KR20140083166A - Stainless steel based on ferrite and method for manufacturing the same - Google Patents

Abstract

The present invention relates to ferrite-based stainless steel and a manufacturing method thereof. The ferrite-based stainless steel consists of 12.5 to 16.5 wt% of Cr, 0.001 to 0.05 wt% of C, 0.005 to 0.05 wt% of N, 0.05 to 0.3 wt% of Ti, 0.05 to 0.3 wt% of Al, 0.01 to 0.5 wt% Si, 0.01 to 0.5 wt% Mn, 0.01 to 0.5 wt% Cu, 0.01 to 0.5 wt% of Mo, 0.01 to 0.5 wt% Nb, and remaining amount of Fe and unavoidable impurities. The stainless steel with a fine grain size can be casted by adding Ti, Al and N. The stainless steel is manufactured by continuous annealing, thereby improving corrosion resistance, anti-ridging properties, and moldability.

Description

TECHNICAL FIELD [0001] The present invention relates to a ferritic stainless steel and a method of manufacturing the ferritic stainless steel.

The present invention relates to a ferritic stainless steel and a method for producing the same, and more particularly, to a ferritic stainless steel capable of casting with fine grain size by adding Ti, Al and N, .

In recent years, ferritic stainless steels have been inexpensive, have a low coefficient of thermal expansion, are excellent in surface gloss, formability and oxidation resistance compared with austenitic stainless steels and are widely used in heaters, sink top plates, exterior materials, have.

On the other hand, ferritic stainless steels are produced through a hot rolling process, an annealing pickling process for removing the surface scale of the hot rolled coils, and a cold rolling and annealing process for removing internal stresses. The ferritic stainless steels There is a problem that the surface quality is deteriorated due to corrosion such as formation of rust and rust.

Therefore, an expensive element such as chromium (Cr), molybdenum (Mo) and tungsten (W) is usually added to improve the corrosion resistance and corrosion resistance of the ferritic stainless steel in order to prevent deterioration of the ferritic stainless steel . The above-mentioned methods cause a rise in the unit price of the ferritic stainless steel, and cause the ferritic stainless steel to become highly alloyed to lower the formability.

On the other hand, in the ferritic stainless steel, wrinkle-like surface defects are generated parallel to the rolling direction in the molding process, and this phenomenon is called ridging. The cause of ridging is due to the coarse casting organization. That is, when the cast structure remains in the coarse band structure without being broken in the rolling or annealing process, it is expressed as a ridging defect due to the width and thickness direction deformation behavior different from the surrounding recrystallized structure during the tensile processing.

Such ridging defects not only deteriorate the appearance of the product but also cause necking during molding, thereby deteriorating moldability. Further, if severe ridging occurs, an additional polishing step is required after molding, which may cause an increase in manufacturing cost of the final product.

Particularly, ferritic stainless steel 430 steel is 16Cr steel containing 16% by weight or more of chromium (Cr), and is widely used for household appliances and household appliance parts. In recent years, there is a continuing need to develop low-cost steels capable of replacing the 430 steel used in washing machine bodies and decorative tubes. Ferritic stainless steels having physical properties comparable to ordinary 430 steels are required while reducing high-alloy alloying elements such as Cr.

The present invention for solving the above problems is to provide a ferritic stainless steel excellent in corrosion resistance, anti-ridging property and formability even in a low cost production process by controlling the content of Ti, Al and N, And to provide a manufacturing method thereof.

In one or more embodiments of the present invention, the alloy of the present invention contains 12.5 to 16.5% of Cr, 0.001 to 0.05% of C, 0.005 to 0.05% of N, 0.05 to 0.3% of Ti, 0.05 to 0.3% of Al, : 0.01 to 0.5% of Mn, 0.01 to 0.5% of Mn, 0.01 to 0.5% of Cu, 0.01 to 0.5% of Mo, 0.01 to 0.5% of Nb and the balance of Fe and impurities, Based stainless steel may be provided.

-0.15? (Ti + Al) - (5.3N + 4C)? 0.15 (1)

However, Ti, Al, N and C are the weight percent of each of these.

Further, the following formula (2) can be satisfied.

1.5? N / C? 6 (2)

However, N and C are weight percent of N and C, respectively.

Further, the following formula (3) can be satisfied.

gmax? 20 ------------------------------- (3)

The C, N, Ni, Cu, Mn, Cr, Si, Mo, and Al of each of these weight ratios are expressed by the following formulas: gmax = 420C + 470N + 23Ni + 9Cu + 10Mn + 180-11.5Cr-11.5Si-12Mo- %to be.

Further, the following formula (4) can be satisfied.

2? Ti / N? 13 - (4)

However, Ti and N are each% by weight.

Further, the average diameter of the equiaxed crystals present in the region from the center slab layer to 1/3 of the total thickness is 3 mm or less, and the following formula (5) can be satisfied.

5? (Ti + Al) / N? 23 (5)

However, Ti, Al and N are the weight percent of each of them.

Further, the following formula (6) can be satisfied.

gmax? 5 -------------------------------- (6)

The C, N, Ni, Cu, Mn, Cr, Si, Mo, and Al of each of these weight ratios were measured in terms of gmax = 420C + 470N + 23Ni + 9Cu + 10Mn + 180-11.5Cr - 11.5Si - 12Mo - %to be.

In one or more embodiments of the present invention, it is preferable that Cr: 12.5 to 16.5%, C: 0.001 to 0.05%, N: 0.005 to 0.05%, Ti: 0.05 to 0.3%, Al: 0.05 to 0.3% 0.01 to 0.5% of Si, 0.01 to 0.5% of Mn, 0.01 to 0.5% of Cu, 0.01 to 0.5% of Mo, 0.01 to 0.5% of Mo, 0.01 to 0.5% of Nb and the balance Fe and impurities are hot- A method of producing ferritic stainless steel in which the temperature (THA) of the continuous annealing satisfies the following formula (7) can be provided: the annealing step is followed by pickling and cold rolling.

800 + 500 * (Ti-4C-3.4N)? THA? AC ----------------- (7)

Wherein the symbol of AC is 35 * (- 7.14C + 2.09Si - 1.89Mn + Cr - 3.28Ni + 1.72Mo + 1.77Ti - 0.51Cu + 21.4Al + 4.86Nb - 8N) + 430, ≪ / RTI >

When the pickling is carried out by a mixed acid composed of nitric acid (HNO 3) and hydrofluoric acid (HF), the concentration of the mixed acid can satisfy the following formula (8).

15? HNO3 + HF? 80 (8)

However, the unit of HNO 3 + HF is g / L.

More specifically, the following expression (9) can be satisfied.

10? HNO3 / HF? 25 (9)

However, the unit of HNO 3 + HF is g / L.

According to the embodiment of the present invention, a low-chromium ferritic stainless steel excellent in corrosion resistance, anti-ridging property and moldability can be provided.

Further, according to the present invention, it is possible to provide a low chromium ferritic stainless steel excellent in corrosion resistance, anti-ridging property and moldability while controlling the content of chromium and silicon to reduce the production process.

1A is a photograph showing the microstructure of a slab of a ferritic stainless steel according to an embodiment of the present invention.
1B is a photograph showing a microstructure of a slab of a conventional ferritic stainless steel.
2 is a graph showing the ridging resistance of a ferritic stainless steel according to the equiaxed grain size.
Fig. 3 is a graph showing the elongation according to the (Ti + Al) / N ratio of a ferritic stainless steel.
4 is a photograph showing the microstructure of the ferritic stainless steel produced according to the present invention according to the annealing temperature.
5 is a photograph showing the microstructure of the ferritic stainless steel produced according to the embodiment of the present invention in accordance with pickling conditions.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

Cr: 12.5 to 16.5, C: 0.001 to 0.05, N: 0.005 to 0.05, Ti: 0.05 to 0.3, in terms of% by weight, the low-chromium ferritic stainless steel having improved corrosion resistance, anti- (1) to (3), wherein the alloy contains Fe and impurities of Al, 0.05 to 0.3, Si: 0.01 to 0.5, Mn: 0.01 to 0.5, Cu: 0.01 to 0.5, Mo: 0.01 to 0.5, Nb: A ferritic stainless steel excellent in corrosion resistance, anti-ridging property and moldability satisfying the formulas (3) are disclosed.

-0.15? (Ti + Al) - (5.3N + 4C)? 0.15 (1)

1.5? N / C? 6 -------------------------------------- (2)

gmax? 20 -------------------------------------------- (3)

In this case, gmax = 420C + 470N + 23Ni + 9Cu + 10Mn + 180 - 11.5Cr - 11.5Si - 12Mo - 52Al, and the symbol of each element represents the content of each component in weight%.

When nitrogen is included in the range of the examples according to the present invention, it is necessary to solve the chromium-depleted layer formed due to the chromium-nitride by BAF heat treatment in a conventional steel. If the chromium-depleted layer is not removed, corrosion resistance and surface gloss are deteriorated.

However, according to the embodiment of the present invention, by forming a TiN compound through addition of titanium (Ti), the content of chromium-nitride can be lowered so that ferritic stainless steel excellent in corrosion resistance can be manufactured without passing through BAF heat treatment.

In addition, unlike conventional ferritic stainless steels, it is possible to manufacture ferritic stainless steels having a high degree of anti-ridging ability by controlling the N / C ratio to a high level and promoting the formation of TiN compounds. Do.

Also, it is possible to manufacture ferritic stainless steels excellent in moldability without deterioration of elongation by controlling the content of solid solution N by adding Ti and Al in spite of high N content.

Hereinafter, the reason for limiting the numerical value of the component content in the examples according to the present invention will be described. Unless otherwise stated, the unit is wt%.

Cr: 12.5 to 16.5%

The amount of chromium (Cr) is 12.5 wt% to 16.5 wt%. Cr is an alloy element added to improve the corrosion resistance of steel. When the chromium content is less than 13.5 wt%, corrosion resistance of the ferritic stainless steel is lowered in the composition range of the present invention. On the other hand, when the chromium content is more than 16.5% by weight, the ferritic stainless steel containing carbon and nitrogen may cause grain boundary strain and unnecessarily increase the production cost. Therefore, in the embodiment of the present invention, Chromium is limited to 13.5 to 16.5% by weight.

C: 0.001 to 0.05%

The amount of carbon (C) is 0.001 wt% to 0.05 wt%. Since the carbon is an austenite stabilizing element of steel, it acts to maximize the austenite fraction and has an effect of inhibiting roping and ridging. The excessive amount of carbon is required to be refined, so that it is preferably contained in an amount of 0.001 wt% or more. On the other hand, if the carbon is excessively contained, the elongation is lowered to lower the workability of the product and reduce the corrosion resistance, so that the content is limited to 0.05% by weight or less. The elongation is a term commonly used as one of quality characteristics that shows the workability of a cold rolled product of a ferritic stainless steel. The amount of the elongation until the fracture occurs when the cold rolled product of the ferritic stainless steel is uniaxially stretched is referred to as an initial length Calculate from divided values.

N: 0.005 to 0.05%

The amount of nitrogen (N) is 0.005 wt% to 0.05 wt%. The nitrogen is added in an amount of 0.005% by weight or more because it has the effect of refining the microstructure of the slab by bonding with Ti during casting and solidification to form a TiN compound. On the other hand, when nitrogen is added in a large amount, The content thereof is limited to 0.05% by weight or less.

Si: 0.01 to 0.5%

The amount of silicon (Si) is 0.01 wt% to 0.5 wt%. Silicon is an element to be added as a deoxidizing agent in steelmaking, and it is preferably contained in an amount of 0.01 wt% or more since it is a ferrite stabilizing element. On the other hand, when a large amount of the silicon is contained, the material is hardened and the ductility is deteriorated. Therefore, the content is limited to 0.5 wt% or less.

Mn: 0.01 to 0.5%

The amount of manganese (Mn) is 0.01 wt% to 0.5 wt%. Manganese is an impurity inevitably included in the steel, but if it is contained in a large amount, a manganese fume is generated at the time of welding and causes a precipitation of MnS phase, which deteriorates the elongation. Therefore, .

Ti: 0.05 to 0.3%

The amount of titanium (Ti) is 0.05% by weight to 0.30% by weight. Titanium is an element that serves to refine the equiaxed crystal grain size of the cast steel, and is used to fix the carbon, nitrogen and the like to improve the workability. Therefore, it is added in an amount of 0.05 wt% or more. On the other hand, when the titanium is added in an amount exceeding 0.30% by weight, the production cost of stainless steel increases and it causes sliver defects in the cold rolled product. Therefore, in the examples according to the present invention, do.

Al: 0.05 to 0.3%

The amount of aluminum (Al) is 0.05 wt% to 0.3 wt%. Aluminum has an effect of improving elongation by reducing the content of solid solution N in combination with solid N, so that it is added in an amount of 0.05 wt% or more. On the other hand, when the aluminum is added in an amount exceeding 0.3% by weight, it is present as a nonmetallic inclusion, causing a defect in the sleeve of the cold-rolled strip and deteriorating weldability, so that the content of Al in the embodiment of the present invention is limited to the above- do.

Cu: 0.01 to 0.5%

Cu is added in an amount of 0.01% or more for the purpose of improving corrosion resistance, and if it is added in an amount exceeding 0.5%, the workability is lowered. Therefore, the content of Cu in the examples according to the present invention is limited to the above range.

Mo: 0.01 to 0.5%

Mo is an element added to improve corrosion resistance, especially pitting resistance. However, addition of a large amount decreases the workability, so that the content of Mo is limited to the above range in the examples according to the present invention.

Nb: 0.01 to 0.5%

Nb is an element which is effective in improving corrosion resistance and moldability by precipitating solid C and N as carbonitride. However, addition of a large amount causes poor appearance and toughness due to inclusions, so the content of Nb in the examples according to the present invention is limited to the above range.

The remainder of the ferritic stainless steels except for the above-mentioned elements consists of iron (Fe) and other unavoidable impurities.

Further, in the ferritic stainless steel according to the embodiment of the present invention, the following formula should be satisfied in terms of% by weight for corrosion resistance and surface gloss.

gmax? 5 ----------------------------------- (4)

The above symbol gmax represents the content expressed by weight%, gmax = 420C + 470N + 23Ni + 9Cu + 10Mn + 180 - 11.5Cr - 11.5Si - 12Mo - 52Al.

If the gmax is high, corrosion resistance is deteriorated by the chromium-nitride formed when the austenite formed during hot rolling is changed to phase change to ferrite, and the grain boundary is eroded during the pickling, thereby deteriorating the gloss. According to the embodiment of the present invention, when gmax is limited to 20 or less, it is preferable that it is excellent in corrosion resistance and surface gloss, more preferably 5 or less.

The ferritic stainless steel is characterized in that the average particle size of the equiaxed crystals existing in the region defined as the point from the center slab center to the 1/3 of the total thickness in the cast slab satisfying the following formula is 3 mm or less . ≪ / RTI >

2? Ti / N? 13 (5)

The cause of ridging in ferritic stainless steels is that coarse grains formed during casting are rolled without being removed during hot rolling. According to the embodiment of the present invention, it is possible to manufacture a ferritic stainless steel having improved toughness by producing a ferrite-based stainless steel slab having a fine structure by forming minute equiaxed crystals by a TiN compound formed at the time of casting.

The ferritic stainless steel can more satisfactorily satisfy the following formula (6) in terms of weight% for moldability.

5? (Ti + Al) / N? 23 (6)

However, in the examples according to the present invention, Ti and Al are added to control the content, thereby making it possible to manufacture a ferritic stainless steel having excellent moldability without deterioration of elongation.

Since the BAF process is not performed in the continuous annealing of the ferritic stainless steels as described above, the range of the annealing temperature (THA) in the continuous annealing after the hot rolling of the slab is made to satisfy the following formula (7) in terms of% by weight.

800 + 500 * (Ti-4C-3.4N)? THA? AC (7)

The AC = 35 * (- 7.14C + 2.09Si - 1.89Mn + Cr - 3.28Ni + 1.72Mo + 1.77Ti - 0.51Cu + 21.4Al + 4.86Nb - 8N) + 430.

Since the steel containing a large amount of Ti and N forms a TiN compound and is distributed in a large amount at the grain boundaries, the recrystallization temperature of the ferritic stainless steel is lowered at the time of continuous annealing. Therefore, in the embodiment according to the present invention, 800 + 4C-3.4N) or more.

Further, ferritic stainless steels containing a large amount of N may have a temperature at which they transform into austenite phase at high temperature. In this case, in order to prevent corrosion, deterioration of corrosion resistance is caused. In the embodiment according to the present invention, Annealing is performed.

In carrying out the pickling after the hot rolling and the continuous annealing of the ferritic stainless steel, the concentration of the mixed acid composed of nitric acid (HNO 3) and hydrofluoric acid (HF) is represented by the following formulas (8) and (9) Satisfaction.

15 ≦ HNO 3 + HF ≦ 80 --------------------------------- (8)

10? HNO3 / HF? 25 (9)

In the examples according to the present invention, when a chromium nitride is present in addition to a TiN compound due to the presence of a large amount of N, grain boundary erosion may occur during pickling, so the pickling is carried out in the ranges of the above formulas (8) and (9).

FIG. 1A is a photograph showing a microstructure of a slab of a ferritic stainless steel according to an embodiment of the present invention, and FIG. 1B is a photograph showing a microstructure of a slab of a conventional ferritic stainless steel. FIG. The microstructures were observed on the surface where all thickness layers could be observed by cutting the slab cross section. Referring to FIG. 1, a slab having a finer equiaxed crystal grain size as shown in FIG. 1A can be manufactured according to an embodiment of the present invention, while a coarse slab is manufactured as shown in FIG. 1B in a conventional ferritic stainless steel .

FIG. 2 is a graph showing the roughness according to the embodiment of the present invention. FIG. 2 is a graph showing the equilibrium particle size of a slab of a ferritic stainless steel manufactured in the range provided by the embodiment of the present invention. It is understood that excellent anti-glare properties can be obtained.

FIG. 3 is a graph showing the elongation according to the (Ti + Al) / N ratio of a ferritic stainless steel according to an embodiment of the present invention, showing excellent moldability of the ferritic stainless steel produced in the range provided by the present invention.

FIG. 4 is a photograph showing the microstructure of the ferritic stainless steel produced in the composition range of the example according to the present invention, according to the annealing temperature.

Since the steel containing a large amount of Ti and N forms a TiN compound and is distributed in a large number of grain boundaries, the recrystallization temperature of the ferritic stainless steel is lowered during the continuous annealing. Therefore, in order to prevent incomplete recrystallization, 4C-3.4N) or more. 4A is a microstructure photograph of a comparative example which does not satisfy this requirement. In addition, ferritic stainless steels containing a large amount of N may have a temperature at which they transform into austenite at high temperatures. In this case, since corrosion resistance deteriorates, continuous annealing is performed below the range satisfying the formula AC to prevent this . Fig. 4c is a microstructure of a comparative example which does not satisfy this requirement, and Fig. 4b shows a microstructure of a preferred embodiment. That is, the photograph of FIG. 4A shows a case where the temperature of continuous annealing is low, and the photograph of FIG. 4C shows a case where the temperature of continuous annealing is excessively high.

FIG. 5 is a photograph showing the microstructure of the ferritic stainless steel produced in the composition range of the present invention according to the present invention. It contains a large amount of N. When chromium-nitride is present in addition to the TiN compound, Erosion may occur. Therefore, it is preferable to pickle in the range suggested by the present invention.

FIG. 5A is a microstructure of the cross-section of the surface of the ferritic stainless steel pickled in the range of the example according to the present invention, and FIG. 5B is a microstructure of the ferritic stainless steel pickled in such a range that it does not satisfy.

Hereinafter, examples and comparative examples according to the present invention will be described.

However, the following examples are only a preferred embodiment of the present invention, and the scope of the present invention is not limited by the following examples.

Table 1 below shows the alloying elements of Examples and Comparative Examples which are ferritic stainless steels. In Examples of Table 1, the contents of titanium (Ti), aluminum (Al), nitrogen (N) and chromium (Cr) were controlled.

The examples and comparative examples according to Table 1 were made into a ferritic stainless steel of a hot rolled sheet by a roughing mill and a continuous finishing mill, followed by continuous annealing and pickling, followed by cold rolling and cold rolling annealing. Table 2 shows (Ti + Al) - (5.3N + 4C), N / C, and gmax of Examples and Comparative Examples according to Table 1 and Table 3 shows the results of Examples and Comparative Examples The corrosion resistance grade, the lowering grade, and the moldability grade, which are typical quality of the final cold rolled products, were confirmed.

Steel grade Alloy component (% by weight) C Si Mn Cr Ni Mo Ti Cu Al N Nb Example 1 0.0050 0.20 0.20 15.2 0.18 0.02 0.12 0.05 0.10 0.0220 0.02 Example 2 0.0100 0.30 0.20 15.2 0.15 0.03 0.12 0.05 0.10 0.0220 0.03 Example 3 0.0040 0.30 0.40 15.2 0.01 0.02 0.14 0.05 0.10 0.0300 0.02 Example 4 0.0100 0.30 0.40 15.2 0.18 0.02 0.14 0.05 0.10 0.0150 0.02 Example 5 0.0100 0.30 0.15 16.0 0.15 0.03 0.15 0.05 0.15 0.0220 0.02 Example 6 0.0050 0.40 0.10 16.2 0.15 0.02 0.11 0.05 0.15 0.0250 0.02 Example 7 0.0050 0.30 0.20 16.2 0.15 0.02 0.15 0.10 0.14 0.0180 0.03 Example 8 0.0050 0.40 0.10 16.2 0.15 0.02 0.08 0.05 0.08 0.0270 0.02 Example 9 0.0035 0.48 0.10 13.4 0.05 0.45 0.19 0.04 0.15 0.0150 0.006 Comparative Example 1 0.0380 0.30 0.50 16.2 0.20 0.02 0.04 0.05 0.06 0.0400 0.007 Comparative Example 2 0.0045 0.60 0.20 13.0 0.05 0.02 0.20 0.02 0.08 0.0045 0.008 Comparative Example 3 0.0080 0.30 0.30 17.1 0.15 0.03 0.01 0.04 0.07 0.0100 0.009 Comparative Example 4 0.0250 1.00 0.30 16.3 0.10 2.00 0.08 0.05 0.01 0.0290 0.5 Comparative Example 5 0.0050 0.60 0.30 11.5 0.20 0.05 0.20 0.05 0.05 0.0080 0.006 Comparative Example 6 0.0510 0.30 0.30 16.2 0.30 0.10 0.07 0.05 0.04 0.0350 0.005

Steel grade (Ti + Al) - (5.3N + 4C) N / C gmax Example 1 0.08 4.4 16 Example 2 0.06 2.2 17 Example 3 0.07 7.5 17 Example 4 0.12 1.5 16 Example 5 0.14 2.2 4 Example 6 0.11 5.0 0 Example 7 0.15 3.6 0 Example 8 0.00 5.4 4 Example 9 0.15 4.3 18 Comparative Example 1 -0.26 1.1 32 Comparative Example 2 0.24 1.0 27 Comparative Example 3 0.00 1.3 -9 Comparative Example 4 -0.16 1.2 -14 Comparative Example 5 0.19 1.6 52 Comparative Example 6 -0.28 0.7 35

Steel grade Quality characteristics Corrosion resistance rating Rise Gong rating Formability grade Example 1 2 One One Example 2 2 One One Example 3 2 2 2 Example 4 2 One One Example 5 One One One Example 6 One 2 One Example 7 One One One Example 8 One 2 2 Example 9 2 One One Comparative Example 1 4 3 4 Comparative Example 2 4 One One Comparative Example 3 One 4 2 Comparative Example 4 One 4 3 Comparative Example 5 4 One One Comparative Example 6 4 4 3

In Table 3, the corrosion resistance grade is the official dislocation grade (mV), 150mV ~ 200mV for [1st grade], 150mV ~ 80mV for 2nd grade, 80mV ~ 30mV for 3rd grade and less than 30mV for [4th grade] The surface potential was polished based on the standard (JIS G 0577), and the surface was polished in 3.5% NaCl solution (Icrit = 100 ° A). Here, the first grade and the second grade correspond to the target range of the present invention. The grading grade of the underlapping grade is 10 탆 to 12 탆 for [grade 1], 12 탆 to 14 탆 for [grade 2], and 14 탆 to 16 탆 for grade [3] in the surface roughness grade (Rt standard) , And [4th grade] indicates 16 占 퐉 or more, where the first grade and the second grade correspond to the target ranges in the present invention.

In addition, the formability grade is an average elongation grade. Specifically, the elongation is widely used as one of the quality characteristics that indicate the workability of the stainless steel cold rolled product. It is a term widely used until a break occurs when a stainless steel cold rolled product is uniaxially pulled Calculate from the value obtained by dividing the stretched amount by the initial length. The average El value represents the average value of 0.5 mm thick cold rolled annealed material. That is, the average El value = (El0 + 2El45 + El90) / 4. In this case, the average Ela value indicates an El value when the angle between the rolling direction and the tensile direction of the cold-rolled product is a. [1st grade] is more than 29%, [2nd grade] is 27% ~ 29%, [3rd grade] is 22% ~ 27% and [4th grade] is less than 22% It falls within the scope of the invention.

Referring to Tables 1 to 3, Examples 1 to 9 show that (Ti + Al) - (5.3N + 4C) satisfies -0.15 to 0.15, N / C satisfies 1.5 to 6, gmax is 20 Or less. On the other hand, in Comparative Examples 1, 2, 4, 5 and 6, (Ti + Al) - (5.3N + 4C) did not satisfy -0.15 to 0.15, and in Comparative Example 3, N / And in Comparative Examples 1, 2, 5 and 6, it was confirmed that gmax exceeded 20.

(1) to (3), satisfying the composition range of the present invention by controlling carbon (C), chromium (Cr), silicon (Ti), aluminum (3), it can be seen that as shown in Table 3, it has corrosion resistance grade 2 or higher, lowering grade 2 or higher, and moldability grade 2 or higher. The 430 steel to which the BAF process is applied is equivalent to grade 2 of corrosion resistance, grade 1 of ridging resistance and grade 2 of moldability. Therefore, in Examples 1 to 9, it was confirmed that the BAF process was omitted to lower the unit cost as compared with the 430 steel, and at the same time, it had a quality corresponding to the 430 steel which is commonly used.

While the present invention has been described in connection with certain exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (10)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet comprises, by weight, 12.5 to 16.5% of Cr, 0.001 to 0.05% of C, 0.005 to 0.05% of N, 0.05 to 0.3% of Ti, 0.05 to 0.3% of Al, Wherein the ferritic stainless steel satisfies the following conditions (1), (2), (3), (5), (5),
-0.15? (Ti + Al) - (5.3N + 4C)? 0.15 (1)
However, Ti, Al, N and C are the weight percent of each of these. The method according to claim 1,
A ferritic stainless steel satisfying the following formula (2).
1.5? N / C? 6 (2)
However, N and C are weight percent of N and C, respectively. 3. The method of claim 2,
A ferritic stainless steel satisfying the following formula (3).
gmax? 20 ------------------------------- (3)
The C, N, Ni, Cu, Mn, Cr, Si, Mo, and Al of each of these weight ratios are expressed by the following formulas: gmax = 420C + 470N + 23Ni + 9Cu + 10Mn + 180-11.5Cr-11.5Si-12Mo- %to be. The method of claim 3,
A ferritic stainless steel satisfying the following formula (4).
2? Ti / N? 13 - (4)
However, Ti and N are each% by weight. 5. The method of claim 4,
Wherein the average diameter of the equiaxed crystals existing in the region from the central layer of the slab to 1/3 of the total thickness is 3 mm or less. 5. The method of claim 4,
A ferritic stainless steel satisfying the following formula (5).
5? (Ti + Al) / N? 23 (5)
However, Ti, Al and N are the weight percent of each of them. The method of claim 3,
A ferritic stainless steel satisfying the following formula (6).
gmax? 5 -------------------------------- (6)
The C, N, Ni, Cu, Mn, Cr, Si, Mo, and Al of each of these weight ratios were measured in terms of gmax = 420C + 470N + 23Ni + 9Cu + 10Mn + 180-11.5Cr - 11.5Si - 12Mo - %to be. The steel sheet according to any one of claims 1 to 3, wherein the steel sheet comprises, by weight, 12.5 to 16.5% of Cr, 0.001 to 0.05% of C, 0.005 to 0.05% of N, 0.05 to 0.3% of Ti, 0.05 to 0.3% of Al, Hot rolling the slab containing 0.5 to 0.5% of Cu, 0.01 to 0.5% of Mo, 0.01 to 0.5% of Mo, 0.01 to 0.5% of Nb and the balance of Fe and impurities and performing continuous annealing,
Wherein the temperature (THA) range of the continuous annealing satisfies the following formula (7).
800 + 500 * (Ti-4C-3.4N)? THA? AC ----------------- (7)
Wherein the symbol of AC is 35 * (- 7.14C + 2.09Si - 1.89Mn + Cr - 3.28Ni + 1.72Mo + 1.77Ti - 0.51Cu + 21.4Al + 4.86Nb - 8N) + 430, ≪ / RTI > 9. The method of claim 8,
Wherein the mixed acid concentration satisfies the following formula (8) when the acid pickling is carried out by a mixed acid composed of nitric acid (HNO3) and hydrofluoric acid (HF).
15? HNO3 + HF? 80 (8)
However, the unit of HNO 3 + HF is g / L. 10. The method of claim 9,
A ferritic stainless steel satisfying the following formula (9).
10? HNO3 / HF? 25 (9)
However, the unit of HNO 3 + HF is g / L.

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