JP5953647B2 - Laser welded joint of steel material with excellent toughness of weld metal part and manufacturing method of laser beam welded joint of steel material with excellent toughness of weld metal part - Google Patents
Laser welded joint of steel material with excellent toughness of weld metal part and manufacturing method of laser beam welded joint of steel material with excellent toughness of weld metal part Download PDFInfo
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本発明は、鋼材のレーザビーム溶接継手に関し、特に引張強度が７８０ＭＰａ以上の鋼材で溶接金属部の引張強度が７８０ＭＰａ以上、且つ靭性に優れたものに関する。 The present invention relates to a laser beam welded joint of steel, and particularly relates to a steel material having a tensile strength of 780 MPa or more and a weld metal part having a tensile strength of 780 MPa or more and excellent toughness.
レーザビーム溶接は、エネルギー密度が高いことから深溶け込みの高速溶接が可能で、高能率な溶接方法として期待されている。また、極めて局所的な溶融となるため母材への熱影響も小さく、歪や変形が小さい高品質な溶接継手を得ることができる。 Laser beam welding is expected to be a high-efficiency welding method because of its high energy density and capable of deep penetration and high-speed welding. Moreover, since it becomes very local melting, the heat influence on a base material is also small, and a high quality welded joint with little distortion and deformation can be obtained.
このため、自動車など薄板分野においては、既に部材や車体の組立工程に実用化が進んでおり、多くの適用実績がある。一方、厚板分野においても、近年、高出力で光ファイバー伝送が可能な高性能のレーザビーム溶接機が市販されるようになり、溶接可能な板厚が増大したことから実用化に向けた本格的な検討がなされるようになった。 For this reason, in the field of thin plates such as automobiles, practical application has already progressed in the assembly process of members and vehicle bodies, and there are many application results. On the other hand, in the field of thick plates, high-performance laser beam welders capable of transmitting optical fibers with high output have been put on the market in recent years. Consideration has come to be made.
しかしながら、レーザビーム溶接は従来アーク溶接に比べて小入熱溶接であるため溶接後の冷却速度が速く、その結果、溶接金属部や熱影響部が硬化して靭性が劣化する場合が多いという問題がある。 However, since laser beam welding is a small heat input welding compared to conventional arc welding, the cooling rate after welding is fast, and as a result, the weld metal part and the heat-affected part often harden and deteriorate toughness. There is.
このような問題に対して、例えば特許文献１では、鋼材の化学組成やＡｌ含有量を調整すると共に、酸化性雰囲気中で溶接することにより、レーザビーム溶接金属中の酸素含有量やＡｌ／Ｏ比を制御し、レーザビーム溶接金属組織をアシキュラーフェライトの発達した組織とすることで高靭化を図る技術が開示されている。 For such a problem, for example, in Patent Document 1, by adjusting the chemical composition and Al content of a steel material and welding in an oxidizing atmosphere, the oxygen content and Al / O in the laser beam weld metal are adjusted. A technique for increasing the toughness by controlling the ratio and making the laser beam weld metal structure a structure in which acicular ferrite is developed is disclosed.
特許文献２では、鋼材および溶接材料のＴｉ、Ｂ含有量および炭素当量をそれぞれ規定すると共に、酸素供給ガスを含有するシールドガスを用いて溶接することにより、レーザビーム溶接金属をアシキュラーフェライト主体の組織にして、溶接金属部と熱影響部の高靭化を図る技術が開示されている。 In Patent Document 2, the Ti and B contents and the carbon equivalent of the steel material and the welding material are respectively defined, and the laser beam welding metal is mainly composed of acicular ferrite by welding using a shielding gas containing an oxygen supply gas. A technique for making the weld metal part and the heat-affected part tougher in the structure is disclosed.
特許文献３では、鋼材の化学組成を選択すると共に、最適なシールドガス雰囲気下でレーザビーム溶接することにより、溶接金属中の介在物組成や酸素、Ａｌ、Ｔｉ含有量のバランスを規定範囲に制御し、その結果、レーザビーム溶接金属組織のアシキュラーフェライト化を確実に実現させることで溶接金属部の高靭化を図る技術が開示されている。 In Patent Document 3, the chemical composition of the steel material is selected, and the balance of the inclusion composition and oxygen, Al, Ti content in the weld metal is controlled within the specified range by laser beam welding in an optimum shielding gas atmosphere. As a result, there has been disclosed a technique for increasing the toughness of the weld metal part by reliably realizing the acicular ferrite of the laser beam weld metal structure.
特許文献４では、鋼材の化学組成や焼入臨界直径ＤＩを調整することで、レーザビーム溶接熱影響部の加熱オーステナイト粒径や組織に占めるマルテンサイトの割合を規定範囲に制御し、その結果、レーザビーム溶接熱影響部の高靭化を図る技術が開示されている。 In Patent Document 4, by adjusting the chemical composition of steel and the critical quenching diameter DI, the heating austenite particle size of the laser beam welding heat-affected zone and the ratio of martensite in the structure are controlled within a specified range. A technique for increasing the toughness of a laser beam welding heat-affected zone is disclosed.
特許文献５では、鋼材の化学組成や炭素当量を調整することで、レーザビーム溶接金属部のオーステナイト粒径や組織に占めるマルテンサイトの割合を規定範囲に制御し、その結果、レーザビーム溶接金属部と熱影響部の高靭化を図る技術が開示されている。 In Patent Document 5, by adjusting the chemical composition and carbon equivalent of the steel material, the austenite grain size of the laser beam weld metal part and the ratio of martensite in the structure are controlled within a specified range. As a result, the laser beam weld metal part And a technology for increasing the toughness of the heat-affected zone.
しかし、特許文献１では炭素当量を０．１７〜０．３５％に、特許文献２では炭素当量を０．１７〜０．４２％にそれぞれ規定されていることから、その適用できる鋼材の強度レベルは４９０ＭＰａあるいは５９０ＭＰａ級を対象としたものである。 However, since the carbon equivalent is defined as 0.17 to 0.35% in Patent Document 1 and the carbon equivalent is defined as 0.17 to 0.42% in Patent Document 2, the applicable steel strength level can be applied. Is intended for the 490 MPa or 590 MPa class.
特許文献３で提案された手法は、レーザビーム溶接金属組織のアシキュラーフェライト面積率を８０％以上にすることで高靭化を図ったものであり、その適用できる鋼材の強度レベルは４９０ＭＰａ級が限界である。 The technique proposed in Patent Document 3 is to increase the toughness by making the acicular ferrite area ratio of the laser beam weld metal structure 80% or more, and the applicable steel material has a strength level of 490 MPa class. It is a limit.
特許文献４および特許文献５では、鋼材の強度レベルが５９０ＭＰａあるいは７８０ＭＰａ級といった高強度鋼を対象としたもので、ミクロ組織をマルテンサイト化することで高靭化を図っている。 In patent document 4 and patent document 5, the strength level of steel materials is intended for high-strength steel having a level of 590 MPa or 780 MPa, and the toughening is achieved by martensifying the microstructure.
しかしながら、特許文献４で提案された手法は、レーザビーム溶接熱影響部の靭性改善を図ったものであり、レーザビーム溶接金属部の靭性向上に関しては考慮されていない。また特許文献５で提案された手法は、レーザビーム溶接金属部の靭性についても考慮されているが、レーザビーム溶接金属の化学組成についての明記はなく、例えばフィラーワイヤなどを用いた場合にその効果が得られるかは疑問である。 However, the technique proposed in Patent Document 4 is intended to improve the toughness of the laser beam welding heat-affected zone, and does not take into account the improvement of the toughness of the laser beam weld metal. The technique proposed in Patent Document 5 also considers the toughness of the laser beam weld metal part, but there is no specification about the chemical composition of the laser beam weld metal, and the effect is obtained when, for example, a filler wire is used. It is doubtful that can be obtained.
そこで、本発明は、上記した従来技術の問題点を鑑みて、引張強度が７８０ＭＰａ以上の高強度鋼において、溶接金属部の靭性に優れたレーザビーム溶接継手およびその製造方法を提案することを目的とする。 Accordingly, in view of the above-described problems of the prior art, the present invention aims to propose a laser beam welded joint excellent in toughness of a weld metal part in a high strength steel having a tensile strength of 780 MPa or more and a method for manufacturing the same. And
本発明者らは、上記課題を解決するために、引張強度が７８０ＭＰａレベルの高強度鋼におけるレーザビーム溶接金属部の靭性におよぼす溶接金属の化学組成やミクロ組織について詳細な調査を行った。 In order to solve the above-mentioned problems, the present inventors conducted a detailed investigation on the chemical composition and microstructure of the weld metal affecting the toughness of the laser beam weld metal part in high-strength steel having a tensile strength of 780 MPa.
その結果、レーザビーム溶接金属部の靭性は、マトリックス組織中に微細なアシキュラーフェライト相をある割合以上含んだ組織を呈する場合に良好であった。従来より、微細なアシキュラーフェライトはＴｉ系酸化物を核生成サイトとして形成されることが知られており、７８０ＭＰａレベルの高強度鋼のレーザビーム溶接金属においても酸素量やＴｉ含有量などを適正に制御することで高靭化が達成されることを知見した。 As a result, the toughness of the laser beam welded metal part was good when the matrix structure exhibited a structure containing a certain proportion of fine acicular ferrite phases. Conventionally, it has been known that fine acicular ferrite is formed by using Ti-based oxides as nucleation sites. Even in laser beam weld metal of 780 MPa level high-strength steel, oxygen content and Ti content are appropriate. It has been found that high toughness can be achieved by controlling to a low level.
また、このような靭性に良好な微細アシキュラーフェライトを多く含んだミクロ組織は、酸素供給ガスを含んだシールドガス中でレーザビーム溶接を行った場合に得られ、酸素供給ガスを含まない不活性ガスをシールドガスに用いた場合には得られないことも判明した。すなわち、本発明は、
１．鋼材のレーザビーム溶接継手であって、溶接金属が、ｍａｓｓ％で、Ｃ：０．０２〜０．１４％、Ｔｉ：０．００６〜０．０５％、Ａｌ：０．０２％以下、Ｂ：０．００１％以下、Ｏ：０．０２〜０．０５％、下記（１）式で定義されるＣｅｑが０．３３〜０．５３％の組成と、面積率で４０％以上のアシキュラーフェライト相を含むミクロ組織を有することを特徴とする溶接金属部の靭性に優れたレーザビーム溶接継手。
Ｃｅｑ＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４
（１）
ここで、Ｃｅｑ：炭素当量（ｍａｓｓ％）
Ｃ、Ｍｎ、Ｓｉ、Ｎｉ、Ｃｒ、Ｍｏ、Ｖ：各合金元素の含有量（ｍａｓｓ％）
２．レーザビーム溶接のシールドガスとして酸素供給ガスを含有するガスを用いたことを特徴とする１記載の溶接金属部の靭性に優れたレーザビーム溶接継手。
In addition, a microstructure containing a large amount of fine acicular ferrite with good toughness is obtained when laser beam welding is performed in a shielding gas containing an oxygen supply gas, and is inert without oxygen supply gas. It has also been found that gas cannot be obtained when used as shielding gas. That is, the present invention
1. This is a laser beam welded joint of steel, and the weld metal is mass%, C: 0.02 to 0.14%, Ti: 0.006 to 0.05%, Al: 0.02% or less, B: 0.001% or less, O: 0.02 to 0.05%, Ceq defined by the following formula (1) is 0.33 to 0.53% and an acicular ferrite having an area ratio of 40% or more A laser beam welded joint excellent in toughness of a weld metal part characterized by having a microstructure including a phase.
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
(1)
Here, Ceq: carbon equivalent (mass%)
C, Mn, Si, Ni, Cr, Mo, V: Content of each alloy element (mass%)
2. 2. The laser beam welded joint excellent in toughness of the weld metal part according to 1, wherein a gas containing an oxygen supply gas is used as a shield gas for laser beam welding.
本発明によれば、引張強度が７８０ＭＰａ級以上の高強度鋼で、溶接金属部の靭性に優れたレーザビーム溶接継手を提供することができ、産業上格段の効果を奏する。 According to the present invention, it is possible to provide a laser beam welded joint which is made of high strength steel having a tensile strength of 780 MPa or more and excellent in the toughness of the weld metal part, and has a remarkable industrial effect.
まず、本発明のレーザビーム溶接継手の溶接金属の化学成分に関する限定理由について説明する。説明において％はｍａｓｓ％とする。 First, the reason for limitation regarding the chemical composition of the weld metal of the laser beam welded joint of the present invention will be described. In the explanation,% is mass%.
Ｃ：０．０２〜０．１４％
Ｃは、焼入れ性を増加させる元素であるため、溶接金属の強度確保に重要な元素である。しかし、０．０２％未満では十分な強度の確保が困難である。一方、０．１４％を超えて含有すると、レーザビーム溶接金属のマトリックス組織中におけるマルテンサイト相の硬さが上昇すると共に、Ｍ−Ａ組織（島状マルテンサイト）の生成が顕著となる。その結果、レーザビーム溶接金属部の靭性は著しく劣化する。このため、溶接金属のＣは０．０２〜０．１４％に限定する。
C: 0.02-0.14%
Since C is an element that increases hardenability, it is an important element for securing the strength of the weld metal. However, if it is less than 0.02%, it is difficult to ensure sufficient strength. On the other hand, if the content exceeds 0.14%, the hardness of the martensite phase in the matrix structure of the laser beam weld metal increases, and the formation of an MA structure (island martensite) becomes significant. As a result, the toughness of the laser beam weld metal part is significantly deteriorated. For this reason, C of a weld metal is limited to 0.02 to 0.14%.
Ｔｉ：０．００６〜０．０５％
Ｔｉは、Ｔｉ系酸化物を介してアシキュラーフェライト生成に有効に働き、レーザビーム溶接金属部の高靭化に寄与する重要な元素である。レーザビーム溶接を酸素供給ガスを含有するシールドガス中で行うことで、鋼材や溶接材料に含まれるＴｉは酸素と結合してＴｉ系酸化物を形成する。このＴｉ系酸化物がアシキュラーフェライトの核生成サイトとして働き、レーザビーム溶接金属は微細なアシキュラーフェライト相を含んだミクロ組織となり、溶接金属の靭性が向上する。溶接金属中のＴｉ含有量が０．００６％未満では、アシキュラーフェライトの核生成サイトとなる酸化物の量が十分に確保できない。一方、溶接金属中のＴｉ含有量が０．０５％を超えて含有すると、溶接金属中に不要な析出物を増加させ、靭性を低下させる。このため、溶接金属のＴｉは０．００６〜０．０５％に限定する。
Ti: 0.006 to 0.05%
Ti is an important element that works effectively for the generation of acicular ferrite via a Ti-based oxide and contributes to the toughening of the laser beam weld metal part. By performing laser beam welding in a shield gas containing an oxygen supply gas, Ti contained in the steel material or welding material combines with oxygen to form a Ti-based oxide. This Ti-based oxide functions as a nucleation site of acicular ferrite, and the laser beam weld metal has a microstructure containing a fine acicular ferrite phase, and the toughness of the weld metal is improved. When the Ti content in the weld metal is less than 0.006%, it is not possible to sufficiently secure the amount of oxide that becomes the nucleation site of acicular ferrite. On the other hand, if the Ti content in the weld metal exceeds 0.05%, unnecessary precipitates are increased in the weld metal and the toughness is lowered. For this reason, Ti of a weld metal is limited to 0.006 to 0.05%.
Ａｌ：０．０２％以下
Ａｌは、Ｔｉよりも酸素との親和力が強いため、溶接金属の凝固過程初期段階に酸化物（Ａｌ２Ｏ３）を形成する。しかしながら、Ａｌ２Ｏ３はアシキュラーフェライトの核生成サイトとして機能しない酸化物である。
Al: 0.02% or less Since Al has a stronger affinity for oxygen than Ti, an oxide (Al 2 O 3 ) is formed in the initial stage of the solidification process of the weld metal. However, Al 2 O 3 is an oxide that does not function as a nucleation site for acicular ferrite.
従って、本発明ではアシキュラーフェライトの核生成サイトとして機能するＴｉ系酸化物を優先的に生成させるという観点からは、レーザビーム溶接金属中のＡｌ含有量は低減することが好ましいが、０．０２％までは許容する。Ａｌが０．０２％を超えて含有された場合、Ｔｉ系酸化物による溶接金属組織のアシキュラーフェライトを確保するため多量の酸素を含有させることが必要となり、酸化物が過剰となって靭性は劣化する。このため、溶接金属のＡｌは０．０２％以下に限定する。 Therefore, in the present invention, from the viewpoint of preferentially generating a Ti-based oxide that functions as a nucleation site of acicular ferrite, it is preferable to reduce the Al content in the laser beam weld metal. % Is allowed. When Al is contained in excess of 0.02%, it is necessary to contain a large amount of oxygen in order to ensure acicular ferrite of the weld metal structure by the Ti-based oxide, and the toughness becomes excessive due to the oxide being excessive. to degrade. For this reason, Al of a weld metal is limited to 0.02% or less.
Ｂ：０．００１％以下
Ｂは、焼入れ性を増加させる元素であるため、溶接金属の強度確保に有効な元素である。しかし、本発明で対象とする引張強度が７８０ＭＰａレベルの高強度鋼のレーザビーム溶接金属では、Ｂ含有量が０．００１％を超えるとレーザビーム溶接金属のマトリックス組織はマルテンサイトが９０％以上を占めるような組織となり、溶接金属部の靭性が劣化する。このため、溶接金属のＢは０．００１％以下に限定する。
B: 0.001% or less B is an element that increases the hardenability and is therefore an effective element for securing the strength of the weld metal. However, in the laser beam weld metal of high strength steel having a tensile strength of 780 MPa, which is the subject of the present invention, when the B content exceeds 0.001%, the matrix structure of the laser beam weld metal has a martensite of 90% or more. As a result, the toughness of the weld metal part deteriorates. For this reason, B of a weld metal is limited to 0.001% or less.
Ｏ：０．０２〜０．０５％
Ｏは、溶接金属中でＴｉと結合した酸化物系介在物の形態で存在し、アシキュラーフェライトの核生成サイトとして働き、レーザビーム溶接金属部の高靭化に寄与する重要な元素である。溶接金属のＯ含有量が０．０２％未満では、十分な量のＴｉ系酸化物が確保できないため、このような高靭化効果を得ることはできない。一方、溶接金属のＯ含有量が０．０５％を超えると、酸化物が過剰になるとともに粗大な介在物も生成して靭性は劣化する。このため、溶接金属のＯは０．０２〜０．０５％に限定する。
O: 0.02 to 0.05%
O exists in the form of oxide inclusions combined with Ti in the weld metal, and serves as an nucleation site for acicular ferrite, and is an important element contributing to the toughening of the laser beam weld metal part. When the O content of the weld metal is less than 0.02%, a sufficient amount of Ti-based oxide cannot be secured, and thus such a toughening effect cannot be obtained. On the other hand, if the O content of the weld metal exceeds 0.05%, the oxide becomes excessive and coarse inclusions are generated, and the toughness deteriorates. For this reason, O of a weld metal is limited to 0.02 to 0.05%.
Ｃｅｑ：０．３３〜０．５３％
Ｃｅｑ（＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４、ここで、Ｃ、Ｍｎ、Ｓｉ、Ｎｉ、Ｃｒ、Ｍｏ、Ｖ：各元素の含有量（ｍａｓｓ％））は、溶接硬化性および焼入れ性を示す指標であり、溶接継手部の強度や靭性に大きな影響を与える。レーザビーム溶接のように冷却速度が速い溶接においては、溶接金属のＣｅｑが０．５３％を超えると、溶接金属が著しく硬化し、靭性が低下する。一方、溶接金属のＣｅｑが０．３３％未満の場合、レーザビーム溶接のような冷却速度が速い溶接においても十分な焼入れ性が確保されず、粒界フェライトあるいはポリゴナルフェライトが生成するようになる。その結果、７８０ＭＰａ級の引張強度を満足することが困難となり、靭性も低下する。このため、溶接金属のＣｅｑは０．３３〜０．５３％、好ましくは、０．３５〜０．５０％である。
Ceq: 0.33-0.53%
Ceq (= C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14, where C, Mn, Si, Ni, Cr, Mo, V: content of each element (mass%)) is weld hardenability and It is an index showing hardenability and has a great influence on the strength and toughness of the welded joint. In welding with a high cooling rate such as laser beam welding, if the Ceq of the weld metal exceeds 0.53%, the weld metal is significantly hardened and the toughness is reduced. On the other hand, if the Ceq of the weld metal is less than 0.33%, sufficient hardenability is not ensured even in welding with a high cooling rate such as laser beam welding, and grain boundary ferrite or polygonal ferrite is generated. . As a result, it becomes difficult to satisfy the tensile strength of 780 MPa class, and the toughness also decreases. For this reason, Ceq of a weld metal is 0.33-0.53%, Preferably, it is 0.35-0.50%.
引張強度が７８０ＭＰａ級以上の高強度鋼の場合、その成分組成として、Ｃ、Ｓｉ、Ｍｎ、Ｃｕ、Ｎｉ、Ｃｒ、Ｍｏ、Ｎｂ、Ｖ、Ｔｉが含有され、レーザビーム溶接金属には各合金元素の含有量の一部が含有される。更に、溶接材料（フィラーワイヤ）から各種合金元素が添加されるため、本発明では、溶接金属におけるＣ、Ｔｉ、Ａｌ、Ｂ、Ｏの含有量とＣｅｑの上下限を規定し、残部Ｆｅ及び不可避的不純物とする。しかしながら、本発明で用いる母材の成分組成としては、Ｃ：０．１５％以下、Ｓｉ：０．４％以下、Ｍｎ：２．０％以下、Ｐ：０．０１％以下、Ｓ：０．０１％以下、Ｔｉ：０．０４％以下であることが好ましい。またフィラーワイヤの成分組成としては、Ｃ：０．１４％以下、Ｓｉ：０．８％以下、Ｍｎ：３．０％以下、Ｐ：０．０２％以下、Ｓ：０．０２％以下、Ｔｉ：０．０１〜０．０６％であることが好ましい。 In the case of high-strength steel with a tensile strength of 780 MPa or higher, the component composition includes C, Si, Mn, Cu, Ni, Cr, Mo, Nb, V, and Ti. A part of the content of is contained. Furthermore, since various alloying elements are added from the welding material (filler wire), the present invention defines the content of C, Ti, Al, B, O and the upper and lower limits of Ceq in the weld metal, the remaining Fe and unavoidable Impurities. However, as a component composition of the base material used in the present invention, C: 0.15% or less, Si: 0.4% or less, Mn: 2.0% or less, P: 0.01% or less, S: 0.00. It is preferable that the content is 01% or less and Ti: 0.04% or less. The component composition of the filler wire is as follows: C: 0.14% or less, Si: 0.8% or less, Mn: 3.0% or less, P: 0.02% or less, S: 0.02% or less, Ti : 0.01 to 0.06% is preferable.
次にミクロ組織について説明する。レーザビーム溶接金属部の高靭化を図るためには、上記化学成分の限定を前提とした上で、ミクロ組織を面積率で４０％以上のアシキュラーフェライト相を含む組織とする。 Next, the microstructure will be described. In order to increase the toughness of the laser beam weld metal part, the microstructure is assumed to be a structure containing an acicular ferrite phase with an area ratio of 40% or more on the premise of limitation of the chemical components.
アシキュラーフェライト相が面積率で４０％未満では、良好な靭性が得られない。このため、本発明においては、アシキュラーフェライト相が面積率で４０％以上に限定する。なお、溶接金属の引張強度が７８０ＭＰａ以上を満足するためには、アシキュラーフェライト相以外の組織は、ベイナイト相および／またはマルテンサイト相とする。 When the acicular ferrite phase is less than 40% by area ratio, good toughness cannot be obtained. For this reason, in this invention, an acicular ferrite phase is limited to 40% or more by an area rate. In order to satisfy the tensile strength of the weld metal of 780 MPa or more, the structure other than the acicular ferrite phase is a bainite phase and / or a martensite phase.
上記化学成分およびミクロ組織を有するレーザビーム溶接金属を製造する方法として、レーザビーム溶接時のシールドガスに酸素供給ガスを含有するガスを用いる。酸素供給ガスとしては、酸素ガス、炭酸ガスあるいはそれらの混合ガスを含む不活性ガスが例示される。 As a method for producing a laser beam weld metal having the above chemical components and microstructure, a gas containing an oxygen supply gas is used as a shield gas during laser beam welding. Examples of the oxygen supply gas include oxygen gas, carbon dioxide gas, or an inert gas containing a mixed gas thereof.
酸素供給ガスを含有する酸化性雰囲気中で溶接することにより、酸素が溶接金属中に供給され、鋼材や溶接材料に含有されるＴｉが酸素と結合してＴｉ系酸化物を形成し、溶接金属中に分散される。 By welding in an oxidizing atmosphere containing an oxygen supply gas, oxygen is supplied into the weld metal, and Ti contained in the steel or welding material combines with oxygen to form a Ti-based oxide, and the weld metal Distributed in.
Ｔｉ系酸化物はアシキュラーフェライトの核生成サイトとして有効に働き、溶接金属組織を微細なアシキュラーフェライト相を含んだ組織にして、高い靭性が得られるようになる。 The Ti-based oxide works effectively as a nucleation site of acicular ferrite, and makes the weld metal structure a structure containing a fine acicular ferrite phase, so that high toughness can be obtained.
以下、実施例に基づいて本発明の効果を示す。 The effects of the present invention will be described below based on examples.
表１に示す化学組成の供試鋼板（板厚１１ｍｍ）と、表２に示す化学組成の溶接材料（フィラーワイヤ、直径１．０ｍｍ）を種々組合わせて、さらにレーザビーム溶接時のシールドガスを変化させてレーザビーム溶接継手を作製した。 Various test steel plates (thickness 11 mm) having the chemical composition shown in Table 1 and welding materials (filler wire, diameter 1.0 mm) having the chemical composition shown in Table 2 are used in combination, and a shielding gas for laser beam welding is further used. Laser beam welded joints were produced by changing the method.
レーザビーム溶接は、ファイバーレーザ溶接装置を用いて、レーザ出力：１０ｋＷ、溶接速度：０．８ｍ／ｍｉｎ、開先形状：Ｉ開先、ルートギャップ：０．５ｍｍの条件にて行った。 Laser beam welding was performed using a fiber laser welding apparatus under the conditions of laser output: 10 kW, welding speed: 0.8 m / min, groove shape: I groove, route gap: 0.5 mm.
得られたレーザビーム溶接継手について、溶接金属の化学組成分析、マトリックス組織のミクロ観察、シャルピー衝撃試験、ビッカース硬さ測定を実施した。レーザビーム溶接金属組織中のアシキュラーフェライト面積率は、光学顕微鏡（×４００）で５視野観察し、画像解析装置により計測した各視野のアシキュラーフェライト面積率の平均値とした。 The obtained laser beam welded joint was subjected to chemical composition analysis of the weld metal, microscopic observation of the matrix structure, Charpy impact test, and Vickers hardness measurement. The acicular ferrite area ratio in the laser beam weld metal structure was observed with five fields of view with an optical microscope (× 400), and was the average value of the acicular ferrite area ratio of each field of view measured by an image analyzer.
シャルピー衝撃試験は、溶接金属中央部から２ｍｍＶノッチシャルピー衝撃試験片を採取し、−２０℃における吸収エネルギー（ｖＥ−２０℃）にて評価した。ビッカース硬さ測定は、溶接金属中央部を板厚方向に荷重９．８Ｎで測定した平均値で評価した。 In the Charpy impact test, a 2 mm V-notch Charpy impact test piece was sampled from the center of the weld metal and evaluated by absorption energy at -20 ° C (vE-20 ° C). The Vickers hardness measurement was evaluated by an average value measured at a load of 9.8 N in the thickness direction of the weld metal center.
表３にこれらの試験結果を示す。継手Ｎｏ．１〜８は、レーザビーム溶接金属部のＣ、Ｔｉ、Ａｌ、Ｂ、Ｏ、Ｃｅｑが本発明で規定する要件を満足し、溶接金属部のミクロ組織も面積率で４０％以上のアシキュラーフェライト相を含む本発明例で、レーザビーム溶接金属部のシャルピー吸収エネルギー（ｖＥ−２０℃）は１００Ｊを超える値となっている。ビッカース硬さも２６０を超えており、７８０ＭＰａ以上の引張強度を有していることが確認された(ＪＩＳハンドブック鉄鋼１（２０１０）硬さ換算表（ＳＡＥＪ４１７）による）。 Table 3 shows the results of these tests. Fitting No. Nos. 1 to 8 satisfy the requirements specified by the present invention for C, Ti, Al, B, O, and Ceq of the laser beam weld metal part, and the microstructure of the weld metal part also has an area ratio of 40% or more. In the example of the present invention including the phase, the Charpy absorbed energy (vE-20 ° C.) of the laser beam weld metal part exceeds 100 J. Vickers hardness also exceeded 260, and it was confirmed that it has a tensile strength of 780 MPa or more (according to JIS Handbook Steel 1 (2010) Hardness Conversion Table (SAEJ417)).
これに対して、継手Ｎｏ．９はシールドガスにＡｒを用いたため、溶接金属のＯ量が本発明で規定する範囲外となり、ミクロ組織においてアシキュラーフェライト相が生成せず、靭性に劣っている。継手Ｎｏ．１０は、溶接金属のＣおよびＣｅｑが本発明で規定する範囲の上限を超えているため、アシキュラーフェライト相が含まれない非常に硬い組織となり、靭性が低い。 On the other hand, the joint No. In No. 9, since Ar was used as the shielding gas, the amount of O of the weld metal was outside the range defined by the present invention, and no acicular ferrite phase was formed in the microstructure, resulting in poor toughness. Fitting No. No. 10 has a very hard structure with no acicular ferrite phase and low toughness because C and Ceq of the weld metal exceed the upper limit of the range defined in the present invention.
継手Ｎｏ．１１は、溶接金属のＯ量が０．０１２％と本発明で規定する範囲の下限未満であるため、ミクロ組織中のアシキュラーフェライト相の割合が少なく、靭性が低い。継手Ｎｏ．１２は、溶接金属のＴｉおよびＡｌが本発明で規定する範囲の上限を超えているため、ミクロ組織はアシキュラーフェライト相を含んでいるものの、靭性は低い。 Fitting No. No. 11 has an O content of the weld metal of 0.012%, which is less than the lower limit of the range defined in the present invention, so that the proportion of the acicular ferrite phase in the microstructure is small and the toughness is low. Fitting No. In No. 12, since Ti and Al of the weld metal exceed the upper limit of the range defined in the present invention, the microstructure contains an acicular ferrite phase, but the toughness is low.
継手Ｎｏ．１３は、溶接金属のＣｅｑが本発明で規定する範囲の下限未満であるため、溶接金属はアシキュラーフェライト相の割合が少なく硬さも低くなり、靭性に劣っている。継手Ｎｏ．１４は、溶接金属のＢが本発明で規定する範囲の上限を超えているため、溶接金属はアシキュラーフェライト相が含まれない硬い組織となり、靭性が低い。 Fitting No. In No. 13, since the Ceq of the weld metal is less than the lower limit of the range defined in the present invention, the weld metal has a low proportion of the acicular ferrite phase and a low hardness, and is inferior in toughness. Fitting No. In No. 14, since B of the weld metal exceeds the upper limit of the range defined in the present invention, the weld metal has a hard structure not including an acicular ferrite phase and has low toughness.
Claims (3)
．１４％、Ｐ：０．００８％以下、Ｓ：０．０１０％以下、Ｔｉ：０．００６〜０．０５
％、Ａｌ：０．０２％以下、Ｂ：０．００１％以下、Ｏ：０．０２６〜０．０４６％、Ｃ
ｕ：０．２２〜０．３０％、Ｎｉ：０．１３〜０．８３％であって、下記（１）式で定義
されるＣｅｑが０．３３〜０．５３％の組成を含有し、残部はＦｅおよび不可避的不純物
からなり、面積率で４０％以上のアシキュラーフェライト相を含むミクロ組織を有するこ
とを特徴とする溶接金属部の靭性に優れたレーザビーム溶接継手。
Ｃｅｑ＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４
（１）
ここで、Ｃｅｑ：炭素当量（ｍａｓｓ％）
Ｃ、Ｍｎ、Ｓｉ、Ｎｉ、Ｃｒ、Ｍｏ、Ｖ：各合金元素の含有量（ｍａｓｓ％） It is a laser beam welded joint of steel material, and the weld metal is mass%, C: 0.02 to 0
. 14%, P: 0.008% or less, S: 0.010% or less, Ti: 0.006 to 0.05
%, Al: 0.02% or less, B: 0.001% or less, O: 0.026 to 0.046%, C
u: 0.22-0.30%, Ni: 0.13-0.83%, Ceq defined by the following formula (1) contains a composition of 0.33-0.53%, A laser beam welded joint excellent in toughness of a weld metal part, characterized in that the balance consists of Fe and inevitable impurities and has a microstructure containing an acicular ferrite phase with an area ratio of 40% or more.
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
(1)
Here, Ceq: carbon equivalent (mass%)
C, Mn, Si, Ni, Cr, Mo, V: Content of each alloy element (mass%)
Ｃｅｑ＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４
（１）
ここで、Ｃｅｑ：炭素当量（ｍａｓｓ％）
Ｃ、Ｍｎ、Ｓｉ、Ｎｉ、Ｃｒ、Ｍｏ、Ｖ：各合金元素の含有量（ｍａｓｓ％） Weld metal, in mass%, C: 0.02~0.14%, P: 0.008% or less, S: 0.010% or less, Ti: 0.006~0.05%, Al: 0 0.02% or less, B: 0.001% or less, O: 0.026 to 0.046%, Cu: 0.22 to 0.30%, Ni: 0.13 to 0.83%, (1) Ceq defined by the formula contains a composition of 0.33 to 0.53%, and the balance is composed of Fe and inevitable impurities, and has a microstructure containing an acicular ferrite phase with an area ratio of 40% or more. Yes, and laser-beam welded joint manufacturing method having excellent toughness of the weld metal portion, characterized in that it is manufactured by laser beam welding.
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
(1)
Here, Ceq: carbon equivalent (mass%)
C, Mn, Si, Ni, Cr, Mo, V: Content of each alloy element (mass%)
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