Scale removal facility for steel sheet, production facility for steel sheet, method for removing scales from steel sheet, and method for producing steel sheet

Abstract

A scale removal facility according to the present invention removes scales from a steel sheet that is being conveyed. The scale removal facility includes, in the order from the upstream side in the conveyance direction of the steel sheet, a first acid pickling device that performs first acid pickling on the steel sheet using a first acid solution, a destruction device that mechanically destroys the scales, and a second acid pickling device that performs second acid pickling on the steel sheet using a second acid solution.

Description

Steel plate descaling equipment, steel plate manufacturing equipment, steel plate descaling method, and steel plate manufacturing method

[0001] The present invention relates to a steel plate descaling equipment, a steel plate manufacturing equipment, a steel plate descaling method, and a steel plate manufacturing method.

[0002] Electrical steel sheets, which are mainly used as iron core materials for electrical equipment, are broadly divided into non-oriented electrical steel sheets and grain-oriented electrical steel sheets. They usually contain large amounts of Si and Al, which increase the resistivity of the steel, in order to reduce iron loss. Non-oriented electrical steel sheets are generally produced by melting steel adjusted to a predetermined composition, forming a slab of steel material by a continuous casting method or the like, hot-rolling the slab, optionally hot-rolling it, pickling, cold-rolling it, and then performing a finish annealing for recrystallization. Grain-oriented electrical steel sheets are generally produced by melting steel adjusted to a predetermined composition, forming a slab of steel material by a continuous casting method or the like, hot-rolling it, optionally hot-rolling it, pickling, cold-rolling it, optionally recrystallizing it and a second cold-rolling, performing a primary recrystallization annealing that also serves as decarburization annealing, applying an annealing separator, and then performing a finish annealing for secondary recrystallization.

[0003] Hot-rolled sheet annealing is a process in which a steel sheet (hot-rolled steel sheet) after hot rolling is subjected to a homogenizing heat treatment. This homogenizing heat treatment can eliminate insufficient recrystallization of the hot-rolled sheet, coarsen and regulate the grain size of the crystals before cold rolling, improve the texture of the steel sheet before cold rolling to be advantageous for magnetic properties, and suppress ridging. Therefore, hot-rolled sheet annealing is often performed on high-grade electrical steel sheets containing a large amount of Si.

[0004] Pickling is a process of removing oxide scale from the surface of a steel sheet (descaling) before cold rolling. If a steel sheet on which oxide scale formed on the surface by hot rolling or hot-rolled sheet annealing remains is cold-rolled without being pickled, the following problems may occur: The oxide scale may be pressed into the steel sheet surface by the rolling rolls, or the peeled oxide scale may adhere to the roll surface and be transferred, causing surface defects, which significantly impair the surface quality of the final product. The acid solution used in the pickling is any of hydrochloric acid, sulfuric acid, hydrofluoric acid, and mixed acids obtained by mixing these acids.

[0005] The oxide scale of hot-rolled steel sheets for electrical steel sheets containing large amounts of Si and Al consists of an outer scale and a subscale. The outer scale is formed by the diffusion of Fe from the inside of the steel sheet to the outside, and consists of FeO and Fe ３ O ４ , Fe ２ O ３ Subscale consists of SiO, which is formed when oxygen diffuses from the outside into the steel sheet. ２ and Fe ２ SiO ４ Si oxides such as Al ２ O ３ etc. In particular, SiO ２ and Al ２ O ３ It is known that subscale containing SiO2 has extremely poor descaling properties. Therefore, in descaling hot-rolled steel sheets for electrical steel sheets, mechanical descaling treatment such as shot blasting is carried out before pickling to mechanically destroy the scale, thereby improving descaling properties.

[0006] However, when high-grade electrical steel sheets with a high Si content are hot-rolled and annealed to ensure magnetic properties, the grain size increases, causing embrittlement of the steel sheet. In particular, when the Si content exceeds 2.5 mass%, shot blasting, which is performed to improve descaling properties, causes twinning deformation on the steel sheet surface, which can easily cause problems such as sheet breakage during cold rolling.

[0007] Patent Document 1 discloses a technique for suppressing twinning deformation, which is likely to occur under low-temperature, high-strain-rate conditions, by reducing the particle diameter of shots projected in shot blasting to less than 0.35 mm and reducing the energy of particles colliding with the steel sheet surface, thereby reducing the amount of strain introduced into the steel sheet surface. Patent Document 2 discloses a technique for suppressing twinning deformation, which is likely to occur under low-temperature, high-strain-rate conditions, when shot blasting an electrical steel sheet containing 2.5 to 3.5 mass% Si, by heating the steel sheet to a temperature Ts according to the Si content so as to satisfy the relational expression Ts [°C] ≥ 80 × Si [mass%] - 180.

[0008] JP-A-61-126919 JP-A-62-048463

[0009] However, while the technology disclosed in Patent Document 1 can suppress twinning by reducing the shot particle diameter and collision energy, it also has the problem of deteriorating descaling properties. Furthermore, the technology disclosed in Patent Document 2 can suppress twinning by increasing the steel sheet temperature Ts. However, the higher the Si content, the higher the required steel sheet temperature. For a steel sheet containing 4.0 [mass%] Si, which is considered the rolling limit, the steel sheet temperature Ts obtained from the above formula is 140 [°C]. This increases the risk of dust explosions due to shot particles. Therefore, it is difficult to apply either of the technologies disclosed in Patent Documents 1 and 2 to actual production.

[0010] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide steel plate descaling equipment, steel plate manufacturing equipment, steel plate descaling method, and steel plate manufacturing method that can achieve both the descaling ability of steel plate and the suppression of fracture occurrence during cold rolling.

[0011] In order to solve the above-mentioned problems and achieve the object, (1) the steel plate descaling equipment of the present invention is a steel plate descaling equipment that removes scale from a steel plate being transported, characterized in that, arranged in this order from upstream in the transport direction of the steel plate, are a first pickling device that performs a first pickling on the steel plate using a first acid solution, a destruction 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 descaling equipment according to the present invention is the equipment according to the above (1), characterized in that a pickling inhibitor is added to the second acid solution.

[0013] (3) The steel plate descaling equipment according to the present invention is the equipment according to the above (1) or (2), characterized in that a pickling accelerator is added to the first pickling solution, and the pickling time in the first pickling is set to 10 to 30 seconds.

[0014] (4) The steel plate scale removal equipment of the present invention is characterized in that, in any one of the above-mentioned (1) to (3), a preliminary destruction device that mechanically destroys the scale is provided upstream of the first pickling device in the conveying direction of the steel plate.

[0015] (5) The steel plate manufacturing equipment according to the present invention is a steel plate manufacturing equipment including: hot rolling equipment for hot rolling a steel material to obtain a hot-rolled plate; hot-rolled plate annealing equipment for annealing the hot-rolled plate as necessary; descaling equipment for removing scale from the hot-rolled plate or the hot-rolled plate that has been annealed; cold rolling equipment for cold-rolling the hot-rolled plate from which the scale has been removed to obtain a cold-rolled plate; and finish annealing equipment for annealing the cold-rolled plate to obtain a cold-rolled annealed plate, wherein the steel plate descaling equipment according to any one of the above (1) to (4) inventions is used as the descaling equipment.

[0016] (6) A method for removing scales from steel plate according to the present invention comprises pickling a hot-rolled steel plate in a first pickling device that pickles the steel plate using a first acid solution, subjecting the steel plate that has been pickled in the first pickling device to a treatment for mechanically destroying scale on the surface of the steel plate that has been pickled in the first pickling device using a destruction device, and pickling the steel plate that has been treated in the destruction device using a second acid solution in a second pickling device.

[0017] (7) The method for removing scale from a steel plate according to the present invention is the method according to the above (6), characterized in that a pickling inhibitor is added to the second acid solution.

[0018] (8) The method for removing scales from a steel plate according to the present invention is characterized in that, in the invention (6) or (7) above, a pickling accelerator is added to the first pickling solution, and the pickling time in the first pickling device is set to 10 to 30 seconds.

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

[0020] (10) A method for producing a steel plate according to the present invention includes a hot rolling step of hot rolling a steel material to obtain a hot-rolled plate, a hot-rolled plate annealing step of annealing the hot-rolled plate as needed, a descaling step of removing scale from the hot-rolled plate or the hot-rolled plate that has been annealed, a cold rolling step of cold-rolling the hot-rolled plate from which the scale has been removed to obtain a cold-rolled plate, and a finish annealing step of annealing the cold-rolled plate to obtain a cold-rolled annealed plate, wherein the descaling step uses the method for descaling a steel plate according to any one of the above-mentioned (6) to (9) inventions.

[0021] The steel plate descaling equipment, steel plate manufacturing equipment, steel plate descaling method, and steel plate manufacturing method according to the present invention have the effect of achieving both descaling properties for steel plate and suppression of fracture occurrence during cold rolling.

[0022] Fig. 1 is a diagram showing a schematic configuration of a steel strip descaling equipment according to an embodiment, and Fig. 2 is a schematic diagram showing external scale and internal scale present on the surface of a steel strip.

[0023] Hereinafter, embodiments of the steel plate descaling equipment, steel plate manufacturing equipment, steel plate descaling method, and steel plate manufacturing method according to the present invention will be described. Note that the present invention is not limited to these embodiments. Furthermore, the term "steel plate" includes "steel strip."

[0024] FIG. 1 is a diagram showing a schematic configuration of a descaling equipment 10 for a steel strip 1 according to an embodiment. This descaling equipment 10 removes scale from the steel strip 1 being transported in the transport direction indicated by the arrow in FIG. 1 . The descaling equipment 10 is configured, in order from upstream to downstream in the transport direction of the steel strip 1, to include a payoff reel 2, a welding machine 3, a first pickling device 4, a breaking device 5, a second pickling device 6, and a tension reel 7. The payoff reel 2 unwinds the hot-rolled steel strip 1 at the inlet side and discharges 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 performs a first pickling on the steel strip 1 using an acid solution (first acid solution) to remove easily pickled scale from the steel strip surface. The breaking device 5 mechanically breaks up film-like, difficult-to-pickle scale on the steel strip surface. The second pickling device 6 performs a second pickling on the steel strip 1 using an acid solution (second acid solution) to remove the destroyed, resistant scale remaining on the steel strip surface while dissolving the base steel. The tension reel 7 winds the steel strip 1 that has been subjected to the second pickling into a coil.

[0025] In the scale removal equipment 10 according to the embodiment, a preliminary destruction device for mechanically destroying scale on the surface of the steel strip may be provided upstream of the first pickling device 4 and downstream of the welding machine 3 in the conveying direction of the steel strip 1. As the preliminary destruction device and the destruction device 5, for example, any of a shot blaster, a tension leveler, a grinding brush, and a laser cleaning device can be used.

[0026] 1, the product (object to be descaled) is a steel strip 1 formed by winding a steel plate, which is a flat plate of metal that is a steel material, into a coil, but the product (object to be descaled) is not limited to the steel strip 1. For example, the product (object to be descaled) may be a steel plate, which is a flat plate of metal that is a steel material. In other words, the descaling equipment 10 can be used in a broad range of steel plate descaling methods.

[0027] Generally, in steel plate scale removal equipment, the scale on the surface of the steel plate is mechanically broken down by a breaking device through a mechanical descaling process, and then the scale is removed by pickling in a pickling device.

[0028] As a result of extensive research, the inventors of the present application have discovered that, as shown in Figure 2, scale 20 on the surface of a steel sheet has a layered structure made up of external scale 21 and internal scale 22, and that film-like internal scale 222 contained in the internal scale 22 is present so as to cover the base steel 23.

[0029] Here, the external scale 21 is iron-based scale formed on the surface of the base steel, generally called black scale, and is mainly formed by external oxidation during hot rolling or annealing of the hot-rolled sheet. ３ O ４ , Fe ２ O ３ , Fe ２ SiO ４ The scale formed by the acid mainly composed of FeO, Fe, etc. is an internal scale 22 formed on the inner layer side of the external scale 21, the formation behavior of which is controlled by the diffusion of oxygen. The scale formed by internal oxidation during hot rolling or annealing of the hot-rolled sheet is the island-like internal scale 221 and the film-like internal scale 222. The island-like internal scale 221 exists in the metallic iron 223 in an island shape, and is composed of FeO, Fe, ２ SiO ４ , SiO ２ , Al ２ O ３ , FeAl ２ O ３The island-like internal scale 221 is a mixture of oxides that are soluble in acid and oxides that are insoluble in acid, but since the metallic iron 223 itself is soluble in acid, the oxides that are insoluble in acid also flake off and can be removed by acid treatment. The film-like internal scale 222 is composed of SiO ２ , Al ２ O ３ , FeAl ２ O ４ The film-like internal scale 222 is composed of amorphous oxides of silicon, silicon, and aluminum, etc. These oxides, which are formed in the innermost layer, which has a low oxygen potential, have a very strong bond with oxygen and are therefore insoluble in acid. Furthermore, because the film-like internal scale 222 is formed in a film-like form to cover the steel substrate 23, it cannot be removed by dissolving the steel substrate 23 through acid treatment.

[0030] First, a first pickling process is performed in a first pickling device 4 to remove all of the external scale 21 and internal scale 22 that are easily soluble in acid except for the film-like internal scale 222 (the island-like internal scale 221 and metallic iron 223). Next, the film-like internal scale 222 is destroyed by a mechanical descaling process in a destruction device 5 such as shot blasting. Then, a second pickling process is performed in a second pickling device 6 to dissolve the base steel 23 and remove the remaining film-like internal scale 222. The present inventors have found that this process effectively completes the removal of scale 20 from the steel sheet surface while suppressing sheet breakage during cold rolling.

[0031] Therefore, in the scale removal equipment 10 according to the embodiment, a first pickling device 4 and a second pickling device 6 are installed upstream and downstream of the breaking device 5 in the conveying direction of the steel strip 1. In the scale removal equipment 10 according to the embodiment, scale is removed from the steel strip 1 by pickling (first pickling and second pickling) using the first pickling device 4 and the second pickling device 6.

[0032] Next, an example of a method for manufacturing the steel strip 1 according to the embodiment will be described. In summary, the method for manufacturing the steel strip 1 according to the embodiment is a method for manufacturing the steel strip 1 by sequentially subjecting a steel material to a hot rolling process, and if necessary, a hot-rolled sheet annealing process, a descaling process, a cold rolling process, and a finish annealing process.

[0033] <Steel Material> The composition of the steel material is not particularly limited. The descaling method according to the embodiment is particularly useful for descaling steel strips (electrical steel sheets) having a high Si content (for example, containing 1.0 [mass%] or more of Si), which are prone to the formation of strong film-like scale, but is also suitably applicable to steel strips having a low Si content. The method for producing the steel material is not particularly limited, and known methods using a converter, an electric furnace, or the like can be employed. Note that, from the viewpoint of productivity and the like, it is preferable to produce a slab (steel material) by continuous casting after the smelting, but the slab (steel material) may also be produced by known casting methods such as ingot making-blooming rolling or thin slab continuous casting.

[0034] <Hot Rolling Process> The hot rolling process is a process of hot-rolling a steel material to obtain a hot-rolled sheet. The hot rolling process is not particularly limited as long as it is a process of heating the steel material and hot-rolling it to obtain a hot-rolled sheet of a predetermined size, and a conventional hot rolling process can be applied. An example of a conventional hot rolling process is a hot rolling process in which the steel material is heated to a temperature of 1000°C or more and 1200°C or less. The heated steel material is then hot-rolled at a finish rolling delivery temperature of 800°C or more and 950°C or less, and after the hot rolling is completed, the steel material is cooled and coiled at a coiling temperature of 400°C or more and 700°C or less to obtain a hot-rolled sheet of a predetermined size and shape.

[0035] <Hot-rolled sheet annealing process> The hot-rolled sheet annealing process is a process of annealing the hot-rolled sheet by heating the hot-rolled sheet and holding it at a high temperature. The hot-rolled sheet annealing process is not particularly limited, and a conventional hot-rolled sheet annealing process can be applied. Note that this process is not essential and can be omitted.

[0036] <Pickling Process> The pickling process is a process of subjecting the steel sheet after the hot-rolled sheet annealing process, or the hot-rolled sheet when the hot-rolled sheet annealing process is omitted, to various treatments including pickling. The pickling process is performed using the descaling equipment 10 according to the embodiment.

[0037] <Cold Rolling Process> The cold rolling process is a process of cold rolling the pickled steel sheet that has been subjected to the pickling process. The cold rolling process is not particularly limited as long as it is a process that can roll down the pickled steel sheet to the desired thickness, and a conventional cold rolling process can be applied. For example, the rolling reduction rate for each pass is 10 to 40% and the strain rate is 10 to 1000 s －１

[0033] A cold rolling process in which the cold rolled sheet is subjected to one or more passes of rolling under the conditions of

[0034] and a cold rolled sheet having a predetermined size and shape can be produced. Alternatively, the cold rolled sheet can be produced by two or more passes of cold rolling with an intermediate annealing step interposed therebetween, as necessary. In this case, the conditions of the intermediate annealing step are not particularly limited, and a conventional intermediate annealing step can be applied.

[0038] <Finish Annealing Step> The finish annealing step is a step of annealing the cold-rolled sheet that has undergone the cold rolling step. The finish annealing step is not particularly limited, and a conventional finish annealing step can be applied. For example, a finish annealing step can be exemplified in which the cold-rolled sheet that has undergone the cold rolling step is heated to an annealing temperature of 700°C or higher and 1050°C or lower and then cooled to obtain a cold-rolled annealed sheet. Note that after the finish annealing step, an insulating coating is applied to the surface of the cold-rolled annealed sheet. The method and type of coating are not particularly limited, and a conventional insulating coating step can be applied.

[0039] The descaling equipment 10 according to the embodiment can be applied to, for example, equipment for manufacturing a steel strip 1 using the above-described method for manufacturing the steel strip 1. In this equipment for manufacturing the steel strip 1, the scale of the steel strip 1 is removed by the descaling equipment 10 to manufacture the steel strip 1. As a result, the steel strip 1 can be manufactured without causing a dust explosion in shot blasting, without reducing descaling properties, and while suppressing breakage due to twin deformation in cold rolling.

[0040] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these. For example, the operating conditions of the destruction device that mechanically destroys the film-like, resistant scale on the surface of the steel strip are for reference only and do not limit the present invention. Although the detailed operating conditions vary depending on the type of destruction device, the type of steel strip to be treated, and the prior heat treatment, a distinctive feature of the present invention is that scale destruction treatment is performed using the destruction device after the removal of external scale by primary pickling. The various conditions for primary pickling, secondary pickling, and destruction device 5 can be appropriately adjusted to find optimal values.

[0041] <Production of Steel Strip> First, a hot-rolled steel sheet containing 0.002 mass% C, 3.7 mass% Si, and 0.5 mass% Mn and having a thickness of 2.2 mm was subjected to hot-rolled sheet annealing under soaking conditions of 1000°C x 30 seconds. In this manner, steel strip 1 for evaluation experiments of descaling properties and cold rolling properties was produced.

[0042] (Evaluation Experiment 1) In Evaluation Experiment 1, a shot blaster was used as the destructive device 5, and the effect of applying the first pickling by the first pickling device 4 provided upstream of the destructive device 5 in the conveying direction of the steel strip 1 was confirmed. For this purpose, as in Examples 1 to 12 and Comparative Examples 1 to 12, evaluation experiments on descaling properties and cold rolling properties were conducted by changing the presence or absence of the first pickling by the first pickling device 4 and the conditions for shot blasting in the destructive device 5.

[0043] Table 1 shows the conditions and results of the pickling and rolling experiments in Examples 1 to 12 and Comparative Examples 1 and 2. In Table 1, "scaling removal" indicates descaling ability, with "◯" indicating that scale removal was completed after the second pickling, and "×" indicating that scale removal was not completed. In Table 1, "fracture occurrence rate in cold rolling" indicates the fracture occurrence rate when cold rolling was performed after the second pickling to obtain a cold-rolled sheet, as cold rolling ability.

[0044]

[0045] In Example 1, a first pickling was performed using the first pickling device 4. The conditions for the first pickling were hydrochloric acid as the pickling solution, a temperature of the pickling solution of 80°C, and a pickling time of 20 seconds. In Example 1, the conditions for shot blasting in the destruction device 5 were a particle velocity of 10 m / s and a shot density of 12.5 kg / m. ２ In Example 1, the conditions for the second pickling by the second pickling device 6 were that the pickling solution was hydrochloric acid, the temperature of the pickling solution was 80°C, and the pickling time was 20 seconds. As a result, in Example 1, scale removal was completed, and the rate of fracture in cold rolling was 0%.

[0046] In Example 2, the conditions for shot blasting in the breaking device 5 were the same as those in Example 1, except that the particle velocity was set to 20 m / s. As a result, in Example 2, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0047] In Example 3, the conditions for shot blasting in the breaking device 5 were the same as those in Example 1, except that the particle velocity was set to 30 m / s. As a result, in Example 3, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0048] In Example 4, the conditions for shot blasting in the breaking device 5 were the same as those in Example 1, except that the particle velocity was set to 40 m / s. As a result, in Example 4, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0049] In Example 5, the conditions for shot blasting in the breaking device 5 were the same as those in Example 1, except that the particle velocity was set to 50 m / s. As a result, in Example 5, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0050] In Example 6, the conditions for shot blasting in the breaking device 5 were the same as those in Example 1, except that the particle velocity was set to 60 m / s. As a result, in Example 6, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0051] In Comparative Example 1, the conditions for shot blasting in the destruction device 5 were the same as those in Example 1, except that the particle velocity was 100 m / s. As a result, in Comparative Example 1, scale removal was completed, and the fracture occurrence rate in cold rolling was 25%.

[0052] [Example 7] In Example 7, the conditions for shot blasting in the destruction device 5 were a projection density of 25 [kg / m ２ The conditions were the same as in Example 1, except that the scale removal was completed in Example 7, and the fracture occurrence rate in cold rolling was 0%.

[0053] [Example 8] In Example 8, the conditions for shot blasting in the destruction device 5 were a projection density of 25 [kg / m ２ The conditions were the same as in Example 2, except that the scale removal was completed in Example 8, and the fracture occurrence rate in cold rolling was 0%.

[0054] [Example 9] In Example 9, the conditions for shot blasting in the destruction device 5 were a projection density of 25 [kg / m ２ The conditions were the same as in Example 3, except that the scale removal was completed in Example 9, and the fracture occurrence rate in cold rolling was 0%.

[0055] [Example 10] In Example 10, the conditions for shot blasting in the destruction device 5 were a projection density of 25 [kg / m ２ The conditions were the same as in Example 4, except that the scale removal was completed in Example 10, and the fracture occurrence rate in cold rolling was 0%.

[0056] [Example 11] In Example 11, the conditions for shot blasting in the destruction device 5 were a projection density of 25 [kg / m ２ The conditions were the same as in Example 5, except that the scale removal was completed in Example 11, and the fracture occurrence rate in cold rolling was 0%.

[0057] [Example 12] In Example 12, the conditions for shot blasting in the destruction device 5 were a projection density of 25 [kg / m２ The conditions were the same as in Example 6, except that the scale removal was completed in Example 12, and the fracture occurrence rate in cold rolling was 0%.

[0058] [Comparative Example 2] In Comparative Example 2, the shot blasting conditions in the destruction device 5 were a projection density of 25 [kg / m ２ The conditions were the same as those of Comparative Example 1, except that the scale removal was completed in Comparative Example 2, and the fracture incidence rate in cold rolling was 27%.

[0059] From Table 1, it can be seen that under conditions such as Comparative Examples 1 and 2, where first pickling is performed using the first pickling device 4 and the particle velocity of shot blasting in the breaking device 5 is extremely high at 100 m / s, scale removal is completed, but the fracture occurrence rate in cold rolling increases.

[0060] On the other hand, as in Examples 1 to 12, under conditions in which the first pickling is performed using the first pickling device 4 and the particle velocity of the shot blasting in the breaking device 5 is low, it is found that it is possible to achieve both scale removal and suppression of fracture occurrence during cold rolling.

[0061] That is, in Examples 1 to 12, the first pickling performed by the first pickling device 4 removes the external scale 21 and internal scale 22 on the steel strip surface, which are easy to pickle, and exposes the film-like internal scale 222, which is difficult to pickle, on the surface. Then, because a mechanical scale destruction process is performed directly on the exposed film-like internal scale 222, the film-like internal scale 222 can be destroyed even if the particle velocity of the shot blasting in the destruction device 5 is low. Therefore, even if the particle velocity of the shot blasting in the destruction device 5 is low, scale removal is completed by performing the second pickling performed by the second pickling device 6. Thus, in Examples 1 to 12, even if the mechanical scale destruction process by the destruction device 5 is weak, scale removal is completed, thereby suppressing processing damage to the base steel 23 and reducing the rate of fractures during cold rolling.

[0062] (Evaluation Experiment 2) In Evaluation Experiment 2, for the purpose of confirming the effect of additives on the acid solution of the second pickling in the second pickling device 6, evaluation experiments were carried out on descaling properties and cold rolling properties by changing conditions such as the time of the second pickling and the presence or absence of additives, as in Examples 13 to 24. Table 2 shows the conditions and evaluation results of Examples 13 to 24 in Evaluation Experiment 2.

[0063]

[0064] In Example 13, the conditions for the first pickling in the first pickling device 4 were as follows: the acid solution was hydrochloric acid, the temperature of the acid solution was 80°C, the pickling time was 20 seconds, and no additives were used. Also, in Example 13, the conditions for shot blasting in the destruction device 5 were as follows: particle velocity was 30 m / s, projection density was 15 kg / m ２ In Example 13, the conditions for the second pickling using the second pickling device 6 were as follows: the pickling solution was hydrochloric acid, the temperature of the pickling solution was 80°C, the pickling time was 10 seconds, and no additives were used. As a result, in Example 13, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0065] In Example 14, the conditions for the second pickling in the second pickling device 6 were the same as those in Example 13, except that the pickling time was set to 20 seconds. As a result, in Example 14, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0066] Example 15 In Example 15, the conditions for the second pickling in the second pickling device 6 were the same as those in Example 13, except that the pickling time was set to 30 seconds. As a result, in Example 15, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0067] In Example 16, the conditions for the second pickling in the second pickling device 6 were the same as those in Example 13, except that the pickling time was 40 seconds. As a result, in Example 16, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0068] In Example 17, the conditions for the second pickling in the second pickling device 6 were the same as those in Example 13, except that the pickling time was set to 50 seconds. As a result, in Example 17, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0069] In Example 18, the conditions for the second pickling in the second pickling device 6 were the same as those in Example 13, except that the pickling time was set to 60 seconds. As a result, in Example 18, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0070] In Example 19, the conditions for the second pickling in the second pickling apparatus 6 were the same as those in Example 13, except that a pickling inhibitor was added to the pickling solution. As a result, in Example 19, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0071] In Example 20, the conditions for the second pickling in the second pickling apparatus 6 were the same as those in Example 14, except that a pickling inhibitor was added to the pickling solution. As a result, in Example 20, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0072] In Example 21, the conditions for the second pickling in the second pickling apparatus 6 were the same as those in Example 15, except that a pickling inhibitor was added to the pickling solution. As a result, in Example 21, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0073] In Example 22, the conditions for the second pickling in the second pickling apparatus 6 were the same as those in Example 16, except that a pickling inhibitor was added to the pickling solution. As a result, in Example 22, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0074] In Example 23, the conditions for the second pickling in the second pickling apparatus 6 were the same as those in Example 17, except that a pickling inhibitor was added to the pickling solution. As a result, in Example 23, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0075] In Example 24, the conditions for the second pickling in the second pickling apparatus 6 were the same as those in Example 18, except that a pickling inhibitor was added to the pickling solution. As a result, in Example 24, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0076] From Table 2, it can be seen that, as in Examples 13 to 24, as a condition for the second pickling using the second pickling apparatus 6, regardless of whether or not a pickling inhibitor is added to the pickling solution, even if the time for the second pickling is increased, it is possible to achieve both scale removal and suppression of fractures during cold rolling.

[0077] (Evaluation Experiment 3) In Evaluation Experiment 3, as in Examples 25 to 41 and Comparative Example 3, the effects of additives in the acid solution of the first pickling were confirmed, and the effect of applying pre-fracturing, which mechanically breaks down the scale on the steel strip surface before the first pickling, was confirmed. For this purpose, evaluation experiments were conducted on descaling properties and cold rolling properties by changing conditions such as the time of the first pickling, the presence or absence of additives, and the presence or absence of pre-fracturing. Table 3 shows the conditions and evaluation results for Examples 25 to 41 and Comparative Example 3 in Evaluation Experiment 3. Note that, of Evaluation Experiment 5, pre-fracturing was not performed except for Evaluation Experiment 3.

[0078]

[0079] In Comparative Example 3, no preliminary destruction treatment was performed before the first pickling in the first pickling device 4, and the conditions for the first pickling in the first pickling device 4 were as follows: the acid solution was hydrochloric acid, the temperature of the acid solution was 80°C, the pickling time was 5 seconds, and no additives were used. Also, in Comparative Example 3, the conditions for shot blasting in the destruction device 5 were: particle velocity was 30 m / s, projection density was 10 kg / m ２ In Comparative Example 3, the conditions for the second pickling using the second pickling device 6 were as follows: the pickling solution was hydrochloric acid, the temperature of the pickling solution was 80°C, the pickling time was 20 seconds, and a pickling inhibitor was added as an additive. As a result, in Comparative Example 3, scale removal was not completed, and the fracture occurrence rate in cold rolling was 0%.

[0080] In Example 25, no preliminary destruction treatment was performed before the first pickling in the first pickling device 4, and the conditions for the first pickling in the first pickling device 4 were as follows: the acid solution was hydrochloric acid, the temperature of the acid solution was 80°C, the pickling time was 10 seconds, and no additives were used. Also in Example 25, the conditions for shot blasting in the destruction device 5 were: particle velocity was 30 m / s, projection density was 10 kg / m ２ In Example 25, the conditions for the second pickling using the second pickling device 6 were as follows: the pickling solution was hydrochloric acid, the temperature of the pickling solution was 80°C, the pickling time was 20 seconds, and a pickling inhibitor was added as an additive. As a result, in Example 25, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0081] Example 26 In Example 26, the conditions for the first pickling in the first pickling device 4 were the same as those in Example 25, except that the pickling time was 15 seconds. As a result, in Example 26, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0082] Example 27 In Example 27, the conditions for the first pickling in the first pickling device 4 were the same as those in Example 25, except that the pickling time was 20 seconds. As a result, in Example 27, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0083] Example 28 In Example 28, the conditions for the first pickling in the first pickling device 4 were the same as those in Example 25, except that the pickling time was set to 25 seconds. As a result, in Example 28, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0084] Example 29 In Example 29, the conditions for the first pickling in the first pickling device 4 were the same as those in Example 25, except that the pickling time was set to 30 seconds. As a result, in Example 29, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0085] In Example 30, the conditions for the first pickling in the first pickling device 4 were the same as those in Example 25, except that the pickling time was 10 seconds and a pickling accelerator was added as an additive to the pickling solution. As a result, in Example 30, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0086] In Example 31, the conditions for the first pickling in the first pickling device 4 were the same as those in Example 25, except that a pickling accelerator was added as an additive to the pickling solution. As a result, in Example 31, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0087] In Example 32, the conditions for the first pickling in the first pickling device 4 were the same as those in Example 26, except that a pickling accelerator was added to the pickling solution. As a result, in Example 32, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0088] In Example 33, the conditions for the first pickling in the first pickling device 4 were the same as those in Example 27, except that a pickling accelerator was added to the pickling solution. As a result, in Example 33, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0089] In Example 34, the conditions for the first pickling in the first pickling device 4 were the same as those in Example 28, except that a pickling accelerator was added to the pickling solution. As a result, in Example 34, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0090] In Example 35, the conditions for the first pickling in the first pickling device 4 were the same as those in Example 29, except that a pickling accelerator was added to the pickling solution. As a result, in Example 35, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0091] [Example 36] In Example 36, shot blasting was performed as a preliminary destruction treatment before the first pickling by the first pickling device 4, and the conditions for this shot blasting were a particle velocity of 30 [m / s] and a projection density of 10 [kg / m ２In Example 36, the conditions for the first pickling by the first pickling device 4 were that the acid solution was hydrochloric acid, the temperature of the acid solution was 80°C, the pickling time was 5 seconds, and no additives were used. In Example 36, the conditions for shot blasting in the destruction device 5 were that the particle velocity was 30 m / s, the projection density was 10 kg / m ２ In Example 36, the conditions for the second pickling using the second pickling device 6 were as follows: the pickling solution was hydrochloric acid, the temperature of the pickling solution was 80°C, the pickling time was 20 seconds, and a pickling inhibitor was added to the pickling solution as an additive. As a result, in Example 36, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0092] In Example 37, shot blasting was performed as a preliminary destruction treatment before the first pickling in the first pickling device 4, and the conditions for this shot blasting were the same as those in Example 25, except that the particle velocity was 30 m / s and the projection density was 10 kg / m. As a result, in Example 37, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0093] [Example 38] In Example 38, shot blasting was performed as a preliminary destruction treatment before the first pickling by the first pickling device 4, and the conditions for this shot blasting were a particle velocity of 30 [m / s] and a projection density of 10 [kg / m ２ The conditions were the same as in Example 26, except that the scale removal was completed in Example 38, and the fracture occurrence rate in cold rolling was 0%.

[0094] [Example 39] In Example 39, shot blasting was performed as a preliminary destruction treatment before the first pickling by the first pickling device 4, and the conditions for this shot blasting were a particle velocity of 30 [m / s] and a projection density of 10 [kg / m ２ The conditions were the same as in Example 27, except that the scale removal was completed in Example 39, and the fracture occurrence rate in cold rolling was 0%.

[0095] [Example 40] In Example 40, shot blasting was performed as a preliminary destruction treatment before the first pickling by the first pickling device 4, and the conditions for this shot blasting were a particle velocity of 30 [m / s] and a projection density of 10 [kg / m ２ The conditions were the same as in Example 28, except that the scale removal was completed in Example 40, and the fracture occurrence rate in cold rolling was 0%.

[0096] [Example 41] In Example 41, shot blasting was performed as a preliminary destruction treatment before the first pickling by the first pickling device 4, and the conditions for this shot blasting were a particle velocity of 30 [m / s] and a projection density of 10 [kg / m ２ The conditions were the same as in Example 29, except that the scale removal was completed in Example 41, and the fracture occurrence rate in cold rolling was 0%.

[0097] Table 3 shows that scale removal was not completed under the conditions of Comparative Example 3. That is, scale removal was not completed under the conditions where no mechanical preliminary destruction treatment of scale was performed before the first pickling in the first pickling apparatus 4, no pickling accelerator was added to the acid solution used in the first pickling in the first pickling apparatus 4, and the pickling time of the first pickling was 5 seconds. This is thought to be because some of the easy-to-pickle scale, such as external scale, was not removed by the preliminary destruction treatment (shot blasting), and the pickling time of the first pickling was too short, so removal of the easy-to-pickle scale, such as external scale, was not completed. As a result, the film-like scale that was difficult to pickle in the inner layer was not exposed, and mechanical destruction did not work sufficiently.

[0098] Furthermore, Table 3 shows that scale removal was completed under the conditions of Examples 30 to 35. That is, scale removal was completed under the conditions that no mechanical preliminary destruction treatment of scale was performed before the first pickling in the first pickling device 4, a pickling accelerator was added to the pickling solution used in the first pickling in the first pickling device 4, and the pickling time of the first pickling was 5 seconds or more. This is thought to be because, due to the effect of the pickling accelerator, removal of easy-to-pickle scale such as external scale was completed early even when the pickling time of the first pickling was as short as 5 seconds as in Example 30.

[0099] Table 3 also shows that scale removal was completed under the conditions of Examples 36 to 41. That is, scale removal was completed under the conditions that a preliminary destructive treatment (shot blasting) was performed before the first pickling in the first pickling apparatus 4, that a pickling accelerator was not added to the pickling solution used in the first pickling in the first pickling apparatus 4, and that the pickling time of the first pickling was 5 seconds or longer. This is thought to be because the preliminary destructive treatment (shot blasting) removes some of the easily pickled scale, such as external scale. Furthermore, the introduction of cracks into the remaining easily pickled scale increases its reactivity with the pickling solution, and therefore removal of the easily pickled scale was completed early even when the pickling time of the first pickling was as short as 5 seconds, as in Example 36.

[0100] (Evaluation Experiment 4) In Evaluation Experiment 4, a grinding brush was used as the breaking device 5, and the effect of applying the first pickling by the first pickling device 4 provided upstream of the breaking device 5 in the conveying direction of the steel strip 1 was confirmed. For this purpose, as in Examples 42 to 47, evaluation experiments on descaling properties and cold rolling properties were conducted by changing the conditions of the grinding brush in the breaking device 5 performed after the first pickling by the first pickling device 4. Table 4 shows the conditions and results of the pickling and rolling experiments in Examples 42 to 47.

[0101]

[0102] Example 42 In Example 42, a first pickling was performed using the first pickling device 4. The conditions for the first pickling were that the pickling solution was hydrochloric acid, the temperature of the pickling solution was 80°C, and the pickling time was 20 seconds. In Example 42, the conditions for the grinding brush in the breaking device 5 were that the torque per 1000 mm of sheet width was 500 Nm. In Example 42, the conditions for the second pickling performed using the second pickling device 6 were that the pickling solution was hydrochloric acid, the temperature of the pickling solution was 80°C, and the pickling time was 20 seconds. As a result, in Example 42, scale removal was completed, and the cold rolling fracture rate was 0%.

[0103] In Example 43, the conditions were the same as in Example 42, except that the torque per 1000 mm of plate width was set to 750 Nm as the condition of the grinding brush in the breaking device 5. As a result, in Example 43, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0104] In Example 44, the conditions were the same as in Example 42, except that the torque per 1000 mm of plate width was set to 1000 Nm as the condition of the grinding brush in the breaking device 5. As a result, in Example 44, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0105] In Example 45, the conditions were the same as in Example 42, except that the torque per 1000 mm of plate width was set to 1250 Nm as the condition of the grinding brush in the breaking device 5. As a result, in Example 45, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0106] In Example 46, the conditions were the same as in Example 42, except that the torque per 1000 mm of plate width was set to 1500 Nm as the condition of the grinding brush in the breaking device 5. As a result, in Example 46, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0107] Example 47 In Example 47, the conditions were the same as those in Example 42, except that the torque per 1000 mm of plate width was set to 1750 Nm as the condition of the grinding brush in the breaking device 5. As a result, in Example 47, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0108] From Table 4, it can be seen that, as in Examples 42 to 47, first pickling is performed using the first pickling device 4, and as a condition of the grinding brush in the breaking device 5, it is possible to achieve both scale removal and suppression of fracture occurrence during cold rolling, regardless of the magnitude of the torque per 1000 mm of plate width.

[0109] (Evaluation Experiment 5) Next, in Evaluation Experiment 5, the effects of the acid solution conditions (type, temperature, and time) and the type of destructive device 5 (shot blast, tension leveler, grinding brush, and laser cleaning device) were confirmed. For this purpose, evaluation experiments on descaling properties and cold rolling properties were conducted under different conditions (Examples 48 to 63 and Comparative Examples 4 to 7) for the acid solution and destructive device 5. Table 5 shows the conditions and evaluation results for Examples 48 to 63 and Comparative Examples 4 to 7 in Evaluation Experiment 5.

[0110]

[0111] Example 48 In Example 48, the conditions for the first pickling using the first pickling device 4 were as follows: the pickling solution was hydrochloric acid, the temperature of the pickling solution was 90°C, the pickling time was 20 seconds, and a pickling accelerator was added to the pickling solution as an additive. In Example 48, the type of destructing device 5 was shot blasting. In Example 48, the conditions for the second pickling using the second pickling device 6 were as follows: the pickling solution was hydrochloric acid, the temperature of the pickling solution was 90°C, the pickling time was 20 seconds, and a pickling inhibitor was added to the pickling solution as an additive. As a result, in Example 48, scale removal was completed, and the fracture rate during cold rolling was 0%.

[0112] Example 49 In Example 49, the conditions for the first pickling in the first pickling device 4 were the acid temperature of 95°C, the type of the breaking device 5 was a tension leveler, and the conditions for the second pickling in the second pickling device 6 were the acid temperature of 95°C, except that the conditions were the same as those in Example 48. As a result, in Example 49, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0113] Example 50 was the same as Example 48 except that the conditions for the first pickling in the first pickling device 4 were that the temperature of the pickling solution was 85°C, the type of the breaking device 5 was a grinding brush, and the conditions for the second pickling in the second pickling device 6 were that the temperature of the pickling solution was 85°C. As a result, in Example 50, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0114] Example 51 was the same as Example 48 except that the conditions for the first pickling in the first pickling device 4 were that the temperature of the acid solution was 75°C, the type of the destructing device 5 was a laser cleaning device, and the conditions for the second pickling in the second pickling device 6 were that the temperature of the acid solution was 75°C. As a result, in Example 51, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0115] [Comparative Example 4] In Comparative Example 4, the conditions for the first pickling using the first pickling device 4 were as follows: the pickling solution was hydrochloric acid, the temperature of the pickling solution was 80°C, the pickling time was 20 seconds, and a pickling accelerator was added to the pickling solution as an additive. Furthermore, in Comparative Example 4, the breaking device 5 was omitted. Furthermore, in Comparative Example 4, the conditions for the second pickling using the second pickling device 6 were as follows: the pickling solution was hydrochloric acid, the temperature of the pickling solution was 80°C, the pickling time was 20 seconds, and a pickling inhibitor was added to the pickling solution as an additive. As a result, in Comparative Example 4, scale removal was not completed, and the rate of fracture in cold rolling was 2%.

[0116] [Example 52] In Example 52, the conditions for the first pickling using the first pickling device 4 were as follows: the pickling solution was sulfuric acid, the temperature of the pickling solution was 90°C, the pickling time was 20 seconds, and no additives were used. Also in Example 52, the type of destructing device 5 was shot blasting. Also in Example 52, the conditions for the second pickling using the second pickling device 6 were as follows: the pickling solution was sulfuric acid, the temperature of the pickling solution was 90°C, the pickling time was 15 seconds, and no additives were used. As a result, in Example 52, scale removal was completed, and the rate of fracture in cold rolling was 0%.

[0117] Example 53 In Example 53, the conditions for the first pickling in the first pickling device 4 were the acid temperature of 95°C, the type of the breaking device 5 was a tension leveler, and the conditions for the second pickling in the second pickling device 6 were the acid temperature of 95°C, except that the conditions were the same as those in Example 52. As a result, in Example 53, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0118] Example 54 In Example 54, the conditions for the first pickling in the first pickling device 4 were the acid temperature of 85°C, the type of the breaking device 5 was a grinding brush, and the conditions for the second pickling in the second pickling device 6 were the acid temperature of 85°C, except that the conditions were the same as in Example 52. As a result, in Example 54, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0119] Example 55 was the same as Example 52 except that the conditions for the first pickling in the first pickling device 4 were that the temperature of the acid solution was 75°C, the type of the breaking device 5 was a laser cleaning device, and the conditions for the second pickling in the second pickling device 6 were that the temperature of the acid solution was 75°C. As a result, in Example 55, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0120] [Comparative Example 5] In Comparative Example 5, the conditions for the first pickling using the first pickling device 4 were as follows: the pickling solution was sulfuric acid, the temperature of the pickling solution was 80°C, the pickling time was 20 seconds, and no additives were used. In Comparative Example 5, the breaking device 5 was not used. In Comparative Example 5, the conditions for the second pickling using the second pickling device 6 were as follows: the pickling solution was sulfuric acid, the temperature of the pickling solution was 80°C, the pickling time was 15 seconds, and no additives were used. As a result, in Comparative Example 5, scale removal was not completed, and the rate of fracture in cold rolling was 3%.

[0121] [Example 56] In Example 56, the conditions for the first pickling using the first pickling device 4 were as follows: the pickling solution was hydrochloric acid + nitric acid, the temperature of the pickling solution was 90 [°C], the pickling time was 25 [s], and no additives were used. Also in Example 56, the type of destructing device 5 was shot blasting. Also in Example 56, the conditions for the second pickling using the second pickling device 6 were as follows: the pickling solution was hydrochloric acid + nitric acid, the temperature of the pickling solution was 90 [°C], the pickling time was 25 [s], and no additives were used. As a result, in Example 56, scale removal was completed, and the fracture occurrence rate in cold rolling was 0 [%].

[0122] Example 57 In Example 57, the conditions for the first pickling in the first pickling device 4 were the acid temperature of 95°C, the type of the breaking device 5 was a tension leveler, and the conditions for the second pickling in the second pickling device 6 were the acid temperature of 95°C, except that the conditions were the same as in Example 56. As a result, in Example 57, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0123] Example 58 In Example 58, the conditions for the first pickling in the first pickling device 4 were the temperature of the pickling solution of 85°C, the type of the breaking device 5 was a grinding brush, and the conditions for the second pickling in the second pickling device 6 were the temperature of the pickling solution of 85°C, except that the conditions were the same as in Example 56. As a result, in Example 58, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0124] Example 59 In Example 59, the conditions for the first pickling in the first pickling device 4 were the acid solution temperature of 75°C, the type of the breaking device 5 was a laser cleaning device, and the conditions for the second pickling in the second pickling device 6 were the acid solution temperature of 75°C, except that the conditions were the same as in Example 56. As a result, in Example 59, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0125] [Comparative Example 6] In Comparative Example 6, the conditions for the first pickling using the first pickling device 4 were as follows: the pickling solution was hydrochloric acid + nitric acid, the temperature of the pickling solution was 80 [°C], the pickling time was 25 [s], and no additives were used. In Comparative Example 6, the breaking device 5 was not used. In Comparative Example 6, the conditions for the second pickling using the second pickling device 6 were as follows: the pickling solution was hydrochloric acid + nitric acid, the temperature of the pickling solution was 80 [°C], the pickling time was 25 [s], and no additives were used. As a result, in Comparative Example 6, scale removal was not completed, and the fracture occurrence rate in cold rolling was 3 [%].

[0126] [Example 60] In Example 60, the conditions for the first pickling using the first pickling device 4 were as follows: the pickling solution was hydrochloric acid + hydrofluoric acid, the pickling solution temperature was 90 [°C], the pickling time was 15 [s], and no additives were used. Also in Example 60, the type of destructing device 5 was shot blasting. Also in Example 60, the conditions for the second pickling using the second pickling device 6 were as follows: the pickling solution was hydrochloric acid + nitric acid, the pickling solution temperature was 90 [°C], the pickling time was 10 [s], and no additives were used. As a result, in Example 60, scale removal was completed, and the fracture occurrence rate in cold rolling was 0 [%].

[0127] Example 61 In Example 61, the conditions for the first pickling in the first pickling device 4 were the acid temperature of 95°C, the type of the breaking device 5 was a tension leveler, and the conditions for the second pickling in the second pickling device 6 were the acid temperature of 95°C, except that the conditions were the same as in Example 60. As a result, in Example 61, scale removal was completed, and the fracture incidence rate in cold rolling was 0%.

[0128] Example 62 In Example 62, the conditions for the first pickling in the first pickling device 4 were the temperature of the pickling solution of 85°C, the type of the breaking device 5 was a grinding brush, and the conditions for the second pickling in the second pickling device 6 were the temperature of the pickling solution of 85°C, except that the conditions were the same as in Example 60. As a result, in Example 62, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0129] Example 63 In Example 63, the conditions for the first pickling in the first pickling device 4 were the acid solution temperature of 75°C, the type of the breaking device 5 was a laser cleaning device, and the conditions for the second pickling in the second pickling device 6 were the acid solution temperature of 75°C, except that the conditions were the same as in Example 60. As a result, in Example 63, scale removal was completed, and the fracture occurrence rate in cold rolling was 0%.

[0130] [Comparative Example 7] In Comparative Example 7, the conditions for the first pickling using the first pickling device 4 were as follows: the pickling solution was hydrochloric acid + hydrofluoric acid, the pickling solution temperature was 80 [°C], the pickling time was 15 [s], and no additives were used. Also in Comparative Example 7, the breaking device 5 was not used. Also in Comparative Example 7, the conditions for the second pickling using the second pickling device 6 were as follows: the pickling solution was hydrochloric acid + nitric acid, the pickling solution temperature was 80 [°C], the pickling time was 10 [s], and no additives were used. As a result, in Comparative Example 7, scale removal was not completed, and the fracture occurrence rate in cold rolling was 2 [%].

[0131] Table 5 shows that, under conditions where the destruction device 5 was not used and no mechanical destruction treatment of the scale was performed, as in Comparative Examples 4 to 7, scale removal was not completed in all cases, and fractures occurred during cold rolling, regardless of the type of acid solution used in the first pickling and the second pickling, or the presence or absence of additives. This is thought to be because a large amount of scale remained, and the remaining scale became the origin of fracture, increasing the fracture occurrence rate during cold rolling. On the other hand, Table 5 shows that, under conditions where mechanical destruction treatment of the scale was performed using the destruction device 5, as in Examples 48 to 63, scale removal was completed regardless of the conditions of the acid solution used in the first pickling and the second pickling, the presence or absence of additives, and the type of destruction device 5. It also shows that no fractures occurred during cold rolling.

[0132] The present invention can provide steel plate descaling equipment, steel plate manufacturing equipment, steel plate descaling method, and steel plate manufacturing method that can achieve both descaling performance of steel plate and suppression of fracture occurrence during cold rolling.

[0133] REFERENCE SIGNS LIST 1 Steel strip 2 Payoff reel 3 Welding machine 4 First pickling device 5 Destruction device 6 Second pickling device 7 Tension reel 10 Scale removal equipment 20 Scale 21 External scale 22 Internal scale 23 Base steel 221 Island-like internal scale 222 Film-like internal scale 223 Metallic iron

Claims

1. A steel plate descaling facility for removing scales from conveyed steel plates, a first pickling device that performs a first pickling on the steel plate using a first acid solution, a destruction 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, arranged in this order from the upstream side in a conveying direction of the steel plate.

2. 2. The steel plate descaling equipment according to claim 1, wherein a pickling inhibitor is added to the second acid solution.

3. 2. The steel plate descaling equipment according to claim 1, wherein a pickling accelerator is added to the first acid solution, and the pickling time in the first pickling is set to 10 to 30 seconds.

4. A steel plate scale removal equipment as described in claim 2, characterized in that a pickling accelerator is added to the first acid solution, and the pickling time in the first pickling is 10 to 30 seconds.

5. 5. The steel plate descaling equipment according to claim 1, further comprising a preliminary destruction device for mechanically destroying the scales, the preliminary destruction device being provided upstream of the first pickling device in the conveying direction of the steel plate.

6. hot rolling equipment for hot rolling a steel material to obtain a hot-rolled sheet; hot-rolled sheet annealing equipment for annealing the hot-rolled sheet as needed; a descaling facility for removing scale from the hot-rolled sheet or the hot-rolled sheet that has been annealed; cold rolling equipment for cold rolling the hot-rolled sheet from which the scale has been removed to obtain a cold-rolled sheet; a finish annealing facility for annealing the cold-rolled sheet to obtain a cold-rolled annealed sheet; A steel plate manufacturing facility comprising: A steel plate manufacturing facility, comprising the steel plate descaling facility according to any one of claims 1 to 4, as the descaling facility.

7. A hot rolling facility for obtaining a hot-rolled sheet by hot-rolling a steel material; hot-rolled sheet annealing equipment for annealing the hot-rolled sheet as needed; a descaling facility for removing scale from the hot-rolled sheet or the hot-rolled sheet that has been annealed; cold rolling equipment for cold rolling the hot-rolled sheet from which the scale has been removed to obtain a cold-rolled sheet; a finish annealing facility for annealing the cold-rolled sheet to obtain a cold-rolled annealed sheet; A steel plate manufacturing facility comprising: A steel plate manufacturing facility, comprising the steel plate descaling facility according to claim 5 as the descaling facility.

8. A method for removing scales from a steel sheet, comprising: pickling a hot-rolled steel sheet in a first pickling device that pickles the steel sheet using a first acid solution; subjecting the steel sheet that has been pickled in the first pickling device to a treatment in which scales on the surface of the steel sheet that has been pickled in the first pickling device are mechanically destroyed by a destruction device; and pickling the steel sheet that has been treated by the destruction device in a second pickling device using a second acid solution.

9. 9. The method for removing scale from steel plate according to claim 8, wherein a pickling inhibitor is added to the second acid solution.

10. 9. The method for removing scales from a steel plate according to claim 8, wherein a pickling accelerator is added to the first pickling solution, and the pickling time in the first pickling device is set to 10 to 30 seconds.

11. A method for removing scale from steel plate as described in Claim 9, characterized in that a pickling accelerator is added to the first acid solution, and the pickling time by the first pickling device is 10 to 30 seconds.

12. 12. The method for removing scales from a steel plate according to claim 8, further comprising the step of mechanically destroying the scales using a preliminary destruction device arranged upstream of the first pickling device in the conveying direction of the steel plate.

13. a hot rolling step of hot rolling a steel material to obtain a hot-rolled sheet; a hot-rolled sheet annealing step of annealing the hot-rolled sheet as needed; a descaling step of removing scale from the hot-rolled sheet or the hot-rolled sheet that has been annealed; a cold rolling step of cold rolling the hot-rolled sheet from which the scale has been removed to obtain a cold-rolled sheet; a finish annealing step of annealing the cold-rolled sheet to obtain a cold-rolled annealed sheet; A method for manufacturing a steel plate comprising: A method for manufacturing a steel plate, comprising the step of: using the method for descaling a steel plate according to any one of claims 8 to 11 in the descaling step.

14. A hot rolling process for obtaining a hot-rolled sheet by hot-rolling a steel material; a hot-rolled sheet annealing step of annealing the hot-rolled sheet as needed; a descaling step of removing scale from the hot-rolled sheet or the hot-rolled sheet that has been annealed; a cold rolling step of cold rolling the hot-rolled sheet from which the scale has been removed to obtain a cold-rolled sheet; a finish annealing step of annealing the cold-rolled sheet to obtain a cold-rolled annealed sheet; A method for manufacturing a steel plate comprising: A method for manufacturing a steel plate, comprising the step of: using the method for descaling a steel plate according to claim 12 in the descaling step.