WO2009110641A1

WO2009110641A1 - Ferritic stainless steel with excellent heat resistance and toughness

Info

Publication number: WO2009110641A1
Application number: PCT/JP2009/054707
Authority: WO
Inventors: 加藤康; 平田知正; 中村徹之; 宇城工
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2008-03-07
Filing date: 2009-03-05
Publication date: 2009-09-11
Also published as: JP5387057B2; KR20130049835A; EP2264202A4; KR20100105800A; ES2519716T3; EP2264202A1; EP2264202B1; CN101965415A; RU2443796C1; US20110123387A1; TWI431122B; BRPI0909643A2; JP2009235573A; TW200946694A; CN101965415B

Abstract

Provided is a ferritic stainless steel having excellent thermal fatigue characteristics and oxidation resistance, without the addition of expensive elements such as molybdenum and tungsten, and having toughness equivalent to or greater than that of Type 429. Specifically, the ferritic stainless steel has, by mass: no more than 0.015% carbon, no more than 0.5% silicon, no more than 0.5% manganese, no more than 0.04% phosphorus, no more than 0.006% sulfur, no more than 16% to 20% chromium, no more than 0.015% nitrogen, between 0.3% and 0.55% niobium, no more than 0.1% titanium, no more than 0.1% molybdenum, no more than 0.1% tungsten, between 1.0% and 2.5% copper, and between 0.2% to 1.2% aluminum, with the remainder comprising iron and unavoidable impurities.

Description

Specification

Ferritic stainless steel with excellent heat resistance and toughness

The present invention relates to a Cr-containing steel, and in particular, an exhaust pipe of a motor vehicle, a exhaust case of a motorcycle, a converter case, and a thermal electric power plant. High heat resistance (thermal fatigue resistance, oxidation resistance) suitable for exhaust system members used in high-temperature environments such as ducts (exhaust air duct) and base metal The present invention relates to ferritic stainless steel having excellent toughness. Background art

Exhaust manifolds, exhaust pipes, compressor cases, mufflers, and other exhaust system members used in the exhaust system environment of automobiles are subject to thermal fatigue, rawness and oxidation resistance (hereinafter referred to as “exhaust manifold”). Both specialties are collectively referred to as “heat resistance.”) In applications where such heat resistance is required, Nb and Si are now added, for example, Cr-containing such as Ty pe 429 (14 C r -0.9 S i -0.4 Nb series) A lot of steel is used. However, as the engine performance improves, the exhaust gas temperature (exhaust gas temperature) rises to a temperature exceeding 900 ° C. It was.

To solve this problem, Cr-containing steel with improved high temperature proof stress by adding Nb and Mo, and SUS 444 (19 9 Cr −0. 2Nb-1.8Mo), ferritic stainless steels with addition of Nb, Mo and W have been developed (see, for example, Japanese Patent Application Laid-Open No. 2004-018921). However, due to the unusually high price of rare metal raw materials such as Mo and W in recent years, the development of materials having equivalent heat resistance using inexpensive raw materials has been required.

As a material with excellent heat resistance without using expensive elements such as Mo and W For example, WO 2003/004714 pamphlet has 10-20 mass% Cr steel, Nb: 0.5 Oma ss% or less, Cu: 0.8-2 Oma ss%, V

: Ferritic stainless steel for automobile exhaust gas flow channel members with 0.03 to 0.2 Oma ss% added, and Japanese Patent Application Laid-Open No. 2006-1 1 7985 discloses 10 to 20 ma ss% Cr steel. T i: 0.05 to 0.30 ma ss%, Nb: 0.1 to 0.60 ma ss%, Cu: 0.8 to 2. Oma ss%, B: 0.0005 to 0.02 ma ss% Ferritic stainless steel with excellent thermal fatigue properties with the addition of

No. 7355 discloses ferritic stainless steel for automotive exhaust system parts in which Cu: 1 to 3 mass% is added to 15 to 25 nxas s s% Cr steel. All of these steels are characterized by improved thermal fatigue properties by adding Cu.

However, according to the researches of the inventors, when Cu is added as in the techniques of Patent Documents 2 to 4 above, although the heat fatigue resistance is improved, the oxidation resistance of the steel itself is rather low. As a whole, it has become clear that heat resistance deteriorates. Also SUS

444 has a higher Cr content than Ty ρ e 429, and a large amount of Mo was added, so that the toughness of the base metal was inferior.

Therefore, the object of the present invention is to develop a technique for preventing the decrease in oxidation resistance due to the addition of Cu, thereby improving thermal fatigue characteristics and oxidation resistance without adding expensive elements such as Mo and W. It is to provide a ferritic stainless steel having excellent toughness equivalent to or better than that of Type 429. Here, “excellent oxidation resistance and thermal fatigue characteristics J” as used in the present invention means that it has the same or better characteristics than SUS 444. Specifically, the oxidation resistance is 9

Oxidation resistance at 50 ° C and thermal fatigue characteristics are 100 ° C-8 Repeated thermal fatigue characteristics between 50 ° C and SUS 444 are equivalent or better. The toughness equivalent to Ty pe 429 means that the brittle fracture surface ratio of a cold-rolled sheet with a thickness of 2 mm when it is subjected to a Charpy impact test at 140 ° C is equivalent to Ty pe 429. Disclosure of the invention In the present invention, C: 0.0 15 mass% or less, S i.: 0.5 mass% or less, Mn: 0.5 mass% or less, P: 0.04 mass% or less, S: 0.006 mass % Or less, Cr: 16 to 20 mass% or less, N: 0.015 mass% or less, N b: 0.3 to 0.55 mass%, T i: 0.01 mass% or less, Mo: 0.1 mass% or less, W: 0.1 mass% or less, Cu: l. 0 to 2.5 mass%, A 1: 0.2 to 1.2 mass%, the balance being Fe and Ferritic stainless steel made of inevitable impurities.

In addition to the above component composition, the fluorescent stainless steel of the present invention further includes B: 0.003 mass% or less, REM: 0.08 mass% or less, Zr: 0.5 mass% or less, V: It is characterized by containing one or more selected from 0.5 mass% or less, Co: 0.5 mass% or less, and Ni: 0.5 mass% or less.

According to the present invention, heat resistance (thermal fatigue characteristics, oxidation resistance) equal to or higher than that of SUS 444 without adding expensive Mo or W, and Ty pe 429 (representative components are steels in Table 1) Ferritic stainless steel with toughness equivalent to or better than No. 24) can be obtained at low cost. Therefore, the steel of the present invention is suitable for use in automobile exhaust system members. Brief Description of Drawings

Fig. 1 is a diagram illustrating a thermal fatigue test piece.

Fig. 2 is a diagram for explaining temperature and restraining conditions in a thermal fatigue test.

Figure 3: A graph showing the effect of Cu content on thermal fatigue properties.

Figure 4: A graph showing the effect of A 1 content on oxidation resistance (weight gain by oxidation).

Figure 5: A graph showing the effect of A 1 content on oxidation resistance (spoiling amounts of scale). Fig. 6: Graph showing the effect of Si content on oxidation resistance (scale peeling) Fig. 7: Graph showing the effect of Mn content on toughness (brittle fracture surface ratio) It is.

Fig. 8 is a graph showing the effect of A 1 content on toughness (brittle fracture surface ratio).

Figure 9: Graph showing the effect of Ti content on toughness (brittle fracture surface ratio). BEST MODE FOR CARRYING OUT THE INVENTION

The inventors have prevented the deterioration of oxidation resistance due to Cu addition in the prior art, and without adding expensive elements such as Mo and W, they have excellent thermal fatigue characteristics and oxidation resistance, and are also tough. In order to develop an excellent ferritic stainless steel, we have made extensive studies. As a result, Nb is changed from 0.3 to 0. & 3 3%, 〇11 in the range of 1.0 to 2.5 mass%, high high-temperature strength can be obtained in a wide temperature range, thermal fatigue characteristics can be improved, and addition of Cu The decrease in oxidation resistance can be prevented by adding more than 0.2 mass% of A 1. Therefore, by controlling Nb, Cu and A 1 within the proper range, Mo and W can be added. However, it was found that heat resistance (thermal fatigue characteristics, oxidation resistance) equivalent to or better than SUS444 was obtained. In addition, the peel resistance of Cu and A 1 added steels by repeated oxidation tests can be improved by optimizing the amount of Si (0.5 mass% or less), and the toughness is Mn, By optimizing the amount of A 1 and T i added (Mn: 0.5 mass% or less, Al: 1.2 mass% or less, T i: 0.0 1 mass% or less) And the present invention was completed.

First, the basic experiment that led to the development of the present invention will be described.

C: 0.005-0.007ina ss ^o / o, N: 0.004-0.006 ma ss%, Si: 0.3 mass% _N Mn: 0.2 mass%, C r: 17 mass% _s N b: 0.45 ma ss. Based on the composition of / o and A 1: 0.35 mass%, steel with various addition amounts of Cu was melted in the laboratory to obtain a 50 kg steel ingot. 1 1 1 After heating to 70 ° C, it was hot rolled to obtain a sheet bar having a thickness of 30 mm X width: 15 Omm. After that, this sheet bar was forged into a par with a cross section of 35 mm X 35 mm, annealed at a temperature of 1030 ° C, machined, and the thermal fatigue test specimen with the dimensions shown in Fig. 1 (thermal fatigue test specimen) ) Was produced. Then, as shown in Fig. 2, a thermal treatment was performed by repeatedly applying a heat treatment in which a restraint ratio was 0.35 at a temperature of 100 ° C-850 at 100 ° C-850, and the thermal fatigue life was measured. The thermal fatigue life is

Calculate the stress by dividing the load detected at 100 ° C by the cross section of the test piece soaking parallel section shown in Fig. 1, and calculate the stress of the previous cycle. In contrast, the minimum number of cycles was obtained when the stress was continuously reduced and reduced. This corresponds to the number of cycles in which cracks occurred in the specimen. For comparison, SUS 444 (C r:

A similar test was conducted on 18 m s s% -Mo: 2 m s s% -Nb: 0.5 m s s% steel.

Figure 3 shows the results of the thermal fatigue test. From this figure, by adding more than 1.0 mass% of 〇11, thermal fatigue life equal to or better than that of SUS 444 (about 1 100 cycles) can be obtained, thus improving thermal fatigue characteristics. It can be seen that it is effective to add Cu by lma ss% or more.

Next, C: 0.006 mass%, N: 0.00 mass Mn: 0.2 mass%, S i: 0.3 mass%, C r: 17 mass%, N b: 0.49 mass% And Cu: A steel composition based on a composition of 1.5 mass%, with various amounts of A 1 added to it, was melted in the laboratory to obtain a 50 kg steel ingot. Hot rolled, hot rolled sheet annealed, cold rolled, finished annealing, and finished into a cold rolled annealed sheet with a thickness of 2 mm. A 3 OmmX 20 mm test piece was cut out from the cold-rolled steel sheet obtained as described above, a 4πιιηφ hole was drilled at the top of the test piece, and the surface and end face were polished with # 320 emery paper, degreased. Later, it was subjected to the following test.

· Continuous oxidation test in air)>

The above test piece is kept in a furnace at 950 ° C in an air atmosphere for 300 hours and heated. The difference in the mass of the test piece before and after the test was measured, and the increase in oxidation per unit area (gZm ² ) was determined.

Using the above test piece, in the atmosphere, heat treatment was repeated for 100 cycles of 100 ° CX 1 min and 950 ° CX 25 min in. Heating and cooling were repeated 600 cycles, and the sample was peeled from the surface of the test piece due to the difference in mass before and after the test. The scale amount (g / m ² ) was measured. The heating rate and the cooling rate in the above test are 5 respectively. C / sec, 1.5 ° C / sec.

Figure 4 shows the measurement results of the increase in oxidation. Fig. 5 shows the measurement results of the amount of scale peeling. From these figures, by adding more than 0.2 mass% of A 1, oxidation resistance equal to or better than SUS 444 (oxidation increase: 27 gZm ² or less, scale peeling: less than 4 _g / in ² ) Is obtained.

Next, C: 0.006 mass%, N: 0.00 mass%, Mn: 0.2 mass%, A 1: 0.45 mass%, C r: 1 7 mass%, N b: 0. A steel with a composition of 49 mass%, Cu: 1.5 mass%, with various amounts of Si added, was melted in the laboratory to form a 50 kg steel ingot. Similarly, a cold-rolled annealed sheet with a thickness of 2 mm was used, and in the same manner as described above, a linear oxidation test was performed, and the amount of scale peeling was measured. The result is shown in FIG. From this, it was found that even when an appropriate amount of A 1 was added, when 3 1 exceeded 0.5%, scale adhesion decreased and the amount of peeling increased, and heat resistance equivalent to SUS 444 could not be obtained.

Finally, C: 0.006 ~ 0.007ma ss%, N: 0.00 6 ~ 0.00 00 7m ass%, S i: 0.3ma ss%, C r: 1 7ma ss%, Nb: 0. A 50 kg steel ingot was prepared by laboratory smelting steel with various contents of Mn, A 1 and Ti based on the composition of 45 mass% and Cu: 1.5 mass%. The steel ingot was hot-rolled, hot-rolled sheet annealed, cold-rolled, and finish-annealed to obtain a cold-rolled annealed sheet with a thickness of 2 mm. A sub-size Charpy impact test specimen was taken from this cold-rolled annealed plate and subjected to a Charpy impact test at a temperature of 40 ° C. The brittle fracture surface ratio was measured and the toughness was evaluated.

Figure 7 shows the effect of Mn content on toughness at A 1: 0.25 mass% and T i: 0.006 mass%. Figure 8 shows the effect of Mn: 0.1 mass% and Ti: 0. The effect of A 1 content on toughness at 0 05 ma ss%. Figure 9 shows the toughness of Ti content at A 1: 25 mass% and Mn: 0.1 mass%. It shows the effect on From these figures, to obtain toughness equivalent to or better than Ty pe 42 9, Mn: 0 · 3 mass% or less, A 1: 1 · 2 ma ss ° / ₀ or less, T i: 0.0 lma ss% It turns out that it must be:

The present invention has been completed by further studying the above findings.

Next, the component composition of the ferritic stainless steel of the present invention will be described.

C: 0. 01 5ma s s% or less

C is an element effective for increasing the strength of steel, but if it exceeds 0.015 mass%, the toughness and formability deteriorate significantly. Therefore, in the present invention, C is set to not more than 0.015 ma s s%. From the viewpoint of ensuring moldability, the lower the C, the better. The lower limit is preferably 0.008 ma s s%. On the other hand, in order to ensure the strength as an exhaust system member, C is preferably 0.001 lma s s% or more. More preferably, it is in the range of 0., 002 to 0.008 ma s s%.

S i: 0.5ma s s% or less

Si is added as a deoxidizer. It is preferable to add more than 0.05 mass%. In addition, Si has an effect of improving the oxidation resistance which is the main subject of the present invention, but cannot be as effective as A 1. On the other hand, as can be seen from FIG. 6, excessive addition of Si exceeding 0.5 mass% reduces the scale peel resistance and does not provide oxidation resistance equal to or better than SUS444. Therefore, the upper limit of S i is 0.5 ma s s%.

Mn: 0.5 ma s s. /. Less than

Mn is an element that increases the strength of steel and also has a function as a deoxidizer. It is preferable to add 0.05 mass% or more. However, excessive addition tends to generate <y phase at high temperatures, which reduces heat resistance. Also, as can be seen from Figure 7, 0.5ina s If added in excess of s%, a toughness equal to or higher than that of Type 4 29 cannot be obtained, and the object of the present invention cannot be achieved. Therefore, in the present invention, Mn is set to 0.5 mass% or less.

P: 0.04 ma s s% or less

P is a harmful element that lowers toughness and should be reduced as much as possible. Therefore, in the present invention, P is set to 0.04 mass% or less. Preferably, it is 0.03 mass% or less.

S: 0.006 s s% or less

S is a harmful element that lowers the elongation value and adversely affects the formability and lowers the corrosion resistance, which is a basic characteristic of stainless steel, so it is desirable to reduce it as much as possible. Therefore, in the present invention, S is set to 0.006 mass s s% or less. Preferably, it is 0.003 s s% or less.

C r: 1 6 ~ 20ma s s%

Cr is an important element effective for improving the corrosion resistance and oxidation resistance characteristic of stainless steel, but if it is less than 16 mass%, sufficient oxidation resistance cannot be obtained. On the other hand, Cr is an element that solidifies and strengthens steel at room temperature and hardens' low ductility.In particular, when it exceeds 20% by mass, the above-mentioned adverse effects become significant, and it is equivalent to or higher than Ty pe 429. The toughness cannot be obtained. Therefore: In the present invention, Cr is in the range of 16-20 mass%. Preferably, it is in the range of 16 to 19 mass%.

N: 0.0 1 5ma s s% or less

N is an element that lowers the toughness and formability of steel, and when the content exceeds 0.015 mass%, the above reduction becomes significant. Therefore, N is set to 0.01 5 ma s s% or less. Note that N is further reduced when higher toughness is required, and is preferably less than 0.010 mass%.

Nb: 0.3 to 0.55 s s%

Nb forms and fixes carbon nitride with C and N, has the effect of improving corrosion resistance and formability, and intergranular corrosion resistance of welds, and also increases the high temperature strength and improves thermal fatigue properties. It is an element that has fruit. Such an effect is recognized with addition of 0.3 mass% or more. 4707. On the other hand, if it exceeds 0.55 mass%, the Laves phase tends to precipitate and the brittleness decreases. Therefore, Nb is in the range of 0.3 to 0.55 mass%. Preferably, it is in the range of 0.4 to 0.5 ma ss%.

T i: 0. Olma s s% or less

T i is an element that easily binds to N and forms coarse T i N compared to Nb, and this coarse T i N acts as a notch and significantly reduces toughness. In particular, as shown in FIG. 9, this adverse effect becomes significant when the Ti content exceeds 0.01 mass%. Therefore, in the present invention, it is limited to T ¾0.0.1% or less.

Mo: 0. lma s s% or less

Mo is an expensive element and is not actively added for the purpose of the present invention. However, it may be mixed in less than 0.1 ma s s% from the raw material scrap. Therefore, Mo is set to 0.1 m a s s% or less.

W: Less than 0.1 ma s s% '

W is an expensive element like Mo, and is not actively added for the purpose of the present invention. However, it may be mixed in less than 0.1 ma s s% from raw materials such as scrap. Therefore, W is less than 0. lma s s%.

C u: 1.0 to 2.5 m a s s%

Cu is an extremely effective element for improving thermal fatigue properties. As shown in Fig. 3, it is necessary to add Cu in an amount of 1.0 mass% or more in order to obtain thermal fatigue characteristics equivalent to or better than SUS444. However, if the addition exceeds 2.5 mass%, ε-Cu precipitates during cooling after heat treatment, hardens the steel, and tends to cause embrittlement during hot working. More importantly, the addition of Cu improves the thermal fatigue resistance, but decreases the oxidation resistance of the steel itself, and overall, the heat resistance decreases. The cause of this is not sufficiently clear, but Cu is concentrated in the decreasing Cr layer immediately below the scale, which suppresses the re-diffusion of Cr, an element that improves the inherent oxidation resistance of stainless steel. It is thought to do. Therefore, Cu is in the range of 1.0 to 2.5 mass%. More preferably, it is in the range of 1.1 to 1.8 ma ss%. 4707

A 1: 0.2 to 1.2 ma s s%

As shown in Fig. 4 and Fig. 5, Al is an indispensable element for improving the oxidation resistance of Cu-added steel. In particular, in order to obtain an oxidation resistance equal to or higher than that of SUS 444, which is the object of the present invention, addition of 0.2 mass% or more is necessary. On the other hand, as shown in Fig. 8, if added over 1.2 mass%, the steel becomes hard and no toughness equivalent to Ty pe 42 9 can be obtained, so the upper limit is 1.2 mass% To do. Preferably, it is in the range of 0.3 to 1. Oma s s%.

In addition to the essential components described above, the ferritic stainless steel of the present invention further contains one or more selected from B, REM, Zr, V, Co and Ni in the following range. Can be added.

B: 0.00 3 ma s s% or less

B is an element effective for improving workability, particularly secondary workability. This remarkable effect can be obtained by addition of 0.005 5 mass% or more. However, if it exceeds 0.03 mass%, BN is formed and workability is lowered. Therefore, when adding B, it should be 0.003 mass s s% or less. More preferably, it is in the range of 0.0 0 0 5 to 0.002 ma s s%.

REM: 0.08 ma s s% or less, Z r: 0.5 m s s% or less

REM (rare earth element) and Zr are both elements that improve oxidation resistance, and can be added as necessary in the present invention. In order to obtain the effect, it is preferable to add 0.01 mass% or more and 0.05 mass% or more, respectively. However, the addition of more than 0.08 mass% of REM causes the steel to become brittle, and the addition of more than 0.5 mass% of Z 、 causes the Zr intermetallic compound to precipitate, making the steel brittle. Therefore, when adding REM, it should be less than 0.08 mass%, and when adding Zr, it should be less than 0.5 mass%.

V: 0.5ma s s% or less

V is an element effective for improving workability and oxidation resistance. In order to obtain an effect of improving oxidation resistance, V is preferably added in an amount of 0.15 mass% or more. Force and 0.5 mas Excessive addition exceeding s% precipitates coarse V (C, N) and degrades the surface properties. Therefore, when V is added, it is preferable to add 0.5 mass% or less, and it is preferable to add in the range of 0.15 to 0.4 mass%.

C o: 0.5ma s s% or less

Co is an element effective in improving toughness, and it is preferable to add 0.02 mass s s% or more. However, Co is an expensive element, and the above effect is saturated even when added in excess of 0.5 mass%. Therefore, when adding Co, it is preferable to be 0.5 mass% or less. More preferably, it is in the range of 0.02 to 0.2 ma s s%. N i: 0.5ma s s% or less

Ni is an element that improves toughness. In order to obtain the effect, 0.05 mass s s% or more is preferable. However, Ni is expensive and is a strong γ-phase-forming element, so it generates a γ-phase at high temperatures and reduces oxidation resistance. Therefore, when Ni is added, the content is preferably 0.5 mass% or less. More preferably, it is in the range of 0.05 to 0.4 ma s s%.

Next, the manufacturing method of the ferritic stainless steel of this invention is demonstrated.

The method for producing stainless steel of the present invention can be suitably used as long as it is an ordinary method for producing fluorescent stainless steel, and is not particularly limited. For example, steel is produced in a known melting furnace such as a converter or an electric furnace, or further subjected to secondary refinement such as ladle or vacuum refinement to obtain steel having the above-described component composition of the present invention, The molten steel is made into a steel slab (slab) by continuous forging or ingot lump rolling, hot-rolled to hot-rolled sheet, and subjected to hot-rolled sheet annealing as necessary. It is preferable to produce a cold-rolled annealed plate through steps such as pickling, cold rolling, finish annealing, and pickling. The cold rolling may be performed once or twice or more with intermediate annealing, and the steps of cold rolling, finish annealing, and pickling may be performed repeatedly. Further, depending on the case, the hot-rolled sheet annealing may be omitted, and when the gloss of the steel sheet surface is required, a skin pass may be applied after cold rolling or after finishing annealing. The slab heating temperature before hot rolling is 1000-1250 ° C, the hot-rolled sheet annealing temperature is 900-1100 ° C, and the final annealing temperature is 900-1 1 2 4707

A range of 0 ° C. is preferred. The ferritic stainless steel of the present invention obtained as described above is then subjected to processing such as cutting, bending, and pressing according to the respective use, and the exhaust pipe of an automobile car pie. It is considered as various exhaust system members used in high temperature environments such as a compressor case and an exhaust duct of a thermal power plant. The stainless steel of the present invention used for the above-mentioned member is not limited to a cold-rolled annealed plate, and may be used as a hot-rolled plate or a hot-rolled plate annealed, and further subjected to descaling as necessary. It may be used. In addition, the welding method for assembling the above-mentioned members is not particularly limited, and normal arc welding such as MIG (Metal Inert Gas), MAG (Metal Active Gas), TIG (Tungsten Inert Gas), or spot welding. Methods such as electric resistance welding such as welding and seam welding, high-frequency resistance welding used in electrical welding, high-frequency induction welding, and laser welding can be used. Example 1

Steel Nos. 1 to 27 having the composition shown in Table 1 were melted in a vacuum melting furnace, forged into 50 kg steel ingots, and forged into two parts. After that, one of the two steel ingots was heated to 1 1700 ° C and hot-rolled to form a hot-rolled sheet with a thickness of 5 mm, and annealed at a temperature of 1020 ° C. Washed, cold-rolled at a rolling reduction of 60%, finish annealed at a temperature of 1030 ° C, cooled at an average cooling rate of 20 ° CZ s, pickled and cold-rolled annealed plate with a thickness of 2 mm The samples were subjected to the following oxidation resistance test and impact test. For reference, S US 444, Type 429 and WO 2003/0047 No. 14 pamphlet shown in No. 28 to 32 of Table 1, JP 2006-1 1 7985, JP 2000-2 9 7355 As for the inventive steel of No. 1, a cold-rolled annealed plate was produced in the same manner as described above and subjected to the same evaluation test.

^ Daiance oxidation test in air)>

Cut a 30 mm x 20 mm sample from the various cold-rolled annealed plates obtained above, drill a 4 mm diameter hole at the top of the sample, polish the surface and edge with # 320 emery paper, and degrease After that, it was suspended in a furnace in an air atmosphere heated and maintained at 950 ° C. and held for 300 hours. After the test, measure the mass of the sample, and measure the mass before the test. The increase in oxidation (gZm ² ) was calculated. Each test was conducted twice, and the average oxidation resistance was evaluated for continuous oxidation resistance.

Cyclic oxidation test in air>

Cut out a sample of 3 OmmX 20 mm from the above various cold-rolled annealed plates, drill a 4 mm diameter hole on the top of the sample, polish the surface and end face with # 320 emery paper, degrease, and in the atmosphere Thus, an oxidation test was repeated in which the temperature was raised and lowered between 100 ° C and 950 ° C. The temperature rising and cooling rates were 5 ° CZsec and 1.5 ° C / sec, respectively, and the holding time was 100 ° C for 1 min and 950 ° C for 25 min, and this was performed for 600 cycles. For the evaluation of the resistance to repeated oxidation, the mass of the sample after the test was measured, the difference from the pre-test mass measured in advance was determined, and the scale peeling amount (g / m ² ) was determined. Each test was conducted twice, and the oxidation resistance was evaluated using the average value.

Kusanorepy Impact Test>

Three Charpy impact specimens with V-notches perpendicular to the rolling direction were sampled from each of the above cold-rolled annealed plates and subjected to a Charpy impact test at a temperature of 40 ° C. Was measured and the average value of the three was obtained to evaluate toughness.

Example 2

The remaining steel ingot of 50 kg copper ingot divided into two in Example 1 was heated to 1 1 70 ° C. and hot-rolled to obtain a sheet par of thickness: 3 OmmX width: 150 mm. The sheet par was then forged into a 35 mm par, annealed at a temperature of 1 030¾, machined, and processed into a thermal fatigue test piece with the dimensions shown in Fig. 1 for the following thermal fatigue test. Provided. As reference examples, as in Example 1, SUS 444, Type 429, and WO 2003/004714 pamphlet, Japanese Patent Application Laid-Open No. 2006-1-17985, and Japanese Patent Application Laid-Open No. 2000-297355. Similarly, a sample was prepared and subjected to a thermal fatigue test. <Thermal fatigue test> ■

In the thermal fatigue test, the thermal fatigue life was measured by raising and lowering the temperature between 100 ° C and 850 ° C with a restraint ratio of 0.35. At this time, the heating rate and the cooling rate are 10 ° O sec and the holding time at 100 ° C is 2 mi. n The holding time at 85 ° C. was 5 min. The thermal fatigue life is calculated by dividing the load detected at 100 ° C by the cross-sectional area of the soaking parallel part of the specimen and calculating the stress continuously. Therefore, the minimum number of cycles when the stress began to decrease was determined.

Table 2 summarizes the results of the atmospheric continuous oxidation test, the atmospheric repeated oxidation test, and the Charpy impact test of Example 1 and the thermal fatigue resistance test of Example 2. As is clear from Table 2, all of the steels of the inventive examples suitable for the present invention have oxidation resistance and thermal fatigue characteristics equal to or better than SUS 4 4 4, and It has toughness equal to or better than 29 and meets the goals of the present invention. On the other hand, comparative steels outside the scope of the present invention or prior art reference steels are not excellent in both oxidation resistance and heat fatigue resistance and toughness of the base metal. The target characteristics of the invention are not obtained. Industrial applicability

The steel of the present invention is not only suitable for exhaust system members such as automobiles, but is also suitable as a solid oxide type fuel cell member for an exhaust system member of a thermal power generation system that requires similar characteristics. Can be used.

Table 1 1 1

2

Reference example 1: Invention steel No.3 of WO2003 / 004714, Reference example 2: Invention steel No.7 of Kai 2006-117985, Reference example 3: Invention steel of Kai 2000-297355 o.5

TJP2009 / 054707 2

(Note) Reference example 1: Invention steel No. 3 of WO 2003/004714

Reference Example 2: Invention Steel No.7 of Kai 2006-117985

Reference Example 3: Invented steel No. 5 of Kai 2000-297355

Claims

The scope of the claims

1. C: 0.0 1 5 mass% or less, S i: 0.5 mass% or less, Mn: 0.5 mass% or less, P: 0.04 mass% or less, S: 0.006 mass% or less, C r: 1 6 ~ 2 Oma ss% or less, N: 0.0 1 5 mass% or less, N b: 0.3 ~ 0.55 mass%, T i: 0.0 1 mass% or less, Mo: 0 1 mass% or less, W: 0. 1 mass ⁰ /. The following is a ferritic stainless steel containing Cu: l. 0 to 2.5 mass% A1: 0.2 to 1.2 mass%, the balance being Fe and inevitable impurities.

2. In addition to the above component composition, B: 0.003 m s s% or less, REM: 0.08 m s s% or less, Z r: 0.5 m s s%. /. Or less, V: 0.5 mass% or less, C o: 0.5 mass% or less, Op N i: One or more selected from 0.5 mass% or less The ferritic stainless steel described.