JP2004018916A - Ferritic stainless steel with excellent high-temperature oxidation resistance and high-temperature salt damage resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce ferritic stainless steel having excellent high-temperature oxidation resistance and high-temperature salt damage resistance and capable of withstanding use at high temperatures exceeding 900°C. <P>SOLUTION: Material components are regulated to a composition range consisting of, by mass, ≤0.02% C, ≤2.0% Si, ≤2.0% Mn, 12.0 to 16.0% Cr, 1.0 to 5.0% Mo, >2.0 to 5.0% W, >0.5 to 7.0% Al, 5(C+N) to 1.0% Nb, ≤0.02% N and the balance Fe with inevitable impurities. <P>COPYRIGHT: (C)2004,JPO

Description

【００３３】
【表２】

【００３４】
表２から明らかなように、この発明に従う鋼板はいずれも、耐高温酸化性および耐高温塩害性とも良好な特性値が得られている。
【００３５】
【発明の効果】
かくして、この発明によれば、耐高温酸化性および耐高温塩害性にも優れたフェライト系ステンレス鋼を安定して得ることができる。
従って、この発明によれば、エンジン性能の向上により、排ガス温度が　９００℃を超えるような自動車関連用途においては言うまでもなく、燃料電池関連用途や発電プラント関連用途においても、それに耐え得るステンレス鋼を安定して供給することができる。
【図面の簡単な説明】
【図１】１４％Ｃｒ−０．１％Ｓｉ−１．５％Ａｌ−０．５％Ｎｂ−１．８％Ｍｏ鋼をベースに、Ｗを種々の割合で添加した時の耐高温酸化性について調べた結果を示したグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention is suitable for high-temperature oxidation resistance and high-temperature resistance suitable for members used in high-temperature environments, such as exhaust pipes of automobiles and motorcycles, catalyst outer cylinders, exhaust ducts of thermal power plants, and fuel cell-related members. The present invention relates to a ferritic stainless steel excellent in salt damage.
[0002]
[Prior art]
Exhaust system members used in the exhaust system environment of automobiles, such as exhaust manifolds, exhaust pipes, converter cases and mufflers, are required to have improved oxidation resistance and salt damage resistance at high temperatures as described later. Have been.
The reason is that an increase in exhaust gas temperature is inevitable to improve engine performance.
[0003]
In the above applications, workability is also important, and from this viewpoint, Type 429 steel (14Cr-0.9Si-0.4Nb-based) is frequently used.
[0004]
[Problems to be solved by the invention]
However, even the exhaust system member described above has a problem in terms of oxidation resistance at high temperatures exceeding 900 ° C., that is, high-temperature oxidation resistance.
That is, in order to further improve engine performance, a further increase in exhaust gas temperature is inevitable, but when the exhaust gas temperature rises above 900 ° C, abnormal oxidation occurs in any of the current materials, The problem was that it could not withstand actual use.
Here, abnormal oxidation means that when a material is exposed to a high-temperature exhaust gas, an Fe oxide is generated. Since the oxidation speed of the Fe oxide is abnormally high, the oxidation proceeds rapidly, and It refers to the phenomenon of becoming ragged.
[0005]
Further, as described above, when the exhaust gas temperature increases, resistance to salt damage at high temperatures, that is, high-temperature salt damage resistance also becomes important.
Here, high-temperature salt damage refers to corrosion caused when salt in road surface freeze inhibitors sprayed on the road surface in cold regions or seawater salt in coastal areas adheres to exhaust pipes and is heated to high temperatures. The plate thickness decreases due to such corrosion.
[0006]
The present invention advantageously solves the above-mentioned problems, and provides a ferritic stainless steel that can withstand use at high temperatures such as an exhaust gas temperature exceeding 900 ° C. and has excellent high-temperature oxidation resistance and high-temperature salt damage resistance. The purpose is to propose.
[0007]
[Hands to solve the problem]
The present inventors have conducted intensive studies to achieve the above-mentioned object. As a result, in order to improve the high-temperature oxidation resistance, the addition of W, especially the combined addition of Mo and W, has the problem that It has been found that the addition of Al is effective in improving Al.
The present invention is based on the above findings.
[0008]
That is, the gist configuration of the present invention is as follows.
1. In mass%,
C: 0.02% or less,
Si: 2.0% or less,
Mn: 2.0% or less,
Cr: 12.0 to 16.0%,
Mo: 1.0 to 5.0%,
W: more than 2.0%, 5.0% or less,
Al: more than 0.5%, not more than 7.0%,
Nb: 5 (C + N) to 1.0% and N: 0.02% or less, with the balance being Fe and inevitable impurities, characterized by high-temperature oxidation resistance and high-temperature salt damage resistance. Excellent ferritic stainless steel.
[0009]
2. In the above item 1, the total amount of Mo and W is (Mo + W) ≧ 4.3% by mass%.
A ferritic stainless steel excellent in high-temperature oxidation resistance and high-temperature salt damage resistance, characterized by satisfying the following conditions.
[0010]
3. In the above 1 or 2, the steel further contains Ti: 0.5% or less by mass%;
A ferritic stainless steel excellent in high-temperature oxidation resistance and high-temperature salt damage resistance, having a composition containing at least one selected from Zr: 0.5% or less and V: 0.5% or less. .
[0011]
4. In the above 1, 2 or 3, the steel further contains Ni: 2.0% or less by mass%;
Cu: 1.0% or less,
A ferritic stainless steel excellent in high-temperature oxidation resistance and high-temperature salt damage resistance, having a composition containing at least one selected from Co: 1.0% or less and Ca: 0.01% or less. .
[0012]
5. In any one of the above 1 to 4, the steel further contains B: 0.01% or less by mass%;
Mg: A ferritic stainless steel excellent in high-temperature oxidation resistance and high-temperature salt damage resistance, having a composition containing at least one selected from 0.01% or less.
[0013]
6. The ferritic stainless steel according to any one of the above items 1 to 5, characterized in that the steel further has a composition containing 0.1% or less of REM by mass%. steel.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the reason for limiting the component composition to the above range in the present invention will be described. In addition, "%" display about a component shall mean the mass% unless there is particular notice.
C: not more than 0.02% C deteriorates toughness and workability, so its inclusion is preferably reduced as much as possible. From this viewpoint, in the present invention, the C content is limited to 0.02% or less. More preferably, it is 0.008% or less.
[0015]
Si: 2.0% or less Si effectively contributes to improvement of high-temperature salt damage resistance, but on the other hand, increases the hardness at room temperature and lowers the workability, so it was limited to 2.0% or less. In the present invention, since the addition of Al improves the high-temperature salt damage resistance, when a sufficient amount of Al is added, it is preferable to reduce the amount of Si in terms of workability, From this viewpoint, the amount of Si is preferably set to 0.5% or less. It is more preferably at most 0.1%.
[0016]
Mn: 2.0% or less Mn effectively contributes as a deoxidizing agent, but excessive addition forms MnS and lowers the corrosion resistance, so it was limited to 2.0% or less. More preferably, it is 1.0% or less. From the viewpoint of scale peeling resistance, the higher the amount of Mn, the better. Therefore, from this viewpoint, it is preferable to contain 0.3% or more.
[0017]
Cr: 12.0 to 16.0%
Cr is a basic element that improves corrosion resistance and oxidation resistance, but has the disadvantage of increasing strength at room temperature and reducing workability. In the present invention, since the oxidation resistance at a high temperature is improved by adding W and Al, the Cr content is set to 16.0% or less from the viewpoint of workability. On the other hand, if the Cr content is less than 12.0%, the corrosion resistance is significantly reduced even if W or Al is added, so the lower limit was set to 12.0%. More preferably, it is in the range of 14.0 to 16.0%.
[0018]
Mo: 1.0 to 5.0%
Mo effectively contributes to improvement of not only high temperature strength but also oxidation resistance and corrosion resistance. Therefore, in the present invention, Mo is contained in an amount of 1.0% or more. However, if the content is too large, the strength at room temperature increases and the workability decreases, so the upper limit was set to 5.0%. More preferably, it is in the range of 1.8 to 2.5%.
[0019]
W: more than 2.0%, 5.0% or less W is an element that is particularly important in the present invention. That is, by adding W in the above-mentioned ferritic stainless steel to which Mo is added, remarkable improvement in high-temperature oxidation resistance can be achieved. Also, it effectively contributes to improvement of high-temperature strength. However, when the W content is 2.0% or less, the effect of the addition is poor. On the other hand, when the W content is more than 5.0%, the cost is increased. Therefore, W is more than 2.0% and 5.0% or less. In the range described above. More preferably, it is in the range of 3.0 to 3.5%.
[0020]
Fig. 1 shows the high temperature oxidation resistance when W is added at various ratios based on 14% Cr-0.1% Si-1.5% Al-0.5% Nb-1.8% Mo steel. The result of examining is shown.
In the high-temperature oxidation resistance test, the test piece was kept in an air atmosphere at 1050 ° C. for 100 hours, and the weight of the test piece after this test was evaluated. If the weight change after the test is 10 mg / cm ² or less, it can be said that the high-temperature oxidation resistance is excellent.
As shown in the figure, when W is contained more than 2.0%, the high-temperature oxidation resistance is remarkably improved.
[0021]
(Mo + W) ≧ 4.3%
As described above, the high-temperature oxidation resistance can be significantly improved by adding Mo and W in combination. For that purpose, the total amount of these elements is preferably set to 4.3% or more. It is more preferably at least 4.7%.
[0022]
Al: more than 0.5%, not more than 7.0% Al effectively contributes to the improvement of high-temperature salt damage resistance. Therefore, in the present invention, it is included as an essential element in a range of more than 0.5%. However, if the content exceeds 7.0%, the embrittlement of the steel material becomes remarkable, so the upper limit of Al is set to 7.0%.
[0023]
Nb: 5 (C + N) to 1.0%
Nb is an element effective for improving the high-temperature strength, and in order to exhibit this effect, it is necessary to contain 5 (C + N) or more in consideration of the amounts of C and N. However, too much addition increases the strength at room temperature and lowers workability, so the upper limit was 1.0%. More preferably, it is in the range of 0.4 to 0.7%.
[0024]
N: 0.02% or less N also deteriorates the toughness and workability similarly to C, so it is preferable to minimize the incorporation of N. From this viewpoint, in the present invention, the N content is limited to 0.02% or less. More preferably, it is 0.008% or less.
[0025]
As described above, the basic components have been described. However, in the present invention, other elements described below can be appropriately contained.
At least one of Ti, Zr and V selected from Ti: 0.5% or less, Zr: 0.5% or less and V: 0.5% or less: From this viewpoint, it is preferable to contain each of them in an amount of 0.02% or more. However, if the content exceeds 0.5%, the steel material will be embrittled. Therefore, each content is set to 0.5% or less.
Since these elements are also effective in improving the high-temperature strength, it is preferable that the total (W + Ti + Zr + V + Cu) amount of the above-mentioned W and Cu described later is more than 3%.
[0026]
Ni: 2.0% or less, Cu: 1.0% or less, Co: 1.0% or less, and Ca: 0.01% or less Ni, Cu, Co and Ca are all toughness. Are effective elements for improving Ni, and are contained at Ni: 2.0% or less, Cu: 1.0% or less, Co: 1.0% or less, and Ca: 0.01% or less, respectively. In particular, Ca, when Ti is contained, effectively contributes to prevention of nozzle clogging during continuous casting. In order to sufficiently exhibit the effects of these elements, Ni: 0.5% or more, Cu: 0.05% or more, Co: 0.03% or more, and Ca: 0.0005% or more. It is preferable to include them.
[0027]
At least one of B and Mg selected from B: 0.01% or less and Mg: 0.01% or less, both of which effectively contribute to improvement of the brittleness in secondary processing, but the content exceeds 0.01%. In addition, since the strength at room temperature is increased and the ductility is reduced, the content of each is set to 0.01% or less. More preferably, B: 0.0003% or more and Mg: 0.0003% or more.
[0028]
REM: 0.1% or less REM effectively contributes to the improvement of oxidation resistance. More preferably, it is 0.002% or more. In the present invention, REM means a lanthanoid element and Y.
[0029]
Next, a preferred method for producing the steel of the present invention will be described. The production conditions of the steel according to the present invention are not particularly limited, and a general production method of Cr-containing steel can be suitably used.
For example, after smelting molten steel adjusted to the above appropriate composition range using smelting furnaces such as converters and electric furnaces, and further using smelting such as ladle refining and vacuum refining, continuous casting or ingot casting -It is preferable that after the slab is formed by the lumping method, each of the steps of hot rolling, hot rolling annealing, pickling, cold rolling, finish annealing, and pickling is sequentially performed to obtain a cold rolled annealed plate. The cold rolling may be performed once or two or more times including intermediate annealing. The steps of cold rolling, finish annealing, and pickling may be repeated. In some cases, the hot-rolled sheet annealing may be omitted. Further, when glossiness is required, it is advantageous to apply a skin pass or the like.
[0030]
【Example】
50 kg steel ingots having the component compositions shown in Table 1 were produced, and these ingots were heated to 1100 ° C., and then hot-rolled into hot-rolled sheets having a thickness of 5 mm. Then, for these hot rolled sheets, hot rolled sheet annealing (annealing temperature: 1000 ° C)-pickling-cold rolling (cold rolling reduction: 60%)-finish annealing (annealing temperature: 1000 ° C)-pickling In order to obtain a cold-rolled annealed plate having a thickness of 2 mm.
Table 2 shows the results of examining the high-temperature oxidation resistance and high-temperature salt damage resistance of the thus obtained cold-rolled annealed sheet.
[0031]
In addition, each characteristic was evaluated as follows.
(1) High-temperature oxidation resistance Two test pieces (2 mm thick x 20 mm width x 30 mm length) were sampled from each cold-rolled annealed plate, and these test pieces were placed in an air atmosphere at 1050 ° C for 100 hours. Held. The weight of each test piece before and after the test was measured, the change in weight before and after the test was calculated, and the average value of the two pieces was obtained. If this weight change is 10 mg / cm ² or less, it can be said that the high-temperature oxidation resistance is excellent.
(2) High-temperature salt damage resistance Two test pieces (2 mm thick x 20 mm width x 30 mm length) were sampled from each cold-rolled annealed plate, immersed in 5% saline for 1 hour, and then heated to 700 ° C in air. The process of heating for 23 hours in an atmosphere and cooling for 5 minutes was defined as one cycle, and the weight change after 10 cycles was measured, and the average value was determined. The smaller the weight change, the better the high-temperature salt damage resistance. In the present invention, the case where the weight change Δw is 40 (mg / cm ² ) or more is x, and the case where 30 ≦ Δw <40 (mg / cm ² ) Was evaluated as ○, 20 ≦ Δw <30 (mg / cm ² ) as ◎, and Δw <20 (mg / cm ² ) as ☆.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
As is clear from Table 2, all the steel sheets according to the present invention have good characteristic values in both high-temperature oxidation resistance and high-temperature salt damage resistance.
[0035]
【The invention's effect】
Thus, according to the present invention, a ferritic stainless steel excellent in high-temperature oxidation resistance and high-temperature salt damage resistance can be stably obtained.
Therefore, according to the present invention, by improving the engine performance, it is possible to stabilize stainless steel that can withstand not only automotive-related applications where the exhaust gas temperature exceeds 900 ° C. but also fuel cell-related applications and power plant-related applications. Can be supplied.
[Brief description of the drawings]
FIG. 1 shows high-temperature oxidation resistance when W is added at various ratios based on 14% Cr-0.1% Si-1.5% Al-0.5% Nb-1.8% Mo steel. 6 is a graph showing the results of examining the results.

Claims (6)

In mass%,
C: 0.02% or less,
Si: 2.0% or less,
Mn: 2.0% or less,
Cr: 12.0 to 16.0%,
Mo: 1.0 to 5.0%,
W: more than 2.0%, 5.0% or less,
Al: more than 0.5%, not more than 7.0%,
Nb: 5 (C + N) to 1.0% and N: 0.02% or less, with the balance being Fe and unavoidable impurities, characterized by high-temperature oxidation resistance and high-temperature salt damage resistance. Excellent ferritic stainless steel. 2. The composition according to claim 1, wherein the total amount of Mo and W is (Mo + W) ≧ 4.3% by mass%.
A ferritic stainless steel excellent in high-temperature oxidation resistance and high-temperature salt damage resistance, characterized by satisfying the following conditions. 3. The steel according to claim 1, wherein the steel further comprises Ti: 0.5% or less by mass%.
A ferritic stainless steel excellent in high-temperature oxidation resistance and high-temperature salt damage resistance, having a composition containing at least one selected from Zr: 0.5% or less and V: 0.5% or less. . The steel according to claim 1, 2, or 3, further comprising: Ni: 2.0% or less by mass%.
Cu: 1.0% or less,
A ferritic stainless steel excellent in high-temperature oxidation resistance and high-temperature salt damage resistance, having a composition containing at least one selected from Co: 1.0% or less and Ca: 0.01% or less. . 5. The steel according to claim 1, wherein the steel further contains B: 0.01% or less by mass%.
Mg: A ferritic stainless steel excellent in high-temperature oxidation resistance and high-temperature salt damage resistance, having a composition containing at least one selected from 0.01% or less. The ferrite system according to any one of claims 1 to 5, wherein the steel further has a composition containing 0.1% or less of REM by mass%. Stainless steel.

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