JP2016196040A - METHOD OF PRODUCING MARTENSITIC HIGH Cr STEEL SEAMLESS STEEL TUBE - Google Patents
METHOD OF PRODUCING MARTENSITIC HIGH Cr STEEL SEAMLESS STEEL TUBE Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 89
- 239000010959 steel Substances 0.000 title claims abstract description 89
- 229910000734 martensite Inorganic materials 0.000 title claims abstract description 41
- 238000000034 method Methods 0.000 title claims abstract description 20
- 238000005096 rolling process Methods 0.000 claims abstract description 79
- 238000010438 heat treatment Methods 0.000 claims abstract description 40
- 238000004519 manufacturing process Methods 0.000 claims abstract description 24
- 238000003303 reheating Methods 0.000 claims abstract description 23
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 14
- 239000000203 mixture Substances 0.000 claims abstract description 12
- 238000001816 cooling Methods 0.000 claims description 37
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052799 carbon Inorganic materials 0.000 claims description 3
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 229910052748 manganese Inorganic materials 0.000 claims description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 3
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 229910052710 silicon Inorganic materials 0.000 claims description 3
- 229910052720 vanadium Inorganic materials 0.000 claims description 3
- 230000037303 wrinkles Effects 0.000 abstract description 19
- 239000000463 material Substances 0.000 abstract description 4
- 229910001566 austenite Inorganic materials 0.000 description 32
- 230000002829 reductive effect Effects 0.000 description 13
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- 230000007797 corrosion Effects 0.000 description 6
- 238000005260 corrosion Methods 0.000 description 6
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- 239000007787 solid Substances 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 3
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- 238000006477 desulfuration reaction Methods 0.000 description 1
- 230000023556 desulfurization Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
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- 229910052758 niobium Inorganic materials 0.000 description 1
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- 238000009628 steelmaking Methods 0.000 description 1
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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Abstract
Description
本発明は、継目無鋼管の製造方法に関し、特に、マルテンサイト系高Ｃｒ鋼の組成を有する中空素管をストレッチ・レデューサもしくはサイザーで縮径圧延する過程で、管の内面に高頻度で発生し易い内面しわ疵を抑制するマルテンサイト系高Ｃｒ鋼継目無鋼管の製造方法に関する。 The present invention relates to a method for producing a seamless steel pipe, and in particular, is frequently generated on the inner surface of a pipe in the process of reducing the diameter of a hollow element pipe having a composition of martensitic high Cr steel with a stretch reducer or sizer. The present invention relates to a method for manufacturing a martensitic high Cr steel seamless steel pipe that suppresses easy internal wrinkling.
継目無鋼管は、一般に、丸ビレットを素材として、穿孔圧延、およびこれに後続する延伸圧延、さらに定径圧延等を施すことにより製造される。 A seamless steel pipe is generally manufactured by subjecting a round billet to a raw material and subjecting it to piercing and rolling, followed by drawing and rolling, and constant diameter rolling.
製管工場における継目無鋼管の製造工程の一例を図４に示す。丸ビレット１は、例えば回転式加熱炉２で、加熱（ビレット加熱）された後、穿孔プラグ４を有する傾斜ロール式穿孔圧延機（ピアサ）３で穿孔圧延（ピアサ圧延）され、中空素管となる。該中空素管は、引き続いて延伸圧延される。該延伸圧延は、管内面拘束用にマンドレルバー６を有するマンドレルミル５を用いるマンドレルミル圧延、あるいは、管内面拘束用にエロンゲータプラグ９を有するエロンゲータ８を用いる圧延（エロンゲータ圧延）と、管内面拘束用にプラグミルプラグ１１を有するプラグミル１０を用いる圧延（プラグミル圧延）と、管内面拘束用にリーラープラグ１３を有するリーラー１２を用いる圧延（リーラー圧延）と、をこの順に行う圧延（エロンゲータ・プラグミル・リーラー圧延）によって施される。前記延伸圧延後の中空素管は、例えばウォーキングビーム式加熱炉７で、再加熱された後、ストレッチ・レデューサ１４を用いるストレッチ・レデューサ圧延、あるいは、サイザー（サイジングミル）１５を用いるサイジングミル圧延によって定径圧延（以下、縮径圧延ともいう）され、製品（継目無鋼管）１６とされる。
An example of the manufacturing process of the seamless steel pipe in a pipe manufacturing factory is shown in FIG. The round billet 1 is heated (billet heating) in, for example, a rotary heating furnace 2, and then pierced and rolled (piercered) by an inclined roll piercing and rolling machine (piercer) 3 having a piercing plug 4. Become. The hollow shell is subsequently drawn and rolled. The stretching rolling includes mandrel mill rolling using a
上述の製造工程において、ストレッチ・レデューサまたはサイザーによる縮径圧延では、中空素管を孔型圧延ロールに通して、マンドレルなどの内面拘束工具を用いることなく、前記中空素管を外径絞り圧延によって縮径して熱間仕上げするので、熱間仕上げされた鋼管の内表面にしわ疵が発生し易い。通常、鋼管の内表面に生じるしわ疵とは、熱間仕上げされた鋼管の内表面に存在する深さ０．２ｍｍ（２００μｍ）程度の管長手方向の縦筋状の凹みをいう。 In the above-described manufacturing process, in the diameter reduction rolling with a stretch reducer or sizer, the hollow shell is passed through a perforated rolling roll and the hollow shell is subjected to outer diameter rolling without using an inner surface constraining tool such as a mandrel. Since it is reduced in diameter and hot-finished, wrinkles are likely to occur on the inner surface of the hot-finished steel pipe. Usually, the wrinkle generated on the inner surface of the steel pipe refers to a longitudinal streak-like dent in the pipe longitudinal direction having a depth of about 0.2 mm (200 μm) existing on the inner surface of the hot-finished steel pipe.
このような問題に対して、特許文献１では、ストレッチ・レデューサを用いて、圧下量を各スタンド間において均一状態にすることで鋼管内面における真円度が高い継目無鋼管を能率的に製造し、この鋼管内面をショットブラスト研削等によって内面切削する自動車用継目無鋼管の製造方法が提案されている。この製造方法によれば、比較的僅少な内面切削によって、内面疵を除去することができるとしている。また、特許文献２ではストレッチ・レデューサによる定径圧延において、圧延機出側での仕上肉厚ｔ（ｍｍ）および仕上外径Ｄ（ｍｍ）とした場合に、ｔ／Ｄと孔型ロールの平均楕円率との関係を一定に保つことにより、熱間仕上げされた鋼管の内表面に発生するしわ疵を抑制する方法が提案されている。 With respect to such a problem, Patent Document 1 efficiently manufactures a seamless steel pipe having a high roundness on the inner surface of the steel pipe by using a stretch reducer to make the reduction amount uniform between the stands. A method for manufacturing a seamless steel pipe for automobiles is proposed in which the inner surface of the steel pipe is internally cut by shot blast grinding or the like. According to this manufacturing method, the inner surface flaws can be removed by relatively little inner surface cutting. Further, in Patent Document 2, in constant diameter rolling by a stretch reducer, when the finishing thickness t (mm) and the finishing outer diameter D (mm) on the delivery side of the rolling mill are set, the average of t / D and perforated roll There has been proposed a method for suppressing wrinkles generated on the inner surface of a hot-finished steel pipe by keeping the relationship with the ellipticity constant.
しかし、特許文献１の製造方法では、熱間圧延された継目無鋼管の内面を２０〜５００μｍ切削加工することによって、鋼管内面に発生した疵および脱炭層を除去するとしているので、ショットブラストによる内面研削に膨大な処理時間が必要になる。 However, in the manufacturing method of Patent Document 1, the inner surface of the hot-rolled seamless steel pipe is cut by 20 to 500 μm to remove the soot and decarburized layer generated on the inner surface of the steel pipe. A huge amount of processing time is required for grinding.
また、特許文献２の製造方法では、定径圧延の仕上げ寸法毎に孔型ロールを準備する必要があり、かつ、ロット毎にロール組替えを要するため、多種に渡る継目無鋼管の製造においては生産能率を阻害するという問題がある。 Moreover, in the manufacturing method of patent document 2, since it is necessary to prepare a perforated roll for every finishing dimension of constant diameter rolling, and a roll recombination is required for every lot, it is produced in the manufacture of various seamless steel pipes. There is a problem of inhibiting efficiency.
本発明は、上述のような問題点に鑑みてなされたものであり、ストレッチ・レデューサまたはサイザーによる縮径圧延によって熱間仕上げされた鋼管の内表面に発生するしわ疵を効率よく抑制することにより、内面品質に優れたマルテンサイト系高Ｃｒ鋼継目無鋼管の製造方法を提供することを目的としている。 The present invention has been made in view of the above-described problems, and efficiently suppresses wrinkles generated on the inner surface of a steel pipe that has been hot-finished by diameter reduction rolling using a stretch reducer or sizer. It aims at providing the manufacturing method of the martensitic high Cr steel seamless steel pipe excellent in inner surface quality.
本発明者等は、上述の課題を解決するため、マルテンサイト系高Ｃｒ鋼継目無鋼管の製造に際し、縮径圧延工程で発生する内面しわ疵と縮径圧延に供される中空素管の内面近傍の組織との関係について鋭意検討を行った。 In order to solve the above-mentioned problems, the present inventors have made inner surface wrinkles generated in the diameter reduction rolling process and inner surface of the hollow shell used for diameter reduction rolling in the production of martensitic high Cr steel seamless steel pipe. We have intensively investigated the relationship with nearby tissues.
縮径圧延工程では、前述したとおり、中空素管を外径絞り圧延によって縮径して仕上げるので、被圧延材である中空素管の内面は拘束の無い状態である。その結果、前記中空素管の内面では周方向の座屈現象が発生し、縮径圧延後には前記内面に微小な凹凸形状が形成され、該凹凸形状が内面しわ疵の原因になると推測される。 In the reduced diameter rolling process, as described above, the hollow shell is finished by reducing the diameter by outside diameter rolling, so that the inner surface of the hollow shell that is the material to be rolled is in an unconstrained state. As a result, a circumferential buckling phenomenon occurs on the inner surface of the hollow shell, and after the diameter reduction rolling, it is estimated that a minute uneven shape is formed on the inner surface, which causes the inner surface to be wrinkled. .
そこで、特に内面しわ疵の発生が顕著なマルテンサイト系高Ｃｒ鋼継目無鋼管からサンプルを採取し、内面しわ疵が発生している部位の周方向断面ミクロ組織を観察した。その結果、鋼管内面の凹凸形状は、該鋼管内面の旧オーステナイト粒界（縮径圧延前のオーステナイト粒界）に沿って形成され、鋼管の内面しわ疵の深さは旧オーステナイト粒が大きいほど深くなっていることが確認された。 Therefore, a sample was taken from a martensitic high Cr steel seamless steel pipe in which the generation of internal wrinkles was particularly remarkable, and the circumferential cross-sectional microstructure of the site where the internal wrinkles were generated was observed. As a result, the uneven shape of the inner surface of the steel pipe is formed along the old austenite grain boundary (austenite grain boundary before diameter reduction rolling) of the inner surface of the steel pipe, and the depth of the inner wrinkle wrinkle of the steel pipe becomes deeper as the old austenite grain becomes larger. It was confirmed that
そこで、縮径圧延前の中空素管のオーステナイト組織を微細化することにより縮径圧延で生じる鋼管内面の凹凸形状の深さを抑制することができ、その結果、内面しわ疵が小さく内面品質が優れた鋼管が得られるということに思い至った。 Therefore, by refining the austenite structure of the hollow shell before diameter reduction rolling, the depth of the irregular shape on the inner surface of the steel pipe caused by diameter reduction rolling can be suppressed. As a result, the inner surface wrinkle is small and the inner surface quality is reduced. It came to mind that an excellent steel pipe could be obtained.
さらに、縮径圧延工程前の再加熱工程において微細なオーステナイト組織を有するマルテンサイト系高Ｃｒ鋼の中空素管を得るためには、延伸圧延した後、該中空素管を前記マルテンサイト系高Ｃｒ鋼のＭｆ点以下の温度まで冷却して鋼組織をマルテンサイト組織とし、その後、Ａｃ３点以上の温度に再加熱することによってマルテンサイト組織から逆変態した微細なオーステナイト組織とすることが有効であることを見出した。 Furthermore, in order to obtain a hollow element tube of martensitic high Cr steel having a fine austenite structure in the reheating step before the diameter reduction rolling step, after the drawing and rolling, the hollow element tube is formed by the martensitic high Cr steel. It is effective to cool the steel structure to a temperature below the Mf point of the steel to make the steel structure a martensite structure, and then reheat it to a temperature of Ac 3 points or more to obtain a fine austenite structure reversely transformed from the martensite structure. I found out.
また、前記延伸圧延後の中空素管をＭｆ点以下まで冷却し、その後Ａｃ３点以上の温度に再加熱するにあたって、冷却速度および／または加熱速度が速くなるほど変態後のオーステナイト組織が微細になるという知見が得られた。
本発明は、上述の知見に基づいて完成されたものであり、下記の要旨からなる。
Further, when the hollow shell after the drawing and rolling is cooled to the Mf point or lower and then reheated to a temperature of Ac 3 point or higher, the austenite structure after transformation becomes finer as the cooling rate and / or the heating rate is increased. That knowledge was obtained.
The present invention has been completed on the basis of the above-mentioned findings and comprises the following gist.
（１）質量％で、Ｃ：０．０１〜０．２５％、Ｓｉ：０．１０〜１．００％、Ｍｎ：０．１０〜２．００％、Ｃｒ：８．０〜１５．０％、Ｎｉ：０．０５〜８．００％、Ｍｏ：０．３０〜４．００％、Ｖ：０．０１〜０．２５％、Ｎ：０．０１０〜０．０７０％を含有し、残部Ｆｅおよび不可避的不純物からなる組成を有する丸ビレットを加熱し、穿孔圧延工程、延伸圧延工程、再加熱工程、及び縮径圧延工程を順次有するマルテンサイト系高Ｃｒ鋼継目無鋼管の製造方法であって、前記延伸圧延工程後の中空素管を内表面温度で前記組成を有するマルテンサイト系高Ｃｒ鋼のＭｆ点以下の温度まで冷却した後、前記再加熱工程でＡｃ３点以上の温度に加熱し、引き続き、前記縮径圧延工程でストレッチ・レデューサあるいはサイザーで縮径圧延することを特徴とするマルテンサイト系高Ｃｒ鋼継目無鋼管の製造方法。 (1) By mass%, C: 0.01 to 0.25%, Si: 0.10 to 1.00%, Mn: 0.10 to 2.00%, Cr: 8.0 to 15.0% Ni: 0.05 to 8.00%, Mo: 0.30 to 4.00%, V: 0.01 to 0.25%, N: 0.010 to 0.070%, and the balance Fe And a round billet having a composition comprising inevitable impurities, and a martensitic high Cr steel seamless steel pipe having a piercing and rolling step, a drawing and rolling step, a reheating step, and a reduced diameter rolling step in order. The hollow shell after the drawing and rolling step is cooled to a temperature below the Mf point of the martensitic high Cr steel having the composition at the inner surface temperature, and then heated to a temperature of Ac 3 point or higher in the reheating step. Subsequently, the diameter is reduced with a stretch reducer or sizer in the diameter reduction rolling process. A method for producing a martensitic high Cr steel seamless steel pipe, characterized by rolling.
（２）前記延伸圧延工程後の冷却を、前記中空素管の内表面温度でＭｆ点以下の温度までの冷却速度が３℃／ｓ以上の冷却とすることを特徴とする（１）に記載のマルテンサイト系高Ｃｒ鋼継目無鋼管の製造方法。 (2) The cooling after the drawing and rolling step is a cooling at a cooling rate of 3 ° C./s or more to a temperature below the Mf point at the inner surface temperature of the hollow shell. Martensitic high Cr steel seamless steel pipe manufacturing method.
（３）前記再加熱工程の加熱を、前記中空素管の内表面温度でＡｃ３点以上の温度までの加熱速度が１０℃／ｓ以上の加熱とすることを特徴とする（１）または（２）に記載のマルテンサイト系高Ｃｒ鋼継目無鋼管の製造方法。 (3) The heating in the reheating step is heating at a heating rate of 10 ° C./s or more up to a temperature of Ac 3 or higher at the inner surface temperature of the hollow shell (1) or ( A method for producing a martensitic high Cr steel seamless steel pipe according to 2).
本発明の製造方法によれば、再加熱工程前の中空素管の組織をマルテンサイト組織とし、再加熱による逆変態で縮径圧延前の中空素管のオーステナイト組織を微細化することにより、ストレッチ・レデューサ、および／または、サイザーによる縮径圧延によって生じるしわ疵を効率よく抑制でき、内面品質に優れたマルテンサイト系高Ｃｒ鋼継目無鋼管を得ることができる。 According to the production method of the present invention, the structure of the hollow shell before the reheating step is changed to a martensite structure, and the austenite structure of the hollow shell before the diameter reduction rolling is refined by reverse transformation by reheating. -It is possible to efficiently suppress wrinkles generated by reduction rolling with a reducer and / or a sizer, and to obtain a martensitic high Cr steel seamless steel pipe excellent in inner surface quality.
まず、本発明に係るマルテンサイト系高Ｃｒ鋼継目無鋼管の組成限定理由について説明する。以下、各元素の含有量に関する「％」は「質量％」を意味する。 First, the reasons for limiting the composition of the martensitic high Cr steel seamless steel pipe according to the present invention will be described. Hereinafter, “%” regarding the content of each element means “mass%”.
Ｃ：０．０１〜０．２５％
Ｃは、マルテンサイト系高Ｃｒ鋼の強度を高めるのに有効な元素であり、鋼管の強度を確保するために０．０１％以上添加するが、０．２５％を超えて含有すると多量のＣｒ炭化物等を形成し、耐食性を劣化させるため、上限を０．２５％とする。なお、好ましくは、０．０２〜０．２１％である。
C: 0.01 to 0.25%
C is an element effective for increasing the strength of martensitic high Cr steel, and is added in an amount of 0.01% or more in order to ensure the strength of the steel pipe, but if it exceeds 0.25%, a large amount of Cr is added. In order to form carbide or the like and deteriorate the corrosion resistance, the upper limit is made 0.25%. In addition, Preferably, it is 0.02 to 0.21%.
Ｓｉ：０．１０〜１．００％
Ｓｉは、脱酸のために添加する。０．１０％未満ではその効果がなく、一方、あまり多量に含有させると鋼の靭性を劣化させるので、１．００％を上限にする。なお、好ましくは、０．１０〜０．３０％である。
Si: 0.10 to 1.00%
Si is added for deoxidation. If the content is less than 0.10%, the effect is not obtained. On the other hand, if the content is too large, the toughness of the steel is deteriorated, so the upper limit is made 1.00%. In addition, Preferably, it is 0.10 to 0.30%.
Ｍｎ：０．１０〜２．００％
Ｍｎは、製鋼上、脱硫のために添加する。０．１０％未満ではその効果がなく、熱間加工性も低下する。一方、あまり過剰に添加すると、結晶粒界の強度を低下させ、鋼の脆性劣化を招くので、２．００％を上限とする。なお、好ましくは、０．３０〜０．８０％である。
Mn: 0.10 to 2.00%
Mn is added for desulfurization on steelmaking. If it is less than 0.10%, the effect is not obtained, and hot workability is also lowered. On the other hand, if added too much, the strength of the grain boundaries is lowered and brittle deterioration of the steel is caused, so the upper limit is made 2.00%. In addition, Preferably, it is 0.30 to 0.80%.
Ｃｒ：８．０〜１５．０％
Ｃｒは、炭酸ガスを含む環境での耐食性を高めるのに有効な元素であり、孔食や隙間腐食を防止するために８．０％以上含有させる必要がある。しかし、Ｃｒ含有量が１５．０％を超えると、δフェライトを生成しマルテンサイト単相の組織が得られない。したがって、Ｃｒの含有量を８．０〜１５．０％とした。なお、好ましくは、８．５〜１３．５％である。
Cr: 8.0 to 15.0%
Cr is an element effective for enhancing the corrosion resistance in an environment containing carbon dioxide gas, and it is necessary to contain 8.0% or more in order to prevent pitting corrosion and crevice corrosion. However, if the Cr content exceeds 15.0%, δ ferrite is generated and a martensite single phase structure cannot be obtained. Therefore, the content of Cr is set to 8.0 to 15.0%. In addition, Preferably, it is 8.5 to 13.5%.
Ｎｉ：０．０５〜８．００％
Ｎｉは、オーステナイト安定化元素でδフェライトの出現を抑制するとともに、靭性を向上させるために添加する。Ｎｉ含有量が０．０５％未満では前記の効果が得られず、また、Ｃｒの含有量が上記の範囲であれば８．００％を超えて含有させてもその効果が飽和してコストが嵩む上に、組織に占める残留オーステナイトの割合が増加して降伏比ＹＲの低下をきたす。したがって、Ｎｉの含有量を０．０５〜８．００％とした。なお、好ましくは、０．１０〜７．００％である。
Ni: 0.05 to 8.00%
Ni is an austenite stabilizing element and is added to suppress the appearance of δ ferrite and improve toughness. If the Ni content is less than 0.05%, the above effect cannot be obtained. If the Cr content is in the above range, the effect is saturated even if the content exceeds 8.00%. In addition, the ratio of retained austenite to the structure increases and the yield ratio YR decreases. Therefore, the Ni content is set to 0.05 to 8.00%. In addition, Preferably, it is 0.10 to 7.00%.
Ｍｏ：０．３０〜４．００％
Ｍｏは、Ｃｒと同様に炭酸ガスを含む環境での耐食性を高めるのに有効な元素であり、特に、耐食性皮膜を保護する作用を有する。Ｍｏの含有量が０．３０％未満では前記の効果が十分に得られない。一方、Ｍｏの含有量が４．００％を超えると熱間加工性の低下をきたす。したがって、Ｍｏの含有量を０．３０〜４．００％とした。なお、好ましくは、０．３５〜３．００％である。
Mo: 0.30 to 4.00%
Mo is an element effective for enhancing the corrosion resistance in an environment containing carbon dioxide gas like Cr, and particularly has an action of protecting the corrosion-resistant film. If the Mo content is less than 0.30%, the above effects cannot be obtained sufficiently. On the other hand, when the Mo content exceeds 4.00%, hot workability is deteriorated. Therefore, the content of Mo is set to 0.30 to 4.00%. In addition, Preferably, it is 0.35-3.00%.
Ｖ：０．０１〜０．２５％
Ｖは、高温強度の向上に有用な元素で、強度確保のために０．０１％以上添加するが、０．２５％を超えて添加すると靱性の劣化を伴う強度上昇をもたらすため、上限を０．２５％とする。また、溶接性を確保するためにため、好ましくは０．０３〜０．２３％とする。
V: 0.01 to 0.25%
V is an element useful for improving the high-temperature strength, and is added in an amount of 0.01% or more to ensure the strength. However, if added over 0.25%, the strength increases with deterioration of toughness, so the upper limit is 0. .25%. Moreover, in order to ensure weldability, it is preferably 0.03 to 0.23%.
Ｎ：０．０１０〜０．０７０％
Ｎは、オーステナイト安定化元素で、高価なＮｉの代替元素として有効な元素であり、この効果を得るためには０．０１０％以上を含有させる必要がある。しかし、その含有量が多くなれば強度上昇が過大となって靱性の低下をきたす。したがって、Ｎの含有量を０．０１０〜０．０７０％とした。なお、好ましくは、０．０２０〜０．０６０％である。
N: 0.010 to 0.070%
N is an austenite stabilizing element and is an effective element as an alternative element to expensive Ni. In order to obtain this effect, it is necessary to contain 0.010% or more. However, if the content increases, the strength rises excessively and the toughness is lowered. Therefore, the N content is set to 0.010 to 0.070%. In addition, Preferably, it is 0.020 to 0.060%.
上記した成分以外の残部は、Ｆｅおよび不可避的不純物である。不可避的不純物としてはＰ：０．０２０％以下、Ｓ：０．０１０％以下が許容できる。
次に、本発明に係るマルテンサイト系高Ｃｒ鋼継目無鋼管製造方法について説明する。
上述の組成を有するマルテンサイト系高Ｃｒ鋼素材の丸ビレットを加熱し、加熱後の丸ビレットを中空素管に成形するピアサによる穿孔圧延とマンドレルミルまたはプラグミルによる延伸圧延を施す。前記穿孔圧延と延伸圧延は通常の方法で行う。また、前記ピアサによる穿孔圧延は、傾斜圧延方式でもプレスピアシング方式でもよい。
The balance other than the above components is Fe and inevitable impurities. As unavoidable impurities, P: 0.020% or less and S: 0.010% or less are acceptable.
Next, the martensitic high Cr steel seamless steel pipe manufacturing method according to the present invention will be described.
A round billet made of a martensitic high Cr steel material having the above composition is heated, and piercing and rolling by a piercer for forming the round billet after heating into a hollow shell and stretching rolling by a mandrel mill or a plug mill are performed. The piercing and stretching are performed by a normal method. Further, the piercing and rolling by the piercer may be a tilt rolling method or a press piercing method.
次に、延伸圧延後の中空素管を内表面温度が前記マルテンサイト系高Ｃｒ鋼のマルテンサイト変態が完了するＭｆ点以下の温度になるまで冷却する。図１に示すように、前記中空素管を内表面温度でＭｆ点以下の温度まで冷却することで、該中空素管の内表面組織を形成するオーステナイトを一度マルテンサイトに変態させ、その後の再加熱工程でマルテンサイトの逆変態によりオーステナイト粒を生成させるので、オーステナイト結晶粒径を小さくできる。なお、図１は、延伸圧延工程後の冷却停止温度が再加熱後のオーステナイト結晶粒径に及ぼす影響を示す図であり、表１に示す鋼Ｎｏ．Ａの組成を有する外径１４０ｍｍの中実丸ビレットを回転炉床式の加熱炉で１２６０℃に加熱して穿孔圧延及び延伸圧延を施して外径１１０ｍｍ、肉厚４．５ｍｍの中空素管Ａ１〜４とした後、該中空素管Ａ１〜４を、内表面温度で、５．０℃／ｓの冷却速度でそれぞれ所定の冷却停止温度まで冷却し、その後、１０℃／ｓの加熱速度で９５０℃まで昇温して１０分間保持した後、室温まで水冷し、９５０℃における内表面のオーステナイト組織を凍結した冷却後の前記中空素管Ａ１〜４の内面側から組織観察用試験片を採取して光学顕微鏡でオーステナイト粒径を測定して得られたものである。 Next, the hollow shell after drawing and rolling is cooled until the inner surface temperature is equal to or lower than the Mf point at which the martensitic transformation of the martensitic high Cr steel is completed. As shown in FIG. 1, by cooling the hollow shell to the temperature below the Mf point at the inner surface temperature, the austenite forming the inner surface structure of the hollow shell is transformed into martensite once, and thereafter Since austenite grains are generated by the reverse transformation of martensite in the heating process, the austenite crystal grain size can be reduced. 1 is a graph showing the effect of the cooling stop temperature after the drawing and rolling process on the austenite crystal grain size after reheating. A hollow round tube A1 having an outer diameter of 110 mm and a thickness of 4.5 mm is obtained by heating a solid round billet having an outer diameter of 140 mm having a composition of A to 1260 ° C. in a rotary hearth-type heating furnace and subjecting it to piercing and rolling. After that, the hollow shells A1 to A4 are cooled to a predetermined cooling stop temperature at an inner surface temperature at a cooling rate of 5.0 ° C / s, and then at a heating rate of 10 ° C / s. After raising the temperature to 950 ° C. and holding it for 10 minutes, water cooling to room temperature was performed, and the specimen for tissue observation was taken from the inner surface side of the hollow shell A1 to 4 after cooling the austenite structure on the inner surface at 950 ° C. Then, the austenite particle size was measured with an optical microscope.
なお、Ｍｆ点は、下記式で算出された値を使用するものとする。
Ｍｆ点（℃）＝３８１．７６−２５２．４４×Ｃ−１１１．１２×Ｍｎ＋５４．５３８×Ｓｉ＋１１４．１７×Ｃｒ−２３．７７９×Ｎｉ−５７．３８１×Ｍｏ＋２１５．７×Ｖ＋９４５．４×Ｎｂ＋１８２１．７×Ｔｉ−１７４６．５×Ｂ
ここで、Ｃ、Ｓｉ、Ｍｎ、Ｃｒ、Ｎｉ、Ｍｏ、Ｖ、Ｎｂ、Ｔｉ、Ｂは各元素の含有量（質量％）であり、Ｍｆ点の計算にあたっては、上記した式に記載された元素を含有しない場合には、当該元素の含有量を零％として算出するものとする。
The Mf point uses a value calculated by the following formula.
Mf point (° C.) = 381.76−252.44 × C−111.12 × Mn + 54.538 × Si + 114.17 × Cr−23.79 × Ni−57.381 × Mo + 215.7 × V + 945.4 × Nb + 1821. 7 x Ti-1746.5 x B
Here, C, Si, Mn, Cr, Ni, Mo, V, Nb, Ti, and B are the contents (mass%) of each element. In calculating the Mf point, the elements described in the above formula In the case where no element is contained, the element content is calculated as 0%.
また、前記中空素管の内表面温度での冷却速度は３℃／ｓ以上とすることが望ましい。図２に示すように、冷却速度が３℃／ｓ以上の加速冷却を行うことで前記中空素管の内表面の組織がマルテンサイト単相組織となるため、後工程の再加熱で前記マルテンサイトがオーステナイトへ逆変態した際、より微細な結晶粒のオーステナイト組織が得られる。なお、図２は、延伸圧延工程後の冷却における冷却速度が再加熱後のオーステナイト結晶粒径に及ぼす影響を示す図であり、表１に示す鋼Ｎｏ．Ａの組成を有する外径１４０ｍｍの中実丸ビレットを回転炉床式の加熱炉で１２６０℃に加熱して穿孔圧延及び延伸圧延を施して外径１１０ｍｍ、肉厚４．５ｍｍの中空素管Ａ５〜９とした後、該中空素管Ａ５〜９を、内表面温度で、それぞれ所定の冷却速度で冷却停止温度５０℃まで冷却し、その後、１０℃／ｓの加熱速度で９５０℃まで昇温して１０分間保持した後、室温まで水冷し、９５０℃における内表面のオーステナイト組織を凍結した冷却後の前記中空素管Ａ５〜９の内面側から組織観察用試験片を採取して光学顕微鏡でオーステナイト粒径を測定して得られたものである。なお、冷却速度の上限は特に限定しないが、管の曲がりや焼割れ等を防止するため、５０℃／ｓ以下とすることが好ましい。この際の冷却手段は特に限定しないが、冷却速度を制御しやすい点から、冷却水によるスプレー冷却を利用することが好ましい。また、内表面の冷却速度の測定方法は、鋼管表面温度履歴に基づいた数値解析で定める方法や接触温度計で直接温度を測定する方法等があるが、いずれの方法でもよい。 The cooling rate at the inner surface temperature of the hollow shell is preferably 3 ° C./s or more. As shown in FIG. 2, the structure of the inner surface of the hollow shell becomes a martensite single-phase structure by performing accelerated cooling at a cooling rate of 3 ° C./s or more. When A is transformed back to austenite, a finer grain austenite structure is obtained. 2 is a graph showing the effect of the cooling rate in the cooling after the drawing and rolling process on the austenite grain size after reheating. A hollow round tube A5 having an outer diameter of 110 mm and a wall thickness of 4.5 mm is obtained by heating a solid round billet having an outer diameter of 140 mm having a composition of A to a temperature of 1260 ° C. in a rotary hearth-type heating furnace to perform piercing and rolling. After that, the hollow shells A5 to 9 are cooled to a cooling stop temperature of 50 ° C. at a predetermined cooling rate at the inner surface temperature, and then heated to 950 ° C. at a heating rate of 10 ° C./s. Then, the sample is cooled to room temperature, cooled to room temperature, and the test piece for observing the structure is collected from the inner surface side of the hollow shell A5 to 9 after freezing the austenite structure on the inner surface at 950 ° C. with an optical microscope. It is obtained by measuring the austenite particle size. In addition, although the upper limit of a cooling rate is not specifically limited, In order to prevent the bending of a pipe | tube, a fire crack, etc., it is preferable to set it as 50 degrees C / s or less. Although the cooling means in this case is not particularly limited, it is preferable to use spray cooling with cooling water from the viewpoint of easy control of the cooling rate. Further, the method for measuring the cooling rate of the inner surface includes a method defined by numerical analysis based on the steel pipe surface temperature history, a method of directly measuring the temperature with a contact thermometer, and the like, and any method may be used.
次に、上記の冷却処理によって管内面の組織がマルテンサイト組織となった前記中空素管を内表面温度で前記マルテンサイト系高Ｃｒ鋼のＡｃ３点以上の温度に再加熱し、マルテンサイトの逆変態による微細なオーステナイト粒を生成させる。逆変態後のオーステナイト粒径は、加熱速度に影響され、図３に示すように、Ｍｆ点以下の温度からＡｃ３点以上の温度までの平均加熱速度が１０℃／ｓ以上になると顕著に微細になる。したがって、前記再加熱の加熱速度を１０℃／ｓ以上とすることが好ましい。なお、より好ましくは、４０℃／ｓ以上である。なお、図３は、マルテンサイト組織の高Ｃｒ鋼をＭｆ点以下の温度からＡｃ３点以上の温度に加熱した場合、Ａｃ３点までの加熱速度が再加熱後のオーステナイト結晶粒径に及ぼす影響を示す図であり、表１に示す鋼Ｎｏ．Ａの組成を有する外径１４０ｍｍの中実丸ビレットを回転炉床式の加熱炉で１２６０℃に加熱して穿孔圧延及び延伸圧延を施して外径１１０ｍｍ、肉厚４．５ｍｍの中空素管Ａ１０〜１４とした後、該中空素管Ａ１０〜１４を、内表面温度で、５．０℃／ｓの冷却速度で冷却停止温度５０℃まで冷却し、その後、それぞれ所定の加熱速度で９５０℃まで昇温して１０分間保持した後、室温まで水冷し、９５０℃における内表面のオーステナイト組織を凍結した冷却後の前記中空素管Ａ１０〜１４の内面側から組織観察用試験片を採取して光学顕微鏡でオーステナイト粒径を測定して得られたものである。 Next, the hollow element tube whose structure on the inner surface of the tube has become a martensite structure by the above cooling treatment is reheated to a temperature of Ac 3 or higher of the martensitic high Cr steel at the inner surface temperature, Fine austenite grains are generated by reverse transformation. The austenite grain size after reverse transformation is affected by the heating rate, and as shown in FIG. 3, the austenite grain size becomes remarkably fine when the average heating rate from the temperature below the Mf point to the temperature above the Ac 3 point is 10 ° C./s or more. become. Therefore, it is preferable that the heating rate of the reheating is 10 ° C./s or more. In addition, More preferably, it is 40 degrees C / s or more. Incidentally, FIG. 3, when heated to a temperature high Cr steel from Mf point below a temperature above Ac 3 point of the martensitic structure, the effect of the heating rate up to the Ac 3 point is on the austenite grain size after reheating The steel No. shown in Table 1 is shown in FIG. A hollow round tube A10 having an outer diameter of 110 mm and a wall thickness of 4.5 mm is obtained by heating a solid round billet having an outer diameter of 140 mm having a composition of A to 1260 ° C. in a rotary hearth-type heating furnace and subjecting it to piercing and rolling. After that, the hollow shells A10 to A14 are cooled at the inner surface temperature to a cooling stop temperature of 50 ° C. at a cooling rate of 5.0 ° C./s, and then to 950 ° C. at a predetermined heating rate, respectively. The temperature was raised and held for 10 minutes, then cooled to room temperature, and the specimen for tissue observation was collected from the inner surface side of the hollow shell A10-14 after cooling after freezing the austenite structure on the inner surface at 950 ° C. It is obtained by measuring the austenite particle size with a microscope.
この際、再加熱の加熱手段は特に限定しないが、生産性を悪化させないためにも誘導加熱装置を利用することが好ましい。Ａｃ３点以上の所定の温度まで昇温後、前記中空素管全体を均熱化する場合には現行の雰囲気制御炉を利用することもできる。 At this time, the heating means for reheating is not particularly limited, but it is preferable to use an induction heating apparatus in order not to deteriorate the productivity. Ac When the temperature is raised to a predetermined temperature of 3 points or more, and the entire hollow shell is soaked, the current atmosphere control furnace can be used.
また、前記中空素管の内表面の加熱速度の測定方法は、鋼管表面温度履歴に基づいた数値解析で定める方法や誘導加熱装置によって加えられる電力量から加熱速度を計算する方法等があるが、いずれの方法でもよい。 In addition, the method for measuring the heating rate of the inner surface of the hollow shell includes a method defined by numerical analysis based on the steel tube surface temperature history, a method of calculating the heating rate from the amount of power applied by the induction heating device, and the like. Either method is acceptable.
再加熱後、Ａｃ３点以上まで加熱された前記中空素管に対して縮径圧延を行う。縮径圧延は、例えばストレッチ・レデューサを用いるストレッチ・レデューサ圧延で行うが、サイザーを用いるサイジングミル圧延で行ってもよい。上記縮径圧延に際し、再加熱温度を高温にしすぎると組織が粗大になってしまうため、再加熱温度の上限は１１５０℃とすることが好ましい。前述の冷却処理と前記再加熱とによって縮径圧延に供される中空素管（被圧延材）の内面が微細なオーステナイト組織となるため、縮径圧延で生じる鋼管内面の凹凸形状の深さが抑制され、内面しわ疵の小さい内面品質が優れた継目無鋼管が得られる。 After reheating, diameter reduction rolling is performed on the hollow shell heated to Ac 3 points or more. The diameter reduction rolling is performed by, for example, stretch-reducer rolling using a stretch reducer, but may be performed by sizing mill rolling using a sizer. At the time of the above-mentioned diameter reduction rolling, if the reheating temperature is too high, the structure becomes coarse. Therefore, the upper limit of the reheating temperature is preferably 1150 ° C. Since the inner surface of the hollow shell (rolled material) subjected to the diameter reduction rolling by the cooling treatment and the reheating described above has a fine austenite structure, the depth of the uneven shape on the inner surface of the steel pipe generated by the diameter reduction rolling is reduced. A seamless steel pipe that is suppressed and has excellent inner surface quality with small inner wrinkles is obtained.
表１に示す化学組成を有する３種類のマルテンサイト系高Ｃｒ鋼の中実丸ビレットを回転炉床式の加熱炉で１２６０℃に加熱し、穿孔圧延及び延伸圧延を施して表２に示す寸法を有する中空素管とした後、表２に示す条件で冷却および再加熱処理を施した。
次いで、前記中空素管に縮径圧延を施し、表２に示す寸法の継目無鋼管を製造した。
なお、表２に示したＭｆ点およびＡｃ３点は、それぞれ前述の計算式により求めた。
Three martensitic high Cr steel solid round billets having the chemical composition shown in Table 1 are heated to 1260 ° C. in a rotary hearth-type heating furnace, subjected to piercing and stretching, and the dimensions shown in Table 2 After that, the tube was cooled and reheated under the conditions shown in Table 2.
Next, the hollow shell was subjected to diameter reduction rolling to produce a seamless steel pipe having the dimensions shown in Table 2.
The Mf point and Ac 3 point shown in Table 2 were obtained by the above-described calculation formulas.
製造後、超音波探傷計を用いて探傷計を周方向に走査しながら前記継目無鋼管を長手方向に送り出し、全長に渡って管内面の内面しわ疵の発生程度を評価した。また、探傷計による異常発生個所を特定し、その位置の鋼管断面を顕鏡することでしわ深さを評価した。評価結果は、最大しわ深さが２００μｍを超える場合を１とし、２００μｍ以下１００μｍ超えの場合を２、１００μｍ以下２０μｍ超えの場合を３、２０μｍ以下の場合を４で示し、評価結果が２以上の場合を合格とした。 After production, the seamless steel pipe was sent out in the longitudinal direction while scanning the flaw gauge in the circumferential direction using an ultrasonic flaw gauge, and the degree of occurrence of wrinkles on the inner surface of the pipe was evaluated over the entire length. Moreover, the location where an abnormality occurred was detected by a flaw detector, and the wrinkle depth was evaluated by observing the cross section of the steel pipe at that position. The evaluation result is 1 when the maximum wrinkle depth exceeds 200 μm, 2 when 200 μm or less and 100 μm or more, 3 when 100 μm or less and 20 μm or more, and 4 when 20 μm or less, and the evaluation result is 2 or more The case was accepted.
表２に示す評価結果から、本発明例では、延伸圧延後の中空素管を内面温度がＭｆ点以下になるまで冷却した後、内表面温度で９５０℃に再加熱し、縮径圧延を行ったことにより、縮径圧延によって生じる鋼管内面の最大しわ深さが２００μｍ以下となり、内表面に発生するしわ疵を低減できていることが分かる。さらに、延伸圧延工程後の冷却を、中空素管の内表面温度でＭｆ点以下の温度までの冷却速度が３℃／ｓ以上の冷却とした場合、および／または、Ｍｆ点以下の温度からＡｃ３点以上の温度までの加熱を、中空素管の内表面温度で加熱速度が１０℃／ｓ以上の加熱とした場合には、より一層しわ深さが低減できていることが分かる。 From the evaluation results shown in Table 2, in the example of the present invention, the hollow shell after drawing and rolling was cooled until the inner surface temperature became Mf point or less, and then reheated to 950 ° C. at the inner surface temperature, and reduced diameter rolling was performed. Thus, it can be seen that the maximum wrinkle depth of the inner surface of the steel pipe generated by the reduced diameter rolling becomes 200 μm or less, and wrinkles generated on the inner surface can be reduced. Further, when the cooling after the drawing and rolling step is the cooling at which the cooling rate to the temperature below the Mf point at the inner surface temperature of the hollow shell is 3 ° C./s or more, and / or from the temperature below the Mf point, Ac3 It can be seen that the wrinkle depth can be further reduced when heating up to a temperature above the point is heating at a heating rate of 10 ° C./s or more at the inner surface temperature of the hollow shell.
１ 丸ビレット
２ 回転式加熱炉
３ ピアサ（傾斜ロール式穿孔圧延機）
４ 穿孔プラグ
５ マンドレルミル
６ マンドレルバー
７ ウォーキングビーム式加熱炉
８ エロンゲータ
９ エロンゲータプラグ
１０ プラグミル
１１ プラグミルプラグ
１２ リーラー
１３ リーラープラグ
１４ ストレッチ・レデューサ
１５ サイザー（サイジングミル）
１６ 製品（継目無鋼管）
1 Round Billet 2 Rotary Heating Furnace 3 Piercer (Inclined Roll Type Punching Roller)
4
16 products (seamless steel pipe)
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113543901A (en) * | 2019-03-15 | 2021-10-22 | 杰富意钢铁株式会社 | Method for manufacturing seamless square steel pipe |
| WO2022038956A1 (en) * | 2020-08-19 | 2022-02-24 | Ｊｆｅスチール株式会社 | Seamless steel pipe and method for manufacturing same |
| CN114589203A (en) * | 2022-01-25 | 2022-06-07 | 大冶特殊钢有限公司 | Preparation method of 09MnNiD seamless steel tube suitable for low temperature |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH01123029A (en) * | 1987-11-07 | 1989-05-16 | Sumitomo Metal Ind Ltd | Production of seamless stainless steel pipe |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01123029A (en) * | 1987-11-07 | 1989-05-16 | Sumitomo Metal Ind Ltd | Production of seamless stainless steel pipe |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113543901A (en) * | 2019-03-15 | 2021-10-22 | 杰富意钢铁株式会社 | Method for manufacturing seamless square steel pipe |
| CN113543901B (en) * | 2019-03-15 | 2023-08-04 | 杰富意钢铁株式会社 | Method for manufacturing seamless square steel tube |
| WO2022038956A1 (en) * | 2020-08-19 | 2022-02-24 | Ｊｆｅスチール株式会社 | Seamless steel pipe and method for manufacturing same |
| JPWO2022038956A1 (en) * | 2020-08-19 | 2022-02-24 | ||
| JP7239019B2 (en) | 2020-08-19 | 2023-03-14 | Ｊｆｅスチール株式会社 | Seamless steel pipe and its manufacturing method |
| EP4169634A4 (en) * | 2020-08-19 | 2024-04-17 | Jfe Steel Corp | Seamless steel pipe and method for manufacturing same |
| CN114589203A (en) * | 2022-01-25 | 2022-06-07 | 大冶特殊钢有限公司 | Preparation method of 09MnNiD seamless steel tube suitable for low temperature |
| CN114589203B (en) * | 2022-01-25 | 2023-09-05 | 大冶特殊钢有限公司 | Preparation method of 09MnNiD seamless steel tube suitable for low temperature |
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