Scale removal device for steel sheet, steel sheet manufacturing device, scale removal method for steel sheet, and steel sheet manufacturing method

Abstract

This scale removal facility for a steel sheet is a facility for removing scale from a conveyed steel sheet, a first pickling device for performing a first pickling on a steel sheet using a first acid solution, a breaking device for mechanically breaking an oxide skin, and a second pickling device for performing a second pickling on the steel sheet using a second acid solution are arranged in this order from the upstream side in the conveying direction of the steel sheet.

Description

Technical Field

[0001] This invention relates to equipment for removing oxide scale from steel plates, equipment for manufacturing steel plates, methods for removing oxide scale from steel plates, and methods for manufacturing steel plates. Background Technology

[0002] Electromagnetic steel sheets, primarily used as core materials for electrical equipment, are broadly classified into non-directional and directional electromagnetic steel sheets. To reduce iron loss, they typically contain large amounts of Si and Al, which increase the inherent impedance of the steel. Non-directional electromagnetic steel sheets are generally manufactured as follows: steel with a specified composition is melted, and a slab is produced using continuous casting or similar methods. This slab is then hot-rolled, and as needed, hot-rolled sheet is annealed, pickled, cold-rolled, and finally recrystallized. Directional electromagnetic steel sheets are generally manufactured as follows: steel with a specified composition is melted, and a slab is produced using continuous casting or similar methods. Then, it is hot-rolled, and as needed, hot-rolled sheet is annealed, pickled, cold-rolled, and as needed, recrystallized annealing and a second cold rolling. A first recrystallization annealing, which also serves as a decarburization annealing, is performed, followed by coating with an annealing separating agent and a final annealing to allow for secondary recrystallization.

[0003] Hot-rolled sheet annealing is a process of homogenizing hot-rolled steel sheets. By homogenizing, insufficient recrystallization in the hot-rolled sheet can be eliminated, or the grains before cold rolling can be coarsened and granulated. This process can also improve the texture of the steel sheet before cold rolling to a texture favorable for magnetic properties or suppress wrinkling. Therefore, most high-grade electromagnetic steel sheets with high Si content undergo hot-rolled sheet annealing.

[0004] Pickling is a process of removing oxide scale from the surface of steel sheets before cold rolling. If steel sheets with residual oxide scale formed on their surface during hot rolling or annealing are cold rolled without pickling, the following problems may occur: the oxide scale may be pressed into the steel sheet surface by the rolls, or the peeled oxide scale may adhere to the roll surface, causing surface defects through transfer and significantly impairing the surface quality of the final product. The acid used in the pickling process can be any one of hydrochloric acid, sulfuric acid, hydrofluoric acid, or a mixture of these acids.

[0005] The oxide scale on hot-rolled steel sheets used for electromagnetic steel plates, which contain a large amount of Si and Al, consists of external and internal oxide scale. External oxide scale is formed by FeO, Fe3O4, Fe2O3, etc., which diffuse from the interior of the steel sheet to the exterior through Fe diffusion. Internal oxide scale is formed by Si oxides such as SiO2 and Fe2SiO4, and Al2O3, which diffuse from the exterior of the steel sheet to the interior through oxygen diffusion. In particular, the descaling properties of internal oxide scale containing SiO2 and Al2O3 are known to be significantly poor. Therefore, for descaling hot-rolled steel sheets used for electromagnetic steel plates, mechanical descaling treatments such as shot peening before pickling can improve descaling performance.

[0006] However, for high-grade electromagnetic steel sheets with high Si content, hot-rolled annealing to ensure magnetic properties leads to larger crystal grains and embrittlement of the steel sheet. Especially if the Si content exceeds 2.5% (mass), the following problems arise: shot peening, used to improve descaling properties, causes twinning deformation on the steel sheet surface, which can easily lead to sheet breakage during cold rolling.

[0007] Patent Document 1 discloses a technique that reduces the strain introduced onto the steel plate surface and suppresses twinning deformation by reducing the diameter of the shot projected during shot peening to less than 0.35 mm and decreasing the energy of the particles impacting the steel plate surface. Patent Document 2 discloses a technique for suppressing twinning deformation that easily occurs under low-temperature, high-strain-rate conditions when shot peening an electromagnetic steel plate containing 2.5–3.5% Si, by heating the steel plate at a temperature Ts such that Ts ≥ 80 × Si ≥ 180, corresponding to the Si content.

[0008] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 61-126919 Patent Document 2: Japanese Patent Application Publication No. 62-048463 Summary of the Invention

[0009] The problem that the invention aims to solve However, the technology disclosed in Patent Document 1 has the following problems: although twinning deformation can be suppressed by reducing the diameter of the pellets and decreasing the impact energy, the descaling properties deteriorate. Furthermore, in the technology disclosed in Patent Document 2, twinning deformation can be suppressed by increasing the steel plate temperature Ts. However, the higher the Si content, the higher the required steel plate temperature. Therefore, in a steel plate containing 4.0 [mass%] Si, which is considered the rolling limit, the steel plate temperature Ts derived from the above formula becomes 140 [°C]. This increases the risk of dust explosions caused by the pellets. Therefore, the technologies disclosed in Patent Documents 1 and 2 are practically unsuitable for actual production.

[0010] The present invention was made in view of the above-mentioned problems, and its object is to provide a steel plate descaling device, a steel plate manufacturing device, a steel plate descaling method, and a steel plate manufacturing method that can take into account both the descaling properties of the steel plate and the suppression of fracture during cold rolling.

[0011] Methods for solving problems To solve the above problems and achieve the goal: (1) The scale removal equipment for steel plates involved in this invention is a scale removal equipment for steel plates that removes scale from transported steel plates. It is characterized in that, from the upstream side in the transport direction of the steel plate, there are arranged in sequence: a first pickling device that performs a first pickling on the steel plate using a first acid solution; a destructive device that mechanically destroys the scale; and a second pickling device that performs a second pickling on the steel plate using a second acid solution.

[0012] (2) The steel plate oxide scale removal equipment of the present invention is characterized in that, in the invention described in (1) above, the second acid solution contains an acid pickling inhibitor.

[0013] (3) The steel plate oxide scale removal equipment of the present invention is characterized in that, in the invention of (1) or (2) above, the first acid solution is added with a pickling accelerator and the pickling time in the first pickling is set to 10 to 30 [s].

[0014] (4) The steel plate oxide scale removal equipment of the present invention is characterized in that, in any one of the inventions (1) to (3) above, a pre-destruction device for mechanically destroying the oxide scale is provided on the upstream side of the first pickling device in the conveying direction of the steel plate.

[0015] (5) The steel plate manufacturing equipment of the present invention comprises: a hot rolling equipment for obtaining a hot-rolled plate by hot rolling a steel raw material; a hot rolling annealing equipment for annealing the hot-rolled plate as needed; an oxide scale removal equipment for removing the oxide scale from the hot-rolled plate or the hot-rolled plate that has undergone the hot rolling annealing; a cold rolling equipment for obtaining a cold-rolled plate by cold rolling the hot-rolled plate to which the oxide scale has been removed; and a final annealing equipment for annealing the cold-rolled plate to obtain a cold-rolled annealed plate, characterized in that, as the oxide scale removal equipment, the oxide scale removal equipment of the invention of any one of (1) to (4) above is used.

[0016] (6) The method for removing oxide scale from steel plates according to the present invention is characterized in that the steel plate is pickled using a first pickling device that pickles the hot-rolled steel plate with a first acid solution, the oxide scale on the surface of the steel plate pickled by the first pickling device is mechanically destroyed by a destructive device, and the steel plate treated by the destructive device is pickled using a second pickling device with a second acid solution.

[0017] (7) The method for removing oxide scale from steel plates according to the present invention is characterized in that, in the invention described in (6) above, the second acid solution contains an acid pickling inhibitor.

[0018] (8) The method for removing oxide scale from steel plates according to the present invention is characterized in that, in the invention described in (6) or (7) above, a pickling accelerator is added to the first acid solution, and the pickling time based on the first pickling device is set to 10 to 30 [s].

[0019] (9) The method for removing scale from steel plates according to the present invention is characterized in that, in any one of the inventions (6) to (8) above, the scale is mechanically destroyed by a pre-destruction device arranged on the upstream side of the first pickling device in the conveying direction of the steel plate.

[0020] (10) The present invention relates to a method for manufacturing steel plates, comprising: a hot rolling process for obtaining a hot-rolled plate by hot rolling a steel raw material; a hot rolling annealing process for annealing the hot-rolled plate as needed; an oxide scale removal process for removing the oxide scale from the hot-rolled plate or the hot-rolled plate that has undergone the hot rolling annealing; a cold rolling process for obtaining a cold-rolled plate by cold rolling the hot-rolled plate to which the oxide scale has been removed; and a final annealing process for annealing the cold-rolled plate to obtain a cold-rolled annealed plate, characterized in that, in the oxide scale removal process, the oxide scale removal method of the invention of any one of (6) to (9) above is used.

[0021] Invention Effects The steel plate oxide scale removal equipment, steel plate manufacturing equipment, steel plate oxide scale removal method, and steel plate manufacturing method disclosed in this invention can achieve the effect of both removing oxide scale from steel plates and suppressing cracking during cold rolling. Attached Figure Description

[0022] [ Figure 1 ] Figure 1 A diagram illustrating the general configuration of the steel strip oxide removal apparatus according to the embodiment.

[0023] [ Figure 2 ] Figure 2 This is a schematic diagram illustrating the outer and inner oxide scale present on the surface of the steel strip. Detailed Implementation

[0024] The following describes embodiments of the steel plate oxide scale removal equipment, steel plate manufacturing equipment, steel plate oxide scale removal method, and steel plate manufacturing method according to the present invention. It should be noted that this invention is not limited to these embodiments. Furthermore, "steel plate" includes "steel strip".

[0025] Figure 1 This diagram illustrates the schematic configuration of the oxide scale removal apparatus 10 for steel strip 1 according to an embodiment. The oxide scale removal apparatus 10 will... Figure 1 The oxide scale of the steel strip 1 conveyed along the conveying direction indicated by the arrow is removed. The oxide scale removal equipment 10 is composed of an uncoiler 2, a welding machine 3, a first pickling device 4, a breaking device 5, a second pickling device 6, and a coiler 7 arranged sequentially from the upstream side in the conveying direction of the steel strip 1. The uncoiler 2 unwinds the coil of hot-rolled steel strip at the inlet side to release the steel strip 1. The welding machine 3 welds the preceding steel strip 1 to the following steel strip 1. The first pickling device 4 uses acid (first acid solution) to perform a first pickling on the steel strip 1 to remove the easily pickled oxide scale on the surface of the steel strip. The breaking device 5 mechanically breaks the film-like difficult-to-pick oxide scale on the surface of the steel strip. The second pickling device 6 uses acid (second acid solution) to perform a second pickling on the steel strip 1 to remove the remaining difficult-to-pick oxide scale on the surface of the steel strip along with the dissolution of the base metal. The coiler 7 coils the steel strip 1, which has undergone the second pickling, into a coil.

[0026] It should be noted that in the oxide scale removal equipment 10 according to the embodiment, a pre-destruction device for mechanically destroying the oxide scale on the surface of the steel strip can also be provided on the upstream side of the first pickling device 4 and the downstream side of the welding machine 3 in the conveying direction of the steel strip 1. In addition, as such a pre-destruction device and destruction device 5, any one of shot peening, tension leveling machine, grinding brush and laser cleaning device can be used.

[0027] in addition, Figure 1In this process, the steel strip 1, obtained by rolling a flat sheet of metal, i.e., a steel plate, into a coil shape, is the manufactured product (object to be removed from oxide scale), but the manufactured product (object to be removed from oxide scale) is not limited to the steel strip 1. For example, the manufactured product (object to be removed from oxide scale) can also be a flat sheet of metal, i.e., a steel plate, which is a steel material. That is, the oxide scale removal equipment 10 can be used for oxide scale removal methods of steel plates in a broad sense.

[0028] Generally speaking, in steel plate oxide scale removal equipment, after mechanical oxide scale removal treatment by mechanically destroying the oxide scale on the surface of the steel plate through a crushing device, the oxide scale is removed by pickling based on a pickling device.

[0029] The inventors of this application conducted repeated and in-depth research, and as a result, discovered that, Figure 2 As shown, the oxide scale 20 on the surface of the steel plate has a layered structure including an outer oxide scale 21 and an inner oxide scale 22, wherein the inner oxide scale 22 contains a film-like inner oxide scale 222 that exists in a manner that covers the base metal 23.

[0030] Here, the external oxide scale 21 is generally an iron-based oxide scale formed on the surface of the base metal, known as black scale. It is mainly formed by external oxidation during hot rolling and annealing of hot-rolled plates, and is likely acid-resistant oxide scale composed of FeO, Fe3O4, Fe2O3, Fe2SiO4, etc. On the inner side relative to the external oxide scale 21, an internal oxide scale 22 is formed, whose formation behavior is limited by the diffusion rate of oxygen. The oxide scale based on internal oxidation during hot rolling and annealing of hot-rolled plates is either island-shaped internal oxide scale 221 or film-shaped internal oxide scale 222. The island-shaped internal oxide scale 221 exists in an island-like form within the metallic iron 223, mainly composed of FeO, Fe2SiO4, SiO2, Al2O3, FeAl2O3, etc. The island-shaped internal oxide scale 221 contains a mixture of acid-soluble oxides and acid-insoluble oxides. Since metallic iron 223 itself is acid-soluble, the acid-insoluble oxides can also be peeled off and removed by acid treatment. The film-like internal oxide scale 222 is composed of amorphous oxides such as SiO2, Al2O3, FeAl2O4, Si, and Al. These oxides, formed on the innermost layer where the oxygen potential is low, are insoluble in acid because they have very strong bonds with oxygen. Furthermore, the film-like internal oxide scale 222 is formed in a film-like manner, covering the base metal 23, and therefore cannot be dissolved and peeled off by acid treatment.

[0031] Furthermore, firstly, using the first pickling apparatus 4, the portion of the acid-soluble outer oxide scale 21 and inner oxide scale 22, excluding the film-like inner oxide scale 222 (island-like inner oxide scale 221 and metallic iron 223), is removed. Next, the film-like inner oxide scale 222 is destroyed by mechanical descaling treatment based on the destroying device 5, such as shot peening. Then, using the second pickling apparatus 6, the remaining film-like inner oxide scale 222 is removed along with the dissolution of the base metal 23. The inventors of this application have discovered that this method can suppress sheet breakage during cold rolling and effectively remove the oxide scale 20 from the surface of the steel sheet.

[0032] Therefore, in the scale removal equipment 10 according to the embodiment, a first pickling device 4 and a second pickling device 6 are respectively provided on the upstream and downstream sides of the crushing device 5 in the conveying direction of the steel strip 1. Furthermore, in the scale removal equipment 10 according to the embodiment, the scale of the steel strip 1 is removed by pickling based on the first pickling device 4 and the second pickling device 6 (first pickling and second pickling).

[0033] Next, an example of the manufacturing method of the steel strip 1 according to the embodiment will be described. In general, the manufacturing method of the steel strip 1 according to the embodiment is a method of manufacturing steel strip 1 by sequentially performing a hot rolling process, a hot-rolled plate annealing process as needed, an oxide scale removal process, a cold rolling process, and a final annealing process on steel raw materials.

[0034] <Steel Raw Materials> The composition of the steel raw material is not particularly limited. The oxide scale removal method described in the embodiments is particularly useful for descaling steel strips (electromagnetic steel sheets) with a high Si content (e.g., containing 1.0 [mass%] or more of Si) that easily form a film-like, firm oxide scale, but it can also be applied to steel strips with a low Si content. The smelting method of the steel raw material is not particularly limited, and known smelting methods using converters or electric furnaces can be used. It should be noted that, considering factors such as productivity, it is preferable to produce slabs (steel raw materials) using continuous casting after smelting, but slabs (steel raw materials) can also be produced using known casting methods such as ingot-rolling or thin slab continuous casting.

[0035] <Hot rolling process> Hot rolling is a process of obtaining hot-rolled sheets by hot rolling steel raw materials. There are no particular limitations on hot rolling processes, as long as they involve heating and hot rolling steel raw materials to obtain hot-rolled sheets of specified dimensions; commonly used hot rolling processes can be applied. For example, a commonly used hot rolling process involves heating steel raw materials to a temperature of 1000°C to 1200°C. Then, the heated steel raw materials are hot-rolled at a finishing run temperature of 800°C to 950°C. After hot rolling, the materials are cooled and coiled at a coiling temperature of 400°C to 700°C to produce hot-rolled sheets of specified dimensions and shapes.

[0036] <Hot-rolled sheet annealing process> The hot-rolled sheet annealing process involves heating and holding the hot-rolled sheet at a high temperature to anneal it. There are no particular limitations on the hot-rolled sheet annealing process; commonly used hot-rolled sheet annealing processes can be applied. It should be noted that this process is not mandatory and can be omitted.

[0037] <Pickling process> The pickling process is a process of performing various treatments, including pickling, on hot-rolled steel sheets after the annealing process, or on hot-rolled steel sheets when the annealing process is omitted. The pickling process is performed using the scale removal equipment 10 described in the embodiment.

[0038] <Cold rolling process> Cold rolling is a process of cold rolling pickled steel sheets that have undergone pickling. There are no particular limitations on cold rolling processes, as long as they can reduce the pickled steel sheet to the desired thickness; commonly used cold rolling processes can be applied. For example, cold rolling processes with a reduction rate of 10–40% in each pass and a strain rate of 10–1000 s can be exemplified. -1 Under certain conditions, one or more rolling passes are performed to produce cold-rolled sheets of specified dimensions and shapes. Alternatively, cold-rolled sheets of specified dimensions and shapes can be produced by cold rolling with an intermediate annealing process in between, as needed. In this case, the conditions of the intermediate annealing process are not particularly limited, and commonly used intermediate annealing processes can be applied.

[0039] Final annealing process The final annealing process is a process of annealing cold-rolled sheets that have undergone the cold rolling process. There are no particular limitations on the final annealing process; any commonly used final annealing process can be applied. For example, a final annealing process can be illustrated by heating the cold-rolled sheet to an annealing temperature of 700°C to 1050°C and then cooling it to obtain a cold-rolled annealed sheet. It should be noted that an insulating coating is applied to the surface of the cold-rolled annealed sheet after the final annealing process, but the method and type of coating are not particularly limited, and any commonly used insulating coating process can be applied.

[0040] The oxide scale removal equipment 10 described in the embodiment can be applied, for example, to a steel strip 1 manufacturing equipment that uses the above-described steel strip 1 manufacturing method. Furthermore, in this steel strip 1 manufacturing equipment, the oxide scale of the steel strip 1 is removed by the oxide scale removal equipment 10 to manufacture the steel strip 1. As a result, the steel strip 1 can be manufactured by suppressing fracture caused by twinning deformation during cold rolling without causing dust explosions during shot peening or reducing descaling properties.

[0041] Example The present invention will be specifically described below with examples. However, the present invention is not limited thereto. For example, the driving conditions of the device for mechanically breaking the film-like, difficult-to-pick oxide scale on the surface of the steel strip are reference values ​​and do not limit the present invention. The detailed driving conditions vary depending on the type of device, the type of steel strip to be processed, and the prior heat treatment. However, the characteristic of the present invention is that the oxide scale is broken by the device after a single pickling to remove the external oxide scale. The various conditions of the single pickling, the double pickling, and the device 5 can be appropriately adjusted to find the optimal values.

[0042] <Steel Strip Manufacturing> First, a hot-rolled steel sheet containing C: 0.002 [mass%], Si: 3.7 [mass%], Mn: 0.5 [mass%], and with a thickness of 2.2 [mm], was subjected to hot-rolled annealing under homogenization conditions of 1000 [°C] × 30 [s]. Steel strip 1, used for evaluation experiments on descaling and cold-rolling properties, was manufactured in this manner.

[0043] (Evaluation Experiment 1) In evaluation experiment 1, shot peening was used as the destructive device 5 to confirm the applicability of the first pickling based on the first pickling device 4, which is located upstream of the destructive device 5 in the conveying direction of the steel strip 1. Furthermore, with this objective, as in Examples 1-12 and Comparative Examples 1-12, evaluation experiments on descaling performance and cold rolling performance were conducted by varying the presence or absence of the first pickling based on the first pickling device 4 and the shot peening conditions in the destructive device 5.

[0044] Table 1 shows the conditions and results of the pickling and rolling experiments in Examples 1-12 and Comparative Examples 1 and 2. It should be noted that, regarding "Oxide Scale Removal" in Table 1, as a measure of oxide scale removal performance, cases where oxide scale removal was completed after the second pickling are marked as "○", and cases where oxide scale removal was not completed are marked as "×". Furthermore, regarding "Cold Rolling Fracture Rate" in Table 1, as a measure of cold rollability, the fracture rate when cold rolling is performed to produce cold-rolled sheets after the second pickling is shown.

[0045] [Table 1] [Example 1] In Example 1, a first pickling process is performed based on the first pickling device 4. The conditions for this first pickling process are: the acid solution is hydrochloric acid, the acid solution temperature is 80°C, and the pickling time is 20 seconds. Additionally, in Example 1, the conditions for shot peening in the destructive device 5 are: the particle velocity is 10 m / s, and the projection density is 12.5 kg / m³. 2 In addition, in Example 1, as the conditions for the second pickling based on the second pickling apparatus 6, the acid solution was set to hydrochloric acid, the temperature of the acid solution was set to 80 [°C], and the pickling time was set to 20 [s]. As a result, in Example 1, the oxide scale removal was completed, and the breakage rate of cold rolling was 0 [%.

[0046] [Example 2] In Example 2, the particle velocity was set to 20 m / s as the shot peening condition in the destructive device 5, and all other conditions were the same as in Example 1. As a result, in Example 2, oxide scale removal was achieved, and the fracture rate of cold rolling was 0%.

[0047] [Example 3] In Example 3, the particle velocity was set to 30 m / s as the shot peening condition in the destructive device 5, and all other conditions were the same as in Example 1. As a result, in Example 3, oxide scale removal was achieved, and the fracture rate during cold rolling was 0%.

[0048] [Example 4] In Example 4, the particle velocity was set to 40 m / s as the shot peening condition in the destructive device 5, and all other conditions were the same as in Example 1. As a result, in Example 4, oxide scale removal was achieved, and the fracture rate during cold rolling was 0%.

[0049] [Example 5] In Example 5, the particle velocity was set to 50 m / s as the shot peening condition in the destructive device 5, and all other conditions were the same as in Example 1. As a result, in Example 5, oxide scale removal was achieved, and the fracture rate during cold rolling was 0%.

[0050] [Example 6] In Example 6, the particle velocity was set to 60 m / s as the shot peening condition in the destructive device 5, and all other conditions were the same as in Example 1. As a result, in Example 6, oxide scale removal was achieved, and the fracture rate of cold rolling was 0%.

[0051] [Comparative Example 1] In Comparative Example 1, the particle velocity was set to 100 m / s as the shot peening condition in the destructive device 5, and all other conditions were the same as in Example 1. As a result, in Comparative Example 1, oxide scale removal was achieved, and the fracture rate of cold rolling was 25%.

[0052] [Example 7] In Example 7, the shot peening density was set to 25 kg / m³ as a condition for shot peening in the destructive device 5. 2 Except for this, the conditions were set to be the same as in Example 1. As a result, in Example 7, the oxide scale removal was completed and the cold rolling breakage rate was 0%.

[0053] [Example 8] In Example 8, the shot peening density was set to 25 kg / m³ as a condition for shot peening in the destructive device 5. 2 Except for this, the conditions were set to be the same as in Example 2. As a result, in Example 8, the oxide scale removal was completed and the cold rolling breakage rate was 0%.

[0054] [Example 9] In Example 9, the shot peening density was set to 25 kg / m³ as a condition for shot peening in the destructive device 5. 2 Except for this, the conditions were the same as in Example 3. As a result, in Example 9, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0055] [Example 10] In Example 10, the shot peening density was set to 25 kg / m³ as a condition for shot peening in the destructive device 5. 2 Except for this, the conditions were the same as in Example 4. As a result, in Example 10, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0056] [Example 11] In Example 11, the shot peening density was set to 25 kg / m³ as a condition for shot peening in the destructive device 5. 2 Except for this, the conditions were the same as in Example 5. As a result, in Example 11, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0057] [Example 12] In Example 12, the shot peening density was set to 25 kg / m³ as a condition for shot peening in the destructive device 5. 2 Except for this, the conditions were the same as in Example 6. As a result, in Example 12, the oxide scale removal was completed and the cold rolling breakage rate was 0%.

[0058] [Comparative Example 2] In Comparative Example 2, the shot peening condition for the destructive device 5 was set to a projection density of 25 kg / m³. 2 The conditions were otherwise the same as those in Comparative Example 1. As a result, in Comparative Example 2, the oxide scale removal was completed and the breakage rate during cold rolling was 27%.

[0059] As shown in Table 1, as in Comparative Examples 1 and 2, under extremely high conditions such as the first pickling based on the first pickling device 4 and the particle velocity of the shot peening device 5 being 100 [m / s], although the oxide scale removal was completed, the fracture rate during cold rolling increased.

[0060] On the other hand, it can be seen that, as in Examples 1 to 12, by performing the first pickling based on the first pickling device 4 and under the condition that the particle velocity of the shot peening device 5 is low, it is possible to simultaneously remove the oxide scale and suppress the breakage that occurs during cold rolling.

[0061] That is, in Examples 1 to 12, the easily pickled external oxide scale 21 and internal oxide scale 22 on the steel strip surface are removed by the first pickling based on the first pickling device 4, and the difficult-to-pickle film-like internal oxide scale 222 is exposed on the surface. Furthermore, mechanical oxide scale destruction treatment is directly applied to the exposed film-like internal oxide scale 222, so even if the shot peening particle velocity in the destruction device 5 is low, the film-like internal oxide scale 222 can be destroyed. Therefore, even when the shot peening particle velocity in the destruction device 5 is low, oxide scale removal is also completed by performing the second pickling based on the second pickling device 6. Thus, in Examples 1 to 12, even if the mechanical oxide scale destruction treatment based on the destruction device 5 is weak, oxide scale removal is still completed, thereby suppressing processing damage to the base metal 23 and reducing the fracture rate during cold rolling.

[0062] (Evaluation Experiment 2) In Evaluation Experiment 2, in order to confirm the effect of the additive in the acid solution of the second pickling based on the second pickling apparatus 6, as in Examples 13-24, the conditions such as the second pickling time and the presence or absence of additives were changed to conduct evaluation experiments on descaling properties and cold rolling properties. Table 2 shows the conditions and evaluation results of Examples 13-24 in Evaluation Experiment 2.

[0063] [Table 2] [Example 13] In Example 13, the conditions for the first pickling based on the first pickling device 4 were: hydrochloric acid, acid temperature of 80°C, pickling time of 20 seconds, and no additives. Additionally, in Example 13, the conditions for shot peening in the destructive device 5 were: particle velocity of 30 m / s and projection density of 15 kg / m³. 2 Furthermore, in Example 13, the conditions for the second pickling based on the second pickling apparatus 6 were set as follows: the acid solution was hydrochloric acid, the acid solution temperature was set to 80°C, the pickling time was set to 10 seconds, and no additives were used. As a result, in Example 13, the oxide scale removal was completed, and the breakage rate of cold rolling was 0%.

[0064] [Example 14] In Example 14, the pickling time was set to 20 seconds as the conditions for the second pickling based on the second pickling apparatus 6, and otherwise the same as in Example 13. As a result, in Example 14, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0065] [Example 15] In Example 15, the pickling time was set to 30 seconds as the conditions for the second pickling based on the second pickling apparatus 6, and otherwise the same as in Example 13. As a result, in Example 15, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0066] [Example 16] In Example 16, the pickling time was set to 40 seconds as the conditions for the second pickling based on the second pickling apparatus 6, and otherwise the same as in Example 13. As a result, in Example 16, the oxide scale removal was completed and the cold rolling breakage rate was 0%.

[0067] [Example 17] In Example 17, the pickling time was set to 50 seconds as the condition for the second pickling based on the second pickling apparatus 6, and otherwise the same as in Example 13. As a result, in Example 17, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0068] [Example 18] In Example 18, the pickling time was set to 60 seconds as the conditions for the second pickling based on the second pickling apparatus 6, and otherwise the same as in Example 13. As a result, in Example 18, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0069] [Example 19] In Example 19, as a condition for the second pickling based on the second pickling apparatus 6, a pickling inhibitor was added to the acid solution, and otherwise the conditions were the same as in Example 13. As a result, in Example 19, oxide scale removal was achieved, and the breakage rate of cold rolling was 0%.

[0070] [Example 20] In Example 20, as part of the second pickling process based on the second pickling apparatus 6, a pickling inhibitor was added to the acid solution, and otherwise the conditions were the same as in Example 14. As a result, in Example 20, oxide scale removal was achieved, and the breakage rate during cold rolling was 0%.

[0071] [Example 21] In Example 21, as the conditions for the second pickling based on the second pickling apparatus 6, a pickling inhibitor was added to the acid solution, and otherwise the conditions were the same as in Example 15. As a result, in Example 21, oxide scale removal was achieved, and the breakage rate of cold rolling was 0%.

[0072] [Example 22] In Example 22, as a condition for the second pickling based on the second pickling apparatus 6, a pickling inhibitor was added to the acid solution, and otherwise the conditions were the same as in Example 16. As a result, in Example 22, oxide scale removal was achieved, and the breakage rate of cold rolling was 0%.

[0073] [Example 23] In Example 23, as a condition for the second pickling based on the second pickling apparatus 6, a pickling inhibitor was added to the acid solution, and otherwise the conditions were the same as in Example 17. As a result, in Example 23, oxide scale removal was achieved, and the breakage rate of cold rolling was 0%.

[0074] [Example 24] In Example 24, as part of the second pickling process based on the second pickling apparatus 6, a pickling inhibitor was added to the acid solution, and otherwise the conditions were the same as in Example 18. As a result, in Example 24, oxide scale removal was achieved, and the breakage rate of cold rolling was 0%.

[0075] As shown in Table 2, as in Examples 13 to 24, as the conditions for the second pickling based on the second pickling apparatus 6, regardless of whether pickling inhibitors are added to the acid solution, even if the time of the second pickling is increased, it is possible to simultaneously remove oxide scale and suppress breakage during cold rolling.

[0076] (Evaluation Experiment 3) In Evaluation Experiment 3, as in Examples 25-41 and Comparative Example 3, the effect of the additives in the acid solution during the first pickling was confirmed, and the applicability of pre-destruction—mechanically breaking down the oxide scale on the steel strip surface before the first pickling—was also confirmed. Furthermore, with this objective in mind, evaluation experiments on descaling properties and cold rolling properties were conducted by varying the first pickling time, the presence or absence of additives, and the presence or absence of pre-destruction. Table 3 shows the conditions and evaluation results for Examples 25-41 and Comparative Example 3 in Evaluation Experiment 3. It should be noted that pre-destruction was not performed in Evaluation Experiment 5, except in Evaluation Experiment 3.

[0077] [Table 3] [Comparative Example 3] In Comparative Example 3, no pre-destructive treatment was performed before the first pickling based on the first pickling apparatus 4. The conditions for the first pickling based on the first pickling apparatus 4 were: hydrochloric acid, acid temperature of 80°C, pickling time of 5 seconds, and no additives. Additionally, in Comparative Example 3, the conditions for shot peening in the destructive apparatus 5 were: particle velocity of 30 m / s and projection density of 10 kg / m³. 2 In Comparative Example 3, the conditions for the second pickling based on the second pickling apparatus 6 were set as hydrochloric acid, the acid temperature was set to 80°C, the pickling time was set to 20 seconds, and a pickling inhibitor was added as an additive. As a result, in Comparative Example 3, the oxide scale removal was not completed, and the breakage rate of cold rolling was 0%.

[0078] [Example 25] In Example 25, no pre-destructive treatment is performed before the first pickling based on the first pickling device 4. The conditions for the first pickling based on the first pickling device 4 are: hydrochloric acid, acid temperature of 80°C, pickling time of 10 seconds, and no additives. Additionally, in Example 25, the conditions for shot peening in the destructive device 5 are: particle velocity of 30 m / s and projection density of 10 kg / m³. 2 Furthermore, in Example 25, as the conditions for the second pickling based on the second pickling apparatus 6, the acid solution was set to hydrochloric acid, the temperature of the acid solution was set to 80°C, the pickling time was set to 20 seconds, and a pickling inhibitor was added as an additive. As a result, in Example 25, the oxide scale removal was completed, and the breakage rate of cold rolling was 0%.

[0079] [Example 26] In Example 26, the pickling time was set to 15 seconds as the condition for the first pickling based on the first pickling apparatus 4, and otherwise the same conditions as in Example 25 were applied. As a result, in Example 26, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0080] [Example 27] In Example 27, the pickling time was set to 20 seconds as the condition for the first pickling based on the first pickling apparatus 4, and otherwise the same conditions as in Example 25 were applied. As a result, in Example 27, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0081] [Example 28] In Example 28, the pickling time was set to 25 seconds as the conditions for the first pickling based on the first pickling apparatus 4, and otherwise the same as in Example 25. As a result, in Example 28, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0082] [Example 29] In Example 29, the pickling time was set to 30 seconds as the condition for the first pickling based on the first pickling apparatus 4, and otherwise the same conditions as in Example 25 were applied. As a result, in Example 29, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0083] [Example 30] In Example 30, the pickling time was set to 10 seconds as the conditions for the first pickling based on the first pickling apparatus 4, and a pickling accelerator as an additive was added to the acid solution. Otherwise, the conditions were the same as in Example 25. As a result, in Example 30, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0084] [Example 31] In Example 31, as the conditions for the first pickling based on the first pickling apparatus 4, a pickling accelerator as an additive was added to the acid solution, and otherwise the conditions were the same as in Example 25. As a result, in Example 31, oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0085] [Example 32] In Example 32, as the conditions for the first pickling based on the first pickling apparatus 4, a pickling accelerator was added to the acid solution, and otherwise the conditions were the same as in Example 26. As a result, in Example 32, oxide scale removal was achieved, and the breakage rate of cold rolling was 0%.

[0086] [Example 33] In Example 33, as the conditions for the first pickling based on the first pickling apparatus 4, a pickling accelerator was added to the acid solution, and otherwise the conditions were the same as in Example 27. As a result, in Example 33, oxide scale removal was completed, and the breakage rate of cold rolling was 0%.

[0087] [Example 34] In Example 34, as the conditions for the first pickling based on the first pickling apparatus 4, a pickling accelerator was added to the acid solution, and otherwise the conditions were the same as in Example 28. As a result, in Example 34, oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0088] [Example 35] In Example 35, as the conditions for the first pickling based on the first pickling apparatus 4, a pickling accelerator was added to the acid solution, and otherwise the conditions were the same as in Example 29. As a result, in Example 35, oxide scale removal was achieved, and the breakage rate of cold rolling was 0%.

[0089] [Example 36] In Example 36, shot peening as a pre-destructive treatment is performed before the first pickling based on the first pickling apparatus 4. The conditions for this shot peening are set as follows: particle velocity 30 m / s and projection density 10 kg / m³. 2 In addition, in Example 36, the conditions for the first pickling based on the first pickling device 4 are as follows: the acid solution is hydrochloric acid, the temperature of the acid solution is set to 80°C, the pickling time is set to 5 seconds, and no additives are used. Furthermore, in Example 36, the conditions for shot peening in the destructive device 5 are as follows: the particle velocity is set to 30 m / s, and the projection density is set to 10 kg / m³. 2Furthermore, in Example 36, as the conditions for the second pickling based on the second pickling apparatus 6, the acid solution was set to hydrochloric acid, the temperature of the acid solution was set to 80°C, the pickling time was set to 20 seconds, and a pickling inhibitor as an additive was added to the acid solution. As a result, in Example 36, the oxide scale removal was completed, and the breakage rate of cold rolling was 0%.

[0090] [Example 37] In Example 37, shot peening as a pre-destructive treatment was performed before the first pickling based on the first pickling apparatus 4. The conditions for this shot peening were set as follows: particle velocity was set to 30 [m / s], projection density was set to 10 [kg / m2], and other conditions were the same as in Example 25. As a result, in Example 37, oxide scale removal was achieved, and the breakage rate of cold rolling was 0 [%.

[0091] [Example 38] In Example 38, shot peening as a pre-destructive treatment is performed before the first pickling based on the first pickling apparatus 4. The conditions for this shot peening are set as follows: particle velocity 30 m / s and projection density 10 kg / m³. 2 Except for this, the conditions were set to be the same as in Example 26. As a result, in Example 38, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0092] [Example 39] In Example 39, shot peening as a pre-destructive treatment is performed before the first pickling based on the first pickling apparatus 4. The conditions for this shot peening are set as follows: particle velocity 30 m / s and projection density 10 kg / m³. 2 Except for this, the conditions were set to be the same as in Example 27. As a result, in Example 39, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0093] [Example 40] In Example 40, shot peening as a pre-destructive treatment is performed before the first pickling based on the first pickling apparatus 4. The conditions for this shot peening are set as follows: particle velocity 30 m / s and projection density 10 kg / m³. 2 Except for this, the conditions were set to be the same as in Example 28. As a result, in Example 40, the oxide scale removal was completed and the breakage rate of cold rolling was 0%.

[0094] [Example 41] In Example 41, shot peening as a pre-destructive treatment is performed before the first pickling based on the first pickling apparatus 4. The conditions for this shot peening are set as follows: particle velocity 30 m / s and projection density 10 kg / m³. 2Except for this, the conditions were set to be the same as in Example 29. As a result, in Example 41, the oxide scale removal was completed and the cold rolling breakage rate was 0%.

[0095] As shown in Table 3, under the conditions of Comparative Example 3, oxide scale removal was not completed. Specifically, no mechanical pre-destruction treatment of the oxide scale was performed before the first pickling based on the first pickling apparatus 4, no pickling accelerator was added to the acid used in the first pickling based on the first pickling apparatus 4, and the pickling time for the first pickling was 5 [s], yet oxide scale removal was not completed. This is because a portion of the easily pickled oxide scale, such as the external oxide scale, based on the pre-destruction treatment (shot peening) was not removed, and the pickling time for the first pickling was short, thus failing to completely remove the easily pickled oxide scale, such as the external oxide scale. Therefore, it is believed that the inner film-like, difficult-to-pickle oxide scale was not exposed, and the mechanical destruction was not sufficiently effective.

[0096] Furthermore, as shown in Table 3, oxide scale removal was achieved under the conditions of Examples 30-35. That is, without performing mechanical pre-destruction treatment of the oxide scale before the first pickling in the first pickling apparatus 4, adding a pickling accelerator to the acid used in the first pickling in the first pickling in the first pickling apparatus 4, and achieving oxide scale removal under the condition that the pickling time of the first pickling is 5 [s] or more. This is believed to be because, as in Example 30, the pickling accelerator, through its effect, allows for the early removal of easily pickled oxide scale such as external oxide scale, even when the pickling time of the first pickling is as short as 5 [s].

[0097] Furthermore, as shown in Table 3, oxide scale removal was achieved under the conditions of Examples 36-41. That is, pre-destruction treatment (shot peening) was performed before the first pickling based on the first pickling apparatus 4, and no pickling accelerator was added to the acid used in the first pickling based on the first pickling apparatus 4, and the pickling time of the first pickling was 5 [s] or more, thus oxide scale removal was achieved. This is believed to be because, through the pre-destruction treatment (shot peening), a portion of easily pickled oxide scale, such as external oxide scale, was removed. In addition, cracks were introduced into the remaining easily pickled oxide scale, thereby increasing its reactivity with the acid. Therefore, as in Example 36, even with a short pickling time of only 5 [s] in the first pickling, the removal of easily pickled oxide scale was achieved earlier.

[0098] (Evaluation Experiment 4) In evaluation experiment 4, a grinding brush was used as the destructive device 5 to confirm the applicability of the first pickling based on the first pickling device 4, which is located upstream of the destructive device 5 in the conveying direction of the steel strip 1. Furthermore, for this purpose, as in Examples 42-47, the conditions of the grinding brush in the destructive device 5, performed after the first pickling based on the first pickling device 4, were changed, and evaluation experiments on descaling and cold rolling properties were conducted. Table 4 shows the conditions and results of the pickling and rolling experiments in Examples 42-47.

[0099] [Table 4] [Example 42] In Example 42, a first pickling was performed using the first pickling apparatus 4. The conditions for the first pickling were hydrochloric acid, a temperature of 80°C, and a pickling time of 20 seconds. Additionally, in Example 42, the torque per 1000 mm plate width was set to 500 Nm as the condition for the abrasive brush in the crushing device 5. Furthermore, in Example 42, the conditions for the second pickling using the second pickling apparatus 6 were hydrochloric acid, a temperature of 80°C, and a pickling time of 20 seconds. As a result, in Example 42, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0100] [Example 43] In Example 43, the torque for the grinding brush in the crushing device 5 was set to 750 Nm per 1000 mm plate width, otherwise the same conditions as in Example 42 were applied. As a result, in Example 43, oxide scale removal was achieved and the cold rolling fracture rate was 0%.

[0101] [Example 44] In Example 44, the torque for each 1000 mm plate width was set to 1000 Nm as the condition for the grinding brush in the crushing device 5, and otherwise the same conditions as in Example 42 were applied. As a result, in Example 44, the oxide scale removal was completed and the cold rolling fracture rate was 0%.

[0102] [Example 45] In Example 45, the torque for each 1000 mm plate width was set to 1250 Nm as the condition for the grinding brush in the crushing device 5, and otherwise the same conditions as in Example 42 were applied. As a result, in Example 45, oxide scale removal was achieved and the cold rolling fracture rate was 0%.

[0103] [Example 46] In Example 46, the torque for the grinding brush in the crushing device 5 was set to 1500 Nm per 1000 mm plate width, otherwise the conditions were the same as in Example 42. As a result, in Example 46, oxide scale removal was achieved and the cold rolling fracture rate was 0%.

[0104] [Example 47] In Example 47, the torque per 1000 mm plate width was set to 1750 Nm as the condition for the grinding brush in the crushing device 5, and otherwise the same conditions as in Example 42 were applied. As a result, in Example 47, oxide scale removal was achieved and the cold rolling fracture rate was 0%.

[0105] As shown in Table 4, as in Examples 42 to 47, when the first pickling based on the first pickling device 4 is performed as a condition for the grinding brush in the destructive device 5, regardless of the magnitude of the torque per 1000 mm plate width, the removal of oxide scale and the suppression of breakage during cold rolling can be achieved simultaneously.

[0106] (Evaluation of Experiment 5) Next, as evaluation experiment 5, the effects of acid conditions (type, temperature, and time) and the type of destructive device 5 (shot peening, tension leveling machine, abrasive brush, and laser cleaning device) were confirmed. Furthermore, with this objective, evaluation experiments on descaling properties and cold rolling properties were conducted by changing the conditions of the acid and destructive device 5 (Examples 48-63 and Comparative Examples 4-7). Table 5 shows the conditions and evaluation results for Examples 48-63 and Comparative Examples 4-7 in evaluation experiment 5.

[0107] [Table 5] [Example 48] In Example 48, as the conditions for the first pickling based on the first pickling apparatus 4, the acid solution was set to hydrochloric acid, the temperature of the acid solution was set to 90°C, the pickling time was set to 20 seconds, and a pickling accelerator as an additive was added to the acid solution. Furthermore, in Example 48, the type of destructive device 5 was shot peening. Additionally, in Example 48, as the conditions for the second pickling based on the second pickling apparatus 6, the acid solution was set to hydrochloric acid, the temperature of the acid solution was set to 90°C, the pickling time was set to 20 seconds, and a pickling inhibitor as an additive was added to the acid solution. As a result, in Example 48, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0108] [Example 49] In Example 49, the acid temperature was set to 95°C for the first pickling based on the first pickling apparatus 4, and the type of destructive device 5 was a tension leveler. The acid temperature was also set to 95°C for the second pickling based on the second pickling apparatus 6. Otherwise, the conditions were the same as in Example 48. As a result, in Example 49, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0109] [Example 50] In Example 50, the acid temperature was set to 85°C for the first pickling based on the first pickling apparatus 4, and the type of abrasive device 5 was set to an abrasive brush. The acid temperature was also set to 85°C for the second pickling based on the second pickling apparatus 6. Otherwise, the conditions were the same as in Example 48. As a result, in Example 50, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0110] [Example 51] In Example 51, the acid temperature was set to 75°C for the first pickling based on the first pickling apparatus 4, and the type of destructive device 5 was set to a laser cleaning device. The acid temperature was also set to 75°C for the second pickling based on the second pickling apparatus 6. Otherwise, the conditions were the same as in Example 48. As a result, in Example 51, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0111] [Comparative Example 4] In Comparative Example 4, as the conditions for the first pickling based on the first pickling apparatus 4, the acid solution was set to hydrochloric acid, the temperature of the acid solution was set to 80°C, the pickling time was set to 20 seconds, and a pickling accelerator as an additive was added to the acid solution. Additionally, in Comparative Example 4, a non-destructive device 5 was used. Furthermore, as the conditions for the second pickling based on the second pickling apparatus 6, in Comparative Example 4, the acid solution was set to hydrochloric acid, the temperature of the acid solution was set to 80°C, the pickling time was set to 20 seconds, and a pickling inhibitor as an additive was added to the acid solution. As a result, in Comparative Example 4, oxide scale removal was not completed, and the cold rolling breakage rate was 2%.

[0112] [Example 52] In Example 52, the conditions for the first pickling based on the first pickling apparatus 4 were sulfuric acid, the acid temperature was set to 90°C, the pickling time was set to 20 seconds, and no additives were used. Additionally, in Example 52, the type of destructive device 5 was shot peening. Furthermore, in Example 52, the conditions for the second pickling based on the second pickling apparatus 6 were sulfuric acid, the acid temperature was set to 90°C, the pickling time was set to 15 seconds, and no additives were used. As a result, in Example 52, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0113] [Example 53] In Example 53, the acid temperature was set to 95°C for the first pickling based on the first pickling apparatus 4, and the type of destructive device 5 was set to a tension leveler. The acid temperature was also set to 95°C for the second pickling based on the second pickling apparatus 6. All other conditions were the same as in Example 52. As a result, in Example 53, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0114] [Example 54] In Example 54, the acid temperature was set to 85°C for the first pickling based on the first pickling apparatus 4, and the type of abrasive device 5 was set to an abrasive brush. The acid temperature was also set to 85°C for the second pickling based on the second pickling apparatus 6. Otherwise, the conditions were the same as in Example 52. As a result, in Example 54, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0115] [Example 55] In Example 55, the acid temperature was set to 75°C for the first pickling based on the first pickling apparatus 4, and the type of destructive device 5 was set to a laser cleaning device. The acid temperature was also set to 75°C for the second pickling based on the second pickling apparatus 6. Otherwise, the conditions were the same as in Example 52. As a result, in Example 55, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0116] [Comparative Example 5] In Comparative Example 5, the conditions for the first pickling based on the first pickling apparatus 4 were sulfuric acid, the acid temperature was set to 80°C, the pickling time was set to 20 seconds, and no additives were used. Additionally, in Comparative Example 5, a non-destructive device 5 was used. Furthermore, in Comparative Example 5, the conditions for the second pickling based on the second pickling apparatus 6 were sulfuric acid, the acid temperature was set to 80°C, the pickling time was set to 15 seconds, and no additives were used. As a result, in Comparative Example 5, oxide scale removal was not completed, and the breakage rate of cold rolling was 3%.

[0117] [Example 56] In Example 56, the conditions for the first pickling based on the first pickling apparatus 4 were hydrochloric acid + nitric acid, the acid temperature was set to 90°C, the pickling time was set to 25 seconds, and no additives were used. Additionally, in Example 56, the type of destructive device 5 was shot peening. Furthermore, in Example 56, the conditions for the second pickling based on the second pickling apparatus 6 were hydrochloric acid + nitric acid, the acid temperature was set to 90°C, the pickling time was set to 25 seconds, and no additives were used. As a result, in Example 56, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0118] [Example 57] In Example 57, the acid temperature was set to 95°C for the first pickling based on the first pickling apparatus 4, and the type of destructive device 5 was a tension leveler. The acid temperature was also set to 95°C for the second pickling based on the second pickling apparatus 6. All other conditions were the same as in Example 56. As a result, in Example 57, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0119] [Example 58] In Example 58, the acid temperature was set to 85°C for the first pickling based on the first pickling apparatus 4, and the type of abrasive device 5 was set to an abrasive brush. The acid temperature was also set to 85°C for the second pickling based on the second pickling apparatus 6. Otherwise, the conditions were the same as in Example 56. As a result, in Example 58, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0120] [Example 59] In Example 59, the acid temperature was set to 75°C for the first pickling based on the first pickling apparatus 4, and the type of destructive device 5 was set to a laser cleaning device. The acid temperature was also set to 75°C for the second pickling based on the second pickling apparatus 6. Otherwise, the conditions were the same as in Example 56. As a result, in Example 59, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0121] [Comparative Example 6] In Comparative Example 6, the conditions for the first pickling based on the first pickling apparatus 4 were hydrochloric acid + nitric acid, the acid temperature was set to 80°C, the pickling time was set to 25 seconds, and no additives were used. Additionally, Comparative Example 6 used a non-destructive device 5. Furthermore, in Comparative Example 6, the conditions for the second pickling based on the second pickling apparatus 6 were hydrochloric acid + nitric acid, the acid temperature was set to 80°C, the pickling time was set to 25 seconds, and no additives were used. As a result, in Comparative Example 6, oxide scale removal was not completed, and the cold rolling breakage rate was 3%.

[0122] [Example 60] In Example 60, the conditions for the first pickling based on the first pickling apparatus 4 were hydrochloric acid + hydrofluoric acid, the acid temperature was set to 90°C, the pickling time was set to 15 seconds, and no additives were used. Additionally, in Example 60, the type of destructive device 5 was shot peening. Furthermore, in Example 60, the conditions for the second pickling based on the second pickling apparatus 6 were hydrochloric acid + nitric acid, the acid temperature was set to 90°C, the pickling time was set to 10 seconds, and no additives were used. As a result, in Example 60, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0123] [Example 61] In Example 61, the acid temperature was set to 95°C for the first pickling based on the first pickling apparatus 4, and the type of destructive device 5 was set to a tension leveler. The acid temperature was also set to 95°C for the second pickling based on the second pickling apparatus 6. All other conditions were the same as in Example 60. As a result, in Example 61, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0124] [Example 62] In Example 62, the acid temperature was set to 85°C for the first pickling based on the first pickling apparatus 4, and the type of abrasive device 5 was set to an abrasive brush. The acid temperature was also set to 85°C for the second pickling based on the second pickling apparatus 6. Otherwise, the conditions were the same as in Example 60. As a result, in Example 62, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0125] [Example 63] In Example 63, the acid temperature was set to 75°C for the first pickling based on the first pickling apparatus 4, and the type of destructive device 5 was set to a laser cleaning device. The acid temperature was also set to 75°C for the second pickling based on the second pickling apparatus 6. Otherwise, the conditions were the same as in Example 60. As a result, in Example 63, oxide scale removal was achieved, and the cold rolling breakage rate was 0%.

[0126] [Comparative Example 7] In Comparative Example 7, the conditions for the first pickling based on the first pickling apparatus 4 were hydrochloric acid + hydrofluoric acid, the acid temperature was set to 80°C, the pickling time was set to 15 seconds, and no additives were used. Additionally, in Comparative Example 7, a non-destructive device 5 was used. Furthermore, in Comparative Example 7, the conditions for the second pickling based on the second pickling apparatus 6 were hydrochloric acid + nitric acid, the acid temperature was set to 80°C, the pickling time was set to 10 seconds, and no additives were used. As a result, in Comparative Example 7, oxide scale removal was not completed, and the breakage rate of cold rolling was 2%.

[0127] As shown in Table 5, in Comparative Examples 4-7, under conditions where no destructive device 5 was used and no mechanical destructive treatment of oxide scale was performed, oxide scale removal was not completed regardless of the type of acid used in the first and second pickling processes or the presence or absence of additives. Furthermore, fracture occurred during cold rolling. This is believed to be because a large amount of oxide scale remained, and the residual oxide scale became the starting point for fracture, thus increasing the fracture rate during cold rolling. On the other hand, as shown in Table 5, in Examples 48-63, under conditions where mechanical destructive treatment of oxide scale was performed using the destructive device 5, oxide scale removal was completed regardless of the conditions of the acid used in the first and second pickling processes, the presence or absence of additives, or the type of destructive device 5. Furthermore, no fracture occurred during cold rolling.

[0128] Industrial availability The present invention provides a steel plate descaling device, a steel plate manufacturing device, a steel plate descaling method, and a steel plate manufacturing method that can simultaneously achieve descaling of steel plates and suppress fracture during cold rolling.

[0129] Explanation of reference numerals in the attached figures 1. Steel strip 2 Uncoiling machine 3 Welding machine 4. First pickling unit 5. Destructive devices 6. Second pickling unit 7. Winding machine 10. Oxide scale removal equipment 20 Oxide Scale 21 External Oxide Scale 22 Internal oxide scale 23 Base metal 221 Island-shaped internal oxide scale 222 Membrane-like internal oxide scale 223 Metallic iron

Claims

1. A steel plate oxide scale removal device, characterized in that, it removes oxide scale from a conveyed steel plate. The steel plate is provided with the following components arranged sequentially from the upstream side in the conveying direction: a first pickling device for performing a first pickling on the steel plate using a first acid solution; a destructive device for mechanically destroying the oxide scale; and a second pickling device for performing a second pickling on the steel plate using a second acid solution.

2. The steel plate oxide scale removal equipment as described in claim 1, characterized in that, The second acid solution contains an acid washing inhibitor.

3. The oxide scale removal equipment for steel plates as described in claim 1 or 2, characterized in that, The first acid solution contains an acid pickling accelerator, and the pickling time in the first acid pickling is set to 10-30 seconds.

4. The scale removal equipment for steel plates according to any one of claims 1 to 3, characterized in that, A pre-destruction device for mechanically destroying the oxide scale is provided on the upstream side of the first pickling device in the conveying direction of the steel plate.

5. Steel plate manufacturing equipment, including: Hot rolling equipment that produces hot-rolled plates by hot rolling steel raw materials; A hot-rolled plate annealing device for performing hot-rolled plate annealing as needed; Oxide removal equipment for removing oxide scale from the hot-rolled plate or the hot-rolled plate that has undergone annealing; A cold rolling apparatus for obtaining a cold-rolled sheet by cold rolling the hot-rolled sheet to which the oxide scale has been removed; and The final annealing equipment for annealing the cold-rolled sheet to obtain the cold-rolled annealed sheet. Its features are, The oxide scale removal device is the same as that used for steel plates according to any one of claims 1 to 4.

6. A method for removing oxide scale from steel plates, characterized in that, The steel plate is pickled using a first pickling device that pickles the hot-rolled steel plate with a first acid solution. The oxide scale on the surface of the steel plate pickled by the first pickling device is mechanically destroyed by a destructive device. The steel plate treated by the destructive device is then pickled using a second pickling device with a second acid solution.

7. The method for removing oxide scale from steel plates as described in claim 6, characterized in that, The second acid solution contains an acid washing inhibitor.

8. The method for removing oxide scale from steel plates as described in claim 6 or 7, characterized in that, The first acid solution contains an acid pickling accelerator, and the pickling time based on the first acid pickling device is set to 10-30 seconds.

9. The method for removing oxide scale from steel plates as described in any one of claims 6 to 8, characterized in that, The oxide scale is mechanically destroyed by a pre-destruction device arranged upstream of the first pickling device in the conveying direction of the steel plate.

10. Methods for manufacturing steel plates, including: The hot rolling process is a process of obtaining hot-rolled plates by hot rolling steel raw materials; The hot-rolled plate is subjected to a hot-rolled plate annealing process as needed; An oxide removal process for removing oxide scale from the hot-rolled plate or the hot-rolled plate that has undergone annealing. A cold rolling process is performed on the hot-rolled sheet to which the oxide scale has been removed, thereby obtaining a cold-rolled sheet; and The final annealing process involves annealing the cold-rolled sheet to obtain a cold-rolled annealed sheet. The feature is that the oxide scale removal process uses the oxide scale removal method for steel plates according to any one of claims 6 to 9.

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