Cooling method for coolant and steel plate

Abstract

This cooling liquid is for cooling a steel sheet, and contains a first ion that can change, in a solution, into a first substance that generates a reducing gas through decomposition, and a second ion that can form, through reaction with ferric oxide, an iron compound or an ionic compound complex including iron. The concentration of the first ion in the cooling liquid is 0.5-6 wt% and the concentration of the second ion in the cooling liquid is 1.0-28 wt%, while the total concentration of the first ion and the second ion is 2.0-33.0 wt%.

Description

[Technical Field]

[0001] This disclosure relates to a cooling liquid and a method for cooling steel plates. [Background technology]

[0002] In the manufacturing process of steel plates, high-temperature steel plates are sometimes cooled.

[0003] For example, Patent Document 1 describes a method in which, in a continuous heat treatment line for steel strips, a liquid or gas-liquid mixed fluid is sprayed onto the steel strip before molten metal plating is performed to cool the steel strip. In Patent Document 1, in order to suppress oxidation of the steel material during cooling using the cooling fluid, a substance having pickling properties for metal oxides such as iron oxide is used as the cooling fluid. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2015 / 083047 [Overview of the project] [Problems that the invention aims to solve]

[0005] In the method described in Patent Document 1, a substance with pickling properties (an acidic substance) is used as the liquid to cool the steel plate, which is thought to suppress the formation of an oxide film on the surface of the steel plate. However, on the other hand, there is a risk that the acidic liquid may corrode the equipment or the steel plate.

[0006] In view of the above circumstances, at least one embodiment of the present invention aims to provide a coolant and a method for cooling a steel plate that can effectively cool a steel plate while suppressing corrosion of equipment and steel plates, and the formation of oxide films on the surface of the steel plate. [Means for solving the problem]

[0007] The coolant according to at least one embodiment of the present invention is A coolant for cooling steel plates, A first ion that can change in solution into a first substance that generates a reducing gas through decomposition, A second ion that can react with iron oxide to form an iron-containing ionic compound, Includes, The concentration of the first ion in the coolant is 0.5% by weight or more and 6% by weight or less. The concentration of the second ion in the coolant is 1.0% by weight or more and 28% by weight or less.

[0008] Furthermore, the method for cooling steel plates according to at least one embodiment of the present invention is: A cooling method for cooling steel plates, The method includes the step of supplying the above-mentioned cooling liquid to the steel plate to cool the steel plate. [Effects of the Invention]

[0009] According to at least one embodiment of the present invention, a cooling liquid and a method for cooling a steel plate are provided that can effectively cool a steel plate while suppressing corrosion of equipment and steel plates, and the formation of an oxide film on the surface of the steel plate. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing a continuous heat treatment facility as an example of an apparatus to which a coolant or cooling method according to several embodiments is applied. [Modes for carrying out the invention]

[0011] Hereinafter, several embodiments of the present invention will be described with reference to the attached drawings. However, the dimensions, materials, shapes, relative arrangements, etc., of the components described as embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples.

[0012] (Configuration of the device to which the coolant / cooling method is applied) FIG. 1 is a schematic configuration diagram of an example of an apparatus to which a coolant or a cooling method according to some embodiments is applied, and is a view showing a continuous heat treatment facility 100 for continuously heat-treating a steel sheet.

[0013] The continuous heat treatment facility 100 shown in FIG. 1 includes a continuous annealing furnace 10 for continuously annealing a strip-shaped steel sheet S. The continuous annealing furnace 10 includes a preheating zone 12, a heating zone 14, and a cooling zone 16. A plurality of conveying rolls 18 are provided in the preheating zone 12, the heating zone 14, and the cooling zone 16. By applying tension to the steel sheet S via the conveying rolls 18, the steel sheet S is conveyed at a conveying speed (line speed) corresponding to this tension.

[0014] The preheating zone 12 is provided upstream of the heating zone 14 and the cooling zone 16 in the conveying direction of the steel sheet S. In order to suppress variations in the temperature of the steel sheet S at the inlet of the heating zone 14, the steel sheet S before entering the heating zone 14 is configured to be preheated by a burner or the like (not shown). The heating zone 14 is provided downstream of the preheating zone 12 and upstream of the cooling zone 16 in the conveying direction of the steel sheet S, and is configured to heat the steel sheet S by a burner or the like (not shown). The temperature of the heating zone 14 can be adjusted, for example, by increasing or decreasing the fuel supply amount to the burner. The cooling zone 16 is located downstream of the preheating zone 12 and the heating zone 14 in the conveying direction of the steel sheet S. A cooling fluid is sprayed onto the surface of the steel sheet S heated in the heating zone 14 by cooling means such as cooling nozzles 22, etc., to gradually cool or rapidly cool the steel sheet S. A reducing or non-oxidizing gas may be supplied into the continuous annealing furnace 10.

[0015] In the continuous annealing furnace 10, the annealing treatment of the steel sheet S is performed by passing the steel sheet S through the above-described preheating zone 12, heating zone 14, and cooling zone 16.

[0016] As shown in FIG. 1, the steel sheet S annealed in the continuous annealing furnace 10 may be sent to the continuous plating processing facility 30. The continuous plating processing facility 30 is a facility for continuously plating the steel sheet S, and includes a pot 32 (molten metal pot) that forms a plating bath 34 of molten metal, a sync roll 36 provided inside the pot 32, and a wiping nozzle 38 for adjusting the amount of plating liquid (molten metal) adhering to the steel sheet S. The molten metal stored as the plating liquid inside the pot 32 may contain zinc, aluminum, or an alloy containing zinc or aluminum.

[0017] The steel sheet S annealed in the continuous annealing furnace 10 is guided to the plating bath 34 of molten metal through a snout 24 provided between the outlet of the continuous annealing furnace 10 and the pot 32 while being tensioned by a bridle roll 20 provided at the outlet of the continuous annealing furnace 10.

[0018] In the cooling zone 16 of the continuous annealing furnace 10 described above, the cooling fluid used to cool the steel sheet S (that is, the cooling fluid supplied to the steel sheet S by the cooling means) may contain the coolant described below. The cooling means may be configured to supply the coolant described below, or a mixed fluid of the coolant and gas, to the surface of the steel sheet S by the cooling means.

[0019] Note that the coolant and the cooling method according to some embodiments may be applied to processes other than the continuous annealing process in the steel sheet manufacturing process. That is, the coolant and the cooling method according to some embodiments may be used to cool the steel sheet S in facilities other than the continuous annealing furnace 10.

[0020] (Coolant) Next, the coolant according to some embodiments will be described.

[0021] In some embodiments, the coolant contains a first ion that can be transformed in solution into a first substance that generates a reducing gas upon decomposition, and a second ion that can react with iron oxide to form an iron-containing ionic compound. The concentration of the first ion in the coolant is 0.5% by weight or more and 6% by weight or less, and the concentration of the second ion in the coolant is 1.0% by weight or more and 28% by weight or less. The coolant contains water. The ion concentrations in this specification are those at room temperature (25°C).

[0022] The coolant according to the above embodiment contains the first ion described above, so reducing gas is generated in the coolant by the decomposition of the first substance. Therefore, when cooling a steel plate S using this coolant, the oxidation reaction of iron on the surface of the steel plate S can be suppressed, thereby suppressing the formation of an oxide film (scale, iron oxide) on the surface of the steel plate S. Furthermore, since the coolant according to the above embodiment contains the second ion described above, even if an oxide film (iron oxide) is formed on the surface of the steel plate S during cooling using this coolant, an ionic compound can be formed by reaction with the second ion iron oxide, dissolving and removing the oxide film (iron oxide). In addition, since the concentration of the first ion in the coolant according to the above embodiment is 0.5% by weight or more and the concentration of the second ion is 1.0% by weight or more, these effects are easily obtained. Furthermore, since the concentration of the first ion in the coolant according to the above embodiment is 6% by weight or less and the concentration of the second ion is 28% by weight or less, the residue of solute components on the surface of the steel material due to evaporation and concentration of the coolant during steel plate cooling can be suppressed. Furthermore, the coolant according to the above embodiment has a concentration of 0.5% to 6% by weight of the first ion and a concentration of 1.0% to 28.0% by weight of the second ion, so its pH tends to be higher than that of acidic liquids (such as hydrochloric acid) used for pickling steel plates S. Therefore, corrosion of equipment and steel plates S due to the adhesion of the coolant can be suppressed. Thus, the coolant according to the above embodiment can effectively cool the steel plates S while suppressing corrosion of equipment and steel plates S, and the formation of oxide films on the surface of steel plates S.

[0023] In some embodiments, the total concentration of the first and second ions in the coolant may be 2.0% by weight or more and 33.0% by weight or less.

[0024] According to the above embodiment, since the total concentration of the first and second ions is 2.0% by weight or more, the effect of suppressing the formation of an oxide film on the surface of the steel plate S is relatively high. Furthermore, since the total concentration is 33.0% by weight or less, the pH tends to be higher than that of acidic liquids (such as hydrochloric acid) used for pickling the steel plate S. Therefore, corrosion of equipment and steel plate S can be effectively suppressed, as well as the formation of an oxide film on the surface of the steel plate S.

[0025] As mentioned above, the first ion is an ion that can be transformed in solution into a first substance that generates a reducing gas through decomposition. The reducing gas is, for example, hydrogen (H2) gas.

[0026] The first ion may be an ion containing a nitrogen atom (N). The first ion may also be an ion containing a nitrogen atom (N) and a hydrogen atom (H).

[0027] The first ion is, for example, the ammonium ion (NH4). + ), hydrazine ions (N2H5 + or N2H6 + ), or ions of alcoholamines (for example, ethanolamine ions or triethanolamine ions, etc.).

[0028] The ammonium ion, as the first ion, can be converted to ammonia (NH3; the first substance) in solution (coolant). Furthermore, ammonia decomposes to produce hydrogen gas, a reducing gas.

[0029] That is, as shown in equation (A) below, ammonia and ammonium ions exist in the solution in a state of ionization equilibrium. NH4 + + OH - ⇔ NH3 + H2O …(A) Then, the ammonia dissolved in the solution decomposes according to the following equation (B), generating hydrogen gas. 2NH3 → N2 + 3H2…(B) In other words, as shown by the above formulas (A) and (B), hydrogen gas, which is a reducing gas, can be generated in a coolant containing ammonium ions.

[0030] Furthermore, when a solution (coolant) containing ammonia (and ammonium ions) is supplied to the surface of the steel plate S, the iron (Fe) present on the surface of the steel plate S acts as a catalyst in the reaction represented by formula (B) above. Therefore, the reaction of formula (B) above (i.e., the generation of hydrogen gas) is promoted.

[0031] The ions of hydrazine as the first ion can change into hydrazine (N2H4; the first substance) in solution (coolant). Furthermore, hydrazine decomposes to produce hydrogen gas, a reducing gas.

[0032] The ions of alcoholamines, acting as the first ions, can be converted into alcoholamines (the first substance) in solution (coolant). Furthermore, alcoholamines decompose to produce hydrogen gas, a reducing gas.

[0033] A coolant containing the first ion can be obtained, for example, by dissolving a first substance corresponding to the first ion (such as ammonia corresponding to ammonia as the first ion) or an ionic compound (salt) containing the first ion in water.

[0034] As already mentioned, the first substance is a substance obtained when the first ion changes in solution, and it is a substance that decomposes to produce a reducing gas. The first substance may be a nitrogen compound containing a nitrogen atom. Alternatively, the first substance may be a compound containing a nitrogen atom and a hydrogen atom. The first substances corresponding to the ammonium ion, hydrazine ion, and alcoholamine ions, which are the first ions mentioned above, are ammonia, hydrazine, and alcoholamines, respectively. These first substances are compounds containing a nitrogen atom and a hydrogen atom, respectively.

[0035] When the first ion contains an ammonium ion, the concentration of the ammonium ion in the coolant may be 0.5% by weight or more and 5.3% by weight or less. If the concentration of the ammonium ion in the coolant is within this range, the pH of the coolant is likely to be higher than that of an acidic liquid (such as hydrochloric acid) used for pickling the steel sheet S. Therefore, corrosion of equipment and the steel sheet S due to the adhesion of the coolant can be effectively suppressed.

[0036] The coolant according to some embodiments may contain ammonia. That is, the coolant may be a solution of ammonia dissolved in water. Note that the coolant containing ammonia can be obtained by mixing water with aqueous ammonia having a predetermined concentration in which ammonia has been previously dissolved. In this case, the first ion in the coolant is an ammonium ion. The ammonia concentration in the coolant may be 1.8% by weight or more and 4.5% by weight or less. If the ammonia concentration in the coolant is within this range, the pH of the coolant is likely to be higher than that of an acidic liquid (such as hydrochloric acid) used for pickling the steel sheet S. Therefore, corrosion of equipment and the steel sheet S due to the adhesion of the coolant can be effectively suppressed.

[0037] As described above, the second ion is an ion that can react with iron oxide to form an ion compound containing iron. Note that the ion compound may be a complex. The ion compound containing iron is generally soluble in water. That is, iron oxide can be dissolved by reacting the second ion with iron oxide.

[0038] The second ion may contain, for example, an organic acid ion (such as an acetate ion (CH3COO - ), etc.), an ionized amino acid (such as an ionized glycine (H3 + NCH2COO - ), etc.), a sulfate ion (SO4 2- ) or a chloride ion (Cl - ).

[0039] For example, an organic acid ion (R-COO -) is produced by the ionization of organic acids in an aqueous solution (coolant), and as shown in the reaction equation (C) below, it reacts with iron oxide to produce an organic iron salt (R-COOFe). Organic iron salts (e.g., iron acetate) are soluble in water. 2R-COOH + FeO → (R-COO)2Fe + H2O …(C)

[0040] Also, for example, sulfate ions (SO4) as second ions. 2- Iron sulfate (FeSO4) is produced when sulfates (such as ammonium sulfate) dissociate in an aqueous solution (coolant), but as shown in the reaction equation (D) below, it reacts with iron oxide to produce iron sulfate (FeSO4). Iron sulfate (ferrous sulfate) is soluble in water. (NH4)2SO4+ FeO → 2NH4+ FeSO4…(D)

[0041] A coolant containing a secondary ion can be obtained, for example, by dissolving a substance that can be converted into a secondary ion in solution in water. When the secondary ion is an organic acid ion (such as an acetate ion), an ionized amino acid (such as ionized glycine), a sulfate ion, or a chloride ion, a coolant containing the secondary ion can be obtained by dissolving an organic acid (such as acetic acid), an amino acid (such as glycine), a sulfate compound, or a chloride in water.

[0042] If the second ion contains sulfate ions, the concentration of sulfate ions in the coolant may be between 1.5% by weight and 14.0% by weight. If the concentration of sulfate ions in the coolant is within this range, the pH of the coolant tends to be higher than that of acidic liquids (such as hydrochloric acid) used for pickling steel plates S. Therefore, corrosion of equipment and steel plates S due to coolant adhesion can be effectively suppressed.

[0043] If the second ion contains acetate ions, the concentration of acetate ions in the coolant may be between 7.2% by weight and 17.8% by weight. If the concentration of acetate ions in the coolant is within this range, the pH of the coolant tends to be higher than that of acidic liquids (such as hydrochloric acid) used for pickling steel plates S. Therefore, corrosion of equipment and steel plates S due to coolant adhesion can be effectively suppressed.

[0044] If the second ion contains ionized glycine, the concentration of ionized glycine in the coolant may be 1.0% by weight or more and 10.0% by weight or less. If the concentration of ionized glycine in the coolant is within this range, the pH of the coolant tends to be higher than that of acidic liquids (such as hydrochloric acid) used for pickling steel plates S. Therefore, corrosion of equipment and steel plates S due to coolant adhesion can be effectively suppressed.

[0045] The coolant in some embodiments may contain ammonium sulfate. That is, the coolant may be a solution of ammonium sulfate in water. In this case, the first ion in the coolant is ammonium ions, and the second ion is sulfate ions. The concentration of ammonium sulfate in the coolant may be between 2.0% by weight and 19.3% by weight. If the concentration of ammonium sulfate in the coolant is within this range, the pH of the coolant tends to be higher than that of acidic liquids (such as hydrochloric acid) used for pickling steel plates S. Therefore, corrosion of equipment and steel plates S due to the adhesion of the coolant can be effectively suppressed.

[0046] The coolant in some embodiments may contain ammonium chloride. That is, the coolant may be a solution of ammonium chloride in water. In this case, the first ion in the coolant is ammonium ion, and the second ion is chloride ion. The concentration of ammonium sulfate in the coolant may be 1.5% by weight or more and 15.7% by weight or less. If the concentration of ammonium chloride in the coolant is within this range, the pH of the coolant tends to be higher than that of acidic liquids (such as hydrochloric acid) used for pickling steel plates S. Therefore, corrosion of equipment and steel plates S due to the adhesion of the coolant can be effectively suppressed.

[0047] In some embodiments, the pH of the coolant is 5 or higher. In some embodiments, the pH of the coolant may be between 5 and 14.

[0048] In the above embodiment, the pH of the coolant is higher than the pH of the acidic liquid (such as hydrochloric acid) used for pickling the steel plate S. Therefore, corrosion of the equipment and steel plate S due to the adhesion of coolant can be effectively suppressed. Thus, the steel plate S can be cooled while effectively suppressing corrosion of the equipment and steel plate S, as well as the formation of an oxide film on the surface of the steel plate S.

[0049] (Method for preparing coolant) Cooling liquids according to some embodiments can be obtained by dissolving a solute from which the first or second ions are derived in water.

[0050] For example, a coolant containing ammonium ions as the primary ion can be obtained by dissolving ammonia or ammonia water in water. Similarly, a coolant containing acetate ions or ionized glycine as the secondary ion can be obtained by dissolving acetate ions or glycine in water. Furthermore, a coolant containing ammonium ions as the primary ion and sulfate ions as the secondary ion can be obtained by dissolving ammonium sulfate in water.

[0051] (Method for cooling steel plates) A method for cooling a steel plate according to some embodiments includes the step of cooling the steel plate by supplying the above-mentioned cooling liquid to the surface of the steel plate.

[0052] In some embodiments, the steel sheet may be cooled by supplying the above-described coolant during the annealing process. The annealing process of the steel sheet can be carried out, for example, using the continuous annealing furnace 10 described above. The coolant can be supplied to the surface of the steel sheet S using, for example, cooling means (cooling nozzle 22, etc.) provided in the cooling zone 16 of the continuous annealing furnace 10 described above.

[0053] In the above-described embodiment, the steel plate is cooled using the above-described coolant under relatively high-temperature conditions where corrosion is likely to occur. Therefore, under such conditions, the steel plate can be cooled while effectively suppressing corrosion of the equipment and the steel plate, as well as the formation of an oxide film on the surface of the steel plate.

[0054] In some embodiments, the temperature of the steel plate may be lowered by 300°C or more while supplying a coolant to the steel plate.

[0055] In the above-described embodiment, the steel plate is cooled using the above-described coolant under relatively high-temperature conditions where corrosion is likely to occur. Therefore, under such conditions, the steel plate can be cooled while effectively suppressing corrosion of the equipment and the steel plate, as well as the formation of an oxide film on the surface of the steel plate. [Examples]

[0056] Coolants according to Examples 1 to 25 shown in Tables 1 and 2 were prepared, and the tests and evaluations described below were performed.

[0057] (Method for preparing coolant) The coolants in Examples 4 to 25 were prepared by dissolving the solutes listed in Tables 1 and 2 (ammonia, ammonium sulfate, ammonium chloride, acetic acid, and / or glycine) in water to the concentrations listed in Tables 1 and 2, respectively. Note that the coolants in Examples 1 to 3 are simply water without solutes.

[0058] (Composition and pH of the coolant) For the coolants in Examples 1 to 25, the types and concentrations of the first and second ions in the coolant are shown in Tables 1 and 2. Furthermore, the pH of the coolants in Examples 1 to 25 is shown in Tables 1 and 2. Note that the pH of the coolants in Examples 8 to 11 and 18 is the result of measurement using test strips, while the pH of the coolants in Examples 1 to 3, 7, 16, and 17 is the result of calculation using calculation software (OLI stream analyzer).

[0059] (Test method) For each of Examples 1 to 25, a sample of ordinary steel (1.6 mm thick) heated to 800°C in a 4% hydrogen + nitrogen atmosphere was immersed in a coolant under a room temperature argon gas atmosphere for the specified duration (immersion time) shown in Tables 1 and 2. Note that an oxide film had formed on the surface of the steel plate sample heated to 800°C.

[0060] (Evaluation method) Based on visual inspection of the sample and elemental analysis results obtained by EDS (energy-dispersive X-ray spectroscopy), each sample from Example 1 to Example 26 was evaluated on a two-point scale, A and B. The evaluation criteria are as follows: A: The oxide film was almost completely gone from the surface, and no nitrogen (N) peak was detected in the EDS analysis. B: The oxide film is almost completely intact in appearance, or a nitrogen (N) peak was confirmed as a result of EDS analysis.

[0061] Before heating the steel plate sample to 800°C, the sample is grayish-white. After heating to 800°C (when the oxide film is formed), the surface of the steel plate sample is dark gray. Therefore, it is possible to visually determine whether the oxide film remains or has decreased.

[0062] [Table 1]

[0063] [Table 2]

[0064] (Evaluation results) The evaluation results for Examples 1 through 25 are shown in Tables 1 and 2. In Examples 7-14 and 16-25, which are embodiments of the present invention, the evaluation result was A, indicating a clear reduction in the oxide film on the surface of the steel plate sample compared to before immersion in the coolant. Therefore, it was found that by cooling the steel plate using the coolant according to these examples, the oxide film on the steel plate can be removed or its formation can be suppressed.

[0065] Furthermore, in examples 16, 18, 19, and 20, the oxide film on the surface of the steel plate samples was clearly reduced compared to before immersion in the coolant, even though the immersion time in the coolant was relatively short at 0.6 seconds. Therefore, it was found that the coolants in these examples are particularly effective in removing the oxide film from steel plates or in suppressing the formation of oxide films.

[0066] On the other hand, in comparative examples 1 to 3 of the present invention, visual inspection of the samples revealed that the oxide film remained almost entirely intact. Therefore, it was found that the coolants in these examples could not effectively remove the oxide film or effectively suppress its formation. Furthermore, in comparative examples 4 to 6 and 15 of the present invention, visual inspection of the samples revealed that the oxide film was removed to some extent, but EDS analysis showed a nitrogen (N) peak on the surface of the samples, indicating that the sample surface had undergone nitriding. Therefore, it was found that even if the formation of the oxide film could be suppressed to some extent with the coolants in these examples, the surface of the steel plate would still undergo nitriding, potentially leading to a deterioration in product quality.

[0067] Furthermore, visual inspection of the samples revealed no signs of corrosion in Examples 1 to 25, nor was there any significant loss of mass in the test specimens.

[0068] From the above, it can be seen that the cooling liquid according to the embodiment of the present invention can effectively suppress the formation of oxide films and corrosion on the surface of steel plates when the steel plates are cooled.

[0069] The contents described in each of the above embodiments can be understood, for example, as follows:

[0070] (1) The coolant according to at least one embodiment of the present invention is A coolant for cooling steel plates, A first ion that can change in solution into a first substance that generates a reducing gas through decomposition, A second ion that can react with iron oxide to form an iron-containing ionic compound, Includes, The concentration of the first ion in the coolant is 0.5% by weight or more and 6% by weight or less. The concentration of the second ion in the coolant is 1.0% by weight or more and 28% by weight or less.

[0071] The coolant described in (1) above contains the first ion described above, and a reducing gas is generated in the coolant by the decomposition of the first substance. Therefore, the oxidation reaction of iron on the surface of the steel plate can be suppressed when the steel plate is cooled using this coolant, thereby suppressing the formation of an oxide film (iron oxide) on the surface of the steel plate. Furthermore, since the coolant described in (1) above contains the second ion described above, even if an oxide film (iron oxide) is formed on the surface of the steel plate when the steel plate is cooled using this coolant, the oxide film (iron oxide) can be dissolved and removed by the reaction between the second ion and iron oxide. In addition, since the coolant described in (1) above has a concentration of 0.5% by weight or more for the first ion and a concentration of 1.0% by weight or more for the second ion, these effects are easily obtained. Furthermore, since the coolant described in (1) above has a concentration of 6% by weight or less for the first ion and a concentration of 28% by weight or less for the second ion, the residue of solute components on the surface of the steel material due to evaporation and concentration of the coolant during steel plate cooling can be suppressed. Furthermore, the coolant described in (1) above has a concentration of 0.5% to 6% by weight of the first ion and a concentration of 1.0% to 28.0% by weight of the second ion, so its pH is higher than that of the acidic liquid used for pickling steel plates. For this reason, corrosion of equipment and steel plates due to the adhesion of the coolant can be suppressed. Therefore, according to the configuration of (1) above, the steel plate can be cooled while effectively suppressing corrosion of the equipment and steel plate, as well as the formation of an oxide film on the surface of the steel plate.

[0072] (2) In some embodiments, in the configuration of (1) above, The total concentration of the first ion and the second ion in the coolant is 2.0% by weight or more and 33.0% by weight or less.

[0073] According to the configuration described in (2) above, the total concentration of the first and second ions is 2.0% by weight or more, so the effect of suppressing the formation of oxide film on the surface of the steel plate is relatively high. Furthermore, since the total concentration is 33.0% by weight or less, the pH tends to be higher than that of the acidic liquid used for pickling steel plates. Therefore, it is possible to effectively suppress corrosion of equipment and steel plates, as well as effectively suppress the formation of oxide film on the surface of the steel plate.

[0074] (3) In some embodiments, in the configuration of (1) or (2) above, The first substance includes a nitrogen compound.

[0075] According to the configuration described in (3) above, the first substance that generates reducing gas (such as hydrogen gas) upon decomposition contains a nitrogen compound, so the pH of the coolant in which the first substance is dissolved tends to increase. Therefore, corrosion of equipment and steel plates due to the adhesion of the coolant can be effectively suppressed.

[0076] (4) In some embodiments, in any of the configurations (1) to (3) above, The first substance includes ammonia, hydrazine, or alcoholamines.

[0077] According to the configuration described in (4) above, the first substance that generates a reducing gas upon decomposition includes ammonia, hydrazine, or alcoholamines, so the pH of the coolant in which the first substance is dissolved tends to increase. Therefore, corrosion of equipment and steel plates due to the adhesion of the coolant can be effectively suppressed. Note that ammonia, hydrazine, or alcoholamines are the first substances that generate hydrogen (H2) gas, which is a reducing gas, upon decomposition.

[0078] (5) In some embodiments, in any of the configurations (1) to (4) above, The second ion includes organic acid ions, ionized amino acids, sulfate ions, or chloride ions.

[0079] According to the configuration described in (5) above, even if an oxide film (iron oxide) forms on the surface of the steel plate during cooling with the coolant, the oxide film (iron oxide) can be dissolved and removed by reaction with organic acid ions, ionized amino acids, sulfate ions, or chloride ions. Therefore, the formation of an oxide film on the surface of the steel plate can be suppressed more effectively.

[0080] (6) In some embodiments, in any of the configurations (1) to (5) above, The aforementioned first ion contains an ammonium ion, The concentration of ammonium ions in the coolant is 0.5% by weight or more and 5.3% by weight or less.

[0081] According to the configuration described in (6) above, hydrogen gas, a reducing gas, is generated by the decomposition of ammonia converted from ammonium ions in the solution. Therefore, during the cooling of steel plates using the coolant, the oxidation reaction of iron on the surface of the steel plates can be suppressed by the hydrogen gas. Furthermore, since the ammonium ion concentration in the coolant is between 0.5% and 5.3% by weight, the pH tends to be higher than that of the acidic liquid used for pickling steel plates. Thus, corrosion of equipment and steel plates due to the adhesion of the coolant can be effectively suppressed.

[0082] (7) In some embodiments, in any of the configurations (1) to (6) above, The aforementioned second ion contains sulfate ions, The concentration of sulfate ions in the coolant is 1.5% by weight or more and 14.0% by weight or less.

[0083] According to the configuration described in (7) above, since sulfate ions are present in the solution, even if an oxide film (iron oxide) forms on the surface of the steel plate during cooling with the coolant, the oxide film (iron oxide) can be dissolved and removed as iron sulfate through a reaction with sulfate ions. Therefore, the formation of oxide films on the surface of the steel plate can be effectively suppressed. In addition, since the sulfate ion concentration in the coolant is between 1.5% by weight and 14.0% by weight, the pH tends to be higher than that of the acidic liquid used for pickling steel plates. Therefore, corrosion of equipment and steel plates due to the adhesion of the coolant can be effectively suppressed.

[0084] (8) In some embodiments, in any of the configurations (1) to (7) above, The coolant contains ammonia, The concentration of ammonia in the coolant is 1.8% by weight or more and 4.5% by weight or less.

[0085] According to the configuration described in (8) above, hydrogen gas, a reducing gas, is generated by the decomposition of ammonia present in the solution. Therefore, during the cooling of the steel plate using the coolant, the oxidation reaction of iron on the surface of the steel plate can be suppressed by the hydrogen gas. Furthermore, since the ammonia ion concentration in the coolant is between 1.8% and 4.5% by weight, the pH tends to be higher than that of the acidic liquid used for pickling steel plates. Thus, corrosion of equipment and steel plates due to the adhesion of the coolant can be effectively suppressed.

[0086] (9) In some embodiments, in any of the configurations (1) to (7) above, The coolant contains ammonium sulfate, The concentration of ammonium sulfate in the coolant is 2.0% by weight or more and 19.3% by weight or less.

[0087] According to the configuration described in (9) above, hydrogen gas, a reducing gas, is generated by the decomposition of ammonia converted from ammonium ions in the solution. Therefore, during the cooling of the steel plate using the coolant, the oxidation reaction of iron on the surface of the steel plate can be suppressed by the hydrogen gas. Furthermore, because sulfate ions are present in the solution, even if an oxide film (iron oxide) is formed on the surface of the steel plate during the cooling of the steel plate using the coolant, the oxide film (iron oxide) can be dissolved and removed by reaction with sulfate ions. Thus, the formation of an oxide film on the surface of the steel plate can be effectively suppressed. In addition, since the ammonium sulfate concentration in the coolant is between 2.0% by weight and 19.3% by weight, the pH tends to be higher than that of acidic liquids used for pickling steel plates. Therefore, corrosion of equipment and steel plates due to the adhesion of the coolant can be effectively suppressed.

[0088] (10) In some embodiments, in any of the configurations (1) to (7) above, The coolant contains ammonium chloride, The concentration of ammonium chloride in the coolant is 1.5% by weight or more and 15.7% by weight or less.

[0089] According to the configuration described in (10) above, hydrogen gas, a reducing gas, is generated by the decomposition of ammonia converted from ammonium ions in the solution. Therefore, during the cooling of steel plates using the coolant, the oxidation reaction of iron on the surface of the steel plates can be suppressed by the hydrogen gas. Furthermore, because chloride ions are present in the solution, even if an oxide film (iron oxide) is formed on the surface of the steel plates during the cooling of steel plates using the coolant, the oxide film (iron oxide) can be dissolved and removed by reaction with chloride ions. Thus, the formation of an oxide film on the surface of the steel plates can be effectively suppressed. In addition, since the ammonium chloride concentration in the coolant is between 1.5% by weight and 15.7% by weight, the pH tends to be higher than that of acidic liquids used for pickling steel plates. Therefore, corrosion of equipment and steel plates due to the adhesion of the coolant can be effectively suppressed.

[0090] (11) In some embodiments, in any of the configurations (1) to (6) above, The aforementioned second ion contains an acetate ion, The concentration of acetate ions in the coolant is 7.2% by weight or more and 17.8% by weight or less.

[0091] According to the configuration described in (11) above, since acetate ions are present in the solution, even if an oxide film (iron oxide) forms on the surface of the steel plate during cooling with the coolant, the oxide film (iron oxide) can be dissolved and removed as iron acetate through a reaction with the acetate ions. Therefore, the formation of oxide films on the surface of the steel plate can be effectively suppressed. In addition, since the acetate ion concentration in the coolant is between 7.2% by weight and 17.8% by weight, the pH tends to be higher than that of the acidic liquid used for pickling steel plates. Therefore, corrosion of equipment and steel plates due to the adhesion of the coolant can be effectively suppressed.

[0092] (12) In some embodiments, in any of the configurations (1) to (6) above, The aforementioned second ion contains ionized glycine, The concentration of the ionized glycine in the coolant is 1.0% by weight or more and 10.0% by weight or less.

[0093] According to the configuration described in (12) above, since ionized glycine is present in the solution, even if an oxide film (iron oxide) forms on the surface of the steel plate during cooling with the coolant, the oxide film (iron oxide) can be dissolved and removed as an ionic compound with ionized glycine through a reaction with the ionized glycine. Therefore, the formation of an oxide film on the surface of the steel plate can be effectively suppressed. In addition, since the concentration of ionized glycine in the coolant is between 1.0% by weight and 10.0% by weight, the pH tends to be higher than that of the acidic liquid used for pickling steel plates. Therefore, corrosion of equipment and steel plates due to the adhesion of the coolant can be effectively suppressed.

[0094] (13) In some embodiments, in any of the configurations (1) to (12) above, The pH of the coolant is 5 or higher.

[0095] According to the configuration described in (13) above, the pH of the coolant is 5 or higher, which is higher than the pH of the acidic liquid used for pickling steel plates. Therefore, corrosion of equipment and steel plates due to the adhesion of coolant can be effectively suppressed. Thus, the steel plates can be cooled while effectively suppressing corrosion of equipment and steel plates, as well as the formation of oxide films on the surface of the steel plates.

[0096] (14) A method for cooling a steel plate according to at least one embodiment of the present invention is: A cooling method for cooling steel plates, The method includes a step of supplying the steel plate with a cooling liquid described in any one of the above items (1) to (13) to cool the steel plate.

[0097] According to the method described in (14) above, since the coolant contains the first ion described above, reducing gas is generated in the coolant by the decomposition of the first substance. Therefore, the oxidation reaction of iron on the surface of the steel plate can be suppressed during the cooling of the steel plate using the coolant, thereby suppressing the formation of an oxide film (iron oxide) on the surface of the steel plate. Furthermore, according to the method described in (14) above, since the coolant contains the second ion described above, even if an oxide film (iron oxide) is formed on the surface of the steel plate during the cooling of the steel plate using the coolant, the oxide film (iron oxide) can be dissolved and removed by reaction with the second ion. In addition, the coolant described above has a concentration of the first ion of 0.5% by weight or more and 6% by weight or less, and a concentration of the second ion of 1.5% by weight or more and 28.0% by weight or less, so its pH is higher than that of acidic liquids used for pickling steel plates. Therefore, corrosion of equipment and steel plates due to the adhesion of coolant can be suppressed. Thus, according to the method of (14) above, the steel plates can be cooled while effectively suppressing corrosion of equipment and steel plates, as well as the formation of oxide films on the surface of the steel plates.

[0098] (14') In some embodiments, in the method of (14) above, In the cooling step, the temperature of the steel plate is lowered to 300°C or more while supplying the cooling liquid.

[0099] According to the method described in (14') above, the steel plate is cooled using the aforementioned coolant under relatively high-temperature conditions where corrosion is likely to occur. Therefore, under such conditions, the steel plate can be cooled while effectively suppressing corrosion of the equipment and the steel plate, as well as the formation of an oxide film on the surface of the steel plate.

[0100] (15) In some embodiments, in the method of (14) or (14') above, The aforementioned cooling method is The process includes the step of adding at least one of ammonia, ammonium sulfate, acetic acid, or glycine to water to obtain the coolant, In the cooling step, the cooling liquid is supplied to the steel plate to cool it.

[0101] According to the above configuration (15), a coolant can be easily obtained by adding ammonia, ammonium sulfate, acetic acid, or glycine to water.

[0102] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and also includes modified forms of the embodiments described above, as well as forms that combine these forms as appropriate.

[0103] In this specification, expressions describing relative or absolute arrangements such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" shall not only describe such arrangements strictly, but also describe states of relative displacement with tolerances or angles or distances that allow for the same function to be achieved. For example, expressions such as "identical," "equal," and "homogeneous" that describe things being in an equal state not only describe a state of being strictly equal, but also describe a state in which there is a tolerance or a difference that is sufficient to achieve the same function. Furthermore, in this specification, expressions describing shapes such as quadrilaterals and cylindrical shapes shall not only represent geometrically precise quadrilaterals and cylindrical shapes, but also shapes that include uneven surfaces, chamfered surfaces, etc., to the extent that the same effect can be achieved. Furthermore, in this specification, the expressions “equipment,” “includes,” or “possess” of a component are not exclusive expressions that exclude the existence of other components. [Explanation of Symbols]

[0104] 10 Continuous Annealing Furnaces 12. Pre-tropical 14. Heating Zone 16 Cooling Zones 18 Conveyor Rolls 20 Bridle Rolls 22 Cooling nozzles 24 Snout 30 Continuous Plating Equipment 32 pots 34 Plating bath 36 Syncroll 38 Wiping nozzles 100 Continuous Heat Treatment Equipment S steel plate

Claims

1. A coolant for cooling steel plates, The first ion containing ammonium ions, A second ion containing organic acid ions or ionized amino acids, Includes, The concentration of the first ion in the coolant is 1.9% by weight or more and 4.8% by weight or less. The concentration of the second ion in the coolant is 1.0% by weight or more and 27.8% by weight or less. coolant.

2. The total concentration of the first ion and the second ion in the coolant is 5.8% by weight or more and 32.6% by weight or less. The coolant according to claim 1.

3. A coolant for cooling steel plates, The first ion containing ammonium ions, A second ion containing sulfate ions, Includes, The concentration of the first ion in the coolant is 0.5% by weight or more and 5.3% by weight or less. The concentration of sulfate ions in the coolant is 1.5% by weight or more and 14.0% by weight or less. coolant.

4. A coolant for cooling steel plates, The first ion containing ammonium ions, A second ion containing sulfate ions, Includes, The concentration of the first ion in the coolant is 0.5% by weight or more and 5.3% by weight or less. The concentration of the second ion in the coolant is 1.5% by weight or more and 14.0% by weight or less. coolant.

5. A coolant for cooling steel plates, The first ion containing ammonium ions, A second ion containing organic acid ions or ionized amino acids, Includes, The concentration of the first ion in the coolant is 1.9% by weight or more and 4.8% by weight or less. The concentration of the second ion in the coolant is 7.2% by weight or more and 27.8% by weight or less. The aforementioned second ion includes an acetate ion, The concentration of acetate ions in the coolant is 7.2% by weight or more and 17.8% by weight or less. coolant.

6. A coolant for cooling steel plates, The first ion containing ammonium ions, A second ion containing organic acid ions or ionized amino acids, Includes, The concentration of the first ion in the coolant is 1.9% by weight or more and 4.8% by weight or less. The concentration of the second ion in the coolant is 1.0% by weight or more and 27.8% by weight or less. The aforementioned second ion contains ionized glycine, The concentration of the ionized glycine in the coolant is 1.0% by weight or more and 10.0% by weight or less. coolant.

7. A coolant for cooling steel plates, The first ion containing ammonium ions, A second ion containing organic acid ions, ionized amino acids, or sulfate ions, Includes, The concentration of the first ion in the coolant is 1.9% by weight or more and 5.3% by weight or less. The concentration of the second ion in the coolant is 1.0% by weight or more and 27.8% by weight or less. The pH of the coolant is 5 or higher. coolant.

8. A cooling method for cooling steel plates, The method comprises the step of supplying a cooling liquid according to any one of claims 1 to 7 to the steel plate to cool the steel plate. A method for cooling steel plates.

9. A cooling method for cooling steel plates, A step of obtaining a coolant by adding at least one of ammonia, ammonium sulfate, acetic acid, or glycine to water, The steps include supplying the cooling liquid to the steel plate to cool the steel plate, Equipped with, In the cooling step, the cooling liquid is supplied to the steel plate to cool the steel plate. The aforementioned coolant is The first ion containing ammonium ions, A second ion containing organic acid ions, ionized amino acids, or sulfate ions, Includes, The concentration of the first ion in the coolant is 0.5% by weight or more and 5.3% by weight or less. The concentration of the second ion in the coolant is 1.0% by weight or more and 27.8% by weight or less. A method for cooling steel plates.

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