: 0.03%, Si: 0.003%, Mn: 0.20%, S: 0.009%, P: 0.08%, Al: 0.03%, and the rest is iron and residue. The slab thickness is 237mm, the heating time of the heating furnace is 160 minutes, and the steel tapping temperature is 1030℃. The rough rolling adopts the 3+3 mode, and the full pass descaling is adopted. The outlet temperature of the rough rolling R2 is 860℃; the finishing rolling F1~F7 is put into rolling lubrication, the inlet temperature is 820℃, the final rolling temperature is 720℃, and the cooling water between the F1, F2, F3, and F5 frames is put into; the laminar cooling adopts the front-stage centralized cooling process, and the coiling temperature is 580℃. 1,200 tons were produced this time, and the color difference defect degradation rate of the final electro-galvanized product was 0.3%.

[0061] The morphology of the iron oxide layer on the surface of the electrogalvanized sheet obtained in this example is shown in the figure Figure 2 As shown, the thickness of the iron oxide layer is 6 μm.

[0062] Example 2

[0063] This example provides a method for reducing the color difference defect on the surface of an electro-galvanized sheet, the method comprising: smelting molten steel to obtain a continuous casting billet; heating the continuous casting billet before rolling, rough rolling, finishing rolling, cooling after rolling and coiling to obtain a hot-rolled coil; pickling, cold rolling, annealing, leveling and electro-galvanizing the hot-rolled coil to obtain an electro-galvanized sheet. Specifically comprising the following steps:

[0064] The IF steel plate composition system is selected for production. The composition of typical steel grades is: C: 0.002%, Si: 0.003%, Mn: 0.11%, S: 0.009%, P: 0.08%, Ti: 0.04%, and the rest is iron and residue. The slab thickness is 237mm, the heating time in the heating furnace is 175 minutes, and the steel tapping temperature is 1050℃. The rough rolling adopts the 3+3 mode, and the full pass descaling is adopted. The outlet temperature of the rough rolling R2 is 890℃; the finishing rolling F1~F7 is put into rolling lubrication, the inlet temperature is 850℃, the final rolling temperature is 750℃, and the cooling water between the F1, F2, F3, and F5 frames is put into; the laminar cooling adopts the front-stage centralized cooling process, and the coiling temperature is 650℃. 800 tons were produced this time, and the color difference defect degradation rate of the final electrogalvanized product was 0.25%.

[0065] Comparative Example 1

[0066] Based on Example 1, this example provides a method for reducing the color difference defect on the surface of an electro-galvanized sheet, and the process parameters in the method are different in that:

[0067] Conventional production process is carried out using a low-carbon steel component system. The composition of typical steel grades is: C: 0.03%, Si: 0.003%, Mn: 0.20%, S: 0.009%, P: 0.08%, Al: 0.03%, and the rest is iron and residue. The slab thickness is 237mm, the heating time in the heating furnace is 200 minutes, and the steel tapping temperature is 1200℃. The rough rolling adopts the 3+3 mode, and 4 passes of descaling are used. The outlet temperature of the rough rolling R2 is 1060℃; the inlet temperature of the finishing rolling is 1050℃, the final rolling temperature is 890℃, and cooling water is added between the F1 and F2 frames; the laminar cooling adopts the front-stage centralized cooling process, and the coiling temperature is 650℃. This production is 1,000 tons, and the final electrogalvanized product color difference defect degradation rate is 8.5%.

[0068] The morphology of the iron oxide layer on the surface of the electrogalvanized sheet obtained in this example is shown in the figure Figure 3 As shown, the thickness of the iron oxide skin layer is 12 μm.

[0069] Comparative Example 2

[0070] Based on Example 2, this example provides a method for reducing the color difference defect on the surface of an electro-galvanized sheet, and the process parameters in the method are different in that:

[0071] The IF steel plate composition system is selected for conventional production. The composition of typical steel grades is: C: 0.002%, Si: 0.003%, Mn: 0.11%, S: 0.009%, P: 0.08%, Ti: 0.04%, and the rest is iron and residue. The slab thickness is 237mm, the heating time in the heating furnace is 210 minutes, and the steel tapping temperature is 1220℃. The rough rolling adopts the 3+3 mode, and 4 passes are used for descaling. The outlet temperature of the rough rolling R2 is 1070℃; the entrance temperature of the finishing rolling is 1060℃, the final rolling temperature is 930℃, and cooling water is added between the F1 and F2 frames; the laminar cooling adopts the front-stage centralized cooling process, and the coiling temperature is 710℃. 1,500 tons were produced this time, and the color difference defect degradation rate of the final electrogalvanized product was 12%.

[0072] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0073] In the present application, in the absence of any contrary description, the directional words used, such as "upper" and "lower", are specifically the directions of the drawings in the accompanying drawings. In addition, in the description of the present specification, the terms "including", "comprising", etc. refer to "including but not limited to". In this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of the associated objects, indicating that there may be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A, B can be singular or plural. In this article, "at least one" refers to one or more, and "plural" refers to two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0074] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for reducing the color difference defect on the surface of an electro-galvanized sheet, characterized in that: The method comprises: Smelting the molten steel to obtain continuous casting billets; The continuous casting slab is subjected to pre-rolling heating, rough rolling, finish rolling, post-rolling cooling and coiling to obtain a hot-rolled coil; The hot-rolled coil is pickled, cold-rolled, annealed, flattened and electro-galvanized to obtain an electro-galvanized sheet; During the pre-rolling heating process, the heating temperature is controlled to be 950°C to 1150°C, and the furnace heating time is controlled to be greater than 120 minutes; The outlet temperature of the rough rolling is 800°C to 950°C. During the rough rolling process, full-pass descaling is used for descaling. At least two inter-stand cooling waters are used for finishing rolling, and the final rolling temperature is controlled at 700-850℃. At the same time, the strip is rolled in the ferrite zone in the downstream stand of the finishing mill, and the finishing rolling stands F1 to F7 are put into rolling lubrication; The chemical composition of the molten steel is: C: 0.03%, Si: 0.003%, Mn: 0.20%, S: 0.009%, P: 0.08%, Al: 0.03%, and the rest are iron and inevitable impurities; or C: 0.002%, Si: 0.003%, Mn: 0.11%, S: 0.009%, P: 0.08%, Ti: 0.04%, and the rest are iron and inevitable impurities.

2. The method for reducing the color difference defect on the surface of the electro-galvanized sheet according to claim 1, characterized in that: The thickness of the iron oxide layer in the electrogalvanized sheet is 3 to 8 μm.

3. The method for reducing the color difference defect on the surface of the electro-galvanized sheet according to claim 1, characterized in that: The coiling process parameters include: the coiling temperature is 580-650°C.

4. The method for reducing the color difference defect on the surface of the electro-galvanized sheet according to claim 1, characterized in that: The process parameters of the post-rolling cooling include: the terminal temperature of the post-rolling cooling is 550-680°C.

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