KR20200131038A - Ferritic stainless steel with improved corrosion resistance - Google Patents

Abstract

Disclosed is a ferritic stainless steel having an improved corrosion resistance. The disclosed ferritic stainless steel includes: 0.003 to 0.03 wt% of C; 0.1 to 2.0 wt% of Si; 0.01 to 1.5 wt% of Mn; 10.0 to 20.0 wt% of Cr; 0.01 to 0.30 wt% of Nb; 0.003 to 0.10 wt% of Al; 0.003 to 0.03 wt% of N; 0.01 to 0.30 wt% of Ti; and the remaining of iron (Fe) and inevitable impurities, and satisfies the following formation 1: Cr + 3*Si - 30*Al + Ti + 10*Nb >= 16, wherein Cr, Si, Al, Ti, and Nb mean the content (wt%) of each element.

Description

Ferritic stainless steel with improved corrosion resistance {FERRITIC STAINLESS STEEL WITH IMPROVED CORROSION RESISTANCE}

The present invention relates to a ferritic stainless steel, and more particularly, to a ferritic stainless steel with improved corrosion resistance.

Stainless steel refers to steel that has strong corrosion resistance by suppressing corrosion, a weak point of carbon steel. In general, stainless steel is classified according to its chemical composition or metal structure. According to the metal structure, stainless steel can be classified into austenite-based, ferrite-based, martensite-based and dual phase-based.

Among them, ferritic stainless steel is widely used in building materials, transportation equipment, kitchen equipment, etc., because it has excellent corrosion resistance while adding less expensive alloying elements, and has high price competitiveness compared to austenitic stainless steel. In particular, when used as a material for home appliances such as washing machines and dryers, corrosion resistance is required, and in order to reduce the cost of parts, materials at a lower price than conventional steel materials are continuously required.

As a means to secure the corrosion resistance of ferritic stainless steel, attempts have been made to secure price competitiveness of steel by reducing the added chromium (Cr) content and replacing low-cost alloy components. The technology for deriving the relationship between alloy components to satisfy the corrosion resistance has not been developed.

The present invention is to provide a ferritic stainless steel with improved corrosion resistance by controlling the content between Si, Ti, Nb, and Al.

Ferritic stainless steel with improved corrosion resistance according to an embodiment of the present invention is, by weight, C: 0.003 to 0.03%, Si: 0.1 to 2.0%, Mn: 0.01 to 1.5%, Cr: 10.0 to 20.0%, Nb : 0.01 to 0.30%, Al: 0.003 to 0.10%, N: 0.003 to 0.03%, Ti: 0.01 to 0.30%, the remaining Fe and inevitable impurities are included, and the following formula (1) is satisfied.

(1) Cr + 3*Si-30*Al + Ti + 10*Nb ≥ 16

Here, Cr, Si, Al, Ti, and Nb mean the content (% by weight) of each element.

In addition, according to an embodiment of the present invention, V: may further include 0.005% to 0.2%.

In addition, according to an embodiment of the present invention, any one or more selected from the group consisting of P: 0.05% or less (excluding 0) and S: 0.005% or less (excluding 0) may be further included.

In addition, according to an embodiment of the present invention, the following equation (2) may be satisfied.

(2) Si + Al + Ti + Nb ≥ 20

Here, Si, Al, Ti, and Nb mean the content (% by weight) of each element present in the 5 nm-thick passivation film formed on the surface of the ferritic stainless steel.

Further, according to an embodiment of the present invention, the official potential value may be 200mV or more.

According to an embodiment of the present invention, it is possible to provide a ferritic stainless steel with improved corrosion resistance.

1 is a graph for explaining the relationship between the value of Equation (1) of the present invention and the official potential value of a stainless steel cold rolled sheet.
2 is a graph for explaining the relationship between the value of the formula (2) and the formula potential value of the alloy component content in the passivation film of the stainless steel cold rolled sheet.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are presented in order to sufficiently convey the spirit of the present invention to those of ordinary skill in the art to which the present invention pertains. The present invention is not limited to the exemplary embodiments presented here, but may be embodied in other forms. In the drawings, in order to clarify the present invention, portions not related to the description may be omitted, and sizes of components may be slightly exaggerated to aid understanding.

Throughout the 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.

Singular expressions include plural expressions, unless the context clearly has exceptions.

In the present invention, while attempting to reduce the cost of ferritic stainless steel, which is commonly used as parts such as building materials, transportation equipment, kitchen equipment, etc., in consideration of corrosion resistance, it is intended to secure an official potential of 200 mV or more.

The present invention proposes a component system and parameters for securing the desired corrosion resistance with respect to the optimal design method of ferritic stainless steel for improving corrosion resistance.

In general, it is known that the corrosion resistance of stainless steel is mainly exhibited by a passivation film composed of Cr, Fe, and O components. However, it is analyzed that Si, Al, Ti, and Nb elements added as alloy elements in addition to the main elements of the passivation film, such as Cr, Fe, and O, are also present in the passivation film. In the case of ferritic stainless steels that do not have a high Cr content, it was confirmed that the added Si, Al, Ti, Nb composition in the passivation film was changed according to the added Si, Al, Ti, and Nb content, and the corrosion resistance was changed accordingly. The present invention has been completed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Ferritic stainless steel according to an embodiment of the present invention, by weight, C: 0.003 to 0.03%, Si: 0.1 to 2.0%, Mn: 0.01 to 1.5%, Cr: 10.0 to 20.0%, Nb: 0.01 to 0.30%, Al: 0.003 to 0.10%, N: 0.003 to 0.03%, Ti: 0.01 to 0.30%, remaining Fe and unavoidable impurities.

Hereinafter, the reason for limiting the numerical value of the alloy element content of the present invention will be described. Hereinafter, unless otherwise specified, the unit is% by weight.

The content of C is 0.003 to 0.03%.

Carbon (C) is an interstitial solid solution strengthening element and serves to improve the strength of ferritic stainless steel, and thus can be added by 0.003% or more. However, if the content is excessive, the strength of the steel material is excessively increased and the ductility is decreased, and the upper limit thereof may be limited to 0.03%.

The content of Si is 0.1 to 2.0%.

Silicon (Si) is an essential element for securing the target corrosion resistance in the present invention. In general, Si is added for deoxidation of molten steel and stabilization of ferrite during steel making, and if the content is excessive, since there is a problem of reducing the ductility by hardening the material of the ferritic stainless steel, it is generally managed at 0.4% or less. However, in order to improve the corrosion resistance of ferritic stainless steel, it is necessary to optimally use Si. Accordingly, in the present invention, the Si content was controlled to 0.1 to 2.0% to enhance the passivation film to improve corrosion resistance.

The content of Mn is 0.01 to 1.5%.

Manganese (Mn) is an element effective in improving the corrosion resistance of ferritic stainless steel, and in the present invention, it may be added by 0.01% or more, and more preferably 0.5% or more. However, if the content is excessive, manganese fumes are generated during welding and cause MnS phase precipitation to reduce ductility, so the upper limit is limited to 1.5%, more preferably 1.0% or less can be added. have.

The content of Cr is 10.0 to 20.0%.

Chromium (Cr) is a silver ferrite stabilizing element and may be added by 10.0% or more in order to secure the corrosion resistance required for stainless steel. However, if the content is excessive, there is a problem that the manufacturing cost increases and the moldability is inferior, so the upper limit may be limited to 20.0%.

The content of Nb is 0.01 to 0.3%.

Niobium (Nb) is an element that improves corrosion resistance by lowering the solid solution C content by preferentially bonding with interstitial elements such as carbon (C) and nitrogen (N) to form carbonitrides. In the present invention, in order to secure high temperature strength It can be added at least 0.01%. However, if the content is excessive, it causes an increase in cost, forms laves precipitates, causes deterioration in formability and brittle fracture, and decreases in toughness, and the upper limit can be limited to 0.3%.

The content of Al is 0.003 to 0.1%.

Aluminum (Al) is a strong deoxidizing agent and serves to lower the content of oxygen in molten steel, and in the present invention, it is added by 0.003% or more. However, when the content is excessive, a sleeve defect of the cold-rolled strip occurs due to an increase in non-metallic inclusions, and at the same time, the weldability is deteriorated, and thus the content is limited to 0.1% or less, and more preferably 0.05% or less.

The content of N is 0.003 to 0.03%.

Nitrogen (N) is an element that promotes recrystallization by depositing austenite during hot rolling, and in the present invention, 0.003% or more is added to secure strength. However, if the content is excessive, it not only lowers the ductility of the steel, but also causes the stretcher strain of the cold-rolled product, and the upper limit may be limited to 0.03%.

The content of Ti is 0.01 to 0.3%.

Titanium (Ti) preferentially combines with interstitial elements such as carbon (C) and nitrogen (N) to form precipitates (carbonitrides), thereby reducing the amount of solid solution C and solid solution N in steel, and is effective in securing corrosion resistance of steel. As an element, in the present invention, 0.01% or more can be added, more preferably 0.1% or more can be added. However, if the content is excessive, it is difficult to manufacture by forming Ti-based inclusions, and there is a problem that surface defects such as scabs occur, so the upper limit is limited to 0.3%, more preferably 0.20% It can be limited to the following.

Further, according to an embodiment of the present invention, any one or more selected from the group consisting of V: 0.005% to 0.2%, P: 0.05% or less (excluding 0), and S: 0.005% or less (excluding 0) It may contain more.

The content of V is 0.005 to 0.2%.

Vanadium (V) serves to form carbonitrides by fixing C and N, and is an element effective in suppressing and miniaturizing the growth of carbonitrides.In the present invention, it is added at least 0.005% and more preferably at least 0.03%. . However, when the content is excessive, the manufacturing cost increases rapidly, and thus it may be limited to 0.2% or less, and more preferably 0.1% or less.

The content of P is 0.05% or less.

Phosphorus (P) is an impurity that is unavoidably contained in steel, and is an element that causes grain boundary corrosion during pickling or impairs hot workability, so it is desirable to control its content as low as possible. In the present invention, the upper limit of the P content is managed as 0.05%.

The content of S is 0.005% or less.

Sulfur (S) is an impurity that is inevitably contained in steel, and is an element that segregates at grain boundaries and is the main cause of impairing hot workability, so it is desirable to control its content as low as possible. In the present invention, the upper limit of the S content is managed as 0.005%.

The remaining component of the present invention is iron (Fe). However, since unintended impurities from the raw material or the surrounding environment may inevitably be mixed in the normal manufacturing process, this cannot be excluded. Examples of inevitable impurities include P (phosphorus) and S (sulfur). Since these impurities are known to anyone of ordinary skill in the manufacturing process, all the contents are not specifically mentioned in the present specification.

In addition, the ferritic stainless steel according to the disclosed embodiment satisfies the following formula (1) at the same time as the above-described component composition.

(One) Cr + 3*Si-30*Al + Ti + 10*Nb ≥ 16

Here, Cr, Si, Al, Ti, and Nb mean the content (% by weight) of each element.

In the present invention, by appropriately controlling the content of Si, Al, Ti, and Nb, a formula potential value of 200 mV or more can be exhibited as an effect of improving corrosion resistance due to an increase in the content of Si, Al, Ti, and Nb in the passivation film on the surface of the stainless steel.

When the value of Cr + 3*Si-30*Al + Ti + 10*Nb is less than 16, the official potential value is less than 200mV, making it difficult to secure the desired corrosion resistance.

In addition, the ferritic stainless steel according to the disclosed embodiment satisfies the following equation (2).

(2) Si + Al + Ti + Nb ≥ 20

Here, Si, Al, Ti, and Nb mean the content (% by weight) of each element present in the 5 nm-thick passivation film formed on the surface of the ferritic stainless steel.

In general, it is known that the corrosion resistance of ferritic stainless steel is related to the composition of the passivation film, and the passivation film is mainly composed of Fe, Cr, and O, and the corrosion resistance tends to improve as the Si content increases.

On the surface of the ferritic stainless steel of the present invention according to the above-described alloy element control, a 5 nm-thick, uniform passivation film containing Si, Al, Ti, and Nb components is formed, thereby improving the corrosion resistance of the ferritic stainless steel.

Hereinafter, it will be described in more detail through a preferred embodiment of the present invention.

Example

For the various alloy component ranges shown in Table 1 below, a 200mm-thick slab is prepared by melting ingots, and the slab is reheated at 1,000 to 1,200°C, and then finish-rolled at 800°C or higher by a rough rolling mill and a continuous finishing mill. A hot-rolled sheet was manufactured by rolling at the completion temperature. Then, hot rolling annealing and pickling were performed, followed by cold rolling and cold rolling annealing.

C Si Mn Cr Al Ti Nb V N Example 1 0.006 0.13 0.1 17.26 0.027 0.107 0.190 0 0.0075 Example 2 0.006 0.12 0.1 18.3 0.056 0.110 0.210 0 0.0081 Example 3 0.006 0.15 0.1 19.37 0.040 0.091 0.200 0 0.009 Example 4 0.006 0.14 0.1 17.31 0.054 0.102 0.200 0 0.0087 Example 5 0.005 0.38 0.1 17.18 0.040 0.100 0.200 0 0.0078 Example 6 0.006 0.81 0.1 17.29 0.040 0.090 0.200 0 0.0081 Example 7 0.007 0.15 0.1 17.34 0.040 0.093 0.200 0 0.02 Example 8 0.006 0.49 0.2 13.9 0.003 0.030 0.090 0.1 0.0081 Example 9 0.004 0.83 0.2 14.2 0.003 0.030 0.110 0.1 0.008 Example 10 0.006 1.09 0.2 14 0.005 0.030 0.090 0.1 0.0082 Comparative Example 1 0.004 0.20 0.2 14 0.044 0.210 0.000 0 0.0081 Comparative Example 2 0.005 0.51 0.2 14 0.048 0.210 0.000 0 0.0075 Comparative Example 3 0.005 0.79 0.2 13.9 0.046 0.210 0.000 0 0.0077 Comparative Example 4 0.004 1.10 0.2 13.9 0.041 0.190 0.000 0 0.0076 Comparative Example 5 0.005 0.18 0.2 14 0.003 0.000 0.100 0.1 0.0077

Table 2 below shows Cr+3*Si-30*Al+Ti+10*Nb, Si, Al, and Si, Al, which exist in a 5 nm-thick passivation film formed on the surface of ferritic stainless steel for the steel having the alloying component of Table 1. The values of Equations (1) and (2) defined as the sum of Nb and Ti elements are shown, and the official potential measurement values based on KS D 0238 are shown.

The official potential was measured using a Potentiostat equipment, and the potential value at which the current reaches 100㎂ by observing the current change while raising the voltage at a scan rate of 20mV/min in a 3.5% NaCl solution at 30℃. Was defined as the official potential (Pitting Potential, Epit). In Table 2 below, the higher the pitting potential value, the better the corrosion resistance of the ferritic stainless steel.

On the other hand, the value of equation (2) was derived by measuring the content of component elements in the thickness direction of the passivation film on the surface of the cold-rolled sheet of each Example and Comparative Example using a glow discharge spectrometer. Specifically, the sum of Si, Al, Nb, and Ti elements measured from the surface of the ferritic stainless steel to a thickness of 5 nm at intervals of about 0.5 nm in the thickness direction is shown in Table 2.

C Si Al Ti Nb Equation (1) Equation (2) Official potential
(mV) Example 1 0.006 0.13 0.027 0.107 0.190 18.9 68.9 229 Example 2 0.006 0.12 0.056 0.110 0.210 19.2 69.8 301 Example 3 0.006 0.15 0.040 0.091 0.200 20.7 82.3 231 Example 4 0.006 0.14 0.054 0.102 0.200 18.2 91.4 300 Example 5 0.005 0.38 0.040 0.100 0.200 19.2 114.6 262 Example 6 0.006 0.81 0.040 0.090 0.200 20.6 124.4 268 Example 7 0.007 0.15 0.040 0.093 0.200 18.7 81.9 251 Example 8 0.006 0.49 0.003 0.030 0.090 16.6 26.8 233 Example 9 0.004 0.83 0.003 0.030 0.110 17.7 39.7 261 Example 10 0.006 1.09 0.005 0.030 0.090 18.0 39.3 270 Comparative Example 1 0.004 0.20 0.044 0.210 0.000 13.5 14.7 171 Comparative Example 2 0.005 0.51 0.048 0.210 0.000 14.3 13.7 144 Comparative Example 3 0.005 0.79 0.046 0.210 0.000 15.1 15.2 154 Comparative Example 4 0.004 1.10 0.041 0.190 0.000 15.8 16.4 177 Comparative Example 5 0.005 0.18 0.003 0.000 0.100 15.5 9.7 179

1 is a graph for explaining the relationship between the value of Equation (1) of the present invention and the official potential value of a stainless steel cold rolled sheet.

Referring to Table 2 and FIG. 1, Examples 1 to 7 control the value of Cr + 3 * Si-30 * Al + Ti + 10 * Nb to 16% or more, thereby setting the target corrosion resistance index of the formula potential value of 200 mV. It could be implemented as above

Examples 8 to 10 additionally including 0.005% to 0.2% V also satisfy the formula potential (mV) ≥ 200 mV as Cr + 3 * Si-30 * Al + Ti + 10 * Nb ≥ 16%. have.

Comparative Examples 1 to 5 satisfies the range of the alloy components of the present invention, but it can be seen that the value of Cr+3Si-30Al+Ti+10Nb is 16% or less, and the formula potential (mV) value is as low as 144 to 179mV.

2 is a graph for explaining the relationship between the value of the formula (2) and the formula potential value of the alloy component content in the passivation film of the stainless steel cold rolled sheet.

Referring to FIG. 2, Examples 1 to 10 are formulas that are target corrosion resistance indicators as the sum of Si, Al, Nb, and Ti elements measured from the surface of ferritic stainless steel to a thickness of 5 nm in the thickness direction satisfies 20% or more. The potential value could be implemented with 200mV or more.

As described above, although exemplary embodiments of the present invention have been described, the present invention is not limited thereto, and those of ordinary skill in the art are within the scope not departing from the concept and scope of the following claims. It will be appreciated that various modifications and variations are possible.

Claims (5)

In% by weight, C: 0.003 to 0.03%, Si: 0.1 to 2.0%, Mn: 0.01 to 1.5%, Cr: 10.0 to 20.0%, Nb: 0.01 to 0.30%, Al: 0.003 to 0.10%, N: 0.003 to 0.03%, Ti: 0.01 to 0.30%, including the remaining Fe and inevitable impurities,
Ferritic stainless steel with improved corrosion resistance satisfying the following formula (1).
(1) Cr + 3*Si-30*Al + Ti + 10*Nb ≥ 16
(Here, Cr, Si, Al, Ti, and Nb mean the content (% by weight) of each element.) The method of claim 1,
V: ferritic stainless steel with improved corrosion resistance further comprising 0.005% to 0.2%. The method of claim 1,
Ferritic stainless steel with improved corrosion resistance further comprising at least one selected from the group consisting of P: 0.05% or less (excluding 0) and S: 0.005% or less (excluding 0). The method of claim 1,
Ferritic stainless steel with improved corrosion resistance satisfying the following formula (2).
(2) Si + Al + Ti + Nb ≥ 20
(Here, Si, Al, Ti, and Nb mean the content (% by weight) of each element present in the 5 nm-thick passivation film formed on the surface of the ferritic stainless steel.) The method of claim 1,
Ferritic stainless steel with improved corrosion resistance with a formula potential value of 200mV or more.

Images