JP3750619B2 - Manufacturing method of high Cr ferritic heat resistant steel pipe - Google Patents
Manufacturing method of high Cr ferritic heat resistant steel pipe Download PDFInfo
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- resistant steel
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Description
【０００１】
【発明の属する技術分野】
本発明は、高Ｃｒフェライト系耐熱鋼管を製造する方法に関するものである。
【０００２】
【従来の技術】
火力発電等のボイラ熱交換器用鋼管には、例えばＪＩＳ Ｇ ３４６２に規定されるＳＴＢＡ２６やＡＳＴＭ Ａ２１３に規定されるＴ９１等に代表される９％Ｃｒ系や、ＤＩＮ １７１７５に規定されるＸ２０ＣｒＭｏＶ１２１に代表される１２％Ｃｒ系の高Ｃｒフェライト系耐熱鋼管が用いられる。
【０００３】
上記の高Ｃｒフェライト系耐熱鋼管は種々の方法によって製造されるが、多くの場合、高い寸法精度を得るために冷間引抜加工を施して所定の寸法に仕上げた後、内外面を洗浄した上で所定の性能を付与すべく、例えば焼ならし−焼戻し等の適宜な熱処理を施している。
【０００４】
ところで、鋼管の冷間引抜加工において、炭素鋼やＣｒ含有量が２質量％以下の低合金鋼の場合には、リン酸塩被膜潤滑が施されているが、Ｃｒ含有量が５質量％以上の高Ｃｒ鋼ではリン酸塩被膜は反応しないので、蓚酸塩被膜潤滑が施されている。
【０００５】
そして、高Ｃｒフェライト系耐熱鋼管は用途上要求される高いクリープ強度を確保する目的から１０００℃を超える高温で焼ならしを行うため、管内面に潤滑剤成分が残存すると容易に浸炭する。
従って、高Ｃｒフェライト系耐熱鋼管を製造する場合には、熱処理時の浸炭を防止するために、熱処理前に前記潤滑剤を脱脂除去しておく必要がある。
【０００６】
しかるに、蓚酸塩被膜は鋼と反応しているので、油性潤滑剤のようにアルカリ水溶液による脱脂では除去できず、酸洗が必要になるが、弗硝酸を使用した場合は短時間で鋼の表面と反応し酸荒れを起こすので、長時間（１〜３時間）浸漬しても大きな反応を起すことなく表面の蓚酸塩被膜を除去できる硫酸酸洗が実施される。
【０００７】
【発明が解決しようとする課題】
しかしながら、本発明者の実験によれば、Ｃｒ含有量が８〜１３質量％の高Ｃｒフェライト鋼の場合、冷間引抜加工を行ったままで硫酸酸洗を行うと、特にそのＴ／Ｄが１５％以上で加工度が１５〜３５％の場合には、割れが発生することを知見した。
【０００８】
なお、特開平９−２４８６１９号には、鋼管の冷間引抜加工の潤滑法として化成処理法、樹脂被膜法及び油潤滑法があると記載されている。しかしながら、化成処理法の一つである蓚酸塩被膜潤滑では、引抜加工後に脱脂を行うことなく直接熱処理すると記載されていることから、高Ｃｒフェライト系耐熱鋼管の熱処理において浸炭発生の懸念があること、及び、その対策として熱処理前に潤滑剤を脱脂除去することは想定していないことが判る。
【０００９】
また、特開平１０−３１０８１９号には高Ｃｒ合金鋼鋼管の熱処理時に浸炭が発生する懸念があること、及び、引抜後に潤滑剤を除去する目的で酸洗を行うことについて記載されている。しかしながら、アルカリ水溶液による脱脂洗浄後と記載されていることから、冷間引抜の潤滑は油性潤滑を前提としており、高Ｃｒ合金鋼鋼管の場合に蓚酸塩被膜潤滑が適している一方、蓚酸塩被膜の除去には酸洗が必須であること、及び、酸洗した場合に割れが発生することについては全く記載されていない。これは、実施例を見ると管の肉厚Ｔと外径Ｄの比（以下、「Ｔ／Ｄ」と略す。）が１０％以下であり、特に本発明が対象としているＴ／Ｄが１５％以上のような厚肉品を想定していないからである。
【００１０】
本発明は、上記した従来の問題点に鑑みてなされたものであり、蓚酸塩被膜潤滑して冷間引抜を行った後、熱処理前に脱脂酸洗しても割れを生じない高Ｃｒフェライト系耐熱鋼管の製造方法を提供することを目的としている。
【００１１】
【課題を解決するための手段】
上記した目的を達成するために、本発明に係る高Ｃｒフェライト系耐熱鋼管の製造方法は、引抜加工後に６００℃〜Ａｃl 変態点の温度で５分以上加熱した後、最終熱処理の前に脱脂酸洗して蓚酸塩被膜潤滑剤を除去することとしている。そして、このようにすることで、高Ｃｒフェライト系耐熱鋼管に蓚酸塩被膜潤滑して冷間引抜を行った後最終熱処理前に脱脂酸洗しても、割れを生じることがなくなる。
【００１２】
【発明の実施の形態】
本発明者は高Ｃｒフェライト系耐熱鋼管に蓚酸塩被膜潤滑を施して冷間引抜した後、熱処理前に脱脂し硫酸酸洗すると、管寸法及び引抜加工度によっては割れが発生する場合があることを見出した。そして、この割れは、引抜によって管の後端に発生した切り欠き部を起点に発生していた。
【００１３】
これは、高Ｃｒフェライト系耐熱鋼は、通常は、Ｃを０．０７〜０．２５質量％、Ｃｒを８．０〜１３．０質量％含有し、鋼によってはＭｏ、Ｗ等を含有する場合もあるが、いずれにしても焼入れ性が高く、引抜加工後は高硬度となって酸洗時の水素吸収による割れ感受性が高いからと考えられる。また、割れの起点となる切り欠きは、引抜き前の素管切断によって生じた管端の凹凸が、引抜加工によって絞り込まれて鋭角化することで発生するものである。
【００１４】
そして、本発明者の実験によれば、前記割れは、Ｔ／Ｄが１５％以上で、引抜加工度が１５％以上の場合に多く発生していることから、引抜加工による残留応力が大きいことが要因となっていると考えられる。
【００１５】
また、硫酸による酸洗時に割れが発生する主な要因は、引抜加工によって硬度が上昇することと、加工による応力が残存すること、及び、硫酸による酸洗時に水素が鋼中に拡散するためであると考えられる。
【００１６】
このような各種の知見に基づき、本発明者が各種の実験を行った結果、高Ｃｒフェライト系耐熱鋼管の製造時において、冷間引抜き後に、６００℃〜Ａｃl 変態点の温度で５分以上加熱すると、材料が軟化すると共に残留応力が除去され、酸洗時の割れの発生を防止することができることが判明した。
【００１７】
本発明に係る高Ｃｒフェライト系耐熱鋼管の製造方法は、上記した知見に基づく各種の実験により判明した新規な事項に基づいてなされたものであり、蓚酸塩被膜潤滑を施した冷間引抜加工による高Ｃｒフェライト系耐熱鋼の製造法であって、引抜加工後に６００℃〜Ａｃl 変態点の温度で５分以上加熱した後、最終熱処理の前に脱脂酸洗して前記潤滑剤を除去するものである。
【００１８】
本発明に係る高Ｃｒフェライト系耐熱鋼管の製造方法によれば、高Ｃｒフェライト系耐熱鋼管に蓚酸塩被膜潤滑して冷間引抜を行った後最終熱処理前に脱脂酸洗しても、材料の軟化と残留応力の除去により酸洗時の割れ発生を効果的に抑制することができるようになる。
【００１９】
そして、上記の本発明に係る高Ｃｒフェライト系耐熱鋼管の製造方法によれば、特に蓚酸塩被膜潤滑を施した冷間引抜加工による高Ｃｒフェライト系耐熱鋼管製造時の、酸洗時における割れ発生率が高い、Ｃが０．０７〜０．２５質量％、Ｃｒが８．０〜１３．０質量％含有されたフェライト系耐熱鋼である場合や、Ｔ／Ｄが１５％以上の素管を用い、１５％以上の加工度で冷間引抜する場合であっても、酸洗時の割れ発生を効果的に抑制することができるようになる。
【００２０】
【実施例】
以下、本発明に係る高Ｃｒフェライト系耐熱鋼管の製造方法の効果を確認するために行った実施結果について説明する。
【００２１】
（実施例１）
材質がＡＳＴＭ Ａ２１３に規定されるＴ９１の材料をマンドレルミルを使用し、▲１▼引抜加工度が１２％のものは、外径Ｄ0 が４８．６ｍｍ、肉厚Ｔ0 が９．９ｍｍの素管に、また、▲２▼引抜加工度が１７％のものは、外径Ｄ0 が５０．８ｍｍ、肉厚Ｔ0 が９．９ｍｍの素管に、また、▲３▼引抜加工度が２２％のものは、外径Ｄ0 が５４．０ｍｍ、肉厚Ｔ0 が９．８ｍｍの素管となるように圧延した後、蓚酸塩被膜潤滑を施して下記表１に示した加工度にて引抜いた後、下記表１に示した軟化熱処理後に脱脂酸洗して蓚酸塩被膜を除去し、その後、１０４５℃で１０分間空冷する焼ならしと、７８０℃で６０分間空冷する焼戻しを行い、外径Ｄが４５．０ｍｍ、肉厚Ｔが９．５ｍｍ（Ｔ／Ｄ＝２１％）の製品を製造した。その際の加工度と軟化熱処理の条件を各種変更した場合の結果を下記表１に併せて示す。
【００２２】
【表１】
上記表１より、本発明の条件を満足する実施例では、何れの場合も内面浸炭のない高Ｃｒフェライト系耐熱鋼管を、酸洗時の割れを発生させることなく、確実に製造することができた。
【００２４】
一方、＊印を付した部分が本発明を満足しない比較例の場合は、何れの場合も、熱処理時に内面浸炭が発生したか、或いは、酸洗時に割れが発生した。
【００２５】
（実施例２）
材質がＤＩＮ１７１７５に規定されるＸ２０ＣｒＭｏＶ１２１の材料をユジーンセジュルネ法により、▲１▼Ｔ／Ｄが１０％のものは、外径Ｄ0 が５１．０ｍｍ、肉厚Ｔ0 が５．０ｍｍの素管に、また、▲２▼Ｔ／Ｄが１７％のものは、外径Ｄ0 が５１．０ｍｍ、肉厚Ｔ0 が８．５ｍｍの素管に、また、▲３▼Ｔ／Ｄが２０％のものは、外径Ｄ0 が５０．８ｍｍ、肉厚Ｔ0 が９．９ｍｍの素管となるように製造した後、蓚酸塩被膜潤滑を施して２０％の加工度で引抜いた後、下記表２に示した軟化熱処理後に脱脂酸洗して蓚酸塩被膜を除去し、その後、１０４５°で１５分間空冷する焼ならしと、７８０℃で９０分間空冷する焼戻しを行い、▲１▼Ｔ／Ｄが１０％のものは、外径Ｄが４５．０ｍｍ、肉厚Ｔが４．５５ｍｍ、▲２▼Ｔ／Ｄが１７％のものは、外径Ｄが４５．０ｍｍ、肉厚Ｔが７．８ｍｍ、▲３▼Ｔ／Ｄが２０％のものは、外径Ｄが４５．０ｍｍ、肉厚Ｔが９．０ｍｍの製品を製造した。その際のＴ／Ｄと軟化熱処理の条件を各種変更した場合の結果を下記表２に併せて示す。
【００２６】
【表２】
上記表２より、本発明の条件を満足する実施例では、何れの場合も内面浸炭のない高Ｃｒフェライト系耐熱鋼管を、酸洗時の割れを発生させることなく、確実に製造することができた。
【００２８】
一方、＊印を付した部分が本発明を満足しない比較例の場合は、何れの場合も、熱処理時に内面浸炭が発生したか、或いは、酸洗時に割れが発生した。
【００２９】
【発明の効果】
以上説明したように、本発明の製造方法によれば、内面浸炭のない高Ｃｒフェライト系耐熱鋼管を確実に製造することができる。特に、Ｔ／Ｄが１５％以上の厚肉品を加工度が１５％以上で加工するに際し、蓚酸塩被膜潤滑を適用して引抜加工した場合にも、潤滑皮膜除去の酸洗時の割れを防止することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a high Cr ferritic heat resistant steel pipe.
[0002]
[Prior art]
Steel tubes for boiler heat exchangers such as thermal power generation are represented by, for example, STBA26 defined in JIS G 3462, 9% Cr represented by T91 defined in ASTM A213, and X20CrMoV121 defined in DIN 17175. 12% Cr high Cr ferritic heat resistant steel pipe is used.
[0003]
The above-mentioned high Cr ferritic heat-resistant steel pipes are manufactured by various methods. In many cases, in order to obtain high dimensional accuracy, after cold-drawing and finishing to a predetermined dimension, the inner and outer surfaces are washed. In order to give predetermined performance, an appropriate heat treatment such as normalizing and tempering is performed.
[0004]
By the way, in cold drawing of a steel pipe, in the case of carbon steel or low alloy steel having a Cr content of 2% by mass or less, phosphate coating lubrication is applied, but the Cr content is 5% by mass or more. In this high Cr steel, the phosphate coating does not react, so oxalate coating lubrication is applied.
[0005]
The high Cr ferritic heat-resistant steel pipe is normally carburized when the lubricant component remains on the inner surface of the pipe because the high Cr ferritic heat-resistant steel pipe is normalized at a high temperature exceeding 1000 ° C. for the purpose of ensuring the high creep strength required for applications.
Therefore, when manufacturing a high Cr ferritic heat resistant steel pipe, it is necessary to degrease and remove the lubricant before the heat treatment in order to prevent carburization during the heat treatment.
[0006]
However, since the oxalate film reacts with the steel, it cannot be removed by degreasing with an alkaline aqueous solution like oil-based lubricants, and pickling is necessary. The acid pickling is carried out, so that even if immersed for a long time (1 to 3 hours), sulfuric acid pickling capable of removing the surface oxalate film without causing a large reaction is performed.
[0007]
[Problems to be solved by the invention]
However, according to the experiments of the present inventors, in the case of high Cr ferritic steel having a Cr content of 8 to 13% by mass, when the sulfuric acid pickling is performed while cold drawing is performed, the T / D is particularly 15. It has been found that cracking occurs when the degree of processing is 15 to 35% at a rate of 15% or more.
[0008]
JP-A-9-248619 describes that there are a chemical conversion treatment method, a resin coating method, and an oil lubrication method as a lubrication method for cold drawing of a steel pipe. However, in the oxalate coating lubrication, which is one of the chemical conversion treatment methods, it is described that the heat treatment is directly performed without degreasing after the drawing process, so there is a concern that carburization may occur in the heat treatment of the high Cr ferritic heat resistant steel pipe. As a countermeasure, it is understood that the lubricant is not degreased and removed before the heat treatment.
[0009]
Japanese Patent Application Laid-Open No. 10-310819 describes that carburization may occur during heat treatment of a high Cr alloy steel pipe and that pickling is performed for the purpose of removing the lubricant after drawing. However, since it is described as after degreasing and cleaning with an alkaline aqueous solution, cold drawing lubrication is premised on oil-based lubrication, and silicate coating lubrication is suitable for high Cr alloy steel pipes. There is no description at all about the fact that pickling is essential for the removal, and that cracking occurs when pickling. In the embodiment, the ratio of the wall thickness T to the outer diameter D (hereinafter abbreviated as “T / D”) is 10% or less, and the T / D targeted by the present invention is 15 in particular. This is because thick products such as% or more are not assumed.
[0010]
The present invention has been made in view of the above-mentioned conventional problems, and is a high Cr ferrite system that does not cause cracking even after degrease pickling after heat treatment and cold drawing after oxalate film lubrication. It aims at providing the manufacturing method of a heat-resistant steel pipe.
[0011]
[Means for Solving the Problems]
In order to achieve the above-described object, the high Cr ferritic heat resistant steel pipe manufacturing method according to the present invention is a method of heating after drawing at a temperature of 600 ° C. to Ac 1 transformation point for 5 minutes or more and then degreasing before the final heat treatment. The oxalate coating lubricant is removed by pickling. And by doing in this way, even if it carries out degreasing pickling before the final heat processing, after carrying out cold drawing after lubricating a high Cr ferritic heat-resistant steel pipe and carrying out cold drawing, it does not produce a crack.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
When the present inventor performs oxalate coating lubrication on a high Cr ferritic heat-resistant steel pipe and cold-draws and then degreases and heat-washes before heat treatment, cracks may occur depending on the pipe dimensions and the degree of drawing. I found. And this crack had started from the notch part which arose at the rear end of the pipe by drawing.
[0013]
This is because the high Cr ferritic heat-resisting steel usually contains 0.07 to 0.25% by mass of C and 8.0 to 13.0% by mass of Cr. Depending on the steel, it contains Mo, W and the like. In any case, it is considered that in any case, the hardenability is high, the hardness becomes high after the drawing process, and the cracking sensitivity due to hydrogen absorption during pickling is high. In addition, the notch that becomes the starting point of the crack is generated when the irregularities at the end of the tube generated by cutting the raw tube before drawing are narrowed down by the drawing process and sharpened.
[0014]
And according to the experiment of the present inventor, since the crack is frequently generated when the T / D is 15% or more and the drawing degree is 15% or more, the residual stress due to the drawing process is large. Is considered to be a factor.
[0015]
The main causes of cracking during pickling with sulfuric acid are the increase in hardness due to drawing, the remaining stress due to processing, and the diffusion of hydrogen into the steel during pickling with sulfuric acid. It is believed that there is.
[0016]
Based on such various findings, the present inventor conducted various experiments, and as a result, at the time of producing a high Cr ferritic heat resistant steel pipe, after cold drawing, at a temperature of 600 ° C. to Ac 1 transformation point for 5 minutes or more. It has been found that, when heated, the material softens and the residual stress is removed, thereby preventing the occurrence of cracks during pickling.
[0017]
The manufacturing method of the high Cr ferritic heat-resistant steel pipe according to the present invention is based on novel matters found by various experiments based on the above-described knowledge, and is by cold drawing with oxalate coating lubrication. A method for producing high Cr ferritic heat resistant steel, which is heated at 600 ° C. to Ac 1 transformation point for 5 minutes or more after drawing and then degreased and pickled before final heat treatment to remove the lubricant. It is.
[0018]
According to the method for producing a high Cr ferritic heat resistant steel pipe according to the present invention, the high Cr ferritic heat resistant steel pipe is lubricated with oxalate coating and cold drawn, and then degreased and pickled before final heat treatment. The generation of cracks during pickling can be effectively suppressed by softening and removal of residual stress.
[0019]
And according to the manufacturing method of the high Cr ferritic heat resistant steel pipe according to the present invention described above, the crack generation at the time of pickling, especially at the time of manufacturing the high Cr ferritic heat resistant steel pipe by cold drawing with silicate coating lubrication When the ferritic heat-resistant steel has a high rate, C is 0.07 to 0.25% by mass, and Cr is 8.0 to 13.0% by mass, or a T / D is 15% or more. Even if it is a case where it uses and cold-draws with a workability of 15% or more, the crack generation at the time of pickling can be suppressed effectively.
[0020]
【Example】
Hereinafter, the implementation result performed in order to confirm the effect of the manufacturing method of the high Cr ferritic heat-resistant steel pipe concerning the present invention is explained.
[0021]
(Example 1)
The material of T91 specified in ASTM A213 using a mandrel mill and (1) with a drawing degree of 12% is an element having an outer diameter D 0 of 48.6 mm and a wall thickness T 0 of 9.9 mm. For pipes, and (2) with a drawing degree of 17%, it is a raw pipe with an outer diameter D 0 of 50.8 mm and a wall thickness T 0 of 9.9 mm, and (3) a drawing degree of 22 %, After rolling so that the outer diameter D 0 is 54.0 mm and the wall thickness T 0 is 9.8 mm, the oxalate coating is lubricated and the degree of processing shown in Table 1 below is applied. After drawing, the oxalate film is removed by degreasing pickling after the softening heat treatment shown in Table 1 below, followed by normalizing by air cooling at 1045 ° C. for 10 minutes and tempering by air cooling at 780 ° C. for 60 minutes, A product having an outer diameter D of 45.0 mm and a wall thickness T of 9.5 mm (T / D = 21%) was produced. Table 1 below also shows the results when various changes were made to the processing degree and softening heat treatment conditions at that time.
[0022]
[Table 1]
From Table 1 above, in Examples satisfying the conditions of the present invention, high Cr ferritic heat-resistant steel pipes with no internal carburization in any case can be reliably produced without causing cracks during pickling. It was.
[0024]
On the other hand, in the case of the comparative example where the part marked with * does not satisfy the present invention, internal carburization occurred during heat treatment or cracking occurred during pickling.
[0025]
(Example 2)
The material of X20CrMoV121 specified by DIN17175 by the Eugene Sejurne method, (1) T / D of 10% is an uncoated tube having an outer diameter D 0 of 51.0 mm and a wall thickness T 0 of 5.0 mm In addition, (2) T / D of 17% is a tube having an outer diameter D 0 of 51.0 mm and a wall thickness T 0 of 8.5 mm, and (3) T / D is 20%. After being manufactured so as to be a blank tube having an outer diameter D 0 of 50.8 mm and a wall thickness T 0 of 9.9 mm, the oxalate film was lubricated and pulled out at a processing rate of 20%, After the softening heat treatment shown in Table 2, degreasing pickling to remove the oxalate film, followed by normalizing by air cooling at 1045 ° for 15 minutes and tempering by air cooling at 780 ° C. for 90 minutes, (1) T / When D is 10%, outer diameter D is 45.0mm, wall thickness T is 4.55mm, (2) T / D is 17% For products with an outer diameter D of 45.0 mm, wall thickness T of 7.8 mm, and (3) T / D of 20%, products with an outer diameter D of 45.0 mm and wall thickness T of 9.0 mm Manufactured. The results when various changes are made to the T / D and softening heat treatment conditions are shown in Table 2 below.
[0026]
[Table 2]
From Table 2 above, in Examples satisfying the conditions of the present invention, high Cr ferritic heat-resistant steel pipes without internal carburization in any case can be reliably produced without causing cracking during pickling. It was.
[0028]
On the other hand, in the case of the comparative example where the part marked with * does not satisfy the present invention, internal carburization occurred during heat treatment or cracking occurred during pickling.
[0029]
【The invention's effect】
As described above, according to the manufacturing method of the present invention, a high Cr ferritic heat-resistant steel pipe without internal carburization can be reliably manufactured. In particular, when processing a thick-walled product with a T / D of 15% or more at a processing degree of 15% or more, even when the oxalate film lubrication is applied and the drawing process is performed, cracks during pickling for removing the lubricant film are caused. Can be prevented.
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