JP2002003984A - Structure having laser or electron beam welded joint excellent in fatigue strength, and its manufacturing method - Google Patents
Structure having laser or electron beam welded joint excellent in fatigue strength, and its manufacturing methodInfo
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- JP2002003984A JP2002003984A JP2000183331A JP2000183331A JP2002003984A JP 2002003984 A JP2002003984 A JP 2002003984A JP 2000183331 A JP2000183331 A JP 2000183331A JP 2000183331 A JP2000183331 A JP 2000183331A JP 2002003984 A JP2002003984 A JP 2002003984A
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Abstract
Description
【0001】[0001]
【発明の属する技術分野】本発明は、レーザーまたは電
子ビーム溶接継ぎ手及びそれらの製造方法に関するもの
であり、特に、疲労強度、静的強度、靭性の機械的特性
に優れたレーザーまたは電子ビーム溶接継ぎ手を備えた
構造物及びそれらの製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser or electron beam welding joint and a method for producing the same, and more particularly, to a laser or electron beam welding joint having excellent mechanical properties such as fatigue strength, static strength and toughness. And a method for manufacturing the same.
【0002】[0002]
【従来の技術】溶接構造物の信頼性は、その溶接部の特
性でほぼ決定されているといって過言ではない。そのた
め、従来から、溶接部の特性向上には多大な関心が注が
れてきた。例えば溶接部の疲労特性については、最近で
は、溶接学会論文集、第18巻、第1号、141〜14
5頁に高合金化した溶接材料を用いて溶接することによ
り溶接金属の変態温度を低下させて、溶接終了後の変態
による膨張を利用して溶接部の残留応力の低減を行う方
法が報告されている。しかしながら、この方法は、高価
な合金元素を多く添加した溶接材料を用いるため、溶接
材料コストの増大を招き、経済的な面で問題がある。2. Description of the Related Art It is no exaggeration to say that the reliability of a welded structure is substantially determined by the characteristics of the welded portion. Therefore, much attention has been paid to improving the characteristics of the welded portion. For example, regarding the fatigue properties of welds, recently, Journal of the Japan Welding Society, Vol. 18, No. 1, 141-14.
On page 5, a method of reducing the transformation temperature of the weld metal by welding using a highly alloyed welding material and reducing the residual stress in the weld by utilizing the expansion due to transformation after the completion of welding is reported. ing. However, since this method uses a welding material to which a large amount of expensive alloying elements are added, the cost of the welding material is increased, and there is a problem in terms of economy.
【0003】また、溶接部の疲労特性を向上させるため
の他の方法としては、被接合材の成分の調整により溶接
熱影響部の軟化を抑制するか、最高硬さを低化させるこ
とにより溶接部の硬さ分布を平坦化し相対的な軟化部へ
の歪み集中を軽減する方法が知られている。この溶接部
の硬さ分布を平坦化する具体的な方法としては、溶接熱
影響部の軟化を抑制するためにC等の焼き入れ性元素を
添加したり、最高硬さを低化させるために焼き入れ性元
素を低減させることにより、相対的に軟化部と最高硬さ
の硬度差を減少させる方法が一般的である。しかしなが
ら、前者のC等の焼き入れ性元素を添加する方法は、溶
接熱影響部の軟化を抑制するために効果はあるが、マル
テンサイトなど硬質組織が多くなり最高硬さが高くなり
過ぎて靭性が低下するという問題が生じる。また、後者
の焼き入れ性元素を低減させる方法は、溶接熱影響部の
最高硬さを低化させるために効果はあるが、軟化部が拡
大して溶接継ぎ手の必要強度の確保が困難になるという
問題が生じる。[0003] Further, as another method for improving the fatigue properties of the welded portion, the softening of the weld heat affected zone is suppressed by adjusting the components of the materials to be joined, or the maximum hardness is reduced to reduce the weldability. There is known a method of flattening the hardness distribution of a portion and reducing the concentration of strain on a relatively softened portion. As a specific method of flattening the hardness distribution of the welded portion, a hardenable element such as C is added to suppress the softening of the weld heat affected zone, or to reduce the maximum hardness. Generally, a method of relatively reducing the hardness difference between the softened portion and the highest hardness by reducing the hardenable element. However, although the former method of adding a hardenable element such as C is effective in suppressing the softening of the heat affected zone, the hard structure such as martensite increases and the maximum hardness becomes too high, resulting in toughness. Is reduced. In addition, the latter method of reducing the quenchable element is effective for lowering the maximum hardness of the heat affected zone, but the softened portion expands, making it difficult to secure the required strength of the welding joint. The problem arises.
【0004】従って、従来の母材成分の調整による溶接
熱影響部の軟化抑制、または最高硬さの低減は、疲労強
度を改善できるものの、強度及び靭性の何れかを劣化さ
せるという問題があった。[0004] Therefore, the conventional softening suppression of the weld heat affected zone or the reduction of the maximum hardness by adjusting the base metal component can improve the fatigue strength, but has a problem of deteriorating either strength or toughness. .
【0005】一方、今までに鋼板の成分組成と制御圧延
冷却による組織制御により疲労特性に優れた鋼板が提案
されており、例えば、特開平6−49593号公報に
は、鋼板表裏層から所定範囲に所定アスペクト比(長径
/短径)の集合組織を有した溶接構造物用厚鋼板が開示
され、また、特開平6−49587号公報には、鋼板表
裏層から所定範囲の硬度が板厚内部よりも所定以上高い
組織を有する溶接継ぎ手用高疲労強度厚鋼板が開示され
ている。On the other hand, a steel sheet having excellent fatigue properties has been proposed by controlling the composition of the steel sheet and controlling the structure by controlled rolling cooling. For example, Japanese Patent Application Laid-Open No. 6-49593 discloses a steel sheet having a predetermined range from the front and back layers of the steel sheet. Discloses a thick steel plate for a welded structure having a texture having a predetermined aspect ratio (major axis / minor axis), and JP-A-6-49587 discloses that a predetermined range of hardness from the front and back layers of the steel sheet is equal to the internal thickness. A high fatigue-strength steel plate for a welded joint having a structure higher than a predetermined level is disclosed.
【0006】しかしながら、特開平6−49593号公
報等の組織制御された鋼板を溶接する場合は、溶接金属
はもちろん、その近傍の熱影響部においても溶接熱によ
って、本来の鋼板組織は消失してしまい、本来の鋼板の
特性を維持することはできない。また、特開平6−49
587号公報に開示されている鋼板は、鋼板表層部に溶
接する隅肉溶接用の厚鋼板であり、鋼板表層部の組織制
御(硬度向上)により、隅肉溶接時に、鋼板表層部にあ
る溶接部から発生する疲労亀裂を遅延し疲労強度を向上
できるが、一般の鋼板の突き合わせ溶接時には、適用で
きないものであり、汎用性の問題がある。However, when welding a steel sheet whose structure is controlled as disclosed in Japanese Patent Application Laid-Open No. 6-49593, the original steel sheet structure disappears due to welding heat not only in the weld metal but also in the heat affected zone in the vicinity. As a result, the original properties of the steel sheet cannot be maintained. Also, Japanese Patent Application Laid-Open No. 6-49
The steel sheet disclosed in Japanese Patent No. 587 is a thick steel sheet for fillet welding to be welded to a surface layer of a steel sheet. Although the fatigue strength can be improved by delaying the fatigue crack generated from the part, it cannot be applied to butt welding of a general steel sheet, and there is a problem of versatility.
【0007】[0007]
【発明が解決しようとする課題】本発明は、以上のよう
な従来技術の問題を鑑み、鋼板の成分及び組織等を制御
するとともに、溶接材料を用いずに低入熱量でも良好な
溶け込み深さが得られるレーザー溶接や電子ビーム溶接
を用いることにより疲労強度、静的強度、靱性等の機械
的特性に優れたレーザーまたは電子ビーム溶接継ぎ手を
備えた構造物及びそれらの製造方法を提供することを目
的とする。SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention controls the composition and structure of a steel sheet, and has a good penetration depth even at a low heat input without using a welding material. To provide a structure provided with a laser or electron beam welding joint having excellent mechanical properties such as fatigue strength, static strength, and toughness by using laser welding or electron beam welding, and a method for producing the same. Aim.
【0008】[0008]
【課題を解決するための手段】本発明は、上記課題を達
成するものであり、その要旨は次の通りである。The present invention achieves the above object, and the gist thereof is as follows.
【0009】(1) 鋼板板厚が4〜20mmであり、
成分として、質量%で、C:0.005〜0.15%、
Si:0.01〜0.8%、Mn:0.2〜2.0%、
Al:0.001〜0.2%、N:0.02%以下、
P:0.01%以下、S:0.01%以下を含有し、残
部が鉄及び不可避不純物からなり、鋼板表面及び裏面の
それぞれから板厚方向に板厚の5%以上までの範囲にお
いて、平均円相当径で3μm以下の細粒フェライト組織
を有することを特徴とするレーザー溶接継ぎ手を備えた
構造物。(1) The thickness of the steel plate is 4 to 20 mm,
As a component, in mass%, C: 0.005 to 0.15%,
Si: 0.01 to 0.8%, Mn: 0.2 to 2.0%,
Al: 0.001 to 0.2%, N: 0.02% or less,
P: 0.01% or less, S: 0.01% or less, the balance being iron and unavoidable impurities, in the range of 5% or more of the sheet thickness in the sheet thickness direction from each of the front and back surfaces of the steel sheet, A structure provided with a laser welding joint, which has a fine-grained ferrite structure having an average equivalent circle diameter of 3 μm or less.
【0010】(2) さらにNi、Cr、Mo、Cu、
V、Nb、Ti、Ca、B、Mgの内の1種または2種
以上を合計量で4.5質量%以下含有することを特徴と
する上記(1)に記載のレーザー溶接継ぎ手を備えた構
造物。(2) Ni, Cr, Mo, Cu,
The laser welding joint according to the above (1), wherein one or more of V, Nb, Ti, Ca, B, and Mg are contained in a total amount of 4.5% by mass or less. Structure.
【0011】(3) 前記レーザー溶接継ぎ手の溶接部
の熱影響部の幅が1.6mm以下であることを特徴とす
る上記(1)または(2)の何れかに記載のレーザー溶
接継ぎ手を備えた構造物。(3) The laser welded joint according to any one of (1) and (2), wherein a width of a heat affected zone of a welded portion of the laser welded joint is 1.6 mm or less. Structure.
【0012】(4) 鋼板板厚が10〜50mmであ
り、成分として、質量%で、C:0.005〜0.15
%、Si:0.01〜0.8%、Mn:0.2〜2.0
%、Al:0.001〜0.2%、N:0.02%以
下、P:0.01%以下、S:0.01%以下を含有
し、残部が鉄及び不可避不純物からなり、鋼板表面及び
裏面のそれぞれから板厚方向に板厚の5%以上までの範
囲において、平均円相当径で3μm以下の細粒フェライ
ト組織を有し、且つ溶接部の熱影響部の幅が1.6mm
以下であることを特徴とする電子ビーム溶接継ぎ手を備
えた構造物。(4) The thickness of the steel sheet is 10 to 50 mm, and as a component, in mass%, C: 0.005 to 0.15
%, Si: 0.01 to 0.8%, Mn: 0.2 to 2.0
%, Al: 0.001 to 0.2%, N: 0.02% or less, P: 0.01% or less, S: 0.01% or less, the balance being iron and unavoidable impurities. In the range of 5% or more of the plate thickness in the plate thickness direction from each of the front surface and the back surface, it has a fine-grained ferrite structure with an average equivalent circle diameter of 3 μm or less, and the width of the heat-affected zone of the welded portion is 1.6 mm.
A structure provided with an electron beam welding joint, characterized in that:
【0013】(5) さらにNi、Cr、Mo、Cu、
V、Nb、Ti、Ca、B、Mgの内の1種または2種
以上を合計量で4.5質量%以下含有することを特徴と
する上記(4)に記載の電子ビーム溶接継ぎ手を備えた
構造物。(5) Further, Ni, Cr, Mo, Cu,
The electron beam welding joint according to the above (4), wherein one or more of V, Nb, Ti, Ca, B, and Mg are contained in a total amount of 4.5% by mass or less. Structure.
【0014】(6) 前記電子ビーム継ぎ手の溶接部の
熱影響部の幅が1.6mm以下であることを特徴とする
上記(4)または(5)の何れかに記載のレーザー溶接
継ぎ手を備えた構造物。(6) The laser welded joint according to (4) or (5), wherein the width of the heat affected zone of the welded portion of the electron beam joint is 1.6 mm or less. Structure.
【0015】(7) 鋼板板厚が4〜20mmであり、
成分として、質量%で、C:0.005〜0.15%、
Si:0.01〜0.8%、Mn:0.2〜2.0%、
Al:0.001〜0.2%、N:0.02%以下、
P:0.01%以下、S:0.01%以下を含有し、残
部が鉄及び不可避不純物からなり、鋼板表面及び裏面の
それぞれから板厚方向に板厚の5%以上までの範囲にお
いて、平均円相当径で3μm以下の細粒フェライト組織
を有する鋼板を熱影響部の幅が1.6mm以下になるよ
うにレーザー溶接することを特徴とするレーザー溶接継
ぎ手を備えた構造物の製造方法。(7) The thickness of the steel plate is 4 to 20 mm,
As a component, in mass%, C: 0.005 to 0.15%,
Si: 0.01 to 0.8%, Mn: 0.2 to 2.0%,
Al: 0.001 to 0.2%, N: 0.02% or less,
P: 0.01% or less, S: 0.01% or less, the balance being iron and unavoidable impurities, in the range of 5% or more of the sheet thickness in the sheet thickness direction from each of the front and back surfaces of the steel sheet, A method for manufacturing a structure provided with a laser welding joint, wherein a steel sheet having a fine-grained ferrite structure having an average circle equivalent diameter of 3 μm or less is laser-welded such that the width of the heat-affected zone is 1.6 mm or less.
【0016】(8) さらにNi、Cr、Mo、Cu、
V、Nb、Ti、Ca、B、Mgの内の1種または2種
以上を合計量で4.5質量%以下含有することを特徴と
する上記(7)に記載のレーザー溶接継ぎ手を備えた構
造物の製造方法。(8) Ni, Cr, Mo, Cu,
The laser welding joint according to (7), wherein one or more of V, Nb, Ti, Ca, B, and Mg are contained in a total amount of 4.5% by mass or less. The method of manufacturing the structure.
【0017】(9) 鋼板板厚が10〜50mmであ
り、成分として、質量%で、C:0.005〜0.15
%、Si:0.01〜0.8%、Mn:0.2〜2.0
%、Al:0.001〜0.2%、N:0.02%以
下、P:0.01%以下、S:0.01%以下を含有
し、残部が鉄及び不可避不純物からなり、鋼板表面及び
裏面のそれぞれから板厚方向に板厚の5%以上までの範
囲において、平均円相当径で3μm以下の細粒フェライ
ト組織を有する鋼板を熱影響部の幅が1.6mm以下に
なるように電子ビーム溶接することを特徴とする電子ビ
ーム溶接継ぎ手を備えた構造物の製造方法。(9) The thickness of the steel sheet is 10 to 50 mm, and as a component, in mass%, C: 0.005 to 0.15
%, Si: 0.01 to 0.8%, Mn: 0.2 to 2.0
%, Al: 0.001 to 0.2%, N: 0.02% or less, P: 0.01% or less, S: 0.01% or less, the balance being iron and unavoidable impurities. A steel sheet having a fine-grained ferrite structure with an average equivalent circle diameter of 3 μm or less in a range from the front surface and the back surface to 5% or more of the thickness in the thickness direction so that the width of the heat-affected zone is 1.6 mm or less. A method for manufacturing a structure provided with an electron beam welding joint, wherein the structure is subjected to electron beam welding.
【0018】(10) さらにNi、Cr、Mo、C
u、V、Nb、Ti、Ca、B、Mgの内の1種または
2種以上を合計量で4.5質量%以下含有することを特
徴とする上記(9)に記載の電子ビーム溶接継ぎ手を備
えた構造物の製造方法。(10) Ni, Cr, Mo, C
The electron beam welding joint according to (9), wherein one or more of u, V, Nb, Ti, Ca, B, and Mg are contained in a total amount of 4.5% by mass or less. A method for manufacturing a structure comprising:
【0019】[0019]
【発明の実施の形態】初めに、本発明の技術思想につい
て述べる。DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the technical concept of the present invention will be described.
【0020】一般に、レーザー溶接や電子ビーム溶接
は、アーク溶接に比べて高エネルギー密度で溶接ができ
るため、溶接材料を用いなくても溶接が可能であるとと
もに、アーク溶接に比べて低入熱量でも完全溶け込み溶
接を行うことができることができる。Generally, laser welding and electron beam welding can be performed at a higher energy density than arc welding, so that welding can be performed without using a welding material, and even with a lower heat input than arc welding. Complete penetration welding can be performed.
【0021】また、本発明者らの実験等の検討結果か
ら、レーザー溶接や電子ビーム溶接はアーク溶接に比べ
て溶接金属部近傍の溶接熱影響部の軟化部が大幅に低下
できることが判った。これは、アーク溶接のような溶接
熱影響部の軟化が発生しやすい溶接方法に比べて、レー
ザー溶接や電子ビーム溶接は、強度等の溶接継ぎ手特性
の向上のために鋼板の組織制御が有効となることを示唆
するものである。Further, from the examination results of the inventors of the present invention and the like, it was found that the softening portion of the weld heat affected zone near the weld metal portion can be significantly reduced in laser welding and electron beam welding as compared with arc welding. This is because laser welding and electron beam welding are more effective in controlling the microstructure of the steel sheet to improve welding joint characteristics such as strength, compared to welding methods in which the heat affected zone tends to soften, such as arc welding. This suggests that
【0022】一方、レーザー溶接や電子ビーム溶接は、
アーク溶接に比べて低入熱量で溶接するために溶接部の
冷却速度が速く、マルテンサイト等の硬質な焼き入れ組
織が生成しやすく、最高硬さが高くなるとともに溶接継
ぎ手靱性の低下が生じる。On the other hand, laser welding and electron beam welding
Since the welding is performed with a lower heat input compared to arc welding, the cooling rate of the welded portion is high, a hard quenched structure such as martensite is easily generated, the maximum hardness is increased, and the weld joint toughness is reduced.
【0023】そこで、本発明者らは、これらのレーザー
溶接や電子ビーム溶接のメリットである溶接熱影響部の
軟化部の大幅低下を活かしつつ、そのデメリットである
焼き入れ組織に起因する最高硬さ増大の問題を解決し、
溶接継ぎ手の疲労強度、静的強度、靭性に優れた溶接継
ぎ手を備えた構造物の製造法について、鋭意検討を行っ
た。レーザー溶接や電子ビーム溶接のデメリット、つま
り溶接継ぎ手靱性低下の要因となる最高硬さ増大を抑制
し、且つ溶接継ぎ手の必要強度を確保する方法として、
鋼板の焼き入れ成分の低減による靱性向上と組織細粒化
による強度確保に着目して検討を行った。Therefore, the present inventors take advantage of the drastic reduction of the softened portion of the weld heat-affected zone, which is an advantage of laser welding and electron beam welding, and have the highest hardness due to the hardened structure, which is a disadvantage thereof. Solve the problem of growth,
We studied the manufacturing method of the structure with the welded joint excellent in the fatigue strength, static strength and toughness of the welded joint. Disadvantages of laser welding and electron beam welding, that is, a method of suppressing the increase in maximum hardness, which causes a decrease in toughness of the weld joint, and securing the required strength of the weld joint,
The study focused on improving the toughness by reducing the quenching component of the steel sheet and ensuring the strength by refining the structure.
【0024】図1に、本発明のレーザー溶接または電子
ビーム溶接による溶接継ぎ手(左図)と、従来のアーク
溶接による溶接継ぎ手(右図)における硬さ分布図を示
す。FIG. 1 shows a hardness distribution diagram of a welding joint by laser welding or electron beam welding according to the present invention (left figure) and a welding joint by conventional arc welding (right figure).
【0025】なお、図中で点線は、実線の鋼板に比べて
焼き入れ成分を低減して鋼材を溶接した場合の硬さ分布
を示す。The dotted line in the figure shows the hardness distribution when the quenching component is reduced and the steel material is welded as compared with the solid line steel plate.
【0026】図1からレーザー溶接または電子ビーム溶
接は、アーク溶接に比べて最高硬さが高く、母材より硬
さが低くなる軟化部が大幅に低減するか、なくすことが
できることが判る。これは、レーザー溶接または電子ビ
ーム溶接などの高エネルギー密度での溶接を行うと、ア
ーク溶接等の溶接法に比べて低入熱量で良好な溶け込み
状態で溶接できるため、熱影響部の軟化部の幅が大幅に
減少し、一方で、低入熱量により冷却が速くなる分、溶
接部の溶接金属(母材が溶融して冷却凝固した領域)に
は硬質焼き入れ組織が生成しやすくなるためと考えられ
る。From FIG. 1, it can be seen that laser welding or electron beam welding has a higher maximum hardness than arc welding and can greatly reduce or eliminate the softened portions that are lower in hardness than the base metal. This is because when welding at a high energy density such as laser welding or electron beam welding, welding can be performed with a low heat input and good penetration compared to welding methods such as arc welding. The width is greatly reduced, and on the other hand, the hardened structure is easily generated in the weld metal (the region where the base metal is melted and solidified by cooling) in the weld metal because the cooling speed becomes faster due to the low heat input. Conceivable.
【0027】また、図1から、レーザー溶接または電子
ビーム溶接では、鋼板の焼き入れ成分を低減することに
より熱影響部の軟化部がない状態で、最高硬さのみを抑
えられることが判る。一方、アーク溶接では、鋼板の焼
き入れ成分の低減により最高硬さは抑えられるが、熱影
響部の軟化部は、さらに広がり、溶接継ぎ手強度が低下
するだけでなく、歪み集中による疲労亀裂発生の要因に
なる軟化部の拡大かつ硬さ低下により疲労特性はむしろ
悪くなっていることが予想される。FIG. 1 also shows that in laser welding or electron beam welding, only the maximum hardness can be suppressed in a state where there is no softened portion of the heat-affected zone by reducing the quenching component of the steel sheet. On the other hand, in arc welding, the maximum hardness is suppressed by reducing the quenching component of the steel sheet, but the softened part of the heat-affected zone is further expanded, which not only reduces the strength of the weld joint, but also causes fatigue cracks due to strain concentration. It is expected that the fatigue characteristics are rather deteriorated due to the expansion of the softened portion and the decrease in hardness, which are factors.
【0028】上記の結果から焼き入れ成分を低く規定し
た鋼材をレーザー溶接または電子ビーム溶接することに
より、熱影響部の最高硬さ及び軟化部生成を抑制するこ
とができ、疲労特性、靭性が良好な溶接継ぎ手を備えた
構造物が得られることが判る。From the above results, it is possible to suppress the maximum hardness of the heat-affected zone and the formation of a softened portion by laser welding or electron beam welding of a steel material in which the quenching component is specified to be low, and the fatigue characteristics and toughness are good. It can be seen that a structure having a suitable welding joint can be obtained.
【0029】また、レーザー溶接または電子ビーム溶接
は、アーク溶接に比べて熱影響部の軟化部が大幅に低減
できるため、鋼材の焼き入れ成分の低下による溶接継ぎ
手の強度低下を抑制する方法として、鋼材組織の細粒化
による強度向上が有効となることが判る。Laser welding or electron beam welding can significantly reduce the softened portion of the heat-affected zone as compared with arc welding. It turns out that the improvement of the strength by making the steel structure finer is effective.
【0030】すなわち、本発明は、上記の知見を基に、
溶接継ぎ手として、レーザー溶接または電子ビーム溶接
を適用するとともに、鋼材の焼き入れ成分を低減するこ
とにより溶接熱影響部の最高硬さを抑え、且つ鋼材の組
織の細粒化により焼き入れ成分を低減による溶接継ぎ手
強度の低下を抑制することを技術思想とするものであ
る。また、溶接継ぎ手を備えた構造物としては、鋼板等
の鋼材や建築構造物等を意味するものである。That is, the present invention, based on the above findings,
Laser welding or electron beam welding is used as the welding joint, and the maximum hardness of the weld heat affected zone is suppressed by reducing the quenching component of the steel material, and the quenching component is reduced by refining the structure of the steel material. The technical idea is to suppress a decrease in the strength of the welding joint due to the above. Further, the structure provided with a welding joint means a steel material such as a steel plate, a building structure, or the like.
【0031】なお、レーザー溶接や電子ビーム溶接など
の溶接では、アーク溶接等に比べて溶接継ぎ手の溶接熱
影響部に軟化部が大幅に低減できるメカニズムは、次の
ように考えることができる。In the welding such as laser welding and electron beam welding, the mechanism by which the softened portion in the weld heat-affected zone of the welding joint can be significantly reduced as compared with arc welding or the like can be considered as follows.
【0032】すなわち、これら溶接方法は、高エネルギ
ー密度の集中熱源を用いて溶接するため、アーク溶接等
に比べて低い入熱量で完全溶け込みが達成される。その
ためその溶接ビード形状は細長くなり、溶接熱影響部の
幅は、入熱量が同じ条件のアーク溶接に比べて狭くなる
傾向にある。特に熱影響部の軟化領域は、ピーク温度で
せいぜい900〜750℃の領域であるが、この領域
は、高エネルギー密度溶接部の方がアーク溶接部に比べ
大幅に狭くなる。この理由は、溶接時の完全溶け込みが
達成される入熱量を比較すると、レーザー溶接や電子ビ
ーム溶接等の高エネルギー密度溶接では、アーク溶接と
比べて、その必要入熱量を数分の一以下に低減すること
ができるため、軟化部に対応する上記温度領域が格段に
狭くなるためであると考えられる。That is, in these welding methods, since welding is performed using a concentrated heat source having a high energy density, complete penetration is achieved with a lower heat input than in arc welding or the like. Therefore, the shape of the weld bead becomes elongated, and the width of the weld heat affected zone tends to be narrower than that of arc welding with the same heat input. In particular, the softened region of the heat-affected zone is a region having a peak temperature of at most 900 to 750 ° C., and this region is much narrower in the high energy density welded portion than in the arc welded portion. The reason for this is that when comparing the heat input that achieves complete penetration at the time of welding, the required heat input for high energy density welding such as laser welding and electron beam welding is reduced to a fraction of that of arc welding. This is considered to be because the temperature region corresponding to the softened portion is significantly narrowed because the temperature can be reduced.
【0033】次に、本発明の詳細について、説明する。Next, the details of the present invention will be described.
【0034】本発明の溶接継ぎ手の鋼材成分の限定理由
は以下の通りである。なお、以下に示す%は質量%を意
味する。The reasons for limiting the steel components of the welding joint of the present invention are as follows. In addition,% shown below means mass%.
【0035】Cは、鋼板に添加する元素の内、最も焼入
性を上げる元素である。また、レーザー溶接のように、
冷却速度が速い場合は、熱影響部の融合線近傍ではミク
ロ組織がほぼ100%マルテンサイト組織になるが、こ
のマルテンサイトの硬さそのものは、Cを代表とする侵
入形固溶元素の含有量でほぼ決定される。従って、C含
有量を抑えることは熱影響部の最高硬さを抑制する最も
有効な手段である。これは、母材が溶接時に一度溶融し
て凝固した、いわゆる溶接金属の硬さに対しても、全く
同じことがいえる。特に、レーザー溶接や電子ビーム溶
接では、溶加材を用いないため、溶接金属と母材の成分
は同じである。従って、鋼板のC含有量を抑えることに
よって溶接金属の硬さをも抑えることが可能である。本
発明では、C含有量を0.005〜0.15%に規定す
る。 C含有量を過度に低減すると、後述の鋼板組織の
細粒化を用いても充分な溶接継ぎ手の強度を確保するこ
とができないため、その下限を0.005%とした。ま
た、上限の0.15%は、これ以上添加すると融合線の
硬さが高くなりすぎ、母材強度を細粒化によって向上さ
せたとしても硬さ分布が平坦にならず、溶接継ぎ手の疲
労特性を向上することができず、また、圧延時の変形抵
抗が大きくなり過ぎるために規定する。C is an element which enhances hardenability most among the elements added to the steel sheet. Also, like laser welding,
When the cooling rate is high, the microstructure becomes almost 100% martensite near the fusion line of the heat-affected zone, but the hardness itself of this martensite is determined by the content of the interstitial solid solution element represented by C. Is almost determined by Therefore, suppressing the C content is the most effective means for suppressing the maximum hardness of the heat-affected zone. This is exactly the same for the hardness of the so-called weld metal, in which the base material is once melted and solidified during welding. In particular, in laser welding and electron beam welding, since no filler material is used, the components of the weld metal and the base metal are the same. Therefore, it is possible to suppress the hardness of the weld metal by suppressing the C content of the steel sheet. In the present invention, the C content is defined as 0.005 to 0.15%. If the C content is excessively reduced, it is not possible to secure a sufficient strength of the welded joint by using the grain refinement of the steel sheet structure described later. Therefore, the lower limit is set to 0.005%. If the upper limit of 0.15% is added more than this, the hardness of the fusion wire becomes too high, and even if the base metal strength is improved by refining, the hardness distribution is not flattened and the fatigue of the weld joint is reduced. It is specified because characteristics cannot be improved and deformation resistance during rolling becomes too large.
【0036】Siは脱酸元素として有効に利用すべき元
素であり、その含有量を0.01〜0.8%とする。S
iの下限0.01%は、この脱酸効果が得られる最低限
の値として設定した。上限の0.8%は、過大なSi添
加は鋼材の加工性を下げ、且つ焼入性を上げ、溶接部の
靱性劣化を招くためこの値を設定した。Si is an element to be effectively used as a deoxidizing element, and its content is set to 0.01 to 0.8%. S
The lower limit of 0.01% of i was set as the minimum value at which this deoxidizing effect was obtained. The upper limit of 0.8% was set because excessive addition of Si lowers the workability of the steel material, increases the hardenability, and causes deterioration in the toughness of the welded portion.
【0037】Mnは、鋼材の強度を向上させる成分とし
て有効活用すべき元素である。また、Mnによる強度確
保は、その分、鋼材に添加すべきCを減らすことができ
る。一方、既に述べたように、100%マルテンサイト
の硬さはCのみで決定されるため、溶接熱影響部の最高
硬さを抑える意味でもMnは有効活用すべきである。本
発明では、その含有量を0.2〜2.0%に規定する。
下限0.2%は、強度確保、C添加抑制の効果が得られ
る最低限の値として設定した。しかし、過剰のMn添加
は、2相域圧延温度を下げすぎ変形抵抗が上昇してしま
うため上限を2.0%とした。Mn is an element to be effectively utilized as a component for improving the strength of a steel material. Further, securing the strength by Mn can reduce the amount of C to be added to the steel material. On the other hand, as described above, since the hardness of 100% martensite is determined only by C, Mn should be used effectively in order to suppress the maximum hardness of the weld heat affected zone. In the present invention, the content is specified to be 0.2 to 2.0%.
The lower limit of 0.2% was set as the minimum value at which the effect of securing strength and suppressing the addition of C was obtained. However, excessive Mn addition lowers the two-phase region rolling temperature too much and increases the deformation resistance, so the upper limit was made 2.0%.
【0038】Al及びNはAl窒化物による鋼材の微細
化のほか、圧延過程での固溶、析出による鋼材の再結晶
のために添加するが、添加量が少ないときは効果がな
く、過剰の添加は鋼材の靭性を劣化させるので、Alは
0.001〜0.2%に、Nは0.02%以下にそれぞ
れ規定する。Al and N are added for refining steel by solid solution and precipitation in the rolling process, in addition to refining steel by Al nitride, but there is no effect when the added amount is small, and there is no effect. Since the addition deteriorates the toughness of the steel material, the content of Al is set to 0.001 to 0.2%, and the content of N is set to 0.02% or less.
【0039】P及びSは、本発明では不純物として扱う
成分である。しかし、これら元素が過剰に存在すると鋼
材の靱性劣化を招くため、それぞれ0.01%以下、
0.01%以下とした。P and S are components treated as impurities in the present invention. However, if these elements are present in excess, the toughness of the steel material is degraded.
It was set to 0.01% or less.
【0040】以上が、本発明の溶接継ぎ手における鋼材
の基本成分であるが、さらに、鋼材の強度、靭性などの
要求特性に応じて、 Ni、Cr、Mo、Cu、V、N
b、Ti、Ca、B、Mgを添加することができる。し
かしながら、これらの成分元素を過度に添加すると、後
述の鋼材組織の細粒化を達成させるための2相域圧延時
の変形抵抗が増加し、圧延負荷増大等の問題が生じるた
め、これらの添加元素の含有合計量の上限を4.5%に
規制する必要がある。The above are the basic components of the steel material in the welded joint of the present invention. Further, Ni, Cr, Mo, Cu, V, and N, depending on the required properties such as the strength and toughness of the steel material.
b, Ti, Ca, B, Mg can be added. However, if these component elements are added excessively, the deformation resistance during the two-phase region rolling for achieving the grain refinement of the steel material structure described later increases, and problems such as an increase in the rolling load occur. It is necessary to regulate the upper limit of the total content of elements to 4.5%.
【0041】次に、本発明の溶接継ぎ手の鋼材組織の限
定理由について説明する。Next, the reasons for limiting the steel structure of the welding joint of the present invention will be described.
【0042】本発明では、溶接部の最高硬さの低減のた
めに鋼板に添加する焼き入れ成分元素を低減し、それに
よって生じる溶接継ぎ手の強度低下を鋼板のミクロ組織
を細粒化することを技術思想とする。上述の焼き入れ成
分を低減した成分系で、溶接継ぎ手の必要強度を確保す
るためには、鋼板表面及び裏面のそれぞれから板厚方向
に板厚の5%以上までの範囲において、平均円相当径で
3μm以下の細粒フェライト主体組織が存在することが
必要である。In the present invention, the quenching component elements added to the steel sheet to reduce the maximum hardness of the welded portion are reduced, and the reduction in the strength of the welded joint caused by the reduction in the microstructure of the steel sheet is considered. Technical philosophy. In order to secure the required strength of the welded joint in the component system in which the quenching component is reduced, in order to secure the required strength of the welded joint, the average equivalent circle diameter in the range of 5% or more of the thickness in the thickness direction from each of the front and back surfaces of the steel plate. It is necessary that a fine-grain ferrite-based structure of 3 μm or less exists.
【0043】細粒フェライト主体組織の存在範囲を鋼板
表面及び裏面のそれぞれから板厚方向に板厚の5%以上
と規定したのは、板厚の5%未満では、レーザー溶接ま
たは電子ビーム溶接継ぎ手の溶接熱影響部の最高硬さを
低減し、靭性が劣化しない焼き入れ成分の低い成分系に
おいて、充分な強度を確保することができないためであ
る。The existence range of the fine-grained ferrite-based structure is defined as 5% or more of the sheet thickness in the sheet thickness direction from each of the front and back surfaces of the steel sheet. This is because it is not possible to secure a sufficient strength in a component system having a low quenching component that does not deteriorate the toughness and reduces the maximum hardness of the weld heat affected zone.
【0044】また、細粒フェライト主体組織の粒径を3
μm以下に規定した理由は、粒径が3μmを超えると、
鋼材の全厚を同じ粒径の組織としてもレーザー溶接また
は電子ビーム溶接継ぎ手の溶接熱影響部の最高硬さを低
減し、靭性が劣化しない焼き入れ成分の低い成分系にお
いて、充分な強度を確保することができないためであ
る。The grain size of the fine-grain ferrite-based structure is set to 3
The reason specified below μm is that if the particle size exceeds 3 μm,
Reduces the maximum hardness of the heat affected zone of laser welds or electron beam welded joints even when the entire thickness of the steel material is the same grain size, ensuring sufficient strength in a low quenching component system where toughness does not deteriorate. Because they cannot do it.
【0045】なお、上記の細粒フェライト主体組織を達
成するためには、例えば、圧延パス間に冷却を行いなが
ら繰り返し熱間圧延する等の方法により、昇温過程中の
フェライト組織に必要量の加工を加え、且つオーステナ
イト化への逆変態を防止すればよい。この方法によれ
ば、熱間圧延により加工フェライトに導入された転位は
回復、再配列をおこし、フェライトの超微細化が可能と
なる。そこで、熱間圧延中に、厚鋼板の表裏面を水冷
し、一旦、フェライト変態させてしまい、その後、冷却
によってもほとんど温度が低下しない板厚中心部の顕熱
を利用して、表裏面部のフェライト組織を昇温させなが
らさらに圧延を行い、最終的に表裏面の特定板厚範囲の
フェライト組織を3μm以下に制御することができる。In order to attain the above-mentioned fine-grain ferrite-based structure, for example, a necessary amount of the ferrite structure during the temperature raising process is reduced by a method such as repeated hot rolling while cooling between rolling passes. What is necessary is just to add a process and prevent the reverse transformation to austenitization. According to this method, dislocations introduced into the processed ferrite by hot rolling are recovered and rearranged, and ultrafine ferrite can be obtained. Therefore, during hot rolling, the front and back surfaces of the thick steel plate are water-cooled and once transformed into ferrite, and then the sensible heat at the center of the plate thickness, where the temperature hardly decreases even by cooling, is applied to the front and back surfaces. Rolling is further performed while raising the temperature of the ferrite structure, and finally the ferrite structure in the specific thickness range on the front and back surfaces can be controlled to 3 μm or less.
【0046】また、本発明では、上記細粒フェライト主
体組織に、不可避的に存在するパーライト、ベイナイ
ト、マルテンサイト等の組織が含有されても本発明の所
要特性を阻害する問題はないが、これらの組織の粒径
は、3μm以下であることが必要である。Further, in the present invention, there is no problem that the required properties of the present invention are hindered even if the fine grain ferrite-based microstructure contains an unavoidable microstructure such as pearlite, bainite and martensite. It is necessary that the grain size of the structure is 3 μm or less.
【0047】次に、本発明の溶接継ぎ手の板厚を限定し
た理由について述べる。Next, the reason why the plate thickness of the welding joint of the present invention is limited will be described.
【0048】本発明では、溶接継ぎ手の溶接熱影響部の
軟化部を低減させるための条件として、アーク溶接等に
比べて低入熱溶接で完全溶け込みが得られる高エネルギ
ー密度のレーザー溶接または電子ビーム溶接を用いる
が、このような高エネルギー密度の集中熱源をもって溶
接する場合にも、板厚の増加に伴って溶接ビード及び溶
接熱影響部の幅が広がり、軟化部を低減できない。この
軟化部が低減できない板厚の上限は、エネルギー密度等
の熱源特性によりレーザー溶接と電子ビーム溶接で異な
るため、それぞれの溶接方法において板厚を規定する必
要がある。In the present invention, as a condition for reducing the softened portion of the welding heat affected zone of the welding joint, a high energy density laser welding or an electron beam that can achieve complete penetration by low heat input welding compared to arc welding or the like is used. Although welding is used, even when welding is performed using such a concentrated heat source having a high energy density, the width of the weld bead and the weld heat affected zone increases with an increase in the plate thickness, and the softened portion cannot be reduced. Since the upper limit of the sheet thickness at which the softened portion cannot be reduced differs between laser welding and electron beam welding depending on heat source characteristics such as energy density, it is necessary to define the sheet thickness in each welding method.
【0049】本発明でレーザー溶接を用いる場合は、板
厚を4〜20mmに規定する。When laser welding is used in the present invention, the thickness is set to 4 to 20 mm.
【0050】板厚の上限の20mmは、その上限板厚を
超えると、レーザー溶接の集中熱源を用いても溶接ビー
ド及び溶接熱影響部の幅が広がり過ぎて軟化部の幅を低
減できず、疲労特性向上が得られなくなるため、規定し
た。また、板厚の下限の4mmは、その下限板厚を下回
ると、鋼板の熱間圧延時の放冷により板厚中心部の温度
低下が大きくなり、圧延パス間冷却の熱間圧延時の冷却
後の鋼板表裏面領域の鋼板中心部の顕熱による昇温効果
を利用できず、結果として上述の本発明の細粒フェライ
ト主体組織を生成できなくなるため、規定した。If the upper limit of the plate thickness of 20 mm exceeds the upper limit of the plate thickness, the width of the weld bead and the weld heat affected zone becomes too wide even if a concentrated heat source of laser welding is used, and the width of the softened zone cannot be reduced. Since the improvement of the fatigue characteristics cannot be obtained, it is specified. When the lower limit of the sheet thickness is 4 mm is less than the lower limit of the sheet thickness, the temperature drop at the center of the sheet thickness becomes large due to the cooling during the hot rolling of the steel sheet, and the cooling during the hot rolling of the cooling between the rolling passes. Since the effect of increasing the temperature by the sensible heat of the central part of the steel sheet in the front and back regions of the steel sheet cannot be used later, as a result, the fine grain ferrite-based structure of the present invention cannot be generated, so that it is specified.
【0051】また、本発明で電子ビーム溶接を用いる場
合は、板厚を10〜50mmに規定する。In the case where electron beam welding is used in the present invention, the thickness is set to 10 to 50 mm.
【0052】電子ビーム溶接は、レーザー溶接よりもエ
ネルギー密度が高いため、厚い板に対して適用可能であ
る。しかしながら、電子ビーム溶接は、溶接部近傍を真
空にする必要があるため、その分、溶接作業性はレーザ
ー溶接よりも低くならざるを得ない。板厚の下限の10
mmは、溶接作業性を考慮したうえで電子ビーム溶接の
適用メリットが得られる最低板厚とした。また、板厚の
上限の50mmは、その上限板厚を上回ると、電子ビー
ム溶接のような高エネルギー密度溶接でも、溶接熱影響
部の幅が広くなり過ぎて、軟化部を低減することができ
なくなるために規定する。Since electron beam welding has a higher energy density than laser welding, it can be applied to thick plates. However, electron beam welding requires a vacuum in the vicinity of the welded portion, so that the welding workability must be lower than that for laser welding. The lower limit of the plate thickness is 10
The mm was set to the minimum thickness at which the advantages of applying electron beam welding can be obtained in consideration of welding workability. In addition, if the upper limit of the plate thickness of 50 mm exceeds the upper limit plate thickness, even in high energy density welding such as electron beam welding, the width of the welding heat affected zone becomes too wide, and the softened portion can be reduced. Stipulate to be eliminated.
【0053】次に、本発明の溶接継ぎ手の溶接熱影響部
の幅を限定した理由について説明する。Next, the reason why the width of the heat affected zone of the welding joint of the present invention is limited will be described.
【0054】本発明のレーザー溶接または電子ビーム溶
接を適用した場合の溶接部は、溶接時に母材が一度溶融
した後、冷却凝固する領域である溶接金属と、溶接入熱
により影響を受け、母材のミクロ組織とは異なる組織と
なる領域である溶接熱影響部とに大きく区分できる。本
発明の溶接金属は、溶接材料を用いないため、その成分
組成は、母材とほぼ同等あるが、他の溶接方法に比べて
レーザー溶接または電子ビーム溶接は低入熱量かつ冷却
速度が高いため、溶融後の冷却強固過程で硬質焼き入れ
組織が生成されやすく硬さが高い領域である。When the laser welding or the electron beam welding according to the present invention is applied, the welded portion is affected by the weld metal, which is a region where the base material is once melted and then solidified by cooling, and the heat input from the weld. The microstructure of the material can be broadly divided into a weld heat affected zone, which is a region having a different structure. Since the weld metal of the present invention does not use a welding material, its component composition is almost the same as that of the base metal, but laser welding or electron beam welding has a low heat input and a high cooling rate compared to other welding methods. This is a region where a hard quenched structure is easily generated in a cooling and solidifying process after melting, and the hardness is high.
【0055】一方、溶接熱影響部は、溶接金属から母材
の方向に離れるに従って硬さが低くなり、一般的に、溶
接熱影響部の範囲でも特に母材部に近傍領域に母材の硬
さよりも軟らかく最も硬度が低い領域である軟化部が形
成される。この軟化部は、他の溶接熱影響部より最高到
達温度が低い領域のために、他の溶接熱影響部に比べて
旧オーステナイト粒径が小さくなった領域である。従っ
て、溶接金属と溶接熱影響部、つまり溶接部の幅が一定
の条件であれば、溶接金属の幅を増大させることによっ
て、溶接熱影響部の幅を低減でき、必然的に溶接熱影響
部中の母材近傍に存在する軟化部を低減、または実質的
に消失できる。On the other hand, the hardness of the weld heat affected zone decreases with increasing distance from the weld metal in the direction of the base metal. A softened portion, which is softer and has the lowest hardness, is formed. The softened portion is a region in which the prior austenite grain size is smaller than that of the other heat affected zones because the highest temperature is lower than the other heat affected zones. Therefore, if the width of the weld metal and the weld heat-affected zone, that is, the width of the weld zone, is constant, the width of the weld heat-affected zone can be reduced by increasing the width of the weld metal. The softened portion existing in the vicinity of the base material therein can be reduced or substantially eliminated.
【0056】上記の知見を踏まえて、本発明では、溶接
継ぎ手の軟化部を低減することにより、疲労強度特性を
向上し、強度低下を抑制するために溶接熱影響部の幅を
1.6mm以下に規定する。上限の1.6mmは、その
上限値を上回ると、軟化部生成による疲労強度特性及び
強度低下の影響が顕著になるため規定する。Based on the above findings, in the present invention, the width of the weld heat-affected zone is reduced to 1.6 mm or less in order to improve the fatigue strength characteristics by reducing the softened portion of the welding joint and to suppress the reduction in strength. Defined in The upper limit of 1.6 mm is specified because if the upper limit is exceeded, the effects of fatigue strength characteristics and strength reduction due to the formation of softened portions become significant.
【0057】なお、溶接熱影響部の幅を上記の範囲に制
御する方法としては、例えば、電子ビーム溶接の場合に
は、溶接入熱量が同じ条件で、溶接ビームに適当な磁場
を加え、溶接ビームをオッシレーションさせながら溶接
金属の幅を調整することで溶接熱影響部の幅を制御でき
る。As a method of controlling the width of the welding heat affected zone to the above range, for example, in the case of electron beam welding, an appropriate magnetic field is applied to the welding beam under the same welding heat input condition, The width of the weld heat affected zone can be controlled by adjusting the width of the weld metal while oscillating the beam.
【0058】また、レーザー溶接の場合は、溶接ビーム
をオッシレーションさせることも可能ではあるが、電子
ビームの場合よりは難しい。これに変わる方法として
は、適当なレンズを用いてレーザービームを溶接線に対
し直角な方向に横長形状となるように制御することで、
オッシレーションの場合と同じ効果が得られ、溶接熱影
響部の幅を狭く制御できる。In the case of laser welding, it is possible to oscillate the welding beam, but it is more difficult than in the case of electron beam. An alternative method is to use a suitable lens to control the laser beam so that it is oblong in the direction perpendicular to the weld line.
The same effect as in the case of oscillation can be obtained, and the width of the heat affected zone can be controlled to be narrow.
【0059】図2には、電子ビーム溶接で、溶接ビーム
のオッシレーションを実施しない場合(上図)と実施し
た場合(下図)での溶接熱影響部及び溶接金属の模式図
(断面図)を示した。図2の溶接ビームのオッシレーシ
ョンを実施しない場合(上図)と実施した場合(下図)
を比較して明らかなように、両者の溶接熱影響部と母材
の境界(点線)位置、つまり、溶接部(溶接金属+溶接
熱影響部)の全幅は一定であるが、オッシレーションを
実施した場合(下図)は、溶接金属の幅が広くすること
で、溶接熱影響部の幅を狭くすることができる。つま
り、溶接入熱量が同じ条件で、溶接ビームに適当な磁場
を加え、溶接ビームをオッシレーションさせながら溶接
金属の幅を拡げることで溶接熱影響部の幅を低減でき
る。FIG. 2 is a schematic view (cross-sectional view) of the weld heat affected zone and the weld metal when the oscillation of the welding beam is not performed (upper figure) and when the oscillation is performed (lower figure) in electron beam welding. Indicated. The case where the oscillation of the welding beam in FIG. 2 is not performed (upper figure) and the case where it is performed (lower figure)
As is clear from the comparison, the position of the boundary (dotted line) between the weld heat-affected zone and the base metal, that is, the entire width of the weld zone (weld metal + weld heat-affected zone) is constant, but oscillation was performed. In this case (lower figure), the width of the weld heat-affected zone can be reduced by increasing the width of the weld metal. That is, under the same welding heat input, an appropriate magnetic field is applied to the welding beam, and the width of the weld metal is increased while oscillating the welding beam, whereby the width of the welding heat affected zone can be reduced.
【0060】[0060]
【実施例】以下に本発明の実施例及び比較例により本発
明の効果について説明する。EXAMPLES The effects of the present invention will be described below with reference to examples and comparative examples of the present invention.
【0061】表1に示した本発明で規定した範囲にある
成分組成を有する鋼板を表2に示す製造条件にて、最終
板厚が10〜75mmの範囲にある鋼板を製造した。表
2において、鋼板番号1〜13及び20は、製造条件を
厳格にした圧延パス間冷却による制御圧延を実施したも
のであり、鋼板番号14〜19は、加熱温度が、約12
00℃、900〜1000℃の温度領域で熱間圧延し、
その後空冷する通常圧延を実施したものである。得られ
た鋼板の板厚、組織及び特性を表3に示す。表3で、本
発明例の鋼板番号1〜12は、本発明で規定する鋼板の
表裏層から板厚方向の範囲に本発明で規定する平均粒径
の細粒フェライト主体組織が存在し、鋼板全厚の強度が
440MPa以上を維持している鋼板であり、比較例の
鋼板番号13は、フェライト主体組織の平均粒径が本発
明で規定する範囲から外れ、鋼板全厚の強度が低く、比
較例の鋼板番号20は、表裏層組織は本発明範囲内であ
るが、板厚が発明範囲外のものである。また、比較例の
鋼板番号14〜19は、上記の通常圧延条件で製造した
鋼板であり、鋼板組織の平均粒径は約50μmであり、
本発明範囲から外れ、鋼板全厚の強度が低いものであっ
た。A steel sheet having a component composition in the range specified in the present invention shown in Table 1 was manufactured under the manufacturing conditions shown in Table 2, and the final sheet thickness was in the range of 10 to 75 mm. In Table 2, steel plate numbers 1 to 13 and 20 are obtained by performing controlled rolling by cooling between rolling passes with strict production conditions, and steel plate numbers 14 to 19 have heating temperatures of about 12
Hot rolling in the temperature range of 00 ° C, 900 to 1000 ° C,
Thereafter, normal rolling for air cooling was performed. Table 3 shows the thickness, structure and properties of the obtained steel sheet. In Table 3, the steel sheet Nos. 1 to 12 of the present invention have a fine-grain ferrite-based structure having an average grain size defined by the present invention in the range from the front and back layers of the steel sheet defined by the present invention to the thickness direction. A steel sheet having a total thickness strength of 440 MPa or more, and the steel sheet number 13 of the comparative example has an average grain size of the ferrite-based structure out of the range specified in the present invention, and the strength of the steel sheet total thickness is low. In the steel sheet No. 20 of the example, the front and back layer structure is within the scope of the present invention, but the sheet thickness is outside the scope of the invention. Further, the steel sheet numbers 14 to 19 of the comparative examples are steel sheets manufactured under the above-described normal rolling conditions, and the average grain size of the steel sheet structure is about 50 μm,
Out of the range of the present invention, the strength of the entire steel sheet was low.
【0062】[0062]
【表1】 [Table 1]
【0063】[0063]
【表2】 [Table 2]
【0064】次に、これらの鋼板をレーザー溶接法また
は電子ビーム溶接法により突き合わせ溶接した。Next, these steel plates were butt-welded by laser welding or electron beam welding.
【0065】レーザー溶接及び電子ビーム溶接時の溶接
に必要なパワーは、板厚によって異なるため、板厚によ
って以下のようにパワーを調整した。レーザー溶接の場
合は、板厚が14mmまでは10kW、1m/min
で、18mmまでは15kW、1m/minで、23m
mまでは20kW、0.8m/minで溶接した。Since the power required for laser welding and electron beam welding differs depending on the plate thickness, the power was adjusted according to the plate thickness as follows. In case of laser welding, 10kW, 1m / min up to 14mm thickness
And up to 18mm, 15kW, 1m / min, 23m
Up to m, welding was performed at 20 kW and 0.8 m / min.
【0066】また、電子ビーム溶接の場合は、板厚が2
5mm以下の場合は、150mA、150kV、60c
m/minで、板厚が40〜50mmの場合は、200
mA、160kV、50cpmで、板厚が75mmの場
合は、210mA、150kV、16cm/minで溶
接した。In the case of electron beam welding, the thickness is 2
In the case of 5 mm or less, 150 mA, 150 kV, 60 c
m / min, and when the plate thickness is 40 to 50 mm, 200
In the case of mA, 160 kV, 50 cpm and a plate thickness of 75 mm, welding was performed at 210 mA, 150 kV, 16 cm / min.
【0067】溶接終了後、疲労試験片を継ぎ手部より採
取し、表裏面のビード形状が疲労試験結果に影響しない
よう、表裏面を機械加工によりなめらかな表面に仕上げ
た。After the welding was completed, a fatigue test piece was sampled from the joint portion, and the front and back surfaces were finished to a smooth surface by machining so that the bead shape on the front and back surfaces did not affect the results of the fatigue test.
【0068】これらの試験片を用い、疲労試験を実施し
た。疲労特性の比較は、応力振幅が400MPaの場合
(10Hz)における疲労寿命(cycle)と、疲労
限で行った。A fatigue test was performed using these test pieces. The comparison of the fatigue characteristics was performed between the fatigue life (cycle) when the stress amplitude was 400 MPa (10 Hz) and the fatigue limit.
【0069】表4に、レーザー溶接及び電子ビーム溶接
を行った溶接継ぎ手の溶接熱影響部の幅と、溶接熱影響
部の最高硬さ及び疲労特性を示す。なお、表4中のLは
レーザー溶接を、EBは電子ビーム溶接をそれぞれ示
す。Table 4 shows the width of the weld heat affected zone of the welded joint subjected to laser welding and electron beam welding, and the maximum hardness and fatigue properties of the weld heat affected zone. In Table 4, L indicates laser welding, and EB indicates electron beam welding.
【0070】表4の溶接部最高硬さを比較すると判るよ
うに、本発明例では、鋼材全厚強度が高くとも、最高硬
さは比較材とほぼ同程度のレベルであることが理解でき
る。これは、鋼材強度を高くしたとしても、溶接部の最
高硬さを従来と同じ程度に抑えることが可能であること
を意味し、溶接部の機械的特性上好ましいことを示して
いる。As can be seen from the comparison of the maximum hardness of the weld in Table 4, it can be understood that the maximum hardness of the present invention example is almost the same level as that of the comparative material even if the total thickness strength of the steel material is high. This means that even if the steel material strength is increased, it is possible to suppress the maximum hardness of the welded portion to the same level as in the past, and this is preferable in terms of the mechanical properties of the welded portion.
【0071】表4において、比較例の試験番号:17〜
22は、表3に示す通常圧延条件で製造し、本発明の組
織規定範囲から外れる鋼板番号:14〜19の鋼板をレ
ーザー溶接または電子ビーム溶接して溶接継ぎ手を作製
したものであり、もともと母材の硬さが低くなっている
ため溶接熱影響部に母材より軟らかくなる部分(軟化
部)は認められなかったが、母材部の強度が低くなって
しまっているため、400MPaでの疲労寿命が0.5
×105以下に低く、また、疲労限も260MPa以下
であった。In Table 4, the test numbers of the comparative examples: 17 to
No. 22 is a steel plate having a steel plate number: 14 to 19, which is manufactured under the normal rolling conditions shown in Table 3 and which is out of the range specified by the microstructure of the present invention, is produced by laser welding or electron beam welding, and is originally made of a welded joint. Due to the low hardness of the material, there was no part (softened portion) that was softer than the base metal in the heat affected zone, but the strength of the base material was low, so fatigue at 400 MPa was observed. 0.5 life
× 10 5 or less, and the fatigue limit was 260 MPa or less.
【0072】比較例の試験番号16は、表3に示す制御
圧延材であるが、フェライト主体組織の平均粒径が本発
明で規定する範囲から高め(21mm)に外れ、鋼板強
度が低い鋼板番号:13の鋼板をレーザー溶接して溶接
継ぎ手を作製したものであり、母材部の強度が低く、硬
さが低くなり、本発明例と比べ充分な疲労特性が得られ
ていない。比較例の試験番号23は、表3に示す制御圧
延材であり、表裏層組織は本発明範囲内であるが、板厚
が75mmと厚く、発明範囲外である鋼板番号:20の
鋼板を電子ビーム溶接して溶接継ぎ手を作製したもので
あり、板厚が厚過ぎるために種々のオッシレーション条
件で電子ビーム溶接を行っても溶接熱影響部幅が広が
り、硬さが160と低い軟化部が発生し、軟化部にひず
みが集中して疲労特性が劣化した。Test No. 16 of the comparative example is a controlled rolled material as shown in Table 3, in which the average grain size of the ferrite-based structure deviates from the range specified by the present invention to a higher value (21 mm), and the steel plate strength is lower. : Laser welding of the steel sheet of No. 13 to produce a welded joint, in which the strength and hardness of the base material were low, and sufficient fatigue characteristics were not obtained as compared with the examples of the present invention. Test No. 23 of the comparative example is a control rolled material shown in Table 3, and the front and back layer structure is within the scope of the present invention. The welding joint is manufactured by beam welding, and the width of the weld heat affected zone is widened even when electron beam welding is performed under various oscillation conditions because the plate thickness is too thick. This occurred, and strain was concentrated on the softened portion, resulting in deterioration of fatigue characteristics.
【0073】比較例の試験番号4、7、11は、表3に
示す制御圧延材であり、表裏層組織は本発明範囲内であ
る鋼板番号:3、5、8の鋼板を電子ビーム溶接して溶
接継ぎ手を作製したものであるが、溶接熱影響部の幅が
本発明範囲からはずれているため、表4に示すように溶
接熱影響部に表裏面の細粒化層より軟らかい部分、すな
わち軟化部が発生し、疲労特性が劣化し、疲労限もすべ
て300MPaに達しなかった。比較例の試験番号14
は、表3に示す制御圧延材であり、表裏層組織は本発明
範囲内であるが、板厚が23mmとレーザー溶接を適用
するためには厚い板厚の鋼板番号:11の鋼板をレーザ
ー溶接したため、レーザービーム形状を横長にして熱影
響部の幅を制御しても熱影響部の幅を1.6mm以下に
抑えることができず、硬さが175と、表裏面の細粒化
層より軟らかい部分が発生し、疲労強度特性が低くなっ
た。Test Nos. 4, 7, and 11 of the comparative examples are the control rolled materials shown in Table 3, and the front and back layer structures are within the scope of the present invention. However, since the width of the weld heat-affected zone is out of the range of the present invention, as shown in Table 4, the weld heat-affected zone is softer than the fine-grained layer on the front and back surfaces, that is, A softened portion was generated, fatigue characteristics were deteriorated, and all fatigue limits did not reach 300 MPa. Test No. 14 of Comparative Example
Is a rolled control material shown in Table 3, and the front and back layer structure is within the scope of the present invention. However, in order to apply laser welding to a sheet thickness of 23 mm, a steel sheet having a thicker steel sheet number: 11 is laser-welded. Therefore, the width of the heat-affected zone cannot be suppressed to 1.6 mm or less even when the laser beam shape is horizontally elongated to control the width of the heat-affected zone, and the hardness is 175. Soft parts were generated, and the fatigue strength characteristics became low.
【0074】一方、本発明例の試験番号1〜3、5、
6、8〜10、12、13、15は、表3に示す制御圧
延材であり、成分組成及び表裏層組織は本発明範囲内で
ある鋼板番号:1〜10、12の鋼板をレーザー溶接ま
たは電子ビーム溶接して溶接継ぎ手を作製したものであ
り、溶接継ぎ手強度が440Mpa以上、400MPa
での疲労寿命がすべて0.5×105を上回っており、
また疲労限もすべて300MPa以上であり、良好な溶
接継ぎ手強度及び疲労特性が得られた。On the other hand, Test Nos. 1 to 3, 5
6, 8 to 10, 12, 13, and 15 are control rolled materials shown in Table 3, and the component composition and the front and back layer structure are within the scope of the present invention. A welded joint produced by electron beam welding, with a welded joint strength of 440 Mpa or more and 400 MPa
Fatigue life exceeds 0.5 × 10 5 ,
The fatigue limits were all 300 MPa or more, and good weld joint strength and fatigue characteristics were obtained.
【0075】[0075]
【表3】 [Table 3]
【0076】[0076]
【表4】 [Table 4]
【0077】[0077]
【発明の効果】本発明は、以上のように、レーザー溶接
及び電子ビーム溶接継ぎ手の機械的特性を向上させるこ
とを可能にした。本発明を用いれば、母材強度を上げ、
且つ溶接熱影響部を抑え、さらには疲労特性をも改善さ
せることができる。特に、レーザー溶接は、今後そのパ
ワー増大の恩恵を受け、重工業分野にも適用範囲を広げ
ていくものと期待されるプロセスである。これらのこと
を考えると、構造物の信頼性を決定する溶接部の機械的
特性を向上できる本発明は、産業上のメリットはきわめ
て大きい。As described above, the present invention has made it possible to improve the mechanical properties of a laser welding and an electron beam welding joint. By using the present invention, the base material strength is increased,
In addition, the heat affected zone can be suppressed, and the fatigue characteristics can be improved. In particular, laser welding is a process that is expected to benefit from the increased power in the future and expand its application to heavy industry. In view of these facts, the present invention, which can improve the mechanical properties of a weld that determines the reliability of a structure, has a great industrial advantage.
【図1】レーザー溶接及び電子ビーム溶接の溶接部の硬
さ分布をアーク溶接部の硬さと比較した概念図である。FIG. 1 is a conceptual diagram comparing the hardness distribution of a welded portion in laser welding and electron beam welding with the hardness of an arc welded portion.
【図2】レーザー溶接または電子ビーム溶接において、
溶接金属の幅と溶接熱影響部の幅におけるオッシレーシ
ョンの影響を示した概念図である。FIG. 2 In laser welding or electron beam welding,
It is the conceptual diagram which showed the influence of the oscillation in the width | variety of a weld metal and the width | variety of a welding heat affected zone.
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.7 識別記号 FI テーマコート゛(参考) // B23K 103:04 B23K 103:04 (72)発明者 小関 敏彦 富津市新富20−1 新日本製鐵株式会社技 術開発本部内 Fターム(参考) 4E066 CA14 CB04 4E068 DA00 DA14 DB01 ──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. 7 Identification symbol FI Theme coat ゛ (Reference) // B23K 103: 04 B23K 103: 04 (72) Inventor Toshihiko Koseki 20-1 Shintomi, Futtsu Nippon Steel Corporation F-term in Technology Development Division, Inc. (reference) 4E066 CA14 CB04 4E068 DA00 DA14 DB01
Claims (10)
して、質量%で、C:0.005〜0.15%、Si:
0.01〜0.8%、Mn:0.2〜2.0%、Al:
0.001〜0.2%、N:0.02%以下、P:0.
01%以下、S:0.01%以下を含有し、残部が鉄及
び不可避不純物からなり、鋼板表面及び裏面のそれぞれ
から板厚方向に板厚の5%以上までの範囲において、平
均円相当径で3μm以下の細粒フェライト組織を有する
ことを特徴とするレーザー溶接継ぎ手を備えた構造物。1. The steel sheet has a thickness of 4 to 20 mm, and contains C: 0.005 to 0.15% by mass, Si:
0.01-0.8%, Mn: 0.2-2.0%, Al:
0.001-0.2%, N: 0.02% or less, P: 0.
S: 0.01% or less, S: 0.01% or less, the balance being iron and unavoidable impurities, and the average equivalent circle diameter in a range of 5% or more of the thickness in the thickness direction from each of the front and back surfaces of the steel plate. A structure provided with a laser welding joint, characterized by having a fine-grained ferrite structure of 3 μm or less.
b、Ti、Ca、B、Mgの内の1種または2種以上を
合計量で4.5質量%以下含有することを特徴とする請
求項1に記載のレーザー溶接継ぎ手を備えた構造物。2. Ni, Cr, Mo, Cu, V, N
The structure provided with a laser welding joint according to claim 1, wherein one or more of b, Ti, Ca, B, and Mg are contained in a total amount of 4.5% by mass or less.
響部の幅が1.6mm以下であることを特徴とする請求
項1または2の何れかに記載のレーザー溶接継ぎ手を備
えた構造物。3. The structure provided with a laser welding joint according to claim 1, wherein a width of a heat affected zone of a welding portion of the laser welding joint is 1.6 mm or less.
として、質量%で、C:0.005〜0.15%、S
i:0.01〜0.8%、Mn:0.2〜2.0%、A
l:0.001〜0.2%、N:0.02%以下、P:
0.01%以下、S:0.01%以下を含有し、残部が
鉄及び不可避不純物からなり、鋼板表面及び裏面のそれ
ぞれから板厚方向に板厚の5%以上までの範囲におい
て、平均円相当径で3μm以下の細粒フェライト主体組
織を有し、且つ溶接部の熱影響部の幅が1.6mm以下
であることを特徴とする電子ビーム溶接継ぎ手を備えた
構造物。4. The steel sheet has a thickness of 10 to 50 mm, and contains C: 0.005 to 0.15% by mass% as a component.
i: 0.01 to 0.8%, Mn: 0.2 to 2.0%, A
l: 0.001 to 0.2%, N: 0.02% or less, P:
0.01% or less, S: 0.01% or less, the balance being iron and unavoidable impurities, the average circle in the range of 5% or more of the thickness in the thickness direction from each of the front and back surfaces of the steel plate. A structure provided with an electron beam welding joint, which has a fine-grain ferrite-based structure having an equivalent diameter of 3 µm or less and a width of a heat-affected zone of a welded portion is 1.6 mm or less.
b、Ti、Ca、B、Mgの内の1種または2種以上を
合計量で4.5質量%以下含有することを特徴とする請
求項4に記載の電子ビーム溶接継ぎ手を備えた構造物。5. Ni, Cr, Mo, Cu, V, N
The structure having an electron beam welding joint according to claim 4, wherein one or more of b, Ti, Ca, B, and Mg are contained in a total amount of 4.5% by mass or less. .
部の幅が1.6mm以下であることを特徴とする請求項
4または5の何れかに記載のレーザー溶接継ぎ手を備え
た構造物。6. The structure provided with a laser welding joint according to claim 4, wherein a width of a heat-affected zone of a welding portion of the electron beam joint is 1.6 mm or less.
して、質量%で、C:0.005〜0.15%、Si:
0.01〜0.8%、Mn:0.2〜2.0%、Al:
0.001〜0.2%、N:0.02%以下、P:0.
01%以下、S:0.01%以下を含有し、残部が鉄及
び不可避不純物からなり、鋼板表面及び裏面のそれぞれ
から板厚方向に板厚の5%以上までの範囲において、平
均円相当径で3μm以下の細粒フェライト組織を有する
鋼板を熱影響部の幅が1.6mm以下になるようにレー
ザー溶接することを特徴とするレーザー溶接継ぎ手を備
えた構造物の製造方法。7. The steel sheet has a thickness of 4 to 20 mm, and contains C: 0.005 to 0.15% by mass% and Si:
0.01-0.8%, Mn: 0.2-2.0%, Al:
0.001-0.2%, N: 0.02% or less, P: 0.
S: 0.01% or less, S: 0.01% or less, the balance being iron and unavoidable impurities, and the average equivalent circle diameter in a range of 5% or more of the thickness in the thickness direction from each of the front and back surfaces of the steel plate. A method for producing a structure having a laser welding joint, wherein a steel sheet having a fine grain ferrite structure of 3 μm or less is laser-welded so that the width of the heat-affected zone is 1.6 mm or less.
b、Ti、Ca、B、Mgの内の1種または2種以上を
合計量で4.5質量%以下含有することを特徴とする請
求項7に記載のレーザー溶接継ぎ手を備えた構造物の製
造方法。8. Further, Ni, Cr, Mo, Cu, V, N
The structure having a laser welding joint according to claim 7, wherein one or more of b, Ti, Ca, B, and Mg are contained in a total amount of 4.5% by mass or less. Production method.
として、質量%で、C:0.005〜0.15%、S
i:0.01〜0.8%、Mn:0.2〜2.0%、A
l:0.001〜0.2%、N:0.02%以下、P:
0.01%以下、S:0.01%以下を含有し、残部が
鉄及び不可避不純物からなり、鋼板表面及び裏面のそれ
ぞれから板厚方向に板厚の5%以上までの範囲におい
て、平均円相当径で3μm以下の細粒フェライト組織を
有する鋼板を熱影響部の幅が1.6mm以下になるよう
に電子ビーム溶接することを特徴とする電子ビーム溶接
継ぎ手を備えた構造物の製造方法。9. The steel sheet has a thickness of 10 to 50 mm, and contains C: 0.005 to 0.15% by mass% as a component.
i: 0.01 to 0.8%, Mn: 0.2 to 2.0%, A
l: 0.001 to 0.2%, N: 0.02% or less, P:
0.01% or less, S: 0.01% or less, the balance being iron and unavoidable impurities, the average circle in the range of 5% or more of the thickness in the thickness direction from each of the front and back surfaces of the steel plate. A method for manufacturing a structure having an electron beam welding joint, wherein an electron beam is welded to a steel sheet having a fine-grained ferrite structure having an equivalent diameter of 3 μm or less so that the width of the heat-affected zone is 1.6 mm or less.
Nb、Ti、Ca、B、Mgの内の1種または2種以上
を合計量で4.5質量%以下含有することを特徴とする
請求項9に記載の電子ビーム溶接継ぎ手を備えた構造物
の製造方法。10. Ni, Cr, Mo, Cu, V,
The structure having an electron beam welding joint according to claim 9, wherein one or more of Nb, Ti, Ca, B, and Mg are contained in a total amount of 4.5% by mass or less. Manufacturing method.
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JP2000183331A JP4267183B2 (en) | 2000-06-19 | 2000-06-19 | Structures with laser or electron beam welded joints with excellent fatigue strength characteristics and methods for manufacturing them |
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