JP3258207B2 - Ultra high strength steel with excellent low temperature toughness - Google Patents
Ultra high strength steel with excellent low temperature toughnessInfo
- Publication number
- JP3258207B2 JP3258207B2 JP19535995A JP19535995A JP3258207B2 JP 3258207 B2 JP3258207 B2 JP 3258207B2 JP 19535995 A JP19535995 A JP 19535995A JP 19535995 A JP19535995 A JP 19535995A JP 3258207 B2 JP3258207 B2 JP 3258207B2
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- JP
- Japan
- Prior art keywords
- steel
- low
- ferrite
- temperature toughness
- strength
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Description
【０００１】[0001]
【発明の属する技術分野】本発明は９５０MPa 以上の引
張強さ（ＴＳ）を有する低温靭性・溶接性の優れた超高
張力鋼に関するもので、原油・天然ガス輸送用ラインパ
イプをはじめ、各種圧力容器、産業機械などの溶接用鋼
材として広く使用できる。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-high tensile strength steel having a tensile strength (TS) of 950 MPa or more and excellent in low-temperature toughness and weldability. Can be widely used as welding steel materials for containers and industrial machines.
【０００２】[0002]
【従来の技術】近年、原油・天然ガスを長距離にわたっ
て輸送する大径パイプラインに使用されるラインパイプ
は、（１）高圧化による輸送効率の向上や（２）ライン
パイプの外径・重量の低減による現地施工能率の向上の
ため、ますます高張力（高強度）化する傾向にある。こ
れまでに米国石油協会（ＡＰＩ）規格でＸ８０（降伏強
さ５５１MPa 以上、引張強さ６２０MPa 以上）までのラ
インパイプが実用化されているが、さらに高強度のライ
ンパイプに対するニーズが強くなってきた。2. Description of the Related Art In recent years, line pipes used for large-diameter pipelines for transporting crude oil and natural gas over long distances include (1) improvement in transportation efficiency by increasing pressure and (2) outer diameter and weight of line pipes. In order to improve on-site construction efficiency by reducing the amount of steel, there is a tendency to increase the tension (high strength). Up to now, line pipes up to X80 (yield strength of 551 MPa or more, tensile strength of 620 MPa or more) according to the American Petroleum Institute (API) standard have been put to practical use, but the need for even higher-strength line pipes has increased. .
【０００３】現在、超高強度ラインパイプの製造法の研
究は、従来のＸ８０ラインパイプの製造技術（たとえば
ＮＫＫ技報 No．138 (1992), pp24-31 およびThe 7th
Offshore Mechanics and Arctic Engineering (1988),
Volume V, pp179-185)を基本に検討されているが、これ
ではせいぜい、Ｘ１００（降伏強さ６８９MPa 以上、引
張強さ７６０MPa 以上）ラインパイプが製造限界と考え
られる。パイプラインの超高強度化は強度・低温靭性バ
ランスをはじめとして溶接熱影響部（ＨＡＺ）靭性、現
地溶接性、継手軟化など多くの問題を抱えており、これ
らを克服した画期的な超高張力ラインパイプ（Ｘ１００
超）の早期開発が要望されている。[0003] At present, research on a method for manufacturing an ultra-high-strength line pipe is based on the conventional X80 line pipe manufacturing technology (for example, NKK Technical Report No. 138 (1992), pp24-31 and The 7th
Offshore Mechanics and Arctic Engineering (1988),
Volume V, pp. 179-185) is considered, but it is considered that, at most, X100 (yield strength of 689 MPa or more, tensile strength of 760 MPa or more) line pipe is the production limit. The ultra-high strength of pipeline has many problems such as strength-low temperature toughness balance, welding heat affected zone (HAZ) toughness, on-site weldability, and softening of joints. Tension line pipe (X100
There is a demand for early development.
【０００４】[0004]
【発明が解決しようとする課題】本発明は強度と低温靭
性のバランスに優れ、かつ現地溶接性の優れた引張強さ
９５０MPa 以上（ＡＰＩ規格Ｘ１００超）の超高張力鋼
（厚板、ホットコイル、鋼管などに使用）を提供するも
のである。SUMMARY OF THE INVENTION The present invention relates to an ultra-high tensile steel (thick plate, hot coil) having an excellent balance between strength and low-temperature toughness, and excellent tensile strength of at least 950 MPa (API standard X100 or more) excellent in on-site weldability. , Steel pipes, etc.).
【０００５】[0005]
【課題を解決するための手段】本発明者らは、引張強さ
が９５０MPa 以上で、かつ優れた低温靭性・現地溶接性
を有する超高張力鋼を得るために鋼の化学成分（組成）
とそのミクロ組織について鋭意研究を行い、新しい超高
張力鋼を発明するに至った。Means for Solving the Problems In order to obtain an ultra-high-strength steel having a tensile strength of 950 MPa or more and excellent low-temperature toughness and on-site weldability, the present inventors have determined the chemical composition (composition) of the steel.
And research on its microstructure, and came to invent a new ultra-high strength steel.
【０００６】すなわち本発明の要旨は、重量％で、 Ｃ ：０．０５〜０．１０％、 Ｓｉ：０．６％以
下、 Ｍｎ：１．８〜２．５％、 Ｐ ：０．０１５％
以下、 Ｓ ：０．００３％以下、 Ｍｏ：０．３０〜
０．６０％、 Ｎｂ：０．０１〜０．１０％、 Ｖ ：０．０３〜
０．１０％、 Ｔｉ：０．００５〜０．０３０％、Ａｌ：０．０６％以
下、 Ｎ ：０．００１〜０．００６％を含有し、 さらに必要に応じ、上記成分に加えて Ｃｅ：０．００５〜０．０２０％、Ｍｇ：０．００１〜
０．００５％、 Ｙ ：０．００５〜０．０３０％の１種または２種以上
を含有し 、またさらに必要に応じ、上記成分に加えて Ｎｉ：０．１〜１．０％、 Ｃｕ：０．１〜１．
２％、 Ｃｒ：０．１〜０．８％、 Ｃａ：０．００１〜
０．００５％ の１種または２種以上を含有し、残部が鉄および不可避
的不純物からなるとともに、 Ｐ＝２．７Ｃ＋０．４Ｓｉ＋Ｍｎ＋０．８Ｃｒ ＋０．４５（Ｎｉ＋Ｃｕ）＋Ｍｏ＋Ｖ−１ で定義されるＰ値が、１．９≦Ｐ≦２．８を満足し、さ
らに、そのミクロ組織が、マルテンサイト・ベイナイト
と分率にして２０〜９０％のフェライトとによって形成
された２相混合組織からなり、かつ、フェライト中に加
工フェライトを５０〜１００％含有し、フェライト平均
粒径が５μｍ以下であることを特徴とする低温靭性の優
れた超高張力鋼である。また、こうして得られた鋼を、
４００℃以上Ａｃ1 点以下の温度で焼戻し処理すること
により、降伏強さが向上する。ここで、フェライト平均
粒径は鋼材の厚み方向に測定したフェライトの平均粒界
間隔と定義する。That is, the gist of the present invention is as follows: C: 0.05 to 0.10%, Si: 0.6% or less, Mn: 1.8 to 2.5%, P: 0.015% by weight%.
Below, S: 0.003% or less, Mo: 0.30
0.60%, Nb: 0.01 to 0.10%, V: 0.03 to
0.10%, Ti: 0.005~0.030%, Al: 0.06% or less, N: containing from 0.001 to 0.006%, if necessary, Ce in addition to the above ingredients: 0.005 to 0.020%, Mg: 0.001 to
0.005%, Y: One or more of 0.005 to 0.030%
Contain, or even necessary, in addition to the above components Ni: 0.1~1.0%, Cu: 0.1~1 .
2%, Cr : 0.1-0.8 %, Ca: 0.001-
One or more of 0.005% , the balance being iron and unavoidable impurities, and P value defined by P = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + Mo + V-1 Satisfies 1.9 ≦ P ≦ 2.8, and the microstructure is a two-phase mixed structure formed by martensite bainite and a fraction of 20 to 90% ferrite, and An ultra-high tensile steel excellent in low-temperature toughness, characterized in that ferrite contains 50-100% of processed ferrite and has an average ferrite grain size of 5 μm or less. Also, the steel thus obtained is
By performing tempering at a temperature of 400 ° C. or more and one point of Ac or less, the yield strength is improved. Here, the average ferrite grain size is defined as the average grain boundary distance of ferrite measured in the thickness direction of the steel material.
【０００７】[0007]
【発明の実施の形態】以下、本発明の内容について詳細
に説明する。本発明の特徴は、（１）Ｎｂ−Ｍｏ−Ｖ−
微量Ｔｉを複合添加した低炭素・高Ｍｎ系（１．８％以
上）であること、（２）そのミクロ組織が微細なフェラ
イト（平均粒径が５μｍ以下で、一定量以上の加工フェ
ライトを含む）とマルテンサイト・ベイナイトの２相混
合組織からなることである。従来より、低炭素−高Ｍｎ
−Ｎｂ−Ｍｏ鋼は微細なアシキュラーフェライト組織を
有するラインパイプ用鋼としてよく知られているが、そ
の引張強さはせいぜい７５０MPa が上限であった。この
ような基本成分系で加工フェライトを含む微細フェライ
トとマルテンサイト・ベイナイトの硬軟２相混合微細組
織を有する超高強度ラインパイプ用鋼はまったく存在し
ない。これはフェライト主体の低炭素−Ｎｂ−Ｍｏ鋼に
おいて、９５０MPa 以上の引張強さを達成することは到
底不可能であり、低温靭性や現地溶接性も不十分と考え
られていたためである。BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the contents of the present invention will be described in detail. The feature of the present invention is (1) Nb-Mo-V-
It is a low carbon / high Mn system (1.8% or more) to which a trace amount of Ti is added in a complex manner. (2) The ferrite has a fine microstructure (the average grain size is 5 μm or less and contains a certain amount or more of processed ferrite. ) And martensite-bainite. Conventionally, low carbon-high Mn
-Nb-Mo steel is well known as a linepipe steel having a fine acicular ferrite structure, but its upper limit of tensile strength is 750 MPa at most. There is no ultrahigh-strength linepipe steel having a hard / soft two-phase mixed microstructure of fine ferrite containing processed ferrite and martensite / bainite in such a basic component system. This is because it was considered impossible to achieve a tensile strength of 950 MPa or more in ferrite-based low carbon-Nb-Mo steel, and low-temperature toughness and on-site weldability were considered to be insufficient.
【０００８】しかしながら、本発明者らは、低炭素−Ｎ
ｂ−Ｍｏ鋼においても化学成分、ミクロ組織を厳密に制
御することにより、超高強度と優れた低温靭性が同時に
達成できることを見出した。本発明鋼の特徴は、（１）
焼戻し処理なしでも優れた超高強度、低温靭性・現地溶
接性バランスが得られること、（２）焼入れ・焼戻し処
理鋼に比較して降伏比が低く、鋼管成形性、低温靭性
（シャルピー遷移温度）に著しく優れていること、
（３）溶接熱による軟化（強度低下）が非常に少ないこ
と、などが挙げられる。なお本発明鋼では、鋼板の状態
で降伏強さが低くても、鋼管成形（加工硬化）によって
降伏強さが上昇し、目的とする降伏強さを得ることが可
能である。[0008] However, the present inventors have found that low carbon-N
By strictly controlling the chemical composition and microstructure of b-Mo steel, it has been found that ultra-high strength and excellent low-temperature toughness can be simultaneously achieved. The features of the steel of the present invention are (1)
Excellent balance of ultra-high strength, low temperature toughness and on-site weldability without tempering. (2) Low yield ratio compared to quenched and tempered steel, formability of steel pipe, low temperature toughness (Charpy transition temperature) Remarkably superior to
And (3) very little softening (strength reduction) due to welding heat. In the steel of the present invention, even if the yield strength is low in the state of the steel sheet, the yield strength is increased by forming the steel pipe (work hardening), and it is possible to obtain a target yield strength.
【０００９】まず本発明鋼のミクロ組織について説明す
る。引張強さ９５０MPa 以上の超高強度を達成するため
には、鋼のミクロ組織中に一定量以上のマルテンサイト
・ベイナイトを含有させることが不可欠であり、その必
要量は１０〜８０％である。この時残りの組織はフェラ
イトで、その量（フェライト分率）は２０〜９０％とな
る。フェライト分率が９０％を超えて、マルテンサイト
・ベイナイト分率が小さくなりすぎて、如何にフェライ
トを強化しても目的とする引張強さは達成できない。本
発明鋼において強度、低温靭性の面から、最も望ましい
フェライト分率は６０〜８０％である。First, the microstructure of the steel of the present invention will be described. In order to achieve an ultra-high strength of 950 MPa or more, it is essential to include a certain amount or more of martensite bainite in the microstructure of steel, and the necessary amount is 10 to 80%. At this time, the remaining structure is ferrite, and the amount (ferrite fraction) is 20 to 90%. The ferrite fraction exceeds 90%, the martensite-bainite fraction becomes too small, and the desired tensile strength cannot be achieved no matter how much the ferrite is strengthened. In the steel of the present invention, the most desirable ferrite fraction is 60 to 80% from the viewpoint of strength and low-temperature toughness.
【００１０】しかし、本来フェライトは軟らかいもので
あり、フェライト分率が大きい場合には、従来の技術で
は目的とする強度（特に降伏強さ）・低温靭性を達成す
ることは不可能である。そこでＶを０．０３％以上添加
し、かつミクロ組織フェライト中の加工フェライトの分
率を５０〜１００％とした。一般にＮがＴｉによりＴｉ
Ｎとして固定された低炭素鋼では、Ｖ炭窒化物による析
出硬化が十分に得られないが、フェライトの強加工（圧
延）による歪によってＶの析出が促進され、フェライト
を著しく強化できることがわかった。フェライトの加工
はＶの析出に加え、転位強化やサブグレイン強化によっ
てフェライトの降伏強さを高めると同時に、後で述べる
ようにシャルピー遷移温度の改善にも極めて有効であ
る。However, ferrite is soft by nature, and when the ferrite fraction is large, it is impossible to achieve the desired strength (particularly yield strength) and low-temperature toughness by the conventional technology. Therefore, V was added at 0.03% or more, and the fraction of processed ferrite in the microstructure ferrite was set to 50 to 100%. Generally, N is Ti
In the low carbon steel fixed as N, precipitation hardening due to V carbonitride cannot be sufficiently obtained, but it has been found that precipitation of V is promoted by strain due to strong working (rolling) of ferrite, and ferrite can be significantly strengthened. . The processing of ferrite is extremely effective in improving the Charpy transition temperature as described later, while increasing the yield strength of ferrite by dislocation strengthening and subgrain strengthening in addition to the precipitation of V.
【００１１】上述のようにミクロ組織の種類と量を限定
しても、優れた低温靭性を達成するには不十分である。
このためには、加工フェライトの導入によるセパレーシ
ョンを利用するとともに、フェライト平均粒径を５μｍ
以下に微細化する必要がある。超高張力鋼においても、
加工フェライト（集合組織）の導入により、シャルピー
衝撃試験などの破面にセパレーションが発生し、破面遷
移温度は飛躍的に低下することがわかった。なお、セパ
レーションはシャルピー衝撃試験などの破面に発生する
板面に平行な層状剥離現象で、脆性亀裂先端での３軸応
力度を低下させ、脆性亀裂伝播停止特性を改善すると考
えられている。さらにフェライト平均粒径を５μｍ以下
とすることによって、当然ながらフェライト以外のマル
テンサイト・ベイナイト組織も同時に微細化することが
でき、遷移温度の著しい改善や降伏強さの増加が得られ
た。[0011] Even if the type and amount of the microstructure are limited as described above, it is insufficient to achieve excellent low-temperature toughness.
For this purpose, separation by introducing processed ferrite is used, and the average ferrite grain size is 5 μm.
It is necessary to miniaturize below. Even in ultra high strength steel,
It was found that the introduction of the processed ferrite (texture) caused separation on the fracture surface such as the Charpy impact test, and the fracture surface transition temperature dropped dramatically. Separation is a layered peeling phenomenon parallel to the plate surface generated on a fractured surface such as a Charpy impact test, and is considered to reduce triaxial stress at a brittle crack tip and improve brittle crack propagation stopping characteristics. Further, by setting the average ferrite grain size to 5 μm or less, a martensite-bainite structure other than ferrite can be naturally refined at the same time, and a remarkable improvement in transition temperature and an increase in yield strength can be obtained.
【００１２】以上の研究により、従来低温靭性が低いと
考えられていたＮｂ−Ｍｏ鋼のフェライトとマルテンサ
イト・ベイナイト２相混合組織における強度・低温靭性
バランスを大幅に向上させることに成功し、引張強さ９
５０MPa 級超高張力鋼を発明するに至った。しかしなが
ら、上述のように、鋼のミクロ組織を厳密に制御しても
目的とする特性を有する鋼は得られない。このため、ミ
クロ組織と同時に化学成分を限定する必要がある。そこ
で、以下に成分元素の限定理由について説明する。From the above research, the balance between strength and low-temperature toughness in the ferrite and martensite-bainite two-phase mixed structure of Nb-Mo steel, which was conventionally considered to have low low-temperature toughness, was significantly improved. Strength 9
Invented a 50 MPa class ultra-high tensile steel. However, as described above, even if the microstructure of the steel is strictly controlled, a steel having desired properties cannot be obtained. For this reason, it is necessary to limit the chemical composition simultaneously with the microstructure. Therefore, the reasons for limiting the component elements will be described below.
【００１３】Ｃ量は０．０５〜０．１０％に限定する。
炭素は鋼の強度向上に極めて有効な元素であり、フェラ
イトとマルテンサイト・ベイナイト２相混合組織におい
て目的とする強度を得るためには、最低０．０５％は必
要である。またこの量は、Ｎｂ，Ｖ添加による析出硬
化、結晶粒の微細化効果の発現や溶接部強度の確保のた
めの必要最小量でもある。一方、Ｃ量が多すぎると母
材、ＨＡＺの低温靭性や現地溶接性の著しい劣化を招く
ので、その上限を０．１０％とした。The C content is limited to 0.05 to 0.10%.
Carbon is an extremely effective element for improving the strength of steel, and at least 0.05% is required to obtain the desired strength in a two-phase mixed structure of ferrite and martensite / bainite. This amount is also a minimum necessary for precipitation hardening due to the addition of Nb and V, the effect of refining crystal grains, and ensuring the strength of a weld. On the other hand, if the C content is too large, the low-temperature toughness and the on-site weldability of the base material and HAZ are remarkably deteriorated, so the upper limit is set to 0.10%.
【００１４】Ｓｉは、脱酸や強度向上のために添加する
元素であるが、添加量が多いとＨＡＺ靭性、現地溶接性
を著しく劣化させるので、上限を０．６％とした。鋼の
脱酸はＴｉあるいはＡｌでも十分可能であり、Ｓｉは必
ずしも添加する必要はない。[0014] Si is an element added for deoxidation and strength improvement, but if the addition amount is large, the HAZ toughness and on-site weldability are remarkably deteriorated, so the upper limit was made 0.6%. Steel can be sufficiently deoxidized with Ti or Al, and Si need not always be added.
【００１５】Ｍｎは、本発明鋼のミクロ組織を微細なフ
ェライトとマルテンサイト・ベイナイトの２相混合組織
とし、優れた強度・低温靭性バランスを確保する上で不
可欠な元素であり、その下限は１．８％である。一方、
Ｍｎ量が多すぎると鋼の焼入れ性が増してＨＡＺ靭性、
現地溶接性を劣化させるだけでなく、連続鋳造鋼片（鋳
片）の中心偏析を助長し、母材の低温靭性をも劣化させ
るので、上限を２．５％とした。なお、望ましいＭｎ量
は１．９〜２．１％である。Mn is an element indispensable for securing the excellent balance between strength and low-temperature toughness by forming the microstructure of the steel of the present invention into a two-phase mixed structure of fine ferrite and martensite / bainite. 0.8%. on the other hand,
If the amount of Mn is too large, the hardenability of the steel increases, and the HAZ toughness increases.
The upper limit is set to 2.5%, because it not only deteriorates the on-site weldability but also promotes the center segregation of the continuously cast steel slab (cast slab) and also deteriorates the low-temperature toughness of the base material. The desirable Mn content is 1.9 to 2.1%.
【００１６】Ｍｏを添加する理由は、鋼の焼入れ性を向
上させ、目的とする２相混合組織を得るためである。ま
た、ＭｏはＮｂと共存して制御圧延時にオーステナイト
の再結晶を強力に抑制し、オーステナイト組織の微細化
にも効果がある。このような効果を得るために、Ｍｏは
最低０．３０％必要である。一方、過剰なＭｏ添加はＨ
ＡＺ靭性、現地溶接性を劣化させるので、その上限を
０．６０％とした。なお、最も望ましいＭｏ量は０．４
０〜０．５０％である。The reason for adding Mo is to improve the hardenability of steel and obtain the desired two-phase mixed structure. In addition, Mo coexists with Nb and strongly suppresses austenite recrystallization during controlled rolling, and is also effective in refining the austenite structure. In order to obtain such an effect, Mo must be at least 0.30%. On the other hand, excessive Mo addition
Since the AZ toughness and the on-site weldability deteriorate, the upper limit is set to 0.60%. The most desirable Mo amount is 0.4.
0 to 0.50%.
【００１７】本発明鋼では、必須の元素としてＮｂ：
０．０１〜０．１０％、Ｔｉ：０．００５〜０．０３０
％を含有している。ＮｂはＭｏと共存して制御圧延時に
オーステナイトの再結晶を抑制し、結晶粒を微細化する
だけでなく、析出硬化や焼入れ性増大にも寄与し、鋼を
強靭化する作用を有する。しかしＮｂ添加量が多すぎる
と、ＨＡＺ靭性や現地溶接性に悪影響をもたらすので、
その上限を０．１０％とした。In the steel of the present invention, Nb:
0.01 to 0.10%, Ti: 0.005 to 0.030
%. Nb coexists with Mo to suppress recrystallization of austenite during controlled rolling, not only to refine crystal grains, but also to contribute to precipitation hardening and hardenability, and has an effect of toughening steel. However, if the added amount of Nb is too large, it adversely affects HAZ toughness and on-site weldability.
The upper limit was set to 0.10%.
【００１８】一方、Ｔｉ添加は微細なＴｉＮを形成し、
スラブ再加熱時および溶接ＨＡＺのオーステナイト粒粗
大化を抑制してミクロ組織を微細化し、母材およびＨＡ
Ｚの低温靭性を改善する。さらに、Ａｌ量が少ない時
（たとえば０．００５％以下）、Ｔｉは酸化物を形成
し、ＨＡＺにおいて粒内フェライト生成核として作用し
て、ＨＡＺ組織を微細化する効果も有する。このような
Ｔｉ添加効果を発現させるには、最低０．００５％のＴ
ｉ添加が必要である。しかしＴｉ量が多すぎると、Ｔｉ
Ｎの粗大化やＴｉＣによる析出硬化が生じ、低温靭性を
劣化させるので、その上限を０．０３０％に限定した。On the other hand, the addition of Ti forms fine TiN,
When the slab is reheated and the austenite grains in the weld HAZ are suppressed from coarsening, the microstructure is refined, and the base material and HA
Improves the low-temperature toughness of Z. Furthermore, when the amount of Al is small (for example, 0.005% or less), Ti forms an oxide, acts as a nucleus for generating intragranular ferrite in the HAZ, and has an effect of making the HAZ structure finer. In order to exhibit such Ti addition effect, at least 0.005% of T
i addition is required. However, if the amount of Ti is too large,
Since the coarsening of N and precipitation hardening due to TiC occur to deteriorate the low-temperature toughness, the upper limit thereof is limited to 0.030%.
【００１９】ＶはＮｂとほぼ同様の効果を有するが、そ
の効果はＮｂに比較して弱いと考えられている。しか
し、超高強度鋼におけるＶ添加の効果は大きく、Ｎｂと
Ｖの複合添加は本発明鋼の優れた特徴をさらに顕著なも
のとすることがわかった。本発明鋼では、フェライト強
化のため、最低０．０３％のＶ添加が必須である。また
Ｖは、フェライトの加工（熱間圧延）によって歪誘起析
出し、フェライトを著しく強化することがわかった。Ｖ
の上限はＨＡＺ靭性、現地溶接性の点から０．１０％ま
で許容できる。V has almost the same effect as Nb, but its effect is considered to be weaker than Nb. However, it was found that the effect of V addition in the ultrahigh-strength steel was great, and that the combined addition of Nb and V further enhanced the excellent characteristics of the steel of the present invention. In the steel of the present invention, V addition of at least 0.03% is essential for strengthening ferrite. It was also found that V was strain-induced precipitated by ferrite processing (hot rolling) and significantly strengthened ferrite. V
The upper limit is 0.10% from the viewpoint of HAZ toughness and on-site weldability.
【００２０】Ａｌは通常脱酸剤として鋼に含まれる元素
である。しかし、Ａｌ量が０．０６％を超えると、非金
属介在物が増加して鋼の清浄度を害するので、上限を
０．０６％とした。脱酸はＴｉあるいはＳｉでも可能で
あり、必ずしもＡｌを添加する必要はない。Al is an element usually contained in steel as a deoxidizing agent. However, if the Al content exceeds 0.06%, nonmetallic inclusions increase and impair the cleanliness of the steel, so the upper limit was made 0.06%. Deoxidation is possible with Ti or Si, and it is not always necessary to add Al.
【００２１】Ｎは、ＴｉＮを形成し、スラブ再加熱時お
よび溶接ＨＡＺのオーステナイト粒粗大化を抑制して母
材、ＨＡＺの低温靭性を向上させる。このための必要最
低量は０．００１％である。一方、Ｎ量が多すぎると、
スラブ表面疵や固溶ＮによるＨＡＺ靭性の劣化の原因と
なるので、その上限は０．００６％に抑える必要があ
る。N forms TiN and suppresses coarsening of austenite grains in the slab during reheating and in the welded HAZ, thereby improving the low-temperature toughness of the base material and the HAZ. The minimum required for this is 0.001%. On the other hand, if the N amount is too large,
Since the HAZ toughness is degraded by slab surface flaws and solid solution N, the upper limit must be suppressed to 0.006%.
【００２２】さらに、本発明では、不純物元素である
Ｐ，Ｓ量をそれぞれ０．０１５％以下、０．００３％以
下とする。この主たる理由は母材およびＨＡＺの低温靭
性をより一層向上させるためである。Ｐ量の低減は鋳片
の中心偏析を軽減するとともに、粒界破壊を防止して低
温靭性を向上させる。またＳ量の低減は制御圧延で延伸
化したＭｎＳを低減して延靭性を向上させる効果があ
る。Further, in the present invention, the contents of P and S as impurity elements are set to 0.015% or less and 0.003% or less, respectively. The main reason for this is to further improve the low-temperature toughness of the base material and the HAZ. Reducing the P content reduces the center segregation of the slab, prevents grain boundary fracture, and improves low temperature toughness. Also, the reduction of the S content has the effect of reducing MnS stretched by controlled rolling and improving ductility.
【００２３】次に、Ｎｉ，Ｃｕ，ＣｒおよびＣａを添加
する目的について説明する。すなわち、以上に述べてき
た基本となる成分に、さらにこれらの元素を必要に応じ
て添加する主たる目的は、本発明鋼の優れた特徴を損な
うことなく、強度・低温靭性などの特性の一層の向上や
製造可能な鋼材サイズの拡大をはかるためである。した
がって、その添加量は自ら制限されるべき性質のもので
ある。Next, the purpose of adding Ni, Cu, Cr and Ca will be described. That is, the main purpose of further adding these elements to the basic components described above as necessary is to further improve the properties such as strength and low-temperature toughness without impairing the excellent characteristics of the steel of the present invention. This is for the purpose of improving and expanding the size of steel products that can be manufactured. Therefore, the amount of addition is of a nature that should be restricted.
【００２４】Ｎｉを添加する目的は、低炭素の本発明鋼
の強度、低温靭性や現地溶接性を劣化させずに向上させ
るためである。Ｎｉ添加は、ＭｎやＣｒ，Ｍｏ添加と比
較して圧延組織（特に鋳片の中心偏析帯）中に低温靭性
に有害な硬化組織を形成させることが少ないだけでな
く、微量のＮｉを添加すればＨＡＺ靭性の改善にも有効
であることが判明した（ＨＡＺ靭性改善上、特に有効な
Ｎｉ添加量は０．３％以上である）。一方、添加量が多
すぎると、ＨＡＺ靭性や現地溶接性を劣化させるばかり
でなく、経済性をも損なうので、その上限を１．０％と
した。なお、Ｎｉ添加は連続鋳造時、および熱間圧延時
におけるＣｕクラック発生の防止にも有効である。この
場合、ＮｉはＣｕ量の１／３以上添加する必要がある。The purpose of adding Ni is to improve the strength, low temperature toughness and on-site weldability of the low carbon steel of the present invention without deteriorating. The addition of Ni not only causes less formation of a hardened structure harmful to low-temperature toughness in the rolled structure (especially the center segregation zone of the slab) than the addition of Mn, Cr, and Mo, but also adds a small amount of Ni. For example, it has been found that the addition of Ni is effective in improving the HAZ toughness (the amount of Ni particularly effective in improving the HAZ toughness is 0.3% or more). On the other hand, if the addition amount is too large, not only deteriorates HAZ toughness and on-site weldability, but also impairs economic efficiency, so the upper limit was made 1.0%. The addition of Ni is also effective in preventing the occurrence of Cu cracks during continuous casting and hot rolling. In this case, Ni needs to be added at least 1/3 of the Cu amount.
【００２５】Ｃｕは、Ｎｉとほぼ同様な効果をもつとと
もに、耐食性、耐水素誘起割れ特性の向上にも効果があ
る。また、０．５％以上のＣｕ添加は析出硬化によって
強度を大幅に増加させる。しかし過剰に添加すると、析
出硬化により母材、ＨＡＺの靭性低下や熱間圧延時にＣ
ｕクラックが生じるので、その上限を１．２％とした。Cu has almost the same effect as Ni, and also has an effect on improving corrosion resistance and resistance to hydrogen-induced cracking. Further, the addition of 0.5% or more of Cu greatly increases the strength by precipitation hardening. However, if added in excess, the precipitation hardening lowers the toughness of the base material and HAZ, and the C
Since u cracks occur, the upper limit is set to 1.2%.
【００２６】Ｃｒは母材、溶接部の強度を増加させる
が、多すぎるとＨＡＺ靭性や現地溶接性を著しく低下さ
せる。このためＣｒ量の上限は０．８％である。Ｎｉ，
ＣｕおよびＣｒ量の下限０．１％は、それぞれの元素添
加による材質上の効果が顕著になる最低量である。[0026] Cr increases the strength of the base material and the welded portion, but if too much, the HAZ toughness and the on-site weldability are remarkably reduced. For this reason, the upper limit of the amount of Cr is 0.8%. Ni,
The lower limit of 0.1% of the amounts of Cu and Cr is the minimum amount at which the effect on the material by adding each element becomes remarkable.
【００２７】ＣａはＯ，Ｓと結合して硫化物（ＭｎＳ）
の形態を制御し、低温靭性を向上（シャルピー衝撃試験
の吸収エネルギーの増加など）させる。特に超高強度ラ
インパイプを主用途とする本発明鋼では、不安定延性破
壊の伝播防止のため、高シャルピー吸収エネルギーが要
求されるので、Ｓ量の低減とＣａ処理は重要である。し
かし、Ｃａ添加量が０．００１％未満では実用上効果が
なく、また０．００５％を超えて添加するとＣａＯ−Ｃ
ａＳが大量に生成して大型クラスター、大型介在物とな
り、鋼の清浄度を害するだけでなく、現地溶接性にも悪
影響をおよぼす。このためＣａ添加量の上限を０．００
５％に制限した。なお、超高強度鋼では、Ｓ，Ｏの含有
量をそれぞれ０．００１％以下、０．００３％以下に低
減し、かつＥＳＳＰ＝（Ｃａ）〔１−１２４（Ｏ）〕／
１．２５（Ｓ）を０．５≦ＥＳＳＰ≦１０．０とするこ
とが特に有効である。なおＣａ添加鋼において強脱酸元
素であるＡｌを０．０１％以下に低減すると、微細分散
したＣａ酸化物が得られ、これはＨＡＺのγ粒粗大化を
抑制し、低温靭性の改善に有効である。Ca combines with O and S to form a sulfide (MnS)
To improve the low-temperature toughness (such as increasing the absorbed energy in the Charpy impact test). Particularly, in the steel of the present invention mainly used for ultra-high-strength line pipes, a high Charpy absorbed energy is required to prevent propagation of unstable ductile fracture, and therefore, reduction of the S content and Ca treatment are important. However, if the added amount of Ca is less than 0.001%, there is no practical effect, and if the added amount exceeds 0.005%, CaO—C
aS is generated in large amounts to form large clusters and large inclusions, which not only impairs the cleanliness of steel but also adversely affects on-site weldability. Therefore, the upper limit of the amount of Ca added is 0.00
Limited to 5%. In the ultrahigh-strength steel, the contents of S and O were reduced to 0.001% or less and 0.003% or less, respectively, and ESSP = (Ca) [1-124 (O)] /
It is particularly effective to set 1.25 (S) to 0.5 ≦ ESSP ≦ 10.0. When Al, which is a strong deoxidizing element, is reduced to 0.01% or less in Ca-added steel, a finely dispersed Ca oxide is obtained, which suppresses coarsening of γ grains in HAZ and is effective in improving low-temperature toughness. It is.
【００２８】以上の個々の添加元素の限定に加えて本発
明では、さらにＰ＝２，７Ｃ＋０．４Ｓｉ＋Ｍｎ＋０．
８Ｃｒ＋０．４５（Ｎｉ＋Ｃｕ）＋Ｍｏ＋Ｖ−１で定義
されるＰ値を１．９≦Ｐ≦２．８に制限する。これは、
ＨＡＺ靭性、現地溶接性を損なうことなく、目的とする
強度・低温靭性バランスを達成するためである。Ｐ値の
下限を１．９としたのは９５０MPa 以上の強度と優れた
低温靭性を得るためである。またＰ値の上限を２．８と
したのは優れたＨＡＺ靭性、現地溶接性を維持するため
である。In the present invention, in addition to the limitation of the individual additive elements described above, P = 2,7C + 0.4Si + Mn + 0.
The P value defined by 8Cr + 0.45 (Ni + Cu) + Mo + V-1 is limited to 1.9 ≦ P ≦ 2.8. this is,
This is to achieve a desired strength-low temperature toughness balance without impairing HAZ toughness and on-site weldability. The lower limit of the P value is set to 1.9 in order to obtain a strength of 950 MPa or more and excellent low-temperature toughness. The upper limit of the P value is set to 2.8 in order to maintain excellent HAZ toughness and on-site weldability.
【００２９】次に、Ｃｅ，ＭｇおよびＹを添加する目的
について説明する。すなわち、その目的は、ＨＡＺ靭性
や現地溶接性（耐低温割れ性）などを一層改善するため
に必要に応じて添加するものであり、添加により本発明
鋼の優れた特徴をさらに顕著なものとする。Next, the purpose of adding Ce, Mg and Y will be described. That is, the purpose is to add as necessary to further improve the HAZ toughness and the on-site weldability (low-temperature cracking resistance), and the addition makes the excellent features of the steel of the present invention more remarkable. I do.
【００３０】ＣｅはＣａとほぼ同様な効果を有し、Ｏ，
Ｓと結合して硫化物形態を制御し、低温靭性を向上（シ
ャルピー衝撃試験の吸収エネルギーの増加など）させる
他、低Ａｌ鋼（０．０１％以下）にＣｅを添加すると、
微細分散したＣｅ酸化物が得られ、ＨＡＺのγ粒粗大化
を抑制してＨＡＺ靭性を改善する。しかしＣｅ添加量が
０．００５％未満では実用上効果がなく、また０．０２
０％を超えて添加すると鋼の清浄度を害するだけでな
く、現地溶接性にも悪影響をおよぼす。このためＣｅ添
加量の上限を０．０２０％に制限した。Ce has almost the same effect as Ca, and O,
In addition to controlling the sulfide form by combining with S to improve low-temperature toughness (increased absorption energy in Charpy impact test, etc.), when Ce is added to low Al steel (0.01% or less),
A finely dispersed Ce oxide is obtained, and HAZ toughness is improved by suppressing coarsening of γ grains in HAZ. However, if the Ce content is less than 0.005%, there is no practical effect, and 0.02% or less.
Addition of more than 0% not only impairs the cleanliness of the steel, but also adversely affects on-site weldability. Therefore, the upper limit of the added amount of Ce is limited to 0.020%.
【００３１】Ｍｇは強脱酸元素であり、酸素と結合して
微細な酸化物（微量のＴｉなどを含んだ複合酸化物）を
形成する。鋼中に微細分散したＭｇ酸化物はＴｉＮに比
べて高温でも安定であり、ＨＡＺ全域のγ粒粗大化を抑
制してＨＡＺ靭性を改善する。そのために、Ｍｇは最低
０．００１％必要である。しかしＭｇ量が多すぎると鋼
の清浄度が低下するので、その上限は０．００５％であ
る。Mg is a strongly deoxidizing element and combines with oxygen to form a fine oxide (composite oxide containing a small amount of Ti or the like). Mg oxide finely dispersed in steel is stable even at high temperatures compared to TiN, and suppresses coarsening of γ grains in the entire HAZ to improve HAZ toughness. Therefore, Mg must be at least 0.001%. However, if the amount of Mg is too large, the cleanliness of the steel decreases, so the upper limit is 0.005%.
【００３２】ＹはほぼＣｅ，Ｍｇと同様な効果を有する
のに加え、溶接時に水素がＹ酸化物に捕獲され、溶接低
温割れを抑制する効果も有する。Ｙの下限は０．００５
％、上限は０．０３０％である。なおＭｇ，Ｙ添加時に
微細酸化物を十分に得るためには、強脱酸元素Ａｌの量
を極力低減し、Ｏ量を０．００２〜０．０１０％に制御
することが有効である。In addition to Y having substantially the same effect as Ce and Mg, hydrogen has the effect of trapping hydrogen in the Y oxide during welding and suppressing welding low-temperature cracking. The lower limit of Y is 0.005
%, And the upper limit is 0.030%. In order to sufficiently obtain a fine oxide at the time of adding Mg and Y, it is effective to reduce the amount of the strongly deoxidizing element Al as much as possible and to control the amount of O to 0.002 to 0.010%.
【００３３】以上のような成分を有する鋼を４００℃以
上Ａｃ1 点以下の温度で焼戻し処理を行うことによっ
て、得られた鋼の特性はさらに良好なものとなる。すな
わち焼戻し処理は脱水素やマルテンサイトの分解による
降伏強さの向上に効果がある。また、焼戻し処理はミク
ロ組織分率などを変えず、本発明鋼の優れた特徴を損な
うものではないことを付記しておく。By subjecting the steel having the above components to tempering at a temperature of 400 ° C. or more and one point of Ac or less, the properties of the obtained steel are further improved. That is, the tempering treatment is effective in improving yield strength due to dehydrogenation and decomposition of martensite. Also, it should be noted that the tempering treatment does not change the microstructure fraction or the like and does not impair the excellent characteristics of the steel of the present invention.
【００３４】[0034]
【実施例】以下、本発明の実施例について述べる。実験
室溶解（５０kg，１２０mm厚鋼塊）または転炉−連続鋳
造法（２４０mm厚）で種々の鋼成分の鋳片を製造した。
これらの鋳片を種々の条件で厚みが１３〜３０mmの鋼板
に圧延し、諸機械的性質、ミクロ組織を調査した。な
お、一部の鋼板については焼戻し処理を付加した。鋼板
の機械的性質（降伏強さ：ＹＳ、引張強さ：ＴＳ、シャ
ルピー衝撃試験の−４０℃での吸収エネルギー：ｖＥ
-40 と５０％破面遷移温度：ｖＴｒｓ）は圧延と直角方
向で調査した。ＨＡＺ靭性（シャルピー衝撃試験の−２
０℃での吸収エネルギー：ｖＥ-20 ）は再現熱サイクル
装置で再現したＨＡＺで評価した（最高加熱温度：１４
００℃，８００〜５００℃の冷却時間〔Δ
ｔ800-500 〕：２５秒）。また現地溶接性はｙ−スリッ
ト溶接割れ試験（ＪＩＳ Ｇ３１５８）においてＨＡＺ
の低温割れ防止に必要な最低予熱温度で評価した（溶接
方法：ガスメタルアーク溶接、溶接棒：引張強さ１００
MPa 、入熱：０．５kJ／mm、溶着金属の水素量：３cc／
１００ｇ）。Embodiments of the present invention will be described below. Slabs of various steel components were produced by laboratory melting (50 kg, 120 mm thick steel ingot) or converter-continuous casting (240 mm thick).
These slabs were rolled into steel plates having a thickness of 13 to 30 mm under various conditions, and various mechanical properties and microstructures were investigated. In addition, tempering treatment was added to some steel sheets. Mechanical properties of steel sheet (yield strength: YS, tensile strength: TS, absorbed energy at −40 ° C. in Charpy impact test: vE
-40 and 50% fracture surface transition temperature (vTrs) were investigated in the direction perpendicular to the rolling. HAZ toughness (-2 of Charpy impact test)
Absorbed energy at 0 ° C .: vE −20 ) was evaluated by HAZ reproduced with a reproduction thermal cycler (maximum heating temperature: 14).
00 ° C, 800-500 ° C cooling time [Δ
t 800-500 ]: 25 seconds). The on-site weldability was determined by HAZ in the y-slit welding crack test (JIS G3158).
(Welding method: gas metal arc welding, welding rod: tensile strength 100)
MPa, heat input: 0.5 kJ / mm, hydrogen content of deposited metal: 3 cc /
100 g).
【００３５】鋼の化学成分、板厚条件を表１に示す。ま
た、表２に組織および試験結果（特性）を示す。本発明
に従って製造した鋼板は優れた強度・低温靭性バラン
ス、ＨＡＺ靭性および現地溶接性を有する。これに対し
て比較鋼は化学成分またはミクロ組織が不適切なため、
いずれかの特性が著しく劣る。The chemical components of the steel, the matter plate Atsujo shown in Table 1. Table 2 shows the structure and test results (characteristics). The steel sheet manufactured according to the present invention has excellent strength-low temperature toughness balance, HAZ toughness and on-site weldability. In contrast, the comparative steel has an inappropriate chemical composition or microstructure,
Either property is significantly inferior.
【００３６】すなわち、具体的には以下の通りである。
鋼９はＣ量が多すぎるため、母材およびＨＡＺのシャル
ピー吸収エネルギーが低く、かつ溶接時の予熱温度も高
い。鋼１０はＶが添加されていないため、母材の降伏強
さが低すぎる（ＵＯＥ鋼管では成形時に加工効果によっ
て、降伏強さは増加するが、鋼１０の降伏強さでは低す
ぎて目標値を満足できない）。鋼１１はＭｎ添加量が多
すぎるため、ＨＡＺの低温靭性が低く、かつ溶接時の予
熱温度も高い。鋼１２はＭｏ添加量が多すぎるため、母
材の低温靭性が低く、かつ溶接時に予熱を要する。鋼１
３は個々の元素は本発明の範囲内にあるが、Ｐ値が高す
ぎるため、母材靭性が低く、かつ溶接時の予熱温度も高
い。鋼１４はＮｂが添加されていないため、強度不足
で、母材の低温靭性も今一歩である。鋼１５はＳ量が多
すぎるため、母材およびＨＡＺのシャルピー吸収エネル
ギーが低い。鋼１６はフェライト分率が少なすぎるた
め、母材の降伏強さがやや低く、シャルピー遷移温度が
やや高い。鋼１７は加工フェライト分率が小さすぎるた
め、強度が不十分で、かつシャルピー遷移温度がやや高
い。鋼１８はフェライト粒径が大きいために、母材の低
温靭性が劣る。鋼１９はフェライト分率、加工フェライ
ト分率がともに小さすぎ、フェライト粒径も大きいた
め、母材の低温靭性が低い。That is, the details are as follows.
Since the steel 9 has too much carbon content, the Charpy absorbed energy of the base metal and the HAZ is low, and the preheating temperature during welding is high. Since V is not added to steel 10, the yield strength of the base material is too low (in the case of UOE steel pipe, the yield strength increases due to the processing effect at the time of forming, but the yield strength of steel 10 is too low and the target value is too low. Cannot be satisfied). Since the amount of Mn added to steel 11 is too large, the low-temperature toughness of HAZ is low and the preheating temperature during welding is high. Since the amount of Mo added to the steel 12 is too large, the low-temperature toughness of the base material is low, and preheating is required during welding. Steel 1
In No. 3, although the individual elements are within the range of the present invention, since the P value is too high, the base material toughness is low and the preheating temperature during welding is high. Steel 14 does not contain Nb, and thus has insufficient strength, and the low-temperature toughness of the base metal is just one step away. Since the steel 15 has too much S content, the Charpy absorbed energy of the base metal and the HAZ is low. Steel 16 has a ferrite fraction that is too low, so that the base metal has a slightly lower yield strength and a slightly higher Charpy transition temperature. Steel 17 has an insufficiently processed ferrite fraction, so that the strength is insufficient and the Charpy transition temperature is slightly high. Since steel 18 has a large ferrite grain size, the low-temperature toughness of the base material is inferior. In steel 19, both the ferrite fraction and the processed ferrite fraction are too small and the ferrite grain size is large, so that the base material has low low-temperature toughness.
【００３７】[0037]
【表１】 [Table 1]
【００３８】[0038]
【表２】 [Table 2]
【００３９】[0039]
【発明の効果】本発明により低温靭性、現地溶接性の優
れた超高張力鋼（引張強さ９５０MPa以上、ＡＰＩ規格
Ｘ１００超）が安定して大量に製造できるようになっ
た。その結果、パイプラインの安全性が著しく向上する
とともに、パイプラインの輸送効率、施工能率の飛躍的
な向上が可能となった。According to the present invention, ultra-high-strength steel (tensile strength of 950 MPa or more, API standard X100 or more) excellent in low-temperature toughness and on-site weldability can be stably mass-produced. As a result, the safety of the pipeline has been remarkably improved, and the transportation efficiency and construction efficiency of the pipeline have been dramatically improved.
フロントページの続き (72)発明者 寺田 好男 千葉県君津市君津１番地 新日本製鐵株 式会社 君津製鐵所内 (56)参考文献 特開 平８−209288（ＪＰ，Ａ) 特開 平８−209287（ＪＰ，Ａ) 特開 平８−209291（ＪＰ，Ａ) 特開 平８−209290（ＪＰ，Ａ) 特開 平８−269545（ＪＰ，Ａ) 特開 平３−97809（ＪＰ，Ａ) 特開 昭52−85917（ＪＰ，Ａ) 特開 平５−195057（ＪＰ，Ａ) 特開 平５−163527（ＪＰ，Ａ) (58)調査した分野(Int.Cl.7，ＤＢ名) C22C 38/00 - 38/60 Continuation of the front page (72) Inventor Yoshio Terada 1 Kimitsu, Kimitsu City, Chiba Prefecture Nippon Steel Corporation Kimitsu Works (56) References JP-A-8-209288 (JP, A) JP-A-8 JP-209287 (JP, A) JP-A-8-209291 (JP, A) JP-A-8-209290 (JP, A) JP-A 8-269545 (JP, A) JP-A-3-97809 (JP, A) JP-A-52-85917 (JP, A) JP-A-5-195057 (JP, A) JP-A-5-163527 (JP, A) (58) Fields investigated (Int. Cl. 7 , DB name) C22C 38/00-38/60
Claims (4)
もに、下記式で定義されるＰ値が、 Ｐ＝２．７Ｃ＋０．４Ｓｉ＋Ｍｎ＋Ｍｏ＋Ｖ−１：１．
９〜２．８ を満足し、さらに、そのミクロ組織が、マルテンサイト
・ベイナイトと分率にして２０〜９０％のフェライトと
によって形成された２相混合組織からなっており、かつ
フェライト中に加工フェライトを５０〜１００％含有
し、フェライト平均粒径が５μｍ以下であることを特徴
とする低温靭性の優れた超高張力鋼。C: 0.05 to 0.10%, Si: 0.6% or less, Mn: 1.8 to 2.5%, P: 0.015% or less, S: 0% by weight 0.003% or less, Mo: 0.30 to 0.60%, Nb: 0.01 to 0.10%, V: 0.03 to 0.10%, Ti: 0.005 to 0.030%, Al : 0.06% or less, N: 0.001 to 0.006%, the balance being iron and unavoidable impurities, and the P value defined by the following formula: P = 2.7C + 0.4Si + Mn + Mo + V- 1: 1.
9 to 2.8, and the microstructure is a two-phase mixed structure formed by martensite bainite and a fraction of 20 to 90% ferrite, and is processed into ferrite. An ultra-high-strength steel excellent in low-temperature toughness, comprising 50 to 100% of ferrite and having an average ferrite grain size of 5 μm or less.
量％で、 Ｃｅ：０．００５〜０．０２０％、 Ｍｇ：０．００１〜０．００５％、 Ｙ ：０．００５〜０．０３０％ の１種または２種以上を含有することを特徴とする請求
項１記載の低温靭性の優れた超高張力鋼。Wherein in addition to the components of claim 1, wherein, in weight%, Ce: 0.005~0.020%, Mg : 0.001~0.005%, Y: 0.005~0. The ultra-high-strength steel excellent in low-temperature toughness according to claim 1, comprising one or more kinds of 030%.
量％で、 Ｎｉ：０．１〜１．０％、 Ｃｕ：０．１〜１．２％、 Ｃｒ：０．１〜０．８％、 Ｃａ：０．００１〜０．００５％ の１種または２種以上を含有し、下記式で定義されるＰ
値が、 Ｐ＝２．７Ｃ＋０．４Ｓｉ＋Ｍｎ＋０．８Ｃｒ＋０．４５（Ｎｉ＋Ｃｕ） ＋Ｍｏ＋Ｖ−１：１．９〜２．８ を満足することを特徴とする請求項２記載の低温靭性の
優れた超高張力鋼。3. In addition to the components according to claim 2, in weight%, Ni: 0.1~1.0%, Cu : 0.1~1.2%, Cr: 0.1~0. 8% Ca: contain one or two or more from 0.001 to 0.005%, defined by the following formula P
3. The ultra-high-strength steel excellent in low-temperature toughness according to claim 2 , wherein the value satisfies the following condition: P = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + Mo + V-1: 1.9 to 2.8. .
の鋼を、４００℃以上Ａｃ1 点以下の温度で焼戻し処理
してなることを特徴とする低温靭性の優れた超高張力
鋼。4. An ultra-high tensile steel excellent in low-temperature toughness, wherein the steel according to claim 1, 2, or 3 is tempered at a temperature of 400 ° C. or more and 1 point or less of Ac. .
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP19535995A JP3258207B2 (en) | 1995-07-31 | 1995-07-31 | Ultra high strength steel with excellent low temperature toughness |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP19535995A JP3258207B2 (en) | 1995-07-31 | 1995-07-31 | Ultra high strength steel with excellent low temperature toughness |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH0941074A JPH0941074A (en) | 1997-02-10 |
| JP3258207B2 true JP3258207B2 (en) | 2002-02-18 |
Family
ID=16339870
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP19535995A Expired - Fee Related JP3258207B2 (en) | 1995-07-31 | 1995-07-31 | Ultra high strength steel with excellent low temperature toughness |
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| Country | Link |
|---|---|
| JP (1) | JP3258207B2 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009008281A1 (en) * | 2007-07-10 | 2009-01-15 | Usui Kokusai Sangyo Kaisha, Ltd. | Steel tube for fuel injection tube and process for producing the same |
| CN108603266A (en) * | 2016-01-29 | 2018-09-28 | 杰富意钢铁株式会社 | High-intensity and high-tenacity steel for steel pipes plate and its manufacturing method |
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|---|---|---|---|---|
| ATE330040T1 (en) | 1997-07-28 | 2006-07-15 | Exxonmobil Upstream Res Co | ULTRA HIGH STRENGTH WELDABLE STEELS WITH EXCELLENT ULTRA LOW TEMPERATURE TOUGHNESS |
| KR100386767B1 (en) | 1997-07-28 | 2003-06-09 | 닛폰 스틸 가부시키가이샤 | Method for producing ultra-high strength, weldable steels with superior toughness |
| ES2251096T3 (en) | 1997-07-28 | 2006-04-16 | Exxonmobil Upstream Research Company | HYPERERRISTLY STEELS ESSENTIALLY BORO FREE, SOLDABLE WITH HIGHER TENACITY. |
| US6228183B1 (en) | 1997-07-28 | 2001-05-08 | Exxonmobil Upstream Research Company | Ultra-high strength, weldable, boron-containing steels with superior toughness |
| US6254698B1 (en) * | 1997-12-19 | 2001-07-03 | Exxonmobile Upstream Research Company | Ultra-high strength ausaged steels with excellent cryogenic temperature toughness and method of making thereof |
| GB0005023D0 (en) * | 2000-03-03 | 2000-04-26 | British Steel Ltd | Steel composition and microstructure |
| JP2003105439A (en) * | 2001-10-01 | 2003-04-09 | Kawasaki Steel Corp | Low yield ratio steel for low temperature use, and production method therefor |
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1995
- 1995-07-31 JP JP19535995A patent/JP3258207B2/en not_active Expired - Fee Related
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009008281A1 (en) * | 2007-07-10 | 2009-01-15 | Usui Kokusai Sangyo Kaisha, Ltd. | Steel tube for fuel injection tube and process for producing the same |
| JP2009019503A (en) * | 2007-07-10 | 2009-01-29 | Usui Kokusai Sangyo Kaisha Ltd | Steel pipe for fuel injection pipe and its manufacturing method |
| CN108603266A (en) * | 2016-01-29 | 2018-09-28 | 杰富意钢铁株式会社 | High-intensity and high-tenacity steel for steel pipes plate and its manufacturing method |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0941074A (en) | 1997-02-10 |
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