JP5245476B2 - Steel plate for line pipe - Google Patents
Steel plate for line pipe Download PDFInfo
- Publication number
- JP5245476B2 JP5245476B2 JP2008066903A JP2008066903A JP5245476B2 JP 5245476 B2 JP5245476 B2 JP 5245476B2 JP 2008066903 A JP2008066903 A JP 2008066903A JP 2008066903 A JP2008066903 A JP 2008066903A JP 5245476 B2 JP5245476 B2 JP 5245476B2
- Authority
- JP
- Japan
- Prior art keywords
- less
- steel plate
- steel
- hic
- value
- 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.)
- Active
Links
- 229910000831 Steel Inorganic materials 0.000 title claims description 73
- 239000010959 steel Substances 0.000 title claims description 73
- 238000005204 segregation Methods 0.000 claims description 63
- 239000013256 coordination polymer Substances 0.000 claims description 21
- 229910052799 carbon Inorganic materials 0.000 claims description 6
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 229910052758 niobium Inorganic materials 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 229910052720 vanadium Inorganic materials 0.000 claims description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 2
- 238000001816 cooling Methods 0.000 description 20
- 238000012360 testing method Methods 0.000 description 19
- 238000000034 method Methods 0.000 description 12
- 239000000463 material Substances 0.000 description 11
- 238000005336 cracking Methods 0.000 description 10
- 230000001965 increasing effect Effects 0.000 description 8
- 238000005096 rolling process Methods 0.000 description 8
- 239000002436 steel type Substances 0.000 description 8
- 229910052739 hydrogen Inorganic materials 0.000 description 7
- 239000001257 hydrogen Substances 0.000 description 7
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 6
- 239000000126 substance Substances 0.000 description 5
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 238000005098 hot rolling Methods 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 230000009466 transformation Effects 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 230000003749 cleanliness Effects 0.000 description 3
- 238000001514 detection method Methods 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 238000007711 solidification Methods 0.000 description 3
- 230000008023 solidification Effects 0.000 description 3
- 230000001629 suppression Effects 0.000 description 3
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 229910001563 bainite Inorganic materials 0.000 description 2
- 239000010953 base metal Substances 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 239000010779 crude oil Substances 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 2
- 229910000734 martensite Inorganic materials 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000003345 natural gas Substances 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- YZCKVEUIGOORGS-UHFFFAOYSA-N Hydrogen atom Chemical compound [H] YZCKVEUIGOORGS-UHFFFAOYSA-N 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 238000004453 electron probe microanalysis Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- -1 hydrogen ions Chemical class 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 238000013507 mapping Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 125000000896 monocarboxylic acid group Chemical group 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 230000000644 propagated effect Effects 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000012932 thermodynamic analysis Methods 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Images
Landscapes
- Heat Treatment Of Steel (AREA)
Description
本発明は、原油や天然ガスなどの輸送用ラインパイプに使用される耐水素誘起割れ性（耐ＨＩＣ性）に優れた高強度ラインパイプ用鋼板に関するものであり、特に、厳しい耐ＨＩＣ性能が要求されるラインパイプに好適なラインパイプ用鋼板に関するものである。 The present invention relates to a steel plate for high-strength line pipes having excellent resistance to hydrogen-induced cracking (HIC resistance) used for transportation line pipes such as crude oil and natural gas. The present invention relates to a steel plate for a line pipe suitable for a line pipe.
一般に、ラインパイプは、厚板ミルや熱延ミルにより製造された鋼板を、ＵＯＥ成形、プレスベンド成形、ロール成形などで鋼管に成形することで製造される。硫化水素を含む原油や天然ガスの輸送に用いられるラインパイプ（以下、「耐サワーラインパイプ」という場合がある）は、強度、靭性、溶接性の他に、耐水素誘起割れ性（耐ＨＩＣ性）や耐応力腐食割れ性（耐ＳＣＣ性）などのいわゆる耐サワー性が必要とされる。耐サワー性に関しては、近年、ＴＯＴＡＬ仕様と呼ばれる、超音波探傷での割れ指示部の割れ長さの個値が規定される厳格仕様の耐サワー性が要求される場合も増えてきている。鋼材のＨＩＣ（水素誘起割れ）は、腐食反応による水素イオンが鋼材表面に吸着し、原子状の水素として鋼内部に侵入し、鋼中のＭｎＳなどの非金属介在物や硬い第２相組織のまわりに拡散・集積して、その内圧により割れを生ずるものとされている。 Generally, a line pipe is manufactured by forming a steel plate manufactured by a thick plate mill or a hot rolling mill into a steel pipe by UOE forming, press bend forming, roll forming or the like. Line pipes used to transport crude oil and natural gas containing hydrogen sulfide (hereinafter sometimes referred to as “sour line pipes”) are not only strong, tough, and weldable, but also resistant to hydrogen-induced cracking (HIC resistance). ) And stress corrosion cracking resistance (SCC resistance) and so-called sour resistance is required. With regard to sour resistance, in recent years, there is an increasing demand for sour resistance of a strict specification called the TOTAL specification, in which the individual value of the crack length of the crack indicating part in ultrasonic flaw detection is defined. HIC (hydrogen-induced cracking) of steel is a phenomenon in which hydrogen ions due to corrosion reaction are adsorbed on the surface of the steel, penetrate into the steel as atomic hydrogen, and include non-metallic inclusions such as MnS in the steel and a hard second phase structure. It is said that it diffuses and accumulates around it and causes cracks due to its internal pressure.
従来、このような水素誘起割れを防ぐために、幾つかの方法が提案されている。例えば、特許文献１には、鋼中のＳ含有量を下げるとともに、ＣａやＲＥＭなどを適量添加することにより、長く伸展したＭｎＳの生成を抑制し、微細に分散した球状のＣａＳ介在物に形態を変える技術が提案されている。これにより、硫化物系介在物による応力集中を小さくし、割れの発生・伝播を抑制することによって、耐ＨＩＣ性を改善するというものである。
特許文献２、３には、偏析傾向の高い元素（Ｃ、Ｍｎ、Ｐ等）の低減やスラブ加熱段階での均熱処理による偏析の低減、および圧延後の冷却時の変態途中で加速冷却を行う技術が提案されている。これにより、中心偏析部での割れの起点となる島状マルテンサイトの生成、および割れの伝播経路となるマルテンサイトなどの硬化組織の生成を抑制するというものである。
また、特許文献４では、偏析係数に基づいた炭素等量式が示され、これを一定値以下にすることで中心偏析部の割れを抑制する方法が提案されている。
Conventionally, several methods have been proposed to prevent such hydrogen-induced cracking. For example, in Patent Document 1, while lowering the S content in steel and adding an appropriate amount of Ca, REM, or the like, the formation of long extended MnS is suppressed, and a finely dispersed spherical CaS inclusion is formed. A technology to change this has been proposed. As a result, the stress concentration due to the sulfide inclusions is reduced, and the generation and propagation of cracks is suppressed, thereby improving the HIC resistance.
In Patent Documents 2 and 3, accelerated cooling is performed in the middle of transformation during cooling after rolling, reduction of elements having a high segregation tendency (C, Mn, P, etc.), reduction of segregation by soaking in the slab heating stage. Technology has been proposed. This suppresses the generation of island martensite that becomes the starting point of cracks in the center segregation part and the generation of hardened structures such as martensite that becomes the propagation path of cracks.
Moreover, in patent document 4, the carbon equivalence formula based on a segregation coefficient is shown, and the method of suppressing the crack of a center segregation part by making this into below a fixed value is proposed.
さらに、中心偏析部の割れの対策として、特許文献５には、中心偏析部におけるＮｂとＭｎの偏析度を一定以下に規定する方法が提案され、また、特許文献６には、ＨＩＣの起点となる介在物の大きさと中心偏析部の硬さをそれぞれ規定する方法が提案されている。
しかしながら、近年の耐サワーラインパイプでは、前述したように厳格仕様の耐サワー性が要求される場合が増えており、加えて耐サワー材の高強度化或いは厚肉化の傾向もみられ、このような耐サワー材では、強度を確保するために合金元素の添加量を増やす必要がある。この場合、上記のような従来技術の手法でＭｎＳの生成を抑制し、また中心偏析部の組織を改善したとしても、中心偏析部の硬さが上昇し、Ｎｂ炭窒化物を起点にＨＩＣが発生してしまう。Ｎｂ炭窒化物からの割れは、その割れ長さ率が小さいため、従来の耐ＨＩＣ性能の要求基準では特に問題とされなかったが、近年、より厳格な耐サワー性能が要求されるようになり、より厳格なＭｎＳの抑制並びにＮｂ炭窒化物を起点としたＨＩＣの抑制が必要となっている。 However, recent sour-resistant line pipes are increasingly required to have strict specifications for sour resistance as described above, and in addition, there is a tendency for sour-resistant materials to become stronger or thicker. In such a sour-resistant material, it is necessary to increase the amount of alloying element added to ensure strength. In this case, even if the generation of MnS is suppressed by the conventional technique as described above and the structure of the center segregation part is improved, the hardness of the center segregation part increases, and the HIC starts from Nb carbonitride. Will occur. Cracks from Nb carbonitrides were not particularly problematic in the conventional requirements for anti-HIC performance because the crack length ratio was small, but in recent years, more stringent sour-proof performance has been required. Therefore, more strict suppression of MnS and suppression of HIC starting from Nb carbonitride are necessary.
特許文献６のようにＮｂを含む炭窒化物を５μｍ以下という非常に小さなサイズにする方法は、中心偏析部のＨＩＣ発生を抑制するには効果的である。しかし、実際には、造塊または連続鋳造時に最終凝固部で粗大なＮｂ炭窒化物が晶出する場合があり、上述したようなより厳しい耐サワー性能の要求に対しては、ＨＩＣの発生の抑制とともに、ある頻度で生成するＮｂ炭窒化物などを基点として発生した割れの伝播を抑制するために、中心偏析部の材質を極めて厳格に管理する必要が生じている。中心偏析部の材質を管理する方法としては、特許文献４が提案した偏析係数を考慮した炭素等量式を用いる方法が挙げられる。しかし、同文献では偏析係数をマイクロアナライザー分析で実験的に求めているため、例えばスポットサイズが１０μｍ程度の測定範囲内での平均値としてしか求めることができず、厳格に中心偏析部の濃度を予測できる方法とはなっていない。 The method of making the carbonitride containing Nb as very small as 5 μm or less as in Patent Document 6 is effective in suppressing the occurrence of HIC in the central segregation part. In practice, however, coarse Nb carbonitrides may crystallize in the final solidified part during ingot casting or continuous casting, and HIC may be generated in response to the more severe requirements for sour resistance as described above. In addition to the suppression, in order to suppress the propagation of cracks generated from Nb carbonitride and the like generated at a certain frequency, it is necessary to manage the material of the central segregation portion very strictly. As a method for managing the material of the center segregation part, there is a method using a carbon equivalence formula considering the segregation coefficient proposed in Patent Document 4. However, since the segregation coefficient is experimentally obtained by microanalyzer analysis in the same document, for example, it can be obtained only as an average value within a measurement range where the spot size is about 10 μm, and the concentration of the central segregation part is strictly determined. It is not a predictable method.
したがって本発明の目的は、上記のような従来技術の課題を解決し、耐サワー性に優れた高強度ラインパイプ用鋼板、特に厳しい耐サワー性能の要求に対しても十分対応できる優れた耐サワー性を有する高強度ラインパイプ用鋼板を提供することにある。 Accordingly, the object of the present invention is to solve the above-mentioned problems of the prior art and to provide a high strength line pipe steel sheet having excellent sour resistance, particularly excellent sour resistance capable of sufficiently responding to severe demands for sour resistance performance. An object of the present invention is to provide a high-strength linepipe steel sheet having properties.
本発明者らは、ＨＩＣ試験での割れの発生及びその伝播挙動を、割れの起点と中心偏析部の組織の観点から詳細に調査した結果、以下の知見を得るに至った。
まず、中心偏析部の割れを抑制するには、起点となる介在物の種類に応じた中心偏析部の材質の適正化が必要である。図１に、中心偏析部にＭｎＳまたはＮｂ炭窒化物が生成している鋼板を用いてＨＩＣ試験（試験方法は後述する実施例と同様）を行った結果の一例を示す。これによれば、中心偏析部にＭｎＳがある場合は、低い硬さでも割れ面積率が上昇するため、ＭｎＳの生成を抑制することは極めて重要であることが判る。しかし、ＭｎＳの生成が抑制できても、Ｎｂ炭窒化物がある場合は、中心偏析部の硬さが或るレベル（ここではＨｖ２５０）を超えるとＨＩＣ試験で割れが発生するようになる。
As a result of detailed investigations on the occurrence of cracks and their propagation behavior in the HIC test from the viewpoint of the crack origin and the structure of the central segregation part, the present inventors have obtained the following knowledge.
First, in order to suppress the cracking of the center segregation portion, it is necessary to optimize the material of the center segregation portion according to the type of inclusions as the starting point. FIG. 1 shows an example of a result of an HIC test (test method is the same as the example described later) using a steel plate in which MnS or Nb carbonitride is generated at the center segregation part. According to this, when MnS is present in the center segregation part, the crack area ratio is increased even with low hardness, so that it is understood that it is extremely important to suppress the generation of MnS. However, even if the generation of MnS can be suppressed, if there is Nb carbonitride, cracking occurs in the HIC test when the hardness of the center segregation part exceeds a certain level (here, Hv250).
このような問題を解決するためには、鋼板の化学成分を厳密に制御してＭｎＳ生成を抑制し、中心偏析部の硬さを所定レベル以下（好ましくはＨｖ２５０以下）とする必要がある。本発明者らは、中心偏析部における化学成分の濃化挙動を熱力学的に解析し、合金元素毎の偏析係数を導出した。この偏析係数の導出は、以下の手順に従って行った。まず、鋳造時の最終凝固部には凝固収縮またはバルジングによる空隙が生成し、その部分に周辺の濃化した溶鋼が流入し、成分が濃化した偏析スポットを形成する。次に、濃化した偏析スポットが凝固する過程は、熱力学的な平行分配係数に基づいて凝固界面での成分変化が生じるため、最終的に形成される偏析部の濃度を熱力学的に求めることが可能である。以上のような熱力学的な解析で求めた偏析係数を用い、下式で示す中心偏析部の炭素等量式に対応するＣＰ値を得るに至った。そして、このＣＰ値を一定値以下とすることで、中心偏析部の硬さを割れが発生する限界硬さ以下に抑制できることを見出した。図２に、下式で示されるＣＰ値とＨＩＣ試験（試験方法は後述する実施例と同様）での割れ面積率との関係を示す。これによれば、ＣＰ値が高くなると割れ面積率が急激に上昇するが、ＣＰ値を一定値以下に抑制することでＨＩＣでの割れを低減することが可能であることが判る。
ＣＰ＝４．４６Ｃ（％）＋２．３７Ｍｎ（％）／６＋{１．１８Ｃｒ（％）＋１．９５Ｍｏ（％）＋１．７４Ｖ（％）}／５＋{１．７４Ｃｕ（％）＋１．７Ｎｉ（％）}／１５＋２２．３６Ｐ（％）
In order to solve such a problem, it is necessary to strictly control the chemical composition of the steel sheet to suppress the generation of MnS and set the hardness of the center segregation part to a predetermined level or less (preferably
CP = 4.46C (%) + 2.37Mn (%) / 6+ {1.18Cr (%) + 1.95Mo (%) + 1.74V (%)} / 5+ {1.74Cu (%) + 1.7Ni (% )} / 15 + 22.36P (%)
また、ＨＩＣ試験での割れの発生起点となるＮｂ炭窒化物の大きさを一定値以下に抑制すること、さらには、下記式で示されるＩＰ値を一定の範囲に管理することによってＭｎＳ生成を抑制することにより、上記の対策と相まって、安定してより優れた耐サワー性能を得ることが可能となることが判った。
ＩＰ＝［Ｃａ（％）−｛０．１８＋１３０Ｃａ（％）｝＊Ｏ（％）］／１．２５Ｓ（％）
In addition, by suppressing the size of Nb carbonitride, which is the starting point of cracking in the HIC test, to a certain value or less, and further, by managing the IP value represented by the following formula within a certain range, MnS generation is achieved. It has been found that, by suppressing, in combination with the above-mentioned measures, it is possible to stably obtain better sour resistance performance.
IP = [Ca (%) − {0.18 + 130Ca (%)} * O (%)] / 1.25S (%)
本発明は、以上のような知見に基づきなされたもので、以下を要旨とするものである。
［1］質量％にて、Ｃ：０．０２〜０．０６％、Ｓｉ：０．５％以下、Ｍｎ：０．８〜１．６％、Ｐ：０．００８％以下、Ｓ：０．０００８％以下、Ａｌ：０．０８％以下、Ｎｂ：０．００５〜０．０３５％、Ｔｉ：０．００５〜０．０２５％、Ｃａ：０．０００５〜０．００３５％を含有し、残部がＦｅおよび不可避不純物からなり、下記（1）式で表わされるＣＰ値が０．９２以下、下記（2）式で表わされるＣｅｑ値が０．２８以上、下記（3）式で表わされるＩＰ値が１．０〜２．８であることを特徴とするラインパイプ用鋼板。
ＣＰ＝４．４６Ｃ（％）＋２．３７Ｍｎ（％）／６＋{１．１８Ｃｒ（％）＋１．９５Ｍｏ（％）＋１．７４Ｖ（％）}／５＋{１．７４Ｃｕ（％）＋１．７Ｎｉ（％）}／１５＋２２．３６Ｐ（％） …（1）
Ｃｅｑ＝Ｃ（％）＋Ｍｎ（％）／６＋{Ｃｒ（％）＋Ｍｏ（％）＋Ｖ（％）}／５＋{Ｃｕ（％）＋Ｎｉ（％）}／１５ …（2）
ＩＰ＝［Ｃａ（％）−｛０．１８＋１３０Ｃａ（％）｝＊Ｏ（％）］／１．２５Ｓ（％） …（3）
The present invention has been made on the basis of the above-described findings and has the following gist.
[1] In mass%, C: 0.02 to 0.06%, Si: 0.5% or less, Mn: 0.8 to 1.6%, P: 0.008% or less, S: 0.00. 0008% or less, Al: 0.08% or less, Nb: 0.005-0.035%, Ti: 0.005-0.025%, Ca: 0.0005-0.0035%, the balance being Fe and inevitable impurities, CP value represented by the following formula (1) is 0.92 or less, Ceq value represented by the following formula (2) is 0.28 or more, IP value represented by the following formula (3) is A steel plate for line pipes, wherein the steel plate is 1.0 to 2.8.
CP = 4.46C (%) + 2.37Mn (%) / 6+ {1.18Cr (%) + 1.95Mo (%) + 1.74V (%)} / 5+ {1.74Cu (%) + 1.7Ni (% )} / 15 + 22.36P (%) (1)
Ceq = C (%) + Mn (%) / 6+ {Cr (%) + Mo (%) + V (%)} / 5+ {Cu (%) + Ni (%)} / 15 (2)
IP = [Ca (%) − {0.18 + 130Ca (%)} * O (%)] / 1.25S (%) (3)
［2］上記［1］の鋼板において、中心偏析部の硬さがＨＶ２５０以下、中心偏析部のＮｂ炭窒化物の長さが２０μｍ以下であることを特徴とするラインパイプ用鋼板。
［3］上記［1］または［2］の鋼板において、さらに、Ｎｉ：０．２８％以下を含有し、これに加えて、Ｃｕ：０．５％以下、Ｃｒ：０．５％以下、Ｍｏ：０．５％以下、Ｖ：０．１％以下の中から選ばれる１種または２種以上を含有することを特徴とするラインパイプ用鋼板。
[2] A steel plate for a line pipe according to [1], wherein the center segregation part has a hardness of
[3] The steel sheet of [1] or [2] further contains Ni: 0.28% or less, and in addition to this, Cu: 0.5% or less , Cr : 0.5% or less, Mo A steel sheet for line pipes, containing one or more selected from: 0.5% or less, V: 0.1% or less.
本発明のラインパイプ用鋼板は優れた耐サワー性を有し、特に高強度ラインパイプで要求される厳しい耐サワー性能にも十分対応することができる。 The steel plate for line pipes of the present invention has excellent sour resistance, and can sufficiently cope with the severe sour resistance performance particularly required for high-strength line pipes.
以下、本発明のラインパイプ用鋼板の詳細について説明する。
まず、本発明の化学成分の限定理由について説明する。なお、成分量の％は全て「質量％」である。
Ｃは、加速冷却によって製造される鋼板の強度を高めるために最も有効な元素である。しかし、Ｃ量が０．０２％未満では十分な強度を確保できず、一方、０．０６％を超えると靭性および耐ＨＩＣ性が劣化する。このためＣ量は０．０２〜０．０６％とする。
Ｓｉは脱酸のために添加するが、Ｓｉ量が０．５％を超えると靭性や溶接性が劣化する。このためＳｉ量は０．５％以下とする。
Ｍｎは鋼の強度および靭性の向上のために添加するが、Ｍｎ量が０．８％未満ではその効果が十分ではなく、一方、１．６％を超えると溶接性と耐ＨＩＣ性が劣化する。このためＭｎ量は０．８〜１．６％とする。
Hereinafter, the details of the steel plate for line pipes of the present invention will be described.
First, the reasons for limiting the chemical components of the present invention will be described. In addition,% of component amount is "mass%" altogether.
C is the most effective element for increasing the strength of the steel sheet produced by accelerated cooling. However, if the amount of C is less than 0.02%, sufficient strength cannot be secured, while if it exceeds 0.06%, toughness and HIC resistance deteriorate. Therefore, the C content is 0.02 to 0.06%.
Si is added for deoxidation, but when the amount of Si exceeds 0.5%, toughness and weldability deteriorate. For this reason, the amount of Si shall be 0.5% or less.
Mn is added to improve the strength and toughness of the steel, but if the amount of Mn is less than 0.8%, the effect is not sufficient, while if it exceeds 1.6%, the weldability and HIC resistance deteriorate. . For this reason, the amount of Mn shall be 0.8 to 1.6%.
Ｐは不可避不純物元素であり、中心偏析部の硬さを上昇させることで耐ＨＩＣ性を劣化させ、この傾向はＰ量が０．００８％を超えると顕著となる。このためＰ量は０．００８％以下、好ましくは０．００６％以下とする。
Ｓは、鋼中においては一般にＭｎＳ系の介在物となるが、Ｃａ添加によりＭｎＳ系からＣａＳ系介在物に形態制御される。しかし、Ｓ量が多いとＣａＳ系介在物の量も多くなり、高強度材では割れの起点となり得る。この傾向は、Ｓ量が０．０００８％を超えると顕著となる。このためＳ量は０．０００８％以下とする。
Ａｌは脱酸剤として添加されるが、Ａｌ量が０．０８％を超えると清浄度の低下により延性が劣化する。このためＡｌ量は０．０８％以下とする。
Ｎｂは、圧延時の粒成長を抑制し、微細粒化により靭性を向上させる。しかし、Ｎｂ量が０．００５％未満ではその効果が十分でなく、一方、０．０３５％を超えると溶接熱影響部の靭性が劣化するだけでなく、粗大なＮｂ炭窒化物の生成を招き、耐ＨＩＣ性能が劣化する。このためＮｂ量は０．００５〜０．０３５％とする。
P is an inevitable impurity element, and the HIC resistance is deteriorated by increasing the hardness of the central segregation part, and this tendency becomes remarkable when the amount of P exceeds 0.008%. Therefore, the P content is 0.008% or less, preferably 0.006% or less.
S is generally MnS-based inclusions in steel, but the form is controlled from MnS-based to CaS-based inclusions by the addition of Ca. However, if the amount of S is large, the amount of CaS-based inclusions also increases, and a high-strength material can be a starting point for cracking. This tendency becomes remarkable when the S amount exceeds 0.0008%. For this reason, the amount of S is made 0.0008% or less.
Al is added as a deoxidizer, but if the Al content exceeds 0.08%, ductility deteriorates due to a decrease in cleanliness. For this reason, the amount of Al is made into 0.08% or less.
Nb suppresses grain growth during rolling, and improves toughness by making fine grains. However, if the Nb content is less than 0.005%, the effect is not sufficient. On the other hand, if the Nb content exceeds 0.035%, not only the toughness of the weld heat affected zone is deteriorated, but also coarse Nb carbonitride is produced. The anti-HIC performance deteriorates. Therefore, the Nb amount is set to 0.005 to 0.035%.
Ｔｉは、ＴｉＮを形成してスラブ加熱時の粒成長を抑制するだけでなく、溶接熱影響部の粒成長を抑制し、母材および溶接熱影響部の微細粒化により靭性を向上させる。しかし、Ｔｉ量が０．００５％未満ではその効果が十分でなく、一方、０．０２５％を超えると靭性が劣化する。このためＴｉ量は０．００５〜０．０２５％とする。
Ｃａは硫化物系介在物の形態を制御し、延性の改善と耐ＨＩＣ性能の向上に有効な元素であるが、Ｃａ量が０．０００５％未満ではその効果が十分でなく、一方、０．００３５％を超えて添加しても効果が飽和し、むしろ清浄度の低下により靭性が劣化するとともに、鋼中のＣａ系酸化物量が増え、それらを起点として割れが発生する結果、耐ＨＩＣ性能も劣るようになる。このためＣａ量は０．０００５〜０．００３５％とする。
Ti not only suppresses grain growth during slab heating by forming TiN, but also suppresses grain growth in the weld heat affected zone and improves toughness by making the base material and the weld heat affected zone finer. However, if the amount of Ti is less than 0.005%, the effect is not sufficient, while if it exceeds 0.025%, the toughness deteriorates. Therefore, the Ti amount is set to 0.005 to 0.025%.
Ca is an element that controls the form of sulfide inclusions and is effective in improving ductility and improving HIC resistance. However, when the Ca content is less than 0.0005%, the effect is not sufficient. Even if added in excess of 0035%, the effect is saturated, but rather the toughness deteriorates due to a decrease in cleanliness, the amount of Ca-based oxide in the steel increases, and cracks occur starting from them, resulting in HIC resistance performance. Become inferior. Therefore, the Ca content is set to 0.0005 to 0.0035%.
本発明の鋼板は、さらに、Ｃｕ、Ｎｉ、Ｃｒ、Ｍｏ、Ｖの中から選ばれる１種または２種以上を以下のような範囲で含有することができる。
Ｃｕは、靭性の改善と強度の上昇に有効な元素であるが、０．５％を超えて添加すると溶接性が劣化する。このためＣｕを添加する場合は０．５％以下とする。
Ｎｉは、靭性の改善と強度の上昇に有効な元素であるが、１％を超えて添加すると溶接性が劣化する。このためＮｉを添加する場合は１．０％以下とする。
Ｃｒは、焼き入れ性を高めることで強度の上昇に有効な元素であるが、０．５％を超えて添加すると溶接性が劣化する。このためＣｒを添加する場合は０．５％以下とする。
Ｍｏは、靭性の改善と強度の上昇に有効な元素であるが、０．５％を超えて添加すると溶接性が劣化する。このためＭｏを添加する場合は０．５％以下とする。
Ｖは、靭性を劣化させずに強度を上昇させる元素であるが、０．１％を超えて添加すると溶接性を著しく損なう。このためＶを添加する場合は０．１％以下とする。
本発明の鋼板の残部はＦｅおよび不可避不純物である。
The steel plate of the present invention can further contain one or more selected from Cu, Ni, Cr, Mo, and V in the following ranges.
Cu is an effective element for improving toughness and increasing strength, but if added over 0.5%, weldability deteriorates. For this reason, when adding Cu, it is 0.5% or less.
Ni is an element effective for improving toughness and increasing strength, but if it exceeds 1%, weldability deteriorates. For this reason, when adding Ni, it is 1.0% or less.
Cr is an element effective for increasing the strength by enhancing the hardenability, but if added over 0.5%, the weldability deteriorates. For this reason, when adding Cr, it is 0.5% or less.
Mo is an element effective for improving toughness and increasing strength, but if added over 0.5%, weldability deteriorates. For this reason, when adding Mo, it is 0.5% or less.
V is an element that increases the strength without deteriorating the toughness, but if added over 0.1%, the weldability is significantly impaired. For this reason, when adding V, it is made into 0.1% or less.
The balance of the steel sheet of the present invention is Fe and inevitable impurities.
本発明では、さらに、下記（1）式で表わされるＣＰ値、下記（2）式で表わされるＣｅｑ値、下記（3）式で表わされるＩＰ値を、それぞれ規定する。ここで、Ｃ（％）、Ｍｎ（％）、Ｃｒ（％）、Ｍｏ（％）、Ｖ（％）、Ｃｕ（％）、Ｎｉ（％）、Ｐ（％）、Ｃａ（％）、Ｏ（％）、Ｓ（％）は、それぞれの元素の含有量である。
ＣＰ＝４．４６Ｃ（％）＋２．３７Ｍｎ（％）／６＋{１．１８Ｃｒ（％）＋１．９５Ｍｏ（％）＋１．７４Ｖ（％）}／５＋{１．７４Ｃｕ（％）＋１．７Ｎｉ（％）}／１５＋２２．３６Ｐ（％） …（1）
Ｃｅｑ＝Ｃ（％）＋Ｍｎ（％）／６＋{Ｃｒ（％）＋Ｍｏ（％）＋Ｖ（％）}／５＋{Ｃｕ（％）＋Ｎｉ（％）}／１５ …（2）
ＩＰ＝［Ｃａ（％）−｛０．１８＋１３０Ｃａ（％）｝＊Ｏ（％）］／１．２５Ｓ（％） …（3）
In the present invention, a CP value represented by the following formula (1), a Ceq value represented by the following formula (2), and an IP value represented by the following formula (3) are respectively defined. Here, C (%), Mn (%), Cr (%), Mo (%), V (%), Cu (%), Ni (%), P (%), Ca (%), O ( %) And S (%) are the contents of the respective elements.
CP = 4.46C (%) + 2.37Mn (%) / 6+ {1.18Cr (%) + 1.95Mo (%) + 1.74V (%)} / 5+ {1.74Cu (%) + 1.7Ni (% )} / 15 + 22.36P (%) (1)
Ceq = C (%) + Mn (%) / 6+ {Cr (%) + Mo (%) + V (%)} / 5+ {Cu (%) + Ni (%)} / 15 (2)
IP = [Ca (%) − {0.18 + 130Ca (%)} * O (%)] / 1.25S (%) (3)
ＣＰ値に関する上記（1）式は、各合金元素の含有量から中心偏析部の材質を推定するために創案された式であり、ＣＰ値が高いほど中心偏析部の濃度が高くなり、中心偏析部の硬さが上昇する。図２に示すように、このＣＰ値を０．９２以下とすることで中心偏析部の硬さを十分小さくする（好ましくはＨｖ２５０以下とする）ことができ、厳格な耐サワー性能に対応可能となる。このためＣＰ値は０．９２以下とする。また、ＣＰ値が低いほど中心偏析部の硬さが低くなるため、ＣＰ値は０．９０以下とすることが好ましい。
Ｃｅｑ値は鋼の焼き入れ性指数であり、Ｃｅｑ値が高いほど鋼材の強度が高くなる。本発明は、Ｘ６５グレードなどのような高強度の耐サワーラインパイプのＨＩＣ性能向上を目的としており、Ｘ６５グレードとして十分な強度を得るためにはＣｅｑ値が０．２８以上であることが必要である。このためＣｅｑ値は０．２８以上とする。
The above equation (1) relating to the CP value is an equation created to estimate the material of the central segregation part from the content of each alloy element. The higher the CP value, the higher the concentration of the central segregation part, and the central segregation part. The hardness of the part increases. As shown in FIG. 2, by setting the CP value to 0.92 or less, the hardness of the central segregation part can be sufficiently reduced (preferably to
The Ceq value is a hardenability index of steel, and the higher the Ceq value, the higher the strength of the steel material. The present invention aims to improve the HIC performance of high strength sour line pipes such as the X65 grade, and in order to obtain sufficient strength as the X65 grade, the Ceq value needs to be 0.28 or more. is there. For this reason, the Ceq value is set to 0.28 or more.
ＩＰ値に関する上記（3）式は、Ｃａ添加によりＣａＳを生成させることでＭｎＳの生成を抑制させるための指標として創案された式であり、ＩＰ値を所定の範囲に制御することによりＭｎＳ生成を抑制させることができる。ＩＰ値が１．０未満では、十分なＭｎＳ生成の抑制効果が得られず、ＭｎＳが生成して厳格な耐サワー仕様には対応できない。一方、ＩＰ値が２．８を超えると、ＭｎＳ生成は抑制されるものの、多量のＣａ系酸化物が生成し、鋼板の清浄性を損なうとともに、耐サワー性能も劣化するため厳格な耐サワー仕様に対応できなくなる。このためＩＰ値は１．０〜２．８とする。 The above expression (3) relating to the IP value is an expression created as an index for suppressing the generation of MnS by generating CaS by adding Ca, and the MnS generation is controlled by controlling the IP value within a predetermined range. Can be suppressed. When the IP value is less than 1.0, a sufficient effect of suppressing MnS generation cannot be obtained, and MnS is generated and cannot meet the strict sour resistance specification. On the other hand, when the IP value exceeds 2.8, MnS generation is suppressed, but a large amount of Ca-based oxides are generated, which impairs the cleanliness of the steel sheet and deteriorates the sour-resistant performance. It becomes impossible to correspond to. For this reason, the IP value is set to 1.0 to 2.8.
また、本発明の鋼板は、中心偏析部の硬さと、ＨＩＣの起点となるＮｂ炭窒化物の大きさについて、次のような条件を満たすことが好ましい。
さきに説明したように、ＨＩＣにおける割れ成長のメカニズムは、鋼中の介在物などの周りに水素が集積し割れが発生し、介在物周囲に割れが伝播することで大きな割れに成長することにある。このとき、中心偏析部が最も割れが発生・伝播しやすい場所であり、中心偏析部の硬さが大きいほど、割れを生じやすくなる。中心偏析部の硬さがＨＶ２５０以下の場合は、中心偏析部に微小なＮｂ炭窒化物が残存していても割れの伝播が生じにくいため、ＨＩＣ試験での割れ面積率を抑制できる。しかし、中心偏析部の硬さがＨＶ２５０を超えると割れが伝播しやすくなり、特に、Ｎｂ炭窒化物で発生した割れが周囲に伝播しやすくなる。このため中心偏析部の硬さは、ＨＶ２５０以下とすることが好ましい。
Moreover, it is preferable that the steel plate of this invention satisfy | fills the following conditions regarding the hardness of a center segregation part, and the magnitude | size of Nb carbonitride used as the starting point of HIC.
As explained earlier, the mechanism of crack growth in HIC is that hydrogen accumulates around inclusions in steel and cracks occur, and cracks propagate around the inclusions to grow into large cracks. is there. At this time, the center segregation portion is the place where cracks are most likely to be generated and propagated, and the greater the hardness of the center segregation portion, the easier it is to crack. When the hardness of the center segregation part is HV250 or less, crack propagation hardly occurs even if minute Nb carbonitride remains in the center segregation part, so that the crack area ratio in the HIC test can be suppressed. However, if the hardness of the center segregation portion exceeds HV250, cracks are likely to propagate, and in particular, cracks generated in Nb carbonitride are likely to propagate to the surroundings. For this reason, it is preferable that the hardness of the center segregation part is HV250 or less.
中心偏析部に生成するＮｂ炭窒化物は、ＨＩＣ試験において水素の集積場所となり、それを起点として割れが発生する。この時、Ｎｂ炭窒化物のサイズが大きいほど割れが伝播しやすくなり、中心偏析部の硬さがＨＶ２５０以下であっても割れが伝播してしまう。そして、Ｎｂ炭窒化物の長さが２０μｍ以下であれば、中心偏析部の硬さをＨＶ２５０以下とすることで割れの伝播を抑制できる。このためＮｂ炭窒化物の長さは２０μｍ以下、好ましくは１０μｍ以下とする。ここで、Ｎｂ炭窒化物の長さは、その粒子の最大長とする。
なお、ＭｎＳの生成については、上述したようにＩＰ値を所定範囲に制御することにより抑制できる。
本発明は、高強度の耐サワーラインパイプ用鋼板に好適である。また、鋼板が厚肉になるほど合金元素の添加が必要となり、中心偏析部の硬さを低減することが難しくなることから、特に板厚が２５ｍｍを超えるような厚肉鋼板において、その効果をより発揮することができる。
The Nb carbonitride generated in the center segregation part becomes a hydrogen accumulation site in the HIC test, and cracks are generated starting from that. At this time, the larger the size of the Nb carbonitride, the easier the crack propagates, and the crack propagates even if the hardness of the central segregation part is HV250 or less. And if the length of Nb carbonitride is 20 micrometers or less, propagation of a crack can be suppressed by making the hardness of a center segregation part into HV250 or less. For this reason, the length of Nb carbonitride is 20 μm or less, preferably 10 μm or less. Here, the length of the Nb carbonitride is the maximum length of the particles.
Note that generation of MnS can be suppressed by controlling the IP value within a predetermined range as described above.
The present invention is suitable for high strength steel plates for sour line pipes. Also, the thicker the steel plate, the more the alloy element needs to be added, making it difficult to reduce the hardness of the center segregation part. It can be demonstrated.
本発明の鋼板は、上述した化学成分と中心偏析部の硬さおよびＮｂ炭窒化物のサイズを規定することで、優れた耐サワー性能が得られるため、基本的には従来法と同様の製造方法で製造すればよい。ただし、耐ＨＩＣ性能のみならず、最適な強度および靭性を得るためには、以下に示すような条件で製造することが望ましい。
スラブを熱間圧延する際のスラブ加熱温度については、１０００℃未満では十分な強度が得られず、一方、１２００℃を超えると靭性やＤＷＴＴ特性が劣化する。このためスラブ加熱温度は１０００〜１２００℃とすることが好ましい。
熱間圧延工程において、高い母材靭性を得るには圧延終了温度は低いほどよいが、その反面圧延能率が低下するため、圧延終了温度は必要な母材靭性と圧延能率を考慮して適宜な温度に設定される。また、高い母材靭性を得るためには、未再結晶温度域での圧下率を６０％以上とすることが好ましい。
Since the steel sheet of the present invention provides excellent sour resistance performance by defining the above-described chemical components, the hardness of the central segregation part, and the size of Nb carbonitride, it is basically produced in the same manner as in the conventional method. What is necessary is just to manufacture by the method. However, in order to obtain not only the HIC resistance performance but also the optimum strength and toughness, it is desirable to manufacture under the following conditions.
As for the slab heating temperature when the slab is hot-rolled, if the temperature is less than 1000 ° C., sufficient strength cannot be obtained, while if it exceeds 1200 ° C., toughness and DWTT characteristics deteriorate. For this reason, it is preferable that slab heating temperature shall be 1000-1200 degreeC.
In the hot rolling process, a lower rolling end temperature is better for obtaining a high base metal toughness. However, since the rolling efficiency is lowered, the rolling end temperature is appropriately determined in consideration of the required base material toughness and rolling efficiency. Set to temperature. In order to obtain high base metal toughness, it is preferable that the rolling reduction in the non-recrystallization temperature region is 60% or more.
熱間圧延後、加速冷却を以下のような条件で実施することが好ましい。
加速冷却における冷却速度は、十分な強度を安定して得るために５℃／sec以上とすることが好ましい。また、加速冷却開始時の鋼板温度が低いと、加速冷却前のフェライト生成量が多くなり、特に、Ａｒ３変態点からの温度低下が１０℃を超えると耐ＨＩＣ性が劣化する。このため、加速冷却開始時の鋼板温度は（Ａｒ３−１０℃）以上とすることが好ましい。ここで、Ａｒ３温度は鋼の成分から、Ａｒ３（℃）＝９１０−３１０Ｃ（％）−８０Ｍｎ（％）−２０Ｃｕ（％）−１５Ｃｒ（％）−５５Ｎｉ（％）−８０Ｍｏ（％）で与えられる。
加速冷却は、ベイナイト変態によって高強度を得るために重要なプロセスである。しかし、加速冷却停止時の鋼板温度が６００℃を超えると、ベイナイト変態が不完全であり、十分な強度が得られない。また、加速冷却停止時の鋼板温度が２５０℃未満では、鋼板表層部の硬度が高くなりすぎるだけでなく、鋼板に歪みを生じやすくなり成形性が劣化する。このため加速冷却停止時の鋼板温度は２５０〜６００℃とすることが好ましい。
After hot rolling, accelerated cooling is preferably performed under the following conditions.
The cooling rate in the accelerated cooling is preferably 5 ° C./sec or more in order to stably obtain a sufficient strength. Moreover, if the steel plate temperature at the start of accelerated cooling is low, the amount of ferrite produced before accelerated cooling increases, and particularly when the temperature drop from the Ar 3 transformation point exceeds 10 ° C., the HIC resistance deteriorates. Therefore, the steel plate temperature at the start of accelerated cooling is preferably set to (Ar 3 -10 ℃) or higher. Here, the Ar 3 temperature is Ar 3 (° C.) = 910−310C (%) − 80Mn (%) − 20Cu (%) − 15Cr (%) − 55Ni (%) − 80Mo (%) from the steel components. Given.
Accelerated cooling is an important process for obtaining high strength by bainite transformation. However, if the steel plate temperature when the accelerated cooling is stopped exceeds 600 ° C., the bainite transformation is incomplete and sufficient strength cannot be obtained. Moreover, if the steel plate temperature at the time of accelerated cooling stop is less than 250 ° C., not only the hardness of the surface portion of the steel plate becomes too high, but also the steel plate tends to be distorted and formability deteriorates. For this reason, it is preferable that the steel plate temperature at the time of accelerated cooling stop shall be 250-600 degreeC.
なお、上述した鋼板温度は、鋼板の板厚方向で温度分布がある場合には、板厚方向での平均温度であるが、板厚方向での温度分布が比較的小さい場合には、鋼板表面の温度を鋼板温度としてよい。また、加速冷却直後は鋼板表面と内部とで温度差があるが、その温度差はしばらくすると熱伝導によって解消され、板厚方向で均一な温度分布となるため、このような均熱化後の鋼板表面温度に基づいて加速冷却停止時の鋼板温度を求めてもよい。
加速冷却後はそのまま空冷により鋼板を冷却すればよいが、鋼板内部の材質の均一化を目的として、ガス燃焼炉または誘導加熱炉などにおいて再加熱を行ってもよい。
The steel plate temperature mentioned above is the average temperature in the plate thickness direction when there is a temperature distribution in the plate thickness direction of the steel plate, but if the temperature distribution in the plate thickness direction is relatively small, the steel plate surface The temperature may be the steel plate temperature. In addition, there is a temperature difference between the steel plate surface and the interior immediately after accelerated cooling, but the temperature difference is eliminated by heat conduction after a while, and a uniform temperature distribution is obtained in the plate thickness direction. You may obtain | require the steel plate temperature at the time of an acceleration cooling stop based on a steel plate surface temperature.
After accelerated cooling, the steel plate may be cooled as it is by air cooling, but may be reheated in a gas combustion furnace or induction heating furnace for the purpose of uniformizing the material inside the steel plate.
表１に示す化学成分の鋼（鋼種Ａ〜Ｔ）を連続鋳造法によりスラブとし、これを用いて板厚１２．７ｍｍ、１９．１ｍｍ、２５．４ｍｍ及び３３．０ｍｍの厚鋼板を製造した。
加熱したスラブを熱間圧延により圧延し、その後、加速冷却を施して所定の強度とした。この時のスラブ加熱温度は１０５０℃、圧延終了温度は８４０〜８００℃、加速冷却開始温度は８００〜７６０℃、加速冷却停止温度は４５０〜５５０℃とした。得られた鋼板の強度はいずれもＡＰＩＸ６５を満足するものであり、引張強度は５７０〜６３０ＭＰａであった。
Steel having the chemical components shown in Table 1 (steel types A to T) was made into a slab by a continuous casting method, and thick steel plates having thicknesses of 12.7 mm, 19.1 mm, 25.4 mm, and 33.0 mm were manufactured using the slab.
The heated slab was rolled by hot rolling and then subjected to accelerated cooling to a predetermined strength. The slab heating temperature at this time was 1050 ° C., the rolling end temperature was 840 to 800 ° C., the accelerated cooling start temperature was 800 to 760 ° C., and the accelerated cooling stop temperature was 450 to 550 ° C. The strength of the obtained steel sheet satisfied APIX65, and the tensile strength was 570 to 630 MPa.
これらの鋼板について、複数の位置から各６〜９個のＨＩＣ試験片を採取し、耐ＨＩＣ特性を調べた。耐ＨＩＣ特性は、ｐＨが約３の硫化水素を飽和させた５％ＮａＣｌ＋０．５％ＣＨ３ＣＯＯＨ水溶液（通常のＮＡＣＥ溶液）中に試験片を９６時間浸漬した後、超音波探傷により試験片全面の割れの有無を調査し、割れ面積率（ＣＡＲ）で評価した。ここで、それぞれの鋼板の６〜９個の試験片のうち割れ面積率が最大のものを、その鋼板を代表する割れ面積率とし、割れ面積率２％以下を合格とした。さらに、ＴＯＴＡＬ仕様で要求される超音波探傷の割れ指示部での断面の個々の割れの長さを測定し、個々の割れの最大長さが５ｍｍ以下を合格とした。 About these steel plates, 6 to 9 HIC test pieces were sampled from a plurality of positions and examined for anti-HIC characteristics. The anti-HIC characteristic is that the test piece is immersed for 96 hours in 5% NaCl + 0.5% CH 3 COOH aqueous solution (ordinary NACE solution) saturated with hydrogen sulfide having a pH of about 3, and then the entire surface of the test piece is subjected to ultrasonic flaw detection. The presence or absence of cracks was investigated, and the crack area ratio (CAR) was evaluated. Here, among the 6 to 9 test pieces of each steel plate, the one with the largest crack area rate was set as the crack area rate representing the steel plate, and the crack area rate of 2% or less was set as acceptable. Furthermore, the length of each crack in the cross section at the crack indicating part for ultrasonic flaw detection required by the TOTAL specification was measured, and the maximum length of each crack was determined to be 5 mm or less.
中心偏析部の硬さは、鋼板から採取した複数のサンプルの板厚方向断面を研磨後、軽くエッチングし、偏析線が見られる部分を荷重５０ｇのビッカース硬さ計で測定し、その最大の値を中心偏析部の硬さとした。
中心偏析部のＮｂ炭窒化物の長さは、ＨＩＣ試験で割れが発生した部分の破面を電子顕微鏡で観察し、破面上のＮｂ炭窒化物粒の最大の長さとした。また、ＨＩＣ試験で割れが発生しない場合は、ＨＩＣ試験片の複数の断面を研磨後軽くエッチングし、偏析線が見られる部分をＥＰＭＡ（電子線マイクロアナライザー）によるＮｂの元素マッピングを行ってＮｂ炭窒化物を識別し、その粒の最大の長さをＮｂ炭窒化物の長さとした。
以上の試験および測定結果を表２に示す。
The hardness of the center segregation part is the maximum value of the part where the segregation line is observed with a Vickers hardness meter with a load of 50 g after polishing the cross section in the thickness direction of a plurality of samples taken from the steel sheet. Is the hardness of the central segregation part.
The length of the Nb carbonitride in the central segregation part was the maximum length of the Nb carbonitride grains on the fracture surface by observing the fracture surface of the portion where cracks occurred in the HIC test with an electron microscope. If cracks do not occur in the HIC test, a plurality of cross sections of the HIC test piece are polished and lightly etched, and the portion where segregation lines are seen is subjected to element mapping of Nb by EPMA (electron beam microanalyzer). Nitride was identified, and the maximum length of the grains was defined as the length of Nb carbonitride.
The above test and measurement results are shown in Table 2.
表１および表２において、本発明例である鋼板（鋼種）Ａ，Ｃ〜Ｇ，Ｉ，Ｊはいずれも、ＨＩＣ試験による割れ面積率が小さく、且つ個々の割れの最大長さも小さく、耐サワー性能が極めて良好である。
これに対して、比較例である鋼板（鋼種）Ｌ〜Ｎは、ＣＰ値が０．９２を超えているため、ＨＩＣ試験において高い割れ面積率を示し、個々の割れの最大長さも大きく、耐サワー性が劣っている。また、同じく鋼板（鋼種）Ｏは、Ｎｂ量が本発明範囲より高いため、中心偏析部に粗大なＮｂ炭窒化物が生成し、ＣＰ値ならびにＩＰ値が本発明範囲内であっても耐ＨＩＣ性能が劣っている。また、同じく鋼板（鋼種）Ｐは、Ｍｎ量、Ｓ量が本発明範囲より高いため中心偏析部にＭｎＳが生成し、ＭｎＳを起点とした割れが発生する結果、耐ＨＩＣ性能が劣っている。また、同じく鋼板（鋼種）Ｑは、ＩＰ値が１．０より低いためＣａによる硫化物の形態制御が不十分となってＭｎＳが生成し、ＭｎＳを起点とした割れが発生する結果、耐ＨＩＣ性能が劣っている。同じく鋼板（鋼種）ＲはＣａ無添加であり、Ｃａによる硫化物系介在物の形態制御がなされないため、ＭｎＳが生成し、耐ＨＩＣ性能が劣っている。同じく鋼板（鋼種）Ｓ，ＴはＩＰ値が２．８を超えているか、Ｃａ量が本発明範囲より高いため、鋼中のＣａ系酸化物量が増え、それらを起点として割れが発生する結果、耐ＨＩＣ性能が劣っている。
In Tables 1 and 2, the steel sheets (steel types) A, C to G, I, and J, which are examples of the present invention, all have a small crack area ratio by the HIC test, and the maximum length of each crack is small, sour resistance The performance is very good.
In contrast, the steel plates (steel types) L to N, which are comparative examples, have a CP value exceeding 0.92, and thus show a high crack area ratio in the HIC test, and the maximum length of each crack is large. Sourness is inferior. Similarly, the steel plate (steel type) O has a Nb content higher than the range of the present invention, so that coarse Nb carbonitride is generated at the center segregation portion, and even if the CP value and the IP value are within the range of the present invention, the HIC resistance The performance is inferior. Similarly, the steel sheet (steel type) P has Mn content and S content higher than the scope of the present invention, so that MnS is generated in the central segregation part and cracks starting from MnS occur, resulting in poor HIC resistance. Similarly, the steel plate (steel type) Q has an IP value lower than 1.0, so the sulfide morphology control by Ca is insufficient and MnS is generated, resulting in cracks starting from MnS. The performance is inferior. Similarly, the steel sheet (steel type) R is Ca-free, and since the form control of sulfide inclusions by Ca is not performed, MnS is generated and the HIC resistance is inferior. Similarly, the steel plates (steel types) S and T have an IP value exceeding 2.8, or the Ca content is higher than the range of the present invention, so that the Ca-based oxide amount in the steel increases, and as a result, cracks occur starting from them. HIC resistance is inferior.
Claims (3)
ＣＰ＝４．４６Ｃ（％）＋２．３７Ｍｎ（％）／６＋{１．１８Ｃｒ（％）＋１．９５Ｍｏ（％）＋１．７４Ｖ（％）}／５＋{１．７４Ｃｕ（％）＋１．７Ｎｉ（％）}／１５＋２２．３６Ｐ（％） …（1）
Ｃｅｑ＝Ｃ（％）＋Ｍｎ（％）／６＋{Ｃｒ（％）＋Ｍｏ（％）＋Ｖ（％）}／５＋{Ｃｕ（％）＋Ｎｉ（％）}／１５ …（2）
ＩＰ＝［Ｃａ（％）−｛０．１８＋１３０Ｃａ（％）｝＊Ｏ（％）］／１．２５Ｓ（％） …（3） In mass%, C: 0.02 to 0.06%, Si: 0.5% or less, Mn: 0.8 to 1.6%, P: 0.008% or less, S: 0.0008% or less Al: 0.08% or less, Nb: 0.005 to 0.035%, Ti: 0.005 to 0.025%, Ca: 0.0005 to 0.0035%, the balance being Fe and inevitable The CP value represented by the following formula (1) is 0.92 or less, the Ceq value represented by the following formula (2) is 0.28 or more, and the IP value represented by the following formula (3) is 1.0. A steel plate for line pipes, which is ˜2.8.
CP = 4.46C (%) + 2.37Mn (%) / 6+ {1.18Cr (%) + 1.95Mo (%) + 1.74V (%)} / 5+ {1.74Cu (%) + 1.7Ni (% )} / 15 + 22.36P (%) (1)
Ceq = C (%) + Mn (%) / 6+ {Cr (%) + Mo (%) + V (%)} / 5+ {Cu (%) + Ni (%)} / 15 (2)
IP = [Ca (%) − {0.18 + 130Ca (%)} * O (%)] / 1.25S (%) (3)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2008066903A JP5245476B2 (en) | 2008-03-15 | 2008-03-15 | Steel plate for line pipe |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2008066903A JP5245476B2 (en) | 2008-03-15 | 2008-03-15 | Steel plate for line pipe |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2009221534A JP2009221534A (en) | 2009-10-01 |
| JP5245476B2 true JP5245476B2 (en) | 2013-07-24 |
Family
ID=41238610
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2008066903A Active JP5245476B2 (en) | 2008-03-15 | 2008-03-15 | Steel plate for line pipe |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP5245476B2 (en) |
Families Citing this family (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102666899A (en) * | 2009-11-25 | 2012-09-12 | 杰富意钢铁株式会社 | Welded steel pipe for linepipe with superior compressive strength and superior toughness, and process for producing same |
| EP2505683B1 (en) * | 2009-11-25 | 2017-04-05 | JFE Steel Corporation | Process for producing a welded steel pipe for linepipe with superior compressive strength and excellent sour resistance |
| KR101511617B1 (en) * | 2009-11-25 | 2015-04-13 | 제이에프이 스틸 가부시키가이샤 | Method for manufacturing welded steel pipe for linepipe with high compressive strength |
| JP5299579B2 (en) * | 2010-09-03 | 2013-09-25 | 新日鐵住金株式会社 | High-strength steel sheet with excellent fracture and HIC resistance |
| JP5177310B2 (en) * | 2011-02-15 | 2013-04-03 | Ｊｆｅスチール株式会社 | High tensile strength steel sheet with excellent low temperature toughness of weld heat affected zone and method for producing the same |
| JP5751013B2 (en) * | 2011-05-24 | 2015-07-22 | Ｊｆｅスチール株式会社 | Manufacturing method of high-strength line pipe with excellent crush resistance and sour resistance |
| JP5796351B2 (en) * | 2011-05-24 | 2015-10-21 | Ｊｆｅスチール株式会社 | High strength sour line pipe excellent in crush resistance and manufacturing method thereof |
| JP5803270B2 (en) * | 2011-05-24 | 2015-11-04 | Ｊｆｅスチール株式会社 | High strength sour line pipe excellent in crush resistance and manufacturing method thereof |
| JP5751012B2 (en) * | 2011-05-24 | 2015-07-22 | Ｊｆｅスチール株式会社 | Manufacturing method of high-strength line pipe with excellent crush resistance and sour resistance |
| JP5900303B2 (en) * | 2011-12-09 | 2016-04-06 | Ｊｆｅスチール株式会社 | High-strength steel sheet for sour-resistant pipes with excellent material uniformity in the steel sheet and its manufacturing method |
| RU2620837C2 (en) | 2012-06-18 | 2017-05-30 | ДжФЕ СТИЛ КОРПОРЕЙШН | Thick high-tensile acid-resistant main pipe and method of its manufacture |
| EP2871252A4 (en) | 2012-07-09 | 2016-03-02 | Jfe Steel Corp | Thick-walled high-strength sour-resistant line pipe and method for producing same |
| CN104018071B (en) * | 2014-06-18 | 2016-08-24 | 内蒙古包钢钢联股份有限公司 | The production method of low-carbon-equivalent high tenacity Q420E steel plate |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH06293919A (en) * | 1993-04-08 | 1994-10-21 | Nippon Steel Corp | Production of high tensile strength steel plate excellent in sour resistance and toughness at low temperature |
| JP2000199029A (en) * | 1999-01-07 | 2000-07-18 | Nippon Steel Corp | Steel sheet and steel pipe excellent in carbon dioxide corrosion resistance and sulfide stress cracking resistance and production thereof |
| JP2000226633A (en) * | 1999-02-04 | 2000-08-15 | Nkk Corp | Steel for electron beam welding excellent in toughness |
| JP5151008B2 (en) * | 2005-03-29 | 2013-02-27 | Ｊｆｅスチール株式会社 | Hot-rolled steel sheet for sour-resistant and high-strength ERW pipe with excellent HIC resistance and weld toughness and method for producing the same |
| RU2481415C2 (en) * | 2007-11-07 | 2013-05-10 | ДжФЕ СТИЛ КОРПОРЕЙШН | Steel sheet and steel pipe for pipelines |
-
2008
- 2008-03-15 JP JP2008066903A patent/JP5245476B2/en active Active
Also Published As
| Publication number | Publication date |
|---|---|
| JP2009221534A (en) | 2009-10-01 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP5343519B2 (en) | Steel plate and pipe for line pipe | |
| JP5245476B2 (en) | Steel plate for line pipe | |
| JP5098256B2 (en) | Steel sheet for high-strength line pipe with low yield stress reduction due to the Bauschinger effect with excellent hydrogen-induced cracking resistance and method for producing the same | |
| JP5353156B2 (en) | Steel pipe for line pipe and manufacturing method thereof | |
| JP6064955B2 (en) | Manufacturing method of high strength seamless steel pipe for oil wells with excellent resistance to sulfide stress cracking | |
| WO2015030210A1 (en) | Steel sheet for thick-walled high-strength line pipe having exceptional souring resistance, crush resistance properties, and low-temperature ductility, and line pipe | |
| WO2013147197A1 (en) | High-strength steel pipe for line pipe having excellent hydrogen-induced cracking resistance, high-strength steel pipe for line pipe using same, and method for manufacturing same | |
| WO2015012317A1 (en) | Steel plate for line pipe, and line pipe | |
| JP2008101242A (en) | High-strength steel plate with excellent hic resistance for line pipe, and its manufacturing method | |
| JP5910792B2 (en) | Thick steel plate and method for manufacturing thick steel plate | |
| KR101601000B1 (en) | Method of manufacturing sheet steel for sour-resistant line pipe | |
| JP6108116B2 (en) | Steel plates for marine, marine structures and hydraulic iron pipes with excellent brittle crack propagation stopping properties and methods for producing the same | |
| WO2016157863A1 (en) | High strength/high toughness steel sheet and method for producing same | |
| JP2020012168A (en) | Thick steel sheet for sour resistant linepipe, and manufacturing method therefor | |
| JP5509654B2 (en) | High-strength steel sheet excellent in PWHT resistance and uniform elongation characteristics and method for producing the same | |
| JP6241434B2 (en) | Steel plate for line pipe, steel pipe for line pipe, and manufacturing method thereof | |
| JP2008150656A (en) | High-strength steel plate resistant to strength reduction resulting from stress relief annealing and excellent in weldability | |
| JP6036645B2 (en) | Ferritic-martensitic duplex stainless steel with excellent low-temperature toughness and method for producing the same | |
| JPH11229075A (en) | High strength steel excellent in delayed breakdown resistance, and its production | |
| JP2018168411A (en) | Manufacturing method of high strength/high toughness steel plate | |
| JP2017053028A (en) | Ferrite-martensite two-phase stainless steel and manufacturing method therefor | |
| JPWO2019064459A1 (en) | High-strength steel sheet for sour line pipes, method for producing the same, and high-strength steel pipe using high-strength steel sheets for sour line pipes | |
| JP3714232B2 (en) | High strength steel plate with excellent HIC resistance and method for producing the same | |
| JP2003301236A (en) | High-strength steel material showing excellent resistance to hydrogen-induced cracking (hic) | |
| JP3896915B2 (en) | High strength steel plate with excellent HIC resistance and method for producing the same |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20110128 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20120924 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20121002 |
|
| A521 | Request for written amendment filed |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20121122 |
|
| TRDD | Decision of grant or rejection written | ||
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20130312 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20130325 |
|
| R150 | Certificate of patent or registration of utility model |
Ref document number: 5245476 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R150 Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20160419 Year of fee payment: 3 |
|
| R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |
|
| R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |
|
| R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |
|
| R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |