JP4741528B2 - Steel plates and steel pipes for steam transport piping having excellent high temperature characteristics and methods for producing them - Google Patents
Steel plates and steel pipes for steam transport piping having excellent high temperature characteristics and methods for producing them Download PDFInfo
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本発明は、特に、３００〜４００℃の蒸気輸送用配管に好適な高温特性に優れた蒸気輸送配管用鋼管およびその製造方法、並びに、蒸気輸送配管用鋼管の素材である鋼板およびその製造方法に関するものである。 In particular, the present invention relates to a steel pipe for steam transport piping excellent in high-temperature characteristics suitable for a steam transport pipe at 300 to 400 ° C., a manufacturing method thereof, a steel plate as a material of the steel pipe for steam transport piping, and a manufacturing method thereof. Is.
オイルサンド中に含有されるビチュメンのような重質油などの粘性の高い原油は、通常の方法で油井から天然のまま採取できない。そのため、オイルサンド含有層に蒸気を注入して原油の粘性を下げて採取し、回収効率を高める方法が採用されている。 Highly viscous crude oil such as heavy oil such as bitumen contained in the oil sand cannot be collected naturally from the oil well by a normal method. Therefore, a method has been adopted in which steam is injected into the oil sand containing layer to collect crude oil with reduced viscosity, thereby increasing the recovery efficiency.
このオイルサンド含有層に蒸気を注入する方法として、例えばスチームインジェクション法がある。この方法では、高温に加熱された高圧の蒸気を輸送用パイプラインによって運搬し、注入用鋼管を通じて注入する。 As a method for injecting steam into the oil sand-containing layer, for example, there is a steam injection method. In this method, high-pressure steam heated to a high temperature is conveyed by a transportation pipeline and injected through an injection steel pipe.
オイルサンド含有層に注入される高温、高圧の蒸気の温度は３００〜４００℃であり、内圧は１５０ＭＰａ程度である。この蒸気を輸送する配管に好適な高温強度に優れた蒸気輸送配管用鋼管として、従来、ＡＰＩ Ｘ６５、Ｘ７０グレード相当の継目無鋼管が提案されている（例えば、特許文献１〜３）。これらの鋼管の外径は最大で１６インチであった。
The temperature of the high-temperature and high-pressure steam injected into the oil sand-containing layer is 300 to 400 ° C., and the internal pressure is about 150 MPa. As steel pipes for steam transport pipes excellent in high-temperature strength suitable for pipes for transporting steam, seamless steel pipes equivalent to API X65 and X70 grades have been proposed (for example,
近年、エネルギー需要旺盛によりカナダなどでオイルサンド事業が活況となり、ビチュメンの回収効率を向上させるために配管の大径化が要求され、また、配管の軽量化による敷設コスト低減のため、鋼管の大径化及び高強度化が要求されている。しかし、特許文献１〜３によって提案されているような継目無鋼管は大径化が困難であり、ＡＰＩ Ｘ８０グレードの高強度も得られていない。
In recent years, the oil sands business has become active in Canada and other countries due to the energetic demand for energy, and it has been required to increase the diameter of piping in order to improve bitumen recovery efficiency. There is a demand for increasing diameter and strength. However, it is difficult to increase the diameter of a seamless steel pipe as proposed by
これに対して、高温強度に優れ、大径化が可能な溶接鋼管の製造技術が提案されている（例えば、特許文献４）。しかし、特許文献４によって提案されている蒸気配管用鋼管は、３００〜４００℃という中温域で長時間使用する際には、クリープによる破断が懸念される。 On the other hand, a technique for manufacturing a welded steel pipe that is excellent in high-temperature strength and capable of increasing the diameter has been proposed (for example, Patent Document 4). However, when the steel pipe for steam piping proposed by Patent Document 4 is used for a long time in an intermediate temperature range of 300 to 400 ° C., there is a concern about breakage due to creep.
本発明は、３００〜４００℃の中温度域での強度及び長時間クリープ特性に優れ、特に、常温及び中温度域での降伏強さが５５０ＭＰａ以上（ＡＰＩグレードＸ８０以上）の蒸気輸送配管用高強度鋼管及びその素材である高強度鋼板、並びにそれらの製造方法の提供を目的とする。 The present invention is excellent in strength at a medium temperature range of 300 to 400 ° C. and long-term creep characteristics, and particularly has a high yield strength for steam transport piping having a yield strength of 550 MPa or more (API grade X80 or more) at room temperature and medium temperature range. An object is to provide a high-strength steel pipe, a high-strength steel plate as a raw material thereof, and a method for producing them.
本発明は、特に、低合金鋼において、Ｔｉ／Ｎが適正な範囲になるようにＴｉを添加して、ＴｉＮを微細に析出させ、固溶Ｎｂを確保して高温強度を高め、更に、Ｂを有効に活用して、３００〜４００℃におけるクリープ特性の向上を図った、高温特性に優れる高強度鋼板及びそれを素材とする高強度溶接鋼管であり、その要旨は、以下のとおりである。
（１） 質量％で、Ｃ：０．０２〜０．１０％、Ｓｉ：０．０１〜０．５０％、Ｍｎ：０．５〜２．０％、Ｎｂ：０．００５〜０．０５０％、Ｔｉ：０．００５〜０．０５０％、Ｎ：０．００１〜０．０１０％、Ｂ：０．０００１〜０．００５０％を含有し、Ｐ：０．０２０％以下、Ｓ：０．００５％以下、Ａｌ：０．０４％以下に制限し、Ｔｉ／Ｎ：２．０〜４．０を満足し、残部Ｆｅ及び不可避的不純物からなることを特徴とする高温特性に優れた蒸気輸送配管用高強度鋼板。
（２） 質量％で、さらに、Ｍｏ：０．５０％以下、Ｃｒ：０．５０％以下の１種又は２種を合計で０．５０％以下含有し、Ｍｏ、Ｃｒ、Ｎｂ、Ｂの含有量が下記（１）式を満たすことを特徴とする上記（１）に記載の高温特性に優れた蒸気輸送配管用高強度鋼板。
０．０１５≦Ｍｏ＋Ｃｒ＋Ｎｂ＋１００Ｂ≦１．３５ … （１）
（３） 質量％で、さらに、Ｖ：０．５０％以下を含有することを特徴とする上記（１）又は（２）に記載の高温特性に優れた高温特性に優れた蒸気輸送配管用高強度鋼板。
（４） 質量％で、さらに、Ｃｕ：０．５０％以下、Ｎｉ：０．５０％以下の１種又は２種を含有することを特徴とする上記（１）〜（３）の何れか１項に記載の高温特性に優れた蒸気輸送配管用高強度鋼板。
（５） 質量％で、さらに、Ｃａ：０．０００５〜０．００５０％、ＲＥＭ：０．０００５〜０．０１００％の一方又は双方を含有することを特徴とする上記（１）〜（４）の何れか１項に記載の高温特性に優れた蒸気輸送配管用高強度鋼板。
（６） 上記（１）〜（４）の何れか１項に記載の鋼板を管状に成形し、突合わせ部を溶接したことを特徴とする高温特性に優れた蒸気輸送配管用高強度鋼管。
（７） 上記（１）〜４の何れか１項に記載の成分からなる鋼片を、１０００〜１２５０℃に加熱し、９００℃以下での累積圧下率を５０％以上とし、終了温度を８５０℃以下として熱間圧延した後、４００〜５５０℃の範囲まで、５℃／ｓ以上の冷却速度で加速冷却することを特徴とする高温特性に優れた蒸気輸送配管用高強度鋼板の製造方法。
（８） 上記（６）に記載の方法により製造された高強度鋼板を管状に成形し、突合せ部を溶接することを特徴とする高温特性に優れた蒸気輸送配管用高強度鋼管の製造方法。
In the present invention, in particular, in low alloy steel, Ti is added so that Ti / N is in an appropriate range, TiN is finely precipitated, solid solution Nb is secured to increase high temperature strength, and B Is a high-strength steel sheet excellent in high-temperature characteristics, and a high-strength welded steel pipe made from the same, which has improved creep characteristics at 300 to 400 ° C. by effectively utilizing the above, and the gist thereof is as follows.
(1) By mass%, C: 0.02 to 0.10%, Si: 0.01 to 0.50%, Mn: 0.5 to 2.0%, Nb: 0.005 to 0.050% , Ti: 0.005 to 0.050%, N: 0.001 to 0.010%, B: 0.0001 to 0.0050%, P: 0.020% or less, S: 0.005 % Or less, Al: 0.04% or less, satisfying Ti / N: 2.0 to 4.0, consisting of the remainder Fe and inevitable impurities High strength steel plate.
(2) By mass%, Mo: 0.50% or less, Cr: 0.50% or less, or a total of 0.50% or less, Mo, Cr, Nb, B content The high-strength steel sheet for steam transport piping excellent in high-temperature characteristics as described in (1) above, wherein the amount satisfies the following formula (1).
0.015 ≦ Mo + Cr + Nb + 100B ≦ 1.35 (1)
(3) High in steam transport piping excellent in high temperature characteristics and excellent in high temperature characteristics as described in (1) or (2) above, further comprising V: 0.50% or less by mass% Strength steel plate.
(4) Any one of the above-mentioned (1) to (3), further comprising one or two of Cu: 0.50% or less and Ni: 0.50% or less in mass%. A high-strength steel sheet for steam transport piping having excellent high-temperature characteristics as described in the paragraph.
(5) The above-mentioned (1) to (4), characterized by containing one or both of Ca: 0.0005 to 0.0050% and REM: 0.0005 to 0.0100% by mass%. The high-strength steel sheet for steam transport piping excellent in high-temperature characteristics according to any one of the above.
(6) A high-strength steel pipe for steam transport piping excellent in high-temperature characteristics, wherein the steel plate according to any one of (1) to (4) is formed into a tubular shape and a butt portion is welded.
(7) The steel slab comprising the component described in any one of (1) to (4) above is heated to 1000 to 1250 ° C., the cumulative rolling reduction at 900 ° C. or less is set to 50% or more, and the end temperature is 850 A method for producing a high-strength steel sheet for steam transport piping excellent in high-temperature characteristics, characterized by performing accelerated rolling at a cooling rate of 5 ° C./s or higher after hot rolling at a temperature of 400 ° C. or less after hot rolling.
(8) A method for producing a high-strength steel pipe for steam transport piping excellent in high-temperature characteristics, wherein the high-strength steel sheet produced by the method described in (6) above is formed into a tubular shape and a butt portion is welded.
本発明によれば、高温、高圧の蒸気を輸送する配管に好適な、高温強度及び長時間クリープ特性に優れた蒸気輸送配管用高強度鋼管を得ることができ、これにより、蒸気輸送用配管の重量軽減による敷設コストの削減が可能になり、又は蒸気輸送用配管の大径化によって蒸気輸送効率が向上するなど、産業上の貢献が顕著である。 According to the present invention, it is possible to obtain a high-strength steel pipe for steam transport piping excellent in high-temperature strength and long-term creep characteristics, suitable for piping for transporting high-temperature and high-pressure steam. Industrial contributions such as reduction in weight due to weight reduction, and improvement in steam transport efficiency due to an increase in diameter of steam transport pipes are significant.
本発明は、Ｔｉの添加によって、微細なＴｉＮの析出による強化を活用し、高温強度を向上させた蒸気輸送配管用高強度鋼板及びその鋼板を素材とする蒸気輸送配管用高強度鋼管である。ＴｉＮの析出状態は、Ｔｉ／Ｎに大きく影響され、これを適正な範囲に規定することにより、ＴｉＮを鋼中に微細に分散させることができる。ＴｉＮは、析出強化だけでなく、溶接熱影響部（ＨＡＺという。）の旧オーステナイト粒の微細化にも有効であり、Ｔｉ／Ｎの適正化によってＨＡＺの靭性も向上する。 The present invention is a high-strength steel plate for steam transport piping that uses high-strength steel plate for steam transport piping that uses high-strength strength due to precipitation of fine TiN by adding Ti, and a high-strength steel pipe for steam transport piping that uses the steel plate as a raw material. The precipitation state of TiN is greatly influenced by Ti / N, and TiN can be finely dispersed in the steel by defining this in an appropriate range. TiN is effective not only for precipitation strengthening but also for refining the prior austenite grains in the weld heat affected zone (referred to as HAZ), and the toughness of the HAZ is improved by optimizing Ti / N.
したがって、本発明において、Ｔｉ／Ｎは重要な因子である。Ｔｉ／Ｎは、Ｔｉの添加量の、Ｎの添加量に対する比であり、ＴｉＮの析出状態を示すパラメータである。Ｔｉ／Ｎが２．０未満であると、ＴｉＮの析出量が少ないため析出強化の効果が不十分になり、高温強度が低下する。一方、Ｔｉ／Ｎが４．０を超えると、ＴｉＮが析出する温度が高温になり、ＴｉＮが粗大化する。そのため、特に、ＨＡＺにおいて、ＴｉＮによる結晶粒成長の抑制が不十分になり、旧オーステナイト粒が粗大化して、靭性が劣化する。 Therefore, Ti / N is an important factor in the present invention. Ti / N is a ratio of the addition amount of Ti to the addition amount of N, and is a parameter indicating the precipitation state of TiN. When Ti / N is less than 2.0, the precipitation amount of TiN is small, so that the effect of precipitation strengthening becomes insufficient, and the high-temperature strength decreases. On the other hand, when Ti / N exceeds 4.0, the temperature at which TiN precipitates becomes high and TiN becomes coarse. Therefore, in particular, in HAZ, the suppression of crystal grain growth by TiN becomes insufficient, the prior austenite grains become coarse, and the toughness deteriorates.
本発明者らは、Ｃ：０．０２〜０．１０％、Ｓｉ：０．０１〜０．５０％、Ｍｎ：０．５〜２．０％、Ｎｂ：０．００５〜０．０５０％、Ｔｉ：０．００５〜０．０５０％、Ｎ：０．００１〜０．０１０％、Ｂ：０．０００１〜０．００５０％を含有し、Ｐ：０．０２０％以下、Ｓ：０．００５％以下、Ａｌ：０．０４％以下に制限し、Ｔｉ／Ｎを変化させた鋼を溶製して鋳造した。得られた鋼片を１０００〜１２５０℃に加熱し、９００℃以下での累積圧下率を５０％以上として、圧延し、８５０℃以下で熱間圧延を終了して、４００〜５５０℃まで５℃／ｓ以上の冷却速度で加速冷却し、鋼板を製造した。 The inventors have C: 0.02 to 0.10%, Si: 0.01 to 0.50%, Mn: 0.5 to 2.0%, Nb: 0.005 to 0.050%, Ti: 0.005 to 0.050%, N: 0.001 to 0.010%, B: 0.0001 to 0.0050%, P: 0.020% or less, S: 0.005% In the following, Al was limited to 0.04% or less, and steel with varying Ti / N was melted and cast. The obtained steel slab is heated to 1000 to 1250 ° C., rolled at a cumulative reduction rate of 900 ° C. or less at 50% or more, hot-rolled at 850 ° C. or less and finished to 400 to 550 ° C. to 5 ° C. The steel plate was manufactured by accelerated cooling at a cooling rate of at least / s.
これらの鋼板用いて、高温強度及びＨＡＺの靭性を評価した。高温強度は、ＪＩＳ Ｇ ０５６７に準拠し、３５０℃の引張強度を測定して評価した。ＨＡＺの靭性は、鋼板から採取した小片に再現熱サイクル試験を施した後、シャルピー試験を行って評価した。再現熱サイクル試験は、高周波加熱とガス冷却によって、溶接熱影響部の温度履歴を模擬した熱処理を施すものである。本発明では、１４００℃に加熱し、８００℃から５００℃までの冷却時間を１０ｓとして冷却する条件で再現熱サイクル試験を行い、シャルピー試験をＪＩＳ Ｚ ２２４２に準拠して行った。 Using these steel plates, high temperature strength and HAZ toughness were evaluated. The high temperature strength was evaluated by measuring the tensile strength at 350 ° C. according to JIS G 0567. The toughness of HAZ was evaluated by conducting a repetitive thermal cycle test on a small piece taken from a steel plate and then performing a Charpy test. The reproducible heat cycle test is a heat treatment that simulates the temperature history of the heat affected zone by high frequency heating and gas cooling. In the present invention, a reproducible thermal cycle test was performed under the conditions of heating to 1400 ° C. and cooling the cooling time from 800 ° C. to 500 ° C. as 10 s, and the Charpy test was performed in accordance with JIS Z 2242.
結果を図１及び図２に示す。図１及び図２に示したように、Ｔｉ／Ｎが２．０〜４．０の範囲内であれば、高温強度及びＨＡＺ靭性が良好であることがわかる。また、図１から、Ｔｉ／Ｎが、２．０〜４．０の範囲内では、大きい方が高温強度の向上には好ましいことがわかる。したがって、良好な高温強度及びＨＡＺ靭性を得るためにはＴｉ／Ｎを２．０〜４．０とすることが必要であり、高温強度を向上させるためにはＴｉ／Ｎを３．０〜４．０とすることが好ましい。 The results are shown in FIGS. As shown in FIG.1 and FIG.2, if Ti / N exists in the range of 2.0-4.0, it turns out that a high temperature strength and HAZ toughness are favorable. Moreover, it can be seen from FIG. 1 that when Ti / N is in the range of 2.0 to 4.0, a larger value is preferable for improving high-temperature strength. Therefore, in order to obtain good high-temperature strength and HAZ toughness, it is necessary to set Ti / N to 2.0 to 4.0, and in order to improve high-temperature strength, Ti / N is set to 3.0 to 4 0.0 is preferable.
また、本発明は、Ｂを添加し、析出するＢＮを有効に活用して、３００〜４００℃におけるクリープ特性を向上させたことを最大の特徴とするものである。高強度鋼板及び鋼管は、長時間、３００〜４００℃に加熱されると、Ｍ23Ｃ6が粗大なＭ6Ｃとなり、高温強度及びクリ−プ強度が低下する。これに対して、Ｂを添加するとＭ23Ｃ6が安定化し、粗大なＭ6Ｃの生成が抑制され、高温強度やクリ−プ強度の低下が抑制される。Ｍは、主にＦｅであり、鋼の成分組成に選択的にＣｒ、Ｍｏが含有される場合は、Ｆｅに加えて、Ｃｒ、Ｍｏが含まれることがある。 Further, the present invention is characterized in that the creep characteristics at 300 to 400 ° C. are improved by adding B and effectively utilizing the precipitated BN. When a high-strength steel plate and a steel pipe are heated to 300 to 400 ° C. for a long time, M 23 C 6 becomes coarse M 6 C, and high-temperature strength and creep strength are lowered. On the other hand, when B is added, M 23 C 6 is stabilized, generation of coarse M 6 C is suppressed, and a decrease in high temperature strength and creep strength is suppressed. M is mainly Fe, and when Cr and Mo are selectively contained in the steel component composition, Cr and Mo may be contained in addition to Fe.
特に、Ｍｏ、Ｃｒの１種又は２種を含有させて、高温強度の向上を図る場合には、粗大なＭ6Ｃの生成が問題になる。そのため、本発明者らは、Ｃ、Ｓｉ、Ｍｎ、Ｔｉ、Ｎ、Ｐ、Ｓ、Ａｌの含有量が上述の範囲であり、Ｔｉ／Ｎが２．０〜４．０であり、Ｎｂ及びＢの含有量が、Ｎｂ：０．００１〜０．０５０％、Ｂ：０〜０．００５０％であり、更に、Ｍｏ：０．５０％以下、Ｃｒ：０．５０％以下の１種又は２種を合計で０．５０％以下を添加した鋼を溶製し、上述の条件で製造した鋼板を製造し、鋼板から試験片を採取して、３５０℃におけるクリープ破断特性を評価した。 In particular, when one or two of Mo and Cr are contained to improve the high-temperature strength, the generation of coarse M 6 C becomes a problem. Therefore, the present inventors have the contents of C, Si, Mn, Ti, N, P, S, and Al in the above range, Ti / N is 2.0 to 4.0, Nb and B The content of Nb is 0.001 to 0.050%, B is 0 to 0.0050%, Mo is 0.50% or less, and Cr is 0.50% or less. Steels added with 0.50% or less in total were melted, steel plates manufactured under the above-mentioned conditions were manufactured, specimens were taken from the steel plates, and creep rupture properties at 350 ° C. were evaluated.
クリープ破断特性の評価は、直径６ｍｍ、平行部３０ｍｍの丸棒試験片を用いて、４００℃及び４５０℃のクリープ破断強度を測定し、ラルソンミラーパラメータ法で３５０℃、３０万時間後の推定クリープ破断強度を算出した。 Creep rupture characteristics were evaluated by measuring the creep rupture strength at 400 ° C and 450 ° C using a round bar test piece with a diameter of 6 mm and a parallel part of 30 mm, and estimated creep after 300,000 hours at 350 ° C by the Larson Miller parameter method. The breaking strength was calculated.
その結果、図３に示すように、クリープ破断強度には、Ｍｏ、Ｃｒ、Ｎｂ、Ｂの含有量との相関が認められた。図３から下記（１）式
０．０１５≦Ｍｏ＋Ｃｒ＋Ｎｂ＋１００Ｂ≦１．３５ … （１）
を満たすことにより、３５０℃におけるクリープ特性が良好になることが明らかである。ここで、Ｍｏ、Ｃｒ、Ｎｂ、Ｂは質量％で表された各元素の含有量である。
As a result, as shown in FIG. 3, the creep rupture strength was correlated with the contents of Mo, Cr, Nb, and B. From FIG. 3, the following equation (1) 0.015 ≦ Mo + Cr + Nb + 100B ≦ 1.35 (1)
It is clear that the creep characteristics at 350 ° C. are improved by satisfying the above. Here, Mo, Cr, Nb, and B are the contents of each element expressed in mass%.
上記（１）式のＭｏ＋Ｃｒ＋Ｎｂ＋１００Ｂを適正な範囲に規定することにより、クリープ特性が向上することから、Ｂの添加による長時間加熱時の高温強度の劣化の抑制、クリープ特性の向上の効果が、特に、Ｃｒ、Ｍｏを含有する低合金鋼において、極めて有効であることがわかる。この理由は、低合金鋼に添加されたＢは、Ｃと共偏析するため、Ｍ23Ｃ6がＭ23ＣＢ6となり、安定化するためであると考えられる。特に、Ｃｒ、Ｍｏを含有する低合金鋼は、高温で長時間加熱されるとＭ23Ｃ6にＣｒ、Ｍｏが濃化するため、粗大なＭ6Ｃが生成し易い。しかし、Ｂを添加すると、Ｍ23ＣＢ6がＭ23Ｃ6の周辺に析出し、粗大なＭ6Ｃの生成が抑制される。 By defining Mo + Cr + Nb + 100B in the above formula (1) within an appropriate range, the creep characteristics are improved. Therefore, the effect of suppressing the deterioration of high-temperature strength during long-time heating due to the addition of B, and the improvement of the creep characteristics are particularly effective. It can be seen that this is extremely effective in a low alloy steel containing Cr, Mo. The reason for this is considered that B added to the low alloy steel co-segregates with C, so that M 23 C 6 becomes M 23 CB 6 and stabilizes. In particular, low alloy steels containing Cr and Mo tend to produce coarse M 6 C because Cr and Mo concentrate in M 23 C 6 when heated for a long time at a high temperature. However, when B is added, M 23 CB 6 precipitates around M 23 C 6 and the production of coarse M 6 C is suppressed.
次に、本発明の鋼板及び鋼管の成分組成について説明する。 Next, the component composition of the steel plate and steel pipe of the present invention will be described.
Ｃは、焼入性を向上させ、また、Ｆｅ、Ｎｂ、Ｔｉ、更に、選択的に添加されるＣｒ、Ｍｏ、と炭化物を形成し、常温及び高温における強度の向上に寄与する元素である。Ｃ量が、０．０２％未満では、焼入性が下するため十分な強度を保持できない。また、炭化物の析出強化を十分に発現させるためには、Ｃを０．０４％以上添加することが好ましい。一方、Ｃ量が、０．１０％を超えると炭化物が粗大化し、析出強化に寄与する微細な炭化物の析出量が減少し、強度が低下する。 C is an element that improves hardenability and forms carbides with Fe, Nb, Ti, and selectively added Cr, Mo, and carbides, and contributes to improvement in strength at normal and high temperatures. If the amount of C is less than 0.02%, the hardenability is lowered and sufficient strength cannot be maintained. Moreover, in order to fully develop the precipitation strengthening of carbides, it is preferable to add 0.04% or more of C. On the other hand, if the amount of C exceeds 0.10%, the carbides become coarse, the amount of fine carbides that contribute to precipitation strengthening decreases, and the strength decreases.
Ｓｉは、脱酸剤として作用する元素であり、その効果を得るには０．０１％以上の添加が必要である。強力な脱酸剤であるＡｌの含有量が少ない場合には、Ｓｉを０．０５％以上添加することが好ましい。一方、Ｓｉ量が０．５０％を超えると溶接熱影響部の靭性が低下し、クリープ特性も劣化する。 Si is an element that acts as a deoxidizer, and in order to obtain the effect, addition of 0.01% or more is necessary. When the content of Al, which is a strong deoxidizer, is small, it is preferable to add 0.05% or more of Si. On the other hand, if the amount of Si exceeds 0.50%, the toughness of the weld heat affected zone decreases, and the creep characteristics also deteriorate.
Ｍｎは、脱酸剤として作用し、強度も向上させる元素である。Ｍｎ含有量が０．５％未満では脱酸の効果が不十分であり、強度を確保するためには、１．０％以上を添加することが好ましい。一方、Ｍｎ量が２．０％を超えるとクリープ破断強度が低下する。 Mn is an element that acts as a deoxidizer and improves strength. If the Mn content is less than 0.5%, the effect of deoxidation is insufficient, and in order to ensure strength, it is preferable to add 1.0% or more. On the other hand, when the amount of Mn exceeds 2.0%, the creep rupture strength decreases.
Ｂは、上述のように、ＢＮ、Ｍ23ＣＢ6を生じ、特に、Ｃｒ、Ｍｏを含有する場合には、粗大なＭ6Ｃの析出が抑えられ、高温強度、クリ−プ強度の向上に寄与する極めて重要な元素である。また、Ｂは、焼入性を著しく向上させる元素であり、強度の向上にも寄与する。これらの効果を得るには、Ｂを０．０００１％以上添加することが必要である。一方、Ｂ含有量が０．００５０％を超えるとＢが結晶粒界に過剰に偏析し、加工性、靭性及び溶接性を損なう。また、Ｃとの共偏析による炭化物の凝集粗大化を抑制して、常温及び高温での強度を確保し、クリープ特性の劣化を抑制するには、Ｂ含有量の上限を０．００３０％以下にすることが好ましい。 As described above, B produces BN and M 23 CB 6 , and particularly when Cr and Mo are contained, the precipitation of coarse M 6 C is suppressed, and the high temperature strength and the creep strength are improved. It is a very important element that contributes. B is an element that remarkably improves hardenability and contributes to the improvement of strength. In order to obtain these effects, it is necessary to add 0.0001% or more of B. On the other hand, if the B content exceeds 0.0050%, B is excessively segregated at the grain boundaries, thereby impairing workability, toughness, and weldability. Moreover, in order to suppress the agglomeration and coarsening of carbides due to co-segregation with C, to ensure the strength at normal temperature and high temperature, and to suppress the deterioration of creep characteristics, the upper limit of the B content is set to 0.0030% or less. It is preferable to do.
Ｎｂは、Ｃ、Ｎと結合してＮｂ（Ｃ，Ｎ）などの炭窒化物を形成する元素である。この炭窒化物が微細に析出すると、高温強度やクリープ破断強度の向上に寄与し、更に、結晶粒を微細化して、靭性の改善にも有効に作用する。これらの効果を得るには、Ｎｂ含有量を０．００５％以上とすることが必要である。一方、Ｎｂ含有量が０．０５０％を超えるとＮｂの炭窒化物が粗大になり、高温強度及び靭性を損なう。 Nb is an element that combines with C and N to form a carbonitride such as Nb (C, N). If this carbonitride precipitates finely, it contributes to the improvement of high-temperature strength and creep rupture strength, and further refines the crystal grains and effectively acts to improve toughness. In order to obtain these effects, the Nb content needs to be 0.005% or more. On the other hand, if the Nb content exceeds 0.050%, the Nb carbonitride becomes coarse and the high-temperature strength and toughness are impaired.
Ｔｉは、上述のように、本発明において極めて重要な元素である。Ｔｉは、Ｎとの結合力がＮｂよりも強いため、固溶Ｎの固定に有効であり、生成した微細なＴｉＮは、強度、特に高温強度の向上への寄与が顕著である。この効果を得るには、Ｔｉ含有量を０．００５％以上とすることが必要である。一方、Ｔｉ量が０．０５０％を超えるとＴｉＮが高温で析出して粗大化し、ＨＡＺの靭性が低下するため、上限を０．０５０％以下とすることが必要である。また、ＴｉＮが粗大化すると高温強度を向上させる効果が不十分になるため、Ｔｉの含有量の上限を０．０３０％以下とすることが好ましい。 As described above, Ti is an extremely important element in the present invention. Since Ti has a stronger binding force with N than Nb, Ti is effective for fixing solute N, and the fine TiN produced has a significant contribution to improving strength, particularly high-temperature strength. In order to acquire this effect, it is necessary to make Ti content 0.005% or more. On the other hand, if the amount of Ti exceeds 0.050%, TiN precipitates at a high temperature and becomes coarse, and the toughness of the HAZ decreases. Therefore, the upper limit needs to be 0.050% or less. Moreover, since the effect of improving the high-temperature strength becomes insufficient when TiN is coarsened, the upper limit of the Ti content is preferably 0.030% or less.
Ｎは、鋼中に固溶し、また、Ｎｂ、Ｔｉ、更にＶと窒化物、炭窒化物を形成する元素であり、固溶強化及び析出強化に寄与するため、０．００１％以上を添加する。更に、本発明では、Ｎは、ＢＮを生じて、クリープ破断強度の向上にも寄与する。この効果を得るには、Ｎを０．００２％以上添加することが好ましい。一方、Ｎ量が０．０１０％を超えると、靭性と強度が低下する。また、ＨＡＺ靭性を確保するには、Ｎ量の上限を０．００６％以下とすることが好ましい。 N is an element that forms a solid solution in steel and forms Nb, Ti, V, nitride, and carbonitride, and contributes to solid solution strengthening and precipitation strengthening, so 0.001% or more is added. To do. Further, in the present invention, N generates BN and contributes to the improvement of creep rupture strength. In order to acquire this effect, it is preferable to add N 0.002% or more. On the other hand, if the N content exceeds 0.010%, the toughness and strength decrease. Moreover, in order to ensure HAZ toughness, it is preferable to make the upper limit of N amount 0.006% or less.
Ｐ、Ｓは、本発明では不純物であり、過剰に含有すると機械特性を損なう。Ｐ、Ｓの含有量が、それぞれ、０．０２０％、０．００５％を超えると強度が低下する。 P and S are impurities in the present invention, and if contained excessively, mechanical properties are impaired. If the P and S contents exceed 0.020% and 0.005%, the strength decreases.
Ａｌは、脱酸剤として有効であるが、０．０４０％を超えると高温強度が低下する。脱酸の効果を十分に得るには、下限を０．００２％以上とすることが好ましい。 Al is effective as a deoxidizing agent, but when it exceeds 0.040%, the high-temperature strength decreases. In order to sufficiently obtain the effect of deoxidation, the lower limit is preferably set to 0.002% or more.
本発明において、高温強度を向上させるには、Ｃｒ、Ｍｏの１種又は２種を更に含有させることが好ましい。 In the present invention, in order to improve the high temperature strength, it is preferable to further contain one or two of Cr and Mo.
Ｃｒは、強度向上に有効な元素であり、高温強度の向上にも有効である。しかし、Ｃｒ含有量が０．５０％を超えると、溶接性を損なうことがあるため、上限を０．５０％以下とすることが好ましい。また、靭性及び製造コストの観点から、０．３５％以下とすることが更に好ましい。 Cr is an element effective for improving the strength, and is also effective for improving the high-temperature strength. However, if the Cr content exceeds 0.50%, weldability may be impaired, so the upper limit is preferably made 0.50% or less. Moreover, from a viewpoint of toughness and manufacturing cost, it is still more preferable to set it as 0.35% or less.
Ｍｏは、固溶強化と微細炭化物析出による強化作用に有効な元素であり、高温強度の向上には極めて有効である。しかし、Ｍｏ含有量が０．５０％を超えると、溶接性、靭性を損うことがあるため、上限を０．５０％以下とすることが好ましい。また、Ｍｏは高価で、価格が不安定であるため、製造コストの観点から、０．１０％未満を上限とすることが更に好ましい。 Mo is an element effective for strengthening by solid solution strengthening and fine carbide precipitation, and is extremely effective for improving high-temperature strength. However, if the Mo content exceeds 0.50%, weldability and toughness may be impaired, so the upper limit is preferably made 0.50% or less. Moreover, since Mo is expensive and its price is unstable, it is more preferable that the upper limit is less than 0.10% from the viewpoint of manufacturing cost.
更に、Ｃｒ、Ｍｏの１種又は２種を添加する場合には、添加量の合計の上限を０．５０％以下とすることが好ましい。これは、Ｃｒ、Ｍｏの合計含有量が０．５０％を超えると、溶接性及び靭性を損なうことがあるためである。なお、Ｃｒ及びＭｏの含有量を、更に好ましい上限、それぞれ、０．３５％以下、０．１０％未満とする場合には、Ｃｒ、Ｍｏの合計の含有量を０．４５％未満とすることが好ましい。 Furthermore, when adding 1 type or 2 types of Cr and Mo, it is preferable to make the upper limit of the total of addition amount into 0.50% or less. This is because if the total content of Cr and Mo exceeds 0.50%, weldability and toughness may be impaired. In addition, when the content of Cr and Mo is further more preferable, respectively, 0.35% or less and less than 0.10%, the total content of Cr and Mo should be less than 0.45%. Is preferred.
更に、Ｖ、Ｃｕ、Ｎｉ、Ｃａ、ＲＥＭの１種又は２種以上を含有しても良い。 Furthermore, you may contain 1 type (s) or 2 or more types of V, Cu, Ni, Ca, and REM.
Ｖは、Ｎｂと同様、Ｖ（Ｃ，Ｎ）の微細炭窒化物を形成し、高温長時間側のクリープ断強度や高温強度の向上に寄与する。しかし、０．５０％を超えるＶを添加すると粗大なＶ（Ｃ，Ｎ）が析出し、クリープ強度、高温強度、引張強度、靭性を損なうことがある。したがって、Ｖ含有量は０．５０％以下とすることが好ましい。 V, like Nb, forms fine carbonitrides of V (C, N) and contributes to the improvement of the creep breaking strength and the high temperature strength on the high temperature long time side. However, when V exceeding 0.50% is added, coarse V (C, N) is precipitated, which may impair the creep strength, high temperature strength, tensile strength, and toughness. Therefore, the V content is preferably 0.50% or less.
Ｃｕ、Ｎｉは、靭性及び強度の向上に有効な元素であり、１種又は２種を添加しても良い。０．５０％超のＣｕ、Ｎｉを添加する場合には、粗大な金属間化合物の析出、粒界への偏析に起因する脆化が生じることがあるため、上限を０．５０％以下とすることが好ましい。 Cu and Ni are elements effective for improving toughness and strength, and one or two of them may be added. When adding more than 0.50% Cu or Ni, embrittlement may occur due to precipitation of coarse intermetallic compounds and segregation to grain boundaries, so the upper limit is made 0.50% or less. It is preferable.
Ｃａ、ＲＥＭは介在物の形態の制御に有効な元素である。Ｃａは硫化物系介在物の形態を制御し、靭性を改善させるため、０．０００５％以上を添加することが好ましい。一方、０．００５０％を超えるＣａを添加すると、粗大な酸化物を形成して靭性を損なうことがある。したがって、Ｃａ含有量は０．０００５〜０．００５０％とすることが好ましい。ＲＥＭは、不純物元素（Ｐ、Ｓ、Ｏ）とそれらの析出物（介在物）の形態の制御を目的として添加される元素である。不純物を安定で無害な析出物として固定し、強度と靭性を向上させるには、ＲＥＭを０．０００５％以上添加することが好ましい。一方、ＲＥＭの添加量が０．０１００％を超えると、介在物が増加して、靭性を損なうことがある。したがって、ＲＥＭの含有量は０．０００５〜０．０１００％以下とすることが好ましい。 Ca and REM are effective elements for controlling the form of inclusions. Ca controls the form of sulfide inclusions and improves toughness, so 0.0005% or more is preferably added. On the other hand, when Ca exceeding 0.0050% is added, a coarse oxide may be formed and toughness may be impaired. Therefore, the Ca content is preferably 0.0005 to 0.0050%. REM is an element added for the purpose of controlling the form of impurity elements (P, S, O) and their precipitates (inclusions). In order to fix impurities as stable and harmless precipitates and improve strength and toughness, it is preferable to add REM 0.0005% or more. On the other hand, if the amount of REM added exceeds 0.0100%, inclusions may increase and the toughness may be impaired. Therefore, the REM content is preferably 0.0005 to 0.0100% or less.
次に、本発明の鋼板の製造方法について説明する。 Next, the manufacturing method of the steel plate of this invention is demonstrated.
鋼の溶製及び鋳造は常法で行えば良く、鋳造は生産性の観点から連続鋳造が好ましい。得られた鋼片を熱間圧延し、冷却して鋼板とする。なお、熱間圧延の条件は、特に規定する必要はなく、素材である鋼片の形状及び厚みと熱間圧延後の鋼板の板厚、目的とする機械特性を考慮して、条件を決定すれば良い。熱間圧延後は空冷でも良いが、加速冷却を行うことが好ましい。加速冷却は、水冷、ミスト冷却、送風など、目的とする機械特性を考慮して、適宜選択することができる。 The melting and casting of steel may be performed by a conventional method, and the casting is preferably continuous casting from the viewpoint of productivity. The obtained steel slab is hot-rolled and cooled to obtain a steel plate. The conditions for hot rolling need not be specified, and should be determined in consideration of the shape and thickness of the steel slab, the thickness of the steel sheet after hot rolling, and the desired mechanical properties. It ’s fine. Although air cooling may be performed after hot rolling, accelerated cooling is preferably performed. Accelerated cooling can be appropriately selected in consideration of target mechanical characteristics such as water cooling, mist cooling, and air blowing.
以下、熱間圧延及び制御冷却の好ましい条件について説明する。 Hereinafter, preferable conditions for hot rolling and controlled cooling will be described.
熱間圧延の加熱温度は、鋼片の組織をオーステナイトとするため、１０００℃以上とすることが好ましい。これは、炭化物の固溶を十分に進行させるためであり、特に、室温強度、高温強度及び長時間クリープ特性を得るためには、加熱温度を１１００℃以上にすることが好ましい。一方、加熱温度が１２５０℃を超えると、鋼のオーステナイトが粒成長し、圧延、加速冷却後の鋼板の靱性が劣化することがある。 The heating temperature of the hot rolling is preferably set to 1000 ° C. or higher so that the structure of the steel slab is austenite. This is to sufficiently advance the solid solution of the carbide. In particular, in order to obtain room temperature strength, high temperature strength, and long-term creep characteristics, it is preferable to set the heating temperature to 1100 ° C. or higher. On the other hand, when the heating temperature exceeds 1250 ° C., the austenite of the steel grows and the toughness of the steel sheet after rolling and accelerated cooling may deteriorate.
熱間圧延では、オーステナイトからフェライトへの変態温度以上で、再結晶が進行しない温度（オーステナイト未再結晶域という。）での圧下率を確保することが好ましい。本発明の鋼は、Ｎｂ添加によってオーステナイト未再結晶域の上限が９００℃程度にまで上昇する。したがって、鋼片を熱間圧延する際には、９００℃以下での累積の圧下率を５０％以上とすることが好ましい。これにより、オーステナイト粒が圧延方向に延伸し、板厚、板幅方向で細粒になると共に、圧延により導入される粒内の転位密度が増加し、高強度が得られ、靭性が向上する。 In hot rolling, it is preferable to ensure a reduction rate at a temperature at which the recrystallization does not proceed (referred to as an austenite non-recrystallized region) above the transformation temperature from austenite to ferrite. In the steel of the present invention, the upper limit of the austenite non-recrystallized region rises to about 900 ° C. by adding Nb. Therefore, when the steel slab is hot-rolled, it is preferable that the cumulative rolling reduction at 900 ° C. or less is 50% or more. As a result, the austenite grains are stretched in the rolling direction and become fine grains in the plate thickness and plate width directions, the dislocation density in the grains introduced by rolling is increased, high strength is obtained, and toughness is improved.
また、圧延の終了温度が８５０℃を超えると、結晶粒が成長して粗大になり、転位が回復して、強度が低下することがある。なお、圧延の終了温度が低すぎると、相変態によりフェライトが生成して、加速冷却後の組織に加工フェライトが含まれることがあり、７００℃以上とすることが好ましい。 On the other hand, when the rolling end temperature exceeds 850 ° C., crystal grains grow and become coarse, dislocations recover, and the strength may decrease. In addition, when the completion | finish temperature of rolling is too low, a ferrite will produce | generate by a phase transformation and a process ferrite may be contained in the structure | tissue after accelerated cooling, It is preferable to set it as 700 degreeC or more.
熱間圧延の終了後は、結晶粒の成長、転位の回復を抑制するために、加速冷却を行うことが好ましい。加速冷却は、熱間圧延の終了後、直ちに開始することが好ましいが、６０ｓ以内に行えば良い。搬送時に温度が低下する場合には、開始温度を７００℃以上とすることが好ましい。 After the hot rolling is completed, accelerated cooling is preferably performed in order to suppress the growth of crystal grains and the recovery of dislocations. Accelerated cooling is preferably started immediately after the end of hot rolling, but may be performed within 60 s. In the case where the temperature decreases during transportation, the starting temperature is preferably set to 700 ° C. or higher.
加速冷却での冷却速度を速くすると、鋼の組織において、ベイナイト、マルテンサイトなど、低温変態の生成量が増加し、強度が向上する。そのため、高い強度を確保するためには、加速冷却の冷却速度を５℃／ｓ以上とすることが好ましい。加速冷却の冷却速度が５℃／ｓ未満であると、フェライトの生成量が増加し、冷却中に転位の回復も進行するため、室温及び高温での強度が低下する傾向にある。加速冷却の上限は、冷却設備の性能により適宜決定されるが、３００℃／ｓを超えることは困難である。 When the cooling rate in accelerated cooling is increased, the amount of low-temperature transformation such as bainite and martensite is increased in the steel structure, and the strength is improved. Therefore, in order to ensure high strength, it is preferable to set the cooling rate of accelerated cooling to 5 ° C./s or more. If the cooling rate of accelerated cooling is less than 5 ° C./s, the amount of ferrite produced increases and the recovery of dislocations also proceeds during cooling, so the strength at room temperature and high temperature tends to decrease. The upper limit of accelerated cooling is appropriately determined depending on the performance of the cooling facility, but it is difficult to exceed 300 ° C./s.
また、加速冷却の停止温度が低下すると、強度が上昇して、靭性が低下することがある。そのため、強度及び靭性を確保するには、加速冷却の冷却停止温度を適正な範囲とすることが好ましい。加速冷却の冷却停止温度が５５０℃を超えると、炭化物の成長が促進され、固溶炭素量が少なくなり、強度、特に高温強度が低下することがあるため、上限を５５０℃とすることが好ましい。一方、冷却停止温度が４００℃未満になると、低温変態生成物の析出が顕著になり靭性が劣化することがある。 Moreover, when the stop temperature of accelerated cooling falls, intensity | strength will rise and toughness may fall. Therefore, in order to ensure strength and toughness, it is preferable to set the cooling stop temperature for accelerated cooling to an appropriate range. When the cooling stop temperature of accelerated cooling exceeds 550 ° C., the growth of carbides is promoted, the amount of dissolved carbon decreases, and the strength, particularly the high temperature strength may be lowered. Therefore, the upper limit is preferably set to 550 ° C. . On the other hand, when the cooling stop temperature is less than 400 ° C., precipitation of the low-temperature transformation product becomes remarkable and the toughness may deteriorate.
上述の方法によって得られた鋼板を造管し、アーク溶接して、本発明の鋼管、例えば、ＵＯＥ鋼管、電縫鋼管、スパイラル鋼管、レーザー溶接鋼管を製造する。 The steel plate obtained by the above method is piped and arc welded to produce the steel pipe of the present invention, for example, UOE steel pipe, ERW steel pipe, spiral steel pipe, laser welded steel pipe.
ＵＯＥ鋼管の場合、上述の熱間圧延工程で製造した鋼板を、冷間加工、具体的には、Ｃプレス、Ｕプレス及びＯプレスによって管状に成形し、突合された鋼板の端部をアーク溶接、好ましくは、サブマージアーク溶接によって溶接する。更に、真円度を高める場合には、拡管を行うことが好ましい。 In the case of UOE steel pipe, the steel plate manufactured in the above hot rolling process is cold-worked, specifically formed into a tube by C press, U press and O press, and the ends of the butt steel plates are arc welded. The welding is preferably performed by submerged arc welding. Furthermore, in order to increase the roundness, it is preferable to perform tube expansion.
電縫鋼管やレーザー溶接鋼管の場合、熱間圧延工程で製造した熱延鋼板を、ロール成形などの冷間曲げ加工によって管状に成形し、入熱、鋼板の突き合わせ角度（Ｖ角）、鋼板の通板速度等を制御して、電縫溶接又はレーザー溶接する。スパイラル鋼管の場合は、熱延工程で製造した鋼板を螺旋状に送給して管状に成形し、溶接して製造する。 In the case of ERW and laser welded steel pipes, the hot-rolled steel sheet produced in the hot rolling process is formed into a tubular shape by cold bending such as roll forming, and heat input, the butt angle (V angle) of the steel sheet, Electrically welded or laser welded by controlling the plate passing speed. In the case of a spiral steel pipe, the steel plate manufactured in the hot rolling process is spirally fed, formed into a tubular shape, and welded.
表１に示す化学成分の鋼を溶製し、鋳造して得られた鋼片を表２に示した条件で熱間圧延し、鋼板を製造した。鋼板をＵＯＥ工程で造管してサブマージアーク溶接し、鋼管を製造した。鋼管のサイズは、肉厚が表２に示した鋼板の板厚と同等であり、外径は７６２ｍｍである。 Steel pieces obtained by melting and casting steels having chemical components shown in Table 1 were hot-rolled under the conditions shown in Table 2 to produce steel plates. A steel plate was piped in the UOE process and submerged arc welded to manufacture a steel pipe. The size of the steel pipe is equivalent to the plate thickness of the steel plate shown in Table 2, and the outer diameter is 762 mm.
造管前の鋼板から、圧延方向と垂直な方向を長手方向として引張試験片を採取した。また、鋼管は、平板状にプレスして、鋼管周方向に引張試験片を採取した。これらの試験片を用いて、室温及び３５０℃で引張試験を行い、降伏強度を求めた。室温での試験にはＡＰＩ全厚引張試験を用いた。３５０℃での試験には直径６ｍｍ、平行部３０ｍｍの丸棒試験片を用いた。室温及び３５０℃での降伏強度が５５０ＭＰａ以上であるものを良好として評価した。 Tensile specimens were taken from the steel plate before pipe making with the direction perpendicular to the rolling direction as the longitudinal direction. Moreover, the steel pipe was pressed into a flat plate shape, and tensile test pieces were collected in the circumferential direction of the steel pipe. Using these test pieces, a tensile test was performed at room temperature and 350 ° C. to determine the yield strength. The API full thickness tensile test was used for the test at room temperature. For the test at 350 ° C., a round bar test piece having a diameter of 6 mm and a parallel part of 30 mm was used. Those having a yield strength of 550 MPa or more at room temperature and 350 ° C. were evaluated as good.
また、平板状にプレスした鋼管からは、クリープ破断特性を評価するために、鋼管周方向に直径６ｍｍ、平行部３０ｍｍの丸棒試験片を採取し、試験温度４００℃及び４５０℃にてクリープ破断強度を測定した。これは、加速評価試験であり、ラルソンミラーパラメータ法を用いることによって３５０℃、３０万時間後の推定クリープ破断強度を算出した。 Moreover, in order to evaluate creep rupture characteristics, a round bar test piece having a diameter of 6 mm and a parallel part of 30 mm was collected from a steel tube pressed into a flat plate shape and subjected to creep rupture at test temperatures of 400 ° C. and 450 ° C. The strength was measured. This is an accelerated evaluation test, and the estimated creep rupture strength after 300,000 hours at 350 ° C. was calculated by using the Larson Miller parameter method.
更に、鋼管周方向からＪＩＳ Ｚ ２２４１のＶノッチシャルピー試験片を採取し、溶接部境界（Ｆｕｓｉｏｎ Ｌｉｎｅ）から１ｍｍ位置にノッチ位置を設けてシャルピー衝撃試験を行った。ＨＡＺ靭性の評価は、試験温度は０℃として、脆性破面率により評価した。 Furthermore, a V-notch Charpy test piece of JIS Z 2241 was sampled from the circumferential direction of the steel pipe, and a Charpy impact test was performed by providing a notch position at a position of 1 mm from the weld line boundary (Fusion Line). The HAZ toughness was evaluated based on the brittle fracture surface ratio at a test temperature of 0 ° C.
表２に結果を示す。表２の製造Ｎｏ．１〜１６は本発明例であり、鋼板および鋼管の室温および３５０℃の降伏強度が５５０ＭＰａ以上を有し、かつ３５０℃、３０万時間後の推定クリープ破断強度も非常に良好な値を得ることができた。なお、鋼板の製造条件が好ましい範囲外である製造Ｎｏ．１２〜１６は、鋼板および鋼管の室温および３５０℃の降伏強度、および３５０℃、３０万時間後の推定クリープ破断強度のうち、何れかが、製造Ｎｏ．１よりも若干劣っている。 Table 2 shows the results. Production No. in Table 2 1 to 16 are examples of the present invention, the yield strength of steel sheets and pipes at room temperature and 350 ° C. is 550 MPa or more, and the estimated creep rupture strength after 350 ° C. and 300,000 hours is also very good. I was able to. In addition, manufacturing No. whose manufacturing conditions of a steel plate are outside a preferable range. Nos. 12 to 16 indicate that any of the yield strength at 350 ° C. and 350 ° C. after 300,000 hours of steel plate and steel pipe is the production No. Slightly inferior to 1.
一方、化学成分が本発明の範囲外である製造Ｎｏ．１７〜２５は、鋼板および鋼管の室温および３５０℃の降伏強度、および３５０℃、３０万時間後の推定クリープ破断強度のうち、何れかが本発明例よりも劣っている。 On the other hand, production No. whose chemical component is out of the scope of the present invention. Nos. 17 to 25 are inferior to the examples of the present invention among the room temperature and the yield strength at 350 ° C. of the steel plate and the steel pipe, and the estimated creep rupture strength after 350 ° C. and 300,000 hours.
Claims (8)
Ｃ ：０．０２〜０．１０％、
Ｓｉ：０．０１〜０．５０％、
Ｍｎ：０．５〜２．０％、
Ｎｂ：０．００５〜０．０５０％、
Ｔｉ：０．００５〜０．０５０％、
Ｎ ：０．００１〜０．０１０％、
Ｂ ：０．０００１〜０．００５０％
を含有し、
Ｐ：０．０２０％以下、
Ｓ：０．００５％以下、
Ａｌ：０．０４％以下
に制限し、
Ｔｉ／Ｎ：２．０〜４．０
を満足し、残部がＦｅ及び不可避的不純物からなることを特徴とする高温特性に優れた蒸気輸送配管用高強度鋼板。 % By mass
C: 0.02-0.10%,
Si: 0.01 to 0.50%,
Mn: 0.5 to 2.0%
Nb: 0.005 to 0.050%,
Ti: 0.005 to 0.050%,
N: 0.001 to 0.010%,
B: 0.0001 to 0.0050%
Containing
P: 0.020% or less,
S: 0.005% or less,
Al: limited to 0.04% or less,
Ti / N: 2.0 to 4.0
A high-strength steel sheet for steam transport piping excellent in high temperature characteristics, characterized in that the balance is composed of Fe and inevitable impurities.
Ｍｏ：０．５０％以下、
Ｃｒ：０．５０％以下
の一方又は双方を合計で０．５０％以下含有し、Ｍｏ、Ｃｒ、Ｎｂ、Ｂの含有量が下記（１）式を満たすことを特徴とする請求項１に記載の高温特性に優れた蒸気輸送配管用高強度鋼板。
０．０１５≦Ｍｏ＋Ｃｒ＋Ｎｂ＋１００Ｂ≦１．３５ … （１） In mass%,
Mo: 0.50% or less,
The content of Mo, Cr, Nb, and B satisfies the following formula (1), containing one or both of Cr: 0.50% or less in total and 0.50% or less. High strength steel plate for steam transport piping with excellent high temperature characteristics.
0.015 ≦ Mo + Cr + Nb + 100B ≦ 1.35 (1)
Ｖ：０．５０％以下
を含有することを特徴とする請求項１又は２に記載の高温特性に優れた蒸気輸送配管用高強度鋼板。 In mass%,
V: 0.50% or less, The high-strength steel sheet for steam transport piping excellent in high temperature characteristics according to claim 1 or 2.
Ｃｕ：０．５０％以下、
Ｎｉ：０．５０％以下
の１種又は２種を含有することを特徴とする請求項１〜３の何れかの項に記載の高温特性に優れた蒸気輸送配管用高強度鋼板。 In mass%,
Cu: 0.50% or less,
Ni: 0.50% or less of 1 type or 2 types is contained, The high strength steel plate for steam transport piping excellent in the high temperature characteristic of any one of Claims 1-3 characterized by the above-mentioned.
Ｃａ ：０．０００５〜０．００５０％、
ＲＥＭ：０．０００５〜０．０１００％
の１種又は２種を含有することを特徴とする請求項１〜４の何れか１項に記載の高温特性に優れた蒸気輸送配管用高強度鋼板。 In mass%,
Ca: 0.0005 to 0.0050%,
REM: 0.0005 to 0.0100%
One type or two types of these are contained, The high strength steel plate for steam transport piping excellent in the high temperature characteristic of any one of Claims 1-4 characterized by the above-mentioned.
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