JP4154932B2 - Ferritic stainless steel with excellent high-temperature strength, high-temperature oxidation resistance, and high-temperature salt damage resistance - Google Patents

Ferritic stainless steel with excellent high-temperature strength, high-temperature oxidation resistance, and high-temperature salt damage resistance Download PDF

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Publication number
JP4154932B2
JP4154932B2 JP2002173697A JP2002173697A JP4154932B2 JP 4154932 B2 JP4154932 B2 JP 4154932B2 JP 2002173697 A JP2002173697 A JP 2002173697A JP 2002173697 A JP2002173697 A JP 2002173697A JP 4154932 B2 JP4154932 B2 JP 4154932B2
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Prior art keywords
temperature
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resistance
oxidation resistance
salt damage
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JP2002173697A
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JP2004018914A (en
Inventor
淳 宮崎
研治 高尾
修 古君
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JFE Steel Corp
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JFE Steel Corp
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Priority to JP2002173697A priority Critical patent/JP4154932B2/en
Application filed by JFE Steel Corp filed Critical JFE Steel Corp
Priority to KR1020047019453A priority patent/KR100676659B1/en
Priority to US10/512,782 priority patent/US7806993B2/en
Priority to PCT/JP2003/006950 priority patent/WO2003106722A1/en
Priority to EP07016111.2A priority patent/EP1873271B1/en
Priority to EP03733230A priority patent/EP1553198A1/en
Priority to CNB038138328A priority patent/CN100370048C/en
Priority to CNB2006101690870A priority patent/CN100471975C/en
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Description

【0001】
【発明の属する技術分野】
この発明は、自動車やオートバイの排気管、触媒外筒材および火力発電プラントの排気ダクトあるいは燃料電池関連部材等の高温環境下で使用される部材に供して好適な、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼に関するものである。
【0002】
【従来の技術】
自動車の排気系環境で使用される、例えばエキゾーストマニホールド、排気パイプ、コンバーターケースおよびマフラー等に代表される排気系部材には、成形性と耐熱性に優れることが要求されている。現在、このような用途には、室温で軟質で成形性に優れ、高温耐力も比較的高い、NbとSiを添加したCr含有鋼、例えば Type429(14Cr−0.9Si −0.4Nb 系)鋼が多用されている。
しかしながら、この Type429鋼は、エンジン性能の向上により排ガス温度が現行温度より高い 900℃から1000℃のような高温にまで上昇すると、高温耐力や耐酸化性が不足するいう問題があった。
【0003】
このため、高温強度がType429 鋼より高い優れた高温強度を有する材料に対する要求が強まっている。また、排気部材材料の高温強度を高めることは、部材の薄肉化を可能とし、自動車車体の軽量化に大きく寄与できるという利点もある。
【0004】
上記の要請に応えるものとして、特開2000−73147 号公報には、 排気系部材の高温部から低温部までの広い範囲にわたって適用可能な、高温強度、加工性および表面性状に優れたCr含有鋼が開示されている。この素材は、C:0.02mass%以下、 Si:0.10mass%以下、 Cr:3.0 〜20mass%、Nb:0.2 〜1.0 mass%を含有するCr含有鋼であり、 Siを0.10mass%以下に低減し、 Fe2Nb ラーベス相の析出を抑制して室温降伏強さの上昇を抑制すると共に、優れた高温強度と加工性、さらには良好な表面性状を付与しようとするものである。
【0005】
【発明が解決しようとする課題】
しかしながら、上記したような排気系部材であっても、 900℃から1000℃のような高温における耐酸化性すなわち耐高温酸化性の面に問題を残していた。
すなわち、エンジン性能をより向上させるためには、排ガス温度の一層の上昇が避けられないが、排ガス温度が 900℃から1000℃のような高温に上昇した場合には、現行の材料ではいずれも異常酸化が生じて、実使用に耐え得ないという問題が生じたのである。また、さらなる高温強度の向上も必要とされていた。
ここに、異常酸化とは、材料が高温の排ガスに曝された場合に、Fe酸化物が生成し、このFe酸化物は酸化速度が異常に速いことから、酸化が急激に進行し、素材がぼろぼろになる現象をいう。
【0006】
この発明は、上記の問題を有利に解決するもので、高温強度および耐高温酸化性に優れ、さらには耐高温塩害性にも優れるフェライト系ステンレス鋼を提案することを目的とする。
ここに、高温塩害とは、特に寒冷地において路面に散布された路面凍結阻止剤中の塩分や海岸地方における海水の塩分が排気パイプに付着したのち、高温に加熱された場合の腐食のことであり、このような腐食で板厚が減少していく。
【0007】
【課題を解決するための手投】
さて、発明者らは、上記の目的を達成すべく鋭意研究を重ねた結果、Wの添加特にMoとWとを複合添加することが、耐高温酸化性および高温強度の改善に有効に寄与することの知見を得た。
また、一定量以上のSiを添加することによって、耐高温塩害性が改善されることも併せて見出した。
この発明は、上記の知見に立脚するものである。
【0008】
すなわち、この発明の要旨構成は次のとおりである。
1.質量%で、
C:0.02%以下、
Si:0.5 〜2.0 %、
Mn:2.0 %以下、
Cr:12.0〜16.0%、
Mo:1.0 〜5.0 %、
W:2.0 %超、5.0 %以下、
Nb:5(C+N)〜1.0 %および
N:0.02%以下
を含有し、残部はFeおよび不可避的不純物の組成になることを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
【0009】
2.上記1において、MoおよびWの合計量が、質量%で
(Mo+W)≧4.3 %
を満足することを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
【0010】
3.上記1または2において、鋼がさらに、質量%で
Ti:0.5 %以下、
Zr:0.5 %以下および
V:0.5 %以下
のうちから選んだ少なくとも一種を含有する組成になることを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
【0011】
4.上記1,2または3において、鋼がさらに、質量%で
Ni:2.0 %以下、
Cu:1.0 %以下、
Co:1.0 %以下および
Ca:0.01%以下
のうちから選んだ少なくとも一種を含有する組成になることを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
【0012】
5.上記1〜4のいずれかにおいて、鋼がさらに、質量%で
Al:0.5 %以下
を含有する組成になることを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
【0013】
6.上記1〜5のいずれかにおいて、鋼がさらに、質量%で
B:0.01%以下、
Mg:0.01%以下
のうちから選んだ少なくとも一種を含有する組成になることを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
【0014】
7.上記1〜6のいずれかにおいて、鋼がさらに、質量%で
REM:0.1 %以下
を含有する組成になることを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
【0015】
【発明の実施の形態】
以下、この発明において、成分組成を上記の範囲に限定した理由について説明する。なお、成分に関する「%」表示は特に断らない限り質量%を意味するものとする。
C:0.02%以下
Cは、靱性や加工性を劣化させるので、その混入は極力低減することが好ましい。この観点から、この発明ではC量を0.02%以下に限定した。より好ましくは 0.008%以下である。
【0016】
Si:0.5 〜2.0 %
Siは、耐高温塩害性の向上に有効に寄与するので、この発明では 0.5%以上含有させることにした。しかしながら、含有量が 2.0%を超えると室温での強度が増大し、加工性を低下させるので、上限を 2.0%とした。より好ましくは 0.6〜1.2 %の範囲である。
【0017】
Mn:2.0 %以下
Mnは、脱酸剤として有効に寄与するが、過剰の添加はMnSを形成して耐食性を低下させるので、2.0 %以下に限定した。より好ましくは 1.0%以下である。なお、耐スケール剥離性の観点からは、Mn量は高いほど好ましくいので、この観点からは 0.3%以上含有させることが好ましい。
【0018】
Cr:12.0〜16.0%
Crは、耐食性および耐酸化性を向上させる基本元素であるが、一方で室温での強度が増大して加工性を低下させる不利がある。この発明では、Wの添加によって耐高温酸化性の向上を図っているので、加工性の観点からCr量は16.0%以下で含有させるものとした。一方、Cr量が12.0%を下回ると、Wが添加されていても耐食性の低下が著しいので、その下限をは12.0%とした。より好ましくは14.0〜16.0%の範囲である。
【0019】
Mo:1.0 〜5.0 %
Moは、高温強度のみならず、耐酸化性および耐食性の向上に有効に寄与するので、この発明では 1.0%以上含有させるものとした。しかしながら、含有量があまりに多くなると室温での強度が増大して加工性が低下するので、5.0 %を上限とした。より好ましくは 1.8〜2.5 %の範囲である。
【0020】
W:2.0 %超、5.0 %以下
Wは、この発明において特に重要な元素である。すなわち、上記したMoを添加したフェライト系ステンレス鋼に、Wを複合含有させることによって、耐高温酸化性の著しい向上を図ることができる。また、高温強度の向上にも有効に寄与する。しかしながら、W量が 2.0%以下ではその添加効果に乏しく、一方 5.0%を超えて多量に含有させるとコストの上昇を招くので、Wは 2.0%超、5.0 %以下の範囲で含有させるものとした。より好ましくは 3.0〜3.5 %の範囲である。
【0021】
図1に、 14%Cr−0.8%Si−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す。
耐高温酸化性試験は、1050℃の大気雰囲気中に 100時間保持し、この試験後の試験片の重量変化で評価した。この重量変化が小さいほど耐高温酸化性に優れていることを意味する。そして、試験後の重量変化が 10 mg/cm2以下であれば耐高温酸化性に優れているといえる。
同図に示したとおり、Wを 2.0%超含有させることによって、耐高温酸化性は格段に向上する。
【0022】
(Mo+W)≧4.3 %
上述したとおり、MoとWとを複合含有させることによって、耐高温酸化性の著しい向上を図ることができる。そのためには、これら元素の合計量は 4.3%以上とすることが好ましい。より好ましくは 4.7%以上である。
【0023】
Nb:5(C+N)〜1.0 %
Nbは、高温強度の改善に有効な元素であり、この効果を発揮させるためには、CおよびN量との兼ね合いで5(C+N)以上含有させる必要がある。しかしながら、あまりに多量の添加は、室温での強度が増大して加工性が低下するので、1.0 %を上限とした。より好ましくは 0.4〜0.7 %の範囲である。
【0024】
N:0.02%以下
Nも、Cと同様、靱性や加工性を劣化させるので、その混入は極力低減することが好ましい。この観点から、この発明ではN量を0.02%以下に限定した。より好ましくは 0.008%以下である。
【0025】
以上、基本成分について説明したが、この発明ではその他にも、以下に述べる元素を適宜含有させることができる。
Ti:0.5 %以下、Zr:0.5 %以下およびV:0.5 %以下のうちから選んだ少なくとも一種
Ti,ZrおよびVはいずれも、CやNを固定して耐粒界腐食性を向上させる作用があり、この観点からはそれぞれ0.02%以上含有させることが好ましい。しかしながら、含有量が 0.5%を超えると、鋼材の脆化を招くので、それぞれ 0.5%以下で含有させるものとした。
なお、これらの元素は、高温強度の向上にも有効であるので、前記したWおよび後述するCuを合わせた(W+Ti+Zr+V+Cu)量は、3%超で含有させることが好適である。
【0026】
Ni:2.0 %以下、Cu:1.0 %以下、Co:1.0 %以下およびCa:0.01%以下のうちから選んだ少なくとも一種
Ni,Cu,CoおよびCaはいずれも、靱性の改善に有用な元素であり、それぞれNi:2.0 %以下、Cu:1.0 %以下、Co:1.0 %以下、Ca:0.01%以下で含有させるものとした。特にCaは、Tiが含有された場合、連続鋳造時のノズル詰まりの防止にも有効に寄与する。なお、これらの元素の効果を十分に発揮させるためには、それぞれNi:0.5 %以上、Cu:0.05%以上、Co:0.03%以上、Ca:0.0005%以上の範囲で含有させることが好ましい。
【0027】
Al:0.5 %以下
Alは、脱酸剤として有用であり、そのためには0.01%以上含有させることが好ましい。また、Alは、溶接部の表面に緻密なスケールを形成して、溶接中に酸素や窒素の吸収を防止し、溶接部の靱性向上にも有効に寄与する。この目的のためには0.02%以上含有させることが好ましい。しかしながら、含有量が 0.5%を超えるとその効果は飽和に達するので、この発明では 0.5%以下で含有させるものとした。
【0028】
B:0.01%以下、Mg:0.01%以下のうちから選んだ少なくとも一種
BおよびMgいずれも、2次加工脆性の改善に有効に寄与するが、含有量が0.01%を超えると室温での強度が増して延性の低下を招くので、それぞれ0.01%以下で含有させるものとした。より好ましくはB:0.0003%以上、Mg:0.0003%以上である。
【0029】
REM:0.1 %以下
REM は、耐酸化性の向上に有効に寄与するので 0.1%以下で含有させるものとした。より好ましくは 0.002%以上である。なお、この発明において REMとは、ランタノイド系元素およびYを意味する。
【0030】
次に、この発明鋼の好適製造方法について説明する。この発明鋼の製造条件はとくに限定されるものではなく、Cr含有鋼の一般的な製造方法を好適に利用できる。
例えば、上記した適正組成範囲に調整した溶鋼を、転炉、 電気炉等の溶製炉、さらには取鍋精錬、 真空精錬等の精錬を利用して溶製したのち、連続鋳造法または造塊−分塊法でスラブとしたのち、 熱間圧延、熱延板焼鈍、酸洗、冷間圧延、仕上げ焼鈍、酸洗の各工程を順次に経て、冷延焼鈍板板とするのが好ましい。 また、冷間圧延は、1回または中間焼鈍を含む2回以上の冷間圧延としてもよい。冷間圧延、仕上げ焼鈍、酸洗の工程は繰り返し打ってもよい。なお、場合によっては熱延板焼鈍は省略してもよい。さらに、光沢性が要求される場合には、スキンパス等を施すことが有利である。
【0031】
【実施例】
表1に示す成分組成になる50kg鋼塊を作製し、 これらの鋼塊を1100℃に加熱後、 熱間圧延により5mm厚の熱延板とした。 ついで、これらの熱延板に対し、熱延板焼鈍(焼鈍温度:1000℃)−酸洗−冷間圧延(冷延圧下率:60%)−仕上げ焼鈍(焼鈍温度:1000℃)−酸洗を順次施して、2mm厚の冷延焼鈍板とした。
かくして得られた冷延焼鈍板の高温強度、耐高温酸化性および耐高温塩害性について調べた結果を、表2に示す。
【0032】
なお、各特性は次のようにして評価した。
(1) 高温強度
各冷延焼鈍板から、圧延方向を引張り方向とする JIS 13 号B引張試験片を各2 本ずつ採取し、 JIS G 0567の規定に準拠して、 引張り温度:900 ℃ 、歪速度:0.3 %/minの条件で引張り試験を行い、2本の試験片の 900℃における 0.2%耐力を求めた。 なお、 この 900℃における 0.2%耐力の値は高ければ高いほど好ましいが、特に 20 MPa 以上であれば高温強度に優れているといえる。
(2) 耐高温酸化性
各冷延焼鈍板から、試験片(2mm厚×20mm幅×30mm長さ)を各2本ずつ採取し、これらの試験片を、1050℃の大気雰囲気中に 100時間保持した。試験前後における各試験片の重量を測定し、試験前後の重量変化を算出して、2本の平均値を求めた。この重量変化が 10 mg/cm2以下であれば耐高温酸化性に優れているといえる。
(3) 耐高温塩害性
各冷延焼鈍板から、試験片(2mm厚×20mm幅×30mm長さ)を各2本ずつ採取し、5%食塩水に1時間浸漬したのち、700 ℃の大気雰囲気中で23時間加熱し、5分冷却する工程を1サイクルとし、10サイクル後の重量変化を測定し、その平均値を求めた。この重量変化が小さいほど耐高温塩害性に優れており、この発明では、重量変化量Δwが40(mg/cm2)以上の場合を×、30≦Δw<40(mg/cm2)の場合を○、20≦Δw<30(mg/cm2)の場合を◎、Δw<20(mg/cm2)の場合を☆と評価した。
【0033】
【表1】

Figure 0004154932
【0034】
【表2】
Figure 0004154932
【0035】
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、高温強度はいうまでもなく、優れた耐高温酸化性および耐高温塩害性が得られている。
【0036】
【発明の効果】
かくして、この発明によれば、高温強度および耐高温酸化性に優れ、さらには耐高温塩害性にも優れるフェライト系ステンレス鋼を得ることができる。
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℃を超えるような使途においても、それに耐え得る排気系部材を安定して供給することができる。また、同様な特性を必要とする燃料電池関連部材等への適用も可能である。
【図面の簡単な説明】
【図1】 14%Cr−0.8%Si−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]
BACKGROUND OF THE INVENTION
The present invention provides high temperature strength and high temperature oxidation resistance suitable for use in high temperature environments such as automobile and motorcycle exhaust pipes, catalyst outer cylinder materials and exhaust ducts of thermal power plants or fuel cell related members. Further, the present invention relates to a ferritic stainless steel excellent in high temperature salt damage resistance.
[0002]
[Prior art]
For example, exhaust system members such as exhaust manifolds, exhaust pipes, converter cases, and mufflers used in the exhaust system environment of automobiles are required to have excellent moldability and heat resistance. Currently, Cr-containing steels containing Nb and Si, such as Type 429 (14Cr-0.9Si-0.4Nb series) steel, are often used for such applications. Has been.
However, this Type 429 steel has a problem that high temperature proof stress and oxidation resistance are insufficient when the exhaust gas temperature rises from 900 ° C, which is higher than the current temperature, to a high temperature such as 1000 ° C due to improvement in engine performance.
[0003]
For this reason, there is an increasing demand for materials having superior high temperature strength, which has a higher high temperature strength than Type 429 steel. Further, increasing the high-temperature strength of the exhaust member material has the advantage that the member can be thinned and can greatly contribute to the weight reduction of the automobile body.
[0004]
In response to the above request, Japanese Patent Application Laid-Open No. 2000-73147 discloses a Cr-containing steel that is applicable to a wide range of exhaust system members from a high temperature part to a low temperature part and that has excellent high temperature strength, workability, and surface properties. Is disclosed. This material is Cr-containing steel containing C: 0.02 mass% or less, Si: 0.10 mass% or less, Cr: 3.0-20 mass%, Nb: 0.2-1.0 mass%, and Si is reduced to 0.10 mass% or less. In addition to suppressing the precipitation of the Fe 2 Nb Laves phase to suppress the increase in yield strength at room temperature, it is intended to impart excellent high-temperature strength and workability, as well as good surface properties.
[0005]
[Problems to be solved by the invention]
However, even the exhaust system member as described above has a problem in terms of oxidation resistance at high temperatures such as 900 ° C. to 1000 ° C., that is, high temperature oxidation resistance.
In other words, in order to further improve engine performance, a further increase in exhaust gas temperature is inevitable, but if the exhaust gas temperature rises to a high temperature such as 900 ° C to 1000 ° C, all current materials are abnormal. Oxidation occurred, causing a problem that it could not withstand actual use. In addition, further improvement in high temperature strength has been required.
Here, abnormal oxidation means that when a material is exposed to high-temperature exhaust gas, Fe oxide is generated, and since the oxidation rate of this Fe oxide is abnormally fast, the oxidation proceeds rapidly, and the material It is a phenomenon that becomes shabby.
[0006]
An object of the present invention is to advantageously solve the above-mentioned problems, and an object of the present invention is to propose a ferritic stainless steel which is excellent in high-temperature strength and high-temperature oxidation resistance and also in high-temperature salt damage resistance.
Here, high-temperature salt damage refers to corrosion when heated to high temperatures after the salt content in road surface freeze inhibitors sprayed on the road surface in cold regions and the salt content of seawater in the coastal area adheres to the exhaust pipe. Yes, the plate thickness decreases due to such corrosion.
[0007]
[Hand throws to solve problems]
As a result of intensive studies to achieve the above object, the inventors have made an effective contribution to the improvement of high-temperature oxidation resistance and high-temperature strength by the addition of W, particularly the combined addition of Mo and W. I got that knowledge.
It was also found that high temperature salt damage resistance was improved by adding a certain amount or more of Si.
The present invention is based on the above findings.
[0008]
That is, the gist configuration of the present invention is as follows.
1. % By mass
C: 0.02% or less,
Si: 0.5-2.0%
Mn: 2.0% or less,
Cr: 12.0-16.0%
Mo: 1.0-5.0%,
W: Over 2.0%, up to 5.0%,
Nb: 5 (C + N) -1.0% and N: 0.02% or less, with the balance being Fe and inevitable impurities, excellent high temperature strength, high temperature oxidation resistance and high temperature salt damage resistance Ferritic stainless steel.
[0009]
2. In the above 1, the total amount of Mo and W is (Mo + W) ≧ 4.3% in mass%.
Ferritic stainless steel excellent in high temperature strength, high temperature oxidation resistance and high temperature salt damage resistance, characterized by satisfying
[0010]
3. In the above 1 or 2, the steel is further in mass%.
Ti: 0.5% or less,
A ferritic stainless steel excellent in high-temperature strength, high-temperature oxidation resistance and high-temperature salt damage resistance, characterized in that the composition contains 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 is further in mass%.
Ni: 2.0% or less,
Cu: 1.0% or less,
Co: 1.0% or less and
Ca: Ferritic stainless steel excellent in high-temperature strength, high-temperature oxidation resistance, and high-temperature salt damage resistance, characterized by having a composition containing at least one selected from 0.01% or less.
[0012]
5. In any one of the above 1 to 4, the steel is further in mass%.
Al: Ferritic stainless steel excellent in high-temperature strength, high-temperature oxidation resistance and high-temperature salt damage resistance, characterized by having a composition containing 0.5% or less.
[0013]
6). In any one of the above 1 to 5, the steel is further B: 0.01% or less by mass%,
Mg: Ferritic stainless steel excellent in high-temperature strength, high-temperature oxidation resistance, and high-temperature salt damage resistance, characterized by having a composition containing at least one selected from 0.01% or less.
[0014]
7). In any one of the above 1 to 6, the steel is further in mass%.
REM: Ferritic stainless steel excellent in high-temperature strength, high-temperature oxidation resistance and high-temperature salt damage resistance, characterized by having a composition containing 0.1% or less.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the reason why the component composition is limited to the above range in the present invention will be described. Unless otherwise specified, “%” in relation to ingredients means mass%.
C: 0.02% or less Since C deteriorates toughness and workability, its mixing 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.
[0016]
Si: 0.5-2.0%
Since Si contributes effectively to the improvement of the high temperature salt damage resistance, it was decided to contain 0.5% or more in this invention. However, if the content exceeds 2.0%, the strength at room temperature increases and the workability decreases, so the upper limit was made 2.0%. More preferably, it is 0.6 to 1.2% of range.
[0017]
Mn: 2.0% or less
Mn contributes effectively as a deoxidizer, but excessive addition reduces the corrosion resistance by forming MnS, so it was limited to 2.0% or less. More preferably, it is 1.0% or less. In addition, from the viewpoint of scale peel resistance, the higher the amount of Mn, the better. From this viewpoint, it is preferable to contain 0.3% or more.
[0018]
Cr: 12.0 to 16.0%
Cr is a basic element that improves the corrosion resistance and oxidation resistance, but has the disadvantage of increasing the strength at room temperature and reducing the workability. In this invention, the addition of W improves the high-temperature oxidation resistance, so from the viewpoint of workability, the Cr content is made 16.0% or less. On the other hand, if the Cr content is less than 12.0%, the corrosion resistance is remarkably lowered even if W is added, so the lower limit was made 12.0%. More preferably, it is 14.0 to 16.0% of range.
[0019]
Mo: 1.0-5.0%
Mo effectively contributes not only to high-temperature strength but also to improvement of oxidation resistance and corrosion resistance. Therefore, in the present invention, Mo is included in an amount of 1.0% or more. However, if the content is too high, the strength at room temperature increases and the workability decreases, so 5.0% was made the upper limit. More preferably, it is 1.8 to 2.5% of range.
[0020]
W: more than 2.0% and 5.0% or less W is an especially important element in the present invention. That is, by adding W to the ferritic stainless steel to which Mo is added, the high temperature oxidation resistance can be remarkably improved. It also contributes effectively to the improvement of high temperature strength. However, if the amount of W is 2.0% or less, the effect of addition is poor. On the other hand, if it contains more than 5.0%, the cost increases. Therefore, W should be contained in the range of more than 2.0% and 5.0% or less. . More preferably, it is 3.0 to 3.5% of range.
[0021]
FIG. 1 shows the results of investigation on high-temperature oxidation resistance when W is added in various proportions based on 14% Cr-0.8% Si-0.5% Nb-1.8% Mo steel.
The high temperature oxidation resistance test was held in an air atmosphere at 1050 ° C. for 100 hours, and the change in the weight of the test piece after this test was evaluated. The smaller this weight change, the better the high-temperature oxidation resistance. And 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, the high-temperature oxidation resistance is remarkably improved by containing W in excess of 2.0%.
[0022]
(Mo + W) ≧ 4.3%
As described above, the high temperature oxidation resistance can be remarkably improved by combining Mo and W. For that purpose, the total amount of these elements is preferably 4.3% or more. More preferably, it is 4.7% or more.
[0023]
Nb: 5 (C + N) to 1.0%
Nb is an element effective for improving the high-temperature strength, and in order to exert this effect, it is necessary to contain 5 (C + N) or more in consideration of the amount of C and N. However, too much addition increases the strength at room temperature and decreases the workability, so 1.0% was made the upper limit. More preferably, it is 0.4 to 0.7% of range.
[0024]
N: 0.02% or less N, as well as C, deteriorates toughness and workability, so it is preferable to reduce the mixing thereof as much as possible. From this point of view, in the present invention, the N content is limited to 0.02% or less. More preferably, it is 0.008% or less.
[0025]
Although the basic components have been described above, in the present invention, other elements described below can be appropriately contained.
At least one selected from Ti: 0.5% or less, Zr: 0.5% or less, and V: 0.5% or less
All of Ti, Zr and V have the effect of fixing C and N and improving the intergranular corrosion resistance. From this viewpoint, it is preferable to contain 0.02% or more. However, if the content exceeds 0.5%, the steel material becomes brittle, so each content was 0.5% or less.
Since these elements are also effective for improving the high-temperature strength, it is preferable that the amount of (W + Ti + Zr + V + Cu) combined with the above-described W and Cu described later is more than 3%.
[0026]
At least one selected from 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 elements that are useful for improving toughness. Ni: 2.0% or less, Cu: 1.0% or less, Co: 1.0% or less, Ca: 0.01% or less did. 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, it is preferable to contain Ni in a range of 0.5% or more, Cu: 0.05% or more, Co: 0.03% or more, and Ca: 0.0005% or more.
[0027]
Al: 0.5% or less
Al is useful as a deoxidizer, and for that purpose, it is preferable to contain 0.01% or more. Further, Al forms a dense scale on the surface of the welded portion, prevents oxygen and nitrogen from being absorbed during welding, and contributes effectively to improving the toughness of the welded portion. For this purpose, it is preferable to contain 0.02% or more. However, since the effect reaches saturation when the content exceeds 0.5%, in this invention, the content is set to 0.5% or less.
[0028]
At least one of B and Mg selected from B: 0.01% or less and Mg: 0.01% or less contributes to the improvement of secondary work brittleness. However, if the content exceeds 0.01%, the strength at room temperature is increased. In addition, it causes a decrease in ductility, so each content was made 0.01% or less. More preferably, B is 0.0003% or more, and Mg is 0.0003% or more.
[0029]
REM: 0.1% or less
Since REM contributes effectively to the improvement of oxidation resistance, it was added at 0.1% or less. More preferably, it is 0.002% or more. In the present invention, REM means a lanthanoid element and Y.
[0030]
Next, the suitable manufacturing method of this invention steel is demonstrated. The production conditions of the steel of the present invention are not particularly limited, and general production methods for Cr-containing steel can be suitably used.
For example, molten steel adjusted to the above-mentioned proper composition range is melted using a refining furnace such as a converter, electric furnace, etc., and ladle refining, vacuum refining, etc. -After making into a slab by a block method, it is preferable to go through each process of hot rolling, hot-rolled sheet annealing, pickling, cold-rolling, finish annealing, and pickling sequentially to make a cold-rolled annealed sheet. Further, the cold rolling may be one or two or more cold rolling including intermediate annealing. The steps of cold rolling, finish annealing, and pickling may be repeated. In some cases, hot-rolled sheet annealing may be omitted. Further, when gloss is required, it is advantageous to apply a skin pass or the like.
[0031]
【Example】
50 kg steel ingots having the composition shown in Table 1 were prepared. These steel 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 ratio: 60%)-finish annealing (annealing temperature: 1000 ° C)-pickling Were applied 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 strength, high temperature oxidation resistance and high temperature salt damage resistance of the cold-rolled annealed sheet thus obtained.
[0032]
Each characteristic was evaluated as follows.
(1) High temperature strength Two JIS 13 B tensile test specimens each with the rolling direction as the tensile direction were sampled from each cold-rolled annealed sheet, and in accordance with the provisions of JIS G 0567, the tensile temperature: 900 ℃, A tensile test was performed at a strain rate of 0.3% / min, and the 0.2% proof stress at 900 ° C. of the two test pieces was determined. The 0.2% proof stress value at 900 ° C is preferably as high as possible, but it can be said that it is excellent in high-temperature strength particularly at 20 MPa or more.
(2) High-temperature oxidation resistance Two test pieces (2 mm thickness 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. Retained. 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.
(3) High temperature salt resistance Two specimens (2mm thickness x 20mm width x 30mm length) were taken from each cold-rolled annealed plate, immersed in 5% saline solution for 1 hour, and then air at 700 ° C. The process of heating in an atmosphere for 23 hours and cooling for 5 minutes was taken as one cycle, the weight change after 10 cycles was measured, and the average value was obtained. The smaller the change in weight, the better the resistance to salt damage at high temperatures. In this invention, the case where the weight change Δw is 40 (mg / cm 2 ) or more is x, and 30 ≦ Δw <40 (mg / cm 2 ) Was evaluated as ○, 20 ≦ Δw <30 (mg / cm 2 ) as ◎, and Δw <20 (mg / cm 2 ) as ☆.
[0033]
[Table 1]
Figure 0004154932
[0034]
[Table 2]
Figure 0004154932
[0035]
As is clear from Table 2, all the steel sheets according to the present invention have excellent high temperature oxidation resistance and high temperature salt damage resistance, not to mention high temperature strength.
[0036]
【The invention's effect】
Thus, according to the present invention, it is possible to obtain a ferritic stainless steel that is excellent in high-temperature strength and high-temperature oxidation resistance, and also excellent in high-temperature salt damage resistance.
Therefore, according to the present invention, by improving the engine performance, it is possible to stably supply an exhaust system member that can withstand the exhaust gas temperature even when the exhaust gas temperature exceeds 900 ° C. Further, it can be applied to fuel cell-related members and the like that require similar characteristics.
[Brief description of the drawings]
FIG. 1 is a graph showing the results of examining high-temperature oxidation resistance when W is added in various proportions based on 14% Cr-0.8% Si-0.5% Nb-1.8% Mo steel.

Claims (7)

質量%で、
C:0.02%以下、
Si:0.5 〜2.0 %、
Mn:2.0 %以下、
Cr:12.0〜16.0%、
Mo:1.0 〜5.0 %、
W:2.0 %超、5.0 %以下、
Nb:5(C+N)〜1.0 %および
N:0.02%以下
を含有し、残部はFeおよび不可避的不純物の組成になることを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
% By mass
C: 0.02% or less,
Si: 0.5-2.0%
Mn: 2.0% or less,
Cr: 12.0-16.0%
Mo: 1.0-5.0%,
W: Over 2.0%, up to 5.0%,
Nb: 5 (C + N) -1.0% and N: 0.02% or less, with the balance being Fe and inevitable impurities, excellent high temperature strength, high temperature oxidation resistance and high temperature salt damage resistance Ferritic stainless steel.
請求項1において、MoおよびWの合計量が、質量%で
(Mo+W)≧4.3 %
を満足することを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
In Claim 1, the total amount of Mo and W is (Mo + W) ≧ 4.3% in mass%.
Ferritic stainless steel excellent in high temperature strength, high temperature oxidation resistance and high temperature salt damage resistance, characterized by satisfying
請求項1または2において、鋼がさらに、質量%で
Ti:0.5 %以下、
Zr:0.5 %以下および
V:0.5 %以下
のうちから選んだ少なくとも一種を含有する組成になることを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
3. The steel according to claim 1 or 2, further comprising mass%.
Ti: 0.5% or less,
A ferritic stainless steel excellent in high-temperature strength, high-temperature oxidation resistance and high-temperature salt damage resistance, characterized in that the composition contains at least one selected from Zr: 0.5% or less and V: 0.5% or less.
請求項1,2または3において、鋼がさらに、質量%で
Ni:2.0 %以下、
Cu:1.0 %以下、
Co:1.0 %以下および
Ca:0.01%以下
のうちから選んだ少なくとも一種を含有する組成になることを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
The steel according to claim 1, 2 or 3, further in mass%.
Ni: 2.0% or less,
Cu: 1.0% or less,
Co: 1.0% or less and
Ca: Ferritic stainless steel excellent in high-temperature strength, high-temperature oxidation resistance, and high-temperature salt damage resistance, characterized by having a composition containing at least one selected from 0.01% or less.
請求項1〜4のいずれかにおいて、鋼がさらに、質量%で
Al:0.5 %以下
を含有する組成になることを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
In any one of Claims 1-4, steel is further in the mass%.
Al: Ferritic stainless steel excellent in high-temperature strength, high-temperature oxidation resistance and high-temperature salt damage resistance, characterized by having a composition containing 0.5% or less.
請求項1〜5のいずれかにおいて、鋼がさらに、質量%で
B:0.01%以下、
Mg:0.01%以下
のうちから選んだ少なくとも一種を含有する組成になることを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
In any one of Claims 1-5, steel is further mass% B: 0.01% or less,
Mg: Ferritic stainless steel excellent in high-temperature strength, high-temperature oxidation resistance, and high-temperature salt damage resistance, characterized by having a composition containing at least one selected from 0.01% or less.
請求項1〜6のいずれかにおいて、鋼がさらに、質量%で
REM:0.1 %以下
を含有する組成になることを特徴とする、高温強度、耐高温酸化性および耐高温塩害性に優れたフェライト系ステンレス鋼。
In any one of Claims 1-6, steel is further in the mass%.
REM: Ferritic stainless steel excellent in high-temperature strength, high-temperature oxidation resistance and high-temperature salt damage resistance, characterized by having a composition containing 0.1% or less.
JP2002173697A 2002-06-14 2002-06-14 Ferritic stainless steel with excellent high-temperature strength, high-temperature oxidation resistance, and high-temperature salt damage resistance Expired - Lifetime JP4154932B2 (en)

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