KR102254006B1 - Corrosion resistant steel having high resistance to corrosion at sulfuric and sulfuric/hydrochloric acid condensing environment and manufacturing method the same - Google Patents

Abstract

The present invention relates to a steel sheet having corrosion resistance in a sulfuric acid and sulfuric acid/hydrochloric acid complex environment, and a method of manufacturing the same.
Corrosion-resistant steel sheet according to an embodiment of the present invention, by weight %, carbon (C): 0.15% or less (excluding 0%), copper (Cu): 0.05 to 0.5%, nickel (Ni): 0.02 to 0.3 %, antimony (Sb): 0.05 to 0.45%, and tin (Sn): 0.05 to 0.45%, contains the balance iron (Fe) and inevitable impurities, and satisfies the following formula 1, a corrosion-resistant steel sheet, steel sheet When immersed in 50wt% sulfuric acid solution for 6 hours, a concentrated layer of sulfuric acid immersion is formed from the surface of the steel sheet in the inner direction, and the steel sheet is immersed in a solution of 16.9 vol% sulfuric acid solution and 0.35 vol% hydrochloric acid solution for 24 hours. , A composite immersion thickening layer is formed in the inner direction from the surface of the steel sheet, and the thickness of the sulfuric acid immersion thickening layer and the composite immersion thickening layer is 360 to 500 nm, respectively.
[Equation 1]
1 <Cu + 3ｘSb + 5ｘSn + 5ｘW + Mo ≤ 1.15 (wt%)

Description

Corrosion-resistant steel sheet in a condensation environment of sulfuric acid and sulfuric acid/hydrochloric acid, and its manufacturing method {CORROSION RESISTANT STEEL HAVING HIGH RESISTANCE TO CORROSION AT SULFURIC AND SULFURIC/HYDROCHLORIC ACID CONDENSING ENVIRONMENT AND MANUFACTURING METHOD THE SAME}

The present invention relates to a steel sheet having corrosion resistance in a sulfuric acid and sulfuric acid/hydrochloric acid complex condensation environment, and a method of manufacturing the same. More specifically, it relates to a steel plate having corrosion resistance against corrosion of the steel plate due to condensate generated as the exhaust gas temperature decreases, such as _{SO x} , Cl, etc. present in the exhaust gas after combustion of fossil fuels, and a method of manufacturing the same.

Fossil fuels contain various impurity elements such as S and Cl. There is always a problem of deterioration due to corrosion in piping and equipment, which are passages through which combustion gases pass by using such fossil fuels. In particular, this corrosion phenomenon is called condensate corrosion, and typical uses are exhaust gas piping and environmental facilities of thermal power plants, automobile exhaust systems, and the like. _{As the type of condensation corrosion, SO x} is formed as S contained in the exhaust gas is combusted. In particular, _{sulfuric acid condensation in which SO 3} meets moisture in the exhaust gas to form sulfuric acid, and chlorine contained in the exhaust gas or industrial water is various. There are hydrochloric acid condensation, in which hydrochloric acid is produced through a reaction, and sulfuric acid/hydrochloric acid complex condensation, which occurs in a state in which sulfuric acid and hydrochloric acid are mixed in combination. The starting temperature of this acid condensation is related to the content of _{SO x, Cl and water vapor in the flue gas.}

Recently, there is a trend of lowering the exhaust gas temperature in order to utilize power generation efficiency or waste heat discharged to the outside in places of use such as power plants, and in general, when the exhaust gas temperature drops to a temperature below 150℃ where sulfuric acid begins to condense, As the formed sulfuric acid gas is liquefied and condensed on the steel surface, the amount causing corrosion increases, and when the exhaust gas temperature drops to a temperature below 80℃ where hydrochloric acid can be condensed, a complex corrosion phenomenon occurs in which sulfuric acid and hydrochloric acid are condensed in combination. do.

As an example of a solution to this problem, there may be a method of using a high alloy-based high corrosion-resistant steel such as a duplex-based STS steel, or a method of increasing the exhaust gas temperature, but this leads to a high cost of equipment and a decrease in power generation efficiency.

On the other hand, when Cu-added corrosion-resistant steel known as sulfuric acid condensed corrosion-resistant steel is used, the Cu-rich layer generated on the steel surface exhibits corrosion resistance against sulfuric acid condensation to form a corrosion-inhibiting layer that suppresses corrosion. In preparation for the case, it has the effect of greatly improving the life of the facility. However, since the aforementioned low temperature reduction of the exhaust gas and the combination of the corrosive environment deteriorated the corrosion resistance properties of the existing sulfuric acid condensed corrosion resistant steel, there has been a continuing demand from customers for higher performance corrosion resistant steel. As alloy STS steel, there has been a problem in that it does not exhibit performance in complex and severe corrosion-resistant environments.

An object of the present invention is to provide a steel sheet having corrosion resistance in a sulfuric acid and sulfuric acid/hydrochloric acid complex condensation environment, and a method of manufacturing the same. More specifically, it is intended to provide a steel plate having corrosion resistance against a phenomenon in which the steel plate is corroded due to condensate generated as the exhaust gas temperature decreases, such as _{SO x} and Cl present in the exhaust gas after combustion of fossil fuels, and a method of manufacturing the same.

Corrosion-resistant steel sheet according to an embodiment of the present invention, by weight %, carbon (C): 0.15% or less (excluding 0%), copper (Cu): 0.05 to 0.5%, nickel (Ni): 0.02 to 0.3 % Antimony (Sb): 0.05 to 0.45%, and tin (Sn): 0.05 to 0.45%, and the balance iron (Fe) and inevitable impurities are included, and the following formula 1 is satisfied.

[Equation 1]

Cu + 3ｘSb + 5ｘSn + 5ｘW + Mo> 1 (wt%)

The steel sheet further contains one or more of manganese (Mn): 0.5 to 1.5%, aluminum (Al): 0.05% or less (excluding 0%) and chromium (Cr): 8% or less (excluding 0%). Can include.

The steel sheet can satisfy the following formula (2).

[Equation 2]

Cu/Ni ≤ 2

The steel sheet can satisfy the following formula (3).

[Equation 3]

[Sulfuric acid immersion corrosion reduction ratio] ｘ [Complex immersion corrosion reduction ratio] <35 (mg/cm ² /hr.)

At this time, the sulfuric acid immersion corrosion loss ratio is a value obtained by measuring the weight loss per unit time and per unit surface area after immersing the steel sheet in 50wt% sulfuric acid solution at 70°C for 6 hours. It is a value obtained by measuring the weight loss per unit time and per unit surface area after immersion at 80°C for 6 hours in a mixture of 16.9 vol% sulfuric acid solution and 0.35 vol% hydrochloric acid solution.

When the steel sheet is immersed in 50wt% sulfuric acid solution for 6 hours, a sulfuric acid immersion thickening layer is formed from the surface of the steel sheet in the inner direction, and the steel sheet is 24 in a solution of 16.9vol% sulfuric acid solution and 0.35vol% hydrochloric acid solution. During time immersion, a composite immersion thickening layer may be formed from the surface of the steel sheet in an inward direction.

The sulfuric acid immersion thickening layer and the composite immersion thickening layer include Cu, Sb, and Sn, and the total amount of Cu, Sb, and Sn may be 3.5% by weight or more.

The sulfuric acid immersion thickening layer may include Cu: 7.05 to 23.06%, Sb: 4.3 to 15.58%, and Sn: 3.5 to 18%, and the composite immersion thickening layer is Cu: 3.5 to 24.58%, Sb: 3.5 to 17.5% , And Sn: 1.5 to 22% may be included.

The steel plate can satisfy the following formula (4).

[Equation 4]

I1 + I2 ≥ 55

At this time, I refers to the corrosion resistance index, and is expressed by the following formula (5).

[Equation 5]

Corrosion resistance index I = Cu + Sb + Sn + 20ｘW + 10ｘMo (component content, wt%)

In addition, I1 refers to the corrosion resistance index of the sulfuric acid immersion thickened layer, and I2 refers to the corrosion resistance index of the complex immersion thickened layer.

In the steel sheet, the sum of the thicknesses of the formed thickening layers can satisfy the following formula (6).

[Equation 6]

[Sulfuric acid immersion thickening layer thickness] + [Composite immersion thickening layer thickness] ≥ 170nm

In the steel plate, the average length of cracks occurring at the corners of the steel plate may be 10 mm or less.

On the other hand, the manufacturing method of the corrosion-resistant steel sheet according to an embodiment of the present invention, in weight%, carbon (C): 0.15% or less (excluding 0%), copper (Cu): 0.05 to 0.5%, nickel (Ni ): 0.02 to 0.3%, antimony (Sb): 0.05 to 0.45%, and tin (Sn): 0.05 to 0.45%, containing the balance iron (Fe) and inevitable impurities, and satisfying the following formula 1 Preparing a; Heating the slab; Manufacturing a hot-rolled steel sheet by hot rolling the heated slab; And winding the hot-rolled steel sheet.

[Equation 1]

Cu + 3ｘSb + 5ｘSn + 5ｘW + Mo> 1 (wt%)

The slab further comprises one or more of manganese (Mn): 0.5 to 1.5%, aluminum (Al): 0.05% or less (excluding 0%), and chromium (Cr): 8% or less (excluding 0%). Can include.

Heating the slab; may be made at 1,000 to 1,300 ℃.

In the step of producing a hot-rolled steel sheet by hot rolling the heated slab; In, the finish rolling temperature may be 750°C or higher.

Winding the hot-rolled steel sheet; It may be made at 550 to 750 ℃.

Winding a hot-rolled steel sheet; Thereafter, the step of pickling the wound hot-rolled steel sheet; Cold rolling the pickled hot-rolled steel sheet to manufacture a cold-rolled steel sheet; And annealing and heat treatment of the cold-rolled steel sheet.

The cold rolled steel sheet may have a thickness of 3 mm or less.

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

1 is a table showing the concentration of elements on the surface of a steel sheet according to an embodiment of the present invention, (a) is a surface observation view after immersion at 70° C. for 6 hours in a 50 wt% sulfuric acid environment of Inventive Example 1, (b) Is a surface observation diagram after immersion for 24 hours in an environment of 16.9 vol% of sulfuric acid and 0.35 vol% of hydrochloric acid of Inventive Example 1.
FIG. 2 is a photograph showing the degree of cracking of the hot-rolled edge during hot rolling of a steel sheet according to an embodiment of the present invention, (a) is a photograph of the steel sheet of Inventive Example 1, and (b) is a comparative example 5.

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

In the present specification, the term "combination of these" included in the expression of the Makushi form refers to a mixture or combination of one or more selected from the group consisting of the constituent elements described in the expression of the Makushi form, and the constituent elements 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 another part may be involved in between. In contrast, when a part is referred to as being "directly above" another part, no other part is interposed between them.

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

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

In an embodiment of the present invention, the meaning of further including an additional element means to include the remaining iron (Fe) as much as an 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 may easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

Among the studies to solve the problems of the prior art, the present inventors have investigated corrosion generated according to the type and content of elements in the steel, and the complex relationship when a conventional low-carbon steel sheet is subjected to a sulfuric acid or sulfuric acid/hydrochloric acid complex corrosion environment. It was confirmed that additional corrosion was inhibited by the product. At this time, if two or more special elements such as Cu, Sb, Sn, W, and Mo are added to the steel in combination, corrosion resistance in a high concentration of sulfuric acid and a complex condensation of sulfuric acid/hydrochloric acid can be greatly improved at the same time. It was concluded that the corrosion resistance performance of equipment in the environment could be dramatically increased.

Continued to be met as dissolution ^- if the ordinary low-carbon steel plate placed in a sulfuric acid or a sulfuric acid / hydrochloric acid complex condensation environment generally and the Fe in the steel melt with Fe ions, it is again the steel surface and then dissociated in the aqueous solution of SO ₄ ^2-, Cl As a result of the reaction, the steel plate is corroded, resulting in a reduction in thickness and weight. However, if Cu, Sb, Sn, W, Mo, etc., which are noble metals than Fe, are used, stable corrosion products are formed even in an acidic solution on the surface of the steel sheet after immersion corrosion, thereby inhibiting the generation of additional corrosion.

Using the same principle as described above, it was confirmed that a corrosion-resistant layer containing corrosion-resistant elements generated between the steel material and the corrosion product can be densely formed when a corrosion reaction is performed on a low-carbon steel sheet.Through this, the manufactured steel sheet has excellent corrosion resistance in an immersion corrosion environment. Found out to have.

Hereinafter, a steel sheet having corrosion resistance in a sulfuric acid or sulfuric acid/hydrochloric acid complex condensation environment, which is an aspect of the present invention, and a manufacturing method thereof will be described in detail.

First, the corrosion-resistant steel sheet according to an embodiment of the present invention is in wt%, carbon (C): 0.15% or less (excluding 0%), copper (Cu): 0.05 to 0.5%, nickel (Ni): 0.02 to 0.3%, antimony (Sb): 0.05 to 0.45%, and tin (Sn): 0.05 to 0.45%, the balance iron (Fe) and inevitable impurities are included, and the following formula (1) is satisfied.

[Equation 1]

Cu + 3ｘSb + 5ｘSn + 5ｘW + Mo> 1 (wt%)

The steel sheet further contains one or more of manganese (Mn): 0.5 to 1.5%, aluminum (Al): 0.05% or less (excluding 0%) and chromium (Cr): 8% or less (excluding 0%). Can include.

The steel plate can satisfy Formula 2.

[Equation 2]

Cu/Ni ≤ 2

First, the reason for limiting the components of the steel sheet will be described. The steel plate may be a low carbon steel plate.

Carbon (C): 0.15% by weight or less (excluding 0%)

The carbon content of the low-carbon steel sheet may be 0.15% or less. If the content of carbon in the steel is too high, there is a possibility that a phase containing carbides such as pearlite and bainite, which causes local corrosion, is formed in the steel, thereby reducing the corrosion resistance. More specifically, it may be 0.10% or less.

Manganese (Mn): 0.5 to 1.5% by weight

Mn helps to improve the strength and hardenability of steel by solid solution strengthening, and may be included in the present invention to exhibit such an effect. However, if too much is added, segregation such as central segregation or micro segregation may become severe and adversely affect the quality of the product. More specifically, it may be 0.5 to 1.0%.

Copper (Cu): 0.05 to 0.5% by weight

When Cu is corroded in an acid immersion environment, it is concentrated between the steel surface and the corrosion product and is a representative element that prevents further corrosion. In order to exhibit the effect, it is preferable to add 0.05% or more, but if too much is added, there is a possibility of causing cracks during manufacturing due to the low melting point of Cu. More specifically, it may be 0.10 to 0.35%.

Nickel (Ni): 0.02 to 0.3% by weight

In this steel type, nickel can be added by limiting it to the range shown in the following formula (2).

[Equation 2]

Cu/Ni ≤ 2

The reason that can be limited to the above range is to limit the phenomenon that liquid Cu penetrates into the grain boundary due to the low melting point of Cu and causes cracking due to the low melting point of Cu when added to steel with only Cu without Ni by raising the melting point due to the addition of Ni. For the sake of

If the content of Ni is too small, the role of increasing the melting point of Cu cannot be sufficiently increased, and if the content is too high, surface defects due to Ni may occur. More specifically, it may be 0.05 to 0.2%.

Antimony (Sb): 0.05 to 0.45% by weight

Sb is added to form a stable thickening layer on the surface like Cu. If the content of Sb is too small, a sufficient thickening layer cannot be formed, and if the content of Sb is too high, it may cause surface cracking. More specifically, it may be 0.05 to 0.2%.

Chrome (Cr): 8% by weight or less (excluding 0%)

Although a large amount of Cr is required in general stainless steel, ^{since it is oxidized to Cr 2+} in the film in a strong acid environment immersion, there is a problem in that the corrosion resistance is rather reduced. More specifically, it may contain 5% by weight or less. More specifically, it may contain 1% by weight or less.

On the other hand, in the present invention, tin (Sn): 0.05 to 0.45% is included as a corrosion resistant element that helps in corrosion resistance properties other than the above elements.

On the other hand, when W and Mo are not included in Equation 1, it is calculated as 0 in Equation 1.

Hereinafter, the above elements will be described.

Tin (Sn): 0.05 to 0.45% by weight

Sn is an element that forms a concentrated layer such as Cu and Sb between the steel surface and corrosion products after corrosion. In addition, it is formed on the electrode surface of the corrosion product, and plays a role of suppressing further corrosion. However, if too much Sn is added, it may cause slab cracks during manufacturing and edge cracks during hot rolling. More specifically, it may be 0.10 to 0.45%.

Tungsten (W)

W is characterized by a very small concentration between the steel surface and corrosion products during corrosion. In addition, it is an element that greatly improves the density of the formed amorphous layer and corrosion products. If the content of W is too small, it may not play a sufficient role, and if there is too much W, defects may occur due to the formation of WC by W.

Molybdenum (Mo)

Mo is a representative element that increases the hardenability of steel. In addition, it is concentrated on the electrode surface of steel and corrosion products to stabilize the layer of corrosion products. If the content of Mo is too high, the strength increases due to the formation of a hard phase, and cracks may occur during manufacturing.

In addition to the above components, the present invention contains Fe and unavoidable impurities. Since inevitable impurities are widely known in the art, detailed descriptions are omitted. In one embodiment of the present invention, the addition of effective ingredients other than the above ingredients is not excluded.

In addition, the content of the special corrosion resistant element is controlled by Equation 1 below.

[Equation 1]

Cu + 3ｘSb + 5ｘSn + 5ｘW + Mo> 1 (wt%)

By controlling in this way, it is possible to promote the concentration of surface corrosion products and improve the density of the resulting corrosion products.

Corrosion-resistant steel sheet according to an embodiment of the present invention is very excellent in corrosion resistance by the above-described alloy component. Specifically, the following formula 3 may be satisfied.

[Equation 3]

[Sulfuric acid immersion corrosion reduction ratio] ｘ [Complex immersion corrosion reduction ratio] <35 (mg/cm ² /hr.)

At this time, the sulfuric acid immersion corrosion loss ratio is a value obtained by measuring the weight loss per unit time and per unit surface area after immersing the steel sheet in 50wt% sulfuric acid solution at 70°C for 6 hours. It is a value obtained by measuring the weight loss per unit time and per unit surface area after immersion at 80°C for 6 hours in a mixture of 16.9 vol% sulfuric acid solution and 0.35 vol% hydrochloric acid solution.

The corrosion-resistant steel sheet according to an embodiment of the present invention has excellent corrosion resistance properties because an appropriate thickening layer is formed in a state in which sulfuric acid or sulfuric acid and hydrochloric acid are mixed in combination. Specifically, in the corrosion-resistant steel sheet according to an embodiment of the present invention, when the steel sheet is immersed in a 50 wt% sulfuric acid solution for 6 hours, a sulfuric acid immersion thickening layer is formed in the inner direction from the surface of the steel sheet, and the steel sheet is 16.9 vol% sulfuric acid solution When immersed for 24 hours in a solution of a mixture of and 0.35 vol% hydrochloric acid solution, a composite immersion thickening layer may be formed from the surface of the steel sheet in the inner direction.

The sulfuric acid immersion thickening layer and the composite immersion thickening layer include Cu, Sb, and Sn, and the total amount of Cu, Sb, and Sn may be 3.5% by weight or more. It is distinguished from a steel plate base material that is not a thickened layer in that the total amount of Cu, Sb, and Sn forming the thickening layer is 3.5% by weight or more.

The sulfuric acid immersion concentrated layer may include Cu: 7.05 to 23.06%, Sb: 4.3 to 15.58%, and Sn: 3.5 to 18%. The composite immersion thickening layer may include Cu: 3.5 to 24.58%, Sb: 3.5 to 17.5%, and Sn: 1.5 to 22%. More specifically, Sn may be 15 to 17.5%.

Corrosion-resistant steel sheet according to an embodiment of the present invention may satisfy Equation 4 below.

[Equation 4]

I1 + I2 ≥ 55

At this time, I refers to the corrosion resistance index, and is expressed by the following formula (5).

[Equation 5]

Corrosion resistance index I = Cu + Sb + Sn + 20ｘW + 10ｘMo (component content, wt%)

In addition, I1 refers to the corrosion resistance index of the sulfuric acid immersion thickened layer, and I2 refers to the corrosion resistance index of the complex immersion thickened layer.

In the corrosion-resistant steel sheet according to an embodiment of the present invention, the sum of the thicknesses of the formed thickening layer may satisfy Equation 6 below.

[Equation 6]

[Sulfuric acid immersion thickening layer thickness] + [Composite immersion thickening layer thickness] ≥ 170nm

At this time, the enrichment layer may contain one or more of the above-described elements. In addition, although it may vary depending on the immersion environment, the thickness of the sulfuric acid immersion thickening layer and the composite immersion thickening layer may have a thickness of 70 to 500 nm or less between the corrosion product and the raw steel material.

In the corrosion-resistant steel sheet according to an embodiment of the present invention, the average length of cracks occurring at the corners of the steel sheet may be 10 mm or less.

The method of manufacturing a corrosion-resistant steel sheet according to an embodiment of the present invention is in weight%, carbon (C): 0.15% or less (excluding 0%), copper (Cu): 0.05 to 0.5%, nickel (Ni): 0.02 To prepare a slab containing to 0.3%, antimony (Sb): 0.05 to 0.45%, and tin (Sn): 0.05 to 0.45%, the balance iron (Fe) and inevitable impurities, and satisfying the following formula 1 step; Heating the slab; Manufacturing a hot-rolled steel sheet by hot rolling the heated slab; And winding the hot-rolled steel sheet.

[Equation 1]

Cu + 3ｘSb + 5ｘSn + 5ｘW + Mo> 1 (wt%)

The slab further comprises one or more of manganese (Mn): 0.5 to 1.5%, aluminum (Al): 0.05% or less (excluding 0%), and chromium (Cr): 8% or less (excluding 0%). Can include.

Hereinafter, each step will be described in detail.

First, a slab that satisfies the above-described composition is prepared. 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 explanation is omitted. Since the composition of the slab does not change substantially during the manufacturing process of hot rolling, hot rolled sheet annealing, cold rolling, and final annealing, which will be described later, the composition of the slab and the composition of the non-oriented electrical steel sheet are substantially the same.

Next, the manufactured slab is heated. By heating, the subsequent hot rolling process can be smoothly performed, and the slab can be homogenized. More specifically, heating may mean reheating. In this case, the slab heating temperature may be 1,000 to 1,300 °C. If the heating temperature of the slab is too high, the precipitate may be redissolved and finely precipitated after hot rolling. More specifically, the step of heating the slab; may be made at 1,100 to 1,250 °C.

Next, the heated slab is hot-rolled to manufacture a hot-rolled steel sheet. The finish rolling temperature of hot rolling may be 750°C or higher.

Winding the hot-rolled steel sheet; It may be made at 550 to 750 ℃.

Thereafter, the step of pickling the wound hot-rolled steel sheet; Cold rolling the pickled hot-rolled steel sheet to manufacture a cold-rolled steel sheet; And annealing and heat treating the cold-rolled steel sheet.

Next, the hot-rolled sheet is pickled and cold-rolled to a predetermined sheet thickness to manufacture a cold-rolled steel sheet. Although it may be applied differently depending on the thickness of the hot-rolled steel sheet, a reduction ratio of 70 to 95% may be applied, and the cold-rolled steel sheet may have a thickness of 3 mmt or less.

Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by matters described in the claims and matters reasonably inferred therefrom.

Example

First, a conventional low-carbon steel sheet (thickness: 2.0 mm) having the composition shown in Table 1 was prepared.

Component system C Mn Si Al Sb Cu Ni W Sn Mo Cr Equation 1 Comparative Example 1 0.07 0.50 0.10 0.035 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0 Comparative Example 2 0.07 1.00 0.30 0.035 0.10 0.30 0.15 0.00 0.00 0.00 0.00 0.6 Comparative Example 3 0.07 1.00 0.30 0.035 0.00 0.30 0.15 0.00 0.00 0.00 0.00 0.3 Invention Example 1 0.07 1.00 0.30 0.035 0.10 0.30 0.15 0.00 0.11 0.00 0.00 1.15 Comparative Example 4 0.07 1.00 0.30 0.035 0.10 0.30 0.15 0.00 0.02 0.00 0.00 0.7 Comparative Example 5 0.07 1.00 0.30 0.035 0.10 0.30 0.15 0.00 0.50 0.00 0.00 3.1 Comparative Example 6 0.07 1.00 0.30 0.035 0.10 0.00 0.00 0.00 0.10 0.00 0.00 0.8 Invention Example 2 0.07 1.00 0.30 0.035 0.10 0.30 0.15 0.10 0.00 0.00 0.00 1.1 Comparative Example 7 0.07 1.00 0.30 0.035 0.10 0.30 0.15 0.50 0.00 0.00 0.00 3.1 Comparative Example 8 0.07 1.00 0.30 0.035 0.10 0.30 0.15 0.02 0.00 0.00 0.00 0.7 Comparative Example 9 0.07 1.00 0.30 0.035 0.10 0.00 0.00 0.10 0.00 0.00 0.00 0.8 Inventive Example 3 0.07 1.00 0.30 0.035 0.10 0.30 0.15 0.00 0.00 0.50 0.00 1.1 Comparative Example 10 0.07 1.00 0.30 0.035 0.10 0.30 0.15 0.00 0.00 1.50 0.00 2.1 Comparative Example 11 0.07 1.00 0.30 0.035 0.10 0.30 0.15 0.00 0.00 0.05 0.00 0.65 Comparative Example 12 0.07 1.00 0.30 0.035 0.10 0.00 0.00 0.00 0.00 0.50 0.00 0.8 Comparative Example 13 0.07 1.00 0.30 0.035 0.10 0.30 0.15 0.00 0.00 0.00 8.50 0.6

After preparing the hot rolled material of the low carbon steel sheet, an immersion test was performed by the method described in ASTM G31. The immersion test was carried out by preparing a 50wt% sulfuric acid aqueous solution 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 test piece according to ASTM G1. It was measured. In addition, a mixed aqueous solution of 16.9 vol% sulfuric acid and 0.35 vol% hydrochloric acid was prepared to simulate the complex condensation of sulfuric acid/hydrochloric acid encountered during low-temperature condensation in a Korean thermal power plant, and after immersion for 6 hours, the above corrosion reduction ratio was measured. Experiments were also conducted. The results are shown in Table 2 below. The unit is mg/cm ² /hr. to be.

Material Sulfuric acid alone immersion Complex acid immersion Equation 3 Comparative Example 1 398 38 15,124 Comparative Example 2 16.8 2.5 42 Comparative Example 3 80 21 1,680 Invention Example 1 9.2 1.5 14 Comparative Example 4 16 2.3 37 Comparative Example 5 8.5 1.2 10 Comparative Example 6 35 12 420 Invention Example 2 26 0.56 15 Comparative Example 7 24 0.44 11 Comparative Example 8 16.2 2.4 39 Comparative Example 9 55 14 770 Inventive Example 3 40.7 0.29 12 Comparative Example 10 36 0.18 6 Comparative Example 11 44 2.6 114 Comparative Example 12 68 18 1,224 Comparative Example 13 240 80 19,200

At this time, since the sulfuric acid and sulfuric acid/hydrochloric acid complex corrosion reduction ratio must simultaneously satisfy excellent properties, the scope of the present invention may follow Equation 3 below.

[Equation 3]

[Sulfuric acid immersion corrosion reduction ratio] ｘ [Complex immersion corrosion reduction ratio] <35 (mg/cm ² /hr.)

In order to grasp the principle from which these results are derived, the inventor confirmed that after several attempts, through elemental analysis from the surface of the steel plate to the inside of the steel, a concentrated layer of corrosion resistant elements was formed in the layer of corrosion products after the surface of the steel. Table 3 below shows the concentrated layer of corrosion resistant elements and the content of each element formed between the corrosion product layer from the steel surface after immersion in 50% sulfuric acid for 6 hours. The content of each component was expressed by finding the maximum value in the thickening layer.

Material Cu Sb W Sn Mo Cr I 1
(Corrosion resistance index) Thickening layer
Forming thickness Comparative Example 1 0 12 0 0 0 0 12 50nm Comparative Example 2 15 7.74 0 0 0 0 22.74 70nm Comparative Example 3 3.5 0 0 0 0 0 3.5 10nm Invention Example 1 24.58 5.84 0 18 0 0 48.42 370nm Comparative Example 4 8.5 3.5 0 1.5 0 0 13.5 40nm Comparative Example 5 25 4.5 0 22 0 0 51.5 130nm Comparative Example 6 0 5.87 0 8.5 0 0 14.37 20nm Invention Example 2 10.2 5.23 0.26 0 0 0 20.63 90nm Comparative Example 7 9.5 5.5 0.45 0 0 0 24 120nm Comparative Example 8 6.5 4.1 0.12 0 0 0 13 40nm Comparative Example 9 0 6.5 0.32 0 0 0 12.9 28nm Inventive Example 3 5.6 10.58 0 0 1.2 0 28.18 75nm Comparative Example 10 5.2 9.52 0 0 2.1 0 35.72 75nm Comparative Example 11 4.5 9.2 0 0 0.4 0 17.7 32nm Comparative Example 12 0 7.5 0 0 0.8 0 15.5 20nm

In addition, the sulfuric acid/hydrochloric acid composite immersion test was performed, and the result of measuring the surface corrosion product after 24 hours is shown in Table 4 below. In the sulfuric acid/hydrochloric acid complex immersion test, the test piece was immersed in a mixed aqueous solution of 16.9 vol% sulfuric acid and 0.35 vol% hydrochloric acid, and after 24 hours, the content of component elements from the steel surface was measured, and the thickness from the interface where Fe and Oxide were formed. The thickness of the thickening layer was measured through.

Material Cu Sb W Sn Mo Cr I 2
(Corrosion resistance index) Thickening layer
Forming thickness Comparative Example 1 0 12 0 0 0 0 12 30nm Comparative Example 2 23.06 11.85 0 0 0 0 34.91 400nm Comparative Example 3 22 0 0 0 0 0 22 80nm Invention Example 1 12.81 5.35 0 17.28 0 0 35.44 360nm Comparative Example 4 10.54 4.35 0 3.5 0 0 18.39 45nm Comparative Example 5 12.82 5.32 0 18 0 0 36.14 400nm Comparative Example 6 0 8.74 0 10.5 0 0 19.24 75nm Invention Example 2 20.09 10.79 0.3 0 0 0 36.88 100nm Comparative Example 7 17.21 12.45 0.35 0 0 0 36.66 120nm Comparative Example 8 15 7.24 0.14 0 0 0 25.04 50nm Comparative Example 9 0 11.24 0.28 0 0 0 16.84 80nm Inventive Example 3 7.5 15.58 0 0 1.2 0 35.08 100nm Comparative Example 10 7.8 11.25 0 0 2.1 0 40.05 110nm Comparative Example 11 8.2 10.11 0 0 0.62 0 24.51 50nm Comparative Example 12 0 8.5 0 0 1.1 0 19.5 30nm

Through this, it was confirmed that in order to have the corrosion resistance to the sulfuric acid alone condensed water and the corrosion resistance to the sulfuric acid/hydrochloric acid complex water of Equation 3 at the same time, the content of the corrosion resistant component of the surface thickening layer must satisfy a specific value in a specific corrosion resistance index. Corrosion resistance index I is defined as follows.

[Equation 5]

Corrosion resistance index I = Cu + Sb + Sn + 20ｘW + 10ｘMo (component content, wt%)

At this time, a value that satisfies the sulfuric acid and sulfuric acid/hydrochloric acid complex corrosion resistance at the same time is represented by Equation 4 below.

[Equation 4]

I1 + I2 ≥ 55

At this time, I1 means the corrosion resistance index of the sulfuric acid immersion thickening layer, and I2 means the corrosion resistance index of the complex immersion thickening layer.

In addition, in the case of forming an amorphous thickening layer in which the corrosion resistant elements are concentrated on the base material on which the corrosion product is formed, it was found that the thickness of the formed thickening layer has a specific value or more, which is related to corrosion resistance. This can be expressed by Equation 6 below.

[Equation 6]

[Sulfuric acid immersion thickening layer thickness] + [Composite immersion thickening layer thickness] ≥ 170nm

With respect to the above characteristic values, in the case of Comparative Example 5, Comparative Example 7, and Comparative Example 10, all of the above corrosion resistance indexes were satisfied. However, in the case of performing hot rolling with the component systems of Comparative Examples 5, 7 and 10, it was confirmed that cracks as shown in FIG. 2 occurred on the surface after hot rolling, and are shown in Table 5. Referring to Table 5, after hot rolling was performed under the previously described rolling conditions, whether cracks were formed at the edge of the hot-rolled material and the average length of the formed cracks were measured, when manufactured with the components of Comparative Examples 5, 7 and 10. Since the length of the crack is formed at an average edge of 10 mm or more, it was judged that it could be a problem when using the product in the future, and the length of the crack at the average edge after hot rolling was limited to an average of 10 mm or less.

Material Occurrence Crack average length Comparative Example 1 X 0 Comparative Example 2 X 0 Comparative Example 3 X 0 Invention Example 1 X 2 Comparative Example 4 X One Comparative Example 5 O 15 Comparative Example 6 O 10 Invention Example 2 X One Comparative Example 7 O 12 Comparative Example 8 X 2 Comparative Example 9 X 11 Inventive Example 3 X 3 Comparative Example 10 O 20

The reason for the appearance of the above characteristics is that when a steel sheet is placed in a sulfuric acid or sulfuric acid/hydrochloric acid complex corrosion environment, an amorphous thickened layer is formed that inhibits the reaction of Fe and acid to prevent further corrosion. This is because the loss of the thickened layer occurs repeatedly, and the thickness of the thickened layer where the equilibrium thickening/corrosion occurs is related to the steel component. In the present invention, the researcher found that the components and thickness of the thickened layer are closely related to the corrosion resistance of sulfuric acid or sulfuric acid/hydrochloric acid based on the results of a large amount of experiments. In addition, it was confirmed that Sn and W play the same role, and the effect is large compared to the content.

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

Claims (16)

In% by weight, carbon (C): 0.15% or less (excluding 0%), copper (Cu): 0.05 to 0.5%, nickel (Ni): 0.02 to 0.3%, antimony (Sb): 0.05 to 0.45%, And molybdenum (Mo): 0.2 to 1.45%,
Contains the balance iron (Fe) and inevitable impurities,
It is a corrosion-resistant steel sheet that satisfies the following formula 1,
When the steel sheet is immersed in 50 wt% sulfuric acid solution for 6 hours, a sulfuric acid immersion thickening layer is formed from the surface of the steel sheet in the inner direction,
When the steel sheet is immersed in a solution of 16.9 vol% sulfuric acid solution and 0.35 vol% hydrochloric acid solution for 24 hours, a composite immersion thickening layer is formed from the surface of the steel sheet in the inner direction,
The thickness of the sulfuric acid immersion thickening layer and the composite immersion thickening layer is 70 to 500 nm, respectively, a corrosion-resistant steel sheet.
[Equation 1]
1 <Cu + 3ｘSb + 5ｘSn + 5ｘW + Mo ≤ 1.15 (wt%)
The method of claim 1,
Manganese (Mn): 0.5 to 1.5%, aluminum (Al): 0.05% or less (excluding 0%), and chromium (Cr): 8% or less (excluding 0%), which further includes at least one corrosion resistance Grater.
The method of claim 1,
Corrosion-resistant steel sheet that satisfies Equation 2 below.
[Equation 2]
Cu/Ni ≤ 2
The method of claim 1,
Corrosion-resistant steel sheet that satisfies the following formula (3).
[Equation 3]
[Sulfuric acid immersion corrosion reduction ratio] ｘ [Complex immersion corrosion reduction ratio] <35 (mg/cm ² /hr.)
(At this time, the corrosion loss ratio by sulfuric acid immersion is a value obtained by measuring the weight loss per unit time and per unit surface area after immersing the steel sheet in 50wt% sulfuric acid solution at 70°C for 6 hours, and the composite immersion corrosion reduction ratio is the steel sheet. Is a value obtained by measuring the weight loss per unit time and per unit surface area after immersion at 80°C for 6 hours in a solution of 16.9 vol% sulfuric acid solution and 0.35 vol% hydrochloric acid solution.)
The method of claim 1,
The sulfuric acid immersion thickening layer and the composite immersion thickening layer include Cu, Sb, and Mo,
The corrosion-resistant steel sheet in which the sum of the Cu, Sb, and Mo is 3.5% by weight or more.
The method of claim 1,
The sulfuric acid immersion concentrated layer includes Cu: 7.05 to 23.06%, Sb: 4.3 to 15.58%, and Mo: 0.6 to 2.1%,
The composite immersion thickening layer is a corrosion-resistant steel sheet comprising Cu: 3.5 to 24.58%, Sb: 3.5 to 17.5%, and Mo: 0.4 to 2.1%.
The method of claim 1,
Corrosion-resistant steel sheet that satisfies the following formula 4.
[Equation 4]
I1 + I2 ≥ 55
(At this time, I means the corrosion resistance index, it is expressed by the following formula (5).
[Equation 5]
Corrosion resistance index I = Cu + Sb + Sn + 20ｘW + 10ｘMo (component content, wt%)
In addition, I1 refers to the corrosion resistance index of the sulfuric acid immersion thickened layer, and I2 refers to the corrosion resistance index of the complex immersion thickened layer.)
The method of claim 1,
Corrosion-resistant steel sheet in which the sum of the thicknesses of the formed thickening layer satisfies the following formula (6).
[Equation 6]
[Sulfuric acid immersion thickening layer thickness] + [Composite immersion thickening layer thickness] ≥ 170nm
The method of claim 1,
Corrosion-resistant steel plate with an average length of 10 mm or less of cracks occurring at the edge of the steel plate.
By weight%, carbon (C): 0.15% or less (excluding 0%), copper (Cu): 0.05 to 0.5%, nickel (Ni): 0.02 to 0.3%, antimony (Sb): 0.05 to 0.45%, And molybdenum (Mo): 0.2 to 1.45%,
Contains the balance iron (Fe) and inevitable impurities,
Preparing a slab that satisfies Equation 1 below;
Heating the slab;
Manufacturing a hot-rolled steel sheet by hot rolling the heated slab; And
The method of manufacturing a corrosion-resistant steel sheet comprising; winding the hot-rolled steel sheet,
When the steel sheet is immersed in 50 wt% sulfuric acid solution for 6 hours, a sulfuric acid immersion thickening layer is formed from the surface of the steel sheet in the inner direction,
When the steel sheet is immersed in a solution of 16.9 vol% sulfuric acid solution and 0.35 vol% hydrochloric acid solution for 24 hours, a composite immersion thickening layer is formed from the surface of the steel sheet in the inner direction,
The thickness of the sulfuric acid immersion thickening layer and the composite immersion thickening layer is 70 to 500 nm, respectively, a method of manufacturing a corrosion-resistant steel sheet.
[Equation 1]
1 <Cu + 3ｘSb + 5ｘSn + 5ｘW + Mo ≤ 1.15 (wt%)
The method of claim 10,
The slab contains at least one of manganese (Mn): 0.5 to 1.5%, aluminum (Al): 0.05% or less (excluding 0%), and chromium (Cr): 8% or less (excluding 0%). Method for producing a corrosion-resistant steel sheet further comprising.
The method of claim 10,
Heating the slab; A method of manufacturing a corrosion-resistant steel sheet made at 1,000 to 1,300 °C.
The method of claim 10,
Hot-rolling the heated slab to prepare a hot-rolled steel sheet; In,
A method of manufacturing a corrosion-resistant steel sheet having a finish rolling temperature of 750°C or higher.
The method of claim 10,
The step of winding the hot-rolled steel sheet; The method of manufacturing a corrosion-resistant steel sheet made at 550 to 750 ℃.
The method of claim 10,
Winding the hot-rolled steel sheet; after,
Pickling the wound hot-rolled steel sheet;
Manufacturing a cold-rolled steel sheet by cold rolling the pickled hot-rolled steel sheet; And
Annealing heat treatment of the cold-rolled steel sheet;
A method of manufacturing a corrosion-resistant steel sheet further comprising a.
The method of claim 15,
The cold-rolled steel sheet is a method of manufacturing a corrosion-resistant steel sheet having a thickness of 3 mm or less.

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