Uncoated austenitic steel sheet having improved corrosion resistance in alkaline environments and method for manufacturing same

Abstract

The uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment may contain, in wt%, more than 0% and 0.04% or less of C, more than 0% and 0.4% or less of Si, more than 0% and 0.5% or less of Mn, more than 0% and 2.0% or less of Cr, 33-40% of Ni, more than 0% and 4.0% or less of Co, and a remainder of Fe and other unavoidable impurities, and the value of formula (1) may be 0.83 or less. Formula (1): 9.0 to 0.2495 * Ni + 0.9 * Cr-0.005 * Co. In formula (1), Ni, Cr, and Co represent the content (wt%) of each element.

Description

Technical Field

[0001] The present invention relates to an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment and a method for producing the same. Background Art

[0002] In recent years, efforts to prevent global warming have been underway to utilize hydrogen as an environmentally friendly fuel. In particular, water electrolysis, which utilizes water electrolysis in conjunction with new renewable energy sources, is being explored for hydrogen production. Water electrolysis methods include high-temperature water electrolysis, cationic membrane water electrolysis, and alkaline water electrolysis, with alkaline water electrolysis being the most commercially available method.

[0003] An alkaline water electrolysis device consists of an electrolyte, a positive electrode, a negative electrode, a diaphragm, a separator, and other components. The electrolyte can contain a strong alkaline solution, such as a 25-30% KOH solution. Therefore, the components of an alkaline water electrolysis device need to be made of materials with high corrosion resistance in strong alkaline solutions.

[0004] Conventionally, pure Ni metal or Ni-coated stainless steel has been used as a diaphragm used in alkaline water electrolysis devices.

[0005] However, the existing technology uses expensive nickel, which reduces price competitiveness and suffers from defects in the Ni coating, which reduces overall battery performance. Furthermore, the existing technology uses large separators, making coating difficult. Furthermore, the better the corrosion resistance of the stainless steel used as the base material, the more difficult the coating becomes. Summary of the Invention

[0006] (1) Technical issues to be resolved

[0007] An object of the present invention, which is intended to solve the above-mentioned problems, is to provide an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment by controlling alloy components and a manufacturing method.

[0008] (2) Technical solution

[0009] An uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment may contain, in terms of weight %, C: greater than 0% and 0.04% or less, Si: greater than 0% and 0.4% or less, Mn: greater than 0% and 0.5% or less, Cr: greater than 0% and 2.0% or less, Ni: 33-40%, Co: greater than 0% and 4.0% or less, and the balance being Fe and other inevitable impurities, and the value of the following formula (1) may be 0.83 or less.

[0010] Formula (1): 9.0-0.2495×Ni+0.9×Cr-0.005×Co

[0011] In formula (1), Ni, Cr, and Co represent the content (wt %) of each element.

[0012] The uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment may have a current density ratio represented by the following formula (2) of 1.9 or less.

[0013] Formula (2): Current density of uncoated austenitic steel sheet with improved corrosion resistance in alkaline environment / Current density of pure Ni metal

[0014] In the uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment, the alkaline environment has a molar concentration of [OH - ] ions can have a concentration of 0.3 molar to 7.5 molar.

[0015] A method for manufacturing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment may include the following steps: manufacturing a steel ingot, the steel ingot comprising, in weight %, C: greater than 0% and 0.04% or less, Si: greater than 0% and 0.4% or less, Mn: greater than 0% and 0.5% or less, Cr: greater than 0% and 2.0% or less, Ni: 33-40%, Co: greater than 0% and 4.0% or less, and the balance being Fe and other inevitable impurities; reheating the steel ingot and hot rolling it to manufacture a hot-rolled steel sheet; and solution heat treating the hot-rolled steel sheet.

[0016] In the method for manufacturing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment, the value of the following formula (1) of the slab may be 0.83 or less.

[0017] Formula (1): 9.0-0.2495×Ni+0.9×Cr-0.005×Co

[0018] In formula (1), Ni, Cr, and Co represent the content (wt %) of each element.

[0019] In the method for manufacturing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment, the reheating may be performed at 1150°C to 1350°C.

[0020] In the method for manufacturing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment, the solution heat treatment may be performed at 800°C to 900°C.

[0021] (3) Beneficial effects

[0022] According to one embodiment of the disclosed invention, an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment can be provided by controlling alloy composition and manufacturing methods. DETAILED DESCRIPTION

[0023] The following detailed description of the embodiments of the disclosed invention is provided with reference to the accompanying drawings. The following embodiments are provided to fully convey the concepts of the present invention to those skilled in the art. The present invention is not limited to the embodiments set forth herein and may be embodied in other forms. To further clarify the present invention, portions not relevant to the present invention are omitted from the accompanying drawings, and the dimensions of components may be exaggerated to facilitate understanding.

[0024] Throughout the specification, unless otherwise specifically stated, when describing a part as “including” or “comprising” a certain component, it means that other components may also be included, rather than excluding other components.

[0025] Unless clearly excepted otherwise in the context, expressions in the singular also include expressions in the plural.

[0026] The following describes the reasons for limiting the numerical values of the alloy component contents according to the embodiment of the present invention. Hereinafter, unless otherwise specified, the unit is weight %.

[0027] An uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment may contain, in weight %, C: greater than 0% and 0.04% or less, Si: greater than 0% and 0.4% or less, Mn: greater than 0% and 0.5% or less, Cr: greater than 0% and 2.0% or less, Ni: 33-40%, Co: greater than 0% and 4.0% or less, and the balance Fe and other inevitable impurities.

[0028] The carbon (C) content may be greater than 0% and 0.04% or less.

[0029] Carbon (C) forms carbides, reducing the quality of steel. Various decarburization processes can be used to minimize its content. However, using extremely low decarburization processes can increase process costs. To account for this, the C content can be greater than 0% and less than 0.04%. Preferably, the C content can be between 0.01% and 0.02%.

[0030] The content of silicon (Si) may be greater than 0% and 0.4% or less.

[0031] Si is an essential element added during alloy refining for deoxidation. Therefore, adding Si facilitates deoxidation during refining, reducing the oxygen content and facilitating inclusion control. However, adding too much Si can reduce the quality of the steel due to inclusions. To account for this, the Si content should be greater than 0% and less than 0.4%. Preferably, the Si content is between 0.1% and 0.2%.

[0032] The content of manganese (Mn) may be greater than 0% and 0.5% or less.

[0033] Mn is an element effective for solid solution strengthening and improving hot workability. In particular, Mn can be used as a deoxidizing agent along with Si during alloy refining. However, excessive Mn content may form sulfides such as MnS, potentially degrading corrosion resistance. To account for this, the Mn content can be greater than 0% and less than 0.5%. Preferably, the Mn content can be between 0.15% and 0.35%.

[0034] The content of chromium (Cr) may be greater than 0% and 2.0% or less.

[0035] Cr dissolves in alkaline environments at 0V relative to a hydrogen electrode. Therefore, the presence of Cr may reduce corrosion resistance in alkaline environments. However, since Cr is an essential element in the stainless steel manufacturing process, removing Cr introduced from scrap and other sources may incur additional costs. Considering this, the Cr content may be greater than 0% and less than 2.0%. Preferably, the Cr content may be between 0.02% and 2.0%.

[0036] The content of nickel (Ni) may be 33-40%.

[0037] Nickel is an essential element for ensuring corrosion resistance in alkaline environments. Considering this, the Ni content can be 33% or higher. However, Ni is an expensive element, and excessive addition of Ni may reduce price competitiveness. Considering this, the upper limit of the Ni content can be limited to 40%.

[0038] The content of cobalt (Co) may be greater than 0% and 4.0% or less.

[0039] Co, along with Ni, is a very stable element in alkaline environments and is an effective element for improving corrosion resistance. However, Co is an expensive element, and excessive addition of Co may reduce price competitiveness. Considering this, the Co content can be greater than 0% and less than 4.0%. Preferably, the Co content can be greater than 0.01% and less than 4.0%, and more preferably, greater than 0.01% and less than 2.0%.

[0040] The remaining component of the present invention is iron (Fe). However, during typical manufacturing processes, unwanted impurities inevitably enter from the raw materials or the surrounding environment, and therefore cannot be completely eliminated. These impurities are well known to those skilled in the art, and therefore, all of them are not specifically mentioned in this specification.

[0041] The uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment may have a value of the following formula (1) of 0.83 or less.

[0042] Formula (1): 9.0-0.2495×Ni+0.9×Cr-0.005×Co

[0043] In formula (1), Ni, Cr, and Co represent the content (wt %) of each element.

[0044] Ni, Cr, and Co are elements that can directly affect corrosion resistance in an alkaline environment. Therefore, in the present invention, by controlling the value of formula (1) composed of Ni, Cr, and Co to be 0.83 or less, an austenitic steel sheet with improved corrosion resistance in an alkaline environment is provided. Specifically, the value of formula (1) of the uncoated austenitic steel sheet with improved corrosion resistance in an alkaline environment according to one embodiment can be -1 to 0.83, more specifically 0.001 to 0.83, and further specifically 0.003-0.8. Within the above range, the uncoated austenitic steel sheet can achieve a current density at a level equivalent to or higher than that of pure Ni metal, while further improving alkali resistance and corrosion resistance.

[0045] The uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment may have a current density ratio represented by the following formula (2) of 1.9 or less.

[0046] Formula (2): Current density of uncoated austenitic steel sheet with improved corrosion resistance in alkaline environment / Current density of pure Ni metal

[0047] The current density ratio is the value obtained by dividing the current density of the uncoated austenitic steel sheet with improved corrosion resistance in an alkaline environment by the current density of pure Ni metal. Therefore, when the current density ratio is 1.0, it can be evaluated as having the same level of corrosion resistance as pure Ni metal.

[0048] In addition, the stronger the corrosion resistance in an alkaline environment, the lower the current density may tend to be. In addition, when the current density ratio is less than 1.0, it can be evaluated as having better corrosion resistance than pure Ni metal.

[0049] In this regard, the lower limit of the current density ratio represented by formula (2) can be 0.001, specifically 0.01, more specifically 0.1, and further specifically 0.5. Within the above range, the uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment of the present invention can achieve physical properties that are more favorable for use as a material for water electrolysis cells such as high-temperature water electrolysis, cationic diaphragm water electrolysis, and alkaline water electrolysis. In addition, the productivity improvement and cost-saving effects for achieving the desired physical properties can be further increased.

[0050] The current density ratio represented by formula (2) of the uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment may be 1.9 or less. Preferably, the current density ratio may be 0.001 to 1.9, more preferably 0.1 to 1.5, further preferably 0.5 to 1.07, and most preferably 0.8 to 1.07.

[0051] The alkaline environment is based on the molar concentration of [OH - ] ions can have a concentration of 0.3 molar to 7.5 molar.

[0052] Furthermore, the uncoated austenitic steel sheet with improved corrosion resistance in alkaline environments according to one embodiment of the present invention does not undergo a separate coating process, thereby preventing the problem of reduced battery performance due to poor coating. Furthermore, the uncoated austenitic steel sheet with improved corrosion resistance in alkaline environments according to one embodiment of the present invention does not undergo a large-area coating process, thereby offering excellent price competitiveness.

[0053] Next, a method for producing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one aspect of the present invention will be described.

[0054] A method for manufacturing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment may include the following steps: manufacturing a steel ingot, the steel ingot comprising, in weight %, C: greater than 0% and 0.04% or less, Si: greater than 0% and 0.4% or less, Mn: greater than 0% and 0.5% or less, Cr: greater than 0% and 2.0% or less, Ni: 33-40%, Co: greater than 0% and 4.0% or less, and the balance being Fe and other inevitable impurities; reheating the steel ingot and hot rolling it to manufacture a hot-rolled steel sheet; and solution heat treating the hot-rolled steel sheet.

[0055] The value of the following formula (1) of the slab may be 0.83 or less.

[0056] Formula (1): 9.0-0.2495×Ni+0.9×Cr-0.005×Co

[0057] In formula (1), Ni, Cr, and Co represent the content (wt %) of each element.

[0058] Specifically, the value of the formula (1) may be -1 to 0.83, more specifically 0.001 to 0.83, and further specifically 0.003 to 0.8.

[0059] The reasons for limiting the component ranges of the above-mentioned alloy compositions and the numerical values of formula (1) are as described above. Below, each production step will be described in more detail.

[0060] A slab satisfying the above alloy composition and formula (1) is produced, and then a series of reheating, hot rolling and solution heat treatment processes can be performed.

[0061] First, the slab may be reheated at 1150-1350° C. and then hot rolled.

[0062] By reheating and hot rolling at 1150-1350°C, coarse precipitates generated during slab production can be re-decomposed, and internal grains can be controlled to an appropriate size.

[0063] After hot rolling to produce hot rolled steel sheets, solution heat treatment is performed at 800-900°C.

[0064] In addition, the method of manufacturing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one example of the present invention does not perform a separate Ni coating process, and thus has excellent productivity and outstanding price competitiveness.

[0065] The present invention will be described in more detail below by way of examples. However, these examples are intended only to illustrate the present invention and are not intended to limit the present invention. The scope of the present invention is determined by the claims and any reasonable derivations therefrom.

[0066] [Example]

[0067] Steel ingots measuring 150 × 150 × 280 mm were produced by melting in a vacuum melting furnace for the various alloy composition ranges shown in Table 1. These ingots were reheated at 1240°C and then hot-rolled to a thickness of 3 mm to produce hot-rolled steel sheets. These hot-rolled steel sheets were solution-heat treated at 850°C to produce test pieces.

[0068] [Table 1]

[0069]

[0070] The values of the formula (1) and the current density ratio are shown in Table 2. The values of the formula (1) are obtained by calculating the following formula (1): Formula (1): 9.0-0.2495×Ni+0.9×Cr-0.005×Co

[0071] In formula (1), Ni, Cr, and Co represent the content (wt %) of each element.

[0072] The current density ratio is calculated as shown below.

[0073] Current density ratio = (current density of uncoated austenitic steel sheet with improved corrosion resistance in alkaline environment / current density of pure Ni metal)

[0074] The current density was measured by applying a voltage of 0.4 V relative to a standard hydrogen electrode to the test piece and pure Ni metal in a 30% KOH solution for 6 hours.

[0075] In addition, the stronger the corrosion resistance in an alkaline environment, the lower the current density may tend to be. In addition, when the current density ratio is 1.0, it can be evaluated as having the same level of corrosion resistance as pure Ni metal, and when the current density ratio is less than 1.0, it can be evaluated as having better corrosion resistance than pure Ni metal.

[0076] [Table 2]

[0077]

[0078] Referring to Table 2, Examples 1 to 9 satisfy the alloy composition, formula (1) and manufacturing method proposed in the present invention. Therefore, the current density ratio of Examples 1 to 9 satisfies 1.9 or less. That is, it can be evaluated that Examples 1 to 9 have improved corrosion resistance in an alkaline environment. However, the Cr content of Comparative Example 1 and Comparative Example 6 is too high, and the Ni content of Comparative Example 1 is too low. Therefore, the value of formula (1) of Comparative Example 1 and Comparative Example 6 does not satisfy 0.83 or less. Therefore, the current density ratio of Comparative Example 1 and Comparative Example 6 does not satisfy 1.9 or less. That is, the corrosion resistance of Comparative Example 1 and Comparative Example 6 in an alkaline environment is very poor. Although Comparative Examples 2 to 5 satisfy the alloy composition, the value of formula (1) does not satisfy 0.83 or less. Therefore, the current density ratio of Comparative Examples 2 to 5 does not satisfy 1.9 or less. That is, the corrosion resistance of Comparative Examples 2 to 5 in an alkaline environment is poor.

[0079] According to one embodiment of the present invention, an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment can be provided by controlling the alloy composition and the manufacturing method.

[0080] Furthermore, according to one embodiment of the present invention, it is possible to produce an uncoated austenitic steel sheet while reducing the amount of expensive Ni added and without introducing a separate coating process. Therefore, according to one embodiment of the present invention, it is possible to produce an uncoated austenitic steel sheet with excellent price competitiveness.

Claims

1. An uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment, comprising, in weight %, C: greater than 0% and less than 0.04%, Si: greater than 0% and less than 0.4%, Mn: greater than 0% and less than 0.5%, Cr: greater than 0% and less than 2.0%, Ni: 33-40%, Co: greater than 0% and less than 4.0%, and the balance being Fe and other unavoidable impurities. And the value of the following formula (1) is 0.83 or less, Formula (1): 9.0-0.2495×Ni+0.9×Cr-0.005×Co In formula (1), Ni, Cr, and Co represent the content of each element in wt %.

2. The uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to claim 1, wherein The current density ratio represented by the following formula (2) is 1.9 or less, Formula (2): Current density of uncoated austenitic steel sheet with improved corrosion resistance in alkaline environment / current density of pure Ni metal.

3. The uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to claim 1, wherein The alkaline environment is based on the molar concentration of [OH - ] ions have a concentration of 0.3 molar to 7.5 molar.

4. A method for producing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment, comprising the steps of: Producing a steel ingot, wherein the steel ingot comprises, in weight %, C: greater than 0% and less than 0.04%, Si: greater than 0% and less than 0.4%, Mn: greater than 0% and less than 0.5%, Cr: greater than 0% and less than 2.0%, Ni: 33-40%, Co: greater than 0% and less than 4.0%, and the balance Fe and other inevitable impurities; reheating the steel ingot and hot rolling it to produce a hot-rolled steel sheet; and The hot-rolled steel plate is subjected to solution heat treatment.

5. The method for producing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to claim 4, wherein: The value of the following formula (1) of the slab is 0.83 or less, Formula (1): 9.0-0.2495×Ni+0.9×Cr-0.005×Co In formula (1), Ni, Cr, and Co represent the content of each element in wt %.

6. The method for producing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to claim 4, wherein: The reheating is performed at 1150°C to 1350°C.

7. The method for producing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to claim 4, wherein: The solution heat treatment is performed at 800°C to 900°C.

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