JP5119574B2 - Heat treatment method for seamless steel pipe made of Ti-added low carbon steel - Google Patents
Heat treatment method for seamless steel pipe made of Ti-added low carbon steel Download PDFInfo
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本発明は、Ｔｉ添加系低炭素鋼からなる継目無鋼管の焼き戻し条件の決定方法に係わり、特に、海洋構造物のブレース（補強材）等に用いられる中径（例えば、外径：１７８〜４０６ｍｍφ程度）のＴｉ添加系低炭素鋼からなる継目無鋼管を強度の規格を外すことなく安定して製造する技術に関する。 The present invention relates to a method for determining a tempering condition of a seamless steel pipe made of a Ti-added low carbon steel, and in particular, a medium diameter (for example, an outer diameter: 178 to 178- The present invention relates to a technique for stably manufacturing a seamless steel pipe made of Ti-added low carbon steel (about 406 mmφ) without removing the strength standard.
一般に、所謂「中径継目無鋼管」は、図３に示すような製造工程（ラインともいう）を経て製造されている。まず、素材としての鋼鋳片（丸ビレット等）１を加熱炉２で一定温度に加熱し、ピアサー３で穿孔して素管４とする。そして、この素管４を、エロンゲータ５で拡管、プラグミル６で延伸、リーラー７で磨管のための圧延を施し、再加熱炉８で温度を再度調整してから、多段にロールスタンドを配設したサイザー９なる絞り圧延機で最終製品の寸法に調整する。ここまで製造した継目無鋼管１０は、引き続き、焼入れ水槽１１、熱処理装置１２に装入され、所定の熱処理（焼き入れ、焼き戻し、焼きならし等）を施し、製品規格を満たすか又はユーザーが所望する品質特性にしてから、図示していない検査、表示工程を経て出荷される。 In general, so-called “medium-diameter seamless steel pipes” are manufactured through a manufacturing process (also referred to as a line) as shown in FIG. First, a steel slab (round billet or the like) 1 as a raw material is heated to a certain temperature in a heating furnace 2, and is pierced by a piercer 3 to form a raw pipe 4. The base tube 4 is expanded by an elongator 5, stretched by a plug mill 6, rolled for polishing by a reeler 7, the temperature is adjusted again by a reheating furnace 8, and roll stands are arranged in multiple stages. The size of the final product is adjusted by a drawing mill called sizer 9. The seamless steel pipe 10 manufactured so far is continuously inserted into the quenching water tank 11 and the heat treatment apparatus 12 and subjected to a predetermined heat treatment (quenching, tempering, normalizing, etc.) to satisfy the product standard or After the desired quality characteristics are obtained, the product is shipped through an inspection and display process (not shown).
ところで、最近、石油業界の事情により、油井リグのような海洋構造物が増設される状況にあり、それに伴い、造管メーカーでは、該構造物に利用する材料の受注量が拡大している。その材料の一つに、Ｔｉ添加系低炭素鋼を素材とした中径の継目無鋼管（以下、単に鋼管ともいう）がある。 By the way, recently, due to circumstances in the oil industry, the number of offshore structures such as oil well rigs has been increased, and as a result, pipe manufacturers have increased orders for materials used for the structures. One of the materials is a medium-diameter seamless steel pipe (hereinafter also simply referred to as a steel pipe) made of Ti-added low carbon steel.
ところが、このＴｉ添加系低炭素鋼からなる鋼管を大量生産するに際して、当該材の過去の「引張り試験」の実績では、その降伏点強度は、顧客の規格から実に最大で１００ＭＰａ以上オーバーする場合もあり、引張り強度も大きくなる傾向が見られた。かかる降伏点強度が高すぎるＴｉ添加系低炭素鋼からなる鋼管は、ユーザーがそれを後に構造材に加工のが難しくなるので、その発生はできるだけ回避しなければならない。また、降伏点強度が高くなり過ぎた場合、再度の熱処理を施して、その降伏点強度を適正な値に戻すため、生産速度が遅くなり、製品の納期が遅れてしまうという問題も生じる可能性がある。 However, when mass-producing steel pipes made of this Ti-added low carbon steel, the yield point strength may exceed the maximum of 100 MPa or more from the customer's standard in the past “tensile test” results of the material. There was a tendency for the tensile strength to increase. Such a steel pipe made of a Ti-added low carbon steel having a yield strength that is too high is difficult to be processed by a user into a structural material later, so that its generation must be avoided as much as possible. Also, if the yield point strength becomes too high, the heat treatment is performed again to return the yield point strength to an appropriate value, which may cause problems such as production speed slowing and product delivery time being delayed. There is.
本発明は、かかる事情に鑑み、１回の熱処理で確実に目標とする降伏点強度を有する製品が得られるＴｉ添加系低炭素鋼からなる継目無鋼管の熱処理方法を提供することを目的としている。 In view of such circumstances, an object of the present invention is to provide a heat treatment method for a seamless steel pipe made of a Ti-added low-carbon steel that can provide a product having a desired yield strength with a single heat treatment. .
発明者は、上記目的を達成するため鋭意研究を重ね、その成果を本発明に具現化した。 The inventor has intensively studied to achieve the above object, and the results have been embodied in the present invention.
すなわち、本発明は、継目無鋼管の製造ライン上で、鋼組成がＴｉ含有量が０．０１６〜０．０１８質量％である低炭素鋼を素材として、それに穿孔、拡管、延伸及び磨管のための圧延を順次施した後、サイザーで絞り圧延した管体に、引き続き焼き入れ及び焼き戻しを順次行って継目無鋼管を製造するに際し、前記管体の焼き戻し温度及び時間を、下記（１）式に基づき定めることを特徴とするＴｉ添加系低炭素鋼からなる継目無鋼管の熱処理方法である。
（Ｔ＋２７３）×（２０＋ｌｏｇ（ｔｍ））
＝１７１６８×〔Ａ０＋Ａ１×（Ｔｉ／Ｎ）＋Ａ２×Ｂｒ＋Ａ３×（ｔ／Ｄ）＋Ａ４×Ｒ〕
・・（１）式
ここで、Ｔ：焼き戻し温度（℃），ｔｍ：焼き戻し時間（ｈｒ），Ｔｉ：素材のチタン含有量（質量％），Ｎ：素材の窒素含有量（質量％），Ｂｒ：素材のほう素含有量（Ｂ：質量％）と基準ほう素含有量（Ｂｏ：０．０００１質量％）との比（Ｂ／Ｂｏ），ｔ：管体の肉厚（ｍｍ），Ｄ：管体の外径（ｍｍφ），Ｒ：目標降伏点強度と基準降伏点強度との比、Ａ０、Ａ１、Ａ２、Ａ３、Ａ４：回帰式の定数
この場合、前記サイザーで絞り圧延した管体の外径を１７８〜４０６ｍｍφとするのが好ましい。
That is, the present invention uses a low carbon steel having a Ti composition of 0.016 to 0.018% by mass as a raw material on a production line for seamless steel pipes. In order to produce a seamless steel pipe by successively performing quenching and tempering sequentially on a pipe body that has been subjected to rolling for the purpose, and then drawing and rolling with a sizer, the tempering temperature and time of the pipe body are set as follows (1 This is a heat treatment method for a seamless steel pipe made of a Ti-added low carbon steel, characterized in that it is determined based on the formula (1).
(T + 273) × (20 + log (tm))
= 17168 × [A 0 + A 1 × (Ti / N) + A 2 × Br + A 3 × (t / D) + A 4 × R]
・ ・ Formula (1) where T: tempering temperature (° C.), tm: tempering time (hr), Ti: titanium content of material (mass%), N: nitrogen content of material (mass%) , Br: ratio (B / Bo) of the boron content (B: mass%) of the material to the reference boron content (Bo: 0.0001 mass%), t: wall thickness (mm) of the tubular body, D: tube outer diameter (mmφ), R: ratio of target yield strength to reference yield strength , A 0 , A 1 , A 2 , A 3 , A 4 : regression equation constant In this case, the sizer It is preferable that the outer diameter of the pipe body drawn and drawn at 178 to 406 mmφ.
本発明によれば、Ｔｉ添加系低炭素鋼からなる継目無鋼管の製造に際して、造管後の鋼管に対し適切な焼き戻し条件を適用できる。その結果、１回の熱処理で確実に目標とする降伏点強度を有する製品が得られるようになる。 According to the present invention, when producing a seamless steel pipe made of Ti-added low carbon steel, appropriate tempering conditions can be applied to the steel pipe after pipe making. As a result, a product having the desired yield strength can be obtained with a single heat treatment.
以下、発明をなすに至った経緯をまじえ、本発明の最良の実施形態を説明する。 Hereinafter, the best embodiment of the present invention will be described based on the background of the invention.
まず、発明者は、Ｔｉ添加系低炭素鋼からなる素材で造管した後に「焼き入れ」、「焼き戻し」の熱処理を順次施した鋼管の降伏点強度（記号：ＹＳ）及び引張強度（記号：ＴＳ）が、ユーザーから求められている目標とする値よりも高くなる原因を究明した。その結果、熱処理の温度及び時間は、製造対象の鋼種からなる鋼管に予め定められている通りであることが確認された。ところが、鋼管縦断面のマクロ組織を調査したところ、規格内に収まる低強度品は、図２（ｂ）に示すように、外面側の近傍に結晶粒が粗大な部分があるが、規格より外れる高強度品は、図２（ａ）に示すように、外面側から内面側にかけてほぼ全体が粗大な結晶粒になっていることが判明した。そして、実験室でこれらの試験片について加熱温度を種々変更して再焼き入れ実験を行ったが、結晶粒の粗大化に対する加熱温度の影響は見出せなかった。つまり、前記の低強度品と高強度品との間には、素材による影響があると判断された。 First, the inventor made a pipe made of a material made of a Ti-added low carbon steel and subsequently subjected to “quenching” and “tempering” heat treatment in sequence, yield strength (symbol: YS) and tensile strength (symbol). : TS) is, to investigate the RuHara-ins higher than the target value, which is determined from the user. As a result, it was confirmed that the temperature and time of the heat treatment were as determined in advance for the steel pipe made of the steel type to be manufactured. However, as a result of investigating the macro structure of the longitudinal section of the steel pipe, as shown in FIG. 2 (b), the low-strength product that falls within the standard has a coarse crystal grain in the vicinity of the outer surface side, but is out of the standard. As shown in FIG. 2A, the high-strength product was found to have coarse crystal grains almost entirely from the outer surface side to the inner surface side. In the laboratory, these test pieces were subjected to re-quenching experiments with various heating temperatures changed, but no influence of the heating temperature on the coarsening of the crystal grains was found. That is, it was determined that there is an influence of the material between the low-strength product and the high-strength product.
そこで、素材の炉番（溶製チャージの番号）毎に試料を採取し、プラズマ発光分光分析法により多数の化学成分について調査を行った。この分析結果の一例を表１に一括して示す。 Therefore, a sample was collected for each furnace number (melting charge number) of the material, and many chemical components were investigated by plasma emission spectroscopy. An example of the analysis results is collectively shown in Table 1.
表１より、各元素の値ともバラツキが小さいが、詳細に観察すると、炉番が３−３３５５９の試料が他の炉番のものより窒素（記号：Ｎ）含有量において若干の差が認められた。鋼鋳片は、同一転炉で溶製した溶鋼をＲＨ脱真空ガス装置で二次精錬し、連続鋳造されたものであるが、炉番が３−３３５５９の素材は、他と異なるＲＨ脱真空ガス装置を用いて溶製されたものであった。従って、装置のシール程度や排気装置の違いで窒素含有量に差が生じることが有り得る。 According to Table 1, the variation of each element value is small, but when observed in detail, a sample with a furnace number of 3-33559 has a slight difference in nitrogen (symbol: N) content from those of other furnace numbers. It was. The steel slab is obtained by continuously refining the molten steel melted in the same converter using an RH devacuum gas device and continuously casting it. It was melted using a gas apparatus. Therefore, there may be a difference in the nitrogen content depending on the degree of sealing of the device and the difference in the exhaust device.
そのため、発明者は、凝固あるいは熱処理時における窒化物の析出が結晶粒の大きさに影響していると考え、窒化物としてＴｉＮに着眼した。そして、素材のＴｉ／Ｎ比と製品の降伏点強度との関係を整理してみた。その結果、図１に示すように、両者間には相関があり、Ｔｉ／Ｎ比が大きいと、降伏点強度が大きくなっていた。このことは、熱処理時に、窒素が低いことから粗大ＴｉＮが少量析出し、オーステナイト粒を粗大化し、焼き入れ性が促進することを示唆している。つまり、Ｔｉ／Ｎ比の大きい素材で製造した鋼管の降伏点強度及び引張り強度がユーザーより求められている目標とする値よりも大きくなる原因と結論した。 For this reason, the inventor considered that precipitation of nitride during solidification or heat treatment has an influence on the size of crystal grains, and has focused on TiN as nitride. Then, the relationship between the Ti / N ratio of the material and the yield point strength of the product was arranged. As a result, as shown in FIG. 1, there was a correlation between them, and when the Ti / N ratio was large, the yield point strength was large. This suggests that a small amount of coarse TiN precipitates due to low nitrogen during heat treatment, coarsening the austenite grains and promoting hardenability. That is, it was concluded that the yield point strength and the tensile strength of the steel pipe manufactured with the material having a large Ti / N ratio are larger than the target values required by the user.
次に、発明者は、上記の問題点に対する対策を検討することにした。まず、Ｔｉ添加系低炭素鋼からなる継目無鋼管を製造する場合、素材のチタン（記号：Ｔｉ）の含有量は予め定まっており、窒素含有量以外はほぼ目標鋼種の基準値になっているので、上記知見に基づくと、窒素含有量の調整が重要なポイントになる。従って、まっ先に考えられる対策は、素材としての鋼鋳片を製造する溶鋼の溶製に際して、窒素含有量を低下させないことである。 Next, the inventor decided to examine a countermeasure for the above-mentioned problem. First, when producing a seamless steel pipe made of Ti-added low carbon steel, the content of titanium (symbol: Ti) of the material is determined in advance, and is almost the reference value of the target steel type other than the nitrogen content. Therefore, based on the above knowledge, adjustment of the nitrogen content is an important point. Therefore, the first conceivable measure is not to lower the nitrogen content when producing molten steel for producing a steel slab as a raw material.
ところが、この窒素含有量の調整は、溶鋼を溶製する装置であるＲＨ真空脱ガス装置の排気能力やシール性に大きな影響を受ける。そして、溶鋼の生産性のことを配慮すると、目標とするＴｉ添加系低炭素鋼からなる継目無鋼管の素材を常に同一のＲＨ真空脱ガス装置で溶製するわけにはいかない。また、Ｔｉ添加系低炭素鋼からなる継目無鋼管の素材を溶製する専用のＲＨ真空脱ガス装置を準備するのは、製鉄所として経済的なデメリットが大き過ぎる。 However, the adjustment of the nitrogen content is greatly affected by the exhaust capacity and sealing performance of the RH vacuum degassing apparatus, which is an apparatus for melting molten steel. Considering the productivity of molten steel, it is not always possible to melt the raw material of the seamless steel pipe made of the target Ti-added low carbon steel with the same RH vacuum degassing apparatus. In addition, preparing an exclusive RH vacuum degassing apparatus for melting a raw material of a seamless steel pipe made of Ti-added low carbon steel has too much economic disadvantage as an ironworks.
そこで、発明者は、継目無鋼管製造ライン上にある既存の装置を利用するだけで、対策を取ることにした。つまり、造管後の鋼管のＴｉ／Ｎ比は迅速に知れるので、熱処理を適切に行えば良いと考えたのである。そして、目標とする強度特性を満足するような「焼き入れ」や「焼き戻し」の条件を見出すことに鋭意努力した。その結果、造管後に「焼き入れ」を従来通りの条件で行い、「焼き戻し」だけを下記のように決定した条件で行えば良いことを見出したのである。 Therefore, the inventor decided to take measures only by using an existing apparatus on the seamless steel pipe production line. In other words, since the Ti / N ratio of the steel pipe after pipe forming is known quickly, it was thought that heat treatment should be performed appropriately. And we made an intensive effort to find the conditions of “quenching” and “tempering” that satisfy the target strength characteristics. As a result, it was found that “quenching” should be performed under conventional conditions after pipe making, and only “tempering” should be performed under the conditions determined as follows.
具体的には、今回得られた知見であるＴｉ／Ｎ比に加え、微量ながらも焼入れ性向上に効果のある元素であるほう素（記号：Ｂ）及び焼入れ時の冷却速度に影響を及ぼす肉厚（記号：ｔ）／外径（記号：Ｄ）比を重要因子として考慮し、過去の操業データを用いて、「焼き戻し」における温度及び時間と他の操業因子間との重相関分析を行い、下記（１）式を得た。
（Ｔ＋２７３）×（２０＋ｌｏｇ（ｔｍ））
＝１７１６８×〔Ａ0＋Ａ1×（Ｔｉ／Ｎ）＋Ａ2×Ｂｒ＋Ａ3×（ｔ／Ｄ）＋Ａ4×Ｒ〕
・・（１）式
ここで、Ｔ：焼き戻し温度（℃），ｔｍ：焼き戻し時間（ｈｒ），Ｔｉ：素材のチタン含有量（質量％），Ｎ：素材の窒素含有量（質量％），Ｂｒ：素材のほう素含有量（Ｂ：質量％）と基準ほう素含有量（Ｂｏ：０．０００１質量％）との比（Ｂ／Ｂｏ），ｔ：管体の肉厚（ｍｍ），Ｄ：管体の外径（ｍｍφ），Ｒ：目標降伏点強度と基準降伏点強度との比、Ａ0、Ａ1、Ａ2、Ａ3、Ａ4：回帰式の定数
この（１）式によれば、造管後の鋼管のＴｉ：素材のチタン含有量（質量％），Ｎ：素材の窒素含有量（質量％），Ｂｒ：素材のほう素含有量（Ｂ：質量％）と基準ほう素含有量（Ｂｏ：０．０００１質量％）との比（Ｂ／Ｂｏ），ｔ：管体の肉厚（ｍｍ），Ｄ：管体の外径（ｍｍφ），Ｒ：目標降伏点強度と基準降伏点強度との比等の値を代入することで、その鋼管に適切な「焼き戻し」の条件を「焼き戻しの温度」×「焼き戻しの時間」の形で見出せることになる。そして、「焼き戻しの温度」か「焼き戻しの時間」のどちらか一方を常識的な値に定めれば、それに対応した他方が決まることになり、それらの条件で焼き戻しをすれば、１回の熱処理で確実に目標とする強度特性を有するＴｉ添加系継目無鋼管を製造できるようになる。
Specifically, in addition to the Ti / N ratio that has been obtained this time, boron (symbol: B), which is an element that is effective in improving hardenability in a small amount, and meat that affects the cooling rate during quenching. Considering the ratio of thickness (symbol: t) / outer diameter (symbol: D) as an important factor, using the past operating data, perform a multiple correlation analysis between temperature and time in “tempering” and other operating factors. The following equation (1) was obtained.
(T + 273) × (20 + log (tm))
= 17168 × [A 0 + A 1 × (Ti / N) + A 2 × Br + A 3 × (t / D) + A 4 × R]
・ ・ Formula (1) where T: tempering temperature (° C.), tm: tempering time (hr), Ti: titanium content of material (mass%), N: nitrogen content of material (mass%) , Br: ratio (B / Bo) of the boron content (B: mass%) of the material to the reference boron content (Bo: 0.0001 mass%), t: wall thickness (mm) of the tubular body, D: tube outer diameter (mmφ), R: ratio of target yield strength to reference yield strength, A 0 , A 1 , A 2 , A 3 , A 4 : constant of regression equation (1) According to the above, Ti of the steel pipe after pipe making: titanium content (mass%) of the material, N: nitrogen content (mass%) of the material, Br: boron content (B: mass%) of the material and the standard Ratio (B / Bo) with boron content (Bo: 0.0001% by mass), t: tube thickness (mm), D: outer diameter of tube (mmφ), R: target yield strength And standard yield point By substituting the value of the ratio or the like of a degree, so that be found the conditions of the steel pipe "tempering" appropriate in the form of a "temperature tempering" × "tempering of time". If one of “tempering temperature” and “tempering time” is set to a common value, the other corresponding to it is determined. If tempering is performed under these conditions, 1 It becomes possible to manufacture a Ti-added seamless steel pipe having a desired strength characteristic by a single heat treatment.
なお、本発明では、製造するＴｉ添加系低炭素鋼からなる継目無鋼管のサイズは特に限定するものではないが、前記サイザーで絞り圧延した管体（鋼管）の外径を１７８〜４０６ｍｍφとするのが好ましい。Ｔｉ添加系低炭素鋼の継目無鋼管は、１７８ｍｍφ未満の小径よりもそれ以上の中径サイズで製造されることが多いからである。 In the present invention, the size of the seamless steel pipe made of Ti-added low carbon steel to be manufactured is not particularly limited, but the outer diameter of the pipe body (steel pipe) drawn by the sizer is 178 to 406 mmφ. Is preferred. This is because a Ti-added low carbon steel seamless steel pipe is often manufactured with a medium diameter larger than a small diameter of less than 178 mmφ.
図３に示した中径の継目無鋼管の製造ラインを利用して、Ｔｉ添加系低炭素鋼からなる継目無鋼管を製造した。その際、素材の鋼鋳片１としては、製鋼工場で転炉、ＲＨ真空脱ガス装置を順次経て連続鋳造したので、造管後の鋼管のＴｉ／Ｎ比は、表２に示すように異なっている。そして、従来通りに造管後の鋼管を再加熱炉８でＡｃ3変態点直上に加熱してから焼入れ水槽１１に浸漬する「焼き入れ」を行ってから、本発明により決定した「焼き戻し」の条件に従い、「焼き戻し」を熱処理装置１２で行った。その「焼き戻し」条件及び製品鋼管の特性を表２に一緒に示す。表２より、いずれの鋼管も目標とする降伏点強度及び引張強度を満足していた。 A seamless steel pipe made of a Ti-added low-carbon steel was manufactured using the production line for medium-diameter seamless steel pipes shown in FIG. At that time, as the steel slab 1 of the raw material, the Ti / N ratio of the steel pipe after the pipe making is different as shown in Table 2 because it is continuously cast through a converter and an RH vacuum degassing device in the steelmaking factory. ing. Then, immersed is heated to re in a heating furnace 8 directly above Ac 3 transformation point to steel pipe after pipe conventionally quenching water tank 11 after performing "quenching", "tempering" it was determined by the present invention In accordance with the above conditions, “tempering” was performed by the heat treatment apparatus 12. The “tempering” conditions and the properties of the product steel pipe are shown together in Table 2. From Table 2, all the steel pipes satisfied the target yield point strength and tensile strength.
１ 鋼鋳片
２ 加熱炉
３ ピアサー
４ 素管
５ エロンゲータ
６ プラグミル
７ リーラー
８ 再加熱炉
９ サイザー
１０ 継目無鋼管
１１ 焼入れ水槽
１２ 熱処理装置
DESCRIPTION OF SYMBOLS 1 Steel slab 2 Heating furnace 3 Piercer 4 Base pipe 5 Elongator 6 Plug mill 7 Reeler 8 Reheating furnace 9 Sizer 10 Seamless steel pipe 11 Quenching water tank 12 Heat treatment apparatus
Claims (2)
前記管体の焼き戻し温度及び時間を、下記（１）式に基づき定めることを特徴とするＴｉ添加系低炭素鋼からなる継目無鋼管の熱処理方法。
（Ｔ＋２７３）×（２０＋ｌｏｇ（ｔｍ））
＝１７１６８×〔Ａ０＋Ａ１×（Ｔｉ／Ｎ）＋Ａ２×Ｂｒ＋Ａ３×（ｔ／Ｄ）＋Ａ４×Ｒ〕
・・（１）式
ここで、Ｔ：焼き戻し温度（℃），ｔｍ：焼き戻し時間（ｈｒ），Ｔｉ：素材のチタン含有量（質量％），Ｎ：素材の窒素含有量（質量％），Ｂｒ：素材のほう素含有量（Ｂ：質量％）と基準ほう素含有量（Ｂｏ：０．０００１質量％）との比（Ｂ／Ｂｏ），ｔ：管体の肉厚（ｍｍ），Ｄ：管体の外径（ｍｍφ），Ｒ：目標降伏点強度と基準降伏点強度との比、Ａ０、Ａ１、Ａ２、Ａ３、Ａ４：回帰式の定数 On the seamless steel pipe production line, low carbon steel with a Ti composition of 0.016 to 0.018 mass% is used as a raw material, and it is sequentially subjected to drilling, expansion, drawing and rolling for polishing pipes. After that, when producing a seamless steel pipe by successively performing quenching and tempering sequentially on the pipe body drawn and rolled with a sizer,
The tempering temperature and time of the said pipe body are defined based on following (1) Formula, The heat processing method of the seamless steel pipe which consists of Ti addition type | system | group low carbon steel characterized by the above-mentioned.
(T + 273) × (20 + log (tm))
= 17168 × [A 0 + A 1 × (Ti / N) + A 2 × Br + A 3 × (t / D) + A 4 × R]
・ ・ Formula (1) where T: tempering temperature (° C.), tm: tempering time (hr), Ti: titanium content of material (mass%), N: nitrogen content of material (mass%) , Br: ratio (B / Bo) of the boron content (B: mass%) of the material to the reference boron content (Bo: 0.0001 mass%), t: wall thickness (mm) of the tubular body, D: outer diameter (mmφ) of tube, R: ratio of target yield strength to reference yield strength , A 0 , A 1 , A 2 , A 3 , A 4 : constants of regression equation
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| DE102013108803A1 (en) | 2013-08-14 | 2015-02-19 | Vallourec Deutschland Gmbh | Process for producing a tempered seamless hot-worked steel tube |
| CN105032976A (en) * | 2015-05-28 | 2015-11-11 | 攀钢集团成都钢钒有限公司 | Production method of titanium alloy seamless pipe |
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| JPS5974221A (en) * | 1982-10-19 | 1984-04-26 | Kawasaki Steel Corp | Production of high strength seamless steel pipe |
| JPS62149814A (en) * | 1983-09-21 | 1987-07-03 | Kawasaki Steel Corp | Production of low-carbon high-strength seamless steel pipe by direct hardening method |
| JPS6067623A (en) * | 1983-09-21 | 1985-04-18 | Kawasaki Steel Corp | Preparation of high strength low carbon seamless steel pipe by direct hardening method |
| JPS6075523A (en) * | 1983-09-30 | 1985-04-27 | Kawasaki Steel Corp | Manufacture of seamless steel pipe for oil well pipe with high strength |
| JPS6077926A (en) * | 1983-10-05 | 1985-05-02 | Kawasaki Steel Corp | Production of seamless steel pipe having high toughness, high strength and low yield ratio |
| JPS61238917A (en) * | 1985-04-15 | 1986-10-24 | Kawasaki Steel Corp | Manufacture of low alloy tempered high tensile seamless steel pipe |
| JPS62151545A (en) * | 1985-12-25 | 1987-07-06 | Kawasaki Steel Corp | Thick-walled, high-strength, low-pcm bended steel pipe and its production |
| JPH09235617A (en) * | 1996-02-29 | 1997-09-09 | Sumitomo Metal Ind Ltd | Production of seamless steel tube |
| JPH11302785A (en) * | 1998-04-20 | 1999-11-02 | Sumitomo Metal Ind Ltd | Steel for seamless steel pipe |
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| US6540848B2 (en) * | 2000-02-02 | 2003-04-01 | Kawasaki Steel Corporation | High strength, high toughness, seamless steel pipe for line pipe |
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