JPH07179943A - Production of high toughness martensitic strainless steel pipe excellent in corrosion resistance - Google Patents
Production of high toughness martensitic strainless steel pipe excellent in corrosion resistanceInfo
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- JPH07179943A JPH07179943A JP5325395A JP32539593A JPH07179943A JP H07179943 A JPH07179943 A JP H07179943A JP 5325395 A JP5325395 A JP 5325395A JP 32539593 A JP32539593 A JP 32539593A JP H07179943 A JPH07179943 A JP H07179943A
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- corrosion resistance
- transformation point
- temperature
- steel pipe
- high toughness
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Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は耐ＣＯ2 腐食特性に優
れ、耐硫化物応力割れ性（以下、耐ＳＳＣ性という。Ｓ
ＳＣ；Sulfide Stress Cracking の略）を有する高靭性
マルテンサイト系ステンレス鋼継目無鋼管の製造法に関
する。The present invention has excellent CO 2 corrosion resistance and sulfide stress cracking resistance (hereinafter referred to as SSC resistance. S
SC: abbreviation for Sulfide Stress Cracking) and a method for producing a high toughness martensitic stainless steel seamless steel pipe.
【０００２】[0002]
【従来の技術】近年、ＣＯ2 を多量に含むガスを生産す
るガス井の開発や２次回収のためのＣＯ2 インジェクシ
ョンが広く行われるようになっている。このような環境
では鋼管の腐食が激しいため耐ＣＯ2 腐食特性に優れた
マルテンサイト系ステンレス鋼管が多く使用されてい
る。特に、耐食性に優れたマルテンサイト系ステンレス
鋼として、特公昭５９−１５９７７号公報に開示されて
いるようなＣ：０．０１５％未満、Ｓｉ：０．１〜０．
８％、Ｍｎ：０．１〜２．０％、Ｃｒ：１１〜１７％、
Ｎｉ：０．１〜３．０％、Ｎｂ：０．０１〜０．０５
％、Ｎ：０．０１５％以下、Ａｌ：０．０１〜０．１０
％、必要によっては少量のＣｏ，Ｃｕを含有するマルテ
ンサイト組織の継目無鋼管などが挙げられる。これらの
鋼は従来鋼であるＳＵＳ４１０，ＳＵＳ４２０Ｊ１，Ｊ
２などと比べてＣ含有量を低く制限しているためＣｒ炭
化物の析出量が少なく、耐食性に有効な固溶Ｃｒ量を確
保できることから耐食性の向上を達成している。また、
さらにＣＯ2 環境での耐食性を向上させるにはＮｉ，Ｃ
ｕの複合添加が有効であることも明らかとなっている。2. Description of the Related Art In recent years, development of gas wells for producing gas containing a large amount of CO 2 and CO 2 injection for secondary recovery have been widely performed. In such an environment, since the steel pipe is severely corroded, a martensitic stainless steel pipe excellent in CO 2 corrosion resistance is often used. In particular, as a martensitic stainless steel excellent in corrosion resistance, C: less than 0.015%, Si: 0.1 to 0. 0, as disclosed in Japanese Patent Publication No. 59-15977.
8%, Mn: 0.1 to 2.0%, Cr: 11 to 17%,
Ni: 0.1-3.0%, Nb: 0.01-0.05
%, N: 0.015% or less, Al: 0.01 to 0.10.
%, And if necessary, a seamless steel pipe having a martensite structure containing a small amount of Co or Cu. These steels are conventional steels, SUS410, SUS420J1, J
Since the C content is limited to be lower than that of No. 2 and the like, the precipitation amount of Cr carbide is small, and the amount of solid solution Cr effective for corrosion resistance can be secured, so that the corrosion resistance is improved. Also,
To improve the corrosion resistance in CO 2 environment, Ni, C
It has also been clarified that the combined addition of u is effective.
【０００３】[0003]
【発明が解決しようとする課題】しかしながら、このよ
うにマルテンサイト系ステンレス鋼においてＣならびに
Ｎの添加量を著しく低下させると、鋼塊加熱時にオース
テナイト基地に熱間加工性を低下させるδフェライト相
が生成しやすくなる欠点を持つ。したがって、シームレ
ス圧延のように苛酷な加工条件下では割れや疵を発生
し、歩留り低下によるコストアップは避けられなかっ
た。また、Ｎｉ，Ｃｕを複合添加すると耐食性は向上す
るが、Ｈ2 Ｓを含む環境において不均一腐食に起因する
微小な割れが発生するという問題があった。したがっ
て、これまで、耐ＣＯ2 腐食特性ならびに耐ＳＳＣ性の
良好なマルテンサイト系ステンレス鋼継目無鋼管の製造
は困難であった。However, when the addition amounts of C and N are remarkably reduced in the martensitic stainless steel as described above, the δ ferrite phase which deteriorates the hot workability in the austenite matrix during the heating of the steel ingot is formed. It has the drawback of being easy to generate. Therefore, under severe processing conditions such as seamless rolling, cracks and flaws are generated, and it is unavoidable that the yield is reduced and the cost is increased. Further, although the corrosion resistance is improved by adding Ni and Cu in combination, there is a problem that minute cracks are generated due to uneven corrosion in an environment containing H 2 S. Therefore, it has heretofore been difficult to manufacture a martensitic stainless steel seamless steel pipe having excellent CO 2 corrosion resistance and SSC resistance.
【０００４】[0004]
【課題を解決するための手段】本発明者らは多くの実験
結果から耐ＣＯ2 腐食性はＣを低減化し必要量のＣｒ，
Ｎｉ，Ｃｕを添加しておけば維持されること、耐ＳＳＣ
性は割れ抵抗性を示す組織制御を行い、かつＭｏを添加
すれば向上することを知見した。また、熱間加工性は、
Ｐ，Ｓなどを低減化して介在物の形成を抑えること、
Ｃ，Ｎの添加量を制御してさらにＮｉを添加することに
より、変形抵抗の異なる異相の相分率および形状を制御
するような冶金的操作を行うことを知見した。The present inventors have found from many experimental results that the CO 2 corrosion resistance reduces C and reduces the required amount of Cr,
It can be maintained by adding Ni and Cu, SSC resistance
It was found that the property is improved by controlling the structure showing crack resistance and adding Mo. The hot workability is
To reduce the formation of inclusions by reducing P, S, etc.,
It has been found that a metallurgical operation is performed to control the phase fraction and shape of different phases having different deformation resistances by controlling the addition amounts of C and N and further adding Ni.
【０００５】特に、本発明者らはまずＣならびにＮの効
果に着目し次のような知見を得た。図１に、ベース成分
を２％Ｃｕ−４％Ｎｉ−１５％Ｃｒ鋼としてＣおよびＮ
含有量を変えた場合の耐ＣＯ2 腐食特性ならびに熱間加
工時の絞り値を示す。図１において、Ｃ．Ｒ．は４０at
m のＣＯ2 と平衡した２００℃の人工海水中における年
間の腐食速度であり、Ｃ．Ｒ．＜０．１mm/yであれば十
分な耐食性を有すると評価できる。また、Ｒ．Ａ．は１
２５０℃に加熱した試料を９００℃で歪速度３sec -1の
条件にて単軸引張変形したときの絞り率であり、Ｒ．
Ａ．＞７０％となれば熱間変形能は良好であると言え
る。なお、ＣＯ2 腐食試験には熱間加工後、焼入れ・焼
戻し処理を行い、降伏強度が７２０MPa 程度を示すもの
を用いた。図１より、耐ＣＯ2 腐食特性を満足するため
にはＣ＜０．０５％にする必要があり、また、良好な熱
間加工性を有するためには、Ｃ＋０．８Ｎ＞０．０６に
する必要があるということが読み取れる（各元素記号の
含有量の単位はwt．％）。In particular, the present inventors first focused on the effects of C and N and obtained the following findings. In FIG. 1, C and N are used as base components with 2% Cu-4% Ni-15% Cr steel.
The CO 2 corrosion resistance characteristics when the content is changed and the drawing value during hot working are shown. In FIG. 1, C.I. R. Is 40 at
is the annual corrosion rate in 200 ° C. artificial seawater equilibrated with m 2 CO 2 . R. If it is <0.1 mm / y, it can be evaluated as having sufficient corrosion resistance. In addition, R. A. Is 1
It is the reduction ratio when a sample heated to 250 ° C. is uniaxially tensile deformed at a strain rate of 3 sec −1 at 900 ° C.
A. If it is> 70%, it can be said that the hot deformability is good. In the CO 2 corrosion test, the one having a yield strength of about 720 MPa was used after quenching and tempering after hot working. From FIG. 1, it is necessary to set C <0.05% in order to satisfy the CO 2 corrosion resistance characteristic, and to set C + 0.8N> 0.06 in order to have good hot workability. It can be read that it is necessary (the unit of the content of each element symbol is wt.%).
【０００６】次に、図２に２５℃，４MPa のＣＯ2 環境
において人工海水を使用した時の２％Ｃｕ−４％Ｎｉ−
１５％Ｃｒ鋼の割れ感受性におよぼすＨ2 Ｓ分圧、Ｍｏ
量の影響を示す。Ｍｏ量が０．５％以下の場合にはＳＳ
Ｃもしくは微小割れが発生するが、０．５％を超えると
割れが発生しなくなることが読み取れる。これはＮｉ，
Ｃｕの複合添加により全面腐食の抑制に伴う水素侵入量
が低下し、さらにＭｏの添加により局部腐食が低減され
ることに起因するものである。Next, in FIG. 2, 2% Cu-4% Ni-when artificial seawater was used in a CO 2 environment of 25 ° C. and 4 MPa.
Partial pressure of H 2 S, Mo on crack susceptibility of 15% Cr steel
The effect of quantity is shown. If the Mo content is 0.5% or less, SS
It can be read that C or minute cracks occur, but cracks do not occur when the content exceeds 0.5%. This is Ni,
This is because the combined addition of Cu reduces the amount of hydrogen intrusion accompanying the suppression of general corrosion, and the addition of Mo further reduces the local corrosion.
【０００７】本発明は以上に述べた知見を組み合わせて
構成したものであって、その要旨は下記の通りである。
Ｃ≦０．０５％、 Ｓｉ≦０．５０％、Ｍｎ
≦１．０％、 Ｐ≦０．０３％、Ｓ≦０．０
１％、 Ｃｒ：１１〜１７％、Ｎｉ：１．５
〜５％、 Ｃｕ：０．２〜４％、Ｍｏ：０．５〜
２％、 Ａｌ≦０．０５％、Ｎ：０．０２〜０．
１％、かつＣ＋０．８Ｎ＞０．０６を満足する成分（w
t．％）を含み、残部が実質的にＦｅおよび不可避的不
純物からなる鋼を熱間加工し室温まで自然放冷した後、
Ａｃ3 変態点＋１０℃〜Ａｃ3変態点＋２００℃の温度
に加熱し続いて室温まで空冷以上の冷却速度にて冷却
し、続いて、Ａｃ1 変態点以下の温度にて焼戻し処理す
るか、あるいは、上記成分の鋼を熱間加工し室温まで自
然放冷した後、Ａｃ3 変態点＋１０℃〜Ａｃ3 変態点＋
２００℃の温度に加熱し室温まで空冷以上の冷却速度に
て冷却し、Ａｃ1 変態点〜Ａｃ3 変態点の温度に加熱し
室温まで空冷以上の速度にて冷却し、続いて、Ａｃ1 変
態点以下の温度にて焼戻し処理する耐食性に優れたマル
テンサイト系ステンレス鋼継目無鋼管の製造法である。The present invention is constructed by combining the findings described above, and the gist thereof is as follows.
C ≦ 0.05%, Si ≦ 0.50%, Mn
≦ 1.0%, P ≦ 0.03%, S ≦ 0.0
1%, Cr: 11 to 17%, Ni: 1.5
~ 5%, Cu: 0.2-4%, Mo: 0.5-
2%, Al ≦ 0.05%, N: 0.02 to 0.
Component satisfying 1% and C + 0.8N> 0.06 (w
t. %), With the balance consisting essentially of Fe and unavoidable impurities, after hot working and spontaneous cooling to room temperature,
It is heated to a temperature of Ac 3 transformation point + 10 ° C to Ac 3 transformation point + 200 ° C and then cooled to room temperature at a cooling rate of air cooling or higher, and subsequently tempered at a temperature of Ac 1 transformation point or lower, or After the steel having the above components is hot worked and naturally cooled to room temperature, the Ac 3 transformation point + 10 ° C to the Ac 3 transformation point +
Heating to a temperature of 200 ° C. and cooling to room temperature at a cooling rate of air cooling or higher, heating to a temperature of Ac 1 transformation point to Ac 3 transformation point and cooling to room temperature at a rate of air cooling or higher, and subsequently Ac 1 transformation This is a method for producing a seamless martensitic stainless steel pipe, which is excellent in corrosion resistance and is tempered at a temperature below the point.
【０００８】以下に本発明について詳細に説明する。ま
ず、鋼成分の限定理由について述べる。ＣはＣｒ炭化物
などを形成し耐食性を劣化させる元素であるが、典型的
なオーステナイト形成元素であり、熱間加工温度域であ
る９００〜１２５０℃でδフェライト相の発生を抑制す
る効果があるために添加する。ただし、０．０５％を超
える量を添加するとＣｒ炭化物などの炭化物が多量に析
出してＣｒ欠乏層を形成するために耐ＣＯ2 腐食特性が
低下し、また、粒界に炭化物が析出しやすくなるために
耐硫化物応力割れ性が著しく低下する。したがってＣ含
有量は０．０５％以下とした。The present invention will be described in detail below. First, the reasons for limiting the steel components will be described. C is an element that forms Cr carbide and deteriorates the corrosion resistance, but is a typical austenite forming element and has an effect of suppressing the occurrence of the δ ferrite phase in the hot working temperature range of 900 to 1250 ° C. Added to. However, when an amount exceeding 0.05% is added, a large amount of carbides such as Cr carbides precipitate to form a Cr-deficient layer, which lowers the CO 2 corrosion resistance and also causes carbides to easily precipitate at grain boundaries. Therefore, the sulfide stress cracking resistance is significantly reduced. Therefore, the C content is set to 0.05% or less.
【０００９】Ｓｉは製鋼上脱酸材として添加され残有さ
れたもので、鋼の中に０．５０％を超えて含有されると
靭性および耐硫化物応力割れ性が低下するために、０．
５０％以下とした。Ｍｎは介在物を形成し腐食環境下で
割れ抵抗性を損なう元素であるが、オーステナイト単相
化するために有用な成分であるために添加する。ただ
し、１．０％を超えて添加すると多量の介在物を形成す
るために、腐食環境下での割れ抵抗性と靭性が低下す
る。したがって、Ｍｎの含有量は１．０％以下とした。Si is added as a deoxidizing agent in steelmaking and remains. When it is contained in the steel in an amount of more than 0.50%, toughness and sulfide stress cracking resistance are deteriorated. ．
It was set to 50% or less. Mn is an element that forms inclusions and impairs crack resistance in a corrosive environment, but is added because it is a useful component for forming a single phase of austenite. However, if added in excess of 1.0%, a large amount of inclusions are formed, so that the crack resistance and toughness in a corrosive environment deteriorate. Therefore, the Mn content is set to 1.0% or less.
【００１０】Ｐは粒界に偏析して粒界強度を弱め、熱間
加工性および耐硫化物応力割れ性を低下させるので０．
０３％以下とした。Ｓは硫化物として介在物を形成し熱
間加工性を低下させるため、その上限を０．０１％とし
た。Ｃｒは本発明の目的とする耐ＣＯ2 腐食性を付与
し、ステンレス鋼としての腐食性を有するためには、１
１％以上の含有が必要である。しかし、１７％を超えて
添加するとフェライト相が生成しやすくなるために、そ
の限定範囲を１１〜１７％とした。P segregates at the grain boundaries, weakens the grain boundary strength, and reduces hot workability and sulfide stress cracking resistance.
It was set to 03% or less. Since S forms inclusions as sulfides and deteriorates hot workability, the upper limit was made 0.01%. Cr imparts the CO 2 corrosion resistance which is the object of the present invention, and in order to have the corrosion resistance as stainless steel, 1
It is necessary to contain 1% or more. However, if it is added in excess of 17%, a ferrite phase is likely to be formed, so the limited range is set to 11 to 17%.
【００１１】ＮｉはＣｒ含有鋼においては耐食性を向上
させる効果がある。しかも、強力なオーステナイト形成
元素であり、高温加熱時にδフェライト相の形成を抑制
するうえ、その形状を細く短くし熱間加工時にδフェラ
イト相内部に形成されるクラックの成長を抑える効果が
あることから、熱間加工性を向上させる効果も有する。
ただし、Ｎ：０．０２％の場合にＮｉ：１．５％以下の
添加ではそれらの効果を示さず、また、５％を超えて添
加するとＡｃ1 点が非常に低くなり調質が困難になるこ
とと、残留オーステナイト相が形成されて強度・靭性を
損なうために、その限定範囲を１．５〜５％とした。Ni has the effect of improving the corrosion resistance of Cr-containing steel. Moreover, it is a strong austenite forming element, and it has the effect of suppressing the formation of the δ ferrite phase during high temperature heating, and also of suppressing the growth of cracks formed inside the δ ferrite phase during hot working by making the shape thin and short. Therefore, it also has an effect of improving hot workability.
However, when N: 0.02%, addition of Ni: 1.5% or less does not show these effects, and when it exceeds 5%, the Ac 1 point becomes extremely low and tempering becomes difficult. In addition, since the retained austenite phase is formed and the strength and toughness are impaired, the limiting range is set to 1.5 to 5%.
【００１２】ＣｕはＮｉと複合添加した場合にのみＣＯ
2 環境での腐食速度を低下させる効果がある。したがっ
て、Ｎｉ，Ｃｕは必ず同時に添加する。また、オーステ
ナイト安定化元素でありＡｃ1 変態点を低下させないと
いう利点も有する。ただし、含有量が０．２％以下では
耐食性向上効果が十分でないこと、４％を超えると加熱
時に粒界に過剰に偏析して粒界強度を低下させるために
熱間加工性の低下をもたらすことから、添加量を０．２
〜４％の範囲に限定した。Cu is CO only when combined with Ni.
2 Effective to reduce the corrosion rate in the environment. Therefore, Ni and Cu are always added at the same time. It is also an austenite stabilizing element and has the advantage of not lowering the Ac 1 transformation point. However, if the content is 0.2% or less, the effect of improving the corrosion resistance is not sufficient, and if it exceeds 4%, it is excessively segregated at the grain boundaries during heating to reduce the grain boundary strength, resulting in a decrease in hot workability. Therefore, add 0.2
The range was limited to 4%.
【００１３】ＡｌはＳｉと同様に脱酸剤として添加され
含有されたもので、０．０５％を超えて添加するとＡｌ
Ｎが多数形成されて著しく靭性が低下する。したがっ
て、添加量の上限を０．０５％とした。Similar to Si, Al is added as a deoxidizer, and if added in excess of 0.05%, Al is added.
A large amount of N is formed and the toughness is significantly reduced. Therefore, the upper limit of the amount added is set to 0.05%.
【００１４】Ｎは耐食性に対し無害であるうえに、Ｃと
同様に典型的なオーステナイト形成元素であり、熱間加
工温度域である９００〜１２５０℃でフェライト相の形
成を抑える効果がある。その効果は、Ｃ＋０．８Ｎ＞
０．０６（Ｃ，Ｎはwt．％）を満たす添加量の範囲にお
いて有効である。したがって、Ｃ＜０．０５％の場合に
熱間加工温度域にてフェライト相を発生させず、良好な
熱間加工性を得るためにはＮを０．０２％以上添加する
必要がある。また、通常の溶製工程においては０．１％
以上の添加は困難であるためにその添加量の範囲を０．
０２〜０．１％とした。N is harmless to the corrosion resistance and is a typical austenite forming element like C, and has the effect of suppressing the formation of the ferrite phase in the hot working temperature range of 900 to 1250 ° C. The effect is C + 0.8N>
It is effective in the range of the added amount satisfying 0.06 (C and N are wt.%). Therefore, when C <0.05%, it is necessary to add 0.02% or more of N in order to obtain a good hot workability without generating a ferrite phase in the hot working temperature range. Also, 0.1% in the usual melting process
Since the above addition is difficult, the range of addition amount is set to 0.
It was set to 02 to 0.1%.
【００１５】Ｍｏは耐孔食性を向上させるのに有効な元
素であり、Ｈ2 Ｓを含む環境において割れ感受性を低下
させる効果があることから添加元素として必須である。
ただし、０．５％以下の添加ではその効果が小さい。ま
た、Ｍｏ単独では全面腐食特性は改善されないことか
ら、Ｃｕ，Ｎｉとの複合添加が必要である。さらに、２
％を超えて添加しても上記効果は改善されないこと、強
力なフェライト安定化元素であり２％を超える添加によ
りδ相を生成しやすくなることから、限定範囲を０．５
〜２％とした。Mo is an element effective for improving pitting corrosion resistance and is essential as an additional element because it has an effect of reducing cracking susceptibility in an environment containing H 2 S.
However, the effect is small with the addition of 0.5% or less. Also, since Mo alone does not improve the general corrosion characteristics, it is necessary to add Cu and Ni in combination. Furthermore, 2
%, The above effect is not improved, and since it is a strong ferrite stabilizing element and the addition of more than 2% tends to generate the δ phase, the limited range is 0.5.
~ 2%.
【００１６】次に熱処理条件の限定理由について述べ
る。まず、オーステナイト化加熱温度は、Ｃｒ含有ステ
ンレス鋼のγループ内において、炭化物が完全に固溶せ
ず結晶粒の粗大化が生じない温度を上限とし、また、オ
ーステナイト層が安定となる最低の温度を下限とした。
すなわち、Ａｃ3 変態点＋２００℃以上の温度に加熱す
ると炭化物が完全に固溶するために、冷却時にＣｒ炭化
物などが粒界に多量に析出し耐食性が著しく低下し、さ
らに結晶粒の粗大化が生じるために、靭性が低下する。
またＡｃ3 変態点＋１０℃以下の低い温度に加熱した場
合には、オーステナイト相が安定化せず、安定した強度
を得ることが困難である。したがって、加熱処理温度は
Ａｃ3 変態点＋１０℃〜Ａｃ3変態点＋２００℃とし
た。この加熱後の冷却速度が空冷よりも遅いと粒界に炭
化物が析出し、靭性が著しく低下するために空冷以上の
冷却速度に限定した。Next, the reasons for limiting the heat treatment conditions will be described. First, the austenitizing heating temperature is the upper limit of the temperature at which carbides do not completely form a solid solution and coarsening of crystal grains does not occur in the γ loop of Cr-containing stainless steel, and the minimum temperature at which the austenite layer becomes stable. Was set as the lower limit.
That is, when heated to a temperature of Ac 3 transformation point + 200 ° C. or higher, the carbide completely dissolves in solid solution, so that a large amount of Cr carbide and the like precipitates at the grain boundaries during cooling, the corrosion resistance is significantly reduced, and the crystal grains are coarsened. As a result, the toughness decreases.
When heated to a low temperature of Ac 3 transformation point + 10 ° C. or lower, the austenite phase is not stabilized and it is difficult to obtain stable strength. Therefore, the heat treatment temperature was set to Ac 3 transformation point + 10 ° C to Ac 3 transformation point + 200 ° C. If the cooling rate after this heating is slower than that of air cooling, carbide precipitates at the grain boundaries and the toughness is significantly reduced, so the cooling rate was limited to air cooling or higher.
【００１７】こうして室温まで冷却するとマルテンサイ
ト変態が生じて、マルテンサイト単相組織となる。この
マルテンサイト組織中の残留応力を回復により消滅さ
せ、過飽和炭素原子を炭化物として析出させることによ
って、靭性・延性を高め、所望の強度を得るために焼戻
し処理を施す。特に、本成分系ではＭｏ，Ｃｕを添加し
ており焼戻し処理によりＭｏ炭化物およびＣｕクラスタ
ーの析出が生じるために油井管のグレードでＣ９５級以
上の高強度に調質できる一方、Ｎｉを含有するために高
い靭性が得られる。また、この焼戻し処理時に、Ａｃ1
変態点以上の温度に加熱すると逆変態が生じて靭性が著
しく低下するために、焼戻し処理はＡｃ1変態点以下の
温度にて行う。When cooled to room temperature in this way, martensitic transformation occurs to form a martensitic single-phase structure. The residual stress in this martensitic structure is eliminated by recovery, and supersaturated carbon atoms are precipitated as carbides to enhance toughness and ductility, and tempering treatment is performed to obtain desired strength. In particular, since Mo and Cu are added to this component system and precipitation of Mo carbide and Cu clusters is caused by the tempering treatment, the grade of oil country tubular goods can be tempered to a high strength of C95 or higher, while Ni is contained. Very high toughness is obtained. In addition, during this tempering treatment, Ac 1
When heated to a temperature above the transformation point, reverse transformation occurs and the toughness decreases significantly, so the tempering treatment is performed at a temperature below the Ac 1 transformation point.
【００１８】さらに、優れた靭性ならびに耐ＳＳＣ性を
得ることを目的とする場合には、オーステナイト化処理
後の焼戻し処理を行う前に、必要によってはＡｃ1 変態
点〜Ａｃ3 変態点の温度範囲に加熱することによる２相
域加熱処理を行う。これは、鋼を１回の焼戻し処理では
得られない比較的低い強度に調質することを目的とす
る。この温度域に加熱することにより、ＣｕおよびＭｏ
炭化物のサイズが大きくなるために析出硬化能は低減
し、より低い強度にも調質し得る。本処理を用いてＣ９
５級以下の強度に調質することにより、鋼にさらに優れ
た靭性ならびに耐ＳＳＣ性を付与することが可能とな
る。以上のような本発明法により製造された鋼管は、耐
ＣＯ2 腐食特性・耐ＳＳＣ性および靭性に優れている。Further, for the purpose of obtaining excellent toughness and SSC resistance, if necessary, before the tempering treatment after the austenitizing treatment, the temperature range from the Ac 1 transformation point to the Ac 3 transformation point may be satisfied. A two-phase region heat treatment is performed by heating to the above. This aims to temper the steel to a relatively low strength which cannot be obtained by a single tempering treatment. By heating to this temperature range, Cu and Mo
Since the size of the carbides is increased, the precipitation hardenability is reduced, and it is possible to temper even lower strength. C9 using this process
By tempering to a grade 5 or lower strength, it becomes possible to impart more excellent toughness and SSC resistance to the steel. The steel pipe manufactured by the method of the present invention as described above is excellent in CO 2 corrosion resistance, SSC resistance and toughness.
【００１９】[0019]
【実施例】表１に示される化学成分の鋼を通常の溶製工
程にて鋳造した後、熱間圧延により鋼管を製造した。ま
ず圧延ままの鋼管の表面を観察し疵の発生の有無を調査
した。次に、加熱処理と焼戻し処理を施したものを用い
て、強度、靭性、耐ＣＯ2腐食性、耐ＳＳＣ性を調査し
た。そのときの熱処理温度と強度などの材質については
表２に示す。EXAMPLE Steels having the chemical composition shown in Table 1 were cast in a usual melting process and then hot rolled to produce steel pipes. First, the surface of the as-rolled steel pipe was observed to investigate the occurrence of flaws. Next, the heat treatment and the tempering treatment were performed, and the strength, toughness, CO 2 corrosion resistance and SSC resistance were investigated. Table 2 shows materials such as heat treatment temperature and strength at that time.
【００２０】耐ＣＯ2 腐食性は４０気圧のＣＯ2 と平衡
した２００℃の人工海水中での腐食速度（mm/y）で評価
した。腐食速度が０．１mm/y以下であれば耐食性を有す
ると見なせる。耐ＳＳＣ性は丸棒引張試験片を２５℃の
５％ＮａＣｌ溶液中に１気圧の９０％ＣＯ2 ＋１０％Ｈ
2 Ｓガスを飽和した腐食環境中で単軸引張応力を加え、
７２０時間で破壊が生じない最大初期応力と降伏応力の
比（Ｒｓ値）を求めた。Ｒｓ≧０．８であれば優れた特
性であるといえる。The resistance to CO 2 corrosion was evaluated by the corrosion rate (mm / y) in 200 ° C. artificial seawater equilibrated with CO 2 at 40 atm. If the corrosion rate is 0.1 mm / y or less, it can be considered to have corrosion resistance. The SSC resistance was measured by applying a round bar tensile test piece to a 5% NaCl solution at 25 ° C. under 1 atmosphere of 90% CO 2 + 10% H.
2 In a corrosive environment saturated with S gas, uniaxial tensile stress is applied,
The ratio (Rs value) of the maximum initial stress and the yield stress at which breakage did not occur at 720 hours was determined. If Rs ≧ 0.8, it can be said that the characteristics are excellent.
【００２１】[0021]
【表１】 [Table 1]
【００２２】[0022]
【表２】 [Table 2]
【００２３】表２の結果より、本発明法により製造され
た鋼管は、良好な耐ＣＯ2 腐食性、耐ＳＳＣ性ならびに
高靭性を示すのに対し、本発明の範囲から外れた比較法
ではいずれかの特性が劣っていることが明らかである。From the results shown in Table 2, the steel pipes produced by the method of the present invention show good CO 2 corrosion resistance, SSC resistance and high toughness, whereas the comparative pipes out of the scope of the present invention show It is clear that these properties are inferior.
【００２４】[0024]
【発明の効果】以上のように本発明によれば構成する成
分元素と処理条件を特定することにより、耐ＣＯ2 腐食
性に優れ、かつ耐ＳＣＣ性ならびに高靭性を有するマル
テンサイト系ステンレス継目無鋼管を容易に得ることが
できる。As described above, according to the present invention, the martensitic stainless steel seamless steel having excellent CO 2 corrosion resistance, SCC resistance and high toughness can be obtained by specifying the constituent elements and the treatment conditions. A steel pipe can be easily obtained.
【図１】ＣおよびＮ含有量と耐ＣＯ2 腐食性ならびに熱
間加工時の絞り値との関係を示す図。FIG. 1 is a graph showing the relationship between C and N contents, CO 2 corrosion resistance, and drawing value during hot working.
【図２】人工海水を使用した割れ感受性におよぼすＨ2
Ｓ分圧とＭｏ含有量との関係を示す図。Fig. 2 H 2 influence on cracking susceptibility using artificial seawater
The figure which shows the relationship between S partial pressure and Mo content.
Claims (2)
および不可避的不純物からなる鋼を熱間加工し室温まで
自然放冷した後、Ａｃ3 変態点＋１０℃〜Ａｃ3変態点
＋２００℃の温度に加熱し続いて室温まで空冷以上の冷
却速度にて冷却し、しかる後、Ａｃ1 変態点以下の温度
にて焼戻し処理することを特徴とする耐食性に優れた高
靭性マルテンサイト系ステンレス鋼継目無鋼管の製造
法。1. C ≦ 0.05%, Si ≦ 0.50%, Mn ≦ 1.0%, P ≦ 0.03%, S ≦ 0.01%, Cr: 11-17%, Ni: 1 0.5 to 5%, Cu: 0.2 to 4%, Mo: 0.5 to 2%, Al ≦ 0.05%, N: 0.02 to 0.1%, and C + 0.8N> 0.06 Content (wt.%) Is satisfied, and the balance is substantially Fe.
And, steel consisting of unavoidable impurities is hot-worked and naturally cooled to room temperature, then heated to a temperature of Ac 3 transformation point + 10 ° C to Ac 3 transformation point + 200 ° C, and then cooled to room temperature at a cooling rate of air cooling or higher. Then, a method of producing a high toughness martensitic stainless steel seamless steel pipe having excellent corrosion resistance, which is characterized by performing a tempering treatment at a temperature not higher than the Ac 1 transformation point.
および不可避的不純物からなる鋼を熱間加工し室温まで
自然放冷した後、Ａｃ3 変態点＋１０℃〜Ａｃ3変態点
＋２００℃の温度に加熱し続いて室温まで空冷以上の速
度にて冷却し、さらにＡｃ1 変態点〜Ａｃ3 変態点の温
度に加熱し続いて室温まで空冷以上の速度にて冷却し、
しかる後、Ａｃ1 変態点以下の温度にて焼戻し処理する
ことを特徴とする耐食性に優れた高靭性マルテンサイト
系ステンレス鋼継目無鋼管の製造法。2. C ≦ 0.05%, Si ≦ 0.50%, Mn ≦ 1.0%, P ≦ 0.03%, S ≦ 0.01%, Cr: 11-17%, Ni: 1 0.5 to 5%, Cu: 0.2 to 4%, Mo: 0.5 to 2%, Al ≦ 0.05%, N: 0.02 to 0.1%, and C + 0.8N> 0.06 Content (wt.%) Is satisfied, and the balance is substantially Fe.
And, steel consisting of unavoidable impurities is hot-worked and naturally cooled to room temperature, then heated to a temperature of Ac 3 transformation point + 10 ° C to Ac 3 transformation point + 200 ° C, and subsequently cooled to room temperature at a rate of air cooling or higher. , Further heating to a temperature from the Ac 1 transformation point to the Ac 3 transformation point, and then cooling to room temperature at a rate of air cooling or higher,
Thereafter, a method of producing a high toughness martensitic stainless steel seamless steel pipe having excellent corrosion resistance, which is characterized by performing a tempering treatment at a temperature not higher than an Ac 1 transformation point.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5325395A JPH07179943A (en) | 1993-12-22 | 1993-12-22 | Production of high toughness martensitic strainless steel pipe excellent in corrosion resistance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5325395A JPH07179943A (en) | 1993-12-22 | 1993-12-22 | Production of high toughness martensitic strainless steel pipe excellent in corrosion resistance |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH07179943A true JPH07179943A (en) | 1995-07-18 |
Family
ID=18176365
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP5325395A Pending JPH07179943A (en) | 1993-12-22 | 1993-12-22 | Production of high toughness martensitic strainless steel pipe excellent in corrosion resistance |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH07179943A (en) |
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1993
- 1993-12-22 JP JP5325395A patent/JPH07179943A/en active Pending
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| US7238434B2 (en) | 2003-09-05 | 2007-07-03 | Sumitomo Metal Industries, Ltd. | Welded structure having improved resistance to stress corrosion cracking |
| WO2005023478A1 (en) | 2003-09-05 | 2005-03-17 | Sumitomo Metal Industries, Ltd. | Welded structure excellent in resistance to stress corrosion cracking |
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