JP5793283B2 - Ferritic stainless steel with few black spots - Google Patents

Ferritic stainless steel with few black spots Download PDF

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Publication number
JP5793283B2
JP5793283B2 JP2010177998A JP2010177998A JP5793283B2 JP 5793283 B2 JP5793283 B2 JP 5793283B2 JP 2010177998 A JP2010177998 A JP 2010177998A JP 2010177998 A JP2010177998 A JP 2010177998A JP 5793283 B2 JP5793283 B2 JP 5793283B2
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less
stainless steel
ferritic stainless
black
black spot
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JP2012036444A (en
JP2012036444A5 (en
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透 松橋
透 松橋
潮雄 中田
潮雄 中田
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Nippon Steel and Sumikin Stainless Steel Corp
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Nippon Steel and Sumikin Stainless Steel Corp
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Priority to JP2010177998A priority Critical patent/JP5793283B2/en
Application filed by Nippon Steel and Sumikin Stainless Steel Corp filed Critical Nippon Steel and Sumikin Stainless Steel Corp
Priority to KR1020137003262A priority patent/KR20130034042A/en
Priority to US13/813,511 priority patent/US20130129560A1/en
Priority to TW100127716A priority patent/TWI526549B/en
Priority to EP11814699.2A priority patent/EP2602351B1/en
Priority to PCT/JP2011/067850 priority patent/WO2012018074A1/en
Priority to CN2011800382369A priority patent/CN103052731A/en
Priority to AU2011286685A priority patent/AU2011286685A1/en
Publication of JP2012036444A publication Critical patent/JP2012036444A/en
Publication of JP2012036444A5 publication Critical patent/JP2012036444A5/ja
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • C—CHEMISTRY; METALLURGY
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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    • C22C—ALLOYS
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    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
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    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
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    • C22C—ALLOYS
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • C—CHEMISTRY; METALLURGY
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C—CHEMISTRY; METALLURGY
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
    • F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
    • F28F21/081—Heat exchange elements made from metals or metal alloys
    • F28F21/082—Heat exchange elements made from metals or metal alloys from steel or ferrous alloys
    • F28F21/083—Heat exchange elements made from metals or metal alloys from steel or ferrous alloys from stainless steel

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Description

本発明は、ＴＩＧ溶接部のブラックスポットの生成の少ないフェライト系ステンレス鋼に関するものである。   The present invention relates to a ferritic stainless steel that generates less black spots in a TIG weld.

フェライト系ステンレス鋼は一般に耐食性に優れるだけでなく、オーステナイト系ステ
ンレス鋼に比較して熱膨張係数が小さいことや、耐応力腐食割れ性に優れる等の特徴を有
する。このため、食器、厨房機器や屋根材をはじめとする建築外装材料、貯水・貯湯用材料などに広く用いられている。さらに近年、Ｎｉ原料の価格高騰により、オーステナイト系ステンレス鋼からの切り替え需要も多く、その用途は広まってきている。 Ferritic stainless steel generally has not only excellent corrosion resistance, but also has features such as a smaller thermal expansion coefficient and superior stress corrosion cracking resistance than austenitic stainless steel. For this reason, it is widely used for building exterior materials such as tableware, kitchen equipment and roofing materials, and materials for water storage and hot water storage. Furthermore, in recent years, due to soaring prices of Ni raw materials, there is also a great demand for switching from austenitic stainless steel, and its application is widespread.

このようなステンレス鋼の構造体においては、溶接施工は不可欠なものである。元来フ
ェライト系ステンレス鋼はそのＣ，Ｎ固溶限が小さいことから溶接部で鋭敏化を生じ、耐
食性が低下する問題があった。この問題を解決するために、Ｃ，Ｎ量の低減やＴｉやＮｂ
などの安定化元素の添加によるＣ，Ｎの固定等により、溶接金属部の鋭敏化を抑制する方
法（例えば特許文献１参照）が提案されており、広く実用化されている。 In such a stainless steel structure, welding is indispensable. Originally, ferritic stainless steel has a problem in that its C and N solid solubility limit is small, so that sensitization occurs at the weld and corrosion resistance is lowered. In order to solve this problem, the amount of C and N is reduced, and Ti and Nb
A method for suppressing the sensitization of the weld metal part by fixing C and N by adding a stabilizing element such as (for example, see Patent Document 1) has been proposed and widely used.

また、フェライト系ステンレス鋼の溶接部における耐食性については、溶接の入熱で生
じたスケール部は耐食性が劣化することが知られており、オーステナイト系ステンレス鋼
に比較して不活性ガスによるシールドを十分に実施することが重要であることが知られて
いる。
また、特許文献２には、式Ｐ１＝５Ｔｉ＋２０(Ａｌ−０．０１)≧１．５（式中のＴｉ
，Ａｌは鋼中のそれぞれの含有量を示す）を満たすようにＴｉとＡｌを添加することで、
溶接熱影響部の耐食性を改善するＡｌ酸化皮膜を、溶接時の鋼の表層部に形成させる技術
が開示されている。 In addition, regarding the corrosion resistance of welded parts of ferritic stainless steel, it is known that the scale part produced by heat input during welding deteriorates in corrosion resistance, and a shield with inert gas is sufficient compared to austenitic stainless steel. It is known to be important to implement.
Patent Document 2 discloses that the formula P1 = 5Ti + 20 (Al−0.01) ≧ 1.5 (Ti in the formula
, Al indicates the respective contents in the steel) and by adding Ti and Al to satisfy,
A technique is disclosed in which an Al oxide film that improves the corrosion resistance of a weld heat affected zone is formed on the surface layer of steel during welding.

また、特許文献３には、ＡｌとＴｉとの複合添加に加え、Ｓｉを一定量以上添加するこ
とで、溶接部の耐すき間腐食性を向上させる技術が開示されている。
また、特許文献４には、４Ａｌ＋Ｔｉ≦０．３２（式中のＴｉ，Ａｌは鋼中のそれぞれ
の含有量を示す）を満足することで、溶接時の入熱を低減させて溶接部のスケール生成を
抑制し、溶接部の耐食性を向上させる技術が開示されている。
前述の従来技術は、溶接部や溶接熱影響部の耐食性を改善させることを目的としたもの
である。 Patent Document 3 discloses a technique for improving the crevice corrosion resistance of a welded part by adding a certain amount or more of Si in addition to the combined addition of Al and Ti.
Further, Patent Document 4 satisfies 4Al + Ti ≦ 0.32 (Ti and Al in the formulas indicate respective contents in steel), thereby reducing the heat input during welding and reducing the scale of the welded portion. A technique for suppressing generation and improving corrosion resistance of a welded portion is disclosed.
The above-described prior art is intended to improve the corrosion resistance of the welded portion and the weld heat affected zone.

その他に、溶接部ではなく素材自身の耐候性および耐すき間腐食性を向上させる手段と
して、Ｐを積極的に添加し、ＣａおよびＡｌを適正量添加する技術がある（例えば、特許
文献５参照）。特許文献５において、ＣａおよびＡｌは、鋼中の非金属介在物の形状と分
布を制御するために添加されている。なお、特許文献５の最大の特徴はＰを０．０４％超
えで添加することであり、特許文献５には溶接時の効果については一切記載がない。 In addition, as a means for improving the weather resistance and crevice corrosion resistance of the material itself, not the welded portion, there is a technique of positively adding P and adding appropriate amounts of Ca and Al (see, for example, Patent Document 5). . In Patent Document 5, Ca and Al are added to control the shape and distribution of nonmetallic inclusions in steel. The greatest feature of Patent Document 5 is that P is added in an amount exceeding 0.04%, and Patent Document 5 does not describe any effect at the time of welding.

特公昭５５−２１１０２号公報Japanese Patent Publication No.55-21102 特開平５−７０８９９号公報JP-A-5-70899 特開２００６−２４１５６４号公報JP 2006-241564 A 特開２００７−２７０２９０号公報JP 2007-270290 A 特開平７−３４２０５号公報JP-A-7-34205

従来のフェライト系ステンレス鋼においては、溶接部におけるシールド条件を適正化し
ても、溶接後の溶接裏ビード上に一般にブラックスポットやスラグスポットと呼ばれる黒
点が点在することがあった。ブラックスポットは、ＴＩＧ（Ｔｕｎｇｓｔｅｎ Ｉｎｅｒ
ｔ Ｇａｓ）溶接の凝固時に、酸素との親和力の強いＡｌ、Ｔｉ、Ｓｉ、Ｃａが酸化物と
して溶接金属上に固化したものである。ブラックスポットの発生には、溶接条件、特に不
活性ガスによるシールド条件が大きく影響しており、シールドが不十分なほどブラックス
ポットが多く発生する。 In conventional ferritic stainless steel, even if the shielding conditions in the welded portion are optimized, black spots generally called black spots or slag spots may be scattered on the weld back bead after welding. The black spot is TIG (Tungsten Inner
t Gas) During welding solidification, Al, Ti, Si, and Ca having strong affinity for oxygen are solidified as oxides on the weld metal. The generation of black spots is greatly influenced by welding conditions, particularly shielding conditions by inert gas, and more black spots are generated as the shielding is insufficient.

なお、ブラックスポット自身は酸化物であるため、ブラックスポットが少量点在してい
ても、溶接部の耐食性及び加工性には全く問題がない。しかしながら、ブラックスポット
が多量に生成したり連続的に生成したりすると、溶接部を研磨処理せずにそのままで用い
る場合の外観を損ねるだけでなく、溶接部を加工した際にブラックスポット部の剥離が生
じる場合がある。ブラックスポット部の剥離が生じると、加工性が低下したり、剥離した
ブラックスポット部とのすき間において、すき間腐食が生じたりする等の問題が発生する
場合がある。また、溶接後に加工を施さない場合でも、ブラックスポットが厚く生成する
と、構造上、溶接部に応力がかかるものではブラックスポットが剥離して耐食性が低下す
る場合がある。 Since the black spot itself is an oxide, there is no problem in the corrosion resistance and workability of the welded portion even if a small amount of black spot is scattered. However, if black spots are generated in large quantities or continuously, not only the appearance of the welded part is used without being polished, but also the appearance of the black spot is removed when the welded part is processed. May occur. When the black spot part is peeled off, there are cases where workability is deteriorated or a gap corrosion occurs between the black spot part and the peeled black spot part. Even when the processing is not performed after welding, if the black spot is generated thickly, if the stress is applied to the welded portion due to the structure, the black spot may be peeled off and the corrosion resistance may be lowered.

したがって、ＴＩＧ溶接部の耐食性を向上させるには、単に溶接ビード部や溶接スケー
ル部自体の耐食性を向上させるだけでなく、溶接部に生成するブラックスポットを制御す
ることが重要である。しかしながら、溶接時に生じる変色を伴うスケールについては、溶
接のシールド条件を強化する方法により、ほぼ抑制可能であるが、ＴＩＧ溶接部に生成す
るブラックスポットについては、シールド条件を強化したとしても従来の技術では十分に
抑制することはできなかった。 Therefore, in order to improve the corrosion resistance of the TIG welded part, it is important not only to improve the corrosion resistance of the weld bead part or the weld scale part itself, but also to control the black spots generated in the welded part. However, scales with discoloration that occur during welding can be suppressed almost by the method of strengthening the shield condition of welding. However, the black spot generated in the TIG welded part is the conventional technology even if the shield condition is strengthened. Then, it was not able to suppress enough.

本発明は、このような事情に鑑みてなされたものであって、ＴＩＧ溶接部にブラックス
ポットが生成しにくく、溶接部の耐食性および加工性に優れたフェライト系ステンレス鋼
を提供することを課題とするものである。 This invention is made in view of such a situation, Comprising: It is hard to produce | generate a black spot in a TIG weld part, and it aims at providing the ferritic stainless steel excellent in the corrosion resistance and workability of a weld part. To do.

本発明者は、ブラックスポットの生成量を抑制するために以下に示すように鋭意研究を
重ねた。その結果、Ａｌ、Ｔｉ、Ｓｉ、Ｃａ量を最適化することにより、ＴＩＧ溶接部に
おけるブラックスポットの生成を抑制できることを見出し、本発明のブラックスポットの
生成の少ないフェライト系ステンレス鋼を想到した。 The present inventor conducted extensive research as described below in order to suppress the amount of black spots generated. As a result, the inventors have found that by optimizing the amounts of Al, Ti, Si, and Ca, it is possible to suppress the generation of black spots in the TIG welded portion, and the present inventors have devised a ferritic stainless steel according to the present invention that generates less black spots.

本発明の要旨は以下のとおりである。
（１）質量％で，Ｃ：０．０２０％以下，Ｎ：０．０２５％以下，Ｓｉ：１．０％以下，Ｍｎ：１．０％以下，Ｐ：０．０３５％以下，Ｓ：０．０１％以下，Ｃｒ：１６．０〜２５．０％，Ａｌ：０．０４〜０．１２％，Ｔｉ：０．０５〜０．３５％，Ｎｂ：０．０５〜０．６％、Ｃａ：０．０００２〜０．００１５％を含有し，残部がＦｅおよび不可避的不純物からなり，下記（１）式を満足することを特徴とする，溶接部のブラックスポットの生成の少ないフェライト系ステンレス鋼。
ＢＩ＝３Ａｌ＋Ｔｉ＋０．５Ｓｉ＋２００Ｃａ≦０．３９ …（１）
（なお、（１）式中のＡｌ、Ｔｉ、Ｓｉ、Ｃａは、鋼中の各成分の含有量［質量％］である。） The gist of the present invention is as follows.
(1) By mass%, C: 0.020% or less, N: 0.025% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.035% or less, S: 0 0.01% or less, Cr: 16.0 to 25.0%, Al: 0.04 to 0.12%, Ti: 0.05 to 0.35%, Nb: 0.05 to 0.6%, Ca : Ferritic stainless steel containing 0.0002 to 0.0015%, the balance being Fe and inevitable impurities, and satisfying the following formula (1): .
BI = 3Al + Ti + 0.5Si + 200Ca ≦ 0.39 (1)
(Al, Ti, Si, and Ca in the formula (1) are the content [% by mass] of each component in the steel.)

（２）さらに、質量％で、Ｍｏ：３．０％以下を含むことを特徴とする（１）に記載の溶接部のブラックスポットの生成の少ないフェライト系ステンレス鋼。
（３）さらに、質量％で、Ｃｕ：２．０％以下、Ｎｉ：２．０％以下から選ばれる一種又は二種を含むことを特徴とする（１）または（２）に記載の溶接部のブラックスポットの生成の少ないフェライト系ステンレス鋼。
（４）さらに、質量％で、Ｖ：０．２％以下、Ｚｒ：０．２％以下から選ばれる一種又は二種を含むことを特徴とする（１）から（３）のいずれかに記載の溶接部のブラックスポットの生成の少ないフェライト系ステンレス鋼。
（５）さらに、質量％で、Ｂ：０．００５％以下を含有することを特徴とする（１）から（４）のいずれかに記載の溶接部のブラックスポットの生成の少ないフェライト系ステンレス鋼。 (2) The ferritic stainless steel with less generation of black spots in the welded portion according to (1) , further comprising Mo: 3.0% or less by mass.
(3) Further, the welded portion according to (1) or (2) , further comprising one or two kinds selected from Cu: 2.0% or less and Ni: 2.0% or less by mass%. Ferritic stainless steel with less black spot formation.
(4) The composition according to any one of (1) to (3) , further comprising one or two kinds selected from V: 0.2% or less and Zr: 0.2% or less by mass%. Ferritic stainless steel with little black spot formation in welds.
(5) Further, B: 0.005% or less by mass%, Ferritic stainless steel with less black spot generation in welds according to any one of (1) to (4) .

本発明によれば、ＴＩＧ溶接部にブラックスポットが生成しにくく、ＴＩＧ溶接部の耐
食性および加工性に優れたフェライト系ステンレス鋼を提供できる。 ADVANTAGE OF THE INVENTION According to this invention, a black spot is hard to produce | generate at a TIG weld part, and the ferritic stainless steel excellent in the corrosion resistance and workability of a TIG weld part can be provided.

図１は、ＴＩＧ溶接時に裏側に生じたブラックスポットの外観を示した写真である。FIG. 1 is a photograph showing the appearance of black spots generated on the back side during TIG welding. 図２は、試験片の裏側におけるブラックスポットおよび溶接ビード部の元素深さプロファイルをＡＥＳで測定した結果を示したグラフである。FIG. 2 is a graph showing the results of measuring the element depth profile of the black spot and the weld bead on the back side of the test piece by AES. 図３は、ＢＩ値とブラックスポット生成長さ比との関係を示したグラフである。FIG. 3 is a graph showing the relationship between the BI value and the black spot generation length ratio. 図４は、ＢＩ値と腐食との関係を示したグラフである。FIG. 4 is a graph showing the relationship between BI value and corrosion.

以下、本発明について詳細に説明する。
本発明の溶接部のブラックスポットの生成の少ないフェライト系ステンレス鋼は、下記
(１)式を満足するものである。
ＢＩ＝３Ａｌ＋Ｔｉ＋０．５Ｓｉ＋２００Ｃａ≦０．８ …（１）
（なお、（１）式中のＡｌ、Ｔｉ、Ｓｉ、Ｃａは、鋼中の各成分の含有量［質量％］であ
る。） Hereinafter, the present invention will be described in detail.
Ferritic stainless steel with less black spot formation in the weld zone of the present invention is
The expression (1) is satisfied.
BI = 3Al + Ti + 0.5Si + 200Ca ≦ 0.8 (1)
(Al, Ti, Si, and Ca in the formula (1) are the content [% by mass] of each component in the steel.)

Ａｌ、Ｔｉ、Ｓｉ、Ｃａは、酸素との親和力が特に強い元素であり、ＴＩＧ溶接時にブ
ラックスポットを生成させる元素である。また、鋼中に含まれるＡｌ、Ｔｉ、Ｓｉ、Ｃａ
の含有量を多くするほど、ブラックスポットが生成されやすくなる。上記(１)式における
Ａｌ、Ｔｉ、Ｓｉ、Ｃａの係数は、ブラックスポットの生成を促進する作用の大きさ（強
さ）と鋼中の含有量とに基づいて決定されている。より詳細には、Ａｌは、後述する実験
例に示されるように、ブラックスポットに最も高濃度で含まれており、ブラックスポット
の生成を促進する作用が特に大きい元素である。このため、上記(１)式において、Ａｌの
係数を３としている。また、Ｃａは鋼中の含有量が少ないにもかかわらず、ブラックスポ
ットに高濃度で含まれており、ブラックスポットの生成を促進する作用が大きい元素であ
る。このため、Ｃａの係数を２００としている。 Al, Ti, Si, and Ca are elements that have a particularly strong affinity with oxygen, and are elements that generate black spots during TIG welding. In addition, Al, Ti, Si, Ca contained in steel
As the content of increases, black spots are more easily generated. The coefficients of Al, Ti, Si, and Ca in the above formula (1) are determined based on the magnitude (strength) of the action that promotes the generation of black spots and the content in steel. More specifically, Al is an element that is contained in the black spot at the highest concentration and has a particularly large effect of promoting the generation of the black spot, as shown in an experimental example described later. For this reason, in the above equation (1), the coefficient of Al is set to 3. Further, Ca is an element that is contained in the black spot at a high concentration despite its low content in the steel and has a large effect of promoting the generation of the black spot. For this reason, the coefficient of Ca is set to 200.

上記ＢＩ値が０．８を超えると、ブラックスポットの生成が顕著になる。これに対して
、ＢＩ値が０．８以下であると、ＴＩＧ溶接部のブラックスポットの生成が十分に少なく
なり、耐食性に優れたものとなる。また、ＢＩ値が０．６以下である場合には、ブラック
スポットの生成をより効果的に抑制でき、更にＢＩ値が０．４以下である場合には、ブラックスポットの生成はほとんど抑制可能となり、ＴＩＧ溶接部の耐食性をより一層向上させることができる。 When the BI value exceeds 0.8, the generation of black spots becomes significant. On the other hand, when the BI value is 0.8 or less, the generation of black spots in the TIG welded portion is sufficiently reduced and the corrosion resistance is excellent. In addition, when the BI value is 0.6 or less, the generation of black spots can be more effectively suppressed, and when the BI value is 0.4 or less, the generation of black spots can be almost suppressed. Further, the corrosion resistance of the TIG welded portion can be further improved.

これは、ブラックスポットが多量に発生するような条件では、ブラックスポットの厚みも厚くなるため、加工時に剥離しやすいと推定され、その場合には張り出し加工のような厳しい加工において剥離が生じ腐食の起点になると考えられる。逆にブラックスポットの発生率が少ない条件では、その厚みも薄くなるため、ブラックスポットが生成しても剥離しにくいと推定される。   This is presumed that when the black spots are generated in large quantities, the thickness of the black spots also increases, so that it is likely to be peeled off during processing. It is considered to be a starting point. On the other hand, under conditions where the occurrence rate of black spots is small, the thickness is reduced, and it is estimated that even if black spots are generated, it is difficult to peel off.

次に、本発明のフェライト系ステンレス鋼の成分組成について、詳細に説明する。
まず、上記(１)式を規定する各元素について説明する。
Ａｌは脱酸元素として重要であり，また非金属介在物の組成を制御して組織を微細化す
る効果もある。しかし、Ａｌはブラックスポットの生成に最も寄与する元素である。また
、Ａｌの過剰な添加は、非金属介在物の粗大化を招き，製品の疵発生の起点になる恐れも
ある。そのため，Ａｌ含有量の上限値を０．１２％以下とした。脱酸のためにはＡｌを０
．０１％以上含有させることが好ましい。Ａｌ含有量は、より望ましくは０．０３％〜０．１０％である。 Next, the component composition of the ferritic stainless steel of the present invention will be described in detail.
First, each element that defines the above equation (1) will be described.
Al is important as a deoxidizing element and also has an effect of controlling the composition of non-metallic inclusions to refine the structure. However, Al is an element that contributes most to the generation of black spots. Moreover, excessive addition of Al leads to coarsening of non-metallic inclusions, which may be a starting point for product wrinkling. Therefore, the upper limit of the Al content is set to 0.12% or less. Al is 0 for deoxidation.
. It is preferable to contain 01% or more. The Al content is more desirably 0.03% to 0.10%.

Ｔｉは，Ｃ，Ｎを固定し，溶接部の粒界腐食を抑制して加工性を向上させる上で非常に
重要な元素である。しかしながら、Ｔｉの過剰な添加は、ブラックスポットを生成させる
だけでなく、製造時の表面疵の原因となる。このため，Ｔｉ含有量の範囲を０．０５％〜
０．３５％とした。より望ましくは０．０７％〜０．２０％である。
Ｓｉは，脱酸元素として重要な元素であり，耐食性，耐酸化性の向上にも有効である。
しかし、Ｓｉの過剰な添加はブラックスポットの生成を促進するだけでなく、加工性，製
造性を低下させる。そのため、Ｓｉの含有量の上限値を１．０％とした。脱酸のためには
Ｓｉを０．０１％以上含有させることが好ましい。Ｓｉ含有量は、より望ましくは０．０
５％〜０．５５％である． Ti is an extremely important element for fixing C and N and suppressing intergranular corrosion of the welded portion to improve workability. However, excessive addition of Ti not only generates black spots, but also causes surface defects during manufacturing. For this reason, the range of Ti content is 0.05% to
0.35%. More desirably, it is 0.07% to 0.20%.
Si is an important element as a deoxidizing element, and is also effective in improving corrosion resistance and oxidation resistance.
However, excessive addition of Si not only promotes the formation of black spots, but also reduces workability and manufacturability. Therefore, the upper limit of Si content is set to 1.0%. For deoxidation, it is preferable to contain 0.01% or more of Si. The Si content is more preferably 0.0.
5% to 0.55%.

Ｃａは脱酸元素として非常に重要であり、非金属介在物として鋼中に微量に含まれる。
ただしＣａは非常に酸化されやすいため、溶接時にブラックスポットを生成させる大きな
要因となる。また、Ｃａは、水溶性介在物を生成させて、耐食性を低下させる場合もある
。このため、Ｃａの含有量は極力低いことが望ましく、Ｃａの含有量の上限値を０．００
１５％以下とした。より好ましくは０．００１２％以下である。 Ca is very important as a deoxidizing element and is contained in a small amount in steel as a nonmetallic inclusion.
However, since Ca is very easily oxidized, it becomes a major factor for generating black spots during welding. Moreover, Ca produces | generates a water-soluble inclusion and may reduce corrosion resistance. For this reason, it is desirable that the Ca content is as low as possible, and the upper limit value of the Ca content is 0.00.
15% or less. More preferably, it is 0.0012% or less.

次に、本発明のフェライト系ステンレス鋼を構成するその他元素について説明する。
Ｃは，耐粒界腐食性および加工性を低下させるため，その含有量を低減させる必要があ
る。このため，Ｃの含有量の上限値を０．０２０％以下とした。しかし、Ｃの含有量を過
度に低減させると、精錬コストが悪化するため，０．００２％〜０．０１５％であること
がより望ましい。
Ｎは，Ｃと同様に耐粒界腐食性，加工性を低下させるため，その含有量を低減させる必
要がある。このため，Ｎの含有量の上限を０．０２５％以下とした。しかし、Ｎの含有量
を過度に低減させると、精錬コストが悪化するため、０．００２％〜０．０１５％である
ことがより望ましい。 Next, other elements constituting the ferritic stainless steel of the present invention will be described.
Since C lowers intergranular corrosion resistance and workability, its content needs to be reduced. For this reason, the upper limit of the C content is set to 0.020% or less. However, if the C content is excessively reduced, the refining cost deteriorates, so 0.002% to 0.015% is more desirable.
N, like C, reduces intergranular corrosion resistance and workability, so its content needs to be reduced. For this reason, the upper limit of the content of N is set to 0.025% or less. However, if the N content is excessively reduced, the refining cost is deteriorated, so 0.002% to 0.015% is more desirable.

Ｍｎは，脱酸元素として重要な元素であるが，過剰に添加すると腐食の起点となるＭｎ
Ｓを生成しやすくなり，またフェライト組織を不安定化させる。このため，Ｍｎの含有量
を１．０％以下とした。脱酸のためにはＭｎを０．０１％以上含有させることが好ましい。より望ましくは，０．０５％〜０．５％である。さらに望ましくは、０．０５％〜０．３％である。
Ｐは，溶接性，加工性を低下させるだけでなく，粒界腐食を生じやすくするため，低く
抑える必要がある。そのためＰの含有量を０．０３５％以下とした。より望ましくは０．
００１％〜０．０２％である。 Mn is an important element as a deoxidizing element, but if added excessively, Mn becomes a starting point of corrosion.
S is likely to be generated, and the ferrite structure is destabilized. Therefore, the Mn content is set to 1.0% or less. For deoxidation, it is preferable to contain 0.01% or more of Mn. More desirably, it is 0.05% to 0.5%. More desirably, it is 0.05% to 0.3%.
P not only deteriorates weldability and workability, but also tends to cause intergranular corrosion, so P needs to be kept low. Therefore, the content of P is set to 0.035% or less. More desirably, 0.
001% to 0.02%.

Ｓは，ＣａＳやＭｎＳ等の腐食の起点となる水溶性介在物を生成させるため，低減させ
る必要がある。そのため、Ｓの含有量は０．０１％以下とする。ただし、過度の低減はコ
ストの悪化を招く。このため，Ｓの含有量は、０．０００１％〜０．００５％であること
がより望ましい。 S needs to be reduced because it generates water-soluble inclusions that cause corrosion such as CaS and MnS. Therefore, the S content is 0.01% or less. However, excessive reduction causes cost deterioration. For this reason, the S content is more preferably 0.0001% to 0.005%.

Ｃｒは，ステンレス鋼の耐食性を確保する上で最も重要な元素であり，フェライト組織
を安定化するために１６．０％以上含有させる必要がある。しかし、Ｃｒは、加工性，製造性を低下させるため，上限を２５．０％以下とした。Ｃｒの含有量は、望ましくは１６．５％〜２３．０％であり，より望ましくは１８．０％〜２２．５％である。 Cr is the most important element for securing the corrosion resistance of stainless steel, and needs to be contained by 16.0% or more in order to stabilize the ferrite structure. However, Cr lowers the workability and manufacturability, so the upper limit was made 25.0% or less. The content of Cr is desirably 16.5% to 23.0%, and more desirably 18.0% to 22.5%.

Ｎｂは，その特性上単独またはＴｉと複合して添加することが可能である。ＮｂをＴｉ
とともに含有させる場合（Ｔｉ＋Ｎｂ）／（Ｃ＋Ｎ）≧６（式中のＴｉ、Ｎｂ、Ｃ、Ｎは
、鋼中の各成分の含有量［質量％］である。）を満たすことが好ましい。
Ｎｂは，Ｔｉと同様にＣ，Ｎを固定し，溶接部の粒界腐食を抑制して加工性を向上させ
る元素である。ただし、Ｎｂの過剰な添加は，加工性を低下させるため，Ｎｂの含有量の
上限を０．６％以下とすることが好ましい。また、Ｎｂを含有させることにより、上記の
特性を向上させるためには、Ｎｂを０．０５％以上含有させることが好ましい。Ｎｂの含
有量は、望ましくは０．１５％〜０．５５％である。 Nb can be added alone or in combination with Ti because of its characteristics. Nb to Ti
It is preferable to satisfy (Ti + Nb) / (C + N) ≧ 6 (Ti, Nb, C, N in the formula is the content [% by mass] of each component in the steel).
Nb is an element that fixes C and N similarly to Ti and suppresses intergranular corrosion of the welded portion to improve workability. However, excessive addition of Nb reduces workability, so the upper limit of Nb content is preferably 0.6% or less. Moreover, in order to improve said characteristic by containing Nb, it is preferable to contain Nb 0.05% or more. The Nb content is desirably 0.15% to 0.55%.

Ｍｏは，不働態皮膜の補修に効果があり，耐食性を向上させるのに非常に有効な元素で
ある。また、ＭｏはＣｒとともに含有されることにより耐孔食性を効果的に向上させる効
果がある。またＭｏは，Ｎｉとともに含有されることにより耐流れさび性を改善する効果
がある。しかし、Ｍｏを増加させると，加工性が低下し，コストが高くなる。このため、
Ｍｏの含有量の上限を３．０％以下とすることが好ましい。また、Ｍｏを含有させること
により、上記の特性を向上させるためには、Ｍｏを０．３０％以上含有させることが好ま
しい。Ｍｏの含有量は、望ましくは，０．６０％〜２．５％であり，より望ましくは０．
９％〜２．０％である。 Mo is an element that is effective in repairing a passive film and is very effective in improving corrosion resistance. Further, when Mo is contained together with Cr, there is an effect of effectively improving the pitting corrosion resistance. Moreover, Mo is effective together with Ni to improve flow rust resistance. However, when Mo is increased, the workability is lowered and the cost is increased. For this reason,
The upper limit of the Mo content is preferably 3.0% or less. Moreover, in order to improve said characteristic by containing Mo, it is preferable to contain 0.30% or more of Mo. The Mo content is preferably 0.60% to 2.5%, more preferably 0.
9% to 2.0%.

Ｎｉは，活性溶解速度を抑制させる効果を有し，また水素過電圧が小さいために再不働
態化特性に優れる。ただし、Ｎｉの過剰な添加は，加工性を低下させ，フェライト組織を
不安定にする。このため，Ｎｉの含有量の上限を２．０％以下とすることが好ましい。ま
た、Ｎｉを含有させることにより、上記の特性を向上させるためには、Ｎｉを０．０５％
以上含有させることが好ましい。Ｎｉの含有量は、望ましくは０．１％〜１．２％であり
，より望ましくは０．２％〜１．１％である。 Ni has the effect of suppressing the active dissolution rate and has excellent repassivation characteristics due to a small hydrogen overvoltage. However, excessive addition of Ni degrades workability and makes the ferrite structure unstable. For this reason, it is preferable to make the upper limit of Ni content 2.0% or less. Moreover, in order to improve said characteristic by containing Ni, 0.05% of Ni is included.
It is preferable to contain above. The Ni content is desirably 0.1% to 1.2%, and more desirably 0.2% to 1.1%.

Ｃｕは，Ｎｉと同様に活性溶解速度を低下させるだけでなく，再不働態化を促進する効
果を有する。しかし、Ｃｕの過剰な添加は，加工性を低下させる。このため，Ｃｕを添加
する場合は上限を２．０％以下とすることが好ましい。Ｃｕを含有させることにより、上
記の特性を向上させるためには、Ｃｕは０．０５％以上含有させることが好ましい。Ｃｕ
の含有量は、望ましくは，０．２％〜１．５％であり、更に望ましくは０．２５％〜１．
１％である。 Cu not only lowers the active dissolution rate in the same manner as Ni, but also has the effect of promoting repassivation. However, excessive addition of Cu reduces workability. For this reason, when adding Cu, it is preferable to make an upper limit into 2.0% or less. In order to improve said characteristic by containing Cu, it is preferable to contain Cu 0.05% or more. Cu
Is desirably 0.2% to 1.5%, and more desirably 0.25% to 1.%.
1%.

ＶおよびＺｒは、耐候性や耐すき間腐食性を改善する。また，Ｃｒ，Ｍｏの使用を抑え
てＶを添加すれば優れた加工性も担保することができる。ただし、Ｖおよび／またはＺｒ
の過度の添加は加工性を低下させる上，耐食性向上効果も飽和するため，Ｖおよび／また
はＺｒを含有する場合の含有量の上限を０．２％以下とすることが好ましい。また、Ｖお
よび／またはＺｒを含有させることにより、上記の特性を向上させるためには、Ｖおよび
／またはＺｒは０．０３％以上含有させることが好ましい。また、Ｖおよび／またはＺｒ
の含有量は、より望ましくは０．０５％〜０．１％である。 V and Zr improve weather resistance and crevice corrosion resistance. Further, if V is added while suppressing the use of Cr and Mo, excellent workability can be secured. However, V and / or Zr
Excessive addition of this lowers the workability and also saturates the effect of improving the corrosion resistance. Therefore, the upper limit of the content when V and / or Zr is contained is preferably 0.2% or less. Moreover, in order to improve said characteristic by containing V and / or Zr, it is preferable to contain V and / or Zr 0.03% or more. V and / or Zr
The content of is more preferably 0.05% to 0.1%.

Ｂは二次加工脆性改善に有効な粒界強化元素であるが，過度の添加はフェライトを固溶
強化して延性低下の原因になる。このため、Ｂを添加する場合は下限を０．０００１％以
下，上限を０．００５％以下とすることが好ましく、０．０００２％〜０．００２０％と
することがより望ましい。 B is an effective grain boundary strengthening element for improving secondary work embrittlement, but excessive addition causes solid solution strengthening of ferrite and causes a drop in ductility. Therefore, when B is added, the lower limit is preferably 0.0001% or less and the upper limit is preferably 0.005% or less, and more preferably 0.0002% to 0.0020%.

表１に示す化学成分（組成）を有するフェライト系ステンレス鋼からなる試験片を、以下に示す方法で製造した。まず、表１に示す化学成分（組成）の鋳鋼を真空溶解にて溶製して４０ｍｍ厚のインゴットを製造し、これを熱間圧延で５ｍｍ厚に圧延した。その後、各々の再結晶挙動に基づいて温度８００〜１０００℃で１分間の熱処理を行って、スケールを研削除去し、さらに冷間圧延により厚み０．８ｍｍの鋼板を製造した。その後、最終焼鈍として各々の再結晶挙動に基づいて温度８００〜１０００℃で１分間の熱処理を行い、表面の酸化スケールを酸洗除去して供試材とし、これを用いてＮｏ．１〜２８の試験片を製造した。なお、表１に示す化学成分（組成）において、残部は、鉄及び不可避的不純物である。   Test pieces made of ferritic stainless steel having the chemical components (composition) shown in Table 1 were produced by the method shown below. First, a cast steel having a chemical composition (composition) shown in Table 1 was melted by vacuum melting to produce a 40 mm thick ingot, which was hot rolled to a thickness of 5 mm. Thereafter, heat treatment was performed at a temperature of 800 to 1000 ° C. for 1 minute based on each recrystallization behavior, the scale was ground and removed, and a steel plate having a thickness of 0.8 mm was manufactured by cold rolling. Then, as final annealing, heat treatment was performed at a temperature of 800 to 1000 ° C. for 1 minute based on each recrystallization behavior, and the surface oxide scale was removed by pickling to obtain a test material. 1-28 specimens were produced. In the chemical components (compositions) shown in Table 1, the balance is iron and inevitable impurities.

このようにして得られたＮｏ１〜２８の試験片に対し、以下に示す溶接条件でＴＩＧ溶
接し、以下に示すようにしてブラックスポット生成長さ比を算出した。また、Ｎｏ１〜２８の試験片に対し、以下に示す腐食試験を行った。
「溶接条件」
ＴＩＧ溶接は、送り速度５０ｃｍ／ｍｉｎ、入熱５５０〜６５０Ｊ／ｃｍ２で同鋼種を
突合せて行った。シールドにはトーチ側、裏面側ともアルゴンを用いた。 The test pieces No. 1 to 28 thus obtained were TIG welded under the welding conditions shown below, and the black spot generation length ratio was calculated as shown below. Moreover, the corrosion test shown below was done with respect to the test piece of No. 1-28.
"Welding conditions"
TIG welding was performed by abutting the same steel type at a feed rate of 50 cm / min and a heat input of 550 to 650 J / cm 2 . Argon was used for the shield on the torch side and back side.

「ブラックスポット生成長さ比」
ブラックスポット生成長さ比は、ＴＩＧ溶接後のブラックスポットの生成量を表す基準
として求めた。ブラックスポット生成長さ比は、溶接部に生じた各ブラックスポットの溶
接方向の長さを積算し、この積算値を、全溶接長さで割って求めた。溶接長さ約１０ｃｍ
分をデジタルカメラで撮影して各ブラックスポットの長さを測定し、画像処理を用いて溶
接長さ中におけるブラックスポットの長さの総和の溶接長さに対する比を計算させること
により求めた。 "Black spot generation length ratio"
The black spot generation length ratio was determined as a standard representing the generation amount of black spots after TIG welding. The black spot generation length ratio was obtained by integrating the lengths in the welding direction of the black spots generated in the welded portion, and dividing the integrated value by the total weld length. Welding length about 10cm
Minutes were photographed with a digital camera, the length of each black spot was measured, and image processing was used to calculate the ratio of the sum of the black spot length in the weld length to the weld length.

「腐食試験」
腐食試験片は、ＴＩＧ溶接部を張り出し加工したものを用いた。張り出し条件は、ＪＩ
Ｓ２２４７に準拠したエリクセン試験条件で、溶接試験片の裏波側を表面として、２０ｍ
ｍφのポンチを用いた。ただし張り出し高さは、加工条件を合わせるため、加工を途中で
停止した。停止高さ（張り出し高さ）は、６ｍｍおよび７ｍｍで統一した。腐食性評価は、ＪＩＳ Ｚ ２３７１に準拠して、５％ＮａＣｌの連続噴霧試験を実施し、４８時間後の流れさびの有無で評価した。張り出し高さ６ｍｍの加工材において５％ＮａＣｌの連続噴霧試験で溶接部に流れさびが認められなかった場合を○、張り出し高さ７ｍｍの加工材において同様にさびが認められなかったものを◎とした。連続噴霧試験で流れさびが発生した場合を×とした。 "Corrosion test"
As the corrosion test piece, a TIG welded portion was used. The overhang condition is JI
Under the Eriksen test conditions according to S2247, the back side of the weld specimen is the surface, 20 m
An mφ punch was used. However, for the overhang height, the machining was stopped halfway to match the machining conditions. The stop height (overhang height) was unified at 6 mm and 7 mm. Corrosion evaluation was performed by performing a continuous spray test of 5% NaCl according to JIS Z 2371 and evaluating the presence or absence of flow rust after 48 hours. In the case of a workpiece with an overhang height of 6 mm, the case where no flow rust was observed in the welded part in a continuous spray test of 5% NaCl, and in the case of a workpiece with an overhang height of 7 mm, no rust was observed. did. The case where flow rust occurred in the continuous spray test was evaluated as x.

表１に示すように、化学成分（組成）が本発明の範囲であってＢＩ値が０．８以下である試験片Ｎｏ１〜２１では、ブラックスポット生成長さ比が小さく、ＴＩＧ溶接後のブラックスポットの生成が少なかった。
このうちＢＩ値が０．６以下のＮｏ１〜１５，１８，１９ではよりブラックスポットの生成が抑制されており、更にＢＩ値が０．４以下のＮｏ１〜１３ではその生成長さが１０％以下とほぼその発生が抑制されていた。
さらに張り出し高さ６ｍｍの試験片Ｎｏ１〜２１では、エリクセン試験機で加工した後の耐食性試験片における５％ＮａＣｌの連続噴霧試験で溶接部からのさびは認めらなかった。更に、より加工の厳しい張り出し高さ７ｍｍの試験片Ｎｏ１〜２１においては、ＢＩ値が０．４以下の試験片では溶接部のさびは認められず、０．４を超える試験片ではさびが認められた。 As shown in Table 1, in the test pieces No1 to 21 whose chemical components (composition) are within the scope of the present invention and the BI value is 0.8 or less, the black spot generation length ratio is small, and black after TIG welding. There was little generation of spots.
Among these, the generation of black spots is further suppressed in Nos. 1 to 15, 18, and 19 having a BI value of 0.6 or less, and the generation length of Nos. 1 to 13 having a BI value of 0.4 or less is 10% or less. The occurrence was almost suppressed.
Further, in test pieces Nos. 1 to 21 having an overhang height of 6 mm, no rust from the welded portion was observed in a continuous spray test of 5% NaCl on the corrosion resistance test piece processed by the Erichsen tester. Furthermore, in the test pieces No1 to 21 having a bulging height of 7 mm, which is more severely processed, rust of the welded portion is not recognized in the test piece having a BI value of 0.4 or less, and rust is recognized in the test piece exceeding 0.4. It was.

一方、ＢＩ値が０．８を超える試験片Ｎｏ２２、２４，２６〜２８では、ＴＩＧ溶接後のブラックスポット生成長さ比が大きく、何れも腐食試験において溶接部からのさびが確認された。試験片Ｎｏ２２、２４，２６〜２８のさび発生部をルーペで拡大観察したところ、ブラックスポットと溶接ビード部の境界で剥離が認められた。Ａｌ，Ｔｉ、Ｓｉ，Ｃａが規定以上の濃度となったＮｏ２２，２６，２７，２８は、腐食試験でさびが発生した。
また、Ｃｒの組成比が１６％未満である試験片Ｎｏ２５及びＴｉの組成比が０．０５％
未満である試験片Ｎｏ２３では、腐食試験でさびの発生が認められた。 On the other hand, in test pieces Nos. 22, 24, and 26 to 28 having a BI value exceeding 0.8, the black spot generation length ratio after TIG welding was large, and rust from the weld was confirmed in the corrosion test. When the rust generation part of test piece No22, 24, 26-28 was expanded and observed with the loupe, peeling was recognized by the boundary of a black spot and a weld bead part. In No22, 26, 27, and 28 where Al, Ti, Si, and Ca had a concentration higher than the specified level, rust occurred in the corrosion test.
In addition, the composition ratio of the specimen No. 25 and Ti in which the Cr composition ratio is less than 16% is 0.05%.
In test piece No23 which is less than this, generation | occurrence | production of rust was recognized by the corrosion test.

「実験例１」
以下に示す化学成分（組成）を有するフェライト系ステンレス鋼を、冷間圧延により厚
み１ｍｍの鋼板を製造したこと以外はＮｏ１の試験片の製造方法と同様にして供試材を製
造した。これを用いて試験片Ａおよび試験片Ｂを得た。
「化学成分（組成）」
試験片Ａ
Ｃ：０．００７％，Ｎ：０．０１１％，Ｓｉ：０．１２％，Ｍｎ：０．１８％，Ｐ：０．
２２％，Ｓ：０．００１％，Ｃｒ：１９．４％，Ａｌ：０．０６％，Ｔｉ：０．１５％、
Ｃａ：０．０００５％、残部：鉄と不可避的不純物
試験片Ｂ
Ｃ：０．００９％，Ｎ：０．０１０％，Ｓｉ：０．２５％，Ｍｎ：０．１５％，Ｐ：０．
２１％，Ｓ：０．００１％，Ｃｒ：２０．２％，Ａｌ：０．１５％，Ｔｉ：０．１９％、
Ｃａ：０．００１５％、残部：鉄と不可避的不純物
このようにして得られた試験片Ａおよび試験片Ｂに対し、Ｎｏ１の試験片と同様の溶接
条件でＴＩＧ溶接し、ＴＩＧ溶接時に裏側に生じたブラックスポットの外観を観察した。
その結果を図１に示す。 "Experiment 1"
A test material was manufactured in the same manner as the method for manufacturing the test piece of No. 1 except that a ferritic stainless steel having the chemical composition (composition) shown below was manufactured by cold rolling to produce a steel plate having a thickness of 1 mm. Using this, a test piece A and a test piece B were obtained.
"Chemical composition (composition)"
Specimen A
C: 0.007%, N: 0.011%, Si: 0.12%, Mn: 0.18%, P: 0.00.
22%, S: 0.001%, Cr: 19.4%, Al: 0.06%, Ti: 0.15%,
Ca: 0.0005%, balance: iron and inevitable impurities Test piece B
C: 0.009%, N: 0.010%, Si: 0.25%, Mn: 0.15%, P: 0.00.
21%, S: 0.001%, Cr: 20.2%, Al: 0.15%, Ti: 0.19%,
Ca: 0.0015%, balance: iron and inevitable impurities The test piece A and the test piece B thus obtained were TIG welded under the same welding conditions as the No. 1 test piece, and on the back side during TIG welding. The appearance of the generated black spot was observed.
The result is shown in FIG.

図１（ａ）は、ＴＩＧ溶接時に裏側に生じたブラックスポットの外観を示した写真であ
る。また、図１（ｂ）は、ＴＩＧ溶接時に裏側に生じたブラックスポットの外観を示した
模式図であり、図１（ａ）に示す写真に対応する図面である。
図１（ａ）および図１（ｂ）において左側はＢＩ値が０．４９の試験片Ａの写真であり
、右側はＢＩ値が１．０７の試験片Ｂの写真である。
図１において矢印で示すように、ＢＩ値が０．４９の試験片Ａ及びＢＩ値が１．０７の
試験片Ｂの双方に、斑点状のブラックスポットが散見される。しかし、ＢＩ値が大きい試
験片Ｂ（右側の写真）において、ブラックスポットはより多く発生しているのが分かる。 Fig.1 (a) is the photograph which showed the external appearance of the black spot which arose on the back side at the time of TIG welding. Moreover, FIG.1 (b) is the schematic diagram which showed the external appearance of the black spot which arose on the back side at the time of TIG welding, and is drawing corresponding to the photograph shown to Fig.1 (a).
1 (a) and 1 (b), the left side is a photograph of test piece A having a BI value of 0.49, and the right side is a photograph of test piece B having a BI value of 1.07.
As indicated by the arrows in FIG. 1, spotted black spots are scattered on both the test piece A having a BI value of 0.49 and the test piece B having a BI value of 1.07. However, it can be seen that more black spots are generated in the test piece B (right photo) having a large BI value.

また、ＢＩ値が１．０７の試験片Ｂについて、溶接ビード部とブラックスポット部の２
カ所について、オージェ電子分光分析（ＡＥＳ）測定を行った。その結果を図２に示す。
なお、ＡＥＳ測定においては、走査型ＦＥオージェ電子分光装置を用い、加速電圧１０
ｋｅＶ、スポット径約４０ｎｍ、スパッタ速度１５ｎｍ／ｍｉｎの条件で、酸素の強度が
殆ど観測されなくなるまで測定を実施した。なお、ＡＥＳの測定スポットは小さいため、
測定位置により誤差が生じる場合があるが、概略の厚さを示すものとして今回採用した。 Further, for the test piece B having a BI value of 1.07, 2 of the weld bead part and the black spot part.
The Auger electron spectroscopy analysis (AES) measurement was performed about the place. The result is shown in FIG.
In the AES measurement, a scanning FE Auger electron spectrometer is used and an acceleration voltage of 10 is used.
The measurement was carried out under conditions of keV, spot diameter of about 40 nm, and sputtering rate of 15 nm / min until almost no oxygen intensity was observed. Since the AES measurement spot is small,
Although an error may occur depending on the measurement position, this was adopted as an indication of the approximate thickness.

図２は、試験片の裏側におけるブラックスポットおよび溶接ビード部の元素深さプロフ
ァイル（深さ方向の元素の濃度分布）をＡＥＳで測定した結果を示したグラフである。図
２（ａ）は溶接ビード部の結果であり、図２（ｂ）はブラックスポットの結果である。
図２（ａ）に示すように、溶接ビード部は、Ｔｉが主体であり、Ａｌ、Ｓｉを含む厚さ
数百Åの酸化物であった。一方、図２（ｂ）に示すように、ブラックスポットは、Ａｌが
主体であり、Ｔｉ、Ｓｉ、Ｃａを含む厚さ数千Åの厚い酸化物であった。また、図２（ｂ
）に示すブラックスポットのグラフより、Ａｌは、ブラックスポットに最も高濃度で含ま
れており、Ｃａは鋼中の含有量が少ないにもかかわらず、ブラックスポットに高濃度で含
まれていることが確認できた。 FIG. 2 is a graph showing the results of AES measurement of the element depth profile (element concentration distribution in the depth direction) of the black spot and the weld bead on the back side of the test piece. 2A shows the result of the weld bead, and FIG. 2B shows the result of the black spot.
As shown in FIG. 2 (a), the weld bead portion was mainly composed of Ti, and was an oxide having a thickness of several hundreds of microns including Al and Si. On the other hand, as shown in FIG. 2B, the black spots were mainly oxides of Al, and were thick oxides having a thickness of several thousand Å containing Ti, Si, and Ca. Further, FIG.
From the graph of black spot shown in Fig. 4), Al is contained at the highest concentration in the black spot, and Ca is contained in the black spot at a high concentration even though the content in the steel is small. It could be confirmed.

「実験例２」
Ｃ：０．００２〜０．０１５％，Ｎ：０．０２〜０．０１５％，Ｃｒ：１６．５〜２３
％，Ｎｉ：０〜１．５％，Ｍｏ：０〜２．５％を基本組成とし、ブラックスポットの主成
分であるＡｌ、Ｔｉ、Ｓｉ、Ｃａ等の含有量の異なる種々の化学成分（組成）を有するフ
ェライト系ステンレス鋼の供試材を、試験片Ａと同様の製造方法により製造した。これを
用いて、複数の試験片を得た。
このようにして得られた複数の試験片に対し、Ｎｏ１の試験片と同様の溶接条件でＴＩ
Ｇ溶接し、Ｎｏ１の試験片と同様にしてブラックスポット生成長さ比を算出した。 "Experimental example 2"
C: 0.002-0.015%, N: 0.02-0.015%, Cr: 16.5-23
%, Ni: 0 to 1.5%, Mo: 0 to 2.5%, and various chemical components (compositions) having different contents such as Al, Ti, Si, and Ca, which are the main components of black spots A ferritic stainless steel test material having a) was produced by the same production method as that for the test piece A. Using this, a plurality of test pieces were obtained.
The plurality of test pieces thus obtained were subjected to TI under the same welding conditions as those for the No. 1 test piece.
G-welding was performed, and the black spot generation length ratio was calculated in the same manner as for the No. 1 test piece.

その結果、ブラックスポット生成長さ比は、Ａｌ、Ｔｉ、Ｓｉ、Ｃａが増加するほど大
きくなる傾向を示した。これらの元素は酸素との親和力が特に強い元素であり、このうち
特にＡｌの効果が大きく、またＣａは鋼中の含有量が少ないにもかかわらずブラックスポ
ットへの影響が大きいことが判明した。またＴｉ、Ｓｉに関しても同様にブラックスポッ
トの生成に寄与することが分かった。 As a result, the black spot generation length ratio tended to increase as Al, Ti, Si, and Ca increased. These elements are elements having a particularly strong affinity with oxygen, and among these, the effect of Al is particularly great, and it has been found that Ca has a great influence on black spots despite its low content in steel. Further, it has been found that Ti and Si also contribute to the generation of black spots.

このことから、Ａｌ、Ｔｉ、Ｓｉ、Ｃａの添加量が多い場合には、シールドを施しても
ブラックスポットが発生する懸念が大きく、とくにＡｌ、Ｔｉはブラックスポットの生成
に大きな影響を与えることが分かった。 For this reason, when Al, Ti, Si, and Ca are added in a large amount, there is a great concern that black spots will be generated even if shield is applied. In particular, Al and Ti may greatly affect the generation of black spots. I understood.

また、複数の試験片それぞれについて下記(１)式で示されるＢＩ値を算出し、ブラック
スポット生成長さ比との関係を調べた。
ＢＩ＝３Ａｌ＋Ｔｉ＋０．５Ｓｉ＋２００Ｃａ≦０．８ …（１）
（なお、（１）式中のＡｌ、Ｔｉ、Ｓｉ、Ｃａは、鋼中の各成分の含有量［質量％］であ
る。）
その結果を図３に示す。図３は、ＢＩ値とブラックスポット生成長さ比との関係を示し
たグラフである。図３に示すように、ＢＩ値が大きいほどブラックスポット生成長さ比が
大きくなることが分かる。 In addition, a BI value represented by the following formula (1) was calculated for each of the plurality of test pieces, and the relationship with the black spot generation length ratio was examined.
BI = 3Al + Ti + 0.5Si + 200Ca ≦ 0.8 (1)
(Al, Ti, Si, and Ca in the formula (1) are the content [% by mass] of each component in the steel.)
The result is shown in FIG. FIG. 3 is a graph showing the relationship between the BI value and the black spot generation length ratio. As shown in FIG. 3, it can be seen that the larger the BI value, the larger the black spot generation length ratio.

また、複数の試験片それぞれに対し、Ｎｏ１の試験片と同様にして腐食試験を行った。
その結果を、図４に示す。図４は、ＢＩ値と加工後に噴霧試験した後の耐食性評価結果との関係を示したグラフである。図４に示すように、ＢＩ値が０．８以下である場合、張り出し高さが６ｍｍの試験片では腐食が発生せず、特に０．４以下では、張り出し高さが７ｍｍの試験片においても、腐食も認められないため、非常に良好であった。 Moreover, the corrosion test was done with respect to each of the plurality of test pieces in the same manner as the No1 test piece.
The result is shown in FIG. FIG. 4 is a graph showing the relationship between the BI value and the corrosion resistance evaluation result after a spray test after processing. As shown in FIG. 4, when the BI value is 0.8 or less, corrosion does not occur in the test piece with the overhang height of 6 mm, and particularly with a test piece with the overhang height of 7 mm when the BI value is 0.4 or less. Since corrosion was not observed, it was very good.

本発明のフェライト系ステンレス鋼は、外装材、建材、屋外機器類、貯水・貯湯タンク
、家電製品、浴槽、厨房機器、潜熱回収型ガス給湯器のドレン水回収器とその熱交換器、
各種溶接パイプなどのように、その他屋外・屋内の一般的な用途で、ＴＩＧ溶接されて形
成される構造体において、耐食性を必要とする部材に好適に用いることができる。特に、
本発明のフェライト系ステンレス鋼は、ＴＩＧ溶接後に加工を施す部材に好適である。ま
た、本発明のフェライト系ステンレス鋼は、耐食性のみならずＴＩＧ溶接部の加工性にも
優れるため、加工の厳しい用途においても広く適用可能である。 Ferritic stainless steel of the present invention includes exterior materials, building materials, outdoor equipment, water storage / hot water storage tanks, home appliances, bathtubs, kitchen equipment, drain water recovery devices for latent heat recovery type gas water heaters and their heat exchangers,
It can be suitably used for a member that requires corrosion resistance in a structure formed by TIG welding, such as various types of welded pipes, for general outdoor / indoor use. In particular,
The ferritic stainless steel of the present invention is suitable for a member to be processed after TIG welding. Moreover, since the ferritic stainless steel of the present invention is excellent not only in corrosion resistance but also in workability of a TIG welded part, it can be widely applied in severe processing applications.

Claims (5)

Ｃ：０．０２０％以下，
Ｎ：０．０２５％以下，
Ｓｉ：１．０％以下，
Ｍｎ：１．０％以下，
Ｐ：０．０３５％以下，
Ｓ：０．０１％以下，
Ｃｒ：１６．０〜２５．０％，
Ａｌ：０．０４〜０．１２％，
Ｔｉ：０．０５〜０．３５％，
Ｎｂ：０．０５〜０．６％、
Ｃａ：０．０００２〜０．００１５％を含有し，残部がＦｅおよび不可避的不純物からなり，
下記（１）式を満足することを特徴とする，溶接部のブラックスポットの生成の少ないフェライト系ステンレス鋼。
ＢＩ＝３Ａｌ＋Ｔｉ＋０．５Ｓｉ＋２００Ｃａ≦０．３９（１）
（なお、（１）式中のＡｌ、Ｔｉ、Ｓｉ、Ｃａは、鋼中の各成分の含有量［質量％］である。） C: 0.020% or less,
N: 0.025% or less,
Si: 1.0% or less,
Mn: 1.0% or less,
P: 0.035% or less,
S: 0.01% or less,
Cr: 16.0 to 25.0%,
Al: 0.04 to 0.12%,
Ti: 0.05 to 0.35%,
Nb: 0.05 to 0.6%,
Ca: 0.0002 to 0.0015% is contained, the balance consists of Fe and inevitable impurities,
A ferritic stainless steel that satisfies the following formula (1) and generates less black spots in the weld zone.
BI = 3Al + Ti + 0.5Si + 200Ca ≦ 0.39 (1)
(Al, Ti, Si, and Ca in the formula (1) are the content [% by mass] of each component in the steel.) さらに、質量％で、Ｍｏ：３．０％以下を含むことを特徴とする、請求項１に記載の溶接部のブラックスポットの生成の少ないフェライト系ステンレス鋼。  Furthermore, the ferritic stainless steel with few generation | occurrence | production of the black spot of the weld part of Claim 1 characterized by including Mo: 3.0% or less by mass%. さらに、質量％で、Ｃｕ：２．０％以下、Ｎｉ：２．０％以下から選ばれる一種又は二種を含むことを特徴とする、請求項１または請求項２に記載の溶接部のブラックスポットの生成の少ないフェライト系ステンレス鋼。  Furthermore, it contains 1 type or 2 types chosen from Cu: 2.0% or less and Ni: 2.0% or less by mass%, The black of the weld part of Claim 1 or Claim 2 characterized by the above-mentioned. Ferritic stainless steel with less spot formation. さらに、質量％で、Ｖ：０．２％以下、Ｚｒ：０．２％以下から選ばれる一種又は二種を含むことを特徴とする、請求項１から請求項３のいずれか一項に記載の溶接部のブラックスポットの生成の少ないフェライト系ステンレス鋼。  Furthermore, it contains the 1 type (s) or 2 types chosen from V: 0.2% or less and Zr: 0.2% or less in the mass%, It is any one of Claims 1-3 characterized by the above-mentioned. Ferritic stainless steel with little black spot formation in welds. さらに、質量％で、Ｂ：０．００５％以下を含有することを特徴とする、請求項１から請求項４のいずれか一項に記載の溶接部のブラックスポットの生成の少ないフェライト系ステンレス鋼。  Furthermore, B: 0.005% or less in mass%, Ferritic stainless steel with less black spot generation in welds according to any one of claims 1 to 4 .
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