JP2011190470A - High-strength ferritic stainless steel for welding operation having excellent corrosion resistance in weld zone and having no gap - Google Patents
High-strength ferritic stainless steel for welding operation having excellent corrosion resistance in weld zone and having no gap Download PDFInfo
- Publication number
- JP2011190470A JP2011190470A JP2010054842A JP2010054842A JP2011190470A JP 2011190470 A JP2011190470 A JP 2011190470A JP 2010054842 A JP2010054842 A JP 2010054842A JP 2010054842 A JP2010054842 A JP 2010054842A JP 2011190470 A JP2011190470 A JP 2011190470A
- Authority
- JP
- Japan
- Prior art keywords
- corrosion resistance
- stainless steel
- less
- welding
- mass
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Images
Abstract
Description
本発明は、溶接熱影響部の耐食性に優れるフェライト単相高強度複相ステンレス鋼帯・鋼板に関するものである。詳しくは、母材部はもちろんのこと溶接熱影響部の硬度低下が小さく、溶接熱影響部の耐食性が要求される、例えば各種スチールベルト、物干竿等のパイプ、自転車リム材等、溶接構造物、温水器缶体容器等に好適な、隙間のない溶接施工用のステンレス鋼に関するものである。
ここで「隙間のない溶接」とは、突合せ溶接や隅肉溶接など、隙間部を形成しない状態で溶接施工を行うものを指す。
The present invention relates to a ferrite single-phase high-strength dual-phase stainless steel strip / steel plate excellent in corrosion resistance of a weld heat-affected zone. Specifically, not only the base metal part but also the welded heat-affected zone has a small decrease in hardness, and the corrosion resistance of the welded heat-affected zone is required. The present invention relates to stainless steel for welding construction without gaps, which is suitable for objects, water heater can bodies and the like.
Here, “welding without a gap” refers to welding performed without forming a gap, such as butt welding or fillet welding.
既存の高強度ステンレス鋼は、(1)マルテンサイト系ステンレス鋼、(2)準安定オーステナイト系ステンレス鋼、(3)析出硬化型ステンレス鋼に大別される。
マルテンサイト系ステンレス鋼は主にＦｅ−Ｃｒ−Ｃ系からなる焼入温度領域ではオーステナイト単相であるが、室温までの冷却中に完全にマルテンサイト変態してしまう。この系の鋼は焼入れ状態あるいは焼入れ焼戻し状態では硬くて加工性が乏しい。そのため、通常は焼きなまし状態で、曲げ、切削、切断などの加工が加えられ、所定の形状が与えられた後に焼入れ焼戻しの熱処理が施されて高強度が付与される。しかし、大きな部材は焼入れ処理が困難であり、また溶接に際してマルテンサイト単相は溶接割れを起しやすく、溶接後に熱影響部に焼戻し熱処理を施さねばならないとの欠点がある。
Existing high-strength stainless steels are broadly classified into (1) martensitic stainless steel, (2) metastable austenitic stainless steel, and (3) precipitation hardened stainless steel.
Martensitic stainless steel is an austenite single phase mainly in the quenching temperature region composed of Fe-Cr-C, but completely martensite transforms during cooling to room temperature. This type of steel is hard and poor in workability in the quenched or tempered state. Therefore, processing such as bending, cutting, and cutting is usually performed in an annealed state, and after a predetermined shape is given, a heat treatment of quenching and tempering is performed to impart high strength. However, the large member is difficult to quench, and the martensite single phase is liable to cause cracks during welding, and has a drawback that the heat-affected zone must be tempered after welding.
マルテンサイト系ステンレス鋼を構造部材として使用することを考慮する場合、上記の欠点を補う手段として、Ｃを低く抑えた組成で、焼入れ状態でマルテンサイト相を呈することが考えられる。例えば、日新製鋼技報（昭和49年 第31号p.32）に紹介されているように、Ｔｉを０．３０％程度添加して、固溶ＣをＴｉＣとして固定することで溶接熱影響部の耐食性を得ている。これも非常に有効な手段であるが、Ｔｉの過度の添加はＴｉクラスター起因の表面疵を発生さえ、製造性の面で不具合がある。 When considering the use of martensitic stainless steel as a structural member, it is conceivable to exhibit a martensitic phase in a quenched state with a composition with low C as a means to compensate for the above-mentioned drawbacks. For example, as introduced in Nisshin Steel Technical Report (Showa 49, No. 31, p.32), about 0.30% of Ti is added, and solid solution C is fixed as TiC. The corrosion resistance of the part is obtained. This is also a very effective means, but excessive addition of Ti has a problem in terms of manufacturability even if surface defects due to Ti clusters are generated.
準安定オーステナイト系ステンレス鋼は、ＳＵＳ３０１、ＳＵＳ３０４などの焼鈍後はオーステナイト単相であり、冷間圧延で加工誘起マルテンサイト相が生成する加工硬化型ステンレス鋼である。この系は冷間圧延率、合金成分の調整で所望の強度・延性バランスをとりうるが、溶接を行なうと冷間加工で生成した加工誘起マルテンサイトがオーステナイトに逆変態して軟化してしまう不具合が生じる。また、この系は溶接熱影響部でＣｒ炭化物析出によるＣｒ欠乏層が生じ、粒界応力腐食割れが発生することがある。 The metastable austenitic stainless steel is a work hardening type stainless steel that is an austenite single phase after annealing of SUS301, SUS304, etc., and a work induction martensite phase is generated by cold rolling. This system can achieve a desired balance between strength and ductility by adjusting the cold rolling rate and alloy composition. However, when welding is performed, the work-induced martensite generated by cold working reversely transforms to austenite and softens. Occurs. In this system, a Cr-deficient layer due to Cr carbide precipitation occurs in the weld heat affected zone, and intergranular stress corrosion cracking may occur.
析出硬化型ステンレス鋼はマトリックスの組成によりマルテンサイト系、フェライト系、オーステナイト系などに分類されるが、いずれも時効硬化に貢献するＡｌ，Ｔｉ，Ｎｂ，Ｃｕなどが１種もしくは２種以上含有し、これら元素が過飽和状態で時効処理することで、金属間化合物を析出させて強化するものである。これら金属間化合物主体での析出効果は、置換型元素の拡散律速で時効処理自体高温長時間になり、設備能力等の面で制約を受ける。
以上に述べたように、高強度ステンレス鋼として知られている鋼は、加工性、溶接軟化、表面欠陥、設備制約等の経済面でいくつかの問題がある。
Precipitation hardening type stainless steel is classified into martensite, ferrite, and austenite depending on the matrix composition, and all contain one or more of Al, Ti, Nb, Cu, etc. that contribute to age hardening. These elements are aging treated in a supersaturated state to precipitate and strengthen intermetallic compounds. The precipitation effect mainly composed of these intermetallic compounds is limited in terms of equipment capacity and the like because the aging treatment itself takes a high temperature and a long time due to the diffusion-controlled diffusion-type element.
As described above, steels known as high-strength stainless steels have several problems in terms of economy such as workability, weld softening, surface defects, equipment constraints, and the like.
本発明は前述のように、従来の高強度ステンレス鋼で問題となっていた、加工性、溶接軟化、表面欠陥などの欠点のない新規な溶接熱影響部の耐食性に優れた高強度フェライト系ステンレス鋼材を提供するものである。 As described above, the present invention is a high-strength ferritic stainless steel excellent in the corrosion resistance of a new weld heat-affected zone without defects such as workability, weld softening, and surface defects, which has been a problem with conventional high-strength stainless steel. It provides steel materials.
発明者らは上記目的を達成すべく詳細な研究を行った結果、以下のようなことを見出した。
（i）２２質量％を超えるＣｒ含有量を確保して基本的耐食性レベルを向上させることが、バックガスシールを行わないＴＩＧ溶接により形成された裏ビード側溶接隙間部の耐食性向上に極めて有効である。
（ii）溶接部の耐食性向上に有効であるとされてきたＳｉは、一定量以上添加するとバックガスシールを行わないＴＩＧ溶接においては耐食性を低下させる。
（iii）Ｓｉは溶接部の高強度化には必須の元素であるが、(ii)で述べたように溶接部耐食性には悪影響を及ぼす。これを回避する手段として、一定以上のＮｉ量を添加して、溶接スケール中のＣｒ濃度を向上させることを見出した。
本発明は、これら知見の中で特に（iii）に基づいて成分設計された新たな高強度フェライト系ステンレス鋼を提供するものである。
As a result of detailed studies to achieve the above object, the inventors have found the following.
(I) It is extremely effective to improve the corrosion resistance of the back bead side weld gap formed by TIG welding without back gas sealing to secure the Cr content exceeding 22 mass% and improve the basic corrosion resistance level. is there.
(Ii) Si, which has been said to be effective for improving the corrosion resistance of the welded portion, lowers the corrosion resistance in TIG welding in which back gas sealing is not performed when a certain amount or more is added.
(Iii) Si is an essential element for increasing the strength of the weld, but as described in (ii), it adversely affects the corrosion resistance of the weld. As means for avoiding this, it has been found that the Ni concentration above a certain level is added to improve the Cr concentration in the weld scale.
The present invention provides a new high-strength ferritic stainless steel whose components are designed based on (iii) among these findings.
すなわち本発明では、質量％で、Ｃ：０.０２％以下、Ｓｉ：１〜３％、Ｍｎ：１％以下、Ｐ：０.０４％以下、Ｓ：０.０３％以下、Ｎｉ：1〜３％以下、Ｃｒ：２２〜２６％、Ｍｏ：１．０％以下、Ｎｂ：０.０５〜０.６％、Ｔｉ：０.０５〜０.４％、Ｎ：０.０２５％以下、Ａｌ：０.０２〜０.３％であり、必要に応じてＣｕ：２.０％以下、Ｖ：１．０％以下、Ｂ １００ｐｐｍ以下の１種以上を含有した残部Ｆｅおよび他の不可避的不純物からなる、溶接部の耐食性に優れることを特徴とする高強度フェライト系ステンレス鋼が提供される。 That is, in the present invention, by mass%, C: 0.02% or less, Si: 1-3%, Mn: 1% or less, P: 0.04% or less, S: 0.03% or less, Ni: 1 to 3% or less, Cr: 22-26%, Mo: 1.0% or less, Nb: 0.05-0.6%, Ti: 0.05-0.4%, N: 0.025% or less, Al : Fe of 0.02 to 0.3%, if necessary, Cu: 2.0% or less, V: 1.0% or less, B containing 100 ppm or less of the balance Fe and other inevitable impurities A high-strength ferritic stainless steel characterized by being excellent in the corrosion resistance of the welded portion is provided.
具体的には、以下の構成を有するものである。
請求項１に記載の発明は、
質量％で、
Ｃ：０.０２％以下、
Ｓｉ：１〜３％、
Ｍｎ：１％以下、
Ｐ：０.０４％以下、
Ｓ：０.０３％以下、
Ｎｉ：１〜３％、
Ｃｒ：２２〜２６％、
Ｍｏ：１.０％以下、
Ｎｂ：０.０５〜０.６％、
Ｔｉ：０.０５〜０.４％、
Ｎ：０.０２５％以下、
Ａｌ：０.０２〜０.３％であり、
残部Ｆｅおよび他の不可避的不純物からなる、溶接部耐食性に優れる隙間のない溶接施工用高強度フェライト系ステンレス鋼である。
Specifically, it has the following configuration.
The invention described in
% By mass
C: 0.02% or less,
Si: 1-3%
Mn: 1% or less,
P: 0.04% or less,
S: 0.03% or less,
Ni: 1-3%
Cr: 22-26%
Mo: 1.0% or less,
Nb: 0.05-0.6%
Ti: 0.05-0.4%,
N: 0.025% or less,
Al: 0.02 to 0.3%,
It is a high-strength ferritic stainless steel for welding work that has no gap and is excellent in welded portion corrosion resistance, consisting of the balance Fe and other inevitable impurities.
請求項２に記載の発明は、
質量％において Ｃｕ ２.０％以下、Ｂ １００ｐｐｍ以下の１種以上を含有した請求項１記載の溶接隙間部の耐食性に優れる隙間のない溶接施工用高強度フェライト系ステンレス鋼である。
The invention described in
The high-strength ferritic stainless steel for welding work having no gap and excellent in corrosion resistance of the weld gap portion according to
請求項３に記載の発明は、
さらに、Ｃｏ、ＶおよびＷの1種以上を合計４質量％以下の範囲で含有する請求項1ならびに請求項２に記載の隙間のない溶接施工用高強度フェライト系ステンレス鋼である。
The invention according to claim 3
Furthermore, it is a high-strength ferritic stainless steel for welding construction without gaps according to
請求項４に記載の発明は、
冷延焼鈍酸洗鋼板とした後、その鋼板を大気中でＴＩＧ溶接した試験片に対し、母材溶接熱影響部の酸化スケールの平均Ｃｒ比率が全金属元素の割合で２５質量％以上を有する請求項１、２、３記載のＴＩＧ溶接部の引張強さが５５０Ｎ／ｍｍ2以上を特徴とする隙間のない溶接施工用高強度フェライト系ステンレス鋼である。
The invention according to claim 4
After making a cold-rolled annealed pickled steel sheet, the average Cr ratio of the oxide scale of the base metal welding heat-affected zone has a mass ratio of 25% by mass or more with respect to the test piece obtained by TIG welding the steel sheet in the atmosphere. It is a high-strength ferritic stainless steel for welding construction having no gap, characterized in that the tensile strength of the TIG welded portion according to
この鋼は、冷延焼鈍酸洗鋼板とした後、アルゴンバックガスシールなしでＴＩＧ溶接隙間のない試験片に対し、無手入れのまま母材熱影響部の溶接隙間部の酸化スケールの平均Ｃｒ比率が全金属元素の割合で２５質量％以上を有する。このＣｒ比率は、主として合金成分の影響により定まるものである。 This steel is a cold-rolled annealed pickled steel sheet, and then the average Cr ratio of the oxide scale of the weld gap in the base metal heat-affected zone remains untreated relative to the test piece without TIG weld gap without an argon back gas seal. Has a ratio of all metal elements of 25% by mass or more. This Cr ratio is determined mainly by the influence of alloy components.
ここで、「無手入れのまま」とは、溶接部に生じた酸化スケールを除去する手段（研磨等の機械的除去手段および酸洗等の化学的除去手段）が施されておらず、溶接されたままの状態であることを意味する。「溶接部」は溶接ビード部と熱影響部からなる領域であり溶接芯線有無両方のケースを想定する。 Here, “as-maintained” means that no means (removal such as polishing and chemical removal such as pickling) that removes oxide scale from the welded part has been applied, and welding is performed. It means that it is in an untouched state. A “welded part” is an area composed of a weld bead part and a heat-affected part, and assumes both cases with and without a weld core.
ステンレス鋼にとって溶接熱影響部の酸化皮膜の存在が耐食性の劣化をもたらす主要因であるが、鋭意予備検討した結果、本組成の範囲で酸化スケール中のＣｒ比率が全金属元素の割合で２５質量％以上を有することで、溶接部の耐食性を向上させるのに有効であることを見出した。 For stainless steel, the presence of the oxide film in the weld heat affected zone is the main factor causing deterioration of the corrosion resistance. As a result of intensive investigations, the Cr ratio in the oxide scale is 25% in terms of the total metal elements within the range of this composition. It has been found that it is effective to improve the corrosion resistance of the welded portion.
本発明の高強度フェライト系ステンレス鋼を使用すると、溶接部の耐食性が顕著に改善される。例えば、本発明によれば、高耐食性が要求される上水環境での温水容器において設計自由度の拡大が可能になる。また、今後需要増が見込まれるＣＯ２冷媒ヒートポンプ給湯器、燃料電池の温水缶体では高強度化により缶体の軽量化につながる。 When the high-strength ferritic stainless steel of the present invention is used, the corrosion resistance of the welded portion is remarkably improved. For example, according to the present invention, it is possible to expand the degree of design freedom in a hot water container in a water supply environment where high corrosion resistance is required. In addition, CO 2 refrigerant heat pump water heaters and fuel cell hot water cans, which are expected to increase in demand in the future, lead to weight reduction of the cans by increasing the strength.
本発明のフェライト系ステンレス鋼を構成する成分元素について説明する。
Ｃ、Ｎは、鋼中に不可避的に含まれる元素である。Ｃ、Ｎの含有量を低減すると鋼は軟質になり加工性が向上するとともに炭化物、窒化物の生成が少なくなり、溶接性および溶接部の耐食性が向上する。このため本発明ではＣ、Ｎとも含有量は少ない方が良く、Ｃは０.０２質量％まで、Ｎは０.０２５質量％まで含有が許容される。
The component elements constituting the ferritic stainless steel of the present invention will be described.
C and N are elements inevitably contained in the steel. When the content of C and N is reduced, the steel becomes soft and the workability is improved, and the formation of carbides and nitrides is reduced, and the weldability and the corrosion resistance of the welded portion are improved. For this reason, in the present invention, it is better that the contents of both C and N are small, and C is allowed to be contained up to 0.02 mass% and N is contained up to 0.025 mass%.
Ｓｉは、Ａｒガスシールを行ってＴＩＧ溶接する場合、溶接部の耐食性改善に有効に作用する。しかしながら発明者らの詳細な検討によれば、ガスシールなしでＴＩＧ溶接する場合、Ｓｉは逆に溶接部の耐食性を阻害する要因になることがわかった。また、Ｓｉは母材および溶接部の靭性を損なう要因となる。このため、耐食性および靭性の点ではＳｉ含有量は低い方が好ましいが、本発明の特徴である高強度化のためには必須である。Ｓｉ添加による溶接部耐食性低下は、Ｎｉの必須で補うことができる。Ｓｉ範囲の規制はＮｉと並び、本発明で特に大事な元素であり、Ｓｉ含有量を１以上３質量％以下の範囲にコントロールする。 Si effectively acts to improve the corrosion resistance of the weld when performing Ar gas sealing and TIG welding. However, according to detailed examinations by the inventors, it has been found that when TIG welding is performed without a gas seal, Si becomes a factor that inhibits corrosion resistance of the welded portion. Moreover, Si becomes a factor which impairs the toughness of a base material and a welding part. For this reason, in terms of corrosion resistance and toughness, a lower Si content is preferable, but it is essential for increasing the strength, which is a feature of the present invention. The deterioration of the weld corrosion resistance due to the addition of Si can be compensated for by the necessity of Ni. The regulation of the Si range, along with Ni, is an especially important element in the present invention, and the Si content is controlled in the range of 1 to 3% by mass.
Ｍｎは、ステンレス鋼の脱酸剤として使用される。しかしＭｎは不動態皮膜中のＣｒ濃度を低下させ、耐食性低下を招く要因となるので、本発明ではＭｎ含有量は低い方が好ましく、１質量％以下の含有量に規定される。スクラップを原料とするステンレス鋼ではある程度のＭｎ混入は避けられないので、過剰に含有されないよう管理が必要である。 Mn is used as a deoxidizer for stainless steel. However, Mn lowers the Cr concentration in the passive film and causes a decrease in corrosion resistance. Therefore, in the present invention, the Mn content is preferably low, and is defined as a content of 1% by mass or less. Since some amount of Mn is unavoidable in the stainless steel made from scrap, it is necessary to manage it so that it is not excessively contained.
Ｐは、母材および溶接部の靭性を損なうので低い方が望ましい。ただし、含Ｃｒ鋼の溶製において精錬による脱りんは困難であることから、Ｐ含有量を極低化するには原料の厳選などに過剰なコスト増を伴う。したがって本発明では一般的なフェライト系ステンレス鋼と同様に、０.０４質量％までのＰ含有を許容する。 P is desirable to be low because it impairs the toughness of the base metal and the weld. However, since dephosphorization by refining is difficult in the production of Cr-containing steel, excessively increasing the cost, such as careful selection of raw materials, is required to minimize the P content. Therefore, in the present invention, the P content up to 0.04% by mass is allowed as in the general ferritic stainless steel.
Ｓは、孔食の起点となりやすいＭｎＳを形成して耐食性を阻害することが知られているが、本発明では適量のＴｉを必須添加するので、Ｓを特に厳しく規制する必要はない。すなわち、ＴｉはＳとの親和力が強く、化学的に安定な硫化物を形成するので、耐食性低下の原因になるＭｎＳの生成が十分に抑止される。一方、あまり多量にＳが含まれると溶接部の高温割れが生じやすくなるので、Ｓ含有量は０.０３質量％以下に規定される。 It is known that S forms MnS that tends to be a starting point of pitting corrosion and inhibits corrosion resistance. However, since an appropriate amount of Ti is essentially added in the present invention, it is not necessary to regulate S particularly severely. That is, since Ti has a strong affinity for S and forms a chemically stable sulfide, the generation of MnS that causes a decrease in corrosion resistance is sufficiently suppressed. On the other hand, if too much S is contained, hot cracking of the welded portion is likely to occur, so the S content is specified to be 0.03 mass% or less.
Ｃｒは、不動態皮膜の主要構成元素であり、耐孔食性や耐隙間腐食性などの局部腐食性の向上をもたらす。バックガスシールなしでＴＩＧ溶接した溶接部の耐食性はＣｒ含有量に大きく依存することから、Ｃｒは本発明において特に重要な元素である。発明者らの検討の結果、バックガスシールなしで溶接した溶接部に温水環境で要求される耐食性を付与するには２１質量％を超えるＣｒ含有量を確保すべきであることがわかった。耐食性向上効果はＣｒ含有量が多くなるに伴って向上する。しかし、Ｃｒ含有量が多くなるとＣ、Ｎの低減が難しくなり、機械的性質や靭性を損ねかつコストを増大させる要因となる。
本発明では、Ｃｒ含有量が２２質量％以上の鋼ではＮｉの溶接部の耐食性改善効果が大きくなることを明らかにした。したがって本発明ではＣｒ含有量を２２〜２６質量％とする。
Cr is a main constituent element of the passive film, and improves local corrosion properties such as pitting corrosion resistance and crevice corrosion resistance. Cr is a particularly important element in the present invention because the corrosion resistance of a welded portion TIG welded without a back gas seal depends greatly on the Cr content. As a result of investigations by the inventors, it has been found that a Cr content exceeding 21% by mass should be ensured in order to impart corrosion resistance required in a hot water environment to a welded portion welded without a back gas seal. The corrosion resistance improving effect is improved as the Cr content is increased. However, when the Cr content is increased, it is difficult to reduce C and N, which causes a deterioration in mechanical properties and toughness and an increase in cost.
In the present invention, it has been clarified that the steel having a Cr content of 22% by mass or more has a large effect of improving the corrosion resistance of the welded portion of Ni. Therefore, in this invention, Cr content shall be 22-26 mass%.
Ｍｏは、Ｃｒとともに耐食性レベルを向上させるための有効な元素であり、その耐食性向上作用は高Ｃｒになるほど大きくなることが知られている。
ところが、発明者らの詳細な検討によれば、バックガスシールなしでＴＩＧ溶接した溶接部については、Ｍｏによってもたらされる耐食性向上作用はあまり大きくないことがわかった。本発明の主な用途である上水の温水環境に対しては０.２質量％以上のＭｏを含有させることが効果的であるが、１.０質量％を超えて増量しても溶接部の腐食性の改善効果は小さく、徒にコスト上昇を招くのみで得策ではない。したがってＭｏ含有量は１.０質量％以下とする。
Mo is an effective element for improving the corrosion resistance level together with Cr, and it is known that the effect of improving the corrosion resistance increases as the Cr content increases.
However, according to detailed examinations by the inventors, it has been found that the effect of improving the corrosion resistance caused by Mo is not so great for a welded portion that is TIG welded without a back gas seal. Although it is effective to contain 0.2% by mass or more of Mo for the warm water environment of clean water, which is the main use of the present invention, the weld zone is increased even if the amount exceeds 1.0% by mass. The effect of improving the corrosivity is small, and it is not a good idea because it only causes an increase in cost. Therefore, the Mo content is 1.0% by mass or less.
Ｎｂは、Ｔｉと同様にＣ、Ｎとの親和力が強く、フェライト系ステンレス鋼で問題となる粒界腐食を防止するのに有効な元素である。その効果を十分発揮させるには０.０５質量％以上のＮｂ含有量を確保することが望ましい。しかし、過剰に添加すると溶接高温割れが生じるようになり、溶接部靭性も低下するので、Ｎｂ含有量の上限は０.６質量％とする。 Nb has a strong affinity for C and N like Ti, and is an effective element for preventing intergranular corrosion, which is a problem in ferritic stainless steel. In order to sufficiently exhibit the effect, it is desirable to secure an Nb content of 0.05% by mass or more. However, if added in excess, welding hot cracking occurs, and the weld zone toughness also decreases, so the upper limit of the Nb content is set to 0.6 mass%.
Ｔｉは、Ａｒバックガスシールを行う従来のＴＩＧ溶接において溶接部の耐食性向上に寄与する元素であるが、バックガスシールなしのＴＩＧ溶接においても溶接部の耐食性を顕著に改善する作用を有することがわかった。そのメカニズムについては必ずしも明確ではないが、Ａｒバックガスシールを行うＴＩＧ溶接の場合は、Ａｌとの複合添加により溶接時に鋼表面にＡｌ主体の酸化皮膜が優先的に形成され、結果的にＣｒの酸化ロスが抑制されるものと考えられる。他方、バックガスシールなしのＴＩＧ溶接の場合は、その溶接部においてＴｉは腐食発生後の再不動態化を促進する作用を発揮し、それによって耐食性が向上するものと推察される。このようなＴｉの作用を十分に享受するには０.０５質量％以上のＴｉ含有量を確保することが望ましい。しかし、Ｔｉ含有量が多くなると素材の表面品質が低下したり、溶接ビードに酸化物が生成して溶接性が低下したりしやすいので、Ｔｉ含有量の上限は０.４質量％とする。 Ti is an element that contributes to improving the corrosion resistance of welds in conventional TIG welding that performs Ar back gas sealing, but it may have the effect of significantly improving the corrosion resistance of welds even in TIG welding without back gas sealing. all right. Although the mechanism is not necessarily clear, in the case of TIG welding with Ar back gas sealing, an oxide film mainly composed of Al is preferentially formed on the steel surface during the welding due to the combined addition with Al. It is thought that oxidation loss is suppressed. On the other hand, in the case of TIG welding without a back gas seal, it is presumed that Ti exhibits an action of promoting repassivation after the occurrence of corrosion, thereby improving corrosion resistance. In order to fully enjoy the effect of such Ti, it is desirable to secure a Ti content of 0.05% by mass or more. However, if the Ti content is increased, the surface quality of the material is deteriorated or oxides are generated in the weld bead and the weldability is likely to be lowered. Therefore, the upper limit of the Ti content is set to 0.4% by mass.
Ａｌは、Ｔｉとの複合添加によって溶接による耐食性低下を抑制する。その作用を十分に得るためには０.０２質量％以上のＡｌ含有量を確保することが望ましい。一方、過剰のＡｌ含有は素材の表面品質の低下や、溶接性の低下を招くので、Ａｌ含有量は０.３質量％以下とする。 Al suppresses a decrease in corrosion resistance due to welding by the combined addition with Ti. In order to obtain the effect sufficiently, it is desirable to secure an Al content of 0.02% by mass or more. On the other hand, excessive Al content causes deterioration of the surface quality of the material and weldability, so the Al content is 0.3 mass% or less.
Ｎｉは、Ｓｉと並び本発明を構成する重要な元素である。ＡｒバックガスシールなしのＴＩＧ溶接において溶接スケール中のＣｒ濃度を高め、化学的に安定なＣｒ２Ｏ３の生成量を増加しスケールの耐食性を向上させる。さらに、溶接金属部（ビード部）および熱影響部ともに腐食の進行を抑えることでバックガスシールなしのＴＩＧ溶接部の耐食性を向上させる。この作用はＳｉ添加により溶接部酸化皮膜中のＣｒ濃度が低くなるところを抑えてくれる。また酸化皮膜中の金属元素比率でＣｒ比率を向上させる手段としてはＦｅ系の酸化物を出させないようにすることが有効であり、母相中のＦｅの酸化反応を抑制し結果的に酸化皮膜中のＣｒ比率を上昇させるのにＮｉは有効である。一方で、Ｎｉは靭性を改善する効果がある。特にフェライト系ステンレス鋼で問題となる溶接部の靭性には有効である。Ｓｉ添加鋼の中でその効果を出すためには予備検討の結果、Ｎｉが１.０質量％以上必要である。ただし多量のＮｉ含有は素材費を向上させさらには加工性を阻害するので、上限を３質量％とした。 Ni is an important element constituting the present invention along with Si. In TIG welding without an Ar back gas seal, the Cr concentration in the weld scale is increased, the amount of chemically stable Cr 2 O 3 is increased, and the corrosion resistance of the scale is improved. Furthermore, the corrosion resistance of the TIG welded part without the back gas seal is improved by suppressing the progress of corrosion in both the weld metal part (bead part) and the heat-affected part. This action suppresses the reduction of the Cr concentration in the welded oxide film due to the addition of Si. In addition, as a means of improving the Cr ratio by the metal element ratio in the oxide film, it is effective not to emit Fe-based oxides, and as a result, the oxidation reaction of Fe in the matrix phase is suppressed and the oxide film Ni is effective in increasing the Cr ratio in the medium. On the other hand, Ni has an effect of improving toughness. This is particularly effective for the toughness of welds, which is a problem with ferritic stainless steel. As a result of preliminary studies, Ni is required to be 1.0% by mass or more in order to exert the effect in the Si-added steel. However, a large amount of Ni increases the material cost and further hinders workability, so the upper limit was made 3 mass%.
Ｃｕは、ＡｒバックガスシールなしのＴＩＧ溶接部の耐食性において、溶接裏面熱影響部での孔食発生を抑制する。製造性の面から上限を２質量％とする。 Cu suppresses the occurrence of pitting corrosion at the weld back heat affected zone in the corrosion resistance of the TIG weld without an Ar back gas seal. From the standpoint of manufacturability, the upper limit is 2% by mass.
Ｖはフェライト系ステンレス鋼の高強度化に寄与するために添加をされることもあり、靭性や製造性の問題から1質量％以下とした。 V may be added to contribute to increasing the strength of ferritic stainless steel, and is set to 1% by mass or less because of problems of toughness and manufacturability.
Ｂはフェライト系ステンレス鋼の加工部分の低温靭性を改善する効果があるが、過度の添加は熱間加工性を低下させるため、上限を１００ｐｐｍとした。 B has the effect of improving the low temperature toughness of the processed part of ferritic stainless steel, but excessive addition reduces the hot workability, so the upper limit was made 100 ppm.
Ｃｏはフェライト系ステンレス鋼の靭性改善、ＶおよびＷはフェライト系ステンレス鋼の高強度化に寄与するために添加をされることもあり、靭性や製造性の問題から３元素の合計を４％以下とした。 Co is added to improve the toughness of ferritic stainless steel, and V and W are sometimes added to contribute to increasing the strength of ferritic stainless steel. Due to toughness and manufacturability, the total of 3 elements is 4% or less. It was.
以上で説明した合金成分以外は不純物である。ステンレス鋼に不可避的に混入しやすい不純物としては、酸素、Ｃａ、Ｃｏ、ＲＥＭ、Ｖ等が挙げられる。これらは、副原料、電気炉を構成する耐火煉瓦や炉壁の付着物、スラグ等からの混入が考えられる。Ｃａ、Ｂ及びＲＥＭは耐食性を阻害したり、表面性状を悪化したりすることのない許容量である、０．０１０質量％を上限とする。 Except for the alloy components described above, impurities are impurities. Oxygen, Ca, Co, REM, V etc. are mentioned as an impurity which is inevitably mixed in stainless steel. These may be mixed from auxiliary materials, refractory bricks constituting the electric furnace, deposits on the furnace wall, slag, and the like. Ca, B, and REM have an upper limit of 0.010% by mass, which is an allowable amount that does not hinder corrosion resistance or deteriorate surface properties.
溶接部高強度化の指標としてＴＩＧ溶接部の引張強さを用い、従来のフェライト単相鋼に対しての高強度化によるメリットを生み出すには、ＴＩＧ溶接部の引張強さが５５０Ｎ／ｍｍ２以上必要である。
本発明においては、基本成分がＣｒ：２２〜２６質量％、Ｍｏ：１.０質量％以下である成分系において更にＮｉを１〜３質量％添加することにより耐食性を確保するとともに、Ｓｉを１〜３質量％添加することによってこの強度レベルを達成している。耐食性及び靭性を確保しつつ高強度化を達成するには、ＮｉとＳｉの添加バランスが重要である。
In order to use the tensile strength of the TIG weld as an index for increasing the strength of the weld and to produce the benefits of higher strength compared to conventional ferritic single phase steel, the tensile strength of the TIG weld is 550 N / mm 2 This is necessary.
In the present invention, the corrosion resistance is ensured by adding 1 to 3% by mass of Ni in the component system in which the basic components are Cr: 22 to 26% by mass and Mo: 1.0% by mass or less, and Si is added to 1%. This strength level is achieved by adding ~ 3 wt%. In order to achieve high strength while ensuring corrosion resistance and toughness, the balance of addition of Ni and Si is important.
表１の化学組成をもつフェライト系ステンレス鋼を３０ｋｇ真空溶解炉で溶製した後、熱間圧延にて板厚４ｍｍの熱延板を得た。その後、冷間圧延、仕上げ焼鈍、酸洗を施し、板厚０．９ｍｍの冷延焼鈍板を製造した。表中で下線を施した数値は、特許請求の範囲から外れるものである。 Ferritic stainless steel having the chemical composition shown in Table 1 was melted in a 30 kg vacuum melting furnace, and a hot rolled sheet having a thickness of 4 mm was obtained by hot rolling. Thereafter, cold rolling, finish annealing, and pickling were performed to produce a cold-rolled annealed plate having a thickness of 0.9 mm. Numerical values underlined in the table are outside the scope of the claims.
製造された冷延焼鈍板について、表２に示す条件で溶接芯線を使用せずにＴＩＧ溶接を実施した。溶接はＡｒバックガスシールを施さずに行った。 About the manufactured cold-rolled annealing board, TIG welding was implemented on the conditions shown in Table 2 without using a welding core wire. Welding was performed without an Ar back gas seal.
このＴＩＧ溶接材を用い、溶接部の引張試験を行い、溶接部の引張強さを調査した。なお、引張試験片には、ＪＩＳ Ｚ ２２０１に規定される５号試験片を用いた。 Using this TIG welding material, a tensile test of the welded portion was performed, and the tensile strength of the welded portion was investigated. In addition, the No. 5 test piece prescribed | regulated to JISZ2201 was used for the tensile test piece.
また、隙間のない母材熱影響部の耐食性も調査した。図１になめづけ溶接試験片の外観を示す。溶接で生じた酸化スケールを除去せず、溶接ビードが試験片長手方向中央位置を横切るように試験片を採取した。この試験片には溶接ビード部、熱影響部および母材部が含まれる。母材部の端にリード線をスポット溶接にて接続し、リード線およびその接続部分のみを樹脂被覆した。 In addition, the corrosion resistance of the base metal heat-affected zone without gaps was also investigated. FIG. 1 shows the appearance of a tanned weld specimen. The test piece was collected such that the weld bead crossed the central position in the longitudinal direction of the test piece without removing the oxide scale generated by welding. This test piece includes a weld bead part, a heat-affected part, and a base material part. A lead wire was connected to the end of the base material portion by spot welding, and only the lead wire and its connecting portion were coated with resin.
浸漬試験は８０℃の２，０００ｐｐｍＣｌ−水溶液で３０日間行った。図２に浸漬試験方法を模擬的に示す。「浸漬試験片２」には「Ｐｔ補助カソード１」を接続した。「Ｐｔ補助カソード１」は４０×６０ｍｍのＴｉ板の表面にＰｔめっきを施したものである。この補助カソードは、ここでの試験片に対し容量３００Ｌの温水器缶体に相当するカソード能力を有している。「浸漬試験片２」と「Ｐｔ補助カソード１」を「試験液３」に浸漬し、試験中、「エアレーションノズル４」からエアーを「試験液３」中に送り込んだ。試験はｎ＝３で行った。
腐食深さは、浸漬試験後の溶着金属部、母材部での最大侵食深さを測定した。
Immersion test of 80 ℃ 2,000ppmCl - was carried out for 30 days in an aqueous solution. FIG. 2 schematically shows the immersion test method. “Pt
The corrosion depth was determined by measuring the maximum erosion depth in the weld metal part and base metal part after the immersion test.
さらに、母材熱影響部の酸化スケールの平均Ｃｒ比率についても調査した。分析は母材金属でボンド部から何箇所か測定した。測定手段は微小部Ｘ線発光電子分析法（μ−ＸＰＳ）で行った。ビーム径は５０μｍで酸化スケールの深さ方向５ｎｍおきに各金属元素量を求め、Ｃｒ比率をＣｒ量／Σ（全金属元素量）で評価した。そのときの各深さでのＣｒ比率の平均を平均Ｃｒ比率とした。母材部で何箇所が測定し、スケール中の平均Ｃｒ比率が低い値を用いた。なお、このスケール中のＣｒ比率が低い場所は、母材部熱影響部で最大浸食深さを示すボンド部から５ｍｍ離れた位置である。これらの調査結果を表３に示す。
Furthermore, the average Cr ratio of the oxide scale in the base material heat-affected zone was also investigated. In the analysis, the base metal was measured at several points from the bond part. The measuring means was a micro part X-ray emission electron analysis method (μ-XPS). The beam diameter was 50 μm, the amount of each metal element was determined every 5 nm in the depth direction of the oxide scale, and the Cr ratio was evaluated by Cr amount / Σ (total metal element amount). The average Cr ratio at each depth at that time was defined as the average Cr ratio. Several points were measured in the base material part, and a value with a low average Cr ratio in the scale was used. In addition, the place where the Cr ratio in this scale is low is a
Ｎｏ．１〜７では、溶接部引張強さが５５０Ｎ／ｍｍ２以上、最大侵食深さが０．１５ｍｍ以下と良好な溶接部の引張特性と耐食性を示した。また、母材部熱影響部で最も低い箇所での平均Ｃｒ比率は２５質量％以上であった。
これに対し、Ｎｏ．８〜１１では、溶接部引張強さが５５０Ｎ／ｍｍ２以下と強度不足であった。一方、Ｎｏ.１０と１２では最大侵食深さが０．３ｍｍ以上と良好な耐食性が得られなかった。これらの母材部熱影響部で最も低い箇所での平均Ｃｒ比率はいずれも２５質量％以下であった。このことから、平均Ｃｒ比率が２５質量％以上でないと良好な耐食性は得られない。
No. In Nos. 1 to 7, the tensile strength and corrosion resistance of the welded portion were good, with a welded portion tensile strength of 550 N / mm 2 or more and a maximum erosion depth of 0.15 mm or less. Moreover, the average Cr ratio in the lowest place in a base material part heat affected zone was 25 mass% or more.
In contrast, no. In 8-11, weld part tensile strength was 550 N / mm < 2 > or less, and the intensity | strength was insufficient. On the other hand, in No. 10 and 12, the maximum erosion depth was 0.3 mm or more, and good corrosion resistance was not obtained. The average Cr ratio at the lowest point in these base material part heat-affected zones was 25% by mass or less. From this, good corrosion resistance cannot be obtained unless the average Cr ratio is 25% by mass or more.
本発明は、各種スチールベルト、物干竿等のパイプ、自転車リム材等、溶接構造物、温水器缶体のみでなく、溶接隙間構造を有する給油管や燃料タンクの給油系部材や燃料噴射レールならびに熱交換機部材にも適用できる。 The present invention is not limited to various steel belts, pipes for clothespins, bicycle rim materials, etc., welded structures, water heater cans, as well as fuel pipes and fuel tank oil supply system members and fuel injection rails having weld gap structures. It can also be applied to heat exchanger members.
１ Ｐｔ補助カソード
２ 浸漬試験片
３ 試験液
４ エアレーションノズル
５ 参照電極
1 Pt
Claims (4)
Ｃ：０.０２％以下、
Ｓｉ：１〜３％、
Ｍｎ：１％以下、
Ｐ：０.０４％以下、
Ｓ：０.０３％以下、
Ｎｉ：１〜３％、
Ｃｒ：２２〜２６％、
Ｍｏ：１.０％以下、
Ｎｂ：０.０５〜０.６％、
Ｔｉ：０.０５〜０.４％、
Ｎ：０.０２５％以下、
Ａｌ：０.０２〜０.３％であり、
残部Ｆｅおよび他の不可避的不純物からなる、溶接部耐食性に優れる隙間のない溶接施工用高強度フェライト系ステンレス鋼。 % By mass
C: 0.02% or less,
Si: 1-3%
Mn: 1% or less,
P: 0.04% or less,
S: 0.03% or less,
Ni: 1-3%
Cr: 22-26%
Mo: 1.0% or less,
Nb: 0.05-0.6%
Ti: 0.05-0.4%,
N: 0.025% or less,
Al: 0.02 to 0.3%,
A high-strength ferritic stainless steel for welding that is free of gaps and has excellent weld corrosion resistance, comprising the balance Fe and other inevitable impurities.
After making a cold-rolled annealed pickled steel sheet, the average Cr ratio of the oxide scale of the base metal welding heat-affected zone has a mass ratio of 25% by mass or more with respect to the test piece obtained by TIG welding the steel sheet in the atmosphere. A high-strength ferritic stainless steel for welding without gaps, characterized in that the tensile strength of the TIG welded portion according to claim 1, 2 and 3 is 550 N / mm 2 or more.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2010054842A JP2011190470A (en) | 2010-03-11 | 2010-03-11 | High-strength ferritic stainless steel for welding operation having excellent corrosion resistance in weld zone and having no gap |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2010054842A JP2011190470A (en) | 2010-03-11 | 2010-03-11 | High-strength ferritic stainless steel for welding operation having excellent corrosion resistance in weld zone and having no gap |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JP2011190470A true JP2011190470A (en) | 2011-09-29 |
Family
ID=44795692
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2010054842A Withdrawn JP2011190470A (en) | 2010-03-11 | 2010-03-11 | High-strength ferritic stainless steel for welding operation having excellent corrosion resistance in weld zone and having no gap |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2011190470A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2023020772A (en) * | 2021-07-28 | 2023-02-09 | 國立清華大學 | High chromium and silicon-rich corrosion resistant steel and use application thereof |
-
2010
- 2010-03-11 JP JP2010054842A patent/JP2011190470A/en not_active Withdrawn
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2023020772A (en) * | 2021-07-28 | 2023-02-09 | 國立清華大學 | High chromium and silicon-rich corrosion resistant steel and use application thereof |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP3704306B2 (en) | Hot-dip galvanized high-strength steel sheet excellent in weldability, hole expansibility and corrosion resistance, and method for producing the same | |
| JP5928405B2 (en) | Tempered steel sheet excellent in resistance to hydrogen-induced cracking and method for producing the same | |
| JP6027302B2 (en) | High strength tempered spring steel | |
| JP2010065272A (en) | High-strength steel sheet and method for manufacturing the same | |
| JP2008190035A (en) | Ferritic stainless steel sheet for water heater | |
| CA2861030C (en) | Ferrite-based stainless steel plate having excellent resistance against scale peeling, and method for manufacturing same | |
| JP2014005532A (en) | High strength spring steel wire with excellent coiling property and hydrogen embrittlement resistance and manufacturing method thereof | |
| JP2009161836A (en) | Ferritic stainless steel sheet excellent in corrosion resistance in welding crevice part | |
| JP2005105367A (en) | High yield ratio and high strength cold-rolled steel plate and high yield ratio and high strength galvanized steel plate excellent in weldability and ductility, and high yield ratio and high strength alloyed galvanized steel plate and its manufacturing method | |
| JP2007262441A (en) | Steel for crude oil tank and its production method | |
| JP2018080379A (en) | Manufacturing method of hot rolled steel sheet and manufacturing method of cold rolled full hard steel sheet | |
| WO1996010654A1 (en) | Highly corrosion-resistant martensitic stainless steel with excellent weldability and process for producing the same | |
| JP2009185382A (en) | Ferritic stainless steel sheet having excellent corrosion resistance in welding gap oxide film | |
| JP2011174122A (en) | Low-chromium-containing stainless steel superior in corrosion resistance at welded part | |
| JP2008291303A (en) | Ferrittic stainless steel sheet excellent in blanking property for water heater and production method therefor | |
| JP2021075758A (en) | Fe-Ni-Cr-Mo-Cu ALLOY HAVING EXCELLENT CORROSION RESISTANCE | |
| JP2002212684A (en) | Martensitic stainless steel having high temperature strength | |
| JP2010090406A (en) | Low yield ratio steel for low temperature use, and producing method of the same | |
| JP2011190470A (en) | High-strength ferritic stainless steel for welding operation having excellent corrosion resistance in weld zone and having no gap | |
| JP2009167439A (en) | Ferritic stainless steel for welding gap structural warm-water vessel | |
| JP2008285718A (en) | Ferritic stainless steel sheet having high strength of welded joint for water heater, and manufacturing method therefor | |
| JP3713833B2 (en) | Ferritic stainless steel for engine exhaust members with excellent heat resistance, workability, and weld corrosion resistance | |
| JP3705161B2 (en) | High tensile steel plate | |
| JP7311808B2 (en) | Steel plate and its manufacturing method | |
| JP4288085B2 (en) | Hot-dip galvanized high-strength steel sheet excellent in hole expansibility and method for producing the same |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A300 | Withdrawal of application because of no request for examination |
Free format text: JAPANESE INTERMEDIATE CODE: A300 Effective date: 20130604 |