Steel plate with excellent abrasion resistance and composite corrosion resistance and manufacturing method thereof

Abstract

The present invention provides a steel plate having excellent wear resistance and combined corrosion resistance, and a method for producing the same. SOLUTION: A corrosion-resistant steel sheet according to one embodiment of the present invention contains, by weight, carbon (C): 0.04 to 0.10%, silicon (Si): 0.1% or less (excluding 0%), copper (Cu): 0.20 to 0.35%, nickel (Ni): 0.1% to 0.2%, antimony (Sb): 0.05 to 0.15%, tin (Sn): 0.07 to 0.22%, titanium (Ti): 0.05 to 0.15%, sulfur (S): 0.01% or less (excluding 0%), nitrogen (N): 0.005% or less (excluding 0%), the balance being iron (Fe) and inevitable impurities, and satisfies the following formulas 1 and 2. [Formula 1] [Ni] / [Cu]≧0.5 [Formula 2] 48x([Ti] / 48-[S] / 32-[N] / 14)≧0.04 In this case, in Formula 1 and Formula 2, [Ni], [Cu], [Ti], [S], and [N] represent the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively.

Description

[Technical field]

[0001] The present invention relates to a steel plate having excellent abrasion resistance and composite corrosion resistance, and a manufacturing method thereof. More specifically, the present invention relates to a steel plate having excellent abrasion resistance and composite corrosion resistance, and a manufacturing method thereof. x The present invention relates to a steel plate that is resistant to corrosion caused by sulfuric acid / hydrochloric acid combined condensate and sulfuric acid condensate, which are generated as exhaust gas temperature decreases, and has high strength and excellent abrasion resistance, and a method for manufacturing the same. [Background technology]

[0002] Fossil fuels contain a variety of impurity elements such as S and Cl. When burning such fossil fuels, there is always the problem of deterioration due to corrosion of the pipes and equipment through which the combustion gas passes. This type of corrosion phenomenon is called condensate corrosion, and typical applications of pipes and equipment exposed to such corrosive environments include exhaust gas pipes and environmental equipment at thermal power plants and automobile exhaust systems. One type of condensation corrosion is when S contained in exhaust gas is burned to produce SO x In particular, sulfuric acid condensation corrosion occurs when SO3 comes into contact with moisture in the exhaust gas to form sulfuric acid; chlorine contained in the exhaust gas or industrial water reacts in various ways to produce hydrochloric acid, and sulfuric acid / hydrochloric acid combined condensation corrosion occurs when sulfuric acid and hydrochloric acid are mixed together. The temperature at which acid condensation begins depends on the temperature of the exhaust gas itself and the SO in the exhaust gas. x , Cl content, and water vapor content.

[0003] In recent years, there has been a sustained demand for lowering the exhaust gas temperature itself in order to improve the power generation efficiency at power plants and other users or to utilize waste heat discharged to the outside. In general, when the exhaust gas temperature drops to a temperature at which sulfuric acid begins to condense, not only does the amount of sulfuric acid gas formed in the exhaust gas liquefy and condense on the steel surface, causing corrosion, increase, but when the exhaust gas temperature drops to a temperature lower than the temperature at which hydrochloric acid can condense, a composite corrosion phenomenon occurs in which sulfuric acid and hydrochloric acid condense together.

[0004] In addition, in recent years, research into equipment modifications to increase the desulfurization efficiency of thermal power plant environmental facilities has been ongoing. One representative example is the change in the type of GGH (Gas Gas Heater), which is a heat exchange device in the front and rear stages of desulfurization equipment. Existing GGHs are located in the rear stage of electrostatic precipitators (EPs), and research into the development of steel materials used in these equipment focused on corrosion resistance. However, in recent GGHs, some desulfurization equipment is located in the front stage of electrostatic precipitators, which causes corrosion due to wear as well as erosion of steel materials caused by dust that cannot be removed. Therefore, the steel materials used in these equipment need to simultaneously solve the problems of wear resistance as well as corrosion resistance.

[0005] As an example of the measures to solve such problems, there are methods to use high alloy corrosion resistant steel such as Duplex stainless steel (Duplex STS steel) or to raise the temperature of exhaust gas, but these lead to high equipment costs and reduced power generation efficiency. There is also a movement to adopt high strength steel, but even if this solves the strength problem, it may cause other equipment deterioration problems due to corrosion resistance problems.

[0006] Meanwhile, when using Cu-added corrosion-resistant steel, known as sulfuric acid condensation corrosion-resistant steel, the Cu-enriched layer formed on the steel surface exhibits corrosion resistance against sulfuric acid condensation, forming a corrosion-inhibiting layer that inhibits corrosion, and is effective in significantly improving equipment life compared to when general steel is used. However, the previously mentioned lower temperatures of exhaust gases, the complex corrosive environment, and the demand for wear resistance have reduced the corrosion resistance properties of existing sulfuric acid condensation corrosion-resistant steel, and there has been a continuous demand for corrosion-resistant steel with better performance.

[0007] Furthermore, there has been a problem with existing sulfuric acid condensation corrosion-resistant steels and high-alloy stainless steels in that they are unable to demonstrate their inherent performance in complex and severe corrosion-resistant environments. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention provides a steel plate having excellent abrasion resistance and composite corrosion resistance, and a manufacturing method thereof. More specifically, the present invention provides a method for producing the same by using SO2, which is present in the exhaust gas after the combustion of fossil fuels. x The present invention aims to provide a steel sheet that is resistant to corrosion caused by sulfuric acid / hydrochloric acid combined condensate and sulfuric acid condensate, which are generated as exhaust gas temperature decreases, and has high strength and excellent abrasion resistance, and a manufacturing method thereof. [Means for solving the problem]

[0009] The corrosion-resistant steel plate according to one embodiment of the present invention contains, by weight, 0.04 to 0.10% carbon (C), 0.1% or less (excluding 0%) silicon (Si), 0.20 to 0.35% copper (Cu), 0.1 to 0.2% nickel (Ni), 0.05 to 0.15% antimony (Sb), 0.07 to 0.22% tin (Sn), 0.05 to 0.15% titanium (Ti), 0.01% or less (excluding 0%) sulfur (S), 0.005% or less (excluding 0%) nitrogen (N), the balance being iron (Fe) and unavoidable impurities, and satisfies the following formulas 1 and 2. [Formula 1] [Ni] / [Cu]≧0.5 [Formula 2] 48x([Ti] / 48-[S] / 32-[N] / 14)≧0.04 In this case, in formulas 1 and 2, [Ni], [Cu], [Ti], [S], and [N] represent the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively.

[0010] The corrosion-resistant steel plate contains TiC precipitates, and the TiC precipitates and the aggregates of TiC precipitates are 1 cm 3 10 per 16 Contains more than one.

[0011] The grain size of the TiC precipitates may be 1 to 10 nm.

[0012] The corrosion-resistant steel plate can further satisfy the following formula 3. [Formula 3] 12x[Sn]+22x[Sb]+50x[Cu]≧15 In this case, in formula 3, [Sn], [Sb], and [Cu] respectively represent the contents (wt%) of Sn, Sb, and Cu in the steel sheet.

[0013] When a steel sheet is immersed in a mixed solution of 28.5 wt % sulfuric acid solution and 0.5 wt % hydrochloric acid solution at 40 to 80° C., a thickened layer is formed on the surface of the steel sheet.

[0014] When a steel sheet is immersed in a 50 wt % sulfuric acid solution at 50 to 90°C, a thickened layer is formed on the surface of the steel sheet.

[0015] The enriched layer may include Cu, Sb, and Sn.

[0016] The thickening amount of the thickened layer may be 15% by weight or more.

[0017] In this case, the enrichment amount refers to the total content (wt%) of enriched elements Mo, Cu, Sb, and Sn at the boundary point where Fe and O become the same in wt%.

[0018] The thickness of the thickened layer may be 10 nm or more.

[0019] The recrystallization fraction of the steel sheet after the annealing heat treatment may be 80% or more.

[0020] When a steel sheet is immersed in a mixed solution of 28.5% by weight sulfuric acid and 0.5% by weight hydrochloric acid at 60°C for 6 hours, the corrosion weight loss ratio is 1.0 mg / cm 2 / hr. or less.

[0021] When a steel plate is immersed in a 50% by weight sulfuric acid solution at 70°C for 6 hours, the corrosion weight loss ratio is 25mg / cm 2 / hr. or less.

[0022] When the steel plate is a hot-rolled steel plate, the hot-rolled steel plate may have a tensile strength of 550 MPa or more and a surface hardness of 85 or more on the HRB scale.

[0023] When the steel sheet is a cold-rolled steel sheet, the cold-rolled steel sheet may have a tensile strength of 500 MPa or more and a surface hardness of 80 or more on the HRB scale.

[0024] A method for producing a corrosion-resistant steel sheet according to an embodiment of the present invention includes the steps of: preparing a steel slab containing, by weight percent, 0.04-0.10% carbon (C), 0.1% or less (excluding 0%) silicon (Si), 0.20-0.35% copper (Cu), 0.1-0.2% nickel (Ni), 0.05-0.15% antimony (Sb), 0.07-0.22% tin (Sn), 0.05-0.15% titanium (Ti), 0.01% or less (excluding 0%) sulfur (S), 0.005% or less (excluding 0%) nitrogen (N), the balance being iron (Fe) and unavoidable impurities, and satisfying the following formulas 1 and 2; heating the slab at 1,200°C or higher; and hot rolling the heated slab at a finish rolling temperature of 850-1,000°C to produce a hot-rolled steel sheet. [Formula 1] [Ni] / [Cu]≧0.5 [Formula 2] 48x([Ti] / 48-[S] / 32-[N] / 14)≧0.04 In this case, in formulas 1 and 2, [Ni], [Cu], [Ti], [S], and [N] represent the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively.

[0025] Meanwhile, after the step of producing a hot-rolled steel sheet, the method may further include the steps of coiling the hot-rolled steel sheet at 450 to 750°C; cold rolling the coiled hot-rolled steel sheet at a rolling reduction of 54 to 70% to produce a cold-rolled steel sheet; and annealing the cold-rolled steel sheet at 750 to 880°C.

[0026] In the step of heating the slab to 1,200° C. or higher, the slab may be left in the furnace for 150 minutes or longer. Effect of the Invention

[0027] The corrosion-resistant steel sheet according to one embodiment of the present invention can be effectively used as a raw material for pipes through which exhaust gas passes after the combustion of fossil fuels, and for hot-rolled and cold-rolled products for fossil fuel combustion facilities.

[0028] Regardless of whether the heat exchanger GGH (Gas Gas Heater) used in desulfurization equipment for thermal power plants is installed before or after the electrostatic precipitator (EP), when the corrosion-resistant steel plate according to one embodiment of the present invention is applied to the GGH equipment, it can meet all the requirements for wear resistance and complex corrosion resistance despite the large difference in environmental changes. [Brief description of the drawings]

[0029] [Figure 1] 4 is a graph showing the concentration of elements in the surface portion of the steel sheet obtained by measuring the element distribution from the surface to the inside by GDS measurement after immersing the steel sheet of Example 2 in a 50 wt % sulfuric acid solution for 24 hours. [Diagram 2] Photographs comparing (a) the tendency of cracks to occur at the hot-rolled edge of Example 4 after hot rolling under condition 1 and (b) the tendency of cracks to occur at the hot-rolled edge of Example 4 after hot rolling under condition 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] In this specification, the terms such as first, second and third are used to describe various parts, components, regions, layers and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Therefore, the first part, component, region, layer or section described below is referred to as the second part, component, region, layer or section within the scope of the present invention.

[0031] In this specification, when a part "comprises" a certain component, this means that it can further include other components, not excluding other components, unless otherwise specified.

[0032] The terminology used in this specification is merely for the purpose of referring to specific embodiments and is not intended to limit the present invention. As used herein, the singular form includes the plural form unless the text clearly indicates otherwise. The meaning of "comprising" as used in the specification embodies certain properties, regions, integers, steps, operations, elements and / or components and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements and / or components.

[0033] As used herein, the term "combinations thereof" contained in a Markush form expression means a mixture or combination of one or more selected from the group of components set forth in the Markush form expression, and means including one or more selected from the group of components.

[0034] As used herein, when a part is referred to as being "on" another part, this means that it is exactly on top of the other part, or there may be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them.

[0035] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless defined.

[0036] Moreover, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0037] In one embodiment of the present invention, the term "additionally contain an additional element" means that the remaining iron (Fe) is replaced by an additional amount of the additional element.

[0038] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0039] The inventors of the present invention have confirmed that when an element capable of forming precipitates, such as Ti, is added to a normal medium to low carbon steel sheet, the hardness and strength of the hot-rolled intermediate material and the cold-rolled final material can be significantly increased by utilizing appropriate manufacturing conditions in the manufacturing process.

[0040] In other words, when such steel plate is placed in a sulfuric acid or combined sulfuric acid / hydrochloric acid corrosive environment, further corrosion is inhibited despite the formation of precipitates due to the corrosion products generated by the types and amounts of elements contained in the steel plate and their combined relationship.

[0041] In this regard, it was concluded that by adding two or more special component elements such as Cu, Sb, and Sn to the steel plate, it is possible to significantly improve corrosion resistance in high concentration sulfuric acid and combined condensed sulfuric acid / hydrochloric acid environments at the same time, thereby dramatically improving the corrosion resistance of equipment in condensed water corrosive environments.

[0042] Using this principle, it has been confirmed that a dense concentrated layer containing corrosion-resistant elements generated between the steel material and the corrosion products during a corrosion reaction can be formed in a low-carbon steel sheet, and it has been found that the manufactured steel sheet has excellent corrosion resistance in an immersion corrosion environment.

[0043] Hereinafter, a steel plate having excellent abrasion resistance and combined corrosion resistance and a method for producing the same will be described in detail as one embodiment of the present invention.

[0044] The corrosion-resistant steel plate according to one embodiment of the present invention contains, by weight, 0.04 to 0.10% carbon (C), 0.1% or less (excluding 0%) silicon (Si), 0.20 to 0.35% copper (Cu), 0.1% to 0.2% nickel (Ni), 0.05 to 0.15% antimony (Sb), 0.07 to 0.22% tin (Sn), 0.05 to 0.15% titanium (Ti), 0.01% or less (excluding 0%) sulfur (S), 0.005% or less (excluding 0%) nitrogen (N), the balance being iron (Fe) and unavoidable impurities, and satisfies the following formulas 1 and 2.

[0045] [Formula 1] [Ni] / [Cu]≧0.5

[0046] [Formula 2] 48x([Ti] / 48-[S] / 32-[N] / 14)≧0.04

[0047] In this case, in formulas 1 and 2, [Ni], [Cu], [Ti], [S], and [N] represent the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively.

[0048] On the other hand, the corrosion-resistant steel plate can further satisfy the following formula 3.

[0049] [Formula 3] 12x[Sn]+22x[Sb]+50x[Cu]≧15

[0050] In this case, in formula 3, [Sn], [Sb], and [Cu] respectively represent the contents (wt%) of Sn, Sb, and Cu in the steel sheet.

[0051] First, the reasons for limiting the components of the steel sheet and the formulas 1, 2, and 3 will be explained.

[0052] Carbon (C): 0.04~0.10% by weight The carbon content of the low carbon steel sheet may be 0.04 to 0.10% by weight. If the carbon content in the steel is too high, excessive TiC formation and carbide formation may cause a decrease in corrosion resistance, particularly a decrease in sulfuric acid / hydrochloric acid combined corrosion resistance. Conversely, if the carbon content is too low, it may not be possible to ensure the strength aimed at in the present invention. More specifically, it may be 0.042 to 0.10% by weight.

[0053] Silicon (Si): 0.1% by weight or less (excluding 0% by weight) The silicon content of the low carbon steel sheet may be 0.1% by weight or less. If the silicon content in the steel is excessively high, a large amount of red scale due to a composite phase of SiO2 and Fe oxides may be induced on the surface. Therefore, the Si content is in the above range to eliminate surface defects. More specifically, it may be 0.05% by weight or less. Even more specifically, it may be 0.01 to 0.05% by weight.

[0054] Copper (Cu): 0.20~0.35% by weight Cu is a typical element that prevents further corrosion by concentrating between the steel surface and the corrosion product when corroded in an acid immersion environment. To achieve this effect, an appropriate amount of Cu is added. However, if too much is added, it may cause cracks during manufacturing due to the low melting point of Cu.

[0055] Nickel (Ni): 0.1% to 0.2% by weight When only Cu is added to steel without Ni, the low melting point of Cu may cause liquid Cu to penetrate into grain boundaries, resulting in cracks. Ni is added to increase the melting point and limit the occurrence of cracks. If the Ni content is too low, it cannot adequately fulfill its role of increasing the melting point of Cu, and conversely, if the Ni content is too high, surface defects due to Ni may occur. More specifically, the Ni content may be 0.11 to 0.19% by weight.

[0056] [Formula 1][Ni] / [Cu]≧0.5 For the same reason as for adding Ni together with Cu, Ni and Cu can be added in the above ranges to appropriately increase the melting point and not induce surface defects due to Ni. If the value of formula 1 is too high, surface defects due to Ni may occur, and if the value of formula 1 is too low, the effect of increasing the melting point by Ni may be small. In this case, [Ni] and [Cu] in formula 1 represent the contents (weight%) of Ni and Cu in the steel plate, respectively.

[0057] Antimony (Sb): 0.05 to 0.15% by weight Sb, like Cu, is added to form a stable concentrated layer on the surface. If the Sb content is too low, a sufficient concentrated layer may not be formed. Conversely, if the Sb content is too high, it may induce surface cracks.

[0058] Tin (Sn): 0.07 to 0.22% by weight Sn, like Cu and Sb, is added to form a stable concentrated layer on the surface. In particular, it has been confirmed that Sn plays a role in significantly improving the corrosion resistance of steels by dissolving first in an acid immersion environment such as sulfuric acid. To explain more specifically, although it is not clear, it is thought that Sn improves the corrosion resistance of steels through the following mechanism. When a steel sheet is placed in an immersion environment of sulfuric acid or complex acid, Sn and Cu dissolve, but Sn dissolves before Cu. As Sn dissolves before Cu, Sn dissociates in the solution. The dissociated Sn lowers the corrosion potential of the solution, which is thought to partially delay the corrosion phenomenon of the steel sheet. At this time, the corrosion potential means the potential with respect to the reference electrode of the metal in which corrosion is progressing. In addition, a corrosion retardation layer can be formed in the process of re-melting Sn that was dissolved on the steel sheet surface, and it is thought that such a corrosion retardation layer can delay the corrosion of the steel sheet. If the Sn content is too low, a sufficient concentrated layer may not be formed. If too much Sn is added, it may cause serious surface cracks during the production process. More specifically, the content may be 0.073 to 0.22 wt %.

[0059] [Formula 3] 12x[Sn]+22x[Sb]+50x[Cu]≧15 The Cu, Sb, and Sn are elements that form an enriched layer on the steel sheet surface in a sulfuric acid / hydrochloric acid combined condensed atmosphere or a sulfuric acid condensed atmosphere, and not only the appropriate content of each element but also the relationship of formula 3 can be satisfied. If the value of formula 3 is too small, there is a disadvantage that a sufficient enriched layer cannot be formed. In this case, in formula 3, [Sn], [Sb], and [Cu] respectively indicate the contents (weight %) of Sn, Sb, and Cu in the steel sheet. More specifically, formula 3 may be 15 to 26. Even more specifically, it may be 15.2 to 23.44.

[0060] Titanium (Ti): 0.05 to 0.15% by weight Ti is added to improve the strength and wear resistance of the steel sheet by acting as an element that forms precipitates. That is, Ti combines with C to form TiC precipitates. TiC is a fine precipitate, and can improve the hardness and wear resistance of the steel sheet by precipitation strengthening, and can increase the strength at the same time. In this regard, specific matters regarding TiC will be described later. Here, if the Ti content is too low, there is a disadvantage that precipitates cannot be formed sufficiently and there is no effect of increasing strength. On the other hand, if the Ti content is too high, there is a disadvantage that excessive TiC is formed, which causes cracks during rolling, and Ti, Al-based composite oxides are formed in the steelmaking stage, which may clog the tundish nozzle, causing manufacturing defects and surface defects. Therefore, Ti may be contained more specifically in an amount of 0.05 to 0.145 wt %. More specifically, Ti may be contained in an amount of 0.052 to 0.145 wt %.

[0061] Sulfur (S): 0.01% by weight or less (excluding 0%) S may have the adverse effect of limiting the Ti content effective in forming Ti carbide. The reason is that, in the present invention, the wear resistance is enhanced by precipitation hardening due to the formation of TiC precipitates, but since TiS is formed before the formation of TiC, if the S content is high, the formation of TiC is hindered. Therefore, the maximum component range can be set to the above range. More specifically, it may be 0.0097 wt% or less. Even more specifically, it may be 0.001 to 0.0097 wt%.

[0062] Nitrogen (N): 0.005% by weight or less (excluding 0%) N may have the adverse effect of limiting the content of Ti that is effective in forming Ti carbide. The reason is that, in the present invention, the wear resistance is enhanced by precipitation hardening due to the formation of TiC precipitates, but since TiN is formed before the formation of TiC, if the content of N is high, the formation of TiC is hindered. For reference, when Ti is formed as a precipitate, it is formed in the order of TiN, TiS, and TiC. Therefore, the range of the maximum component can be the above range. More specifically, it may be 0.004 wt% or less. Even more specifically, it may be 0.001 to 0.004 wt%.

[0063] [Formula 2]48x([Ti] / 48-[S] / 32-[N] / 14)≧0.04 Effective Ti(Ti * ) is calculated by formula 2. Even if the above-mentioned ranges of S and N are satisfied, if the range of formula 2 is not satisfied, sufficient TiC cannot be formed, which may lead to a decrease in strength. In this case, in formula 2, [Ti], [S], and [N] respectively represent the contents (weight%) of Ti, S, and N in the steel plate. More specifically, the range of formula 2 may be 0.04 to 0.12.

[0064] The steel plate may further contain manganese (Mn) and aluminum (Al).

[0065] Manganese (Mn): 0.5 to 1.5% by weight Mn plays a role in improving strength by solid solution strengthening in steel, but if its content is too excessive, coarse MnS is formed, which rather reduces strength. Therefore, in the present invention, it is preferable to limit the Mn content to 0.5 to 1.5 wt%.

[0066] Aluminum (Al): 0.02 to 0.05% by weight Al is an element that is inevitably added when manufacturing aluminum-killed steel, and is preferably added in an appropriate content for its deoxidizing effect. However, if the Al content exceeds 0.02 wt%, not only is there an increased possibility of inducing surface defects in the steel sheet, but there is also a problem of reduced weldability. Therefore, in the present invention, it is preferable to limit the Al content to 0.02 to 0.05 wt%.

[0067] In addition to the above components, the present invention includes Fe and inevitable impurities. Since inevitable impurities are widely known in the art, detailed description is omitted. In one embodiment of the present invention, the addition of effective components in addition to the above components is not excluded, and when an additional component is further included, it is included to replace the remaining Fe.

[0068] Meanwhile, the corrosion-resistant steel sheet according to an embodiment of the present invention has excellent wear resistance, and in this regard, may contain TiC precipitates. The TiC precipitates and aggregates of the TiC precipitates are fine precipitates, and can improve the hardness and wear resistance of the steel sheet by precipitation strengthening, while at the same time increasing the strength.

[0069] TiC precipitates and aggregates of multiple TiC precipitates were observed in the area of ​​1 cm 3 10 per 16 If the precipitate content is too low, the desired strength and wear resistance cannot be achieved. 3 10 per 16 ~10 18 It may be one piece.

[0070] The TiC precipitates may be spherical.

[0071] The particle size of the TiC precipitates may be 1 to 10 nm. The precipitates prevent the movement of electric potential inside the steel material and form an electric potential zone to increase the strength. If the particle size of the precipitates is too small, the electric potential moves easily and there is no effect of increasing the strength. On the other hand, if the particle size of the precipitates is too large, the electric potential passes through the precipitates, making the movement easier, and there is also a disadvantage that the effect of increasing the strength is reduced. More specifically, the particle size may be 2 to 10 nm. More specifically, the particle size may be 2 to 8 nm. Here, the particle size means the diameter of a sphere, assuming that the sphere has the same volume as the particle.

[0072] Moreover, the TiC precipitates can be distributed uniformly within the steel sheet.

[0073] Meanwhile, in the corrosion-resistant steel sheet according to an embodiment of the present invention, Cu, Sb, Sn, etc. form a concentrated layer in a sulfuric acid / hydrochloric acid composite condensed atmosphere or a sulfuric acid condensed atmosphere, which inhibits further corrosion. More specifically, when a steel sheet is immersed in a mixed solution of 28.5 wt % sulfuric acid solution and 0.5 wt % hydrochloric acid solution at 40 to 80°C, a concentrated layer is formed on the surface of the steel sheet. Also, when a steel sheet is immersed in a 50 wt % sulfuric acid solution at 50 to 90°C, a concentrated layer is formed on the surface of the steel sheet. More specifically, when immersed for 4 to 8 hours, a concentrated layer is formed.

[0074] In this case, the concentrated layer means a layer where Cu, Sb, and Sn start to concentrate, and in other respects is similar to the point where oxidation generally starts. In the present invention, the concentrated layer means a layer in which the total amount of Cu, Sb, and Sn in the layer exceeds four times the total amount of Cu, Sb, and Sn in the steel sheet.

[0075] The concentrated layer may also be an amorphous concentrated layer.

[0076] The concentrated layer is formed when the steel sheet is immersed in acid, together with the formation of a corrosion layer. In this case, the corrosion layer refers to a layer in which Fe is oxidized by O. Generally, Fe is oxidized before Cu and Sb, and when immersed in acid, Fe dissociates into Fe ions and escapes into the acid solution, but Cu and Sb are more stable in a solid state and remain on the surface. Therefore, even if the Fe content on the steel sheet surface continues to decrease as the acid reaction continues, Cu and Sb remain on the surface and a highly concentrated layer is formed. This is formed on the surface in the form of a concentrated layer after a certain reaction time has passed, and this concentrated layer inhibits further corrosion by preventing direct contact between the acid and the internal iron.

[0077] The enriched layer may contain Cu, Sb, and Sn, and the enrichment amount of the enriched layer may be 15% by weight or more. At this time, the enrichment amount is taken as the boundary point where Fe and O are the same in weight percent, and means the total content (weight percent) of the enriched elements Mo, Cu, Sb, and Sn at this time. In other words, it is taken as the boundary point where the contents (weight percent) of Fe and O are the same, and means the total content (weight percent) of the enriched elements Cu, Sb, and Sn at this time. If the enrichment amount is too small, there is a disadvantage that the enriched layer cannot be formed sufficiently and the corrosion weight loss ratio increases. More specifically, it may be 15% to 22%.

[0078] The contents of each enriched element at the point where the Fe and O contents (wt %) in the enriched layer become the same may be Cu: 10-15 wt %, Sb: 1-3 wt %, and Sn: 1-3 wt %.

[0079] The thickness of the concentrated layer may be 10 nm or more. More specifically, the concentrated layer is formed to a thickness of 10 to 500 nm. If the concentrated layer is too thin, it is difficult to perform the above-mentioned role of corrosion prevention. If the concentrated layer is formed too thick, cracks may occur inside the concentrated layer, and acid may penetrate along the cracks, causing corrosion. More specifically, the concentrated layer is formed to a thickness of 12 to 100 nm.

[0080] The corrosion-resistant steel sheet according to an embodiment of the present invention may be a hot-rolled steel sheet or a cold-rolled steel sheet.

[0081] In the case of a hot-rolled steel sheet, the thickness of the steel sheet may be 2.5 to 5.5 mm, more specifically, 3.5 to 5.5 mm.

[0082] In the case of a cold-rolled steel sheet, the thickness of the steel sheet may be 1.0 to 2.5 mm, more specifically, 1.0 to 2.0 mm.

[0083] When the corrosion-resistant steel sheet according to an embodiment of the present invention is a cold-rolled steel sheet, the recrystallization fraction after the steel sheet is annealed may be 80% or more. More specifically, it may be 100%. If the recrystallization fraction is too low, the strength increases, but there is a disadvantage that the ductility decreases rapidly and defects are formed during customer processing. Here, the recrystallization fraction means the area of ​​recrystallized grains based on the area of ​​the entire steel sheet.

[0084] When a corrosion-resistant steel sheet according to an embodiment of the present invention is immersed in a mixed solution of 28.5 wt % sulfuric acid solution and 0.5 wt % hydrochloric acid solution at 60° C. for 6 hours, the corrosion weight loss ratio is 1.0 mg / cm 2 / hr. or less.

[0085] When the corrosion-resistant steel sheet according to one embodiment of the present invention is immersed in a 50% by weight sulfuric acid solution at 70° C. for 6 hours, the corrosion weight loss ratio is 25 mg / cm 2 / hr. or less.

[0086] When the corrosion-resistant steel plate according to an embodiment of the present invention is a hot-rolled steel plate, the hot-rolled steel plate may have a tensile strength of 550 MPa or more and a surface hardness of 85 or more based on HRB.

[0087] When the corrosion-resistant steel sheet according to an embodiment of the present invention is a cold-rolled steel sheet, the cold-rolled steel sheet may have a tensile strength of 500 MPa or more and a surface hardness of 80 or more based on HRB.

[0088] A method for producing a corrosion-resistant steel sheet according to an embodiment of the present invention includes the steps of: preparing a steel slab containing, by weight percent, 0.04-0.10% carbon (C), 0.1% or less (excluding 0%) silicon (Si), 0.20-0.35% copper (Cu), 0.1-0.2% nickel (Ni), 0.05-0.15% antimony (Sb), 0.07-0.22% tin (Sn), 0.05-0.15% titanium (Ti), 0.01% or less (excluding 0%) sulfur (S), 0.005% or less (excluding 0%) nitrogen (N), the balance being iron (Fe) and unavoidable impurities, and satisfying the following formulas 1 and 2; heating the slab at 1,200°C or higher; and hot rolling the heated slab at a finish rolling temperature of 850-1,000°C to produce a hot-rolled steel sheet.

[0089] [Formula 1] [Ni] / [Cu]≧0.5

[0090] [Formula 2] 48x([Ti] / 48-[S] / 32-[N] / 14)≧0.04

[0091] In this case, in formulas 1 and 2, [Ni], [Cu], [Ti], [S], and [N] represent the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively.

[0092] In addition, the method may further include, after the step of producing a hot-rolled steel sheet, a step of coiling the hot-rolled steel sheet at 450 to 750°C; a step of cold-rolling the coiled hot-rolled steel sheet at a rolling reduction of 54 to 70% to produce a cold-rolled steel sheet; and a step of annealing the cold-rolled steel sheet at 750 to 880°C.

[0093] Each step will be explained in detail below.

[0094] First, a slab satisfying the above-mentioned composition is heated. The reason for limiting the addition ratio of each component in the slab is the same as the reason for limiting the composition of the steel sheet described above, so a repeated explanation will be omitted. Since the composition of the slab does not substantially change during the manufacturing process such as hot rolling, coiling, pickling, cold rolling, and annealing described below, the composition of the slab and the composition of the finally manufactured corrosion-resistant steel sheet are substantially the same.

[0095] By heating the slab, the subsequent hot rolling process can be smoothly performed and the slab can be homogenized. More specifically, heating can mean reheating. At this time, the heating temperature of the slab can be 1,200°C or more. The reason why the heating temperature of the slab is in the above range is to sufficiently redissolve Ti. Only when Ti is sufficiently redissolved can TiC precipitate later.

[0096] On the other hand, the residence time during heating of the slab may be 150 minutes or more. If the residence time is too short, re-dissolution of Ti may not occur sufficiently.

[0097] Next, the heated slab is hot-rolled to produce a hot-rolled steel sheet. The finish rolling temperature of the hot rolling may be 850 to 1000°C. If the finish rolling temperature is too low, sufficient rolling capacity cannot be exhibited, whereas if the finish rolling temperature is too high, it may be difficult to ensure the strength of the steel sheet. In this case, the thickness of the hot-rolled sheet may be 2.5 to 5.5 mm.

[0098] Next, the method may include a step of coiling the hot-rolled steel sheet. The step of coiling the hot-rolled steel sheet is performed at 450 to 750° C. If the coiling temperature is too low, the initial strength of the hot-rolled steel sheet increases, making the final cold rolling difficult. On the other hand, if the coiling temperature is too high, problems such as buckling and strength reduction due to phase transformation in the coiling section may occur.

[0099] Thereafter, the coiled hot-rolled steel sheet is pickled.

[0100] Next, the coiled hot-rolled steel sheet is cold-rolled at a reduction of 54 to 70% to produce a cold-rolled steel sheet. If the reduction is too low, it may be difficult to ensure complete recrystallization during cold rolling, which may lead to a decrease in the elongation of the material and may lead to cracks during subsequent customer processing. On the other hand, if the reduction is too high, a problem may occur in which the material cannot be rolled due to the load of the motor during the rolling process.

[0101] Next, the cold-rolled steel sheet is annealed at 750 to 880°C. If the annealing temperature is too low, it may be difficult to ensure complete recrystallization, which may lead to a decrease in the elongation rate of the material and may lead to cracks during subsequent customer processing. On the other hand, if the annealing temperature is too high, it may be difficult to ensure the strength of the steel sheet.

[0102] The present invention will be described in more detail with reference to the following examples, which are merely for illustrative purposes and are not intended to limit the scope of the present invention. EXAMPLES

[0103] Working Example First, a low carbon steel slab was produced containing the alloying components summarized in Table 1 below.

[0104] The slabs were heated at 1250°C for 200 min and then hot rolled to a thickness of 3.5 mm to produce hot-rolled sheets. The finish rolling temperature (FDT) was 920°C and coiling was performed at 650°C.

[0105] [Table 1] JPEG0007598379000002.jpg56169

[0106] After the low carbon steel plate was manufactured, an immersion test was performed according to the method described in the ASTM G31 standard. The immersion test was performed by preparing a 50 wt% sulfuric acid aqueous solution and immersing the plate at 70°C for 6 hours. After immersion, the weight loss after cleaning was measured according to the ASTM G1 surface cleaning method of the test piece, and the weight loss per unit time and unit surface area was measured.

[0107] In addition, to simulate the sulfuric acid / hydrochloric acid composite condensation that occurs during low-temperature condensation in Korean thermal power plants, a mixed aqueous solution of 28.5 wt% sulfuric acid solution and 0.5 wt% hydrochloric acid solution was prepared and immersed at 60°C for 6 hours. After immersion, the weight loss after cleaning was measured according to the ASTM G1 surface cleaning method of the test piece as described above, and the weight loss per unit time and unit surface area was measured.

[0108] The results are shown in Table 2 below. The unit is mg / cm 2 / hr.

[0109] On the other hand, in order to clarify the relationship between the corrosion-resistant elements and the surface enriched layer, the hot-rolled sheets of each of the invention examples and comparative examples were immersed in a 50% by weight sulfuric acid solution at 70°C for 24 hours, and then the test pieces were subjected to GDS measurement to measure the element distribution from the surface to the inside. The thickness of the enriched layer and the enrichment amount of the surface enriched elements measured from these are shown in Table 2 below.

[0110] In this case, the enriched layer refers to the layer where Cu, Sb, and Sn start to enrich, and in other respects is similar to the point where oxidation generally begins. Empirically, the thickness of the enriched layer was measured as the thickness of the layer where the total amount of Cu, Sb, and Sn in that layer exceeds four times the total amount of Cu, Sb, and Sn in the steel plate. At this time, it was confirmed that Cu and other elements are enriched at the boundary point where the Fe and O contents (weight%) are the same, and the enrichment amount was calculated as the total content (weight%) of the enriched elements Cu, Sb, and Sn at this point, where the Fe and O contents (weight%) are the same. It was confirmed that the enriched layer consisting of Sb, Sn, and Cu exists on the surface of the steel material and the corrosion product at a level of about 20wt%. It was found that the thickness and enrichment amount of such an enriched layer determine the corrosion resistance during immersion.

[0111] In relation to this, Figure 1 is a graph showing the concentration of elements in the surface of the steel sheet, measured by GDS measurement from the surface to the inside after immersing the steel sheet of Example 2 in a 50 wt% sulfuric acid solution for 24 hours. The total content of Cu, Sb, and Sn in Example 2 is (0.26 + 0.1 + 0.15), or 0.51 wt%, and at a depth of 14 nm, the total amount of Cu, Sb, and Sn exceeds 2.04 wt%, which is four times 0.51 wt%. Therefore, the depth of 14 nm was determined to be the thickness of the concentrated layer. (Red dotted line)

[0112] In addition, the boundary point where Fe and O come into contact, that is, the point where the Fe and O contents are the same, is the layer corresponding to the blue dotted line (left side) in Figure 1, and the enrichment amount, which is the total amount of Cu, Sb, and Sn in that layer, was 17 wt%.

[0113] The strength, hardness and presence or absence of cracks were also confirmed for the produced steel sheets before acid immersion. The hot-rolled materials of the inventive and comparative examples were fabricated into tensile test pieces conforming to the JIS 13B standard, and then tensile tests were performed long in the rolling direction. The results of measuring the HRB surface hardness based on the Rockwell hardness standard are shown in Table 2 below.

[0114] Furthermore, the occurrence of cracks in the slab during the continuous casting process and the occurrence of cracks on the edges of the hot-rolled material during the hot rolling process are also shown in Table 2. Here, the enrichment amount means the total content (wt%) of enrichment elements Cu, Sb, and Sn at the point where the contents (wt%) of Fe and O become the same.

[0115] [Table 2]

[0116] In the case of Comparative Example 1, where the C content was low, the tensile strength of the hot-rolled material was lower than 550 MPa and the surface hardness was low due to the decrease in the TiC precipitate content caused by the low C content, so strength and wear resistance could not be ensured. However, when the C content was excessively high as in Comparative Example 2, a phenomenon was observed in which the composite corrosion resistance decreased due to the increase in TiC precipitates.

[0117] In the present invention, the Si content is characteristically significantly reduced. The reason for this is that it was confirmed that the higher the Si content, as in Comparative Example 3, the more excessive red scale is generated on the surface of the hot-rolled material, which leads to cracks.

[0118] Comparative Example 4, which had a low Cu content, caused a decrease in corrosion resistance, especially when sulfuric acid was used alone, and in the case of Comparative Example 5, which had an excessively high Cu content, cracks in the slab due to Cu liquefaction were observed during the continuous casting process.

[0119] As shown in formula 1, the active addition of Ni plays a role in increasing the melting point of Cu, so it was confirmed that when the Ni / Cu ratio does not satisfy a certain level as in Comparative Example 6, cracks occur in the slab.

[0120] The most important elements for corrosion resistance are Cu, Sb, and Sn. It was confirmed that the corrosion resistance was significantly reduced in Comparative Example 8, which had a low Sb content, and Comparative Example 12, which had a low Sn content, while the surface defects and cracks were induced in the hot-rolled material in Comparative Example 9, which had an excessively high Sb content, and Comparative Example 13, which had an excessively high Sn content.

[0121] In the present invention, Ti was actively added to form precipitates to ensure strength and surface hardness, but it was confirmed that the tensile strength and surface hardness of the hot-rolled material rapidly decreased when the Ti content was low as in Comparative Example 10. Meanwhile, in the case of Comparative Example 11, where the Ti content was high, especially 0.15 wt% or more, nozzle clogging could be induced during the continuous casting process, and serious nozzle clogging was actually confirmed during the testing process of the comparative example.

[0122] For the formation of TiC, not only the adjustment of C and Ti and the temperature are important, but also the effective Ti content capable of precipitating Ti-based carbides is important. Excessive addition of nitrogen and sulfur as in Comparative Examples 14 and 15 reduces the effective Ti content, offsetting the effect of increasing strength.

[0123] In addition, even if the S and N contents are within the ranges described in the invention examples as in Comparative Example 16, the effective Ti (Ti * ) content must be 0.04 or more, otherwise it is difficult to obtain the effects of high strength and high wear resistance. On the other hand, in the case of Comparative Example 16 in which the effective Ti content is low, the density of TiC is low and the grain size of TiC is excessively small, so that there is a disadvantage in that the desired precipitation hardening effect cannot be obtained.

[0124] Table 3 below shows the properties of hot-rolled and cold-rolled materials produced under different production conditions using the composition of Example 4 of the invention, in order to investigate the possibility of producing the materials and the effect of the production conditions on the strength of the materials.

[0125] [Table 3]

[0126] From the results in Table 3, it can be confirmed that in the case of condition 10 where the reheating temperature is lower than 1200°C, the tensile strength of the hot-rolled material and the cold-rolled material decreases even when the composition of the invention is used. This is because Ti that was formed as a precipitate during the slab process could not be sufficiently redissolved during the reheating process.

[0127] In the case of condition 2, where the hot finish rolling temperature (FDT) was high, edge cracks occurred during the hot rolling production process, and this also occurred in the case of condition 4, where the coiling temperature (CT) was low. In relation to this, FIG. 2 is a photograph comparing (a) the tendency of cracks to occur on the hot rolled edge of Example 4 after hot rolling under condition 1, and (b) the tendency of cracks to occur on the hot rolled edge of Example 4 after hot rolling under condition 2.

[0128] In contrast, under condition 3, in which the hot finish rolling temperature (FDT) was high at 1,050°C, the tensile strength of the hot-rolled and cold-rolled materials was low and the target material quality could not be achieved. This also occurred in the case of condition 5, in which the coiling temperature (CT) was high.

[0129] The steel type of the present invention is characterized by its high C and Ti content and high recrystallization temperature after cold rolling, but in the case of condition 6 where the cold rolling reduction is 53%, the recrystallization fraction of the final cold rolled material is at the 70% level, which is not complete recrystallization, and even in the case of condition 8 where the annealing temperature is as low as 740°C, the recrystallization fraction is 65%, which is not complete recrystallization. In the case of the above-mentioned material where complete recrystallization does not occur, cracks may be induced during customer processing due to the decrease in elongation, so in the present invention, when used as a cold rolled material, the rolling reduction is limited to 54% or more and the annealing temperature is limited to 750°C or more.

[0130] In the case of conditions 4 and 7, where the strength of the hot-rolled material was high or the cold reduction rate was high, the rolling process was not completed due to the load on the motor, and the final product could not be obtained.

[0131] The present invention is not limited to the embodiments, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains will understand that the present invention can be embodied in other specific forms without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the embodiments described above are illustrative in all respects and are not limiting.

Claims

1. The alloy contains, by weight, 0.04-0.10% carbon (C), 0.1% or less (excluding 0%) silicon (Si), 0.20-0.35% copper (Cu), 0.1-0.2% nickel (Ni), 0.05-0.15% antimony (Sb), 0.05-0.15% titanium (Ti), 0.07-0.22% tin (Sn), 0.01% or less (excluding 0%) sulfur (S), and 0.005% or less (excluding 0%) nitrogen (N), with the remainder being iron (Fe) and unavoidable impurities; A corrosion-resistant steel plate that satisfies the following formulas 1 and 2. [Formula 1] [Ni] / [Cu]≧0.5 [Formula 2] 48x ([Ti] / 48-[S] / 32-[N] / 14)≧0.04 (In Formula 1 and Formula 2, [Ni], [Cu], [Ti], [S], and [N] respectively represent the contents (wt%) of Ni, Cu, Ti, S, and N in the steel plate.)

2. The grain size of the TiC precipitates is 1-10 nm. The TiC precipitate is 1 cm ３ 10 per １６ The corrosion-resistant steel plate according to claim 1 , comprising at least one of the above.

3. The corrosion-resistant steel plate according to claim 1 or 2, which satisfies the following formula 3: [Formula 3] 12x[Sn]+22x[Sb]+50x[Cu]≧15 (In formula 3, [Sn], [Sb], and [Cu] represent the contents (wt%) of Sn, Sb, and Cu in the steel sheet, respectively.)

4. The corrosion-resistant steel plate according to claim 2 or 3, wherein when the steel plate is immersed in 50% by weight sulfuric acid at 50 to 90° C. for 24 hours, a concentrated layer is formed on the surface of the steel plate.

5. The corrosion-resistant steel plate according to claim 4 , wherein the concentrated layer contains Cu, Sb, and Sn.

6. The corrosion-resistant steel plate according to claim 5 , wherein the concentrated layer has a concentration of 15% by weight or more. (In this case, the enrichment amount is the total content (wt%) of the enriched elements Mo, Cu, Sb, and Sn at the boundary point where Fe and O become the same in wt%.)

7. The corrosion-resistant steel plate according to any one of claims 4 to 6, wherein the concentrated layer has a thickness of 10 nm or more.

8. The corrosion-resistant steel sheet according to any one of claims 1 to 7, wherein the recrystallization fraction after the steel sheet is subjected to an annealing heat treatment is 80% or more.

9. The corrosion weight loss ratio when the steel sheet is immersed in a solution containing 28.5 wt % sulfuric acid and 0.5 wt % hydrochloric acid at 60° C. for 6 hours is 1.0 mg / cm ２ The corrosion-resistant steel sheet according to any one of claims 4 to 8, wherein the corrosion resistance is 0.1 to 1.0 s. / hr. or less.

10. The corrosion weight loss ratio when the steel plate is immersed in a 50 wt % sulfuric acid solution at 70° C. for 6 hours is 25 mg / cm ２ The corrosion-resistant steel plate according to any one of claims 5 to 9, wherein the corrosion resistance is 0.1 to 1.0 MPa.

11. The corrosion-resistant steel plate according to any one of claims 2 to 10, wherein when the steel plate is a hot-rolled steel plate, the hot-rolled steel plate has a tensile strength of 550 MPa or more and a surface hardness of 85 or more based on HRB.

12. The corrosion-resistant steel plate according to any one of claims 2 to 10, wherein when the steel plate is a cold-rolled steel plate, the cold-rolled steel plate has a tensile strength of 500 MPa or more and a surface hardness of 80 or more based on HRB.

13. The alloy contains, by weight, 0.04-0.10% carbon (C), 0.1% or less (excluding 0%) silicon (Si), 0.20-0.35% copper (Cu), 0.1-0.2% nickel (Ni), 0.05-0.15% antimony (Sb), 0.07-0.22% tin (Sn), 0.05-0.15% titanium (Ti), 0.01% or less (excluding 0%) sulfur (S), and 0.005% or less (excluding 0%) nitrogen (N), with the remainder being iron (Fe) and unavoidable impurities; Providing a steel slab that satisfies the following formulas 1 and 2: heating the slab to above 1,200° C.; and hot rolling the heated slab at a finish rolling temperature of 850 to 1000° C. to produce a hot-rolled steel sheet; A method for producing a corrosion-resistant steel plate comprising the steps of: [Formula 1] [Ni] / [Cu]≧0.5 [Formula 2] 48x ([Ti] / 48-[S] / 32-[N] / 14)≧0.04 (In Formula 1 and Formula 2, [Ni], [Cu], [Ti], [S], and [N] respectively represent the contents (wt%) of Ni, Cu, Ti, S, and N in the steel plate.)

14. After the step of producing the hot rolled steel sheet, coiling the hot-rolled steel sheet at 450 to 750°C; cold rolling the coiled hot-rolled steel sheet at a rolling reduction of 54 to 70% to produce a cold-rolled steel sheet; and subjecting the cold-rolled steel sheet to an annealing heat treatment at 750 to 880°C; The method for producing a corrosion-resistant steel plate according to claim 13, further comprising:

15. heating the slab to 1,200° C. or higher; The method for producing a corrosion-resistant steel sheet according to claim 13 or 14, wherein the furnace time is 150 minutes or more.

Images