JP3244984B2 - High strength linepipe steel with low yield ratio and excellent low temperature toughness - Google Patents
High strength linepipe steel with low yield ratio and excellent low temperature toughnessInfo
- Publication number
- JP3244984B2 JP3244984B2 JP01730295A JP1730295A JP3244984B2 JP 3244984 B2 JP3244984 B2 JP 3244984B2 JP 01730295 A JP01730295 A JP 01730295A JP 1730295 A JP1730295 A JP 1730295A JP 3244984 B2 JP3244984 B2 JP 3244984B2
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- Prior art keywords
- steel
- ferrite
- low
- strength
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Description
【０００１】[0001]
【産業上の利用分野】本発明は９５０ＭＰａ以上の引張
強さ（ＴＳ）を有する低温靱性・溶接性の優れた超高強
度鋼に関するももので、天然ガス・原油輸送用ラインパ
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-strength steel having a tensile strength (TS) of 950 MPa or more and excellent in low-temperature toughness and weldability. It can be widely used as welding steel for pressure vessels and industrial machinery.
【０００２】[0002]
【従来の技術】近年、原油・天然ガスを長距離輸送する
パイプラインに使用するラインパイプは、高圧化によ
る輸送効率の向上や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（引張強さ６２０ＭＰａ以上）までのラインハ
パイプの実用化がされているが、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 pipelines for transporting crude oil and natural gas over long distances have been used to improve transportation efficiency by increasing pressure and to improve on-site construction efficiency by reducing the outside diameter and weight of line pipes. , The strength tends to be higher and higher. Up to now, line pipes up to X80 (tensile strength of 620 MPa or more) have been put into practical use according to the American Petroleum Institute (API) standard, but the need for higher-strength line pipes has increased.
【０００３】現在、超高強度ラインパイプ製造法の研究
は、従来のＸ８０ラインパイプの製造技術（たとえばＮ
ＫＫ技報 No.138(1992), pp24-31、およびThe 7th Offs
horeMechanics and Arctic Engineering (1988), Volum
e V, pp179-185) を基本に検討されているが、これでは
せいぜい、Ｘ１００（引張強さ７６０ＭＰａ以上）ライ
ンパイプの製造が限界と考えられる。パイプラインの超
高強度化は強度・低温靱性バランスを始めとして溶接熱
影響部（ＨＡＺ）靱性、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強
度ラインパイプ（Ｘ１００超）の早期開発が要望されて
いる。[0003] At present, research on ultra-high-strength linepipe manufacturing methods is based on conventional X80 linepipe manufacturing techniques (eg, N
KK Technical Report No.138 (1992), pp24-31, and The 7th Offs
horeMechanics and Arctic Engineering (1988), Volum
e V, pp. 179-185), but it is considered that, at most, the production of X100 (tensile strength of 760 MPa or more) line pipe is the 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. There is a demand for early development of a strength line pipe (above X100).
【０００４】[0004]
【発明が解決しようとする問題点】本発明は強度と低温
靱性のバランスが優れ、かつ現地溶接が容易な引張強さ
９５０ＭＰａ以上（ＡＰＩ規格Ｘ１００超）の超高強度
・低降伏比ラインパイプ用鋼を提供するものである。SUMMARY OF THE INVENTION The present invention is directed to an ultra-high-strength, low-yield ratio line pipe having an excellent balance between strength and low-temperature toughness and having a tensile strength of 950 MPa or more (API standard X100 or more), which is easily welded on site. It provides steel.
【０００５】[0005]
【問題点を解決する為の手段】本発明者らは、引張強さ
が９５０ＭＰａ以上で、かつ低温靱性・現地溶接性の優
れた超高強度鋼を得るための鋼材の化学成分（組成）と
そのミクロ組織について鋭意研究を行い、新しい超高強
度溶接用鋼を発明するに至った。Means for Solving the Problems The present inventors have determined that the chemical composition (composition) of a steel material for obtaining an ultra-high-strength steel having a tensile strength of 950 MPa or more and excellent low-temperature toughness and on-site weldability. The enthusiastic research on the microstructure has led to the invention of a new ultra-high strength welding steel.
【０００６】すなわち、本発明の要旨とするところは、 (1) 重量％で、 Ｃ ：０．０５〜０．１０％、 Ｓｉ：０．６％以下、 Ｍｎ：１．７〜２．５％、 Ｐ ：０．０１５％以
下、 Ｓ ：０．００３％以下、 Ｎｉ：０．１〜１．０
％、 Ｃｕ：０．８〜１．２％、 Ｍｏ：０．３５〜０．
５０％、 Ｎｂ：０．０１〜０．１０％、 Ｔｉ：０．００５〜
０．０３０％、 Ａｌ：０．０６％以下、 Ｎ ：０．００１〜
０．００６％、 必要に応じてさらに、 Ｖ ：０．１０％以下、 Ｃｒ：０．６％以下、 Ｃａ：０．００１〜０．００６％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り、下
記式で定義されるＰ値が２．０以上、３．５以下の範囲
にあり、さらにそのミクロ組織がマルテンサイト、ベイ
ナイトおよびフェライトからなり、フェライト分率が２
０〜９０面積％で、かつフェライト中に加工フェライト
を面積％で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降伏比を有する
低温靱性に優れた高強度ラインパイプ用鋼。 Ｐ＝２．７Ｃ＋０．４Ｓｉ＋Ｍｎ＋０．８Ｃｒ＋０．４５（Ｎｉ＋Ｃｕ） ＋Ｍｏ＋Ｖ−１ (2) 前記鋼を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降伏比を有する低温靱性に優れた高
強度ラインパイプ用鋼にある。なお、以下の説明におい
て、フェライト分率やマルテンサイト・ベイナイト分
率、およびフェライト中の加工フェライト量を示す％は
面積％をいう。 That is, the gist of the present invention is as follows: (1) C: 0.05 to 0.10%, Si: 0.6% or less, Mn: 1.7 to 2.5% by weight. , P: 0.015% or less, S: 0.003% or less, Ni: 0.1 to 1.0
%, Cu: 0.8-1.2%, Mo: 0.35-0.
50%, Nb: 0.01-0.10%, Ti: 0.005-
0.030%, Al: 0.06% or less, N: 0.001 to
0.006%, if necessary, one or more of V: 0.10% or less, Cr: 0.6% or less, and Ca: 0.001 to 0.006%, with the balance being It consists of iron and unavoidable impurities, has a P value defined by the following formula in the range of 2.0 or more and 3.5 or less, further has a microstructure of martensite, bainite and ferrite, and has a ferrite fraction of 2
High strength excellent in low-temperature toughness having a low yield ratio, characterized in that the ferrite has a ferrite average particle size of 5 μm or less, containing 0 to 90 area %, and 50 to 100% area ferrite processed ferrite in the ferrite. Steel for line pipe. P = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + Mo + V-1 (2) The steel is tempered at a temperature of not more than one point Ac, and has excellent low-temperature toughness having a low yield ratio. In high-strength linepipe steel. In the following explanation
Ferrite fraction and martensite bainite fraction
And the percentage indicating the amount of processed ferrite in ferrite
It means area%.
【０００７】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、Ｎｉ−Ｃｕ−Ｍｏ−Ｎｂ−微量
Ｔｉを複合添加した低炭素・高Ｍｎ系であること、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、ある一定量以上の加工フェライトを含む）とマル
テンサイト、ベイナイトの硬軟混合組織からなることで
ある。Hereinafter, the contents of the present invention will be described in detail. The feature of the present invention is that it is a low-carbon, high-Mn system to which Ni-Cu-Mo-Nb-trace Ti is added in a complex manner, and its microstructure is fine ferrite (having an average particle size of 5 μm or less and a certain amount or more. And a hard-soft mixed structure of martensite and bainite.
【０００８】従来より、低炭素−高Ｍｎ−Ｎｂ−Ｃｕ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
イプ用鋼として知られているが、その引張強さの上限は
せいぜい７５０ＭＰが限界であった。本基本成分系で加
工フェライトを含む微細フェライトとマルテンサイト、
ベイナイトの硬軟混合微細組織を有する高強度ラインパ
イフ用鋼はまったく存在しない。これはマルテンサイ
ト、ベイナイト２相混合組織では９５０ＭＰａ以上の引
張強さは到底不可能であるばかりか、低温靱性や現地溶
接性も不十分と考えられていたためである。Conventionally, a low carbon-high Mn-Nb-Cu steel has been known as a linepipe steel having a fine acicular ferrite structure, but the upper limit of its tensile strength is at most 750MP. . Fine ferrite including processed ferrite and martensite in this basic component system,
There is no high-strength line pif steel having a hard-soft mixed microstructure of bainite. This is because not only the tensile strength of 950 MPa or more is impossible at all with the martensite-bainite two-phase mixed structure, but also the low-temperature toughness and on-site weldability are considered to be insufficient.
【０００９】しかしながら本発明者らはＮｂ−Ｃｕ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靱性が達成できることを見
いだした。すなわち、本発明鋼の特徴は焼戻し処理な
しでも優れた超高強度、低温靱性が得られること、焼
入れ・焼戻し処理に比較して降伏比が低く、鋼管成形
性、低温靱性（シャルピー遷移温度）に著しく優れるこ
と、などがあげられる（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）。However, the present inventors have found that even in Nb-Cu steel, ultra-high strength and excellent low-temperature toughness can be achieved by strictly controlling the chemical composition and microstructure. In other words, the characteristics of the steel of the present invention are that excellent ultra-high strength and low-temperature toughness can be obtained without tempering, the yield ratio is lower than that of quenching and tempering, and the steel tube formability and low-temperature toughness (Charpy transition temperature) are improved. (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, and the desired yield strength can be obtained.) .
【００１０】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、鋼のミクロ組織を一定量以上のマルテンサイト
・ベイナイトとする必要があり、そのためにはフェライ
ト分率を２０〜９０％（マルテンサイト・ベイナイト分
率１０〜８０％）とする必要がある。フェライト分率が
９０％を超えると、マルテンサイト・ベイナイト分率が
小さくなり過ぎて、目的とする強度は達成出来ない（フ
ェライト分率はＣ量にも依存し、Ｃ量が０．０５％以上
では、実質上フェライトを９０％以上とすることは困難
である）。本発明鋼において強度、低温靱性上、もっと
も望ましいフェライト分率は３０〜８０％である。しか
し、本来フェライトは軟らかいものであり、たとえフェ
ライト分率が２０〜９０％であっても、加工フェライト
の割合が少なすぎると、目的とする強度（とくに降伏強
さ）・低温靱性は達成できない。このため、加工フェラ
イトの割合を５０〜１００％とした。フェライトの加工
（圧延）は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。First, the microstructure of the steel of the present invention will be described. In order to achieve an ultra-high tensile strength of 950 MPa or more, it is necessary that the microstructure of steel be a certain amount or more of martensite bainite, and for that purpose, the ferrite fraction is set to 20 to 90% (martensite. (A bainite fraction of 10 to 80%). When the ferrite fraction exceeds 90%, the desired strength cannot be achieved because the martensite-bainite fraction becomes too small (the ferrite fraction also depends on the C content, and the C content is 0.05% or more. Then, it is practically difficult to increase the ferrite content to 90% or more). In the steel of the present invention, the most desirable ferrite fraction in terms of strength and low-temperature toughness is 30 to 80%. However, ferrite is originally soft, and even if the ferrite fraction is 20 to 90%, if the proportion of the processed ferrite is too small, the desired strength (particularly, yield strength) and low-temperature toughness cannot be achieved. For this reason, the ratio of the processed ferrite is set to 50 to 100%. The processing (rolling) of ferrite increases the yield strength of ferrite by strengthening dislocations and subgrains, and is extremely effective in improving the Charpy transition temperature, as described later.
【００１１】しかしミクロ組織の種類を上述のように限
定しても優れた低温靱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。超高強度鋼においても、
加工フェライトの導入により、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（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層状剥離現象で、脆
性き裂先端での３軸応力度を低下させ、脆性き裂伝播停
止特性を改善すると考えられている）。However, even if the type of microstructure is limited as described above, it is not sufficient 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 caused separation on the fracture surface such as the Charpy impact test, and the fracture surface transition temperature dropped dramatically. (Separation is a layered phenomenon that occurs on the fracture surface such as the Charpy impact test.) It is believed that the triaxial stress at the brittle crack tip is reduced to improve brittle crack propagation arrestability).
【００１２】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ることがわかっ
た。Further, it has been found that by setting the average ferrite grain size to 5 μm or less, the martensite-bainite structure other than ferrite can be simultaneously refined, and a remarkable improvement in transition temperature and an increase in yield strength can be obtained. .
【００１３】以上により、従来低温靱性が悪いと考えら
れていたＮｂ−Ｃｕ鋼のフェライトとマルテンサイト・
ベイナイト硬軟混合組織の強度・低温靱性バランスの大
幅な向上に成功した。As described above, ferrite and martensite of Nb-Cu steel, which were conventionally considered to be poor in low-temperature toughness, were obtained.
The balance between strength and low-temperature toughness of the bainite hard-soft mixed structure was greatly improved.
【００１４】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材は得
られない。このためにはミクロ組織と同時に化学成分を
限定する必要がある。以下に成分元素の限定理由につい
て説明する。[0014] However, even if the microstructure of the steel is strictly controlled as described above, a steel material having desired characteristics cannot be obtained. For this purpose, it is necessary to limit the chemical composition simultaneously with the microstructure. The reasons for limiting the component elements will be described below.
【００１５】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であり、フェライトと
マルテンサイト・ベイナイト硬軟混合組織において目標
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添加による析出効果、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最小
量でもある。しかし、Ｃ量が多すぎると母材、ＨＡＺの
低温靱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。[0015] The amount of C is limited to 0.05 to 0.10%.
Carbon is extremely effective in improving the strength of steel, and at least 0.05% is required in order to obtain a target strength in a hard-soft mixed structure of ferrite and martensite-bainite. Further, this amount is also a minimum amount for exhibiting the effect of precipitation by adding Nb and V, the effect of refining crystal grains, and securing the strength of the welded portion. However, 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%.
【００１６】Ｓｉは脱酸や強度向上のために添加する元
素であるが、多く添加するとＨＡＺ靱性、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ＡｌでもＴｉでも十分可能であり、Ｓｉは必ずしも
添加する必要はない。[0016] Si is an element added for deoxidation and improvement of strength, but if added in a large amount, HAZ toughness and on-site weldability are remarkably deteriorated, so the upper limit was made 0.6%. Deoxidation of steel is sufficiently possible with Al or Ti, and Si need not always be added.
【００１７】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・ベイナイト硬軟混合組織と
し、優れた強度・低温靭性の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１．７％である。しか
し、Ｍｎ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
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。望ましいＭｎ量は１．９〜
２．１％である。Mn is an element indispensable for ensuring a good balance between strength and low-temperature toughness, with the microstructure of the steel of the present invention having a fine ferrite and martensite-bainite hard / soft mixed structure, with a lower limit of 1.7. %. However, if the Mn content is too large, the hardenability of the steel increases and not only deteriorates the HAZ toughness and the on-site weldability, but also promotes the center segregation of the continuously cast steel slab and deteriorates the low-temperature toughness of the base material. 2.5 %. Desirable Mn amount is 1.9 to
2.1%.
【００１８】Ｎｉを添加する目的は低炭素の本発明鋼を
低温靱性や現地溶接性を劣化させることなく向上させる
ためである。Ｎｉ添加はＭｎやＣｒ，Ｍｏ添加に比較し
て圧延組織（とくに連続鋳造鋼片の中心偏析帯）中に低
温靱性に有害な硬化組織を形成することが少ないばかり
か、０．１％以上での微量のＮｉ添加がＨＡＺ靱性の改
善にも有効であることが判明した。ＨＡＺ靱性上、とく
に有効なＮｉ添加量は０．３％以上である。しかし、添
加量が多すぎると、経済性だけでなく、ＨＡＺ靱性や現
地溶接性を劣化させるので、その上限を１．０％とし
た。また、Ｎｉ添加は連続鋳造時、熱間圧延時における
Ｃｕ割れ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 low carbon steel of the present invention without deteriorating the low-temperature toughness and the on-site weldability. Compared with the addition of Mn, Cr, or Mo, Ni addition not only causes less formation of a hardened structure that is detrimental to low-temperature toughness in the rolled structure (particularly, the central segregation zone of continuous cast steel slabs), but also has a content of 0.1% or more. It has been found that the addition of a small amount of Ni is also effective in improving the HAZ toughness. The Ni addition amount that is particularly effective in terms of HAZ toughness is 0.3% or more. However, if the addition amount is too large, not only economic efficiency but also HAZ toughness and on-site weldability are degraded, so the upper limit was made 1.0%. The addition of Ni is also effective in preventing Cu cracking during continuous casting and hot rolling. In this case, Ni is Cu
It is necessary to add at least 1/3 of the amount.
【００１９】Ｃｕはフェライトとマルテンサイト・ベイ
ナイト硬軟混合組織においてマルテンサイト・ベイナイ
ト相の硬化および析出強化により強度を大幅に増加させ
る。０．８％未満では効果が十分でなく、一方、過剰に
添加すると、析出硬化により母材、ＨＡＺの靱性低下
し、また熱間加工時にＣｕ割れが生じるので、その上限
を１．２％とした。Cu greatly increases strength by hardening and precipitation strengthening of the martensite-bainite phase in a hard-soft mixed structure of ferrite and martensite-bainite. If it is less than 0.8%, the effect is not sufficient. On the other hand, if it is added excessively, the toughness of the base material and the HAZ decreases due to precipitation hardening, and Cu cracks occur during hot working, so the upper limit is 1.2%. did.
【００２０】Ｍｏを添加する理由は鋼の焼入れ性を向上
させ、目的とする硬軟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は最低で
も０．３５％必要である。しかし、過剰なＭｏ添加はＨ
ＡＺ靱性、現地溶接性を劣化させるので、その上限を
０．５％とした。The reason for adding Mo is to improve the hardenability of the steel and obtain the desired hard / soft mixed structure. Further, Mo coexists with Nb to suppress recrystallization of austenite during controlled rolling, and is also effective in refining the austenite structure. To obtain such an effect, Mo needs to be at least 0.35%. However, excessive Mo addition is
Since the AZ toughness and the on-site weldability deteriorate, the upper limit is set to 0.5%.
【００２１】また、本発明鋼では、必須の元素としてＮ
ｂ：０．０１〜０．１０％、Ｔｉ：０．００５〜０．０
３０％を含有する。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て組織を微細化するだ
けでなく、析出硬化や焼入れ性増大にも寄与し、鋼を強
靱化する。０．０１％未満では効果が十分でなく、一
方、Ｎｂ添加量が多すぎると、ＨＡＺ靱性や現地溶接性
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, N is an essential element.
b: 0.01 to 0.10%, Ti: 0.005 to 0.0
Contains 30%. Nb coexists with Mo to suppress the recrystallization of austenite during controlled rolling, not only to refine the structure, but also to contribute to precipitation hardening and hardenability, and toughen the steel. If the content is less than 0.01%, the effect is not sufficient. On the other hand, if the Nb content is too large, the HAZ toughness and the on-site weldability are adversely affected, so the upper limit was made 0.10%.
【００２２】一方、Ｔｉ添加は微細なＴｉＮを形成し、
スラブ再加熱時およびＨＡＺのオーステナイト粒の粗大
化を抑制してミクロ組織を微細化し、母材およびＨＡＺ
の低温靱性を改善する。また、Ａｌ量が少ない時（たと
えば０．００５％以下）、Ｔｉは酸化物を形成し、ＨＡ
Ｚにおいて粒内フェライト生成核として作用し、ＨＡＺ
組織を微細化する効果も有する。このようなＴｉＮの効
果を発現させるためには、最低０．００５％のＴｉ添加
が必要である。しかし、Ｔｉ量が多すぎると、ＴｉＮの
粗大化やＴｉＣによる析出硬化が生じ、低温靱性を劣化
させるので、その上限を０．０３％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 of the HAZ are suppressed from coarsening, the microstructure is refined, and the base material and the HAZ are reduced.
To improve the low temperature toughness of steel. When the amount of Al is small (for example, 0.005% or less), Ti forms an oxide and HA
H acts as an intragranular ferrite nucleus in Z
It also has the effect of making the structure finer. In order to exert such an effect of TiN, at least 0.005% of Ti must be added. However, if the amount of Ti is too large, coarsening of TiN and precipitation hardening due to TiC occur, deteriorating low-temperature toughness. Therefore, the upper limit was set to 0.03%.
【００２３】Ａｌは通常脱酸材として鋼に含まれる元素
で、組織の微細化にも効果を有する。しかし、Ａｌ量が
０．０６％を超えるとＡｌ系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、Ａｌは必ずしも添
加する必要はない。Al is an element usually contained in steel as a deoxidizing material, and also has an effect on refining the structure. However, if the Al content exceeds 0.06%, Al-based nonmetallic inclusions increase and impair the cleanliness of the steel, so the upper limit was made 0.06%. Deoxidation can be performed with Ti or Si, and Al need not always be added.
【００２４】ＮはＴｉＮを形成し、スラブ再加熱時およ
びＨＡＺのオーステナイト粒の粗大化を抑制して母材、
ＨＡＺの低温靱性を向上させる。このために、必要な最
小量は０．００１％である。しかし、Ｎ量が多すぎると
スラブ表面疵や固溶ＮによるＨＡＺ靱性の劣化の原因と
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 HAZ during reheating of the slab and in the HAZ.
Improves the low temperature toughness of HAZ. For this, the minimum amount required is 0.001%. However, if the amount of N is too large, it causes deterioration of HAZ toughness due to slab surface flaws and solid solution N, so the upper limit must be suppressed to 0.006%.
【００２５】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％、０．００３％以下と
する。この主たる理由は母材およびＨＡＺの低温靱性を
より一層向上させるためである。Ｐ量の低減は連続鋳造
スラブの中心偏析を軽減するとともに、粒界破壊を防止
して低温靱性を向上させる。また、Ｓ量の低減は熱間圧
延で延伸化するＭｎＳを低減して延性，靱性を向上させ
る効果がある。Further, in the present invention, the amounts of P and S as impurity elements are set to 0.015% and 0.003% or less, respectively. The main reason for this is to further improve the low-temperature toughness of the base material and HAZ. The reduction of the P content reduces the segregation of the center of the continuously cast slab, prevents the grain boundary fracture, and improves the low-temperature toughness. Further, the reduction of the amount of S has the effect of reducing MnS stretched by hot rolling and improving ductility and toughness.
【００２６】つぎに、Ｖ，Ｃｒ，Ｃａを添加する目的に
ついて説明する。基本となる成分に、更にこれらの元素
を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・靱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、必ずし
も含有する必要はなく、また、その添加量は自ずから制
限されるべき性質のものである。Next, the purpose of adding V, Cr, and Ca will be described. The main purpose of adding these elements to the basic components is to further improve the strength and toughness and to expand the size of the steel material that can be manufactured without impairing the excellent characteristics of the steel of the present invention. Therefore, it is not always necessary to contain it, and the amount of addition is of a nature that should be naturally restricted.
【００２７】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。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。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。上限
はＨＡＺ靱性、現地溶接性の点から０．１０％まで許容
でき、特に０．０３〜０．０８％の添加が望ましい範囲
である。V has almost the same effect as Nb, but the effect is weaker than Nb. However, the effect of V addition on ultra-high strength steel is great, and the combined addition of Nb and V makes the excellent features of the steel of the present invention more remarkable. Also, V
It was found that due to the processing (hot rolling) of ferrite, strain-induced precipitation resulted in significant strengthening of ferrite. The upper limit is allowable from the viewpoint of HAZ toughness and on-site weldability up to 0.10%, and particularly, the addition of 0.03 to 0.08% is a desirable range.
【００２８】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劣化さ
せる。このためＣｒ量の上限は０．６％である。Ｖ，Ｃ
ｒ量の下限は特に限定しないが、材質上の効果が顕著に
なる最少量として、Ｖは０．０１％，Ｃｒは０．１％で
ある。[0028] Cr increases the strength of the base material and the welded portion, but if it is too large, the HAZ toughness and on-site weldability are remarkably deteriorated. Therefore, the upper limit of the Cr content is 0.6 %. V, C
The lower limit of the amount of r is not particularly limited, but V is 0.01% and Cr is 0.1% as the minimum amounts at which the effect on the material is remarkable.
【００２９】Ｃａは硫化物（ＭｎＳ）の形態を制御し、
低温靱性を向上（シャルピー試験の吸収エネルギーの増
加など）させる。しかし、Ｃａ量が０．００１％以下で
は実用上効果は無い。また０．００６％を超えて添加す
るとＣａＯ−ＣａＳ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０．００６％に制限した。なお超高強度ラインパ
イプでは、Ｓ，Ｏ量をそれぞれ０．００１％、０．００
２％以下に低減し、かつＥＳＳＰ＝（Ｃａ）〔１−１２
４（Ｏ）〕／１．２５Ｓを０．５≦ＥＳＳＰ≦１０．０
とすることがとくに有効である。ここでＥＳＳＰとは、
有効硫化物形態制御パラメターの略である。Ca controls the form of sulfide (MnS),
Improves low-temperature toughness (increased energy absorbed in Charpy test, etc.). However, there is no practical effect if the Ca content is 0.001% or less. Further, when added in excess of 0.006%, CaO—CaS is generated in large quantities, resulting in large clusters,
It becomes a large inclusion, which not only impairs the cleanliness of the steel, but also adversely affects on-site weldability. For this reason, the upper limit of the amount of Ca added was limited to 0.006%. In the case of ultra-high-strength line pipes, the amounts of S and O are 0.001% and 0.00%, respectively.
2% or less, and ESSP = (Ca) [1-12
4 (O)] / 1.25S with 0.5 ≦ ESSP ≦ 10.0
Is particularly effective. Here, ESSP is
Abbreviation of effective sulfide form control parameter.
【００３０】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を２．
０≦Ｐ≦３．５に制限する。これは、目的とする強度・
低温靱性バランスを達成するためである。Ｐ値の下限は
９５０ＭＰａ以上の強度と優れた低温靱性を得るためで
ある。また、Ｐ値の上限を３．５としたのは優れたＨＡ
Ｚ靱性、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.
8Cr + 0.45 (Ni + Cu) + Mo + V-1
Restrict to 0 ≦ P ≦ 3.5. This is the desired strength
This is to achieve a low-temperature toughness balance. The lower limit of the P value is for obtaining a strength of 950 MPa or more and excellent low-temperature toughness. Further, the reason why the upper limit of the P value is set to 3.5 is that excellent HA is obtained.
This is to maintain Z toughness and on-site weldability.
【００３１】次に、請求項４について説明する。請求項
４は請求項１〜３の鋼をＡｃ1 点以下の温度で焼戻し処
理を行うものである。焼戻し処理によって延性、靭性は
適度に回復する。焼戻し処理はミクロ組織分率そのもの
を変えず、本発明の優れた特徴を損なうものでなく、溶
接熱影響部の軟化幅を狭める効果をも有する。Next, claim 4 will be described. Claim
No. 4 is for tempering the steel of claims 1 to 3 at a temperature not higher than Ac 1 point. The ductility and toughness are appropriately recovered by tempering. The tempering treatment does not change the microstructure fraction itself, does not impair the excellent features of the present invention, and also has the effect of narrowing the softening width of the heat affected zone.
【００３２】[0032]
【実施例】つぎに本発明の実施例について述べる。実験
室溶解（５０kg，１００mm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１５〜２５mmの鋼板
に圧延し、場合によっては焼戻し処理を行い諸性質、ミ
クロ組織を調査した。Next, embodiments of the present invention will be described. Slabs of various steel components were produced by laboratory melting (50 kg, 100 mm thick steel ingot) or converter-continuous casting (240 mm thick).
These slabs were rolled into steel sheets having a thickness of 15 to 25 mm under various conditions, and in some cases, a tempering treatment was performed to investigate various properties and microstructure.
【００３３】鋼板の機械的性質（降伏強さ：ＹＳ，引張
強さ：ＴＳ，シャルピー試験の−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靱性（シャルピー試験の−４
０℃での吸収エネルギー：vE-40 ）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：１４０
０℃，８００〜５００℃の冷却時間〔Δt 800-500 〕：
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１００ＭＰａ，入熱：
０．３kJ/mm ，溶着金属の水素量：３cc／１００ｇ金
属）。The mechanical properties (yield strength: YS, tensile strength: TS, absorbed energy at −40 ° C. of Charpy test at −40 ° C .: vE- 40 and 50% fracture surface transition temperature: vTrs) of the steel sheet are perpendicular to the rolling direction. Investigated. HAZ toughness (-4 in Charpy test)
Absorbed energy at 0 ° C .: vE -40 ) was evaluated by HAZ reproduced with a reproduction thermal cycler (maximum heating temperature: 140).
0 ° C, 800-500 ° C cooling time [Δt 800-500 ]:
25 seconds). The on-site weldability was evaluated in a Y-slit welding crack test (JIS G3158) at the minimum preheating temperature required to prevent low-temperature cracking of the HAZ (welding method: gas metal arc welding, welding rod: tensile strength 100 MPa, heat input:
0.3 kJ / mm, hydrogen amount of deposited metal: 3 cc / 100 g metal).
【００３４】実施例を表１および２に示す。本発明法に
従って製造した鋼板は優れた強度・低温靱性バランス、
ＨＡＺ靱性および現地溶接性を示す。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ことが明らかである。Examples are shown in Tables 1 and 2. The steel sheet manufactured according to the method of the present invention has excellent strength-low temperature toughness balance,
Shows HAZ toughness and field weldability. In contrast, it is clear that the comparative steel is significantly inferior in any of its properties due to inadequate chemical composition or microstructure.
【００３５】[0035]
【表１】 [Table 1]
【００３６】[0036]
【表２】 [Table 2]
【００３７】[0037]
【発明の効果】本発明により、低温靱性、現地溶接性の
優れた低降伏比の超強度ラインパイプ（引張強さ９５０
ＭＰａ以上、ＡＰＩ規格Ｘ１００超）用鋼が安定して大
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, a super-strength line pipe (with a tensile strength of 950) having excellent low-temperature toughness and on-site weldability and a low yield ratio.
It is now possible to stably mass-produce steels for use at a pressure of not less than MPa and API standard X100). 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 東京都千代田区大手町２−６−３ 新日 本製鐵株式会社内 (58)調査した分野(Int.Cl.7，ＤＢ名) C22C 38/00 - 38/60 C21D 6/00 C21D 8/00 - 8/10 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshio Terada 2-6-3 Otemachi, Chiyoda-ku, Tokyo Nippon Steel Corporation (58) Field surveyed (Int.Cl. 7 , DB name) C22C 38/00-38/60 C21D 6/00 C21D 8/00-8/10
Claims (4)
記式で定義されるＰ値が２．０以上、３．５以下の範囲
にあり、さらにそのミクロ組織がマルテンサイト、ベイ
ナイトおよびフェライトからなり、フェライト分率が２
０〜９０面積％で、かつフェライト中に加工フェライト
を面積％で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降伏比を有する
低温靱性に優れた高強度ラインパイプ用鋼。 Ｐ＝２．７Ｃ＋０．４Ｓｉ＋Ｍｎ＋０．８Ｃｒ＋０．４５（Ｎｉ＋Ｃｕ） ＋Ｍｏ＋Ｖ−１C: 0.05 to 0.10%, Si: 0.6% or less, Mn: 1.7 to 2.5%, P: 0.015% or less, S: 0 by weight% 0.003% or less, Ni: 0.1 to 1.0%, Cu: 0.8 to 1.2%, Mo: 0.35 to 0.50%, Nb: 0.01 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 a P value defined by the following formula: Is in the range of 2.0 or more and 3.5 or less, and the microstructure is composed of martensite, bainite and ferrite, and the ferrite fraction is 2
High strength excellent in low-temperature toughness having a low yield ratio, characterized in that the ferrite has a ferrite average particle size of 5 μm or less, containing 0 to 90 area %, and 50 to 100% area ferrite processed ferrite in the ferrite. Steel for line pipe. P = 2.7C + 0.4Si + Mn + 0.8Cr + 0.45 (Ni + Cu) + Mo + V-1
で、 Ｖ ：０．１０％以下、 Ｃｒ：０．６％以下の１種または２種を含有することを
特徴とする請求項１記載の低降伏比を有する低温靱性に
優れた高強度ラインパイプ用鋼。2. In addition to the component according to claim 1, in weight%
2. A high-strength line pipe having a low yield ratio and excellent in low-temperature toughness according to claim 1, wherein one or two of V: 0.10% or less and Cr: 0.6% or less are contained. For steel.
さらに重量％で、 Ｃａ：０．００１〜０．００６％を含有することを特徴
とする請求項１または２記載の低降伏比を有する低温靱
性に優れた高強度ラインパイプ用鋼。3. In addition to the component according to claim 1 or 2,
The high-strength linepipe steel having a low yield ratio and excellent low-temperature toughness according to claim 1 or 2, further comprising Ca: 0.001 to 0.006% by weight.
て、Ａｃ1 以下の温度で焼戻し処理した鋼からなること
を特徴とする低降伏比を有する低温靱性に優れた高強度
ラインパイプ用鋼。4. The high-strength linepipe according to claim 1, wherein the steel is tempered at a temperature of Ac 1 or less and has a low yield ratio and excellent low-temperature toughness. For steel.
Priority Applications (11)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP01730295A JP3244984B2 (en) | 1995-02-03 | 1995-02-03 | High strength linepipe steel with low yield ratio and excellent low temperature toughness |
| CA002187028A CA2187028C (en) | 1995-02-03 | 1996-01-26 | High strength line pipe steel having low yield ratio and excellent low temperature toughness |
| KR1019960705573A KR100222302B1 (en) | 1995-02-03 | 1996-01-26 | High strength line pipe steel having low yield ratio and excellent low temperature |
| EP96901131A EP0757113B1 (en) | 1995-02-03 | 1996-01-26 | High-strength line-pipe steel having low yield ratio and excellent low-temperature toughness |
| RU96121789A RU2136776C1 (en) | 1995-02-03 | 1996-01-26 | High-strength steel for main pipelines with low yield factor and high low-temperature ductility |
| AU44966/96A AU677540B2 (en) | 1995-02-03 | 1996-01-26 | High-strength line-pipe steel having low yield ratio and excellent low-temperature toughness |
| US08/718,567 US5755895A (en) | 1995-02-03 | 1996-01-26 | High strength line pipe steel having low yield ratio and excellent in low temperature toughness |
| PCT/JP1996/000157 WO1996023909A1 (en) | 1995-02-03 | 1996-01-26 | High-strength line-pipe steel having low yield ratio and excellent low-temperature toughness |
| CN96190145A CN1148416A (en) | 1995-02-03 | 1996-01-26 | High strength line-pipe steel having low-yield ratio and excullent low-temp toughness |
| DE69607702T DE69607702T2 (en) | 1995-02-03 | 1996-01-26 | High-strength conduit steel with a low yield strength-tensile strength ratio and excellent low-temperature toughness |
| NO964182A NO964182L (en) | 1995-02-03 | 1996-10-02 | Pipeline steel with high strength, low flow ratio and excellent toughness at low temperatures |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP01730295A JP3244984B2 (en) | 1995-02-03 | 1995-02-03 | High strength linepipe steel with low yield ratio and excellent low temperature toughness |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH08209287A JPH08209287A (en) | 1996-08-13 |
| JP3244984B2 true JP3244984B2 (en) | 2002-01-07 |
Family
ID=11940216
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP01730295A Expired - Lifetime JP3244984B2 (en) | 1995-02-03 | 1995-02-03 | High strength linepipe steel with low yield ratio and excellent low temperature toughness |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3244984B2 (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5900075A (en) * | 1994-12-06 | 1999-05-04 | Exxon Research And Engineering Co. | Ultra high strength, secondary hardening steels with superior toughness and weldability |
| NO320153B1 (en) | 1997-02-25 | 2005-10-31 | Sumitomo Metal Ind | Stable with high toughness and high tensile strength, as well as manufacturing methods |
| KR100518323B1 (en) * | 2001-12-24 | 2005-10-04 | 주식회사 포스코 | High Strength Linepipe Steel and Method for Manufacturing the Steel |
| JP3869747B2 (en) * | 2002-04-09 | 2007-01-17 | 新日本製鐵株式会社 | High-strength steel plate, high-strength steel pipe and manufacturing method excellent in deformation performance |
| WO2004111286A1 (en) * | 2003-06-12 | 2004-12-23 | Jfe Steel Corporation | Steel plate and welded steel tube exhibiting low yield ratio, high strength and high toughness and method for production thereof |
| JP4736374B2 (en) * | 2004-08-06 | 2011-07-27 | 住友金属工業株式会社 | Steel material with super large heat input welding characteristics |
| JP4997805B2 (en) * | 2005-03-31 | 2012-08-08 | Ｊｆｅスチール株式会社 | High-strength thick steel plate, method for producing the same, and high-strength steel pipe |
| KR100851189B1 (en) * | 2006-11-02 | 2008-08-08 | 주식회사 포스코 | Steel plate for linepipe having ultra-high strength and excellent low temperature toughness and manufacturing method of the same |
| KR100833035B1 (en) * | 2006-12-20 | 2008-05-27 | 주식회사 포스코 | High-strength and high-toughness steel plate for linepipe excellent in deformability and method for manufacturing the same |
| KR100868423B1 (en) * | 2006-12-26 | 2008-11-11 | 주식회사 포스코 | High strength api-x80 grade steels for spiral pipes with less strength changes and method for manufacturing the same |
| JP7025950B2 (en) * | 2018-02-16 | 2022-02-25 | 日本製鋼所Ｍ＆Ｅ株式会社 | Cu-containing low alloy steel with high strength and high toughness and its manufacturing method |
| CN113046653B (en) * | 2021-02-01 | 2022-03-01 | 南京钢铁股份有限公司 | Pipeline steel with excellent high heat input welding performance and manufacturing method thereof |
-
1995
- 1995-02-03 JP JP01730295A patent/JP3244984B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPH08209287A (en) | 1996-08-13 |
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