JPH0534419B2

JPH0534419B2 -

Info

Publication number: JPH0534419B2
Application number: JP63264184A
Authority: JP
Inventors: Hiroshi Shimizu; Osamu Hashimoto; Hayao Kurahashi; Hiroyuki Murata; Atsushi Manako; Hidemasa Nonaka; Hiroshi Sano; Hiroshi Iizuka; Jun Kuroda
Original assignee: Yazaki Sogyo KK; Kawasaki Steel Corp
Current assignee: JFE Steel Corp; Yazaki Corp
Priority date: 1988-10-21
Filing date: 1988-10-21
Publication date: 1993-05-24
Also published as: JPH02115346A

Description

[Detailed description of the invention]

〔産業上の利用分野〕本発明は、ハロゲン濃度10重量％以上の高濃度
ハロゲン化物中で、優れた耐食性、特に耐孔食性
を示すフエライト系ステンレス鋼に関する。〔従来の技術〕近年、利用価値の低い工業用廃水としての温水
や低温熱源を熱交換器をもつて利用する傾向にあ
るが、その熱媒体としてハロゲン濃度10重量％以
上の高濃度のハロゲン化物水溶液や、低融点の溶
融塩が利用されようとしている。しかし、このよ
うな高濃度のハロゲン化物中での耐食合金の挙動
については、殆ど研究されていないのが現状であ
る。一般に、オーステナイト系ステンレス鋼は、耐
銹性、耐食性とも優れてはいるが、ハロゲンイオ
ンの存在下では応力腐食割れ（以下SCCという）
を起こすため、上述の熱交換器用材料には適して
いない。また、２相ステンレス鋼は耐SCC性には優れて
いるが、耐孔食性が不十分なため上述の材料には
適さない。最近では、高耐食性のフエライト系ステンレス
鋼も数多く開発されているが、それらは海水を代
表とする低濃度のハロゲン化物水溶液中で使用す
ることを主たる目的としているために、ハロゲン
濃度10重量％以上の高濃度ハロゲン化物中では十
分な耐食性が得られないのが実情である。従来より耐孔食性の優れたステンレス鋼として
は、Cr量、Mo量を高め、Ｃ、Ｎ、Ｐ、Ｓ、Mn
等の不純物元素量を極力下げる方向で開発が行わ
れており、特に海水環境に対しては数々の耐食ス
テンレス鋼が開発されてきた。しかし、これら従
来鋼のハロゲン濃度として10重量％以上含有する
高濃度のハロゲン化物中（水溶液や溶融塩）での
耐食性に関しては殆ど研究が行われていない。本発明者らは、ハロゲン濃度10重量％以上の高
濃度ハロゲン化物中での従来材の耐食性を調査し
た。例を上げると、SUS316鋼を代表とするオース
テナイト系ステンレス鋼は、耐孔食性ではフエラ
イト系ステンレス鋼より優れているが耐SCC性に
劣つており、高濃度ハロゲン化物中では短時間で
貫通割れを起こすものさえある。また、SUS329J1を代表とする２相ステンレス
鋼は耐SCC性に優れており、高濃度ハロゲン化物
中でもSCCを起こしにくいが、耐孔食性はフエラ
イト相に優先的に孔食が発生するため使用できな
い。２相ステンレス鋼に関し、特開昭50−84412
等が開示されているが、同じく十分な耐食性が得
られない。フエライト系ステンレス鋼に関しては、特公昭
59−52226、特公昭59−38300等が開示されている
が、ハロゲン濃度10重量％以上の高濃度ハロゲン
化物中で十分な耐食性を得るに至つていない。〔発明が解決しようとする課題〕本発明は上記従来技術の欠点を解決し、ハロゲ
ン濃度10重量％以上の高濃度ハロゲン化物を利用
する熱交換器などの材料として、十分な耐食性が
得られるステンレス鋼を提供しようとするもので
ある。〔課題を解決するための手段〕本発明は、上記従来技術の問題点を解決するた
めに、研究を重ねた結果、高濃度ハロゲン化物中
では、ステンレス鋼をフエライト単相とし、特に
Al、Ni、Cu、Mo、Crの適量添加が有効である
ことを発見し完成したものである。本発明の要旨とするところは、Ｃ：0.01重量％以下 Si：0.40〜1.50重量％ Mn：2.0重量％以下 Cr：18.1〜23.0重量％ Al：0.01〜1.00重量％Ｎ：0.05重量％以下 Ni：0.60〜3.00重量％ Cu：0.50〜3.00重量％を含み、残部Feおよび不可避的不純物より成る
ハロゲン濃度10重量％以上の高濃度ハロゲン化物
中で優れた耐食性を有するフエライト系ステンレ
ス鋼、上記成分に加え、さらに、 Mo：0.30〜3.00重量％を含み、残部がFeおよび不可避的不純物より成
るハロゲン濃度10重量％以上の高濃度ハロゲン化
物中で優れた耐食性を有するフエライト系ステン
レス鋼、上記２種の成分に加え、さらに、 Ti：0.05〜1.00重量％ Nb：0.05〜1.00重量％Ｖ：0.05〜1.00重量％のうち１種または２種以上を含み、残部Feおよ
び不可避的不純物より成るハロゲン濃度10重量％
以上の高濃度ハロゲン化物中で優れた耐食性を有
するフエライト系ステンレス鋼である。〔作用〕本発明者らは、ハロゲン濃度10重量％以上の高
濃度ハロゲン化物中でステンレス鋼の耐食性に及
ぼす構成元素の影響をくまなく調査した結果、フ
エライト単相状態でAl、Ni、Cu、Mo、Crを添
加することが有効であり、80℃以上の高温とする
場合、特にAlの添加が有効であることを発見し
た。これはAlがフエライト系ステンレス鋼中のＮ
を無害化するのみならず、被膜組成をAlが富化
した酸化物系とするためである。このとき、特に
鋼が80℃以上の高温にさらされた場合には、空気
中あるいは水溶液中の酸素によりAlの酸化が促
進され、優れた耐食性を有する被膜を形成するも
のと考えられる。従つて、腐食環境で使用する場
合には、大気などの酸化雰囲気中で80℃以上の加
熱を行い予備処理すると効果的である。次に、各成分元素の影響について説明する。ＣおよびＮ：ＣおよびＮは、フエライト系ステンレス鋼にお
いては共に固溶限が小さく、主として炭化物、窒
化物として析出し耐食性を劣化させるほか、鋼板
の靭性および延性を低下させるので、出来るだけ
少ない方が望ましい。特に、Ｃにおいては高濃度
ハロゲン化物に対して耐食性を劣化させる作用が
著しいため、極力低くする必要があるが、工業
的、経済的な溶製技術を考慮してそれぞれ上限を
Ｃ：0.01重量％、Ｎ：0.05重量％とした。 Si： Siは脱酸剤として必要なだけでなく高濃度、高
温のハロゲン化物中でステンレス鋼表面に耐食性
の良い皮膜を形成させるため、耐孔食性、耐SCC
性を向上させる効果があり本発明では重要な添加
元素である。その効果を十分に発揮させるために
は0.40重量％以上の添加が必要である。しかし、
1.50重量％を越えて添加すると靭性が低下し製造
性を損なうので範囲を0.40〜1.50重量％とした。 Mn： Mnは一般に脱酸剤として使用されるが、鋼中
で硫化物を形成し、著しく耐食性を劣化させるた
め低い方が望ましいが、製造時の経済性を考慮し
て上限を2.0重量％に規定した。 Cr： Crはステンレス鋼の重要な構成元素である。
本発明者らの研究の結果、Crは高濃度ハロゲン
化物中での耐孔食性を向上させることがわかつ
た。その効果を十分に発揮させるためには、18.1
重量％以上の添加が必要である。しかし、23重量
％を越えて含有させても効果は飽和し、十分な改
善効果は得られないために上限を23.0重量％とし
た。よつて、範囲を18.1〜23.0重量％に限定し
た。 Al： Alは本発明で最も重要な添加元素である。本
発明におけるAlは、フエライト系ステンレス鋼
の脱酸剤として働き鋼中の酸化物系介在物を減少
させることを通じて、または、鋼中のＮを固定無
害化することを通じて、耐食性を向上させるのみ
ならず、上述のように、皮膜組成をAlが富化し
た酸化物系とすることにより、優れた耐食性を与
えるものである。第１図に、ハロゲン濃度が55％の高濃度ハロゲ
ン化物水溶液150℃における22Cr−1.5Ni−0.5Cu
鋼の孔食電位に及ぼすAl含有量の影響を示した。図からも明らかなように、Al量0.01重量％以上
で孔食電位が改善されているのがわかる。これ
は、鋼中酸素を安定化するのに必要なAl量が0.01
重量％程度であるため、0.01重量％未満のAl添加
では脱酸が不十分で、孔食の起点となる酸化物が
多く介在するため孔食電位が低いと考えられる。
また、Al含有量の増加にともない、耐孔食性は
向上するが、その効果はAl量0.05重量％以上で顕
著となる。これは、固溶Alが80℃以上の高温で
皮膜中で酸化物を作るためである。第１図に示すように耐孔食性は0.01重量％以上
のAl添加により飛躍的に向上しており、従つて、
0.01％重量以上の添加が必要である。また、Alは
1.00重量％を越えて含有させると鋼の靭性を劣化
させ、製造性を逸するので上限を1.00重量％と
し、範囲を0.01〜1.00重量％に限定した。なお、
Al添加の効果をより一層発揮させるために、上
述のように酸化雰囲気中で80℃以上の加熱予備処
理を行つてもよい。 Ni、Cu： NiおよびCuは高濃度ハロゲン化物中での耐食
性を改善する効果を有する。その効果を十分に発
揮させるためには、それぞれNi：0.60重量％以
上、Cu：0.50重量％以上の添加が必要である。し
かし、それぞれ3.00重量％を越えて含有させても
上述の効果は飽和の傾向にある上に、Ni、Cu共
に多量の添加により組織がフエライトとオーステ
ナイトあるいはマルテンサイトの２相として、耐
食性を著しく劣化させるため、Ni、Cuの上限を
それぞれ3.00重量％とし、範囲を、Ni：0.60〜
3.00重量％、Cu：0.50〜3.00重量％に限定した。 Mo： Moは、ステンレス鋼の耐食性を向上させる効
果を有する。その効果を十分発揮させるために
は、0.30重量％以上の添加が必要である。しか
し、Moは高価であり、3.00重量％以上添加する
と経済性を損うため上限を3.00重量％とし、範囲
を0.30〜3.00重量％に限定した。 Ti、Nb、Ｖ： Ti、Nb、Ｖは、ステンレス鋼の溶製時の不純
物として残留したＣ、Ｎを無害化する効果を有す
る。その効果を十分発揮させるためには、それぞ
れ0.05重量％以上含有させる必要がある。しか
し、多量の添加は鋼中酸素により酸化物を形成
し、鋼の清浄度を悪化させ耐食性、成形性、靭性
等を劣化させるので、その上限をそれぞれ1.00重
量％とし、範囲をTi、Nb、Ｖ共、0.05〜1.00重
量％に限定した。また、本発明では特にその範囲を規定しなかつ
たが、不純物としてのＰおよびＳは耐食性を劣化
させるので、経済性を損なわない程度に低く抑え
ることが望ましい。本発明鋼は、上記成分の鋼塊をフエライト系ス
テンレス鋼の通常の製造工程、すなわち、熱間圧
延→焼鈍酸洗→冷間圧延→焼鈍によつて得られ、
鋼板および鋼帯等とすることができる。ここで焼鈍温度は、高温でオーステナイト相が
生成する場合には、オーステナイト相生成温度直
下のフエライト単相温度域とし、常温でフエライ
ト単相状態にあるように熱処理する必要がある。〔実施例〕本発明の内容を実施例をもつて説明する。第１表に本発明鋼および比較鋼の化学組成を示
した。 A1〜A3は請求項１記載の発明鋼、B1〜B3は
請求項２記載の発明鋼、C1〜C5は請求項３記載
の発明鋼、D1〜D7は請求項４記載の発明鋼、E1
〜E6は比較鋼で、E1はA1に対して、Alを過小と
した鋼、E2はA1に対して、Ｃを過大とした鋼、
E3はA1に対して、Niを過小とした鋼、E4は２相
ステンレス鋼、E5はSUS316鋼、E6はSiが低い鋼
である。これらの本発明鋼および比較鋼は、比較鋼の一
部を除いて高周波真空溶解により100Kgの鋼塊に
鋳込み、熱間圧延、冷間圧延を経て、板厚１mmの
鋼板とし、850℃〜1100℃の温度範囲内で組織が
フエライト単相となるように仕上焼鈍を行つた。用いた溶液は、MgCl₂、ZnCl₂、LiCl、ZnBr₂、
LiBrを混合して水溶液とし、蒸発することによ
り水分を除去して、ハロゲン濃度が合計で55％
（Cl濃度約20重量％、Br濃度約35重量％）とした
溶液を使用した。なお、この溶液は25℃でPH2.3
程度である。耐食性の評価は、上記ハロゲン化物100℃およ
び150℃中での孔食電位を測定し、それぞれ10回
の平均値を求め、平均値の比較により行つた。また、浸漬試験として、上記ハロゲン化物150
℃中で200時間浸漬した場合の腐食減量も評価の
対象とした。この場合、腐食形態はすべて孔食で
あつた。なお、比液量は1.5／ｄm²とした。さらに、鋼の耐SCC性を評価するために、上記
ハロゲン化物150℃中および35％塩化マグネシウ
ム沸騰液中で200時間のSCC試験法を行つた。
SCC試験法については、基本的にJIS規格に準ず
る。試験片は溶液に１回に２個ずつ浸漬し、３回
の同一試験を行い、計６個の試験片の割れの有無
で判断した。なお、比液量は１／２個とした。第２表に、前記高濃度ハロゲン化物水溶液中、
100℃、150℃での孔食電位、150℃×200hr後の腐
食減量、150℃×200hr浸漬によるSCC試験結果お
よび35％MgCl₂水溶液沸騰200hr浸漬によるSCC
試験結果をまとめて示した。表中○および×は、
それぞれSCCの「なし」および「あり」を示す。各鋼の孔食電位を比較すると、100℃、150℃、
いずれも本発明鋼は比較鋼E1〜E4、E6に対し、
貴な値となつており、耐孔食性が良好であること
がわかる。浸漬試験による腐食減量を比較すると、比較鋼
は全て50mg／ｄm²以上であるのに対し、本発明鋼
では、40mg／ｄm²未満となつており、良好な耐食
性を示していることがわかる。特に、本発明鋼の中には、腐食減量が20mg／ｄ
m²未満と少ない鋼もあり、成分バランスの適正化
を図れば耐食性が改善されることを示している。 SCC試験結果を比較すると、本発明鋼は、高濃
度ハロゲン化物中、MgCl₂中いずれの環境におい
てもSCCは見られず、耐SCC性も良好であること
がわかる。 [Industrial Application Field] The present invention relates to a ferritic stainless steel that exhibits excellent corrosion resistance, particularly pitting corrosion resistance, in a high concentration halide with a halogen concentration of 10% by weight or more. [Prior art] In recent years, there has been a trend to use hot water or low-temperature heat sources in the form of industrial waste water with low utility value, with heat exchangers. Aqueous solutions and molten salts with low melting points are being used. However, the behavior of corrosion-resistant alloys in such high concentrations of halides has hardly been studied. Generally, austenitic stainless steel has excellent rust resistance and corrosion resistance, but in the presence of halogen ions, stress corrosion cracking (hereinafter referred to as SCC) occurs.
It is not suitable for the heat exchanger materials mentioned above. Further, although duplex stainless steel has excellent SCC resistance, it has insufficient pitting corrosion resistance and is therefore not suitable for the above-mentioned materials. Recently, many ferritic stainless steels with high corrosion resistance have been developed, but because they are mainly intended for use in low-concentration halide aqueous solutions such as seawater, they have halogen concentrations of 10% by weight or more. The reality is that sufficient corrosion resistance cannot be obtained in high-concentration halides. Stainless steels with better pitting corrosion resistance than conventional stainless steels have higher amounts of Cr and Mo, and contain C, N, P, S, and Mn.
Development efforts are underway to reduce the amount of impurity elements such as, as much as possible, and a number of corrosion-resistant stainless steels have been developed, especially for seawater environments. However, little research has been conducted on the corrosion resistance of these conventional steels in high-concentration halides (aqueous solutions and molten salts) containing halogen concentrations of 10% by weight or more. The present inventors investigated the corrosion resistance of conventional materials in a high concentration halide with a halogen concentration of 10% by weight or more. For example, austenitic stainless steel, such as SUS316 steel, has superior pitting corrosion resistance to ferritic stainless steel, but is inferior to SCC resistance, and can easily undergo through cracking in a short period of time in high-concentration halides. Some even cause it. In addition, duplex stainless steels such as SUS329J1 have excellent SCC resistance and do not easily cause SCC even in high concentration halides, but cannot be used because pitting corrosion occurs preferentially in the ferrite phase. Regarding duplex stainless steel, JP-A-50-84412
etc. have been disclosed, but similarly, sufficient corrosion resistance cannot be obtained. Regarding ferritic stainless steel, please contact Tokkosho
No. 59-52226, Japanese Patent Publication No. 59-38300, etc. have been disclosed, but sufficient corrosion resistance has not yet been achieved in high-concentration halides with a halogen concentration of 10% by weight or more. [Problems to be Solved by the Invention] The present invention solves the above-mentioned drawbacks of the prior art and provides stainless steel that has sufficient corrosion resistance as a material for heat exchangers and the like that utilize high-concentration halides with a halogen concentration of 10% by weight or more. The aim is to provide steel. [Means for Solving the Problems] In order to solve the problems of the above-mentioned prior art, the present invention has been made as a result of repeated research.In high concentration halides, stainless steel is made into a single phase of ferrite, and in particular,
This was completed after discovering that adding appropriate amounts of Al, Ni, Cu, Mo, and Cr was effective. The gist of the present invention is as follows: C: 0.01% by weight or less Si: 0.40 to 1.50% by weight Mn: 2.0% by weight or less Cr: 18.1 to 23.0% by weight Al: 0.01 to 1.00% by weight N: 0.05% by weight or less Ni: A ferritic stainless steel containing 0.60 to 3.00 wt% Cu: 0.50 to 3.00 wt%, the balance consisting of Fe and unavoidable impurities, which has excellent corrosion resistance in high concentration halides with a halogen concentration of 10 wt% or more, in addition to the above components. , furthermore, a ferritic stainless steel containing Mo: 0.30 to 3.00% by weight, the balance consisting of Fe and unavoidable impurities, which has excellent corrosion resistance in a high concentration halide with a halogen concentration of 10% by weight or more, the above two components In addition, it further contains one or more of Ti: 0.05 to 1.00% by weight, Nb: 0.05 to 1.00% by weight, V: 0.05 to 1.00% by weight, and the balance is Fe and unavoidable impurities with a halogen concentration of 10% by weight.
This is a ferritic stainless steel that has excellent corrosion resistance in the presence of high-concentration halides. [Function] The present inventors thoroughly investigated the effects of constituent elements on the corrosion resistance of stainless steel in high-concentration halides with a halogen concentration of 10% by weight or more, and found that Al, Ni, Cu, It has been discovered that adding Mo and Cr is effective, and that adding Al is particularly effective when the temperature is 80°C or higher. This is because Al is N in ferritic stainless steel.
This is not only to make it harmless, but also to make the coating composition an oxide system enriched with Al. At this time, especially when the steel is exposed to high temperatures of 80° C. or higher, the oxidation of Al is promoted by oxygen in the air or in the aqueous solution, and it is thought that a film with excellent corrosion resistance is formed. Therefore, when used in a corrosive environment, it is effective to perform pretreatment by heating at 80° C. or higher in an oxidizing atmosphere such as the air. Next, the influence of each component element will be explained. C and N: Both C and N have a small solid solubility limit in ferritic stainless steel, and they mainly precipitate as carbides and nitrides, deteriorating the corrosion resistance as well as reducing the toughness and ductility of the steel sheet, so they should be kept as low as possible. is desirable. In particular, C has a significant effect on deteriorating corrosion resistance due to high concentrations of halides, so it must be kept as low as possible, but in consideration of industrial and economic melting technology, the upper limit for each is set at 0.01% by weight. , N: 0.05% by weight. Si: Si is not only necessary as a deoxidizing agent, but also forms a highly corrosion-resistant film on the stainless steel surface in high-concentration, high-temperature halides, making it resistant to pitting corrosion and SCC.
It is an important additive element in the present invention because it has the effect of improving properties. In order to fully exhibit its effect, it is necessary to add 0.40% by weight or more. but,
If added in excess of 1.50% by weight, the toughness decreases and manufacturability is impaired, so the range was set to 0.40 to 1.50% by weight. Mn: Mn is generally used as a deoxidizing agent, but since it forms sulfides in steel and significantly deteriorates corrosion resistance, it is preferable to keep it low, but considering economic efficiency during manufacturing, the upper limit has been set at 2.0% by weight. stipulated. Cr: Cr is an important constituent element of stainless steel.
As a result of research conducted by the present inventors, it was found that Cr improves pitting corrosion resistance in high concentration halides. In order to fully demonstrate its effect, 18.1
It is necessary to add more than % by weight. However, even if the content exceeds 23% by weight, the effect is saturated and a sufficient improvement effect cannot be obtained, so the upper limit was set at 23.0% by weight. Therefore, the range was limited to 18.1-23.0% by weight. Al: Al is the most important additive element in the present invention. Al in the present invention not only improves corrosion resistance by acting as a deoxidizing agent for ferritic stainless steel and reducing oxide inclusions in the steel, but also by fixing and rendering N in the steel harmless. First, as mentioned above, by making the coating composition an oxide-based film enriched with Al, it provides excellent corrosion resistance. Figure 1 shows 22Cr−1.5Ni−0.5Cu in a highly concentrated halide aqueous solution at 150°C with a halogen concentration of 55%.
The influence of Al content on the pitting potential of steel is shown. As is clear from the figure, it can be seen that the pitting corrosion potential is improved when the Al content is 0.01% by weight or more. This means that the amount of Al required to stabilize oxygen in steel is 0.01
Since the amount of Al added is about 0.01% by weight, deoxidation is insufficient and the pitting corrosion potential is thought to be low due to the presence of many oxides that become pitting corrosion starting points.
Further, as the Al content increases, the pitting corrosion resistance improves, but this effect becomes noticeable when the Al content is 0.05% by weight or more. This is because solid solution Al forms oxides in the film at high temperatures of 80°C or higher. As shown in Figure 1, pitting corrosion resistance is dramatically improved by adding 0.01% by weight or more of Al.
It is necessary to add 0.01% or more by weight. Also, Al
If the content exceeds 1.00% by weight, the toughness of the steel deteriorates and manufacturability is lost, so the upper limit was set at 1.00% by weight and the range was limited to 0.01 to 1.00% by weight. In addition,
In order to further exhibit the effect of Al addition, a preheating treatment at 80° C. or higher may be performed in an oxidizing atmosphere as described above. Ni, Cu: Ni and Cu have the effect of improving corrosion resistance in high concentration halides. In order to fully exhibit their effects, it is necessary to add 0.60% by weight or more of Ni and 0.50% by weight or more of Cu, respectively. However, even if the content exceeds 3.00% by weight, the above-mentioned effects tend to be saturated, and addition of large amounts of both Ni and Cu causes the structure to form two phases of ferrite and austenite or martensite, significantly deteriorating corrosion resistance. In order to achieve
Cu was limited to 3.00% by weight, and Cu: 0.50 to 3.00% by weight. Mo: Mo has the effect of improving the corrosion resistance of stainless steel. In order to fully exhibit its effect, it is necessary to add 0.30% by weight or more. However, Mo is expensive, and adding more than 3.00% by weight impairs economic efficiency, so the upper limit was set at 3.00% by weight, and the range was limited to 0.30 to 3.00% by weight. Ti, Nb, V: Ti, Nb, and V have the effect of rendering C and N, which remain as impurities during the melting of stainless steel, harmless. In order to fully exhibit their effects, each must be contained in an amount of 0.05% by weight or more. However, if large amounts are added, oxygen in the steel forms oxides, which deteriorates the cleanliness of the steel and deteriorates corrosion resistance, formability, toughness, etc., so the upper limit is set at 1.00% by weight for each, and the range is set as Ti, Nb, Both V and V were limited to 0.05 to 1.00% by weight. Further, although the present invention does not particularly define the range, since P and S as impurities deteriorate corrosion resistance, it is desirable to keep them low to the extent that they do not impair economic efficiency. The steel of the present invention is obtained by a steel ingot having the above-mentioned components through the normal manufacturing process of ferritic stainless steel, that is, hot rolling → annealing pickling → cold rolling → annealing,
It can be a steel plate, a steel strip, etc. Here, when the austenite phase is generated at a high temperature, the annealing temperature must be set to a ferrite single phase temperature range immediately below the austenite phase generation temperature, and the heat treatment must be performed so that the ferrite single phase state is maintained at room temperature. [Example] The content of the present invention will be explained using an example. Table 1 shows the chemical compositions of the invention steel and comparative steel. A1 to A3 are the invention steels according to claim 1, B1 to B3 are the invention steels according to claim 2, C1 to C5 are the invention steels according to claim 3, D1 to D7 are the invention steels according to claim 4, and E1
~ E6 is a comparative steel, E1 is a steel with too little Al compared to A1, E2 is a steel with too much C compared to A1,
E3 is a steel with less Ni than A1, E4 is a duplex stainless steel, E5 is SUS316 steel, and E6 is a steel with a lower Si content. These inventive steels and comparative steels, except for a part of the comparative steels, were cast into a 100 kg steel ingot by high frequency vacuum melting, hot rolled and cold rolled to form a steel plate with a thickness of 1 mm. Finish annealing was carried out within the temperature range of °C so that the structure became a single ferrite phase. The solutions used were MgCl ₂ , ZnCl ₂ , LiCl, ZnBr ₂ ,
Mix LiBr to form an aqueous solution, remove water by evaporation, and achieve a total halogen concentration of 55%.
(Cl concentration: about 20% by weight, Br concentration: about 35% by weight) was used. Note that this solution has a pH of 2.3 at 25℃.
That's about it. Corrosion resistance was evaluated by measuring the pitting potential of the halide at 100°C and 150°C, calculating the average value of each test 10 times, and comparing the average values. In addition, as an immersion test, the above halide 150
The corrosion loss when immersed for 200 hours in °C was also evaluated. In this case, all forms of corrosion were pitting corrosion. Note that the specific liquid amount was 1.5/dm ² . Furthermore, in order to evaluate the SCC resistance of the steel, a 200-hour SCC test method was conducted in the above-mentioned halide at 150°C and in a 35% magnesium chloride boiling liquid.
The SCC test method basically follows JIS standards. The test pieces were immersed in the solution two at a time, and the same test was conducted three times, and the presence or absence of cracks was judged based on the presence or absence of cracks in a total of six test pieces. Note that the specific liquid amount was 1/2. Table 2 shows that in the high concentration halide aqueous solution,
Pitting corrosion potential at 100℃ and 150℃, corrosion loss after 150℃×200hr, SCC test results by immersion at 150℃×200hr, and SCC by immersion in 35% MgCl ₂ aqueous solution boiling for 200hr
The test results are summarized below. ○ and × in the table are
Indicates “without” and “with” SCC, respectively. Comparing the pitting corrosion potential of each steel, 100℃, 150℃,
In both cases, the steels of the present invention have a lower
It is clear that the pitting corrosion resistance is good. Comparing the corrosion weight loss in the immersion test, all comparative steels had a loss of 50 mg/dm ² or more, while the steel of the present invention had a loss of less than 40 mg/dm ² , indicating good corrosion resistance. In particular, some of the steels of the present invention have a corrosion loss of 20 mg/d.
There are some steels with less than m ² , indicating that corrosion resistance can be improved by optimizing the component balance. Comparing the SCC test results, it can be seen that the steel of the present invention shows no SCC in either environments of high concentration halide or _MgCl2 , and has good SCC resistance.

【表】【table】

【表】［発明の効果］本発明鋼は、従来鋼では成し得なかつたハロゲ
ン濃度10重量％以上の高濃度ハロゲン化物中での
優れた耐食性を得ることができるフエライト系ス
テンレス鋼であり、高濃度のハロゲン化物を利用
する装置、例えば熱交換器等の構成材料として最
適である。[Table] [Effects of the Invention] The steel of the present invention is a ferritic stainless steel that can obtain excellent corrosion resistance in high-concentration halides with a halogen concentration of 10% by weight or more, which could not be achieved with conventional steels. It is ideal as a constituent material for devices that utilize high-concentration halides, such as heat exchangers.

[Brief explanation of the drawing]

第１図はCl濃度20重量％、Br濃度35重量％、
PH2.3の高濃度ハロゲン化物水溶液を用い、150℃
で測定された22Cr−1.5Ni−0.5Cu鋼の孔食電位
V′_C100に及ぼすAl含有量の影響を示す線図であ
る。 Figure 1 shows Cl concentration 20% by weight, Br concentration 35% by weight,
Using a highly concentrated halide aqueous solution with a pH of 2.3, at 150℃
Pitting potential of 22Cr−1.5Ni−0.5Cu steel measured at
FIG. 2 is a diagram showing the influence of Al content on V′ _C100 .

Claims

[Claims] 1 C: 0.01 wt% or less Si: 0.40 to 1.50 wt% Mn: 2.0 wt% or less Cr: 18.1 to 23.0 wt% Al: 0.01 to 1.00 wt% N: 0.05 wt% or less Ni: 0.60 to A ferritic stainless steel having excellent corrosion resistance in a high concentration halide with a halogen concentration of 10% by weight or more, containing 3.00% by weight Cu: 0.50 to 3.00% by weight, and the remainder consisting of Fe and unavoidable impurities. 2. In addition to the components described in claim 1, it further contains Mo: 0.30 to 3.00% by weight, and the balance is Fe and unavoidable impurities. Ferritic stainless steel with corrosion resistance. 3 In addition to the components described in claim 1, it further contains one or more of Ti: 0.05 to 1.00% by weight, Nb: 0.05 to 1.00% by weight, V: 0.05 to 1.00% by weight, and the remainder is Fe and unavoidable components. A ferritic stainless steel that has excellent corrosion resistance in high-concentration halides with a halogen concentration of 10% by weight or more, which is characterized by consisting of impurities. 4 In addition to the components described in claim 2, it further contains one or more of Ti: 0.05 to 1.00% by weight, Nb: 0.05 to 1.00% by weight, V: 0.05 to 1.00% by weight, and the remainder is Fe and unavoidable components. A ferritic stainless steel that has excellent corrosion resistance in high-concentration halides with a halogen concentration of 10% by weight or more, which is characterized by consisting of impurities.