WO2021125729A1 - Steel plate having excellent wear resistance and composite corrosion resistance and method for manufacturing same - Google Patents

Abstract

The present invention provides a steel sheet having excellent wear resistance and composite corrosion resistance, and a method for manufacturing same. A corrosion-resistant steel sheet according to an embodiment of the present invention comprises, in wt%: 0.04 to 0.10% of carbon (C); 0.1% or less (excluding 0%) of silicon (Si); 0.20 to 0.35% of copper (Cu); 0.1% to 0.2% of nickel (Ni); 0.05 to 0.15% of antimony (Sb); 0.07 to 0.22% of tin (Sn); 0.05 to 0.15% of titanium (Ti); 0.01% or less (excluding 0%) of sulfur (S); 0.005% or less (excluding 0%) of nitrogen (N); the remainder iron (Fe); and unavoidable impurities, and satisfies formulas 1 and 2 below: [Formula 1] [Ni]/[Cu] ≥ 0.5; and [Formula 2] 48 x ([Ti]/48 - [S]/32 - [N]/14) ≥ 0.04, wherein, in formulas 1 and 2, [Ni], [Cu], [Ti], [S], and [N] represent contents (wt%) of Ni, Cu, Ti, S, and N contained in the steel sheet, respectively.

Description

Steel sheet with excellent wear resistance and composite corrosion resistance and manufacturing method therefor

The present invention relates to a steel sheet having excellent wear resistance and composite corrosion resistance and a method for manufacturing the same. _{More specifically, SO x} , Cl, etc. present in the exhaust gas after combustion of fossil fuels have high strength and abrasion resistance as well as corrosion resistance against the corrosion of steel sheets due to sulfuric acid/hydrochloric acid complex condensate and sulfuric acid condensate generated as the flue gas temperature decreases. The present invention relates to an excellent steel sheet and a method for manufacturing the same.

Fossil fuels contain various impurity elements such as S and Cl. Since these fossil fuels are used for combustion, there is always a problem in that pipes and equipment, which are passages through which combustion gases pass, deteriorate due to corrosion. This corrosion phenomenon is called condensate corrosion, and typical uses where piping and equipment are exposed to these corrosive environments are exhaust gas piping and environmental equipment of thermal power plants, and automobile exhaust systems. _{As the types of condensation corrosion, SO x} is formed as S contained in the flue gas is burned. In particular, _{sulfuric acid condensate corrosion where SO 3} meets moisture in the flue gas to form sulfuric acid, and chlorine contained in the flue gas or industrial water is diverse. Hydrochloric acid is generated through the reaction, corrosion by the generated hydrochloric acid condensate, and sulfuric acid/hydrochloric acid composite condensate corrosion occurring in a state in which sulfuric acid and hydrochloric acid are mixed. The starting temperature of the acid condensation is related to the temperature of the flue-gas itself _{, the content of SO x} , Cl and the water vapor content in the flue-gas.

Recently, there has been a continuous demand for lowering the temperature of the flue gas itself for the purpose of utilizing the waste heat emitted to the outside or power generation efficiency in the place of use such as a power plant. In general, when the flue gas temperature is lowered to the temperature at which sulfuric acid starts to condense, the sulfuric acid gas formed in the flue gas is liquefied and condensed on the steel surface to increase the amount of corrosion, as well as the flue gas temperature to a lower temperature at which hydrochloric acid can be condensed. When is decreased, a complex corrosion phenomenon in which sulfuric acid and hydrochloric acid are condensed complexly occurs.

In addition, recent studies related to facility change to increase the desulfurization efficiency of environmental facilities of thermal power plants are continuing. As a representative example, the type of GGH (Gas Gas Heater), which is a heat exchange device before/after the desulfurization facility, is being changed. Existing GGH is located at the rear end of the electrostatic precipitator (EP), and the development of steel used here has been researched focusing on corrosion resistance, but recently GGH could not be removed as some desulfurization facilities were placed in front of the electrostatic precipitator. In addition to corrosion due to corrosion of steel materials by dust, corrosion due to wear is occurring, so there is a need to solve the problem of wear resistance in addition to corrosion resistance of steel materials used in these facilities at the same time.

As an example of a method to solve this problem, there is a method of using high-alloy high corrosion-resistant steel such as duplex stainless steel (Duplex-based STS steel), or increasing the temperature of the exhaust gas, but this increases the cost of the equipment and decreases the power generation efficiency will cause In addition, there is a movement to adopt high-strength steel, but this may lead to deterioration of other equipment due to corrosion resistance problem even if the strength problem is solved.

On the other hand, when Cu-added corrosion-resistant steel known as sulfuric acid condensation corrosion-resistant steel is used, the Cu-concentrated layer formed on the steel surface exhibits corrosion resistance against sulfuric acid condensation to form a corrosion-inhibiting layer that suppresses corrosion. It has the effect of greatly improving the life of the equipment in preparation for such a case. However, the aforementioned lower temperature of flue gas, complex corrosive environment, and demand for wear resistance have lowered the corrosion resistance of the existing sulfuric acid condensed corrosion steel, and there has been a continuous demand for corrosion-resistant steel with better performance.

And there has been a problem that the existing sulfuric acid condensation corrosion-resistant steel or high-alloy stainless steel cannot exhibit its original performance in a complex and severe corrosion-resistant environment.

An object of the present invention is to provide a steel sheet having excellent wear resistance and composite corrosion resistance and a method for manufacturing the same. _{More specifically, SO x} , Cl, etc. present in the exhaust gas after combustion of fossil fuels have high strength and abrasion resistance as well as corrosion resistance against the corrosion of steel sheets due to sulfuric acid/hydrochloric acid complex condensate and sulfuric acid condensate generated as the flue gas temperature decreases. An object of the present invention is to provide an excellent steel sheet and a method for manufacturing the same.

Corrosion-resistant steel sheet according to an embodiment of the present invention, 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 remainder including iron (Fe) and unavoidable impurities, and satisfies Formulas 1 and 2 below.

[Equation 1]

[Ni]/[Cu] ≥ 0.5

[Equation 2]

48 x ([Ti]/48 - [S]/32 - [N]/14) ≥ 0.04

At this time, in Equations 1 and 2, [Ni], [Cu], [Ti], [S], and [N] are the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively. indicates.

The corrosion-resistant steel sheet includes TiC precipitates, and TiC precipitates and aggregates made of TiC precipitates may be included in an amount of 10 ^{16 or more per 1 cm 3 .}

The TiC precipitate may have a particle diameter of 1 to 10 nm.

The corrosion-resistant steel sheet may further satisfy the following formula (3).

[Equation 3]

12 x [Sn] + 22 x [Sb] + 50 x [Cu] ≥ 15

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

When the steel sheet is immersed in a mixture of 28.5 wt% sulfuric acid solution and 0.5 wt% hydrochloric acid solution at 40 to 80° C., a thickening layer may be formed on the surface of the steel sheet.

When the steel sheet is immersed in a 50 wt% sulfuric acid solution at 50 to 90°C, a thickening layer may be formed on the surface of the steel sheet.

The thickening layer may include Cu, Sb, and Sn.

The concentration of the thickening layer may be 15% by weight or more.

At this time, the concentration means the sum (weight %) of the content of the concentration elements Mo, Cu, Sb, and Sn holding the boundary point at which Fe and O are equal in weight %.

The thickening layer thickness may be 10 nm or more.

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

When the steel sheet is immersed in a solution of 28.5 wt% sulfuric acid solution and 0.5 wt% hydrochloric acid solution at 60° C. for 6 hours, the corrosion loss ratio is 1.0 mg/cm ² /hr. may be below.

When the steel sheet is immersed in 50 wt% sulfuric acid solution at 70° C. for 6 hours, the corrosion loss ratio is 25 mg/cm ² /hr. may be below.

When the steel sheet is a hot-rolled steel sheet, the tensile strength of the hot-rolled steel sheet may be 550 MPa or more, and the surface hardness may be 85 or more based on HRB.

In the case of a cold-rolled steel sheet of the steel sheet, the tensile strength of the cold-rolled steel sheet may be 500 MPa or more, and the surface hardness may be 80 or more based on HRB.

The method of manufacturing a corrosion-resistant steel sheet according to an embodiment of the present invention, in 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%), remaining iron (Fe) and unavoidable impurities, and the steel slab satisfying the following formulas 1 and 2 preparing; heating the slab above 1,200 °C; and preparing a hot-rolled steel sheet by hot-rolling the heated slab to a finish rolling temperature of 850 to 1000 °C.

[Equation 1]

[Ni]/[Cu] ≥ 0.5

[Equation 2]

48 x ([Ti]/48 - [S]/32 - [N]/14) ≥ 0.04

At this time, in Equations 1 and 2, [Ni], [Cu], [Ti], [S], and [N] are the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively. indicates.

On the other hand, manufacturing a hot-rolled steel sheet; Thereafter, winding the hot-rolled steel sheet at 450 to 750 ℃; manufacturing a cold rolled steel sheet by cold rolling the wound hot rolled steel sheet at a reduction ratio of 54 to 70%; and annealing and heat-treating the cold-rolled steel sheet at 750 to 880°C.

In addition, the step of heating the slab at 1,200 ° C. or higher; in, the re-route time may be 150 minutes or more.

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

Regardless of whether the heat exchange device GGH (Gas Gas Heater) used in the desulfurization facility for thermal power plants is installed at the front or rear end of the electrostatic precipitator (EP), the corrosion-resistant steel sheet according to an embodiment of the present invention can be applied to the GGH facility. In this case, it can satisfy both wear resistance and complex corrosion resistance requirements despite the large environmental change.

1 is a graph showing the element concentration of the surface portion of the steel sheet by measuring the element distribution from the surface to the inside through GDS measurement after immersing the steel sheet of Inventive Example 2 in a 50 wt% sulfuric acid solution for 24 hours.

2 is (a) Inventive Example 4 after hot rolling under condition 1, the tendency of cracks in the hot rolling edge (Edge), and (b) after hot rolling in Inventive Example 4 under condition 2, cracks in the hot rolling edge ( It is a photograph comparing the tendency of crack) occurrence.

In this specification, terms such as first, second and third are used to describe, but are not limited to, various parts, components, regions, layers and/or sections. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first part, component, region, layer or section described below may be referred to as a second part, component, region, layer or section without departing from the scope of the present invention.

In the present specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

In this specification, the terminology used is for the purpose of referring to specific embodiments only, and is not intended to limit the present invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite. The meaning of "comprising," as used herein, specifies a particular characteristic, region, integer, step, operation, element and/or component, and includes the presence or absence of another characteristic, region, integer, step, operation, element and/or component. It does not exclude additions.

In the present specification, the term "combination of these" included in the expression of the Markush form means one or more mixtures or combinations selected from the group consisting of the components described in the expression of the Markush form, and the components It means to include one or more selected from the group consisting of.

In this specification, when a part is referred to as being “on” or “on” another part, it may be directly on or on the other part, or the other part may be accompanied in between. In contrast, when a part refers to being "directly above" another part, the other part is not interposed therebetween.

Although not defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Commonly used terms defined in the dictionary are additionally interpreted as having a meaning consistent with the related technical literature and the presently disclosed content, and unless defined, they are not interpreted in an ideal or very formal meaning.

In addition, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

In an embodiment of the present invention, the meaning of further including the additional element means that the remaining iron (Fe) is included by replacing the additional amount of the additional element.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

The inventors of the present invention, when adding an element capable of forming precipitates, such as Ti, to a normal medium to low carbon steel sheet, if appropriate manufacturing conditions are used in the manufacturing process, the intermediate material of the hot rolled material and the final material of the cold rolled material It was confirmed that hardness and strength can be significantly increased.

That is, when these steel sheets are subjected to sulfuric acid or sulfuric acid/hydrochloric acid complex corrosion environment, it is necessary to prevent further corrosion even though precipitates are formed by corrosion products generated according to the type and content of elements contained in the steel sheet and the complex relationship. Confirmed.

At this time, if two or more special element elements, such as Cu, Sb, Sn, etc., are added in combination to the steel sheet, corrosion resistance in high sulfuric acid concentration and sulfuric acid/hydrochloric acid complex condensing environment can be greatly improved at the same time. We have come to the conclusion that it is possible to dramatically increase the corrosion resistance performance of equipment.

Using the same principle as above, it was confirmed that a thickening layer containing corrosion resistance elements generated between the steel and corrosion products during a corrosion reaction on a low-carbon steel sheet can be densely formed, and the steel sheet manufactured through this can be formed in an immersion corrosion environment. It was found to have excellent corrosion resistance.

Hereinafter, as an embodiment of the present invention, a steel sheet having excellent wear resistance and composite corrosion resistance and a manufacturing method thereof will be described in detail.

Corrosion-resistant steel sheet according to an embodiment of the present invention, 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 remainder including iron (Fe) and unavoidable impurities, and satisfy the following formulas 1 and 2.

[Equation 1]

[Ni]/[Cu] ≥ 0.5

[Equation 2]

48 x ([Ti]/48 - [S]/32 - [N]/14) ≥ 0.04

At this time, in Equations 1 and 2, [Ni], [Cu], [Ti], [S], and [N] are the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively. indicates.

On the other hand, the corrosion-resistant steel sheet may further satisfy the following formula (3).

[Equation 3]

12 x [Sn] + 22 x [Sb] + 50 x [Cu] ≥ 15

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

First, the reason for limiting the components of the steel sheet and Equations 1, 2, and 3 will be described.

Carbon (C): 0.04 to 0.10% by weight

The carbon content of the low-carbon steel sheet may be 0.04 to 0.10 wt%. If the content of carbon in the steel is too large, corrosion resistance may be deteriorated due to excessive TiC formation and carbide formation, in particular, deterioration of sulfuric acid/hydrochloric acid composite corrosion resistance may occur. Conversely, if the carbon content is too small, it may be impossible to secure the strength desired in the present invention. More specifically, it may be 0.042 to 0.10 wt%.

Silicon (Si): 0.1 wt% or less (excluding 0 wt%)

The silicon content of the low-carbon steel sheet may be 0.1 wt% or less. If the silicon content in the steel is too large, a large amount of scale may be induced on the _{surface due to the complex phase shape of SiO 2 and Fe oxide.} Accordingly, the Si content may be within the above range for resolving surface defects. More specifically, it may be 0.05 wt% or less. More specifically, it may be 0.01 to 0.05 wt%.

Copper (Cu): 0.20 to 0.35 wt%

Cu is a representative element that, when corroded in an acid immersion environment, is concentrated between the steel surface and corrosion products to prevent further corrosion. In order to exhibit the effect, an appropriate amount of Cu may be added. However, when too much is added, there is a possibility of causing cracks during manufacturing due to the low melting point of Cu.

Nickel (Ni): 0.1% to 0.2% by weight

When only Cu is added to steel without Ni, liquid Cu may penetrate into grain boundaries and cause cracks due to Cu's low melting point. Ni is added for the purpose of limiting the occurrence of cracks by raising the melting point by adding Ni. When the content of Ni is too small, it does not sufficiently serve to increase the melting point of Cu. Conversely, when the content of Ni is too large, surface defects due to Ni may occur. More specifically, it may be 0.11 to 0.19 wt%.

[Equation 1] [Ni]/[Cu] ≥ 0.5

For the same reason as adding Ni together with Cu, Ni and Cu may be added in the above ranges in order to properly increase the melting point and not cause surface defects due to Ni. If the value of Equation 1 is too high, surface defects may occur due to Ni, and if the value of Equation 1 is too low, the effect of increasing the melting point by Ni may be insignificant. In this case, in Equation 1, [Ni] and [Cu] represent Ni and Cu contents (weight %) in the steel sheet, respectively.

Antimony (Sb): 0.05 to 0.15 wt%

Sb, like Cu, is added to form a stable thickening layer on the surface. When the content of Sb is too small, a sufficient thickening layer may not be formed. Conversely, too much may cause surface cracks.

Tin (Sn): 0.07 to 0.22 wt%

Sn, like Cu and Sb, is added to form a stable thickening layer on the surface. In particular, it was confirmed that Sn was first dissolved in an acid immersion environment such as sulfuric acid, thereby greatly improving the corrosion resistance of steel grades. More specifically, although it is not clear, it is thought that Sn improves the corrosion resistance of steel grades by the following mechanism. When the steel sheet is placed in an immersion environment of sulfuric acid or complex acid, Sn and Cu are dissolved, and Sn is dissolved before Cu. As Sn dissolves out before Cu, Sn dissociates in solution. It is thought that the dissociated Sn lowers the corrosion potential of the solution, thereby partially delaying the corrosion phenomenon of the steel sheet. At this time, the corrosion potential (Corrosion Potential) means a potential with respect to the combination electrode (Reference Electrode) of the metal corrosion is in progress. In addition, a corrosion retardation layer may be formed in the process of re-fusion of Sn dissolved on the surface of the steel sheet, and it is believed that this corrosion retardation layer may delay corrosion of the steel sheet. When Sn is included too little, it may not be possible to form a sufficient thickening layer. If Sn is added too much, it can cause serious surface cracks in the production process. More specifically, it may be 0.073 to 0.22 wt%.

[Equation 3] 12 x [Sn] + 22 x [Sb] + 50 x [Cu] ≥ 15

The Cu, Sb, and Sn are elements that form a concentrated layer on the surface of the steel sheet in a sulfuric acid/hydrochloric acid complex condensing atmosphere or a sulfuric acid condensing atmosphere, and may satisfy the relation of Equation 3 as well as an appropriate content of each element. If the value of Equation 3 is too small, there is a disadvantage that a sufficient thickening layer cannot be formed. In this case, in Equation 3, [Sn], [Sb], and [Cu] represent the contents (weight %) of Sn, Sb, and Cu in the steel sheet, respectively. More specifically, Equation 3 may be 15 to 26. More specifically, it may be 15.2 to 23.44.

Titanium (Ti): 0.05 to 0.15 wt%

Ti acts as an element for forming precipitates and is added to increase the strength and wear resistance of the steel sheet. That is, Ti combines with C to form TiC precipitates. TiC as a fine precipitate may improve the hardness and wear resistance of the steel sheet due to precipitation strengthening, and may also increase strength. In this regard, specific details of TiC will be described later. Here, if the content of Ti is too small, there is a disadvantage in that there is no effect of increasing the strength because precipitates are not sufficiently formed. On the other hand, if too much TiC is formed excessively, cracks occur during rolling, and Ti and Al-based composite oxides are formed in the steelmaking step, which can block the tundish nozzle, causing manufacturing defects and surface defects. Therefore, more specifically, Ti may include 0.05 to 0.145 wt%. More specifically, it may contain 0.052 to 0.145 wt%.

Sulfur (S): 0.01 wt% or less (excluding 0%)

S may have an adverse effect of limiting the effective content of Ti in forming Ti carbides. The reason is that, in the present invention, although the wear resistance is improved by precipitation hardening according to the formation of TiC precipitates, since TiS is formed first before TiC formation, a large amount of S interferes with the formation of TiC. Therefore, the range of the largest component can be made into said range. More specifically, it may be 0.0097 wt% or less. More specifically, it may be 0.001 to 0.0097 wt%.

Nitrogen (N): 0.005 wt% or less (excluding 0%)

N may have an adverse effect of limiting the effective content of Ti in forming Ti carbide. The reason is that, in the present invention, the wear resistance is improved by precipitation hardening according to the formation of TiC precipitates, but since TiN is first formed before TiC formation, a large amount of N interferes with the formation of TiC. 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 largest component can be made into said range. More specifically, it may be 0.004 wt% or less. More specifically, it may be 0.001 to 0.004 wt%.

[Equation 2] 48 x ([Ti]/48 - [S]/32 - [N]/14) ≥ 0.04

The effective content of Ti(Ti ^* ) can be calculated by Equation 2. Even if the component ranges of S and N are satisfied, if the range of Equation 2 is not satisfied, sufficient TiC may not be formed, resulting in a decrease in strength. At this time, in Equation 2, [Ti], [S], and [N] represent the contents (weight %) of Ti, S, and N in the steel sheet, respectively. More specifically, the range of Equation 2 may be 0.04 to 0.12.

In addition, the steel sheet may further include manganese (Mn) and aluminum (Al).

Manganese (Mn): 0.5 to 1.5 wt%

Mn plays a role in improving strength through solid solution strengthening in steel, but if the content is too large, coarse MnS is formed, which reduces strength. Therefore, the content of Mn in the present invention is preferably limited to 0.5 to 1.5% by weight.

Aluminum (Al): 0.02 to 0.05 wt%

Al is an element that is unavoidably added during the production of aluminum-killed steel, and is preferably added in an appropriate amount for the deoxidation effect. However, when the Al content exceeds 0.02% by weight, there is a problem that not only increases the possibility of causing surface defects of the steel sheet, but also deteriorates weldability. Therefore, in the present invention, it is preferable to limit the Al content to 0.02 to 0.05 wt%.

In addition to the above components, the present invention contains Fe and unavoidable impurities. Since unavoidable impurities are widely known in the art, a detailed description thereof will be omitted. In one embodiment of the present invention, the addition of effective components other than the above components is not excluded, and when additional components are further included, the remaining Fe is included.

On the other hand, the corrosion-resistant steel sheet according to an embodiment of the present invention has excellent wear resistance, and may include TiC precipitates in relation thereto. TiC precipitates and the aggregate formed of the TiC precipitates may improve hardness and wear resistance of the steel sheet due to precipitation strengthening as fine precipitates, and may also increase strength.

TiC precipitates and aggregates made of a plurality of TiC precipitates may be included in an amount of 10 ^{16 or more per 1 cm 3 .} If the content of the precipitates is too small, there is a disadvantage in that the desired strength and wear resistance cannot be secured. More specifically, it may be 10 ¹⁶ to 10 ^{18 pieces per 1 cm 3 .}

The TiC precipitate may be spherical.

The TiC precipitate may have a particle diameter of 1 to 10 nm. The precipitates interfere with the movement of dislocations inside the steel and increase the strength by forming bands of dislocations. If the particle size of the precipitates is too small, the dislocations can easily move, so there is a disadvantage that there is no strength-increasing effect. If it is too large, dislocations cut and pass through the precipitates to facilitate movement, so there is a disadvantage that the effect of increasing the strength is also reduced. More specifically, it may be 2 to 10 nm. More specifically, it may be 2 to 8 nm. Here, the particle diameter means a diameter of the sphere, assuming a sphere having the same volume as the particle.

In addition, TiC precipitates may be uniformly distributed in the steel sheet.

Meanwhile, in the corrosion-resistant steel sheet according to an embodiment of the present invention, Cu, Sb, and Sn form a thickening layer in a sulfuric acid/hydrochloric acid complex condensing atmosphere or a sulfuric acid condensing atmosphere, which suppresses additional corrosion. More specifically, when the steel sheet is immersed in a mixture of 28.5 wt% sulfuric acid solution and 0.5 wt% hydrochloric acid solution at 40 to 80° C., a thickening layer may be formed on the surface of the steel sheet. In addition, when the steel sheet is immersed in a 50 wt% sulfuric acid solution at 50 to 90°C, a thickening layer may be formed on the surface of the steel sheet. More specifically, when immersed for 4 to 8 hours, a thickening layer may be formed.

In this case, the thickening layer means a layer in which Cu, Sb, and Sn begin to be concentrated, and in other respects, it is similar to the point where oxidation generally starts. The thickened layer in the present invention means a layer in which the sum of Cu, Sb, and Sn in the layer exceeds four times the sum of Cu, Sb, and Sn of the steel sheet.

In addition, the thickening layer may be an amorphous thickening layer.

The thickening layer is generated along with the formation of a corrosion layer when immersed in acid. In this case, the corrosion layer means a layer in which Fe is oxidized by O. In general, Fe is oxidized before Cu and Sb, and when immersed in acid, Fe is dissociated into Fe ions and escapes into an acid solution, but Cu and Sb are stable in a solid state and remain on the surface. Therefore, even if the reduction of the Fe content on the surface of the steel sheet continues to occur due to the continued acid reaction, Cu and Sb remain on the surface to form a high-concentration layer. It is formed on the surface in the form of a thickening layer after a certain reaction time has passed, and the thickening layer prevents direct contact between the acid and the internal iron to suppress further corrosion.

The concentrating layer may include Cu, Sb, and Sn, and the concentrating amount of the concentrating layer may be 15% by weight or more. At this time, the concentration means the sum (weight %) of the content of the concentration elements Mo, Cu, Sb, and Sn holding the boundary point at which Fe and O are equal in weight %. That is, the boundary point at which Fe and O contents (wt%) are equal, mean the sum (wt%) of the concentrations of Cu, Sb, and Sn concentrating elements at this time. If the amount of thickening is too small, the thickening layer may not be sufficiently formed, so that the corrosion reduction ratio increases. More specifically, it may be 15% to 22%.

The content of each enriching element at the point where the content (wt%) of Fe and O in the enriched layer becomes the same is Cu: 10 to 15 wt%, Sb: 1 to 3 wt%, and Sn: 1 to 3 wt% can be

The thickening layer thickness may be 10 nm or more. More specifically, the thickening layer may be formed to a thickness of 10 to 500 nm. When the thickness of the thickening layer is too thin, it is difficult to prevent the above-mentioned corrosion. If the thickened layer is formed too thickly, cracks may occur inside the thickened layer, and acid may penetrate along the crack to cause corrosion. More specifically, the thickening layer may be formed to a thickness of 12 to 100 nm.

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.

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, it may be 3.5 to 5.5 mm.

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, it may be 1.0 to 2.0 mm.

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 annealing heat treatment of the steel sheet may be 80% or more. More specifically, it may be 100%. If the recrystallization fraction is too low, the strength is increased, but the ductility is sharply decreased, so there is a disadvantage of forming defects during customer processing. In this case, the recrystallized fraction means the area of the recrystallized grain (grain) based on the total area of the steel sheet.

When the 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 loss ratio is 1.0 mg/cm ² /hr. may be below.

When the corrosion-resistant steel sheet according to an embodiment of the present invention is immersed in a 50 wt% sulfuric acid solution at 70° C. for 6 hours, the corrosion loss ratio is 25 mg/cm ² /hr. may be below.

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

In the case of the cold-rolled steel sheet of the corrosion-resistant steel sheet according to an embodiment of the present invention, the tensile strength of the cold-rolled steel sheet may be 500 MPa or more, and the surface hardness may be 80 or more based on HRB.

The method of manufacturing a corrosion-resistant steel sheet according to an embodiment of the present invention, in 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%), remaining iron (Fe) and unavoidable impurities, and the steel slab satisfying the following formulas 1 and 2 preparing; heating the slab at 1,200° C. or higher; and preparing a hot-rolled steel sheet by hot-rolling the heated slab to a finish rolling temperature of 850 to 1000 °C.

[Equation 1]

[Ni]/[Cu] ≥ 0.5

[Equation 2]

48 x ([Ti]/48 - [S]/32 - [N]/14) ≥ 0.04

At this time, in Equations 1 and 2, [Ni], [Cu], [Ti], [S], and [N] are the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively. indicates.

In addition, manufacturing a hot-rolled steel sheet; Thereafter, winding the hot-rolled steel sheet at 450 to 750 °C; manufacturing a cold rolled steel sheet by cold rolling the wound hot rolled steel sheet at a reduction ratio of 54 to 70%; and annealing and heat-treating the cold-rolled steel sheet at 750 to 880°C.

Hereinafter, each step will be described in detail.

First, the slab that satisfies the above-described composition is heated. The reason for limiting the addition ratio of each composition in the slab is the same as the reason for limiting the composition of the steel sheet described above, and thus repeated description will be omitted. Since the composition of the slab does not substantially change in the manufacturing process of hot rolling, winding, pickling, cold rolling, annealing, etc. to be described later, the composition of the slab and the composition of the finally manufactured corrosion-resistant steel sheet are substantially the same.

By heating the slab, the subsequent hot rolling process can be smoothly performed, and the slab can be homogenized. More specifically, heating may refer to reheating. At this time, the slab heating temperature may be 1,200 ℃ or more. The reason why the heating temperature of the slab is in the above range is for sufficient Ti re-dissolution. This is because TiC precipitates are later precipitated only when Ti is sufficiently re-dissolved.

On the other hand, the ash furnace time at the time of heating the slab may be 150 minutes or more. If the time for ash is too short, the re-recruitment of Ti may not occur sufficiently.

Next, a hot-rolled steel sheet is manufactured by hot rolling the heated slab. The finish rolling temperature of the hot rolling may be 850 to 1000 °C. If the finish rolling temperature is too low, sufficient rolling ability may not be exhibited. On the other hand, if the finish rolling temperature is too high, it may be difficult to secure the strength of the steel sheet. In this case, the thickness of the hot-rolled sheet may be 2.5 to 5.5 mm.

Next, it may include winding the hot-rolled steel sheet. The step of winding the hot-rolled steel sheet; may be made at 450 to 750 °C. If the coiling temperature is too low, the final cold rolling may be difficult due to an increase in the initial strength of the hot rolled material. On the other hand, if the coiling temperature is too high, there may be problems of buckling and strength drop due to phase transformation in the winding section.

Thereafter, the step of pickling the wound hot-rolled steel sheet; may include.

Next, cold rolling the wound hot-rolled steel sheet at a reduction ratio of 54 to 70% to manufacture a cold-rolled steel sheet; may include. If the reduction ratio is too low, it may be difficult to secure complete recrystallization during cold rolling, which may cause a decrease in the elongation of the material and may cause cracks during customer processing in the future. On the other hand, if the reduction ratio is too high, there may be a problem in that rolling is not performed due to a motor load during the rolling process.

Next, annealing the cold-rolled steel sheet at 750 to 880 °C; may include. If the annealing heat treatment temperature is too low, it may be difficult to secure complete recrystallization, which may cause a decrease in the elongation of the material, and may cause cracks during customer processing in the future. On the other hand, if the annealing heat treatment temperature is too high, there is a problem in that it is difficult to secure the strength of the steel sheet.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are only for illustrating the present invention, and the present invention is not limited thereto.

Example

First, a low-carbon steel slab containing the alloy components summarized in Table 1 was prepared.

The slab was heated at 1250° C. for 200 minutes and then hot-rolled to a thickness of 3.5 mm to prepare a hot-rolled sheet. The finish rolling temperature (FDT) was 920 °C, and the winding was performed at 650 °C.

ingredient system	C	Si	Cu	Ni	Sb	Ti	Sn	S	N	expression (One)	Equation (2) (Ti * )	expression (3)
Invention Example 1	0.043	0.015	0.28	0.14	0.11	0.072	0.18	0.005	0.0018	0.50	0.0583	18.58
Invention Example 2	0.1	0.035	0.26	0.13	0.1	0.07	0.15	0.007	0.0023	0.50	0.0516	17.00
Invention example 3	0.072	0.035	0.21	0.11	0.12	0.068	0.18	0.005	0.0021	0.52	0.0533	15.30
Invention Example 4	0.072	0.032	0.34	0.19	0.1	0.065	0.13	0.005	0.0022	0.56	0.0500	20.76
Invention Example 5	0.078	0.044	0.28	0.15	0.052	0.075	0.22	0.005	0.0032	0.54	0.0565	17.78
Invention example 6	0.075	0.035	0.32	0.16	0.145	0.078	0.15	0.005	0.0038	0.50	0.0575	20.99
Invention Example 7	0.076	0.032	0.22	0.11	0.11	0.053	0.15	0.003	0.0018	0.50	0.0423	15.22
Invention Example 8	0.071	0.022	0.24	0.13	0.11	0.143	0.16	0.0085	0.0028	0.54	0.1207	16.34
Invention Example 9	0.073	0.028	0.26	0.14	0.12	0.12	0.075	0.0065	0.0018	0.54	0.1041	16.54
Invention example 10	0.076	0.026	0.28	0.14	0.09	0.09	0.21	0.0095	0.0023	0.50	0.0679	18.50
Invention Example 11	0.07	0.055	0.3	0.15	0.1	0.07	0.2	0.005	0.0032	0.50	0.0515	19.60
Comparative Example 1	0.035	0.032	0.22	0.15	0.09	0.068	0.15	0.005	0.0021	0.68	0.0533	14.78
Comparative Example 2	0.12	0.022	0.3	0.15	0.1	0.07	0.2	0.007	0.0022	0.50	0.0520	19.60
Comparative Example 3	0.07	0.11	0.3	0.15	0.1	0.07	0.2	0.005	0.0032	0.50	0.0515	19.60
Comparative Example 4	0.072	0.035	0.15	0.14	0.12	0.068	0.18	0.005	0.0038	0.93	0.0475	12.30
Comparative Example 5	0.072	0.032	0.45	0.15	0.09	0.07	0.15	0.005	0.0036	0.33	0.0502	26.28
Comparative Example 6	0.078	0.044	0.34	0.1	0.09	0.12	0.09	0.005	0.0028	0.29	0.1029	20.06
Comparative Example 7	0.075	0.035	0.32	0.22	0.1	0.09	0.13	0.005	0.0018	0.69	0.0763	19.76
Comparative Example 8	0.076	0.032	0.22	0.16	0.045	0.068	0.22	0.0085	0.0023	0.73	0.0474	14.63
Comparative Example 9	0.071	0.022	0.24	0.11	0.155	0.07	0.15	0.0065	0.0021	0.46	0.0531	17.21
Comparative Example 10	0.073	0.028	0.26	0.13	0.12	0.045	0.15	0.0095	0.0022	0.50	0.0232	17.44
Comparative Example 11	0.076	0.026	0.28	0.14	0.09	0.155	0.16	0.005	0.0032	0.50	0.1365	17.90
Comparative Example 12	0.075	0.032	0.22	0.14	0.09	0.068	0.06	0.007	0.0038	0.64	0.0445	13.70
Comparative Example 13	0.076	0.022	0.3	0.15	0.1	0.07	0.23	0.005	0.0045	0.50	0.0471	19.96
Comparative Example 14	0.075	0.035	0.32	0.16	0.11	0.05	0.15	0.012	0.002	0.50	0.0251	20.22
Comparative Example 15	0.075	0.035	0.32	0.16	0.11	0.065	0.15	0.005	0.0055	0.50	0.0386	20.22
Comparative Example 16	0.075	0.035	0.32	0.16	0.11	0.06	0.15	0.01	0.0049	0.50	0.0282	20.22

After manufacturing the low-carbon steel sheet, an immersion test was performed by the method described in the standard of ASTM G31. The immersion test was performed by preparing a 50% by weight aqueous solution of sulfuric acid and immersing it at 70° C. for 6 hours. After immersion, the weight loss per unit time and per unit surface area was measured by measuring the weight loss after washing through the method of cleaning the surface of the specimen in ASTM G1.

In addition, in order to simulate the sulfuric acid/hydrochloric acid complex condensation subjected to low-temperature condensation in a Korean thermal power plant, 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. did. After immersion, the weight loss per unit time and per unit surface area was measured by measuring the weight loss after washing through the method of cleaning the surface of the specimen in ASTM G1 in the same manner as above.

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

On the other hand, in order to investigate the relationship between the corrosion resistance element and the surface thickening layer, the hot-rolled sheet of each invention example and comparative example was immersed in a 50 wt% sulfuric acid solution at 70° C. for 24 hours, and then the specimen was distributed from the surface to the inside through GDS measurement. was measured. In Table 2 below, the thickness of the concentrating layer measured therefrom and the concentrating amount of the surface concentrating elements were measured and shown.

In this case, the thickening layer means a layer in which Cu, Sb, and Sn begin to be concentrated, and in other respects, it is similar to the point where oxidation generally starts. Empirically, the thickness of the thickening layer was measured as the thickness of the layer in which the sum of Cu, Sb, and Sn in the layer exceeds four times the sum of Cu, Sb, and Sn of the steel sheet. At this time, it is confirmed that Cu is maximally concentrated at the boundary point where the content (wt%) of Fe and O is equal to the weight%, and the concentration is the point where the content (wt.%) of Fe and O is equal, and at this time It was calculated as the sum (wt%) of the content of enriching elements Cu, Sb, and Sn. It was confirmed that the thickening layer made of Sb, Sn, and Cu was present on the surface of steel and corrosion products at a level of about 20 wt%. It was found that the thickness and amount of the thickening layer determine the corrosion resistance during immersion.

1 is a graph showing the element concentration of the surface portion of the steel sheet by measuring the element distribution from the surface to the inside through GDS measurement after immersing the steel sheet of Inventive Example 2 in a 50 wt% sulfuric acid solution for 24 hours. The sum of the contents of Cu, Sb, and Sn of Invention Example 2 is (0.26+0.1+0.15), which is 0.51% by weight, and the sum of Cu, Sb, and Sn at a depth of 14nm exceeds 2.04% by weight, which is four times of 0.51% by weight. do. Therefore, the depth of 14 nm was set as the thickness of the thickening layer. (red dotted line)

In addition, the boundary point where Fe and O meet, that is, the point where the content of Fe and O are equal is the layer corresponding to the blue dotted line (left) of FIG. 1, and the concentration amount, which is the sum of Cu, Sb, and Sn, in the layer is 17% by weight.

In addition, with respect to the manufactured steel sheet, strength, hardness, and cracks were checked before acid immersion. The hot-rolled materials of the Inventive Examples and Comparative Examples were temporarily processed into tensile test pieces conforming to the JIS13B standard, and then a tensile test was performed in the rolling direction, and the results of measuring the HRB surface hardness, which is the Rockwell hardness standard, are shown in Table 2 below.

In addition, whether cracks occurred in the slab during the continuous casting process during the manufacturing of the hot-rolled sheet or whether cracks occurred at the edge of the hot-rolled material during the hot rolling process are also shown in Table 2 below. Here, the concentration means the sum (weight %) of the contents of the enriched elements Cu, Sb, and Sn at the point at which the contents (weight %) of Fe and O are the same.

ingredient system	Sulfuric Acid Sole Corrosion reduction ratio mg/(cm 2 xhr.)	complex acid Corrosion reduction ratio mg/(cm 2 xhr.)	thickening layer thickness (nm)	thickening amount (wt%)	TiC density (pcs/cm 3 )	TiC particle size (nm)	The tensile strength (MPa)	hot rolled hardness (HRB)	playing, performing Crack
Invention Example 1	18	0.82	15	18.6	2.9E+16	3.7	630	93	X
Invention Example 2	22	0.94	14	17.0	2.0E+16	3.0	668	96	X
Invention example 3	24.5	0.74	16	15.3	2.2E+16	3.2	652	95.5	X
Invention Example 4	23	0.85	12	20.8	1.8E+16	2.8	650	95.5	X
Invention Example 5	23.5	0.95	14	17.8	2.6E+16	3.5	654	93.5	X
Invention example 6	20.8	0.74	15	21.0	2.7E+16	3.6	665	94.5	X
Invention Example 7	21.9	0.88	14	15.2	1.1E+16	2.1	550	85	X
Invention Example 8	21.6	0.98	14	16.3	1.0E+18	9.6	920	106	X
Invention Example 9	24.6	0.95	12	16.5	4.0E+17	8.1	725	101	X
Invention example 10	20.8	0.65	14	18.5	5.0E+16	4.6	690	97	X
presentation example 11	23.5	0.85	14	19.6	2.2E+16	3.2	635	91	X
Comparative Example 1	25.8	0.85	9	14.8	1.7E+16	2.8	510	82	X
Comparative Example 2	22.9	1.03	12	19.6	1.7E+16	2.8	640	91.6	X
Comparative Example 3	22.5	0.75	14	18.5	2.1E+16	3.1	639	91.5	O (Hot rolling crack generation)
Comparative Example 4	48.5	2.35	7.5	12.3	2.0E+16	3.0	615	90.2	X
Comparative Example 5	20.5	0.68	15	26.3	1.9E+16	3.0	580	90	O (Crack of cast steel)
Comparative Example 6	21	0.72	15	20.1	1.5E+16	2.6	910	102	O (Crack of cast steel)
Comparative Example 7	20.6	1.52	13	19.8	1.8E+16	2.9	685	94	X
Comparative Example 8	56.9	2.65	8.9	14.6	3.7E+17	7.9	590	90	X
Comparative Example 9	18	0.68	11	17.2	8.1E+16	5.4	610	90	O (Hot rolling crack generation)
Comparative Example 10	19.5	0.55	13	17.4	1.5E+16	2.6	460	73	X
Comparative Example 11	22.5	2.31	14	17.9	2.1E+16	3.1	930	108	O (Crack of cast steel)
Comparative Example 12	85.5	8.95	6.8	13.7	3.8E+15	0.3	608	90	X
Comparative Example 13	24.5	0.56	14	20.0	2.6E+18	11.2	605	90	O (Hot rolling crack generation)
Comparative Example 14	22.3	1.55	13	18.0	1.3E+16	2.3	480	76	X
Comparative Example 15	21.5	2.36	12	18.0	1.5E+16	2.6	520	83	X
Comparative Example 16	20.8	2.08	13	18.0	4.3E+15	0.5	490	79	X

In the case of Comparative Example 1 having a low C content, the tensile strength of the hot rolled material was lower than 550 MPa and the surface hardness was low due to a decrease in the TiC precipitate content due to the low C content, so that strength and abrasion could not be secured. However, when the C content was excessively high as in Comparative Example 2, a phenomenon in which the composite corrosion resistance was decreased due to the increase of TiC precipitates was observed.

In the present invention, the content of Si was characteristically significantly lowered, because as in Comparative Example 3, the higher the Si content, the excessively the red scale occurred on the surface of the hot rolled material, and it was confirmed that this leads to cracks. to be.

Comparative Example 4 having a low Cu content resulted in a decrease in corrosion resistance of sulfuric acid alone, and in Comparative Example 5 having an excessively high Cu content, cracks in the cast slab due to Cu liquefaction during continuous casting were confirmed.

As shown in Equation 1, since the active addition of Ni serves to increase the melting point of Cu, as in Comparative Example 6, it was confirmed that cracks occurred in the cast steel when the Ni/Cu ratio did not satisfy a certain level or more.

The most important elements for corrosion resistance are Cu, Sb, and Sn. In Comparative Example 8 with a low Sb content and Comparative Example 12 with a low Sn content, the corrosion resistance was greatly reduced, and Comparative Example 9 with an excessively high Sb content In the case of Comparative Example 13 having an excessively high Sn content, it was confirmed that surface defects and cracks of the hot rolled material were induced.

In the present invention, Ti was actively added to form precipitates to ensure strength and surface hardness. When the Ti content is low as in Comparative Example 10, it can be seen that the tensile strength and surface hardness of the hot rolled material are rapidly decreased. On the other hand, in the case of Comparative Example 11 having a high Ti content, particularly 0.15 wt% or more, nozzle clogging may be caused in the continuous casting process, and severe nozzle clogging was confirmed in the actual test process of Comparative Example.

For TiC formation, not only C and Ti control and temperature control are important, but an effective Ti content capable of precipitating Ti-based carbides is important. As in Comparative Examples 14 and 15, the addition of excessive nitrogen and sulfur offsets the effect of increasing the strength by lowering the effective Ti content.

In addition, as in Comparative Example 16, even if the content of S and N described in the invention example is within the effective Ti (Ti ^* ) content of Equation 2 is not 0.04 or more, it is difficult to obtain the effect of high strength and high wear resistance. On the other hand, in the case of Comparative Example 16 having a low effective Ti content, the TiC density was small and the TiC particle size was too small, so that the desired precipitation hardening effect could not be obtained.

Table 3 below shows the characteristics of the hot-rolled material and the cold-rolled material after manufacturing under different manufacturing conditions with the component system of Invention Example 4 in order to examine the influence of the manufacturing conditions on the production possibility and strength.

Manufacturing conditions	reheat temperature (℃)	FDT (℃)	CT (℃)	cold reduction rate (%)	Annealing temperature (℃)	Tensile strength of hot rolled material	Tensile strength of cold rolled material	recrystallization fraction	Possibility of cold rolling	Edge Crack or not
Condition 1	1250	920	650	64	810	650	550	100%	O	X
condition 2	1250	800	650	64	810	680	594	100%	O	O
condition 3	1250	1050	650	64	810	540	485	100%	O	X
condition 4	1250	920	440	64	-	690	-	100%	X	O
condition 5	1250	920	755	64	810	530	490	100%	O	X
condition 6	1250	920	650	53	810	650	650	70%	O	X
condition 7	1250	920	650	72	-	650	-	100%	X	X
condition 8	1250	920	650	64	740	650	670	65%	O	X
condition 9	1250	920	650	64	890	650	450	100%	O	X
condition 10	1180	920	650	64	810	530	480	100%	O	X

Looking at the results in Table 3, it can be seen 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 inventive component system is used. It was because they were not sufficiently rehired in the process.

In the case of condition 2 where the hot finish rolling temperature (FDT) was high, edge cracks occurred during the hot rolling production process, which also occurred in the case of condition 4 where the coiling temperature (CT) was low. In relation to this, FIG. 2 shows (a) the tendency of cracks in the hot rolling edge part after hot rolling in Inventive Example 4 under condition 1 and (b) hot rolling edge after hot rolling in Inventive Example 4 under condition 2. This is a picture comparing the tendency of minor cracks.

On the other hand, in condition 3, where the hot finish rolling temperature (FDT) was high at 1050 ° C, the target material could not be obtained due to the low tensile strength of the hot and cold rolled materials, which also occurred in condition 5 when the coiling temperature (CT) was high.

The steel grade of the present invention has a high recrystallization temperature after cold rolling due to high C and Ti content. In the case of condition 6, where the cold rolling reduction ratio was 53%, the recrystallization fraction of the final cold rolled material was 70%, so complete recrystallization was not achieved. Even in the case of condition 8, where the annealing temperature was as low as 740 °C, the recrystallization fraction was 65% and complete recrystallization was not achieved. In the case of the material in which complete recrystallization does not occur, cracks may be induced during customer processing due to a drop in elongation. In the present invention, when used as a cold rolled material, the reduction ratio is 54% or more, and the annealing temperature is limited to 750 ° C or more. do.

In addition, in the case of conditions 4 and 7, in which the strength of the hot-rolled material is high or the cold-rolling ratio is high, a problem occurred in that rolling was not performed due to a motor load during the rolling process, and thus the final product could not be obtained.

The present invention is not limited to the embodiments, but may be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains can use other specific forms without changing the technical spirit or essential features of the present invention. It will be appreciated that this may be practiced. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (17)

1. 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%, titanium (Ti): 0.05 to 0.15%, tin (Sn): 0.07 to 0.22%, sulfur (S): 0.01% or less (excluding 0%), nitrogen (N) : 0.005% or less (excluding 0%), including the remainder iron (Fe) and unavoidable impurities,

   A corrosion-resistant steel sheet satisfying the following formulas 1 and 2.

   [Equation 1]

   [Ni]/[Cu] ≥ 0.5

   [Equation 2]

   48 x ([Ti]/48 - [S]/32 - [N]/14) ≥ 0.04

   (In Equations 1 and 2, [Ni], [Cu], [Ti], [S], and [N] represent the contents (% by weight) of Ni, Cu, Ti, S, and N in the steel sheet, respectively. .)
2. According to claim 1,

   TiC precipitates,

   The TiC precipitate and the aggregate made of the TiC precipitate are included in an amount of 10 ^{16 or more per 1 cm 3} Corrosion-resistant steel sheet.
3. 3. The method of claim 2,

   The particle size of the TiC precipitate is 1 to 10nm corrosion-resistant steel sheet.
4. According to claim 1,

   A corrosion-resistant steel sheet satisfying the following Equation 3.

   [Equation 3]

   12 x [Sn] + 22 x [Sb] + 50 x [Cu] ≥ 15

   (In Equation 3, [Sn], [Sb], and [Cu] represent the contents (weight %) of Sn, Sb, and Cu in the steel sheet, respectively.)
5. 3. The method of claim 2,

   When the steel sheet is immersed in a solution of 28.5 wt% sulfuric acid solution and 0.5 wt% hydrochloric acid solution at 40 to 80°C, a thickening layer is generated on the surface of the steel sheet.
6. 3. The method of claim 2,

   When the steel sheet is immersed in a 50 wt% sulfuric acid solution at 50 to 90°C, a thickening layer is generated on the surface of the steel sheet.
7. 7. The method of claim 5 or 6,

   The thickening layer is a corrosion-resistant steel sheet comprising Cu, Sb, and Sn.
8. 8. The method of claim 7,

   The concentration of the thickening layer is 15% by weight or more of the corrosion-resistant steel sheet.

   (At this time, the concentration means the sum (wt%) of the content of the concentration elements Mo, Cu, Sb, and Sn at the boundary point where Fe and O are equal in weight %.)
9. 7. The method of claim 5 or 6,

   The thickness of the thickening layer is 10 nm or more corrosion-resistant steel sheet.
10. According to claim 1,

    A corrosion-resistant steel sheet having a recrystallization fraction of 80% or more after the annealing heat treatment of the steel sheet.
11. 6. The method of claim 5,

    When the steel sheet is immersed in a solution of 28.5 wt% sulfuric acid solution and 0.5 wt% hydrochloric acid solution at 60° C. for 6 hours, the corrosion loss ratio is 1.0 mg/cm ² /hr. Corrosion-resistant steel sheet below.
12. 7. The method of claim 6,

    ^{A corrosion-resistant steel sheet having a corrosion loss ratio of 25 mg/cm 2} /hr or less when the steel sheet is immersed in a 50 wt% sulfuric acid solution at 70° C. for 6 hours.
13. 3. The method of claim 2,

    When the steel sheet is a hot-rolled steel sheet, the tensile strength of the hot-rolled steel sheet is 550 MPa or more, and the surface hardness is 85 or more based on HRB.
14. 3. The method of claim 2,

    When the steel sheet is a cold-rolled steel sheet, the tensile strength of the cold-rolled steel sheet is 500 MPa or more, and the surface hardness of the cold-rolled steel sheet is 80 or more based on HRB.
15. 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%), including the remainder iron (Fe) and unavoidable impurities,

    Preparing a steel slab that satisfies the following Equations 1 and 2;

    heating the slab at 1,200 °C or higher; and

    preparing a hot-rolled steel sheet by hot-rolling the heated slab to a finish rolling temperature of 850 to 1000 °C;

    A method of manufacturing a corrosion-resistant steel sheet comprising a.

    [Equation 1]

    [Ni]/[Cu] ≥ 0.5

    [Equation 2]

    48 x ([Ti]/48 - [S]/32 - [N]/14) ≥ 0.04

    (In Equations 1 and 2, [Ni], [Cu], [Ti], [S], and [N] represent the contents (% by weight) of Ni, Cu, Ti, S, and N in the steel sheet, respectively. .)
16. 16. The method of claim 15,

    manufacturing the hot-rolled steel sheet; Since the,

    winding the hot-rolled steel sheet at 450 to 750 °C;

    manufacturing a cold rolled steel sheet by cold rolling the wound hot rolled steel sheet at a reduction ratio of 54 to 70%; and

    annealing the cold-rolled steel sheet at 750 to 880°C;

    A method of manufacturing a corrosion-resistant steel sheet further comprising a.
17. 16. The method of claim 15,

    In the step of heating the slab at 1,200 ℃ or more;

    A method of manufacturing a corrosion-resistant steel sheet with a burning time of 150 minutes or more.

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