JPH0352527B2 - - Google Patents
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- Publication number
- JPH0352527B2 JPH0352527B2 JP58186418A JP18641883A JPH0352527B2 JP H0352527 B2 JPH0352527 B2 JP H0352527B2 JP 58186418 A JP58186418 A JP 58186418A JP 18641883 A JP18641883 A JP 18641883A JP H0352527 B2 JPH0352527 B2 JP H0352527B2
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- Japan
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- less
- scc
- solution treatment
- resistance
- treatment
- 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.)
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Links
- 230000007797 corrosion Effects 0.000 claims description 22
- 238000005260 corrosion Methods 0.000 claims description 22
- 229910000851 Alloy steel Inorganic materials 0.000 claims description 12
- 239000000203 mixture Substances 0.000 claims description 11
- 229910052759 nickel Inorganic materials 0.000 claims description 10
- 229910052804 chromium Inorganic materials 0.000 claims description 8
- 238000004519 manufacturing process Methods 0.000 claims description 7
- 238000005336 cracking Methods 0.000 claims description 5
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 229910052698 phosphorus Inorganic materials 0.000 claims description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 3
- 229910052710 silicon Inorganic materials 0.000 claims description 3
- 229910052719 titanium Inorganic materials 0.000 claims description 3
- 238000001816 cooling Methods 0.000 claims description 2
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 229910052802 copper Inorganic materials 0.000 claims 1
- 239000000243 solution Substances 0.000 description 31
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 22
- 238000010438 heat treatment Methods 0.000 description 18
- 230000000694 effects Effects 0.000 description 17
- 239000011651 chromium Substances 0.000 description 14
- 238000005275 alloying Methods 0.000 description 9
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 8
- 238000005097 cold rolling Methods 0.000 description 7
- 229910000831 Steel Inorganic materials 0.000 description 6
- 238000011105 stabilization Methods 0.000 description 6
- 239000010959 steel Substances 0.000 description 6
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 5
- 238000005098 hot rolling Methods 0.000 description 4
- 230000003993 interaction Effects 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 230000006641 stabilisation Effects 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 239000011572 manganese Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000011574 phosphorus Substances 0.000 description 3
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 2
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 2
- 230000002411 adverse Effects 0.000 description 2
- 238000000137 annealing Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 239000011733 molybdenum Substances 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- CADICXFYUNYKGD-UHFFFAOYSA-N sulfanylidenemanganese Chemical compound [Mn]=S CADICXFYUNYKGD-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 229910001030 Iron–nickel alloy Inorganic materials 0.000 description 1
- 229910000990 Ni alloy Inorganic materials 0.000 description 1
- 206010070834 Sensitisation Diseases 0.000 description 1
- CKUAXEQHGKSLHN-UHFFFAOYSA-N [C].[N] Chemical compound [C].[N] CKUAXEQHGKSLHN-UHFFFAOYSA-N 0.000 description 1
- YUWBVKYVJWNVLE-UHFFFAOYSA-N [N].[P] Chemical compound [N].[P] YUWBVKYVJWNVLE-UHFFFAOYSA-N 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 150000001805 chlorine compounds Chemical class 0.000 description 1
- BIJOYKCOMBZXAE-UHFFFAOYSA-N chromium iron nickel Chemical compound [Cr].[Fe].[Ni] BIJOYKCOMBZXAE-UHFFFAOYSA-N 0.000 description 1
- 230000001143 conditioned effect Effects 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 229910001629 magnesium chloride Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000002250 progressing effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 230000008313 sensitization Effects 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 230000008685 targeting Effects 0.000 description 1
Landscapes
- Heat Treatment Of Steel (AREA)
Description
本発明は耐応力腐食割れ性に優れた合金鋼の製
造方法に関し、合金元素を経済的な範囲に限定し
た成分組成と熱処理条件との組み合せにより、優
れた耐応力腐食割れ性を有する合金鋼を得さしめ
るようにしたものである。
塩化物応力腐食割れ（以下単に「SCC」と称
す）に及ぼす合金元素の影響に関する報告のう
ち、最も一般的なものは、Copsonによるニツケ
ルの耐SCC性への影響に関する報告（Physical
metallurgy of stresscorrosion fracture，P247、
Interscience，N.Y.（1959））である。これによれ
ば、18％程度のクロムを含有するクロム−ニツケ
ル−鉄系合金の耐SCC性は８％のニツケル程度で
最も劣り、ニツケルの添加量の減少、或いは高ニ
ツケル化により耐SCC性は向上するとし、またオ
ーステナイト系ステンレス鋼を対象とした場合に
は、ニツケル含有量を45％以上とすることによ
り、極めて高い耐SCC性が得られるとしている。
ニツケル以外の合金元素で耐SCC性に有効と一般
に認められているのは炭素と珪素であり、また、
悪影響を及ぼす元素としては、リン、窒素、モリ
ブデン、クロムなどが知られている。だが、ここ
に述べた各成分元素の耐SCC性に対する影響につ
いては、主として着目成分濃度のみを変動因子と
して採つたものであり、これに対して成分元素相
互の作用については検討例が少なく、含有量の小
さい炭素−窒素、リン−窒素の組合せについてわ
ずかに報告（「遅沢、深瀬、横田：日本金属学会
誌，36（1972）170.」「小若、富士川：日本金属学
会誌，34（1970）1047.」）があるに過ぎない。そ
こでは、炭素と窒素の組合せにおいては、炭素の
対SCC効果が窒素量の増加とともに失なわれてい
き、またリン−窒素の組み合せではリンの低減が
極めて有効であることが確認されている。
塩化物を含む厳しい腐食環境で用いられる耐食
合金は、耐SCC性と耐孔食性とが要求されその成
分設計には耐SCC性向上のためにニツケルの添加
が、また耐孔食性向上のためにクロム、モリブデ
ンの添加が行われ、ともにその添加量は増す傾向
にある。しかし、前述したように、従来各々の合
金元素の添加量は、個別元素の個別現象への効果
を基に定められており、耐SCC性等の向上のため
経済性を考慮しつつニツケル、モリブデン、クロ
ム等の合金元素の相互的な最適バランスが定量的
に考慮されている材料は未だ知られていない。さ
らに、実際の製品製造において最も重要な要素の
１つである熱履歴、特に溶体化処理条件と耐SCC
性、耐孔食性との相互作用についても十分な解明
がなされていないのが現状である。
本発明はこのような現状に鑑み創案されたもの
で、耐SCC性に対する合金元素の相互作用及びこ
れと溶体化（又は準溶体化）処理条件との関係を
解明し、従来のSUS304，316等の材料より優れ
た耐SCC性を有する合金鋼を経済的な合金元素の
範囲で得ることに成功したものである。
即ち、本発明においては、Ｃ：0.03wt％以下、
Si：2wt％以下、Mn：2wt％以下、Ｐ：0.02wt％
以下、Ｓ：0.01wt％以下、Ni：20wt％以上30wt
％未満、Cr：12〜25wt％、Mo：10wt％以下、
Ｎ：0.3％wt以下、Cu：2wt％以下、Ti：1wt％
以下を含有し残部鉄及び不可避不純物からなる組
成であつて、
Cr＋1.5Mo＋0.8Ti＋0.5Cu15
の条件を満し、且つ
Δ＝（Ni＋30C＋25N）−〔｛（Cr＋1.5Mo
＋0.8Ti＋0.5Cu−19）2／12｝＋13〕
で求められるΔ値が５以上である組成を有する合
金鋼を、950〜1200℃の温度範囲であつて且つ下
式の条件を満す温度Tfにて溶体化又は準溶体化
処理後急冷するようにしたものである。
Tf12Δ＋900
以下本発明の成分組成及び熱処理条件の限定理
由を詳細に説明する。
本発明の成分組成の限定理由は以下の通りであ
る。
Ｃは、粒内型SCCの抑制に対して有効との説も
あるが、Ｃ含有量が0.03wt％を超えると粒界型
SCCを起し易くなり、特にＣ固溶度が減少する高
Ni合金でそのおそれが大きくなる。このような
ことからＣは0.03wt％以下に制限される。
Siは脱酸成分として必要であり、また耐SCC性
の向上に有効な元素であるが、2wt％を超えると
熱間加工性を劣化させ、したがつてその上限が
2wt％と定められる。
MnはSiと同様脱酸作用がある。このMnは耐
SCC性にはほとんど影響を与えないが、2wt％を
超えるとマンガン硫化物等の析出物が孔食の起点
となり易く、したがつて2wt％が上限とされる。
不可避不純物としてのＰはSCC感受性を高める
作用があるため、極力低減させる必要があり、こ
のためその上限が0.02wt％と定められる。
不可避不純物としてのＳには熱間加工性を劣化
させる作用があり、マンガン硫化物等を作つて耐
孔食性を悪化させるので、その上限が0.01wt％と
定められる。
Niは、耐SCC性を向上させるのに有効な元素
であつて、20wt％以上でその効果が顕著になり、
したがつて、20wt％が下限とされる。一方、下
記するCr量の上限が25wt％であることから、こ
のCr量上限とのバランス上、Niの上限は30wt％
未満に抑えられる。また本発明は合金元素の添加
を経済的な範囲としつつ従来のSUS304，316よ
り優れた耐SCC性を得んとするものであり、した
がつて30wt％以上の添加は経済性を損ね、本発
明の目的を逸脱することになる。
Crは高合金鋼の耐食性、とくに不働態皮膜の
強化による耐食性向上に有効な元素であるが
12wt％未満ではその効果が十分でなく、また
25wt％を超えると熱間加工性の劣化が避け難く、
したがつて12〜25wt％の範囲とされる。
Moは不働態皮膜の強化に対してCrの1.5倍程度
の効果があるが、その含有量が10wt％を超える
と熱間工程時に耐食性を劣化させるσ相を容易に
生成するようになり、このためその上限が10wt
％と定められる。
Ｎは耐SCC性の向上に対し必ずしも有効な元素
とはいい難いが、本発明鋼では耐孔食性を増すこ
とが期待できる。高合金鋼のSCCは孔食を起点に
伝播することが多く、孔食の発生を防止すること
は、SCCの防止につながる。また、Ｎは粒界鋭敏
化を抑制し、粒界型SCCの発生をおさえる作用を
有する。但し、Ｎは0.3％を超えるとCr，Nb，Ti
等の窒化物を形成して耐孔食性を劣化せしめると
ともに、加工性も低下せしめるので、0.3％を上
限とする。
Cuは材料の耐食性を向上させるのに役立つが、
2wt％を超えると熱間加工性の劣化を招き、この
ため2wt％が上限と定められる。
Tiは熱間加工性を向上させる作用があり、Ｃ
を固定して結果的に粒界SCCを抑制する効果をも
つ。Tiは1wt％を超えて含有せしめてもそれ以上
の効果は期待できず、従つて1wt％を上限にして
含有せしめられる。
本発明では、以上のような成分元素の組成条件
に、さらに成分元素間で、次のような条件を満足
させる必要があり、このような成分元素相互の関
係を満足させることによつて、本発明が目的とす
る優れた耐SCC性が得られる。すなわち、本発明
ではまず、
Cr＋1.5Mo＋0.8Ti＋0.5Cu15
となるよう各成分値が調整されう必要がある。全
面腐食及び孔食を含む耐食性を得るためには上記
条件を満足させる必要がある。さらに本発明で
は、上記組成条件に加え、
Δ＝（Ni＋30C＋25N）−〔｛（Cr＋1.5Mo
＋0.8Ti＋0.5Cu−19）2／12｝＋13〕
の式で定義されるΔ値が５以上となるよう組成条
件が調整される必要があり、組成条件上このΔ値
を満足しないと所望の耐SCC性が得られない。第
１図は上記Δ値と耐SCC性との関係を調べ、これ
を％（Cr＋1.5Mo＋0.8Ti＋0.5Cu）をＸ軸に、ま
た％（Ni＋30C＋25N）をＹ軸に取つて表わした
ものであり、この場合もSCC感受性は、950℃で
熱処理した試験片に降伏強さの1.2倍の応力を負
荷したまま、154℃沸騰塩化マグネシウム溶液に
浸漬し、600時間経過後の割れの有無で判定した
ものである。同付から明らかなように、（Cr＋
1.5Mo＋0.8Ti＋0.5Cu）15の範囲であつても、
Δ≧５の範囲においてのみ満足すべき耐SCC性が
得られており、したがつて本発明が目的とする耐
SCC性を十分満足させるには、少なくとも上記組
成条件を満足しなければならないことが判る。な
お同図中破線に示すように、（Ni＋30C＋25N）
の値は30以下に抑えられることが好ましい。
本発明では上記した成分条件の合金鋼を溶製し
た後、熱間圧延以降の工程で所謂溶体化処理又は
準溶体化処理が行われ、しかる後急冷される。こ
こで準溶体化処理とは、完全とはいかないまでも
組織中のカーバイトの溶解が進行し成分元素の不
均一が均一化される状態を示す。そして、本発明
ではまず、かかる熱処理を950〜1200℃の温度範
囲で行うことが条件とされる。ここで、熱処理温
度が950℃未満では金属組織の均一化が必要とさ
れる程度まで得られないため十分な耐SCC性が期
待できず、また、1200℃を超えた熱処理では、結
晶粒が粗大化して降伏応力が低下するので好まし
くない。成分組成によつて差はあるが、一般的に
はこのような950〜1200℃の温度範囲中、高温側
での熱処理が溶体化処理、低温側での熱処理が準
溶体化処理となる。本発明の熱処理は、このよう
な温度範囲において、さらにΔとの関係で下式の
条件を満す温度Tfで行うことが条件とされる。
Tf12Δ＋900
温度Tfは成分元素相互の含有量に関係して求め
られるΔ値に基づき決定されるもので、このよう
に成分元素の相互的な関係から決定される温度で
溶体化処理又は準溶体化処理を行うことにより、
本発明の目的とする優れた耐SCC性が得られる。
第２図は、Δ値と熱処理温度Tfとの関係から耐
SCC性を調べたものであるが、同図から明らかな
ように、950〜1200℃の温度範囲であつても、Δ
値との関係からTf＞12Δ＋900の範囲では耐SCC
性が劣り、耐SCC性を十分満足させるには、成分
元素相互の関係で求められるΔの値に基づいた温
度で熱処理することが不可欠であることが判る。
上記した溶体化処理又は準溶体化処理は、熱間
加工以降の種々の段階で行うことができ、例えば
熱間圧延−冷間圧延−溶体化処理又は準溶体化
処理、熱間圧延−溶体化処理又は準溶体化処理
−冷間圧延、等の各工程を採ることができる。ま
た溶体化処理（若しくは準溶体化処理）後、固溶
Ｃを過飽和の状態から飽和状態にして組織の安定
化を図るための熱処理、所謂安定化処理を行うこ
とができ、この場合には、例えば熱間圧延−溶
体化処理−冷間圧延−安定化処理、熱間圧延−
溶体化処理−安定化処理−冷間圧延、熱間圧延
−冷間圧延−溶体化処理−冷間圧延−安定化処
理、等の各工程を採ることができる。ここで上記
準溶体化処理は、組織中のカーバイドの溶解をあ
る程度進行せしめることによつて成分元素の均一
化（ミクロ的な成分濃度の均一化を含む）が図ら
れるようにした熱処理であることは前述した通り
であり、このようにして得られる組織は溶体化処
理は−安定化処理を経て均一化、安定化された組
織にも近いものとなる。なお、上記した、で
示すような工程では、溶体化処理と安定化処理の
工程で冷間圧延が行われ、この冷間圧延によつて
NbC、TiC等の析出が促進されるためより安定化
した組織を得ることができる。
〔実施例〕
第１表に本発明鋼（Ａ−１〜Ａ−６）及び比較
鋼（Ｂ−１〜Ｂ−４）の化学成分を示す。これら
はいずれも通常のステンレス鋼の製造ラインで製
造されたもので、熱間圧延−焼鈍−冷間圧延後、
950〜1050℃の温度範囲で10〜30分間加熱して急
冷する溶体化処理又は準溶体化処理を行つた。な
お、いくつかの条件では上記焼鈍工程に相当する
段階で溶体化処理又は準溶体化処理を行い、冷間
圧延後の熱処理は省略した。工程上における熱処
理の位置或いは当該熱処理における保持時間は結
果に影響を与えないので、それらの項目は省略し
た。各供試鋼の耐SCC性に関する試験結果を第１
表に併せて示した。
The present invention relates to a method for producing an alloy steel with excellent stress corrosion cracking resistance, and the present invention relates to a method for producing alloy steel with excellent stress corrosion cracking resistance.The present invention relates to a method for producing alloy steel with excellent stress corrosion cracking resistance. It was designed to encourage people to benefit from it. Of the reports on the effects of alloying elements on chloride stress corrosion cracking (hereinafter simply referred to as "SCC"), the most common one is Copson's report on the effects of alloying elements on the SCC resistance of nickel (Physical
metallurgy of stresscorrosion fracture, P247,
Interscience, NY (1959)). According to this, the SCC resistance of a chromium-nickel-iron alloy containing about 18% chromium is the lowest at about 8% nickel, and the SCC resistance decreases by decreasing the amount of nickel added or increasing the nickel content. Furthermore, when targeting austenitic stainless steel, extremely high SCC resistance can be obtained by increasing the nickel content to 45% or more.
The alloying elements other than nickel that are generally recognized as effective for SCC resistance are carbon and silicon.
Phosphorus, nitrogen, molybdenum, chromium, etc. are known as elements that have an adverse effect. However, regarding the influence of each component element on SCC resistance described here, only the concentration of the component of interest was taken as a variable factor; on the other hand, there are few studies on the interaction of component elements, and There are only a few reports on the combinations of carbon-nitrogen and phosphorus-nitrogen in small amounts ("Sayasawa, Fukase, Yokota: Journal of the Japan Institute of Metals, 36 (1972) 170.""Kowaka, Fujikawa: Journal of the Japan Institute of Metals, 34 (1970). ) 1047.”). It has been confirmed that in the combination of carbon and nitrogen, the effect of carbon on SCC disappears as the amount of nitrogen increases, and in the combination of phosphorus and nitrogen, the reduction of phosphorus is extremely effective. Corrosion-resistant alloys used in severe corrosive environments containing chlorides are required to have SCC resistance and pitting corrosion resistance, and in their component design, nickel is added to improve SCC resistance, and nickel is added to improve pitting corrosion resistance. Chromium and molybdenum are being added, and the amounts of both are increasing. However, as mentioned above, the amount of each alloying element added has conventionally been determined based on the effect of each individual element on individual phenomena. There is still no known material in which the optimal mutual balance of alloying elements such as chromium and chromium is quantitatively considered. Furthermore, thermal history, which is one of the most important factors in actual product manufacturing, especially solution treatment conditions and SCC resistance.
At present, the interaction between corrosion resistance and pitting corrosion resistance has not been sufficiently elucidated. The present invention was devised in view of the current situation, and aims to elucidate the interaction of alloying elements with respect to SCC resistance and the relationship between this and solution treatment (or quasi-solution treatment) conditions, thereby improving conventional SUS304, 316, etc. We have succeeded in obtaining an alloy steel with SCC resistance superior to that of other materials using an economical range of alloying elements. That is, in the present invention, C: 0.03wt% or less,
Si: 2wt% or less, Mn: 2wt% or less, P: 0.02wt%
Below, S: 0.01wt% or less, Ni: 20wt% or more 30wt
%, Cr: 12~25wt%, Mo: 10wt% or less,
N: 0.3%wt or less, Cu: 2wt% or less, Ti: 1wt%
The composition contains the following, with the balance consisting of iron and unavoidable impurities, and satisfies the conditions of Cr + 1.5Mo + 0.8Ti + 0.5Cu15, and Δ = (Ni + 30C + 25N) - [{(Cr + 1.5Mo + 0.8Ti + 0.5Cu - 19) 2 /12}+13] An alloy steel having a composition with a Δ value of 5 or more is subjected to solution treatment or quasi-solution treatment at a temperature Tf in the temperature range of 950 to 1200℃ and satisfying the conditions of the following formula. It is designed to be rapidly cooled after the chemical treatment. Tf12Δ+900 Below, the reason for limiting the component composition and heat treatment conditions of the present invention will be explained in detail. The reasons for limiting the component composition of the present invention are as follows. There is a theory that C is effective in suppressing intragranular type SCC, but if the C content exceeds 0.03 wt%, grain boundary type SCC
SCC is more likely to occur, especially at high temperatures where C solid solubility decreases.
This possibility increases with Ni alloys. For this reason, C is limited to 0.03wt% or less. Si is necessary as a deoxidizing component and is an effective element for improving SCC resistance, but if it exceeds 2wt%, it deteriorates hot workability, and therefore its upper limit is
It is defined as 2wt%. Like Si, Mn has a deoxidizing effect. This Mn is
It has little effect on SCC properties, but if it exceeds 2wt%, precipitates such as manganese sulfide tend to become a starting point for pitting corrosion, so 2wt% is the upper limit. Since P as an unavoidable impurity has the effect of increasing SCC susceptibility, it must be reduced as much as possible, and therefore the upper limit is set at 0.02 wt%. S as an unavoidable impurity has the effect of deteriorating hot workability and creates manganese sulfide, etc., which deteriorates pitting corrosion resistance, so its upper limit is set at 0.01 wt%. Ni is an effective element for improving SCC resistance, and its effect becomes noticeable at 20wt% or more.
Therefore, 20wt% is set as the lower limit. On the other hand, since the upper limit of Cr amount described below is 25wt%, in balance with this upper limit of Cr amount, the upper limit of Ni is 30wt%.
can be kept below. Furthermore, the present invention aims to achieve SCC resistance superior to conventional SUS304 and 316 while keeping the addition of alloying elements within an economical range. Therefore, addition of 30wt% or more impairs economic efficiency and This would deviate from the purpose of the invention. Cr is an effective element for improving the corrosion resistance of high alloy steel, especially by strengthening the passive film.
If it is less than 12wt%, the effect is not sufficient, and
If it exceeds 25wt%, it is difficult to avoid deterioration of hot workability.
Therefore, it is in the range of 12 to 25 wt%. Mo is about 1.5 times as effective as Cr in strengthening the passive film, but if its content exceeds 10wt%, it easily forms a σ phase that deteriorates corrosion resistance during hot processing. Therefore, the upper limit is 10wt
%. Although N is not necessarily an effective element for improving SCC resistance, it can be expected to increase pitting corrosion resistance in the steel of the present invention. SCC in high-alloy steel often propagates starting from pitting corrosion, and preventing the occurrence of pitting corrosion will lead to the prevention of SCC. Further, N has the effect of suppressing grain boundary sensitization and suppressing the occurrence of grain boundary type SCC. However, if N exceeds 0.3%, Cr, Nb, Ti
The upper limit is set at 0.3% because it forms nitrides such as, which deteriorates pitting corrosion resistance and also reduces workability. Although Cu helps improve the corrosion resistance of materials,
If it exceeds 2wt%, hot workability deteriorates, and for this reason, 2wt% is set as the upper limit. Ti has the effect of improving hot workability, and C
This has the effect of suppressing grain boundary SCC as a result. Even if Ti is contained in an amount exceeding 1 wt%, no further effect can be expected, and therefore the content is limited to 1 wt%. In the present invention, it is necessary to satisfy the compositional conditions of the component elements as described above, as well as the following conditions between the component elements. The excellent SCC resistance aimed at by the invention can be obtained. That is, in the present invention, first, the values of each component must be adjusted to become Cr+1.5Mo+0.8Ti+0.5Cu15. In order to obtain corrosion resistance including general corrosion and pitting corrosion, it is necessary to satisfy the above conditions. Furthermore, in the present invention, in addition to the above composition conditions, the Δ value defined by the formula Δ=(Ni+30C+25N)−[{(Cr+1.5Mo+0.8Ti+0.5Cu−19) 2 /12}+13] is 5 or more. It is necessary to adjust the composition conditions so that the desired SCC resistance cannot be obtained unless the composition conditions satisfy this Δ value. Figure 1 examines the relationship between the above Δ value and SCC resistance, and expresses this with % (Cr + 1.5Mo + 0.8Ti + 0.5Cu) on the X axis and % (Ni + 30C + 25N) on the Y axis. In this case as well, SCC susceptibility was determined by immersing a specimen heat-treated at 950°C in a magnesium chloride solution boiling at 154°C while applying a stress 1.2 times the yield strength, and determining the presence or absence of cracks after 600 hours. It is something. As is clear from the attachment, (Cr+
1.5Mo+0.8Ti+0.5Cu) Even if it is in the range of 15,
Satisfactory SCC resistance was obtained only in the range of Δ≧5, and therefore the resistance aimed at by the present invention was not achieved.
It can be seen that in order to fully satisfy the SCC property, at least the above composition conditions must be satisfied. As shown by the broken line in the same figure, (Ni + 30C + 25N)
It is preferable that the value of is suppressed to 30 or less. In the present invention, after the alloy steel having the above-mentioned composition conditions is produced, so-called solution treatment or quasi-solution treatment is performed in the steps after hot rolling, and then it is rapidly cooled. Here, the semi-solution treatment refers to a state in which dissolution of carbide in the structure progresses, although not completely, and non-uniformity of component elements is made uniform. The present invention first requires that such heat treatment be performed at a temperature range of 950 to 1200°C. If the heat treatment temperature is less than 950℃, sufficient SCC resistance cannot be expected because the metal structure cannot be made uniform to the required degree, and if the heat treatment temperature exceeds 1200℃, the crystal grains will become coarse. This is not preferable because the yield stress decreases. Although there are differences depending on the component composition, in general, within this temperature range of 950 to 1200°C, heat treatment on the high temperature side is solution treatment, and heat treatment on the low temperature side is quasi-solution treatment. The heat treatment of the present invention is conditioned to be carried out within such a temperature range and at a temperature Tf that satisfies the condition of the following formula in relation to Δ. Tf12Δ+900 The temperature Tf is determined based on the Δ value determined in relation to the mutual content of the component elements, and solution treatment or quasi-solution treatment is performed at the temperature determined from the mutual relationship of the component elements. By doing
Excellent SCC resistance, which is the objective of the present invention, can be obtained.
Figure 2 shows the relationship between the Δ value and the heat treatment temperature Tf.
The SCC property was investigated, and as is clear from the figure, even in the temperature range of 950 to 1200℃, Δ
From the relationship with the value, SCC resistance is achieved in the range of Tf>12Δ+900.
It can be seen that in order to fully satisfy the SCC resistance, it is essential to perform heat treatment at a temperature based on the value of Δ determined from the relationship between the component elements. The solution treatment or quasi-solution treatment described above can be performed at various stages after hot working, such as hot rolling-cold rolling-solution treatment or quasi-solution treatment, hot rolling-solution treatment. Processes such as treatment or quasi-solution treatment-cold rolling can be employed. Further, after the solution treatment (or quasi-solution treatment), a so-called stabilization treatment, which is a heat treatment to stabilize the structure by changing the solid solution C from a supersaturated state to a saturated state, can be performed. For example, hot rolling - solution treatment - cold rolling - stabilization treatment, hot rolling -
Each process such as solution treatment-stabilization treatment-cold rolling, hot rolling-cold rolling-solution treatment-cold rolling-stabilization treatment, etc. can be taken. Here, the quasi-solution treatment described above is a heat treatment that achieves uniformity of component elements (including uniformity of microscopic component concentration) by progressing the dissolution of carbide in the structure to a certain extent. As described above, the structure obtained in this way becomes similar to a structure that has been homogenized and stabilized through solution treatment and stabilization treatment. In addition, in the process shown above, cold rolling is performed in the solution treatment and stabilization treatment steps, and this cold rolling
Since the precipitation of NbC, TiC, etc. is promoted, a more stable structure can be obtained. [Example] Table 1 shows the chemical components of the invention steels (A-1 to A-6) and comparative steels (B-1 to B-4). All of these were manufactured on a normal stainless steel production line, and after hot rolling, annealing, and cold rolling,
Solution treatment or quasi-solution treatment was performed by heating in a temperature range of 950 to 1050°C for 10 to 30 minutes and rapidly cooling. Note that under some conditions, solution treatment or quasi-solution treatment was performed at a stage corresponding to the above-mentioned annealing step, and heat treatment after cold rolling was omitted. Since the position of the heat treatment in the process or the holding time in the heat treatment do not affect the results, these items were omitted. The test results regarding the SCC resistance of each sample steel are
It is also shown in the table.
【表】
同表からも明らかなように、本発明鋼は耐SCC性
に優れた性質を有しているのに対し、比較鋼で
は、いずれの熱処理温度においても悪影響が現わ
れていることが判る。
以上述べたように本発明によれば、耐SCC性に
対する合金元素の相互作用及びそれらと熱処理条
件との関係を解明し、それらを特定の範囲に選定
することにより、優れた耐SCC性を有する合金鋼
の製造を可能ならしめたものであつて、この種の
合金鋼に関する工業的な効果の大きい発明であ
る。[Table] As is clear from the table, the steel of the present invention has excellent SCC resistance, while the comparative steel shows an adverse effect at all heat treatment temperatures. . As described above, according to the present invention, by elucidating the interaction of alloying elements on SCC resistance and the relationship between them and heat treatment conditions, and selecting them within a specific range, excellent SCC resistance can be achieved. This invention has made it possible to manufacture alloy steel, and has great industrial effects regarding this type of alloy steel.
第１図はΔ値と耐SCC性との関係を示すもので
ある。第２図はΔ値と熱処理温度との関係から耐
SCC性を調べたものである。
FIG. 1 shows the relationship between Δ value and SCC resistance. Figure 2 shows the relationship between the Δ value and the heat treatment temperature.
This study investigated SCC properties.
Claims (1)
2wt％以下、Ｐ：0.02wt％以下、Ｓ：0.01wt％以
下、Ni：20wt％以上30wt％未満、Cr：12〜25wt
％、Mo：10wt％以下、Ｎ：0.3wt％以下、Cu：
2wt％以下、Ti：1wt％以下を含有し残部鉄及び
不可避不純物からなる組成であつて、 Cr＋1.5Mo＋0.8Ti＋0.5Cu15 の条件を満し、且つ、 Δ＝（Ni＋30C＋25N）−〔｛（Cr＋1.5Mo ＋0.8Ti＋0.5Cu−19）2／12｝＋13〕 で求められるΔ値が５以上である組成を有する合
金鋼を、950〜1200℃の範囲であつて、且つ下式
の条件を満す温度Tfにて溶体化又は準溶体化処
理後急冷することを特徴とする耐応力腐食割れ性
に優れた合金鋼の製造方法。 Tf12Δ＋900[Claims] 1 C: 0.03wt% or less, Si: 2wt% or less, Mn:
2wt% or less, P: 0.02wt% or less, S: 0.01wt% or less, Ni: 20wt% or more and less than 30wt%, Cr: 12 to 25wt
%, Mo: 10wt% or less, N: 0.3wt% or less, Cu:
2wt% or less, Ti: 1wt% or less, with the balance consisting of iron and unavoidable impurities, satisfying the conditions of Cr + 1.5Mo + 0.8Ti + 0.5Cu15, and Δ = (Ni + 30C + 25N) - [{(Cr + 1. 5Mo + 0.8Ti + 0.5Cu - 19) 2 / 12} + 13] Alloy steel with a composition whose Δ value calculated by A method for producing an alloy steel with excellent stress corrosion cracking resistance, characterized by rapid cooling after solution treatment or quasi-solution treatment at a temperature of Tf. Tf12Δ+900
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP18641883A JPS6077917A (en) | 1983-10-05 | 1983-10-05 | Manufacture of alloy steel having superior resistance to stress corrosion cracking |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP18641883A JPS6077917A (en) | 1983-10-05 | 1983-10-05 | Manufacture of alloy steel having superior resistance to stress corrosion cracking |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS6077917A JPS6077917A (en) | 1985-05-02 |
| JPH0352527B2 true JPH0352527B2 (en) | 1991-08-12 |
Family
ID=16188075
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP18641883A Granted JPS6077917A (en) | 1983-10-05 | 1983-10-05 | Manufacture of alloy steel having superior resistance to stress corrosion cracking |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS6077917A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4911886A (en) * | 1988-03-17 | 1990-03-27 | Allegheny Ludlum Corporation | Austentitic stainless steel |
-
1983
- 1983-10-05 JP JP18641883A patent/JPS6077917A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6077917A (en) | 1985-05-02 |
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