JP2003342694A - Ferritic stainless steel excellent in spinning workability and used for diameter-enlarged member of gas exhaust system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ferritic stainless steel which is used for a diameter-enlarged member of a gas exhaust system, is excellent in spinning workability, and undergoes a bread at the material end or at the raw-pipe welded section with a very low probability even when subjected to high-speed spinning. <P>SOLUTION: This ferritic stainless steel has a composition comprising 0.020 mass% or less C, 0.40 mass% or less Si, 0.80 mass% or less Mn, 0.040 mass% or less P, 0.010 mass% or less S, 10.0-19.0 mass% Cr, 0.6 mass% or less Ni, 0.10 mass% or less Al, 0.10-0.80 mass% Ti, and the balance being Fe and unavoidable impurities provided that inequalities (1): Ti≥15(C+N) and (2): Ni+30C +0.5Mn≤1.00 are satisfied. <P>COPYRIGHT: (C)2004,JPO

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 as a material for an exhaust system expansion member such as a muffler or a housing of a catalytic converter, and more particularly to a steel having excellent spinnability.

[0002]

2. Description of the Related Art Ferritic stainless steels such as SUH 409L, SUS429, and SUS 436L, which have excellent workability and corrosion resistance, have been widely used for automobile exhaust system members. For example, a housing or muffler of a catalytic converter that processes exhaust gas emitted from an engine of an automobile is one example.

The general shape of the housing described above is shown in FIG.
Shown in. As shown in the figure, the housing of the catalytic converter has a relatively large-diameter body r ₁ for accommodating the catalyst carrier and a relatively small-diameter connecting portion r ₃ connected to the exhaust pipe.
And a tapered cone portion r ₂ having a gradually decreasing diameter from the main body r ₁ toward the connecting portion r ₃ .

In many cases, the housing of such a catalytic converter is manufactured by forming a raw tube having substantially the same diameter as the main body r ₁ by spinning. For example, Japanese Patent Publication No. 4-46647 discloses a method in which one end of a raw pipe is fixed on a core metal and a plurality of rollers equipped with guide rolls are symmetrically arranged on the outer periphery of the raw pipe to perform ironing. Is disclosed. Further, Japanese Patent Laid-Open No. 10-24323 discloses a method of gripping a raw pipe with three rollers, defining an inclination angle of the rollers, and rotating the raw pipe to perform ironing.

The method of forming a pipe material having a taper by such a spinning process is as follows: 1) The material yield is good, and 2) Integral, as compared with the method in which plate materials are pressed and joined by welding. It has the advantages that it can be molded and does not reduce the reliability of the welded part, 3) no mold is required, and 4) there is a small number of man-hours. On the other hand, the spinning process takes a relatively long time compared to the method using a press. That is, it was inferior in terms of production efficiency.

In this respect, as a method for improving the production efficiency, for example, in Japanese Unexamined Patent Publication No. 2000-33443, the material pipe and the forming tool are rotated in opposite directions to increase the relative rotation speed. A method of performing high speed processing is disclosed. However, if the processing speed is increased according to the above method, the probability of breakage at the material end and breakage from the raw pipe weld W increases as shown in FIGS. 2 (a) and 2 (b). Was left.

[0007]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the above problems, and in the case of performing a spinning process, the probability of breakage at the material end and breakage at the bare pipe weld is extremely low. An object of the present invention is to propose a ferritic stainless steel for an exhaust expansion member, which can exhibit excellent spinning workability even when the processing speed is increased.

[0008]

By the way, the inventors of the present invention have found that even if the same steel grade is used as the material, the probability of breakage at the material end during spinning and breakage from the raw pipe welded portion is high. Since it is different for each coil, it is considered that the components in the steel and the impurity components in the steel affect the spinnability, and a detailed investigation and examination of the effects of these in-steel components on the spinnability I went. As a result, regarding steel components, C, Si, Mn, P, S, Ni and Al
It was found that the probability of breakage during spinning can be dramatically reduced by controlling the content and adding a certain amount of Ti. The present invention is based on the above findings.

That is, the gist of the present invention is as follows. 1. Mass%: C: 0.020% or less, Si: 0.40% or less, Mn: 0.80% or less, P: 0.040% or less, S: 0.010% or less, Cr: 10.0 to 19.0%, Ni: 0.6% or less, Al: 0.10 % Or less and Ti: 0.10 to 0.80% by the following formula (1), (2) Ti ≧ 15 (C + N) --- (1) Ni + 30C + 0.5Mn ≦ 1.00 --- (2) (however, formula (1) , (2), Ti, C, N, Ni and
Mn is contained in a range satisfying the relationship of the content (mass%) of each element), and the balance is Fe and inevitable impurities composition. Ferritic stainless steel for bulging members.

2. In the above 1, S content is mass%
Is less than 0.005%, and is a ferritic stainless steel with excellent spinnability for exhaust system expansion members.

3. In 1 or 2 above, the steel has a composition which, in mass%, further contains one or two selected from V: 0.01 to 0.5% and W: 0.001 to 0.05%. Ferritic stainless steel with excellent properties for exhaust system expansion members.

4. In any one of 1 to 3 above, a spinning process characterized in that the steel has a composition containing, in mass%, one or two selected from Cu: 3.0% or less and Mo: 3.0% or less. Ferritic stainless steel with excellent properties for exhaust system expansion members.

5. In any one of the above 1 to 4, the steel has a composition that further contains B: 0.0002 to 0.0030% by mass%, and is a ferritic stainless steel for an exhaust system expanding member having excellent spinning workability, characterized in that .

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. First, the reason why the composition of the steel in the present invention is limited to the above range will be described. In addition, unless otherwise indicated, "%" display regarding components means mass%. C: 0.020% or less C lowers not only the toughness but also the oxidation resistance, which is an important characteristic when applied to automobile exhaust system members, so a lower content is desirable. Therefore, in the present invention, the amount of C is limited to 0.020% or less.

Si: 0.40% or less Si is an important element in the present invention. That is, Si
Reduces the spinnability and toughness, so it is desirable to reduce the content from these aspects, but on the other hand, it has the function of increasing the oxidation resistance. Therefore, in the present invention, Si
Was 0.40% or less. More preferably
It is 0.30% or less.

Mn: 0.80% or less Mn is an element effective for improving strength, but if added in a large amount, it decreases toughness, so 0.80%
Limited to:

P: 0.040% or less P is also an element effective for increasing the strength, but if it is contained in a large amount, it lowers the toughness, so it is limited to 0.040% or less.

S: 0.010% or less S is an important element in the present invention. That is, S
Forms precipitates and inclusions with Ti and the like, and these become the starting points of fracture during spinning. In particular, when the raw pipe is formed by electric resistance welding, the precipitates and inclusions segregated in the center of the plate thickness due to the metal flow are exposed on the surface of the pipe, which easily becomes a starting point of fracture. Therefore, in the present invention, the S amount is
Limited to 0.010% or less. It is more preferably 0.005% or less.

Cr: 10.0 to 19.0% Cr is an essential element for heat-resistant steel, and its content is 10.0.
If it is less than%, sufficient oxidation resistance cannot be obtained, while 19.0%
If Cr exceeds 1.0, the toughness decreases, so Cr is contained in the range of 10.0 to 19.0%.

Ni: 0.6% or less Ni contributes to the improvement of toughness, but its content is 0.6%.
If it exceeds 0.1%, the oxidation resistance is deteriorated, so Ni is limited to 0.6% or less.

Al: 0.10% or less Al is added for deoxidation during steelmaking, but 0.10% or less is sufficient for this purpose, so the amount of Al was limited to 0.10% or less.

Ti: 0.10 to 0.80% Ti preferentially forms carbonitrides to reduce the solute C and N and suppresses the formation of Cr carbonitrides, so that ductility, toughness, weldability and It is a useful element for improving corrosion resistance. However, if the content is less than 0.10%, the effect of addition is poor, and if it exceeds 0.80%, the toughness is adversely deteriorated. Therefore, Ti is contained in the range of 0.10 to 0.80%.

Although the proper composition range of the basic components has been described above, in the present invention, it is not sufficient that each component simply satisfies the above composition range, and the relations of the following formulas (1) and (2) are also satisfied. It is necessary to be satisfied at the same time. Ti ≧ 15 (C + N) --- (1) Ni + 30C + 0.5Mn ≦ 1.00 --- (2) The above formula (1) is a condition necessary for preferentially fixing solid solution C and N by Ti. By satisfying the relationship of the above formula, formation of carbonitrides by Cr can be effectively suppressed. The above formula (2) is a condition for suppressing the formation of martensite, and by satisfying the relation of the above formula, spinning workability, toughness, weldability,
It is possible to effectively suppress the formation of martensite, which adversely affects the corrosion resistance.

Although the basic components have been described above, other elements described below can be appropriately contained in the present invention. V: 0.01 to 0.5% and / or W: 0.001 to 0.05% V and W are both elements useful for improving the weld crack susceptibility of the heat affected zone, but their respective contents are less than the lower limits. And the effect of addition thereof is poor, while if it exceeds the upper limit, the toughness of the base material and the weld heat affected zone will be deteriorated, so the respective contents were made to fall within the above ranges. A more preferable range is V: 0.05 to 0.3 mass%, W: 0.005 to
It is 0.03 mass%.

Cu: 3.0% or less Cu is an element that improves the corrosion resistance, and it is effective to add it when high corrosion resistance is required. However, if added in excess of 3.0%, there is a risk of hot cracking in hot rolling, etc. Therefore, Cu was included in 3.0% or less. Further, more preferably, the lower limit is 0.1% at which the effect is remarkable, and it is desirable that the content be 1.0% or less.

Mo: 3.0% or Less Like Cu, Mo is also an element effective for improving the corrosion resistance. However, if added in excess of 3.0%, not only the spinnability deteriorates, but also the stability of the austenite phase deteriorates, especially the toughness of the weld heat affected zone decreases. Therefore, Mo should be contained at 3.0% or less. From the viewpoint of achieving both spinnability and corrosion resistance, 0.1-
A range of 1.0% is preferred.

B: 0.0002 to 0.0030% B is particularly effective in improving the toughness of the weld heat affected zone through improving the hardenability. However, the content is 0.0002%
If it is less than 0.003%, the effect is poor. On the other hand, if it exceeds 0.0030%, the hardening becomes large, and the toughness and workability of both the base metal and the weld heat affected zone are impaired. Therefore, B is 0.0002
It was made to contain in the range of -0.0030%. The range is more preferably 0.0005 to 0.0010%.

Next, a preferred method for producing the steel of the present invention will be described. Molten steel having the above-described suitable component composition is melted by a known method such as a converter, an electric furnace, and a vacuum melting furnace, and is made into a steel material (slab) by a continuous casting method or an ingot-casting method. This steel material is then heated or directly hot-rolled without heating to form a hot-rolled sheet. The hot-rolled sheet is usually annealed, but the hot-rolled sheet may be omitted depending on the application. Then, after pickling, a cold rolled sheet is obtained by cold rolling, and then recrystallization annealing is performed to obtain a product.

[0029]

The present invention will be described in more detail based on the following examples. Steel having the composition shown in Table 1 was melted in a small vacuum melting furnace to make a 100 kg steel ingot. After heating these steel ingots to 1050-1250 ℃, finishing temperature: 750-950
Hot rolling was performed under conditions of ℃ and coiling temperature: 650 to 850 ℃ to make a hot rolled sheet with a thickness of 3.0 mm. Then, some of these hot-rolled sheets were annealed at 800 to 1000 ° C., pickled, and then cold-rolled to obtain cold-rolled sheets with a plate thickness of 1.2 mm. Test pieces were taken from each of the steel sheets obtained as described above, and the spinnability was evaluated based on the following test method.

<Spinning workability> A test piece was formed into a 1.2 mm t x 120 mm φ x 500 mm L electric resistance welded tube by high frequency welding. For these ERW pipes, the spinning speed shown in FIGS. 3 and 4 was used to rotate at a rotation speed of 500 rpm or 10 rpm.
Under the conditions of 00 rpm, drawing amount: 2 mm / time, and relative parallel moving speed of forming roll: 8000 mm / min, the drawing part (r ₃ part in FIG. 1) has a diameter of 60 mmφ and a length of 50 mm as shown in FIG. Spinning was performed such that the length of the tapered portion (r ₂ portion in FIG. 1) was 60 mm. The tightening amount represents the amount of increase in the pressing amount of the forming roll per one reciprocation when the forming roll reciprocates relative to the raw pipe.

The spinning machine shown in FIG. 3 has a rotation driving means for gripping the raw tube 1 and rotating it about its axis CC.
Forming roller moving means for moving the forming roller 4 in order to give the base tube 1 a predetermined shape is provided. The rotary drive means comprises a gripping mechanism 3 such as a chuck provided on the spindle 2 for gripping the raw tube, and a motor (not shown) for rotationally driving the spindle 2. Is gripped and rotated about its axis C-C. The moving means of the forming roller 4 comprises a servo mechanism (not shown) capable of numerical control, and the forming roller 4 and the forming pipe 1 are formed on the basis of data set and input to form the forming pipe 1 into a desired shape. And are relatively moved in the axis C-C direction and the diameter D direction. The forming roller 4 is pressed against the base pipe 1 while being moved as shown by an arrow A in the figure, whereby the base pipe 1 is subjected to a spinning drawing process into a shape having a conical portion.

On the other hand, the spinning apparatus shown in FIG. 4 comprises a parallel moving means for fixing and holding the raw pipe 1 and moving it in the direction of the axis C-C, and a forming roller 4 for imparting a predetermined shape to the raw pipe 1. The rotary table 5 with 4'and 4 "is mounted on its axis CC.
It is provided with forming roller rotation moving means for revolving the forming rollers by revolving around and moving the forming rollers 4, 4 ', 4 "in the direction D perpendicular to the axis C-C. Is a base 6 for supporting the raw tube 1, and a holding mechanism 7 such as a chuck for holding the raw tube 1.
And the like, and can be translated in the direction of the axis C-C along the moving table 8 by a driving means (not shown). The forming roller rotation moving means includes a rotary table 5 to which three forming rollers 4, 4 ', 4 "are attached, and a motor housed in a motor case 9 for rotating the rotating table 5 around a set axis C-C. , Further embedded in the turntable 5 and forming rollers 4, 4 ′, 4 ″ each being orthogonal to the axis CC.
It is equipped with a mechanism to move in the direction by numerical control.
In the case of this type, the rotation speed represents the revolution speed of the forming roll.

Here, the spinning workability is as follows. The above-mentioned processing is applied to 200 electric resistance welded pipes,
0 was evaluated as ⊚, 1 to 2 was evaluated as ○, 3 to 9 was evaluated as Δ, and 10 or more was evaluated as ×. Tables 2 and 3 show the test results of the obtained spinnability.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

As shown in Tables 2 and 3, all the steel sheets obtained according to the present invention have extremely excellent spinning workability as compared with the conventional materials.

[0038]

As described above, according to the present invention, it is possible to remarkably reduce the breakage at the end of the material and the breakage at the welded portion of the raw pipe when performing the spinning process, especially when the working speed is increased. Even if it is, good spinning workability can be obtained. Therefore, by using the ferritic stainless steel of the present invention, it is possible to advantageously provide a steel material for an exhaust system expanding member.

[Brief description of drawings]

FIG. 1 is a diagram showing a typical shape of a housing of a catalytic converter.

FIG. 2 is a diagram showing a fractured state at a material end portion or a raw pipe welded portion which occurs when a spinning process is performed.

FIG. 3 is an explanatory diagram showing a first embodiment of a spinning processing device.

FIG. 4 is an explanatory diagram showing a second embodiment of a spinning processing device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Elementary tube 2 Spindle 3 Gripping mechanism 4, 4 ', 4 "Forming roller 5 Rotating table 6 Base 7 Gripping mechanism 8 Moving table 9 Motor case r ₁ Body part of housing r ₂ Cone part of housing r ₃ Connection part of housing

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshihiro Ozaki             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. (72) Inventor Takaro Iguchi             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. (72) Inventor Yukihiro Baba             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Chiba Steel Works, Ltd. F-term (reference) 3G004 FA04 GA00                 3G091 AA02 AB01 BA39 GB01Z

Claims (5)

[Claims] 1. In mass%, C: 0.020% or less, Si: 0.40% or less, Mn: 0.80% or less, P: 0.040% or less, S: 0.010% or less, Cr: 10.0 to 19.0%, Ni: 0.6% Below, Al: 0.10% or less and Ti: 0.10 to 0.80% are calculated by the following formulas (1), (2) Ti ≧ 15 (C + N) --- (1) Ni + 30C + 0.5Mn ≦ 1.00 --- (2) (However, , In formulas (1) and (2), Ti, C, N, Ni and
Mn is contained in a range satisfying the relationship of the content (mass%) of each element), and the balance is Fe and inevitable impurities composition. Ferritic stainless steel for bulging members. 2. The S content according to claim 1, wherein the S content is% by mass.
Is less than 0.005%, and is a ferritic stainless steel with excellent spinnability for exhaust system expansion members. 3. The composition according to claim 1 or 2, wherein the steel further contains, in mass%, one or two selected from V: 0.01 to 0.5% and W: 0.001 to 0.05%. A ferritic stainless steel with excellent spinnability for exhaust system swelling members. 4. The composition according to any one of claims 1 to 3, wherein the steel further contains, in mass%, one or two selected from Cu: 3.0% or less and Mo: 3.0% or less. A ferritic stainless steel with excellent spinnability for exhaust system swelling members. 5. The exhaust system expanding member excellent in spinning workability according to any one of claims 1 to 4, wherein the steel has a composition further containing B: 0.0002 to 0.0030% in mass%. Ferritic stainless steel for use.