JP2012077325A - High strength steel sheet for line pipe and method for producing the same, and high strength steel pipe using high strength steel sheet for line pipe - Google Patents
High strength steel sheet for line pipe and method for producing the same, and high strength steel pipe using high strength steel sheet for line pipe Download PDFInfo
- Publication number
- JP2012077325A JP2012077325A JP2010221496A JP2010221496A JP2012077325A JP 2012077325 A JP2012077325 A JP 2012077325A JP 2010221496 A JP2010221496 A JP 2010221496A JP 2010221496 A JP2010221496 A JP 2010221496A JP 2012077325 A JP2012077325 A JP 2012077325A
- Authority
- JP
- Japan
- Prior art keywords
- less
- steel sheet
- steel
- mass
- cooling
- 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.)
- Granted
Links
Images
Landscapes
- Heat Treatment Of Steel (AREA)
Abstract
Description
本発明は、建築、海洋構造物、造船、土木、建設産業用機械の分野のラインパイプに使用して好適な、鋼板内の材質均一性に優れたラインパイプ用高強度鋼板及びその製造方法に関するものである。
また、本発明は、上記のラインパイプ用高強度鋼板を用いた高強度鋼管に関するものである。
The present invention relates to a high-strength steel plate for line pipes excellent in material uniformity in a steel plate and a method for producing the same, which is suitable for use in line pipes in the fields of architecture, offshore structures, shipbuilding, civil engineering, and construction industry machines. Is.
The present invention also relates to a high-strength steel pipe using the above-described high-strength steel sheet for line pipes.
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。鋼板の特性の向上や合金元素の削減、さらには熱処理の省略などを目的として、通常、高強度鋼板の製造に際しては、制御圧延と制御冷却を組み合わせた、いわゆるTMCP技術が適用されている。この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。
特に、ラインパイプ用高強度鋼板では、外面での耐応力腐食割れ性(耐SCC性)や溶接部割れ防止の観点から鋼板表層部の硬さを抑制する技術が求められており、また強度や成形性の観点から、鋼板内の材質均一性の確保は重要な課題である。
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, the so-called TMCP technique, which combines controlled rolling and controlled cooling, is usually applied in the production of high-strength steel sheets. In order to increase the strength of steel using this 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.
In particular, for high-strength steel sheets for line pipes, a technique for suppressing the hardness of the steel sheet surface layer from the viewpoint of stress corrosion cracking resistance (SCC resistance) on the outer surface and cracking of welded parts is required. From the viewpoint of formability, securing the material uniformity within the steel sheet is an important issue.
上記の問題や課題を解決するために、従来から種々の解決策が提案されている。例えば特許文献1には、制御冷却に際して、冷却速度を3〜12℃/sという比較的低い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。
また、特許文献2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、板厚方向の材質差が小さい鋼板の製造方法が開示されている。
さらに、特許文献3,4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うことにより、板厚方向の材質差が小さい鋼板の製造方法が開示されている。
In order to solve the above problems and problems, various solutions have been proposed. For example, Patent Document 1 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. .
Patent Document 2 discloses that the structure of the steel sheet is made into a two-phase structure of ferrite and bainite by waiting in the temperature range where ferrite precipitates during the cooling process, and the difference in hardness between the surface layer and the center of the sheet thickness is indicated. A method for producing a reduced steel sheet with a small material difference in the thickness direction is disclosed.
Furthermore, in Patent Documents 3 and 4, after rolling, by performing controlled cooling at a high cooling rate that reheats the surface before the surface layer portion completes the bainite transformation, the manufacture of a steel sheet with a small material difference in the thickness direction is produced. A method is disclosed.
他方、鋼板表面のスケール性状にむらがあった場合、冷却時の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が生じ、ひいては鋼板内で局所的に冷却停止温度のばらつきが生じる結果、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ことになる。
これに対し、特許文献5,6には、冷却直前にデスケーリングを行うことにより、スケール性状に起因した冷却むらを低減して、鋼板形状を改善する方法が開示されている。
On the other hand, if there is unevenness in the scale properties of the steel sheet surface, the cooling rate of the steel sheet below varies depending on the scale thickness during cooling, and as a result, the cooling stop temperature varies locally within the steel sheet. The steel plate material varies in the plate width direction corresponding to the scale properties.
On the other hand,
しかしながら、特許文献1に記載の技術では、冷却速度が制限されるため、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。また、特許文献2に開示の製造方法は、Ar3変態点以下での冷却待機でフェライトを析出させるものであるため、強度が低下するだけでなく、冷却待機時間が必要になるため製造効率が悪化する。さらに、特許文献3,4に記載の製造方法では、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。しかも、高精度な冷却制御を必要とするため、適用範囲が限られると共に、製造効率の低下を余儀なくされる。 However, in the technique described in Patent Document 1, since the cooling rate is limited, it is possible to fully utilize the effects of controlled cooling such as high strength by high cooling rate, reduction of alloy elements, simplified control rolling, and the like. Can not. In addition, since the manufacturing method disclosed in Patent Document 2 deposits ferrite in a cooling standby at an Ar 3 transformation point or lower, not only the strength is reduced, but a cooling standby time is required, so that the manufacturing efficiency is improved. Getting worse. Furthermore, in the manufacturing methods described in Patent Documents 3 and 4, if the transformation behavior differs depending on the components of the steel sheet, sufficient material homogenization effect due to recuperation may not be obtained. In addition, since highly accurate cooling control is required, the application range is limited, and the production efficiency is inevitably reduced.
他方、特許文献5,6に記載の方法では、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は何ら配慮がなされていない。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いて硬さのばらつきが生じるおそれがある。すなわち、冷却速度が遅い場合、鋼板表面が冷却する際に、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、表面の冷却速度がばらつくおそれがある。そのため、鋼板表面の硬さにばらつきを生じることになる。
一方、鋼板の高強度化を図るために、冷却速度を速くした場合、表面の冷却停止温度のばらつきは低減し、鋼板の表層部の硬さは向上する。しかしながら、鋼板の表層部の硬さは、スケール厚さの影響も鋭敏に受けるため、高冷却速度で冷却する場合は、スケール厚さを均一にしておくことが課題となる。
On the other hand, the methods described in
On the other hand, when the cooling rate is increased in order to increase the strength of the steel sheet, the variation in the surface cooling stop temperature is reduced, and the hardness of the surface layer portion of the steel sheet is improved. However, since the hardness of the surface layer portion of the steel plate is also sensitively influenced by the scale thickness, it is a problem to keep the scale thickness uniform when cooling at a high cooling rate.
本発明は、上記の現状に鑑み開発されたもので、鋼板の板厚方向および板幅方向の硬さのばらつきを効果的に軽減して、鋼板内の材質均一性を向上させつつ、スケール厚さのむらを抑えたラインパイプ用高強度鋼板を、その有利な製造方法と共に提案することを目的とする。
また、そのラインパイプ用高強度鋼板を用いた高強度鋼管を提案することを目的とする。
The present invention was developed in view of the above situation, effectively reducing the variation in hardness in the plate thickness direction and the plate width direction of the steel plate, improving the material uniformity in the steel plate, and improving the thickness of the scale. The purpose of the present invention is to propose a high-strength steel sheet for line pipes that suppresses unevenness along with its advantageous manufacturing method.
Moreover, it aims at proposing the high strength steel pipe using the high strength steel plate for the line pipe.
本発明は、高強度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、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、ミクロ組織および製造条件について、数多くの実験と検討を繰り返した末に、開発されたものである。 In order to reduce the variation in hardness in the plate thickness direction and the plate width direction of the high-strength steel sheet and to improve the material uniformity in the steel sheet, the present invention provides a large number of chemical components, microstructures and manufacturing conditions of the steel material. It was developed after repeated experiments and examinations.
すなわち、本発明の要旨構成は次のとおりである。
1.質量%で、C:0.03〜0.12%、Si:0.01〜0.5%、Mn:1.5〜3.0%、P:0.01%以下、S:0.002%以下及びAl:0.01〜0.08%を含有し、下記(1)式で示されるCeq値が0.33以上であって、残部がFeおよび不可避的不純物の組成からなり、鋼組織がベイナイト組織であり、さらに板厚方向の硬さのばらつきがビッカース硬さのばらつきΔHVで50以下で、かつ板幅方向の硬さのばらつきがビッカース硬さのばらつきΔHVで50以下であり、引張強度が650MPa以上であることを特徴とする、ラインパイプ用高強度鋼板。
記
Ceq(質量%)=[%C]+[%Mn]/6+([%Cu]+[%Ni])/15+([%Cr]+[%Mo]+[%V])/5
・・・(1)
ただし、[%X]はX元素の鋼中含有量(質量%)を示す。
That is, the gist configuration of the present invention is as follows.
1. In mass%, C: 0.03-0.12%, Si: 0.01-0.5%, Mn: 1.5-3.0%, P: 0.01% or less, S: 0.002 % Or less and Al: 0.01 to 0.08%, the Ceq value represented by the following formula (1) is 0.33 or more, the balance is composed of Fe and inevitable impurities, and the steel structure Is a bainite structure, the hardness variation in the plate thickness direction is 50 or less Vickers hardness variation ΔHV, and the hardness variation in the plate width direction is 50 or less Vickers hardness variation ΔHV. A high-strength steel sheet for line pipes, wherein the strength is 650 MPa or more.
Ceq (mass%) = [% C] + [% Mn] / 6 + ([% Cu] + [% Ni]) / 15 + ([% Cr] + [% Mo] + [% V]) / 5
... (1)
However, [% X] indicates the content (mass%) of element X in steel.
2.前記鋼が、さらに、質量%で、Cu:0.50%以下、Ni:0.50%以下、Cr:0.50%以下及びMo:0.50%以下のうちから選んだ1種又は2種以上を含有することを特徴とする、前記1に記載のラインパイプ用高強度鋼板。 2. Further, the steel is one or two selected from the following by mass: Cu: 0.50% or less, Ni: 0.50% or less, Cr: 0.50% or less, and Mo: 0.50% or less. The high-strength steel sheet for line pipes according to 1 above, which contains seeds or more.
3.前記鋼が、さらに、質量%で、Nb:0.005〜0.1%、V:0.005〜0.1%及びTi:0.005〜0.1%のうちから選んだ1種又は2種以上を含有することを特徴とする、前記1または2に記載のラインパイプ用高強度鋼板。 3. Further, the steel may be one selected from Nb: 0.005 to 0.1%, V: 0.005 to 0.1%, and Ti: 0.005 to 0.1% by mass%. The high-strength steel sheet for line pipes according to 1 or 2 above, which contains two or more kinds.
4.質量%で、C:0.03〜0.12%、Si:0.01〜0.5%、Mn:1.5〜3.0%、P:0.01%以下、S:0.002%以下及びAl:0.01〜0.08%を含有し、下記(1)式で示されるCeq値が0.33以上であって、残部がFeおよび不可避的不純物の組成からなる鋼片を、1000〜1300℃の温度に加熱したのち、熱間圧延し、引き続く制御冷却の直前に鋼板表面での噴射流の衝突圧が1MPa以上の条件でデスケーリングを行い、その後冷却開始時の鋼板表面温度:(Ar3−10℃)以上、鋼板表面の冷却速度:200℃/s以下、鋼板平均の冷却速度:15℃/s以上及び鋼板平均温度で冷却停止温度:250〜550℃の条件で制御冷却を行うことを特徴とする、ラインパイプ用高強度鋼板の製造方法。
記
Ceq(質量%)=[%C]+[%Mn]/6+([%Cu]+[%Ni])/15+([%Cr]+[%Mo]+[%V])/5
・・・(1)
ただし、[%X]はX元素の鋼中含有量(質量%)を示す。
4). In mass%, C: 0.03-0.12%, Si: 0.01-0.5%, Mn: 1.5-3.0%, P: 0.01% or less, S: 0.002 % Or less and Al: 0.01 to 0.08%, a Ceq value represented by the following formula (1) is 0.33 or more, and the balance is Fe and an inevitable impurity composition. After heating to 1000 to 1300 ° C., hot rolling, descaling is performed under the condition that the impinging pressure of the jet flow on the steel plate surface is 1 MPa or more immediately before the subsequent controlled cooling, and then the steel plate surface at the start of cooling Temperature: (Ar 3 −10 ° C.) or more, steel sheet surface cooling rate: 200 ° C./s or less, steel sheet average cooling rate: 15 ° C./s or more, and steel sheet average temperature and cooling stop temperature: 250 to 550 ° C. Production of high-strength steel sheets for line pipes, characterized by controlled cooling Law.
Ceq (mass%) = [% C] + [% Mn] / 6 + ([% Cu] + [% Ni]) / 15 + ([% Cr] + [% Mo] + [% V]) / 5
... (1)
However, [% X] indicates the content (mass%) of element X in steel.
5.前記鋼片が、さらに、質量%で、Cu:0.50%以下、Ni:0.50%以下、Cr:0.50%以下及びMo:0.50%以下のうちから選んだ1種又は2種以上を含有することを特徴とする、前記4にラインパイプ用記載の高強度鋼板の製造方法。 5. The steel slab further comprises, in mass%, Cu: 0.50% or less, Ni: 0.50% or less, Cr: 0.50% or less, and Mo: 0.50% or less, or The method for producing a high-strength steel sheet as described in 4 above, which comprises 2 or more types.
6.前記鋼片が、さらに、質量%で、Nb:0.005〜0.1%、V:0.005〜0.1%及びTi:0.005〜0.1%のうちから選んだ1種又は2種以上を含有することを特徴とする、前記4また5に記載のラインパイプ用高強度鋼板の製造方法。 6). The steel slab is further selected by mass% from Nb: 0.005 to 0.1%, V: 0.005 to 0.1%, and Ti: 0.005 to 0.1%. Or the manufacturing method of the high strength steel plate for line pipes of said 4 or 5 characterized by containing 2 or more types.
7.前記1〜3のいずれかに記載のラインパイプ用高強度鋼板を用いた高強度鋼管。 7). The high strength steel pipe using the high strength steel plate for line pipes in any one of said 1-3.
本発明に従い、制御冷却技術およびデスケーリング技術を併せて活用することにより、従来の制御冷却技術では達成が困難とされた、低廉な成分系を用いて高冷却速度で冷却を行った場合における高強度鋼板内での材質均一性を格段に向上させることができる。
また、本発明の高強度鋼板は、プレスベンド成形、ロール成形、UOE成形等で鋼管に成形して、原油や天然ガスを輸送する鋼管(電縫鋼管、スパイラル鋼管、UOE鋼管等)に成形することができる。この様に成形された鋼管は、高強度でかつ鋼板内の材質均一性に優れているので、原油や天然ガス等の輸送に供した場合、従来品よりもより安定して長寿命な性能を有する。
According to the present invention, by utilizing the control cooling technology and the descaling technology together, it is difficult to achieve the high speed when cooling at a high cooling rate using an inexpensive component system, which is difficult to achieve with the conventional control cooling technology. The material uniformity within the strength steel plate can be remarkably improved.
The high-strength steel sheet of the present invention is formed into a steel pipe by press bend forming, roll forming, UOE forming, etc., and formed into a steel pipe (such as an electric resistance steel pipe, spiral steel pipe, UOE steel pipe, etc.) that transports crude oil or natural gas. be able to. The steel pipe formed in this way has high strength and excellent material uniformity within the steel plate, so when used for transportation of crude oil, natural gas, etc., it has a more stable and long-life performance than conventional products. Have.
以下、本発明を具体的に説明する。
〔化学成分〕
まず、本発明の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。
C:0.03〜0.12%
Cは、強度の向上に有効に寄与するが、含有量が0.03%未満では十分な強度が確保できず、一方0.12%を超えると靭性の劣化を招くため、C量は0.03〜0.12%の範囲に限定する。なお、溶接部の軟化防止および溶接熱影響部靭性劣化防止の観点から0.04〜0.08%とすることが好ましい。
Hereinafter, the present invention will be specifically described.
〔Chemical composition〕
First, chemical components of the high-strength steel plate of the present invention will be described. In the following description, all units represented by% are mass%.
C: 0.03-0.12%
C contributes effectively to the improvement of strength, but if the content is less than 0.03%, sufficient strength cannot be ensured. On the other hand, if it exceeds 0.12%, the toughness is deteriorated. It is limited to the range of 03 to 0.12%. In addition, it is preferable to set it as 0.04 to 0.08% from a viewpoint of softening prevention of a welding part and welding heat affected zone toughness deterioration prevention.
Si:0.01〜0.5%
Siは、脱酸のため添加するが、含有量が0.01%未満では脱酸効果が十分でなく、一方0.5%を超えると靭性や溶接性を劣化させるため、Si量は0.01〜0.5%の範囲に限定する。
Si: 0.01 to 0.5%
Si is added for deoxidation, but if the content is less than 0.01%, the deoxidation effect is not sufficient. On the other hand, if it exceeds 0.5%, the toughness and weldability are deteriorated. It is limited to the range of 01 to 0.5%.
Mn:1.5〜3.0%
Mnは、強度、靭性の向上に有効に寄与するが、含有量が1.5%未満ではその添加効果に乏しく、一方3.0%を超えると溶接性が劣化するため、Mn量は1.5〜3.0%の範囲に限定する。
Mn: 1.5 to 3.0%
Mn contributes effectively to the improvement of strength and toughness. However, if the content is less than 1.5%, the effect of addition is poor. On the other hand, if it exceeds 3.0%, the weldability deteriorates. It is limited to a range of 5 to 3.0%.
P:0.01%以下
Pは不可避不純物元素であり、鋼板の靭性や溶接性を劣化させる。経済的に可能な範囲で低減することが好ましいが、性能への影響を考慮して0.01%までは許容される。好ましくは0.008%以下である。
P: 0.01% or less P is an inevitable impurity element, and deteriorates the toughness and weldability of the steel sheet. Although it is preferable to reduce as much as possible economically, up to 0.01% is allowed in consideration of the effect on performance. Preferably it is 0.008% or less.
S:0.002%以下
Sは不可避不純物元素であり、鋼板の靭性や溶接性を劣化させる。経済的に可能な範囲で低減することが好ましいが、性能への影響を考慮して0.002%までは許容される。好ましくは0.001%以下である。
S: 0.002% or less S is an inevitable impurity element, and deteriorates the toughness and weldability of the steel sheet. Although it is preferable to reduce as much as possible economically, up to 0.002% is allowed in consideration of the effect on performance. Preferably it is 0.001% or less.
Al:0.01〜0.08%
Alは脱酸剤として添加するが、0.01%未満では添加効果がなく、一方、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 of addition. On the other hand, if it exceeds 0.08%, the cleanliness of the steel decreases and the toughness deteriorates, so the content is 0.01. It is specified to ˜0.08%.
以上、本発明の基本成分について説明したが、本発明では、鋼板の強度や靱性の一層の改善のために、Cu,Ni,Cr及びMoのうちから選んだ1種又は2種以上を、以下の範囲で適宜含有させることができる。
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り、この効果を得るには0.05%以上を含有することが好ましいが、含有量が多すぎると溶接性が劣化するため、Cuを添加する場合は0.50%を上限とする。
The basic components of the present invention have been described above. In the present invention, one or more selected from Cu, Ni, Cr, and Mo are selected in order to further improve the strength and toughness of the steel sheet. It can contain suitably in the range.
Cu: 0.50% or less Cu is an element effective for improving toughness and increasing strength. To obtain this effect, it is preferable to contain 0.05% or more, but if the content is too large, welding is performed. When Cu is 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り、この効果を得るには0.05%以上を含有することが好ましいが、含有量が多すぎると経済的に不利なだけでなく、溶接熱影響部の靱性が劣化するため、Niを添加する場合は0.50%を上限とする。
Ni: 0.50% or less Ni is an element effective for improving toughness and increasing strength. To obtain this effect, it is preferable to contain 0.05% or more, but if the content is too large, it is economical. This is not only disadvantageous, but also the toughness of the weld heat affected zone deteriorates. Therefore, when Ni is added, the upper limit is 0.50%.
Cr:0.50%以下
Crは、Mnと同様、低Cでも十分な強度を得るために有効な元素であり、この効果を得るには0.05%以上を含有することが好ましいが、含有量が多すぎると溶接性が劣化するため、Crを添加する場合は0.50%を上限とする。
Cr: 0.50% or less Cr, like Mn, is an element effective for obtaining sufficient strength even at low C. To obtain this effect, it is preferable to contain 0.05% or more. If the amount is too large, weldability deteriorates, so when Cr is added, the upper limit is 0.50%.
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り、この効果を得るには0.05%以上を含有することが好ましいが、含有量が多すぎると溶接性が劣化するため、Moを添加する場合は0.50%を上限とする。
Mo: 0.50% or less Mo is an element effective in improving toughness and increasing strength. To obtain this effect, it is preferable to contain 0.05% or more, but if the content is too large, welding is performed. When the Mo is added, the upper limit is 0.50%.
本発明では、さらに、Nb,VおよびTiのうちから選んだ1種又は2種以上を、以下の範囲で含有させることもできる。
Nb:0.005〜0.1%、V:0.005〜0.1%及びTi:0.005〜0.1%のうちから選んだ1種又は2種以上
Nb,VおよびTiはいずれも、鋼板の強度および靭性を高めるために添加することができる任意元素であり、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、含有量が0.005%未満ではその添加効果に乏しく、一方0.1%を超えると溶接部の靭性が劣化するので、添加する場合はいずれも0.005〜0.1%の範囲とするのが好ましい。
In the present invention, one or more selected from Nb, V and Ti can be further contained in the following range.
Nb: 0.005 to 0.1%, V: 0.005 to 0.1% and Ti: One or more selected from 0.005 to 0.1% Nb, V and Ti are either Is an optional element that can be added to increase the strength and toughness of the steel sheet, and one or more elements can be added depending on the required strength. For each element, if the content is less than 0.005%, the effect of addition is poor. On the other hand, if it exceeds 0.1%, the toughness of the welded portion deteriorates. It is preferable to be in the range.
本発明では、以下の式(1)で表されるCeq値が、質量%で0.33以上とする必要がある。というのは、Ceq値が0.33以上で、鋼板の引張強度が650MPa以上を確保することができるためである。
Ceq(質量%)=[%C]+[%Mn]/6+([%Cu]+[%Ni])/15+([%Cr]+[%Mo]+[%V])/5 ・・・(1)
ただし、[%X]はX元素の鋼中含有量(質量%)を示す。
上記した元素以外の残部は、Feおよび不可避的不純物からなる。ただし、本発明の作用効果を害しない限り、他の微量元素の含有を妨げない。たとえば、靱性改善の観点から、Ca:0.003%以下、Mg:0.02%以下、REM(希土類金属):0.02%以下の1種または2種以上を含有させることができる。
In the present invention, the Ceq value represented by the following formula (1) needs to be 0.33 or more by mass%. This is because the Ceq value is 0.33 or more and the tensile strength of the steel sheet can be secured to 650 MPa or more.
Ceq (mass%) = [% C] + [% Mn] / 6 + ([% Cu] + [% Ni]) / 15 + ([% Cr] + [% Mo] + [% V]) / 5)・ (1)
However, [% X] indicates the content (mass%) of element X in steel.
The balance other than the above elements is made of Fe and inevitable impurities. However, the content of other trace elements is not hindered unless the effects of the present invention are impaired. For example, from the viewpoint of improving toughness, one or more of Ca: 0.003% or less, Mg: 0.02% or less, and REM (rare earth metal): 0.02% or less can be contained.
次に、本発明鋼の鋼組織(ミクロ組織)について説明する。
引張強度が650MPa以上の高強度化を図るために、鋼組織は、ベイナイト組織とする必要がある。特に、表層部は、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た場合、表層硬さが上昇し、鋼板内の硬さのばらつきが増大して材質均一性が阻害される。表層硬さの上昇を抑制するために、鋼組織とくに表層部についてはベイナイト組織とする。ベイナイト組織中に、フェライトやマルテンサイト、パーライト、島状マルテンサイト、残留オーステナイトなどの異種組織が混在すると、強度の低下や靭性の劣化、表層硬さの上昇などが生じるため、ベイナイト相以外の組織分率は少ない程良い。ただし、ベイナイト相以外の組織の体積分率が十分に低い場合には、それらの影響が無視できるので、ある程度の量であれば許容される。具体的に、本発明では、ベイナイト相以外の鋼組織(フェライト、マルテンサイト、パーライト、島状マルテンサイト、残留オーステナイト等)の合計が体積分率で5%未満であれば、大きな影響がないので許容されるものとする。
Next, the steel structure (microstructure) of the steel of the present invention will be described.
In order to increase the tensile strength of 650 MPa or more, the steel structure needs to be a bainite structure. In particular, in the surface layer portion, when a hard phase such as martensite or island martensite (MA) is generated, the surface layer hardness is increased, the hardness variation in the steel sheet is increased, and the material uniformity is inhibited. . In order to suppress the increase in surface hardness, the steel structure, particularly the surface layer portion, is made a bainite structure. When different types of structures such as ferrite, martensite, pearlite, island-like martensite, and retained austenite are mixed in the bainite structure, the strength decreases, the toughness deteriorates, and the surface hardness increases. The smaller the fraction, the better. However, when the volume fraction of the structure other than the bainite phase is sufficiently low, the influence thereof can be ignored, so that a certain amount is acceptable. Specifically, in the present invention, if the sum of the steel structures other than the bainite phase (ferrite, martensite, pearlite, island martensite, residual austenite, etc.) is less than 5% in volume fraction, there is no significant effect. Shall be acceptable.
〔硬さのばらつき〕
板厚方向の硬さのばらつき:ビッカース硬さのばらつき(ΔHV)で50以下で、かつ
板幅方向の硬さのばらつき:ビッカース硬さのばらつき(ΔHV)で50以下
鋼板の強度や伸び、成形性、耐HIC性、耐SSCC性能などの観点から、鋼板内の硬さのばらつきを抑制することが要求される。板厚方向の硬さのばらつきがΔHVで50を超えた場合や、板幅方向の硬さのばらつきがΔHVで50を超えた場合は、上記特性に悪影響を及ぼす。例えば、鋼板表層部の硬さのばらつきが鋼板内部に比べてΔHVで50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易くなったり、硫化水素に対する割れ感受性が高まったりする。また、板幅方向の硬さのばらつきがΔHVで50を超えた場合は、成形時に硬い部分と軟らかい部分とで変形の仕方に差が生じて所望の形状が得られなかったり、小板に切断した場合にそれぞれの小板で強度や伸びが異なったりする。
そこで、鋼板内の材質均一性の観点から、板厚方向および板幅方向の硬さのばらつきはいずれもΔHVで50以下とした。好ましくは、ΔHVで40以下である。
[Hardness variation]
Hardness variation in the plate thickness direction: Vickers hardness variation (ΔHV) of 50 or less and hardness variation in the plate width direction: Vickers hardness variation (ΔHV) of 50 or less From the viewpoints of performance, HIC resistance, SSCC resistance, etc., it is required to suppress variation in hardness within the steel sheet. When the hardness variation in the plate thickness direction exceeds 50 in ΔHV, or the hardness variation in the plate width direction exceeds 50 in ΔHV, the above characteristics are adversely affected. For example, when the variation in hardness of the steel sheet surface layer portion is greater than 50 in ΔHV compared to the inside of the steel plate, springback is likely to occur after forming, and cracking susceptibility to hydrogen sulfide is increased. Also, if the variation in hardness in the plate width direction exceeds 50 in ΔHV, there will be a difference in the deformation method between the hard part and the soft part at the time of molding, and the desired shape cannot be obtained, or it is cut into small plates If this is the case, the strength and elongation of each platelet may vary.
Therefore, from the viewpoint of material uniformity in the steel sheet, the variation in hardness in the sheet thickness direction and the sheet width direction is set to 50 or less in ΔHV. Preferably, ΔHV is 40 or less.
[引張強度]
引張強度:650MPa以上
本発明に従う高強度鋼板は、APIX80グレード以上の強度を十分に満足するために、引張強度で650MPa以上とする。より好ましくは700MPa以上である。
[Tensile strength]
Tensile strength: 650 MPa or more The high-strength steel sheet according to the present invention has a tensile strength of 650 MPa or more in order to sufficiently satisfy the strength of APIX 80 grade or more. More preferably, it is 700 MPa or more.
次に、本発明に係る高強度鋼板の製造条件について説明する。
〔スラブ加熱温度〕
スラブ加熱温度:1000〜1300℃
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、一方1300℃を超えると靭性が劣化するため、スラブ加熱温度は1000〜1300℃とする。なお、この温度は加熱炉の炉内温度であり、スラブは中心部までこの温度に加熱されるものとする。
Next, manufacturing conditions for the high-strength steel sheet according to the present invention will be described.
[Slab heating temperature]
Slab heating temperature: 1000-1300 ° C
If the heating temperature is less than 1000 ° C., the required strength cannot be obtained because the solid solution of the carbide is insufficient. On the other hand, if it exceeds 1300 ° C., the toughness deteriorates, so the slab heating temperature is 1000 to 1300 ° C. This temperature is the furnace temperature of the heating furnace, and the slab is heated to this temperature up to the center.
〔圧延終了温度〕
熱間圧延工程において、高い母材靱性を得るには、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、鋼板表面温度での圧延終了温度は、必要な母材靱性と圧延能率を勘案して設定する必要がある。強度の観点からは、圧延終了温度は鋼板表面温度でAr3変態点以上とすることが好ましい。ここで、Ar3変態点とは、冷却中におけるフェライト変態開始温度を意味し、例えば、鋼の成分から以下の式で求めることができる。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。
Ar3(℃)=910−310[%C]−80[%Mn]−20[%Cu]−15[%Cr]−55[%Ni]−80[%Mo]
ただし、[%X]はX元素の鋼中含有量(質量%)を示す。
[Rolling end temperature]
In the hot rolling process, in order to obtain high base metal toughness, the lower the rolling end temperature, the better. However, since the rolling efficiency decreases, the rolling end temperature at the steel sheet surface temperature is the required base material toughness and rolling. It is necessary to set in consideration of efficiency. From the viewpoint of strength, it is preferable that the rolling end temperature is not less than the Ar 3 transformation point at the steel sheet surface temperature. Here, the Ar 3 transformation point means a ferrite transformation start temperature during cooling, and can be obtained from the steel components by the following formula, for example. 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.
Ar 3 (° C.) = 910-310 [% C] -80 [% Mn] -20 [% Cu] -15 [% Cr] -55 [% Ni] -80 [% Mo]
However, [% X] indicates the content (mass%) of element X in steel.
〔デスケーリング〕
さらに、制御冷却の直前に高衝突圧の噴射流によるデスケーリングを行う。鋼板内の材質均一性に優れた高強度鋼板とするためには、鋼板内の硬さのばらつきを低減することが必要であり、特に鋼板内部の強度を保ちながら、表層部の硬さのばらつきを抑制することが重要である。圧延後の鋼板においては、圧延前および圧延中のデスケーリング等により幅方向にスケールの厚さにむらが生じることがある。また、スケール厚さが大きい場合には、部分的にスケールの剥離が生じることがある。圧延後の冷却の際に、スケール厚さにばらつきがあると、その厚さに応じて鋼板表面の冷却速度も変化してしまい、その冷却速度に応じて鋼板表面の硬さも変化してしまう。鋼板を高強度化するためには、制御冷却時の冷却速度を大きくすることが有効であるが、高冷却速度での冷却では表層硬さに及ぼすスケール厚さの影響が顕著になるため、スケール厚さにむらがあると硬さのばらつきが増大して鋼板内の材質均一性が劣化する。
[Descaling]
Further, the descaling by the jet flow of high collision pressure is performed immediately before the control cooling. In order to obtain a high-strength steel sheet with excellent material uniformity within the steel sheet, it is necessary to reduce the variation in hardness within the steel sheet, and in particular, while maintaining the strength inside the steel sheet, the variation in surface layer hardness. It is important to suppress this. In a steel sheet after rolling, unevenness in the thickness of the scale may occur in the width direction due to descaling or the like before rolling and during rolling. Further, when the scale thickness is large, the scale may be partially peeled off. When the scale thickness varies during cooling after rolling, the cooling rate of the steel plate surface changes according to the thickness, and the hardness of the steel plate surface also changes according to the cooling rate. In order to increase the strength of steel sheets, it is effective to increase the cooling rate during controlled cooling, but the effect of scale thickness on the surface hardness becomes significant when cooling at a high cooling rate. If the thickness is uneven, the variation in hardness increases and the material uniformity in the steel sheet deteriorates.
その対策として、制御冷却の直前に高衝突圧の噴射流によるデスケーリングを実施し、これによりスケール厚さを冷却速度に大きな差が生じない程度まで均一に薄くすることが本発明の特徴である。すなわち、制御冷却後の鋼板のスケール厚さを15μm以下とした場合に、板厚方向の硬さのばらつきがΔHVで50以下、且つ板幅方向の硬さのばらつきがΔHVで50以下となる。
なお、制御冷却直前の鋼板のスケール厚みを測定することは事実上困難であるが、制御冷却前のスケール厚みは制御冷却後のスケール厚みによって推定することができ、冷却後の鋼板のスケール厚みが15μm以下となるように冷却直前にデスケーリングを行うことによって、所望の効果が得られることが解明された。
このように、冷却直前での高衝突圧の噴射流によるデスケーリングによって、高冷却速度下での高強度と鋼板内の材質均一性を両立することができる。
As a countermeasure, it is a feature of the present invention that the descaling by the jet flow of high collision pressure is performed immediately before the control cooling, and thereby the thickness of the scale is uniformly reduced to such an extent that a large difference in the cooling rate does not occur. . That is, when the scale thickness of the steel sheet after controlled cooling is 15 μm or less, the variation in hardness in the thickness direction is 50 or less in ΔHV, and the variation in hardness in the sheet width direction is 50 or less in ΔHV.
Although it is practically difficult to measure the scale thickness of the steel plate immediately before the controlled cooling, the scale thickness before the controlled cooling can be estimated by the scale thickness after the controlled cooling, and the scale thickness of the steel plate after the cooling is It has been clarified that a desired effect can be obtained by performing descaling immediately before cooling so as to be 15 μm or less.
Thus, the descaling by the jet flow of the high collision pressure immediately before cooling can achieve both high strength at a high cooling rate and material uniformity in the steel sheet.
デスケーリング圧(鋼板表面での噴射流の衝突圧):1MPa以上
本発明では、制御冷却の直前に鋼板表面での噴射流の衝突圧が1MPa以上となる条件で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、噴射流の衝突圧は1MPa以上とする。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問題はない。より好ましくは2MPa以上である。
Descaling pressure (impact pressure of jet flow on steel plate surface): 1 MPa or more In the present invention, descaling is performed under the condition that the impingement pressure of jet flow on the steel plate surface is 1 MPa or more immediately before control cooling. If the collision pressure of the jet flow on the surface of the steel sheet is less than 1 MPa, the descaling may be insufficient and unevenness in scale may occur, resulting in variations in surface hardness. Therefore, the collision pressure of the jet flow is set to 1 MPa or more. Although descaling is performed using high-pressure water, there is no problem even if another jet flow is used as long as the collision pressure of the jet flow on the steel plate surface is 1 MPa or more. More preferably, it is 2 MPa or more.
また、デスケーリング後、5秒以内に制御冷却を行うことが望ましい。デスケーリング後、制御冷却を行うまでの時間が5秒を超えると、スケールが成長するため表層部の冷却速度が上昇し、硬さのばらつきが大きくなる。特に、スケール厚さが15μmを超える場合、表層硬さの上昇および鋼板内の硬さのばらつきが増大して材質均一性の劣化が顕著となる。この点、デスケーリング後、5秒以内に制御冷却を行えば、スケール厚さを15μm以下とすることができる。従って、デスケーリングから制御冷却までの時間は5秒以内とすることが望ましい。 Moreover, it is desirable to perform control cooling within 5 seconds after descaling. If the time until the controlled cooling is performed after descaling exceeds 5 seconds, the scale grows, the cooling rate of the surface layer portion increases, and the variation in hardness increases. In particular, when the scale thickness exceeds 15 μm, the increase in the surface layer hardness and the variation in the hardness in the steel sheet increase, and the deterioration of the material uniformity becomes remarkable. In this regard, if controlled cooling is performed within 5 seconds after descaling, the scale thickness can be reduced to 15 μm or less. Therefore, it is desirable that the time from descaling to control cooling be within 5 seconds.
〔冷却開始温度〕
冷却開始温度:鋼板表面温度で(Ar3−10℃)以上
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、特にAr3変態点からの温度降下量が10℃を超えると体積分率で5%を超えるフェライトが生成して、強度低下が大きくなるため、冷却開始時の鋼板表面温度は(Ar3−10℃)以上とする。
[Cooling start temperature]
Cooling start temperature: (Ar 3 −10 ° C.) or more at the steel sheet surface temperature When the steel sheet surface temperature at the start of cooling is low, the amount of ferrite produced before controlled cooling increases, and in particular, the temperature drop from the Ar 3 transformation point is 10 If it exceeds ° C., ferrite with a volume fraction exceeding 5% is generated and the strength decreases greatly, so 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:200℃/s以下、鋼板平均の冷却速度:15℃/s以上
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内の平均冷却速度を制御することが重要である。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。
また、鋼板平均の冷却速度が15℃/s未満では、鋼板表面の冷却状態において膜沸騰と核沸騰とが混在する場合があり、硬さのばらつきの原因となる。冷却状態を核沸騰状態として均一な冷却とするため、鋼板平均の冷却速度は15℃/s以上とする。鋼板強度と硬さのばらつきの観点からは、鋼板平均の冷却速度は20℃/s以上とすることが好ましい。また、鋼板表面の冷却速度を200℃/s以下で、かつ鋼板平均の冷却速度を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、その結果、鋼板形状が良好となる。
なお、鋼板平均の温度および冷却速度については、物理的に直接測定することはできないが、鋼板表面の温度変化を基にしたシミュレーション計算を行うことで、リアルタイムに求めることができる。
(Cooling rate)
Steel sheet surface cooling rate: 200 ° C./s or less, Steel sheet average cooling rate: 15 ° C./s or more In order to reduce hardness variation and improve material uniformity while increasing strength It is important to control the cooling rate of the surface layer part and the average cooling rate in the steel sheet. 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 hardness increases, so the cooling rate of the steel sheet surface is 200 ° C. / S or less. Preferably it is 150 degrees C / s or less.
In addition, when the average cooling rate of the steel sheet is less than 15 ° C./s, film boiling and nucleate boiling may be mixed in the cooling state of the steel sheet surface, which causes variations in hardness. In order to achieve uniform cooling by setting the cooling state to the nucleate boiling state, the average cooling rate of the steel sheet is set to 15 ° C./s or more. From the viewpoint of variations in steel plate strength and hardness, the average cooling rate of the steel plate is preferably 20 ° C./s or more. Further, by setting the cooling rate of the steel sheet surface to 200 ° C./s or less and the average cooling rate of the steel sheet to 15 ° C./s or more, variation in cooling stop temperature can be suppressed. It becomes good.
The average temperature and cooling rate of the steel sheet cannot be directly measured physically, but can be obtained in real time by performing a simulation calculation based on the temperature change of the steel sheet surface.
〔冷却停止温度〕
冷却停止温度:鋼板平均温度で250〜550℃
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。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。そこで、鋼板内の材質均一性の劣化を抑制するため、制御冷却の冷却停止温度は鋼板平均温度250〜550℃とする。
[Cooling stop temperature]
Cooling stop temperature: 250-550 ° C. at the average temperature of the 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. When the cooling stop temperature exceeds 550 ° C., the bainite transformation is incomplete and sufficient strength cannot be obtained. In addition, 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 is remarkably increased, resulting in a large variation in hardness. Therefore, in order to suppress deterioration of material uniformity in the steel plate, the cooling stop temperature of the controlled cooling is set to a steel plate average temperature of 250 to 550 ° C.
図1に、本発明鋼板の製造に使用して好適な圧延ラインの一例を示す。圧延ライン1には、鋼板搬送ライン5の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および制御冷却装置4を配置する。また、デスケーリング装置の前に熱間矯正機を設置することもできる。この熱間矯正機で鋼板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なデスケーリングの実施が可能となる。
In FIG. 1, an example of a suitable rolling line used for manufacture of this invention steel plate is shown. In the rolling line 1, a hot rolling mill 2, a high collision pressure descaling device 3, and a control cooling device 4 are arranged from the upstream side to the downstream side of the steel
表1に示す化学成分になる鋼(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:28mmの厚鋼板(No.1〜No.22)を製造した。
ついで、スラブを加熱後、熱間圧延により所定の板厚とし、ついで制御冷却直前に高衝突圧のデスケーリングを行ったのち、水冷型の制御冷却装置を用いて制御冷却を行った。各鋼板(No.1〜No.22)の製造条件を表2に示す。
Steels (steel types A to L) having chemical components shown in Table 1 were made into slabs by a continuous casting method, and using this, thick steel plates (No. 1 to No. 22) having a plate thickness of 28 mm were manufactured.
Next, after heating the slab, it was hot rolled to a predetermined plate thickness, and after high-impact pressure descaling was performed immediately before control cooling, control cooling was performed using a water-cooled control cooling device. Table 2 shows the production conditions of each steel plate (No. 1 to No. 22).
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、画像解析装置を用いて相分率を測定した。また、スケール厚さを測定し、10視野の平均値で評価した。特性は、圧延方向に直角な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。また、圧延方向に直角な断面について、JIS Z 2244に準拠して、ビッカース硬さを測定し、板厚方向の硬さ分布と板幅方向の硬さ分布を求めた。板厚方向については、1mmピッチで全厚の硬さを測定し、板幅方向については、20mmピッチで全幅の硬さを測定した。なお、板幅方向の硬さ分布は、表層1mm位置(表層から1mm内側の位置)、t/4位置(板厚1/4位置)、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。
本発明の目標範囲は、高強度鋼として引張強度:650MPa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、板厚方向および板幅方向の硬さのばらつきはいずれもΔHV50以下である。
得られた結果を表2に併せて示す。
The microstructure and scale properties of the obtained steel sheet were observed with an optical microscope and a scanning electron microscope. Ten cross-sectional structure photographs were obtained, and the phase fraction was measured using an image analyzer. Moreover, the scale thickness was measured and evaluated by the average value of 10 fields of view. For the characteristics, a tensile test was performed using a full thickness test piece in a direction perpendicular to the rolling direction as a tensile test piece, and the tensile strength was measured. Moreover, the Vickers hardness was measured about the cross section orthogonal to a rolling direction based on JISZ2244, and the hardness distribution of the board thickness direction and the hardness distribution of the board width direction were calculated | required. For the plate thickness direction, the hardness of the entire thickness was measured at a pitch of 1 mm, and for the plate width direction, the hardness of the full width was measured at a pitch of 20 mm. The hardness distribution in the plate width direction was measured at the surface layer 1 mm position (position 1 mm inside from the surface layer), t / 4 position (plate thickness 1/4 position), and t / 2 position (plate thickness center). Since all the steel sheets showed the largest variation in hardness at the surface layer of 1 mm, the variation in hardness in the plate width direction was evaluated at the surface layer of 1 mm.
The target range of the present invention is that the tensile strength is 650 MPa or more as high strength steel, the microstructure is bainite structure at both the 1 mm position and the t / 2 position of the surface layer, and variations in hardness in the plate thickness direction and the plate width direction are both ΔHV50 or less. is there.
The obtained results are also shown in Table 2.
No.1〜No.11は、化学成分および製造条件が本発明の適正範囲を満足する発明例である。いずれも、引張強度:650MPa以上、板厚方向および板幅方向の硬さのばらつき:ΔHVで50以下で、か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った。
一方、No.12〜No.18は、化学成分は本発明の範囲内であるが、製造条件が本発明の範囲外の比較例である。No.12は、スラブ加熱温度が低いため、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。No.13は、冷却開始温度が低く、フェライトが析出したため、低強度である。No.14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、低強度であった。No.15は、冷却停止温度が低く、硬質相である島状マルテンサイト(MA)が生成したため、硬さのばらつきがΔHV50を超えていた。No.16〜No.18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いか、行っていても衝突圧が低いため、スケール厚さが15μmを超え、また板厚方向と板幅方向の硬さのばらつきがΔHV50を超えて、鋼板内の材質均一性に劣っていた。No.19〜No.22は、化学成分が本発明の範囲外である。No.19、No.21、No.22は、引張強度が650MPaに満たない低強度であり、No.20は、板厚方向の硬さのばらつきがΔHV50を超えており、鋼板内の材質均一性に劣っていた。
No. 1-No. 11 is an invention example in which chemical components and production conditions satisfy the appropriate range of the present invention. In all cases, the tensile strength was 650 MPa or more, the hardness variation in the plate thickness direction and the plate width direction: ΔHV was 50 or less, and the microstructure of the steel plate was a bainite structure at both the surface layer 1 mm position and the t / 2 position.
On the other hand, no. 12-No. 18 is a comparative example in which the chemical components are within the scope of the present invention but the production conditions are outside the scope of the present invention. No. No. 12 had a low strength because the slab heating temperature was low, so that the homogenization of the microstructure and the solid solution of carbides were insufficient. No. No. 13 has low strength because the cooling start temperature is low and ferrite is precipitated. No. No. 14 had a low strength because the controlled cooling conditions were outside the scope of the present invention, and a bainite structure was not obtained as the microstructure in the center of the plate thickness, and pearlite was precipitated. No. No. 15 had a low cooling stop temperature and island-shaped martensite (MA), which was a hard phase, was generated, and thus the hardness variation exceeded ΔHV50. No. 16-No. No. 18 is not descaling immediately before control cooling, or even if it is performed, the impact pressure is low, so the scale thickness exceeds 15 μm, and the variation in hardness in the plate thickness direction and the plate width direction is ΔHV50. The material uniformity in the steel sheet was inferior. No. 19 to No. 22 have chemical components outside the scope of the present invention. No. 19, No. 21, and No. 22 are low strengths with a tensile strength of less than 650 MPa, and No. 20 has a hardness variation in the plate thickness direction exceeding ΔHV50, and the material in the steel plate is uniform. It was 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 鋼板搬送ライン
DESCRIPTION OF SYMBOLS 1 Rolling line 2 Hot rolling mill 3 High collision pressure descaling device 4
Claims (7)
記
Ceq(質量%)=[%C]+[%Mn]/6+([%Cu]+[%Ni])/15+([%Cr]+[%Mo]+[%V])/5
・・・(1)
ただし、[%X]はX元素の鋼中含有量(質量%)を示す。 In mass%, C: 0.03-0.12%, Si: 0.01-0.5%, Mn: 1.5-3.0%, P: 0.01% or less, S: 0.002 % Or less and Al: 0.01 to 0.08%, the Ceq value represented by the following formula (1) is 0.33 or more, the balance is composed of Fe and inevitable impurities, and the steel structure Is a bainite structure, the hardness variation in the plate thickness direction is 50 or less Vickers hardness variation ΔHV, and the hardness variation in the plate width direction is 50 or less Vickers hardness variation ΔHV. A high-strength steel sheet for line pipes, wherein the strength is 650 MPa or more.
Ceq (mass%) = [% C] + [% Mn] / 6 + ([% Cu] + [% Ni]) / 15 + ([% Cr] + [% Mo] + [% V]) / 5
... (1)
However, [% X] indicates the content (mass%) of element X in steel.
記
Ceq(質量%)=[%C]+[%Mn]/6+([%Cu]+[%Ni])/15+([%Cr]+[%Mo]+[%V])/5
・・・(1)
ただし、[%X]はX元素の鋼中含有量(質量%)を示す。 In mass%, C: 0.03-0.12%, Si: 0.01-0.5%, Mn: 1.5-3.0%, P: 0.01% or less, S: 0.002 % Or less and Al: 0.01 to 0.08%, a Ceq value represented by the following formula (1) is 0.33 or more, and the balance is Fe and an inevitable impurity composition. After heating to 1000 to 1300 ° C., hot rolling, descaling is performed under the condition that the impinging pressure of the jet flow on the steel plate surface is 1 MPa or more immediately before the subsequent controlled cooling, and then the steel plate surface at the start of cooling Temperature: (Ar 3 −10 ° C.) or more, steel sheet surface cooling rate: 200 ° C./s or less, steel sheet average cooling rate: 15 ° C./s or more, and steel sheet average temperature and cooling stop temperature: 250 to 550 ° C. Production of high-strength steel sheets for line pipes, characterized by controlled cooling Law.
Ceq (mass%) = [% C] + [% Mn] / 6 + ([% Cu] + [% Ni]) / 15 + ([% Cr] + [% Mo] + [% V]) / 5
... (1)
However, [% X] indicates the content (mass%) of element X in steel.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2010221496A JP5640614B2 (en) | 2010-09-30 | 2010-09-30 | High-strength steel pipe for line pipe, its manufacturing method, and high-strength steel pipe using high-strength steel sheet for line pipe |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2010221496A JP5640614B2 (en) | 2010-09-30 | 2010-09-30 | High-strength steel pipe for line pipe, its manufacturing method, and high-strength steel pipe using high-strength steel sheet for line pipe |
Publications (2)
Publication Number | Publication Date |
---|---|
JP2012077325A true JP2012077325A (en) | 2012-04-19 |
JP5640614B2 JP5640614B2 (en) | 2014-12-17 |
Family
ID=46237912
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP2010221496A Active JP5640614B2 (en) | 2010-09-30 | 2010-09-30 | High-strength steel pipe for line pipe, its manufacturing method, and high-strength steel pipe using high-strength steel sheet for line pipe |
Country Status (1)
Country | Link |
---|---|
JP (1) | JP5640614B2 (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2014156175A1 (en) * | 2013-03-29 | 2014-10-02 | Jfeスチール株式会社 | Steel plate for thick steel pipe, method for manufacturing same, and high strength thick steel pipe |
WO2016031168A1 (en) * | 2014-08-26 | 2016-03-03 | Jfeスチール株式会社 | Thick steel plate manufacturing facility and manufacturing method |
WO2016031169A1 (en) * | 2014-08-26 | 2016-03-03 | Jfeスチール株式会社 | Thick steel plate manufacturing method |
CN111183238A (en) * | 2017-09-28 | 2020-05-19 | 杰富意钢铁株式会社 | High-strength steel sheet for acid-resistant line pipe, method for producing same, and high-strength steel pipe using high-strength steel sheet for acid-resistant line pipe |
JP2022106590A (en) * | 2021-01-07 | 2022-07-20 | Jfeスチール株式会社 | Electroseamed steel pipe, and production method of electroseamed steel pipe |
Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS61165207A (en) * | 1985-01-14 | 1986-07-25 | Nippon Steel Corp | Manufacture of unrefined steel plate excellent in sour-resistant property |
JPS63179020A (en) * | 1987-01-20 | 1988-07-23 | Nippon Steel Corp | Production of steel sheet having excellent strength and toughness and small difference in sectional hardness in thickness direction of sheet |
JPH0841536A (en) * | 1994-07-29 | 1996-02-13 | Kawasaki Steel Corp | Production of high tensile strength steel plate small in nonuniformity of hardness in plate thickness direction and excellent in dwtt property |
JPH0957327A (en) * | 1995-08-22 | 1997-03-04 | Sumitomo Metal Ind Ltd | Scale removal method of steel plate |
JP2000129350A (en) * | 1998-10-22 | 2000-05-09 | Nkk Corp | Production of low yield ratio high tensile strength steel small in difference in material in plate thickness direction |
JP2006265577A (en) * | 2005-03-22 | 2006-10-05 | Jfe Steel Kk | Method for producing high strength, high toughness steel sheet |
-
2010
- 2010-09-30 JP JP2010221496A patent/JP5640614B2/en active Active
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS61165207A (en) * | 1985-01-14 | 1986-07-25 | Nippon Steel Corp | Manufacture of unrefined steel plate excellent in sour-resistant property |
JPS63179020A (en) * | 1987-01-20 | 1988-07-23 | Nippon Steel Corp | Production of steel sheet having excellent strength and toughness and small difference in sectional hardness in thickness direction of sheet |
JPH0841536A (en) * | 1994-07-29 | 1996-02-13 | Kawasaki Steel Corp | Production of high tensile strength steel plate small in nonuniformity of hardness in plate thickness direction and excellent in dwtt property |
JPH0957327A (en) * | 1995-08-22 | 1997-03-04 | Sumitomo Metal Ind Ltd | Scale removal method of steel plate |
JP2000129350A (en) * | 1998-10-22 | 2000-05-09 | Nkk Corp | Production of low yield ratio high tensile strength steel small in difference in material in plate thickness direction |
JP2006265577A (en) * | 2005-03-22 | 2006-10-05 | Jfe Steel Kk | Method for producing high strength, high toughness steel sheet |
Cited By (16)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2014156175A1 (en) * | 2013-03-29 | 2014-10-02 | Jfeスチール株式会社 | Steel plate for thick steel pipe, method for manufacturing same, and high strength thick steel pipe |
US10240226B2 (en) * | 2013-03-29 | 2019-03-26 | Jfe Steel Corporation | Steel plate for thick-walled steel pipe, method for manufacturing the same, and thick-walled high-strength steel pipe |
KR101788152B1 (en) * | 2013-03-29 | 2017-10-19 | 제이에프이 스틸 가부시키가이샤 | Steel plate for thick-walled steel pipe, method for manufacturing the same, and thick-walled high strength steel pipe |
JP6008042B2 (en) * | 2013-03-29 | 2016-10-19 | Jfeスチール株式会社 | Steel plate for thick-walled steel pipe, method for producing the same, and thick-walled high-strength steel pipe |
JPWO2014156175A1 (en) * | 2013-03-29 | 2017-02-16 | Jfeスチール株式会社 | Steel plate for thick-walled steel pipe, method for producing the same, and thick-walled high-strength steel pipe |
EP3187275A4 (en) * | 2014-08-26 | 2017-09-06 | JFE Steel Corporation | Thick steel plate manufacturing method |
JPWO2016031168A1 (en) * | 2014-08-26 | 2017-04-27 | Jfeスチール株式会社 | Manufacturing equipment and manufacturing method for thick steel plate |
JPWO2016031169A1 (en) * | 2014-08-26 | 2017-04-27 | Jfeスチール株式会社 | Thick steel plate manufacturing method |
KR20170033423A (en) * | 2014-08-26 | 2017-03-24 | 제이에프이 스틸 가부시키가이샤 | Thick steel plate manufacturing method |
WO2016031169A1 (en) * | 2014-08-26 | 2016-03-03 | Jfeスチール株式会社 | Thick steel plate manufacturing method |
KR101940429B1 (en) * | 2014-08-26 | 2019-01-18 | 제이에프이 스틸 가부시키가이샤 | Method for manufacturing steel plate |
WO2016031168A1 (en) * | 2014-08-26 | 2016-03-03 | Jfeスチール株式会社 | Thick steel plate manufacturing facility and manufacturing method |
CN111183238A (en) * | 2017-09-28 | 2020-05-19 | 杰富意钢铁株式会社 | High-strength steel sheet for acid-resistant line pipe, method for producing same, and high-strength steel pipe using high-strength steel sheet for acid-resistant line pipe |
EP3677698A4 (en) * | 2017-09-28 | 2020-07-08 | JFE Steel Corporation | High-strength steel plate for sour resistant line pipe, method for manufacturing same, and high-strength steel pipe using high-strength steel plate for sour resistant line pipe |
JP2022106590A (en) * | 2021-01-07 | 2022-07-20 | Jfeスチール株式会社 | Electroseamed steel pipe, and production method of electroseamed steel pipe |
JP7388371B2 (en) | 2021-01-07 | 2023-11-29 | Jfeスチール株式会社 | ERW steel pipe and method for manufacturing ERW steel pipe |
Also Published As
Publication number | Publication date |
---|---|
JP5640614B2 (en) | 2014-12-17 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
JP5672916B2 (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 | |
JP5900303B2 (en) | High-strength steel sheet for sour-resistant pipes with excellent material uniformity in the steel sheet and its manufacturing method | |
JP5348386B2 (en) | Thick high-strength steel sheet with excellent low yield ratio and brittle crack resistance and its manufacturing method | |
JP5991175B2 (en) | High-strength steel sheet for line pipes with excellent material uniformity in the steel sheet and its manufacturing method | |
JP4951997B2 (en) | A method for producing a high-tensile steel sheet having a tensile strength of 550 MPa or more. | |
JP2008101242A (en) | High-strength steel plate with excellent hic resistance for line pipe, and its manufacturing method | |
JP2008056962A (en) | Steel sheet for high strength line pipe which is excellent in resistance to crack induced by hydrogen and has small reduction in yield stress due to bauschinger effect, and manufacturing method therefor | |
JP2005048224A (en) | Method for producing low yield ratio, high strength and high toughness steel plate excellent in weld heat affected zone toughness | |
JP5625694B2 (en) | High-strength, high-toughness thick-walled steel plate with excellent material uniformity in the steel plate and method for producing the same | |
JP2006291349A (en) | Line pipe steel sheet having high deformation performance and its manufacturing method | |
JP4830330B2 (en) | Manufacturing method of thick-walled low yield ratio high-tensile steel sheet | |
JP2013194316A (en) | High strength steel plate for high heat input welding excellent in material uniformity in steel plate and method for manufacturing the same | |
JP2017057449A (en) | Steel sheet excellent in sour resistance and production method therefor | |
JP2007270349A (en) | Steel tube for hollow part, and its manufacturing method | |
JP2015190026A (en) | Thick high strength electroseamed steel pipe for linepipe and manufacturing method therefor | |
JP2012031509A (en) | High strength low yield ratio steel with highly uniform elongation characteristic, method of producing the same and high strength low yield ratio welded steel pipe | |
JP5640614B2 (en) | High-strength steel pipe for line pipe, its manufacturing method, and high-strength steel pipe using high-strength steel sheet for line pipe | |
JP6288288B2 (en) | Steel plate for line pipe, manufacturing method thereof and steel pipe for line pipe | |
JP5991174B2 (en) | High-strength steel sheet for sour-resistant pipes with excellent material uniformity in the steel sheet and its manufacturing method | |
JP5605136B2 (en) | High strength steel plate with excellent material uniformity in steel plate and method for producing the same | |
JP5439889B2 (en) | Thick steel plate for thick and high toughness steel pipe material and method for producing the same | |
JP2019131840A (en) | Method for producing high strength steel sheet for sour resistant line pipes, high strength steel sheet for sour resistant line pipes, and high strength steel pipe made of high strength steel sheet for sour resistant line pipes | |
JP6521196B1 (en) | High strength steel plate for sour line pipe, manufacturing method thereof and high strength steel pipe using high strength steel plate for sour line pipe | |
JP2009127072A (en) | Method for manufacturing thick high strength high toughness steel pipe base stock provided with high deformability | |
JP5891748B2 (en) | High-strength, high-toughness thick-walled steel plate with excellent material uniformity in the steel plate 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: 20130823 |
|
A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20140529 |
|
A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20140603 |
|
A521 | Request for written amendment filed |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20140724 |
|
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: 20140930 |
|
A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20141013 |
|
R150 | Certificate of patent or registration of utility model |
Ref document number: 5640614 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
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 |