JP3684895B2 - Manufacturing method of high toughness martensitic stainless steel with excellent stress corrosion cracking resistance - Google Patents
Manufacturing method of high toughness martensitic stainless steel with excellent stress corrosion cracking resistance Download PDFInfo
- Publication number
- JP3684895B2 JP3684895B2 JP02776299A JP2776299A JP3684895B2 JP 3684895 B2 JP3684895 B2 JP 3684895B2 JP 02776299 A JP02776299 A JP 02776299A JP 2776299 A JP2776299 A JP 2776299A JP 3684895 B2 JP3684895 B2 JP 3684895B2
- Authority
- JP
- Japan
- Prior art keywords
- tempering
- stainless steel
- temperature
- martensitic stainless
- stress corrosion
- 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.)
- Expired - Lifetime
Links
Description
【0001】
【発明の属する技術分野】
本発明は、耐応力腐食割れ性に優れた高靭性マルテンサイト系ステンレス鋼の製造方法に関し、詳しくは、例えば石油、天然ガスの掘削や輸送等の湿潤炭酸ガスや湿潤硫化水素ガスを含む環境において、高い応力腐食割れ抵抗を有する高靭性マルテンサイト系ステンレス鋼の製造方法に関するものである。
【0002】
【従来の技術】
近年生産される石油、天然ガスは、湿潤炭酸ガスや湿潤硫化水素ガスを多量に含む場合が増加しており、その掘削、輸送においては従来の炭素鋼に代り、13Crステンレス鋼等のマルテンサイト系ステンレス鋼が用いられるようになった。しかし、従来のマルテンサイト系ステンレス鋼は、湿潤炭酸ガスに対する耐食性(以下、単に「耐食性」と呼ぶ)は優れているが、湿潤硫化水素ガスに対する耐応力腐食割れ性(以下、単に「耐応力腐食割れ性」と呼ぶ)は十分でなく、強度、靭性、耐食性を維持しつつ、耐応力腐食割れ性に優れたマルテンサイト系ステンレス鋼が望まれていた。
【0003】
強度、靭性、耐食性に加えて、耐応力腐食割れの要求を満たすマルテンサイト系ステンレス鋼として、例えば、特開昭58−199850号公報には、C:0.16〜0.25wt%、Si:1.0wt%未満、Mn:1.0wt%未満、Cr:12.5〜13.5wt%、Ni:0.3〜3wt%、Mo:0.5〜3.5wt%、Cu:0.5〜2wt%を含み、残部がFe及び不可避不純物からなるマルテンサイト系ステンレス鋼が開示され、又、特開昭61−207550号公報には、C:0.03〜0.20wt%、Si:1.0wt%未満、Mn:1.0wt%未満、Cr:12.0〜14.0wt%、B:0.0010〜0.0060wt%を含有し、且つ、Mo:0.5〜4.0wt%、Ni:0.5〜6.0wt%の1種又は2種を含有し、残部がFe及び不可避的不純物からなるマルテンサイト系ステンレス鋼が開示されている。
【0004】
しかしこれらは、極微量の硫化水素ガスを含む環境では耐応力腐食割れ性を示すものの、硫化水素ガス分圧が0.01気圧を越える環境では、応力腐食割れが生じるため、硫化水素ガスを多く含む環境では使用できないという問題があった。
【0005】
一方、硫化水素ガス分圧が0.01気圧を越える環境での耐応力腐食割れ性を改善したマルテンサイト系ステンレス鋼も提案されており、例えば、特開昭60−174859号公報には、C:0.02wt%以下、Si:0.50wt%以下、Mn:0.50〜1.50wt%、S:0.005wt%以下、Cr:12〜15wt%、Ni:3.5〜6wt%、Mo:0.5〜3wt%を含有し、残部がFe及び不可避不純物からなるマルテンサイト系ステンレス鋼が開示され、又、特開昭62−54063号公報には、C:0.001〜0.05wt%、Si:1.0wt%以下、Mn:0.3〜2.0wt%、Cr:11.0〜15.0wt%、Ni:3.0〜6.0wt%、Ca:0.0005〜0.005wt%、Al:0.01〜0.1wt%、O:0.0040wt%以下、を含み、P:0.01wt%以下、S:0.005wt%以下であって、更に、N:0.01〜0.20wt%とMo:0.05〜3.0wt%のうち1種以上を含有して、残部はFe及び不可避不純物からなるマルテンサイト系ステンレス鋼が開示されている。しかし、これらの鋼も硫化水素ガスによる応力腐食割れを完全に防止できるものではない。
【0006】
更に、強度について検討すると、上述したマルテンサイト系ステンレス鋼は、何れも高強度化を試みると靭性及び耐応力腐食割れ性が著しく劣化し、そのため、強度又は靭性と耐応力腐食割れ性とのどちらか一方を犠牲にせざるを得ないという問題もあった。そのため、例えば高強度、耐応力腐食割れ性、耐食性、高靭性が同時に要求される高深度の油井管には適用できないという難点があった。
【0007】
【発明が解決しようとする課題】
本発明は、上述した従来技術における問題点を解決するためになされたもので、その目的は、マルテンサイト系ステンレス鋼の耐食性を維持しつつ、強度、耐応力腐食割れ性、及び靭性を同時に改善することにより、硫化水素ガスを多く含む環境でも応力腐食割れを生じることなく使用できる高靭性のマルテンサイト系ステンレス鋼の製造方法を提供することである。ここで、目的とする性能は炭酸ガス、硫化水素ガスを含む石油、天然ガスの掘削、輸送用鋼材に要求される性能に鑑み、以下の如くとした。
【0008】
(1)強度:0.2%耐力が655MPa以上、(2)靭性:−20℃でのシャルピー・フルサイズ試験片での吸収エネルギー値(以下、「シャルピー衝撃値」と呼ぶ)が180J以上、(3)耐食性:30気圧のCO2 環境下の180℃の5%NaCl溶液中で腐食速度が0.5mm/y以下、(4)耐応力腐食割れ性:0.1気圧の硫化水素ガスを飽和させた5%NaCl溶液中で試験片に0.2%耐力の80%の応力を負荷して、720時間以上破断しないこと。
【0009】
【課題を解決するための手段】
本発明者等は、上記課題を解決すべく鋭意研究を重ねた結果、以下の知見を得るに至った。
【0010】
マルテンサイト系ステンレス鋼の耐食性向上にはCrの増加が有功である。しかしCrの増加は、一方でδ−フェライト相を生成させて、強度及び靭性を劣化させる。そこで、オーステナイト生成元素であるNiを増加して、δ−フェライト相の生成を抑制する方法があるが、Niの増加はAc1の変態点温度を下げて焼戻し温度に制約を及ぼすため、その上限に制約がある。Cの増加もδ−フェライト相の生成抑制に有効であるが、焼戻し時に炭化物が析出して、却って耐食性及び耐応力腐食割れ性を劣化させるため、その含有量はむしろ制限されるべきである。
【0011】
一方、一般に鋼を高強度化させると、靭性及び耐応力腐食割れ性が劣化するが、Vを適量含有させ、且つ熱処理によりVの炭化物をこのステンレス鋼の基地に微細な析出物として分散させることにより、靭性及び耐応力腐食割れ性を劣化させることなく高強度化することができる。又、マルテンサイト相中にオーステナイト相を残留させることにより、靭性と耐食性を向上させることができる。そして、微細なV炭化物を均一に分散析出させると同時に、マルテンサイト相中にオーステナイト相を残留させるためには、焼戻し条件を制御することが特に重要である。
【0012】
本発明は、これらの知見に基づきなされたもので、第1の発明による耐応力腐食割れ性に優れた高靭性マルテンサイト系ステンレス鋼の製造方法は、C:0.005〜0.05wt%、Si:1wt%以下、Mn:0.05〜0.3wt%、Cr:12〜16wt%、Ni:3.5〜6wt%、Mo:1.5〜2.5wt%、V:0.01〜0.05wt%、N:0.02wt%以下を含有して、残部がFe及び不可避的不純物からなり、熱間加工されたマルテンサイト系ステンレス鋼を、Ac3〜980℃の範囲に加熱してオーステナイト化した後冷却し、次いで、下記の(1)式を満足する温度(T)で焼戻しを行い、焼戻し後のマルテンサイト相中にオーステナイト相を残留させることを特徴とするものである。
【0013】
第2の発明による耐応力腐食割れ性に優れた高靭性マルテンサイト系ステンレス鋼の製造方法は、C:0.005〜0.05wt%、Si:1wt%以下、Mn:0.05〜0.3wt%、Cr:12〜16wt%、Ni:3.5〜6wt%、Mo:1.5〜2.5wt%、V:0.01〜0.05wt%、N:0.02wt%以下を含有し、更に、Nb:0.01〜0.1wt%、Ti:0.01〜0.1wt%の1種以上を含有して、残部がFe及び不可避的不純物からなり、熱間加工されたマルテンサイト系ステンレス鋼を、Ac3〜980℃の範囲に加熱してオーステナイト化した後冷却し、次いで、下記の(1)式を満足する温度(T)で焼戻しを行い、焼戻し後のマルテンサイト相中にオーステナイト相を残留させることを特徴とするものである。
【0014】
第3の発明による耐応力腐食割れ性に優れた高靭性マルテンサイト系ステンレス鋼の製造方法は、第1の発明又は第2の発明に記載の化学成分組成を有し、熱間加工されたマルテンサイト系ステンレス鋼を、Ac3〜980℃の範囲に加熱してオーステナイト化した後冷却し、次いで、下記の(2)式を満足する温度(T1)で1回目の焼戻しを行い、更に、温度(T1)以下で且つ下記の(3)式を満足する温度(T2)で2回目の焼戻しを行い、焼戻し後のマルテンサイト相中にオーステナイト相を残留させることを特徴とするものである。
Ac1≦T≦Ac1+(1/10)×(Ac3−Ac1) …(1)
Ac1≦T1≦Ac1+(7/10)×(Ac3−Ac1) …(2)
Ac1 <T2≦Ac1+(1/10)×(Ac3−Ac1) …(3)
尚、(1)〜(3)式において、Ac1及びAc3はマルテンサイト系ステンレス鋼の化学成分組成により定まる変態点温度である。
【0015】
以下に、本発明においてマルテンサイト系ステンレス鋼の化学成分組成及び熱処理条件を上述したように限定した理由を、それぞれの作用と共に説明する。
【0016】
(1)化学成分組成
(a)C:Cは強力なオーステナイト生成元素であり、又、高強度を得るためにも欠かせない元素である。しかし、焼戻し時にCrと結合して炭化物となって析出し、耐食性、耐応力腐食割れ性、及び靭性を劣化させる。Cの含有量が0.05wt%を越えると、この炭化物による劣化が顕著になる。一方、含有量が0.005wt%未満では十分な強度が得られない。従って、C含有量は0.005〜0.05wt%の範囲内に限定しなければならない。
【0017】
(b)Si:Siは脱酸剤として必要な元素であるが、強力なフェライト生成元素でもあり、1wt%を越えて含有させるとδ−フェライト相の生成を助長させる。従って、Si含有量は1wt%以下に限定しなければならない。
【0018】
(c)Mn:Mnは脱酸、脱硫剤として有効であると共に、δ−フェライト相の出現を抑えるオーステナイト生成元素である。しかし、Mnは耐応力腐食割れ性に対して有害であり、0.3wt%以下にする必要がある。一方、0.05wt%未満では脱酸が不十分となり、鋼中の介在物が増加する。従って、Mn含有量は0.05〜0.3wt%の範囲内に限定しなければならない。
【0019】
(d)Cr:Crはマルテンサイト系ステンレス鋼を構成する基本的な元素で、しかも耐食性を発現する重要な元素であるが、含有量が12wt%未満では十分な耐食性が得られず、一方、16wt%を越えると他の合金成分をどのように調整してもδ−フェライト相の生成量が増加して、強度及び靭性が劣化する。従って、Cr含有量は12〜16wt%の範囲内に限定しなければならない。
【0020】
(e)Ni:Niは耐食性を向上させると共に、オーステナイトの生成に極めて有効な元素であるが、3.5wt%未満ではその効果が少なく、一方、含有量が増加するとAc1変態点を下げて、焼戻し温度に制約を及ぼすため、6wt%以下にする必要がある。従って、Ni含有量は3.5〜6wt%の範囲内に限定しなければならない。
【0021】
(f)Mo:Moは特に耐応力腐食割れ性及び耐食性に有効な元素であるが、1.5wt%未満ではその効果が少なく、一方、2.5wt%を越えると過剰なδ−フェライトを出現させる。従って、Mo含有量は1.5〜2.5wt%の範囲内に限定しなければならない。
【0022】
(g)V:Vは強力な炭化物生成元素であり、微細な炭化物を析出させて結晶粒を微細化し、耐応力腐食割れ性を向上させる。又、微細な炭化物の析出は強度向上にも寄与する。しかし、フェライト生成元素でもあり、δ−フェライト相を増加させる。含有量が0.01wt%未満では耐応力腐食割れ性の向上効果が現れず、一方、0.05wt%を越えると、その効果は飽和すると共にδ−フェライト相が増加する。従って、V含有量は0.01〜0.05wt%の範囲内に限定しなければならない。
【0023】
(h)N:Nは耐食性向上に有害な元素であるが、オーステナイト生成元素でもある。0.02wt%を越えて含有させると、焼戻し時に窒化物となって析出し、耐食性、耐応力腐食割れ性、及び靭性を劣化させる。従って、N含有量は0.02wt%以下に限定しなければならない。
【0024】
(i)付加成分としてのNb及びTi:Nb及びTiは強力な炭化物生成元素であり、微細な炭化物を析出させて結晶粒を微細化し、耐応力腐食割れ性を向上させる。しかし、共にフェライト生成元素でもあり、δ−フェライト相を増加させる。Nb及びTiの含有量が0.01wt%未満では耐応力腐食割れ性の向上効果が現れず、一方、0.10wt%を越えると、その効果は飽和すると共にδ−フェライト相が増加する。従って、Nb含有量及びTi含有量は、共に0.01〜0.10wt%の範囲内に限定することが好ましい。
【0025】
(2)熱処理条件
(a)オーステナイト化温度:加熱温度がAc3温度より低いと、組織全体が均一にはオーステナイト化されないため、均質な焼入れマルテンサイト組織が得られない。この段階で均質なマルテンサイト組織が得られていないと、これ以降の熱処理によっても焼戻し効果が十分に得られないばかりか、最終製品の特性も安定しない。一方、加熱温度が980℃を越えると、結晶粒が粗大化して十分な強度が得られないばかりでなく、靭性が劣化する。従って、オーステナイト化温度はAc3〜980℃の範囲内に限定しなければならない。
【0026】
(b)焼戻し温度(T):焼戻し処理は、Vの微細な炭化物を均一に分散析出させて高強度化させると共に、オーステナイト相を残留させて、靭性及び耐応力腐食割れ性を向上させるために必要である。しかし、焼戻し温度(T)が(1)式の右辺を越えると、変態したオーステナイト相全てが冷却時に全て新たに生成するフレッシュ−マルテンサイト相となり、目的とするオーステナイト相の残留が発生しない。(1)式を満足する温度域に加熱すると、オーステナイト相に変態する割合が少ないため、鋼中の化学成分の拡散によりオーステナイト相の安定化が起こり、冷却時にマルテンサイト相への変態が起こらず、オーステナイト相が残留する。一方、焼戻し温度(T)がAc1温度より低くなると、焼入れマルテンサイト相が焼戻しマルテンサイト相となるだけで、やはりオーステナイト相は残留せず、靭性及び耐応力腐食割れ性の向上が得られない。従って、焼戻し温度(T)は(1)式を満足する範囲内に限定しなければならない。
【0027】
(c)2段焼戻し時の焼戻し温度(T1)及び焼戻し温度(T2):焼戻し処理を2回行う2段焼戻しは、より多くのオーステナイト相を残留させるための有効な方法である。1回目の焼戻し温度(T1)の下限は、1段焼戻しの際の焼戻し温度(T)の下限と同一理由で同一温度であるが、フレッシュ−マルテンサイト相が形成されても2回目の焼戻しがあるため、その上限は焼戻し温度(T)の上限より高い範囲としても良く、従って、上限を(2)式の右辺とした。2回目の焼戻し温度(T2)の上限は、フレッシュ−マルテンサイト相が生成しない温度とする必要があり、1段焼戻しの際の焼戻し温度(T)の上限と同等であるが、1回目の焼戻し温度(T1)を越えると、残留オーステナイト相が減少してしまうため、1回目の焼戻し温度(T1)以下の温度で、且つ、フレッシュ−マルテンサイト相が生成しない温度とする必要がある。一方、1回目の焼戻し時に鋼中の化学成分の拡散が生じているため、2回目の焼戻しではAc1温度以下でも残留オーステナイト相を得ることができ、その下限はAc1温度より20℃低い温度であるが、下限値は、1回目と同様、Ac1温度とする。従って、1回目の焼戻し温度(T1)は(2)式を満足する範囲内に限定しなければならず、2回目の焼戻し温度(T2)は焼戻し温度(T1)以下で、且つ(3)式を満足する範囲内に限定しなければならない。
【0028】
【発明の実施の形態】
転炉、電気炉、及び、炉外精錬炉等により上記化学成分組成に溶製された溶鋼を普通造塊法又は連続鋳造法により鋼片にする。それを、熱間加工により鋼板又は継目無鋼管に製造した後、Ac3〜980℃の範囲に加熱してオーステナイト化した後冷却し、次いで焼戻し処理を行う。焼戻し処理は1回の焼戻し処理で熱処理を完了する1段焼戻しと、2回の焼戻し処理を行う2段焼戻しとがあり、目標とする製品特性を考慮して、どちらかを選択する。一般的には、高靭性を確保する場合には2段焼戻しを選択し、高強度を確保する場合には1段焼戻しを選択すれば良い。
【0029】
1段焼戻しの場合には、(1)式を満足する焼戻し温度(T)で焼戻し、2段焼戻しの場合には、1回目の焼戻し温度を(2)式を満足する焼戻し温度(T1)で行い、2回目の焼戻し温度(T2)は1回目の焼戻し温度(T1)以下で、且つ(3)式を満足する範囲とする。尚、焼戻し温度を決めるAc1温度及びAc3温度は、溶製されたマルテンサイト系ステンレス鋼の化学成分組成から予め定めておくこととする。
【0030】
上記溶製の際に、不可避不純物として硫黄(S)及び燐(P)が残留する。これらは何れも鋼の熱間加工性及び耐応力腐食割れ性を劣化させる元素であり、少ない程好ましい。しかし、本発明者らの経験では、Sは0.01wt%以下、Pは0.04wt%以下であれば、本発明の目的とする耐応力腐食割れ性を確保できると共に、熱間圧延鋼板及び継目無鋼管の製造に支障を来すことがないので、この程度まで低減すれば十分である。
【0031】
このように、Crの増加による金属組織の制約を考慮しつつ、低C高Cr系のマルテンサイト系ステンレス鋼にVを一定量含有させ、且つ熱処理条件を一定範囲内に調整して、Vの炭化物を粒内に均一に分散析出させると同時に、オーステナイト相を残留させてマルテンサイト系ステンレス鋼を製造することで、従来のマルテンサイト系ステンレス鋼では実現し得なかった高靭性、高強度で、且つ、耐応力腐食割れ性に優れたマルテンサイト系ステンレス鋼を製造することが可能となる。
【0032】
【実施例】
12種類の化学成分組成のマルテンサイト系ステンレス鋼を真空溶解炉により溶製し、鋼片とした後、この鋼片を熱間圧延にて厚み12mmの鋼板とした。表1に、これら12種類の供試鋼の化学成分組成を示す。表1に示すように、鋼No.1〜6の化学成分組成は本発明の範囲内であるのに対し、鋼No.7はMnとMoが、鋼No.8はMnとVが、鋼No.9はCとNが、鋼No.10はNiが、鋼No.11はCrとMoとVが、又、鋼No.12はNiが、それぞれ本発明の範囲を外れている。
【0033】
【表1】
【0034】
その後、これらの鋼板を加熱してオーステナイト化した後空冷し、次いで、1回当たり30分間の焼戻し処理を行った後、残留オーステナイト量の測定、機械的性質、耐食性、及び耐応力腐食割れ性を調査した。その際、鋼の化学成分組成と熱処理条件との組み合せを変更して、合計19水準の試験を行った。表2に19水準の各試験における供試鋼のAc1温度、Ac3温度、熱処理温度、及び調査結果を示す。機械的性質、耐食性、及び耐応力腐食割れ性の調査は、前述した条件下で実施した。尚、表2において、熱処理温度の欄に2つの温度を記入した試験は1段焼戻しを行った試験で、最初の温度がオーステナイト化温度を表わし、後段の温度が焼戻し温度(T)を表わしており、又、熱処理温度の欄に3つの温度を記入した試験は2段焼戻しを行った試験で、最初の温度がオーステナイト化温度を表わし、中段の温度が焼戻し温度(T1)を表わし、後段の温度が焼戻し温度(T2)を表わしている。
【0035】
【表2】
【0036】
オーステナイト化温度は全ての試験において本発明の範囲内とし、又、焼戻し温度は試験No.15〜19を除き本発明の範囲内とした。試験No.15〜18は焼戻し温度が本発明の範囲外であり、試験No.19は2回目の焼戻し温度が本発明の範囲外である。
【0037】
表2に示すように、本発明の範囲内の化学成分組成の鋼を、本発明の範囲内の熱処理条件で処理することにより、0.2%耐力の目標値及びシャルピー衝撃値の目標値を上回り、又、腐食速度も目標値を達成すると共に応力腐食割れ(SSC)も発生せず、耐食性及び耐応力腐食割れ性も目標値を達成した。一方、化学成分組成が本発明の範囲内であっても、本発明の範囲外の熱処理条件で処理した場合、及び、化学成分組成が本発明の範囲外の場合には、耐食性や耐応力腐食割れ性が目標値を達成していなかった。尚、表2の備考欄に、本発明の範囲内の化学成分組成の鋼を本発明の範囲内の熱処理条件で処理した試験を実施例とし、それ以外の試験を比較例として表示した。
【0038】
【発明の効果】
本発明では、化学成分組成及び熱処理条件を特定してマルテンサイト系ステンレス鋼を製造するので、高靭性及び高強度を維持しつつ、炭酸ガス腐食に対する耐食性はもとより、硫化水素ガスを多量に含む環境での耐応力腐食割れ性に極めた優れたマルテンサイト系ステンレス鋼を製造することが可能となる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a high toughness martensitic stainless steel excellent in stress corrosion cracking resistance, and more specifically, in an environment containing wet carbon dioxide gas or wet hydrogen sulfide gas, such as oil and natural gas drilling and transportation. The present invention relates to a method for producing a high toughness martensitic stainless steel having high stress corrosion cracking resistance.
[0002]
[Prior art]
Oil and natural gas produced in recent years have increased in cases where they contain a large amount of wet carbon dioxide or wet hydrogen sulfide gas, and in their excavation and transportation, martensitic systems such as 13Cr stainless steel are used instead of conventional carbon steel. Stainless steel has been used. However, conventional martensitic stainless steel has excellent corrosion resistance against wet carbon dioxide gas (hereinafter simply referred to as “corrosion resistance”), but stress corrosion cracking resistance against wet hydrogen sulfide gas (hereinafter simply referred to as “stress corrosion resistance”). Martensitic stainless steel having excellent stress corrosion cracking resistance while maintaining strength, toughness, and corrosion resistance has been desired.
[0003]
In addition to strength, toughness, and corrosion resistance, martensitic stainless steel that satisfies the requirements for stress corrosion cracking is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-199850, C: 0.16-0.25 wt%, Si: Less than 1.0 wt%, Mn: less than 1.0 wt%, Cr: 12.5-13.5 wt%, Ni: 0.3-3 wt%, Mo: 0.5-3.5 wt%, Cu: 0.5 A martensitic stainless steel containing ˜2 wt%, the balance being Fe and inevitable impurities is disclosed, and Japanese Patent Laid-Open No. 61-207550 discloses C: 0.03 to 0.20 wt%, Si: 1 Less than 0.0 wt%, Mn: less than 1.0 wt%, Cr: 12.0 to 14.0 wt%, B: 0.0010 to 0.0060 wt%, and Mo: 0.5 to 4.0 wt% , Ni: 0.5 to 6.0 wt% It contains two, martensitic stainless steel balance being Fe and inevitable impurities.
[0004]
However, they exhibit stress corrosion cracking resistance in an environment containing a very small amount of hydrogen sulfide gas, but stress corrosion cracking occurs in an environment where the hydrogen sulfide gas partial pressure exceeds 0.01 atm. There was a problem that it could not be used in the environment that included.
[0005]
On the other hand, martensitic stainless steel having improved stress corrosion cracking resistance in an environment where the hydrogen sulfide gas partial pressure exceeds 0.01 atm has been proposed. For example, Japanese Patent Laid-Open No. 60-174859 discloses C : 0.02 wt% or less, Si: 0.50 wt% or less, Mn: 0.50 to 1.50 wt%, S: 0.005 wt% or less, Cr: 12 to 15 wt%, Ni: 3.5 to 6 wt%, A martensitic stainless steel containing Mo: 0.5 to 3 wt%, the balance being Fe and inevitable impurities is disclosed, and Japanese Patent Application Laid-Open No. 62-54063 discloses C: 0.001 to. 05 wt%, Si: 1.0 wt% or less, Mn: 0.3-2.0 wt%, Cr: 11.0-15.0 wt%, Ni: 3.0-6.0 wt%, Ca: 0.0005 0.005 wt%, Al: 0.01- 0.1 wt%, O: 0.0040 wt% or less, P: 0.01 wt% or less, S: 0.005 wt% or less, and further, N: 0.01-0.20 wt% and Mo: 0 A martensitic stainless steel is disclosed that contains one or more of 0.05 to 3.0 wt%, with the balance being Fe and inevitable impurities. However, these steels cannot completely prevent stress corrosion cracking caused by hydrogen sulfide gas.
[0006]
Further, when examining the strength, the above-described martensitic stainless steels are significantly deteriorated in toughness and stress corrosion cracking resistance when attempting to increase the strength. There was also a problem that one had to be sacrificed. Therefore, for example, there is a problem that it cannot be applied to a deep oil well pipe that requires high strength, stress corrosion cracking resistance, corrosion resistance, and high toughness at the same time.
[0007]
[Problems to be solved by the invention]
The present invention was made to solve the above-described problems in the prior art, and its purpose is to simultaneously improve the strength, stress corrosion cracking resistance, and toughness while maintaining the corrosion resistance of martensitic stainless steel. Thus, it is to provide a method for producing a high toughness martensitic stainless steel that can be used without causing stress corrosion cracking even in an environment containing a large amount of hydrogen sulfide gas. Here, the target performance was as follows in view of the performance required for steel for transportation of petroleum and natural gas, including carbon dioxide gas and hydrogen sulfide gas.
[0008]
(1) Strength: 0.2% proof stress is 655 MPa or more, (2) Toughness: Absorption energy value (hereinafter referred to as “Charpy impact value”) at −20 ° C. at 180 ° C. or more is 180 J or more. (3) Corrosion resistance: corrosion rate is 0.5 mm / y or less in 5% NaCl solution at 180 ° C. in a CO 2 environment of 30 atm. (4) Stress corrosion cracking resistance: hydrogen sulfide gas at 0.1 atm. The test piece must be loaded with 80% stress of 0.2% proof stress in a saturated 5% NaCl solution and should not break for more than 720 hours.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge.
[0010]
Increasing Cr is effective for improving the corrosion resistance of martensitic stainless steel. However, an increase in Cr, on the other hand, produces a δ-ferrite phase and degrades strength and toughness. Therefore, there is a method for increasing the austenite-forming element Ni to suppress the formation of the δ-ferrite phase, but the increase in Ni lowers the transformation temperature of Ac1 and restricts the tempering temperature. There are limitations. An increase in C is also effective in suppressing the formation of the δ-ferrite phase, but carbides are precipitated during tempering, and on the contrary, the corrosion resistance and stress corrosion cracking resistance are deteriorated, so the content should rather be limited.
[0011]
On the other hand, generally, when steel is strengthened, toughness and stress corrosion cracking resistance deteriorate, but an appropriate amount of V is contained, and V carbide is dispersed as fine precipitates on the base of this stainless steel by heat treatment. Therefore, the strength can be increased without deteriorating the toughness and the stress corrosion cracking resistance. Moreover, toughness and corrosion resistance can be improved by allowing the austenite phase to remain in the martensite phase. It is particularly important to control the tempering conditions in order to disperse and precipitate the fine V carbide uniformly and at the same time to leave the austenite phase in the martensite phase.
[0012]
The present invention has been made based on these findings, and the method for producing a high toughness martensitic stainless steel excellent in stress corrosion cracking resistance according to the first invention has a C: 0.005 to 0.05 wt%, Si: 1 wt% or less, Mn: 0.05 to 0.3 wt%, Cr: 12 to 16 wt%, Ni: 3.5 to 6 wt%, Mo: 1.5 to 2.5 wt%, V: 0.01 to Austenite containing 0.05 wt%, N: 0.02 wt% or less, with the balance consisting of Fe and inevitable impurities and hot-worked martensitic stainless steel heated to a range of Ac3 to 980 ° C Then, it is cooled and then tempered at a temperature (T) that satisfies the following formula (1) to leave the austenite phase in the martensite phase after tempering.
[0013]
The manufacturing method of the high toughness martensitic stainless steel excellent in stress corrosion cracking resistance according to the second invention is as follows: C: 0.005-0.05 wt%, Si: 1 wt% or less, Mn: 0.05-0. 3 wt%, Cr: 12-16 wt%, Ni: 3.5-6 wt%, Mo: 1.5-2.5 wt%, V: 0.01-0.05 wt%, N: 0.02 wt% or less In addition, it contains at least one of Nb: 0.01 to 0.1 wt%, Ti: 0.01 to 0.1 wt%, the balance being Fe and inevitable impurities, and hot-worked martens The site-based stainless steel is heated to a range of Ac3 to 980 ° C. to austenite and then cooled, and then tempered at a temperature (T) satisfying the following formula (1), and in the martensite phase after tempering Austenite phase remains in It is intended to.
[0014]
A method for producing a high toughness martensitic stainless steel excellent in stress corrosion cracking resistance according to the third invention has the chemical composition described in the first invention or the second invention and is hot-worked martensite. The site-based stainless steel is heated to a range of Ac3 to 980 ° C. to austenite and then cooled, and then tempered at the temperature (T1) satisfying the following expression (2), and further the temperature ( The tempering is performed for the second time at a temperature (T2) that is equal to or less than T1) and satisfies the following expression (3), and the austenite phase remains in the martensite phase after tempering.
Ac1 ≦ T ≦ Ac1 + (1/10) × (Ac3-Ac1) (1)
Ac1 ≦ T1 ≦ Ac1 + (7/10) × (Ac3-Ac1) (2)
Ac1 < T2 ≦ Ac1 + (1/10) × (Ac3-Ac1) (3)
In the equations (1) to (3), Ac1 and Ac3 are transformation point temperatures determined by the chemical composition of the martensitic stainless steel.
[0015]
The reason why the chemical component composition and the heat treatment conditions of the martensitic stainless steel are limited as described above in the present invention will be described together with the respective actions.
[0016]
(1) Chemical component composition (a) C: C is a strong austenite-forming element and is also an indispensable element for obtaining high strength. However, it combines with Cr during tempering and precipitates as carbide, which degrades corrosion resistance, stress corrosion cracking resistance, and toughness. When the C content exceeds 0.05 wt%, the deterioration due to this carbide becomes remarkable. On the other hand, if the content is less than 0.005 wt%, sufficient strength cannot be obtained. Therefore, the C content must be limited to a range of 0.005 to 0.05 wt%.
[0017]
(B) Si: Si is an element necessary as a deoxidizing agent, but is also a strong ferrite-forming element. When it is contained in an amount exceeding 1 wt%, the formation of a δ-ferrite phase is promoted. Therefore, the Si content must be limited to 1 wt% or less.
[0018]
(C) Mn: Mn is an austenite generating element that is effective as a deoxidizing and desulfurizing agent and suppresses the appearance of a δ-ferrite phase. However, Mn is harmful to the stress corrosion cracking resistance and needs to be 0.3 wt% or less. On the other hand, if it is less than 0.05 wt%, deoxidation becomes insufficient, and inclusions in the steel increase. Therefore, the Mn content must be limited to the range of 0.05 to 0.3 wt%.
[0019]
(D) Cr: Cr is a basic element constituting martensitic stainless steel, and is an important element that expresses corrosion resistance. However, if the content is less than 12 wt%, sufficient corrosion resistance cannot be obtained, If it exceeds 16 wt%, the amount of δ-ferrite phase generated increases and strength and toughness deteriorate regardless of how other alloy components are adjusted. Therefore, the Cr content must be limited to a range of 12 to 16 wt%.
[0020]
(E) Ni: Ni is an element that improves corrosion resistance and is extremely effective in the formation of austenite. However, if it is less than 3.5 wt%, its effect is small. On the other hand, when the content increases, the Ac1 transformation point is lowered. In order to limit the tempering temperature, it is necessary to make it 6 wt% or less. Therefore, the Ni content must be limited to the range of 3.5 to 6 wt%.
[0021]
(F) Mo: Mo is an element particularly effective for stress corrosion cracking resistance and corrosion resistance. However, if it is less than 1.5 wt%, its effect is small, while if it exceeds 2.5 wt%, excessive δ-ferrite appears. Let Therefore, the Mo content must be limited to a range of 1.5 to 2.5 wt%.
[0022]
(G) V: V is a strong carbide-forming element, which precipitates fine carbides to refine crystal grains and improves stress corrosion cracking resistance. Moreover, the precipitation of fine carbides also contributes to the strength improvement. However, it is also a ferrite-forming element and increases the δ-ferrite phase. If the content is less than 0.01 wt%, the effect of improving the stress corrosion cracking resistance does not appear. On the other hand, if the content exceeds 0.05 wt%, the effect is saturated and the δ-ferrite phase increases. Therefore, the V content must be limited to a range of 0.01 to 0.05 wt%.
[0023]
(H) N: N is an element harmful to the improvement of corrosion resistance, but is also an austenite generating element. When the content exceeds 0.02 wt%, it precipitates as nitrides during tempering, and deteriorates corrosion resistance, stress corrosion cracking resistance, and toughness. Therefore, the N content must be limited to 0.02 wt% or less.
[0024]
(I) Nb and Ti as additional components: Nb and Ti are strong carbide generating elements, and precipitate fine carbides to refine crystal grains and improve stress corrosion cracking resistance. However, both are ferrite-forming elements and increase the δ-ferrite phase. When the content of Nb and Ti is less than 0.01 wt%, the effect of improving the stress corrosion cracking resistance does not appear. On the other hand, when the content exceeds 0.10 wt%, the effect is saturated and the δ-ferrite phase increases. Therefore, it is preferable to limit both the Nb content and the Ti content within the range of 0.01 to 0.10 wt%.
[0025]
(2) Heat treatment conditions (a) Austenitizing temperature: When the heating temperature is lower than the Ac3 temperature, the entire structure is not uniformly austenitized, so that a homogeneous quenched martensite structure cannot be obtained. If a homogeneous martensite structure is not obtained at this stage, not only a sufficient tempering effect can be obtained by the subsequent heat treatment, but also the properties of the final product are not stable. On the other hand, when the heating temperature exceeds 980 ° C., the crystal grains become coarse and sufficient strength cannot be obtained, and the toughness deteriorates. Therefore, the austenitizing temperature must be limited to the range of Ac3 to 980 ° C.
[0026]
(B) Tempering temperature (T): The tempering treatment is performed in order to improve the toughness and stress corrosion cracking resistance by uniformly dispersing and precipitating fine carbides of V to increase the strength and leaving the austenite phase. is necessary. However, when the tempering temperature (T) exceeds the right side of the formula (1), all the transformed austenite phases become fresh-martensite phases that are newly formed during cooling, and the target austenite phase does not remain. When heated to a temperature range that satisfies the formula (1), since the rate of transformation to the austenite phase is small, the austenite phase is stabilized by diffusion of chemical components in the steel, and transformation to the martensite phase does not occur during cooling. The austenite phase remains. On the other hand, when the tempering temperature (T) is lower than the Ac1 temperature, the quenched martensite phase only becomes the tempered martensite phase, and the austenite phase does not remain, and the toughness and the stress corrosion cracking resistance cannot be improved. Therefore, the tempering temperature (T) must be limited to a range satisfying the expression (1).
[0027]
(C) Tempering temperature (T1) and tempering temperature (T2) at the time of two-stage tempering: Two-stage tempering in which the tempering treatment is performed twice is an effective method for leaving more austenite phase. The lower limit of the first tempering temperature (T1) is the same for the same reason as the lower limit of the tempering temperature (T) in the first stage tempering, but the second tempering is performed even if a fresh-martensite phase is formed. Therefore, the upper limit may be higher than the upper limit of the tempering temperature (T), and therefore the upper limit is set to the right side of the equation (2). The upper limit of the second tempering temperature (T2) needs to be a temperature at which the fresh-martensite phase is not generated, and is equivalent to the upper limit of the tempering temperature (T) at the first stage tempering. When the temperature (T1) is exceeded, the retained austenite phase decreases, so it is necessary to set the temperature to be equal to or lower than the first tempering temperature (T1) and not to produce a fresh martensite phase. On the other hand, since chemical components in the steel are diffused during the first tempering , the second austenite can obtain a retained austenite phase even at a temperature below the Ac1 temperature, and the lower limit is 20 ° C. lower than the Ac1 temperature. However, the lower limit is set to the Ac1 temperature as in the first time. Accordingly, the first tempering temperature (T1) must be limited to a range satisfying the equation (2), and the second tempering temperature (T2) is equal to or lower than the tempering temperature (T1) and the equation (3). Must be limited to a range that satisfies the above.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Molten steel melted to the above chemical composition by a converter, electric furnace, out-of-furnace refining furnace, or the like is made into a steel slab by ordinary ingot casting or continuous casting. After manufacturing it into a steel plate or a seamless steel pipe by hot working, it is cooled to an austenite by heating to a range of Ac 3 to 980 ° C., and then tempering. The tempering process includes one-stage tempering in which the heat treatment is completed by one tempering process and two-stage tempering in which the tempering process is performed twice, and either one is selected in consideration of target product characteristics. In general, two-stage tempering is selected to ensure high toughness, and one-stage tempering is selected to ensure high strength.
[0029]
In the case of the first stage tempering, the tempering temperature (T) satisfying the formula (1) is tempered. In the case of the second stage tempering, the first tempering temperature is set to the tempering temperature (T1) satisfying the formula (2). The second tempering temperature (T2) is set to be equal to or lower than the first tempering temperature (T1) and satisfies the expression (3). The Ac1 temperature and Ac3 temperature that determine the tempering temperature are determined in advance from the chemical component composition of the melted martensitic stainless steel.
[0030]
During the melting, sulfur (S) and phosphorus (P) remain as inevitable impurities. These are all elements that degrade the hot workability and stress corrosion cracking resistance of steel, and the smaller the better. However, in the experience of the present inventors, if S is 0.01 wt% or less and P is 0.04 wt% or less, the stress corrosion cracking resistance intended by the present invention can be secured, and a hot-rolled steel plate and Since there is no hindrance to the production of seamless steel pipes, it is sufficient to reduce to this extent.
[0031]
In this way, while taking into consideration the restriction of the metal structure due to the increase in Cr, a certain amount of V is contained in the low C high Cr martensitic stainless steel, and the heat treatment conditions are adjusted within a certain range. Carbide is uniformly dispersed and precipitated in the grains, and at the same time, the austenite phase is left to produce martensitic stainless steel, thereby providing high toughness and high strength that could not be achieved with conventional martensitic stainless steel. And it becomes possible to manufacture the martensitic stainless steel excellent in stress corrosion cracking resistance.
[0032]
【Example】
After martensitic stainless steel having 12 kinds of chemical composition was melted in a vacuum melting furnace to form a steel slab, the steel slab was hot rolled to form a steel sheet having a thickness of 12 mm. Table 1 shows the chemical composition of these 12 types of test steels. As shown in Table 1, steel no. While the chemical composition of 1-6 is within the scope of the present invention, steel no. 7 shows that Mn and Mo are steel No. 7. 8 shows that Mn and V are steel No. 9 and C and N are steel No. 10 is Ni, steel No. 10; 11 is Cr, Mo and V, and steel No. No. 12 is outside the scope of the present invention.
[0033]
[Table 1]
[0034]
Thereafter, these steel sheets were heated to austenite and then air-cooled, and then subjected to a tempering treatment for 30 minutes per time, followed by measurement of the amount of retained austenite, mechanical properties, corrosion resistance, and stress corrosion cracking resistance. investigated. At that time, the combination of the chemical composition of the steel and the heat treatment conditions was changed, and a total of 19 tests were conducted. Table 2 shows the Ac1 temperature, Ac3 temperature, heat treatment temperature, and investigation results of the test steel in each of 19 levels of tests. The investigation of mechanical properties, corrosion resistance, and stress corrosion cracking resistance was performed under the conditions described above. In Table 2, the test in which two temperatures are entered in the heat treatment temperature column is a test in which the first stage tempering was performed, the first temperature representing the austenitizing temperature, and the latter stage temperature representing the tempering temperature (T). In addition, the test in which three temperatures are entered in the heat treatment temperature column is a test in which two-stage tempering was performed. The first temperature represents the austenitizing temperature, the middle temperature represents the tempering temperature (T1), and the latter stage The temperature represents the tempering temperature (T2).
[0035]
[Table 2]
[0036]
The austenitizing temperature is within the range of the present invention in all tests, and the tempering temperature is the test number. Except for 15 to 19, it was within the scope of the present invention. Test No. Nos. 15 to 18 have a tempering temperature outside the range of the present invention. No. 19 has a second tempering temperature outside the range of the present invention.
[0037]
As shown in Table 2, by treating a steel having a chemical composition within the scope of the present invention under the heat treatment conditions within the scope of the present invention, the target value of 0.2% proof stress and the target value of Charpy impact value are obtained. In addition, the corrosion rate achieved the target value and the stress corrosion cracking (SSC) did not occur, and the corrosion resistance and stress corrosion cracking resistance achieved the target value. On the other hand, even if the chemical component composition is within the scope of the present invention, when it is processed under heat treatment conditions outside the scope of the present invention, and when the chemical component composition is outside the scope of the present invention, corrosion resistance and stress corrosion resistance Crackability did not achieve the target value. In addition, in the remarks column of Table 2, the test which processed the steel of the chemical component composition in the range of this invention on the heat processing conditions in the range of this invention was set as the Example, and the other test was displayed as a comparative example.
[0038]
【The invention's effect】
In the present invention, since the martensitic stainless steel is manufactured by specifying the chemical composition and heat treatment conditions, the environment containing a large amount of hydrogen sulfide gas as well as corrosion resistance against carbon dioxide corrosion while maintaining high toughness and high strength. This makes it possible to produce an excellent martensitic stainless steel with excellent resistance to stress corrosion cracking.
Claims (3)
Ac1≦T≦Ac1+(1/10)×(Ac3−Ac1) …(1)C: 0.005 to 0.05 wt%, Si: 1 wt% or less, Mn: 0.05 to 0.3 wt%, Cr: 12 to 16 wt%, Ni: 3.5 to 6 wt%, Mo: 1.5 to A martensitic stainless steel containing 2.5 wt%, V: 0.01 to 0.05 wt%, N: 0.02 wt% or less, the balance being Fe and inevitable impurities, and hot-worked, Heating to a range of Ac3 to 980 ° C to austenite and then cooling, then tempering at a temperature (T) satisfying the formula (1), leaving the austenite phase in the martensite phase after tempering A method for producing a high toughness martensitic stainless steel with excellent stress corrosion cracking resistance.
Ac1 ≦ T ≦ Ac1 + (1/10) × (Ac3-Ac1) (1)
Ac1≦T≦Ac1+(1/10)×(Ac3−Ac1) …(1)C: 0.005 to 0.05 wt%, Si: 1 wt% or less, Mn: 0.05 to 0.3 wt%, Cr: 12 to 16 wt%, Ni: 3.5 to 6 wt%, Mo: 1.5 to 2.5 wt%, V: 0.01 to 0.05 wt%, N: 0.02 wt% or less, Nb: 0.01 to 0.1 wt%, Ti: 0.01 to 0.1 wt% The martensitic stainless steel, which is composed of one or more of the following, the balance being Fe and inevitable impurities and hot-worked, is heated to a range of Ac3 to 980 ° C. to austenite, then cooled, A high toughness martensitic stainless steel excellent in stress corrosion cracking resistance, characterized by tempering at a temperature (T) satisfying the formula (1) and leaving the austenite phase in the martensite phase after tempering. Production method.
Ac1 ≦ T ≦ Ac1 + (1/10) × (Ac3-Ac1) (1)
Ac1≦T1≦Ac1+(7/10)×(Ac3−Ac1) …(2)
Ac1 <T2≦Ac1+(1/10)×(Ac3−Ac1) …(3)The martensitic stainless steel having the chemical component composition according to claim 1 or 2 and hot-worked is heated to a range of Ac3 to 980 ° C. to be austenitized and then cooled, and then (2 ) The first tempering is performed at a temperature (T1) satisfying the formula, and the second tempering is performed at a temperature (T2) which is equal to or lower than the temperature (T1) and satisfies the formula (3). A method for producing a high toughness martensitic stainless steel excellent in stress corrosion cracking resistance, characterized in that an austenite phase remains in the phase.
Ac1 ≦ T1 ≦ Ac1 + (7/10) × (Ac3-Ac1) (2)
Ac1 < T2 ≦ Ac1 + (1/10) × (Ac3-Ac1) (3)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP02776299A JP3684895B2 (en) | 1999-02-04 | 1999-02-04 | Manufacturing method of high toughness martensitic stainless steel with excellent stress corrosion cracking resistance |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP02776299A JP3684895B2 (en) | 1999-02-04 | 1999-02-04 | Manufacturing method of high toughness martensitic stainless steel with excellent stress corrosion cracking resistance |
Publications (2)
Publication Number | Publication Date |
---|---|
JP2000226614A JP2000226614A (en) | 2000-08-15 |
JP3684895B2 true JP3684895B2 (en) | 2005-08-17 |
Family
ID=12230030
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP02776299A Expired - Lifetime JP3684895B2 (en) | 1999-02-04 | 1999-02-04 | Manufacturing method of high toughness martensitic stainless steel with excellent stress corrosion cracking resistance |
Country Status (1)
Country | Link |
---|---|
JP (1) | JP3684895B2 (en) |
Families Citing this family (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP4570221B2 (en) * | 2000-09-20 | 2010-10-27 | 新日鐵住金ステンレス株式会社 | Martensitic stainless steel with excellent fire resistance |
JP4529269B2 (en) * | 2000-10-05 | 2010-08-25 | Jfeスチール株式会社 | High Cr martensitic stainless steel pipe for line pipe excellent in corrosion resistance and weldability and method for producing the same |
JP2003129190A (en) | 2001-10-19 | 2003-05-08 | Sumitomo Metal Ind Ltd | Martensitic stainless steel and manufacturing method therefor |
KR100613082B1 (en) | 2004-12-01 | 2006-08-16 | 두산중공업 주식회사 | Manufacturing method for products desired erosion resistance using 17-Cr stainless steel |
CN104254625A (en) * | 2012-04-26 | 2014-12-31 | 杰富意钢铁株式会社 | Cr-containing steel pipe for linepipe excellent in intergranular stress corrosion cracking resistance of welded heat affected zone |
JP6102798B2 (en) * | 2014-02-28 | 2017-03-29 | Jfeスチール株式会社 | Manufacturing method of martensitic stainless steel pipe for line pipe excellent in reel barge laying |
JP6390677B2 (en) * | 2015-08-18 | 2018-09-19 | Jfeスチール株式会社 | Low carbon martensitic stainless steel welded pipe and method for producing the same |
-
1999
- 1999-02-04 JP JP02776299A patent/JP3684895B2/en not_active Expired - Lifetime
Also Published As
Publication number | Publication date |
---|---|
JP2000226614A (en) | 2000-08-15 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
KR101657828B1 (en) | Steel plate for pressure vessel having excellent strength and toughness after post weld heat treatment and method for manufacturing the same | |
EP1873270B1 (en) | Low alloy steel | |
WO2011061812A1 (en) | High-toughness abrasion-resistant steel and manufacturing method therefor | |
JP4926447B2 (en) | Manufacturing method of high strength steel with excellent weld crack resistance | |
JP4369612B2 (en) | Steel plate for low quenching or normalizing type low alloy boiler steel pipe excellent in toughness, and method of manufacturing steel pipe using the same | |
JP3852248B2 (en) | Manufacturing method of martensitic stainless steel with excellent stress corrosion cracking resistance | |
KR20070116561A (en) | Steel sheets having superior haz toughness and reduced lowering of strength by post weld heat treatment | |
JP3684895B2 (en) | Manufacturing method of high toughness martensitic stainless steel with excellent stress corrosion cracking resistance | |
JP3539250B2 (en) | 655 Nmm-2 class low C high Cr alloy oil country tubular good with high stress corrosion cracking resistance and method of manufacturing the same | |
JP5206056B2 (en) | Manufacturing method of non-tempered steel | |
KR102142782B1 (en) | Chromium-molybdenum steel sheet having excellent creep strength and method of manufacturing the same | |
KR20040054198A (en) | Method for manufacturing high-tensile steel sheets having excellent low temperature toughness | |
JP2001279383A (en) | High temperature carburizing steel excellent in high temperature carburizability, and hot forged member for high temperature carburizing | |
JP2000160300A (en) | 655 Nmm-2 CLASS LOW-C HIGH-Cr ALLOY OIL WELL PIPE WITH HIGH CORROSION RESISTANCE, AND ITS MANUFACTURE | |
JP3774697B2 (en) | Steel material for high strength induction hardening and method for manufacturing the same | |
JP3485034B2 (en) | 862N / mm2 Class Low C High Cr Alloy Oil Well Pipe Having High Corrosion Resistance and Method of Manufacturing the Same | |
JP3536687B2 (en) | Low-C high-Cr alloy steel having high corrosion resistance and high strength, and method for producing the same | |
JP3228008B2 (en) | High-strength martensitic stainless steel excellent in stress corrosion cracking resistance and method for producing the same | |
JP3620099B2 (en) | Method for producing Cr-Mo steel excellent in strength and toughness | |
JP3267653B2 (en) | Manufacturing method of high strength steel sheet | |
JPH0225969B2 (en) | ||
KR100262440B1 (en) | Cr-mo alloy steel and the manufacturing method of low-temperature bolt-nut | |
KR102259806B1 (en) | Ferritic stainless steel with improved creep resistance at high temperature and method for manufacturing the ferritic stainless steel | |
KR100311791B1 (en) | METHOD FOR MANUFACTURING QUENCHED AND TEMPERED STEEL WITH SUPERIOR TENSILE STRENGTH OF AROUND 600MPa AND IMPROVED TOUGHNESS IN WELDED PART | |
JP4271311B2 (en) | Ferritic heat resistant steel |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
TRDD | Decision of grant or rejection written | ||
A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20050510 |
|
A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20050523 |
|
R150 | Certificate of patent or registration of utility model |
Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20080610 Year of fee payment: 3 |
|
FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20090610 Year of fee payment: 4 |
|
FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20100610 Year of fee payment: 5 |
|
FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20100610 Year of fee payment: 5 |
|
FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20110610 Year of fee payment: 6 |
|
FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120610 Year of fee payment: 7 |
|
FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120610 Year of fee payment: 7 |
|
FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130610 Year of fee payment: 8 |
|
FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20140610 Year of fee payment: 9 |
|
EXPY | Cancellation because of completion of term |