JPH10102208A - Ferritic stainless steel for engine exhaust parts with excellent heat resistance, workability and corrosion resistance at welds - Google Patents

Abstract

(57) [Summary] The present invention has excellent heat resistance and 17% Cr-0.1% Si- which has been conventionally used for a muffler.
It is an object of the present invention to provide an inexpensive ferritic stainless steel for an engine exhaust member having better corrosion resistance of a weld portion than a ferritic stainless steel containing 0.2% Ti-0.8% Mo. SOLUTION: In weight%, C: less than 0.02%, Si:
0.8% or more, less than 1.6%, Mn: less than 0.20%,
P: less than 0.04%, S: less than 0.02%, Cr: 10
% Or more, less than 16%, Ni: 0.05% or more, 1.0%
, N: less than 0.02%, Ti: 0.002% or more,
Less than 0.03%, Nb: 0.43 or more, less than 0.6%,
This is a ferritic stainless steel for an engine exhaust member excellent in heat resistance, workability, and corrosion resistance of a welded portion of a muffler, comprising Fe and inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferritic stainless steel suitable for use in automobile exhaust members,
Ferritic stainless steel for engine exhaust parts with excellent heat resistance, workability, and welded part corrosion resistance, assuming use in parts requiring corrosion resistance, such as mufflers, from the side close to the engine of the automobile (high heat resistance is required). Related to steel.

[0002]

2. Description of the Related Art Generally, ferritic stainless steel is
Since it is inexpensive compared to austenitic stainless steel, it is widely used as a material for automobile exhaust systems. In this automobile exhaust system, as in the exhaust manifold, 900
In a region where the temperature rises to a level exceeding ℃, particularly excellent heat resistance is required, and SUS430 JIL (19)
Cr-0.4Si-0.4Nb-0.5Cu) has been used. On the other hand, as represented by a muffler, condensed water from the exhaust gas easily accumulates in a portion where the exhaust temperature is relatively low, and corrosion of the muffler becomes a problem. Therefore, SUS436 LT (17Cr-0. 1Si-0.
2Ti-0.8Mo) has been used.

As described above, materials used in automobile exhaust systems are required to have completely different characteristics depending on the temperature of a use site, and the problem that "users must distinguish materials" and "particularly, mufflers The cost of the material for use is high due to the high Cr and Mo added steel. " Therefore, there has been a strong demand for the development of a low-cost unified material that can be widely applied from a high-temperature portion to a low-temperature portion. In addition, since the unified material has a great merit in terms of quality control and production efficiency for the material supply side, there has been a strong demand from both the user and the supplier for the development of the unified material. However, at present, there is no such unified material.

Here, a conventional material which is assumed to be used in a high-temperature portion is introduced.
No. 06 discloses a ferrite stainless steel sheet for automobile exhaust system members. This material was developed for the purpose of integrating the exhaust system with one steel type.
As specified in page 4, column 4 [0017],
It clearly states "from the exhaust manifold to the center pipe", and assumes that the materials will be unified only in the high temperature part of the exhaust system, not the muffler. Further, the gazette states that the developed steel material has a Si content of 0.6 to 1.5%,
r: Despite relatively high Si and Cr levels such as 16-22%, they cannot withstand a corrosive environment such as a muffler material. " In fact, experimental investigations by the inventor have confirmed that application to a muffler material cannot be achieved only by increasing the Cr content. The reason will be described later in the section “Detailed description of the invention”.

Further, Japanese Patent Application Laid-Open No. 57-85960 (US Pat.
attain No. No. 4,331,474) discloses Nb,
Disclosed are Al-added steel. The steel is characterized in that Ti is maintained at an unavoidable residual level, and Al is strictly adjusted to 0.1% or more and Nb to 0.45% or less in order to eliminate an adverse effect on toughness. In particular, as disclosed in
In JP-A-7-85960, there is no recognition of the effects of Si and Ti. Therefore, in the steels disclosed in any of the invention examples and the comparative examples, Si is less than 0.6%, and Ti is residual (not described). ) Or 0.23%.

[0006] Japanese Patent Application Laid-Open No. 6-248394 discloses that
As described in Column 2 [0007], a ferritic stainless steel excellent in high-temperature salt damage characteristics in consideration of use in a front pipe and a center pipe is disclosed. That is, as specified in column 4 “0020”, Nb and Ti are added to improve the corrosion resistance of the welded portion, and the effect is recognized as being equivalent. For this reason, only the addition of Nb alone to the invention steel and the comparative steel described in the publication, the addition of a small amount of Ti to the steel with high Si and low Cr and 0.43% or more of the Nb added is scarfed. Knowledge that it has a significant effect on corrosion,
No suggestion is found.

Also, Japanese Patent Publication No. 3-4617 (US Pat.
ent No. Japanese Patent No. 4461811) discloses a component of a stabilized ferritic stainless steel having good brazing properties. Here, Ti is strictly limited because it has an adverse effect on the brazing property, but no consideration is given to improving the corrosion resistance of the welded portion. In fact, both the invention examples and the comparative examples disclosed in this publication have relatively low Si contents (0.6% or less).

Further, US Pat. Patent No. 441
7921 has a welded ferriticst
There is a disclosure of an ainless steel article. There, Nb and Ti are equivalent,
There is no knowledge or suggestion that the increase in Si and the addition of a small amount of Ti to a relatively large amount of Nb are significantly effective in improving the muffler corrosion resistance of welding. Furthermore, since the effect of the addition of Si has not been found, 1% or less, preferably 0.1% or less.
3 to 0.6% (claim 3, and text column 3, line 29). In addition, each of Examples and Comparative Examples is a steel containing only 0.2% or more of Ti.

[0009] Japanese Patent Application Laid-Open No. 7-268554 discloses that
A ferritic stainless steel sheet for automobile exhaust systems having excellent formability and heat resistance is disclosed. However, this steel material is also supposed to be on the high temperature side, and there is no consideration for muffler corrosion. Therefore, both the invention examples and the comparative examples have a Si level of less than 0.8%, Insufficient corrosion resistance.

The present inventor has disclosed in Japanese Patent Application Laid-Open No. 8-3698 an inexpensive hot-rolled ferritic steel which can be used as an automobile exhaust system material. However, this steel material has a main purpose of improving the workability of a hot-rolled sheet, and has a technical idea of lowering Ti as much as possible and actively adding P. At the time of filing of the Japanese Patent Application Laid-Open No. 8-3698, it was generally recognized that a high corrosion-resistant material of a base material also improved the corrosion resistance of a welded portion and, as a result, improved the muffler life.
It has been found that even if the base material has high corrosion resistance, the weld corrosion resistance of the muffler does not always improve. for that reason,
According to the knowledge at the time of JP-A-8-3698, Cr, S
There is no knowledge about the corrosion resistance of the muffler welds of i, Nb, Ti, and P.

On the other hand, as an example of a steel material assumed to be used in the low-temperature part side, there is a steel described in Japanese Patent Application Laid-Open No. HEI 5-112848, characterized by adding Mo by 1% or more. This steel material improves the corrosion resistance of the base material part, especially in consideration of muffler corrosion. The inventor recently stated, `` The site that poses a problem in muffler corrosion is the weld, and the most problematic point is that, starting from significant corrosion there, cracks are propagated by external stress and the weld is fractured. The corrosion level of the material is small compared to the welded part and does not significantly affect the muffler life. " Since the welded portion corrodes most, it is only necessary to reduce the occurrence of corrosion pits at this portion, thereby preventing the base point of fracture. However, the addition of Mo as disclosed in JP-A-5-112848 has little effect on the corrosion resistance of the welded portion and is disadvantageous in terms of cost, as described later.

In order to improve the corrosion resistance of the weld,
It is known to add stabilizing elements such as Ti and Nb. For example, Japanese Patent Application Laid-Open No. 5-112848 also describes that the reason for adding Ti and Nb is to improve the intergranular corrosion resistance of the welded portion. However, in recent years,
It has been found that the problem with muffler corrosion is the breakage of the connection (weld structure) originating from the significant corrosion of the weld, and the addition of Mo, Ti, and Nb simply results in the corrosion resistance of the weld. Turned out not to be enough. The reason is that, as described in JP-A-5-112848, the condensed water in the muffler is changed from a high pH (（9) to a low pH.
H (~ 2), it is extremely difficult to calculate Mo, T
It is considered that the addition of i and Nb alone does not provide sufficient weld corrosion resistance of the muffler. Since no material was developed in consideration of this point, an inexpensive material having excellent muffler corrosion resistance has not been developed at present.

Further, in addition to the above-mentioned problem that there is no unified material, in the existing ferritic stainless steel for muffler, there is also a problem that the production cost is increased by adding 0.8% or more of Mo. Therefore, recently there has been a strong demand for improved corrosion resistance of the welded part of the muffler,
There is a problem of cost reduction by saving Mo. Japanese Patent Application Laid-Open No. 4-22847 discloses a ferritic stainless steel excellent in intergranular corrosion resistance, tube forming properties and high-temperature strength. However, there is an attempt to improve the intergranular corrosion resistance, but it is merely evaluated by a so-called Strauss test. As described above, since the condensed water of the muffler changes extremely from a high pH (〜9) to a low pH (〜2), the muffler corrosion cannot be correctly evaluated in the Strauss test. Therefore, both of the invention examples and the comparative examples have low Si of 0.6% or less, which is insufficient for the corrosion resistance of the welded portion of the muffler, as described later.

[0014]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention has excellent heat resistance and has been used in conventional mufflers for 17% Cr-0.1% Si-0.2% Ti.
It is an object of the present invention to provide an inexpensive ferritic stainless steel for an engine exhaust member that has better corrosion resistance at a welded portion than a ferritic stainless steel added with -0.8% Mo. It is another object of the present invention to provide a unified material that eliminates the need to distinguish materials used in a high temperature part and a low temperature part in an engine exhaust system.

[0015]

Means for Solving the Problems In order to achieve the above object, the inventor has improved the heat resistance (high-temperature strength) required for an engine exhaust member and the workability required for the steel material by adding Nb. First, based on the known fact that the muffler does, the improvement in the corrosion resistance of the welded portion of the muffler was examined in detail. The problem with the durability of the muffler is mainly the breakage of the weld. It is known that the welded portion has lower corrosion resistance than the base material portion, and it is also clear that stress is most concentrated on the welded portion. Therefore, even if only the base material shows excellent corrosion resistance, the most susceptible to corrosion is the welded portion, and the welded portion is subjected to the highest stress concentration, so that large stress in the corrosion pit portion induces rupture. Therefore, improving the corrosion resistance of the welded portion improves the life of the muffler.

Based on the results of the actual vehicle survey, the improvement of the weld corrosion resistance of the muffler was examined in detail, and the important findings obtained are shown below. The test conditions for FIGS. 1 and 2 below will be described in detail in the “Examples” section. (1) It is clear that the base metal part has better corrosion resistance than the welded part, but a material with good corrosion resistance in the base material part has a large difference in corrosion resistance from the welded part, and corrosion concentrates on the welded part. It was found that it was difficult to improve the corrosion resistance of the weld. As a result, as shown in FIG.
A system (10 to 16% Cr) material is advantageous for improving the corrosion resistance of the muffler at the weld.

(2) As shown in FIGS.
8% or more is added to make Cr relatively low, 10 to 16%,
If Ti is positively added to the component system to which Nb is added at 0.4% or more with the upper limit being 0.03%, the corrosion resistance of the welded portion of the muffler is significantly improved, and 17% Cr-0.1%
The characteristics more than the weld of Si-0.2% Ti-0.8% Mo steel are obtained.

This is because the scale of the weld is Si, Nb,
It is presumed that corrosion was not concentrated on the welded portion because it was strengthened by Ti and approached the corrosion resistance of the base material portion. on the other hand,
Conventional 17% Cr-0.1% Si-0.2% Ti
In the case of -0.8% Mo steel, the base material shows remarkably excellent corrosion resistance, so that the corrosion concentrates on the weld, and as a result,
It can be estimated that the corrosion resistance of the welded portion is inferior to that of the low Cr-high Si-Nb-trace Ti steel.

FIG. 2 shows that 11% Cr-0.1%
The effect of Mo on the weld corrosion resistance of Si-0.2% Ti is also shown. Surprisingly, the effect of adding Mo to the weld was significantly smaller than the effect of adding Si. In other words, it was confirmed that the addition of Mo had almost no effect on the improvement of the corrosion resistance of the welded portion, and it was confirmed that the steel material needed to be made Cr-high Si, Nb was added, and a small amount of Ti was added. The detailed reason for the effect of each element on the corrosion resistance of the welded portion will be described in “Limited components” described later. (3) Further, by adding a relatively small amount of Al and Cu to the above-mentioned steel material, the weld corrosion resistance of the muffler is further improved. (4) Further, the P content greatly affects the corrosion resistance of the welded portion of the muffler, and is preferably as low as possible. (5) The above-described component system does not deteriorate the heat resistance and workability of the base Nb-added steel.

The inventor of the present invention has made intensive efforts to realize the above-mentioned novel findings, and has invented a ferritic stainless steel excellent in heat resistance, workability and corrosion resistance at a welded portion. That is, in the present invention, C: 0.02% by weight.
%, Si: 0.8% or more and less than 1.6%, Mn:
Less than 0.20%, P: less than 0.04%, S: 0.02%
, Cr: 10% or more, less than 16%, Ni: 0.05
% Or more, less than 1.0%, N: less than 0.02%, Ti:
0.002% or more, less than 0.03%, Nb: 0.43%
It is a ferritic stainless steel for an engine exhaust member excellent in heat resistance, workability, and welded portion corrosion resistance, which contains less than 0.6%, the balance being Fe and inevitable impurities.

Further, the present invention further provides one or two types selected from the group consisting of Al: 0.02% or more and less than 0.5% and Cu: 0.02% or more and less than 0.3% by weight. Additional content or Mo: 0.05% or more and less than 0.8%, further Ca: 0.001% or more and less than 0.03%, B: 0.0002% or more and less than 0.005%, It is a ferritic stainless steel for an engine exhaust member which is excellent in heat resistance, workability, and corrosion resistance at a welded portion.

In the present invention, since the ferritic stainless steel for the engine exhaust member is formed from the above-described component system, it has excellent heat resistance and workability, and
17% Cr-0.1% S conventionally used for mufflers
The corrosion resistance of the welded portion can be simultaneously improved more than the ferritic stainless steel added with i-0.2% Ti-0.8% Mo. As a result, in the engine exhaust system, conventionally, the materials used were distinguished between the high-temperature part and the low-temperature part.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention limit the content of each component element of ferritic stainless steel, and the reasons for the limitation will be described below. All units are% by weight. C is an element that deteriorates toughness and workability. If the content of C is 0.02% or more, the deterioration of toughness and workability becomes remarkable, and thus C is limited to less than 0.02% by weight. For good toughness and workability, the lower the C content, the better, and preferably 0.01% or less.

[0024] Si is one of the important elements for the steel of the present invention. As shown in FIG. 2, when a trace amount of Ti of 0.03% or less is added, by adding 0.8% or more of Si, the weld corrosion resistance of the muffler is significantly improved, and the conventional steel (17% Cr-0.1% Si-0.2% Ti
-0.8% Mo) or higher. This is because the scale generated in the weld is strengthened by Si-Nb-Ti, and since the difference from the corrosion resistance level of the base material is relatively small, corrosion does not concentrate on the weld. It is considered to show good weld corrosion resistance of the muffler, but details are unknown.

When the content of Si is 1.6% or more, the workability is greatly deteriorated, so that the content should not exceed 1.6%. Preferably, it is 1.0% or more and 1.3% or less.
Mn is known as a deoxidizing agent for steel, but excessive addition forms MnS, lowers workability and lowers the corrosion resistance of the muffler at the weld, so that the Mn content is 0.2%.
It was less than 0% by weight. Preferably, it is less than 0.15%. The lower the better, the better.

P is an element that deteriorates the toughness and the corrosion resistance of the muffler at the welded portion, and is set to less than 0.04% by weight. S is the elongation and r-value (Rankford value) of the steel material
As it is an element that reduces the corrosion resistance, which is the basic property of stainless steel,
The content was less than 0.02%.

Cr is an element that improves the corrosion resistance, which is a basic property of stainless steel. However, as shown in FIG. 1, if it is too much, it becomes harmful to the corrosion resistance of the muffler welded portion and increases the cost. Therefore, it is limited to less than 16%.
On the other hand, if the content is less than 10%, the corrosion resistance of the welded portion is extremely poor, so the lower limit is 10%. Therefore, in the present invention, Cr
The content is limited to 10% or more and less than 16%. Cr content is 10% or more and 12% for the corrosion resistance of the muffler weld
The following is preferred. More preferably, 10.
More than 5% and less than 11.5%.

Ni is added in an amount of 0.05% or more because it has the effect of improving the corrosion resistance of the welded portion of the muffler. On the other hand, a large amount of addition makes 1%
Restrict to less than. Preferably, it is 0.1% or more and 0.8% or less. More preferably, it is 0.5% or more and 0.8% or less. N is an element that deteriorates the toughness and workability of steel. If the content is 0.02% or more, the deterioration of toughness and workability becomes remarkable, so the content is limited to less than 0.02%. The smaller the content of N, the better, and preferably 0.01% or less.

Nb is an element having an effect of improving high-temperature strength, workability, and corrosion resistance of a welded portion of a muffler. To obtain properties higher than those of conventional steel, it is necessary to add 0.43% or more. However, if added in excess of 0.6%, the strength of the steel material at room temperature is significantly increased, and formability and workability are degraded, so the upper limit is 0.6%. Preferably, 0.4
More than 5% and less than 0.6%. More preferably,
0.5% or more and less than 0.6%.

[0030] Ti is a particularly important element for the steel of the present invention. As shown in Table 1, Table 2 and Table 3, the Ti-less material (0.001
% Or less), the corrosion resistance of the welded portion of the muffler is not improved even when the Si content and the Cr content are reduced (Nos. 24 and 28 in Table 2).
When 0.002% or more of Ti was added, the corrosion resistance of the muffler at the weld was significantly improved. Although the reason is not clear, it is thought that the trace amount of Ti changes the composition of the scale generated at the time of welding. However, 0.
If it exceeds 03%, muffler corrosion of the welded portion deteriorates.
The reason for this is that Ti is easier to combine with N than Nb and Al and absorbs N in the atmosphere. Excessive addition of Ti absorbs C and N from the atmosphere during welding, and the It is thought that the corrosion resistance is reduced. Therefore, T
The i content is limited to 0.002% or more and less than 0.03%. Preferably it is 0.005% or more and 0.02% or less.

Al is an optional additive element. Generally, it may be inevitably contained as a steel deoxidizing agent, but there is no particular adverse effect. In the present invention, Al deoxidation is optional in order to contain Si. On the other hand, when 0.02% or more is added, the corrosion resistance of the muffler at the welded portion is further improved. Although the reason for this is not clear, Al is an element that is easily oxidized, and it is considered that sufficient addition of Al is due to the effect of preventing absorption of C and N from the atmosphere by the alumina coating during welding. Therefore, in order to further improve the muffler corrosion resistance, 0.02% or more may be added. However, when the content is 0.5% or more, the workability is significantly deteriorated. Therefore, the content is limited to 0.02% or more and less than 0.5%. Preferably, it is more than 0.1% and less than 0.2%.

Cu is an optional additive element. 0.02%
When the above addition is performed, the corrosion resistance of the welded portion is improved. 0.
When the content is 3% or more, the workability deteriorates. Therefore, in the present invention, the content is limited to 0.02% or more and less than 0.3%. Preferably, it is more than 0.15% and less than 0.3%. The present invention is applicable to conventional steel (17
% Cr-0.1% Si-0.2% Ti-0.8% Mo)
It has been proposed as a steel material that achieves the same level of corrosion resistance of welds in mufflers.

On the other hand, Mo is a solid solution strengthening element, and is also effective for improving the high temperature strength.
Appears from%. Therefore, even in the present invention, when it is desired to increase the high-temperature strength, 0.05% or more may be added. However, Mo is an expensive element, which causes an increase in cost, and has almost no effect on the weld corrosion resistance of the muffler as shown in FIG. Therefore, in the present invention, 0.8%
Limited to less than.

Ca is an element having an effect of suppressing nozzle clogging due to Ti-based inclusions during casting from molten steel to a slab. The effect appears from 0.001%. However, even if it is added in excess of 0.03% by weight, not only the effect is saturated, but also Ca-containing inclusions become the starting point of pitting corrosion and the corrosion resistance deteriorates.
%.

B is effective for improving the workability of the steel material. The effect appears from 0.0002%, but 0.005%
If it exceeds, the toughness deteriorates due to the generation of a large amount of BN, so the content is made less than 0.005%.

[0036]

【Example】

(Example 1) After melting the steel of the present invention having the composition shown in Tables 1 and 2 and a comparative steel, heating to 1250 ° C,
A hot-rolled sheet having a thickness of 5 mm was formed by hot rolling. Annealing this,
Pickling, cold rolling, finish annealing, and pickling were sequentially performed to obtain a cold-rolled annealed steel sheet having a thickness of 2 mm.

The samples obtained from the cold-rolled annealed steel sheets thus obtained were evaluated for the high-temperature strength, the workability at room temperature, and the corrosion resistance of the weld between the base material and the muffler by the following methods.

[0038]

[Table 1]

[0039]

[Table 2]

(1) High Temperature Strength A 0.2% proof stress was measured at a tensile rate of 0.3% / min using a plate-like test piece having a thickness of 2 mm. The high-temperature strength was evaluated by the following index (for example, AA is excellent, A is good, B is normal, and C is acceptable). 18 MPa or more is AA 15 MPa or more but less than 18 MPa A 10 MPa or more and less than 15 MPa B is less than 10 MPa C 2.

(2) Workability at room temperature The elongation was measured with a B-shaped tensile test piece (plate thickness 2 mm) defined in JIS No. 13 at 0 °, 45 °, and 90 ° directions with respect to the rolling direction. , El = ｛El (0 °) + 2 × El
(45 °) + El (90 °)｝ / 4. The evaluation is performed by indexing in the same manner as described above.

(A) Muffler corrosion resistance of the welded portion The bead-on type TIG welding was performed on a 2 mm-thick material. The welding conditions were: welding speed: 600 mm / min, welding current: 200 amps, shielding gas: Ar gas, 15 liter / min (surface only).

As shown in FIG. 3, a 50 mm × 100 mm square sample was suspended in the beaker 1 and repeatedly subjected to an evaporation test to evaluate an average of five maximum erosion depths. In addition,
The sample was obtained by heat-treating a steel material (or base metal) after welding at 400 ° C. for 5 hours. In addition, as shown in FIG. 3, the test was performed by immersing the sample in a test solution maintained at 80 ° C. and evaporating the solution until it became empty, as one cycle.
This was repeated 10 times. The composition of the test solution used, (the unit, ppm) for simulating the muffler ^{_{environment, Cl: 250, NO 2 -}} : 100, NO 3 -: 20, CO 3
_{^{2-: 2000, SO 3 2-:}} 1250, SO 4 2-: 12
50, CH ₃ COO ⁻ : 400, HCHO 250, H
COO ^-: 100, pH: was 8.5.

(4) Muffler Corrosion of Base Material A muffler corrosion test similar to that of (3) was performed using a base material instead of the test piece of the welded portion. The average of the five maximum erosion depths was classified and evaluated as follows, and evaluated. 0.1 mm or more and less than 0.2 mm are A and 0.2 mm or more and less than 0.3 mm are B and 0.3 mm or more and less than 0.4 mm are C.

The results of these tests are summarized in Table 3.

[0046]

[Table 3]

According to Table 3, the comparative steel 17 has too low Si and the weld corrosion resistance of the muffler is as poor as SUH409L. Since the comparative steel 18 has too much Si, the workability is poor. Comparative steel 19 contains excessive Ti,
The weld corrosion resistance of the muffler is worse than SUS436 LT. Comparative steel 20 has an excessive amount of Mn, and the weld corrosion resistance of the muffler is lower than SUS436 LT. Comparative steel 21 is N
Since b and Ti are excessive, both the workability and the corrosion resistance of the muffler weld are poor. The workability of the comparative steel 22 is poor because Ni is excessive. In Comparative Steel 23, since Nb was too small,
Both high-temperature strength and corrosion resistance of muffler welds are poor. The comparative steel 24 has poor corrosion resistance at the welded portion of the muffler because Ti is too small. Comparative steel 25 has an excessively large P, and has poor corrosion resistance at the welded portions of the base metal and the muffler. Comparative steel 26 is SUH
409 L, and the high-temperature strength, and the corrosion resistance of the base material and the muffler at the weld zone are all poor. Comparative steel 27 is SUS436
Comparative steel 28 is SUS430 J1L, which is LT, and has poor workability and poor muffler weld corrosion resistance.

On the other hand, the steels 1 to 16 of the present invention have high-temperature strengths as follows:
It shows a value equal to or higher than the current material (SUS430 JIL), and the corrosion resistance of the muffler welded part is the same as the current material (SUS436 L).
T) It shows excellent properties as described above. Further, the workability is more than that of the current materials (SUS430 J1L, SUS436 LT), and furthermore, it is lower in cost because it is a low Cr and Mo saving steel. The muffler corrosion resistance of the base material is SUS436
Although it is inferior to LT, it has a level of B or higher, that is, a slight corrosion level of 0.3 mm or less.
436 LT better than the weld value, SUS43
It can be judged that it is superior to the 6LT muffler. This is because the location of the most severe corrosion becomes a problem.

As described above, the ferritic stainless steel according to the present invention has heat resistance equal to or higher than that of a currently used high-temperature member (SUS430 J1L) in an automobile exhaust system, and a low-temperature member (SUS436) currently used. LT) and more than muffler corrosion resistance, and also more than both processability,
In addition, it can be seen that they are lower in Cr, less in Mo, and inexpensive.

[0050]

As described above, according to the present invention, it is possible to provide inexpensively ferritic stainless steel for an engine exhaust member having excellent heat resistance, workability, and corrosion resistance at a welded portion. That is, even if the Mo-low Cr material is used, heat resistance and muffler corrosion resistance higher than conventional materials can be obtained. Therefore, even if it is used for exhaust manifolds, front pipes, outer tubes of converters, center pipes, mufflers, etc. of automobile engines that require high-temperature strength, oxidizing properties, and corrosion resistance, the properties are superior to those of conventional materials. And even cheaper. Further, the exhaust path member of the thermal power generation system is required to have the same characteristics as the exhaust member of the automobile engine, and thus is suitable for the use of the steel of the present invention.

[Brief description of the drawings]

FIG. 1 is a view showing the effect of adding Cr on the corrosion resistance of a welded portion of a steel muffler (however, the base steel material is 0.5% N
b-0.02% Ti-1.2% Si based).

FIG. 2 shows the effect of S on the corrosion resistance of the base material and the muffler in the weld zone.
It is a figure which shows the addition effect of i or Mo.

FIG. 3 is a diagram showing an example of an apparatus for performing a muffler corrosion test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Beaker 2 80 degreeC water 3 Test solution 4 Weld part 5 Constant temperature bath 6 Evaporation direction

Continued on the front page (72) Inventor Kazuhide Ishii 1 Kawasaki-cho, Chuo-ku, Chiba City, Kawasaki Steel Engineering Co., Ltd. (72) Inventor Susumu Sato 1 Kawasaki-cho, Chuo-ku, Chiba City, Kawasaki Steel Co., Ltd.

Claims (4)

[Claims] 1. In weight%, C: less than 0.02%, Si: 0.8% or more and less than 1.6%, Mn: less than 0.20%, P: less than 0.04%, S: 0 0.02%, Cr: 10% or more, less than 16%, Ni: 0.05% or more, less than 1.0%, N: less than 0.02%, Ti: 0.002% or more, less than 0.03% , Nb: 0.43% or more and less than 0.6%, and comprising a balance of Fe and unavoidable impurities, and having excellent heat resistance, workability, and corrosion resistance at welded portions, for engine exhaust members. 2. In addition, one or two selected from the following: Al: 0.02% or more and less than 0.5%, Cu: 0.02% or more and less than 0.3% by weight. The ferritic stainless steel for an engine exhaust member according to claim 1, which is excellent in heat resistance, workability, and weld corrosion resistance. 3. The composition according to claim 1, further comprising Mo: 0.05% or more and less than 0.8% by weight. Ferritic stainless steel for engine exhaust parts. 4. The composition according to claim 1, further comprising, by weight%, Ca: 0.001% or more and less than 0.03%, and B: 0.0002% or more and less than 0.005%. 4. A ferritic stainless steel for an engine exhaust member having excellent heat resistance, workability, and corrosion resistance at a weld portion according to any one of (1) to (3).