KR20000027022A - Ferritic stainless steel for exterior ornament of building having good tenacity and ductility at weld zone and method for preparation thereof - Google Patents

Abstract

PURPOSE: Aferritic stainless steel for exterior ornament of a building and preparation method thereof are provided which has good tenacity and ductility at weld zone. CONSTITUTION: A ferritic stainless steel for exterior ornament of a building is obtained by: i) homogenizing, hot-rolling, annealing a steel slab which comprises: 0.015 wt.% or less of C, 0.02 wt.% or less of N, 0.5 wt.% or less of Si, 0.5 wt.% or less of Mn, 0.03 wt.% or less of P, 0.004 wt.% or less of S, 0.005 wt.% or less of O, 0.36 wt.% or less of Nb, 0.15 wt.% or less of Ti, 0.5 wt.% or less of Cu, 0.15 wt.% or less of Al, 4 wt.% or less of MO and 24-32 wt.% of Cr and the stabilization ratio of which satisfies that (Nb+Ti)/(C+N) is 8-24, and washing with an acid; ii) cold-stripping, annealing, washing with an acid; iii) dull rolling by which a surface roughness becomes 1.5 plus or minus 0.5 micro meter, annealing, and washing with an acid.

Description

Ferritic stainless steel for building exterior with excellent toughness and ductility of welds, and its manufacturing method

The present invention relates to a ferritic stainless steel used as a building roofing material and a wall material, and more particularly, to a ferritic stainless steel with improved corrosion resistance and toughness, and weld ductility.

In general, stainless steel having excellent corrosion resistance is used for exterior materials of roofs and walls of buildings. Corrosion resistance, toughness and weldability are required for stainless steels for this purpose, and double weldability is determined by the construction method. In the case of roofs, welding of some corners is unavoidable, even if folding, batten type is used. Today, the shape of buildings tends to be complicated in consideration of architectural beauty. Therefore, weldability is an important requirement.

Until now, austenitic stainless steel has been widely used in architectural exterior materials in consideration of corrosion resistance and welding characteristics. However, the use of austenitic stainless steel is limited due to the increase in the material price due to expensive Ni. Recently, there is a tendency to use inexpensive ferritic stainless steel as a building exterior material, for example, the Republic of Korea Patent Publication No. 95-3159.

Republic of Korea Patent Publication No. 95-3159 relates to a technique for solving the problem of workability (occurrence of pocket wake) occurs when applying ferritic stainless steel as a building exterior material. Specifically, the prior art is Cr: 10-32%, C + N: 0.005-0.1%, Mo: 0.2-3.5%, Cu: 0.1-3.0%, Nb: 0.1-0.9% and Ti, V, Zr , The four-membered sum of B consists of at least one element selected from the group consisting of 0.15-1.0% and the remaining Fe and other unavoidable elements; A stainless steel sheet for building exterior materials having a strain ratio of 2.5 or more, measured at an elastic limit reached in a tensile test on a specimen taken in the width direction of cold rolling, wherein the strain ratio is 5 at a temperature of 200-500 ° C. It is stated that it is obtained by aging for -48 seconds.

However, the stainless steel proposed in the prior art does not take into account weldability, which is an important characteristic in building exterior materials, and further, corrosion resistance and toughness are required to be improved. In particular, the stainless steel sheet for building exterior materials should have a low glossiness of the surface due to the nature of the exterior material, but the prior art has no consideration therefor. In addition, the prior art is subjected to the aging heat treatment at low temperature after the temper rolling, in this case there is a problem that a dense oxide film is formed, the final pickling is difficult.

On the other hand, in order to increase toughness in ferritic stainless steel, Cr, Mo, C, N content should be reduced. However, the reduction of Cr and Mo content lowers the corrosion resistance, and the reduction of the content of C and N is not only difficult in process but also requires a high cost. Therefore, toughness should be increased without decreasing the corrosion resistance at constant Cr, Mo, C and N concentrations. In addition, nitrogen is contaminated during welding, which leads to a decrease in toughness and corrosion resistance. Therefore, in order to be used as a material for building exterior use, which requires welding, component design considering both toughness, corrosion resistance, and weldability is required, but research on this is inadequate, and the same is true of the aforementioned prior art.

Accordingly, an object of the present invention is to provide a ferritic stainless steel having improved corrosion resistance, toughness and weldability.

It is another object of the present invention to provide a method for producing ferritic stainless steel which can have appropriate glossiness, which is important as corrosion resistance, toughness and weldability as well as building exterior materials.

Ferritic stainless steel of the present invention for achieving the above object, in weight%, C: 0.015% or less, N: 0.02% or less, Si: 0.5% or less, Mn: 0.5% or less, P: 0.03% or less, S : 0.004% or less, O: 0.005% or less, Nb: 0.36% or less, Ti: 0.15% or less, Cu: 0.5% or less, Al: 0.15% or less, Mo: 4% or less, Cr: 24-32% And the stabilization ratio (Nb + Ti / C + N) is configured to satisfy 8-24.

In addition, the production method of the present invention for achieving the above another object, in weight%, C: 0.015% or less, N: 0.02% or less, Si: 0.5% or less, Mn: 0.5% or less, P: 0.03% or less, S: 0.004% or less, O: 0.005% or less, Nb: 0.36% or less, Ti: 0.15% or less, Cu: 0.5% or less, Al: 0.15% or less, Mo: 4% or less, Cr: 24-32% The steel slab having a stabilization ratio ((Nb + Ti) / (C + N)) of 8-24 is homogenized, hot rolled, annealed and pickled, and then cold rolled, annealed and pickled. It consists of a process of rolling, annealing and pickling so that the surface roughness (Ra) of the steel sheet becomes 1.5 ± 0.5 μm.

Hereinafter, the present invention will be described in detail.

[Ferritic stainless steel]

Features of the ferritic stainless steel of the present invention,

First, in the present invention, Ti + Nb is added as a stable element similar to the existing ferritic stainless steel, but the purpose of addition is different. In the present invention, the effect (function) of Ti on weld ductility and corrosion resistance after pickling is newly identified. Based on the results of the study, the amount of Ti is adjusted in consideration of the relationship with Nb. That is, the content of Ti necessary to secure toughness by optimizing coarse TiN (2 μm or less) and suppressing precipitation of coarse TiN is improved. In addition, the stabilization element content required for the inhibition of sensitization adds Nb instead of Ti.

Second, although Al is added as a deoxidizer in existing ferritic stainless steels, in the present invention, the Al content is managed based on the results of a study that has revealed the effect of Al on the toughness, and in consideration of the adverse effect of Al oxide on the corrosion resistance, While suppressing the content of Al limits the size of the oxide.

In addition, C + N, Si, Mn, P, S, O, Nb, Ti, Cu, Al, Mo, Cr, and Nb + Ti are managed in consideration of various characteristics required for ferritic stainless steel. same.

The C and N is limited to less than 0.015%, 0.02% or less, respectively, in order to minimize the reduction of toughness, the smaller the content of the content is improved because the properties of the material is not limited at least. In addition, C + N is preferably 0.03% or less in consideration of sensitization.

The Si is an element that increases deoxidation and oxidation resistance and is within 0.5% in order to suppress a decrease in toughness.

The Mn is an element that increases deoxidation and thus reduces corrosion of inclusions, MnS, and is within 0.5%.

P is less than 0.03% because it reduces toughness as well as corrosion resistance.

S is limited to within 0.004% because it reduces the corrosion resistance.

Since the O increases the inclusion content to reduce toughness and corrosion resistance, it is preferable to suppress the oxygen content as much as possible, and is limited to within 0.005%.

The Cu increases the corrosion resistance in a reducing atmosphere, but when added to 0.5% or more, it reduces the corrosion resistance, stress corrosion resistance and hot workability, so it is limited to within 0.5%.

Al has been added mainly for deoxidation until now, and inhibited as much as possible from being contained in steel for corrosion resistance. On the other hand, in the present invention, Al is an element actively added in consideration of the effect on Al toughness, and has an effect of preventing a decrease in toughness caused by addition of Ti. However, when Al is added in excess, Al oxide is formed to reduce corrosion resistance, so the Al is controlled within 0.15%. In the present invention, it is more preferable to suppress the size of the Al oxide to about 1 μm or less in order to suppress the decrease in corrosion resistance according to the addition of Al.

Ti has been managed as an element so far to suppress the formation of MnS, which inhibits sensitization and lowers the corrosion resistance of steel. In contrast, in the present invention, the amount of Ti is adjusted on the basis of a new experiment on the effect of Ti on the toughness and ductility of the weld, and the corrosion resistance after pickling. If welding is inevitable due to the use of construction materials, the welded toughness of Ti-added steel is similar to the welded toughness of Ti-free steel, but Ti is advantageous in terms of weld ductility. In addition, corrosion resistance after pickling of Ti-added steel is superior to that of Ti-free steel. Therefore, Ti is added in consideration of the ductility of the weld and corrosion resistance after pickling. The upper limit thereof is limited to 0.15% or less in consideration of deterioration of toughness. Such Ti is formed of TiN during coagulation, resulting in deterioration of toughness, but it is possible to prevent the deterioration of the toughness to some extent by making the size of TiN as approximately 2 µm as possible. It is advantageous not to add such Ti, considering only the toughness of the product.

The Nb is an element added to prevent sensitization, and the addition of more than 0.36% leads to a decrease in toughness due to the precipitated phase, so the maximum content is 0.36%.

Stabilization ratio ((Ti + Nb) / (C + N)) is determined in consideration of corrosion resistance and toughness. In terms of corrosion resistance, an appropriate stabilization ratio of about 8 can prevent intergranular corrosion. By the way, if the building exterior steel is actually applied through the welding process, the increase in the C + N due to the penetration of nitrogen should increase the stabilization ratio. However, as mentioned above, since the toughness decreases with increasing Ti, the optimum stabilization ratio should be determined in consideration of the toughness along with the increase in the amount of C + N due to welding. Normally, the degree of nitrogen contamination depends on the welding method, but about 300ppm is contaminated. Considering this, the maximum stabilization ratio of the base metal should be 24 so that the welding stabilization ratio should be maintained at 8-10 even if C + N is contaminated during welding. . This stabilization ratio can also prevent a sharp drop in toughness. As described above, in the present invention, in order to optimize the properties (corrosion resistance and toughness) of the material, the optimum stabilization ratio is 8 to 24 in order to ensure the toughness without intergranular corrosion resistance due to sensitization.

Therefore, what is necessary is just to determine the content of titration Nb as% Nb = (8-24) *% (C + N)-% Ti.

Here,% (C + N) = weight content of the welded portion (C + N), Ti may be determined in consideration of welded ductility, corrosion resistance and toughness. That is, the content of (C + N) of the base metal is limited to 0.03%, but the concentration of nitrogen may increase due to the contamination of nitrogen in the air during welding, so the appropriate Nb content is determined by the degree of contamination and Ti content. To lose.

The Cr increases the corrosion resistance, but as the Cr content increases, the increase in the precipitation degree of Cr (C, N) and Cr oxides causes a decrease in toughness, so the appropriate range of Cr is 24-32%.

Mo increases the corrosion resistance but causes a decrease in toughness due to high temperature (σ, χ) precipitation, so the proper range of Mo is within 4%.

[Production method of ferritic stainless steel]

The steel slab prepared as described above is manufactured in a conventional manner through a series of processes such as homogenization, hot rolling, hot rolled sheet annealing, pickling, cold rolling, cold rolled sheet annealing, and second pickling, according to the present invention. According to the rolling (dull), annealing, the final pickling process to produce a ferritic stainless steel sheet for building exterior materials having an appropriate gloss.

The manufacturing method for obtaining a cold rolled plate before the less rolling process is performed according to a conventional method, and the specific manufacturing conditions will be described as follows. The steel slab is homogenized and rolled at about 30 minutes to 2 hours at 1100-1200 ° C. At this time, water cooling is preferably performed to suppress embrittlement of the hot rolled plate, and water cooling is preferably performed at a temperature of about 500-600 ° C. After hot rolling as described above, the hot rolled sheet is annealed at about 980 -1050 ° C for about 1-5 minutes, and pickled by immersion for about 1-5 minutes in mixed acid solution (nitric acid + hydrofluoric acid) to remove the annealing scale. . The pickled hot rolled sheet is cold rolled according to the application to obtain a cold rolled sheet. Annealing and secondary pickling of cold rolled sheets are similar to the annealing and pickling conditions after hot rolling mentioned above. Since the cold rolled sheet is thin, the annealing and pickling times are smaller than those of the hot rolled sheet.

After pickling the cold rolled steel sheet annealed as described above, less rolling is performed according to the present invention. Dull (dull) rolling is to conventionally make a pattern by the chemical method on the surface of the roll to make a pattern on the surface of the stainless steel sheet, in the present invention is to be performed to reduce the gloss of the steel sheet. At this time, it should be noted that if the V roughness of the steel surface is increased to reduce gloss, that is, if the roughness shape of the steel surface is extremely deep or a corner occurs, contaminants present in the air during use are easily attached and cause corrosion. It is easy to make. Therefore, a streamlined shape in which the pattern of the steel sheet is not deep and does not have corners is preferable, which is obtained by constantly adjusting the roughness of the surface of the steel sheet.

That is, it is preferable to roll less so that the surface roughness (roughness, Ra) of the steel sheet is 1.5 ± 0.5 μm, which is set in consideration of the glossiness and resistance to corrosion.

Less rolling and annealing as described above. In general, the purpose of annealing is to soften the material. However, the rolling reduction rate is less than about 6% in less rolling, so softening of the material occurs too much when the annealing under the above-mentioned conditions, thus weakening the properties of the material. For example, after cold rolling, the hardness (Hv) was 190 and the annealing of the material was about 150. However, after rolling, the hardness of the material (Hv) was about 130 at the time of annealing, similar to the previous condition. Therefore, the annealing condition performed after the less rolling requires a lower temperature and a shorter holding time than the cold rolling annealing condition, for example, at a temperature of 850-1100 ° C. The pickling solution is used in the same way as the primary pickling solution, but it is preferable to slightly increase the pickling time because the roughness of the plate after annealing is high and the pickling is difficult.

The ferritic stainless steel produced according to the present invention not only satisfies low glossiness characteristics, but does not generate pocket waves even when the aging heat treatment is not performed at low temperature as in the prior art (Korean Patent Publication No. 95-3159).

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

The chemical composition of the 25Kg ingot used in the embodiment of the present invention is shown in Table 1 below.

division Chemical composition (% by weight) Cr Mo Nb Ti Al C + N Si Mn P S O One 26.2 4.1 ^* - ^* - - ^* 0.0113 0.29 0.30 0.030 0.0020 0.016 ^* 2 25.9 4.2 ^* - ^* - - ^* 0.0250 0.29 0.30 0.029 0.0020 0.018 ^* 3 25.95 4.07 ^* 0.11 0.094 - ^* 0.0270 0.29 0.29 0.029 0.0024 0.0046 4 25.9 4.1 ^* 0.25 0.072 - ^* 0.0250 0.30 0.29 0.029 0.0025 0.01 ^* 5 26.1 4.1 ^* 0.34 - - ^* 0.0250 0.28 0.30 0.029 0.0026 0.014 ^* 6 26.0 4.2 ^* 0.10 0.12 0.065 0.0248 0.30 0.29 0.029 0.0023 0.0038 7 26.0 4.0 0.34 - 0.055 0.0260 0.29 0.29 0.029 0.0026 0.006 ^* 8 25.8 4.1 ^* 0.24 0.13 0.06 0.0234 0.29 0.29 0.029 0.0024 0.0039 9 26.2 2.0 - ^* - - ^* 0.021 0.29 0.3 0.029 0.0022 0.013 ^* 10 26.2 2.1 0.23 0.09 - ^* 0.024 0.3 0.3 0.029 0.0021 0.0096 ^* 11 26 2.1 0.33 - - ^* 0.024 0.3 0.3 0.029 0.0022 0.0079 ^* 12 26.2 2.0 0.23 0.11 0.062 0.024 0.29 0.3 0.029 0.0022 0.0040 13 26.2 2.0 0.33 - 0.0064 0.027 0.29 0.3 0.029 0.0022 0.0034 14 26.2 2.0 0.3 0.025 0.0065 0.0254 0.29 0.3 0.028 0.0022 0.0045 15 26.1 2.0 0.32 - 0.003 0.0260 0.29 0.3 0.028 0.0024 0.0038 16 26.2 2.1 0.34 - 0.02 0.0255 0.29 0.3 0.030 0.0022 0.0034 17 26 2.0 0.33 - 0.015 0.0250 0.29 0.3 0.028 0.0022 0.0035 The * mark is outside the conditions of the present invention.

Each ingot prepared as described above was homogenized by heat treatment at 1200 ° C. for 2 hours in an Ar atmosphere after melting in a vacuum induction furnace, and hot rolled to 6 mm thickness, followed by water cooling, annealing and pickling, and cold rolling at 1050 ° C. Cold roll annealing was performed for 30 seconds at. Each specimen was polished up to SIC # 200 before the experiment. To evaluate the quality characteristics of the welded specimens, the welds were welded according to the conditions shown in Table 2 below.

thickness Weld Joint Shape welding method Welding condition Protective gas (ℓ / min) Remarks Torch gas Post torch Backing gas 1.5 Bead On Plate Inspection GTAW 45A-9V-12cm / min (2.0KJ / cm) 18 18 18 Arc distance: 2 mm tungsten electrode: 2.4 mm dia. 3.0 100 ~ 110A-10V-12cm / min (5.0 ~ 5.5KJ / cm)

The specimens obtained as described above were evaluated for (1) sensitivity, (2) toughness change of the base metal of the weld, (3) weld ductility, (4) corrosion resistance, and (5) glossiness.

(1) sensitivity

The sensitivity of the base metal was measured by EPR test (Corrosion vol 40 1984, 584-593) and the immersion test proposed by Lee (Corrosion vol 37 1981, 437-443). -91A-F)). The base material specimens used in the sensitization test were subjected to sensitization for 10 minutes at 620 ℃ before the test. Thus, the degree of sensitivity was measured and the results are shown in Table 3 below.

According to the parent material test results shown in Table 3, the sensitization did not occur when the stabilization ratio was 7.6, but the sensitization occurred when the stabilization ratio was zero. In addition, in the case of welding, the stabilization ratio was not sensitive near 10, but in the case of 7.6, the sensitization occurred. Therefore, the stabilization ratio is appropriate around 10.

(2) Toughness change of welded part and base metal

Changes in toughness of the base metal of the weld zone according to the stabilization element and Al are shown in Table 4 below. Here, the lower the ductile-brittle transition temperature (DBTT), the higher the toughness.

Steel number and main components of Table 1 DBTT (℃) Mother and child department Weld One 26Cr-4Mo-0.011 (C + N) -5 ± 11 - 2 26Cr-4Mo-0.025 (C + N) 75 ± 5 130 4 26Cr-4Mo-0.025 (C + N) -Ti-Nb 24 ± 6 45 5 26Cr-4Mo-0.025 (C + N) -Nb 5 ± 3 45 6 26Cr-4Mo-0.025 (C + N) -Ti-Nb-Al 20 ± 4 40 7 26Cr-4Mo-0.026 (C + N) -Nb-Al -25 ± 9 30 9 26Cr-2Mo-0.021 (C + N) 80 ± 5 110 10 26Cr-2Mo-0.024 (C + N) -Ti-Nb 20 ± 5 55 11 26Cr-2Mo-0.024 (C + N) -Nb -12 ± 3 35 12 26Cr-2Mo-0.024 (C + N) -Ti-Nb-Al 15 ± 5 50 13 26Cr-2Mo-0.027 (C + N) -Nb-Al -50 ± 10 30 14 26Cr-2Mo-0.025 (C + N) -Ti-Nb-Al 10 ± 5 40 15 26Cr-2Mo-0.026 (C + N) -Nb-Al -60 ± 5 35 16 26Cr-2Mo-0.026 (C + N) -Nb-Al -40 ± 6 35 17 26Cr-2Mo-0.025 (C + N) -Nb-Al -42 ± 5 35

As can be seen in Table 4, the toughness of the base material was increased in the following order.

Unadded Steel <Ti + Nb Additive Steel <Ti + Nb + Al <Nb Additive Steel <Nb + Al Additive Steel

(In this case, no additive steel means no addition of Ti, Nb, or Al)

Thus, the toughness of ferritic stainless steel for building exterior materials is determined by the addition of stabilizing elements (Ti, Nb) and Al. Specifically, the toughness is very weak due to the formation of Cr (C, N) in the steel (1-2) without Ti, Nb and Al is added. In addition, in the steel grades (6, 12) to which 0.1% Ti is added, the toughness of the steel grades (13, 15, 16, and 17), which is not Ti-added Nb + Al (Nb), is increased due to the formation of angualr type TiN in the material. This degradation was observed. Toughness increased with decreasing Ti content in the steel (12,14) in which Ti + Nb + Al was added, which is due to less TiN formed with decreasing Ti content. Therefore, it is preferable not to add Ti in order to improve toughness.

Among the steels with excellent toughness (steel without Ti and Nb or Nb + Al added compared to Ti steel), the toughness was the highest in steel with Al added to Nb (5,7,11,13,15,16 , 17). The addition of Al increased the toughness in steel compared to the non-Al addition, but the tendency did not show a linear relationship. In other words, the toughness increased with Al addition, but the toughness decreased again above a certain threshold concentration (13, 15-17). The addition of a small amount of Al improves the toughness by reducing the oxygen concentration in the steel and suppressing the formation of oxides. Therefore, the optimum amount of Al is about 0.03% to minimize the amount of addition in the range where the reduction of oxygen concentration in steel does not occur rapidly. However, since the addition amount of Al is determined by the oxygen content of the steel in the pre-deoxidation step by Al, the maximum value of Al is set to about 0.15%. As mentioned above, the toughness of the base material increases in the order of the following additive elements and the toughness of the welded part shows the same tendency, but the change of the toughness of the welded part according to the alloy element compared to the base material ratio is very insignificant.

(3) Ductility of welded parts according to stabilization element and Al

The change in ductility of the weld according to the stabilization element and Al is shown in Table 5 below. In this case, a higher Erichen value means better ductility.

Alloy number Alloy component Erichen value (r, mm, JIS B 7777) Base material Erichen value (mm) Weld part Erichen ratio (%) 4 Nb, Ti 9.84 97 5 Nb 9.67 96 7 Nb, Al 9.74 96 8 Nb, Ti, Al 9.83 98 9 - 9.47 65 10 Nb, Ti 9.89 99 11 Nb 9.76 93 13 Nb, Al 9.77 94 14 Nb, Ti, Al 9.95 97

As can be seen in Table 4, the ductility of the Ti, Nb composite addition steel was superior to the Nb alone addition steel.

(4) corrosion resistance

Corrosion resistance was measured and the results are shown in Table 6 below. Corrosion resistance was measured at the formal potential and the passive film by polarization test in a 20% NaCl solution (salt atmosphere) at 80 ℃. The surface of the specimen before polarization was treated with two types (polishing or final pickling).

Alloy number Microalloy Components Base Material Potential Potential (mV vs. SCE) After polishing After pickling 10 Ti, Nb 700 640 11 Nb 900 800 12 Ti, Nb, Al 350 950 13 Nb, Al 780 650 14 Ti, Nb, Al 450 900

As can be seen in Table 5, the polished specimens had the highest pitting resistance in Nb-only steel, but the final pickled specimens had excellent pitting resistance in Nb + Ti + Al addition steel. In general, pickling is used as the final process in the production process, and considering that the addition of Al is required to improve the toughness, it is judged that the steel with Nb + Ti + Al is added in terms of corrosion resistance.

(5) glossiness and surface characteristics

Glossiness and surface characteristics according to the surface treatment are shown in Table 6 below. AP is a general cold-roll pickling process, followed by pickling after cold rolling, and BA is a cold-annealed method after annealing and pickling. DR is a surface treatment method in which rolling is performed by a roll having a high roughness (Ra = 1.5 μm) during cold rolling and annealing after pickling to improve the roughness of the steel sheet, followed by annealing and pickling (less rolling). In the less rolling method, the reduction ratio is about 6% so that only the pattern engraved on the roll is engraved on the steel sheet during the secondary rolling.

As can be seen in Table 6, when less rolling in accordance with the present invention it was possible to effectively reduce the gloss compared to the BA, AP method. Generally, after cold rolling, steel sheet is produced through annealing, pickling, and temper rolling for surface treatment of the steel sheet. However, in order to reduce the high gloss, which is an intrinsic property of aesthetics and metals, it is effective to perform less rolling instead of temper rolling in order to be used as a roofing material.

The conclusion obtained through the above embodiment is as follows.

Steels with added Nb + Al are most appropriate in terms of corrosion resistance and toughness when using materials for applications that require no welding. However, in the case where the welding is required, the change of the weld toughness according to the alloying element is insignificant, and the weld ductility is excellent in the steel to which Ti + Nb + Al is added. In order to be used for building exterior materials, it is necessary to reduce glossiness, and for this purpose, pickling after rolling by a roll having high roughness is essential. Corrosion resistance after pickling surface treatment, which is a process required to reduce glossiness, was the best in steels with Ti + Nb + Al. Therefore, pickling and welding are inevitable in order to be used as building exterior materials, and for this, steel with Ti, Nb, Al complex is most effective in improving corrosion resistance and toughness. More preferably, in the case of Ti and Al, it is effective to appropriately suppress the size of TiN precipitates and oxidative inclusions.

As described above, according to the present invention, there is an effect of providing a ferritic stainless steel for building exterior having excellent general characteristics required for building exterior materials such as corrosion resistance, toughness, weldability, and glossiness.

Claims (5)

By weight%, C: 0.015% or less, N: 0.02% or less, Si: 0.5% or less, Mn: 0.5% or less, P: 0.03% or less, S: 0.004% or less, O: 0.005% or less, Nb: 0.36% Ti: 0.15% or less, Cu: 0.5% or less, Al: 0.15% or less, Mo: 4% or less, Cr: 24-32%, C + N: 0.03% or less, and stabilization ratio ((Nb + Ferritic stainless steel for building exterior materials with excellent toughness and ductility of welds satisfying Ti) / (C + N)) 8-24. The ferritic stainless steel according to claim 1, wherein Al is 0.003-0.15% and Al oxide has a size of 1 μm or less. The ferritic stainless steel according to claim 1, wherein the Ti is 0.025-0.15% and the precipitates of Ti and N are 2 µm or less. By weight%, C: 0.015% or less, N: 0.02% or less, Si: 0.5% or less, Mn: 0.5% or less, P: 0.03% or less, S: 0.004% or less, O: 0.005% or less, Nb: 0.36% Ti: 0.15% or less, Cu: 0.5% or less, Al: 0.15% or less, Mo: 4% or less, Cr: 24-32%, and contain a stabilization ratio ((Nb + Ti) / (C + N) ) Hot-rolled, annealed and pickled after homogenizing steel slab satisfying 8-24 A method for producing ferritic stainless steel for building exterior materials having low glossiness, annealing and pickling. The method of claim 1, wherein the surface of the less rolled steel sheet is characterized in that the streamlined irregularities are formed.