A kind of steel for automobile outer panel and preparation method thereof

Abstract

The present application relates to a steel for automobile outer panel and a preparation method thereof, belonging to the technical field of steel preparation, the method comprising: rolling and annealing a cast ingot to obtain a steel strip; leveling the steel strip; electroplating the leveled steel strip to obtain the steel for automobile outer panel; wherein the electroplating adopts gravity electroplating, the pH value of the electroplating satisfies the set pH value, and the temperature of the electroplating solution satisfies the set temperature; by adopting gravity electroplating and controlling the pH value and the electroplating temperature of the electroplating solution, the roughness attenuation caused by the electroplating process is effectively reduced, and the steel is prepared by the method, so that the roughness Ra of the electroplating process can be attenuated ≤0.1μm, which is about 0.2-0.4μm compared with the current process roughness Ra attenuation, the attenuation value is reduced by more than half, and the attenuation of the peak count RPc is ≤10 / cm 2 , compared with the current process peak count RPc attenuation of 20-30 / cm 2 , the attenuation value is also reduced by more than half.

Description

Technical Field

[0001] The present application relates to the technical field of steel preparation, and in particular to a steel for automobile outer panels and a preparation method thereof. Background Art

[0002] In the automobile stamping process, surface roughness will directly affect the stamping's ability to contain lubricants and the glossiness of the paint. A higher surface roughness has a higher storage capacity for lubricants, which affects the sliding properties of the material flowing into the mold, and is related to the stamping performance of the steel plate. On the other hand, in the painting process, the larger waviness of the steel plate will affect the bonding area with the paint film, resulting in poor adhesion of the paint film, thus affecting the surface roughness and appearance after painting and reducing the brightness. Waviness is a periodic wave-shaped deviation on the strip surface caused by roll shape errors and mill vibrations.

[0003] Automobile outer panels generally require the steel plate surface to have higher roughness Ra, RPc and lower waviness, but the roughness will be attenuated after the electroplating process. Generally, the roughness Ra attenuation of the electroplating process is about 0.2-0.4μm, and the peak count RPc attenuation is 20-30 / cm 2 , which is not conducive to the precise and stable control of product roughness. Summary of the invention

[0004] The present application provides a steel for automobile outer panel and a preparation method thereof, so as to solve the problem of roughness attenuation caused by current electroplating.

[0005] In a first aspect, the present application provides a method for preparing steel for automobile outer panels, the method comprising:

[0006] Rolling and annealing the ingot to obtain strip steel;

[0007] Leveling the steel strip;

[0008] Electroplating the flattened steel strip to obtain steel for automobile outer panels;

[0009] Wherein, the electroplating adopts gravity electroplating, the pH value of the electroplating meets the set pH value, and the plating solution temperature of the electroplating meets the set temperature.

[0010] As an optional embodiment, the set pH value is 1.2-1.8, and the set temperature is 50-52° C.;

[0011] Preferably, the set pH value is 1.4-1.6, and the set temperature is 51-52°C.

[0012] As an optional embodiment, the electroplating is zinc electroplating, and the mass concentration of zinc ions in the zinc electroplating solution is 100-140 g / L; and / or

[0013] The mass concentration of free acid in the electro-galvanizing solution is 5-7 g / L.

[0014] As an optional embodiment, the impurity ions in the electrogalvanizing solution are controlled within a set range, and the impurity ions include Fe 2+ , Fe 3+ , Pb 2+ and Cu 2+ , the setting range includes Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0015] As an optional implementation, the moving speed of the electroplated steel strip is 60-100 m / min.

[0016] As an optional implementation, the surface roughness Ra of the roller used for the flattening is 2.5-3 μm, and the roller surface RPc value of the roller used for the flattening is not less than 90;

[0017] Preferably, the surface roughness Ra of the roller used for the smoothing is 2.6-2.9 μm, and the roller surface RPc value of the roller used for the smoothing is not less than 95.

[0018] More preferably, the surface roughness Ra of the roller used for the smoothing is 2.7-2.8 μm, and the roller surface RPc value of the roller used for the smoothing is not less than 100.

[0019] As an optional implementation, the flattening tension is 20-25.

[0020] As an optional implementation, the flattened elongation is 0.6%-0.7%.

[0021] As an optional embodiment, the annealing soaking temperature is 840-860° C.; and / or

[0022] The annealing strip moving speed is 120-150m / min.

[0023] In a second aspect, the present application provides a steel for automobile outer panel, wherein the steel is produced by the method for producing the steel for automobile outer panel provided in the first aspect.

[0024] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0025] The method provided in the embodiment of the present application adopts the gravity electroplating method and controls the pH value and electroplating temperature of the electroplating solution to effectively reduce the roughness attenuation caused by the electroplating process. The method is used to prepare steel, and the roughness Ra of the electroplating process can be attenuated by ≤0.1μm. Compared with the current process roughness Ra attenuation of about 0.2-0.4μm, the attenuation value is reduced by more than half, and the attenuation of the peak count RPc is ≤10 / cm 2 , compared with the current process peak count RPc attenuation of 20-30 / cm 2 , the attenuation value is also reduced by more than half. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] 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.

[0028] Figure 1 A flowchart of the method provided in the embodiment of the present application. DETAILED DESCRIPTION

[0029] 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.

[0030] 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.

[0031] like Figure 1 As shown, the embodiment of the present application provides a method for preparing steel for automobile outer panel, the method comprising:

[0032] S1. rolling and annealing the ingot to obtain a strip;

[0033] In some embodiments, the ingot steel plate is designed with an ultra-low carbon composition containing Nb, and the specific composition is shown in the following table by mass fraction:

[0034]

[0035] In some embodiments, rolling includes hot rolling and cold rolling.

[0036] The final rolling temperature of hot rolling is 910-950°C, the coiling temperature of hot rolling is 710-740°C; the total reduction rate of cold rolling is 80%-83%.

[0037] In some embodiments, the annealing soaking temperature is 840-860°C, and the temperature is required to remain stable during the production process; the annealing strip moving speed is 120-150m / min, and the strip moving speed is preferably controlled near a fixed value within this range.

[0038] The use of this soaking temperature and strip moving speed can promote the initial nucleation and growth of γ-oriented textured grains, thereby obtaining good deep drawing performance.

[0039] S2. leveling the strip;

[0040] In some embodiments, the surface roughness Ra of the roller used for the leveling is 2.5-3 μm, and the RPc value of the roller surface of the roller used for the leveling is not less than 90; preferably, the surface roughness Ra of the roller used for the leveling is 2.6-2.9 μm, and the RPc value of the roller surface of the roller used for the leveling is not less than 95. More preferably, the surface roughness Ra of the roller used for the leveling is 2.7-2.8 μm, and the RPc value of the roller surface of the roller used for the leveling is not less than 100.

[0041] According to the roughness transfer principle, the rolling force transfers the surface roughness of the roller to the strip during the leveling process. The strip surface requires a roughness of about 0.8-0.9μm. Taking into account the attenuation of electro-galvanizing, the plate surface roughness after continuous annealing and leveling needs to be about 0.9-1.0μm. The strip surface RPc is required to reach 75. To ensure that the plate surface reaches 90 after continuous annealing and leveling, the surface roughness Ra of the roller used for leveling is controlled to be 2.5-3.0μm, and the roller surface RPc value is not less than 90. The roller with this roughness can be copied to the strip to meet the plate surface roughness requirements.

[0042] In order to ensure that the roller has a larger replication coefficient, in some embodiments, the tension in the leveling process is reduced by 20% to 25% compared with the 25-30KN in the prior art. Specifically, the leveling tension is 20-25KN.

[0043] In some embodiments, the flattened elongation is 0.6%-0.7%.

[0044] S3. Electroplating the flattened steel strip to obtain steel for automobile outer panels; wherein the electroplating is performed by gravity plating, the pH value of the electroplating satisfies a set pH value, and the temperature of the electroplating solution satisfies a set temperature.

[0045] Those skilled in the art should be aware that after annealing is completed and before electroplating, cleaning steps such as alkali washing, brushing, electrolytic degreasing, and rinsing are also included.

[0046] In some embodiments, the set pH value is 1.2-1.8, and the set temperature is 50-52°C; preferably, the set pH value is 1.4-1.6, and the set temperature is 51-52°C.

[0047] The plating solution temperature and free acid concentration will affect the roughness attenuation. If the value is too low, it will affect the electroplating process, and if it is too high, it will cause excessive attenuation. The applicant believes that controlling the set pH value to 1.2-1.8 and the set temperature to 50-52°C is the best choice considering the electroplating process and attenuation.

[0048] In some embodiments, the electroplating is zinc electroplating, and the main salt component of the zinc electroplating solution is zinc sulfate to provide zinc ions in the plating solution. The mass concentration of zinc ions in the zinc electroplating solution is 100-140g / L; the mass concentration of free acid in the zinc electroplating solution is 5-7g / L.

[0049] Controlling the mass concentration of zinc ions to 100-140 g / L can improve the conductivity and electrodeposition efficiency and maintain the stability of the interface between the plating solution and the electrodeposition.

[0050] Acid has a corrosive effect on the zinc layer. If the value is too low, it will affect the electroplating, and if it is too high, it will lead to corrosion of the surface roughness and excessive attenuation. The applicant believes that controlling the mass concentration of free acid to 5-7g / L is a better choice considering the impact on electroplating and roughness attenuation.

[0051] In some embodiments, the impurity ions in the electrogalvanizing solution are controlled within a set range, and the impurity ions include Fe 2+ , Fe 3+ , Pb 2+ and Cu 2+ , the setting range includes Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0052] Impurities will enter the coating, deteriorate the zinc layer crystallization, and affect the surface quality of the coating, so it is necessary to control the impurity ions.

[0053] In some embodiments, the electroplated steel strip moves at a speed of 60-100 m / min.

[0054] Based on a general inventive concept, an embodiment of the present application further provides a steel for automobile outer panel, wherein the steel is prepared by the preparation method for automobile outer panel steel provided in the first aspect.

[0055] The automobile outer panel steel is produced based on the above-mentioned automobile outer panel steel preparation method. The specific steps of the automobile outer panel steel preparation method can refer to the above-mentioned embodiment. Since the automobile outer panel steel adopts part or all of the technical solutions of the above-mentioned embodiment, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiment, which will not be described one by one here.

[0056] The properties of the steel are shown below:

[0057]

[0058] 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.

[0059] Example 1

[0060] A method for preparing steel for automobile outer panels, the method comprising:

[0061] S1. rolling and annealing the ingot to obtain a strip;

[0062] The composition of the ingot is, by mass fraction, C: 0.0017%, Si: 0.014%, Mn: 0.10%, P: ≤0.015%, S: ≤0.010%, Nb: 0.04%, Als: 0.030%, N: 0.002%; the rest is iron and unavoidable impurities.

[0063] The rolling process includes hot rolling and cold rolling. The final rolling temperature of the hot rolling is 910°C; the coiling temperature of the hot rolling is 710°C; and the total reduction rate of the cold rolling is 80%.

[0064] The soaking temperature of the annealing is 840°C, and the rapid cooling endpoint temperature of the annealing is 440°C.

[0065] S2. leveling the strip;

[0066] Among them, the flat elongation is: 0.6%, the flat roller surface roughness Ra needs to be controlled between 2.5μm, the roller surface RPc is controlled at 90, and the flat tension is 20KN.

[0067] S3. After the flattening is completed, the strip steel is cleaned by alkali washing, brushing, electrolytic degreasing, rinsing and other processes, and then enters the vertical electrogalvanizing tank, and adopts the gravity electroplating process to obtain steel for automobile outer panels.

[0068] Among them, the main component of the electrogalvanizing bath is zinc sulfate, which provides zinc ions in the bath. The zinc ion concentration in the bath is 100g / L, the pH value range is 1.2, the bath temperature is strictly controlled at 50°C, the free acid concentration in the bath is 5g / l, and the speed of the strip passing through the electroplating tank is 60m / min. Impurity ions in the bath must be strictly controlled: Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0069] Example 2

[0070] A method for preparing steel for automobile outer panels, the method comprising:

[0071] S1. rolling and annealing the ingot to obtain a strip;

[0072] The composition of the ingot is, by mass fraction, C: 0.0017%, Si: 0.014%, Mn: 0.10%, P: ≤0.015%, S: ≤0.010%, Nb: 0.04%, Als: 0.030%, N: 0.002%; the rest is iron and unavoidable impurities.

[0073] The rolling process includes hot rolling and cold rolling. The final rolling temperature of the hot rolling is 950°C; the coiling temperature of the hot rolling is 740°C; and the total reduction rate of the cold rolling is 83%.

[0074] The soaking temperature of annealing is 860°C, and the rapid cooling endpoint temperature of annealing is 470°C.

[0075] S2. leveling the strip;

[0076] Among them, the flat elongation is: 0.7%, the flat roller surface roughness Ra needs to be controlled between 3.0μm, the roller surface RPc is controlled at 95, and the flat tension is 25KN.

[0077] S3. After the flattening is completed, the strip steel is cleaned by alkali washing, brushing, electrolytic degreasing, rinsing and other processes, and then enters the vertical electrogalvanizing tank, and adopts the gravity electroplating process to obtain steel for automobile outer panels.

[0078] Among them, the main component of the electrogalvanizing bath is zinc sulfate, which provides zinc ions in the bath. The zinc ion concentration in the bath is 140g / L, the pH value range is 1.8, the bath temperature is strictly controlled at 52°C, the free acid concentration in the bath is 7g / l, and the speed of the strip passing through the electroplating tank is 100m / min. Impurity ions in the bath must be strictly controlled: Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2 + <1.4ppm,Cu 2+ <5ppm.

[0079] Example 3

[0080] A method for preparing steel for automobile outer panels, the method comprising:

[0081] S1. rolling and annealing the ingot to obtain a strip;

[0082] The composition of the ingot is, by mass fraction, C: 0.0017%, Si: 0.014%, Mn: 0.10%, P: ≤0.015%, S: ≤0.010%, Nb: 0.04%, Als: 0.030%, N: 0.002%; the rest is iron and unavoidable impurities.

[0083] The rolling process includes hot rolling and cold rolling. The final rolling temperature of the hot rolling is 930°C; the coiling temperature of the hot rolling is 725°C; and the total reduction rate of the cold rolling is 81.5%.

[0084] The soaking temperature of annealing is 850°C, and the rapid cooling endpoint temperature of annealing is 455°C.

[0085] S2. leveling the strip;

[0086] Among them, the flat elongation is: 0.65%, the flat roller surface roughness Ra needs to be controlled between 2.75μm, the roller surface RPc is controlled at 95, and the flat tension is 23KN.

[0087] S3. After the flattening is completed, the strip steel is cleaned by alkali washing, brushing, electrolytic degreasing, rinsing and other processes, and then enters the vertical electrogalvanizing tank, and adopts the gravity electroplating process to obtain steel for automobile outer panels.

[0088] Among them, the main component of the electrogalvanizing bath is zinc sulfate, which provides zinc ions in the bath. The zinc ion concentration in the bath is 120g / L, the pH value range is 1.6, the bath temperature is strictly controlled at 51°C, the free acid concentration in the bath is 6g / l, and the speed of the strip passing through the electroplating tank is 80m / min. Impurity ions in the bath must be strictly controlled: Fe 2+ ≤3000ppm,Fe3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0089] Example 4

[0090] A method for preparing steel for automobile outer panels, the method comprising:

[0091] S1. rolling and annealing the ingot to obtain a strip;

[0092] The composition of the ingot is, by mass fraction, C: 0.0017%, Si: 0.014%, Mn: 0.10%, P: ≤0.015%, S: ≤0.010%, Nb: 0.04%, Als: 0.030%, N: 0.002%; the rest is iron and unavoidable impurities.

[0093] The rolling process includes hot rolling and cold rolling. The final rolling temperature of the hot rolling is 920°C; the coiling temperature of the hot rolling is 720°C; and the total reduction rate of the cold rolling is 81%.

[0094] The soaking temperature of the annealing is 845°C, and the rapid cooling endpoint temperature of the annealing is 450°C.

[0095] S2. leveling the strip;

[0096] Among them, the flat elongation is: 0.62%, the flat roller surface roughness Ra needs to be controlled between 2..6μm, the roller surface RPc is controlled at 95, and the flat tension is 22KN.

[0097] S3. After the flattening is completed, the strip steel is cleaned by alkali washing, brushing, electrolytic degreasing, rinsing and other processes, and then enters the vertical electrogalvanizing tank, and adopts the gravity electroplating process to obtain steel for automobile outer panels.

[0098] Among them, the main component of the electrogalvanizing bath is zinc sulfate, which provides zinc ions in the bath. The zinc ion concentration in the bath is 110g / L, the pH value range is 1.4, the bath temperature is strictly controlled at 50.5℃, the free acid concentration in the bath is 5.5g / l, and the speed of the strip passing through the electroplating tank is 70m / min. Impurity ions in the bath must be strictly controlled: Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0099] Example 5

[0100] A method for preparing steel for automobile outer panels, the method comprising:

[0101] S1. rolling and annealing the ingot to obtain a strip;

[0102] The composition of the ingot is, by mass fraction, C: 0.0017%, Si: 0.014%, Mn: 0.10%, P: ≤0.015%, S: ≤0.010%, Nb: 0.04%, Als: 0.030%, N: 0.002%; the rest is iron and unavoidable impurities.

[0103] The rolling process includes hot rolling and cold rolling. The final rolling temperature of the hot rolling is 940°C; the coiling temperature of the hot rolling is 730°C; and the total reduction rate of the cold rolling is 82%.

[0104] The soaking temperature of annealing is 855°C, and the rapid cooling endpoint temperature of annealing is 460°C.

[0105] S2. leveling the strip;

[0106] Among them, the flat elongation is: 0.67%, the flat roller surface roughness Ra needs to be controlled at 2.8μm, the roller surface RPc is controlled at 95, and the flat tension is 24KN.

[0107] S3. After the flattening is completed, the strip steel is cleaned by alkali washing, brushing, electrolytic degreasing, rinsing and other processes, and then enters the vertical electrogalvanizing tank, and adopts the gravity electroplating process to obtain steel for automobile outer panels.

[0108] Among them, the main salt of the electrogalvanizing bath is zinc sulfate, which provides zinc ions in the bath. The zinc ion concentration in the bath is 130g / L, the pH value range is 1.6, the bath temperature is strictly controlled at 51.5℃, the free acid concentration in the bath is 6.8g / l, and the speed of the strip passing through the electroplating tank is 90m / min. Impurity ions in the bath must be strictly controlled: Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0109] Comparative Example 1

[0110] A method for preparing steel for automobile outer panels, the method comprising:

[0111] S1. rolling and annealing the ingot to obtain a strip;

[0112] The composition of the ingot is, by mass fraction, C: 0.0017%, Si: 0.014%, Mn: 0.10%, P: ≤0.015%, S: ≤0.010%, Nb: 0.04%, Als: 0.030%, N: 0.002%; the rest is iron and unavoidable impurities.

[0113] The rolling process includes hot rolling and cold rolling. The final rolling temperature of the hot rolling is 930°C; the coiling temperature of the hot rolling is 725°C; and the total reduction rate of the cold rolling is 81.5%.

[0114] The soaking temperature of annealing is 850°C, and the rapid cooling endpoint temperature of annealing is 455°C.

[0115] S2. leveling the strip;

[0116] Among them, the flat elongation is: 0.65%, the flat roller surface roughness Ra needs to be controlled between 2.75μm, the roller surface RPc is controlled at 95, and the flat tension is 23KN.

[0117] S3. After the flattening is completed, the strip steel is cleaned by alkali washing, brushing, electrolytic degreasing, rinsing and other processes, and then enters the vertical electrogalvanizing tank, and adopts the gravity electroplating process to obtain steel for automobile outer panels.

[0118] Among them, the main component of the electrogalvanizing bath is zinc sulfate, which provides zinc ions in the bath. The zinc ion concentration in the bath is 120g / L, the pH value range is 1, the bath temperature is strictly controlled at 51°C, the free acid concentration in the bath is 6g / l, and the speed of the strip passing through the electroplating tank is 80m / min. Impurity ions in the bath must be strictly controlled: Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0119] Comparative Example 2

[0120] A method for preparing steel for automobile outer panels, the method comprising:

[0121] S1. rolling and annealing the ingot to obtain a strip;

[0122] The composition of the ingot is, by mass fraction, C: 0.0017%, Si: 0.014%, Mn: 0.10%, P: ≤0.015%, S: ≤0.010%, Nb: 0.04%, Als: 0.030%, N: 0.002%; the rest is iron and unavoidable impurities.

[0123] The rolling process includes hot rolling and cold rolling. The final rolling temperature of the hot rolling is 930°C; the coiling temperature of the hot rolling is 725°C; and the total reduction rate of the cold rolling is 81.5%.

[0124] The soaking temperature of annealing is 850°C, and the rapid cooling endpoint temperature of annealing is 455°C.

[0125] S2. leveling the strip;

[0126] Among them, the flat elongation is: 0.65%, the flat roller surface roughness Ra needs to be controlled between 2.75μm, the roller surface RPc is controlled at 95, and the flat tension is 23KN.

[0127] S3. After the flattening is completed, the strip steel is cleaned by alkali washing, brushing, electrolytic degreasing, rinsing and other processes, and then enters the vertical electrogalvanizing tank, and adopts the gravity electroplating process to obtain steel for automobile outer panels.

[0128] Among them, the main component of the electrogalvanizing bath is zinc sulfate, which provides zinc ions in the bath. The zinc ion concentration in the bath is 120g / L, the pH value range is 2, the bath temperature is strictly controlled at 51°C, the free acid concentration in the bath is 6g / l, and the speed of the strip passing through the electroplating tank is 80m / min. Impurity ions in the bath must be strictly controlled: Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0129] Comparative Example 3

[0130] A method for preparing steel for automobile outer panels, the method comprising:

[0131] S1. rolling and annealing the ingot to obtain a strip;

[0132] The composition of the ingot is, by mass fraction, C: 0.0017%, Si: 0.014%, Mn: 0.10%, P: ≤0.015%, S: ≤0.010%, Nb: 0.04%, Als: 0.030%, N: 0.002%; the rest is iron and unavoidable impurities.

[0133] The rolling process includes hot rolling and cold rolling. The final rolling temperature of the hot rolling is 930°C; the coiling temperature of the hot rolling is 725°C; and the total reduction rate of the cold rolling is 81.5%.

[0134] The soaking temperature of annealing is 850°C, and the rapid cooling endpoint temperature of annealing is 455°C.

[0135] S2. leveling the strip;

[0136] Among them, the flat elongation is: 0.65%, the flat roller surface roughness Ra needs to be controlled between 2.75μm, the roller surface RPc is controlled at 95, and the flat tension is 23KN.

[0137] S3. After the flattening is completed, the strip steel is cleaned by alkali washing, brushing, electrolytic degreasing, rinsing and other processes, and then enters the vertical electrogalvanizing tank, and adopts the gravity electroplating process to obtain steel for automobile outer panels.

[0138] Among them, the main component of the electrogalvanizing bath is zinc sulfate, which provides zinc ions in the bath. The zinc ion concentration in the bath is 120g / L, the pH value range is 1.6, the bath temperature is strictly controlled at 48°C, the free acid concentration in the bath is 6g / l, and the speed of the strip passing through the electroplating tank is 80m / min. Impurity ions in the bath must be strictly controlled: Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0139] Comparative Example 4

[0140] A method for preparing steel for automobile outer panels, the method comprising:

[0141] S1. rolling and annealing the ingot to obtain a strip;

[0142] The composition of the ingot is, by mass fraction, C: 0.0017%, Si: 0.014%, Mn: 0.10%, P: ≤0.015%, S: ≤0.010%, Nb: 0.04%, Als: 0.030%, N: 0.002%; the rest is iron and unavoidable impurities.

[0143] The rolling process includes hot rolling and cold rolling. The final rolling temperature of the hot rolling is 930°C; the coiling temperature of the hot rolling is 725°C; and the total reduction rate of the cold rolling is 81.5%.

[0144] The soaking temperature of annealing is 850°C, and the rapid cooling endpoint temperature of annealing is 455°C.

[0145] S2. leveling the strip;

[0146] Among them, the flat elongation is: 0.65%, the flat roller surface roughness Ra needs to be controlled between 2.75μm, the roller surface RPc is controlled at 95, and the flat tension is 23KN.

[0147] S3. After the flattening is completed, the strip steel is cleaned by alkali washing, brushing, electrolytic degreasing, rinsing and other processes, and then enters the vertical electrogalvanizing tank, and adopts the gravity electroplating process to obtain steel for automobile outer panels.

[0148] Among them, the main component of the electrogalvanizing bath is zinc sulfate, which provides zinc ions in the bath. The zinc ion concentration in the bath is 120g / L, the pH value range is 1.6, the bath temperature is strictly controlled at 55°C, the free acid concentration in the bath is 6g / l, and the speed of the strip passing through the electroplating tank is 80m / min. Impurity ions in the bath must be strictly controlled: Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0149] Comparative Example 5

[0150] A method for preparing steel for automobile outer panels, the method comprising:

[0151] S1. rolling and annealing the ingot to obtain a strip;

[0152] The composition of the ingot is, by mass fraction, C: 0.0017%, Si: 0.014%, Mn: 0.10%, P: ≤0.015%, S: ≤0.010%, Nb: 0.04%, Als: 0.030%, N: 0.002%; the rest is iron and unavoidable impurities.

[0153] The rolling process includes hot rolling and cold rolling. The final rolling temperature of the hot rolling is 930°C; the coiling temperature of the hot rolling is 725°C; and the total reduction rate of the cold rolling is 81.5%.

[0154] The soaking temperature of annealing is 850°C, and the rapid cooling endpoint temperature of annealing is 455°C.

[0155] S2. leveling the strip;

[0156] Among them, the flat elongation is: 0.65%, the flat roller surface roughness Ra needs to be controlled between 2.5μm, the roller surface RPc is controlled at 80, and the flat tension is 23KN.

[0157] S3. After the flattening is completed, the strip steel is cleaned by alkali washing, brushing, electrolytic degreasing, rinsing and other processes, and then enters the vertical electrogalvanizing tank, and adopts the gravity electroplating process to obtain steel for automobile outer panels.

[0158] Among them, the main component of the electrogalvanizing bath is zinc sulfate, which provides zinc ions in the bath. The zinc ion concentration in the bath is 120g / L, the pH value range is 1.6, the bath temperature is strictly controlled at 51°C, the free acid concentration in the bath is 6g / l, and the speed of the strip passing through the electroplating tank is 80m / min. Impurity ions in the bath must be strictly controlled: Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0159] Comparative Example 6

[0160] A method for preparing steel for automobile outer panels, the method comprising:

[0161] S1. rolling and annealing the ingot to obtain a strip;

[0162] The composition of the ingot is, by mass fraction, C: 0.0017%, Si: 0.014%, Mn: 0.10%, P: ≤0.015%, S: ≤0.010%, Nb: 0.04%, Als: 0.030%, N: 0.002%; the rest is iron and unavoidable impurities.

[0163] The rolling process includes hot rolling and cold rolling. The final rolling temperature of the hot rolling is 930°C; the coiling temperature of the hot rolling is 725°C; and the total reduction rate of the cold rolling is 81.5%.

[0164] The soaking temperature of annealing is 850°C, and the rapid cooling endpoint temperature of annealing is 455°C.

[0165] S2. leveling the strip;

[0166] Among them, the flat elongation is: 0.65%, the flat roller surface roughness Ra needs to be controlled between 3.1μm, the roller surface RPc is controlled at 95, and the flat tension is 23KN.

[0167] S3. After the flattening is completed, the strip steel is cleaned by alkali washing, brushing, electrolytic degreasing, rinsing and other processes, and then enters the vertical electrogalvanizing tank, and adopts the gravity electroplating process to obtain steel for automobile outer panels.

[0168] Among them, the main component of the electrogalvanizing bath is zinc sulfate, which provides zinc ions in the bath. The zinc ion concentration in the bath is 120g / L, the pH value range is 1.6, the bath temperature is strictly controlled at 51°C, the free acid concentration in the bath is 6g / l, and the speed of the strip passing through the electroplating tank is 80m / min. Impurity ions in the bath must be strictly controlled: Fe 2+ ≤3000ppm,Fe 3+≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0169] Comparative Example 7

[0170] A method for preparing steel for automobile outer panels, the method comprising:

[0171] S1. rolling and annealing the ingot to obtain a strip;

[0172] The composition of the ingot is, by mass fraction, C: 0.0017%, Si: 0.014%, Mn: 0.10%, P: ≤0.015%, S: ≤0.010%, Nb: 0.04%, Als: 0.030%, N: 0.002%; the rest is iron and unavoidable impurities.

[0173] The rolling process includes hot rolling and cold rolling. The final rolling temperature of the hot rolling is 930°C; the coiling temperature of the hot rolling is 725°C; and the total reduction rate of the cold rolling is 81.5%.

[0174] The soaking temperature of annealing is 850°C, and the rapid cooling endpoint temperature of annealing is 455°C.

[0175] S2. leveling the strip;

[0176] Among them, the flat elongation is: 0.6%, the flat roller surface roughness Ra needs to be controlled between 2.8μm, the roller surface RPc is controlled at 80, and the flat tension is 23KN.

[0177] S3. After the flattening is completed, the strip steel is cleaned by alkali washing, brushing, electrolytic degreasing, rinsing and other processes, and then enters the vertical electrogalvanizing tank, and adopts the gravity electroplating process to obtain steel for automobile outer panels.

[0178] Among them, the main salt of the electrogalvanizing bath is zinc sulfate, which provides zinc ions in the bath. The zinc ion concentration in the bath is 120g / L, the pH value range is 1.6, the bath temperature is strictly controlled at 58°C, the free acid concentration in the bath is 12g / l, and the speed of the strip passing through the electroplating tank is 80m / min. Impurity ions in the bath must be strictly controlled: Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm.

[0179] The roughness attenuation values ​​of the steel plates provided in Examples 1-5 and Comparative Examples 1-6 during the electroplating process are shown in the following table:

[0180]

[0181] As can be seen from the above table, the method provided by this application can effectively reduce the roughness attenuation caused by the electroplating process, making the roughness Ra of the electroplating process attenuated ≤0.1μm, which is more than half of the attenuation of the current process roughness Ra attenuation of about 0.2-0.4μm, and the attenuation of the peak count RPc is ≤10 / cm 2 , compared with the current process peak count RPc attenuation of 20-30 / cm 2 , the attenuation value is also reduced by more than half.

[0182] 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.

[0183] In this application, unless otherwise specified, directional words such as "upper" and "lower" used refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of the specification of this application, the terms "include", "comprise", etc. mean "including but not limited to".

[0184] 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 associated objects, indicating that there can 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 "multiple" refers to two or more. "At least one", "the following at least one (individual)" or similar expressions refer to any combination of these items, including any combination of single (individual) or plural (individual). For example, "at least one (individual) of a, b, or c", or "at least one (individual) of a, b, and c", can all represent: a, b, c, ab (i.e. a and b), ac, bc, or abc, wherein a, b, c can be single or multiple respectively.

[0185] 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 preparing steel for automobile outer panel, characterized in that: The method comprises: Rolling and annealing the ingot to obtain strip steel; Leveling the steel strip; Electroplating the flattened steel strip to obtain steel for automobile outer panels; Wherein, the electroplating is gravity electroplating, the electroplating is zinc electroplating, and the mass concentration of zinc ions in the zinc electroplating solution is 100-140 g / L; and / or The mass concentration of free acid in the electro-galvanizing solution is 5-7 g / L; The impurity ions in the electrogalvanizing solution are controlled within a set range, and the impurity ions include Fe 2+ , Fe 3+ , Pb 2+ and Cu 2+ , the setting range includes Fe 2+ ≤3000ppm,Fe 3+ ≤1000ppm, Pb 2+ <1.4ppm,Cu 2+ <5ppm; The pH value of the electroplating is 1.4-1.6, and the plating solution temperature of the electroplating is 51-52° C.; The composition of the ingot steel plate includes, by mass fraction, C: ≤0.0018%, Si: ≤0.015%, Mn: 0.05% to 0.18%, P: ≤0.015%, S: ≤0.01%, Als: 0.015%-0.040%, Nb: 0.03%-0.05%, N: ≤0.003%; The surface roughness Ra of the roller used for the flattening is 2.6-2.9 μm, and the roller surface RPc value of the roller used for the flattening is not less than 95; The tension of the flattening is 20-25 KN, and the elongation of the flattening is 0.6%-0.7%.

2. The method for preparing steel for automobile outer panel according to claim 1, characterized in that: The moving speed of the electroplated steel strip is 60-100 m / min.

3. The method for preparing the steel for automobile outer panel according to claim 1, characterized in that: The surface roughness Ra of the roller used for the smoothing is 2.7-2.8 μm, and the roller surface RPc value of the roller used for the smoothing is not less than 100.

4. The method for preparing steel for automobile outer panel according to claim 1, characterized in that: The annealing soaking temperature is 840-860° C.; and / or The annealing strip moving speed is 120-150m / min.

5. A steel for automobile outer panel, characterized in that: The steel for automobile outer panel is prepared by the preparation method as described in any one of claims 1 to 4.

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