Method for improving surface quality of pickling plate for automobile outer plate and pickling plate

Abstract

The invention provides a method for improving the surface quality of a pickled plate for an automobile outer plate and the pickled plate, and belongs to the field of steel preparation. The method comprises the following steps: obtaining a plate blank with set chemical components; the plate blank is heated and then rolled, and a hot rolled plate is obtained; the hot-rolled plate is coiled at the set coiling temperature and then rapidly cooled, and a hot-rolled coil is obtained; the hot-rolled coil is subjected to acid pickling at the set acid pickling speed, and an acid pickling plate is obtained; a pickling solution for pickling contains a pickling accelerant with a set concentration. By reasonably designing the chemical components of the pickling plate and controlling the technological parameters of heating, the influence of sulfides and phosphides of the microalloy element Ti in the steel on the surface quality can be reduced; by controlling the coiling temperature, the influence of over-thick oxide scale and surface intergranular oxidation on the surface quality under the high-temperature coiling process can be reduced. Therefore, the surface quality of the pickling plate for the automobile outer plate is improved.

Description

Technical Field

[0001] The present application relates to the technical field of steel material preparation, and in particular to a method for improving the surface quality of a pickled plate for an automobile outer panel, and a pickled plate. Background Art

[0002] High-grade automobile outer panels generally add Ti to fix C and N elements in steel. At the same time, the TiC formed can improve the strength to a certain extent. Ti is a relatively economical element with good strengthening effect. However, in the production process of ultra-low carbon automobile outer panels containing Ti, the surface quality after pickling is prone to poor, which is mainly manifested in iron sheet residue and strip color difference defects, resulting in leakage and slag defects on the subsequent galvanized surface.

[0003] At present, the control of zinc plating leakage and slag point defects is limited to the zinc plating process, which at most involves the surface cleanliness of the raw materials, and there is no coordinated control from the hot rolling to cold rolling process. For example, the annealing temperature and dew point temperature are controlled to avoid the generation of bright spot defects; the pickling process adjustment such as acid concentration and acid temperature is controlled to improve the surface quality. However, the surface quality controlled by the above methods is not ideal. Therefore, it is urgent to develop a method that can improve the surface quality of pickled plates for automotive exterior panels. Summary of the invention

[0004] The present application provides a method for improving the surface quality of a pickled plate for an automobile outer panel and a pickled plate, so as to solve the following technical problem: how to improve the surface quality of a pickled plate for an automobile outer panel.

[0005] In a first aspect, the present application provides a method for improving the surface quality of a pickled plate for an automobile outer panel, the method comprising:

[0006] A slab with a set chemical composition is obtained;

[0007] The slab is heated, and the following heating parameters are controlled: heating temperature, holding time and excess air coefficient of the heating atmosphere, and then rolled to obtain a hot-rolled plate;

[0008] Coiling the hot-rolled sheet at a set coiling temperature, and then rapidly cooling the sheet to obtain a hot-rolled coil;

[0009] The hot-rolled coil is pickled at a set pickling speed to obtain a pickled plate; the pickling solution contains a pickling accelerator of a set concentration.

[0010] Optionally, the set chemical composition includes, by mass fraction: C: 0.0010% to 0.0025%, Mn: 0.10% to 0.15%, Si: 0.005% to 0.01%, P≤0.02%, Ti: 0.03% to 0.07%, and the remainder is Fe and unavoidable impurities.

[0011] Optionally, the heating temperature is 1180° C. to 1200° C., the insulation time is 170 min to 200 min, and the excess air coefficient of the heating atmosphere is 1.05 to 1.20.

[0012] Optionally, the finishing rolling F1-F7 stands use high-speed steel rollers.

[0013] Optionally, the set coiling temperature is 680°C to 710°C.

[0014] Optionally, the rapid cooling method includes water cooling tank cooling.

[0015] Optionally, the time interval between the coiling and the rapid cooling is ≤60 min.

[0016] Optionally, the pickling speed is set to 100m / min to 140m / min.

[0017] Optionally, the set concentration of the pickling accelerator is 0.15% to 0.25%.

[0018] In a second aspect, the present application provides a pickling plate prepared by the method described in any one of the embodiments of the first aspect.

[0019] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0020] The present application provides a method for improving the surface quality of pickled plates for automobile outer panels, and pickled plates, comprising: obtaining a slab with a set chemical composition; heating the slab, and controlling the following parameters of the heating: heating temperature, holding time, and air excess coefficient of the heating atmosphere, and then rolling to obtain a hot-rolled plate; coiling the hot-rolled plate at a set coiling temperature, and then rapidly cooling to obtain a hot-rolled coil; pickling the hot-rolled coil at a set pickling speed to obtain a pickled plate; the pickling solution of the pickling contains a pickling accelerator of a set concentration. By reasonably designing the chemical composition of the pickled plate and controlling the heating process parameters, the influence of sulfides and phosphides of the microalloying element Ti in the steel on the surface quality can be reduced; by controlling the coiling temperature, the influence of excessively thick iron oxide scale and surface intergranular oxidation on the surface quality under the high-temperature coiling process can be reduced; by controlling the pickling process parameters, the iron oxide scale and surface intergranular oxidation defects can be effectively removed. Thereby, the surface quality of the pickled plates for automobile outer panels is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] 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.

[0022] 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.

[0023] Figure 1 A schematic flow chart of a method for improving the surface quality of a pickled plate for an automobile outer panel provided in an embodiment of the present application;

[0024] Figure 2 A surface morphology of the pickled plate provided in Example 1 of the present application;

[0025] Figure 3 The surface morphology of the pickled plate provided in Comparative Example 1 of the present application;

[0026] Figure 4 A surface morphology diagram of a pickled plate provided in Example 2 of the present application;

[0027] Figure 5 The surface morphology of the pickled plate provided in Comparative Example 2 of the present application;

[0028] Figure 6 The surface morphology of the pickled plate provided in Example 3 of the present application;

[0029] Figure 7 The surface morphology of the pickled plate provided in Comparative Example 3 of the present application;

[0030] Figure 8 A surface morphology diagram of a pickled plate provided in Example 4 of the present application;

[0031] Fig. 9 This is a surface morphology of the pickled plate provided in Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0032] 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.

[0033] 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.

[0034] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply 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 three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0035] 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.

[0036] High-grade automobile outer panels generally add Ti to fix C and N elements in steel. At the same time, the TiC formed can improve the strength to a certain extent. Ti is a relatively economical element with good strengthening effect. However, compared with the Fe element in the steel matrix, Ti is easily oxidized and combined with S to form TiS to weaken the grain boundary. The gas in the hot rolling furnace comes from the blast furnace and the coking furnace, which inevitably contains S. When the S element in the gas in the heating furnace is abnormal, TiS is enriched on the surface of the billet in the heating furnace, resulting in the production of iron oxide scale on the substrate during the rolling process, which is exposed after being pressed into pickling. Therefore, the strong oxidizing atmosphere of the heating furnace is properly controlled to burn off the TiS enriched on the surface of the billet in the heating furnace to reduce the occurrence of defects. In addition, the P element is also easy to enrich at the grain boundary. When Ti exists in the steel, the surface of the Ti phosphide formed during the hot rolling process may crack at the grain boundary.

[0037] Therefore, the present application comprehensively considers the influence of sulfide and phosphide of microalloying element Ti in steel on surface quality, and considers the influence of excessively thick scale and surface intergranular oxidation on surface quality under high temperature coiling process, and provides a method for improving the pickling surface quality of ultra-low carbon automobile outer plate by adjusting the process during hot rolling and pickling. The method solves the problem of poor pickling surface of ultra-low carbon automobile outer plate without increasing cost, and the method is simple and effective.

[0038] Figure 1 A schematic flow chart of a method for improving the surface quality of a pickled plate for an automobile outer panel provided in an embodiment of the present application.

[0039] See also Figure 1 The present application provides a method for improving the surface quality of a pickled plate for an automobile outer panel, the method comprising:

[0040] S1. Obtaining a slab with a set chemical composition;

[0041] In some embodiments, the set chemical composition includes, by mass fraction: C: 0.0010% to 0.0025%, Mn: 0.10% to 0.15%, Si: 0.005% to 0.01%, P≤0.02%, Ti: 0.03% to 0.07%, and the remainder is Fe and unavoidable impurities.

[0042] In actual production, it is found that due to the presence of a certain amount of Ti in steel, the sulfide combines with the S element in the heating furnace atmosphere during the heating process of the ingot, and the sulfide has an adverse effect on the surface quality of the slab. Therefore, certain restrictions are placed on the Ti element of the slab, and the Ti element is controlled at 0.03% to 0.07%. When the Ti element is lower than 0.03%, it is difficult to completely remove the solid solution C and N atoms, causing aging of the strip steel; when the Ti element is higher than 0.07%, the sulfide invades the surface of the ingot, and the iron sheet press-in defects increase significantly after rolling. In addition, the P element content is controlled, and the P element is lower than 0.02% to reduce the harm of Ti phosphide; the Mn element content is also required during component smelting. The lower limit of the Mn element is 0.1%. On the basis of ensuring strength, the Mn element does not exceed 0.15%, to avoid the diffusion of the Mn element to the grain boundary during the high temperature slow cooling process after coiling, causing intergranular oxidation defects. Exemplarily, the C content can be 0.0010%, 0.0012%, 0.0015%, 0.0018%, 0.0020%, 0.0025%, etc.; the Mn content can be 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, etc.; the Si content can be 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, 0.01%, etc.; the P content can be 0.005%, 0.010%, 0.012%, 0.016%, 0.02%, etc.; the Ti content can be 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, etc.

[0043] S2, heating the slab and controlling the following heating parameters: heating temperature, holding time and excess air coefficient of the heating atmosphere, and then rolling to obtain a hot-rolled plate;

[0044] In some embodiments, the heating temperature is 1180° C. to 1200° C., the holding time is 170 min to 200 min, and the excess air coefficient of the heating atmosphere is 1.05 to 1.20.

[0045] The heating furnace parameters have a great influence on the surface quality. The heating temperature of the heating furnace affects the enrichment of Ti, S and P elements on the slab surface and the morphology of Ti phosphides and sulfides. When the heating temperature exceeds 1200℃ and the time exceeds 200min, the Ti sulfide changes from solid to liquid and extends into the slab along the grain boundary. The Ti phosphide will also adhere to the liquid sulfide and enter the slab, causing incomplete descaling and aggravating the pressure of iron oxide scale. When the temperature is less than 1180℃ and the time is less than 170min, it is not easy to burn out the slag inherited from steelmaking on the surface of the casting. Therefore, the temperature of the billet heating furnace is 1180-1200℃, the holding time is 170-200min, and the air coefficient of the heating furnace is controlled at 1.05-1.20 at the same time, which can effectively remove the slag and is also conducive to the removal of some Ti phosphides and sulfides. Exemplarily, the heating temperature can be 1180°C, 1185°C, 1190°C, 1195°C, 1200°C, etc., the holding time can be 170min, 180min, 190min, 195min, 200min, etc., and the excess air coefficient of the heating atmosphere can be 1.05, 1.10, 1.12, 1.15, 1.18, 1.20, etc.

[0046] In some embodiments, the finishing rolling mills F1 to F7 use high-speed steel rolls.

[0047] Research on the hot rolling process found that when ordinary infinitely cold hardened rolls are used, pickling color difference defects often occur, and the probability of iron sheet residue increases significantly. High-speed steel rolls have good surface wear resistance, and it is not easy to produce grooves on the surface during rolling, which reduces the stress of contact with the strip and reduces the risk of iron sheet pressing. In actual production, it is found that when producing automobile outer panels, the entire F1-F7 frame of the finishing rolling adopts high-speed steel rolls, and they are arranged in the early stage of the rolls, and the surface quality is the best.

[0048] S3, coiling the hot-rolled sheet at a set coiling temperature, and then rapidly cooling the sheet to obtain a hot-rolled coil;

[0049] In some embodiments, the set coiling temperature is 680°C to 710°C.

[0050] In some embodiments, the rapid cooling method includes water cooling tank cooling.

[0051] In some embodiments, the time interval between the coiling and the rapid cooling is ≤ 60 min.

[0052] During the slow natural cooling process after the hot-rolled steel coil is coiled, the iron oxide scale thickens and the thickness is uneven, which can easily cause pickling color difference and defects. In addition, oxygen elements easily invade the grain boundaries of the strip steel matrix and the Mn elements enriched in the grain boundaries to form grain boundary oxides. Therefore, under the effect of solid solution strengthening, the coiling temperature needs to be controlled within a certain range. However, in practice, the coiling temperature cannot be greatly reduced to ensure the mechanical properties of the strip steel. Therefore, the hot-rolled steel coiling temperature is controlled at 680-710°C. After the steel coil is coiled, it is placed in a water cooling tank for rapid cooling within 60 minutes, and the high-temperature residence time is reduced to avoid intergranular oxidation defects during the coiling process. Exemplarily, the set coiling temperature can be 680°C, 682°C, 685°C, 690°C, 695°C, 700°C, 705°C, 710°C, etc.; the time interval between coiling and the rapid cooling can be 20min, 30min, 40min, 50min, 60min, etc.

[0053] S4, pickling the hot-rolled coil at a set pickling speed to obtain a pickled plate; the pickling solution contains a pickling accelerator of a set concentration.

[0054] In some embodiments, the pickling speed is set to 100 m / min to 140 m / min.

[0055] In some embodiments, the set concentration of the pickling accelerator is 0.15% to 0.25%.

[0056] The pickling speed has a great influence on the pickling surface quality. The pickling speed of the pickling process is controlled at 100-140m / min. When the pickling speed is lower than 100m / min, although the scale and intergranular oxidation substances can be removed, the acid on the surface of the pickled plate is more likely to remain on the surface of the strip and easily affect the production capacity of the pickling production line. If the pickling speed is too fast, exceeding 140m / min, intergranular oxidation defects are difficult to remove. Therefore, the appropriate addition of accelerators can greatly improve the removal of intergranular oxidation substances. When the concentration of the pickling accelerator is less than 0.15%, the removal effect is poor. When the concentration of the pickling accelerator is greater than 0.25%, the increase in iron loss is not conducive to the yield rate. Therefore, adding a pickling accelerator with a concentration of 0.15% to 0.25% in the acid solution can remove scale and surface intergranular oxidation defects without causing over-pickling. Exemplarily, the set pickling speed can be 100m / min, 110m / min, 120m / min, 130m / min, 135m / min, 140m / min, etc.; the set concentration of the pickling accelerator can be 0.15%, 0.18%, 0.20%, 0.22%, 0.25%, etc.

[0057] Based on a general inventive concept, the present application provides a pickling plate.

[0058] The pickling plate is realized based on the preparation method of the pickling plate mentioned above. The specific steps of the preparation method of the pickling plate can refer to the above embodiment. Since the pickling plate adopts part or all of the technical solutions of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment, which will not be repeated here one by one.

[0059] 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 industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0060] In the embodiment of the present application, molten iron is smelted to obtain the chemical composition of the slab shown in Table 1.

[0061] Table 1 Chemical composition of slab (wt%), the rest is Fe and unavoidable impurities

[0062] Group C Mn Si P Ti Examples 1 to 4 and Comparative Examples 2 to 4 0.0019％ 0.13％ 0.01％ 0.01％ 0.05％ Comparative Example 1 0.0015％ 0.11％ 0.008％ 0.03％ 0.08％

[0063] Based on the chemical composition of the above-mentioned slab, this embodiment provides a method for improving the surface quality of a pickled plate for an automobile outer panel, comprising the following steps:

[0064] S11, obtaining a slab with a set chemical composition;

[0065] S21, heating the slab, and controlling the following heating parameters: heating temperature, holding time and excess air coefficient of the heating atmosphere, and then rolling to obtain a hot-rolled plate;

[0066] S31, coiling the hot-rolled plate at a set coiling temperature, and then rapidly cooling the hot-rolled plate to obtain a hot-rolled coil;

[0067] S41, pickling the hot-rolled coil at a set pickling speed to obtain a pickled plate; the pickling solution contains a pickling accelerator of a set concentration.

[0068] Table 2 Process parameters of the method for improving the surface quality of pickled plates for automobile outer panels

[0069]

[0070] Attached Figures 2 to 9 Detailed explanation:

[0071] Figure 2 A surface morphology of the pickled plate provided in Example 1 of the present application;

[0072] Figure 3 This is a surface morphology of the pickled plate provided in Comparative Example 1 of the present application.

[0073] Depend on Figure 2 and Figure 3 By comparison, it can be seen that the higher the content of alloying elements Ti and P (Comparative Example 1, Ti = 0.08%, P = 0.03%), the more serious the iron scale residue and color difference defects on the pickling surface are; reducing the Ti and P contents, the iron scale residue phenomenon is alleviated to a certain extent, and the color difference is also reduced; it shows that controlling the content of alloying elements Ti and P can effectively reduce the iron scale residue defects.

[0074] Figure 4 A surface morphology diagram of a pickled plate provided in Example 2 of the present application;

[0075] Figure 5 This is a surface morphology of the pickled plate provided in Comparative Example 2 of the present application.

[0076] Depend on Figure 4 and Figure 5 By comparison, it can be seen that appropriate heating temperature and time, and increasing the excess air coefficient in the heating furnace can reduce the adverse effects of Ti and P elements and alleviate the residual defects of iron scale.

[0077] Figure 6 The surface morphology of the pickled plate provided in Example 3 of the present application;

[0078] Figure 7 This is a surface morphology of the pickled plate provided in Comparative Example 3 of the present application.

[0079] Depend on Figure 6 and Figure 7 By comparison, it can be seen that the use of high-speed steel rolls, lowering the coiling temperature, and reducing the high-temperature residence time after coiling can greatly reduce the severity of surface color difference and defects.

[0080] Figure 8 A surface morphology diagram of a pickled plate provided in Example 4 of the present application;

[0081] Fig. 9 This is a surface morphology of the pickled plate provided in Comparative Example 4 of the present application.

[0082] Depend on Figure 8 and Fig. 9 By comparison, it can be seen that the use of a higher pickling rate and a suitable accelerator concentration can significantly reduce the severity of surface color difference and defects. In addition, the surface quality of the pickled plate provided in Example 4 is better than that of the pickled plates in Examples 1 to 3 and Comparative Examples 1 to 4.

[0083] In addition, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0084] (1) In the embodiments of the present invention, the manufacturing method for improving the pickling surface quality of ultra-low carbon automobile outer panels provided can effectively reduce the incidence of surface quality defects of ultra-low carbon high-grade automobile outer panels after pickling, and can also provide a reference for improving the surface quality of other steel grades with similar compositions.

[0085] (2) In the embodiment of the present invention, the problem of galvanizing slag aggregation caused by hot rolling inheritance is solved, and the degradation rate of the outer plate caused by the slag aggregation is reduced from 2.7% to below 0.1%, which effectively improves the overall level of the outer plate and the normal operation of the production organization.

[0086] (3) In the embodiment of the present invention, a manufacturing method for improving the pickling surface quality of ultra-low carbon automobile outer panels is provided, and the content of elements in steel, especially P element, is controlled. The atmosphere of the heating furnace is adjusted during hot rolling, especially the cooling process after coiling, the pickling speed is adjusted during pickling, and an accelerator is added. Through the control of the above components and key process points, the poor quality problems such as residual iron scale on the pickling surface and intergranular oxidation caused by unreasonable control of the components and hot rolling and pickling processes are solved.

[0087] (4) In the embodiments of the present invention, the manufacturing method for improving the pickling surface quality of ultra-low carbon automobile outer panels is simple, economical and efficient. The present invention can be used to easily improve the pickling quality without increasing the difficulty of production line production and without affecting the performance of the finished product.

[0088] 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 improving the surface quality of pickled plates for automobile outer panels, characterized in that: The method comprises: A slab with a set chemical composition is obtained; The slab is heated, and the following heating parameters are controlled: heating temperature, holding time and excess air coefficient of the heating atmosphere, and then rolled to obtain a hot-rolled plate; Coiling the hot-rolled sheet at a set coiling temperature, and then rapidly cooling the sheet to obtain a hot-rolled coil; The hot-rolled coil is pickled at a set pickling speed to obtain a pickled plate; the pickling solution contains a pickling accelerator of a set concentration.

2. The method according to claim 1, characterized in that In terms of mass fraction, the set chemical composition includes: C: 0.0010% to 0.0025%, Mn: 0.10% to 0.15%, Si: 0.005% to 0.01%, P≤0.02%, Ti: 0.03% to 0.07%, and the remainder is Fe and unavoidable impurities.

3. The method according to claim 1, characterized in that The heating temperature is 1180° C. to 1200° C., the heat preservation time is 170 min to 200 min, and the air excess coefficient of the heating atmosphere is 1.05 to 1.

20.

4. The method according to claim 1, characterized in that: The finishing rolling F1-F7 stands adopt high-speed steel rollers.

5. The method according to claim 1, characterized in that The set coiling temperature is 680°C to 710°C.

6. The method according to claim 1, characterized in that The rapid cooling method includes water cooling tank cooling.

7. The method according to claim 1, characterized in that The time interval between the coiling and the rapid cooling is ≤60 min.

8. The method according to claim 1, characterized in that The pickling speed is set to 100m / min to 140m / min.

9. The method according to claim 1, characterized in that: The set concentration of the pickling accelerator is 0.15% to 0.25%.

10. A pickled plate prepared by the method according to any one of claims 1 to 9.

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