JP2013139630A - High strength steel sheet for sour-resistant line pipe excellent in material uniformity in the steel sheet and method for producing the same - Google Patents
High strength steel sheet for sour-resistant line pipe excellent in material uniformity in the steel sheet and method for producing the same Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 220
- 239000010959 steel Substances 0.000 title claims abstract description 220
- 239000000463 material Substances 0.000 title claims abstract description 38
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 26
- 238000001816 cooling Methods 0.000 claims abstract description 121
- 239000002344 surface layer Substances 0.000 claims abstract description 49
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 18
- 238000005098 hot rolling Methods 0.000 claims abstract description 11
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 7
- 239000002184 metal Substances 0.000 claims abstract description 6
- 229910052751 metal Inorganic materials 0.000 claims abstract description 6
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 6
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 5
- 239000012535 impurity Substances 0.000 claims abstract description 5
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 5
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 5
- 238000010438 heat treatment Methods 0.000 claims description 31
- 230000006698 induction Effects 0.000 claims description 19
- 238000003303 reheating Methods 0.000 claims description 19
- 238000005096 rolling process Methods 0.000 claims description 15
- 239000013256 coordination polymer Substances 0.000 claims description 10
- 239000000126 substance Substances 0.000 claims description 10
- 229910052799 carbon Inorganic materials 0.000 claims description 3
- 229910052748 manganese Inorganic materials 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 229910052758 niobium Inorganic materials 0.000 abstract description 5
- 229910052802 copper Inorganic materials 0.000 abstract description 3
- 239000000203 mixture Substances 0.000 abstract description 3
- 229910000734 martensite Inorganic materials 0.000 description 17
- 238000000034 method Methods 0.000 description 13
- 238000005204 segregation Methods 0.000 description 13
- 230000000694 effects Effects 0.000 description 9
- 230000009466 transformation Effects 0.000 description 9
- 229910052739 hydrogen Inorganic materials 0.000 description 7
- 239000001257 hydrogen Substances 0.000 description 7
- 229910000859 α-Fe Inorganic materials 0.000 description 7
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 6
- 238000005336 cracking Methods 0.000 description 6
- 238000003466 welding Methods 0.000 description 5
- 230000007423 decrease Effects 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 3
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 229910001566 austenite Inorganic materials 0.000 description 3
- 230000001276 controlling effect Effects 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 3
- 229910001567 cementite Inorganic materials 0.000 description 2
- 230000003749 cleanliness Effects 0.000 description 2
- 239000000498 cooling water Substances 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
- 230000006866 deterioration Effects 0.000 description 2
- 238000000265 homogenisation Methods 0.000 description 2
- -1 hydrogen ions Chemical class 0.000 description 2
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 2
- 239000003345 natural gas Substances 0.000 description 2
- 229910001562 pearlite Inorganic materials 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- 230000000171 quenching effect Effects 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- RMLPZKRPSQVRAB-UHFFFAOYSA-N tris(3-methylphenyl) phosphate Chemical compound CC1=CC=CC(OP(=O)(OC=2C=C(C)C=CC=2)OC=2C=C(C)C=CC=2)=C1 RMLPZKRPSQVRAB-UHFFFAOYSA-N 0.000 description 2
- YZCKVEUIGOORGS-UHFFFAOYSA-N Hydrogen atom Chemical compound [H] YZCKVEUIGOORGS-UHFFFAOYSA-N 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
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- 238000007654 immersion Methods 0.000 description 1
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- 238000000465 moulding Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
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- 238000001953 recrystallisation Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000005482 strain hardening Methods 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
- 238000011144 upstream manufacturing Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- Heat Treatment Of Steel (AREA)
Abstract
Description
本発明は、建築、海洋構造物、造船、土木、建設産業用機械、ラインパイプ等の分野で使用される、鋼板内の材質均一性に優れた耐サワーラインパイプ用高強度鋼板とその製造方法に関するものである。 The present invention relates to a high-strength steel plate for sour line pipes having excellent material uniformity in a steel plate used in the fields of architecture, offshore structures, shipbuilding, civil engineering, construction industry, line pipes, and the like, and a method for producing the same. It is about.
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、ロール成形等で鋼管形状に成形して製造する。 The line pipe is manufactured by forming a steel plate manufactured by a thick plate mill or a hot rolling mill into a steel pipe shape by UOE forming, press bend forming, roll forming or the like.
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を備えることが必要とされる。 Line pipes used to transport crude oil and natural gas containing hydrogen sulfide have strength, toughness and weldability, as well as hydrogen-induced crack resistance (HIC resistance) and stress corrosion crack resistance (SCC resistance). It is necessary to provide so-called sour resistance.
鋼材の水素誘起割れ（ＨＩＣ）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、その内圧により割れを生ずるものとされている。 In hydrogen induced cracking (HIC) of steel, hydrogen ions from the 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 hard second phase structure. It is said that it diffuses and accumulates around, and cracks occur due to its internal pressure.
このような水素誘起割れを防ぐためにいく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、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性を改善する技術が提案されている。 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. Has been proposed to improve the HIC resistance by reducing stress concentration due to sulfide inclusions and suppressing the occurrence and propagation of cracks.
特許文献２、特許文献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の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。 In Patent Documents 2 and 3, there is a reduction in elements that have a high segregation tendency (C, Mn, P, etc.), a reduction in segregation by soaking in the slab heating stage, and an acceleration during transformation after cooling after rolling. Techniques for cooling have 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.
また、特許文献４、特許文献５には、高強度鋼板に対して、低ＳかつＣａ添加により硫化物系介在物の形態制御を行いつつ、低Ｃ−低Ｍｎ化により中心偏析を抑制し、それに伴う強度低下をＣｒ、Ｍｏ、Ｎｉ等の添加と加速冷却により補う方法が提案されている。 In Patent Documents 4 and 5, for high-strength steel sheets, while controlling the form of sulfide inclusions with low S and Ca addition, the center segregation is suppressed by low C-low Mn, There has been proposed a method of compensating for the accompanying strength reduction by adding Cr, Mo, Ni or the like and accelerated cooling.
一方、鋼構造物の大型化やコスト削減の観点から、より高強度や高靭性を有する鋼板の需要が高まっている。鋼板の特性向上や合金元素削減、熱処理省略を目的として、通常、高強度鋼板は、制御圧延と制御冷却を組み合わせた、いわゆるＴＭＣＰ技術が適用されて製造される。 On the other hand, from the viewpoint of increasing the size of steel structures and reducing costs, there is an increasing demand for steel sheets having higher strength and higher toughness. For the purpose of improving the properties of steel sheets, reducing alloy elements, and omitting heat treatment, high-strength steel sheets are usually manufactured by applying so-called TMCP technology, which combines controlled rolling and controlled cooling.
ＴＭＣＰ技術を用いて鋼材の高強度化を行うには、制御冷却時の冷却速度を大きくすることが有効である。しかしながら、高冷却速度で制御冷却した場合、鋼板表層部が急冷されるため、鋼板内部に比べて表層部の硬さが高くなり、板厚方向の硬さ分布にばらつきが生じる。したがって、鋼板内の材質均一性を確保する観点で問題となる。 In order to increase the strength of steel using the TMCP technology, it is effective to increase the cooling rate during controlled cooling. However, when controlled cooling is performed at a high cooling rate, the surface layer portion of the steel sheet is rapidly cooled, so that the hardness of the surface layer portion is higher than that inside the steel plate, and the hardness distribution in the thickness direction varies. Therefore, it becomes a problem from the viewpoint of ensuring the material uniformity in the steel plate.
特許文献６には、制御冷却に際して、冷却速度を３〜１２℃／ｓという比較的低冷却速度に制御することにより、板厚中心部に対する表面の硬さ上昇を抑える方法が開示されている。 Patent Document 6 discloses a method of suppressing an increase in surface hardness with respect to the center portion of the plate thickness by controlling the cooling rate to a relatively low cooling rate of 3 to 12 ° C./s during controlled cooling.
特許文献７には、冷却過程で、フェライトが析出する温度域で待機を行うことにより、鋼板の組織をフェライトとベイナイトの２相組織とし、表層と板厚中心部の硬さの差を低減した、板厚方向に材質差の小さい鋼板の製造方法が開示されている。 In Patent Document 7, by waiting in a cooling process at a temperature range where ferrite precipitates, the steel sheet has a two-phase structure of ferrite and bainite, and the difference in hardness between the surface layer and the center of the plate thickness is reduced. A method of manufacturing a steel sheet having a small material difference in the thickness direction is disclosed.
また、特許文献８、特許文献９には、圧延後、表層部がベイナイト変態を完了する前に表面を復熱させる高冷却速度の制御冷却を行った、板厚方向に材質差の小さい鋼板の製造方法が開示されている。 Patent Document 8 and Patent Document 9 include a steel plate having a small material difference in the plate thickness direction, which has been subjected to controlled cooling at a high cooling rate for reheating the surface after the rolling before the surface layer portion completes the bainite transformation. A manufacturing method is disclosed.
特許文献１０、特許文献１１には、高周波誘導加熱装置を用いて、加速冷却後の鋼板表面を内部より高温に加熱して表層部の硬さを低減した、ラインパイプ用鋼板の製造方法が開示されている。 Patent Document 10 and Patent Document 11 disclose a method for manufacturing a steel plate for a line pipe in which the surface of the steel plate after accelerated cooling is heated to a higher temperature from the inside by using a high-frequency induction heating device to reduce the hardness of the surface layer portion. Has been.
また、特許文献１２には、制御冷却を、鋼板表面温度が５００℃以下となるまで鋼板中央部の平均冷却速度５〜１５℃／ｓで冷却した後、後期冷却で鋼板中央部の平均冷却速度２０〜５０℃／ｓで板厚方向平均温度６００℃以下まで冷却することにより、表層の硬化組織を抑制する方法が開示されている。 Patent Document 12 discloses that control cooling is performed at an average cooling rate of 5 to 15 ° C./s at the central part of the steel sheet until the steel sheet surface temperature becomes 500 ° C. or lower, and then at the latter stage cooling. A method for suppressing the hardened structure of the surface layer by cooling to a plate thickness direction average temperature of 600 ° C. or lower at 20 to 50 ° C./s is disclosed.
一方、鋼板表面のスケール性状にむらがあると、冷却時にスケール厚さに応じてその下部の鋼板の冷却速度に違いを生じて、すなわち鋼板内で部分的に冷却停止温度のばらつきが生じて、スケール性状に対応して板幅方向に鋼板材質のばらつきが生じる。 On the other hand, if there is unevenness in the scale properties of the steel sheet surface, the cooling rate of the lower steel sheet varies depending on the scale thickness during cooling, that is, the cooling stop temperature varies partially within the steel sheet, Corresponding to the scale properties, the steel plate material varies in the plate width direction.
特許文献１３、特許文献１４には、冷却直前にデスケーリングを行うことにより、スケール性状による冷却むらを低減し、鋼板形状を改善する方法が開示されている。 Patent Document 13 and Patent Document 14 disclose a method of reducing the uneven cooling due to the scale properties and improving the steel plate shape by performing descaling immediately before cooling.
しかしながら、特許文献１〜５に記載の技術は、いずれも中心偏析部が対象で、中心偏析部以外の部分については考慮されていない。 However, all of the techniques described in Patent Documents 1 to 5 are directed to the center segregation part, and no part other than the center segregation part is considered.
制御冷却又は直接焼入れによって製造されるＡＰＩ規格Ｘ６５グレード以上の強度を有する高強度鋼板においては、冷却速度の高い鋼板表面部が内部に比べて硬化するため、表面近傍から水素誘起割れが発生するという問題がある。 In high-strength steel sheets with API standard X65 grade strength or higher manufactured by controlled cooling or direct quenching, the steel sheet surface portion with a high cooling rate is hardened compared to the inside, so that hydrogen-induced cracking occurs from the vicinity of the surface. There's a problem.
特許文献６記載の技術は、冷却速度の制限により、高冷却速度による高強度化や合金元素の削減、制御圧延の簡略化等といった制御冷却の効果を十分に活用することができない。特許文献７の製造方法は、Ａｒ３変態点以下での冷却待機でフェライトを析出させるため強度が低下するとともに、冷却待機時間が必要なため製造効率が悪化する。 The technology described in Patent Document 6 cannot fully utilize the effect of controlled cooling such as high strength by high cooling rate, reduction of alloy elements, simplification of controlled rolling, etc. due to limitation of cooling rate. In the manufacturing method of Patent Document 7, the ferrite is precipitated in the cooling standby at the Ar 3 transformation point or lower, so that the strength is lowered and the cooling standby time is required, so that the manufacturing efficiency is deteriorated.
特許文献８、特許文献９記載の製造方法は、鋼板の成分により変態挙動が異なると、復熱による十分な材質均質化の効果が得られない場合がある。また、高精度な冷却制御が必要なため、適用範囲が限られるとともに製造効率が悪化する。特許文献１０、特許文献１１記載の製造方法は、加速冷却での表層部の冷却速度が大きいと、鋼板表面の加熱だけでは表層部の硬さを十分に低減できない場合がある。
特許文献１２記載の製造方法は、鋼板の成分により変態挙動が異なると、表層の硬化組織を抑制できない場合があり、十分な材質均質化の効果が得られない場合がある。
In the production methods described in Patent Document 8 and Patent Document 9, if the transformation behavior differs depending on the components of the steel sheet, a sufficient material homogenization effect due to recuperation may not be obtained. Moreover, since highly accurate cooling control is required, the application range is limited and the manufacturing efficiency is deteriorated. In the manufacturing methods described in Patent Document 10 and Patent Document 11, if the cooling rate of the surface layer portion in accelerated cooling is large, the hardness of the surface layer portion may not be sufficiently reduced only by heating the steel sheet surface.
In the production method described in Patent Document 12, if the transformation behavior varies depending on the components of the steel sheet, the hardened structure of the surface layer may not be suppressed, and a sufficient material homogenizing effect may not be obtained.
また、特許文献１３、特許文献１４記載の方法は、デスケーリングにより、熱間矯正時のスケールの押し込み疵による表面性状不良の低減や、鋼板の冷却停止温度のばらつきを低減して鋼板形状を改善しているが、均一な材質を得るための冷却条件に関しての記載はない。 In addition, the methods described in Patent Document 13 and Patent Document 14 improve the steel plate shape by reducing the surface property failure due to the indentation of the scale during hot correction and the variation in the cooling stop temperature of the steel plate by descaling. However, there is no description about cooling conditions for obtaining a uniform material.
鋼板の冷却状態は、表面性状だけでなく冷却の強弱によっても影響を受けるため、鋼板表面の冷却速度がばらつくと硬さのばらつきが生じる危険性がある。冷却速度によっては、鋼板表面の冷却状態において、鋼板表面と冷却水の間に気泡の膜が発生する“膜沸騰”と気泡が膜を形成する前に冷却水によって表面から分離される“核沸騰”とが混在し、表面の冷却速度にばらつきを生じる虞がある。それによって鋼板表面の硬さにばらつきを生じることになる。 Since the cooling state of the steel sheet is affected not only by the surface properties but also by the strength of the cooling, there is a risk that the hardness may vary if the cooling rate of the steel sheet surface varies. Depending on the cooling rate, in the cooling state of the steel sheet surface, a film of bubbles is generated between the steel sheet surface and the cooling water, and “nucleate boiling” where the bubbles are separated from the surface by the cooling water before forming the film. "May be mixed, and the surface cooling rate may vary. As a result, the hardness of the steel sheet surface varies.
従って、本発明は、従来、低廉な成分と高冷却速度冷却を組み合わせた場合、鋼板内の材質均一性と耐ＨＩＣ特性を備えた高強度鋼板を製造するこができなかったことを解決し、中央偏析部のＨＩＣとともに表面近傍から発生するＨＩＣに対して優れた耐ＨＩＣ特性を有し、鋼板の板厚方向および板幅方向の硬さのばらつきを低減した、鋼板内の材質均一性に優れた耐サワーラインパイプ用高強度鋼板とその製造方法を提供することを目的とする。 Therefore, the present invention solves the problem that, conventionally, when a low-cost component and high cooling rate cooling are combined, a high-strength steel sheet with material uniformity and HIC resistance in the steel sheet could not be produced, It has excellent HIC resistance against HIC generated from the vicinity of the surface together with HIC in the central segregation part, and it has excellent material uniformity in the steel sheet with reduced variation in hardness in the sheet thickness direction and sheet width direction. Another object of the present invention is to provide a high-strength steel sheet for sour-resistant pipes and a method for producing the same.
上記課題を解決するため、本発明者らは、ＡＰＩ規格Ｘ６５グレードの強度を有する高強度鋼板において、中央偏析部とともに表面近傍からのＨＩＣ発生を防止し、板厚方向および板幅方向の硬さのばらつきを低減し、鋼板内の材質均一性を向上させるために、鋼材の化学成分、ミクロ組織、製造方法を鋭意検討し、表層部の冷却速度や復熱を含む冷却パターンと鋼板内の平均冷却速度を制御することが重要であるとの知見を得て、本発明を完成した。本発明の課題は以下の手段により達成可能である。
（１）質量％で、Ｃ：０．０２〜０．０８％、Ｓｉ：０．０１〜０．５％、Ｍｎ：０．５〜１．８％、Ｐ：０．０１％以下、Ｓ：０．００１％以下、Ａｌ：０．０１〜０．０８％、Ｃａ：０．０００５〜０．００５％を含有し、残部がＦｅおよび不可避的不純物からなり、金属組織がベイナイト組織であり、板厚方向の硬さのばらつきがΔＨＶ１０２５以下であり、板幅方向の硬さのばらつきがΔＨＶ１０２５以下であり、鋼板表層部の最高硬さがＨＶ１０２２０以下であることを特徴とする、鋼板内の材質均一性に優れた耐サワーラインパイプ用高強度鋼板。
（２）さらに、質量％で、Ｃｕ：０．５０％以下、Ｎｉ：０．５０％以下、Ｃｒ：０．５０％以下、Ｍｏ：０．５０％以下の１種又は２種以上を含有することを特徴とする、（１）に記載の鋼板内の材質均一性に優れた耐サワーラインパイプ用高強度鋼板。
（３）さらに、質量％で、Ｎｂ：０．００５〜０．１％、Ｖ：０．００５〜０．１％、Ｔｉ：０．００５〜０．１％の１種又は２種以上を含有することを特徴とする、（１）または（２）に記載の鋼板内の材質均一性に優れた耐サワーラインパイプ用高強度鋼板。
（４）下記（１）式で示されるＣＰ値（質量％）が１．０以下であり、下記（２）式で示されるＣｅｑ値（質量％）が０．３０以上０．３７以下であることを特徴とする、（１）乃至（３）のいずれか一つに記載の鋼板内の材質均一性に優れた耐サワーラインパイプ用高強度鋼板。
ＣＰ＝４．４６Ｃ（％）＋２．３７Ｍｎ（％）＋｛１．７４Ｃｕ（％）＋１．７Ｎｉ（％）｝／１５＋｛１．１８Ｃｒ（％）＋１．９５Ｍｏ（％）＋１．７４Ｖ（％）｝／５＋２２．３６Ｐ（％） ・・・（１）
Ｃｅｑ＝Ｃ（％）＋Ｍｎ（％）／６＋（Ｃｕ（％）＋Ｎｉ（％））／１５＋（Ｃｒ（％）＋Ｍｏ（％）＋Ｖ（％））／５ ・・・（２）
但し、各式において各元素記号は含有量（質量％）。
（５）（１）乃至（４）の何れか一つに記載の化学成分を有する鋼を、１０００℃以上１３００℃以下の温度に加熱し、圧延終了温度が鋼板表面温度でＡｒ３温度以上で熱間圧延した後、制御冷却の直前に鋼板表面での噴射流の衝突圧が１ＭＰａ以上でデスケーリングを行い、冷却開始時の鋼板表面温度が（Ａｒ３−１０）℃以上から鋼板表面の冷却速度が２００℃／ｓ以下、且つ鋼板の平均冷却速度が１５℃／ｓ以上で、鋼板の平均温度で２５０℃以上５５０℃まで制御冷却し、その後直ちに誘導加熱により、冷却停止温度以上であって且つ鋼板表面温度で５００〜７００℃、鋼板平均温度で３５０〜６００℃まで再加熱を行うことを特徴とする、鋼板内の材質均一性に優れた耐サワーラインパイプ用高強度鋼板の製造方法。
（６）（５）に記載の製造方法で製造された鋼板を用いた材質均一性に優れた耐サワーラインパイプ用高強度鋼管。
In order to solve the above-mentioned problems, the present inventors have prevented the occurrence of HIC from the vicinity of the surface together with the central segregation portion in the high strength steel plate having the strength of API standard X65 grade, and the hardness in the plate thickness direction and the plate width direction. In order to reduce the variation of the material and improve the material uniformity in the steel sheet, we intensively studied the chemical composition, microstructure and manufacturing method of the steel material, the cooling pattern including the cooling rate of the surface layer and the average in the steel sheet The present invention was completed with the knowledge that it is important to control the cooling rate. The object of the present invention can be achieved by the following means.
(1) By mass%, C: 0.02 to 0.08%, Si: 0.01 to 0.5%, Mn: 0.5 to 1.8%, P: 0.01% or less, S: 0.001% or less, Al: 0.01-0.08%, Ca: 0.0005-0.005%, the balance is made of Fe and inevitable impurities, the metal structure is a bainite structure, The variation in hardness in the thickness direction is ΔH V10 25 or less, the variation in hardness in the sheet width direction is ΔH V10 25 or less, and the maximum hardness of the steel sheet surface layer portion is H V10 220 or less. High strength steel plate for sour line pipes with excellent material uniformity in the steel plate.
(2) Further, by mass%, Cu: 0.50% or less, Ni: 0.50% or less, Cr: 0.50% or less, Mo: 0.50% or less, or one or more of them are contained. The high-strength steel plate for sour line pipes having excellent material uniformity in the steel plate according to (1), characterized in that
(3) Further, by mass%, Nb: 0.005 to 0.1%, V: 0.005 to 0.1%, Ti: 0.005 to 0.1%, or one or more A high-strength steel sheet for a sour line pipe excellent in material uniformity in the steel sheet according to (1) or (2).
(4) The CP value (mass%) represented by the following formula (1) is 1.0 or less, and the Ceq value (mass%) represented by the following formula (2) is 0.30 or more and 0.37 or less. The high-strength steel plate for sour line pipes having excellent material uniformity in the steel plate according to any one of (1) to (3).
CP = 4.46C (%) + 2.37Mn (%) + {1.74Cu (%) + 1.7Ni (%)} / 15+ {1.18Cr (%) + 1.95Mo (%) + 1.74V (%) } /5+22.36P (%) (1)
Ceq = C (%) + Mn (%) / 6+ (Cu (%) + Ni (%)) / 15+ (Cr (%) + Mo (%) + V (%)) / 5 (2)
However, each element symbol in each formula is the content (% by mass).
(5) The steel having the chemical component according to any one of (1) to (4) is heated to a temperature of 1000 ° C. or higher and 1300 ° C. or lower, and the rolling end temperature is a steel plate surface temperature of Ar 3 temperature or higher. After hot rolling, just before the controlled cooling, the impact pressure of the jet flow on the steel sheet surface is descaled at 1 MPa or more, and the steel sheet surface temperature is cooled from (Ar 3 -10) ° C. or more at the start of cooling. The rate is 200 ° C./s or less, the average cooling rate of the steel plate is 15 ° C./s or more, the average temperature of the steel plate is controlled to 250 ° C. to 550 ° C., and then immediately after induction cooling, the cooling stop temperature is over And the manufacturing method of the high-strength steel plate for sour-line pipes excellent in the material uniformity in the steel plate characterized by performing reheating to 500-700 degreeC with a steel plate surface temperature and 350-600 degreeC with a steel plate average temperature.
(6) A high-strength steel pipe for a sour line pipe excellent in material uniformity using a steel plate produced by the production method described in (5).
本発明によれば、低廉な化学成分でも鋼板内の材質均一性に優れ、且つ耐ＨＩＣ特性に優れる、高強度の耐サワーラインパイプ用鋼板およびその製造方法が得られ、産業上極めて有用である。 According to the present invention, a high-strength sour line pipe steel plate having excellent material uniformity in a steel plate even with low-cost chemical components and excellent in HIC resistance and a method for producing the same can be obtained, which is extremely useful industrially. .
本発明に係る高強度鋼板の化学成分について説明する。以下の説明において％で示す単位は全て質量％である。 The chemical components of the high-strength steel sheet according to the present invention will be described. In the following description, all units represented by% are mass%.
Ｃ：０．０２〜０．０８％
Ｃは０．０２％未満では十分な強度が確保できず、０．０８％超えでは加速冷却時に表層部の硬さが上昇するとともに、耐ＨＩＣ特性と靭性を劣化させるため、含有量を０．０２〜０．０８％に規定する。
C: 0.02 to 0.08%
If C is less than 0.02%, sufficient strength cannot be ensured, and if it exceeds 0.08%, the hardness of the surface layer portion increases during accelerated cooling, and the HIC resistance and toughness are deteriorated. It is specified at 02 to 0.08%.
Ｓｉ：０．０１〜０．５％
Ｓｉは脱酸のため添加するが、０．０１％未満では脱酸効果が十分でなく、０．５％を超えると靭性や溶接性を劣化させるため、含有量を０．０１〜０．５％に規定する。
Si: 0.01 to 0.5%
Si is added for deoxidation, but if it is less than 0.01%, the deoxidation effect is not sufficient, and if it exceeds 0.5%, the toughness and weldability are deteriorated. %.
Ｍｎ：０．５〜１．８％
Ｍｎは強度、靭性のため添加するが、０．５％未満ではその効果が十分でなく、１．８％を超えると溶接性と耐ＨＩＣ特性が劣化するため、含有量を０．５〜１．８％に規定する。
Mn: 0.5 to 1.8%
Mn is added for strength and toughness, but if it is less than 0.5%, its effect is not sufficient, and if it exceeds 1.8%, the weldability and HIC resistance deteriorate, so the content is 0.5 to 1 .8% is specified.
Ｐ：０．０１％以下
Ｐは不可避的不純物元素であり、溶接性を劣化させるとともに、中心偏析部の硬さを上昇させることで耐ＨＩＣ性を劣化させる。０．０１％を超えるとその傾向が顕著となるため、含有量の上限を０．０１％に規定する。好ましくは０．００８％以下である。
P: 0.01% or less P is an unavoidable impurity element, which deteriorates weldability and HIC resistance by increasing the hardness of the central segregation part. Since the tendency will become remarkable when it exceeds 0.01%, the upper limit of content is prescribed | regulated to 0.01%. Preferably it is 0.008% or less.
Ｓ：０．００１％以下
Ｓは一般的には鋼中においてはＭｎＳ介在物となり耐ＨＩＣ特性を劣化させるため少ないほどよい。しかし、０．００１％以下であれば問題ないため、含有量の上限を０．００１％に規定する。
S: 0.001% or less Generally, S is preferably as small as possible because it becomes MnS inclusions in steel and deteriorates the HIC resistance. However, since there is no problem if it is 0.001% or less, the upper limit of the content is specified to 0.001%.
Ａｌ：０．０１〜０．０８％
Ａｌは脱酸剤として添加されるが、０．０１％未満では効果がなく、０．０８％を超えると鋼の清浄度が低下し、靱性が劣化するため、含有量を０．０１〜０．０８％に規定する。
Al: 0.01 to 0.08%
Al is added as a deoxidizer, but if it is less than 0.01%, there is no effect, and if it exceeds 0.08%, the cleanliness of the steel decreases and the toughness deteriorates, so the content is 0.01-0. .08% is specified.
Ｃａ：０．０００５〜０．００５％
Ｃａは硫化物系介在物の形態制御による耐ＨＩＣ特性向上に有効な元素であるが、０．０００５％未満ではその効果が十分でなく、０．００５％を超えて添加しても効果が飽和し、むしろ、鋼の清浄度の低下により耐ＨＩＣ特性を劣化させるので、含有量を０．０００５〜０．００５％に規定する。上記以外の残部はＦｅおよび不可避的不純物とする。
Ca: 0.0005 to 0.005%
Ca is an element effective for improving the HIC resistance by controlling the form of sulfide inclusions, but the effect is not sufficient if it is less than 0.0005%, and the effect is saturated even if added over 0.005%. However, since the HIC resistance is deteriorated due to a decrease in the cleanliness of the steel, the content is specified to be 0.0005 to 0.005%. The balance other than the above is Fe and inevitable impurities.
ＣＰ＝４．４６Ｃ（％）＋２．３７Ｍｎ（％）＋｛１．７４Ｃｕ（％）＋１．７Ｎｉ（％）｝／１５＋｛１．１８Ｃｒ（％）＋１．９５Ｍｏ（％）＋１．７４Ｖ（％）｝／５＋２２．３６Ｐ（％） ・・・（１）
但し、Ｃ（％）、Ｍｎ（％）、Ｃｕ（％）、Ｎｉ（％）、Ｃｒ（％）、Ｍｏ（％）、Ｖ（％）、Ｐ（％）は各元素の含有量（質量％）であり、添加しない元素は０とする。
CP = 4.46C (%) + 2.37Mn (%) + {1.74Cu (%) + 1.7Ni (%)} / 15+ {1.18Cr (%) + 1.95Mo (%) + 1.74V (%) } /5+22.36P (%) (1)
However, C (%), Mn (%), Cu (%), Ni (%), Cr (%), Mo (%), V (%), P (%) are the contents of each element (mass% The element not added is 0.
ＣＰ値は、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考案された式であり、（１）式で表されるＣＰ値（質量％）を１．０以下とする。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。このＣＰ値を１．０以下とすることでＨＩＣを抑制することが可能となる。また、ＣＰ値が低いほど中心偏析部の硬さが低くなるため、さらに高い耐ＨＩＣ特性が必要な場合はその上限を０．９５とすることが望ましい。 The CP value is an expression devised for estimating the material of the central segregation part from the content of each alloy element, and the CP value (mass%) represented by the expression (1) is 1.0 or less. The higher the CP value, the higher the concentration of the center segregation part and the higher the hardness of the center segregation part. By setting the CP value to 1.0 or less, HIC can be suppressed. Further, the lower the CP value, the lower the hardness of the center segregation part. Therefore, when higher HIC resistance is required, the upper limit is desirably set to 0.95.
以上が本発明の基本化学成分であるが、鋼板の強度靱性をさらに改善する場合、Ｃｕ、Ｎｉ、Ｃｒ、Ｍｏ、Ｎｂ、Ｖ、Ｔｉの１種又は２種以上を含有してもよい。 The above is the basic chemical component of the present invention, but when further improving the strength toughness of the steel sheet, it may contain one or more of Cu, Ni, Cr, Mo, Nb, V, and Ti.
Ｃｕ：０．５０％以下
Ｃｕは靭性の改善と強度の上昇に有効な元素であるが、多く添加すると溶接性が劣化するため、添加する場合は０．５０％を上限とする。
Cu: 0.50% or less Cu is an element effective for improving toughness and increasing strength, but if added in a large amount, weldability deteriorates. Therefore, when added, the upper limit is 0.50%.
Ｎｉ：０．５０％以下
Ｎｉは靭性の改善と強度の上昇に有効な元素であるが、多く添加するとコスト的に不利になり、また、溶接熱影響部靱性が劣化するため、添加する場合は０．５０％を上限とする。
Ni: 0.50% or less Ni is an element effective for improving toughness and increasing strength. However, if added in a large amount, it is disadvantageous in cost, and the weld heat affected zone toughness deteriorates. The upper limit is 0.50%.
Ｃｒ：０．５０％以下
ＣｒはＭｎと同様に低Ｃでも十分な強度を得るために有効な元素であるが、多く添加すると溶接性を劣化するため、添加する場合は０．５０％を上限とする。
Cr: 0.50% or less Cr is an element effective for obtaining sufficient strength even at low C like Mn, but if added in a large amount, the weldability deteriorates, so when added, the upper limit is 0.50% And
Ｍｏ：０．５０％以下
Ｍｏは靭性の改善と強度の上昇に有効な元素であるが、多く添加すると溶接性が劣化するため、添加する場合は０．５０％を上限とする。
Mo: 0.50% or less Mo is an element effective for improving toughness and increasing strength, but if added in a large amount, weldability deteriorates, so when added, the upper limit is 0.50%.
Ｎｂ、Ｖ、Ｔｉの１種又は２種以上
Ｎｂ、ＶおよびＴｉは、鋼板の強度および靭性を高めるために添加する選択元素であり、要求強度に応じて、１種または２種以上を添加することができる。各元素とも、０．００５％未満では効果が無く、０．１％を超えると溶接部の靭性が劣化するので、添加する場合は０．００５〜０．１％の範囲とするのが好ましい。
［金属組織］
金属組織は、引張強度５２０ＭＰａ以上の高強度化を達成するために、板厚方向に均一な、ベイナイト組織の混合したベイナイト主体組織とする。ここでベイナイト組織とは、オーステナイト温度域から加速冷却することにより生成する変態組織であり、ベイニティックフェライトやグラニュラーベイナイトを含む。
One or more of Nb, V, and Ti Nb, V, and Ti are selective elements that are added to increase the strength and toughness of the steel sheet, and one or more of Nb, V, and Ti are added depending on the required strength. be able to. If each element is less than 0.005%, there is no effect, and if it exceeds 0.1%, the toughness of the welded portion deteriorates. Therefore, when added, the content is preferably in the range of 0.005 to 0.1%.
[Metal structure]
In order to achieve a high strength with a tensile strength of 520 MPa or more, the metal structure is a bainite main structure that is uniform in the plate thickness direction and mixed with the bainite structure. Here, the bainite structure is a transformation structure generated by accelerated cooling from the austenite temperature range, and includes bainitic ferrite and granular bainite.
少なくとも表層部がベイナイト組織の場合、表層硬さが低く、耐ＨＩＣ特性が向上する。表層部にマルテンサイトや島状マルテンサイト（ＭＡ）等の硬質相が生成すると、表層硬さが上昇し、耐ＨＩＣ特性が劣化するとともに、鋼板内の硬さのばらつきが増大して材質均一性が低下する。表層部とは鋼板表面から板厚方向に５ｍｍまでとする。 When at least the surface layer portion has a bainite structure, the surface layer hardness is low and the HIC resistance is improved. When a hard phase such as martensite or island martensite (MA) is formed in the surface layer, the surface layer hardness is increased, the HIC resistance is deteriorated, and the hardness variation in the steel sheet is increased, resulting in material uniformity. Decreases. The surface layer portion is defined as 5 mm in the plate thickness direction from the steel plate surface.
ベイナイト組織以外に、マルテンサイト、パーライト、島状マルテンサイト、セメンタイト、残留オーステナイトなどの金属組織が１種または２種以上混在すると、靭性劣化が生じ、表層硬さが上昇するため、これらの組織は少ない程良いが、体積分率で５％未満の場合には、それらの影響が無視できるため、本発明範囲内とする。 In addition to the bainite structure, when one or more metal structures such as martensite, pearlite, island martensite, cementite, and retained austenite are mixed, the toughness deteriorates and the surface hardness increases. The smaller the volume, the better. However, when the volume fraction is less than 5%, the influence thereof can be ignored, so it is within the scope of the present invention.
［硬さのばらつき］
板厚方向の硬さのばらつきは荷重１０ｋｇでのビッカース硬さ（以下、ＨＶ１０）でΔＨＶ１０２５以下、板幅方向の硬さのばらつきはΔＨＶ１０２５以下とする。ΔＨＶ１０は最高硬さと最低硬さの差とする。
[Hardness variation]
The variation in hardness in the sheet thickness direction is ΔH V10 25 or less in terms of Vickers hardness (hereinafter referred to as H V10 ) at a load of 10 kg, and the variation in hardness in the sheet width direction is defined as ΔH V10 25 or less. ΔH V10 is the difference between the highest hardness and the lowest hardness.
耐サワーラインパイプ用高強度鋼板の場合、鋼板の強度や伸び、成形性、耐ＨＩＣ性、耐ＳＣＣ性などを満足させる観点から、鋼板内の硬さのばらつき抑制が要求される。 In the case of a high-strength steel sheet for sour line pipes, from the viewpoint of satisfying the strength and elongation of the steel sheet, formability, HIC resistance, SCC resistance, etc., it is required to suppress variation in hardness within the steel sheet.
板厚方向の硬さのばらつきがΔＨＶ１０２５を超えた場合や、板幅方向の硬さのばらつきがΔＨＶ１０２５を超えた場合は、上記特性に悪影響を及ぼす。例えば、鋼板表層部の硬さが鋼板内部に比べてΔＨＶ１０２５を超えて硬くなった場合は、成形後にスプリングバックが起こりやすくなったり、硫化水素に対する割れ感受性が高まったりする。 When the variation in hardness in the plate thickness direction exceeds ΔH V10 25 or the variation in hardness in the plate width direction exceeds ΔH V10 25, the above characteristics are adversely affected. For example, when the hardness of the steel sheet surface layer part exceeds ΔH V10 25 as compared with the inside of the steel sheet, springback is likely to occur after forming, and cracking susceptibility to hydrogen sulfide is increased.
また、板幅方向の硬さのばらつきがΔＨＶ１０２５を超えた場合は、成形時に硬い部分と軟らかい部分での変形量の差が所望の形状が得られない程度となり、小板に切断した場合に小板毎の強度や伸びが異なったりする。 Also, if the variation in hardness in the plate width direction exceeds ΔH V10 25, the difference in deformation amount between the hard part and the soft part during molding is such that the desired shape cannot be obtained, and it is cut into small plates In addition, the strength and elongation of each platelet differ.
鋼板内の材質均一性と耐ＨＩＣ特性の観点からは、板厚方向の硬さのばらつきはΔＨＶ１０２０以下、板幅方向の硬さのばらつきはΔＨＶ１０２０以下であることがより好ましい。 From the viewpoint of material uniformity in the steel sheet and HIC resistance, it is more preferable that the variation in hardness in the thickness direction is ΔH V10 20 or less, and the variation in hardness in the plate width direction is ΔH V10 20 or less.
［硬さの最大値］
ＡＰＩ規格Ｘ６５グレードの強度を有する高強度鋼板において、鋼板表層部の硬さが上昇すると、水素誘起割れ（ＨＩＣ）を発生する危険性が高まる。鋼板表層部からの水素誘起割れ（ＨＩＣ）を抑制するために、鋼板表層部の硬さ（表面下１ｍｍでの硬さ）をＨＶ１０２２０以下とする。より厳しいサワー環境で鋼板が使用される場合には、耐サワー特性の観点から、鋼板表層部の硬さ（表面下１ｍｍでの硬さ）はＨＶ１０２１０以下とすることが好ましい。
[Maximum hardness]
In the high-strength steel sheet having the strength of API standard X65 grade, when the hardness of the steel sheet surface layer portion is increased, the risk of generating hydrogen induced cracking (HIC) increases. In order to suppress hydrogen-induced cracking (HIC) from the steel plate surface layer portion, the hardness of the steel plate surface layer portion (hardness at 1 mm below the surface) is set to H V10 220 or less. When a steel plate is used in a more severe sour environment, the hardness of the steel plate surface layer portion (hardness at 1 mm below the surface) is preferably H V10 210 or less from the viewpoint of sour resistance characteristics.
なお、冷間成形によりパイプとした後の鋼管表層部（表面下１ｍｍ）の硬さはＨＶ１０２３５以下であることが望ましい。より厳しいサワー環境で鋼板が使用される場合には、耐サワー特性の観点から、鋼板表層部の硬さ（表面下１ｍｍでの硬さ）はＨＶ１０２２５以下とすることが好ましい。これは冷間成形時の加工硬化量を考慮している。 It is desirable hardness of the steel tube surface portion after the pipe by cold forming (subsurface 1mm) is H V10 235 or less. When a steel plate is used in a more severe sour environment, it is preferable that the hardness (hardness at 1 mm below the surface) of the steel plate surface layer is HV10 225 or less from the viewpoint of sour resistance characteristics. This takes into account the work hardening amount during cold forming.
本発明に係る高強度鋼板は、熱間圧延し、制御冷却を施した後、再加熱して製造することができ、各工程における条件は以下の様である。
［スラブ加熱温度］
スラブ加熱温度は、１０００〜１３００℃とする。加熱温度が１０００℃未満では炭化物の固溶が不十分で必要な強度が得られず、１３００℃を超えると靭性が劣化するため、１０００〜１３００℃とする。なお、ここでの温度は加熱炉の炉内温度であり、スラブはこの温度に中心部まで十分に加熱されるものとする。
The high-strength steel sheet according to the present invention can be manufactured by hot rolling, control cooling, and then reheating, and the conditions in each step are as follows.
[Slab heating temperature]
Slab heating temperature shall be 1000-1300 degreeC. If the heating temperature is less than 1000 ° C., the solid solution of the carbide is insufficient and the required strength cannot be obtained, and if it exceeds 1300 ° C., the toughness deteriorates, so the temperature is set to 1000 to 1300 ° C. Here, the temperature is the furnace temperature of the heating furnace, and the slab is sufficiently heated to this temperature to the center.
［熱間圧延］
熱間圧延は、強度および耐ＨＩＣ性能の観点から、圧延終了温度を鋼板表面温度でＡｒ３温度以上とする。Ａｒ３温度は、以下の式で求めることができる。
[Hot rolling]
In the hot rolling, from the viewpoint of strength and HIC resistance, the rolling end temperature is set to the Ar 3 temperature or higher at the steel sheet surface temperature. The Ar 3 temperature can be obtained by the following equation.
Ａｒ３（℃）＝９１０−３１０Ｃ−８０Ｍｎ−２０Ｃｕ−１５Ｃｒ−５５Ｎｉ−８０Ｍｏ、但し、各元素記号は含有量（質量％）とする。 Ar 3 (° C.) = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo, where each element symbol is the content (% by mass).
また、高い母材靱性を得るためにはオーステナイト未再結晶温度域に相当する９５０℃以下の温度域での圧下率を６０％以上とすることが望ましい。なお、鋼板の表面温度は放射温度計等で測定することができる。 In order to obtain high base metal toughness, it is desirable that the rolling reduction in a temperature range of 950 ° C. or lower corresponding to the austenite non-recrystallization temperature range be 60% or more. In addition, the surface temperature of a steel plate can be measured with a radiation thermometer or the like.
［デスケーリング］
熱間圧延後、制御冷却の直前に鋼板表面での噴射流の衝突圧を１ＭＰａ以上とする高衝突圧のデスケーリングを行う。鋼板表面での噴射流の衝突圧が１ＭＰａ未満では、デスケーリングが不十分でスケールむらが生じる場合があり、表層硬さのばらつきが生じるため、１ＭＰａ以上とする。
[Descaling]
After hot rolling, just before controlled cooling, high impact pressure descaling is performed so that the impact pressure of the jet flow on the steel sheet surface is 1 MPa or more. If the impinging pressure of the jet flow on the steel sheet surface is less than 1 MPa, descaling may be insufficient and unevenness in scale may occur, resulting in variations in surface hardness.
制御冷却直前に鋼板表面での噴射流の衝突圧を種々に変化させた予備試験を行い、デスケーリング冷却後の鋼板のスケール厚みが１５μｍ以下となる噴射流の衝突圧として１ＭＰａ以上を求めた。制御冷却後の鋼板のスケール厚さで１５μｍ以下とした場合、板厚方向の硬さのばらつきをΔＨＶ１０２５以下、且つ板幅方向の硬さのばらつきをΔＨＶ１０２５以下とすることが可能である。 Immediately before the controlled cooling, a preliminary test was performed in which the collision pressure of the jet flow on the surface of the steel sheet was changed in various ways, and the collision pressure of the jet flow at which the scale thickness of the steel sheet after descaling cooling was 15 μm or less was determined to be 1 MPa or more. When the scale thickness of the steel plate after controlled cooling is 15 μm or less, it is possible to make the hardness variation in the plate thickness direction ΔH V10 25 or less and the hardness variation in the plate width direction be ΔH V10 25 or less. is there.
デスケーリングは高圧水を用いて行うが、鋼板表面での噴射流の衝突圧が１ＭＰａ以上であれば、他の噴射流を用いても構わない。
［制御冷却］
制御冷却の冷却開始温度は鋼板表面温度で（Ａｒ３−１０℃）以上とする。冷却開始時の鋼板表面温度が低いと、制御冷却前のフェライト生成量が多くなり、Ａｒ３変態点からの温度低下が１０℃を超えると５％を超えるフェライトが生成する虞があり、強度が低下するとともに耐サワー特性が劣化するため、冷却開始時の鋼板表面温度は（Ａｒ３−１０℃）以上とする。
Descaling is performed using high-pressure water, but other jet streams may be used as long as the collision pressure of the jet stream on the steel sheet surface is 1 MPa or more.
[Controlled cooling]
The cooling start temperature of controlled cooling is (Ar 3 −10 ° C.) or higher in terms of the steel sheet surface temperature. If the steel sheet surface temperature at the start of cooling is low, the amount of ferrite produced before controlled cooling increases, and if the temperature drop from the Ar 3 transformation point exceeds 10 ° C., ferrite exceeding 5% may be produced, and the strength is high. Since the sour resistance characteristics deteriorate with decreasing, the steel sheet surface temperature at the start of cooling is set to (Ar 3 -10 ° C) or higher.
[冷却速度]
鋼板表面の冷却速度が２００℃/s以下、且つ鋼板の平均の冷却速度が１５℃/s以上とする。高強度化を図りつつ、鋼板内の硬さのばらつきを低減し、材質均一性を向上させるためには、表層部の冷却速度と鋼板の平均冷却速度の両方を制御することが重要である。鋼板の平均冷却速度とは、板厚方向の冷却速度の平均値を指す。
[Cooling rate]
The cooling rate of the steel sheet surface is 200 ° C./s or less, and the average cooling rate of the steel plate is 15 ° C./s or more. It is important to control both the cooling rate of the surface layer part and the average cooling rate of the steel sheet in order to reduce the variation in hardness in the steel sheet and improve the material uniformity while increasing the strength. The average cooling rate of a steel sheet refers to the average value of cooling rates in the thickness direction.
鋼板表面の冷却速度が２００℃/sを超えると、マルテンサイトや島状マルテンサイト（ＭＡ）等の硬質相が生成して、表層硬さが上昇するとともに耐サワー特性が劣化するため、鋼板表面の冷却速度は、２００℃/s以下とする。好ましくは、１５０℃/s以下である。 When the cooling rate of the steel sheet surface exceeds 200 ° C / s, a hard phase such as martensite and island martensite (MA) is generated, and the surface layer hardness increases and the sour resistance property deteriorates. The cooling rate is set to 200 ° C./s or less. Preferably, it is 150 ° C./s or less.
また、鋼板の平均冷却速度が１５℃/s未満では、ベイナイト組織が得られずに強度低下や耐サワー特性が劣化したり、硬さのばらつきが大きくなるため、鋼板の平均冷却速度は１５℃/s以上とする。より好ましくは、２０℃/s以上である。 Further, if the average cooling rate of the steel sheet is less than 15 ° C / s, the average cooling rate of the steel sheet is 15 ° C because the bainite structure is not obtained, the strength is lowered, the sour resistance is deteriorated, and the hardness is increased. / s or more. More preferably, it is 20 ° C./s or more.
さらに、鋼板表面の冷却速度が２００℃/s以下、且つ鋼板の平均冷却速度が１５℃/s以上とすることにより、冷却停止温度のばらつきを抑制することができ、鋼板形状が良好となる。 Furthermore, when the cooling rate of the steel plate surface is 200 ° C./s or less and the average cooling rate of the steel plate is 15 ° C./s or more, variation in the cooling stop temperature can be suppressed, and the steel plate shape is improved.
[冷却停止温度]
冷却停止温度は、鋼板の平均温度で２５０〜５５０℃とする。圧延終了後、制御冷却でベイナイト変態の温度域である２５０〜５５０℃まで急冷することにより、ベイナイト相を生成させる。なお、鋼板の平均温度は、鋼板板厚方向に温度分布がある場合は、その断面内で平均した温度である。
[Cooling stop temperature]
Cooling stop temperature shall be 250-550 degreeC by the average temperature of a steel plate. After rolling, the bainite phase is generated by quenching to 250 to 550 ° C., which is the temperature range of bainite transformation, by controlled cooling. In addition, the average temperature of a steel plate is the temperature averaged in the cross section, when there exists temperature distribution in the steel plate thickness direction.
冷却停止温度が５５０℃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、冷却停止温度が２５０℃未満では、マルテンサイトや島状マルテンサイト（ＭＡ）が生成し、特に鋼板表層部の硬さ上昇が著しくなり、硬さのばらつきが大きくなるとともに耐サワー特性が劣化する。さらに、鋼板に歪みを生じやすくなり、成形性が劣化する。 When the cooling stop temperature exceeds 550 ° C., the bainite transformation is incomplete and sufficient strength cannot be obtained. Further, when the cooling stop temperature is less than 250 ° C., martensite and island martensite (MA) are generated, and particularly the hardness of the surface layer portion of the steel sheet is remarkably increased, so that the variation in hardness is increased and the sour resistance is deteriorated. To do. Further, the steel sheet is easily distorted, and formability deteriorates.
従って、鋼板内の材質均一性と耐サワー特性の劣化を抑制するため、制御冷却の冷却停止温度は２５０〜５５０℃とする。なお、加速冷却後に生じた鋼板表面温度と鋼板中心温度との差は、しばらくすると熱伝導によって鋼板内でほぼ均一な温度分布となるため、冷却停止温度は、冷却後均熱化された鋼板の鋼板表面温度としても良い。 Therefore, the cooling stop temperature of the controlled cooling is set to 250 to 550 ° C. in order to suppress deterioration of material uniformity and sour resistance in the steel plate. Note that the difference between the steel plate surface temperature and the steel plate center temperature generated after accelerated cooling becomes a substantially uniform temperature distribution within the steel plate due to heat conduction after a while, so the cooling stop temperature is the temperature of the steel plate soaked after cooling. It is good also as steel plate surface temperature.
[再加熱温度]
加速冷却後、直ちに誘導加熱により、冷却停止温度以上であって且つ鋼板表面温度で５００〜７００℃、鋼板平均温度で３５０〜６００℃まで再加熱を行う。再加熱により表層部を焼戻すため、再加熱温度は冷却停止温度以上とする。ここで、誘導加熱装置を用いるのは、急速な加熱が可能で、鋼板の加熱温度を鋼板表層部と板厚中央部とで変化させることが可能であるためである。
[Reheating temperature]
Immediately after accelerated cooling, reheating is performed by induction heating to a temperature equal to or higher than the cooling stop temperature, to a steel plate surface temperature of 500 to 700 ° C., and to a steel plate average temperature of 350 to 600 ° C. In order to temper the surface layer portion by reheating, the reheating temperature is set to the cooling stop temperature or higher. Here, the induction heating device is used because rapid heating is possible, and the heating temperature of the steel sheet can be changed between the steel sheet surface layer part and the plate thickness center part.
高冷却速度の加速冷却によって表層部の一部に硬質相が生成した場合でも、鋼板表層部の加熱によって硬質相が分解され、表層部の硬さが低減される。しかし、鋼板表面温度が５００℃未満では硬質相の分解が十分でないため、硬さ低下が不十分であり、一方、７００℃を超えると、鋼板中央部の加熱温度も上昇するため大きな強度低下を招く。従って、誘導加熱による再加熱での鋼板表面温度は５００〜７００℃とする。 Even when a hard phase is generated in a part of the surface layer portion by accelerated cooling at a high cooling rate, the hard phase is decomposed by heating the surface layer portion of the steel sheet, and the hardness of the surface layer portion is reduced. However, if the steel sheet surface temperature is less than 500 ° C., the hard phase is not sufficiently decomposed, so that the hardness is insufficiently reduced. Invite. Therefore, the steel sheet surface temperature in reheating by induction heating is set to 500 to 700 ° C.
また、誘導加熱により表層部を加熱し、熱伝導によって鋼板内部が加熱されるため、鋼板内部よりも表層部の温度が高くなるが、鋼板平均温度の上昇を抑制し、表層部の硬さを効果的に低減するために、誘導加熱による鋼板表面温度は、鋼板平均温度よりも１００℃以上高い温度とすることが望ましい。 In addition, the surface layer part is heated by induction heating, and the inside of the steel sheet is heated by heat conduction, so the temperature of the surface layer part becomes higher than the inside of the steel sheet, but the increase in the average temperature of the steel sheet is suppressed, and the hardness of the surface layer part is increased. In order to reduce effectively, it is desirable that the surface temperature of the steel plate by induction heating is higher than the average temperature of the steel plate by 100 ° C or more.
加速冷却後の誘導加熱によって、鋼板表層部だけでなく鋼板内部の強度ばらつきも低減できる。しかし、鋼板中央部の加熱温度が３５０℃未満ではバラツキの低減が不十分であり、一方、６００℃を超えると、焼戻しによる強度低下をまねくだけでなく、ＤＷＴＴ性能が劣化する。従って、誘導加熱による再加熱での鋼板の平均温度は３５０〜６００℃とする。 By induction heating after accelerated cooling, not only the surface layer portion of the steel sheet but also the strength variation inside the steel sheet can be reduced. However, when the heating temperature at the central part of the steel sheet is less than 350 ° C., the variation is insufficiently reduced. On the other hand, when it exceeds 600 ° C., not only does the strength decrease due to tempering, but also the DWTT performance deteriorates. Therefore, the average temperature of the steel sheet during reheating by induction heating is set to 350 to 600 ° C.
更に強度のバラツキ低減やＤＷＴＴ性能の劣化を抑制するためには、誘導加熱による再加熱での鋼板の平均温度を４００〜５５０℃の範囲とすることが望ましい。 Furthermore, in order to suppress the variation in strength and the deterioration of the DWTT performance, it is desirable that the average temperature of the steel sheet in the reheating by induction heating is in the range of 400 to 550 ° C.
誘導加熱直後に生じた鋼板表面温度と鋼板中心温度の差は、しばらくすると熱伝導によって鋼板内でほぼ均一な温度分布となるため、誘導加熱後均熱化された鋼板の鋼板表面温度としても良い。 Since the difference between the steel plate surface temperature and the steel plate center temperature generated immediately after induction heating becomes a substantially uniform temperature distribution in the steel plate due to heat conduction after a while, it may be the steel plate surface temperature of the steel plate soaked after induction heating. .
再加熱温度において、特に温度保持時間を設定する必要はなく、再加熱温度に到達後、直ちに冷却してもよい。再加熱温度に保持する場合は、３０分を超えて温度保持を行うと強度低下を招く場合があるので、３０分以内とすることが望ましい。また、再加熱後の冷却速度は任意に適宜選定してよいが、急冷すると鋼板形状が劣化する場合があるので、空冷が望ましい。 In the reheating temperature, it is not necessary to set the temperature holding time in particular, and it may be cooled immediately after reaching the reheating temperature. In the case where the temperature is maintained at the reheating temperature, if the temperature is maintained for more than 30 minutes, the strength may be reduced. Moreover, although the cooling rate after reheating may be selected arbitrarily, air cooling is desirable because the steel plate shape may deteriorate when rapidly cooled.
図１に本発明に係る鋼板の製造に好適な設備の一例を示す。圧延ライン１には上流から下流側に向かって熱間圧延機２、高衝突圧デスケーリング装置３、制御冷却装置４、インライン型誘導加熱装置５を配置する。また、高衝突圧デスケーリング装置３の前に熱間矯正機を設置しても良い。 FIG. 1 shows an example of equipment suitable for manufacturing a steel sheet according to the present invention. In the rolling line 1, a hot rolling mill 2, a high collision pressure descaling device 3, a control cooling device 4, and an in-line induction heating device 5 are arranged from upstream to downstream. A hot straightening machine may be installed in front of the high collision pressure descaling device 3.
熱間矯正機で鋼板６の形状を改善することにより、噴射流の衝突圧を増大させることができるため、低コストでより効率的にデスケーリングを行うことができる。 By improving the shape of the steel plate 6 with a hot straightening machine, it is possible to increase the collision pressure of the jet flow, and therefore it is possible to perform descaling more efficiently at a low cost.
インライン型誘導加熱装置５を圧延ライン上に設置するので、圧延および冷却終了後の鋼板を迅速に再加熱処理することができる。すなわち、圧延して加速冷却した後の鋼板を、冷却停止温度から過度に冷却させることなく、直ちに冷却停止温度以上であって且つ鋼板表面温度で５００〜７００℃、鋼板平均温度で３５０〜６００℃まで再加熱を行うことができる。 Since the in-line induction heating device 5 is installed on the rolling line, the steel sheet after the completion of rolling and cooling can be quickly reheated. That is, the steel sheet after rolling and accelerated cooling is immediately over the cooling stop temperature without being excessively cooled from the cooling stop temperature, and the steel sheet surface temperature is 500 to 700 ° C., and the steel sheet average temperature is 350 to 600 ° C. Can be reheated.
また、インライン型誘導加熱装置５の前に熱間矯正機を設置しても良い。熱間矯正機で鋼板の形状が改善するとともに、誘導加熱装置での再加熱をより均一にすることができる。 A hot straightening machine may be installed in front of the inline type induction heating device 5. While the shape of the steel sheet is improved by the hot straightening machine, the reheating by the induction heating device can be made more uniform.
本発明によれば、制御冷却の直前に高衝突圧デスケーリングを行い、制御冷却の直後に誘導加熱で再加熱処理を行うことにより、板厚方向の硬さのばらつきがΔＨＶ１０２５以下、板幅方向の硬さのばらつきがΔＨＶ１０２５以下とすることができる。 According to the present invention, high impact pressure descaling is performed immediately before the control cooling, and reheating treatment is performed by induction heating immediately after the control cooling, whereby the variation in hardness in the plate thickness direction is ΔH V10 25 or less, the plate The variation in the hardness in the width direction can be ΔH V10 25 or less.
さらに、密着性の良い均一な薄スケールが形成されるため、再加熱処理した鋼板に生じ易いスケールの剥離を抑制し、鋼板内の材質均一性に優れ、且つスケールの耐剥離性に優れた耐サワーラインパイプ用高強度鋼板を製造することができる。 Furthermore, since a uniform thin scale with good adhesion is formed, scale peeling that is likely to occur in a reheat-treated steel sheet is suppressed, excellent material uniformity within the steel sheet, and excellent resistance to scale peeling. High strength steel sheets for sour line pipes can be manufactured.
本発明に係る高強度鋼板を、プレスベンド成形、ロール成形、ＵＯＥ成形等で管状に成形した後、突き合わせ部を溶接することにより、鋼板内の材質均一性に優れ、高強度かつ耐ＨＩＣ特性に優れた硫化水素を含む原油や天然ガスの輸送に好適な耐サワーラインパイプ用高強度鋼管（ＵＯＥ鋼管、電縫鋼管、スパイラル鋼管等）を製造することができる。 The high-strength steel sheet according to the present invention is formed into a tubular shape by press bend forming, roll forming, UOE forming, etc., and then the butt portion is welded to provide excellent material uniformity in the steel sheet, high strength, and HIC resistance. High-strength steel pipes for sour line pipes (UOE steel pipes, ERW steel pipes, spiral steel pipes, etc.) suitable for transporting crude oil and natural gas containing excellent hydrogen sulfide can be manufactured.
例えば、ＵＯＥ鋼管は、鋼板の端部を開先加工し、Ｃプレス、Ｕプレス、Ｏプレスで鋼管形状に成形した後、内面溶接および外面溶接で突き合わせ部をシーム溶接し、さらに必要に応じて拡管工程を経て製造される。また、溶接方法は十分な継手強度と継手靭性が得られる方法であれば、いずれの方法でも良いが、優れた溶接品質と製造能率の観点から、サブマージアーク溶接を用いることが好ましい。 For example, in UOE steel pipe, the end of a steel plate is grooved and formed into a steel pipe shape by C press, U press, and O press, and then the butt portion is seam welded by inner surface welding and outer surface welding. Manufactured through a tube expansion process. Any welding method may be used as long as sufficient joint strength and joint toughness can be obtained, but it is preferable to use submerged arc welding from the viewpoint of excellent welding quality and manufacturing efficiency.
表１に示す化学成分の鋼（鋼種Ａ〜Ｌ）を連続鋳造法によりスラブとし、これを用いて板厚２５ｍｍと３４ｍｍの厚鋼板（Ｎｏ．１〜２７）を製造した。 Steel of chemical composition shown in Table 1 (steel types A to L) was made into a slab by a continuous casting method, and thick steel plates (No. 1 to 27) having a thickness of 25 mm and 34 mm were manufactured using this.
スラブを加熱後、熱間圧延により所定の板厚とした後直ちに、あるいは制御冷却直前に高衝突圧のデスケーリングを行った後、水冷型の制御冷却装置を用いて冷却を行った。 After the slab was heated, immediately after it was made to have a predetermined thickness by hot rolling, or after descaling the high collision pressure just before the controlled cooling, cooling was performed using a water-cooled control cooling device.
得られた鋼板のミクロ組織およびスケール性状を、光学顕微鏡および走査型電子顕微鏡により観察した。１０視野の断面組織写真を得て、スケール厚さを測定し、１０視野の平均値で評価した。 The microstructure and scale properties of the obtained steel sheet were observed with an optical microscope and a scanning electron microscope. A cross-sectional structure photograph of 10 fields of view was obtained, the scale thickness was measured, and the average value of 10 fields of view was evaluated.
また、各鋼板の引張特性、硬さ、耐ＨＩＣ特性およびスケールの耐剥離性を測定した。引張特性は、圧延垂直方向の全厚試験片を引張試験片として引張試験を行い、引張強度を測定した。 Further, the tensile properties, hardness, HIC resistance, and scale peel resistance of each steel plate were measured. Tensile properties were measured by performing a tensile test using a full thickness test piece in the vertical direction of rolling as a tensile test piece, and measuring the tensile strength.
また、ビッカース硬度計で板厚方向の硬さと板幅方向の硬さを測定した。板厚方向の硬さは１ｍｍピッチで全厚を測定し、板幅方向の硬さは２０ｍｍピッチで全幅を測定した。なお、板幅方向の硬さは、表層１ｍｍ位置（表層から板厚（ｔ）方向へ１ｍｍ）、板厚（ｔ）／４位置、板厚（ｔ）／２位置（板厚中心部）で測定したが、いずれの鋼板も表層１ｍｍ位置において硬さのばらつきが最大を示したので、板幅方向の硬さのばらつきは表層１ｍｍ位置で評価した。硬さの測定はいずれも荷重１０ｋｇでおこなった。 Further, the hardness in the plate thickness direction and the hardness in the plate width direction were measured with a Vickers hardness tester. The thickness in the thickness direction was measured at a pitch of 1 mm, and the total thickness was measured at a pitch of 20 mm. In addition, the hardness in the plate width direction is the surface layer 1 mm position (1 mm from the surface layer to the plate thickness (t) direction), plate thickness (t) / 4 position, plate thickness (t) / 2 position (plate thickness center). Although measured, all the steel plates showed the largest variation in hardness at the surface layer position of 1 mm, so the variation in hardness in the plate width direction was evaluated at the surface layer position of 1 mm. The hardness was measured at a load of 10 kg.
耐ＨＩＣ特性は、ＮＡＣＥ Ｓｔａｎｄａｒｄ ＴＭ−０２−８４に準じた浸漬時間９６時間のＨＩＣ試験を行い、割れが認められない場合を耐ＨＩＣ特性良好と判断して○で、割れが発生した場合を×として評価した。 The HIC resistance was evaluated by performing an HIC test with an immersion time of 96 hours in accordance with NACE Standard TM-02-84. If no crack was observed, the HIC resistance was judged good. As evaluated.
スケールの耐剥離性は、鋼板のスケール表面に碁盤目状に切込みを入れた後にテープ剥離を行う碁盤目試験を実施し、スケールの剥離が無い場合を○、剥離がある場合を×としてスケールの耐剥離性を評価した。 The peel resistance of the scale is determined by conducting a cross-cut test in which the tape is peeled after making a grid-like cut on the scale surface of the steel sheet. The peel resistance was evaluated.
ＤＷＴＴ性能は、鋼板の板厚中心で表裏両面から１９ｍｍに減厚したＤＷＴＴ試験片を用いて−３７℃の試験温度で落重試験を実施し、延性破面率で評価した。 The DWTT performance was evaluated by performing a drop weight test at a test temperature of −37 ° C. using a DWTT test piece whose thickness was reduced to 19 mm from both the front and back surfaces at the center of the plate thickness of the steel sheet, and evaluated by the ductile fracture surface ratio.
本発明範囲は、高強度鋼板として引張強度５２０ＭＰａ以上、表層１ｍｍ位置とｔ／２位置ともミクロ組織はベイナイト組織、板厚方向と板幅方向の硬さのばらつきはΔＨＶ１０２５以下、ＨＩＣ試験で割れが認められない、スケールの耐剥離性が良好、およびＤＷＴＴ性能が延性破面率８５％以上とした。
各鋼板（Ｎｏ．１〜２７）の製造条件と測定結果を表２に併せて示す。
The scope of the present invention is that the tensile strength is 520 MPa or more as a high-strength steel plate, the microstructure is a bainite structure at both the 1 mm position and the t / 2 position of the surface layer, the variation in hardness in the plate thickness direction and the plate width direction is ΔH V10 25 or less, No cracks were observed, the peel resistance of the scale was good, and the DWTT performance was a ductile fracture surface ratio of 85% or more.
The manufacturing conditions and measurement results for each steel plate (No. 1 to 27) are shown in Table 2.
Ｎｏ.１〜１２は、化学成分および製造方法が本発明の範囲内の本発明例である。いずれも、引張強度５２０ＭＰａ以上、板厚方向と板幅方向の硬さのばらつきはΔＨＶ１０２５以下で、且つ鋼板のミクロ組織は、表層１ｍｍ位置とｔ／２位置ともベイナイト組織であり、耐ＨＩＣ特性、スケールの耐剥離性およびＤＷＴＴ性能も良好であった。 Nos. 1 to 12 are examples of the present invention in which chemical components and production methods are within the scope of the present invention. In any case, the tensile strength is 520 MPa or more, the variation in hardness in the sheet thickness direction and the sheet width direction is ΔH V10 25 or less, and the microstructure of the steel sheet is a bainite structure in both the 1 mm position of the surface layer and the t / 2 position. Properties, scale peel resistance and DWTT performance were also good.
一方、Ｎｏ.１３〜２２は、化学成分は本発明の範囲内であるが、製造方法が本発明の範囲外の実施例である。Ｎｏ.１３は、スラブ加熱温度が低く、ミクロ組織の均質化と炭化物の固溶が不十分であり低強度であった。 On the other hand, Nos. 13 to 22 are examples whose chemical components are within the scope of the present invention, but whose production methods are outside the scope of the present invention. In No. 13, the slab heating temperature was low, the homogenization of the microstructure and the solid solution of carbides were insufficient, and the strength was low.
Ｎｏ.１４は、冷却開始温度が低く、フェライトが析出したため、低強度であり、且つ耐ＨＩＣ特性が劣っていた。Ｎｏ.１５は、制御冷却条件が本発明範囲外で、ミクロ組織として板厚中心部でベイナイト組織が得られず、パーライトが析出したため、低強度であり、且つ耐ＨＩＣ特性が劣っていた。 No. 14 had a low cooling start temperature and ferrite precipitated, so that it had low strength and inferior HIC resistance. In No. 15, the controlled cooling condition was outside the range of the present invention, and a bainite structure was not obtained as the microstructure at the center of the plate thickness, and pearlite was precipitated, so that the strength was low and the HIC resistance was inferior.
Ｎｏ.１６は、冷却停止温度が低く、マルテンサイトや島状マルテンサイト（ＭＡ）の硬質相が生成したため、鋼板表層部の最高硬さがＨＶ１０２２０を超えて、板厚方向と板幅方向の硬さのばらつきもΔＨＶ１０２５を超えており、鋼板内の材質均一性と耐ＨＩＣ特性が劣っていた。 No. 16 has a low cooling stop temperature, and a hard phase of martensite or island-like martensite (MA) was generated. Therefore, the maximum hardness of the steel sheet surface layer part exceeded HV10 220, and the thickness direction and the sheet width direction The hardness variation of the steel sheet also exceeded ΔH V10 25, and the material uniformity in the steel sheet and the HIC resistance were inferior.
Ｎｏ.１７は、制御冷却直前のデスケーリングの衝突圧が低く、且つ冷制御却条件が本発明範囲外であるため、鋼板表層部の最高硬さがＨＶ１０２２０を超えて、硬さのばらつきもΔＨＶ１０２５を超えて鋼板内の材質均一性に劣っており、スケールの耐剥離性も劣っていた。 No. 17 has a low descaling collision pressure just before the control cooling and the cooling control rejection condition is outside the scope of the present invention. Therefore, the maximum hardness of the steel sheet surface layer exceeds HV10 220 and the hardness varies. Further, ΔH V10 25 was exceeded, the material uniformity in the steel sheet was inferior, and the scale peel resistance was also inferior.
Ｎｏ.１８〜Ｎｏ.２０は、いずれも制御冷却直前のデスケーリングを行っていなか、衝突圧が低いため、表層部の冷却速度が増加してマルテンサイトが生成し、鋼板表層部の最高硬さがＨＶ１０２２０を超えて、板厚方向と板幅方向の硬さのばらつきもΔＨＶ１０２５を超えており、鋼板内の材質均一性と耐ＨＩＣ特性およびスケールの耐剥離性が劣っていた。 No. 18 to No. 20 were not subjected to descaling immediately before control cooling, and because the collision pressure was low, the cooling rate of the surface layer portion increased, martensite was generated, and the maximum hardness of the steel plate surface layer portion Exceeds HV10 220, and the variation in hardness in the plate thickness direction and the plate width direction also exceeds ΔH V10 25, and the material uniformity in the steel sheet, the HIC resistance, and the scale peel resistance were inferior.
Ｎｏ.２１は、再加熱温度が低く本発明範囲外であり、鋼板表層部の最高硬さがＨＶ１０２２０を超えて、硬さのばらつきもΔＨＶ１０２５を超えており、鋼板内の材質均一性に劣っていた。Ｎｏ.２２は、再加熱温度が高く、板厚中心部でセメンタイトが粗大析出するため、ＤＷＴＴ性能が劣っていた。Ｎｏ.２３〜Ｎｏ.２７は、化学成分が本発明の範囲外であり、鋼板表層部の最高硬さがＨＶ１０２２０を超えて、硬さのばらつきがΔＨＶ１０２５を超えているか、耐ＨＩＣ特性が劣っていた。 No. 21 has a low reheating temperature and is outside the scope of the present invention, the maximum hardness of the steel sheet surface layer portion exceeds H V10 220, and the hardness variation also exceeds ΔH V10 25. It was inferior. No. 22 had a high reheating temperature, and cementite precipitated coarsely at the center of the plate thickness, so the DWTT performance was inferior. No.23~No.27, the chemical component is outside the scope of the present invention, or maximum hardness of the steel sheet surface layer portion exceeds the H V10 220, variation in hardness is greater than [Delta] H V10 25, HIC resistant The characteristics were inferior.
１ 圧延ライン
２ 熱間圧延機
３ 高衝突圧デスケーリング装置
４ 制御冷却装置
５ インライン型誘導加熱装置
６ 鋼板
DESCRIPTION OF SYMBOLS 1 Rolling line 2 Hot rolling mill 3 High collision pressure descaling device 4 Control cooling device 5 Inline type induction heating device 6 Steel plate
Claims (6)
ＣＰ＝４．４６Ｃ（％）＋２．３７Ｍｎ（％）＋｛１．７４Ｃｕ（％）＋１．７Ｎｉ（％）｝／１５＋｛１．１８Ｃｒ（％）＋１．９５Ｍｏ（％）＋１．７４Ｖ（％）｝／５＋２２．３６Ｐ（％） ・・・（１）
但し、式において各元素記号は含有量（質量％）。 The CP value (mass%) represented by the following formula (1) is 1.0 or less, and is excellent in material uniformity in the steel sheet according to any one of claims 1 to 3. High strength steel plate for sour line pipes.
CP = 4.46C (%) + 2.37Mn (%) + {1.74Cu (%) + 1.7Ni (%)} / 15+ {1.18Cr (%) + 1.95Mo (%) + 1.74V (%) } /5+22.36P (%) (1)
However, each element symbol in the formula is the content (% by mass).
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