JP2001059141A - Austenitic stainless steel and automotive exhaust system paprts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart excellent welding high temp. cracking resistance and high temp. salt damage corrosion resistance to steel by allowing it to contain respectively specified ratios of elements and specifying Nf value and a forming index. SOLUTION: Austenitic stainless steel contg., by weight, 0.004 to 0.07% C, 2.5 to 4.5% Si, 0.05 to 2% Mn, 14 to 21% Cr, 9 to 16% Ni, 0.005 to 0.1% N, 0 to <1.5% Cu, 0 to 0.25% Nb, 0 to 2% Mo and 0 to 0.003% B, and the balance Fe with inevitable impurities is prepd. At this time, the content of S in the impurities is controlled to <=0.01%, and P to <0.026%, also, as to P, Nf expressed by the inequality I satisfies -3<=Nf<=0.5, in the case the high temp. crack suppressing index Pf=0.02-0.005Nf, P <= Pf is satisfied, and the forming index If expressed by the inequality I satisfies If <=10, where the elemental symbols in the inequalities I and II denote the content (weight%) of each element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention is excellent in oxidation resistance at 1000 ° C. or less and hot cracking resistance at welding.
The present invention relates to an austenitic stainless steel having excellent resistance to high-temperature salt damage and corrosion, and a vehicle exhaust system component such as a flexible tube, an exhaust manifold, and an engine gasket made of the steel.

[0002]

2. Description of the Related Art Steel materials used as exhaust system members of automobiles are exposed to severe corrosive environments. Further, since the corrosive environment differs depending on the part of the exhaust system, the corrosive form differs in each part as described below.

That is, an exhaust manifold, a front center pipe, and the like are required to have excellent oxidation resistance, scale adhesion, and high-temperature strength in a temperature range up to about 1000 ° C. On the other hand, the muffler is required to have corrosion resistance to the condensed liquid generated by cooling the exhaust gas.

In a gasket for an automobile engine, durability against "stiffness" as a spring characteristic when heated to around 700.degree.
High temperature fatigue properties are required.

As described above, in the exhaust system of an automobile, different characteristics are required for each part, and different materials are applied.

[0006] The flexible pipe is 600-
Since the temperature rises to 700 ° C. and is exposed to a corrosive environment to which sodium chloride or calcium chloride such as rock salt used as a snow melting agent adheres, high-temperature salt damage corrosion resistance is required. Further, since the flexible pipe is attached for the purpose of absorbing the vibration of the engine in the exhaust system, the flexible pipe is subjected to bellows processing. The flexible pipe usually has a diameter of about 40 to 70 mm and a thickness of about 0,0 mm.
A thin ERW steel pipe of about 2 to 0.4 mm or TI
It is manufactured by using a G-welded steel pipe as a material and subjecting this material to bellows processing. Therefore, a welded steel pipe made of a material is required to have excellent formability that can withstand severe bellows processing, and a welded part is required to have workability equivalent to that of a base material. Furthermore, fatigue characteristics that can withstand repeated vibrations are also required.

[0007] Conventionally, from the viewpoint of resistance to high-temperature salt damage and corrosion, flexible pipes are mainly made of SUS X with an increased Si content.
Austenitic stainless steels represented by M15J1 have been used.

For example, Japanese Patent Publication No. 57-16187 and Japanese Patent Publication No. 58-42264 disclose 0.1% Si.
An austenitic stainless steel containing up to 5% by weight and suppressing S content to 0.003% or less to improve hot corrosion resistance is disclosed.

In Japanese Patent Publication No. 5-7458, the relationship between high-temperature corrosion resistance in the presence of chloride and the chemical composition of steel is analyzed by a multiple regression analysis method, and based on the obtained regression equation. An austenitic stainless steel with a determined chemical composition is disclosed. However, since all stainless steels have been developed with an emphasis on improving high temperature corrosion resistance, one of the major problems of high Si content steels is mechanical resistance such as high temperature cracking resistance and formability. The component design does not sufficiently satisfy the properties or the high temperature fatigue resistance characteristics.

[0010] In view of the above, recently, there is an increasing need to develop austenitic stainless steel which satisfies the above-mentioned performance and can meet the severe cost reduction required for automotive exhaust system materials.

[0011]

DISCLOSURE OF THE INVENTION The present invention has excellent resistance to high temperature cracking at welding, good resistance to salt damage and corrosion at high temperature, and excellent mechanical properties such as moldability and high temperature fatigue. It is an object of the present invention to provide an austenitic stainless steel and a vehicle exhaust system component suitable for a vehicle exhaust system member such as a flexible pipe having characteristics and excellent economic efficiency.

[0012]

The gist of the present invention is as follows.

(1) C: 0.004 to 0.0% by weight
7%, Si: 2.5 to 4.5%, Mn: 0.05 to 2
%, Cr: 14-21%, Ni: 9-16%, N: 0.
005 to 0.1%, Cu: 0 to less than 1.5%, Nb: 0
~ 0.25%, Mo: 0 ~ 2%, B: 0 ~ 0.003%
And S in the impurities is 0.01% or less, and P is 0.0% or less.
Is less than 26% and satisfies the following expression (1), and furthermore, N _f
Austenitic stainless steel whose value satisfies the following formula (2) and the forming index _If satisfies the following formula (3), and the balance is Fe and unavoidable impurities, and is excellent in welding hot cracking resistance and high temperature salt corrosion resistance. .

P ≦ P _f (1) -3.0 ≦ N _f ≦ 0.5 (2) I _f ≦ 10 (1)・ ・ ・ ・ (3) where P _f = 0.02-0.005N _f N _f = 30 (C + N) + 0.5Mn + Ni + 8.2-1.1 (1.5Si + Cr + Mo) I _f = 497-462 (C + N) -20 (Cu + Ni) -13.7Cr-8.1Mn-9.2Si-18.5M
o Element symbol: Content of each element (% by weight) (2) Above (1)
In addition to the austenitic stainless steel described in
a, an austenitic stainless steel excellent in weldability and high-temperature salt damage corrosion resistance containing one or two or more of REM and Mg in total of 0.0002 to 0.2%;

(3) A vehicle exhaust system component comprising the austenitic stainless steel according to (1) or (2).

Here, the vehicle exhaust system components are components used in a system through which exhaust gas from an automobile engine passes, and typical components include a flexible tube, an exhaust manifold, an engine gasket, and an exhaust gasket. Can be exemplified.

The present inventors have found that chlorides caused by snow-melting salt sprayed on the road adhere to the road, and high S salt corrosion resistance can be maintained in a high-temperature corrosive environment.
For i-containing austenitic stainless steels, with the aim of reducing alloying elements and increasing weld cracking resistance, which lead to increased costs, and improving mechanical properties such as formability required for steel used in flexible pipes and high temperature fatigue properties. , Research and development. As a result, the following findings were obtained.

(A) If a large amount of Si is contained in austenitic stainless steel in order to enhance high-temperature salt damage corrosion resistance, high-temperature cracking is likely to occur during welding.
This is because a P-based low-melting intermetallic compound is generated.

(B) By lowering the P content below the hot cracking suppression index ( _Pf ) described later, the hot cracking resistance can be drastically increased.

(C) In order to improve the high-temperature salt damage corrosion resistance in an environment where snow melting salt adheres, the Cr content is reduced, the C content is reduced, and the Si content is reduced as long as general corrosion resistance can be maintained. It is effective to increase the rate.

(D) For the purpose of cost reduction, steel in which alloying elements such as Cr and Ni are reduced as much as possible approaches a metastable austenitic stainless steel, so that martensitic transformation is likely to occur during processing. When the martensitic transformation occurs, the stainless steel hardens, so that the formability decreases. However, if a predetermined formability index (N _f ) described later is secured, the formability at room temperature required for bellows processing can be obtained.

(E) When the contents of C and Cr are reduced, the high-temperature strength is reduced, and thus sufficient high-temperature fatigue properties cannot be obtained. However, by including appropriate amounts of N and Nb in stainless steel, high-temperature strength higher than that of conventional stainless steel can be obtained. Also, the effect is large after aging,
High temperature fatigue characteristics can be dramatically improved.

(F) By adding Ca, REM, Mg, B, etc. to steel, corrosion resistance and hot workability can be improved. It is also very effective to reduce the amount of S in steel.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The chemical composition and each formula specified in the present invention will be described below. The percentages of the chemical compositions shown below represent% by weight.

Chemical composition: C: C is an extremely harmful element to high-temperature corrosion in a chloride-adhering environment. The reason is that when the steel is heated to a high temperature, Cr carbide precipitates at the crystal grain boundaries, which promotes intergranular corrosion. For high temperature salt corrosion,
Extremely harmful. Therefore, from the viewpoint of preventing intergranular corrosion, the upper limit of the C content is set to 0.07% by weight. However, if the C content is too low, the strength of the steel decreases, so the lower limit is 0.00 from the viewpoint of maintaining the required strength.
4%.

The upper limit is desirably about 0.03%, and more desirably about 0.02%. By setting such a lower limit, the high-temperature salt damage resistance can be remarkably improved.

Si: Si is an element effective not only as a deoxidizing agent but also for improving oxidation resistance. In addition, the content of 2.5% or more exerts an excellent effect on high-temperature corrosion resistance in a chloride-attached environment, and the high-temperature salt corrosion resistance improves with an increase in the Si content. The reason for this is considered to be that an oxide layer mainly composed of Si is formed at the boundary between the oxide scale layer formed on the surface of the steel and the base material, thereby preventing penetration of attached salts into the base material. On the other hand, the Si content is 4.
If it exceeds 5%, the steel becomes harder than necessary and the formability decreases. Therefore, the Si content is 2.5 to 4.5%.
And

Mn: Mn is an element effective for stabilizing the austenite phase and improving hot workability. But,
It is harmful to high-temperature corrosion resistance in an environment where chlorides adhere,
If it exceeds 2%, the high-temperature corrosion resistance is significantly reduced, so the upper limit is made 2% or less. The lower limit of Mn is set to 0.05% in order to obtain the above effects.

Cr: Cr is an important element that determines the corrosion resistance of the steel of the present invention. However, it is a harmful element to high-temperature corrosion in an environment where chlorides adhere. The reason is that Cr and Cr oxide react with chloride to form unprotected chromates (eg, Na ₂ CrO ₄ , CaCrO ₄ ), and in addition, free chlorine is formed at the grain boundaries. It is thought to erode. However, from the viewpoint of high-temperature oxidation resistance and salt-corrosion near room temperature, at least 14% is necessary. On the other hand, if it exceeds 21%, the high-temperature corrosion resistance in a chloride-adhering environment decreases and the cost increases, so the upper limit is set to 21%.

Ni: Ni is an element indispensable for stabilizing the austenite phase, and requires at least 9%. On the other hand, since it is an expensive element, the upper limit is preferably as low as possible. Ni has no significant effect on high-temperature corrosiveness in a chloride-attached environment, so its upper limit is 16%.
And

N: N is an element for stabilizing the austenite phase and has the effect of increasing the high-temperature strength of steel. To obtain the effect, 0.005% or more is required. However, if the N content is too high, the steel becomes hard,
The upper limit was set to 0.1% because the moldability deteriorated.

Cu: Cu is an element having a stabilizing effect on the austenite phase like Mn, and is it effective in improving hot workability? , If necessary. Also,
It also has the effect of improving high-temperature corrosion resistance or high-temperature strength in a chloride-adhered environment. However, when the content is 1.5% or more, the weldability and hot workability decrease, so that
Less than.

Nb: Nb is an optional element to be added as required. When Nb is contained, it has the effect of increasing the high-temperature strength of steel by solid solution strengthening. However, when the content is excessive, the steel is hardened, and the proof stress at room temperature may be too high and the elongation may be reduced. The most preferable condition for improving high-temperature strength without impairing mechanical properties such as formability at room temperature is that steel containing 0.03% or more of N contains 0.25% or less of Nb. That is.
That is, when Nb is contained, the high-temperature strength is improved at room temperature without increasing the proof stress. In particular, since the effect is remarkable after aging, the high-temperature fatigue characteristics can be significantly improved. The lower limit is preferably set to 0.03%. The reason is that steel containing 0.03% or more of N is 600 to
It is considered that when the temperature is maintained at 700 ° C. for a long time, fine Nb carbonitride precipitates in the crystal grains, and the high-temperature strength is improved by the precipitation strengthening action. When the amount of N in steel is as low as less than 0.03%, Nb can be contained at a higher level. The increase in high-temperature strength in this case is considered to be a solid solution effect as a substitutional element. To ensure good processability,
The upper limit is preferably set to 0.25%.

Mo: Mo is an element to be added as necessary, and has an effect of improving high-temperature corrosion resistance and high-temperature strength in a chloride-adhering environment. When the effect of adding Mo is required, it is preferable to set Mo to 0.5% or more. However, since Mo is expensive, the upper limit was set to 2%.

B: B has the effect of improving hot workability and remarkably improving "edge cracks", which are cracks on the end faces of hot-rolled coils, and is contained as necessary. However, an excessive content exceeding 0.003% causes solidification cracking.
The upper limit was made 0.003%.

Ca, REM and Mg: These elements have an effect of improving hot workability, and are contained as necessary. The total of one or more of these elements is 0.0002
%, The effect of improving hot workability is seen, but 0.2%
If it exceeds 300, hot workability will deteriorate. Therefore, when they are contained, these elements are added in a total amount of 0.0002 to 0.2.
%.

Al: Al is used as a deoxidizing agent,
It is mixed as an impurity at 0.2% or less.

S: S is a harmful element, and the lower the better, the better. If it exceeds 0.01%, the hot workability decreases, so the upper limit was made 0.01%.

P: Since P is a very harmful element, the lower the better, the better. If it exceeds 0.026%, the weldability is remarkably deteriorated, and the weld bead portion is liable to undergo hot cracking during welding. The reason why high-temperature cracking easily occurs when the amount of P is high is that remarkable enrichment of P and Si occurs in the final solidified portion, and a low-melting intermetallic compound of Ni-Si-P system is generated. By making the P content 0.026% or less and satisfying the following expression (1), it becomes possible to manufacture a thin-walled welded steel pipe while avoiding welding hot cracking.

P ≦ P _f ... (1) P _f is an exponential rule, which is an index for inhibiting hot cracking, expressed by the following equation.

P _f = 0.02-0.005N _f where N _f is N _f = 30 (C + N) + 0.5Mn + Ni + 8.2-1.1 (1.5Si + Cr +
Mo).

Here, the element symbols represent the contents (% by weight) of each element.

FIG. 1 shows a transvalestrain test using austenitic stainless steels with various contents of C, N, Mn, Ni, Si, Cr, Mo and P,
It is the result which calculated _| required the relationship between _Nf value and P content. As shown by a dotted line in FIG. 1, a P content of less 0.026%, and P _f value it is hot cracking in the following areas 0.02-0.005N _f is smaller.

-3 ≦ N _f ≦ 0.5: The N _f value is an index represented by the above equation, and when the N _f value satisfies the following equation (2), cracking during hot work is reduced. Rule of thumb.

−3.0 ≦ N _f value ≦ 0.5 (2) _If ≦ 10: As in the case of a flexible tube of an automobile exhaust system which is mainly used by the steel of the present invention, Materials subjected to severe bellows processing are required to have excellent formability. Specifically, an elongation percentage corresponding to 55% or more in a tensile test is required in a state where a predetermined annealing treatment is performed after cold rolling. When the formability index _If shown by the following equation satisfies the following equation (3), good moldability with a tensile elongation of 55% or more can be obtained. This is an empirical rule sought by the inventors.

I _f ≦ 10 (3) where I _f = 497-462 (C + N) -20 (Cu + Ni) -13.7Cr-8.1Mn-9.2
Si-18.5Mo.

Here, the symbol of the element indicates the content (% by weight) of each element.

The present inventors investigated the effects of each element on elongation of steel having a chemical composition within the above-mentioned range, thereby examining the combination of each element having the best formability. As a result of performing analysis by a multiple regression analysis method, the above formula (3) was obtained.

As described above, when the chemical composition is within the above range and satisfies the formulas (1) to (3), excellent resistance to high-temperature corrosion in an environment where chlorides are adhered, An austenitic stainless steel having both moldability and high temperature fatigue resistance can be obtained.

Next, a method for producing the austenitic stainless steel of the present invention will be described.

The austenitic stainless steel of the present invention can be produced by equipment and processes used in ordinary commercial production. For melting stainless steel, an electric arc furnace, an argon-oxygen mixed gas decarburization furnace (AOD furnace) or a vacuum oxygen decarburization furnace (VOD)
It is preferable to use a furnace. The molten steel whose composition is adjusted to a predetermined chemical composition is cast into a slab or a steel ingot by a continuous casting method or an ingot making method. When a thin plate for manufacturing a flexible tube or the like is manufactured from the obtained slab or steel ingot, steps such as hot rolling, cold rolling, pickling, and annealing may be performed.

[0052]

EXAMPLES (Example 1) Table 1 shows the chemical composition of the austenitic stainless steel used in the examples. No. 1 to
12 is the steel of the present invention, and 13 to 25 are comparative steels.

[0053]

[Table 1]

The preparation method of the test material was as follows.

The molten steel having the chemical composition shown in Table 1
It is cast into a 10-mm 20-kg steel ingot, and the obtained steel ingot is forged into a slab, then heated to 1200 ° C., hot-rolled, and has a width of 150 mm, a thickness of 3.2 mm, and a length of 90 mm.
A 0 mm material steel plate was produced. In addition, 10
After annealing at 80 ° C., a steel sheet having a thickness of 1 mm was formed by cold rolling. This cold-rolled steel sheet was subjected to finish annealing at 1100 ° C. to obtain a test material. From this test material, a tensile test specimen, a high-temperature salt damage corrosion specimen, and a high-temperature weld crack specimen at normal temperature for evaluating mechanical properties such as formability were prepared by machining. Each test method was as follows.

Tensile test: The test piece for the room temperature tensile test is J
A No. 13 B test piece specified in IS Z 2201 was sampled so that the rolling direction of the test material was the tensile direction.

The tensile test conditions were as follows.

Test temperature: room temperature Peeling speed: 3 mm / min up to proof stress, 3 from proof stress to rupture
Mechanical properties were evaluated by measuring 0.2 mm proof stress and elongation at 0 mm / min.

High-temperature salt damage corrosion test: The test piece had a width of 2
It was 0 mm, 25 mm in length, and 1 mm in thickness. Before the evaluation, it was finished by wet-type No. 600 emery polished paper and degreased with an organic solvent before use. One cycle of the corrosion test was as described below, and this treatment was repeated 60 times. The high-temperature salt damage corrosion resistance was evaluated by measuring the decrease in the thickness of the test piece after 60 cycles.

700 ° C. (hold for 110 minutes) → Cooling (5 minutes)
→ → immersion in 5% NaCl aqueous solution (immersion for 20 minutes) → 50 ° C
Drying (25 minutes) The degree of corrosion was indicated by the total erosion amount obtained by adding the grain boundary erosion depth to the reduction amount of the plate thickness. The reason why the intergranular corrosion amount is added to the reduction amount of the sheet thickness is that, in a high-temperature salt-corrosion environment, the austenite stainless steel is significantly corroded in addition to the general corrosion. Here, the amount of intergranular corrosion was measured by a method of observing the cross section of the test piece with an optical microscope.

Table 2 shows the tensile elongation at room temperature and the results of the high temperature salt damage corrosion test of each material.

[0062]

[Table 2]

FIG. 2 shows the relationship between the formability index (I _f ) shown in Tables 1 and 2 and the tensile elongation at room temperature. It can be seen that a good room temperature elongation value can be obtained stably when the _If value is 10 or less.

As is clear from Table 2 and FIG. 2, it can be judged that the steel of the present invention has good formability that can sufficiently withstand bellows processing. Further, the total erosion amount after the high-temperature salt corrosion test was 228 μm or less as shown in Table 2,
It was confirmed that it had good high-temperature salt damage corrosion resistance.

According to the experience of the inventors, when the total erosion amount under the present test conditions is 300 μm or less, there is substantially no problem of perforated corrosion in an environment where an automobile flexible tube is applied.

High Temperature Weld Cracking Test (Transvarestrain): The transvarestrain test is the most general method for evaluating welding hot cracking and was carried out under the following conditions.

Test piece: thickness 3.2 mm, width 100 mm, length 150
mm Test method: current 100A, voltage 14V, welding speed 15c
TIG welding was performed at a rate of 10 liters / minute with an alcohol flow rate of 10 liters / minute, and then a bending strain of 3.72% and 1.84% was applied. The total crack length of the heat affected zone (HAZ) at that time Was measured.

Table 3 shows the measurement results.

[0069]

[Table 3]

As is clear from Table 3, in the present invention,
The welding hot cracks are all 0.95 mm or less,
In Comparative Examples, cracks were remarkable at 2.84 mm or more, except for steel Nos. 22 and 23. In addition, steel No.
In Nos. 22 and 23, the cracks were as small as 0.48 or less when the strain amount was 1.845, but were large as about 4 mm or more when the strain amount was 3.72%.

Example 2 In this example, the following tests were performed to evaluate high-temperature strength and high-temperature fatigue characteristics.

High temperature strength: The high temperature strength was 60
After the aging treatment at 0 ° C., a tensile test specimen was collected and subjected to a high-temperature tensile test at 600 ° C., which is the same as the aging temperature, for evaluation.

The high temperature fatigue was evaluated by a plane bending fatigue test at a high temperature.

FIG. 3 is a view showing the shape of a high-temperature fatigue test piece. The test piece was sampled such that the length direction of the test piece coincided with the rolling direction of the test material.

FIG. 4 is a diagram showing a high-temperature fatigue test method. As shown in the figure, a cantilever plane bending fatigue test was performed under the conditions of displacement control and complete swinging. The test temperature was 50
The temperature was 0 ° C. and 600 ° C., and the load repetition rate was 660 cycles / min to a maximum of 10 ⁷ cycles. In fatigue test, a load repetition number of relationships to stress amplitude and the test piece was broken was measured, the maximum stress amplitude does not break at 10 ⁷ cycles was determined as a fatigue limit.

Table 2 also shows the results of these tests.

With respect to the high-temperature strength properties, as can be seen from Table 2, the steel of the present invention shows that after aging for 300 hours and at 1000
Even after the time aging, the decrease in tensile strength at 600 ° C. was slight or rather high, and it was confirmed that there was no practical problem.

On the other hand, all of the comparative steels were 300
Time aging, 1000 hours aging and 60 with aging progress
The tensile strength at 0 ° C. is reduced. It is considered that the reason why the strength of the comparative steel is reduced by aging for 300 hours is that Cr carbide precipitates at the crystal grain boundaries due to the aging treatment and solute C is reduced. It is considered that the reason why the strength of the steel of the present invention increases after the aging treatment is that fine precipitates are formed in the crystal grains by the aging treatment.

Regarding the high-temperature fatigue properties, as apparent from Table 2, the steel of the present invention has a relatively small difference between the fatigue limits at 500 ° C. and 600 ° C. Further, the fatigue limit at 600 ° C. is higher than that of the comparative steel. On the other hand, the comparative steels
The difference between 00 ° C is large, and the fatigue limit at 600 ° C is inferior to the steel of the present invention.

Example 3 After melting the raw materials in a 30-ton electric furnace and adjusting the components, refining was performed in a 30-ton VOD furnace. Table 4 shows the results of the ladle analysis.

[0081]

[Table 4]

The ingot is cast by a continuous casting method and has a thickness of 150 m.
m, a width of 800 mm, and a length of 8 m. The slabs were allowed to cool and then groomed cold. The hot rolling was carried out for about 6 hours in a slab heating furnace heated to 1230 ° C., and then hot-rolled to a coil having a thickness of 6 mm. The shape of the hot rolled coil was extremely good. 11
After performing intermediate annealing, forced air cooling, and pickling at 20 ° C., cold rolling was performed using a cold rolling mill to a thickness of 2 mm, 1.2 mm, and 0.3 mm. Intermediate annealing and pickling treatment were performed during cold rolling as needed to soften the coil.

From a cold-rolled coil having a thickness of 2 mm and 1.2 mm, a welded steel pipe having an outer diameter of 38.1 mm was manufactured, an exhaust manifold for an automobile was manufactured, and evaluation was performed using an actual engine. The maximum temperature of the outer surface of the exhaust manifold was 930 ° C., but the durability was good. 0.3m
A double-walled steel pipe having an outer diameter of 52.9 mm and 51.9 mm was manufactured from a cold-rolled coil of m, and a flexible pipe for an automobile was manufactured by hydraulic bulge forming. No high-temperature cracking occurred during welding, and it was confirmed that there was no practical problem in both the fatigue test at room temperature, the high-temperature test with the actual machine connected to the engine, and the outer surface corrosion resistance test of spraying snow melting agent.

[0084]

The austenitic stainless steel of the present invention has excellent weldability and high-temperature salt-corrosion resistance, and has excellent mechanical properties such as formability, strength and fatigue properties at high temperatures. It is extremely suitable as a material for flexible pipes used in automobile exhaust systems. In addition, while having these excellent properties, Ni,
Since the content of expensive alloy elements such as Cr is kept low, it is also excellent in terms of economy. Therefore, there is a great industrial effect, such as a contribution to further improving the durability of the automobile.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between an _Nf value and a P content.

FIG. 2 is a diagram showing the relationship between the formability index and the elongation in a room temperature tensile test.

FIG. 3 is a view showing a shape of a high-temperature fatigue test piece.

FIG. 4 is a diagram for explaining a high-temperature fatigue test method.

Continued on the front page (72) Inventor Yoshitaka Nishiyama 4-5-33 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Inside Sumitomo Metal Industries, Ltd. (72) Inventor Takayuki Kuyoshi 4-5-33 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture No. Sumitomo Metal Industries Co., Ltd.

Claims (3)

[Claims] (1) C: 0.004 to 0.07% by weight,
Si: 2.5 to 4.5%, Mn: 0.05 to 2%, C
r: 14 to 21%, Ni: 9 to 16%, N: 0.005
0.1%, Cu: 0 to less than 1.5%, Nb: 0 to 0.
25%, Mo: 0 to 2%, B: 0 to 0.003%, S in impurities is 0.01% or less, P is 0.026%
And the _Nf value satisfies the following equation (2) and the molding index _If satisfies the following equation (3), and the balance consists of Fe and unavoidable impurities. Austenitic stainless steel with excellent weld hot cracking resistance and high temperature salt corrosion resistance. P ≦ P _f (1) -3 ≦ N _f ≦ 0.5 (2) _If ≦ 10 (10)・ ・ (3) where, Pf = 0.02-0.005N _f N _f = 30 (C + N) + 0.5Mn + Ni + 8.2-1.1 (1.5Si + Cr + Mo) I _f = 497-462 (C + N) -20 (Cu + Ni) -13.7Cr-8.1Mn-9.2Si-18.5M
o Element symbol: Content of each element (% by weight) 2. C: 0.004 to 0.07% by weight,
Si: 2.5 to 4.5%, Mn: 0.05 to 2%, C
r: 14 to 21%, Ni: 9 to 16%, N: 0.005
-0.1%, total of one or more of Ca, REM and Mg: 0.0002-0.2%, Cu: 0
Less than 1.5%, Nb: 0 to 0.25%, Mo: 0 to 2
% B: containing from 0 to 0.003% S in impurities than 0.01%, a P less than 0.026%, and satisfies the following formula (1), further N _f value Satisfies the following equation (2) and the molding index _If satisfies the following equation (3), and the remainder is F
Austenitic stainless steel having excellent resistance to hot cracking at high temperatures and high resistance to salt damage and corrosion, characterized by comprising e and unavoidable impurities. P ≦ P _f (1) -3 ≦ N _f ≦ 0.5 (2) _If ≦ 10 (10)・ ・ (3) where, Pf = 0.02-0.005N _f N _f = 30 (C + N) + 0.5Mn + Ni + 8.2-1.1 (1.5Si + Cr + Mo) I _f = 497-462 (C + N) -20 (Cu + Ni) -13.7Cr-8.1Mn-9.2Si-18.5M
o Element symbol: Content of each element (% by weight) 3. A vehicle exhaust system component comprising the austenitic stainless steel according to claim 1.