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

Abstract

By controlling the alloy components and manufacturing method, we provide an uncoated austenitic steel sheet with improved corrosion resistance in alkaline environments. [Solution] The uncoated austenitic steel sheet of the present invention, which has improved corrosion resistance in alkaline environments, contains, in weight percent, C: more than 0% and not more than 0.04%, Si: more than 0% and not more than 0.4%, Mn: more than 0% and not more than 0.5%, Cr: more than 0% and not more than 2.0%, Ni: 33 to 40%, Co: more than 0% and not more than 4.0%, with the remainder being Fe and other unavoidable impurities, and the value of the following formula (1) can be 0.83 or less. Formula (1): 9.0-0.2495xNi+0.9xCr-0.005xCo 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 technology]

[0002] In recent years, efforts have been made to use hydrogen, an environmentally friendly fuel, in order to prevent global warming. In particular, water electrolysis, which utilizes the electrolysis of water in conjunction with renewable energy, is being considered for hydrogen production. Water electrolysis methods include high-temperature water electrolysis, cation separation membrane water electrolysis, and alkaline water electrolysis, with alkaline water electrolysis being the most commonly commercialized method. An alkaline water electrolysis device comprises an electrolyte, an anode, a cathode, a separation membrane, a separation plate, etc., and the electrolyte contains a strong base solution such as a 25-30% KOH solution. Therefore, the components included in the alkaline water electrolysis device must be made of materials that are highly resistant to corrosion in strong base solutions.

[0003] Conventionally, pure Ni metal or Ni-coated stainless steel has been used as the separator plate for alkaline water electrolysis equipment. However, conventional technologies have had problems such as a decrease in price competitiveness due to the use of expensive Ni, and a decrease in overall cell performance due to defects in the Ni coating layer. Additionally, conventional technologies have had problems such as the difficulty of coating due to the use of large-area separators, and the higher the corrosion resistance of the stainless steel base material, the more difficult it becomes to coat. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made to solve the above problems, and its object is to provide an uncoated austenitic steel sheet with improved corrosion resistance in alkaline environments by controlling the alloy components and manufacturing method. [Means for solving the problem]

[0005] The uncoated austenitic steel sheet of the present invention, which has improved corrosion resistance in an alkaline environment, is characterized by comprising, in weight percent, 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 to 40% of Ni, more than 0% and 4.0% or less of Co, with the remainder being Fe and other unavoidable impurities, and having a value of the following formula (1) of 0.83 or less: Formula (1): 9.0-0.2495xNi+0.9xCr-0.005xCo In formula (1), Ni, Cr, and Co represent the content (wt %) of each element.

[0006] The steel sheet of the present invention may have a current density ratio represented by the following formula (2) of 1.9 or less. Equation (2): Current density of uncoated austenitic steel sheet with improved corrosion resistance in alkaline environments / Current density of pure Ni metal In the uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment, the alkaline environment may have an [OH-] ion concentration of 0.3 mol to 7.5 mol on a molar basis.

[0007] The method for producing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to the present invention includes the steps of producing an ingot containing, by weight, C: more than 0% and not more than 0.04%, Si: more than 0% and not more than 0.4%, Mn: more than 0% and not more than 0.5%, Cr: more than 0% and not more than 2.0%, Ni: 33 to 40%, Co: more than 0% and not more than 4.0%, with the remainder being Fe and other unavoidable impurities; reheating the ingot and hot rolling it to produce a hot-rolled steel sheet; and solution heat treating the hot-rolled steel sheet.

[0008] In the manufacturing method of the present invention, the ingot preferably has a value of the following formula (1) of 0.83 or less. Formula (1): 9.0-0.2495xNi+0.9xCr-0.005xCo In formula (1), Ni, Cr, and Co represent the content (wt %) of each element.

[0009] In the above manufacturing method, the reheating is preferably carried out at a temperature of 1150°C to 1350°C. In the above manufacturing method, the solution heat treatment is preferably carried out at 800 to 900°C. [Effects of the Invention]

[0010] According to one embodiment of the disclosed invention, by controlling the alloying elements and manufacturing method, it is possible to provide an uncoated austenitic steel sheet with improved corrosion resistance in alkaline environments. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are presented to fully convey the spirit of the disclosed invention to those skilled in the art to which the disclosed invention pertains. The disclosed invention is not limited to the embodiments presented herein and may be embodied in other forms. In the drawings, parts irrelevant to the description may be omitted to clarify the disclosed invention, and the sizes of components may be somewhat exaggerated to facilitate understanding. Throughout the specification, when a part is said to "comprise" certain elements, this means that it may further include other elements, rather than excluding other elements, unless specifically stated to the contrary. Singular expressions include plural expressions unless the context clearly indicates otherwise. The reasons for limiting the numerical values ​​of the alloy component contents in the embodiments of the present invention will be explained below. Unless otherwise specified, the units are % by weight.

[0012] The uncoated austenitic steel sheet of the present invention with improved corrosion resistance in alkaline environments contains, by weight, C: more than 0% and not more than 0.04%, Si: more than 0% and not more than 0.4%, Mn: more than 0% and not more than 0.5%, Cr: more than 0% and not more than 2.0%, Ni: 33 to 40%, Co: more than 0% and not more than 4.0%, with the remainder being Fe and other unavoidable impurities.

[0013] The C (carbon) content is more than 0% and not more than 0.04%. C is an element that forms carbides and reduces the quality of steel, and can be maintained at extremely low concentrations through various decarburization processes. However, the use of extremely low decarburization processes may increase manufacturing costs. In consideration of this, the C content is preferably greater than 0% and less than or equal to 0.04%. More preferably, the C content is 0.01% to 0.02%.

[0014] The Si (silicon) content is more than 0% and not more than 0.4%. Si is an essential element added for deoxidation during alloy refining. Therefore, adding Si facilitates deoxidation during refining, reduces the oxygen content, and is advantageous for inclusion control. However, excessive addition of Si may result in a deterioration in the quality of the steel due to inclusions. In consideration of this, the Si content should be more than 0% and not more than 0.4%. More preferably, the Si content is 0.1% to 0.2%.

[0015] The Mn (manganese) content is more than 0% and not more than 0.5%. Mn is an element effective in solid solution strengthening and improving hot workability. In particular, Mn can be used as a deoxidizer together with Si during alloy refining. However, excessive Mn content can lead to the formation of sulfides such as MnS, which may result in poor corrosion resistance. In consideration of this, the Mn content is preferably more than 0% and 0.5% or less. More preferably, the Mn content is 0.15% to 0.35%.

[0016] The Cr (chromium) content is more than 0% and not more than 2.0%. Cr dissolves in an alkaline environment at a level of 0 V versus a hydrogen electrode. Therefore, steels containing Cr may have reduced corrosion resistance in an alkaline environment. However, because Cr is an essential element added in the stainless steel manufacturing process, additional costs may be incurred to remove Cr that has been introduced from the base metal, etc. In consideration of this, the Cr content is preferably more than 0% and not more than 2.0%. More preferably, the Cr content is 0.02% to 2.0%.

[0017] The Ni (nickel) content is 33 to 40%. Ni is an essential element for ensuring corrosion resistance in alkaline environments. Taking this into consideration, the Ni content should be 33% or more. However, Ni is an expensive element, and adding too much may reduce price competitiveness. Taking this into consideration, it is preferable to limit the Ni content to an upper limit of 40%.

[0018] The Co (cobalt) content is more than 0% and not more than 4.0%. Co, along with Ni, is an element that is very stable in alkaline environments and is effective in increasing corrosion resistance. However, Co is an expensive element, and adding too much Co may reduce price competitiveness. In consideration of this, the Co content is preferably more than 0% and not more than 4.0%. More preferably, the Co content is 0.01% to 4.0%, and even more preferably, 0.01% to 2.0%.

[0019] The remaining component of the disclosed invention is iron (Fe). However, it cannot be excluded that unintended impurities may inevitably be introduced from raw materials or the surrounding environment during normal manufacturing processes. These impurities are known to anyone skilled in normal manufacturing processes, and therefore not all of them are specifically mentioned herein.

[0020] In the uncoated austenitic steel sheet of the present invention having improved corrosion resistance in an alkaline environment, the value of the following formula (1) may be 0.83 or less. Formula (1): 9.0-0.2495xNi+0.9xCr-0.005xCo In formula (1), Ni, Cr, and Co represent the content (wt %) of each element. Ni, Cr, and Co are elements that can directly affect corrosion resistance in alkaline environments. Therefore, the disclosed invention aims to provide an austenitic steel sheet with improved corrosion resistance in alkaline environments by controlling the value of formula (1) consisting of Ni, Cr, and Co to 0.83 or less. Specifically, an uncoated austenitic steel sheet with improved corrosion resistance in alkaline environments has a value of formula (1) of -1 to 0.83, more preferably 0.001 to 0.83, and even more preferably 0.003 to 0.8. Within this range, the uncoated austenitic steel sheet can achieve a current density that is equivalent to or better than that of pure Ni metal, and can further improve its alkali resistance and corrosion resistance.

[0021] The uncoated austenitic steel sheet of the present invention with improved corrosion resistance in an alkaline environment preferably has a current density ratio represented by the following formula (2) of 1.9 or less. Equation (2): Current density of uncoated austenitic steel sheet with improved corrosion resistance in alkaline environments / Current density of pure Ni metal The current density ratio is the current density of an uncoated austenitic steel sheet with improved corrosion resistance in an alkaline environment divided by the current density of pure Ni metal. Therefore, a current density ratio of 1.0 can be evaluated as having corrosion resistance at the same level as pure Ni metal.

[0022] On the other hand, the current density may be lower as the corrosion resistance in an alkaline environment increases. Also, the lower the current density ratio is below 1.0, the better the corrosion resistance of the material is than that of pure Ni metal. In this regard, the lower limit of the current density ratio represented by the above formula (2) is 0.001, preferably 0.01, more preferably 0.1, and even more preferably 0.5. Within this range, an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one embodiment of the present invention can exhibit advantageous properties for use as a material for water electrolysis cells such as high-temperature water electrolysis, cation separation membrane water electrolysis, and alkaline water electrolysis. In addition, the productivity and cost reduction effects for achieving desired properties can be further enhanced.

[0023] An uncoated austenitic steel sheet with improved corrosion resistance in an alkaline environment has a current density ratio represented by the above formula (2) of 1.9 or less. The current density ratio is preferably 0.001 to 1.9, more preferably 0.1 to 1.5, even more preferably 0.5 to 1.07, and even more preferably 0.8 to 1.07. The alkaline environment preferably has an [OH-] ion concentration of 0.3 to 7.5 mol in terms of molar concentration.

[0024] Meanwhile, the uncoated austenitic steel sheet with improved corrosion resistance in an alkaline environment according to one example of the disclosed invention does not require a separate coating, so there is no problem of reduced cell performance due to a defective coating layer. Furthermore, the uncoated austenitic steel sheet with improved corrosion resistance in an alkaline environment according to one example of the disclosed invention does not require a large-area coating process, so it is highly price competitive. Next, a method for producing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to another embodiment of the disclosed invention will be described.

[0025] The method for producing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to the present invention includes the steps of producing an ingot containing, by weight, C: more than 0% and not more than 0.04%, Si: more than 0% and not more than 0.4%, Mn: more than 0% and not more than 0.5%, Cr: more than 0% and not more than 2.0%, Ni: 33 to 40%, Co: more than 0% and not more than 4.0%, with the remainder being Fe and other unavoidable impurities; reheating the ingot and hot rolling it to produce a hot-rolled steel sheet; and solution heat treating the hot-rolled steel sheet. The ingot preferably has a value of the following formula (1) of 0.83 or less. Formula (1): 9.0-0.2495xNi+0.9xCr-0.005xCo

[0026] In formula (1), Ni, Cr, and Co represent the content (wt %) of each element. Specifically, the value of the above formula (1) is from −1 to 0.83, more preferably from 0.001 to 0.83, and even more preferably from 0.003 to 0.8. The component ranges of each alloy composition and the reasons for limiting the numerical values ​​in formula (1) are as described above. Each manufacturing step will be described in more detail below.

[0027] After an ingot satisfying the above alloy composition and formula (1) is produced, it undergoes a series of steps of reheating, hot rolling, and solution heat treatment. First, the ingot can be reheated at 1150 to 1350°C and then hot rolled. By reheating the ingot at 1150 to 1350°C and hot rolling it, the coarse precipitates formed during ingot production can be redissolved, and the internal crystal grains can be controlled to an appropriate size. After hot rolling to produce a hot-rolled steel sheet, it can be subjected to solution heat treatment at 800 to 900°C.

[0028] Meanwhile, the method for manufacturing an uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to one example of the disclosed invention does not require a separate Ni coating process, and therefore has excellent productivity and price competitiveness.

[0029] The present invention will be described in more detail below through embodiments. However, the description of these embodiments is for illustrative purposes only and does not limit the scope of the present invention. The scope of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom.

[0030] {Embodiment} Various alloy compositions shown in Table 1 below were melted in a vacuum melting furnace and then ingots measuring 150 x 150 x 280 mm were prepared. The ingots were reheated to 1240°C and hot-rolled to a thickness of 3 mm to prepare hot-rolled steel sheets. The hot-rolled steel sheets were solution-heat-treated at 850°C to prepare test specimens.

[0031] [Table 1]

[0032] Table 2 below shows the values ​​of formula (1) and the current density ratios. The formula (1) value was calculated using the following formula (1): 9.0 - 0.2495xNi + 0.9xCr - 0.005xCo In formula (1), Ni, Cr, and Co represent the content (wt %) of each element.

[0033] The current density ratio was calculated as follows: Current density ratio = (current density of uncoated austenitic steel sheet with improved corrosion resistance in alkaline environment / current density of pure Ni metal) The current density was measured by applying a voltage of 0.4 V vs. a standard hydrogen electrode in a 30% KOH solution to the test piece and pure Ni metal for 6 hours.

[0034] On the other hand, the current density may be lower as the corrosion resistance in an alkaline environment increases. If the current density ratio is 1.0, the corrosion resistance is equivalent to that of pure Ni metal, and if the current density ratio is lower than 1.0, the corrosion resistance is evaluated to be better than that of pure Ni metal.

[0035] [Table 2]

[0036] Referring to Table 2, Examples 1 to 9 satisfied the alloy composition, formula (1), and manufacturing method proposed in the disclosed invention. Therefore, Examples 1 to 9 satisfied the current density ratio of 1.9 or less. That is, Examples 1 to 9 can be evaluated as having improved corrosion resistance in an alkaline environment. However, Comparative Examples 1 and 6 had too high a Cr content and Comparative Example 1 had too low a Ni content, so Comparative Examples 1 and 6 did not satisfy the formula (1) value of 0.83 or less. Therefore, Comparative Examples 1 and 6 did not satisfy the current density ratio of 1.9 or less. That is, Comparative Examples 1 and 6 had very poor corrosion resistance in an alkaline environment. Comparative Examples 2 to 5 satisfied the alloy composition, but did not satisfy the formula (1) value of 0.83 or less. Therefore, Comparative Examples 2 to 5 did not satisfy the current density ratio of 1.9 or less. That is, Comparative Examples 2 to 5 had poor corrosion resistance in an alkaline environment.

[0037] According to one embodiment of the disclosed invention, by controlling the alloy composition and manufacturing method, it is possible to provide an uncoated austenitic steel sheet with improved corrosion resistance in alkaline environments. Furthermore, according to one example of the disclosed invention, it is possible to reduce the amount of expensive Ni element added and to manufacture an uncoated austenitic steel sheet without introducing a separate coating process, thereby making it possible to manufacture an uncoated austenitic steel sheet that is highly cost-competitive.

Claims

1. In weight percent, C: more than 0% and not more than 0.04%, Si: more than 0% and not more than 0.4%, Mn: more than 0% and not more than 0.5%, Cr: more than 0% and not more than 2.0%, Ni: 33 to 40%, Co: more than 0% and not more than 4.0%, with the remainder being Fe and other unavoidable impurities, An uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment, characterized in that the value of the following formula (1) is 0.83 or less: Formula (1): 9.0-0.2495xNi+0.9xCr-0.005xCo (In formula (1), Ni, Cr, and Co represent the content (wt%) of each element.)

2. 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: Equation (2): Current density of uncoated austenitic steel sheet with improved corrosion resistance in alkaline environment / Current density of pure Ni metal

3. 2. The uncoated austenitic steel sheet having improved corrosion resistance in an alkaline environment according to claim 1, wherein the alkaline environment has an [OH-] ion concentration of 0.3 mol to 7.5 mol on a molar basis.

4. producing an ingot consisting of, by weight percent, C: more than 0% but not more than 0.04%, Si: more than 0% but not more than 0.4%, Mn: more than 0% but not more than 0.5%, Cr: more than 0% but not more than 2.0%, Ni: 33-40%, Co: more than 0% but not more than 4.0%, with the remainder being Fe and other unavoidable impurities; reheating and hot rolling the ingot to produce a hot rolled steel sheet; and a step of subjecting the hot-rolled steel sheet to a solution heat treatment;

5. The ingot is 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) is 0.83 or less: Formula (1): 9.0-0.2495xNi+0.9xCr-0.005xCo (In formula (1), Ni, Cr, and Co represent the content (wt%) of each element.)

6. The method for manufacturing an uncoated austenitic steel sheet with improved corrosion resistance in an alkaline environment according to claim 4, wherein the reheating is performed at a temperature of 1150°C to 1350°C.

7. 5. The method for manufacturing 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 a temperature of 800 to 900°C.

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