CA2053175A1 - Aluminum-containing ferritic stainless steel having excellent high temperature oxidation resistance and toughness - Google Patents
Aluminum-containing ferritic stainless steel having excellent high temperature oxidation resistance and toughnessInfo
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- CA2053175A1 CA2053175A1 CA002053175A CA2053175A CA2053175A1 CA 2053175 A1 CA2053175 A1 CA 2053175A1 CA 002053175 A CA002053175 A CA 002053175A CA 2053175 A CA2053175 A CA 2053175A CA 2053175 A1 CA2053175 A1 CA 2053175A1
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- steel
- high temperature
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- oxidation resistance
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- Engineering & Computer Science (AREA)
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- Organic Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
Abstract of the Disclosure There is disclosed a ferritic stainless steel essentially consisting of C: not more than 0.03 %, Si:
less than 0.25 %, Mn: less than 0.25 %, P: not more than 0.03 %, S: less than 0.001 %, N: not more than 0.03 %, Cr: 15 - 25 %, Al: 3 - 6 %, at least one of REM, Y and alkaline earth metals: 0.01 - 0.2 %, optionally at least one of Nb, V and Ti: 0.05 - 1 % and the balance of Fe and unavoidable incidental impurities. This steel has excellent high temperature oxidation resistance, espe-cially resistance to abnormal oxidation and high tough-ness and is suitable for manufacturing foil substrate for metallic catalytic converters for automobile exhaust gas treatment.
less than 0.25 %, Mn: less than 0.25 %, P: not more than 0.03 %, S: less than 0.001 %, N: not more than 0.03 %, Cr: 15 - 25 %, Al: 3 - 6 %, at least one of REM, Y and alkaline earth metals: 0.01 - 0.2 %, optionally at least one of Nb, V and Ti: 0.05 - 1 % and the balance of Fe and unavoidable incidental impurities. This steel has excellent high temperature oxidation resistance, espe-cially resistance to abnormal oxidation and high tough-ness and is suitable for manufacturing foil substrate for metallic catalytic converters for automobile exhaust gas treatment.
Description
~33~ 7~
Title of the Invention Aluminum-containing ferritic stainless steel having excellent high temperature oxidation resistance and toughness Field of the Invention The present invention relates to an aluminum (Al)~
containing ferritic stainless steel for use in automo-bile exhaust-gas-treating apparatuses, heating appara-tuses and the like.
BackgLround of Invention Al-con~aining ferri~ic stainless steels have excel-lent high temperature oxidation resistance and thus are widely used for parts of heating apparatuses such as stove chimneys, electric heating means, etc.
Recently, such steels also have come to be used as the substrate of catalytic converters in place of ceram-ic materials conventionally used therefor. As is well known, ceramics are weak against thermal shock and have large heat capacity and thus they require a long time to e heat up to the ~emperature for the catalytic reaction.
Therefore, metallic catalaytic convertexs, which are free from the defects of ceramic ctalytic converters, are now attracting the attention of those skilled in the art. The substrate of metallic catalytic converters is formed of metal foil having a thickness of around 50 microns.
~ his substrate is used in an exhaust gas atmos-phere, in which catalytic reaction takes place and, therefore, has to have excellent high temperature oxida-tion resistance. In view of this fact, high-Al ferritic stainless steels essentially comprising 20Cr~5Al and containing rare earth metals (R~M), yttrium (Y), etc.
are used for this purpose. However, even these steels are not fully satisfactory in terms of high temperature oxidation resistance and abnormal oxidation occurs if they are subjected to high temperature oxidation ~or a prolonged period of time. Higher power engines, which emit higher temperature exhaust gas, are now coming into , :
. ~ :
,- - - ' .: .
Title of the Invention Aluminum-containing ferritic stainless steel having excellent high temperature oxidation resistance and toughness Field of the Invention The present invention relates to an aluminum (Al)~
containing ferritic stainless steel for use in automo-bile exhaust-gas-treating apparatuses, heating appara-tuses and the like.
BackgLround of Invention Al-con~aining ferri~ic stainless steels have excel-lent high temperature oxidation resistance and thus are widely used for parts of heating apparatuses such as stove chimneys, electric heating means, etc.
Recently, such steels also have come to be used as the substrate of catalytic converters in place of ceram-ic materials conventionally used therefor. As is well known, ceramics are weak against thermal shock and have large heat capacity and thus they require a long time to e heat up to the ~emperature for the catalytic reaction.
Therefore, metallic catalaytic convertexs, which are free from the defects of ceramic ctalytic converters, are now attracting the attention of those skilled in the art. The substrate of metallic catalytic converters is formed of metal foil having a thickness of around 50 microns.
~ his substrate is used in an exhaust gas atmos-phere, in which catalytic reaction takes place and, therefore, has to have excellent high temperature oxida-tion resistance. In view of this fact, high-Al ferritic stainless steels essentially comprising 20Cr~5Al and containing rare earth metals (R~M), yttrium (Y), etc.
are used for this purpose. However, even these steels are not fully satisfactory in terms of high temperature oxidation resistance and abnormal oxidation occurs if they are subjected to high temperature oxidation ~or a prolonged period of time. Higher power engines, which emit higher temperature exhaust gas, are now coming into , :
. ~ :
,- - - ' .: .
2 ~ . 7 ~
use and adoption of manifold con~erters, which are placed nearer to the engine, is contemplated and thus converters inevitably have to treat exhaust gas of higher temperature.
Conventional steel materials for mekallic convert-ers are not satisfactory under such conditions and Al-containing ferritic stainless steels having far betker high temperature oxidation resistance are desired.
Steels of this kind are disclosed in Japanese Laid-Open Patent Publications Nos. 63-76850, 63-45s351, etc. These steels withstand oxidation for less than 200 hours a~ 1150C. However, the oxidation resistance of this level is now no longer a sufficient level of oxidation resistance.
It is well known that Al-con~aining ferritic stain-less steels are inferior in the toughness of slabs and hot-rolled sheets and, especially, that steels for metallic cakaalytic converters containing high levels of chromium (Cr) and Al are poor in toughness and thus cause difficult problems when they are manufactured in a mass production line.
It is known that incr0asing the contents of Cr, Al, REM, Y, etc. is effective for improving high temperature oxidation resistance of high-~l ferritic stainless steels. However, increasing contents of Cr, Al, REM and Y deqrades the toughness of slabs and hot-rolled steel sheets produced therefrom and thus making the manufac-ture more difficult and inviting poor yield or making production impossible. Besides, REM and Y are very expensive materials and thus the increased incorporation threarof raises the cost of the products. Therefore, the contents of Cr, Al, REM and Y cannot be increased so much.
Under the circumstances, a need exists for a no~el ferritic stainless steel that has an excellent high temperature oxidation resistance suitable for a metallic catalytic converter material, good toughness and excel-lent manufacturability and which contains Cr, Al, REM
.
. ~ :, . .. . .
:
- . , .
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and Y of the same le~els as the conventional stainless steels for metallic converters.
The present invention is intended to provide a Fe-Cr-Al-REM, Y ferritic stainless steel for metallic catalytic converters having sufficient high temperature oxidation resistance~ excellent toughness and good manufacturabiliky, wherein the A1203 formed on the surface thereof does not suffer abnormal oxidation. We discovered that manganese (Mn) oxide compounds penetrate 1~ into the A1203 formed on the surface of the steel imme-diately before the abnormal oxidation occurs. So we thought of inhibiting the formation of Mn oxide com-pounds and the penetration thereof into the A12O3 layer and we found that a ferritic stainless steel having ~S excellent high temperature oxidation resistance under ultra-thin condition and further excellen~ toughness as well as good manufacturability can be obtained by re-stricting both the Mn and Si contents to less than 0.25 % respectively and optionally adding V, Ti and Nb to the conventional Al-containing ferritic stainless steel.
Summary of the Invention_ The present invention provides a ferritic stainless steel essentially consisting of:
C: not more than 0.03 Si: less than 0.25 %
Mn: less than Q.25 %
P: not more than 0.03 %
S: less than 0.001 %
N: not more than 0.03 %
Cr: 15 - 25 %
Al: 3 - 6 %
at least one of REM, Y and alkaline earth metals:
0.~1 - 0.2 %
balance of Fe and inevitable incidental impurities 35 and a ferritic stainless steel essentially consisting of the above-described composition and further contains:
at least one of Nb, V and Ti: 0.05 - 1 %.
. . . ,, ' :: .,' 2~3~
In the present invention, the Mn content is prefer-ably 0.21 ~ or less and more preferably 0.13 % or less.
The Si content is preferably 0.22 % or less and more preferably 0.17 ~ or less.
The reason for defining the composition of the steel of the present invention as above is generally as follows.
C: From the viewpoint of oxidation resistance, generally the higher the C content, the higher the 'C~ liability to occurrence of abnormal oxida~ion. The toughness of slabs and hot coils of high-Al-containing ferritic stainless steels deteriorates as the C content increases. In consideration of these facts, the C
content is limited to not more than 0.03 %.
Si: Si content is the most significant factor in the steel of the present invention. Generally, it is considered that Si is effective for high temperature oxidation resistance. In the case of high-Al-containing ferritic steels, however, the high temperature oxidation 20 resistance thereof is markedly improved by reducing the Si content. We found that the high temperature oxidation resistance of high-Al-containing ~erritic stainless steels is marXedly improved by reducing both the Si content and the ~n conten~ simultaneously. Also, ~5 the toughness of the high-Al-containing ferritic stain-less steel can be markedly improved by reducing the Si content. We found that the above-described effects are brought about if the Si content is reduced to less than 0.~5 %.
3Q Mn: In the present invention, the Mn content is significant. Generally Mn is effective for improving hot-workability. In the case of the present invention, however, Mn has a deleterious effect on high temperature oxidation resistance. Ne found that the high tempera-35 ture oxidation resistance of high-Al-containing ferritic - stainless steels is markedly improved by reducing the Mn content and further by increased addition of Cr, Al, - REM, Y, etc. The toughness~of the s~eel of the present .
:
~3~ 7~5 invention is also remarkably improved by reduction of the Mn content and the effect is achieved by reducing the Mn content to less than 0.25 %. That is, the lower the Mn content, the better the effect and thus the Mn content is defined as less than 0.25 %.
P: P is an element which is deleterious to high temperature oxidation resistance as well as toughness of steels and, therefore, the lower the P content~ the better the steel properties in general. In the case of ;~ the present invention, the P content should be not more than 0.03 %.
S: S forms compounds with REM, Y, etc. which degrade the surface properties as non-metallic inclu-sions. Also S consumes metallic REM, Y etc., which are lS effective for high temperature oxidation resistance.
These adverse effects are great when the content is 0.001% or more. That is, the high temperature oxidation resistance is improved by reducing the S content to less than 0.001 %. In the present invention, the S content is defined as less than 0.001 %.
N: N reduces toughness of steels of the kind contemplated by the present invention. Also, it forms AlN consuming Al, which is effective for providing the steel with high temperature oxidation resistance, and thus inducing abnormal oxidation. The lower the N
content, the better the oxidation resistance. In the present invention, the N conten~ is defined as no~ more than 0.03 %.
Cr: Cr is a fundamental element that provides the steel with high temperature oxidation resistance. At least 15 ~ of Cr is required in order to exhibit its effect. On the other hand, Cr in excess of 25 % dete-riorates the toughness of slabs and hot coils, causing difficulty in manufacturing. Thus the Cr content is ~5 defined as-15 - 25 %.
Al: Al is an essential element as well as Cr or providing the steel with high temperature oxidation resistance. In the foil material contemplated by the ' ' , , , ~3 ~
present invention, abnormal oxidation readily occurs.
In this sense, addition of not less than 3 % of Al is necessary. In ~he present invention, however, the Al content need not be excessively high. Rather, Al in excess of 6 % deteriorates the toughness of slabs and hot coils. Thus the Al content is deined as 3 - 6 %.
REM, Y and alkaline earth metals: These are impor-tant elements which improve the high temperature oxida-tion resistance of Fe-Cr-Al alloys. They greatly im-'0 prove the protecting effect of the formed oxide film,well inhibit abnormal oxidation, which easily develops in very thin materials, and improve adherence of the produced oxide film to the substrate. With a content o~
less than 0.01 %, the effect is not exhibited. To the contrary, at a content in excess of 0.2 %, they adverse-ly affect hot-workability, making manufacture difficult, and form non-me~allic inclusions impairing the surface properties. Thus the content of these elements is defined as 0.01 - 0.2 %.
Nb, V and Ti: When contained in suitable amounts, these elements combine with C and N in the steel and greatly improve the toughness of the steel. The steel of the present invention is used in severe high tempera-ture environments and thus is required to be provided 25 with excellent high temperature strength. Addition of these elements is very effective for this purpose.
Addition of O.OS % or more is required. The maximum amount is limited to 1 % since addition of excessive amount hardens the steel.
30 Brief Description of the Attached ~rawinq The invention will now be specifically described with reference to the attached drawingl which is a graph showing the influence of Mn and Si on the impact strength of 20Cr-SAl-O.lTi-O.lLa steels a~ room tempera-3~ ture.Specific Disclosure of_the ~nvention The high temperature oxidation resistance of high-Al-containing ferritic steels is provided by the A12O3 2~.~3~ 7~
which forms on the surface of the steel. Therefore, it is considered that the high temperature oxidation re-sistance will be improved as the Al content is in-creased. Test specimens of the compositions indicated in Table 1 respectively having a thickness of 50 microns were subjec~ed to an oxidation test at 1150 C and the time until abnormal oxidation occurred was measured.
The results are also indicated in Table 1. From ~hese results, it is apparent that with increase in the con-tents of Cr and Al and addition of REM, high temperatureoxidation resistance is improved and the steel becomes less susceptible t.o abnormal oxidation.
Then, ste~ls of the compositions as indicated in Table 2, which further contained REM, were tested. 30 kg heat of each steel was melted in vacuum and casted and the ingot was forged. All the steel samples de-veloped cracking during forging and further working was impossible. This fact proved that increase of Cr, Al and REM is impossible from the viewpoint of manufacture.
So we conducted an extensive study in order to develop a steel having excellent high temperature oxidation with-out increasing contents of Cr, Al and REM. As a result, we found that some Mn oxide compounds had penetrated into the formed A12O3 surface film immediately before abnormal oxidation occurred. Thus we thought that these Mn oxide compounds adversely affected high temper-ature oxidation resistance of the steel and further stud~ was conducted on inhibition of formation of the Mn oxide compounds. Thus we found that the formation of 30` said Mn oxide compound is inhibited by reducing the content of Mn and Si.
Steels of the compositions as indicated in Table 3 were prepared and respectively made into 50 micron thick test specimens, which were sub~ected to oxidation test at 1150 C. The time up to the occurrence of abnormal oxidation was measured and the effect of the contents of Mn and Si was checked. The results are also indicated in Table 3. Table 3 shows that decrease in the Mn and ": :
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2 ~ 7 ~
Si contents prolongs the time until abnormal oxida~ion occurs and is very effective for improving the high temperature oxidation resistance. Specifically, pron-nonced effect was obtained by reducing the contents of 5 Mn and Si respectively to less than 0.25 %. That is to say, a ferritic stainless steel having highly improved high temperature oxidation resistance was obtained by merely reducing the contents of Mn and Si without in-creasing the contents of Cr, Al and REM over that of the '0 conventional steel for metallic catalytic converters.
Further, the effect of Mn and Si on the improvement of toughness of hot-rolled steel sheets was examined.
Respectively 100 kg heats of 20Cr-5AL-O.lTi-O.lLa skeels containing various amounts of Mn and Si were melted in vacuum and casted, and the ingots were forged and hot-rolled. The hot-rolled specimens were subjected to Charpy impact test. The results are shown in the at~
tached drawing. The drawing shows that the impact test value rises as the Mn content decreases and the reduc-2G tion in the Si content also increases the impact testvalue.
As has been described above, various tests wera carried out and it was found that reduction of the Mn and Si contents of a high-Al-containing ferritic stain-less steel brings about excellent high temperatureoxidation resistance without increasing the contents o Cr, Al and REM over those of the conventional composi-tion. The thus obtained high-Al-containing ferritic steel exhibits excellent toughness and is amenable to 3Q the mass production by the conventional equipment, which has been difficult with a steel of this kind.
The invention will now be illustrated by way of working examples.
Respectively 30 kg heats of the steels of the compositions indicated in Table 4 were melted and casted and the ingots were forged, machined, hot-rolled and, thereafter, made into 30 micron thick ~heets b~
repeating annealing and cold rolling. These sampLes .
~3~ ~
were subjected to an oxidation test at 1150 C and the time upto the occurrence of the abnormal oxidation was measured. The results are al50 shown in Table 4. The results show that for the steels of the present inven-5 tion the time required for the occurrence of abnormaloxidation was remarkably prolonged in comparison with conventional steels, that is, the oxidation resistance of the steel of the present invention is greatly im-proved.
1~ Also the results of the test on impact toughness of the hot-rolled specimens are shown in Table 4. The results show that the toughness is also remarkably improved in the steel of the presen~ invention.
As has been described above, the present invention 15 provides an inexpensive steel material having excellent high temperature oxidation resistance and excellent toughness without adding unnecessarily large amounts of Cr, Al, REM and Y.
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use and adoption of manifold con~erters, which are placed nearer to the engine, is contemplated and thus converters inevitably have to treat exhaust gas of higher temperature.
Conventional steel materials for mekallic convert-ers are not satisfactory under such conditions and Al-containing ferritic stainless steels having far betker high temperature oxidation resistance are desired.
Steels of this kind are disclosed in Japanese Laid-Open Patent Publications Nos. 63-76850, 63-45s351, etc. These steels withstand oxidation for less than 200 hours a~ 1150C. However, the oxidation resistance of this level is now no longer a sufficient level of oxidation resistance.
It is well known that Al-con~aining ferritic stain-less steels are inferior in the toughness of slabs and hot-rolled sheets and, especially, that steels for metallic cakaalytic converters containing high levels of chromium (Cr) and Al are poor in toughness and thus cause difficult problems when they are manufactured in a mass production line.
It is known that incr0asing the contents of Cr, Al, REM, Y, etc. is effective for improving high temperature oxidation resistance of high-~l ferritic stainless steels. However, increasing contents of Cr, Al, REM and Y deqrades the toughness of slabs and hot-rolled steel sheets produced therefrom and thus making the manufac-ture more difficult and inviting poor yield or making production impossible. Besides, REM and Y are very expensive materials and thus the increased incorporation threarof raises the cost of the products. Therefore, the contents of Cr, Al, REM and Y cannot be increased so much.
Under the circumstances, a need exists for a no~el ferritic stainless steel that has an excellent high temperature oxidation resistance suitable for a metallic catalytic converter material, good toughness and excel-lent manufacturability and which contains Cr, Al, REM
.
. ~ :, . .. . .
:
- . , .
:: . ' ~3~
and Y of the same le~els as the conventional stainless steels for metallic converters.
The present invention is intended to provide a Fe-Cr-Al-REM, Y ferritic stainless steel for metallic catalytic converters having sufficient high temperature oxidation resistance~ excellent toughness and good manufacturabiliky, wherein the A1203 formed on the surface thereof does not suffer abnormal oxidation. We discovered that manganese (Mn) oxide compounds penetrate 1~ into the A1203 formed on the surface of the steel imme-diately before the abnormal oxidation occurs. So we thought of inhibiting the formation of Mn oxide com-pounds and the penetration thereof into the A12O3 layer and we found that a ferritic stainless steel having ~S excellent high temperature oxidation resistance under ultra-thin condition and further excellen~ toughness as well as good manufacturability can be obtained by re-stricting both the Mn and Si contents to less than 0.25 % respectively and optionally adding V, Ti and Nb to the conventional Al-containing ferritic stainless steel.
Summary of the Invention_ The present invention provides a ferritic stainless steel essentially consisting of:
C: not more than 0.03 Si: less than 0.25 %
Mn: less than Q.25 %
P: not more than 0.03 %
S: less than 0.001 %
N: not more than 0.03 %
Cr: 15 - 25 %
Al: 3 - 6 %
at least one of REM, Y and alkaline earth metals:
0.~1 - 0.2 %
balance of Fe and inevitable incidental impurities 35 and a ferritic stainless steel essentially consisting of the above-described composition and further contains:
at least one of Nb, V and Ti: 0.05 - 1 %.
. . . ,, ' :: .,' 2~3~
In the present invention, the Mn content is prefer-ably 0.21 ~ or less and more preferably 0.13 % or less.
The Si content is preferably 0.22 % or less and more preferably 0.17 ~ or less.
The reason for defining the composition of the steel of the present invention as above is generally as follows.
C: From the viewpoint of oxidation resistance, generally the higher the C content, the higher the 'C~ liability to occurrence of abnormal oxida~ion. The toughness of slabs and hot coils of high-Al-containing ferritic stainless steels deteriorates as the C content increases. In consideration of these facts, the C
content is limited to not more than 0.03 %.
Si: Si content is the most significant factor in the steel of the present invention. Generally, it is considered that Si is effective for high temperature oxidation resistance. In the case of high-Al-containing ferritic steels, however, the high temperature oxidation 20 resistance thereof is markedly improved by reducing the Si content. We found that the high temperature oxidation resistance of high-Al-containing ~erritic stainless steels is marXedly improved by reducing both the Si content and the ~n conten~ simultaneously. Also, ~5 the toughness of the high-Al-containing ferritic stain-less steel can be markedly improved by reducing the Si content. We found that the above-described effects are brought about if the Si content is reduced to less than 0.~5 %.
3Q Mn: In the present invention, the Mn content is significant. Generally Mn is effective for improving hot-workability. In the case of the present invention, however, Mn has a deleterious effect on high temperature oxidation resistance. Ne found that the high tempera-35 ture oxidation resistance of high-Al-containing ferritic - stainless steels is markedly improved by reducing the Mn content and further by increased addition of Cr, Al, - REM, Y, etc. The toughness~of the s~eel of the present .
:
~3~ 7~5 invention is also remarkably improved by reduction of the Mn content and the effect is achieved by reducing the Mn content to less than 0.25 %. That is, the lower the Mn content, the better the effect and thus the Mn content is defined as less than 0.25 %.
P: P is an element which is deleterious to high temperature oxidation resistance as well as toughness of steels and, therefore, the lower the P content~ the better the steel properties in general. In the case of ;~ the present invention, the P content should be not more than 0.03 %.
S: S forms compounds with REM, Y, etc. which degrade the surface properties as non-metallic inclu-sions. Also S consumes metallic REM, Y etc., which are lS effective for high temperature oxidation resistance.
These adverse effects are great when the content is 0.001% or more. That is, the high temperature oxidation resistance is improved by reducing the S content to less than 0.001 %. In the present invention, the S content is defined as less than 0.001 %.
N: N reduces toughness of steels of the kind contemplated by the present invention. Also, it forms AlN consuming Al, which is effective for providing the steel with high temperature oxidation resistance, and thus inducing abnormal oxidation. The lower the N
content, the better the oxidation resistance. In the present invention, the N conten~ is defined as no~ more than 0.03 %.
Cr: Cr is a fundamental element that provides the steel with high temperature oxidation resistance. At least 15 ~ of Cr is required in order to exhibit its effect. On the other hand, Cr in excess of 25 % dete-riorates the toughness of slabs and hot coils, causing difficulty in manufacturing. Thus the Cr content is ~5 defined as-15 - 25 %.
Al: Al is an essential element as well as Cr or providing the steel with high temperature oxidation resistance. In the foil material contemplated by the ' ' , , , ~3 ~
present invention, abnormal oxidation readily occurs.
In this sense, addition of not less than 3 % of Al is necessary. In ~he present invention, however, the Al content need not be excessively high. Rather, Al in excess of 6 % deteriorates the toughness of slabs and hot coils. Thus the Al content is deined as 3 - 6 %.
REM, Y and alkaline earth metals: These are impor-tant elements which improve the high temperature oxida-tion resistance of Fe-Cr-Al alloys. They greatly im-'0 prove the protecting effect of the formed oxide film,well inhibit abnormal oxidation, which easily develops in very thin materials, and improve adherence of the produced oxide film to the substrate. With a content o~
less than 0.01 %, the effect is not exhibited. To the contrary, at a content in excess of 0.2 %, they adverse-ly affect hot-workability, making manufacture difficult, and form non-me~allic inclusions impairing the surface properties. Thus the content of these elements is defined as 0.01 - 0.2 %.
Nb, V and Ti: When contained in suitable amounts, these elements combine with C and N in the steel and greatly improve the toughness of the steel. The steel of the present invention is used in severe high tempera-ture environments and thus is required to be provided 25 with excellent high temperature strength. Addition of these elements is very effective for this purpose.
Addition of O.OS % or more is required. The maximum amount is limited to 1 % since addition of excessive amount hardens the steel.
30 Brief Description of the Attached ~rawinq The invention will now be specifically described with reference to the attached drawingl which is a graph showing the influence of Mn and Si on the impact strength of 20Cr-SAl-O.lTi-O.lLa steels a~ room tempera-3~ ture.Specific Disclosure of_the ~nvention The high temperature oxidation resistance of high-Al-containing ferritic steels is provided by the A12O3 2~.~3~ 7~
which forms on the surface of the steel. Therefore, it is considered that the high temperature oxidation re-sistance will be improved as the Al content is in-creased. Test specimens of the compositions indicated in Table 1 respectively having a thickness of 50 microns were subjec~ed to an oxidation test at 1150 C and the time until abnormal oxidation occurred was measured.
The results are also indicated in Table 1. From ~hese results, it is apparent that with increase in the con-tents of Cr and Al and addition of REM, high temperatureoxidation resistance is improved and the steel becomes less susceptible t.o abnormal oxidation.
Then, ste~ls of the compositions as indicated in Table 2, which further contained REM, were tested. 30 kg heat of each steel was melted in vacuum and casted and the ingot was forged. All the steel samples de-veloped cracking during forging and further working was impossible. This fact proved that increase of Cr, Al and REM is impossible from the viewpoint of manufacture.
So we conducted an extensive study in order to develop a steel having excellent high temperature oxidation with-out increasing contents of Cr, Al and REM. As a result, we found that some Mn oxide compounds had penetrated into the formed A12O3 surface film immediately before abnormal oxidation occurred. Thus we thought that these Mn oxide compounds adversely affected high temper-ature oxidation resistance of the steel and further stud~ was conducted on inhibition of formation of the Mn oxide compounds. Thus we found that the formation of 30` said Mn oxide compound is inhibited by reducing the content of Mn and Si.
Steels of the compositions as indicated in Table 3 were prepared and respectively made into 50 micron thick test specimens, which were sub~ected to oxidation test at 1150 C. The time up to the occurrence of abnormal oxidation was measured and the effect of the contents of Mn and Si was checked. The results are also indicated in Table 3. Table 3 shows that decrease in the Mn and ": :
, : ' .: ~
2 ~ 7 ~
Si contents prolongs the time until abnormal oxida~ion occurs and is very effective for improving the high temperature oxidation resistance. Specifically, pron-nonced effect was obtained by reducing the contents of 5 Mn and Si respectively to less than 0.25 %. That is to say, a ferritic stainless steel having highly improved high temperature oxidation resistance was obtained by merely reducing the contents of Mn and Si without in-creasing the contents of Cr, Al and REM over that of the '0 conventional steel for metallic catalytic converters.
Further, the effect of Mn and Si on the improvement of toughness of hot-rolled steel sheets was examined.
Respectively 100 kg heats of 20Cr-5AL-O.lTi-O.lLa skeels containing various amounts of Mn and Si were melted in vacuum and casted, and the ingots were forged and hot-rolled. The hot-rolled specimens were subjected to Charpy impact test. The results are shown in the at~
tached drawing. The drawing shows that the impact test value rises as the Mn content decreases and the reduc-2G tion in the Si content also increases the impact testvalue.
As has been described above, various tests wera carried out and it was found that reduction of the Mn and Si contents of a high-Al-containing ferritic stain-less steel brings about excellent high temperatureoxidation resistance without increasing the contents o Cr, Al and REM over those of the conventional composi-tion. The thus obtained high-Al-containing ferritic steel exhibits excellent toughness and is amenable to 3Q the mass production by the conventional equipment, which has been difficult with a steel of this kind.
The invention will now be illustrated by way of working examples.
Respectively 30 kg heats of the steels of the compositions indicated in Table 4 were melted and casted and the ingots were forged, machined, hot-rolled and, thereafter, made into 30 micron thick ~heets b~
repeating annealing and cold rolling. These sampLes .
~3~ ~
were subjected to an oxidation test at 1150 C and the time upto the occurrence of the abnormal oxidation was measured. The results are al50 shown in Table 4. The results show that for the steels of the present inven-5 tion the time required for the occurrence of abnormaloxidation was remarkably prolonged in comparison with conventional steels, that is, the oxidation resistance of the steel of the present invention is greatly im-proved.
1~ Also the results of the test on impact toughness of the hot-rolled specimens are shown in Table 4. The results show that the toughness is also remarkably improved in the steel of the presen~ invention.
As has been described above, the present invention 15 provides an inexpensive steel material having excellent high temperature oxidation resistance and excellent toughness without adding unnecessarily large amounts of Cr, Al, REM and Y.
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Claims (10)
1. A ferritic stainless steel essentially consisting of:
C: not more than 0.03 %, Si: less than 0.25 %, Mn: less than 0.25 %, P: not more than 0.03 %, S: less than 0.001 %, N: not more than 0.03 %, Cr: 15 - 25 %, Al: 3 - 6 %, at least of one of REM, Y and alkaline earth metals.
0.01 - 0.2 %
and balance of Fe and unavoidable incidental impurities.
C: not more than 0.03 %, Si: less than 0.25 %, Mn: less than 0.25 %, P: not more than 0.03 %, S: less than 0.001 %, N: not more than 0.03 %, Cr: 15 - 25 %, Al: 3 - 6 %, at least of one of REM, Y and alkaline earth metals.
0.01 - 0.2 %
and balance of Fe and unavoidable incidental impurities.
2. The steel of Claim 1, wherein the Mn content is not more than 0.21 %.
3. The steel of Claim 2, wherein the Mn content is not more than 0.13 %.
4. The steel of Claim 1, wherein the Si content is not more than 0.21 %.
5. The steel of Claim 4, wherein the Si content is not more than 0.17 %.
6. A ferritic stainless steel essentially consisting of:
C: not more than 0.03 %, Si: less than 0.25 %, Mn: less than 0.25 %, P: not more than 0.03 %, S: less than 0.001 %, N: not more than 0.03 %, Cr: 15 - 25 %, Al: 3 - 6 %, at least of one of REM, Y and alkaline earth metals-0.01 - 0.2 %, at least one of Nb, V and Ti:
0.05 - 1 %
and balance of Fe and unavoidable incidental impurities.
C: not more than 0.03 %, Si: less than 0.25 %, Mn: less than 0.25 %, P: not more than 0.03 %, S: less than 0.001 %, N: not more than 0.03 %, Cr: 15 - 25 %, Al: 3 - 6 %, at least of one of REM, Y and alkaline earth metals-0.01 - 0.2 %, at least one of Nb, V and Ti:
0.05 - 1 %
and balance of Fe and unavoidable incidental impurities.
7. The steel of Claim 6, wherein the Mn content is not more than 0.21 %.
8. The steel of Claim 7, wherein the Mn content is not more than 0.13 %.
9. The steel of Claim 6, wherein the Si content is not more than 0.21 %.
10. The steel of Claim 9, wherein the Si content is not more than 0.17 %.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2270521A JPH04147945A (en) | 1990-10-11 | 1990-10-11 | High al-containing ferritic stainless steel excellent in high temperature oxidation resistance and toughness |
| JP2-270521 | 1990-10-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2053175A1 true CA2053175A1 (en) | 1992-04-12 |
Family
ID=17487384
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002053175A Abandoned CA2053175A1 (en) | 1990-10-11 | 1991-10-10 | Aluminum-containing ferritic stainless steel having excellent high temperature oxidation resistance and toughness |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0480461B1 (en) |
| JP (1) | JPH04147945A (en) |
| KR (1) | KR100196984B1 (en) |
| CA (1) | CA2053175A1 (en) |
| DE (1) | DE69112165T2 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3176403B2 (en) * | 1991-12-20 | 2001-06-18 | 新日本製鐵株式会社 | High strength stainless steel foil for corrugating and method for producing the same |
| JP2689208B2 (en) * | 1992-12-11 | 1997-12-10 | 新日本製鐵株式会社 | Steel for internal combustion engine exhaust systems with excellent wet corrosion resistance and workability |
| US5480608A (en) * | 1993-03-19 | 1996-01-02 | Nippon Yakin Kogyo Co., Ltd. | Ferritic stainless steel having an excellent oxidation resistance |
| JPH08117614A (en) * | 1994-10-20 | 1996-05-14 | Matsushita Electric Ind Co Ltd | Catalyst body and its manufacture |
| FR2732360B1 (en) * | 1995-03-29 | 1998-03-20 | Ugine Savoie Sa | FERRITIC STAINLESS STEEL FOR USE, IN PARTICULAR FOR CATALYST SUPPORTS |
| US6652830B2 (en) * | 2001-02-16 | 2003-11-25 | Battelle Memorial Institute | Catalysts reactors and methods of producing hydrogen via the water-gas shift reaction |
| DE10261207A1 (en) * | 2002-12-20 | 2004-07-15 | Mk Metallfolien Gmbh | Iron alloy, in particular for use in an exhaust gas cleaning unit |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3171737A (en) * | 1961-04-28 | 1965-03-02 | Hoskins Mfg Company | Electrical resistance alloy |
| SU552369A1 (en) * | 1975-12-12 | 1977-03-30 | Предприятие П/Я Р-2120 | Heat resistant steel |
| EP0033203A3 (en) * | 1980-01-28 | 1981-08-26 | Allegheny Ludlum Steel Corporation | Substrate for catalytic system and ferritic stainless steel from which it is formed |
| GB2079065B (en) * | 1980-06-27 | 1983-09-07 | Sharetree Ltd | Linear differential transformer |
| DE3780082T2 (en) * | 1986-04-21 | 1993-01-14 | Kawasaki Steel Co | STAINLESS CHROME-ALUMINUM STEEL WITH HIGH RESISTANCE TO OXYDATION AND PEELING AND CHROME-ALUMINUM STEEL FILMS FOR CATALYST CARRIERS IN CATALYTIC CONVERTERS. |
-
1990
- 1990-10-11 JP JP2270521A patent/JPH04147945A/en active Pending
-
1991
- 1991-10-10 CA CA002053175A patent/CA2053175A1/en not_active Abandoned
- 1991-10-11 KR KR1019910017925A patent/KR100196984B1/en not_active IP Right Cessation
- 1991-10-11 EP EP91117384A patent/EP0480461B1/en not_active Revoked
- 1991-10-11 DE DE69112165T patent/DE69112165T2/en not_active Revoked
Also Published As
| Publication number | Publication date |
|---|---|
| DE69112165T2 (en) | 1996-03-21 |
| EP0480461A1 (en) | 1992-04-15 |
| DE69112165D1 (en) | 1995-09-21 |
| JPH04147945A (en) | 1992-05-21 |
| KR100196984B1 (en) | 1999-06-15 |
| EP0480461B1 (en) | 1995-08-16 |
| KR920008206A (en) | 1992-05-27 |
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