Method for solving surface color difference of electrogalvanized steel sheet

Abstract

The application provides a method for solving surface color difference of electro-galvanized steel plate, and belongs to the technical field of steel rolling. The method comprises the following steps: in the heating stage, the slab is subjected to segmented heating at a set temperature for a set time, so that the surface and middle temperature of the slab are stabilized; and in the finishing rolling stage, the slab is subjected to finishing rolling at a set finishing rolling inlet temperature and a set finishing rolling rolling speed, so that the pure rolling time in the finishing rolling stage is reduced. The method is scientific, effective, simple to operate and high in economy, and can easily solve the surface strip-shaped color difference of low-IF steel after electro-galvanizing without increasing equipment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rolling steel, in particular to a method for solving surface color difference of electro-galvanized steel plate. BACKGROUND

[0002] Electro-galvanizing is a widely used anticorrosion technology for steel and iron, which has good protection performance, low price, and convenient operation, and is easy to implement in the electroplating process. In recent years, electro-galvanized steel plate, after being treated by electro-galvanizing and organic resin coating, is directly used as a surface treatment steel plate with good corrosion resistance and fingerprint resistance.

[0003] However, electro-galvanized steel plate is prone to form visible color difference defects, which can be reflected even after being coated with organic resin. SUMMARY

[0004] The embodiments of the present application provide a method for solving surface color difference of electro-galvanized steel plate, so as to solve the technical problem that the existing electro-galvanized steel plate production process is prone to produce color difference defects.

[0005] In a first aspect, the embodiments of the present application provide a method for solving surface color difference of electro-galvanized steel plate, which comprises:

[0006] In the heating stage, the slab is subjected to segmented heating at a set temperature for a set time, so as to stabilize the surface and middle temperature of the slab.

[0007] In the finishing rolling stage, the slab is subjected to finishing rolling at a set finishing rolling inlet temperature and a set finishing rolling rolling speed, so as to reduce the pure rolling time in the finishing rolling stage.

[0008] Further, the set temperature is 1180-1210℃, and the set time is 160-180min.

[0009] Further, the set finishing rolling inlet temperature is 1030-1040℃, and the set finishing rolling rolling speed is 8-10m / s.

[0010] Further,

[0011] The segmented heating comprises a preheating section, a first heating section, a second heating section, and a soaking section, wherein the preheating section and the first heating section respectively adopt an oxidizing gas atmosphere, and the air-fuel ratio is 1.1-1.2; the temperature of the preheating section is ≤900℃, and the temperature of the first heating section is ≤1100℃; and / or

[0012] The second heating section and the soaking section respectively adopt a reducing gas atmosphere, and the air-fuel ratio is 0.9-1.0; the temperature t1 of the second heating section and the temperature t2 of the soaking section satisfy the relationship: t2-t1≥20℃.

[0013] Further, the temperature of the first plus section is 920-980 DEG C, and the time is 30-40 min; and / or

[0014] The temperature of the second plus section is 1140-1180 DEG C, and the time is 10-20 min; and / or

[0015] The temperature of the soaking section is 1180-1210 DEG C, and the time is 30-40 min; and / or

[0016] The time of the preheating section is 60-80 min.

[0017] Further, the finish rolling temperature of the finish rolling stage is 900-920 DEG C.

[0018] Further, in the finish rolling stage, the slab is finish rolled under the condition of the set finish rolling inlet temperature and the set finish rolling rolling speed to reduce the pure rolling time of the finish rolling stage, comprising:

[0019] In the finish rolling stage, the slab is finish rolled under the condition of the set finish rolling inlet temperature and the set finish rolling rolling speed to reduce the pure rolling time of the finish rolling stage, and rolling lubricating oil is put into rolling to establish a lubricating film.

[0020] Further, the amount of the rolling lubricating oil is 0.25-0.3 kg / ton.

[0021] Further, the method further comprises:

[0022] In the rough rolling stage, the slab is rolled by R1 pass and R2 five passes, and rough scale removal is performed in the 1st, 3rd and 5th rolling processes of R2.

[0023] In the finish rolling stage, double-pass scale removal is performed on the slab at the finish rolling inlet.

[0024] Further, the method further comprises:

[0025] In the layer cooling stage, the cooling speed is controlled to be 70-100 DEG C / s to reduce the high-temperature residence time of the layer cooling section;

[0026] In the coiling stage, the coiling temperature is controlled to be 630-650 DEG C, and after coiling, air cooling or water cooling mode is used for cooling.

[0027] Further, the chemical composition of the slab is as follows in terms of percentage by weight: C: 0.0015-0.002%, Al: 0.02-0.05%, Mn: 0.1-0.2%, Si: 0.05-0.07%, Ti: 0.06-0.08%, and the balance is Fe and inevitable impurity elements.

[0028] The above technical solution provided by the embodiment of the application has the following advantages compared with the prior art:

[0029] The method for solving the color difference of the electro-galvanized steel plate provided by the embodiment of the application controls the heating temperature and the heating time of the plate blank, so that the surface and the middle part of the plate blank are stable in temperature, thereby avoiding the generation of a large amount of iron oxide scale in the heating process under the premise of ensuring that the plate blank is burned through, thereby reducing the total thickness of the scale of the heating furnace; the inlet temperature and the rolling speed of the finish rolling are controlled, and the pure rolling time in the finish rolling stage is reduced, so that the problem of scale crushing and pressing is avoided. Therefore, the method can reduce the thickness of the oxidized scale, avoid scale pressing, ensure the uniformity of the scale, and thereby solve the problem of the color difference of the surface of the electro-galvanized steel plate. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the accompanying drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, for those skilled in the art, other drawings can also be obtained based on these drawings without any creative labor.

[0032] Figure 1 Macroscopic morphology of color difference of electro-galvanized strip;

[0033] Figure 2 Growth morphology of abnormal zinc layer on the outer side after electro-galvanizing of electro-galvanized zinc;

[0034] Figure 3 Growth morphology of abnormal zinc layer on the inner side after electro-galvanizing of electro-galvanized zinc;

[0035] Figure 4 Surface defect condition of electro-galvanized zinc substrate;

[0036] Figure 5 Observation condition of electro-galvanized zinc surface after pickling;

[0037] Figure 6 Analysis condition of continuous oxidation characteristics of electro-galvanized steel;

[0038] Figure 7 Influence of rolling lubrication input on the three-dimensional morphology and interface roughness of the electro-galvanized surface;

[0039] Figure 8 Growth morphology of the zinc layer after electro-galvanizing of the electro-galvanized zinc obtained in Embodiment 1 of the application. DETAILED DESCRIPTION

[0040] To make the objects, technical solutions, and advantages of the embodiments of the present application clearer, the following will briefly describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of the present application.

[0041] Electro-galvanizing is a widely used anticorrosion technology for steel and iron, which has good protection performance, low price, and convenient operation, and the electroplating process is easy to implement. In recent years, electro-galvanized steel plates, after galvanizing treatment and organic resin coating treatment, are directly used as surface treatment steel plates with good corrosion resistance and fingerprint resistance.

[0042] However, electro-galvanized steel plates are prone to form visually observable color difference defects, which can be reflected even after being coated with organic resin.

[0043] In view of this, the present application provides a method for solving the color difference of the surface of an electro-galvanized steel plate, which can effectively solve the above problems existing in the production process of the electro-galvanized steel plate.

[0044] The technical solution provided by the embodiments of the present application is to solve the above technical problems, and the general idea is as follows:

[0045] In a first aspect, the embodiments of the present application provide a method for solving the color difference of the surface of an electro-galvanized steel plate, which comprises:

[0046] In the heating stage, the slab is subjected to segmented heating at a set temperature for a set time to stabilize the surface and middle temperature of the slab.

[0047] In the finishing rolling stage, the slab is subjected to finishing rolling at a set finishing rolling inlet temperature and a set finishing rolling rolling speed to reduce the pure rolling time in the finishing rolling stage.

[0048] The method for solving the color difference of the surface of an electro-galvanized steel plate provided by the embodiments of the present application stabilizes the surface and middle temperature of the slab by controlling the heating temperature and heating time of the slab, thereby avoiding the generation of a large amount of oxide scale in the heating process under the premise of ensuring that the slab is fully burned, reducing the overall thickness of the scale in the heating furnace, and reducing the thickness of the oxide scale, avoiding scale indentation, and ensuring the uniformity of the scale, thereby solving the color difference problem of the surface of the electro-galvanized steel plate.

[0049] As an embodiment of the present application, the set temperature is 1180-1210℃, and the set time is 160-180min.

[0050] In the application, by controlling the tapping temperature and heating time, the billet can be prevented from generating a large amount of iron scale in the heating process under the premise of being burnt through, and the coarse precipitates formed in the continuous casting process are also prevented from dissolving.

[0051] In an embodiment of the application, the finish rolling inlet temperature is set to 1030-1040 DEG C, and the finish rolling speed is set to 8-10 m / s.

[0052] In the application, by controlling the finish rolling inlet temperature, the finish rolling inlet temperature can be kept away from the position of the peak of the oxidation weight gain rate of the iron scale, which is beneficial to reducing the proportion of Fe2O3 and Fe3O4, reducing the wear of the roll and reducing the thickness of the scale.

[0053] In an embodiment of the application,

[0054] The preheating section and the first heating section adopt an oxidizing gas atmosphere, and the air-fuel ratio is 1.1-1.2; the temperature of the preheating section is ≤900 DEG C, and the temperature of the first heating section is ≤1100 DEG C; and / or

[0055] The second heating section and the soaking section adopt a reducing gas atmosphere, and the air-fuel ratio is 0.9-1.0; the temperature t1 of the second heating section and the temperature t2 of the soaking section satisfy the relationship: t2-t1≥20 DEG C.

[0056] In the application, the main function of the segmented heating is to make the slab reach a certain temperature, ensure the dissolution of precipitates and austenitization, and ensure the stability of the surface and the middle part of the slab. The gradient control of the soaking temperature and the second heating temperature can realize the differentiation of the slab shell and the slab core. If the difference between the second heating temperature and the soaking temperature is too low, the gas flow of the soaking section of the heating furnace will be small, the surface temperature of the slab will not increase, and on the contrary, the edge temperature at the furnace door will decrease. Controlling the appropriate range of the difference between the soaking temperature and the second heating temperature ≥20 DEG C can improve the gas flow of the soaking section, and fully utilize the heating capacity of the soaking section to ensure the surface temperature of the slab. By controlling the atmosphere and the air-fuel ratio of the second heating section and the soaking section, the billet can be prevented from generating a large amount of iron scale in the heating process under the premise of being burnt through, and the coarse precipitates formed in the continuous casting process are also prevented from dissolving.

[0057] In an embodiment of the application, the slab adopts hot charging technology to control the surface temperature to be 300-400 DEG C in the heating stage; the preheating section and the first heating section adopt an oxidizing atmosphere, and the air-fuel ratio is 1.1-1.2; the temperature of the preheating section is ≤900 DEG C, and the temperature of the first heating section is ≤1100 DEG C.

[0058] As an embodiment of the present application, the temperature of the first heating section is 920-980℃, and the time is 30-40min; and / or

[0059] The temperature of the second heating section is 1140-1180℃, and the time is 10-20min; and / or

[0060] The temperature of the soaking section is 1180-1210℃, and the time is 30-40min; and / or

[0061] The time of the preheating section is 60-80min.

[0062] In the present application, by increasing the heating rate of the first heating section, the heat load is increased from 60% to 80%, and the heat load of the second heating section is decreased from 75% to 60%, so that the heating load is moved forward, and the effect of low-temperature fast burning of the slab is achieved. The heating rate of the second heating section is slowed down, and the comprehensive radiation coefficient is appropriately reduced, so that the heating uniformity can be improved. The low-temperature heating mode is adopted in the present application, which is green and environmentally friendly, and at the same time, the total thickness of the iron skin of the heating furnace can be reduced, so that the subsequent descaling effect is ensured. By controlling the time of the soaking section, the difference between the surface temperature and the center of the slab can be avoided, and thus the temperature uniformity of the slab is weakened.

[0063] As an embodiment of the present application, the finish rolling temperature of the finish rolling is 900-920℃.

[0064] As an embodiment of the present application, in the finish rolling stage, the slab is finish rolled under the condition of the set finish rolling inlet temperature and the set finish rolling rolling speed, so as to reduce the pure rolling time in the finish rolling stage, which comprises:

[0065] In the finish rolling stage, the slab is finish rolled under the condition of the set finish rolling inlet temperature and the set finish rolling rolling speed, so as to reduce the pure rolling time in the finish rolling stage, and rolling lubricating oil is put in, so as to establish a lubricating film.

[0066] In the present application, the purpose of putting in the rolling lubricating oil is to reduce the influence of the shear forming of the Goss texture in the hot rolling process on the subsequent cold rolling and annealing.

[0067] As an embodiment of the present application, the amount of the rolling lubricating oil is 0.25-0.3kg / ton.

[0068] In the present application, the amount of the rolling lubricating oil per ton of steel material is 0.25-0.3kg, the rolling lubrication is not complete, and the lubricating film cannot be effectively established, and too much rolling lubricating oil is easy to cause the problem of mill slip.

[0069] As an embodiment of the present application, the method further comprises:

[0070] In the rough rolling stage, the slab is subjected to R1 pass rolling and R2 five-pass rolling, and rough descaling is carried out during the 1st, 3rd and 5th rolling of R2;

[0071] In the finishing rolling stage, the slab is subjected to double-pass descaling at the entrance of the finishing rolling;

[0072] In the layer cooling stage, the cooling rate is controlled to be 70-100℃ / s to reduce the high-temperature residence time in the layer cooling section;

[0073] In the coiling stage, the coiling temperature is controlled to be 630-650℃, and after coiling, air cooling or water cooling mode is used for cooling.

[0074] In the present application, the multi-pass rough descaling and the double-pass descaling at the entrance of the finishing rolling can ensure the completeness of the removal of the iron scale in the rough rolling process, ensure that there is no residual iron scale, avoid the incomplete removal of the iron scale to cause the surface iron scale to be left and pressed in, and further affect the directionality of the zinc layer growth in the electro-galvanizing process. The ultra-fast cooling mode is used in the layer cooling process, the cooling rate of which can reduce the high-temperature residence time in the layer cooling section, ensure the casting speed, and reduce the oxidation time in the layer cooling process. By reducing the coiling temperature, the thickness of the iron scale after hot rolling can be further reduced, and the problems of the over-thick growth and peeling of the iron scale after coiling and the pressing in can be prevented. By using air cooling and water cooling, the cooling rate can be improved, the steel coil can be prevented from staying in the high-temperature section for a long time, the problem of the over-thick iron scale after hot rolling can be avoided, and the problems of the peeling and pressing in of the iron scale and the incomplete pickling after cold rolling can be avoided, which affect the surface quality after cold rolling.

[0075] As an embodiment of the present application, the chemical composition of the slab is as follows in terms of weight percentage: C: 0.0015-0.002%, Al: 0.02-0.05%, Mn: 0.1-0.2%, Si: 0.05-0.07%, Ti: 0.06-0.08%, and the balance being Fe and inevitable impurity elements.

[0076] In the present application, the control range of the C element in the IF steel composition meets the requirement of mechanical properties, the addition of the TI element is mainly to fix the C\N atoms by using the TI to meet the requirement of deep drawing performance, and the yield strength is controlled to be between 90-110MPa, and A80 is between 45-50%.

[0077] The growth rate of the oxide film of the IF steel is relatively fast due to the absence of obvious addition of alloy elements, and the increase of the adhesion of the iron scale is beneficial to avoiding the pressing in of the iron scale. The Si element can effectively increase the adhesion of the iron scale, and with the increase of the Si content of the steel matrix, the oxidation weight gain of the material rapidly decreases; when the Si content is ≥0.05%, the change tends to be stable, and in the present application, the Si content is added to be 0.03-0.05%, which is beneficial to avoiding the occurrence of the pressing in of the iron scale.

[0078] The application will be further described in connection with the following specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. The experimental methods in the following examples, if no specific conditions are noted, are generally determined according to the national standards. If there is no corresponding national standard, the international standard, the conventional condition, or the condition suggested by the manufacturer is used.

[0079] Example 1

[0080] The present embodiment provides a method for solving the surface color difference of electro-galvanized steel plate, and a flowchart thereof is shown in Figure 2 as shown, specifically comprising:

[0081] (1) Steel smelting: when the steel is smelted into a slab, the chemical elements of the steel are as follows in terms of percentage by weight: C: 0.0017%, Al: 0.035%, Mn: 0.15%, Si: 0.06%, Ti: 0.07%, and the balance is Fe and unavoidable impurity elements;

[0082] (2) Slab heating: the hot charging technology is used to control the slab surface temperature to be 350℃, and then the four-stage heating mode is used for heating, wherein the preheating stage uses the oxidizing atmosphere, the air-fuel ratio is 1.15, the preheating stage temperature is 800℃, and the time is 75min; the first heating stage uses the oxidizing atmosphere, the air-fuel ratio is 1.15, the first heating stage temperature is 950℃, and the time is 35min; the second heating stage uses the reducing atmosphere, the air-fuel ratio is 0.95, the second heating stage temperature is 1160℃, and the time is 20min; the soaking stage uses the reducing atmosphere, the air-fuel ratio is 0.95, the soaking stage temperature is 1183℃, and the time is 35min;

[0083] (3) Slab rough rolling: after the slab is heated, the 1+5 rolling mode of R1 one-pass rolling and R2 five-pass rolling is used for rough rolling, and the rough scale removal is started at the 1st, 3rd and 5th passes of R2 to remove the furnace-born scale;

[0084] (4) Slab finish rolling: after the slab is rough rolled, the finish rolling is performed, wherein the finish rolling inlet temperature is 1035℃, the finish rolling double-pass scale removal is started, the finish rolling rolling speed is 9.5m / s to reduce the pure rolling time in the finish rolling process; the rolling lubrication is started, and the rolling lubricating oil is 0.28kg / ton; and the finish rolling temperature is 910℃;

[0085] (5) Slab layer cooling: the slab after the finish rolling is layer cooled at a cooling speed of 80℃ / s to reduce the high-temperature residence time in the layer cooling stage;

[0086] (6) Slab coiling: the slab after the layer cooling is coiled at 640℃, and the air cooling or water cooling mode is used for cooling after coiling.

[0087] Example 2

[0088] The embodiment provides a method for solving surface color difference of electroplated zinc steel plate, a flowchart is shown in the figure, and the method specifically comprises the following steps: Figure 2

[0089] (1) Steel smelting: when steel is smelted into a slab, the steel chemical elements are as follows in percentage by weight: C: 0.0015%, Al: 0.02%, Mn: 0.1%, Si: 0.05%, Ti: 0.06%, and the balance is Fe and inevitable impurity elements;

[0090] (2) Slab heating: the slab surface temperature is controlled to be 300 DEG C by adopting a hot delivery technology, and then four-stage heating modes are adopted for heating, wherein, the preheating stage adopts an oxidizing atmosphere, the air-fuel ratio is 1.1, the preheating stage temperature is 850 DEG C, and the time is 60 min; the first heating stage adopts an oxidizing atmosphere, the air-fuel ratio is 1.1, the first heating stage temperature is 920 DEG C, and the time is 40 min; the second heating stage adopts a reducing atmosphere, the air-fuel ratio is 0.9, the second heating stage temperature is 1140 DEG C, and the time is 20 min; the soaking stage adopts a reducing atmosphere, the air-fuel ratio is 0.9, the soaking stage temperature is 1180 DEG C, and the time is 40 min;

[0091] (3) Slab rough rolling: after the slab is heated, the 1+5 rolling mode of R1 one-pass rolling and R2 five-pass rolling is adopted for rough rolling, and the rough scale removal is started in the 1st, 3rd and 5th passes of R2;

[0092] (4) Slab finish rolling: after the slab is rough rolled, finish rolling is carried out, wherein, the finish rolling inlet temperature is 1030 DEG C, the double-pass scale removal is started in the finish rolling, the finish rolling rolling speed is 8 m / s, so as to reduce the pure rolling time in the finish rolling process; the rolling lubrication is started, and 0.3 kg / ton of rolling lubricating oil is put in; and the finish rolling temperature is 900 DEG C;

[0093] (5) Slab layer cooling: the slab after the finish rolling is subjected to layer cooling at a cooling speed of 70 DEG C / s, so as to reduce the high-temperature residence time in the layer cooling stage;

[0094] (6) Slab coiling: the slab after the layer cooling is coiled at 630 DEG C, and the air cooling or water cooling mode is adopted for cooling after the coiling.

[0095] Embodiment 3

[0096] The embodiment provides a method for solving surface color difference of electroplated zinc steel plate, a flowchart is shown in the figure, and the method specifically comprises the following steps: Figure 2

[0097] (1) Steel smelting: when steel is smelted into a slab, the steel chemical elements are as follows in percentage by weight: C: 0.002%, Al: 0.05%, Mn: 0.2%, Si: 0.07%, Ti: 0.08%, and the balance is Fe and inevitable impurity elements; ​​

[0098] (2) Slab heating: The surface temperature of the slab is controlled to be 400°C by using hot charging technology, and then the slab is heated by using a four-stage heating mode. In the preheating stage, an oxidizing atmosphere is used, the air-fuel ratio is 1.2, the preheating stage temperature is 880°C, and the time is 80 min. In the first heating stage, an oxidizing atmosphere is used, the air-fuel ratio is 1.2, the first heating stage temperature is 980°C, and the time is 40 min. In the second heating stage, a reducing atmosphere is used, the air-fuel ratio is 1.0, the second heating stage temperature is 1180°C, and the time is 20 min. In the soaking stage, a reducing atmosphere is used, the air-fuel ratio is 1.0, the soaking stage temperature is 1210°C, and the time is 40 min.

[0099] (3) Slab rough rolling: After the slab is heated, the slab is rough-rolled by using a 1+5 rolling mode of R1 one-pass rolling and R2 five-pass rolling, and the rough scale removal is started in the 1st, 3rd and 5th passes of R2 to remove the furnace-born scale.

[0100] (4) Slab finish rolling: After the slab is rough-rolled, the slab is finish-rolled, in which the finish rolling inlet temperature is 1040°C, the double-pass scale removal is started in the finish rolling, the finish rolling rolling speed is 10 m / s to reduce the pure rolling time in the finish rolling, the rolling lubrication is started, and 0.3 kg / ton of rolling lubricating oil is added, and the finish rolling temperature is 920°C.

[0101] (5) Slab layer cooling: The slab after finish rolling is layer-cooled at a cooling rate of 100°C / s to reduce the high-temperature residence time in the layer cooling stage.

[0102] (6) Slab coiling: The slab after layer cooling is coiled at 650°C, and then the slab is cooled by using air cooling or water cooling mode after coiling.

[0103] Example 4

[0104] The embodiment provides a method for solving the surface color difference of a galvanized steel plate, a flowchart of which is shown in Figure 2 , and specifically comprises the following steps:

[0105] (1) Steel smelting: when the steel is smelted into a slab, the chemical elements of the steel are as follows in terms of percentage by weight: C: 0.0018%, Al: 0.04%, Mn: 0.18%, Si: 0.06%, Ti: 0.07%, and the balance is Fe and inevitable impurity elements;

[0106] (2) Slab heating: the hot charging technology is used to control the slab surface temperature to be 380℃, and then the four-stage heating mode is used for heating, wherein the preheating stage uses the oxidizing atmosphere, the air-fuel ratio is 1.17, the preheating stage temperature is within 890℃, and the time is 80min; the first heating stage uses the oxidizing atmosphere, the air-fuel ratio is 1.17, the first heating stage temperature is 950℃, and the time is 30min; the second heating stage uses the reducing atmosphere, the air-fuel ratio is 0.95, the second heating stage temperature is 1160℃, and the time is 20min; the soaking stage uses the reducing atmosphere, the air-fuel ratio is 0.95, the soaking stage temperature is 1195℃, and the time is 30min;

[0107] (3) Slab rough rolling: after the slab heating, the 1+5 rolling mode of R1 one-pass rolling and R2 five-pass rolling is used for rough rolling, and the rough scale removal is started in the 1st, 3rd and 5th passes of R2 to remove the furnace-born scale;

[0108] (4) Slab finish rolling: after the slab rough rolling, the finish rolling is performed, wherein the finish rolling inlet temperature is 1030-1040℃, the finish rolling double-pass scale removal is started, the finish rolling rolling speed is 9m / s to reduce the pure rolling time in the finish rolling process, the rolling lubrication is started, and the rolling lubricating oil 0.25kg / ton is put in; and the final rolling temperature is 910℃;

[0109] (5) Slab layer cooling: the slab after the finish rolling is subjected to the layer cooling at the cooling speed of 85℃ / s to reduce the high-temperature residence time in the layer cooling stage;

[0110] (6) Slab coiling: the slab after the layer cooling is coiled at 640℃, and the air cooling or water cooling mode is used for cooling after the coiling.

[0111] Example 5

[0112] The embodiment provides a method for solving the surface color difference of the galvanized steel plate, a flowchart thereof is shown in Figure 2 , and specifically, the method comprises the following steps:

[0113] (1) Steel smelting: when the steel is smelted into a slab, the steel chemical elements are as follows in terms of percentage by weight: C: 0.0017%, Al: 0.035%, Mn: 0.15%, Si: 0.06%, Ti: 0.07%, and the balance is Fe and inevitable impurity elements;

[0114] (2) Slab heating: the hot charging technology is used to control the slab surface temperature to be 350℃, and then four-stage heating mode is used for heating, wherein, the preheating stage uses oxidizing atmosphere, the air-fuel ratio is 1.15, the preheating stage temperature is 800℃, and the time is 700min; the first heating stage uses oxidizing atmosphere, the air-fuel ratio is 1.15, the first heating stage temperature is 950℃, and the time is 30min; the second heating stage uses reducing atmosphere, the air-fuel ratio is 0.95, the second heating stage temperature is 1160℃, and the time is 20min; the soaking stage uses reducing atmosphere, the air-fuel ratio is 0.95, the soaking stage temperature is 1195℃, and the time is 40min;

[0115] (3) Slab rough rolling: after the slab heating, the 1+5 rolling mode of R1 one-pass rolling and R2 five-pass rolling is used for rough rolling, and the rough scale removal is started in the 1st, 3rd and 5th passes of R2 to remove the furnace-born scale;

[0116] (4) Slab finish rolling: after the slab rough rolling, the finish rolling is carried out, wherein, the finish rolling inlet temperature is 1035℃, the finish rolling double-pass scale removal is started, the finish rolling rolling speed is 9.5m / s to reduce the pure rolling time in the finish rolling process; the rolling lubrication is started, and the rolling lubricating oil 0.3kg / ton is put in; the finish rolling temperature is 910℃;

[0117] (5) Slab layer cooling: the slab after the finish rolling is subjected to the layer cooling at the cooling speed of 80℃ / s to reduce the high-temperature residence time in the layer cooling stage;

[0118] (6) Slab coiling: the slab after the layer cooling is coiled at 640℃, and the air cooling or water cooling mode is used for cooling after the coiling.

[0119] Comparative Example 1

[0120] In the example 1, the soaking stage temperature is changed to 1250℃, the preheating stage time is changed to 90min, the first heating stage time is changed to 50min, the second heating stage time is changed to 30min, the soaking stage time is changed to 50min, the finish rolling temperature is changed to 930℃, the layer cooling speed is changed to 30℃ / s, the coiling temperature is changed to 720℃, and the rest is the same as the example 1.

[0121] Comparative Example 2

[0122] In the example 1, the rolling lubricating oil flow is changed to 0kg / ton, the layer cooling speed is changed to 40℃ / s, the coiling temperature is changed to 710℃, and the rest is the same as the example 1.

[0123] Comparative Example 3

[0124] The following changes were made to Example 1: the soaking zone temperature was changed to 1270℃, the preheating zone time was changed to 90min, the first heating zone time was changed to 50min, the second heating zone time was changed to 40min, the soaking zone time was changed to 50min, the final rolling temperature was changed to 930℃, the rolling lubricating oil flow rate was changed to 0.1kg / ton, the layer cooling rate was changed to 30℃ / s, and the coiling temperature was changed to 710℃. The rest were the same as in Example 1.

[0125] Comparative Example 4

[0126] The rolling lubricating oil in Example 1 is not turned on; otherwise, it is the same as in Example 1.

[0127] Figure 1 The macroscopic morphological characteristics of color difference in electroplated zinc strips are determined by... Figure 1 It can be seen that after electro-galvanizing, there are striped color differences on the surface, with a width of less than 2mm, exhibiting a striped morphological characteristic.

[0128] Figure 2 This refers to the abnormal growth morphology of the outer zinc layer after electroplating, caused by... Figure 2 It can be seen that the zinc layer surface within the defect exhibits a porous and rough morphology. Magnified surface observation and analysis revealed a granular morphology of the zinc layer, slightly poor surface flatness, and a difference in the zinc layer growth state compared to the surrounding area. In normal locations, the zinc layer growth direction is characterized by zinc particles arranged in flakes with a certain orientation, while in defective locations, the zinc layer growth direction is perpendicular to the substrate direction.

[0129] The surface layer of the zinc layer was removed using dilute hydrochloric acid, resulting in an abnormal growth morphology of the inner zinc layer after electroplating, as shown below. Figure 3 As shown, the growth of the inner zinc layer is inconsistent, and the preferential growth area shows obvious large-scale oblique growth morphology.

[0130] The surface condition of the substrate after complete removal of the zinc layer is shown below, along with the surface defects. Figure 4 As shown, after removing the zinc layer with a solution, the surface of the substrate exhibits numerous pits at the defect locations, and particulate matter remains on the substrate surface. Energy dispersive spectroscopy (EDS) analysis reveals the presence of Fe and O elements, with O content ranging from 1% to 5%.

[0131] Therefore, the mechanism of color difference defects in electroplated zinc is as follows: Color difference defects in electroplated zinc are mainly caused by the difference in diffuse light reflection resulting from the directional growth of the zinc layer and the disordered growth of the surrounding zinc layer. The difference in zinc layer growth orientation originates from oxide particles adhering to the substrate surface, which inhibits the epitaxial growth of zinc crystals, alters the crystal growth morphology, and causes a preferential growth pattern at the location of adhesion defects, resulting in coarse and non-dense laminations.

[0132] According to the morphology analysis of the defects, the defects are neither caused by the large-area linden-shaped iron sheet due to the primary iron sheet pressing nor caused by the landscape painting-shaped defects due to the secondary iron sheet pressing, and the key point of the defect formation is the uniformity of the three-time iron sheet pressing in the finish rolling process and the four-time iron sheet formation after coiling.

[0133] Figure 6 For the analysis of the continuous oxidation characteristics of the steel grade, the situation is shown in Table 1. Figure 6 As can be seen, the oxidation weight gain of the steel grade begins to increase at 700°C, the first oxidation weight gain rate peak appears near 910°C, the second peak appears near 1050°C, and then the sample continues to oxidize as the temperature increases, and the oxidation weight gain rate reaches the maximum value at 1150°C, and then the oxidation weight gain rate slows down. As can be seen, controlling the surface temperature of the finish rolling process to avoid the position of the oxidation weight gain rate peak is beneficial to reducing the thickness of the surface oxide film and avoiding the risk of cracking and pressing the surface during the rolling process due to the over-thick oxide film.

[0134] It is found through the comparison of Example 1 and Comparative Example 4 that when the rolling lubrication is not put into the rolling, the average thickness of the iron sheet on the upper surface of the electro-galvanized steel sheet is 7.59 μm, and the average thickness of the iron sheet on the lower surface is 7.63 μm; after the rolling lubrication is put into the rolling, the thickness of the upper surface is 7.22 μm, and the thickness of the lower surface is 6.78 μm. The thickness of the upper surface iron sheet is reduced by 4.8%, and the thickness of the lower surface is reduced by 11.2%. It is found through the comparison of the cross-sectional structure of the iron sheet that the average roughness is 1.38 μm when the rolling lubrication is not turned on, and the average roughness is 1.55 μm when the rolling lubrication is turned on. However, after the rolling lubrication is turned on, the standard deviation of the roughness data set decreases by 60.75%, and the surface uniformity is obviously improved, as shown in Table 1. Figure 7

[0135] During annealing, preferential nucleation and selective growth of grains occur, and during grain recrystallization, the {111} plane texture formed by cold rolling preferentially nucleates and grows, and the {001} <110> texture gradually changes to the {111} <110> texture. With the completion of annealing, the {001} <110> rotating cubic texture and the {100} fiber texture on the surface decrease to a certain extent, and the proportion of the {001} <110> texture decreases from 39% of the cold hard plate to 9.84% of the continuous annealing coil, and the proportion of the {100} texture decreases from 58.9% of the cold hard plate to 19.12% of the continuous annealing coil. It is found through comparison that the rolling lubrication turned on still has an effect on the {111} / {100} texture proportion of the surface layer of the finished product, and the {111} / {100} texture proportion of the surface layer of the finished product is 0.57 when the rolling lubrication is turned off, and the {111} / {100} texture proportion of the surface layer of the finished product is 1.64 when the rolling lubrication is turned on. As shown in Table 1, the increase of the {111} texture proportion is more conducive to the formation of the electro-galvanized layer without color difference after electro-galvanizing.

[0136] Table 1 Effect of rolling lubrication turned on on the change of the surface texture proportion of the continuous annealing plate

[0137] ​

[0138]

[0139] The surface color difference of the electro-galvanized zinc steel plate produced by the embodiments of the present application and the comparative examples was tested, and the results are shown in Table 2.

[0140] Table 2 Surface color difference ratio of electro-galvanized zinc steel plate

[0141]

[0142] In summary, the method for solving the surface color difference of the electro-galvanized zinc steel plate provided by the present application is scientific and effective, simple to operate, and highly economical and efficient, and can easily solve the surface strip-shaped color difference of the low-IF steel after electro-galvanizing without increasing equipment. After the embodiments of the present application are implemented, no obvious color difference defects occur after electro-galvanizing, and the electro-galvanized zinc layer grows as shown in Table 2. Figure 8

[0143] It should be noted that, in this document, relational terms such as“first” and“second”, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms“comprises”,“comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by“comprises a...” does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0144] The above description is merely one specific implementation of the present application, which enables one skilled in the art to 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 scope consistent with the principles and novel features presented herein.​

Claims

1. A method for solving color difference on the surface of electro-galvanized steel sheet, characterized in that, The method includes: During the heating stage, the slab is heated in sections under set temperature and set time conditions to stabilize the surface and center temperature of the slab. In the finishing rolling stage, the slab is finished rolled under the conditions of a set finishing rolling inlet temperature and a set finishing rolling rate, so as to reduce the pure rolling time in the finishing rolling stage. The set temperature is 1180-1210℃, and the set time is 160-180min; The set finishing mill inlet temperature is 1030-1040℃, and the set finishing mill rolling speed is 8-10m / s; The segmented heating includes a preheating section, a first heating section, a second heating section, and a homogenizing section. The preheating section and the first heating section each use an oxidizing gas atmosphere, and the air-fuel ratio is 1.1-1.

2. The temperature of the preheating section is ≤900℃, and the temperature of the first heating section is ≤1100℃. The secondary heating section and the homogenizing section both use a reducing gas atmosphere, and the air-fuel ratio is 0.9-1.0; the temperature t1 of the secondary heating section and the temperature t2 of the homogenizing section satisfy the relationship: t2-t1≥20℃; The finishing rolling temperature is 900-920℃.

2. The method for solving the color difference on the surface of electro-galvanized steel sheet according to claim 1, characterized in that, The temperature of the first stage is 920-980℃, and the time is 30-40 minutes.

3. The method for solving the color difference on the surface of electro-galvanized steel sheet according to claim 1, characterized in that, The temperature of the second stage is 1140-1180℃, and the time is 10-20 minutes.

4. The method for solving the color difference on the surface of electro-galvanized steel sheet according to claim 1, characterized in that, The temperature of the heat spreader is 1180-1210℃, and the time is 30-40 minutes.

5. The method for solving the color difference on the surface of electro-galvanized steel sheet according to claim 1, characterized in that, The preheating period is 60-80 minutes.

6. The method for solving the color difference on the surface of electro-galvanized steel sheet according to claim 1, characterized in that, In the finishing rolling stage, the slab is finished rolled under set finishing rolling inlet temperature and set finishing rolling rate conditions to reduce the pure rolling time in the finishing rolling stage, including: In the finishing rolling stage, the slab is finished rolled under the conditions of a set finishing rolling inlet temperature and a set finishing rolling rate to reduce the pure rolling time in the finishing rolling stage, and rolling lubricating oil is added to establish a lubricating film.

7. The method for solving the color difference on the surface of electro-galvanized steel sheet according to claim 6, characterized in that, The amount of rolling lubricating oil used is 0.25~0.3 kg / ton.

8. The method for solving the color difference on the surface of electro-galvanized steel sheet according to claim 1, characterized in that, The method further includes: In the roughing stage, the slab is subjected to one pass of R1 rolling and five passes of R2 rolling, and rough descaling is performed during the first, third and fifth passes of R2 rolling. During the finishing rolling stage, the slab is descaled in two passes at the finishing rolling inlet; During the laminar cooling stage, the cooling rate is controlled at 70-100℃ / s to reduce the high-temperature residence time in the laminar cooling section; During the winding stage, the winding temperature is controlled at 630-650℃, and after winding, it is cooled by air cooling or water cooling.

9. The method for solving the color difference on the surface of electro-galvanized steel sheet according to claim 1, characterized in that, The chemical composition of the slab, by weight percentage, is: C: 0.0015-0.002%, Al: 0.02-0.05%, Mn: 0.1-0.2%, Si: 0.05-0.07%, Ti: 0.06-0.08%, with the balance being Fe and unavoidable impurity elements.

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