JP4352597B2 - High weather resistant steel - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、耐候性鋼材に係わり、とくに海浜地域など塩分の多い環境で使用可能な海浜耐候性に優れた鋼材に関する。ここでいう海浜耐候性とは、海浜地域の大気中で使用した場合の耐候性をいう。なお、本発明でいう鋼材は、厚鋼板、薄鋼板、棒鋼、形鋼等を含むものとする。
【０００２】
【従来の技術】
鋼中に、Ｐ，Cu，Cr，Ni等の合金元素を添加し大気中における耐食性を向上させた耐候性鋼は、橋梁等の構造物に広く利用されている。耐候性鋼は、屋外において腐食の原因である酸素、水を通しにくい安定さびと呼ばれるさびを数年で形成し、その後の腐食を抑制している。このため、耐候性鋼は防錆塗料の塗布が不要であり、いわゆる裸使用が可能な安価な高耐食性材料である。
【０００３】
一方、近年、建設省から耐候性鋼の適用指針（「耐候性鋼の橋梁への適用に関する共同研究報告著（ＸＸ）」、1993.3, 建設省土木研究所、（社）鋼材倶楽部、（社）日本橋梁建設協会発行）が公表され、飛来塩分量が0.05mg/dm2/day以上の地域、すなわち海浜地域では、従来の耐候性鋼（JIS G 3114：溶接構造用耐候性熱間圧延鋼材）は無塗装で使用できないことになっている。
【０００４】
したがって、海浜地域などの塩分の多い環境下では、普通鋼材にフタル酸樹脂、塩化ゴム、タールエポキシ樹脂等の塗装を行って対処している。しかしながら、河口付近の海浜地域に建設される橋梁は腐食が著しく再塗装の要求が高いが、長大橋が多く、しかも再塗装作業が困難な場合が多い。このようなことから、依然として無塗装で使用できる鋼材への要望が高い。
【０００５】
さらに、海岸地帯といっても、場所により飛来する塩分量は大きく相違する。鋼材の腐食は飛来塩分量が多くなるにしたがい激しくなるため、耐食性と経済性の観点からは、飛来塩分量に応じた耐候性鋼材が必要となる。
また、橋梁といっても、使用される場所により鋼材の腐食環境は同一とは限らない。たとえば、桁外部では、降雨、結露水および日照に曝される。一方、桁内部では、結露水のみに曝され雨掛かりはない。一般に、飛来塩分量が多い環境では、桁外部より桁内部の方が腐食が激しいと言われている。
【０００６】
このような問題に対し、例えば特開平６−136557号公報には、硫酸クロム水溶液あるいは硫酸銅水溶液を塗布し、水分乾燥後さらに有機樹脂被覆を行う鋼材の表面処理方法が提案されている。さらに、特開平８−13158 号公報には、アルミニウムイオンを含む水溶液を塗布し、水分乾燥後さらに有機樹脂被膜を形成する鋼材の表面処理方法が提案されている。しかしながら、特開平６−136557号公報および特開平８−13158 号公報に記載された技術では、安定さびが短期間で形成されるが、工程が複雑であるうえ使用する表面処理剤が高価であるなどの問題を残しており、表面処理を必要としない耐候性鋼材の開発が要望されていた。
【０００７】
この点、特開昭63−255341号公報には、耐塩害性に優れた溶接構造用耐食性鋼板が提案されている。この鋼板は、Ｐ：0.04〜0.15wt％、Cu：0.1 〜0.5wt ％、Cr：３〜10wt％、Al：0.02〜1.0wt ％含有し、海塩粒子が関与する腐食環境下でも無塗装使用に耐え得るとされている。しかし、この鋼板は、Ｐ含有量が高く靱性の低下、溶接性の低下が大きいという問題があった。
【０００８】
また、特開平３−158436号公報には、海浜耐候性構造用鋼が提案され、この鋼は、Ｐを多量添加することなく、Mn、Cu、Cr、Ni、Moの含有量を調整することにより海浜地帯で優れた耐候性を示し、鋼板への塗装を省略できるとされている。しかし、この鋼は、Crの含有量が高く、靱性、溶接性の低下という問題が残されていた。
【０００９】
また、特開平10-251797 号公報には、Ｃ：0.15％以下、Si：0.7 ％以下、Mn：0.2 〜1.5 ％、Ｐ：0.03〜0.15％、Ｓ：0.02％以下、Al：0.01〜0.1 ％、Cr：0.1 ％以下、Ni：0.4 〜４％、Cu：0.4 ％以下、Mo：0.05〜１％と、さらにSn：0.01〜0.5 ％、Sb：0.01〜３％のうちの１種または２種を含有する、0.05mg/dm2/day以上10mg/dm2/day未満の塩分が飛来する環境において高い耐候性を有する溶接構造用鋼が提案されている。しかし、特開平10-251797 号公報に記載された鋼は、強度確保のためにＣを比較的高く含有し、さらに強度向上と耐食性確保のために、Ｐを0.03％以上含有しており、靱性、溶接性に難点がある。
【００１０】
【発明が解決しようとする課題】
本発明は、上記した従来技術の問題に鑑み、海浜地域などの塩分が多く、雨掛かりがない環境下でも、靱性および溶接性を損なわずに優れた海浜耐候性を保持し、塗装、表面処理などを必要としない海浜耐候性に優れた高耐候性鋼材を提供することを目的とする。
【００１１】
【課題を解決するための手段】
本発明者らは、上記した課題を達成するために、耐候性鋼材に形成されるさび層について鋭意研究した。その結果、本発明者らは、耐候性鋼材に形成されるさび層について、つぎのような知見を得た。
耐候性鋼材の初期にできるさび層はγ−FeOOH やFe3O4 が主体である。数年の乾湿繰り返し腐食反応によって、さび層はγ−FeOOH やFe3O4 が減少し、Ｘ線回折レベルでの非晶質さびが主体となる。また、このさび層はTEM （透過型電子顕微鏡）観察レベルでも結晶系を特定できない非晶質さびが多くを占め、このような状態のさびとすることが耐候性の点で好ましい。
【００１２】
しかしながら、海浜地域で暴露された耐候性鋼材に形成されるさび層では、さび粒子として、TEM 観察レベルで笹状のγ−FeOOH あるいはα−FeOOH が主体となっている。これら笹状のさび粒子の形成は、さび層に空隙を生成するため、さび層が水、酸素、Clイオンを通し易い構造となる。したがって、海浜耐候性を改善するためには、これら笹状のさび粒子の形成を抑制したさび層とすることが肝要であることを知見した。
【００１３】
そこで、本発明者らは、笹状のさび粒子の形成を抑制する方策について鋭意研究した。その結果、鋼中にSbを添加することによって、笹状のさび粒子の形成が抑制され、TEM 観察レベルでも非晶質さび主体のさび層となることを見いだした。また、本発明者らは、Ｃ含有量を極低炭素域に低減し、さらにＰ含有量を0.030 ％以下、好ましくは0.025 ％未満と低Ｐ化することにより、耐候性鋼材の溶接性、とくに大入熱溶接における溶接性が顕著に改善されるという新規な知見を得た。
【００１４】
本発明は、上記した知見に基づき、さらに検討を加えて完成されたものである。
すなわち、本発明は、質量％で、Ｃ：0.001 〜0.025 ％、Si：0.60％以下、Mn：0.1 〜3.0 ％、Ｐ：0.005 〜0.030 ％、Ｓ：0.01％以下、Al：0.10％以下、Cu：0.1 〜1.5 ％、Ni：0.1 〜6.0 ％、Sb：0.005 〜1.0 ％を含み、残部Fe及び不可避的不純物からなる組成を有することを特徴とする高耐候性鋼材である。
【００１５】
また、本発明では、前記組成に加えてさらに、質量％で、Mo：0.005 〜0.5 ％、Ｗ：0.005 〜1.0 ％、Co：0.005 〜1.0 ％のうちから選ばれた１種または２種以上を含有することが好ましく、また本発明では、前記各組成に加えてさらに、質量％で、Nb：0.005 〜0.20％、Ti：0.005 〜0.20％、Ｖ：0.005 〜0.20％、Ｂ：0.0001〜0.0050％のうちから選ばれた１種または２種以上を含有することが好ましく、また、本発明では、前記各組成に加えてさらに、質量％で、REM ：0.02％以下、Ca：0.02％以下のうちから選ばれた１種または２種を含有することが好ましい。
【００１６】
【発明の実施の形態】
本発明鋼材の成分限定理由について説明する。以下、質量％は単に％と記す。
Ｃ：0.001 〜0.025 ％
Ｃは、強度を増加する元素であり、所望の強度を確保するためには、0.001 ％以上の含有を必要とするが、0.025 ％を超えて含有すると、靱性、溶接性が劣化する。そこで、Ｃは0.001 〜0.025 ％の範囲に限定した。
【００１７】
Si：0.60％以下
Siは、脱酸剤として作用し、さらに鋼の強度を増加させる元素であるが、0.60％を超えて多量に含有すると、靱性および溶接性を劣化させる。このため、Siは0.60％以下に限定した。なお、好ましくは0.10〜0.30％である。
Mn：0.1 〜3.0 ％
Mnは、鋼の強度および靱性の増加に大きく寄与する元素であり、所望の強度を確保するために、本発明では0.1 ％以上の含有を必要とするが、3.0 ％を超えて多量に含有すると靱性、溶接性に悪影響を及ぼす。このため、Mnは0.1 〜3.0 ％の範囲に限定した。なお、寒冷地等で高靱性が要求される場合には、低Mn化が効果的であり、0.10〜0.50％とするのが好ましい。
【００１８】
Ｐ：0.005 〜0.030 ％
Ｐは、さび粒子を緻密化し耐候性を向上させる元素であり、本発明では0.005 ％以上の含有を必要とする。しかし、0.030 ％を超えて含有すると、溶接性が顕著に劣化する。このため、Ｐは0.005 〜0.030 ％の範囲に限定した。本発明では、Ｃ含有量を極低炭素域に低減し、さらにＰ含有量を0.030 ％以下、好ましくは0.025 ％未満と低Ｐとすることにより、大入熱溶接における溶接性が顕著に改善される。なお、好ましくは0.005 〜0.020 ％である。
【００１９】
Ｓ：0.01％以下
Ｓは、耐候性を劣化させ、さらに溶接性、靱性を劣化させるため、本発明では、Ｓはできるだけ低減するのが好ましいが、0.01％までは許容できる。なお、好ましくは0.005 ％以下である。
Al：0.10％以下
Alは、脱酸剤として添加するが、0.10％を超えて含有すると溶接性に悪影響を及ぼす。このため、Alは0.10％を上限とした。なお、好ましくは0.010 〜0.050 ％である。
【００２０】
Cu：0.1 〜1.5 ％
Cuは、さび粒子を緻密化し耐候性を向上させる元素であり、本発明では0.1 ％以上の含有を必要とする。一方、1.5 ％を超えて含有すると、熱間加工性を阻害するとともに、耐候性向上の効果も飽和し、含有量に見合う効果が期待できず、経済的に不利となる。このため、Cuは0.1 〜1.5 ％の範囲に限定した。なお、好ましくは0.10〜0.60％である。
【００２１】
Ni：0.1 〜6.0 ％
Niは、さび粒子を緻密化し耐候性を向上させる元素であり、本発明では、0.1 ％以上の含有を必要とする。一方、6.0 ％を超えて含有しても、効果が飽和し含有量に見合う効果が期待できず、経済的に不利となる。このため、Niは0.1 〜6.0 ％の範囲とした。なお、飛来塩分量が多い場合には、2.0 ％以上とするのが好ましく、飛来塩分量が少ない場合には2.0 ％未満とするのが好ましい。
【００２２】
Sb：0.005 〜1.0 ％
本発明では、最も重要な元素である。Sbは、さび層で、笹状のさび粒子の形成を抑制し、さび層を非晶質さび主体とする効果を有する。このような効果は、0.005 ％以上の含有で認められるが、1.0 ％を超えて含有しても、効果が飽和し含有量に見合う効果が認められない。このため、Sbは0.005 〜1.0 ％の範囲に限定した。なお、好ましくは0.005 〜0.7 ％である。
【００２３】
Mo：0.005 〜0.5 ％、Ｗ：0.005 〜1.0 ％、Co：0.005 〜1.0 ％のうちから選ばれた１種または２種以上
Mo、Ｗ、Coはいずれも、耐候性を向上させる元素であり、必要に応じ１種または２種以上を選択して含有できる。
Mo：0.005 〜0.5 ％
Moは、耐候性を向上させ、さらに強度を増加させる元素であるが、0.005 ％未満の含有ではその効果が少ない。一方、0.5 ％を超えて含有しても効果が飽和し含有量に見合う効果が認められず、経済的に不利となる。このため、Moは0.005 〜0.5 ％の範囲に限定するのが好ましい。なお、靱性の観点から、0.005 〜0.35％の範囲とするのがより好ましい。
【００２４】
Ｗ：0.005 〜1.0 ％
Ｗは、耐候性を向上させ、さらに強度を増加させる元素であるが、0.005 ％未満の含有ではその効果が少ない。一方、1.0 ％を超えて含有しても効果が飽和し含有量に見合う効果が認められず、経済的に不利となる。このため、Ｗは0.005 〜1.0 ％の範囲に限定するのが好ましい。なお、経済性の観点から、0.005 〜0.6 ％の範囲とするのがより好ましい。
【００２５】
Co：0.005 〜1.0 ％
Coは、耐候性を向上させる元素であるが、0.005 ％未満の含有ではその効果が少ない。一方、1.0 ％を超えて含有しても効果が飽和し含有量に見合う効果が認められず、経済的に不利となる。このため、Coは0.005 〜1.0 ％の範囲に限定するのが好ましい。なお、経済性の観点から、0.005 〜0.6 ％の範囲とするのがより好ましい。
【００２６】
Nb：0.005 〜0.20％、Ti：0.005 〜0.20％、Ｖ：0.005 〜0.20％、Ｂ：0.0001〜0.0050％のうちから選ばれた１種または２種以上
Nb、Ti、Ｖ、Ｂは、鋼材の強度を増加させる元素であり、必要に応じ１種または２種以上を含有できる。
Nb、Ti、Ｖは、いずれも0.005 ％以上の含有で、Ｂは、0.0001％以上の含有で効果が認められるが、Nb、Ti、Ｖはそれぞれ0.20％を超えて、Ｂは0.0050％を超えて含有しても効果が飽和し、含有量に見合う効果が期待できなくなり、経済的に不利となる。このため、Nb、Ti、Ｖはいずれも0.005 ％〜0.20％、Ｂは0.0001〜0.0050％の範囲に限定するのが好ましい。
【００２７】
REM ：0.02％以下、Ca：0.02％以下のうちから選ばれた１種または２種
REM 、Caは、溶接性を向上させる元素であり、必要に応じ選択して含有できる。このような効果は、REM 0.001 ％以上、Ca0.001 ％以上の含有で顕著に認められるようになるが、REM 、Caとも0.02％を超える多量の含有は、鋼材の清浄度を劣化させる。このため、REM ：0.02％以下、Ca：0.02％以下の限定するのが好ましい。
【００２８】
上記した成分以外の残部は、Fe及び不可避的不純物である。
不可避的不純物として、Cr：0.05％以下、Ｎ：0.010 ％以下、Ｏ：0.010 ％以下が許容できる。
Crは、耐候性を向上させる元素といわれてきたが、耐候性を向上させるのは、塩分の少ない環境下における場合であり、本発明が目的とする海浜地域のような塩分の多い環境では、逆に耐候性を劣化させる元素である。このため、本発明では敢えて添加しないが、0.05％までは許容できる。
【００２９】
本発明鋼材は、転炉、電気炉等、通常公知の溶製方法で溶製され、連続鋳造法あるいは造塊法により鋼素材とされる。また、溶製方法は、真空脱ガス精錬等を実施してもよい。
ついで、これら鋼素材は、加熱炉等で加熱され、あるいは加熱なしで直接、熱間圧延により所望の形状に圧延される。
【００３０】
【実施例】
表１に示す化学成分の鋼を転炉で溶製し、連続鋳造法でスラブとした。ついで、これらスラブを加熱し、熱間圧延により25mm×2500mm幅の厚鋼板とした。これら厚鋼板について、引張特性、靱性および溶接性を調査した。
引張特性は、各厚鋼板の全厚（Ｃ方向）からJIS 4 号引張試験片を採取し、JIS Z 2241の規定に準拠して、降伏強さYS、引張強さTS、伸びElを測定した。
【００３１】
靱性は、各厚鋼板の1/2T（Ｃ方向）からJIS 4 号衝撃試験片を採取し、JIS Z 2242の規定に準拠して、試験温度−５℃でシャルピー衝撃試験を実施し、吸収エネルギー vＥ-5を求めた。
溶接性は、各厚鋼板から試験片を採取し、入熱100kJ/cm溶接熱影響部１mm相当の再現熱サイクルを付与したのち、試験温度−５℃におけるシャルピー衝撃試験を実施し、吸収エネルギー vＥ-5を求めた。
【００３２】
また、各厚鋼板から、５mm×50mm×100mm の腐食試験片を採取し、ショットブラスト後、大気暴露試験に供し、海浜耐候性を評価した。
大気暴露試験は、飛来塩分量0.8mg/dm2/day （JIS Z 2381ガーゼ法により測定）の海岸地帯を選定し、雨掛かりのない条件で、それぞれ試験片の地鉄面を水平上向きに設置し、１年間暴露した。暴露試験後、地鉄表面に形成されたさび層を除去し、試験片の重量減少量を測定し、板厚減少量に換算した。
【００３３】
それらの結果を表２に示す。
【００３４】
【表１】
【表２】
本発明例は、いずれも強度、靱性および溶接性ともに優れ、かつ板厚減少量が29〜45μｍと、従来例（鋼板No.12 ）の143 μｍにくらべて著しく減少しており、本発明鋼材が優れた耐候性を有していることが分かる。
一方、本発明範囲の下限からSb含有量が外れる比較例（鋼板 No.８、No.10 ）は、板厚減少量が、それぞれ102 、145 μｍと、大きく、耐候性が劣化している。比較例（鋼板No. ９）は、Sb含有量が1.25％と多いにもかかわらずSb含有量が0.89％と少ない本発明例（鋼板 No.３）と同じ板厚減少量を示し、Sbの効果が本発明範囲を高く外れると飽和していることを示している。なお、Ｐ含有量が本発明の範囲を外れて高い比較例（鋼板 No.11）の板厚減少量は、26μｍと非常に少ない値を示しているが、靱性、溶接性が劣化している。
【００３７】
また、比較例（鋼板No.15 ）は、それぞれＣ、Ｐが本発明の範囲を外れており、溶接性が劣化している。
また、比較例（鋼板No.13 、No.14 ）は、それぞれCu、Niが本発明の範囲を外れており、耐候性が劣化している。
【００３８】
【発明の効果】
以上の説明から明らかなごとく、本発明によれば、海浜地域など塩分が多い環境下で、耐候性を保持できる耐候性鋼材を提供できる。これら鋼材を橋梁などの構造物へ適用すると、塗装、表面処理等の省略が可能となり、保守費用の削減という経済的効果も期待でき、産業上格段の効果を奏する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a weather resistant steel material, and more particularly to a steel material having excellent beach weather resistance that can be used in a salty environment such as a beach area. The beach weather resistance here refers to the weather resistance when used in the atmosphere of the beach area. In addition, the steel materials referred to in the present invention include thick steel plates, thin steel plates, bar steels, shaped steels, and the like.
[0002]
[Prior art]
Weatherproof steel, in which an alloying element such as P, Cu, Cr, or Ni is added to the steel to improve the corrosion resistance in the atmosphere, is widely used for structures such as bridges. Weather-resistant steel forms rust, called stable rust, that prevents the passage of oxygen and water, which cause corrosion outdoors, in several years, and suppresses subsequent corrosion. For this reason, weather resistant steel does not require the application of a rust preventive paint, and is an inexpensive high corrosion resistant material that can be used naked.
[0003]
On the other hand, in recent years, the Ministry of Construction has applied guidelines for the application of weathering steels ("Joint Research Report on the Application of Weathering Steels to Bridges (XX)", 1993.3, Ministry of Construction Public Works Research Institute, Steel Club, Ltd.) Published by the Japan Bridge Construction Association), in areas where the incoming salt content is 0.05 mg / dm 2 / day or more, that is, in the coastal area, conventional weathering steel (JIS G 3114: weathering hot rolled steel for welded structures) Is unpainted and cannot be used.
[0004]
Therefore, in a salty environment such as a beach area, ordinary steel is coated with phthalic acid resin, chlorinated rubber, tar epoxy resin, etc. However, bridges constructed in the coastal area near the estuary are highly corroded and require repainting. However, there are many long bridges and repainting is often difficult. For these reasons, there is still a high demand for steel materials that can be used without painting.
[0005]
Furthermore, even if it is a coastal zone, the amount of salt that flies varies greatly depending on the location. Since corrosion of steel materials increases as the amount of flying salt increases, a weathering steel material corresponding to the amount of flying salt is required from the viewpoint of corrosion resistance and economy.
Moreover, even if it is called a bridge, the corrosive environment of steel materials is not necessarily the same according to the place used. For example, outside the girder, they are exposed to rainfall, condensed water and sunlight. On the other hand, the inside of the girders is exposed only to condensed water and there is no rain. In general, in an environment where the amount of incoming salt is large, it is said that the inside of the girders is more corrosive than the outside of the girders.
[0006]
For example, Japanese Laid-Open Patent Publication No. 6-136557 proposes a surface treatment method for a steel material in which a chromium sulfate aqueous solution or a copper sulfate aqueous solution is applied, followed by moisture drying and further coating with an organic resin. Furthermore, Japanese Patent Laid-Open No. 8-13158 proposes a steel surface treatment method in which an aqueous solution containing aluminum ions is applied, followed by moisture drying to further form an organic resin film. However, in the techniques described in JP-A-6-136557 and JP-A-8-13158, stable rust is formed in a short period of time, but the process is complicated and the surface treatment agent used is expensive. The development of a weathering steel material that does not require surface treatment has been desired.
[0007]
In this regard, Japanese Patent Laid-Open No. 63-255341 proposes a corrosion-resistant steel sheet for welded structures that has excellent salt damage resistance. This steel plate contains P: 0.04 to 0.15 wt%, Cu: 0.1 to 0.5 wt%, Cr: 3 to 10 wt%, Al: 0.02 to 1.0 wt%, and is used without coating even in corrosive environments involving sea salt particles It is supposed to be able to endure. However, this steel plate has a problem that the P content is high and the toughness and weldability are greatly reduced.
[0008]
Japanese Laid-Open Patent Publication No. 3-158436 proposes a beach weathering structural steel, which can adjust the contents of Mn, Cu, Cr, Ni, and Mo without adding a large amount of P. It is said that it has excellent weather resistance in the beach area and can omit painting on the steel sheet. However, this steel has a high Cr content, and there remains a problem of reduced toughness and weldability.
[0009]
JP-A-10-251797 discloses that C: 0.15% or less, Si: 0.7% or less, Mn: 0.2 to 1.5%, P: 0.03 to 0.15%, S: 0.02% or less, Al: 0.01 to 0.1% Cr: 0.1% or less, Ni: 0.4-4%, Cu: 0.4% or less, Mo: 0.05-1%, Sn: 0.01-0.5%, Sb: 0.01-3% containing, 0.05mg / dm 2 / day or more 10 mg / dm 2 / welding structural steel day less of salt has a high weather resistance in an environment where flying is proposed. However, the steel described in Japanese Patent Application Laid-Open No. 10-251797 contains a relatively high amount of C to ensure strength, and further contains 0.03% or more of P to improve strength and ensure corrosion resistance. There is a difficulty in weldability.
[0010]
[Problems to be solved by the invention]
In view of the above-mentioned problems of the prior art, the present invention retains excellent beach weather resistance without sacrificing toughness and weldability even in an environment where there is a lot of salt in the beach area, etc., and there is no rain, paint, surface treatment It is an object of the present invention to provide a highly weather-resistant steel material having excellent beach weather resistance that does not require the above.
[0011]
[Means for Solving the Problems]
In order to achieve the above-described problems, the present inventors have intensively studied a rust layer formed on a weather-resistant steel material. As a result, the present inventors obtained the following knowledge about the rust layer formed on the weathering steel.
The initial rust layer of weathering steel is mainly composed of γ-FeOOH and Fe 3 O 4 . The rust layer is reduced by γ-FeOOH and Fe 3 O 4 due to repeated dry and wet corrosion reactions over several years, and is mainly composed of amorphous rust at the X-ray diffraction level. Further, the rust layer occupies many amorphous rusts whose crystal system cannot be specified even at the TEM (transmission electron microscope) observation level, and it is preferable from the viewpoint of weather resistance that the rust layer is in such a state.
[0012]
However, in the rust layer formed on weathering steel exposed in the beach area, rust-like γ-FeOOH or α-FeOOH is mainly used as rust particles at the TEM observation level. The formation of these ridge-like rust particles creates voids in the rust layer, and thus the rust layer has a structure that allows easy passage of water, oxygen, and Cl ions. Therefore, in order to improve the beach weather resistance, it has been found that it is important to use a rust layer that suppresses the formation of these ridge-like rust particles.
[0013]
Therefore, the present inventors have intensively studied a method for suppressing the formation of ridge-like rust particles. As a result, it was found that by adding Sb to the steel, the formation of rust-like rust particles was suppressed and a rust layer mainly composed of amorphous rust was observed even at the TEM observation level. Further, the present inventors have reduced the C content to an extremely low carbon region, and further reduced the P content to 0.030% or less, preferably less than 0.025%, thereby improving the weldability of the weathering steel material, in particular. The new knowledge that the weldability in high heat input welding is remarkably improved was obtained.
[0014]
The present invention has been completed based on the above findings and further studies.
That is, the present invention is mass%, C: 0.001 to 0.025%, Si: 0.60% or less, Mn: 0.1 to 3.0%, P: 0.005 to 0.030%, S: 0.01% or less, Al: 0.10% or less, Cu : 0.1 to 1.5%, Ni: 0.1 to 6.0%, Sb: 0.005 to 1.0%, a highly weathering steel material characterized by having a composition comprising the balance Fe and inevitable impurities.
[0015]
Moreover, in this invention, in addition to the said composition, 1 type (s) or 2 or more types chosen from Mo: 0.005-0.5%, W: 0.005-1.0%, Co: 0.005-1.0% are further comprised by the mass%. Further, in the present invention, in addition to the above-mentioned compositions, Nb: 0.005 to 0.20%, Ti: 0.005 to 0.20%, V: 0.005 to 0.20%, B: 0.0001 to 0.0050% It is preferable to contain one or more selected from among the above, and in the present invention, in addition to each of the above-mentioned compositions, by mass%, REM: 0.02% or less, Ca: 0.02% or less It is preferable to contain 1 type or 2 types chosen from these.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The reason for limiting the components of the steel of the present invention will be described. Hereinafter, mass% is simply referred to as%.
C: 0.001 to 0.025%
C is an element that increases the strength, and in order to ensure the desired strength, 0.001% or more of content is required, but if it exceeds 0.025%, toughness and weldability deteriorate. Therefore, C is limited to the range of 0.001 to 0.025%.
[0017]
Si: 0.60% or less
Si is an element that acts as a deoxidizer and further increases the strength of the steel, but if contained in a large amount exceeding 0.60%, toughness and weldability are deteriorated. For this reason, Si was limited to 0.60% or less. In addition, Preferably it is 0.10 to 0.30%.
Mn: 0.1-3.0%
Mn is an element that greatly contributes to the increase in strength and toughness of steel, and in order to ensure the desired strength, the present invention needs to contain 0.1% or more, but if it contains more than 3.0% in large quantities It adversely affects toughness and weldability. For this reason, Mn was limited to the range of 0.1 to 3.0%. In addition, when high toughness is required in cold districts or the like, lowering Mn is effective, and it is preferable to set it to 0.10 to 0.50%.
[0018]
P: 0.005 to 0.030%
P is an element that densifies the rust particles and improves the weather resistance. In the present invention, P is required to be contained in an amount of 0.005% or more. However, if the content exceeds 0.030%, the weldability is significantly deteriorated. For this reason, P was limited to the range of 0.005 to 0.030%. In the present invention, by reducing the C content to an extremely low carbon region and further reducing the P content to 0.030% or less, preferably less than 0.025%, the weldability in high heat input welding is remarkably improved. The In addition, Preferably it is 0.005-0.020%.
[0019]
S: 0.01% or less Since S deteriorates the weather resistance and further deteriorates the weldability and toughness, in the present invention, it is preferable to reduce S as much as possible, but up to 0.01% is acceptable. In addition, Preferably it is 0.005% or less.
Al: 0.10% or less
Al is added as a deoxidizer, but if it exceeds 0.10%, the weldability is adversely affected. Therefore, the upper limit of Al is 0.10%. In addition, Preferably it is 0.010 to 0.050%.
[0020]
Cu: 0.1-1.5%
Cu is an element that densifies the rust particles and improves the weather resistance, and in the present invention, it is necessary to contain 0.1% or more. On the other hand, if the content exceeds 1.5%, hot workability is hindered, and the effect of improving weather resistance is saturated. For this reason, Cu was limited to the range of 0.1 to 1.5%. In addition, Preferably it is 0.10 to 0.60%.
[0021]
Ni: 0.1-6.0%
Ni is an element that densifies the rust particles and improves the weather resistance. In the present invention, Ni is required to be contained in an amount of 0.1% or more. On the other hand, if the content exceeds 6.0%, the effect is saturated and an effect commensurate with the content cannot be expected, which is economically disadvantageous. For this reason, Ni was made into the range of 0.1 to 6.0%. When the amount of flying salt is large, it is preferably 2.0% or more, and when the amount of flying salt is small, it is preferably less than 2.0%.
[0022]
Sb: 0.005 to 1.0%
In the present invention, it is the most important element. Sb is a rust layer and has an effect of suppressing formation of ridge-like rust particles and mainly using the rust layer as an amorphous rust. Such an effect is recognized when the content is 0.005% or more. However, if the content exceeds 1.0%, the effect is saturated and an effect commensurate with the content is not recognized. For this reason, Sb was limited to the range of 0.005 to 1.0%. In addition, Preferably it is 0.005-0.7%.
[0023]
One or more selected from Mo: 0.005 to 0.5%, W: 0.005 to 1.0%, Co: 0.005 to 1.0%
Mo, W, and Co are all elements that improve the weather resistance, and can be selected from one or more as required.
Mo: 0.005 to 0.5%
Mo is an element that improves the weather resistance and further increases the strength. However, if it is less than 0.005%, its effect is small. On the other hand, if the content exceeds 0.5%, the effect is saturated and an effect commensurate with the content is not recognized, which is economically disadvantageous. For this reason, Mo is preferably limited to a range of 0.005 to 0.5%. In addition, from the viewpoint of toughness, the range of 0.005 to 0.35% is more preferable.
[0024]
W: 0.005 to 1.0%
W is an element that improves the weather resistance and further increases the strength. However, if it is less than 0.005%, its effect is small. On the other hand, if the content exceeds 1.0%, the effect is saturated and an effect commensurate with the content is not recognized, which is economically disadvantageous. For this reason, W is preferably limited to a range of 0.005 to 1.0%. In addition, it is more preferable to set it as 0.005 to 0.6% of range from an economical viewpoint.
[0025]
Co: 0.005 to 1.0%
Co is an element that improves the weather resistance, but its effect is small when the content is less than 0.005%. On the other hand, if the content exceeds 1.0%, the effect is saturated and an effect commensurate with the content is not recognized, which is economically disadvantageous. For this reason, Co is preferably limited to a range of 0.005 to 1.0%. In addition, it is more preferable to set it as 0.005 to 0.6% of range from an economical viewpoint.
[0026]
Nb: 0.005 to 0.20%, Ti: 0.005 to 0.20%, V: 0.005 to 0.20%, B: One or more selected from 0.0001 to 0.0050%
Nb, Ti, V, and B are elements that increase the strength of the steel material, and may contain one or more as necessary.
Nb, Ti, and V are all contained at 0.005% or more, and B is effective at 0.0001% or more, but Nb, Ti, and V each exceed 0.20%, and B exceeds 0.0050%. Even if contained, the effect is saturated, and an effect commensurate with the content cannot be expected, which is economically disadvantageous. For this reason, it is preferable that Nb, Ti, and V are all limited to 0.005% to 0.20% and B is limited to 0.0001 to 0.0050%.
[0027]
One or two types selected from REM: 0.02% or less, Ca: 0.02% or less
REM and Ca are elements that improve weldability, and can be selected and contained as necessary. Such an effect becomes prominent when the content of REM is 0.001% or more and Ca is 0.001% or more. However, when both REM and Ca are contained in a large amount exceeding 0.02%, the cleanliness of the steel material is deteriorated. For this reason, it is preferable to limit to REM: 0.02% or less and Ca: 0.02% or less.
[0028]
The balance other than the components described above is Fe and inevitable impurities.
As unavoidable impurities, Cr: 0.05% or less, N: 0.010% or less, and O: 0.010% or less are acceptable.
Cr has been said to be an element that improves the weather resistance, but the improvement in weather resistance is in a low-salt environment, and in a high-salt environment such as the beach area targeted by the present invention, Conversely, it is an element that degrades the weather resistance. For this reason, although it does not dare add in this invention, 0.05% is permissible.
[0029]
The steel material of the present invention is melted by a generally known melting method such as a converter or an electric furnace, and is made into a steel material by a continuous casting method or an ingot forming method. Moreover, you may implement vacuum degassing refining etc. as a melting method.
Subsequently, these steel materials are heated in a heating furnace or the like, or directly rolled without being heated into a desired shape.
[0030]
【Example】
Steels having the chemical components shown in Table 1 were melted in a converter and made into slabs by a continuous casting method. Subsequently, these slabs were heated and formed into thick steel plates having a width of 25 mm × 2500 mm by hot rolling. These thick steel plates were examined for tensile properties, toughness and weldability.
For tensile properties, JIS No. 4 tensile test specimens were collected from the total thickness (C direction) of each steel plate, and the yield strength YS, tensile strength TS, and elongation El were measured in accordance with the provisions of JIS Z 2241. .
[0031]
As for toughness, JIS No. 4 impact test specimens were collected from 1 / 2T (C direction) of each thick steel plate, and Charpy impact test was conducted at a test temperature of -5 ° C in accordance with the provisions of JIS Z 2242. vE- 5 was determined.
For weldability, specimens were taken from each thick steel plate and given a reproducible thermal cycle equivalent to 1 mm heat input at a heat input of 100 kJ / cm, followed by a Charpy impact test at a test temperature of -5 ° C, and the absorbed energy vE -5 was sought.
[0032]
In addition, 5 mm x 50 mm x 100 mm corrosion test specimens were taken from each thick steel plate, and after shot blasting, they were subjected to an atmospheric exposure test to evaluate beach weather resistance.
For the atmospheric exposure test, select a coastal area with an incoming salt content of 0.8 mg / dm 2 / day (measured by the JIS Z 2381 gauze method), and place the test piece's ground iron surface horizontally upwards under conditions without rain. And exposed for one year. After the exposure test, the rust layer formed on the surface of the ground iron was removed, the weight reduction amount of the test piece was measured, and converted into the plate thickness reduction amount.
[0033]
The results are shown in Table 2.
[0034]
[Table 1]
[Table 2]
All of the examples of the present invention are excellent in strength, toughness and weldability, and the thickness reduction amount is 29 to 45 μm, which is remarkably reduced compared with 143 μm of the conventional example (steel plate No. 12). It can be seen that has excellent weather resistance.
On the other hand, the comparative examples (steel plates No. 8, No. 10) in which the Sb content deviates from the lower limit of the range of the present invention have large plate thickness reduction amounts of 102 and 145 μm, respectively, and the weather resistance is deteriorated. The comparative example (steel plate No. 9) shows the same reduction in sheet thickness as the present invention example (steel plate No. 3) with a low Sb content of 0.89% despite the high Sb content of 1.25%. It shows that the effect is saturated when it is outside the scope of the present invention. In addition, the thickness reduction amount of the comparative example (steel plate No. 11) whose P content is out of the range of the present invention is very small as 26 μm, but the toughness and weldability are deteriorated. .
[0037]
In the comparative example (steel plate No. 15), C and P are outside the scope of the present invention, and the weldability is deteriorated.
In the comparative examples (steel plates No. 13 and No. 14), Cu and Ni are out of the scope of the present invention, respectively, and the weather resistance is deteriorated.
[0038]
【The invention's effect】
As is apparent from the above description, according to the present invention, it is possible to provide a weather-resistant steel material that can maintain weather resistance in an environment having a high salinity such as a beach area. When these steel materials are applied to structures such as bridges, it is possible to omit painting, surface treatment, etc., and the economic effect of reducing maintenance costs can be expected.
Claims (4)
Ｃ：0.001 〜0.025 ％、 Si：0.60％以下、
Mn：0.1 〜3.0 ％、 Ｐ：0.005 〜0.030 ％、
Ｓ：0.01％以下、 Al：0.10％以下、
Cu：0.1 〜1.5 ％、 Ni：0.1 〜6.0 ％、
Sb：0.005 〜1.0 ％
を含み、残部Fe及び不可避的不純物からなる組成を有することを特徴とする高耐候性鋼材。% By mass
C: 0.001 to 0.025%, Si: 0.60% or less,
Mn: 0.1 to 3.0%, P: 0.005 to 0.030%,
S: 0.01% or less, Al: 0.10% or less,
Cu: 0.1-1.5%, Ni: 0.1-6.0%,
Sb: 0.005 to 1.0%
And having a composition consisting of the balance Fe and inevitable impurities.
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| JP4677714B2 (en) * | 2003-05-15 | 2011-04-27 | 住友金属工業株式会社 | Steel materials for bridges with excellent beach weather resistance and structures using the same |
| JP4586489B2 (en) * | 2004-10-22 | 2010-11-24 | 住友金属工業株式会社 | Steel and structures with excellent beach weather resistance |
| JP5201806B2 (en) * | 2006-05-12 | 2013-06-05 | 日本発條株式会社 | Coated steel with excellent corrosion resistance and corrosion fatigue resistance |
| KR100775339B1 (en) * | 2006-11-21 | 2007-11-08 | 주식회사 포스코 | Cold rolled steel sheet having excellent in-plane anisotropy and workability and the method for manufacturing the same |
| JP5812268B2 (en) * | 2011-07-29 | 2015-11-11 | Ｊｆｅスチール株式会社 | Steel offshore structure |
| CN114774777A (en) * | 2022-03-28 | 2022-07-22 | 包头钢铁（集团）有限责任公司 | Preparation method of rare earth treated weathering structural steel Q355NH |
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| JPS5479115A (en) * | 1977-12-07 | 1979-06-23 | Nippon Steel Corp | Steel for corrosion resistant expanded metal |
| JPS609588B2 (en) * | 1980-04-01 | 1985-03-11 | 新日本製鐵株式会社 | Pitting corrosion resistant low alloy steel |
| JPH0925536A (en) * | 1995-07-06 | 1997-01-28 | Sumitomo Metal Ind Ltd | Acid dew point corrosion resistant steel |
| JPH10251797A (en) * | 1997-03-10 | 1998-09-22 | Nkk Corp | Steel for welded structure, excellent in atmospheric corrosion resistance and its production |
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