JP6466734B2 - Austenitic high Mn stainless steel welded joint for high-pressure hydrogen gas and liquid hydrogen and method for producing the same - Google Patents
Austenitic high Mn stainless steel welded joint for high-pressure hydrogen gas and liquid hydrogen and method for producing the same Download PDFInfo
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- 239000001257 hydrogen Substances 0.000 title claims description 92
- 229910052739 hydrogen Inorganic materials 0.000 title claims description 92
- 239000007788 liquid Substances 0.000 title claims description 42
- 229910001220 stainless steel Inorganic materials 0.000 title claims description 28
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- 229910052751 metal Inorganic materials 0.000 claims description 49
- 239000002184 metal Substances 0.000 claims description 49
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- 239000012535 impurity Substances 0.000 claims description 11
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Description
本発明は、高圧水素ガスおよび液体水素用オーステナイト系高Ｍｎステンレス鋼溶接継手およびその製造方法に関し、特に、高圧水素ガスおよび液体水素環境下で使用され、優れた機械的性質を有する耐水素脆化感受性に優れたオーステナイト系高Ｍｎステンレス鋼溶接継手およびその製造方法に関する。 The present invention relates to an austenitic high-Mn stainless steel welded joint for high-pressure hydrogen gas and liquid hydrogen and a method for producing the same, and in particular, hydrogen embrittlement resistance used in high-pressure hydrogen gas and liquid hydrogen environments and having excellent mechanical properties. The present invention relates to an austenitic high Mn stainless steel welded joint excellent in sensitivity and a method for producing the same.
近年、地球温暖化防止の観点から、温室効果ガス（ＣＯ２、ＮＯｘ、ＳＯｘ）の排出を抑制するため、水素をエネルギーとして利用する技術開発が進んでいる。このような背景から、水素の貯蔵・輸送に用いる金属材料の開発が期待されている。 In recent years, from the viewpoint of preventing global warming, technology development using hydrogen as energy is progressing in order to suppress the emission of greenhouse gases (CO 2 , NO x , SO x ). Against this background, development of metal materials used for hydrogen storage and transport is expected.
従来、圧力４０ＭＰａ程度までの水素ガスは厚肉のＣｒ−Ｍｏ鋼製ボンベに高圧ガスとして充填・貯蔵されている。また、高圧水素ガスの配管用材料あるいは燃料電池自動車の高圧水素ガスタンクライナーとしては、高圧水素ガス環境下での耐水素ガス脆化特性が他の構造用鋼、例えば上記のＣｒ−Ｍｏ鋼を含む炭素鋼や、ＪＩＳ規格のＳＵＳ３０４系オーステナイト系ステンレス鋼（以下、「ＳＵＳ３０４鋼と記載」）と比較して良好である、ＪＩＳ規格のＳＵＳ３１６系オーステナイト系ステンレス鋼（以下、「ＳＵＳ３１６鋼と記載」）も使用されている。 Conventionally, hydrogen gas up to a pressure of about 40 MPa is filled and stored as a high-pressure gas in a thick Cr-Mo steel cylinder. In addition, as a high-pressure hydrogen gas piping material or a high-pressure hydrogen gas tank liner for a fuel cell vehicle, the hydrogen gas embrittlement resistance under a high-pressure hydrogen gas environment includes other structural steels such as the above-described Cr-Mo steel. JIS SUS316 austenitic stainless steel (hereinafter referred to as “SUS316 steel”), which is better than carbon steel and JIS 304 SUS304 austenitic stainless steel (hereinafter referred to as “SUS304 steel”). Has also been used.
また近年、燃料電池自動車の一般販売に先駆けて水素ステーションの公的な試作・実証実験が進行している。大量の水素を液体水素として貯蔵しておき、必要な際に液体水素を昇圧して７０ＭＰａ以上の高圧水素ガスとして供給可能な水素ステーションも実証段階にある。このような水素ステーションが実用化され、普及していく中で、高圧水素ガスと液体水素の両水素環境において使用できる、安価かつ強度の高い金属材料に対するニーズがより一層強くなっている。 In recent years, public trials and demonstration experiments of hydrogen stations are in progress prior to general sales of fuel cell vehicles. A hydrogen station that can store a large amount of hydrogen as liquid hydrogen, pressurize the liquid hydrogen when necessary, and supply it as high-pressure hydrogen gas of 70 MPa or more is also in the demonstration stage. As such hydrogen stations are put into practical use and spread, there is a growing need for inexpensive and high-strength metal materials that can be used in both high-pressure hydrogen gas and liquid hydrogen environments.
極低温となる液体水素の貯蔵・輸送には、従来、オーステナイト系のＳＵＳ３０４鋼もしくはＳＵＳ３１６鋼が使用されている。特に、貯蔵容器内で液体水素が蒸気となる容器上層部は、低温における水素ガス脆化を考慮する必要があり、耐水素脆化特性に優れるＳＵＳ３１６鋼を使用することが望ましい。しかし、ＳＵＳ３１６鋼は、高価なレアメタルであるＮｉを１０％以上、Ｍｏを２％以上含有するステンレス鋼である。そのため、ＳＵＳ３１６鋼は、汎用性と経済性（コスト）に大きな課題がある。
さらに、高圧水素ガス用の容器や配管およびこれらに付属する機器は、溶接、および溶接後に加工して使用されることが多いため、溶接部における耐水素脆化特性が重要となるとともに、溶接材料にも汎用性と経済性が求められている。
Conventionally, austenitic SUS304 steel or SUS316 steel has been used for storage and transport of liquid hydrogen at extremely low temperatures. In particular, it is necessary to consider hydrogen gas embrittlement at a low temperature for the upper layer portion of the container in which liquid hydrogen becomes vapor in the storage container, and it is desirable to use SUS316 steel excellent in hydrogen embrittlement resistance. However, SUS316 steel is a stainless steel containing 10% or more of Ni, which is an expensive rare metal, and 2% or more of Mo. Therefore, SUS316 steel has a big subject in versatility and economical efficiency (cost).
Furthermore, since the containers and pipes for high-pressure hydrogen gas and the devices attached to them are often used after welding and after being welded, the resistance to hydrogen embrittlement at the weld is important, and the welding material In addition, versatility and economy are required.
一般的に、例えば非特許文献１に記載されている通り、ＳＵＳ３０４鋼を母材とする場合は溶接材料としてＳＵＳ３０８系鋼が使用され、一方ＳＵＳ３１６鋼を母材とする場合は溶接材料として母材と同様のＳＵＳ３１６系鋼が使用されている。しかし、これら溶接材料は、Ｎｉを９％以上含有しており、経済性の点で問題がある。 Generally, as described in Non-Patent Document 1, for example, when SUS304 steel is used as a base material, SUS308 series steel is used as a welding material, while when SUS316 steel is used as a base material, the base material is used as a welding material. The same SUS316 steel is used. However, these welding materials contain 9% or more of Ni, which is problematic in terms of economy.
特許文献１において、４０ＭＰａ超の高圧水素ガス環境および液体水素環境での耐水素脆化特性に優れたオーステナイト系高Ｍｎステンレス鋼が開示されている。このオーステナイト系高Ｍｎステンレス鋼は、素材に加工熱処理を施すことで破壊の起点となるδフェライト相の体積率、サイズを制御しているが、このような加工熱処理を溶接部に実施することは困難である。 Patent Document 1 discloses an austenitic high Mn stainless steel having excellent hydrogen embrittlement resistance in a high-pressure hydrogen gas environment and a liquid hydrogen environment exceeding 40 MPa. This austenitic high-Mn stainless steel controls the volume fraction and size of the δ ferrite phase that is the starting point of fracture by subjecting the material to a heat treatment. Have difficulty.
特許文献２において、溶接継手の溶接金属が、質量％で、Ｃ：０．０２％以下、Ｓｉ：１．０％以下、Ｍｎ：３〜３０％、Ｃｒ：２２を超えて３０％まで、Ｎｉ：８〜３０％、Ｖ：０．００１〜１．０％ 、Ｍｏ：０〜３．０％、Ｗ：０〜６．０％、Ｎ：０．１〜０．５％、Ａｌ：０．１０％以下、Ｔｉ、Ｎｂ、Ｚｒ、ＨｆおよびＴａ：それぞれ０〜０．０１％であり、残部がＦｅおよび不純物からなる高圧水素ガス用の容器、配管およびそれらの付属機器が開示されている。しかしながら、特許文献３に記載の発明の溶接継手の溶接金属に含まれるＮｉ量は実質１２％以上であり経済性の点で問題があり、さらに、液体水素環境までの適用は考慮していない。 In Patent Document 2, the weld metal of the welded joint is in mass%, C: 0.02% or less, Si: 1.0% or less, Mn: 3 to 30%, Cr: more than 22 and up to 30%, Ni : 8-30%, V: 0.001-1.0%, Mo: 0-3.0%, W: 0-6.0%, N: 0.1-0.5%, Al: 0.00. 10% or less, Ti, Nb, Zr, Hf, and Ta: 0 to 0.01% each, containers for high-pressure hydrogen gas, the balance of which is composed of Fe and impurities, piping, and their accessories are disclosed. However, the amount of Ni contained in the weld metal of the welded joint of the invention described in Patent Document 3 is substantially 12% or more, which is problematic in terms of economy, and is not considered for application to a liquid hydrogen environment.
特許文献３において、耐水素ガス脆化特性に優れた溶接材料として、Ｃ：０．１％以下、Ｓｉ：０．８％以下、Ｍｎ：１．５〜４．５％、Ｎｉ：８〜１５％、Ｃｒ：１８〜２４％、Ａｌ：０．０５％未満、Ｎ：０．１５〜０．３５％のステンレス鋼が開示されている。この溶接材料は、Ｎｉ含有量が８％以上であり引用文献２、３と同様に経済性の点で問題があり、さらに、液体水素環境下までの適用を考慮したものではない。 In Patent Document 3, as a welding material excellent in hydrogen gas embrittlement resistance, C: 0.1% or less, Si: 0.8% or less, Mn: 1.5 to 4.5%, Ni: 8 to 15 %, Cr: 18-24%, Al: less than 0.05%, N: 0.15-0.35% stainless steel is disclosed. This welding material has a Ni content of 8% or more, which is problematic in terms of economic efficiency as in References 2 and 3, and is not intended for application in a liquid hydrogen environment.
このように、４０ＭＰａ超の高圧水素ガスと液体水素の両水素環境下で適用可能な経済性に優れた溶接継手およびそれに用いることができる溶接材料は、未だ出現していないのが現状である。 Thus, the present condition is that the welding joint excellent in economical efficiency applicable to both the high-pressure hydrogen gas of over 40 Mpa and liquid hydrogen, and the welding material which can be used for it have not yet appeared.
本発明は、４０ＭＰａ超の高圧水素ガスと液体水素の両水素環境下で適用可能な経済性に優れたオーステナイト系高Ｍｎステンレス鋼溶接継手およびその製造方法を提供することを目的とする。 An object of the present invention is to provide an austenitic high Mn stainless steel welded joint excellent in economic efficiency applicable to both high pressure hydrogen gas exceeding 40 MPa and liquid hydrogen, and a method for producing the same.
本発明者らは、前記の課題を解決するために、オーステナイト系高Ｍｎステンレス鋼溶接継手において、主要元素であるＣｒ、Ｍｎ、Ｎｉ、Ｃｕと微量元素で構成されている合金成分組成と溶接部の凝固組織、変形組織、および高圧水素ガスと液体水素の両水素環境下における耐水素脆化特性の関係について鋭意研究を行い、以下の新しい知見を得て本発明を完成するに至った。 In order to solve the above-mentioned problems, the present inventors, in an austenitic high-Mn stainless steel welded joint, have an alloy component composition and a weld zone composed of main elements such as Cr, Mn, Ni, Cu and trace elements. The present inventors completed the present invention by earnestly studying the solidification structure, deformation structure, and relationship between hydrogen embrittlement resistance in both hydrogen environments of high-pressure hydrogen gas and liquid hydrogen.
（ａ）高圧水素ガス環境および液体水素環境において、溶接時の凝固段階で生成するδフェライト相は、オーステナイト相と比較して割れが生成しやすい。さらに、この割れが連結・伝播して材料破断に至る。 (A) In a high-pressure hydrogen gas environment and a liquid hydrogen environment, the δ ferrite phase generated in the solidification stage during welding is more likely to crack than the austenite phase. Furthermore, the cracks are connected and propagated to cause material breakage.
（ｂ）また、溶接時の凝固段階で生成するδフェライト相の体積率および形態はオーステナイト生成元素であるＮｉやＭｎ、Ｃｕ等の含有量、溶接条件に依存し、その形態は針状または球状となる。 (B) The volume fraction and form of the δ ferrite phase produced in the solidification stage during welding depend on the contents of the austenite-forming elements Ni, Mn, Cu, etc., and the welding conditions, and the form is acicular or spherical. It becomes.
（ｃ）δフェライト相の形態が針状である場合、お互いのδフェライト相は連結して存在している。このように連結したδフェライト相組織では、割れが生成した後の割れの伝播が容易となり、高圧水素ガス環境および液体水素環境における溶接部の延性は著しく低下する。 (C) When the form of the δ ferrite phase is acicular, the δ ferrite phases are connected to each other. In the δ ferrite phase structure thus connected, the propagation of the crack after the crack is generated becomes easy, and the ductility of the welded part in the high-pressure hydrogen gas environment and the liquid hydrogen environment is significantly reduced.
（ｄ）δフェライト相の形態が球状である場合、δフェライト相で割れが生成しても、割れの伝播はδフェライト相とオーステナイト相の界面で停止する。 (D) When the shape of the δ ferrite phase is spherical, even if cracks are generated in the δ ferrite phase, the propagation of the cracks stops at the interface between the δ ferrite phase and the austenite phase.
（ｅ）溶接金属中のδフェライト相において、長径の平均が０．０５ｍｍ以下である球状の形態とするとともに、当該形態を有するδフェライト相の体積率を１０％以下にすることで、δフェライト相を起点とした割れの連結・伝播を抑制でき、高圧水素ガス中および液体水素中で優れた耐水素脆化特性が得られる。 (E) The δ ferrite phase in the weld metal has a spherical shape whose average major axis is 0.05 mm or less, and the volume ratio of the δ ferrite phase having the shape is 10% or less, Connection and propagation of cracks originating from the phase can be suppressed, and excellent hydrogen embrittlement resistance can be obtained in high-pressure hydrogen gas and liquid hydrogen.
（ｆ）従来、ステンレス鋼の溶接部の組織はＣｒｅｑとＮｉｅｑの影響を受け、ＮｉｅｑにおいてはＮｉの他、Ｍｎ、Ｃ、Ｎにより整理されることが知られている。しかし本発明者らが検討した結果、Ｃｕも溶接部の組織形成に影響をおよぼすことがわかった。
溶接金属において、以下の式（１）及び式（２）で算出されるＣｒｅｑとＮｉｅｑの比（Ｃｒｅｑ／Ｎｉｅｑ）を１．１０以下にすることで、体積率１０％以下のδフェライト相組織を得ることができる。
ここで、
Ｃｒｅｑ＝［Ｃｒ］＋１．５［Ｓｉ］ ・・・（１）
Ｎｉｅｑ＝［Ｎｉ］＋０．５［Ｍｎ］＋［Ｃｕ］＋３０（［Ｃ］＋［Ｎ］） ・・（２）
であり、［Ｃｒ］、［Ｓｉ］、［Ｎｉ］、［Ｍｎ］、［Ｃｕ］、［Ｃ］、［Ｎ］はそれぞれの元素の質量％を示す。
(F) Conventionally, it is known that the structure of the welded portion of stainless steel is affected by Creq and Nieq, and Nieq is organized by Mn, C, and N in addition to Ni. However, as a result of investigations by the present inventors, it has been found that Cu also affects the structure formation of the weld.
In the weld metal, the ratio of Creq to Nieq (Creq / Nieq) calculated by the following equations (1) and (2) is 1.10 or less, so that a δ ferrite phase structure having a volume ratio of 10% or less can be obtained. Can be obtained.
here,
Creq = [Cr] +1.5 [Si] (1)
Nieq = [Ni] +0.5 [Mn] + [Cu] +30 ([C] + [N]) (2)
[Cr], [Si], [Ni], [Mn], [Cu], [C], and [N] indicate mass% of each element.
（ｇ）溶接部の耐水素脆化特性をより一層高めるためには、δフェライト相の形態を球状で、長径が０．０５ｍｍ以下に制御することが好ましい。既存のＳＵＳ３０４鋼やＳＵＳ３１６鋼等のオーステナイト系ステンレス鋼では、溶接時の入熱量を２０ｋＪ／ｃｍ程度とすることが最適である。しかしながら、本発明の溶接継手では、溶接時の入熱量が大きい場合、溶接終了後も溶接部は高温となり、δフェライト相が粗大化し、さらに、δフェライト相の球状化が阻害されてしまう。上記の溶接部の組織を得るためには、入熱量を７．２ｋＪ／ｃｍ以下とすることが好ましい。なお、既存のオーステナイト系ステンレス鋼において溶接時の入熱量を７．２ｋＪ／ｃｍ以下とした場合、入熱不足のため、上記の本発明に係る溶接部の組織を得ることができない。 (G) In order to further improve the hydrogen embrittlement resistance of the welded portion, it is preferable to control the form of the δ ferrite phase to be spherical and the major axis to be 0.05 mm or less. For austenitic stainless steels such as existing SUS304 steel and SUS316 steel, it is optimal to set the heat input during welding to about 20 kJ / cm. However, in the welded joint of the present invention, when the heat input during welding is large, the welded portion becomes high temperature after the end of welding, the δ ferrite phase becomes coarse, and further, the spheroidization of the δ ferrite phase is inhibited. In order to obtain the structure of the welded portion, it is preferable that the heat input is 7.2 kJ / cm or less. When the heat input during welding is set to 7.2 kJ / cm or less in existing austenitic stainless steel, the structure of the welded portion according to the present invention cannot be obtained due to insufficient heat input.
本発明は、上記（ａ）〜（ｇ）の知見に基づきなされたもので、本発明の要旨は、以下の通りである。 This invention was made | formed based on the knowledge of said (a)-(g), and the summary of this invention is as follows.
（１）オーステナイト系ステンレス鋼の母材と溶接金属とからなる溶接継手であって、前記溶接金属の化学組成が、質量％でＣ：０．２％以下、Ｓｉ：２．０％以下、Ｍｎ：５．５〜１４．５％、Ｃｒ：１３．５〜２２．０％、Ｎｉ：３．５〜１２．５％、Ｃｕ：１〜５％およびＮ：０．０１〜０．４％を含有し、残部がＦｅおよび不可避的不純物であり、以下の式（１）及び（２）で算出されるＣｒｅｑとＮｉｅｑの比（Ｃｒｅｑ／Ｎｉｅｑ）が１．１０以下であり、前記溶接金属中のδフェライト相の体積率が１０％以下であり、前記δフェライト相の長径の平均が０．０５ｍｍ以下であり、かつ前記δフェライト相の形態が、（前記δフェライト相の短径）／（前記フェライト相の長径）で表されるアスペクト比が０．３以上である球状であることを特徴とする高圧水素ガスおよび液体水素用オーステナイト系高Ｍｎステンレス鋼溶接継手。
Ｃｒｅｑ＝［Ｃｒ］＋１．５［Ｓｉ］ … （１）
Ｎｉｅｑ＝［Ｎｉ］＋０．５［Ｍｎ］＋［Ｃｕ］＋３０（［Ｃ］＋［Ｎ］） …（２）ここで、［Ｃｒ］、［Ｓｉ］、［Ｎｉ］、［Ｍｎ］、［Ｃｕ］、［Ｃ］、［Ｎ］はそれぞれの元素の質量％を示す。
（２）前記母材の化学組成が、質量％で、Ｃ：０．１％以下、Ｓｉ：０．４〜１．５％、Ｍｎ：８〜１１％、Ｃｒ：１５〜１７％、Ｎｉ：５〜８％、Ｃｕ：１〜４％およびＮ：０．０１〜０．３％を含有し、残部がＦｅおよび不可避的不純物であることを特徴とする、上記（１）に記載の高圧水素ガスおよび液体水素用オーステナイト系高Ｍｎステンレス鋼溶接継手。
（３）上記（１）または（２）に記載の高圧水素ガスおよび液体水素用オーステナイト系高Ｍｎステンレス鋼溶接継手の製造方法であって、オーステナイト系ステンレス鋼の母材に対して溶接する際、溶接金属を、質量％でＣ：０．１％以下、Ｓｉ：０．４〜１．５％、Ｍｎ：７〜１１％、Ｃｒ：１５〜２０％、Ｎｉ：５〜１２％、Ｃｕ：１〜４％およびＮ：０．０１〜０．３％を含有し、残部がＦｅおよび不可避的不純物であり、かつ以下の式（１）及び（２）で算出されるＣｒｅｑとＮｉｅｑの比（Ｃｒｅｑ／Ｎｉｅｑ）が１．１０以下を満足する化学組成とし、入熱量を７．２ｋＪ／ｃｍ以下として溶接することを特徴とする、高圧水素ガスおよび液体水素用オーステナイト系高Ｍｎステンレス鋼溶接継手の製造方法。
Ｃｒｅｑ＝［Ｃｒ］＋１．５［Ｓｉ］ ・・・ （１）
Ｎｉｅｑ＝［Ｎｉ］＋０．５［Ｍｎ］＋［Ｃｕ］＋３０（［Ｃ］＋［Ｎ］） …（２）ここで、［Ｃｒ］、［Ｓｉ］、［Ｎｉ］、［Ｍｎ］、［Ｃｕ］、［Ｃ］、［Ｎ］はそれぞれの元素の質量％を示す。
（４）前記オーステナイト系ステンレス鋼の母材に対し、質量％でＣ：０．１％以下、Ｓｉ：０．４〜１．５％、Ｍｎ：７．０〜１２％、Ｃｒ：１４〜２０％、Ｎｉ：５〜１２％、Ｃｕ：１〜４％およびＮ：０．０１〜０．４％を含有し、残部がＦｅおよび不可避的不純物である化学組成を有する溶接材料を用いて溶接することを特徴とする、上記（３）に記載の高圧水素ガスおよび液体水素用オーステナイト系高Ｍｎステンレス鋼溶接継手の製造方法。
(1) A welded joint comprising a base metal of austenitic stainless steel and a weld metal, wherein the chemical composition of the weld metal is C: 0.2% or less, Si: 2.0% or less, Mn : 5.5 to 14.5%, Cr: 13.5 to 22.0%, Ni: 3.5 to 12.5%, Cu: 1 to 5% and N: 0.01 to 0.4% And the balance is Fe and inevitable impurities, the ratio (Creq / Nieq) of Creq and Nieq calculated by the following formulas (1) and (2) is 1.10 or less, volume fraction of δ ferrite phase Ri der than 10%, the average major axis of the δ ferrite phase does not exceed 0.05mm or less, and the form of the δ ferrite phase, (minor diameter of the δ ferrite phase) / ( A spherical shape having an aspect ratio of 0.3 or more expressed by the major axis of the ferrite phase) Oh pressure hydrogen gas and liquid hydrogen for austenitic high Mn stainless steel welded joints characterized by Rukoto.
Creq = [Cr] +1.5 [Si] (1)
Nieq = [Ni] +0.5 [Mn] + [Cu] +30 ([C] + [N]) (2) where [Cr], [Si], [Ni], [Mn], [Cu ], [C], and [N] indicate mass% of each element .
(2 ) The chemical composition of the base material is% by mass, C: 0.1% or less, Si: 0.4 to 1.5%, Mn: 8 to 11%, Cr: 15 to 17%, Ni: High-pressure hydrogen according to (1 ) above, containing 5-8%, Cu: 1-4% and N: 0.01-0.3%, the balance being Fe and inevitable impurities Austenitic high Mn stainless steel welded joints for gas and liquid hydrogen.
( 3 ) A method for producing an austenitic high Mn stainless steel welded joint for high pressure hydrogen gas and liquid hydrogen as described in (1) or (2) above, when welding to a base material of austenitic stainless steel, Weld metal in mass% C: 0.1% or less, Si: 0.4-1.5%, Mn: 7-11%, Cr: 15-20%, Ni: 5-12%, Cu: 1 -4% and N: 0.01 to 0.3%, the balance being Fe and inevitable impurities, and the ratio of Creq to Nieq calculated by the following formulas (1) and (2) (Creq / Nieq) having a chemical composition satisfying 1.10 or less and a heat input of 7.2 kJ / cm or less, welding with high pressure hydrogen gas and austenitic high Mn stainless steel welded joint for liquid hydrogen Production method.
Creq = [Cr] +1.5 [Si] (1)
Nieq = [Ni] +0.5 [Mn] + [Cu] +30 ([C] + [N]) (2) where [Cr], [Si], [Ni], [Mn], [Cu ], [C], and [N] indicate mass% of each element .
(4 ) C: 0.1% or less, Si: 0.4 to 1.5%, Mn: 7.0 to 12%, Cr: 14 to 20% by mass with respect to the base material of the austenitic stainless steel. %, Ni: 5 to 12%, Cu: 1 to 4% and N: 0.01 to 0.4%, and the remainder is welded using a welding material having a chemical composition of Fe and inevitable impurities The method for producing an austenitic high Mn stainless steel welded joint for high-pressure hydrogen gas and liquid hydrogen as described in ( 3) above.
本発明によれば、高圧水素ガスおよび液体水素環境下で好適に使用することが可能な、優れた経済性及び優れた機械的性質を有し、かつ耐水素脆化感受性に優れた溶接継手を提供することができる。また、そのような溶接継手を得るための最適な溶接材料を用いた製造方法を提供することができる。 According to the present invention, a welded joint that can be suitably used in a high-pressure hydrogen gas and liquid hydrogen environment, has excellent economic efficiency and excellent mechanical properties, and has excellent resistance to hydrogen embrittlement. Can be provided. Moreover, the manufacturing method using the optimal welding material for obtaining such a welded joint can be provided.
本発明は溶接継手およびその製造方法について規定するものである。
水素環境下で用いられる貯蔵タンクや配管等の構造体の最終的な使用状況において要求されるものは、構造体に用いる溶接継手の特性であり、そのためには溶接継手の化学組成および組織を制御し、規定することは当然かつ重要事項である。
一方で、溶接材料については、溶接継手作成時に、溶解、凝固を経るため、溶接材料自体の特性や組織は、特に規定が必要ではない。さらに溶接材料は溶接母材（以下、単に母材または母鋼材ともいう。）との混合が起きるため、溶接材料の化学組成は、最終的に必要となる溶接継手の化学組成と同じものである必然性はなく、厳密な規定は意味がないとも言える。しかし、最終的な溶接継手の化学組成、組織、さらには特性を制御するためには、溶接材料の化学組成が特定の範囲内に規定されることも当然である。
The present invention defines the welded joint and its manufacturing method.
What is required in the final use situation of structures such as storage tanks and pipes used in a hydrogen environment is the characteristics of the welded joints used in the structures. To that end, the chemical composition and structure of the welded joints are controlled. However, it is a matter of course and important to specify.
On the other hand, since the welding material undergoes melting and solidification at the time of creating a welded joint, the characteristics and structure of the welding material itself do not need to be regulated. Furthermore, since the welding material is mixed with the welding base material (hereinafter also simply referred to as a base material or a base steel material), the chemical composition of the welding material is the same as the chemical composition of the weld joint that is ultimately required. There is no necessity, and it can be said that strict provisions are meaningless. However, in order to control the chemical composition, structure and even properties of the final welded joint, it is natural that the chemical composition of the welding material is defined within a certain range.
以下では、まず、溶接継手の化学組成および組織について説明する。その後、そのような溶接継手を得るために好適な溶接材料を用いた溶接継手の製造方法について、その溶接材料を使用して作成された溶接継手の特性と関連づけて説明することとする。 Below, first, the chemical composition and structure of a welded joint will be described. Then, the manufacturing method of the welded joint using the welding material suitable in order to obtain such a welded joint will be explained in relation to the characteristics of the welded joint created using the welded material.
まず、本発明の溶接継手において、溶接金属の化学組成を限定する理由について説明する。なお、各元素の含有量の「％」は「質量％」を意味する。
溶接継手における溶接金属の化学組成は、溶接する母鋼材の化学組成や用いる溶接材料の化学組成、さらには溶接条件に依存する母鋼材と溶接材料の混合の状況に影響されるものである。しかしながら、本発明では、最終的な溶接金属の化学組成を以下のようにすることで、本発明の目的を達することができる。なお、本発明の溶接継手は、後述する本発明の溶接材料を用いて製造することで、実現が容易になるが、本発明の溶接継手は、当該製造条件に限定されるものでないことは言うまでもない。つまり、溶接する母鋼材、用いる溶接材料、さらに溶接条件を適切に選択することで、最終的な溶接継手における溶接金属の化学組成を本発明の範囲内に制御することができる。
First, the reason for limiting the chemical composition of the weld metal in the welded joint of the present invention will be described. In addition, “%” of the content of each element means “mass%”.
The chemical composition of the weld metal in the welded joint is affected by the chemical composition of the base steel material to be welded, the chemical composition of the welding material used, and the mixing state of the base steel material and the welding material depending on the welding conditions. However, in the present invention, the object of the present invention can be achieved by setting the chemical composition of the final weld metal as follows. The welded joint of the present invention can be easily realized by manufacturing using the welding material of the present invention described later, but it goes without saying that the welded joint of the present invention is not limited to the manufacturing conditions. Yes. That is, the chemical composition of the weld metal in the final welded joint can be controlled within the scope of the present invention by appropriately selecting the base steel material to be welded, the welding material to be used, and the welding conditions.
＜Ｃ：０．２％以下＞
Ｃは本発明の溶接継手において、オーステナイト相の安定化に有効な元素である。さらに、溶接金属のＮｉｅｑを高め、δフェライト相の球状化を促進するのに有効な元素である。しかし、Ｃの過度の添加は、溶接時にＭ２３Ｃ６型炭化物が析出し、水素環境下での延性を著しく低下させるため、Ｃ量の上限を０．２％とする必要がある。好ましいＣ量の上限は０．１０％であり、更に好ましくは０．０８％以下とする。
Ｃの含有量に特に下限を設ける必要はないが、極端な低下は製造コストの著しい上昇を招くため、望ましい下限は０．００２％である。より好ましくは０．０４以上である。
<C: 0.2% or less>
C is an element effective in stabilizing the austenite phase in the welded joint of the present invention. Furthermore, it is an element effective for increasing the Nieq of the weld metal and promoting the spheroidization of the δ ferrite phase. However, excessive addition of C causes M 23 C 6 type carbides to precipitate during welding and significantly lowers the ductility in a hydrogen environment, so the upper limit of the C amount needs to be 0.2%. The upper limit of the preferable amount of C is 0.10%, more preferably 0.08% or less.
Although there is no particular need to set a lower limit for the C content, an extremely lower limit causes a significant increase in manufacturing cost, so a desirable lower limit is 0.002%. More preferably, it is 0.04 or more.
＜Ｓｉ：２．０％以下＞
Ｓｉは、本発明の溶接継手において、常温から極低温環境下でオーステナイト相の安定度を高めて耐水素脆化特性を向上させるために有効な元素である。さらに、材料強度を上昇させる上でも効果的な固溶強化元素である。これら効果を発現させるため、下限は０．１％とすることが好ましい。なお更に好ましくは、Ｓｉ量は０．４％以上であり、最も好ましくは０．５％以上とする。
一方、Ｓｉの過度の含有はＣｒｅｑを増加させ、溶接部に生成するδフェライト相の針状化を促進する。さらに、シグマ相などの金属間化合物の生成を助長し、熱間加工性や靭性の低下を招く可能性がある。そのため、Ｓｉ量の上限を２．０％とする。好ましくは、Ｓｉ量は１．５％以下であり、更に好ましくは１．０％以下とする。
<Si: 2.0% or less>
Si is an effective element for improving the hydrogen embrittlement resistance by increasing the stability of the austenite phase in a welded joint according to the present invention from room temperature to a cryogenic environment. Furthermore, it is a solid solution strengthening element that is also effective in increasing the material strength. In order to express these effects, the lower limit is preferably 0.1%. Even more preferably, the Si content is 0.4% or more, and most preferably 0.5% or more.
On the other hand, excessive inclusion of Si increases Creq and promotes acicularization of the δ ferrite phase generated in the weld. Furthermore, it may promote the formation of intermetallic compounds such as sigma phase, and may cause a decrease in hot workability and toughness. Therefore, the upper limit of Si content is set to 2.0%. Preferably, the Si content is 1.5% or less, more preferably 1.0% or less.
＜Ｍｎ：５．５〜１４．５％＞
Ｍｎは、常温から極低温環境下でオーステナイト安定度を高めて耐水素脆化特性を向上させ、Ｎｉ含有量の低減に有効な元素である。さらに、溶接部のＮｉｅｑを高め、δフェライト相の球状化を促進する。上記効果を十分に得るためには、Ｍｎの下限を５．５％とする必要がある。好ましくは、Ｍｎ量の下限を７．０％とし、更に好ましくは８．５％とする。
一方、Ｍｎの過剰含有は、Ｓ系介在物の増加をもたらし延性の低下を招くため、Ｍｎ量の上限を１４．５％とする。好ましくは、Ｍｎ量の上限を１２％とし、更に好ましくは１０％とする。
<Mn: 5.5 to 14.5%>
Mn is an element effective in increasing the austenite stability from room temperature to a cryogenic environment to improve hydrogen embrittlement resistance and reducing the Ni content. Furthermore, the Nieq of the weld is increased, and the spheroidization of the δ ferrite phase is promoted. In order to sufficiently obtain the above effect, the lower limit of Mn needs to be 5.5%. Preferably, the lower limit of the amount of Mn is 7.0%, more preferably 8.5%.
On the other hand, an excessive Mn content causes an increase in S-based inclusions and a decrease in ductility, so the upper limit of the Mn content is 14.5%. Preferably, the upper limit of the amount of Mn is 12%, more preferably 10%.
＜Ｃｒ：１３．５〜２２．０％＞
Ｃｒは、ステンレス鋼に要求される耐食性を得るために必須の合金元素である。また、Ｃｒは溶接後の加工時に溶接継手に生成する加工誘起マルテンサイト相の延性改善に有効な元素である。この効果を十分に得るためにはＣｒの下限を１３．５％とする必要がある。好ましくはＣｒの下限を１５．０％とする。
一方、Ｃｒの過度の添加は、溶接部のδフェライト相の生成と針状化を促進させ、高圧水素ガスおよび液体水素中での耐水素脆化特性に悪影響をおよぼす。さらに、Ｃｒの過剰の添加は、ＣｒＮ、Ｃｒ２Ｎ等の窒化物やＭ２３Ｃ６型炭化物を生成し、溶接部の延性、靭性、耐食性に悪影響をおよぼす。そのため、Ｃｒ量の上限を２２．０％とする。好ましくは、Ｃｒ量の上限を２０．０％とし、更に好ましくは１７％とする。
<Cr: 13.5 to 22.0%>
Cr is an alloy element essential for obtaining the corrosion resistance required for stainless steel. Cr is an effective element for improving the ductility of the work-induced martensite phase generated in the welded joint during processing after welding. In order to sufficiently obtain this effect, the lower limit of Cr needs to be 13.5%. Preferably, the lower limit of Cr is 15.0%.
On the other hand, excessive addition of Cr promotes the formation and acicularization of the δ ferrite phase in the weld zone, and adversely affects the hydrogen embrittlement resistance in high-pressure hydrogen gas and liquid hydrogen. Furthermore, excessive addition of Cr produces nitrides such as CrN and Cr 2 N and M 23 C 6 type carbides, and adversely affects the ductility, toughness and corrosion resistance of the weld. Therefore, the upper limit of Cr content is 22.0%. Preferably, the upper limit of the Cr content is 20.0%, more preferably 17%.
＜Ｎｉ：３．５〜１２．５％＞
Ｎｉは、既存のＳＵＳ３１６鋼でも周知のように、耐水素脆化特性を改善させるのに極めて有効な元素であり、さらに、溶接部でのＮｉｅｑを高めてδフェライト相の球状化を促進させるのに有効な元素である。これら効果を十分に得るためには、Ｎｉを３．５％以上含有する必要がある。好ましくは、Ｎｉを５．０％以上とし、更に好ましくは５．５％以上とする。
一方、多量のＮｉを含有させるには、溶接材料または母材を高Ｎｉ材とする必要がありコストの増加を招くため、Ｎｉの上限は１２．５％とする。好ましくは、Ｎｉ量の上限は１２．０％であり、更に好ましくは８．０％である。
<Ni: 3.5 to 12.5%>
As is well known in existing SUS316 steel, Ni is an extremely effective element for improving the hydrogen embrittlement resistance. Further, Nieq at the weld is increased to promote the spheroidization of the δ ferrite phase. Is an effective element. In order to obtain these effects sufficiently, it is necessary to contain 3.5% or more of Ni. Preferably, Ni is 5.0% or more, more preferably 5.5% or more.
On the other hand, in order to contain a large amount of Ni, it is necessary to make the welding material or the base material a high Ni material, which causes an increase in cost. Preferably, the upper limit of the Ni content is 12.0%, more preferably 8.0%.
＜Ｃｕ：１．０〜５．０％＞
Ｃｕは、ＭｎやＮｉと同様にオーステナイト相を安定化させる元素であり、本発明が目標とする耐水素脆化特性の向上に有効な元素である。また、ＣｕはＭｎとの相乗効果によって常温から極低温にかけて、変形組織を水素の影響を受けにくい組織に変化させる元素でもある。さらに、Ｃｕは溶接部のＮｉｅｑを増加させ、δフェライト相の球状化を促進させるのに有効な元素でもある。これら効果を得るため、Ｃｕの下限は１．０％とする。好ましくは、Ｃｕ量の下限を１．５％とする。
一方、Ｃｕの過度の含有は、鋼中でのＣｕの析出を促進させ、上記効果が飽和する。そのため、Ｃｕの上限は５．０％とする。好ましくは、Ｃｕ量の上限を４．０％とし、更に好ましくは３．０％とする。
<Cu: 1.0-5.0%>
Cu, like Mn and Ni, is an element that stabilizes the austenite phase, and is an element effective in improving the hydrogen embrittlement resistance targeted by the present invention. Further, Cu is an element that changes a deformed structure into a structure that is hardly affected by hydrogen from room temperature to extremely low temperature by a synergistic effect with Mn. Furthermore, Cu is also an element effective for increasing the Nieq of the weld and promoting the spheroidization of the δ ferrite phase. In order to obtain these effects, the lower limit of Cu is 1.0%. Preferably, the lower limit of the Cu amount is 1.5%.
On the other hand, excessive inclusion of Cu promotes precipitation of Cu in the steel, and the above effect is saturated. Therefore, the upper limit of Cu is 5.0%. Preferably, the upper limit of the Cu amount is 4.0%, more preferably 3.0%.
＜Ｎ：０．０１〜０．４％＞
Ｎは、オーステナイト相の安定化に有効な元素である。さらに、溶接部のＮｉｅｑを増加させ、δフェライト相の球状化を促進するのに有効な元素である。これらの効果を得るため、Ｎ量は０．０１％以上とする。なお、Ｎを０．０１％未満に減らすことは、製鋼コストの負担増加にも繋がる。また、Ｎは固溶強化により鋼の０．２％耐力や引張強度を向上させることが知られており、溶接部の強度向上に有効な元素である。この強度上昇効果を得る場合、Ｎは０．１％以上含有させることが好ましい。
一方、過剰なＮの添加はＣｒＮ、Ｃｒ２Ｎ等の窒化物の生成を促進し、耐水素脆化特性の改善を阻害するため、Ｎ量の上限を０．４％とする。好ましくは、０．３％とし、更に好ましくは、０．２５％以下とする。
<N: 0.01 to 0.4%>
N is an element effective for stabilizing the austenite phase. Furthermore, it is an effective element for increasing the Nieq of the weld and promoting the spheroidization of the δ ferrite phase. In order to obtain these effects, the N content is 0.01% or more. Note that reducing N to less than 0.01% also leads to an increase in steelmaking cost burden. Further, N is known to improve the 0.2% proof stress and tensile strength of steel by solid solution strengthening, and is an element effective for improving the strength of the weld. When obtaining this strength increasing effect, N is preferably contained in an amount of 0.1% or more.
On the other hand, excessive addition of N promotes the formation of nitrides such as CrN and Cr 2 N and inhibits the improvement of hydrogen embrittlement resistance, so the upper limit of N content is set to 0.4%. Preferably, it is 0.3%, more preferably 0.25% or less.
また、本発明に係る溶接継手では、上記で限定した溶接金属の化学組成を満たしつつ、以下の式（１）及び（２）で算出されるＣｒｅｑとＮｉｅｑの比（Ｃｒｅｑ／Ｎｉｅｑ）を１．１０以下とすることが重要である。 Further, in the welded joint according to the present invention, the ratio (Creq / Nieq) of Creq and Nieq calculated by the following formulas (1) and (2) is satisfied while satisfying the chemical composition of the weld metal limited as described above. It is important to set it to 10 or less.
Ｃｒｅｑ＝［Ｃｒ］＋１．５［Ｓｉ］ ・・・ （１）
Ｎｉｅｑ＝［Ｎｉ］＋０．５［Ｍｎ］＋［Ｃｕ］＋３０（［Ｃ］＋［Ｎ］） … （２）
ここで、［Ｃｒ］、［Ｓｉ］、［Ｎｉ］、［Ｍｎ］、［Ｃｕ］、［Ｃ］、［Ｎ］はそれぞれの元素の質量％を示す。
Creq = [Cr] +1.5 [Si] (1)
Nieq = [Ni] +0.5 [Mn] + [Cu] +30 ([C] + [N]) (2)
Here, [Cr], [Si], [Ni], [Mn], [Cu], [C], and [N] indicate mass% of each element.
上記式（１）及び式（２）で算出されるＣｒｅｑとＮｉｅｑの比（Ｃｒｅｑ／Ｎｉｅｑ）を１．１０以下にすることで、溶接金属において、体積率１０％以下のδフェライト相組織を得ることができる。 By setting the ratio (Creq / Nieq) of Creq and Nieq calculated by the above formulas (1) and (2) to 1.10 or less, a δ ferrite phase structure having a volume ratio of 10% or less is obtained in the weld metal. be able to.
次に、本発明の溶接継手の組織について説明する。 Next, the structure of the welded joint of the present invention will be described.
高圧水素ガス環境および液体水素環境において、溶接時の凝固段階で生成するδフェライト相は、オーステナイト相と比較して割れが生成しやすい。さらに、この割れが連結・伝播して材料破断に至る。 In a high-pressure hydrogen gas environment and a liquid hydrogen environment, the δ ferrite phase generated in the solidification stage at the time of welding is more susceptible to cracking than the austenite phase. Furthermore, the cracks are connected and propagated to cause material breakage.
δフェライト相の形態が針状である場合、お互いのδフェライト相は連結して存在している。このように連結したδフェライト相組織では、割れが生成した後の割れの伝播が容易となり、高圧水素ガス環境および液体水素環境における溶接部の延性は著しく低下する。
一方、δフェライト相の形態が球状である場合、δフェライト相で割れが生成しても、割れの伝播はδフェライト相とオーステナイト相の界面で停止するため、溶接部の延性の低下を抑制することが可能となる。
したがって、本発明に係る溶接継手の溶接金属の組織は、球状のδフェライト相とすることが好ましい。
When the form of the δ ferrite phase is acicular, the δ ferrite phases are connected to each other. In the δ ferrite phase structure thus connected, the propagation of the crack after the crack is generated becomes easy, and the ductility of the welded part in the high-pressure hydrogen gas environment and the liquid hydrogen environment is significantly reduced.
On the other hand, when the form of the δ ferrite phase is spherical, even if cracks are generated in the δ ferrite phase, the propagation of the cracks stops at the interface between the δ ferrite phase and the austenite phase, thus suppressing a decrease in ductility of the weld. It becomes possible.
Therefore, the weld metal structure of the welded joint according to the present invention is preferably a spherical δ ferrite phase.
さらに、本発明においては、δフェライト相の体積率を１０％以下とし、かつ溶接金属中のδフェライト相の形態を球状とするとともに、その長径の平均を０．０５ｍｍ以下にすることが好ましい。このように球状のδフェライト相の形態及び体積率を制御することで、δフェライト相を起点とした割れの連結・伝播を抑制でき、高圧水素ガス中および液体水素中でより一層優れた耐水素脆化特性が得られる。
このような溶接部の組織は、上記で限定した溶接継手における溶接金属の化学組成を満たしつつ、さらに上記式（１）及び（２）で算出されるＣｒｅｑとＮｉｅｑの比（Ｃｒｅｑ／Ｎｉｅｑ）を１．１０以下とし、適切な入熱量にて溶接することで得ることができる。
Furthermore, in the present invention, it is preferable that the volume fraction of the δ ferrite phase is 10% or less, the form of the δ ferrite phase in the weld metal is spherical, and the average major axis is 0.05 mm or less. By controlling the shape and volume ratio of the spherical δ-ferrite phase in this way, it is possible to suppress the connection and propagation of cracks starting from the δ-ferrite phase, and even better hydrogen resistance in high-pressure hydrogen gas and liquid hydrogen Embrittlement characteristics are obtained.
The structure of such a welded part satisfies the chemical composition of the weld metal in the weld joint limited as described above, and further calculates the ratio (Creq / Nieq) between Creq and Nieq calculated by the above formulas (1) and (2). It can be obtained by welding at an appropriate heat input with a value of 1.10 or less.
δフェライト相の体積率は、作製した溶接継手の溶接部から試料を５つ切り出した後、フェライトメーターによる測定を行った。５つの試料それぞれから測定したδフェライト相の体積率の平均値を、その溶接継手のδフェライト相の体積率とした。 The volume fraction of the δ ferrite phase was measured with a ferrite meter after five samples were cut out from the welded part of the produced welded joint. The average value of the volume fraction of the δ ferrite phase measured from each of the five samples was taken as the volume fraction of the δ ferrite phase of the welded joint.
本発明では、アスペクト比が０．３以上のδフェライト相を球状のδフェライト相と定義する。
ここで、アスペクト比とはδフェライト相の短径／長径であり、短径とは長径の中心部に対して垂直な位置におけるδフェライト相の長さのことである。
In the present invention, a δ ferrite phase having an aspect ratio of 0.3 or more is defined as a spherical δ ferrite phase.
Here, the aspect ratio is the minor axis / major axis of the δ ferrite phase, and the minor axis is the length of the δ ferrite phase at a position perpendicular to the center of the major axis.
δフェライト相の短径および長径は、δフェライト相の体積率測定で使用した試料を樹脂に埋め込み、観察面を研磨、シュウ酸電解エッチングした後、光学顕微鏡観察により測定した。倍率は２００倍とし、４５０μｍ×６００μｍの長方形の領域内でのδフェライトに対して測定を行った。なお、測定は５つの各樹脂埋め試料に対し３視野で実施した。
観察位置による測定結果のばらつきはほとんど生じていないため、計１５視野における測定結果の平均値をその溶接部のδフェライト相の長径と定めた。また、同時に測定視野内の各δフェライト相のアスペクト比を測定し、各測定結果の平均値を、その溶接部のδフェライト相のアスペクト比と定めた。なお、各測定視野に対しては予め点算法によるδフェライト相の体積率測定を行い、その測定結果が、フェライトメーターによる測定結果と著しく異なっていない視野を抽出した。
The short diameter and long diameter of the δ ferrite phase were measured by observing an optical microscope after embedding a sample used for measuring the volume ratio of the δ ferrite phase in a resin, polishing the observation surface and performing oxalic acid electrolytic etching. The magnification was 200 times, and the measurement was performed on δ ferrite in a rectangular region of 450 μm × 600 μm. In addition, the measurement was implemented by three visual fields with respect to each of five resin embedding samples.
Since there was almost no variation in the measurement results depending on the observation position, the average value of the measurement results in a total of 15 fields was determined as the major axis of the δ ferrite phase of the weld. At the same time, the aspect ratio of each δ ferrite phase in the measurement visual field was measured, and the average value of each measurement result was determined as the aspect ratio of the δ ferrite phase of the weld. In addition, for each measurement visual field, the volume ratio of the δ ferrite phase was previously measured by a point calculation method, and a visual field in which the measurement result was not significantly different from the measurement result by the ferrite meter was extracted.
なお、δフェライト相の体積率は、例えば、市販のフィッシャー製フェライトメーターで簡便に測定することができる。また、光学顕微鏡観察の画像解析でも求めることができる。さらに、δフェライト相の長径は、例えば、試料を樹脂に埋め込み、研磨、エッチングを施した後、光学顕微鏡観察により測定することができる。 The volume ratio of the δ ferrite phase can be easily measured with, for example, a commercially available Fischer meter. It can also be obtained by image analysis of optical microscope observation. Furthermore, the major axis of the δ ferrite phase can be measured, for example, by observation with an optical microscope after the sample is embedded in a resin, polished and etched.
本発明の溶接継手が適用される母鋼材、つまり溶接される鋼材については、オーステナイト系ステンレス鋼である以外は、特に限定されるものではない。ただし、溶接部の耐水素性を高めるという本発明の目的からして、母鋼材についても耐水素性が高い材料（例えば、オーステナイト系高Ｍｎステンレス鋼の母材）であることが好ましい。
背景技術に記述したように、耐水素性が非常に良好で、一般的に広く適用されているＳＵＳ３１６系鋼材を母鋼材として溶接継手を形成することは、本発明の好ましい例である。また、溶接継手の成分制御を容易にする意味では、母鋼材が本発明の溶接継手に近い成分系であることはさらに好ましく、特に耐水素性の向上を目的に設計された、例えば特許文献１（国際公開第２０１２／０４３８７７号公報）に開示された鋼材の溶接継手として形成することは非常に好ましい事例となる。
本発明の好適な母材の化学組成は、質量％で、Ｃ：０．１％以下、Ｓｉ：０．４〜１．５％、Ｍｎ：８〜１１％、Ｃｒ：１５〜１７％、Ｎｉ：５〜８％、Ｃｕ：１〜４％およびＮ：０．０１〜０．３％を含有し、残部がＦｅおよび不可避的不純物である化学組成である。
The base steel material to which the welded joint of the present invention is applied, that is, the steel material to be welded, is not particularly limited except that it is an austenitic stainless steel. However, for the purpose of the present invention to increase the hydrogen resistance of the welded portion, the base steel material is also preferably a material having high hydrogen resistance (for example, a base material of austenitic high Mn stainless steel).
As described in the background art, it is a preferable example of the present invention to form a welded joint using a SUS316 steel material having a very good hydrogen resistance and generally applied as a base steel material. Further, in terms of facilitating the component control of the welded joint, it is further preferable that the base steel material is a component system close to the welded joint of the present invention, and particularly designed for the purpose of improving hydrogen resistance, for example, Patent Document 1 ( It is a very preferable example to form it as a welded joint of steel disclosed in International Publication No. 2012/043877).
The chemical composition of a suitable base material of the present invention is, in mass%, C: 0.1% or less, Si: 0.4 to 1.5%, Mn: 8 to 11%, Cr: 15 to 17%, Ni : 5 to 8%, Cu: 1 to 4% and N: 0.01 to 0.3%, with the balance being Fe and inevitable impurities.
次に、本発明の溶接継手の製造方法について説明する。
本発明の溶接継手は、後述する溶接材料を用いて製造することで、実現が容易になるが、本発明の溶接継手の製造方法は、当該製造条件に限定されるものでない。つまり、溶接する母鋼材、用いる溶接材料、さらに溶接条件を適切に選択することで、最終的な溶接継手における溶接金属の化学組成を本発明の範囲内に制御することができる。
以下、本発明の溶接継手を製造する際に用いる溶接材料の望ましい化学組成について説明する。
Next, the manufacturing method of the welded joint of this invention is demonstrated.
Although the realization of the welded joint of the present invention is facilitated by manufacturing using a welding material described later, the method for manufacturing the welded joint of the present invention is not limited to the manufacturing conditions. That is, the chemical composition of the weld metal in the final welded joint can be controlled within the scope of the present invention by appropriately selecting the base steel material to be welded, the welding material to be used, and the welding conditions.
Hereinafter, the desirable chemical composition of the welding material used when manufacturing the welded joint of the present invention will be described.
本発明の溶接継手を製造する際は、質量％で、Ｃ：０．１％以下、Ｓｉ：０．４〜１．５％、Ｍｎ：７．０〜１２％、Ｃｒ：１４〜２０％、Ｎｉ：５〜１２％、Ｃｕ：１〜４％およびＮ：０．０１〜０．４％を含有し、残部がＦｅおよび不可避的不純物である化学組成を有する溶接材料を用いることが望ましい。
以下に、溶接材料の化学組成について説明する。
When producing the welded joint of the present invention, the mass% is C: 0.1% or less, Si: 0.4 to 1.5%, Mn: 7.0 to 12%, Cr: 14 to 20%, It is desirable to use a welding material having a chemical composition containing Ni: 5 to 12%, Cu: 1 to 4%, and N: 0.01 to 0.4%, the balance being Fe and inevitable impurities.
Below, the chemical composition of a welding material is demonstrated.
＜Ｃ：０．１％以下＞
Ｃは本発明の溶接継手において、オーステナイト相の安定化に有効な元素である。さらに、溶接金属のＮｉｅｑを高め、δフェライト相の球状化を促進するのに有効な元素であるが、過度の添加は、溶接時にＭ２３Ｃ６型炭化物が析出し、水素環境下での延性を著しく低下させるため、溶接材料中のＣ量の上限を０．１％とする必要がある。好ましくは、Ｃ量は０．０８％以下とする。一方、溶接材料中のＣの含有量に特に下限を設ける必要はないが、極端な低下は製造コストの著しい上昇を招くため、望ましい下限は０．００２％である。より好ましくは０．０４％以上である。
<C: 0.1% or less>
C is an element effective in stabilizing the austenite phase in the welded joint of the present invention. Furthermore, it is an element effective for increasing the Nieq of the weld metal and promoting the spheroidization of the δ ferrite phase. However, excessive addition causes precipitation of M 23 C 6 type carbides during welding, resulting in ductility in a hydrogen environment. Therefore, the upper limit of the C content in the welding material needs to be 0.1%. Preferably, the C amount is 0.08% or less. On the other hand, it is not necessary to set a lower limit in particular in the content of C in the welding material. However, since an extreme decrease causes a significant increase in manufacturing cost, the desirable lower limit is 0.002%. More preferably, it is 0.04% or more.
＜Ｓｉ：０．４〜１．５％＞
Ｓｉは、本発明の溶接材料を使用した溶接継手において、常温から極低温環境下でオーステナイト相の安定度を高めて耐水素脆化特性を向上させるために有効な元素である。さらに、継手強度を上昇させる上でも効果的な固溶強化元素である。これら効果を発現させるため、溶接材料中のＳｉ量の下限は０．４％とする。好ましくは０．５％以上である。
一方、Ｓｉの過度の添加はＣｒｅｑを増加させ、溶接部に生成するδフェライト相の針状化を促進する。さらに、シグマ相などの金属間化合物の生成を助長し、熱間加工性や靭性の低下を招く可能性がある。そのため、溶接材料中のＳｉ量の上限を１．５％とする。好ましくは、１．０％以下の範囲である。
<Si: 0.4 to 1.5%>
Si is an effective element for increasing the stability of the austenite phase and improving the hydrogen embrittlement resistance in a welded joint using the welding material of the present invention in a normal temperature to a very low temperature environment. Furthermore, it is a solid solution strengthening element that is also effective in increasing joint strength. In order to express these effects, the lower limit of the amount of Si in the welding material is 0.4%. Preferably it is 0.5% or more.
On the other hand, excessive addition of Si increases Creq and promotes acicularization of the δ ferrite phase generated in the weld. Furthermore, it may promote the formation of intermetallic compounds such as sigma phase, and may cause a decrease in hot workability and toughness. Therefore, the upper limit of the amount of Si in the welding material is 1.5%. Preferably, it is 1.0% or less of range.
＜Ｍｎ：７．０〜１２％＞
Ｍｎは、常温から極低温環境下でオーステナイト安定度を高めて耐水素脆化特性を向上させ、Ｎｉ含有量の低減に有効な元素である。さらに、溶接部のＮｉｅｑを高め、δフェライト相の球状化を促進するのに有効な元素でもある。また、本発明の目的である経済性を向上させるためには、Ｎｉ含有量をＳＵＳ３０４鋼におけるＮｉ含有量以下、つまり８％以下と低減する必要がある。このＮｉの添加量の減少分を補い、かつ上記効果を十分に得るためには、溶接材料中のＭｎ量の下限を７．０％とする必要がある。好ましくは、８．５％以上である。一方、本発明の溶接継手は高Ｍｎが特徴である。溶接時の希釈を考慮し、溶接継手よりもＭｎ含有量を高めておくことが好ましい。ただし、Ｍｎの過剰添加は、溶接部でのＳ系介在物の増加をもたらし延性の低下を招くため、溶接材料におけるＭｎ量の上限を１２％とする。好ましくは、１０％以下の範囲である。
<Mn: 7.0 to 12%>
Mn is an element effective in increasing the austenite stability from room temperature to a cryogenic environment to improve hydrogen embrittlement resistance and reducing the Ni content. Furthermore, it is an element effective for increasing the Nieq of the weld and promoting the spheroidization of the δ ferrite phase. Moreover, in order to improve the economic efficiency which is the object of the present invention, it is necessary to reduce the Ni content to be equal to or less than the Ni content in SUS304 steel, that is, 8% or less. In order to compensate for the decrease in the amount of Ni added and to sufficiently obtain the above effect, the lower limit of the amount of Mn in the welding material needs to be 7.0%. Preferably, it is 8.5% or more. On the other hand, the welded joint of the present invention is characterized by high Mn. In consideration of dilution during welding, it is preferable to increase the Mn content more than the welded joint. However, excessive addition of Mn causes an increase in S-based inclusions in the weld and causes a reduction in ductility, so the upper limit of the amount of Mn in the welding material is set to 12%. Preferably, it is 10% or less.
＜Ｃｒ：１４〜２０％＞
Ｃｒは、ステンレス鋼に要求される耐食性を得るために必須の合金元素である。また、Ｃｒは溶接部の加工時に溶接継手に生成する加工誘起マルテンサイト相の延性改善に有効な元素である。この効果を十分に得るためには、溶接材料中のＣｒ量の下限を１４％とする必要がある。好ましくは、１５％以上である。一方、Ｃｒは溶接部のδフェライト相の生成と針状化を促進し、高圧水素ガスおよび液体水素中での耐水素脆化特性に悪影響をおよぼす。さらに、Ｃｒの過剰の添加は、ＣｒＮ、Ｃｒ２Ｎ等の窒化物やＭ２３Ｃ６型炭化物を生成し、溶接部の延性、靭性、耐食性に悪影響をおよぼす。そのため、溶接材料中のＣｒ量の上限を２０％とする。好ましくは、１７％以下の範囲である。
<Cr: 14 to 20%>
Cr is an alloy element essential for obtaining the corrosion resistance required for stainless steel. Cr is an effective element for improving the ductility of the work-induced martensite phase generated in the weld joint during the processing of the weld. In order to sufficiently obtain this effect, the lower limit of the amount of Cr in the welding material needs to be 14%. Preferably, it is 15% or more. On the other hand, Cr promotes the formation and acicularization of the δ ferrite phase in the weld zone and adversely affects the resistance to hydrogen embrittlement in high-pressure hydrogen gas and liquid hydrogen. Furthermore, excessive addition of Cr produces nitrides such as CrN and Cr 2 N and M 23 C 6 type carbides, and adversely affects the ductility, toughness and corrosion resistance of the weld. Therefore, the upper limit of the amount of Cr in the welding material is set to 20%. Preferably, it is 17% or less.
＜Ｎｉ：５〜１２％＞
Ｎｉは、既存のＳＵＳ３１６鋼でも周知のように、耐水素脆化特性を改善させるのに極めて有効な元素であり、さらに、溶接部でのＮｉｅｑを高めてδフェライト相の球状化を促進させるのに有効な元素である。これら効果を十分に得るためには、溶接材料中のＮｉを５％以上含有する必要がある。好ましくは、５．５％以上である。一方、Ｎｉの過度の含有は材料コストの増加を招くため、材料コスト低減の観点から、溶接材料中のＮｉの上限は１２％とする。好ましくは、８％以下である。
<Ni: 5-12%>
As is well known in existing SUS316 steel, Ni is an extremely effective element for improving the hydrogen embrittlement resistance. Further, Nieq at the weld is increased to promote the spheroidization of the δ ferrite phase. Is an effective element. In order to obtain these effects sufficiently, it is necessary to contain 5% or more of Ni in the welding material. Preferably, it is 5.5% or more. On the other hand, since excessive Ni content causes an increase in material cost, the upper limit of Ni in the welding material is set to 12% from the viewpoint of reducing the material cost. Preferably, it is 8% or less.
＜Ｃｕ：１〜４％＞
Ｃｕは、ＭｎやＮｉと同様にオーステナイト相を安定化させる元素であり、本発明が目標とする溶接継手の耐水素脆化特性の向上に有効な元素である。また、ＣｕはＭｎとの相乗効果によって、常温から極低温にかけて、変形組織を水素の影響を受けにくい組織に変化させることで、溶接継手の加工による特性劣化を抑制することができる。さらに、Ｃｕは溶接部のＮｉｅｑを増加させ、δフェライト相の球状化を促進させる。これら効果を得るため、溶接材料中のＣｕの下限は１％とする。好ましくは、１．５％以上である。一方、Ｃｕの過度の添加は、鋼中でのＣｕの析出を促進させ、上記効果が飽和する。さらに、製鋼時のＣｕ汚染や熱間加工性を低下させる可能性がある。そのため、Ｃｕの上限は４％とする。好ましくは、上記効果と製造性を両立させる観点から、３％以下の範囲である。
<Cu: 1-4%>
Cu, like Mn and Ni, is an element that stabilizes the austenite phase, and is an effective element for improving the hydrogen embrittlement resistance of the welded joint targeted by the present invention. Moreover, Cu can suppress the characteristic deterioration by the process of a welded joint by changing a deformation | transformation structure | tissue into the structure | tissue which is hard to receive the influence of hydrogen from normal temperature to very low temperature by a synergistic effect with Mn. Furthermore, Cu increases the Nieq of the weld and promotes the spheroidization of the δ ferrite phase. In order to obtain these effects, the lower limit of Cu in the welding material is 1%. Preferably, it is 1.5% or more. On the other hand, excessive addition of Cu promotes the precipitation of Cu in the steel, and the above effect is saturated. Furthermore, there is a possibility that Cu contamination and hot workability at the time of steelmaking are lowered. Therefore, the upper limit of Cu is 4%. Preferably, it is 3% or less from the viewpoint of achieving both the above effects and manufacturability.
＜Ｎ：０．０１〜０．４％＞
Ｎは、オーステナイト相の安定化に有効な元素である。さらに、溶接部のＮｉｅｑを増加させ、δフェライト相の球状化を促進するのに有効な元素であり、これらの効果を得るために、溶接材料中のＮ量を０．０１％以上とする。Ｎを０．０１％未満に減らすことは、製鋼コストの負担増加にも繋がる。また、Ｎは固溶強化により鋼の０．２％耐力や引張強度を向上させることが知られており、溶接部の強度向上に有効な元素である。この強度上昇効果を得る場合、０．１％以上含有させることが好ましい。溶接時の希釈を考慮し、溶接継手よりもＮ含有量を高めておくことが好ましい。一方、０．４％を超えるＮの添加は工業的な通常の溶製プロセスにおいて困難であり、製鋼コストの大幅な上昇を招くことから、溶接材料中のＮ量は０．４％以下とする。
<N: 0.01 to 0.4%>
N is an element effective for stabilizing the austenite phase. Furthermore, it is an element effective for increasing the Nieq of the welded portion and promoting the spheroidization of the δ ferrite phase. In order to obtain these effects, the N content in the welding material is set to 0.01% or more. Reducing N to less than 0.01% also leads to an increase in steelmaking cost burden. Further, N is known to improve the 0.2% proof stress and tensile strength of steel by solid solution strengthening, and is an element effective for improving the strength of the weld. When obtaining this strength increasing effect, it is preferable to contain 0.1% or more. In consideration of dilution during welding, it is preferable that the N content is higher than that of the welded joint. On the other hand, addition of N exceeding 0.4% is difficult in a normal industrial melting process and causes a significant increase in steelmaking cost. Therefore, the N content in the welding material is set to 0.4% or less. .
以上説明した化学組成を有する溶接材料によって、上述した化学組成及び所望の形態及び体積率であるδフェライト相を備えた溶接金属を得るためには、ガスタングステンアーク溶接（ＴＩＧ溶接）方法を用いて溶接を施すことが好ましい。 In order to obtain a weld metal having the above-described chemical composition and the δ ferrite phase having the desired form and volume ratio by the welding material having the chemical composition described above, a gas tungsten arc welding (TIG welding) method is used. It is preferable to perform welding.
また、本発明の溶接継手が適用される母鋼材、つまり溶接される鋼材については、特に限定されるものではないが、溶接部の耐水素性を高めるという本発明の目的からして、母鋼材についても耐水素性が高い材料（例えば、オーステナイト系高Ｍｎステンレス鋼の母材）であることが好ましい。なお、このような母鋼材と併せて、上記溶接材料と用いることで、より一層安定的に、上述した、化学組成、所望の形態及び体積率であるδフェライト相を備えた溶接金属を得ることが可能となる。 Further, the base steel material to which the welded joint of the present invention is applied, that is, the steel material to be welded is not particularly limited, but for the purpose of the present invention to improve the hydrogen resistance of the welded portion, Is preferably a material having high hydrogen resistance (for example, a base material of austenitic high Mn stainless steel). In addition, by using with the above-mentioned welding material in combination with such a base steel material, it is possible to obtain a weld metal having the above-described chemical composition, desired form, and δ-ferrite phase having a volume ratio more stably. Is possible.
具体的な溶接条件については特に限定しないが、本発明の溶接継手において、溶接時の入熱量を大きくした場合、溶接終了後も溶接部が高温となり、δフェライト相が粗大化し、さらに、δフェライト相の球状化が阻害されてしまうおそれがある。そのため、上記の溶接金属の組織を得るためには、溶接時の入熱量を７．２ｋＪ／ｃｍ以下とすることが好ましい。 The specific welding conditions are not particularly limited, but in the welded joint of the present invention, when the heat input during welding is increased, the welded portion becomes high temperature after the end of welding, the δ ferrite phase becomes coarse, and δ ferrite The spheroidization of the phase may be hindered. Therefore, in order to obtain the above-described weld metal structure, the heat input during welding is preferably set to 7.2 kJ / cm or less.
また、ＴＩＧ溶接による溶接を行う場合、シールドガスとして、窒素ガスを用いることが好ましい。 Moreover, when welding by TIG welding, it is preferable to use nitrogen gas as shielding gas.
その他の製造条件（溶接条件）については、本発明の効果を損なわない範囲で適宜決定してよく、また、突合せ部の開先形状等も特に限定せずとも、本発明の効果を十分に享受できる。 Other manufacturing conditions (welding conditions) may be appropriately determined within a range that does not impair the effects of the present invention, and the effects of the present invention can be fully enjoyed even if the groove shape of the butted portion is not particularly limited. it can.
以下、実施例により本発明の効果を説明するが、本発明は、以下の実施例で用いた条件に限定されるものではない。 Hereinafter, the effects of the present invention will be described with reference to examples, but the present invention is not limited to the conditions used in the following examples.
表１の化学成分を有するステンレス鋼を溶製した後、熱間圧延、熱延板熱処理により、板厚１５ｍｍの熱延焼鈍板を母鋼材（母材）ａ、ｂ、ｃとして作製した。母鋼材ｂには、高強度化のため、意図的にＮを添加している。
表２の化学成分を有するステンレス鋼を溶製した後、熱間鍛造、熱処理、伸線加工により、直径３．２ｍｍの溶接材料を作製した。なお、Ｎｏ．６〜１６に示す溶接材料は、本発明の好適な範囲を満足しない化学成分としている。
After melting the stainless steel having chemical components shown in Table 1, hot-rolled annealed plates having a thickness of 15 mm were produced as base steel materials (base materials) a, b, and c by hot rolling and hot-rolled sheet heat treatment. N is intentionally added to the base steel material b for high strength.
After melting the stainless steel having the chemical components shown in Table 2, a welding material having a diameter of 3.2 mm was produced by hot forging, heat treatment, and wire drawing. In addition, No. The welding materials shown in 6 to 16 are chemical components that do not satisfy the preferred range of the present invention.
次に、得られた母鋼材に片側２０度のＶ開先を設け、同じ成分の母鋼材を突き合わせ、表２に示す溶接材料を母材と組み合わせて、開先内にＴＩＧ溶接にて８層溶接して、表３に示す溶接継手Ｗ１〜Ｗ２５を作製した。 Next, the obtained base steel is provided with a V groove of 20 degrees on one side, the base steel of the same component is abutted, the welding materials shown in Table 2 are combined with the base material, and eight layers are formed in the groove by TIG welding. Welded joints W1 to W25 shown in Table 3 were prepared by welding.
次に、溶接継手Ｗ１〜Ｗ２５におけるδフェライト相の体積率（％）、長径（ｍｍ）及びアスペクト比を求めた。
具体的には、まず、溶接継手Ｗ１〜Ｗ２５の溶接部から試料を５つ切り出した後、各試料においてフェライトメーター（株式会社フィッシャー・インスツルメンツ製）によりδフェライト相の体積率を測定した。次に、５つの試料それぞれから測定したδフェライト相の体積率の平均値を算出し、求めた平均値をその溶接継手のδフェライト相の体積率とした。
Next, the volume ratio (%), major axis (mm), and aspect ratio of the δ ferrite phase in the welded joints W1 to W25 were determined.
Specifically, first, five samples were cut out from the welded portions of the welded joints W1 to W25, and then the volume fraction of the δ ferrite phase was measured with a ferrite meter (manufactured by Fisher Instruments Co., Ltd.) in each sample. Next, the average value of the volume fraction of the δ ferrite phase measured from each of the five samples was calculated, and the obtained average value was taken as the volume fraction of the δ ferrite phase of the welded joint.
次に、δフェライト相体積率の測定後、前述のδフェライト相の体積率測定で使用した試料から光学顕微鏡観察用の試料を切り出した後、樹脂に埋め込んで、観察面を研磨・シュウ酸電解エッチングを行った。その後、光学顕微鏡を用い、観察視野において、δフェライト相の長径を計測し、その平均値を求めた。この際、倍率は２００倍とし、４５０μｍ×６００μｍの長方形の領域内でのδフェライトに対して測定を行った。なお、測定は５つの各樹脂埋め試料に対し３視野で実施し、計１５視野における測定結果の平均値をその溶接部のδフェライト相の長径と定めた。また、同時に測定視野内の各δフェライト相のアスペクト比を測定し、各測定結果の平均値を、その溶接部のδフェライト相のアスペクト比とした。
なお、観察視野において、連結したδフェライト相の数の割合が４割以上の場合、その組織のδフェライト相は針状であるとみなした。連結した針状δフェライト相のサイズ測定は困難であるため、表３において、測定結果は「−」と記載した。
Next, after measuring the volume ratio of the δ ferrite phase, a sample for optical microscope observation is cut out from the sample used in the volume ratio measurement of the δ ferrite phase described above, and then embedded in a resin, and the observation surface is polished / oxalic acid electrolysis Etching was performed. Thereafter, the major axis of the δ ferrite phase was measured in an observation field using an optical microscope, and the average value was obtained. At this time, the magnification was 200 times, and the measurement was performed on δ ferrite in a rectangular region of 450 μm × 600 μm. The measurement was carried out on three resin-filled samples in three fields of view, and the average value of the measurement results in a total of 15 fields was determined as the major axis of the δ ferrite phase of the weld. At the same time, the aspect ratio of each δ ferrite phase in the measurement field of view was measured, and the average value of each measurement result was taken as the aspect ratio of the δ ferrite phase of the weld.
In the observation field, when the ratio of the number of connected δ ferrite phases was 40% or more, the δ ferrite phase of the structure was considered to be acicular. Since it is difficult to measure the size of the connected acicular δ ferrite phase, in Table 3, the measurement result is described as “−”.
表３に溶接金属の化学組成、Ｃｒｅｑ／Ｎｉｅｑ、δフェライト相の体積率、長径長さ、アスペクト比、および溶接時の入熱量を示す。 Table 3 shows the chemical composition of the weld metal, Creq / Nieq, the volume fraction of the δ ferrite phase, the major axis length, the aspect ratio, and the heat input during welding.
上記の溶接継手Ｗ１〜Ｗ２５から、外径７ｍｍ、長さ３５ｍｍの平行部を持ち、標点間距離が２５ｍｍで、中央に幅６ｍｍの溶接金属を有する引張試験片を、その平行部がそれぞれ溶接線と直交する方向に採取した。この引張試験片Ｗ１〜Ｗ２５を用いて、１）大気中引張試験、２）高圧水素ガス中引張試験、３）液体水素中引張試験に供した。なお、比較のため、各母材からも上記同様の引張試験片を採取し、同様の試験１）〜３）を実施した。 From the above-mentioned welded joints W1 to W25, tensile test pieces having a parallel part with an outer diameter of 7 mm and a length of 35 mm, a distance between gauge points of 25 mm, and a weld metal with a width of 6 mm in the center are welded to the parallel parts. Samples were taken in the direction perpendicular to the line. The tensile test pieces W1 to W25 were used for 1) an atmospheric tensile test, 2) a high-pressure hydrogen gas tensile test, and 3) a liquid hydrogen tensile test. For comparison, the same tensile test pieces were collected from each base material, and the same tests 1) to 3) were performed.
１）大気中引張試験は、試験温度：常温、試験環境：大気、歪速度：８×１０−４／秒で実施し、０．２％耐力（０．２％ＰＳ）及び伸び（ＥＬ）を求めた。 1) The tensile test in air is performed at a test temperature: normal temperature, a test environment: air, and a strain rate: 8 × 10 −4 / sec, and 0.2% proof stress (0.2% PS) and elongation (EL) Asked.
２）高圧水素ガス中引張試験は、試験温度：常温、試験環境：４５ＭＰａ水素中、９０ＭＰａ水素中、１２０ＭＰａ水素中、歪速度：８×１０−５／秒で実施しＥＬを求めた。
溶接部（溶接金属）における高圧水素ガス中での耐水素脆化特性は、（高圧水素ガス中での伸び（ＥＬ））／（大気中での伸び（ＥＬ））の値により評価した。なお、４５ＭＰａ水素中、９０ＭＰａ水素中、１２０ＭＰａ水素中のそれぞれの（高圧水素ガス中での伸び）／（大気中での伸び）は、表４、５においてＥＬ：４５ＭＰａ、ＥＬ：９０ＭＰａ、ＥＬ：１２０ＭＰａと表記し、これら値が０．９（９０％）以上のものを合格とした。
2) Tensile test in high-pressure hydrogen gas was performed at test temperature: normal temperature, test environment: 45 MPa hydrogen, 90 MPa hydrogen, 120 MPa hydrogen, strain rate: 8 × 10 −5 / sec, and EL was determined.
The resistance to hydrogen embrittlement in high-pressure hydrogen gas at the weld zone (welded metal) was evaluated by the value of (elongation in high-pressure hydrogen gas (EL)) / (elongation in the atmosphere (EL)). In Tables 4 and 5, the (elongation in high-pressure hydrogen gas) / (elongation in the atmosphere) in 45 MPa hydrogen, 90 MPa hydrogen, and 120 MPa hydrogen are as follows: EL: 45 MPa, EL: 90 MPa, EL: It was described as 120 MPa, and those having a value of 0.9 (90%) or more were regarded as acceptable.
３）液体水素中の引張試験は、０．２％耐力まで１．７×１０−４／秒、それ以降は６．８×１０−４／秒で実施し、ＥＬ（ＬＨ２）を求めた。
溶接部（溶接金属）における液体水素中での耐水素脆化特性は、（溶接金属の伸び）／（母鋼材の伸び）の値により評価した。なお、（溶接金属の伸び）／（母材の伸び）は、上記の同一の形状での引張試験において、試験片平行部に溶接部を有する試験片での伸び（溶接金属の伸び）と、母鋼材から作成した試験片での伸び（母材の伸び）との比である。
（溶接金属の伸び）／（母鋼材の伸び）はＥＬ：ＬＨ２と表記し、この値が０．９（９０％）以上のものを合格とした。
母鋼材の評価結果を表４に、溶接部の評価結果を表５に示した。
3) The tensile test in liquid hydrogen was carried out at 1.7 × 10 −4 / sec up to 0.2% proof stress, and thereafter at 6.8 × 10 −4 / sec, and EL (LH 2 ) was determined. .
The resistance to hydrogen embrittlement in liquid hydrogen in the weld zone (welded metal) was evaluated by the value of (elongation of weld metal) / (elongation of base metal). In addition, (elongation of the weld metal) / (elongation of the base material) is the elongation (the elongation of the weld metal) in the test piece having the welded portion in the test piece parallel portion in the tensile test with the same shape as described above. It is a ratio to the elongation (elongation of the base material) of a test piece made from the base steel material.
(Elongation of weld metal) / (Elongation of base steel material) is expressed as EL: LH 2, and a value of 0.9 (90%) or more is regarded as acceptable.
Table 4 shows the evaluation results of the base steel, and Table 5 shows the evaluation results of the welds.
発明例である試験片Ｗ１〜Ｗ１１は、本発明の溶接金属の化学組成、溶接部の金属組織が規定の範囲を満足するものであった。さらに、試験片Ｗ１〜Ｗ１１はすべて溶接時の入熱量を７．２ｋＪ／ｃｍ以下とした例である。その結果、高圧水素ガス環境および液体水素環境において、延性が低下しない、すなわち、非常に優れた耐水素脆化特性を示すことが確認できた。 Test pieces W1 to W11, which are examples of the invention, satisfy the specified ranges in the chemical composition of the weld metal of the present invention and the metal structure of the weld. Further, all the test pieces W1 to W11 are examples in which the heat input during welding is set to 7.2 kJ / cm or less. As a result, it was confirmed that the ductility does not decrease in a high-pressure hydrogen gas environment and a liquid hydrogen environment, that is, it exhibits extremely excellent hydrogen embrittlement resistance.
試験片Ｗ１２〜１８は溶接金属が規定の成分範囲を満足できず、本発明で規定する溶接金属組織を得ることができなかった結果、延性の低下に至った。 As for test pieces W12 to 18, the weld metal could not satisfy the prescribed component range, and the weld metal structure prescribed in the present invention could not be obtained, resulting in a decrease in ductility.
試験片Ｗ１９、２０は溶接金属が規定の成分範囲を満足しているが、Ｃｒｅｑ／Ｎｉｅｑが１．１０以上となっているため、本発明で規定する溶接金属組織を得ることができなかった結果、高圧水素ガス環境および液体水素環境において延性が低下した。 Although the test pieces W19 and 20 satisfy the specified component range of the weld metal, Creq / Nieq is 1.10 or more, and thus the weld metal structure specified in the present invention cannot be obtained. The ductility decreased in high-pressure hydrogen gas environment and liquid hydrogen environment.
試験片２１は溶接金属のＮ量が規定の上限を上回った。その結果、金属組織中にＣｒ系窒化物が析出することで高圧水素ガス環境および液体水素環境における延性低下が助長されてしまった。 In the test piece 21, the N amount of the weld metal exceeded the prescribed upper limit. As a result, the precipitation of Cr-based nitrides in the metal structure has promoted a reduction in ductility in a high-pressure hydrogen gas environment and a liquid hydrogen environment.
試験片２２は溶接金属のＣｕ量が規定の上限を上回った。試験片２１は溶接金属のＮ量が規定の上限を上回った。その結果、金属組織中へのＣｕ析出および凝固割れに起因した欠陥生成により、高圧水素ガス環境および液体水素環境における延性低下が助長されてしまった。 In the test piece 22, the Cu amount of the weld metal exceeded the specified upper limit. In the test piece 21, the N amount of the weld metal exceeded the prescribed upper limit. As a result, the generation of defects due to Cu precipitation and solidification cracking in the metal structure has promoted a reduction in ductility in a high-pressure hydrogen gas environment and a liquid hydrogen environment.
発明例である試験片Ｗ２３、２４は溶接金属の成分、およびＣｒｅｑ／Ｎｉｅｑが規定の範囲を満足しているため、高圧水素ガス環境および液体水素環境において延性の低下はごくわずかであり、良好な耐水素脆化特性を示すことが確認できた。 Since the test pieces W23 and 24, which are examples of the invention, satisfy the prescribed range of the weld metal component and Creq / Nieq, the ductility degradation is negligible in the high-pressure hydrogen gas environment and the liquid hydrogen environment. It was confirmed that hydrogen embrittlement resistance was exhibited.
試験片Ｗ２５は母材と溶接材料の成分範囲が本発明の望ましい範囲を満たしていないが、本発明の溶接金属の化学組成、溶接部の金属組織が規定の範囲を満足している。さらに、入熱量を７．２ｋＪ／ｃｍ以下として溶接している。その結果、高圧水素ガス環境および液体水素環境において、延性が低下しない、すなわち、非常に優れた耐水素脆化特性を示すことが確認できた。 In the test piece W25, the component range of the base material and the welding material does not satisfy the desirable range of the present invention, but the chemical composition of the weld metal of the present invention and the metal structure of the welded portion satisfy the specified range. Furthermore, welding is performed with a heat input of 7.2 kJ / cm or less. As a result, it was confirmed that the ductility does not decrease in a high-pressure hydrogen gas environment and a liquid hydrogen environment, that is, it exhibits extremely excellent hydrogen embrittlement resistance.
Claims (4)
前記溶接金属の化学組成が、質量％でＣ：０．２％以下、Ｓｉ：２．０％以下、Ｍｎ：５．５〜１４．５％、Ｃｒ：１３．５〜２２．０％、Ｎｉ：３．５〜１２．５％、Ｃｕ：１〜５％およびＮ：０．０１〜０．４％を含有し、残部がＦｅおよび不可避的不純物であり、以下の式（１）及び（２）で算出されるＣｒｅｑとＮｉｅｑの比（Ｃｒｅｑ／Ｎｉｅｑ）が１．１０以下であり、前記溶接金属中のδフェライト相の体積率が１０％以下であり、前記δフェライト相の長径の平均が０．０５ｍｍ以下であり、かつ前記δフェライト相の形態が、（前記δフェライト相の短径）／（前記フェライト相の長径）で表されるアスペクト比が０．３以上である球状であることを特徴とする高圧水素ガスおよび液体水素用オーステナイト系高Ｍｎステンレス鋼溶接継手。
Ｃｒｅｑ＝［Ｃｒ］＋１．５［Ｓｉ］ ・・・ （１）
Ｎｉｅｑ＝［Ｎｉ］＋０．５［Ｍｎ］＋［Ｃｕ］＋３０（［Ｃ］＋［Ｎ］） ・・・（２）
ここで、［Ｃｒ］、［Ｓｉ］、［Ｎｉ］、［Ｍｎ］、［Ｃｕ］、［Ｃ］、［Ｎ］はそれぞれの元素の質量％を示す。 A weld joint made of austenitic stainless steel base metal and weld metal,
The chemical composition of the weld metal is, by mass%, C: 0.2% or less, Si: 2.0% or less, Mn: 5.5 to 14.5%, Cr: 13.5 to 22.0%, Ni : 3.5 to 12.5%, Cu: 1 to 5% and N: 0.01 to 0.4%, the balance being Fe and inevitable impurities, the following formulas (1) and (2 ) Creq and Nieq ratio calculated by (Creq / Nieq) is 1.10 or less, wherein Ri der volume of not more than 10% of δ ferrite phase in the weld metal, the average of major axis of the δ ferrite phase Is 0.05 mm or less, and the form of the δ ferrite phase is a spherical shape having an aspect ratio expressed by (minor axis of the δ ferrite phase) / (major axis of the ferrite phase) of 0.3 or more. Austenitic high Mn stainless steel for high-pressure hydrogen gas and liquid hydrogen Scan steel welded joints.
Creq = [Cr] +1.5 [Si] (1)
Nieq = [Ni] +0.5 [Mn] + [Cu] +30 ([C] + [N]) (2)
Here, [Cr], [Si], [Ni], [Mn], [Cu], [C], and [N] indicate mass% of each element.
オーステナイト系ステンレス鋼の母材に対して溶接する際、
溶接金属を、質量％でＣ：０．１％以下、Ｓｉ：０．４〜１．５％、Ｍｎ：７〜１１％、Ｃｒ：１５〜２０％、Ｎｉ：５〜１２％、Ｃｕ：１〜４％およびＮ：０．０１〜０．３％を含有し、残部がＦｅおよび不可避的不純物であり、かつ以下の式（１）及び（２）で算出されるＣｒｅｑとＮｉｅｑの比（Ｃｒｅｑ／Ｎｉｅｑ）が１．１０以下を満足する化学組成とし、
入熱量を７．２ｋＪ／ｃｍ以下として溶接することを特徴とする、高圧水素ガスおよび液体水素用オーステナイト系高Ｍｎステンレス鋼溶接継手の製造方法。
Ｃｒｅｑ＝［Ｃｒ］＋１．５［Ｓｉ］ ・・・ （１）
Ｎｉｅｑ＝［Ｎｉ］＋０．５［Ｍｎ］＋［Ｃｕ］＋３０（［Ｃ］＋［Ｎ］） ・・・（２）
ここで、［Ｃｒ］、［Ｓｉ］、［Ｎｉ］、［Ｍｎ］、［Ｃｕ］、［Ｃ］、［Ｎ］はそれぞれの元素の質量％を示す。 A method for producing an austenitic high Mn stainless steel welded joint for high-pressure hydrogen gas and liquid hydrogen according to claim 1 or 2 ,
When welding to austenitic stainless steel base metal,
Weld metal in mass% C: 0.1% or less, Si: 0.4-1.5%, Mn: 7-11%, Cr: 15-20%, Ni: 5-12%, Cu: 1 -4% and N: 0.01 to 0.3%, the balance being Fe and inevitable impurities, and the ratio of Creq to Nieq calculated by the following formulas (1) and (2) (Creq / Nieq) has a chemical composition satisfying 1.10 or less ,
A method for producing an austenitic high Mn stainless steel welded joint for high-pressure hydrogen gas and liquid hydrogen, wherein welding is performed with a heat input of 7.2 kJ / cm or less .
Creq = [Cr] +1.5 [Si] (1)
Nieq = [Ni] +0.5 [Mn] + [Cu] +30 ([C] + [N]) (2)
Here, [Cr], [Si], [Ni], [Mn], [Cu], [C], and [N] indicate mass% of each element.
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