WO2012172808A1

WO2012172808A1 - Ferritic stainless steel

Info

Publication number: WO2012172808A1
Application number: PCT/JP2012/003894
Authority: WO
Inventors: 和秀石井; 山内　克久; 源一石橋; 秋信神丸
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2011-06-15
Filing date: 2012-06-14
Publication date: 2012-12-20
Also published as: TW201303044A; CN103597109B; CN103597109A; KR20140026602A; TWI473891B

Abstract

Provided is ferritic stainless steel which has excellent surface quality, while exhibiting excellent corrosion resistance and excellent acid pickling performance in a welded portion. Ferritic stainless steel which is characterized by containing, in mass%, 0.010% or less of C, 0.15-0.60% of Si, 0.5% or less of Mn, 0.04% or less of P, 0.01% or less of S, 0.2% or less of Al, 17.0-19.0% of Cr, 0.3-0.5% of Cu, 0.6% or less of Ni, 0.10-0.20% of Ti, and 0.015% or less of N, with C + N being 0.02% or less and with the balance made up of Fe and unavoidable impurities. The ferritic stainless steel is also characterized by satisfying formula (1). Ti%/(C% + N%) ≥ 8 (1) In this connection, C%, N% and Ti% respectively represent the contents (mass%) of C, N and Ti.

Description

Ferritic stainless steel

The present invention relates to a ferritic stainless steel (ferritic stainless steel), excellent in surface properties (quality of surface), and excellent in corrosion resistance (corrosion resistance) and pickling (weld zone). It relates to ferritic stainless steel.

Among stainless steels, austenitic stainless steel SUS304 (18% Cr-8% Ni) (Japanese Industrial Standard, JIS G 4305) is widely used due to its excellent corrosion resistance. However, this steel type is expensive because it contains a large amount of Ni.

On the other hand, in Patent Document 1, as component composition, C: 0.03% or less, Si: 1.0% or less, Mn: 0.5% or less, P: 0.04% or less, S: 0 0.02% or less, Al: 0.1% or less, Cr: 20.5% or more, 22.5% or less, Cu: 0.3% or more, 0.8% or less, Ni: 1.0% or less, Ti : 4 × (C% + N%) or more, 0.35% or less, Nb: 0.01% or less, N: 0.03% or less, C + N: 0.05% or less, the balance being Fe and inevitable A ferritic stainless steel sheet characterized by comprising impurities (inevitable impurities) is disclosed. This stainless steel plate is widely used for building members, industrial machines, and kitchens because of its excellent corrosion resistance and economy by not using Ni.

Japanese Patent No. 4396676

However, when the ferritic stainless steel sheet disclosed in Patent Document 1 is used for industrial machines, it is often used by welding not only to the same steel type but also to different steel types, particularly SUS304. Even in that case, it is required to maintain good corrosion resistance. Although this steel type has good corrosion resistance in welded parts of the same steel type, there is a problem that when SUS304 and TIG welding (Tungsten Inert Gas welding), the corrosion resistance of the welded portion is lower than that of the base material.

Corrosion resistance of the weld is determined by the thermal history during welding, where C and N in the steel combine with Cr and precipitate at the grain boundaries as chromium carbonitride (precipitates as Cr-carbides and Cr-nitrides at the grain boundaries during It is caused by the formation of chromium-depletion-layer-at-the-grain-boundaries- at the grain boundary by the cooling-state-of-welding. This phenomenon is called sensitization. In order to prevent this, a method of reducing the amount of C and N in the steel and adding an appropriate amount of Ti to precipitate C and N as titanium carbonitride to prevent the formation of chromium carbonitride is taken. ing. By this method, the TIG welded portion between the ferritic stainless steel plates disclosed in Patent Document 1 maintains good corrosion resistance.

However, while the C content of the steel sheet is about 0.01%, SUS304 has a high C content of 0.04 to 0.05%, so that at the joint between the steel sheet and SUS304, In order to prevent sensitization, the amount of Ti added must be increased to about 0.4 to 1.0%.

However, when Ti is added in this manner, the steel becomes brittle (get brittle), Ti combines with nitrogen to become TiN, and this aggregates, resulting in a large amount of so-called titanium stringers (stringer caused by titanium nitrides) resulting in surface properties. It will be seriously damaged.

Thus, in the prior art, it was difficult to achieve both the corrosion resistance and the surface properties of the different steel type TIG welds with SUS304. In addition, when welding is performed, an oxide film called scale caused by welding is generated on the surface and the aesthetic appearance is impaired. Therefore, it is necessary to remove the oxide film by acid pickling. is there. However, the ferritic stainless steel disclosed in Patent Document 1 has a problem that the oxide film of the welded portion is difficult to be removed by pickling.

In view of such circumstances, the present invention is excellent in surface properties, and not only the same steel type but also different steel types, especially when used welded to SUS304, a ferrite system excellent in corrosion resistance and pickling properties of the welded portion. It aims to provide stainless steel.

When the inventors add an appropriate amount of Si, the precipitation of titanium carbonitride is promoted in the initial stage of solidification, the size of the precipitate is reduced, and the problem of titanium stringers can be solved. It has been found that the formation of the film is suppressed and the oxide film is easily removed by pickling after welding. Furthermore, it has been found that sensitization can be prevented by precipitating a martensite phase in a TIG weld with SUS304 by optimizing the amount of Cr added.

This ensures good surface quality from hot-rolled, annealed and pickled steel sheets with good corrosion resistance and without surface grinding (colding). It has been found that a ferritic stainless steel having good corrosion resistance and pickling properties of a TIG weld with SUS304 can be obtained.

The present invention has been made based on the above findings, and the gist thereof is as follows. In addition, all component% is the mass% (mass%).

[1] C: 0.010% or less, Si: 0.15 to 0.60%, Mn: 0.5% or less, P: 0.04% or less, S: 0.01% or less, Al: 0. 2% or less, Cr: 17.0 to 19.0%, Cu: 0.3 to 0.5%, Ni: 0.6% or less, Ti: 0.10 to 0.20%, N: 0.015 %, C + N: 0.02% or less, consisting of the remaining Fe and inevitable impurities and satisfying the following formula (1).
Ti% / (C% + N%) ≧ 8 (1)
[2] In addition to the above component composition, the composition further contains one or two selected from Ca: 0.0005 to 0.0020% and B: 0.0003 to 0.0020%. The ferritic stainless steel according to [1] above.

[3] The ferritic stainless steel according to the above [1] or [2], which further satisfies the following formula (2) in addition to the component composition.
Si% / Ti% ≧ 1.3 (2)
[4] The ferritic stainless steel according to the above [1] to [3], which satisfies the following formula (3) in addition to the component composition.
Si% / Cr% ≧ 0.013 (3)

According to the present invention, ferritic stainless steel having good corrosion resistance of the welded portion can be obtained not only between the same steel types but also when used with different steel types, particularly SUS304. Moreover, the stainless steel plate of the present invention can prevent generation of titanium stringers by adding an appropriate amount of Si. Therefore, surface grinding with a hot-rolled sheet for preventing the generation of titanium stringers is not necessary, and the production can be performed at a low cost. Furthermore, a good appearance can be obtained by easily removing the oxide film formed on the welded portion by pickling.

Hereinafter, the reasons for limitation of each component of the present invention will be described.

[Ingredient composition]
First, the reason for defining the component composition of the steel of the present invention will be described. In addition, all the component% is the mass%.

C: 0.010% or less, N: 0.015% or less, C + N: 0.02% or less C and N are desirable because they reduce the corrosion resistance of the welded portion. C: 0.010% or less, N: 0 0.15% or less, C + N: 0.02% or less.

Si: 0.15-0.60%
Si is an element necessary for controlling the precipitation of titanium carbonitride and improving the surface properties. However, if the amount is less than 0.15%, the effect cannot be obtained, and if added in a large amount, the workability and pickling properties during cold-rolled sheet annealing are lowered, so the Si amount is in the range of 0.15 to 0.60%. To do. Preferably it is 0.20 to 0.50% of range. More preferably, it is in the range of 0.20 to 0.40%.

Mn: 0.5% or less Although Mn has a deoxidizing action, it is desirable that the addition amount be low because it forms sulfides in the steel and significantly reduces the corrosion resistance. .5% or less. However, if the amount of Mn is too small, inclusions increase, so the content is preferably in the range of 0.1 to 0.4%.

P: 0.04% or less P is preferably smaller in terms of hot workability, and is 0.04% or less.

S: 0.01% or less S is preferably smaller in terms of hot workability and corrosion resistance, and is 0.01% or less. Preferably, it is 0.006% or less.

Al: 0.2% or less Al is an effective component for deoxidation, but excessive addition causes surface flaws due to an increase in Al-based non-metallic inclusions and lowers workability. % Or less. Al is preferably 0.06% or less because it lowers the welding efficiency.

Cr: 17.0 to 19.0%
Cr is effective in improving the corrosion resistance, and in order to obtain good corrosion resistance, addition of 17.0% or more is necessary, but addition exceeding 19.0% is martensite in the TIG welded portion with SUS304. As a result, no reduction of corrosion resistance can be prevented, so the Cr content is in the range of 17.0 to 19.0%. Preferably it is 17.5 to 18.5% of range. More preferably, it is in the range of 18.0 to 18.5%.

Cu: 0.3 to 0.5%
Cu is an element necessary for ensuring corrosion resistance, and for that purpose, it is necessary to add at least 0.3% or more. However, when it exceeds 0.5%, hot workability deteriorates. Therefore, the Cu amount is set to a range of 0.3 to 0.5%.

Ni: 0.6% or less Ni is effective in improving corrosion resistance, but is an expensive element and may cause stress corrosion cracking when added in excess of 0.6%. , 0.6% or less. Preferably it is 0.4% or less.

Ti: 0.10 to 0.20%, Ti% / (C% + N%) ≧ 8
Ti is an indispensable component for ensuring the corrosion resistance of the welded portion, and it is necessary to add Ti% / (C% + N%) ≧ 8 at 0.10% or more. However, if it exceeds 0.20% and is added excessively, the surface properties of the hot-rolled sheet are deteriorated. Therefore, the Ti amount is in the range of 0.10 to 0.20%. In order to ensure the corrosion resistance of the welded portion, it is desirable that Ti% / (C% + N%) ≧ 10.

The above is the basic chemical component of the present invention, but one or two of Ca and B can be further added.

Ca: 0.0005 to 0.0020%
Ca is an effective component for preventing choking of CC nozzles due to precipitation of Ti-based inclusions that are likely to occur during continuous casting. If it is less than 0.0005%, the effect is not obtained, and if it exceeds 0.0020%, the corrosion resistance is lowered. Therefore, the Ca content is set in the range of 0.0005 to 0.0020%.

B: 0.0003 to 0.0020%
B is effective in preventing low temperature secondary working embrittlement. If the content is less than 0.0003%, the effect is not obtained. If the content exceeds 0.0020%, the hot workability deteriorates, so the B content is in the range of 0.0003 to 0.0020%. Preferably it is 0.0003 to 0.0010% of range.

The remainder other than the above is Fe and inevitable impurities. As an example of impurities, V and Co may be mixed from Cr ore (ore), but if mixed, the steel becomes hard and the workability deteriorates.

Si% / Ti% ≧ 1.3
When the amount of Ti added is large, large titanium carbonitride precipitates and the surface properties tend to deteriorate. Therefore, when the amount of Ti added is large, it is necessary to increase the amount of Si added to further promote the precipitation of titanium carbonitride at the initial stage of solidification and prevent the precipitation of large titanium carbonitride. For this reason, Si addition of Si% / Ti% ≧ 1.3 is desirable.

Si% / Cr% ≧ 0.013
When stainless steel is welded, an oxide film is formed on the surface and the aesthetic appearance is impaired. In many applications, this oxide film must be removed by pickling. However, ferritic stainless steel having a high Cr content produces an oxide film containing a large amount of Cr oxide, which is difficult to remove by pickling. Therefore, since Si is more easily oxidized than Cr, increasing the ratio of Si content to Cr content, increasing the amount of Si oxide generated, and suppressing the formation of Cr oxide will remove the oxide film by pickling. I found it easier to do. In order to obtain this effect, Si% / Cr% ≧ 0.013 is desirable.

[Production method]
Next, the manufacturing method of the ferritic stainless steel sheet excellent in the corrosion resistance, pickling property and surface property of the welded portion of the present invention will be described.

As a highly efficient production method of the steel of the present invention, continuous casting is performed on a slab, and the steel is heated to 1100 to 1250 ° C. and hot-rolled to obtain a hot-rolled coil. This is annealed at a temperature of 800 to 1000 ° C. in a continuous annealing / pickling line for hot rolling and pickling. Next, a method of performing cold rolling and finish annealing and pickling as a cold-rolled sheet is recommended. Details are as follows.

First, the above chemical range is achieved by secondary refining by converter, electric furnace, etc. and strong stirring / vacuum oxygen decarburization (Vacuum Oxygen Decarburization) or argon / oxygen decarburization (Argon-Oxygen Decarburization). The adjusted molten steel is melted. Next, the slab is melted from the molten steel by continuous casting or ingot casting. The casting method is preferably continuous casting in terms of productivity and quality.

The slab obtained by casting is heated to 1100 to 1250 ° C, hot-rolled, annealed at a temperature of 800 to 1000 ° C, and then pickled. In order to obtain good mechanical properties and workability, the hot-rolled sheet annealing temperature is preferably 850 to 950 ° C.

The pickled hot-rolled sheet becomes a cold-rolled annealed sheet through the steps of cold rolling, finish annealing, cooling, and pickling.

The rolling reduction during cold rolling is preferably 50% or more in order to ensure mechanical properties such as extensibility, bendability and press formability. Further, the cold rolling may be performed once or twice or more cold rolling including intermediate annealing. The steps of cold rolling, finish annealing, and pickling may be repeated.

Furthermore, cold rolled sheet annealing and pickling are performed in a cold rolled sheet continuous annealing line. Further, if necessary, annealing may be performed with a bright annealing line.

A ferritic stainless steel having the composition of Invention Examples A1 to A5 and Comparative Examples C1 to C5 shown in Table 1 was melted in a 30 kg steel ingot, heated to a temperature of 1150 ° C. and hot-rolled to obtain a plate thickness A 4.0 mm hot-rolled sheet was used. Next, after annealing in an argon gas atmosphere at 950 ° C., cold rolling was performed to produce a cold-rolled sheet having a thickness of 0.8 mm. Next, annealing was performed at 930 ° C. in an argon gas atmosphere, and pickling was performed using a mixed acid of hydrofluoric acid and nitric acid.

With respect to Invention Examples A1 to A5 and Comparative Examples C1 to C5 obtained as described above, the surface was polished with No. 600 polishing paper (polished to # 600 finish) to obtain test materials.

A salt spray cycle test (salt spray cyclic corrosion test) was performed on the test material in accordance with JIS H8502. Salt spray cycle test: 5% NaCl spray (35 ° C, 2 hr) (spraying 5% NaCl aqueous solution at 35 ° C, 2hr) → drying (60 ° C, 4hr, relative humidity 20-30%) (drying at 60 ° C, 4hr, として relative humidity 20 to 30%) → wet (40 ℃, 2hr, relative humidity of 95% or more) (wetting at 40 ℃, 2hr, relative humidity 95% or more) was performed for 15 cycles.

Next, a TIG weld corrosion resistance test with the same steel type was performed on the remaining specimens excluding C1. In this test, two plates taken from each test material were joined by TIG welding, their surfaces were polished with No. 600 abrasive paper, and then the above-mentioned salt spray cycle test was conducted for 15 cycles to improve the corrosion resistance. Examined.

Next, a different steel type TIG weld corrosion resistance test with SUS304 was performed on the remaining specimens excluding C1, C2, and C3. In this test, a plate taken from each test material and SUS304 having a thickness of 0.8 mm were joined by TIG welding, their surfaces were polished with No. 600 abrasive paper, and then the above-mentioned salt spray cycle test was repeated 15 cycles. The corrosion resistance was checked.
The results obtained as described above are shown in Table 1.

In Table 1, the criteria for each test are as follows.
(1) Salt spray cycle test result: The rusting area after the 15-cycle test was determined to be less than 20% as ◯ (pass) and 20% or more as x (fail).
(2) Corrosion resistance test result of the same material (same steel type) TIG welded part: After performing TIG butt welding with the same steel type and polishing the surface with No. 600 abrasive paper, after 15 cycles of salt spray cycle test As for the rusting rate of a welded part (weld metal and heat affected zone (Heat Affected Zone)), less than 20% was judged as ◯ (passed), and 20% or more was judged as x (failed).
(3) Corrosion resistance test result of different steel type TIG welded part with SUS304: SUS304 and TIG butt welding were performed, and the surface was polished with No. 600 polishing paper. Thereafter, the rusting rate of the welded part after 15 cycles of the salt spray cycle test was determined to be less than 20% (good) and 20% or more as x (failed).

In TIG welding of (2) and (3), Ar gas is flowed as shielding gas on both the front and back surfaces, no filler metal is used, and the width of the back bead is about the plate thickness. I went to be. These welding conditions are welding speed: 600 mm / min, welding voltage: 10 to 12 V, welding current: 70 to 110 A, shielding gas amount: Table 10 liter / min, back 5 liter / min.

In the salt spray cycle test, Comparative Example C1 having a low Cr content of 16.5% had a large rusting area and poor corrosion resistance. In the same steel type TIG welded part corrosion resistance test, C2 with a low Ti content of 0.07% and C3 with a low Ti% / (C% + N%) of 6.2 had a large rusting area and poor corrosion resistance. . In the different steel type TIG weld corrosion resistance test with SUS304, Comparative Example C4 with a high Cr addition amount of 19.4% and Comparative Example C5 of the ferritic stainless steel sheet disclosed in Patent Document 1 have a large rusting area. Corrosion resistance was poor.

From the above, it has been clarified that in the examples of the present invention, the corrosion resistance of the base metal, the same steel type TIG welded portion corrosion resistance, and the different steel type TIG welded portion corrosion resistance with SUS304 are excellent.

Ferritic stainless steel having the composition of Invention Examples B1 to B6 and Comparative Examples D1 to D4 (D4 is a ferritic stainless steel disclosed in Patent Document 1) shown in Table 2 is melted at 150 ton VOD, and then continuously cast. Cast into a slab. This was heated to a temperature of 1150 ° C. and hot-rolled to obtain a hot-rolled coil having a plate thickness of 4.0 mm.

Next, after annealing in a combustion gas atmosphere at 950 ° C., pickling is performed using sulfuric acid, followed by pickling using a mixed acid of hydrofluoric acid and nitric acid to perform hot rolling annealing pickling. A coil was used. Next, after cold rolling to a thickness of 0.8 mm and annealing in a combustion gas atmosphere at 930 ° C., neutral salt electrolysis is performed, followed by mixed acid of hydrofluoric acid and nitric acid. The pickling used was made into a cold-rolled annealed pickling coil. The surface properties of the obtained cold-rolled annealed pickling plate were visually determined.

Furthermore, the surface of the obtained cold-rolled annealed pickling plate was polished with No. 600 polishing paper to obtain a test material. In the same manner as in Example 1, a salt spray cycle test according to JIS H 8502, the same steel type TIG welded part corrosion resistance test, and the different steel type TIG welded part corrosion resistance test with SUS304 were conducted.

Table 2 shows the results obtained as described above.

In Table 2, the criteria for each test are as follows.
(1) Salt spray cycle test result: The rusting area after the 15-cycle test was determined to be less than 20% as ◯ (pass) and 20% or more as x (fail).
(2) Corrosion resistance test result of the same steel type TIG welded part: After performing TIG butt welding with the same steel type and polishing the surface with No. 600 abrasive paper, the rusting rate of the welded part after 15 cycles of the salt spray cycle test, Less than 20% was judged as ○ (pass), and 20% or more was judged as × (fail).
(3) Corrosion resistance test result of different steel type TIG welded part with SUS304: SUS304 and TIG butt welded, the surface was polished with No. 600 abrasive paper, and the rusting rate of the welded part after 15 cycles of salt spray cycle test Less than 20% was judged as ◯ (passed), and 20% or more was judged as x (failed).
(4) Surface properties of cold-rolled annealed pickling plates: Length of surface defects (shape defects or color defects due to linear scab or stringers) (less than 1 m) Was converted to 1 m) with respect to the total length of the plate, and the defect rate was less than 10% as ◯ (pass), and 10% or more as x (fail).

The TIG welding of (2) and (3) was performed such that Ar gas was flowed as a shielding gas on the front and back surfaces, no filler material was used, and the width of the back bead was about the plate thickness. The welding conditions are: welding speed: 600 mm / min, welding voltage: 10 to 12 V, welding current: 70 to 110 A, shielding gas amount: table 10 liter / min, back 5 liter / min.

The determination results of the surface properties were as follows: Comparative Example D1 with a low Si addition amount of 0.07%, Comparative Example D2 with a high Ti addition amount of 0.28% and Comparative Example D4 with a high amount of 0.29%, and Cu addition amount of 0 In Comparative Example D3, which was as high as 0.55%, the surface properties of the cold-rolled annealed pickled plates were all inferior. On the other hand, the inventive examples B1 to B6 all had excellent surface properties. Regarding the salt spray cycle test, the same steel type TIG welded portion corrosion resistance test, and the different steel type TIG welded portion corrosion resistance test with SUS304, the inventive examples B1 to B6 showed good corrosion resistance in any of the tests.

Ferritic stainless steels having compositions of Invention Examples E1 to E10 and G1 to G6 shown in Table 3 were melted at 150 ton VOD, and then cast into a slab by continuous casting. Note that the B amount of E3 and E6, the Ca amount, the B amount of E9 and G4, and the Ca amount of G6 are all inevitable impurity level contents. Each slab was heated to a temperature of 1150 ° C. and hot-rolled to form a hot-rolled coil having a plate thickness of 4.0 mm. Subsequently, after annealing in a combustion gas atmosphere at 950 ° C., pickling was performed using sulfuric acid, followed by pickling using a mixed acid of hydrofluoric acid and nitric acid to obtain a hot rolled annealing pickled coil. Next, after cold rolling to a sheet thickness of 1.2 mm and annealing in a combustion gas atmosphere at 930 ° C., neutral salt electrolysis is performed, followed by pickling using a mixed acid of hydrofluoric acid and nitric acid, A cold-rolled annealed pickled coil was obtained.

At this stage, the surface properties of the obtained cold-rolled annealed pickling plate were visually determined. When the plate thickness is reduced by cold rolling, the titanium stringers on the surface are stretched and become assimilated with the surroundings so that they are not noticeable. In Example 2, the plate thickness was set to 0.8 mm by cold rolling, but in Example 3, the thickness was set to 1.2 mm, which is a condition for easily detecting the presence of titanium stringers. Furthermore, the surface of the obtained cold-rolled annealed pickling plate was polished with No. 600 polishing paper to obtain a test material. In the same manner as in Examples 1 and 2, a salt spray cycle test according to JIS H 8502, a TIG welded part corrosion resistance test of the same material, a TIG welded part corrosion resistance test with SUS304, and a new TIG welded pickling test were performed. .
The results obtained as described above are shown in Table 3.

In Table 3, the criteria for each test are as follows.
(1) Salt spray cycle test result: The rusting area after the 15-cycle test was determined to be less than 20% as ◯ (pass) and 20% or more as x (fail).
(2) Corrosion resistance test result of the same steel type TIG welded part: After performing TIG butt welding with the same steel type and polishing the surface with No. 600 abrasive paper, the rusting rate of the welded part after 15 cycles of the salt spray cycle test, Less than 20% was judged as ○ (pass), and 20% or more was judged as × (fail).
(3) Corrosion resistance test result of different steel type TIG welded part with SUS304: After performing butt welding of different steel type TIG welded with SUS304 and polishing the surface with No. 600 abrasive paper, the welded part after 15 cycles of salt spray cycle test When the rust ratio was less than 20%, it was judged as ◯ (passed) and 20% or more as x (failed).
(4) Surface properties of cold-rolled annealed pickling plates: The total length of the length (less than 1 m is converted to 1 m) of the portion with surface defects (shape anomalies and white streak pattern color anomalies due to line shaving and stringers) A defect rate of less than 3% was judged as ◎ (passed, particularly excellent), 3% or more but less than 10% was judged as ◯ (passed), and 10% or more was judged as x (failed).
(5) TIG welded portion pickling test: TIG butt welding was performed between the same steel types and immersed in a mixed acid solution of hydrofluoric acid and nitric acid at 20 ° C. (5% hydrofluoric acid, 35% nitric acid). The removal of the oxide film was observed every 10 minutes by pulling it up from the acid solution and rubbing the oxide film on the welding front side (the surface directly exposed to the welding arc) with a nylon brush. ◎ (particularly excellent) that the oxide film was able to be removed in the total immersion time of 30 minutes or less, ○ (passed) that was able to be removed in excess of 30 minutes to 120 minutes or less, even if the immersion was over 120 minutes What remained was judged as x (failed).

In TIG welding of (2), (3) and (5), Ar gas is flowed as a shielding gas on both the front and back surfaces, no filler material is used, and the width of the back bead is about the plate thickness. went. These welding conditions are: welding speed: 600 mm / min, welding voltage: 10 to 12 V, welding current: 80 to 120 A, shielding gas amount: table 10 liter / min, back 5 liter / min.

The determination result of the surface property is Si% / Ti% ≧ 1.3. E1 to E10 were particularly excellent with a surface defect rate of less than 3%. G1 to G6 with Si% / Ti% <1.3 passed the surface defect rate of 3% or more and less than 10%. Thus, Si% / Ti% ≧ 1.3 is effective for improving the surface properties.

As a result of determination of pickling property of the TIG welded part, E2, E4 to E10, G1, and G2 with Si% / Cr% ≧ 0.013 were particularly excellent when the pickling time was 30 minutes or less. E1, E3, and G3 to G6 with Si% / Cr% <0.013 passed the pickling time exceeding 30 minutes and not exceeding 120 minutes. Thus, Si% / Cr% ≧ 0.013 is effective in improving the pickling property of the surface slope film of the TIG welded part.

E1 to E10 and G1 to G6 showed good corrosion resistance in the salt spray test, the same steel type TIG welded portion corrosion resistance test, and the different steel type TIG welded portion corrosion resistance test with SUS304.

It is suitable as a member that requires corrosion resistance, mainly for furniture, kitchen equipment, interior / exterior materials for buildings, construction hardware, elevator / escalator interior materials, home appliances, automobile parts, and the like.

Claims

In mass%, C: 0.010% or less, Si: 0.15 to 0.60%, Mn: 0.5% or less, P: 0.04% or less, S: 0.01% or less, Al: 0 0.2% or less, Cr: 17.0 to 19.0%, Cu: 0.3 to 0.5%, Ni: 0.6% or less, Ti: 0.10 to 0.20%, N: 0.0. A ferritic stainless steel containing 015% or less, C + N: 0.02% or less, consisting of the balance Fe and inevitable impurities and satisfying the following formula (1).
Ti% / (C% + N%) ≧ 8 (1)
Here, C%, N%, and Ti% represent the contents (mass%) of C, N, and Ti, respectively.
In addition to the component composition, the composition further contains one or two kinds selected from Ca: 0.0005 to 0.0020% and B: 0.0003 to 0.0020% by mass%. The ferritic stainless steel according to claim 1.
The ferritic stainless steel according to claim 1 or 2, further satisfying the following formula (2) in addition to the component composition.
Si% / Ti% ≧ 1.3 (2)
Here, Si% and Ti% represent the contents (mass%) of Si and Ti, respectively.
The ferritic stainless steel according to claim 1, further satisfying the following formula (3) in addition to the component composition.
Si% / Cr% ≧ 0.013 (3)
Here, Si% and Cr% represent the contents (mass%) of Si and Cr, respectively.
The ferritic stainless steel according to claim 2, wherein, in addition to the component composition, the following formula (3) is satisfied.
Si% / Cr% ≧ 0.013 (3)
Here, Si% and Cr% represent the contents (mass%) of Si and Cr, respectively.
The ferritic stainless steel according to claim 3, wherein, in addition to the component composition, the following formula (3) is satisfied.
Si% / Cr% ≧ 0.013 (3)
Here, Si% and Cr% represent the contents (mass%) of Si and Cr, respectively.