Method for controlling zinc defects of noodles of hot-dip galvanized sheet

Abstract

The invention provides a control method for zinc defects of hot galvanized sheet strips, which comprises the following steps: S1, acid rolling: after uncoiling a hot rolled steel coil, carrying out acid pickling, cold rolling and coil merging to obtain a cold hard coil; s2, galvanizing: uncoiling the cold hard coil, annealing and then galvanizing to obtain a galvanized steel plate; and the galvanized steel plate is subjected to finishing and withdrawal and straightening to obtain the hot-dip galvanized steel plate. The pickling quality of the surface of the base plate is guaranteed through control over the pickling and rolling process, and it is finally guaranteed that the FC steel coil with the high surface quality is obtained through control over the galvanizing cleaning process, the in-furnace reduction process, the grate humidifying process, the grate ash removing process and the zinc liquid component control.

Description

Technical Field

[0001] The present application relates to the technical field of hot-dip galvanized sheets, and in particular to a method for controlling zinc defects in hot-dip galvanized sheet noodles. Background Art

[0002] Galvanized sheets are mainly used in household appliances, including air conditioners, washing machines, televisions, computer cases, etc. They have high requirements on the quality of the sheet surface and do not allow defects that can be seen or felt by the naked eye to exist.

[0003] The strip zinc defects generated in the production process of galvanized thin plates are clearly visible because of their linear defects, and some defects can be felt by hand. In the related art, a zinc liquid pump is set on each side of the furnace nose to pump the zinc ash and zinc slag on the zinc liquid surface on both sides of the furnace nose out of the furnace nose to prevent them from adhering to the surface of the strip and affecting the surface quality of the strip. The related art also adopts a two-component cleaning process, which is to change the components of the cleaning liquid from the commonly used single component (alkali + surfactant + defoaming agent, etc.) liquid added together to the alkali, surfactant, defoaming agent and other components added separately according to the process requirements, so as to improve the cleanliness of the strip surface and reduce strip zinc or zinc particle defects. However, after the improvement in the related art, there is still a high problem of strip zinc defects.

[0004] Application Contents

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide a method for controlling zinc defects in hot-dip galvanized sheet strips, through which the control of zinc defects in strips is achieved.

[0006] Specifically, the present application provides a method for controlling zinc defects in hot-dip galvanized sheet strips, comprising the following steps:

[0007] S1, acid rolling:

[0008] The hot-rolled steel coil is uncoiled, pickled, cold-rolled and coiled to obtain a chilled coil;

[0009] The pickling temperature is above 82°C, and the concentration of the acid solution used in the acid process is above 100g / L;

[0010] S2, galvanizing:

[0011] The cold hardened coil is unrolled, annealed and then galvanized to obtain a galvanized steel sheet;

[0012] The annealing heating section temperature is 730°C to 750°C;

[0013] The annealing soaking zone temperature is 730°C to 750°C;

[0014] The galvanized steel sheet is subjected to skin-smoothing and tension-correction to obtain a hot-dip galvanized steel sheet;

[0015] The elongation of the finishing is 1.3% to 1.5%;

[0016] The rolling force of skin pass is above 200t;

[0017] The elongation of the tension straightening is 0.15% to 0.25%.

[0018] According to some embodiments of the present application, the acid washing is preceded by alkali washing;

[0019] The temperature of the alkali washing is 50°C to 90°C.

[0020] According to some embodiments of the present application, the alkalinity of the alkali washing is controlled at 30Pt to 90Pt.

[0021] According to some embodiments of the present application, the atmosphere during the galvanizing process is a reducing atmosphere.

[0022] According to some embodiments of the present application, the volume fraction of hydrogen in the reducing atmosphere is above 5.0%.

[0023] According to some embodiments of the present application, the rotation speed of the zinc extraction pump during the galvanizing process is 700 r / min to 750 r / min.

[0024] According to some embodiments of the present application, the mass content of Al in the zinc solution during the galvanizing process is 0.22% to 0.04%.

[0025] According to some embodiments of the present application, the temperature of zinc in the galvanizing process is 455°C to 460°C.

[0026] According to some embodiments of the present application, the temperature of the zinc solution during the galvanizing process is 450°C to 460°C.

[0027] According to some embodiments of the present application, the speed of the process section during the galvanizing process is above 60 m / min.

[0028] According to some embodiments of the present application, the flow ratio of dry and wet nitrogen during the galvanizing process is 3 to 7:1.

[0029] According to some embodiments of the present application, the flow rate of dry nitrogen during the galvanizing process is 20 Nm 3 / h~25Nm 3 / h.

[0030] According to some embodiments of the present application, the flow rate of wet nitrogen during the galvanizing process is 4Nm 3 / h~6Nm 3 / h.

[0031] According to some embodiments of the present application, the acid solution is hydrochloric acid.

[0032] According to some embodiments of the present application, the surface grade of the hot-dip galvanized steel sheet is above FC.

[0033] This application has at least the following beneficial effects:

[0034] ① Pickling process: During the pickling rolling process of the galvanized substrate, the pickling concentration should be appropriately increased to reduce the source of oxygen from the substrate entering the galvanizing unit.

[0035] ② Galvanizing cleaning section process: Strengthen the process control of the galvanizing cleaning section, accurately control the alkali temperature, alkali alkalinity and free alkalinity of the alkali solution tank in the cleaning section to ensure that the surface of the strip is clean.

[0036] ③Atmosphere in the galvanizing furnace: Optimize the atmosphere in the galvanizing furnace to ensure that the surface of the strip is fully reduced.

[0037] ④ Humidification of the galvanizing furnace grate and the temperature of the zinc pot plate: optimize the process parameters of the furnace nose humidifier, control the flow ratio of dry and wet nitrogen in the furnace nose, reduce the evaporation and condensation of zinc liquid in the furnace nose, reduce the accumulation of zinc ash in the furnace nose, and ensure a good atmosphere environment in the furnace nose.

[0038] ⑤ Galvanizing zinc extraction pump and zinc liquid composition: The speed of the zinc extraction pump should be stably controlled to avoid excessive flow and increased zinc evaporation. At the same time, the Al content in the zinc pot should be controlled to improve the amount of slag in the zinc pot. The Al content in the zinc liquid in the zinc pot, the temperature of the zinc pot, and the temperature of the zinc liquid should be accurately controlled to ensure the stability of the zinc liquid composition, zinc pot temperature and liquid level. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present drawings 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, the drawings described below are only some embodiments of the present drawings. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0040] Figure 1 This is a scanning electron microscope image of the zinc stripe position.

[0041] Figure 2 This is a scanning electron microscope image of the normal position.

[0042] Figure 3 This is an electron probe map of the zinc stripe position.

[0043] Figure 4 This is the electron probe image in normal position.

[0044] Figure 5This is a scanning electron microscope image of white zinc gray.

[0045] Figure 6 This is a scanning electron microscope image of black zinc gray.

[0046] The purpose, features and advantages of this figure will be further described in conjunction with the embodiments with reference to the accompanying drawings. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0048] Obviously, the drawings described below are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios based on these drawings without creative work. In addition, it can also be understood that although the efforts made in this development process may be complicated and lengthy, for ordinary technicians in this field related to the content disclosed in this application, some changes in design, manufacturing or production based on the technical content disclosed in this application are just conventional technical means, and should not be understood as insufficient content disclosed in this application.

[0049] However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0050] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0051] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0052] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0053] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0054] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0055] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0056] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0057] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0058] The purpose of this application is to provide a production method for FC surface grade hot-dip galvanized steel sheet, through in-depth analysis and research on the causes of zinc defects on the surface of galvanized sheet, combined with appropriate pickling concentration and pickling speed of pickling rolling and galvanizing cleaning, annealing and galvanizing technology, to manufacture FC surface grade steel coils that meet the requirements of high-end home appliance plates.

[0059] 1. Scanning electron microscope comparison between zinc strip and normal sample surface

[0060] By comparing the zinc strip defect position with the normal position through scanning electron microscopy, the energy spectrum results show that the oxygen content in the zinc strip defect position is significantly higher, while no oxygen content is found in the normal position. Figure 1 The percentage of elements is shown in Table 1; the scanning electron microscopy results of the normal area are shown in Figure 2 The percentage of elements is shown in Table 2.

[0061] Table 1

[0062] Spectrum C O Al Ca Zn Total Spectrum Figure 1 0.37 7.10 2.88 0.89 88.77 100 Spectrum Figure 2 0.04 42.55 18.04 0 39.38 100 Spectrum Figure 3 0.04 30.59 6.10 0 63.27 100 Spectrum Figure 4 0.04 1.63 0 0 98.33 100

[0063] Table 2

[0064] Spectrum C Fe Zn Total Spectrum Figure 1 0.03 2.09 97.88 100 Spectrum Figure 2 0.02 1.50 98.48 100

[0065] 2. Comparative analysis of the cross-section electron probe at the zinc stripe position and the normal position

[0066] By comparing the cross-sectional electron probe analysis of the zinc strip defect position and the normal position, it is found that the closer the oxygen content of the zinc strip defect position is to the zinc layer surface, the higher the content is, while the distribution of oxygen content in the normal position does not follow this rule. Figures 3-4 shown.

[0067] 3. Comparison of white zinc ash and black zinc ash in the furnace nose

[0068] Through the SEM analysis of the white and black zinc ash in the furnace nose, it was found that both colors of zinc ash contain extremely high oxygen. The SEM results of the grate zinc ash are as follows: Figures 5-6 As shown, Figure 5 The content of elements in the Figure 6 The element contents are shown in Table 4.

[0069] Table 3

[0070] Spectrum C O Zn Spectrum Figure 1 0.04 23.21 76.75 Spectrum Figure 2 0.03 21.69 78.28 Spectrum Figure 3 0.03 22.27 77.70 Spectrum Figure 4 0.04 23.74 76.22 Spectrum Figure 5 0.03 20.03 79.94 average value - 22.19 77.78

[0071] Table 4

[0072] Spectrum C O Zn Spectrum Figure 1 0.09 21.57 78.34 Spectrum Figure 2 0.06 22.10 77.84 Spectrum Figure 3 0.07 9.32 90.61 Spectrum Figure 4 0.05 15.85 84.10 Spectrum Figure 5 0.08 19.11 80.81 average value 0.07 17.59 82.34

[0073] Through the above sample analysis, it can be seen that the zinc defects of the galvanized annealing furnace plate under reducing atmosphere conditions have higher oxygen elements, and the reasons such as insufficient plate surface cleanliness, insufficient reduction in the furnace, and evaporation of zinc liquid in the zinc pot lead to the accumulation of zinc ash with high oxygen content in the grate and dripping onto the surface of the strip.

[0074] Therefore, the root cause of controlling zinc defects in hot-dip galvanized strip lies in controlling the oxygen content on the surface of the strip before it leaves the zinc pot, and the focus is on controlling the generation of oxides in the substrate, galvanizing cleaning section, furnace, grate and zinc pot.

[0075] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0076] The present application provides a method for controlling zinc defects in hot-dip galvanized sheet strips, comprising the following steps:

[0077] S1, acid rolling:

[0078] The hot-rolled steel coil is uncoiled, pickled, cold-rolled and coiled to obtain a chilled coil;

[0079] The pickling temperature is above 82°C, and the concentration of the acid solution used in the acid process is above 100g / L;

[0080] S2, galvanizing:

[0081] The cold hardened coil is unrolled, annealed and then galvanized to obtain a galvanized steel sheet;

[0082] The annealing heating section temperature is 730°C to 750°C;

[0083] The annealing soaking zone temperature is 730°C to 750°C;

[0084] The galvanized steel sheet is subjected to skin-smoothing and tension-correction to obtain a hot-dip galvanized steel sheet;

[0085] The elongation of the finishing is 1.3% to 1.5%;

[0086] The rolling force of skin pass is above 200t;

[0087] The elongation of the tension straightening is 0.15% to 0.25%.

[0088] According to some embodiments of the present application, the acid washing is preceded by alkali washing;

[0089] The temperature of the alkali washing is 50°C to 90°C.

[0090] According to some embodiments of the present application, the alkalinity of the alkali washing is controlled at 30Pt to 90Pt.

[0091] According to some embodiments of the present application, the atmosphere during the galvanizing process is a reducing atmosphere.

[0092] According to some embodiments of the present application, the volume fraction of hydrogen in the reducing atmosphere is above 5.0%.

[0093] According to some embodiments of the present application, the rotation speed of the zinc extraction pump during the galvanizing process is 700 r / min to 750 r / min.

[0094] According to some embodiments of the present application, the mass content of Al in the zinc solution during the galvanizing process is 0.22% to 0.24%.

[0095] According to some embodiments of the present application, the temperature of zinc in the galvanizing process is 455°C to 460°C.

[0096] According to some embodiments of the present application, the temperature of the zinc solution during the galvanizing process is 450°C to 460°C.

[0097] According to some embodiments of the present application, the speed of the process section during the galvanizing process is above 60 m / min.

[0098] According to some embodiments of the present application, the flow ratio of dry and wet nitrogen during the galvanizing process is 3 to 7:1.

[0099] According to some embodiments of the present application, the flow rate of dry nitrogen during the galvanizing process is 20 Nm 3 / h~25Nm 3 / h.

[0100] According to some embodiments of the present application, the flow rate of wet nitrogen during the galvanizing process is 4Nm 3 / h~6Nm 3 / h.

[0101] According to some embodiments of the present application, the pickling temperature is 82°C to 100°C.

[0102] According to some embodiments of the present application, the acid solution is hydrochloric acid.

[0103] According to some embodiments of the present application, the surface grade of the hot-dip galvanized steel sheet is above FC.

[0104] In the technical solution of the present application, the pickling quality of the substrate surface is ensured by controlling the pickling process, and the galvanizing cleaning process, the furnace reduction process, the grate humidification process, the grate cleaning process and the zinc liquid composition control are controlled to ultimately ensure that the steel coil with high FC surface quality is obtained.

[0105] The present application adopts the above-mentioned process method, which has a simple process and convenient control, and can produce a hot-dip galvanized steel plate with FC surface grade, which can meet the requirements of the field of high-end steel plates for home appliances.

[0106] Compared with the prior art, this application has the following significant advantages:

[0107] 1. This application ensures the pickling effect of the steel coil surface by controlling the pickling process.

[0108] 2. This application analyzes and optimizes the galvanizing cleaning process, galvanizing annealing process, galvanizing zinc pot process, and galvanizing furnace nose humidification process, so that the zinc strip defects of galvanized products of the galvanizing line can be effectively controlled.

[0109] The functions of the relevant process steps in this application are as follows:

[0110] ① Pickling process: During the pickling process of galvanized substrate, the pickling concentration should be appropriately increased to reduce the oxygen source of the substrate entering the galvanizing unit.

[0111] ② Galvanizing cleaning section process: Strengthen the process control of the galvanizing cleaning section, accurately control the alkali temperature, alkali alkalinity and free alkalinity of the alkali solution tank in the cleaning section to ensure that the surface of the strip is clean.

[0112] ③Atmosphere in the galvanizing furnace: Optimize the atmosphere in the galvanizing furnace to ensure that the surface of the strip is fully reduced.

[0113] ④ Humidification of the galvanizing furnace grate and the temperature of the zinc pot plate: optimize the process parameters of the furnace nose humidifier, control the flow ratio of dry and wet nitrogen in the furnace nose, reduce the evaporation and condensation of zinc liquid in the furnace nose, reduce the accumulation of zinc ash in the furnace nose, and ensure a good atmosphere environment in the furnace nose.

[0114] ⑤ Galvanizing zinc extraction pump and zinc liquid composition: The speed of the zinc extraction pump should be stably controlled to avoid excessive flow and increased zinc evaporation. At the same time, the Al content in the zinc pot should be controlled in order to improve the amount of slag in the zinc pot. The Al content in the zinc liquid in the zinc pot, the temperature of entering the zinc pot, and the temperature of the zinc liquid should be accurately controlled.

[0115] The humidifying gas in the examples and comparative examples of the present application is prepared in the following manner:

[0116] Pure nitrogen is passed through a pipeline into a humidification tank (a 70 kWh / m heating tape is wrapped around the humidifier tank), and humidification is performed by heating water for 1 hour.

[0117] Example 1

[0118] This embodiment is a method for controlling zinc defects in hot-dip galvanized noodles, which consists of the following steps:

[0119] S1, acid rolling:

[0120] The hot-rolled steel coil is uncoiled, alkali-washed, pickled, cold-rolled and coiled to obtain a chilled coil;

[0121] The pickling temperature is 82°C, and the acid used in the acid process is 100g / L hydrochloric acid;

[0122] The alkali solution temperature in the alkali solution tank of the cleaning section is controlled at 60°C, the alkalinity of the alkali solution is controlled at 30Pt (sodium hydroxide solution), and the free alkalinity of the cleaning tank is controlled at 8Pt to ensure that the surface of the strip is cleaned.

[0123] S2, galvanizing:

[0124] The cold hardened coil is unrolled, annealed and then galvanized to obtain a galvanized steel sheet;

[0125] The volume fraction of hydrogen during the galvanizing process is 5%;

[0126] The heating section temperature of annealing is 740°C;

[0127] The soaking temperature of the annealing section is 740°C;

[0128] The galvanized steel sheet is subjected to skin-smoothing and tension-correction to obtain a hot-dip galvanized steel sheet;

[0129] The elongation of skin-finishing is 1.4%;

[0130] The rolling force of skin-pass is 200t;

[0131] The elongation of tension leveling is 0.2%.

[0132] Control the flow ratio of dry and wet nitrogen at the furnace nose. The flow rate of dry nitrogen is 25m 3 / h, humidified gas (composed of nitrogen and water) is 4m 3 / h.

[0133] The speed of the zinc pump is stably controlled at 750r / min;

[0134] The Al content in the zinc liquid in the zinc pot is controlled at 0.23%;

[0135] The temperature of zinc pot is controlled at 455℃~460℃;

[0136] The temperature of zinc liquid is controlled at 456±2℃.

[0137] Example 2

[0138] This embodiment is a method for controlling zinc defects in hot-dip galvanized noodles, which differs from Embodiment 1 in that:

[0139] The flow rate of dry nitrogen is 24m 3 / h, humidified gas (composed of nitrogen and water) is 5.6m 3 / h.

[0140] Example 3

[0141] This embodiment is a method for controlling zinc defects in hot-dip galvanized noodles, which differs from Embodiment 1 in that:

[0142] The flow rate of dry nitrogen is 18m 3 / h, humidified gas (nitrogen and water) is 3.3m 3 / h.

[0143] Comparative Example 1

[0144] This comparative example is a preparation method of hot-dip galvanizing, which differs from Example 1 in that:

[0145] The flow rate of dry nitrogen is 30m 3 / h, humidified gas (composed of nitrogen and water) is 10.2m 3 / h.

[0146] The Al content in the zinc liquid in the zinc pot is controlled at 0.3%.

[0147] Comparative Example 2

[0148] This comparative example is a preparation method of hot-dip galvanizing, which differs from Example 1 in that:

[0149] The pickling temperature is 70°C.

[0150] The flow rate of dry nitrogen is 13m 3 / h, humidified gas (consisting of nitrogen and water) is 1.8m 3 / h.

[0151] The Al content in the zinc liquid in the zinc pot is controlled at 0.3%.

[0152] Comparative Example 3

[0153] This comparative example is a preparation method of hot-dip galvanizing, which differs from Example 1 in that:

[0154] The flow rate of dry nitrogen is 30m 3 / h, humidified gas (composed of nitrogen and water) is 10.2m 3 / h. The Al content in the zinc liquid in the zinc pot is controlled at 0.28%.

[0155] The speed of the zinc pump is stably controlled at 850r / min.

[0156] Comparative Example 4

[0157] This comparative example is a preparation method of hot-dip galvanizing, which differs from Example 1 in that:

[0158] The pickling temperature is 70°C.

[0159] The flow rate of dry nitrogen is 30m 3 / h, humidified gas (composed of nitrogen and water) is 6.7m 3 / h. The Al content in the zinc liquid in the zinc pot is controlled at 0.3%.

[0160] The temperature of zinc pot is controlled at 470℃~475℃.

[0161] Comparative Example 5

[0162] This comparative example is a preparation method of hot-dip galvanizing, which differs from Example 1 in that:

[0163] The flow rate of dry nitrogen is 8m 3 / h, humidified gas (composed of nitrogen and water) is 0.4m 3 / h. The Al content in the zinc liquid in the zinc pot is controlled at 0.1%.

[0164] The statistical comparison of the zinc defect downgrade and removal of zinc strips in the embodiment and the comparative example is shown in Table 5.

[0165] Table 5

[0166] - Defect ratio of zinc strips (%) Example 1 0.13 Example 2 0.21 Example 3 0.24 Comparative Example 1 0.42 Comparative Example 2 0.56 Comparative Example 3 0.59 Comparative Example 4 0.63 Comparative Example 5 0.71

[0167] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for controlling zinc defects in hot-dip galvanized sheet strips, characterized in that: The following steps are involved: S1, acid rolling: The hot-rolled steel coil is uncoiled, pickled, cold-rolled and coiled to obtain a chilled coil; The pickling temperature is above 82°C, and the concentration of the acid solution used in the acid process is above 100g / L; S2, galvanizing: The cold hardened coil is unrolled, annealed and then galvanized to obtain a galvanized steel sheet; The annealing heating section temperature is 730°C to 750°C; The annealing soaking zone temperature is 730°C to 750°C; The galvanized steel sheet is subjected to skin-smoothing and tension-correction to obtain a hot-dip galvanized steel sheet; The elongation of the finishing is 1.3% to 1.5%; The rolling force of skin pass is above 200t; The elongation of the tension straightening is 0.15% to 0.25%.

2. The control method according to claim 1, characterized in that: Alkali washing before pickling; The temperature of the alkali washing is 50°C to 90°C.

3. The control method according to claim 2, characterized in that: The alkalinity of the alkali washing is controlled at 30Pt to 90Pt.

4. The control method according to claim 1, characterized in that: The atmosphere during the galvanizing process is a reducing atmosphere; And / or, the volume fraction of hydrogen in the reducing atmosphere is greater than 5.0%.

5. The control method according to claim 1, characterized in that: The rotation speed of the zinc pump during the galvanizing process is 700r / min to 750r / min; And / or, the mass content of Al in the zinc solution during the galvanizing process is 0.22% to 0.04%; And / or, the temperature of zinc in the galvanizing process is 455°C to 460°C; And / or, the temperature of the zinc solution during the galvanizing process is 450°C to 460°C.

6. The control method according to claim 1, characterized in that: The speed of the process section during the galvanizing process is above 60m / min.

7. The control method according to claim 1, characterized in that: The flow ratio of dry and wet nitrogen in the galvanizing process is 3 to 7:1; And / or, the flow rate of dry nitrogen during the galvanizing process is 20Nm 3 / h~25Nm 3 / h; And / or, the flow rate of wet nitrogen during the galvanizing process is 4Nm 3 / h~6Nm 3 / h.

8. The control method according to claim 1, characterized in that: The pickling temperature is 82°C to 100°C.

9. The control method according to claim 1, characterized in that: The acid solution is hydrochloric acid.

10. The control method according to any one of claims 1 to 9, characterized in that: The surface grade of the hot-dip galvanized steel sheet is FC or above.

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