JPH1147969A - Manufacture of welded steel tube for line pipe excellent in corrosion resistance - Google Patents
Manufacture of welded steel tube for line pipe excellent in corrosion resistanceInfo
- Publication number
- JPH1147969A JPH1147969A JP9207719A JP20771997A JPH1147969A JP H1147969 A JPH1147969 A JP H1147969A JP 9207719 A JP9207719 A JP 9207719A JP 20771997 A JP20771997 A JP 20771997A JP H1147969 A JPH1147969 A JP H1147969A
- Authority
- JP
- Japan
- Prior art keywords
- less
- welding
- value
- corrosion resistance
- welded
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/346—Working by laser beam, e.g. welding, cutting or boring in combination with welding or cutting covered by groups B23K5/00 - B23K25/00, e.g. in combination with resistance welding
- B23K26/348—Working by laser beam, e.g. welding, cutting or boring in combination with welding or cutting covered by groups B23K5/00 - B23K25/00, e.g. in combination with resistance welding in combination with arc heating, e.g. TIG [tungsten inert gas], MIG [metal inert gas] or plasma welding
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/02—Iron or ferrous alloys
- B23K2103/04—Steel or steel alloys
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/02—Iron or ferrous alloys
- B23K2103/04—Steel or steel alloys
- B23K2103/05—Stainless steel
Landscapes
- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Mechanical Engineering (AREA)
- Laser Beam Processing (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、石油・天然ガスの
輸送に用いて好適な耐食性に優れたラインパイプ用溶接
鋼管の製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a welded steel pipe for line pipes having excellent corrosion resistance and suitable for transporting oil and natural gas.
【０００２】[0002]
【従来の技術】近年、石油・天然ガスは、掘削が容易な
ものはあらかた掘り尽くされ、勢い、腐食が厳しい、深
度が深い、寒冷地や海底といった掘削環境の厳しい坑井
にも手をつけざるを得なくなっている。このような坑井
から生産される石油・天然ガスの中には、炭酸ガスが多
量に含まれる場合が多く、こうした環境に置かれた炭素
鋼あるいは低合金鋼は著しく腐食されることから、従
来、これに対する防食手段としてインヒビタを添加する
ことが行われてきた。しかし、インヒビタの使用はコス
ト高となることや高温での効果が不十分なことから、現
在では、インヒビタを用いる必要のない耐食材料が使わ
れる傾向にある。こういった耐食材料として、油井管で
は、13％Crのマルテンサイト系ステンレス鋼が広く用い
られている。2. Description of the Related Art In recent years, petroleum and natural gas are easily digged out of the easy-to-drill area. I have to help. Oil and natural gas produced from such wells often contain large amounts of carbon dioxide, and carbon steel or low-alloy steel placed in such environments is significantly corroded. Addition of inhibitors as anticorrosion means has been performed. However, since the use of inhibitors increases costs and the effect at high temperatures is insufficient, corrosion-resistant materials that do not require the use of inhibitors tend to be used at present. As such a corrosion-resistant material, 13% Cr martensitic stainless steel is widely used in oil country tubular goods.
【０００３】一方、ラインパイプ用材料としては、ＡＰ
Ｉ規格にはＣ量を低減した12％Cr系マルテンサイト系ス
テンレス鋼が規定されてはいるが、円周溶接に予熱、後
熱が必要となり高コストとなることや、溶接部の靱性に
劣るという欠点があることから、一般にはほとんど採用
されていない。したがって、ラインパイプ用材料には、
溶接性に優れ、また耐食性にも優れた二相ステンレス鋼
が用いられてきた。しかし、二相ステンレス鋼は坑井に
よっては過剰性能であったり、高コストになるという問
題があった。On the other hand, as a material for line pipe, AP
Although the I standard stipulates a 12% Cr martensitic stainless steel with a reduced C content, it requires preheating and postheating for girth welding, resulting in high cost and poor toughness of the weld. Due to the drawback, they are rarely adopted in general. Therefore, materials for line pipes include:
Duplex stainless steels having excellent weldability and excellent corrosion resistance have been used. However, duplex stainless steels have the problem of overperformance or high cost in some wells.
【０００４】これらの問題に対して、例えば特開平８−
295939号公報に開示されるように、シームレス鋼管では
高Crマルテンサイト系ステンレス鋼の開発が行われてい
る。しかしシームレス鋼管では大径、薄肉鋼管が製造困
難なため、すべてのパイプラインに適用することは難し
く、同様の特性を持つ溶接管の開発が望まれていた。こ
れに対し、特開平８−206861号公報に開示されるよう
に、Ｃ≦0.05％、Cr：10〜14％のマルテンサイト系ステ
ンレス鋼を素材としたレーザ溶接鋼管が提案されてはい
るが、高温、高CO2 および塩化物環境下での耐食性、と
くに溶接部の耐選択腐食性が考慮されておらず、溶接部
に選択腐食が発生する危険性がある。To solve these problems, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent Publication No. 295939, high Cr martensitic stainless steel has been developed for seamless steel pipes. However, it is difficult to produce a large-diameter, thin-walled steel pipe in a seamless steel pipe, so that it is difficult to apply the pipe to all pipelines, and development of a welded pipe having similar characteristics has been desired. On the other hand, as disclosed in Japanese Patent Application Laid-Open No. Hei 8-206861, a laser welded steel pipe made of a martensitic stainless steel having a C of 0.05% and a Cr of 10 to 14% has been proposed. The corrosion resistance under high temperature, high CO 2 and chloride environment, especially the selective corrosion resistance of the welded part is not considered, and there is a risk that the selective corrosion occurs in the welded part.
【０００５】[0005]
【発明が解決しようとする課題】そこで本発明は、比較
的安価な高Crマルテンサイト系ステンレス鋼を母材と
し、炭酸ガスおよび塩化物腐食環境中での耐食性、特に
溶接部の耐選択腐食性に優れ、円周溶接で予熱・後熱を
要さないラインパイプ用溶接鋼管の製造方法を提供する
ことを目的とする。SUMMARY OF THE INVENTION Accordingly, the present invention is based on a relatively inexpensive high Cr martensitic stainless steel as a base material, and has a corrosion resistance in a carbon dioxide gas and chloride corrosion environment, particularly a selective corrosion resistance of a welded portion. It is an object of the present invention to provide a method for manufacturing a welded steel pipe for a line pipe which is excellent in girth and does not require preheating and post-heating by circumferential welding.
【０００６】[0006]
【課題を解決するための手段】本発明者らは、鋭意検討
の結果、素材の鋼帯を、Ｃ、Ｎをそれぞれ0.02％以下、
0.05％以下にまで低減し、さらに、Ni、Mo、および炭化
物形成元素であるTi、Ｖ、Zr、Nb、TaをＣ、Ｎに応じた
所定量範囲で添加したCr鋼とし、さらにシーム造管溶接
後の溶接部の冷却速度を規制することで、炭酸ガス環境
下での耐食性、溶接性に優れた溶接鋼管が得られるとい
う知見を得、さらに検討を重ねて本発明を完成した。す
なわち、本発明は、mass％で、Ｃ：0.02％以下、Si：0.
5 ％以下、Mn：0.3 〜3.0 ％、Cr：10〜14％、Ni：0.1
〜7.0 ％、Al：0.1 ％以下、Ｎ：0.03％以下を含有し、
さらに、Mo：3.0 ％以下、Cu：2.0 ％以下、Nb：0.15％
以下、Ti：0.15％以下、Zr：0.15％以下、Ｖ：0.25％以
下、Ta：0.15％以下、Ca：0.006 ％以下のうち１種また
は２種以上を必要に応じて含有し、かつ、下記の式(1)
で定められるP1値が10.5以上、下記の式(2) で定められ
るP2値が4.0 以下であり、残部Feおよび不可避的不純物
からなる鋼帯を、オープン管状に成形し対向する両端部
をレーザ溶接して鋼管にすることを特徴とする耐食性に
優れたラインパイプ用溶接鋼管の製造方法である。Means for Solving the Problems As a result of intensive studies, the present inventors have found that the steel strip of the material has a C and N content of 0.02% or less, respectively.
Cr steel containing Ni, Mo, and carbide forming elements Ti, V, Zr, Nb, and Ta in a predetermined amount range according to C and N. By controlling the cooling rate of the weld after welding, it was found that a welded steel pipe excellent in corrosion resistance and weldability in a carbon dioxide gas environment was obtained, and the present invention was completed by further study. That is, in the present invention, in mass%, C: 0.02% or less, Si: 0.
5% or less, Mn: 0.3 to 3.0%, Cr: 10 to 14%, Ni: 0.1
~ 7.0%, Al: 0.1% or less, N: 0.03% or less,
Further, Mo: 3.0% or less, Cu: 2.0% or less, Nb: 0.15%
In the following, one or more of Ti: 0.15% or less, Zr: 0.15% or less, V: 0.25% or less, Ta: 0.15% or less, Ca: 0.006% or less are contained as necessary, and the following: Equation (1)
The P1 value determined by the above is 10.5 or more, the P2 value determined by the following formula (2) is 4.0 or less, and the steel strip consisting of the balance Fe and unavoidable impurities is formed into an open tubular shape and the opposite ends are laser-welded. This is a method for producing a welded steel pipe for line pipes having excellent corrosion resistance, characterized in that the steel pipe is made into a steel pipe.
【０００７】 記 P1値＝ (％Cr) ＋ (％Mo) ＋0.2(％Ni) ＋3(％Cu) ＋3(％Ti) −7(％Ｃ) −5( ％Ｎ) ………(1) P2値＝150(％Ｃ) ＋100(％Ｎ) − (％Nb) − (％Ti) − (％Ｖ) ………(2) なお、Mo、Cu、Nb、Ti、Ｖを含有しない場合には、前記
の式(1) 、式(2) に代えて下記の式(1A)、式(2B)とす
る。P1 value = (% Cr) + (% Mo) +0.2 (% Ni) +3 (% Cu) +3 (% Ti) −7 (% C) −5 (% N) ) P2 value = 150 (% C) + 100 (% N)-(% Nb)-(% Ti)-(% V) ... (2) When Mo, Cu, Nb, Ti and V are not contained In this case, the following equations (1A) and (2B) are used instead of the above equations (1) and (2).
【０００８】 記 P1値＝ (％Cr) ＋0.2(％Ni) −7(％Ｃ) −5(％Ｎ) ………(1A) P2値＝150(％Ｃ) ＋100(％Ｎ) ………(2B) 本発明では、溶接されてから 500℃までの溶接部の平均
冷却速度が 150℃/s以上となるようにレーザ溶接するの
が好ましく、また、必要に応じて、レーザ溶接後、鋼管
の全体もしくは溶接部近傍を 500℃以上に加熱する、あ
るいは、レーザ溶接後、鋼管の全体もしくは溶接部近傍
を Ac3点以上に加熱し、 300℃以下まで冷却し、 500℃
以上 Ac1点以下に加熱するのが好ましい。P1 value = (% Cr) +0.2 (% Ni) −7 (% C) −5 (% N) (1A) P2 value = 150 (% C) +100 (% N) (2B) In the present invention, it is preferable to perform laser welding so that the average cooling rate of the welded portion from welding to 500 ° C is 150 ° C / s or more, and if necessary, after laser welding. Heat the entire steel pipe or the vicinity of the weld to 500 ° C or higher, or after laser welding, heat the entire steel pipe or the vicinity of the weld to three or more Ac points, cool to 300 ° C or lower, and then 500 ° C
Preferably heated to less than Ac 1 point.
【０００９】[0009]
【発明の実施の形態】まず、本発明要件のうち鋼帯化学
組成の限定理由を述べる。 Ｃ：0.02％以下 Ｃは、溶接割れ回避のため、溶接熱影響部の靱性向上の
ため、溶接熱影響部の硬さ低減のため、また、炭酸ガス
に対する耐食性、耐孔食性確保のために、できるだけ低
いほうが望ましい。特に予熱なしで溶接するためには0.
02％以下とする必要があることから、Ｃ量は0.02％以下
とする。なお、より好ましいのは0.015％以下である。DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the reasons for limiting the chemical composition of a steel strip among the requirements of the present invention will be described. C: 0.02% or less C is to prevent welding cracks, to improve the toughness of the heat affected zone, to reduce the hardness of the heat affected zone, and to ensure the corrosion resistance to carbon dioxide gas and the pitting corrosion resistance. It is desirable to be as low as possible. Especially for welding without preheating.
Since it is necessary to make it 02% or less, the C content is made 0.02% or less. It is more preferable that the content be 0.015% or less.
【００１０】Si：0.5 ％以下 Siは脱酸元素として添加されるが、フェライト生成元素
であり、0.5 ％を超える多量の含有はフェライトを過剰
に生成させ、母材および溶接部の靱性を劣化させるの
で、0.5 ％以下とする。 Mn：0.2 〜3.0 ％ Mnは、脱酸、および強度確保に必要な元素である。ま
た、オーステナイト生成元素であるため、フェライト生
成を抑制し、母材および溶接部の靱性を向上させる働き
もある。これらの効果を得るには0.2 ％以上必要である
が、3.0 ％を超えて添加しても効果が飽和するため、Mn
量は0.2 〜3.0 ％とする。Si: not more than 0.5% Si is added as a deoxidizing element, but is a ferrite-forming element. If it is contained in a large amount exceeding 0.5%, ferrite is excessively formed and the toughness of the base metal and the welded portion is deteriorated. Therefore, it should be 0.5% or less. Mn: 0.2-3.0% Mn is an element necessary for deoxidation and ensuring strength. Further, since it is an austenite forming element, it also has the function of suppressing the formation of ferrite and improving the toughness of the base material and the welded portion. To obtain these effects, 0.2% or more is required. However, even if added over 3.0%, the effects are saturated, so that Mn
The amount is 0.2-3.0%.
【００１１】Cr：10〜14％ Crはマルテンサイト組織を確保し、かつ炭酸ガスに対す
る耐食性および耐孔食性を付与するために必要な基本元
素である。これらの効果を得るためには10％以上の添加
が必要である。また、14％を超えて含有するとフェライ
トの生成が容易になり、マルテンサイト組織を安定して
得るために多量のオーステナイト生成元素の添加が必要
となってコスト高となる。よって、Cr量は10〜14％とす
る。Cr: 10 to 14% Cr is a basic element necessary to secure a martensite structure and to impart corrosion resistance and pitting corrosion resistance to carbon dioxide gas. To obtain these effects, addition of 10% or more is necessary. On the other hand, when the content exceeds 14%, the formation of ferrite is facilitated, and a large amount of austenite-forming element must be added in order to stably obtain a martensitic structure, resulting in an increase in cost. Therefore, the Cr content is set to 10 to 14%.
【００１２】Ni：0.1 〜7.0 ％ Niはオーステナイト生成元素としてＣ、Ｎの低減による
影響を補うとともに、炭酸ガス環境における耐食性、な
らびに靱性を向上させる効果がある。その効果を得るに
は0.1 ％以上の添加が必要である。また、Crが高い場合
やMo添加鋼の場合、熱間加工性を確保するために添加す
る必要がある。しかし、7.0 ％を超えて添加するとAc1
点が下がりすぎ、要求される特性を得るには長時間の焼
戻しが必要となるほかコストも高くなる。したがって、
Niの添加量は0.1 〜7.0 ％とする。Ni: 0.1-7.0% Ni has the effect of improving the corrosion resistance and the toughness in a carbon dioxide gas environment while compensating for the effects of the reduction of C and N as austenite forming elements. To obtain the effect, it is necessary to add 0.1% or more. In addition, when Cr is high or in the case of Mo-added steel, it is necessary to add Cr to ensure hot workability. However, if added over 7.0%, Ac 1
The points are lowered too much, and a long tempering is required to obtain the required properties, and the cost is also high. Therefore,
The amount of Ni added is 0.1-7.0%.
【００１３】Al：0.1 ％以下 AlはSiと同様、脱酸が目的で添加されるが、0.1 ％超の
添加は靱性の低下を引き起こすため0.1 ％以下とした。 Ｎ：0.03％以下 Ｎは、Ｃと同様、溶接割れ回避のため、溶接熱影響部の
靱性向上のため、溶接熱影響部の硬さ低減のためにでき
るだけ低いほうが望ましい。0.03％を超えるとこれらの
効果が十分に得られないことから、Ｎ量は0.03％以下、
好ましくは0.025 ％以下とする。Al: 0.1% or less Al is added for the purpose of deoxidation similarly to Si, but addition of more than 0.1% causes a decrease in toughness, so Al was made 0.1% or less. N: 0.03% or less N, like C, is preferably as low as possible to avoid welding cracks, to improve the toughness of the heat affected zone, and to reduce the hardness of the heat affected zone. If the content exceeds 0.03%, these effects cannot be sufficiently obtained. Therefore, the N content is 0.03% or less,
Preferably it is 0.025% or less.
【００１４】Mo：3.0 ％以下 Moは耐食性を向上させる効果がある。しかし3.0 ％を超
えて含有するとフェライトの生成が容易になり、かつ耐
食性向上に対してもあまり効果がなくなるため、3.0 ％
以下とする。 Cu：2.0 ％以下 CuはNi、Moとともにオーステナイト生成元素としてＣ、
Ｎの低減による影響を補うとともに、溶接熱影響部の靱
性向上、耐全面腐食性向上に効果がある。さらに、炭酸
ガスおよび塩化物が存在する環境での耐孔食性に効果が
ある。しかし、2.0 ％を超えて含有すると一部が固溶せ
ず析出するようになり、溶接熱影響部の靱性に悪影響を
与えるようになる。よって、Cuは2.0 ％以下、好ましく
は0.2 〜0.7 ％とする。Mo: 3.0% or less Mo has an effect of improving corrosion resistance. However, when the content exceeds 3.0%, the formation of ferrite becomes easy, and the effect of improving the corrosion resistance is not so significant.
The following is assumed. Cu: 2.0% or less Cu is C as an austenite forming element together with Ni and Mo.
In addition to compensating for the effects of reducing N, it is effective in improving the toughness of the heat affected zone and improving the overall corrosion resistance. Further, it has an effect on pitting corrosion resistance in an environment where carbon dioxide and chloride are present. However, when the content exceeds 2.0%, a part thereof does not form a solid solution but precipitates, so that the toughness of the heat affected zone is adversely affected. Therefore, the content of Cu is 2.0% or less, preferably 0.2 to 0.7%.
【００１５】Nb：0.15％以下、Ti：0.15％以下、Zr：0.
15％以下、Ｖ：0.25％以下、Ta：0.15％以下 Nb、Ti、Zr、Ｖ、Taは母材および溶接部の靱性向上に効
果がある。また、Cr炭化物をNb、Ti、Zr、Ｖ、Taの炭化
物に置換することによって、耐孔食性に対する有効Cr量
を増加させることになり、耐孔食性を向上させる。しか
し、Nb、Ti、Zr、Taは0.15％を超えて、Ｖは0.25％を超
えて添加すると溶接割れ感受性が高くなることや、逆に
靱性を劣化させることから、Nb、Ti、Zr、Taはそれぞれ
0.15％以下、Ｖは0.25％以下とする。Nb: 0.15% or less, Ti: 0.15% or less, Zr: 0.
15% or less, V: 0.25% or less, Ta: 0.15% or less Nb, Ti, Zr, V, and Ta are effective in improving the toughness of the base material and the welded portion. Further, by replacing Cr carbide with carbides of Nb, Ti, Zr, V, and Ta, the effective Cr amount with respect to pitting corrosion resistance is increased, and pitting corrosion resistance is improved. However, if Nb, Ti, Zr, and Ta exceed 0.15%, and if V exceeds 0.25%, welding crack susceptibility increases, and conversely, toughness deteriorates, so Nb, Ti, Zr, Ta Are each
0.15% or less, V is 0.25% or less.
【００１６】Ca：0.006 ％以下 CaはCaS を形成し、溶解しやすいMnS を減らす効果があ
り、耐食性を向上させる。しかし、0.006 ％以上の添加
はクラスタ状の介在物を生成させ、靱性低下につながる
ため、0.006 ％以下とした。 P1値：10.5以上 炭酸ガスおよび塩化物の存在環境下で耐食性を向上させ
るためには、不働態皮膜を安定化させる必要があり、そ
れにはCrの増量さらにはMoの添加が効果的である。とは
いえCrが炭化物や窒化物を生成すると耐孔食性に対する
有効Cr量が減少するから、Ｃ、Ｎは下げてやる必要があ
る。またNiさらにはCu、Tiの添加は不働態皮膜を安定に
する効果がある。これらの元素の効果を定量的に調べた
結果、十分な耐炭酸ガス腐食性が顕現されるためには、
前記式(1) または式(1A)で定められるP1値を10.5以上に
する必要がある。なお、P1値は、あまり高すぎるとマル
テンサイト組織の確保が困難になるなどの不都合が生じ
るので、10.5〜16.5の範囲とするのが好ましい。Ca: 0.006% or less Ca forms CaS, has an effect of reducing easily soluble MnS, and improves corrosion resistance. However, the addition of 0.006% or more generates cluster-like inclusions and leads to a decrease in toughness. P1 value: 10.5 or more In order to improve corrosion resistance in the presence of carbon dioxide gas and chloride, it is necessary to stabilize the passive film, and it is effective to increase the amount of Cr and to add Mo. Nevertheless, when Cr forms carbides or nitrides, the effective Cr amount with respect to pitting corrosion resistance decreases, so that C and N must be reduced. The addition of Ni, Cu, and Ti has the effect of stabilizing the passive film. As a result of quantitatively examining the effects of these elements, sufficient carbon dioxide gas corrosion resistance becomes apparent in order to
It is necessary to set the P1 value determined by the above equation (1) or equation (1A) to 10.5 or more. If the P1 value is too high, inconveniences such as difficulty in securing a martensite structure occur. Therefore, the P1 value is preferably in the range of 10.5-16.5.
【００１７】P2値：4.0 以下 本発明では造管シーム溶接にレーザ溶接を用いるが、溶
接部近傍に炭化物や窒化物が生成して、靱性の低下や耐
食性の劣化、特に溶接部の選択腐食を引き起こすことが
ある。これを抑制して溶接部においても充分な耐食性を
確保するためには、前記式(2) または式(2A)で定められ
るP2値を4.0 以下にする必要がある。なお、P2値は、あ
まり低すぎるとデルタフェライトの生成などの不都合が
生じるので、0.5 〜4.0 の範囲とするのが好ましい。P2 value: 4.0 or less In the present invention, laser welding is used for pipe-forming seam welding. However, carbides and nitrides are generated in the vicinity of the welded portion to reduce toughness and deterioration of corrosion resistance, and particularly, selective corrosion of the welded portion. May cause. In order to suppress this and secure sufficient corrosion resistance even at the welded portion, the P2 value determined by the above equation (2) or (2A) needs to be 4.0 or less. If the P2 value is too low, problems such as the formation of delta ferrite occur, so that the P2 value is preferably in the range of 0.5 to 4.0.
【００１８】その他元素はFe中に不可避的に含有する
が、できるだけ低減するのが望ましい。例えばＰ、Ｓは
それぞれ0.03％、0.01％まで許容できるができるだけ低
減する。Ｏは0.04％までなら許容できる。次に、造管シ
ーム溶接以後の工程について説明する。本発明では、上
記組成の鋼帯を、オープン管状に成形し対向する両端部
をレーザ溶接して鋼管にする。造管シーム溶接（鋼帯を
オープン管状に成形し対向する両端部を溶接して鋼管に
すること）の手段としては電縫溶接、鍛接、レーザ溶接
があるが、電縫溶接では耐食性に有害なペネトレータを
発生しやすい問題があり、鍛接では接合界面に酸化物が
残りやすくシーム品質の信頼性が低い問題がある。これ
らに対しレーザ溶接では、そのような問題がないほか、
エネルギーを集中できるから選択腐食されやすい溶接熱
影響部の幅を極めて狭くすることができる。よって、造
管シーム溶接にはレーザ溶接を用いる。Other elements are inevitably contained in Fe, but it is desirable to reduce them as much as possible. For example, P and S can be permitted up to 0.03% and 0.01%, respectively, but are reduced as much as possible. O is acceptable up to 0.04%. Next, steps after the pipe forming seam welding will be described. In the present invention, a steel strip having the above composition is formed into an open tubular shape, and the opposite ends are laser-welded to form a steel pipe. As a means of pipe forming seam welding (forming a steel strip into an open tubular shape and welding the opposite ends to form a steel pipe), there are ERW, forging and laser welding, but ERW welding is harmful to corrosion resistance. There is a problem that a penetrator is easily generated, and there is a problem that oxide is easily left at a joint interface in the forging, and reliability of seam quality is low. In contrast, laser welding does not have such a problem,
Since the energy can be concentrated, the width of the weld heat affected zone which is susceptible to selective corrosion can be made extremely narrow. Therefore, laser welding is used for pipe forming seam welding.
【００１９】ところで、レーザ溶接後、凝固から 500℃
までの溶接部の平均冷却速度が 150℃/s未満であると、
溶接部にCrの炭窒化物が析出し、耐食性、靱性を劣化さ
せる危険性があるため、この冷却速度は 150℃/s以上と
するのが望ましい。この冷却速度の調整を行うには、レ
ーザ溶接の入熱を変更する、あるいは溶接後に管体の一
部または全体に水、エア、もしくは気水混合ミストを噴
射する。By the way, after laser welding, 500 ° C.
If the average cooling rate of the weld up to is less than 150 ° C / s,
Since there is a risk that Cr carbonitride precipitates at the weld and deteriorates corrosion resistance and toughness, it is desirable to set the cooling rate to 150 ° C / s or more. In order to adjust the cooling rate, the heat input of laser welding is changed, or water, air, or a gas-water mixed mist is sprayed on a part or the whole of the pipe after welding.
【００２０】また、好ましくは、レーザ溶接後、鋼管の
全体もしくは溶接部近傍を、(A) 500℃以上に加熱す
る、または、(B) Ac3点以上に加熱し、 300℃以下まで
冷却し、 500℃以上 Ac1点以下に加熱する。上記(A) ま
たは(B) の措置により、溶接部の硬さを下げることがで
きて、靱性をより一層向上させることができる。Preferably, after laser welding, the entirety of the steel pipe or the vicinity of the welded portion is heated to (A) 500 ° C. or more, or (B) heated to 3 points or more of Ac and cooled to 300 ° C. or less. Heat to 500 ° C or more and 1 Ac or less. By the above measures (A) or (B), the hardness of the welded portion can be reduced, and the toughness can be further improved.
【００２１】[0021]
【実施例】表１に示す化学組成になる鋼スラブを熱間圧
延して厚み5mm の熱延鋼帯とし、これらの熱延鋼帯を焼
戻し熱処理してＸ80グレードの強度に調整した後、オー
プン管状に成形し、該オープン管の対向する両端部を表
２に示す溶接条件で CO2レーザ溶接して外径60.5mmφの
溶接鋼管とした。溶接後の冷却速度の調整はレーザビー
ムのエネルギーを調節して行った。また、一部の鋼管に
ついては表２に示すように溶接後熱処理を施すことによ
り、全部の鋼管について溶接最高硬さＨmaxを 300〜340
の範囲に収めた。なお、熱処理条件は前記(A) 、(B)
の範囲から鋼管毎に適宜選択した。EXAMPLE A steel slab having the chemical composition shown in Table 1 was hot-rolled into hot-rolled steel strips having a thickness of 5 mm, and these hot-rolled steel strips were tempered and heat-treated to adjust the strength to X80 grade. The open pipe was formed into a tubular shape, and the opposite ends of the open pipe were CO 2 laser-welded under the welding conditions shown in Table 2 to obtain a welded steel pipe having an outer diameter of 60.5 mmφ. The cooling rate after welding was adjusted by adjusting the energy of the laser beam. Further, as shown in Table 2, some steel pipes are subjected to heat treatment after welding so that the maximum welding hardness Hmax of all the steel pipes is 300 to 340.
Within the range. Note that the heat treatment conditions are the above (A) and (B)
Was selected for each steel pipe as appropriate.
【００２２】これら鋼管から、溶接シーム部が試験片幅
中央に位置するように板厚表層部から採取した 3.0mm厚
×25mm幅×50mm長さの試験片を切り出し、この試験片を
オートクレーブで3.0MPaの炭酸ガスを飽和させた20％Na
Cl水溶液中に浸漬し、80℃で７日間保持するという条件
で、炭酸ガスおよび塩化物腐食環境下での耐食性を試験
した。From these steel pipes, a test piece having a thickness of 3.0 mm × 25 mm × 50 mm and cut out from the surface layer was cut out from the steel pipe so that the welded seam portion was positioned at the center of the width of the test piece. 20% Na saturated with MPa carbon dioxide
The corrosion resistance in a carbon dioxide gas and chloride corrosive environment was tested under the condition of immersion in a Cl aqueous solution and holding at 80 ° C. for 7 days.
【００２３】耐全面腐食性は、試験後、試験片を水洗、
乾燥したのち重量を測定し、重量減少速度を１年間の厚
み減少量に換算して評価し、溶接部選択腐食の有無は、
試験片断面の拡大像を観察して母材部と溶接部との肉厚
段差を測定し、腐食減厚量が母材部の1.5 倍以上の場合
を「有」、1.5 倍未満の場合を「なし」と判定した。試
験結果を表２に併せて示す。この結果から明らかなよう
に、本発明により、、比較的安価な高Crマルテンサイト
系ステンレス鋼をベースとして、炭酸ガスおよび塩化物
腐食環境下での全面腐食に対しては無論のこと、溶接部
の選択腐食に対しても耐性に優れた溶接鋼管が得られ
た。After the test, the test piece was washed with water,
After drying, the weight is measured, and the rate of weight loss is converted into the thickness loss for one year and evaluated.
Observe the magnified image of the cross section of the test piece and measure the thickness difference between the base material and the welded part.If the corrosion reduction amount is 1.5 times or more of the base material part, `` Yes '', and if less than 1.5 times, "None" was determined. The test results are also shown in Table 2. As is evident from the results, the present invention, based on a relatively inexpensive high-Cr martensitic stainless steel, has no A welded steel pipe excellent in resistance to selective corrosion was obtained.
【００２４】[0024]
【表１】 [Table 1]
【００２５】[0025]
【表２】 [Table 2]
【００２６】また、本発明鋼管（No.1）および比較鋼管
（No.12 ）を用いて、予熱後熱なしでＭＩＧ溶接にて円
周溶接を行った。なお溶接材料としては、二相ステンレ
ス鋼を使用した。溶接材料および溶接条件を表３に示
す。本発明鋼は円周溶接を行ってもわれは発生しなかっ
たが、Cr量およびP2値が請求範囲を満たさない比較鋼管
ではＨＡＺにわれが発生した。Further, using the steel pipe of the present invention (No. 1) and the comparative steel pipe (No. 12), circumferential welding was performed by MIG welding without heat after preheating. Note that a duplex stainless steel was used as a welding material. Table 3 shows the welding materials and welding conditions. In the steel of the present invention, cracks did not occur even when circumferential welding was performed, but cracks occurred in the HAZ in comparative steel pipes in which the Cr content and the P2 value did not satisfy the claims.
【００２７】[0027]
【表３】 [Table 3]
【００２８】[0028]
【発明の効果】以上の通り、本発明によれば、比較的安
価な高Crマルテンサイト系ステンレス鋼を母材として、
炭酸ガスおよび塩化物腐食環境下での全面腐食と溶接部
の選択腐食との両方に対して耐性に優れ、円周溶接で予
熱・後熱の要らない溶接鋼管が得られるという格段の効
果を奏することから、石油・天然ガスなどの輸送用のラ
インパイプが安価に提供できるようになり、産業の発展
に寄与するところが極めて大きい。As described above, according to the present invention, a relatively inexpensive high Cr martensitic stainless steel is used as a base material.
It has excellent resistance to both general corrosion and selective corrosion of welds under carbon dioxide and chloride corrosion environments, and has the remarkable effect of being able to obtain welded steel pipes that do not require preheating and postheating by circumferential welding. Therefore, it becomes possible to provide inexpensive line pipes for transporting oil, natural gas, and the like, which greatly contributes to industrial development.
Claims (5)
以下、Mn：0.3 〜3.0 ％、Cr：10〜14％、Ni：0.1 〜7.
0 ％、Al：0.1 ％以下、Ｎ：0.03％以下を含有し、か
つ、下記の式(1A)で定められるP1値：10.5以上、下記の
式(2A)で定められるP2値：4.0 以下であり、残部Feおよ
び不可避的不純物からなる鋼帯を、オープン管状に成形
し対向する両端部をレーザ溶接して鋼管にすることを特
徴とする耐食性に優れたラインパイプ用溶接鋼管の製造
方法。 記 P1値＝ (％Cr) ＋0.2(％Ni) −7(％Ｃ) −5(％Ｎ) ………(1A) P2値＝150(％Ｃ) ＋100(％Ｎ) ………(2A)1. Mass%, C: 0.02% or less, Si: 0.5%
Hereinafter, Mn: 0.3 to 3.0%, Cr: 10 to 14%, Ni: 0.1 to 7.
0%, Al: 0.1% or less, N: 0.03% or less, and P1 value defined by the following formula (1A): 10.5 or more, P2 value defined by the following formula (2A): 4.0 or less A method for producing a welded steel pipe for line pipes having excellent corrosion resistance, comprising forming a steel strip comprising the balance of Fe and unavoidable impurities into an open tubular shape and laser-welding the opposite ends to a steel pipe. Note P1 value = (% Cr) + 0.2 (% Ni) -7 (% C) -5 (% N) ... (1A) P2 value = 150 (% C) + 100 (% N) ... ( 2A)
以下、Mn：0.3 〜3.0 ％、Cr：10〜14％、Ni：0.1 〜7.
0 ％、Al：0.1 ％以下、Ｎ：0.03％以下を含有し、さら
に、Mo：3.0 ％以下、Cu：2.0 ％以下、Nb：0.15％以
下、Ti：0.15％以下、Zr：0.15％以下、Ｖ：0.25％以
下、Ta：0.15％以下、Ca：0.006 ％以下のうち１種また
は２種以上を含有し、かつ、下記の式(1) で定められる
P1値：10.5以上、下記の式(2) で定められるP2値：4.0
以下であり、残部Feおよび不可避的不純物からなる鋼帯
を、オープン管状に成形し対向する両端部をレーザ溶接
して鋼管にすることを特徴とする耐食性に優れたライン
パイプ用溶接鋼管の製造方法。 記 P1値＝ (％Cr) ＋ (％Mo) ＋0.2(％Ni) ＋3(％Cu) ＋3(％Ti) −7(％Ｃ) −5( ％Ｎ) ………(1) P2値＝150(％Ｃ) ＋100(％Ｎ) − (％Nb) − (％Ti) − (％Ｖ) ………(2) 2. In mass%, C: 0.02% or less, Si: 0.5%
Hereinafter, Mn: 0.3 to 3.0%, Cr: 10 to 14%, Ni: 0.1 to 7.
0%, Al: 0.1% or less, N: 0.03% or less, Mo: 3.0% or less, Cu: 2.0% or less, Nb: 0.15% or less, Ti: 0.15% or less, Zr: 0.15% or less, V: contains one or more of 0.25% or less, Ta: 0.15% or less, and Ca: 0.006% or less, and is determined by the following formula (1).
P1 value: 10.5 or more, P2 value determined by the following equation (2): 4.0
A method for producing a welded steel pipe for a line pipe excellent in corrosion resistance, characterized in that a steel strip consisting of the balance Fe and unavoidable impurities is formed into an open tubular shape and laser opposite ends are welded into a steel pipe. . P1 value = (% Cr) + (% Mo) + 0.2 (% Ni) + 3 (% Cu) + 3 (% Ti) -7 (% C) -5 (% N) ……… (1) P2 value = 150 (% C) +100 (% N)-(% Nb)-(% Ti)-(% V) ... (2)
均冷却速度が 150℃/s以上となるようにレーザ溶接する
請求項１または２に記載の方法。3. The method according to claim 1, wherein the laser welding is performed so that an average cooling rate of the welded portion from welding to 500 ° C. is 150 ° C./s or more.
部近傍を 500℃以上に加熱する請求項１〜３のいずれか
に記載の方法。4. The method according to claim 1, wherein after laser welding, the entire steel pipe or the vicinity of the weld is heated to 500 ° C. or higher.
部近傍を Ac3点以上に加熱し、 300℃以下まで冷却し、
500℃以上 Ac1点以下に加熱する請求項１〜３のいずれ
かに記載の方法。5. After laser welding, the entire steel pipe or the vicinity of the welded portion is heated to three or more Ac and cooled to 300 ° C. or less,
The method according to claim 1, wherein the heating is performed at a temperature of 500 ° C. or more and 1 point or less of Ac.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9207719A JPH1147969A (en) | 1997-08-01 | 1997-08-01 | Manufacture of welded steel tube for line pipe excellent in corrosion resistance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP9207719A JPH1147969A (en) | 1997-08-01 | 1997-08-01 | Manufacture of welded steel tube for line pipe excellent in corrosion resistance |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH1147969A true JPH1147969A (en) | 1999-02-23 |
Family
ID=16544425
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP9207719A Pending JPH1147969A (en) | 1997-08-01 | 1997-08-01 | Manufacture of welded steel tube for line pipe excellent in corrosion resistance |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH1147969A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1070763A1 (en) * | 1999-02-02 | 2001-01-24 | Kawasaki Steel Corporation | HIGH Cr STEEL PIPE FOR LINE PIPE |
| JP2011089159A (en) * | 2009-10-21 | 2011-05-06 | Jfe Steel Corp | Method for manufacturing martensitic stainless steel welded tube excellent in intergranular stress corrosion cracking resistance |
| EP1930462B1 (en) * | 2006-11-16 | 2014-01-01 | VIEGA GmbH & Co. KG | Fittings for drinking water carrying assembly sections |
-
1997
- 1997-08-01 JP JP9207719A patent/JPH1147969A/en active Pending
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1070763A1 (en) * | 1999-02-02 | 2001-01-24 | Kawasaki Steel Corporation | HIGH Cr STEEL PIPE FOR LINE PIPE |
| EP1070763A4 (en) * | 1999-02-02 | 2002-05-29 | Kawasaki Steel Co | HIGH Cr STEEL PIPE FOR LINE PIPE |
| US6464802B1 (en) | 1999-02-02 | 2002-10-15 | Kawasaki Steel Corporation | High Cr steel pipe for line pipe |
| EP1930462B1 (en) * | 2006-11-16 | 2014-01-01 | VIEGA GmbH & Co. KG | Fittings for drinking water carrying assembly sections |
| JP2011089159A (en) * | 2009-10-21 | 2011-05-06 | Jfe Steel Corp | Method for manufacturing martensitic stainless steel welded tube excellent in intergranular stress corrosion cracking resistance |
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