JP2001064747A - B-added high tensile strength steel excellent in toughness in weld heat-affected zone - Google Patents
B-added high tensile strength steel excellent in toughness in weld heat-affected zoneInfo
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- JP2001064747A JP2001064747A JP23793499A JP23793499A JP2001064747A JP 2001064747 A JP2001064747 A JP 2001064747A JP 23793499 A JP23793499 A JP 23793499A JP 23793499 A JP23793499 A JP 23793499A JP 2001064747 A JP2001064747 A JP 2001064747A
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、引張強さが８０ｋ
ｇｆ／ｍｍ2 以上の溶接熱影響部靭性に優れたＢ添加高
張力鋼に関する。BACKGROUND OF THE INVENTION The present invention relates to a tensile strength of 80 k.
The present invention relates to a B-added high-strength steel having excellent weld heat-affected zone toughness of not less than gf / mm 2 .
【０００２】[0002]
【従来の技術】構造物の高性能化、大型化が進むのに伴
って高強度鋼板の開発の重要性が高まっている。鋼板強
度は、添加元素の増加により達成される。しかし、添加
元素の増加は、一般に、溶接施工時の耐溶接割れ性を低
下させる。このため、添加元素量を増加させることなく
高強度が得られるような組成、製造法に関する種々の検
討がなされてきた。その結果、微量（０．０００３〜
０．００２％程度）のＢ添加により鋼の焼入性が著しく
向上することから、耐溶接割れ性の極端な劣化を生じさ
せることなく引張強さが８０ｋｇｆ／ｍｍ2 を超える高
強度鋼を製造できることが明らかにされている。2. Description of the Related Art The development of high-strength steel sheets has become increasingly important as structures have become more sophisticated and larger. Steel sheet strength is achieved by increasing the additional elements. However, an increase in the added element generally lowers the resistance to weld cracking during welding. For this reason, various studies have been made on compositions and production methods that can provide high strength without increasing the amount of added elements. As a result, a very small amount (0.0003-
Since the hardenability of steel is remarkably improved by the addition of B (about 0.002%), a high-strength steel having a tensile strength exceeding 80 kgf / mm 2 is produced without causing extreme deterioration of weld cracking resistance. It is clear what can be done.
【０００３】溶接構造用の鋼板には、一般に、上記の耐
溶接割れ感受性の他に溶接熱影響部靭性が要求される。
溶接熱影響部靭性の改善方法としては、一般的に、以下
の（イ）〜（ニ）の方法が有効とされている。In general, a steel plate for a welded structure is required to have a weld heat-affected zone toughness in addition to the above-described weld crack resistance.
In general, the following methods (a) to (d) are considered to be effective as methods for improving the toughness of the heat affected zone.
【０００４】（イ）析出物を利用して高温加熱された際
の旧オーステナイト結晶粒の粗大化を防止する。(A) To prevent coarsening of prior austenite crystal grains when heated at a high temperature by utilizing precipitates.
【０００５】（ロ）析出物を利用して粒内変態を促進す
ることにより組織を微細化する。(B) Microstructure is refined by promoting intragranular transformation using precipitates.
【０００６】（ハ）Ｃ、Ｓｉ、Ａｌを低減することによ
り島状マルテンサイト組織などの硬化第二相の生成を抑
制する。(C) The formation of a hardened second phase such as an island martensite structure is suppressed by reducing C, Si and Al.
【０００７】（ニ）Ｎ量を低減することによりマトリッ
クスの靭性を向上させる。(D) The toughness of the matrix is improved by reducing the amount of N.
【０００８】ただし、上記（イ）〜（ニ）の方法が検討
された対象は、引張強さが６０ｋｇｆ／ｍｍ2 程度の比
較的低強度の鋼材においてである。[0008] However, the method (a) to (d) was studied for a relatively low-strength steel material having a tensile strength of about 60 kgf / mm 2 .
【０００９】母材の引張強さが８０ｋｇｆ／ｍｍ2 以上
の高強度Ｂ添加鋼の溶接熱影響部靭性の改善方法として
は、Ｃ、ＳｉおよびＳｏｌ．Ａｌ量を低減して島状マル
テンサイト組織などの硬化第二相の生成量を減らす方法
（特開平９−６７６２０号公報）や、Ｎ量を０．００２
％以下に低減する方法（特公平１−２１８４７号公報）
があるにすぎない。Methods for improving the toughness of the heat-affected zone of a high-strength B-added steel having a base material having a tensile strength of 80 kgf / mm 2 or more include C, Si and Sol. A method of reducing the amount of Al to reduce the amount of a hardened second phase such as an island martensite structure (Japanese Patent Application Laid-Open No. 9-67620), or reducing the amount of N to 0.002
% (Japanese Patent Publication No. 1-28474)
There is only.
【００１０】ところが、安定かつ安価に高強度を確保す
るめには、Ｃ量を無制限に低減することができない。ま
た、実製造を想定した場合、Ａｌ量の極端な低減は脱酸
不足を招く懸念がある。すなわち、上記の特開平９−６
７６２０号公報に示される方法では、実質的に効果を挙
げうるのはＳｉ量の低減だけであるという問題があっ
た。また、特公平１−２１８４７号公報に示されるＮ量
を低減する方法については、Ｎ量が０．００２％以下の
鋼を安定かつ大量に生産することが難しいという問題が
あった。However, in order to secure high strength stably and inexpensively, the amount of carbon cannot be reduced without limit. Further, when assuming actual production, an extreme decrease in the amount of Al may cause insufficient deoxidation. That is, Japanese Patent Application Laid-Open No. 9-6
The method disclosed in Japanese Patent No. 7620 has a problem that only the reduction of the Si amount can be substantially effective. Further, the method of reducing the amount of N disclosed in Japanese Patent Publication No. 21847/1990 has a problem that it is difficult to stably produce a steel having an N amount of 0.002% or less in large quantities.
【００１１】[0011]
【発明が解決しようとする課題】本発明の目的は、Ｃ、
ＮおよびＡｌ量の極端な低減が不要で、安定かつ大量に
生産することが容易であり、所望の母材特性と耐溶接割
れ性を備えるとともに、良好な溶接熱影響部靭性を示す
引張強さが８０ｋｇｆ／ｍｍ2 以上のＢ添加高張力鋼を
提供することにある。SUMMARY OF THE INVENTION The object of the present invention is to provide C,
Extremely low N and Al contents are unnecessary, stable and easy to mass-produce, with desired base metal properties and weld cracking resistance, and tensile strength showing good weld heat affected zone toughness Is to provide a B-added high-strength steel of 80 kgf / mm 2 or more.
【００１２】[0012]
【課題を解決するための手段】本発明の要旨は、次の溶
接熱影響部靭性に優れたＢ添加高張力鋼にある。The gist of the present invention resides in a B-added high-strength steel excellent in the toughness of the weld heat-affected zone as described below.
【００１３】重量％で、Ｃ：０．０５〜０．１５％、Ｓ
ｉ：０．３％以下、Ｍｎ：０．５〜３．５％、Ｐ：０．
０３％以下、Ｓ：０．０１％以下、Ｎｉ：０．３〜２．
５％、Ｔｉ：０．００５％以下、Ｂ：０．０００３〜
０．００２５％、Ａｌ：０．００２〜０．０６％、Ｎ：
０．００４％以下、Ｏ：０．００４％以下、ならびにＣ
ｕ：０．２〜０．８％、Ｃｒ：０．２〜１．０％、Ｍ
ｏ：０．２〜１．０％、Ｖ：０．００５〜０．１％およ
びＮｂ：０．００５〜０．１％のうちの１種または２種
以上を含有し、残部は実質的にＦｅからなり、かつＡｌ
含有量とＯ含有量の関係が式「Ａｌ／Ｏ≧１．１２」を
満たす溶接熱影響部靭性に優れたＢ添加高張力鋼。C: 0.05-0.15% by weight, S
i: 0.3% or less, Mn: 0.5 to 3.5%, P: 0.
03% or less, S: 0.01% or less, Ni: 0.3-2.
5%, Ti: 0.005% or less, B: 0.0003-
0.0025%, Al: 0.002 to 0.06%, N:
0.004% or less, O: 0.004% or less, and C
u: 0.2 to 0.8%, Cr: 0.2 to 1.0%, M
o: one or more of 0.2 to 1.0%, V: 0.005 to 0.1% and Nb: 0.005 to 0.1%, and the balance substantially Fe and Al
A B-added high-strength steel excellent in the weld heat-affected zone toughness in which the relationship between the content and the O content satisfies the expression “Al / O ≧ 1.12”.
【００１４】本発明者らは、Ｂ添加高張力鋼の母材特性
と耐溶接割れ性を劣化させることなく、溶接熱影響部靭
性を向上させる方法について鋭意研究を行った結果、次
のことを知見して上記の本発明を完成させた。The present inventors have conducted intensive studies on a method for improving the toughness of the heat-affected zone of a B-added high-strength steel without deteriorating the properties of the base metal and the resistance to weld cracking. The inventors have found that the present invention has been completed.
【００１５】すなわち、代表的なＢ添加高張力鋼の一つ
であるＨＴ１００相当鋼（０．１１％Ｃ−０．２％Ｓｉ
−０．９％Ｍｎ−１．３％Ｎｉ−０．５％Ｃｒ−０．５
％Ｍｏ−０．０４Ｖ−０．０１％Ｎｂ−０．０１％Ｔｉ
−０．０２％Ａｌ−０．００１％Ｂ−０．００４％Ｎ）
を用いて溶接入熱量４．５ｋＪ／ｍｍの１層溶接を行
い、その溶接部の靭性、硬さ分布およびミクロ組織を詳
細に調査した。That is, HT100 equivalent steel (0.11% C-0.2% Si
-0.9% Mn-1.3% Ni-0.5% Cr-0.5
% Mo-0.04V-0.01% Nb-0.01% Ti
-0.02% Al-0.001% B-0.004% N)
Was used to perform single-layer welding with a welding heat input of 4.5 kJ / mm, and the toughness, hardness distribution and microstructure of the weld were examined in detail.
【００１６】その結果、溶接熱影響部において靭性が最
も低下するのは溶融線近傍である。また、溶接部、具体
的には溶接金属の厚さ方向の中央を通る母材表面に平行
な線上では、図１に示すような硬さ分布を示し、溶融線
近傍には硬さ低下領域が存在していることが判明した。
これは、溶融線近傍のミクロ組織の観察結果と硬さ測定
結果より、溶融線近傍では何らかの理由で焼入性が低下
し、上部ベイナイト組織が生成するためと推定される。As a result, the toughness is most reduced in the heat affected zone near the melting line. In addition, a hardness distribution as shown in FIG. 1 is shown on a line parallel to the surface of the base material passing through the center of the weld metal, specifically, the thickness direction of the weld metal, and a reduced hardness region is shown near the melting line. Turned out to be present.
This is presumed to be from the observation result of the microstructure near the melting line and the hardness measurement result that the hardenability decreases for some reason near the melting line and the upper bainite structure is generated.
【００１７】上記の結果は、溶融線近傍での靭性低下の
原因が下記の２つのうちのいずれかであることを示唆し
ている。The above results suggest that the cause of the decrease in toughness near the melting line is one of the following two.
【００１８】（Ａ）溶融線近傍では旧オーステナイト粒
が粗大化するために靭性が低下する。(A) In the vicinity of the melting line, the prior austenite grains are coarsened and the toughness is reduced.
【００１９】（Ｂ）溶融線近傍では上部ベイナイト組織
が生成するために靭性が低下する。(B) The upper bainite structure is generated near the melting line, so that the toughness is reduced.
【００２０】そこで、これらのいずれが靭性低下の主原
因であるかを究明するために次の実験を行った。すなわ
ち、その実験は、上記のＨＴ１００相当鋼を１３５０℃
に加熱した後に冷却速度１０℃／秒で２００℃まで冷却
した試験片（以下、急冷材という）と、１３５０℃に加
熱した後に冷却速度１０℃／秒で５００℃まで冷却し、
次いで冷却速度１℃／秒で２００℃まで冷却した試験片
（以下、徐冷材という）を作製し、両者の組織、硬さお
よび靭性を調査する実験である。なお、実際の溶接熱サ
イクルは徐冷材に近い。Therefore, the following experiment was conducted to determine which of these is the main cause of the decrease in toughness. That is, in the experiment, the above HT100 equivalent steel was
After cooling to 200 ° C. at a cooling rate of 10 ° C./sec to 200 ° C. (hereinafter referred to as “quenched material”), heating to 1350 ° C., and then cooling to 500 ° C. at a cooling rate of 10 ° C./sec.
Next, a test piece (hereinafter, referred to as a gradually cooled material) cooled to 200 ° C. at a cooling rate of 1 ° C./sec is an experiment for examining the structure, hardness and toughness of both. It should be noted that the actual welding heat cycle is close to the slow cooling material.
【００２１】その結果、急冷材と徐冷材の旧オーステナ
イト粒径は、いずれも約２００μｍで大きな差はなかっ
た。急冷材のビッカース硬さＨｖは３２０であり、粒内
に上部ベイナイト組織の生成は認められなかった。一
方、徐冷材のビッカース硬さＨｖは２７０程度であり、
粒内に上部ベイナイト組織の生成が認められた。また、
急冷材の靭性は−１０℃のシャルピー衝撃試験において
１５０Ｊ以上の吸収エネルギーを示したのに対し、徐冷
材の吸収エネルギーは４０Ｊ程度であった。As a result, the former austenite grain size of the quenched material and the slowly cooled material was about 200 μm, and there was no significant difference. The Vickers hardness Hv of the quenched material was 320, and generation of an upper bainite structure in the grains was not observed. On the other hand, the Vickers hardness Hv of the gradually cooled material is about 270,
The formation of upper bainite structure was observed in the grains. Also,
The toughness of the quenched material showed an absorbed energy of 150 J or more in a Charpy impact test at −10 ° C., whereas the absorbed energy of the slowly cooled material was about 40 J.
【００２２】以上の結果、実際の溶接継手の溶融線近傍
での靭性低下の原因は、結晶粒の粗大化によるのではな
く、焼入性の低下による上部ベイナイト組織の生成が主
たる原因であることが判明した。これは、両者の硬さが
明確に相違することか明らかである。As a result of the above, the cause of the decrease in toughness in the vicinity of the melting line of the actual welded joint is not due to the coarsening of the crystal grains, but mainly to the formation of the upper bainite structure due to the decrease in hardenability. There was found. It is clear that the hardness of the two is clearly different.
【００２３】そこで、溶融線近傍での焼入性の低下（硬
さ低下）を防止し、優れた溶接熱影響部靭性を有する鋼
を得るための条件について種々検討を行った結果、以下
の知見を得た。Therefore, various investigations were made on the conditions for preventing a decrease in hardenability (hardness decrease) near the melting line and obtaining a steel having excellent weld heat affected zone toughness. I got
【００２４】(a) 溶融線近傍の溶接熱影響部靭性に優れ
た鋼では、図１中に示したｍｉｎ．Ｈｖ（ＨＡＺ）は下
記の(1) 式を満たす。(A) In the steel having excellent toughness in the weld heat affected zone near the melting line, the min. Hv (HAZ) satisfies the following equation (1).
【００２５】 ｍｉｎ．Ｈｖ（ＨＡＺ）≧０．７×（８００×Ｃ＋２９５）・・・(1) なお、(1) 式中のＣは母材のＣ含有量（重量％）であ
る。また、(1) 式中の右辺における「８００×Ｃ＋２９
５」は母材のＣ含有量より推定されるマルテンサイト組
織の硬さを示している。Min. Hv (HAZ) ≧ 0.7 × (800 × C + 295) (1) where C in the equation (1) is the C content (% by weight) of the base material. Also, “800 × C + 29” on the right side of the equation (1)
"5" indicates the hardness of the martensite structure estimated from the C content of the base material.
【００２６】(b) 低Ｔｉ化と低Ｎ化は、いずれも、図１
中に示したｍａｘ．Ｈｖ（ＨＡＺ）を上昇させることな
くｍｉｎ．Ｈｖ（ＨＡＺ）のみを上昇させ、溶融線近傍
の硬さを上昇させて靭性を向上させる。その効果は、Ｔ
ｉについては０．００５重量％以下、Ｎについては０．
００２重量％以下に低減した場合に顕著になる。(B) Both the reduction of Ti and the reduction of N are shown in FIG.
The max. Hv (HAZ) without increasing min. Only Hv (HAZ) is increased, and the hardness near the melting line is increased to improve toughness. The effect is T
i is 0.005% by weight or less;
It becomes remarkable when it is reduced to 002% by weight or less.
【００２７】上記のうち、Ｎによる効果は、前述の特公
平１−２１８４７号公報に示されるのと同じであるが、
Ｔｉ量を０．００５重量％以下にした場合、０．００４
重量％までであればＮを含んでも、Ｎ量が０．００１５
重量％、Ｔｉ量が０．０１重量％の鋼と同等の吸収エネ
ルギーを示すことを確認した。Among the above, the effect of N is the same as that shown in the aforementioned Japanese Patent Publication No. 1-28474,
When the Ti content is 0.005% by weight or less, 0.004%
Even if N is contained up to the weight%, the N amount is 0.0015.
It was confirmed that the steel had an absorption energy equivalent to that of steel having a weight% and a Ti content of 0.01 weight%.
【００２８】すなわち、大気中から混入しやすいため
に、商業規模ではＮ含有量を０．００２％以下に低減す
るのは難しい。しかし、Ｎ含有量が０．００４％までで
あれば、Ｎに比べてその含有量を低くしやすいＴｉの含
有量を０．００５％以下に制限することで、溶接熱影響
部靭性に優れた鋼を安定かつ大量生産することが可能で
あることを知見した。That is, it is difficult to reduce the N content to 0.002% or less on a commercial scale because it is easily mixed from the atmosphere. However, when the N content is up to 0.004%, the content of Ti, whose content is easily reduced as compared with N, is limited to 0.005% or less, so that the weld heat affected zone toughness is excellent. It has been found that it is possible to stably and mass-produce steel.
【００２９】なお、ＴｉおよびＮ量を低減した場合、上
記のｍｉｎ．Ｈｖ（ＨＡＺ）のみが上昇する理由の詳細
は不明であるが、次によるものと推定される。When the amounts of Ti and N are reduced, the above min. The details of the reason why only Hv (HAZ) increases are unknown, but are presumed to be due to the following.
【００３０】すなわち、従来の大入熱対策鋼では、Ｔｉ
Ｎが高温でも比較的安定なことと、溶接による加熱冷却
が短時間加熱であることが相まって、溶融線近傍の高温
加熱域においてもＴｉＮの一部が結晶質のまま残留し、
旧オーステナイト結晶粒の粗大化が抑制される。さら
に、冷却過程においては、フェライトの変態生成核とし
て機能するため組織が微細化されて靭性が向上する。こ
れらの作用は、ＴｉＮが溶融線近傍の焼入性を低下させ
る作用を持つことを示している。That is, in the conventional high heat input resistance steel, Ti
The fact that N is relatively stable even at a high temperature and that the heating and cooling by welding is heating for a short time combine, so that even in the high temperature heating region near the melting line, part of the TiN remains crystalline,
The coarsening of prior austenite crystal grains is suppressed. Further, in the cooling process, the structure functions as a transformation nucleus of ferrite, so that the structure is refined and the toughness is improved. These effects indicate that TiN has an effect of reducing the hardenability near the melting line.
【００３１】これに対し、本発明が対象とするＢ添加高
張力鋼では、低Ｔｉ化によってＴｉＮの影響が取り除か
れて焼入性が上昇し、この焼入性の上昇により低靭性な
上部ベイナイト組織の生成量が減少するために靭性が向
上するものと推定される。On the other hand, in the case of the B-added high-strength steel, which is the object of the present invention, the effect of TiN is removed by the reduction of Ti, thereby increasing the hardenability. It is presumed that toughness is improved due to a decrease in the amount of microstructure generated.
【００３２】(c) Ｃ量、Ａｌ量およびＳｉ量の増加に伴
って溶接部の靭性が低下する。その原因は、島状マルテ
ンサイト組織などの硬化第二相の減少に伴うものと推定
される。このため、Ｃ、ＡｌおよびＳｉ含有量は、それ
ぞれ、０．１５％以下、０．０６％以下、０．３％以下
に制限する必要がある。(C) The toughness of the weld decreases as the amounts of C, Al and Si increase. The cause is presumed to be due to a decrease in the hardened second phase such as an island martensite structure. Therefore, it is necessary to limit the contents of C, Al and Si to 0.15% or less, 0.06% or less, and 0.3% or less, respectively.
【００３３】(d) Ａｌ量を低減した場合には靭性が向上
するが、「Ａｌ／Ｏ（酸素）」値が１．１２未満となる
量にまでＡｌ量を低減しすぎると上記のｍｉｎ．Ｈｖ
（ＨＡＺ）が低下し、これに伴って靭性が低下する。こ
れは、「Ａｌ／Ｏ」値が１．１２未満では、Ｔｉ酸化物
が生成するため粒内変態核が増加して変態温度が上昇
し、焼入性が低下して上部ベイナイト組織が生成しやす
くなるためと推定される。したがって、「Ａｌ／Ｏ」値
は、Ｏ量を０．００４重量％以下に制限したうえで、
１．１２以上にする必要がある。(D) When the Al content is reduced, the toughness is improved. However, when the Al content is excessively reduced to an amount where the “Al / O (oxygen)” value is less than 1.12, the above min. Hv
(HAZ) decreases, and accordingly, toughness decreases. This is because when the “Al / O” value is less than 1.12, Ti oxides are formed, so that the intragranular transformation nuclei increase, the transformation temperature rises, the hardenability decreases, and the upper bainite structure is formed. It is presumed to be easier. Therefore, the “Al / O” value is obtained by limiting the amount of O to 0.004% by weight or less.
Must be 1.12 or more.
【００３４】[0034]
【発明の実施の形態】以下、本発明のＢ添加高張力鋼の
化学組成を上記のように定めた理由について詳細に説明
する。なお、以下において、「％」は「重量％」を意味
する。BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the reason why the chemical composition of the B-added high-strength steel of the present invention is determined as described above will be described in detail. In the following, “%” means “% by weight”.
【００３５】Ｃ：０．０５〜０．１５％ Ｃは鋼の強度を上昇させるうえで最も重要な元素であ
る。その効果を得るためには０．０５％以上の含有量が
必要である。一方、Ｃの過剰な添加は溶接熱影響部での
島状マルテンサイト組織などの硬化第二相の生成を助長
するので、その上限を０．１５％とした。好ましい範囲
は０．０５〜０．１２％、より好ましい範囲は０．０７
〜０．１２％である。C: 0.05 to 0.15% C is the most important element for increasing the strength of steel. To obtain the effect, a content of 0.05% or more is required. On the other hand, excessive addition of C promotes the formation of a hardened second phase such as an island-like martensite structure in the weld heat affected zone, so the upper limit was made 0.15%. A preferred range is 0.05 to 0.12%, and a more preferred range is 0.07%.
~ 0.12%.
【００３６】Ｓｉ：０．３％以下 Ｓｉは鋼の脱酸元素または強度上昇元素として重要であ
る。そのためには最低でも０．０５％程度含有させるの
がよい。しかし、過剰なＳｉ添加は溶接熱影響部での島
状マルテンサイト組織の生成量の増加を招き、靭性を低
下させる。このため、上限を０．３％に限定した。好ま
しい上限は０．２０％、より好ましい上限は０．１０％
である。なお、脱酸または強度補償をＳｉ以外の他の元
素で代替することが可能であるため、特に下限値は設け
ない。Si: 0.3% or less Si is important as a deoxidizing element or a strength increasing element of steel. For that purpose, it is preferable to contain at least about 0.05%. However, excessive addition of Si causes an increase in the amount of island martensite structure generated in the heat affected zone by welding, and lowers toughness. For this reason, the upper limit was limited to 0.3%. A preferred upper limit is 0.20%, and a more preferred upper limit is 0.10%.
It is. In addition, since it is possible to substitute deoxidation or intensity | strength compensation by elements other than Si, a lower limit is not specifically provided.
【００３７】Ｍｎ：０．５〜３．５％ Ｍｎは鋼の強度、靭性を調整する上で重要な元素であ
る。これらの効果を得るためには最低でも０．５％が必
要である。一方、過剰なＭｎ添加は中心偏析を助長し、
板厚方向での特性バラツキを生じるため、その上限を
３．５％とした。好ましい範囲は０．５〜２．５％、よ
り好ましい範囲は０．８〜１．５％である。Mn: 0.5 to 3.5% Mn is an important element for adjusting the strength and toughness of steel. To obtain these effects, at least 0.5% is required. On the other hand, excessive Mn addition promotes central segregation,
Since characteristic variations occur in the thickness direction, the upper limit is set to 3.5%. A preferred range is 0.5 to 2.5%, and a more preferred range is 0.8 to 1.5%.
【００３８】Ｐ：０．０３％以下 Ｐは鋼に不可避的に混入する不純物元素であり、その含
有量は低いほど好ましい。実用上許容しうる上限は０．
０３％である。好まし上限は０．０２％、より好ましい
上限は０．０１％である。P: 0.03% or less P is an impurity element inevitably mixed into steel, and the lower the content, the better. The practically acceptable upper limit is 0.
03%. A preferred upper limit is 0.02%, and a more preferred upper limit is 0.01%.
【００３９】Ｓ：０．０１％以下 Ｓは上記のＰと同様に、鋼に不可避的に混入する不純物
元素であり、その含有量は低いほど好ましい。実用上許
容しうる上限は０．０１％である。好まし上限は０．０
０５％、より好ましい上限は０．００２％である。S: 0.01% or less S is an impurity element unavoidably mixed into steel, as in the case of P described above, and the lower the content, the better. A practically acceptable upper limit is 0.01%. Preferred upper limit is 0.0
05%, and a more preferred upper limit is 0.002%.
【００４０】Ｎｉ：０．３〜２．５％ Ｎｉは母材の靭性を損なうことなく強度上昇に寄与する
元素である。また、溶接熱影響部の靭性向上にも効果を
有する。これらの効果を得るためには最低でも０．３％
が必要である。一方、過剰なＮｉ添加は溶接部の硬度上
昇を招いて耐溶接割れ性を劣化させるので上限を２．５
％とした。好ましい範囲は０．５〜２．５％、より好ま
しい範囲は１．０〜２．５％である。Ni: 0.3 to 2.5% Ni is an element that contributes to an increase in strength without impairing the toughness of the base material. It also has the effect of improving the toughness of the heat affected zone. To achieve these effects, at least 0.3%
is necessary. On the other hand, excessive Ni addition causes an increase in the hardness of the welded portion and deteriorates the crack resistance to welding.
%. A preferred range is 0.5 to 2.5%, and a more preferred range is 1.0 to 2.5%.
【００４１】Ｔｉ：０．００５％以下 Ｔｉは本発明鋼を特徴付ける重要な元素で、その含有量
が０．００５％を超えると溶融線近傍での焼入性が低下
し、所望の溶接熱影響部靭性が確保できないので、０．
００５％以下とした。なお、十分な焼入性を確保するに
はＴｉの含有量を０．００５％以下に制限するととも
に、Ｎ含有量を０．００４％以下に抑える必要がある。
それにより、少なくとも溶融線近傍の十分な焼入性が確
保される。好まし上限は０．００３％、より好ましい上
限は０．００１％である。Ti: 0.005% or less Ti is an important element characterizing the steel of the present invention. If its content exceeds 0.005%, the hardenability near the melting line decreases, and the desired welding heat effect is reduced. Since the toughness of the part cannot be secured, 0.
005% or less. In order to secure sufficient hardenability, it is necessary to limit the Ti content to 0.005% or less and to suppress the N content to 0.004% or less.
Thereby, sufficient hardenability at least near the melting line is secured. A preferred upper limit is 0.003%, and a more preferred upper limit is 0.001%.
【００４２】Ｂ：０．０００３〜０．００２５％ Ｂは極微量で焼入性を高める元素である。この効果を得
るには０．０００３％以上の含有量が必要である。しか
し、過剰なＢの添加は溶接性を悪くするので上限を０．
００２５％とした。好ましい範囲は０．０００３〜０．
００２０％、より好ましい範囲は０．０００３〜０．０
０１５％である。B: 0.0003% to 0.0025% B is an element which enhances hardenability in a very small amount. To obtain this effect, a content of 0.0003% or more is required. However, excessive addition of B deteriorates the weldability, so the upper limit is set to 0.
0025%. The preferred range is from 0.0003 to 0.
0020%, a more preferred range is from 0.0003 to 0.0.
015%.
【００４３】Ａｌ：０．００２〜０．０６％ Ａｌは鋼の脱酸に重要な元素である。この効果を得るた
めには０．００２％以上の含有量が必要である。しか
し、過剰なＡｌ添加は溶接熱影響部において島状マルテ
ンサイト組織の生成を助長し、靭性を劣化させる。この
ため、Ａｌ含有量は０．００２〜０．０６％とした。好
ましい範囲は０．００４〜０．０４％、より好ましい範
囲は０．００４〜０．０２％である。Al: 0.002 to 0.06% Al is an important element for deoxidizing steel. To obtain this effect, a content of 0.002% or more is required. However, excessive addition of Al promotes the formation of an island-like martensite structure in the weld heat affected zone and deteriorates toughness. For this reason, the Al content is set to 0.002 to 0.06%. A preferred range is 0.004 to 0.04%, and a more preferred range is 0.004 to 0.02%.
【００４４】Ｎ：０．００４％以下 Ｎは鋼に不可避的に混入する不純物元素である。よって
その含有量は低いほど好ましい。本発明において許容し
うる上限は０．００４％である。好まし上限は０．００
３％、より好ましい上限は０．００１５％である。N: 0.004% or less N is an impurity element inevitably mixed into steel. Therefore, the lower the content, the better. The upper limit allowable in the present invention is 0.004%. Preferred upper limit is 0.00
3%, and a more preferred upper limit is 0.0015%.
【００４５】Ｏ（酸素）：０．００４％以下 Ｏは鋼に不可避的に混入する不純物元素である。よって
その含有量は低いほど好ましい。本発明において許容し
うる上限は０．００４％である Ａｌ／Ｏ：１．１２以上 Ａｌ含有量とＯ含有量の比Ａｌ／Ｏが１．１２以上で
は、酸化物のほぼ全量が実質的にＡｌ2Ｏ3（アルミナ）
となる。これに対し、Ａｌ／Ｏが１．１２未満ではＴｉ
酸化物が形成される。このＴｉ酸化物は、鋼中に均一に
分散し、かつ粒内変態の生成核となる。このことは、Ｔ
ｉ酸化物の形成が実質的には変態温度を上昇させること
を示している。本発明鋼では、溶接熱影響部における焼
入性向上を主眼としており、Ｔｉ酸化物の形成は好まし
くない。よってＴｉ酸化物を実質的に含有しない鋼を得
るために本限定を加えた。O (oxygen): 0.004% or less O is an impurity element inevitably mixed into steel. Therefore, the lower the content, the better. The upper limit allowable in the present invention is 0.004%. Al / O: 1.12 or more When Al / O is 1.12 or more, almost all of the oxide is substantially reduced. Al 2 O 3 (alumina)
Becomes On the other hand, if Al / O is less than 1.12, Ti
An oxide is formed. This Ti oxide is uniformly dispersed in the steel and serves as a nucleus for intragranular transformation. This means that T
This shows that the formation of i-oxide substantially increases the transformation temperature. In the steel of the present invention, the purpose is to improve the hardenability in the weld heat affected zone, and the formation of Ti oxide is not preferred. Therefore, this limitation was added in order to obtain a steel substantially containing no Ti oxide.
【００４６】Ｃｕ、Ｃｒ、Ｍｏ、Ｖ、Ｎｂ：これらの元
素は添加しなくてもよいが、添加すれば、いずれの元素
も鋼の強度を向上させる。したがって、この効果を得た
い場合には、これらのうちから選んだ１種を単独添加ま
たは２種以上を複合添加してよい。その効果は、Ｃｕ、
ＣｒおよびＭｏについては０．２％以上、ＶとＮｂにつ
いては０．００５％以上で顕著になる。しかし、Ｃｕは
０．８％、ＣｒとＭｏは１．０％、ＶとＮｂは０．１％
を超えて含有させると、いずれも溶接性が劣化する。こ
のため、これらの元素を添加する場合の含有量は、Ｃｕ
は０．２〜０．８％、ＣｒとＭｏは０．２〜１．０％、
ＶとＮｂは０．００５〜０．１％とするのがよい。Cu, Cr, Mo, V, Nb: These elements do not need to be added, but if added, any of them improves the strength of steel. Therefore, in order to obtain this effect, one selected from these may be added alone or two or more may be added in combination. The effect is Cu,
It becomes remarkable at 0.2% or more for Cr and Mo, and 0.005% or more for V and Nb. However, Cu is 0.8%, Cr and Mo are 1.0%, V and Nb are 0.1%.
If the content exceeds the above range, the weldability of any of them will deteriorate. Therefore, the content when these elements are added is Cu
Is 0.2-0.8%, Cr and Mo are 0.2-1.0%,
V and Nb are preferably set to 0.005 to 0.1%.
【００４７】上記の化学組成を有する本発明のＢ含有高
張力鋼は、転炉や電気炉などの製鋼炉を用いて溶製し、
必要に応じてその溶湯をＡＯＤ炉やＶＯＤ炉などの製錬
炉を用いて製錬し、次いで造塊法や連続鋳造法などで所
定の大きさの鋳片（スラブ）とすることで容易に製造す
ることができる。また、その鋼板などの製品は、前記の
鋳片（スラブ）を例えば既存の厚板圧延ミルやホットス
トリップミルなどに供して所定寸法に成形することで容
易に製造できる。The B-containing high-strength steel of the present invention having the above chemical composition is melted using a steelmaking furnace such as a converter or an electric furnace.
If necessary, the molten metal is smelted using a smelting furnace such as an AOD furnace or a VOD furnace, and then easily formed into a slab of a predetermined size by an ingot casting method or a continuous casting method. Can be manufactured. The product such as a steel plate can be easily manufactured by subjecting the slab (slab) to, for example, an existing plate rolling mill or hot strip mill to form it into a predetermined size.
【００４８】[0048]
【実施例】容量が２００ｋｇの真空精錬炉を用い、表１
に示す化学組成を有する７種類の鋼を溶解した。そし
て、得られた各鋼の鋼塊を熱間鍛造と熱間圧延によって
板厚５０ｍｍの鋼板に仕上げた後、９８０℃での焼入れ
と６３０℃での焼戻し処理を施して母材とした。EXAMPLE A vacuum refining furnace with a capacity of 200 kg was used.
Seven types of steels having the chemical compositions shown in Table 1 were melted. Then, the obtained ingot of each steel was finished into a steel plate having a thickness of 50 mm by hot forging and hot rolling, and then subjected to quenching at 980 ° C. and tempering at 630 ° C. to obtain a base material.
【００４９】[0049]
【表１】 [Table 1]
【００５０】表２に、各母材鋼板の機械的性質（降伏強
さ、引張強さ、伸び）と試験温度−８０℃のシャルピー
吸収ネルギーを示すが、いずれの母材鋼板も優れた強度
と靭性を備えている。Table 2 shows the mechanical properties (yield strength, tensile strength, elongation) and Charpy absorption energy at a test temperature of −80 ° C. of each base steel sheet. Has toughness.
【００５１】[0051]
【表２】 [Table 2]
【００５２】上記の各母材鋼板を対象に、表３に示す条
件のもとで１層盛りＳＡＷ溶接を行った。A single-layer SAW welding was performed on each of the base steel plates under the conditions shown in Table 3.
【００５３】[0053]
【表３】 [Table 3]
【００５４】そして、得られた各鋼板の溶接部、具体的
には溶接金属の厚さ方向の中央を通る母材表面に平行な
線上母材肉厚の中央位置における硬さ分布を測定して溶
接熱影響部内における最低硬さ（ｍｉｎ．Ｈｖ）と最高
硬さ（ｍａｘ．Ｈｖ）を調べた。また、各鋼板の溶接部
から、溶接金属の厚さ方向の中央と溶融線とがノッチ溝
の長手方向の中央に位置するＪＩＳ Ｚ ２２０２に規
定される４号試験片を採取して試験温度−１０℃のシャ
ルピー衝撃試験に供し、吸収エネルギーを測定すること
によって溶接熱影響部の靭性を調べた。Then, the hardness distribution at the central position of the base material thickness on a line parallel to the base material surface passing through the center of the weld metal in the thickness direction of the obtained steel plate, specifically, the weld metal, was measured. The minimum hardness (min. Hv) and the maximum hardness (max. Hv) in the heat affected zone were examined. Further, a No. 4 test piece defined in JIS Z 2202 where the center in the thickness direction of the weld metal and the melting line are located at the center in the longitudinal direction of the notch groove is sampled from the welded portion of each steel plate, and the test temperature is determined by It was subjected to a Charpy impact test at 10 ° C., and the toughness of the heat affected zone was examined by measuring the absorbed energy.
【００５５】以上の結果を、表４に示した。なお、表４
中のＨｖＣＲは、母材のＣ含有量より推定されるマルテ
ンサイト組織の硬さから予想される溶融線近傍の最低硬
さ（ｍｉｎ．Ｈｖ）を示し、式「０．７×（８００×Ｃ
＋２９５）」で求められる値である。Table 4 shows the above results. Table 4
HvCR in the table indicates the minimum hardness (min.Hv) near the melting line estimated from the hardness of the martensite structure estimated from the C content of the base material, and the equation “0.7 × (800 × C
+295) ".
【００５６】[0056]
【表４】 [Table 4]
【００５７】表４に示す結果からわかるように、本発明
例の鋼（鋼No. １〜３）は、いずれも溶接熱影響部内で
の最低硬さがＨｖＣＲより大きく、吸収エネルギーが１
０５〜１２０Ｊと溶接熱影響部の靭性が良好であった。As can be seen from the results shown in Table 4, the steels of the present invention (Steel Nos. 1 to 3) all have a minimum hardness in the weld heat affected zone greater than HvCR and an absorbed energy of 1
The toughness of the weld heat affected zone was in the range of 0.05 to 120 J.
【００５８】これに対し、比較例の鋼（鋼No. ４〜７）
のうち、鋼No. ４〜６は、いずれも溶接熱影響部内での
最低硬さがＨｖＣＲより小さく、吸収エネルギーも４３
〜５１Ｊと本発明例鋼の１／２以下で、溶接熱影響部の
靭性が悪かった。On the other hand, the steels of the comparative examples (steel Nos. 4 to 7)
Among them, steel Nos. 4 to 6 all have a minimum hardness in the weld heat affected zone smaller than HvCR and an absorbed energy of 43.
The toughness of the weld heat-affected zone was poor at ~ 51J and 1/2 or less of the steel of the present invention.
【００５９】また、鋼No. ７は、最低硬さはＨｖＣＲよ
りも大きいものの、吸収エネルギーが４８Ｊで溶接熱影
響部の靭性が悪かった。これは、Ａｌ量が多すぎるため
に島状マルテンサイト組織などの硬化第二層が生成した
ためと考えられる。Further, steel No. 7 had a minimum hardness greater than that of HvCR, but the absorbed energy was 48 J and the toughness of the heat affected zone was poor. This is considered to be because the hardened second layer such as the island-like martensite structure was generated due to the excessive amount of Al.
【００６０】[0060]
【発明の効果】本発明のＢ添加高張力鋼は、Ｎ含有量が
比較的高いにもかかわらず、溶接部靭性に優れている。
このため、生産性、経済性の面で不利な脱Ｎ処理が不要
で、溶接部靭性に優れたＢ添加高張力鋼を安価に提供で
きる。The B-added high-strength steel of the present invention has excellent weld toughness despite its relatively high N content.
For this reason, denitrification treatment disadvantageous in terms of productivity and economy is unnecessary, and a B-added high tensile steel excellent in weld toughness can be provided at low cost.
【図１】溶接部の硬さ分布の一例を示す模式図である。FIG. 1 is a schematic diagram illustrating an example of a hardness distribution of a welded portion.
Claims (1)
ｉ：０．３％以下、Ｍｎ：０．５〜３．５％、Ｐ：０．
０３％以下、Ｓ：０．０１％以下、Ｎｉ：０．３〜２．
５％、Ｔｉ：０．００５％以下、Ｂ：０．０００３〜
０．００２５％、Ａｌ：０．００２〜０．０６％、Ｎ：
０．００４％以下、Ｏ：０．００４％以下、ならびにＣ
ｕ：０．２〜０．８％、Ｃｒ：０．２〜１．０％、Ｍ
ｏ：０．２〜１．０％、Ｖ：０．００５〜０．１％およ
びＮｂ：０．００５〜０．１％のうちの１種または２種
以上を含有し、残部は実質的にＦｅからなり、かつＡｌ
含有量とＯ含有量の関係が式「Ａｌ／Ｏ≧１．１２」を
満たすことを特徴とする溶接熱影響部靭性に優れたＢ添
加高張力鋼。(1) C: 0.05 to 0.15% by weight, S
i: 0.3% or less, Mn: 0.5 to 3.5%, P: 0.
03% or less, S: 0.01% or less, Ni: 0.3-2.
5%, Ti: 0.005% or less, B: 0.0003-
0.0025%, Al: 0.002 to 0.06%, N:
0.004% or less, O: 0.004% or less, and C
u: 0.2 to 0.8%, Cr: 0.2 to 1.0%, M
o: one or more of 0.2 to 1.0%, V: 0.005 to 0.1% and Nb: 0.005 to 0.1%, and the balance substantially Fe and Al
A B-added high-strength steel excellent in welding heat-affected zone toughness, characterized in that the relationship between the content and the O content satisfies the expression “Al / O ≧ 1.12”.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23793499A JP3449307B2 (en) | 1999-08-25 | 1999-08-25 | B-added high-strength steel with excellent toughness in the heat affected zone |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23793499A JP3449307B2 (en) | 1999-08-25 | 1999-08-25 | B-added high-strength steel with excellent toughness in the heat affected zone |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2001064747A true JP2001064747A (en) | 2001-03-13 |
| JP3449307B2 JP3449307B2 (en) | 2003-09-22 |
Family
ID=17022633
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP23793499A Expired - Lifetime JP3449307B2 (en) | 1999-08-25 | 1999-08-25 | B-added high-strength steel with excellent toughness in the heat affected zone |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3449307B2 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2003027179A (en) * | 2001-07-10 | 2003-01-29 | Nkk Corp | Steel for welding structure having excellent low temperature toughness |
| EP2371982A1 (en) * | 2008-11-26 | 2011-10-05 | Sumitomo Metal Industries, Ltd. | Seamless steel pipe and method for manufacturing same |
| JP2013220431A (en) * | 2012-04-13 | 2013-10-28 | Kobe Steel Ltd | Welded joint excellent in fatigue strength, mag welding method for hot rolled steel sheet, mig welding method for hot rolled steel sheet, and flux-cored wire |
-
1999
- 1999-08-25 JP JP23793499A patent/JP3449307B2/en not_active Expired - Lifetime
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2003027179A (en) * | 2001-07-10 | 2003-01-29 | Nkk Corp | Steel for welding structure having excellent low temperature toughness |
| JP4599770B2 (en) * | 2001-07-10 | 2010-12-15 | Ｊｆｅスチール株式会社 | Welded structural steel with excellent low temperature toughness |
| EP2371982A1 (en) * | 2008-11-26 | 2011-10-05 | Sumitomo Metal Industries, Ltd. | Seamless steel pipe and method for manufacturing same |
| EP2371982A4 (en) * | 2008-11-26 | 2017-03-29 | Nippon Steel & Sumitomo Metal Corporation | Seamless steel pipe and method for manufacturing same |
| JP2013220431A (en) * | 2012-04-13 | 2013-10-28 | Kobe Steel Ltd | Welded joint excellent in fatigue strength, mag welding method for hot rolled steel sheet, mig welding method for hot rolled steel sheet, and flux-cored wire |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3449307B2 (en) | 2003-09-22 |
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