JP7297373B2 - Ferritic steel plate for exhaust systems with excellent corrosion resistance - Google Patents

Ferritic steel plate for exhaust systems with excellent corrosion resistance Download PDF

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JP7297373B2
JP7297373B2 JP2022506185A JP2022506185A JP7297373B2 JP 7297373 B2 JP7297373 B2 JP 7297373B2 JP 2022506185 A JP2022506185 A JP 2022506185A JP 2022506185 A JP2022506185 A JP 2022506185A JP 7297373 B2 JP7297373 B2 JP 7297373B2
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ヒョング カン，
フォン ジェ ハ，
ヨン ジュン キム，
ギュジン ジョ，
ムンスゥ イ，
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ポスコ カンパニー リミテッド
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Description

本発明は、排気系用フェライト系鋼板に係り、より詳しくは、排気系システムに適合した耐食性に優れた排気系用フェライト系鋼板に関する。 TECHNICAL FIELD The present invention relates to a ferritic steel sheet for an exhaust system, and more particularly to a ferritic steel sheet for an exhaust system that is suitable for an exhaust system and has excellent corrosion resistance.

自動車、二輪車の排気系システムは、外部に露出していて、冬季に除雪用塩による汚染から容易に腐食される環境に曝されており、また、化石燃料の排気から発生する酸性凝縮水から容易に腐食される環境に曝されている。 Exhaust systems of automobiles and motorcycles are exposed to the outside and are exposed to an environment that is easily corroded from contamination by salt for snow removal in winter, and is easily exposed to acidic condensate generated from fossil fuel exhaust. exposed to an environment that is corrosive to

排気ガス温度がますます高まる環境下で、腐食を防止するために、排気系システムに使用される素材は、熱容量の大きい鋳物から熱容量の小さいステンレス鋼が主として使用されてきた。特に、オーステナイト系ステンレス鋼材に比べて高価な合金元素の添加が少ないフェライト系ステンレス鋼材は、耐食性も優れていて、価格競争力が高いため、常温～８００℃の排気ガスの温度範囲に対応する排気系部品など（Ｍｕｆｆｌｅｒ、Ｅｘ－ｍａｎｉｆｏｌｄ、Ｃｏｌｌｅｃｔｏｒ ｃｏｎｅなど）に主に使用されてきた。 In order to prevent corrosion in an environment where the exhaust gas temperature is increasing, the materials used for the exhaust system have mainly been cast metal with a large heat capacity and stainless steel with a small heat capacity. In particular, ferritic stainless steel, which contains less expensive alloying elements than austenitic stainless steel, has excellent corrosion resistance and is highly competitive in price. It has been mainly used for system parts (Muffler, Ex-manifold, Collector cone, etc.).

耐腐食性および耐酸化性を確保するための最も一般的な方法は、Ｃｒ含有量の高いステンレス鋼を使用することであるが、Ｃｒを最小１１重量％以上含むフェライト系ステンレス鋼は高価である。また、ステンレス鋼は、Ｃｒ含有量が高くて、難酸洗性および酸洗費用が大きく、Ｎｂなどを多量で含むので、冷延焼鈍温度も高くする必要がある。このため、価格上昇を招くＣｒを低減しながらも、優れた耐食性を確保する排気系用鋼板の必要性が生じている。 The most common way to ensure corrosion resistance and oxidation resistance is to use stainless steel with a high Cr content, but ferritic stainless steel containing at least 11% by weight of Cr is expensive. . In addition, stainless steel has a high Cr content, is difficult to pickle, is expensive to pickle, and contains a large amount of Nb, etc., so that the cold rolling annealing temperature must be raised. Therefore, there is a need for steel sheets for exhaust systems that ensure excellent corrosion resistance while reducing Cr, which causes price increases.

本発明の目的は、高価な元素であるＣｒの含量を低減しながら、排気系用に優れた耐食性を備えたフェライト系鋼板を提供することである。 SUMMARY OF THE INVENTION An object of the present invention is to provide a ferritic steel sheet having excellent corrosion resistance for exhaust systems while reducing the content of Cr, which is an expensive element.

本発明の耐食性に優れた排気系用フェライト系鋼板は、重量％で、Ｃ：０．０２％以下、Ｎ：０．０２％以下、Ｓｉ：２．０％以下、Ｍｎ：０．５％以下、Ｃｒ：３．０～５．５％、Ｔｉ：０．００１～０．３％、Ａｌ：１．０～４．０％を含み、残部がＦｅおよび不可避な不純物からなり、表面スケール層を具備し、下記のように定義されるＡｌ被膜指数１５．０以上およびＳｉ被膜指数３．０以下を満たすことを特徴とする。

［Ａｌ被膜指数］：表面から深さ０．２μｍの範囲でＡｌ含有量の最大値（重量％）
［Ｓｉ被膜指数］：表面から深さ０．２μｍの範囲でＳｉ含有量の最大値（重量％） The ferritic steel sheet for exhaust system with excellent corrosion resistance of the present invention has C: 0.02% or less, N: 0.02% or less, Si: 2.0% or less, and Mn: 0.5% or less by weight %. , Cr: 3.0 to 5.5%, Ti: 0.001 to 0.3%, Al: 1.0 to 4.0%, the balance being Fe and unavoidable impurities, forming a surface scale layer It is characterized by satisfying the Al coating index of 15.0 or more and the Si coating index of 3.0 or less defined as follows.

[Al coating index]: maximum value of Al content (% by weight) in the range from the surface to a depth of 0.2 μm
[Si coating index]: maximum value of Si content (% by weight) in the range from the surface to a depth of 0.2 μm

また、本発明のＡｌ、Ｃｒ、Ｓｉ各元素の含有量は、式（１）を満たし、

（１）５＊Ａｌ－（Ｃｒ＋Ｓｉ）＞０

式（２）で表される腐食減耗率が２０％未満であることを特徴とする。

（２）腐食減耗率（％）＝［（腐食試験前の重さ）－（腐食試験後の重さ）］／（腐食試験前の重さ）×１００

ここで、腐食試験後の重さは、腐食試験後に生成された腐食生成物を除去した後の重さ（ｇ）である。 In addition, the content of each element of Al, Cr, and Si in the present invention satisfies the formula (1),

(1) 5*Al-(Cr+Si)>0

The corrosion loss rate represented by the formula (2) is less than 20%.

(2) Corrosion loss rate (%) = [(Weight before corrosion test) - (Weight after corrosion test)] / (Weight before corrosion test) x 100

Here, the weight after the corrosion test is the weight (g) after removing corrosion products generated after the corrosion test.

また、本発明の耐食性に優れた排気系用フェライト系鋼板表面のＬ＊ａ＊ｂ＊表色系のＬ＊値が５０以上であり、
表面のＬ＊ａ＊ｂ＊表色系のａ＊値が－１０～＋１０およびｂ＊値が－１０～＋１０の範囲であることを特徴とする。 Further, the L* value in the L*a*b* color system of the surface of the ferritic steel plate for exhaust system with excellent corrosion resistance of the present invention is 50 or more,
The a* value of the surface is in the range of -10 to +10 and the b* value is in the range of -10 to +10 in the L*a*b* color system.

本発明のフェライト系鋼板によれば、排気系用途に使用される既存のステンレス鋼に比べて原料価格および工程費用を大きく節減できると共に、優れた耐食性を示すことができる。
また、最終酸洗工程を経ないで、Ｌ＊ａ＊ｂ＊表色系のＬ＊値が５０以上、ａ＊およびｂ＊値が－１０～＋１０の範囲の明るい無彩色の金属性を示し、表面性状に優れている。 According to the ferritic steel sheet of the present invention, raw material costs and process costs can be greatly reduced compared to existing stainless steels used for exhaust systems, and excellent corrosion resistance can be exhibited.
In addition, without going through the final pickling process, the L* value of the L*a*b* color system is 50 or more, and the a* and b* values are in the range of -10 to +10. , excellent surface properties.

Ｌ＊ａ＊ｂ＊表色系を示す色空間（ＣＯＬＯＲ ＳＰＡＣＥ）である。It is a color space (COLOR SPACE) indicating the L*a*b* color system. 本発明による発明鋼２の表面から深さ方向に０．２μｍの範囲に対するグロー放電発光分析法で分析した合金成分の分布である。Fig. 3 shows the distribution of alloy components analyzed by glow discharge optical emission spectrometry in a range of 0.2 µm in the depth direction from the surface of Inventive Steel 2 according to the present invention. 本発明による比較鋼５の表面から深さ方向に０．２μｍの範囲に対するグロー放電発光分析法で分析した合金成分の分布である。10 shows distribution of alloy components analyzed by glow discharge optical emission spectrometry in a range of 0.2 μm in the depth direction from the surface of comparative steel 5 according to the present invention. 本発明による発明鋼２の酸洗後に表面から深さ方向に０．２μｍの範囲に対するグロー放電発光分析法で分析した合金成分の分布である。Fig. 2 shows the distribution of alloy components analyzed by glow discharge emission spectrometry in a range of 0.2 µm in the depth direction from the surface after the pickling of invention steel 2 according to the present invention. 本発明による比較鋼１０の冷延焼鈍鋼板試験片の表面を示す写真である。1 is a photograph showing the surface of a cold-rolled and annealed steel plate test piece of comparative steel 10 according to the present invention. 本発明による発明鋼２の冷延焼鈍鋼板試験片の表面を示す写真である。1 is a photograph showing the surface of a cold-rolled and annealed steel plate test piece of invention steel 2 according to the present invention.

本発明の耐食性に優れた排気系用フェライト系鋼板は、重量％で、Ｃ：０．０２％以下、Ｎ：０．０２％以下、Ｓｉ：２．０％以下、Ｍｎ：０．５％以下、Ｃｒ：３．０～５．５％、Ｔｉ：０．００１～０．３％、Ａｌ：１．０～４．０％を含み、残部がＦｅおよび不可避な不純物からなり、表面スケール層を具備し、下記のように定義されるＡｌ被膜指数１５．０以上およびＳｉ被膜指数３．０以下を満たす。
［Ａｌ被膜指数］：表面から深さ０．２μｍの範囲でＡｌ含有量の最大値（重量％）
［Ｓｉ被膜指数］：表面から深さ０．２μｍの範囲でＳｉ含有量の最大値（重量％） The ferritic steel sheet for exhaust system with excellent corrosion resistance of the present invention has C: 0.02% or less, N: 0.02% or less, Si: 2.0% or less, and Mn: 0.5% or less by weight %. , Cr: 3.0 to 5.5%, Ti: 0.001 to 0.3%, Al: 1.0 to 4.0%, the balance being Fe and unavoidable impurities, forming a surface scale layer and satisfies the Al coating index of 15.0 or more and the Si coating index of 3.0 or less defined below.
[Al coating index]: maximum value of Al content (% by weight) in the range from the surface to a depth of 0.2 μm
[Si coating index]: maximum value of Si content (% by weight) in the range from the surface to a depth of 0.2 μm

以下では、本発明の実施例を添付の図面を参照して詳細に説明する。以下の実施例は、本発明の属する技術分野における通常の知識を有する者に本発明の思想を十分に伝達するために提示するものである。本発明は、ここで提示した実施例のみに限定されず、他の形態に具体化されることもできる。図面は、本発明を明確にするために説明と関係ない部分の図示を省略し、理解を助けるために構成要素のサイズを多少誇張して表現することができる。
また、任意の部分が或る構成要素を「含む」というとき、これは、特に反対になる記載がない限り、他の構成要素を除くものではなく、他の構成要素をさらに含むことができることを意味する。
単数の表現は、文脈上、明白に例外がない限り、複数の表現を含む。 Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The following examples are presented to fully convey the spirit of the invention to those of ordinary skill in the art to which the invention pertains. The present invention is not limited to the embodiments presented herein, and may be embodied in other forms. In the drawings, parts irrelevant to the description may be omitted to clarify the present invention, and the sizes of components may be exaggerated to facilitate understanding.
Also, when we say that any part "includes" a component, this does not exclude other components, but it can further include other components, unless specifically stated to the contrary. means.
Singular references include plural references unless the context clearly dictates otherwise.

排気系用ステンレス鋼、特にフェライト系ステンレス鋼には、高温強度の向上のためにＮｂを添加したり、これの代わりにＳｎなどを添加し、耐酸化性の向上のためにＣｒ含有量を高めることが一般的である。しかしながら、Ｎｂ、Ｓｎなどの固溶強化元素の添加とＣｒ含有量の増加は、製造コストを上昇させる原因となって、好ましい開発方向ではない。 In stainless steel for exhaust systems, especially ferritic stainless steel, Nb is added to improve high-temperature strength, or Sn or the like is added instead, and the Cr content is increased to improve oxidation resistance. is common. However, the addition of solid-solution strengthening elements such as Nb and Sn and the increase in the Cr content increase the manufacturing cost, which is not a desirable development direction.

排気系用フェライト系ステンレス鋼の原料価格を節減するためには、相対的に含有量の高い高価な元素であるＣｒ含有量の低減が必須である。しかしながら、Ｃｒは、排気系用フェライト系ステンレス鋼において耐食性を確保する核心元素であるから、Ｃｒ低減のためには、耐食性を確保できる他の方案が必要である。本発明では、ステンレス鋼としてＣｒの最小含有量である１１重量％より低いＣｒ含有量を有する鋼板でありながらも、従来ステンレス鋼と同等以上の耐食性を確保して原料価格を節減できるフェライト系鋼板を提供する。 In order to reduce the raw material cost of ferritic stainless steel for exhaust systems, it is essential to reduce the content of Cr, which is an expensive element with a relatively high content. However, since Cr is a core element that secures corrosion resistance in ferritic stainless steel for exhaust systems, another method for securing corrosion resistance is required to reduce Cr. In the present invention, a ferritic steel sheet that has a Cr content lower than the minimum Cr content of 11% by weight as a stainless steel can secure corrosion resistance equal to or higher than that of conventional stainless steel and reduce raw material costs. I will provide a.

本発明の耐食性に優れた排気系用フェライト系鋼板は、重量％で、Ｃ：０．０２％以下、Ｎ：０．０２％以下、Ｓｉ：２．０％以下、Ｍｎ：０．５％以下、Ｃｒ：３．０～５．５％、Ｔｉ：０．００１～０．３％、Ａｌ：１．０～４．０％を含み、残部がＦｅおよび不可避な不純物からなる。 The ferritic steel sheet for exhaust system with excellent corrosion resistance of the present invention has C: 0.02% or less, N: 0.02% or less, Si: 2.0% or less, and Mn: 0.5% or less by weight %. , Cr: 3.0-5.5%, Ti: 0.001-0.3%, Al: 1.0-4.0%, and the balance consists of Fe and unavoidable impurities.

以下、本発明の実施例における合金成分の元素含有量の数値限定理由について説明する。以下では、特別な言及がない限り、単位は、重量％である。 The reasons for limiting the numerical values of the element contents of the alloy components in the examples of the present invention will be described below. In the following, the unit is % by weight unless otherwise specified.

Ｃの含有量は、０超過０．０２％以下である。
Ｃ含有量が０．０２％を超過する場合、溶接部の靭性が低下することがあり、Ｃｒと結合してＣｒ２３Ｃ６析出物が生成されて素地内局部Ｃｒ枯渇により耐食性および耐酸化性が低下する。なお、Ｃは、不可避な不純物として０超過で含まれ、極低含有量の制御のためには、製鋼ＶＯＤ工程費用が増加するところ、好ましくは、０．００５％以上含まれ得る。 The content of C is more than 0 and 0.02% or less.
If the C content exceeds 0.02%, the toughness of the weld zone may be reduced, and it may combine with Cr to form Cr 23 C 6 precipitates. decreases. In addition, C is contained in excess of 0 as an unavoidable impurity, and in order to control its extremely low content, the cost of the steelmaking VOD process increases, so it is preferably contained in an amount of 0.005% or more.

Ｎの含有量は、０超過０．０２％以下である。
鋼中Ｎが０．０２％を超過する場合、固溶Ｎの濃度は限界に至り、Ｃｒと結合してＣｒ２Ｎ析出物が生成されて素地内局部Ｃｒ枯渇により耐食性および耐酸化性が低下する。なお、Ｎは、不可避な不純物として０超過で含まれ、極低含有量の制御のためには、製鋼ＶＯＤ工程費用が増加するところ、好ましくは、０．００５％以上含まれ得る。 The content of N is more than 0 and 0.02% or less.
When N in the steel exceeds 0.02%, the concentration of solute N reaches its limit, and it combines with Cr to form Cr 2 N precipitates, resulting in local Cr depletion in the base material, resulting in deterioration of corrosion resistance and oxidation resistance. do. In addition, N is contained in excess of 0 as an unavoidable impurity, and in order to control its extremely low content, the cost of the steelmaking VOD process increases, so it is preferably contained in an amount of 0.005% or more.

Ｓｉの含有量は、２．０％以下である。
Ｓｉは、固溶強化元素であると同時に、表層部にＳｉ濃化酸化膜を形成して耐酸化性を増加させる。しかしながら、本発明では、後述する「酸洗の省略」を具現するために、焼鈍熱処理後にＳｉ被膜指数を３．０以下に制限する必要があり、このために、総含有量を２．０％以下に制限する。しかしながら、変色の防止をより容易に制御するための観点から、１．５％以下含んでもよく、１．０％以下含んでもよい。 The content of Si is 2.0% or less.
Si is a solid-solution strengthening element and at the same time forms a Si-concentrated oxide film on the surface layer to increase the oxidation resistance. However, in the present invention, it is necessary to limit the Si film index to 3.0 or less after the annealing heat treatment in order to implement the "omission of pickling" described later. Limited to: However, from the viewpoint of more easily controlling the prevention of discoloration, the content may be 1.5% or less, or 1.0% or less.

Ｍｎの含有量は、０．５％以下である。
Ｍｎは、鋼中に不可避に含まれる不純物であり、オーステナイトを安定化させる役割をする。Ｍｎ含有量が０．５％を超過する場合、熱延または冷延後の焼鈍熱処理時にオーステナイト逆変態が発生することになって、伸び率に悪影響を及ぼすことになる。したがって、Ｍｎの含有量を上記のように制限する。 The content of Mn is 0.5% or less.
Mn is an impurity that is inevitably contained in steel and plays a role in stabilizing austenite. If the Mn content exceeds 0.5%, reverse austenite transformation occurs during the annealing heat treatment after hot rolling or cold rolling, adversely affecting elongation. Therefore, the content of Mn is limited as described above.

Ｃｒの含有量は、３．０～５．５％である。
Ｃｒは、耐食性を向上させる元素であるが、原料価格の節減のための本発明の趣旨によって５．５％以下に制限する。ただし、最小限の耐食性を確保するために、３．０％以上添加する。 The Cr content is 3.0-5.5%.
Cr is an element that improves corrosion resistance, but it is limited to 5.5% or less according to the purpose of the present invention to reduce raw material costs. However, in order to secure the minimum corrosion resistance, 3.0% or more is added.

Ｔｉの含有量は、０．００１～０．３％である。
Ｔｉは、Ｃ、Ｎと結合してＴｉ（Ｃ、Ｎ）析出物を形成して固溶Ｃ、Ｎの量を低減し、Ｃｒ枯渇層の形成を抑制する役割をし、Ｔｉは、溶接部の耐食性および靭性の向上のために、必須的に０．００１％以上添加しなければならない。しかしながら、Ｔｉ含有量が多すぎる場合、鋳造に悪影響を与えるので、０．３％以下に制限する。 The content of Ti is 0.001 to 0.3%.
Ti combines with C and N to form Ti (C, N) precipitates, thereby reducing the amount of dissolved C and N and suppressing the formation of a Cr-depleted layer. In order to improve the corrosion resistance and toughness of steel, it must be added in an amount of 0.001% or more. However, if the Ti content is too high, casting will be adversely affected, so it is limited to 0.3% or less.

Ａｌの含有量は、１．０～４．０％である。
本発明では、Ａｌが焼鈍熱処理時に酸化被膜を形成させることができるように、１．０％以上十分に添加する。しかしながら、過量添加する場合、鋳造と圧延が難しくなり得るので、上限を４．０％以下に制限する。 The Al content is 1.0 to 4.0%.
In the present invention, 1.0% or more of Al is sufficiently added so that an oxide film can be formed during the annealing heat treatment. However, if it is added in an excessive amount, casting and rolling may become difficult, so the upper limit is limited to 4.0% or less.

本発明の残部の成分は、鉄（Ｆｅ）である。ただし、通常の製造過程では、原料または周囲環境から意図しない不純物が不可避に混入することがあるので、これを排除することはできない。前記不純物は、通常の製造過程の技術者であれば、誰でも知ることができるから、すべての内容について特に本明細書では言及してはいない。 The remaining component of the present invention is iron (Fe). However, unintended impurities from raw materials or the surrounding environment may inevitably be mixed in during normal manufacturing processes, and cannot be excluded. The above impurities are known to anyone who is skilled in the normal manufacturing process, so not all of them are specifically mentioned in this specification.

ただし、上述した合金成分系だけでは耐食性の確保に不十分である。本発明者らが検討したところによれば、原料価格の節減のために、Ｃｒ含有量を低減する場合、外部に露出したとき、腐食が発生するなど腐食抵抗性がきわめて弱くなる問題があった。これより、本発明では、耐食性を確保するために特別な方法を導入した。 However, the above-described alloy composition system alone is insufficient to ensure corrosion resistance. According to the studies by the present inventors, when the Cr content is reduced in order to reduce the cost of raw materials, there is a problem that the corrosion resistance becomes extremely weak, such as corrosion when exposed to the outside. . Therefore, the present invention introduces a special method to ensure corrosion resistance.

排気系用ステンレス鋼の冷延鋼鈑は、冷間圧延後に軟化のために焼鈍熱処理を実施した後、表面のスケール除去のために酸洗処理して製品を出荷することが一般的である。本発明では、上述した合金成分系組成の冷延鋼鈑を焼鈍熱処理するに際して、下記のように定義されるＡｌ被膜指数およびＳｉ被膜指数の範囲を満たす表面を有するように焼鈍熱処理した後、酸洗処理することなく、最終製品を製造する。すなわち、本発明によるフェライト系鋼板は、冷延焼鈍鋼板であって、表面にスケール層を有する。 Cold-rolled stainless steel sheets for exhaust systems are generally subjected to annealing heat treatment for softening after cold rolling, and then pickling for surface scale removal before shipment. In the present invention, when the cold-rolled steel sheet having the above-described alloy composition is subjected to annealing heat treatment, the annealing heat treatment is performed so as to have a surface satisfying the ranges of the Al coating index and the Si coating index defined below. Manufacture the final product without washing. That is, the ferritic steel sheet according to the present invention is a cold-rolled and annealed steel sheet and has a scale layer on its surface.

従来、スケール層が耐食性に不利なＦｅを多量を含有している点から回避の対象であったが、本発明では、耐食性に有利なＡｌ濃化酸化被膜を形成して意図的に含む意味を有する。焼鈍熱処理を通じて表層に濃化して酸化するＡｌとＳｉの含有量を制御することによって、３．０～５．５％Ｃｒのフェライト系鋼板においても、ステンレス鋼と同等水準以上の耐食性および耐酸化性を確保できる。 In the past, the scale layer contained a large amount of Fe, which is disadvantageous to corrosion resistance, and was therefore an object of avoidance. have. By controlling the contents of Al and Si, which concentrate and oxidize on the surface layer through annealing heat treatment, even in ferritic steel sheets with 3.0 to 5.5% Cr, corrosion resistance and oxidation resistance equal to or higher than that of stainless steel. can be ensured.

本発明の排気系用フェライト系鋼板は、表面から深さ方向にスケール層を含む深さ０．２μｍの範囲でのＡｌ被膜指数が１５．０以上、そしてＳｉ被膜指数が３．０以下を満たす。Ａｌ被膜指数とＳｉ被膜指数は、下記のように定義される。
［Ａｌ被膜指数］：表面から深さ０．２μｍの範囲でＡｌ含有量の最大値（重量％）
［Ｓｉ被膜指数］：表面から深さ０．２μｍの範囲でＳｉ含有量の最大値（重量％） The ferritic steel sheet for an exhaust system of the present invention satisfies an Al coating index of 15.0 or more and a Si coating index of 3.0 or less in a depth range of 0.2 μm including a scale layer in the depth direction from the surface. . The Al coating index and the Si coating index are defined as follows.
[Al coating index]: maximum value of Al content (% by weight) in the range from the surface to a depth of 0.2 μm
[Si coating index]: maximum value of Si content (% by weight) in the range from the surface to a depth of 0.2 μm

一般的に、Ｓｉは、表層部にＳｉ濃化酸化膜を形成して高温耐酸化性を増加させることが知られている。ところで、酸洗を実施しない本発明では、Ｓｉ被膜指数が３．０を超過する場合に、表面に暗茶色のスケール層が形成されて、表面状態が不良になり、これによって、Ｓｉ被膜指数は、３．０以下に制限しなければならない。 It is generally known that Si forms a Si-concentrated oxide film on the surface layer to increase high-temperature oxidation resistance. By the way, in the present invention in which pickling is not performed, when the Si coating index exceeds 3.0, a dark brown scale layer is formed on the surface, resulting in a poor surface condition. , must be limited to 3.0 or less.

Ａｌも、表層部の酸素と反応して不均一な酸化層を形成するが、本発明によるＡｌ含有量である１．０～４．０％を添加した後、焼鈍熱処理を実施する場合、Ｓｉの表層への移動および反応を妨害して、優先的にＡｌ濃化酸化膜が形成される。Ａｌ酸化膜が緻密に形成されて、Ａｌ被膜指数が１５．０以上である場合、明るい金属性色相を示すことができる。 Al also reacts with oxygen in the surface layer to form a non-uniform oxide layer. movement and reaction to the surface layer are hindered, and an Al-enriched oxide film is preferentially formed. When the Al oxide film is densely formed and the Al coating index is 15.0 or more, a bright metallic hue can be exhibited.

素材表面の金属性色相は、国際照明委員会が制定したＬ＊ａ＊ｂ＊表色系で示すことができる。Ｌ＊ａ＊ｂ＊表色系は、物体の色を表現するにあたって、現在あらゆる分野において最も大衆的に使用される表色系であって、図１では、Ｌ＊ａ＊ｂ＊表色系を示す色空間（ＣＯＬＯＲ ＳＰＡＣＥ）を示している。この際、Ｌ＊は、０のとき、黒色、１００のとき、白色を強く示し、ａ＊は、正数のとき、赤色（Ｒｅｄ）方向、負数のとき、緑色（Ｇｒｅｅｎ）方向を示し、ｂ＊は、正数のとき、黄色（Ｙｅｌｌｏｗ）方向、負数のとき、青色（Ｂｌｕｅ）方向を示す。ａ＊、ｂ＊が両方と０である場合、無彩色となる。 The metallic hue of the material surface can be represented by the L*a*b* color system established by the International Commission on Illumination. The L*a*b* color system is currently the most widely used color system in all fields for expressing the color of an object. 2 shows a color space (COLOR SPACE) indicating . At this time, when L* is 0, it indicates black, and when it is 100, it strongly indicates white. When a* is a positive number, it indicates the direction of red. * indicates a yellow direction when a positive number and a blue direction when a negative number. If both a* and b* are 0, the color is achromatic.

本発明の一実施例によれば、Ａｌ濃化酸化被膜を形成して、Ｌ＊ａ＊ｂ＊表色系のＬ＊値が５０以上である明るい金属性表面を得ることができる。また、５０以上のＬ＊値と共に、ａ＊値とｂ＊値が同時に－１０～＋１０の範囲の明るい無彩色の金属性表面を得ることができる。 According to one embodiment of the present invention, a bright metallic surface having an L* value of 50 or more in the L*a*b* color system can be obtained by forming an Al-enriched oxide layer. It is also possible to obtain bright achromatic metallic surfaces with a* and b* values simultaneously in the range of -10 to +10, together with L* values of 50 or more.

図２～図４は、本発明による実施例を表面から深さ方向に０．２μｍまでグロー放電発光分析法で分析した合金成分の分布である。 2 to 4 are distributions of alloy components analyzed by glow discharge emission spectrometry in the examples according to the present invention from the surface to a depth of 0.2 μm.

図２は、本発明の実施例による冷延鋼鈑を焼鈍熱処理後に酸洗を実施しない試験片の合金成分の分布を示す。深さ方向への測定値中、Ａｌ含有量の最大値であるＡｌ被膜指数が１５．０以上である。 FIG. 2 shows the distribution of alloy components of a test piece of a cold-rolled steel sheet according to an embodiment of the present invention, which is not subjected to pickling after annealing heat treatment. Among the measured values in the depth direction, the Al coating index, which is the maximum value of the Al content, is 15.0 or more.

図３は、ＳｉとＡｌの含有量の範囲が一般排気系用フェライト系ステンレス鋼と同一であり、原料価格の節減のために、Ｃｒ含有量だけを低減した冷延鋼鈑を、同一に焼鈍熱処理後、酸洗を実施しない試験片の合金成分の分布を示す。すなわち、ＣｒとＡｌの含有量の範囲が本発明の組成範囲から外れる冷延焼鈍鋼板に該当する。図３に示すとおり、Ａｌ被膜指数が低く、最表層でＳｉ被膜指数が５．０に近く現れる。このような場合、耐食性および耐酸化性が不十分であり、Ｓｉ酸化膜に起因して表面変色も発生することになる。 Fig. 3 shows that the range of Si and Al contents is the same as that of ferritic stainless steel for general exhaust systems, and cold-rolled steel sheets with only a reduced Cr content are annealed in the same manner in order to reduce raw material costs. 1 shows the distribution of alloy components of a test piece that is not pickled after heat treatment. In other words, it corresponds to a cold-rolled and annealed steel sheet in which the contents of Cr and Al are outside the composition range of the present invention. As shown in FIG. 3, the Al coating index is low, and the Si coating index appears close to 5.0 at the outermost layer. In such a case, corrosion resistance and oxidation resistance are insufficient, and surface discoloration also occurs due to the Si oxide film.

図４は、図２と同じ合金成分系試験片を本発明の実施例によって冷延鋼鈑を焼鈍熱処理し、以後、酸洗まで実施した後の合金成分の分布を示す。同じ含有量のＣｒ、Ａｌ、Ｓｉを含んでいても、本発明において提示する焼鈍熱処理後に酸洗の省略を行わない場合、Ａｌ被膜指数が低く現れる。 FIG. 4 shows the distribution of the alloy composition of the same alloy composition test piece as in FIG. 2 after the cold-rolled steel sheet is subjected to annealing heat treatment and pickling according to the embodiment of the present invention. Even if the contents of Cr, Al and Si are the same, the Al coating index appears low when the pickling is not omitted after the annealing heat treatment proposed in the present invention.

また、Ａｌ被膜指数およびＳｉ被膜指数を同時に満たすために、フェライト系鋼板は、下記の式（１）を満たすことができる。

（１）５＊Ａｌ－（Ｃｒ＋Ｓｉ）＞０

Ａｌを式（１）のように十分に含有する場合、焼鈍中に十分なＡｌ濃化酸化被膜を形成できる。一方、そうでない場合、ＣｒとＳｉの酸化によってＡｌ濃化酸化被膜を形成する酸素が不十分になるか、ＣｒまたはＳｉ酸化被膜の形成によって一部のＡｌ濃化酸化被膜の形成に必要な酸素の移動が制限され得るので、避けなければならない。 In order to simultaneously satisfy the Al coating index and the Si coating index, the ferritic steel sheet can satisfy the following formula (1).

(1) 5*Al-(Cr+Si)>0

When Al is sufficiently contained as in formula (1), a sufficient Al-enriched oxide film can be formed during annealing. On the other hand, if this is not the case, the oxidation of Cr and Si will result in insufficient oxygen to form an Al-enriched oxide film, or the formation of a Cr or Si oxide film will result in the oxygen required to form a part of the Al-enriched oxide film. movement can be restricted and must be avoided.

なお、スケール層の厚さは、焼鈍熱処理温度および時間によって異なるが、本発明では、Ａｌ被膜指数が半分となる地点での厚さと定義できる。例えば、図１でのスケール層の厚さは、Ａｌ含有量の最大値であるＡｌ被膜指数の中間値に該当する約０．１μｍである。 The thickness of the scale layer varies depending on the annealing temperature and time, but in the present invention, it can be defined as the thickness at the point where the Al coating index is halved. For example, the thickness of the scale layer in FIG. 1 is about 0.1 μm, which corresponds to the middle value of the Al coating index, which is the maximum Al content.

本発明によるＡｌ被膜指数およびＳｉ被膜指数を満足するための焼鈍熱処理は、雰囲気ガスのうち高純度水素を７５％以上使用する高価な光輝焼鈍（ＢＡＬ）工程を利用しなくてもよく、低価のガスを使用する連続焼鈍工程を経ることで可能である。例えば、燃料ガスを熱源として使用し、排ガスの過剰酸素を０．１～１０％範囲に制限することで、本発明の目的を達成可能である。 The annealing heat treatment for satisfying the Al coating index and the Si coating index according to the present invention does not need to use an expensive bright annealing (BAL) process that uses 75% or more of high-purity hydrogen in the atmosphere gas, and is inexpensive. It is possible through a continuous annealing process using a gas of For example, the object of the present invention can be achieved by using fuel gas as a heat source and limiting excess oxygen in the exhaust gas to a range of 0.1-10%.

過剰酸素を０．１％以上にして酸素を付与することによって、焼鈍熱処理中に本発明の含有量の範囲によるＡｌが酸素と反応して高耐食性を付与する被膜を形成する。過剰酸素が不足すると、十分なＡｌ濃化酸化被膜が形成されないことがある。一方、過剰酸素が１０％を超過すると、素材のＦｅ、ＣｒまたはＳｉと酸素が反応してＡｌ濃化酸化被膜の他にＦｅ、Ｃｒ、Ｓｉ酸化被膜が形成されることがあり、この場合、変色が発生するので、不適切である。 By adding oxygen with an excess oxygen content of 0.1% or more, Al according to the content range of the present invention reacts with oxygen during the annealing heat treatment to form a coating that imparts high corrosion resistance. If excess oxygen is insufficient, a sufficient Al-enriched oxide film may not be formed. On the other hand, if the excess oxygen exceeds 10%, the material Fe, Cr or Si may react with oxygen to form an Fe, Cr, or Si oxide film in addition to the Al-concentrated oxide film. Not suitable as it causes discoloration.

なお、容易な製造のために、酸素を０．１％以下に制限したい場合、雰囲気ガス中の水素を０．１％～１０％の範囲で混合すると、Ｆｅ、Ｃｒ、Ｓｉとの酸化が抑制されて、０．１％以下の少ない量の酸素でもＡｌ濃化酸化被膜の形成が可能である。１０％以上で混合することは、上述したように、費用の上昇を招くので、不要であり、０．１％未満の水素では、Ｆｅ、Ｃｒ、Ｓｉの酸化を抑制する能力が不十分で、Ａｌ濃化酸化被膜の形成が不十分になる。 For ease of production, if oxygen is to be limited to 0.1% or less, the oxidation of Fe, Cr, and Si can be suppressed by mixing hydrogen in the atmospheric gas in the range of 0.1% to 10%. Therefore, it is possible to form an Al-enriched oxide film even with a small amount of oxygen of 0.1% or less. Mixing at 10% or more is unnecessary because it causes an increase in cost as described above, and with less than 0.1% hydrogen, the ability to suppress the oxidation of Fe, Cr, and Si is insufficient. Formation of the Al-concentrated oxide film becomes insufficient.

焼鈍熱処理後に酸洗は省略しなければならない。酸洗を未実施することによって、ＡｌおよびＳｉ被膜指数を満足し、スケール層が除去されない最表層を得ることができ、硝酸および／またはフッ酸の混酸溶液を使用する酸洗工程の省略を通じて製造費用をも節減できる。 Pickling should be omitted after the annealing heat treatment. By not performing pickling, it is possible to obtain the outermost layer that satisfies the Al and Si coating indices and that the scale layer is not removed, and manufacturing by omitting the pickling process using a mixed acid solution of nitric acid and/or hydrofluoric acid. Costs can also be saved.

焼鈍熱処理および酸洗省略前の冷延鋼鈑は、通常の製造工程を経て製造でき、例えば、上述した合金成分の組成を含むスラブを熱間圧延し、熱間圧延した熱延鋼板を焼鈍熱処理し、酸洗後に冷間圧延して、冷延鋼鈑に製造できる。 The cold-rolled steel sheet before the annealing heat treatment and the pickling omission can be manufactured through a normal manufacturing process. Then, after pickling, it can be cold-rolled to produce a cold-rolled steel sheet.

本発明の耐食性に優れた排気系用フェライト系鋼板は、式（２）で表される腐食減耗率が２０％未満である。

（２）腐食減耗率（％）＝［（腐食試験前の重さ）－（腐食試験後重さ）］／（腐食試験前の重さ）×１００

ここで、腐食試験後の重さは、腐食試験後に生成された腐食生成物を除去した後の重さ（ｇ）である。 The ferritic steel sheet for exhaust systems of the present invention having excellent corrosion resistance has a corrosion loss rate represented by the formula (2) of less than 20%.

(2) Corrosion loss rate (%) = [(Weight before corrosion test) - (Weight after corrosion test)] / (Weight before corrosion test) x 100

Here, the weight after the corrosion test is the weight (g) after removing corrosion products generated after the corrosion test.

耐食性、すなわち腐食に対する抵抗性は、任意に組成した腐食環境に露出させることで知ることができる。例えば、水中に５％の体積比になるように、ＮａＣｌを含有する溶液を素材に噴霧した後、４時間維持し、６０℃程度で４時間の間加熱して乾燥させる過程を計３０回繰り返して、後述する方法で腐食程度を評価できる。評価環境は、多様に構成できるので、本発明に限定するものではない。 Corrosion resistance, or resistance to corrosion, can be determined by exposure to a randomly composed corrosive environment. For example, after spraying a solution containing NaCl to the material so that the volume ratio is 5% in water, the process is maintained for 4 hours, heated at about 60 ° C. for 4 hours, and dried, which is repeated 30 times in total. Therefore, the degree of corrosion can be evaluated by the method described later. Since the evaluation environment can be configured in various ways, it is not limited to the present invention.

本発明では、［（腐食試験前の重さ）－（腐食試験後重さ）］／（腐食試験前の重さ）を減耗率と定義し、１００を掛けて％単位で表示した。このように腐食試験後に生成された腐食生成物を除去した後の重さ、すなわち「腐食試験後の重さ」を測定し、「腐食試験前の重さ」と比較することによって、減耗率を測定できる。減耗率が腐食生成物の除去が必要であるという点から容易でない場合、重さの代わりに厚さに変えることができる。この場合、腐食生成物の除去は不要であり、断面を光学顕微鏡で観察して、腐食生成物を除いた母材金属の部分の厚さを比較すればよい。 In the present invention, [(Weight before corrosion test)-(Weight after corrosion test)]/(Weight before corrosion test) is defined as the wear rate, which is multiplied by 100 and expressed in %. By measuring the weight after removing the corrosion products generated after the corrosion test, that is, the "weight after the corrosion test" and comparing it with the "weight before the corrosion test", the wear rate can be calculated. can be measured. If the wear rate is not easy in terms of the need to remove corrosion products, thickness can be substituted for weight. In this case, it is not necessary to remove the corrosion products, and the cross section may be observed with an optical microscope to compare the thickness of the base metal portion excluding the corrosion products.

本発明において代替しようとする１１％Ｃｒが含有された鋼において同時にＡｌを１．０％以上添加すると、加工性が悪くなる。Ｓｉも同様であり、このような現象は、Ａｌ、Ｓｉだけでなく、ＣｒがＦｅと原子位置を置換して加工性の代表的な指標である伸び率を阻害するためである。一方、本発明が提示する式（１）を満たす場合、Ａｌを１．０％以上含有していても、伸び率を２８％以上確保できる。この点は、Ａｌ濃化酸化被膜のための効果とともに、本発明を通じて付随的に得ることができる効果である。 If 1.0% or more of Al is added at the same time to the steel containing 11% Cr, which is intended to be substituted in the present invention, workability deteriorates. The same applies to Si, and such a phenomenon is caused not only by Al and Si, but also by Cr substituting the atomic positions of Fe and impairing elongation, which is a typical index of workability. On the other hand, when the formula (1) presented by the present invention is satisfied, an elongation rate of 28% or more can be secured even if the Al content is 1.0% or more. This point is an effect that can be additionally obtained through the present invention together with the effect for the Al-enriched oxide film.

以下、本発明の好ましい実施例に基づいてより詳細に説明することとする。
実施例
表１に記載した合金成分系で鋳造後に３ｍｍまで熱間圧延した。熱間圧延開始温度は、過度な組織成長を防止し、十分な熱間加工性を得るために好ましい１，２００℃前後に調節した。表面酸洗後に１ｍｍまで冷間圧延した後、過剰酸素が５％の雰囲気ガスで９００℃以上の温度で１０秒以上焼鈍した。以後、発明鋼と比較鋼に対して酸洗を実施および未実施した試験片をそれぞれ用意し、外部露出と同一環境での腐食発生の有無を評価し、表２に示した。外部露出に関するシミュレーションは、水中体積比で５％ＮａＣｌを含有する溶液を噴霧した後、７２時間放置した後、表面に点錆の発生の有無によって判断した。腐食の発生は○で表示し、腐食の未発生は×で表示した。 The preferred embodiments of the present invention will be described in more detail below.
Example
After casting with the alloy composition system shown in Table 1, hot rolling was performed to 3 mm. The hot rolling start temperature was adjusted to around 1,200° C., which is preferable for preventing excessive structural growth and obtaining sufficient hot workability. After surface pickling, the steel was cold-rolled to 1 mm, and then annealed at a temperature of 900° C. or higher in an atmosphere gas containing 5% excess oxygen for 10 seconds or longer. After that, test pieces with and without pickling were prepared for the invention steel and the comparative steel, respectively, and the presence or absence of corrosion in the same environment as the external exposure was evaluated. In the simulation of external exposure, a solution containing 5% NaCl by volume in water was sprayed and left for 72 hours. Occurrence of corrosion is indicated by ◯, and non-occurrence of corrosion is indicated by ×.

Figure 0007297373000001
Figure 0007297373000001

Figure 0007297373000002
Figure 0007297373000002

表２は、本発明による合金成分系の組成範囲を満たしても、焼鈍熱処理後に酸洗を実施した素材は、外部に露出したとき、腐食が発生することを示している。ただし、比較鋼１と比較鋼２は、本発明において低減しようとする高価な元素であるＣｒを多量含有するフェライト系ステンレス鋼であり、外部露出環境においても腐食が発生しなかった。本発明による発明鋼は、同じ合金成分系の試験片であるにもかかわらず、焼鈍熱処理後に酸洗を未実施の結果、腐食が発生しないことを確認できた。 Table 2 shows that even if the composition range of the alloy component system according to the present invention is satisfied, corrosion occurs when the material subjected to pickling after the annealing heat treatment is exposed to the outside. However, Comparative Steel 1 and Comparative Steel 2 are ferritic stainless steels containing a large amount of Cr, which is an expensive element to be reduced in the present invention, and did not corrode even in an environment exposed to the outside. It was confirmed that the inventive steel according to the present invention does not corrode as a result of not pickling after the annealing heat treatment, although the test pieces have the same alloy composition.

表３には、Ａｌ被膜指数およびＳｉ被膜指数と、酸洗を実施しない試験片の腐食減耗率と、腐食減耗率２０％を基準として判断した腐食適合性を示した。腐食適合性に適合した場合を○で表示し、適合しない場合を×で表示した。 Table 3 shows the Al coating index, the Si coating index, the corrosion wear rate of test pieces not pickled, and the corrosion suitability determined based on the corrosion wear rate of 20%. The cases where the corrosion compatibility was met were indicated by ◯, and the cases where the corrosion compatibility was not met were indicated by x.

Ａｌ被膜指数およびＳｉ被膜指数は、グロー放電発光分析法で分析でき、この方法は、本技術分野において広く知られた方法で学界で通用するグロー放電発光分析法に準ずる方法で分析できる。ただし、データを十分に確保するために、表面から深さ方向に距離による成分を分析するとき、その解像度は、１０ｎｍ以下であることが要求される。 The Al coating index and the Si coating index can be analyzed by glow discharge optical emission spectrometry, which is a widely known method in this technical field and can be analyzed by a method that conforms to the glow discharge optical emission analysis method that is commonly used in academic circles. However, in order to secure sufficient data, when analyzing the component according to the distance from the surface in the depth direction, the resolution is required to be 10 nm or less.

Figure 0007297373000003
Figure 0007297373000003

比較鋼１～５は、Ｃ、Ｓｉ、Ｍｎ、Ａｌ、Ｔｉ、Ｎの含有量が類似し、単にＣｒの含有量を次第に低減した試験片である。表３に示すとおり、比較鋼１および２は、Ｃｒ含有量が１１％以上のフェライト系ステンレス鋼に該当し、十分な耐食性を有するので、腐食減耗率が低く、腐食適合性も適合した。ただし、本発明によって酸洗を未実施した結果、Ｓｉ被膜指数が１０．６と高く現れ、これによる表面変色が発生した。 Comparative Steels 1-5 are specimens with similar C, Si, Mn, Al, Ti, and N contents, but only with progressively lower Cr contents. As shown in Table 3, Comparative Steels 1 and 2 correspond to ferritic stainless steels with a Cr content of 11% or more and have sufficient corrosion resistance, so the corrosion wear rate is low and the corrosion compatibility is also suitable. However, as a result of not pickling according to the present invention, the Si film index appeared as high as 10.6, and surface discoloration occurred due to this.

比較鋼３、４、５は、Ａｌ含有量が低くて、酸洗の未実施時にもＡｌ被膜指数が低くなり、減耗率が高くて、腐食適合性が不適合であった。また、Ｓｉ含有量は適正量であるが、スケール層を含む酸化被膜内Ｓｉ最大値であるＳｉ被膜指数が高くて、変色が発生したことが分かった。特に、比較鋼５は、Ａｌ含有量を除いた残りの合金元素の含有量が本発明の範囲を満たすが、発明鋼１～３を参照すると、酸洗の未実施時にＡｌ被膜指数を確保するためのＡｌ含有量が不足していることを確認できた。Ａｌ含有量が式（１）を満たすように含まれる場合、発明鋼１～３のように、Ｓｉ被膜指数を低減し、Ａｌ被膜指数を高めることができることが分かった。 Comparative steels 3, 4, and 5 had low Al contents, had a low Al coating index even when pickling was not performed, had a high wear rate, and were unsuitable for corrosion compatibility. Also, it was found that although the Si content was appropriate, the Si film index, which is the maximum value of Si in the oxide film including the scale layer, was high and discoloration occurred. In particular, Comparative Steel 5 satisfies the range of the present invention in terms of the content of the remaining alloying elements excluding the Al content, but with reference to Inventive Steels 1 to 3, the Al coating index is secured when pickling is not performed. It has been confirmed that the Al content for is insufficient. It was found that when the Al content satisfies the formula (1), the Si coating index can be reduced and the Al coating index can be increased, as in Inventive Steels 1-3.

比較鋼６、７、８は、Ｓｉ含有量を高めた試験片に該当する。一般的に、耐食性および耐酸化性に効果的であると知られているＳｉ含有量が高いとしても、酸洗の未実施の場合には、Ａｌ含有量が十分でなくて、腐食評価が不適合であり、表面変色も発生したことが分かった。 Comparative steels 6, 7 and 8 correspond to specimens with increased Si content. In general, even if the Si content is high, which is known to be effective for corrosion resistance and oxidation resistance, if pickling is not performed, the Al content is not sufficient and the corrosion evaluation is unsuitable. , and it was found that surface discoloration also occurred.

比較鋼９は、Ａｌを０．９％含有するが、Ａｌ含有量の範囲および式（１）を満たさないので、Ａｌ被膜指数が目標範囲に達しておらず、これによって、腐食評価が不適合であった。これは、Ａｌ含有量が不十分で、Ｓｉの酸化膜の形成を妨害しなかったと判断でき、これによって、Ｓｉ酸化膜が優勢に形成されて、変色が発生した。 Comparative steel 9 contains 0.9% Al, but does not satisfy the Al content range and formula (1), so the Al coating index does not reach the target range, and as a result, the corrosion evaluation is unsatisfactory. there were. It can be determined that the Al content was insufficient and did not interfere with the formation of the Si oxide film, and as a result, the Si oxide film was predominantly formed, resulting in discoloration.

比較鋼１０は、Ａｌ含有量が十分に含まれていて、Ａｌ被膜指数が１５以上と現れ、腐食評価も適合したが、式（１）を満たさないので、Ｓｉ被膜指数が高まる結果をもたらした。比較鋼１０は、表面変色が発生したが、Ａｌ被膜指数を満足して腐食評価が適合であるとしても、Ｓｉ被膜指数が３．０を超過する場合には、表面の変色を抑制できないことが分かった。 Comparative Steel 10 contained a sufficient amount of Al, appeared to have an Al coating index of 15 or more, and conformed to the corrosion evaluation, but did not satisfy the formula (1), resulting in an increased Si coating index. . Comparative Steel 10 had surface discoloration, but even if the Al coating index was satisfied and the corrosion evaluation was acceptable, the surface discoloration could not be suppressed when the Si coating index exceeded 3.0. Do you get it.

発明鋼１、２、３は、本発明の合金成分系の組成範囲を満たし、酸洗の未実施後に、Ａｌ被膜指数１５．０以上およびＳｉ被膜指数３．０以下を全部満たし、腐食評価が優れており、変色も発生しなかった。 Inventive steels 1, 2, and 3 satisfy the composition range of the alloy composition system of the present invention, and after not pickling, satisfy all of the Al film index of 15.0 or more and the Si film index of 3.0 or less, and the corrosion evaluation is Excellent and no discoloration occurred.

発明鋼４は、本発明の組成範囲内でＣｒ含有量が多少低い方に属するが、式（１）を満たすように、ＳｉおよびＡｌ含有量を調節することによって、Ａｌ被膜指数およびＳｉ被膜指数を目的範囲内に制御できた。 Inventive Steel 4 has a slightly lower Cr content within the composition range of the present invention, but by adjusting the Si and Al contents so as to satisfy the formula (1), the Al coating index and the Si coating index could be controlled within the target range.

なお、発明鋼５は、本発明の組成範囲内でＳｉ含有量が多少高い方に属するが、式（１）を満たすように、ＳｉおよびＡｌ含有量を調節することによって、Ａｌ被膜指数およびＳｉ被膜指数を目的範囲内に制御できた。 Inventive Steel 5 has a slightly higher Si content within the composition range of the present invention, but the Al coating index and the Si The coating index could be controlled within the target range.

Figure 0007297373000004
Figure 0007297373000004

表４は、比較鋼および発明鋼のＬ＊ａ＊ｂ＊表色系値を示し、表３の変色についてより詳しく示している。焼鈍後に酸洗を実施しない場合、比較鋼１～５は、Ｃｒの酸化による赤色を呈するスケール層を示した。また、比較鋼６～１０は、Ｓｉ被膜を制御しないため、紫色ないし青色を呈するスケール層を示した。一方、発明鋼１～５は、本発明が提示する製造方法を通じて明るい金属性色相を呈するスケール層を示した。 Table 4 shows the L*a*b* color system values of the comparative steel and the invention steel, and shows the discoloration in Table 3 in more detail. When no pickling was performed after annealing, comparative steels 1-5 showed a reddish scale layer due to oxidation of Cr. Also, Comparative Steels 6 to 10 showed a purple to blue scale layer because the Si coating was not controlled. On the other hand, Inventive Steels 1 to 5 exhibited a scale layer exhibiting a bright metallic hue through the manufacturing method proposed by the present invention.

図５は、本発明による比較鋼１０の冷延焼鈍鋼板試験片の表面を示す写真である。図５を通じて、通常の鋼種と同様に、焼鈍熱処理により表面に暗茶色のスケールが形成されたことを確認できる。 FIG. 5 is a photograph showing the surface of a cold-rolled and annealed steel plate test piece of comparative steel 10 according to the present invention. From FIG. 5, it can be seen that dark brown scales were formed on the surface due to the annealing heat treatment, as in the case of ordinary steel.

図６は、本発明による発明鋼２の冷延焼鈍鋼板試験片の表面を示す写真である。図６を通じて、発明鋼２の試験片は、酸洗の未実施時にも、明るい金属性の光沢を示すことを確認でき、Ｌ＊ａ＊ｂ＊表色系の値は、Ｌ＊：７９、ａ＊：０、ｂ＊：＋１であった。 FIG. 6 is a photograph showing the surface of a cold-rolled and annealed steel plate test piece of invention steel 2 according to the present invention. 6, it can be confirmed that the test piece of Inventive Steel 2 exhibits a bright metallic luster even when it is not pickled, and the L*a*b* color system values are L*: 79, a*: 0, b*: +1.

以上、本発明の例示的な実施例を説明したが、本発明は、これに限定されず、当該技術分野における通常の知識を有する者なら、下記に記載する請求範囲の概念と範囲を逸脱しない範囲内で多様な変更および変形が可能であることを理解できる。 While exemplary embodiments of the present invention have been described above, the present invention is not limited thereto and a person of ordinary skill in the art will not depart from the concept and scope of the claims set forth below. It can be understood that various modifications and variations are possible within the scope.

本発明による排気系用フェライト系鋼板は、排気系部品など（Ｍｕｆｆｌｅｒ、Ｅｘ－ｍａｎｉｆｏｌｄ、Ｃｏｌｌｅｃｔｏｒ ｃｏｎｅなど）の素材に適用可能である。 The ferritic steel sheet for exhaust systems according to the present invention can be applied to materials such as exhaust system parts (Muffler, Ex-manifold, collector cone, etc.).

Claims (5)

重量％で、Ｃ：０．０２％以下、Ｎ：０．０２％以下、Ｓｉ：２．０％以下、Ｍｎ：０．５％以下、Ｃｒ：３．０～５．５％、Ｔｉ：０．００１～０．３％、Ａｌ：１．０～４．０％を含み、残部がＦｅおよび不可避な不純物からなり、
表面スケール層を具備し、
下記のように定義されるＡｌ被膜指数１５．０以上およびＳｉ被膜指数３．０以下を満たすことを特徴とする耐食性に優れた排気系用フェライト系鋼板。
（ここで、Ａｌ被膜指数は、表面から深さ０．２μｍの範囲でＡｌ含有量の最大値（重量％）、
Ｓｉ被膜指数は表面から深さ０．２μｍの範囲でＳｉ含有量の最大値（重量％）である） % by weight, C: 0.02% or less, N: 0.02% or less, Si: 2.0% or less, Mn: 0.5% or less, Cr: 3.0 to 5.5%, Ti: 0 .001 to 0.3%, Al: 1.0 to 4.0%, the balance being Fe and unavoidable impurities,
comprising a surface scale layer;
A ferritic steel sheet for an exhaust system with excellent corrosion resistance, characterized by satisfying an Al coating index of 15.0 or more and a Si coating index of 3.0 or less defined as follows.
(Here, the Al coating index is the maximum value (% by weight) of the Al content in the range from the surface to a depth of 0.2 μm,
The Si coating index is the maximum value (% by weight) of the Si content in the range from the surface to a depth of 0.2 μm) 前記排気系用フェライト系鋼板は、式（１）を満たすことを特徴とする請求項１に記載の耐食性に優れた排気系用フェライト系鋼板。
（１）５＊Ａｌ－（Ｃｒ＋Ｓｉ）＞０
（ここで、Ａｌ、Ｃｒ、Ｓｉは、各元素の含有量（重量％）を意味する） The ferritic steel sheet for an exhaust system according to claim 1, wherein the ferritic steel sheet for an exhaust system satisfies the formula (1).
(1) 5*Al-(Cr+Si)>0
(Here, Al, Cr, and Si mean the content (% by weight) of each element) 水中に５％の体積比になるように、ＮａＣｌを含有する溶液を素材に噴霧した後、４時間維持し、６０℃で４時間の間加熱して乾燥させる過程を計３０回繰り返して行う腐食試験において、
前記排気系用フェライト系鋼板は、式（２）で表される腐食減耗率が２０％未満であることを特徴とする請求項１に記載の耐食性に優れた排気系用フェライト系鋼板。
（２）腐食減耗率（％）＝［（腐食試験前の重さ）－（腐食試験後の重さ）］／（腐食試験前の重さ）×１００
（ここで、腐食試験後の重さは、腐食試験後に生成された腐食生成物を除去した後の重さ（ｇ）である） Corrosion in which a solution containing NaCl is sprayed onto the material so as to have a volume ratio of 5% in water, maintained for 4 hours, and then dried by heating at 60°C for 4 hours, which is repeated 30 times in total. in the test,
2. The ferritic steel sheet for an exhaust system having excellent corrosion resistance according to claim 1, wherein the corrosion loss rate represented by the formula (2) is less than 20%.
(2) Corrosion loss rate (%) = [(Weight before corrosion test) - (Weight after corrosion test)] / (Weight before corrosion test) x 100
(Here, the weight after the corrosion test is the weight (g) after removing the corrosion products generated after the corrosion test) 前記排気系用フェライト系鋼板の表面のＬ＊ａ＊ｂ＊表色系のＬ＊値は、５０以上であることを特徴とする請求項１に記載の耐食性に優れた排気系用フェライト系鋼板。 2. The ferritic steel sheet for an exhaust system having excellent corrosion resistance according to claim 1, wherein the surface of the ferritic steel sheet for an exhaust system has an L* value of 50 or more in an L*a*b* color system. . 前記表面のＬ＊ａ＊ｂ＊表色系のａ＊値が－１０～＋１０およびｂ＊値が－１０～＋１０の範囲であることを特徴とする請求項４に記載の耐食性に優れた排気系用フェライト系鋼板。
5. Exhaust gas with excellent corrosion resistance according to claim 4, wherein the a* value of the surface L*a*b* color system is in the range of -10 to +10 and the b* value is in the range of -10 to +10 Ferritic steel sheets for systems.
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