JP7261364B1 - steel plate - Google Patents
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- JP7261364B1 JP7261364B1 JP2023007599A JP2023007599A JP7261364B1 JP 7261364 B1 JP7261364 B1 JP 7261364B1 JP 2023007599 A JP2023007599 A JP 2023007599A JP 2023007599 A JP2023007599 A JP 2023007599A JP 7261364 B1 JP7261364 B1 JP 7261364B1
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 68
- 239000010959 steel Substances 0.000 title claims abstract description 68
- 239000011701 zinc Substances 0.000 claims abstract description 33
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims abstract description 26
- 229910052725 zinc Inorganic materials 0.000 claims abstract description 26
- 239000003973 paint Substances 0.000 claims abstract description 16
- 239000012535 impurity Substances 0.000 claims abstract description 14
- 229910000859 α-Fe Inorganic materials 0.000 claims description 19
- 229910001563 bainite Inorganic materials 0.000 claims description 18
- 229910000734 martensite Inorganic materials 0.000 claims description 9
- 229910001562 pearlite Inorganic materials 0.000 claims description 8
- 238000005260 corrosion Methods 0.000 abstract description 83
- 230000007797 corrosion Effects 0.000 abstract description 79
- 239000011248 coating agent Substances 0.000 abstract description 43
- 238000000576 coating method Methods 0.000 abstract description 43
- 229910052802 copper Inorganic materials 0.000 abstract description 4
- 239000000463 material Substances 0.000 description 36
- 230000000694 effects Effects 0.000 description 30
- 229910052761 rare earth metal Inorganic materials 0.000 description 21
- 238000005096 rolling process Methods 0.000 description 20
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 15
- 238000012360 testing method Methods 0.000 description 14
- 230000009467 reduction Effects 0.000 description 13
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- 235000013339 cereals Nutrition 0.000 description 10
- 238000001816 cooling Methods 0.000 description 9
- 239000013078 crystal Substances 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 8
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 8
- 238000000034 method Methods 0.000 description 7
- 239000010953 base metal Substances 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- 239000000047 product Substances 0.000 description 6
- 239000000126 substance Substances 0.000 description 6
- 229910001566 austenite Inorganic materials 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 5
- 238000010828 elution Methods 0.000 description 5
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- 150000003839 salts Chemical class 0.000 description 5
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- 150000001247 metal acetylides Chemical class 0.000 description 4
- 238000009736 wetting Methods 0.000 description 4
- 230000001133 acceleration Effects 0.000 description 3
- 230000002411 adverse Effects 0.000 description 3
- 239000010779 crude oil Substances 0.000 description 3
- 238000000151 deposition Methods 0.000 description 3
- 230000001976 improved effect Effects 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- 229910052759 nickel Inorganic materials 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 230000001681 protective effect Effects 0.000 description 3
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- 229920005989 resin Polymers 0.000 description 3
- 239000011347 resin Substances 0.000 description 3
- 238000010998 test method Methods 0.000 description 3
- 230000009466 transformation Effects 0.000 description 3
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 2
- -1 REM ions Chemical class 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 229910052787 antimony Inorganic materials 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 230000001747 exhibiting effect Effects 0.000 description 2
- 239000011737 fluorine Substances 0.000 description 2
- 229910052731 fluorine Inorganic materials 0.000 description 2
- 238000007602 hot air drying Methods 0.000 description 2
- 239000003112 inhibitor Substances 0.000 description 2
- 230000000977 initiatory effect Effects 0.000 description 2
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- 230000003472 neutralizing effect Effects 0.000 description 2
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- 239000007921 spray Substances 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- 229910052684 Cerium Inorganic materials 0.000 description 1
- 240000007594 Oryza sativa Species 0.000 description 1
- 235000007164 Oryza sativa Nutrition 0.000 description 1
- 229910000746 Structural steel Inorganic materials 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 229910000870 Weathering steel Inorganic materials 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 229910052785 arsenic Inorganic materials 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 238000004210 cathodic protection Methods 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
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- 238000011109 contamination Methods 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 230000032798 delamination Effects 0.000 description 1
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- 239000003822 epoxy resin Substances 0.000 description 1
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- 229910052739 hydrogen Inorganic materials 0.000 description 1
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- 229910052746 lanthanum Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 229910001425 magnesium ion Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
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- 229910052758 niobium Inorganic materials 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
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- 238000010422 painting Methods 0.000 description 1
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- 230000035515 penetration Effects 0.000 description 1
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- 229910052698 phosphorus Inorganic materials 0.000 description 1
- XNGIFLGASWRNHJ-UHFFFAOYSA-L phthalate(2-) Chemical compound [O-]C(=O)C1=CC=CC=C1C([O-])=O XNGIFLGASWRNHJ-UHFFFAOYSA-L 0.000 description 1
- 229920000647 polyepoxide Polymers 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
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- 150000002910 rare earth metals Chemical class 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 235000009566 rice Nutrition 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 239000005413 snowmelt Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- Heat Treatment Of Steel (AREA)
Abstract
【課題】ジンクリッチペイント等の塗装を行って耐食性を向上できる鋼板であって、塗装耐久性に優れた鋼鈑を提供する。【解決手段】Ｃ：０．０２～０．１０質量％、Ｓｉ：０．１０～０．５０質量％、Ｍｎ：０．３０～２．００質量％、Ｃｕ：０．４０質量％～１．００質量％、Ｎｉ：０．４０～１．００質量％、Ｓ：０．０１０質量％以下（０質量％を含む）、Ｐ：０．０３０質量％以下（０質量％を含む）、Ｃｒ：４．００質量％以下（０質量％を含む）、Ｔｉ：０．０２～０．０７質量％、Ａｌ：０．０１０～０．０７０質量％、Ｂ：０．０００５～０．００３０質量％、Ｎ：０．００１０～０．０１００質量％、Ｃａ：０．００５０質量％以下（０質量％を含む）、Ｔａ：０．０１～０．２０質量％、ならびにＭｇ：０．０５質量％以下（０質量％を含まず）およびＲＥＭ：０．０５質量％以下（０質量％を含まず）の一方または両方を含み、残部がＦｅおよび不可避不純物からなる鋼板である。【選択図】なし[Problem] To provide a steel plate which can be coated with zinc-rich paint or the like to improve its corrosion resistance and which has excellent coating durability. SOLUTION: C: 0.02 to 0.10 mass %, Si: 0.10 to 0.50 mass %, Mn: 0.30 to 2.00 mass %, Cu: 0.40 mass % to 1.0 mass %. 00% by mass, Ni: 0.40 to 1.00% by mass, S: 0.010% by mass or less (including 0% by mass), P: 0.030% by mass or less (including 0% by mass), Cr: 4.00% by mass or less (including 0% by mass), Ti: 0.02 to 0.07% by mass, Al: 0.010 to 0.070% by mass, B: 0.0005 to 0.0030% by mass, N: 0.0010 to 0.0100% by mass, Ca: 0.0050% by mass or less (including 0% by mass), Ta: 0.01 to 0.20% by mass, and Mg: 0.05% by mass or less ( 0% by mass) and REM: 0.05% by mass or less (excluding 0% by mass), or both, with the balance being Fe and unavoidable impurities. [Selection figure] None
Description
本開示は、鋼板、とりわけ例えば橋梁等の耐食性を要する用途に用いることができる鋼板に関する。 TECHNICAL FIELD The present disclosure relates to steel sheets, particularly steel sheets that can be used in applications requiring corrosion resistance, such as bridges.
橋梁に用いる鋼板に例示されるように、耐食性を有する鋼板は従来から広く腐食環境で用いられている。例えば、Ｃｒ、Ｃｕ、Ｎｉ、Ｐ等の化学成分を適量添加した耐候性鋼材として日本工業規格（ＪＩＳ）には溶接構造用耐候性熱間圧延鋼材（ＳＭＡ：ＪＩＳ Ｇ ３１１４）と高耐候性圧延鋼材（ＳＰＡ：ＪＩＳＧ ３１２５）の二種が規定されている。これらは塗装を施さずに用いることができるが、より耐食性を向上させることを目的として塗装を施されて用いられることも一般的に行われている。
塗装用耐候性鋼として以下に示す特許文献１～３に係る鋼板が知られている。
Corrosion-resistant steel plates have been widely used in corrosive environments, as exemplified by steel plates used for bridges. For example, the Japanese Industrial Standards (JIS) define weather-resistant hot-rolled steel materials for welded structures (SMA: JIS G 3114) and high-weather-resistant rolled Two types of steel (SPA: JISG 3125) are specified. Although these can be used without coating, they are generally used with coating for the purpose of further improving corrosion resistance.
Steel sheets according to Patent Documents 1 to 3 shown below are known as weathering steel for painting.
特許文献１は、Ｓｉ量を適正な範囲に調整したうえで、Ｃｕ、Ｎｉ、ＳｎおよびＳｂを微量複合添加し、さらにＷを添加することによって、塗装耐久性を向上できる、すなわち再塗装までの期間を延ばすことができ、メンテナンスコストを低減できる鋼板を開示している。 In Patent Document 1, after adjusting the amount of Si to an appropriate range, a trace amount of Cu, Ni, Sn and Sb are added in combination, and further W is added to improve the coating durability. Disclosed is a steel sheet that can extend the life and reduce maintenance costs.
特許文献２は、亜鉛含有被膜をプライマとする鋼材の耐孔食性の向上に関する。Ｓｎ添加により、酸化剤として働く腐食界面のＦｅ３＋の濃度を低下させ、孔食を抑制し、塗装メンテナンスコストを低減できる鋼板を開示している。 Patent Literature 2 relates to improving the pitting corrosion resistance of a steel material primed with a zinc-containing coating. A steel sheet is disclosed in which the addition of Sn reduces the concentration of Fe 3+ at the corrosion interface, which acts as an oxidizing agent, suppresses pitting corrosion, and reduces coating maintenance costs.
特許文献３は、Ｃｕ、ＮｉおよびＴｉを適正量添加することにより錆の緻密化を図り、さらにＣｒ量を低減することにより塗装欠陥部における腐食を抑制できる鋼板を開示している。 Patent Literature 3 discloses a steel sheet capable of densifying rust by adding appropriate amounts of Cu, Ni, and Ti, and further suppressing corrosion in coating defects by reducing the amount of Cr.
また、特許文献４は塗装および電気防食を施さなくても優れた耐食性を示す鋼板を開示している。より詳細には、原油タンカー、貨物船、貨客船、客船、軍艦等の船舶において、主要な構造材として用いられる船舶用鋼板に関するものであり、海水による塩分および高温高湿に曝される環境下における耐食性に優れている。硫黄分を含有する原油と接触するような厳しい腐食環境下でも良好な耐食性を示すことから、殊に原油タンカーのタンク構造材として有用である。特許文献に係る鋼板では、Ｃｕ、Ｃｒ、Ｎｉといった耐食性元素の量が規定され、さらにパーライト、ベイナイト、マルテンサイト、フェライトの体積比、およびパーライトのアスペクト比が規定されている。 Further, Patent Document 4 discloses a steel sheet that exhibits excellent corrosion resistance even without coating and cathodic protection. More specifically, it relates to marine steel plates used as main structural materials in ships such as crude oil tankers, cargo ships, cargo-passenger ships, passenger ships, and warships. Excellent corrosion resistance. Since it exhibits good corrosion resistance even in severe corrosive environments such as contact with sulfur-containing crude oil, it is particularly useful as a tank structural material for crude oil tankers. In the steel sheet according to the patent document, the amounts of corrosion-resistant elements such as Cu, Cr, and Ni are specified, and the volume ratio of pearlite, bainite, martensite, and ferrite, and the aspect ratio of pearlite are specified.
上述のＪＩＳ Ｇ ３１１４溶接構造用耐候性熱間圧延鋼材は、海岸および融雪塩がまかれる地域といった飛来塩分量が多い環境ではうろこ状錆の形成または層状剥離等が生ずることから用いることができない。また、Ｎｉ量を増加させて耐食性を向上させた鋼板があるが、これらも飛来塩分量が多い地域では適用できない。またコストが高くなるという問題を有する。 The above-mentioned JIS G 3114 welded structure weather-resistant hot-rolled steel cannot be used in environments with a large amount of airborne salt, such as coastal areas and areas where snowmelt salt is sprinkled, because of the formation of scaly rust or delamination. Also, there are steel sheets with improved corrosion resistance by increasing the amount of Ni, but these cannot be applied to areas with a large amount of airborne salt. Moreover, there is a problem that the cost becomes high.
そのため、塗装による防食が必要となる。塗装として、従来はA系塗装（一般錆止め＋フタル酸樹脂）が用いられていたが、近年は防食性能向上を目的に、防食下地にジンクリッチプライマ、上塗りに紫外線および高温下での耐久性に優れたフッ素系樹脂を適用し、膜厚を増加させたC系塗装が施されることが多くなっている。
なお、ジンクリッチプライマとは亜鉛を多量（７０質量％以上）に含んだ下塗り塗料（ジンクリッチペイント）が１５～２５μmの膜厚で塗装されたものを指す場合が多い。これ以外にも厚膜型ジンクリッチペイントと呼ばれる５０～７５μmの膜厚の塗装もある。本明細書においては「ジンクリッチペイント」は膜厚によらず亜鉛を多量に（７０質量％以上）含んだ下塗り塗装を意味する。
Therefore, anticorrosion by coating is required. Conventionally, A-type coating (general rust prevention + phthalate resin) was used as the coating, but in recent years, with the aim of improving anti-corrosion performance, zinc-rich primer is used as the anti-corrosion base and durability under ultraviolet rays and high temperatures is used as the top coat. It is becoming more common to apply excellent fluorine-based resin and apply C-based coating with increased film thickness.
In many cases, the zinc-rich primer refers to an undercoat paint (zinc-rich paint) containing a large amount (70% by mass or more) of zinc applied to a film thickness of 15 to 25 μm. In addition to this, there is also a coating with a film thickness of 50 to 75 μm called a thick film type zinc rich paint. As used herein, "zinc-rich paint" means an undercoat paint containing a large amount (70% by mass or more) of zinc regardless of the film thickness.
ジンクリッチペイントのような顕著に耐食性を向上できる塗装を用いてもなお、塗装の疵部および膜厚が局所的に薄い箇所といった塗膜欠陥部においては、鋼材の腐食が塗膜下等で進行する。そして、腐食が進行することで、外観劣化、腐食減肉部での構造的強度低下による損傷事故などのリスクがあるため定期的な再塗装が必要となる。 Even if a coating such as zinc-rich paint that can significantly improve corrosion resistance is used, corrosion of the steel progresses under the coating film in areas where the coating film is defective, such as scratches and locally thin areas. do. As the corrosion progresses, there is a risk of damage such as deterioration of the appearance and deterioration of structural strength at the corrosion-reduced portion, which necessitates periodic repainting.
しかし、再塗装はコストがかかるため、腐食を抑制することで再塗装を最小限に抑え、メンテナンスコストを抑制したいとの要望がある。とりわけ、橋梁の中でも桁端部では、路面からの漏水が多く閉塞的な構造を有するため湿潤環境となり、腐食が特に激しくなるとともに、構造的に点検およびメンテナンスを行いにくい。したがって、橋梁桁端部といった特に厳しい腐食環境で且つメンテナンスが難しい箇所においても十分な塗装耐久性を発揮し、塗装メンテナンスコストを低減できる鋼板が求められている。 However, since repainting is costly, there is a desire to minimize repainting and reduce maintenance costs by suppressing corrosion. In particular, girder ends of bridges have a closed structure due to a large amount of water leakage from the road surface. Therefore, there is a demand for a steel sheet that exhibits sufficient coating durability even in locations such as bridge girder ends that are subject to particularly severe corrosive environments and that are difficult to maintain, and that can reduce coating maintenance costs.
上述の特許文献１～３に係る鋼板では、橋梁桁端部のような濡れ時間が長く、特に厳しい腐食環境下での塗装耐久性が十分でない虞がある。特許文献１～３の鋼板は、腐食に伴い、鋼材に含まれる微量合金成分が溶出し、その溶出した合金成分により錆相を緻密化・安定化することで錆の環境遮断性（Ｃｌ－、Ｏ２、Ｈ２Ｏ等腐食因子の侵入阻害効果）を向上させ、腐食の進行を遅延させることで、塗膜耐久性を向上するものである。腐食により母材の溶出がある程度進行しないと、母材に添加された耐食成分が供給されないため、効果を発現せず（腐食の起点そのものを低減するものでは無く）、安定さびが形成するまでの初期の腐食を抑制できないといった問題もさらにある。 The steel sheets according to Patent Documents 1 to 3 described above have a long wetting time, such as at the ends of bridge girders, and may not have sufficient coating durability especially under severe corrosive environments. In the steel sheets of Patent Documents 1 to 3, trace alloy components contained in the steel material are eluted with corrosion, and the eluted alloy components densify and stabilize the rust phase, thereby improving the environmental barrier properties of rust (Cl − , By improving the penetration inhibition effect of corrosive factors such as O 2 and H 2 O) and delaying the progress of corrosion, the durability of the coating film is improved. If the elution of the base metal does not proceed to some extent due to corrosion, the anti-corrosion component added to the base metal will not be supplied, so the effect will not be manifested (it will not reduce the starting point of corrosion itself), and it will take time until stable rust is formed. There is also the problem of not being able to control early corrosion.
特許文献４は、船舶の石油タンクおよびバラストタンクといった液体浸漬環境において塗装を施さずに使用することを前提とした鋼材であり、大気環境中およびジンクリッチプライマ等の塗布下で使用されることは考慮されていない。ジンクリッチプライマ塗布下では、初期にプライマ中の亜鉛の溶出が生じ、次いでＺｎ腐食生成物が形成することで環境遮断効果を発現するが、石油および海水等の液体浸漬環境においては、Ｚｎ腐食生成物が流出してしまうためにそもそもジンクリッチプライマの耐食効果が期待できない。一方、橋梁が使用される大気環境中ではＺｎ腐食生成物が鋼材および塗膜上に残存することで環境遮断効果を発現し、ひいては塗装耐久性向上に重要な役割を担う。すなわち、対象とする腐食のメカニズムが異なることから、引用文献４に記載の鋼板を用いても十分な塗装耐久性が得られない虞がある。 Patent Document 4 is a steel material that is intended to be used without coating in a liquid immersion environment such as oil tanks and ballast tanks of ships, and it is not possible to use it in an atmospheric environment or under the application of a zinc-rich primer or the like. not considered. When the zinc-rich primer is applied, the elution of zinc in the primer occurs initially, followed by the formation of Zn corrosion products, thereby exhibiting the environmental shielding effect. In the first place, the anti-corrosion effect of the zinc-rich primer cannot be expected because the material flows out. On the other hand, in the atmospheric environment where the bridge is used, the Zn corrosion products remain on the steel material and the coating film, thereby exhibiting an environmental shielding effect and playing an important role in improving coating durability. That is, since the target corrosion mechanisms are different, even if the steel sheet described in Cited Document 4 is used, there is a possibility that sufficient coating durability cannot be obtained.
本開示は、このような状況に鑑みてなされたものであり、ジンクリッチペイント等の塗装を行って耐食性を向上できる鋼板であって、塗装耐久性に優れた鋼板を提供することを目的とする。 The present disclosure has been made in view of such circumstances, and an object of the present disclosure is to provide a steel sheet that can be coated with zinc-rich paint or the like to improve corrosion resistance and has excellent coating durability. .
本発明の態様１は、
Ｃ ：０．０２質量％以上、０．１０質量％以下、
Ｓｉ：０．１０質量％以上、０．５０質量％以下、
Ｍｎ：０．３０質量％以上、２．００質量％以下、
Ｃｕ：０．４０質量％以上、１．００質量％以下、
Ｎｉ：０．４０質量％以上、１．００質量％以下、
Ｓ ：０．０１０質量％以下（０質量％を含む）、
Ｐ ：０．０３０質量％以下（０質量％を含む）、
Ｃｒ：４．００質量％以下（０質量％を含む）、
Ｔｉ：０．０２質量％以上、０．０７質量％以下、
Ａｌ：０．０１０質量％以上、０．０７０質量％以下、
Ｂ ：０．０００５質量％以上、０．００３０質量％以下、
Ｎ ：０．００１０質量％以上、０．０１００質量％以下、
Ｃａ：０．００５０質量％以下（０質量％を含む）、
Ｔａ：０．０１質量％以上、０．２０質量％以下、ならびに
Ｍｇ：０．０５質量％以下（０質量％を含まず）およびＲＥＭ：０．０５質量％以下（０質量％を含まず）の一方または両方、
を含み、残部がＦｅおよび不可避不純物からなる鋼板である。
Aspect 1 of the present invention is
C: 0.02% by mass or more and 0.10% by mass or less,
Si: 0.10% by mass or more and 0.50% by mass or less,
Mn: 0.30% by mass or more and 2.00% by mass or less,
Cu: 0.40% by mass or more and 1.00% by mass or less,
Ni: 0.40% by mass or more and 1.00% by mass or less,
S: 0.010% by mass or less (including 0% by mass),
P: 0.030% by mass or less (including 0% by mass),
Cr: 4.00% by mass or less (including 0% by mass),
Ti: 0.02% by mass or more and 0.07% by mass or less,
Al: 0.010% by mass or more and 0.070% by mass or less,
B: 0.0005% by mass or more and 0.0030% by mass or less,
N: 0.0010% by mass or more and 0.0100% by mass or less,
Ca: 0.0050% by mass or less (including 0% by mass),
Ta: 0.01% by mass or more and 0.20% by mass or less, and Mg: 0.05% by mass or less (excluding 0% by mass) and REM: 0.05% by mass or less (excluding 0% by mass) one or both of
A steel sheet containing and the balance being Fe and unavoidable impurities.
本発明の態様２は、板厚ｔ／４位置における金属組織がフェライトおよびベイナイトの一方または両方を含み、残部がパーライトおよび島状マルテンサイトの一方または両方であり、前記フェライトおよびベイナイトの最大結晶粒径が３０μｍ以下である態様１に記載の鋼板である。 In aspect 2 of the present invention, the metal structure at the plate thickness t/4 position contains one or both of ferrite and bainite, the remainder is one or both of pearlite and island martensite, and the largest grains of ferrite and bainite The steel sheet according to aspect 1, having a diameter of 30 μm or less.
本発明の態様３は、橋梁用鋼板である態様１または２に記載の鋼板である。 Aspect 3 of the present invention is the steel plate according to aspect 1 or 2, which is a steel plate for bridges.
本発明の態様４は、ジンクリッチペイントを施されてなる態様１～３のいずれかに記載の鋼板である。 Aspect 4 of the present invention is the steel sheet according to any one of Aspects 1 to 3, which is coated with zinc-rich paint.
本発明の１つの実施形態によれば、ジンクリッチペイント等の塗装を行って耐食性を向上できる鋼板であって、塗装耐久性に優れた鋼板を提供することができる。 According to one embodiment of the present invention, it is possible to provide a steel sheet that can be coated with zinc-rich paint or the like to improve corrosion resistance and that has excellent coating durability.
本発明者らは、上記課題を解決するため、鋭意検討した。その結果、所定の成分、とりわけ（１）所定量のＴａと、（２）所定量のＭｇおよび所定量のＲＥＭの一方または両方とを含有させることにより、塗装耐久性を大きく向上できることを見出した。 In order to solve the above problems, the inventors have made extensive studies. As a result, the inventors have found that the coating durability can be greatly improved by including predetermined components, particularly (1) a predetermined amount of Ta and (2) one or both of a predetermined amount of Mg and a predetermined amount of REM. .
Ｔａは腐食発生の起点となるＭｎＳ／鋼界面の面積を低減し、腐食の発生自体を抑制すること、また、同時に母材の電位を貴化する効果も有することを見出した。なお、従来Ｔａは金属組織微細化といった強度および靭性向上の観点から添加されるのが一般的であった。一部には耐食性の観点として、Ｔａの添加により鉄錆の微細化による環境遮断効果が図られている。具体的には、本発明と用途が異なるが、ラインパイプの耐サワー環境鋼材などでもＴａが添加されることがある。しかし鉄さびの緻密化を意図したものであり、本発明のように、母材の耐食性そのものを向上させる（腐食起点低減と電位貴化）効果を検討したものはない。 It was found that Ta reduces the area of the MnS/steel interface, which is the starting point of corrosion, and suppresses the occurrence of corrosion itself, and at the same time has the effect of making the potential of the base material noble. Conventionally, Ta has generally been added from the viewpoint of improving strength and toughness, such as refining the metal structure. In some cases, from the viewpoint of corrosion resistance, the addition of Ta has the effect of blocking the environment by miniaturizing iron rust. Specifically, although the application is different from that of the present invention, Ta may also be added to steel materials resistant to sour environments such as line pipes. However, this is intended to densify iron rust, and unlike the present invention, there is no study of the effect of improving the corrosion resistance itself of the base metal (reducing corrosion starting points and increasing the potential).
Ｍｇについては、腐食に伴い鋼板より溶出したＭｇイオンが、ジンクペイント由来のＺｎ腐食生成物の結晶子サイズを緻密化および安定化し、Ｚｎ腐食生成物による環境遮断効果を高める効果があることを見出した。
また、ＲＥＭについては、腐食に伴い鋼板より溶出したＲＥＭイオンが、母材／塗膜界面での腐食環境中性化による耐食性向上効果、および鋼材表層への沈着インヒビターの作用（保護被膜形成）を有することでジンクリッチプライマ中のＺｎ粒子の消耗および母材の溶出を抑制することを見出した。
Regarding Mg, it was found that Mg ions eluted from the steel sheet with corrosion densify and stabilize the crystallite size of Zn corrosion products derived from zinc paint, and have the effect of enhancing the environmental shielding effect of Zn corrosion products. rice field.
Regarding REM, the REM ions eluted from the steel sheet due to corrosion have the effect of improving corrosion resistance by neutralizing the corrosive environment at the base material / coating film interface, and the action of a deposition inhibitor on the steel material surface layer (protective film formation). It was found that the consumption of Zn particles in the zinc-rich primer and the elution of the base material can be suppressed by having it.
本発明に係る鋼板は、橋梁桁端部等の特に厳しい腐食環境での使用を前提とするため、腐食促進評価法である複合サイクル試験の試験条件は、従来よりも厳しい条件を設定する必要がある。すなわち、従来の腐食促進方法では実橋梁の桁端部といった厳しい腐食環境を模擬できないため、このような厳しい腐食環境において優位性を有する鋼板が得られたとしてもその優位性を検証できないといった問題があった。発明者らは、実際の橋梁における長期大気曝露試験より、橋梁桁端部における濡れ時間と腐食量の関係を調査し、それに基づき、ＪＩＳ－Ｋ－５６００－７－９：２００６ サイクルＤ法から湿潤時間を増加させ、乾燥時間を減少させたより厳しい腐食促進試験方法を新たに開発した。こうした、新たな腐食促進試験を適用することで初めて、上述のＴａ、ＭｇおよびＲＥＭが塗装耐久性向上に寄与することを明らかにし、本発明に至ったものである。
なお、この新しい腐食促進試験方法の技術思想を含む詳細については必要に応じて特願２０２２－１１１８４７号の明細書等を参照されたい。
以下、本発明の実施形態で規定する各要件について詳細に説明する。
Since the steel plate according to the present invention is assumed to be used in a particularly severe corrosive environment such as at the end of a bridge girder, it is necessary to set more severe conditions than conventional conditions for the combined cycle test, which is a method for evaluating accelerated corrosion. be. In other words, since the conventional corrosion acceleration method cannot simulate the severe corrosive environment such as the girder end of an actual bridge, even if a steel plate having superiority in such a severe corrosive environment is obtained, the superiority cannot be verified. there were. The inventors investigated the relationship between the wetting time and the amount of corrosion at the end of the bridge girder from a long-term atmospheric exposure test on an actual bridge. A new, more stringent accelerated corrosion test method was developed with increased time and decreased drying time. By applying such a new accelerated corrosion test, it was clarified for the first time that the above-mentioned Ta, Mg and REM contribute to the improvement of coating durability, leading to the present invention.
For details including the technical concept of this new accelerated corrosion test method, please refer to the specification of Japanese Patent Application No. 2022-111847 as necessary.
Each requirement defined in the embodiments of the present invention will be described in detail below.
１．化学組成
本発明の実施形態に係る鋼板は、以下に説明する化学組成を有することで優れた塗装耐久性を得ることができる。
とりわけ、以下の（１）および（２）の一方または両方を含有させることが塗装耐久性向上に大きく寄与する。
（１）Ｔａ：０．０１質量％以上、０．２０質量％以下。
（２）Ｍｇ：０．０５質量％以下（０質量％を含まず）およびＲＥＭ：０．０５質量％以下（０質量％を含まず）の一方または両方。
1. Chemical composition The steel sheet according to the embodiment of the present invention can obtain excellent coating durability by having the chemical composition described below.
In particular, containing one or both of the following (1) and (2) greatly contributes to the improvement of coating durability.
(1) Ta: 0.01% by mass or more and 0.20% by mass or less.
(2) one or both of Mg: 0.05% by mass or less (excluding 0% by mass) and REM: 0.05% by mass or less (excluding 0% by mass);
［Ｔａ：０．０１質量％以上、０．２０質量％以下］
Ｔａは、Ｔａ炭化物として析出し、腐食起点として作用するＭｎＳの周囲を被覆することで、腐食の発生を抑制（腐食起点を低減）する効果を有する。Ｔａはさらに鋼板（母材）の腐食電位を貴化し、腐食の発生を抑制する効果も有する。これらの効果を発揮するためにはＴａを０．０１質量％以上の含有させる必要がある。一方、含有量が過大になると効果が飽和する、コストの上昇を招く、および微細分散析出するＴａ炭化物が新たな腐食起点として作用する等の理由から、Ｔａ含有量の上限を０．２０質量％とした。Ｔａ含有量の上限は好ましくは０．１５質量％、さらに好ましくは０．１０質量％以下である。
[Ta: 0.01% by mass or more and 0.20% by mass or less]
Ta has the effect of suppressing the occurrence of corrosion (reducing the number of corrosion initiation points) by depositing as Ta carbides and covering the periphery of MnS acting as corrosion initiation points. Ta also has the effect of noblening the corrosion potential of the steel sheet (base material) and suppressing the occurrence of corrosion. In order to exhibit these effects, it is necessary to contain 0.01% by mass or more of Ta. On the other hand, if the content is excessive, the effect saturates, the cost increases, and finely dispersed and precipitated Ta carbides act as new corrosion starting points. and The upper limit of the Ta content is preferably 0.15% by mass, more preferably 0.10% by mass or less.
［Ｍｇ：０．０５質量％以下（０質量％を含まず）およびＲＥＭ：０．０５質量％以下（０質量％を含まず）の一方または両方］
本発明の実施形態に係る鋼板は、以下のｉ）およびｉｉ）のいずれか一方または両方を含有する。
ｉ）０．０５質量％以下（０質量％を含まず）のＭｇ
ｉｉ）０．０５質量％以下（０質量％を含まず）のＲＥＭ
[One or both of Mg: 0.05% by mass or less (excluding 0% by mass) and REM: 0.05% by mass or less (excluding 0% by mass)]
A steel sheet according to an embodiment of the present invention contains either one or both of i) and ii) below.
i) 0.05 wt% or less (not including 0 wt%) of Mg
ii) 0.05 wt% or less REM (not including 0 wt%)
Ｍｇは、母材の溶出が進行した際に溶出したＭｇがジンクリッチプライマ由来のＺｎ腐食生成物に供給されることで、保護性のＺｎ腐食生成物の体積比率を増大させ、腐食因子（Ｃｌ－、Ｈ２Ｏ、Ｏ２等）の母材への透過を抑制し（環境遮断効果を高め）、塗装耐久性を向上する。一方、過剰に添加されたＭｇは析出物として新たな腐食起点となる。このため、Ｍｇを添加する場合、その含有量は０．０５質量％以下（０質量％を含まず）とする。Ｍｇ含有量は好ましくは０．０１質量％以下（０質量％を含まず）、さらに好ましくは０．００６質量％以下（０質量％を含まず）である。
なお、本明細書において「０質量％を含まず」とは、当該元素が意図的に添加されていることを意味する。
一方、本明細書において「０質量％を含む」とは、意図的に添加しない実施形態に係る含有量、例えば不可避不純物レベルの含有量である場合を包含する（意図的に添加した場合を排除するものではない）ことを意味する。Ｍｇの通常の不純物レベルは０．０００１質量％未満であり、このため、本発明の実施形態ではＭｇの添加効果をより確実に発揮させるため、好ましくは、Ｍｇを０．０００１質量％以上含有させる。
Mg increases the volume ratio of the protective Zn corrosion products by supplying the eluted Mg to the Zn corrosion products derived from the zinc-rich primer when the elution of the base material progresses, and the corrosion factor (Cl - , H 2 O, O 2, etc.) permeation into the base material (enhances the environmental shielding effect) and improves the coating durability. On the other hand, excessively added Mg becomes a new corrosion starting point as a precipitate. Therefore, when Mg is added, its content should be 0.05% by mass or less (not including 0% by mass). The Mg content is preferably 0.01% by mass or less (excluding 0% by mass), more preferably 0.006% by mass or less (excluding 0% by mass).
In this specification, the expression "not including 0% by mass" means that the element is intentionally added.
On the other hand, in the present specification, "comprising 0% by mass" includes the content according to the embodiment that is not intentionally added, for example, the content at the level of unavoidable impurities (excluding the case of intentionally added not intended to). The normal impurity level of Mg is less than 0.0001% by mass. Therefore, in the embodiment of the present invention, preferably 0.0001% by mass or more of Mg is contained in order to more reliably exhibit the effect of adding Mg. .
ＲＥＭは母材／塗膜界面での腐食環境中性化による耐食性向上効果、および鋼材表層への沈着インヒビターの作用（保護被膜形成）を有することでジンクリッチプライマ中のＺｎ粒子の消耗および母材の溶出を抑制し、塗装耐久性を向上させる。一方、過剰に添加されたＲＥＭは析出物として新たな腐食起点となる。このためＲＥＭを含有する場合、その含有量は０．０５質量％以下（０質量％を含まず）とした。ＲＥＭの含有量は好ましくは、０．０１質量％以下（０質量％を含まず）、さらに好ましくは０．００５質量％以下（０質量％を含まず）である。なお、ＲＥＭは、ＬａおよびＣｅをはじめとした任意の希土類金属の１種または２種以上であってよく、ＲＥＭ含有量は、それぞれの希土類元素の含有量の合計量である。本明細書において「希土類元素」の定義はＹを含む。ＲＥＭの通常の不純物レベルは０．０００１質量％未満であり、このため、本発明の実施形態ではＲＥＭの添加効果をより確実に発揮させるため、好ましくは、ＲＥＭを０．０００１質量％以上含有させる。 REM has the effect of improving corrosion resistance by neutralizing the corrosive environment at the base metal/coating film interface and acting as a deposition inhibitor on the surface of steel materials (forming a protective film). Suppresses the elution of and improves paint durability. On the other hand, excessively added REM becomes a new corrosion starting point as a precipitate. Therefore, when REM is contained, its content is set to 0.05% by mass or less (not including 0% by mass). The content of REM is preferably 0.01% by mass or less (excluding 0% by mass), more preferably 0.005% by mass or less (excluding 0% by mass). REM may be one or more of any rare earth metals including La and Ce, and the REM content is the total content of each rare earth element. As used herein, the definition of "rare earth element" includes Y. The normal impurity level of REM is less than 0.0001% by mass. Therefore, in order to more reliably exhibit the effect of adding REM in the embodiment of the present invention, preferably 0.0001% by mass or more of REM is contained. .
［Ｃ：０．０２質量％以上、０．１０質量％以下］
Ｃは、鋼の強度を増加させる元素であり、構造用鋼としての所定の強度を確保するために、Ｃの含有量は０．０２質量％以上とする。一方、０．１０質量％を超えるＣの含有は靭性の低下を招く。このため、Ｃの含有量は０．０２～０．１０質量％の範囲とする。
[C: 0.02% by mass or more and 0.10% by mass or less]
C is an element that increases the strength of steel, and the content of C is made 0.02% by mass or more in order to ensure a predetermined strength as structural steel. On the other hand, the content of C exceeding 0.10% by mass causes a decrease in toughness. Therefore, the C content should be in the range of 0.02 to 0.10% by mass.
［Ｓｉ：０．１０質量％以上、０．５０質量％以下］
Ｓｉは、脱酸材として有効な元素である。また、Ｓｉは、母材強度の向上に有効な元素であり、これらの効果を発揮させるには、Ｓｉを０．１０質量％以上含有させる。しかし、Ｓｉ含有量が過剰になると、島状マルテンサイト（ＭＡ）が形成され母材強度と靭性の確保が困難となる。加えて、溶接熱影響部の靭性と溶接性の劣化を招きやすくなるので、Ｓｉ含有量は０．５０質量％以下とする。
[Si: 0.10% by mass or more and 0.50% by mass or less]
Si is an element effective as a deoxidizer. Moreover, Si is an element effective in improving the strength of the base material, and in order to exhibit these effects, Si is contained in an amount of 0.10% by mass or more. However, if the Si content becomes excessive, island-shaped martensite (MA) is formed, making it difficult to ensure the strength and toughness of the base material. In addition, the Si content is set to 0.50% by mass or less because it tends to cause deterioration of the toughness and weldability of the weld heat-affected zone.
［Ｍｎ：０．３０質量％以上、２．００質量％以下］
Ｍｎは、オーステナイトを安定化させ、変態温度を低温化させる元素である。また、Ｍｎは、低温変態による結晶粒径微細化効果による衝撃特性の確保に有効な元素である。さらに、Ｍｎは、焼入れ性を向上させて強度向上に有効である。これらの効果を発揮させるために、Ｍｎを０．３０質量％以上含有させる。しかし、Ｍｎを過剰に含有させると、伸び特性、低温靭性およびＨＡＺ靭性が劣化する。そのため、Ｍｎ含有量の上限は２．００質量％とする。
[Mn: 0.30% by mass or more and 2.00% by mass or less]
Mn is an element that stabilizes austenite and lowers the transformation temperature. Moreover, Mn is an element effective in securing impact properties due to the crystal grain size refinement effect of low-temperature transformation. Furthermore, Mn improves hardenability and is effective in improving strength. In order to exhibit these effects, 0.30% by mass or more of Mn is contained. However, excessive Mn content deteriorates elongation properties, low temperature toughness and HAZ toughness. Therefore, the upper limit of the Mn content is set to 2.00% by mass.
［Ｃｕ：０．４０質量％以上、１．００質量％以下］
Ｃｕは、溶接性、溶接熱影響部の靭性に大きな悪影響を及ぼすことなく、母材の強度および靭性を向上させるのに有効な元素である。これらの効果を有効に発揮させるには、Ｃｕを０．４０質量％以上含有させる。しかし、原料コストを低減する観点から、Ｃｕは少ない方がよい。そのため、Ｃｕ含有量は１．００質量％以下とする。
[Cu: 0.40% by mass or more and 1.00% by mass or less]
Cu is an effective element for improving the strength and toughness of the base metal without significantly adversely affecting the weldability and the toughness of the weld heat affected zone. In order to effectively exhibit these effects, 0.40% by mass or more of Cu is contained. However, from the viewpoint of reducing raw material costs, Cu should be as small as possible. Therefore, the Cu content is set to 1.00% by mass or less.
［Ｎｉ：０．４０質量％以上、１．００質量％以下］
Ｎｉは、溶接性、ＨＡＺ靭性に大きな悪影響を及ぼすことなく、母材の強度および靭性を向上させるのに有効な元素である。この効果を有効に発揮させるには、Ｎｉを０．４０質量％以上含有させる。しかし、原料コストを低減する観点から、Ｎｉは少ない方がよい。そのため、Ｎｉ含有量は１．００質量％以下とする。
[Ni: 0.40% by mass or more and 1.00% by mass or less]
Ni is an element effective in improving the strength and toughness of the base material without having a large adverse effect on weldability and HAZ toughness. In order to effectively exhibit this effect, 0.40% by mass or more of Ni is contained. However, from the viewpoint of reducing raw material costs, the smaller the Ni content, the better. Therefore, the Ni content is set to 1.00% by mass or less.
［Ｓ：０．０１０質量％以下（０質量％を含む）］
Ｓは、ＭｎＳを形成して衝撃特性と溶接熱影響部の靭性、更には母材伸びを劣化させる不可避不純物元素である。そのため、Ｓ含有量は０．０1０質量％以下に規制する。
[S: 0.010% by mass or less (including 0% by mass)]
S is an unavoidable impurity element that forms MnS and deteriorates the impact properties, the toughness of the weld heat affected zone, and the elongation of the base metal. Therefore, the S content is restricted to 0.010% by mass or less.
［Ｐ：０．０３０質量％以下（０質量％を含む）］
Ｐは、衝撃特性（母材靭性、曲げ加工後の靭性）と溶接熱影響部の靭性に悪影響を及ぼす不可避不純物元素である。そのため、Ｐ含有量を０．０３０質量％以下に規制する必要がある。
[P: 0.030% by mass or less (including 0% by mass)]
P is an unavoidable impurity element that adversely affects the impact properties (base material toughness, toughness after bending) and the toughness of the weld heat affected zone. Therefore, it is necessary to limit the P content to 0.030% by mass or less.
［Ｃｒ：４．００質量％以下（０質量％を含む）］
Ｃｒは、母材の耐食性を向上させる元素であることから添加してもよい。ただしＣｒは必須の元素でなく添加しなくてもよい。この場合でも製造上、０．０８質量％以下までは不可避不純物元素として混入する可能性がある。一方でＣｒは塗装欠陥部では、ｐH低下の原因となり、欠陥内での凝集水分の酸化性を促進することにより塗装－素地界面での隙間腐食を誘発する作用をもたらす。このためＣｒ含有量が０．０８質量％を超えるように意図的に添加する場合でもその含有量は４．００質量％以下とする。
[Cr: 4.00% by mass or less (including 0% by mass)]
Cr may be added because it is an element that improves the corrosion resistance of the base material. However, Cr is not an essential element and may be omitted. Even in this case, there is a possibility that up to 0.08% by mass or less may be mixed as an unavoidable impurity element in terms of production. On the other hand, Cr causes a decrease in pH at the coating defect portion, and promotes the oxidizability of the moisture condensed in the defect, thereby inducing crevice corrosion at the coating-substrate interface. Therefore, even when Cr content is intentionally added to exceed 0.08% by mass, the content should be 4.00% by mass or less.
［Ｔｉ：０．０２質量％以上、０．０７質量％以下］
Ｔｉは炭化物を生成することで母材の強度を向上させるのに有効であるとともに、生成錆を緻密化し安定錆層の生成を促進する効果がある。これら効果を有効に発揮させるに、Ｔｉを０．０２質量％以上含有させる。しかし、過剰に添加するとＴｉ炭化物生成により母材靱性が劣化することから、Ｔｉ含有量は０．０７質量％以下とする。
[Ti: 0.02% by mass or more and 0.07% by mass or less]
Ti is effective in improving the strength of the base material by forming carbides, and has the effect of densifying the formed rust and promoting the formation of a stable rust layer. In order to effectively exhibit these effects, 0.02% by mass or more of Ti is contained. However, if Ti is added excessively, the toughness of the base material deteriorates due to the formation of Ti carbides.
［Ａｌ：０．０１０質量％以上、０．０７０質量％以下］
Ａｌは、脱酸に必要な元素であり、０．０１０質量％以上含有させる。好ましくは０．０１５質量％以上含有させる。一方、Ａｌを過剰に含有させると、アルミナ系の粗大な介在物を形成し衝撃特性が低下する。そのため、Ａｌ含有量は０．０７０質量％以下とする。
[Al: 0.010% by mass or more and 0.070% by mass or less]
Al is an element necessary for deoxidation and is contained in an amount of 0.010% by mass or more. Preferably, it is contained in an amount of 0.015% by mass or more. On the other hand, if Al is contained excessively, alumina-based coarse inclusions are formed and the impact resistance is lowered. Therefore, the Al content is set to 0.070% by mass or less.
［B：０．０００５質量％以上、０．００３０質量％以下］
Ｂは、溶接熱影響部においてオーステナイト粒界に偏析し粒界からの粗大なフェライト析出を抑制し、ＨＡＺ靭性向上に有効な元素である。そのため、Ｂは０．０００５質量％以上含有させる。好ましくは０．０００８質量％以上含有させる。しかし、Ｂ含有量が過剰になると粗大な析出物を形成し、かえって焼入れ性を低下させる。そのため、Ｂ含有量の上限は０．００３０質量％とする。より好ましい上限は０．００２５質量％である。
[B: 0.0005% by mass or more and 0.0030% by mass or less]
B is an element that segregates at the austenite grain boundary in the weld heat-affected zone, suppresses coarse ferrite precipitation from the grain boundary, and is effective in improving HAZ toughness. Therefore, 0.0005% by mass or more of B is contained. Preferably, it is contained in an amount of 0.0008% by mass or more. However, when the B content becomes excessive, coarse precipitates are formed, which rather deteriorates the hardenability. Therefore, the upper limit of the B content is set to 0.0030% by mass. A more preferable upper limit is 0.0025% by mass.
［Ｎ：０．００１０質量％以上、０．０１００質量％以下］
Ｎは固溶状態では靭性を低下させるためその含有量を０．０１００質量％以下とする必要があるが、ＴｉＮとなり溶接熱影響部の結晶粒を微細化し高靱化に寄与する効果もあるため０．００１０質量％以上含有させる。
[N: 0.0010% by mass or more and 0.0100% by mass or less]
N reduces the toughness in a solid solution state, so the content must be 0.0100% by mass or less. It is contained in an amount of 0.0010% by mass or more.
［Ｃａ：０．００５０質量％以下（０質量％を含む）］
ＣａはＭｎＳ介在物の形態制御による鋳片品質の改善に寄与する。一方、Ｃａは介在物として存在することにより母材の靱性を低下させる。このため、Ｃａは添加してもよく、また添加しなくてもよく、Ｃａの含有量を０．００５０質量％以下とした。Ｃａの通常の不純物レベルは０．０００１質量％未満であり、このため、本発明の実施形態ではＣａの添加効果をより確実に発揮させるため、意図的に添加する場合は、好ましくは、Ｃａを０．０００１質量％以上含有させる。
[Ca: 0.0050% by mass or less (including 0% by mass)]
Ca contributes to the improvement of slab quality by controlling the morphology of MnS inclusions. On the other hand, Ca reduces the toughness of the base material by being present as inclusions. Therefore, Ca may or may not be added, and the content of Ca is set to 0.0050% by mass or less. The normal impurity level of Ca is less than 0.0001% by mass. Therefore, in the embodiment of the present invention, in order to more reliably exhibit the effect of adding Ca, Ca is preferably added when intentionally added. It is contained in an amount of 0.0001% by mass or more.
［残部］
残部は鉄および不可避不純物である。不可避不純物としては、原料、資材、製造設備等の状況によって持ち込まれる元素（例えば、Ａｓ、Ｓｂ、Ｎｂ、Ｏ、Ｈ等）の混入が許容される。
なお、例えば、ＰおよびＳのように、通常、含有量が少ないほど好ましく、従って不可避不純物であるが、その組成範囲について上記のように別途規定している元素がある。このため、本明細書において、残部を構成する「不可避不純物」は、別途その組成範囲が規定されている元素を除いた概念である。
[Remainder]
The balance is iron and unavoidable impurities. As unavoidable impurities, contamination of elements (for example, As, Sb, Nb, O, H, etc.) brought in depending on the situation of raw materials, materials, manufacturing facilities, etc. is allowed.
For example, there are elements, such as P and S, whose content is generally preferably as low as possible and thus are unavoidable impurities, but whose composition range is separately defined as described above. For this reason, in this specification, "inevitable impurities" constituting the balance are concepts excluding elements whose composition ranges are defined separately.
２．金属組織
本発明の実施形態に係る鋼板は上述の化学組成を有することにより優れた塗装耐久性を得ることができる。
一方、橋梁として使用する際により優れた靭性を有することが好ましい。このため以下に規定する金属組織を有することが好ましい。
2. Metallographic Structure The steel sheet according to the embodiment of the present invention can obtain excellent coating durability by having the chemical composition described above.
On the other hand, it is preferable to have better toughness when used as a bridge. Therefore, it is preferable to have the metallographic structure defined below.
［板厚ｔ／４位置における金属組織がフェライトおよびベイナイトの一方または両方を含み、残部がパーライトおよび島状マルテンサイトの一方または両方であり、フェライトおよびベイナイトにおいて最大結晶粒径が３０μｍ以下であってよい。］
厳しい腐食環境下において靭性を確保するために、鋼板の代表的な部位である板厚ｔ／４位置（鋼板の表面（主面）から中心に向かって板厚ｔの４分の１の距離にある位置）における金属組織がフェライトおよびベイナイトの一方または両方を含み、残部がパーライトおよび島状マルテンサイト（ＭＡ）の一方または両方であり、且つこれらのフェライトおよびベイナイトの結晶粒径を３０μｍ以下としてよい。
ここで「フェライトおよびベイナイトの結晶粒径を３０μｍ以下」とはフェライトとベイナイトの両方が存在する場合は、そのそれぞれの最大結晶粒径が３０μｍ以下であり、フェライトとベイナイトの一方のみが存在する場合は存在する方の最大結晶粒径が３０μｍ以下という意味である。
[The metal structure at the plate thickness t/4 position contains one or both of ferrite and bainite, the balance is one or both of pearlite and island martensite, and the maximum grain size of ferrite and bainite is 30 μm or less. good. ]
In order to ensure toughness in a severely corrosive environment, the position of the plate thickness t / 4, which is a typical part of the steel plate (from the surface (main surface) of the steel plate toward the center, at a distance of 1/4 of the plate thickness t The metal structure at a certain position) contains one or both of ferrite and bainite, the balance is one or both of pearlite and island martensite (MA), and the grain size of these ferrite and bainite may be 30 μm or less. .
Here, "the grain size of ferrite and bainite is 30 µm or less" means that when both ferrite and bainite are present, the maximum grain size of each is 30 µm or less, and only one of ferrite and bainite is present. means that the maximum crystal grain size of the existing one is 30 μm or less.
ここで最大結晶粒径は、板厚ｔ／４位置において、光学顕微鏡を用い倍率１００倍で、視野が６００μｍ×８００μｍの領域を観察し、画像解析ソフトを用いて、最大結晶粒が占める面積を測定し、その面積値から円相当径を計算することで得ることができる。 Here, the maximum crystal grain size is obtained by observing a region with a field of view of 600 μm × 800 μm at a position of t / 4 in the plate thickness at a magnification of 100 using an optical microscope, and using image analysis software to determine the area occupied by the maximum crystal grain. It can be obtained by measuring and calculating the equivalent circle diameter from the area value.
上述の本発明の実施形態に係る鋼板は厳しい耐食性が要求される各種の用途、とりわけ優れた塗装耐久性が要求される各種の用途で用いることができる。
好ましい用途の代表例は橋梁であり、とりわけ橋梁桁端部において、優れた塗装耐久性により長期間再塗装を行うことなく（すなわち、メンテナンスコストフリーで）高い耐食性を維持できる。
また、本発明の実施形態に係る鋼板が高い塗装耐久性を示す好ましい塗装形態としてジンクリッチペイント（ジンクリッチプライマ）を挙げることができる。
The steel sheets according to the embodiments of the present invention described above can be used in various applications requiring severe corrosion resistance, especially in various applications requiring excellent coating durability.
A representative example of a preferred application is a bridge, and particularly at the ends of bridge girders, high corrosion resistance can be maintained without repainting for a long period of time (that is, without maintenance costs) due to excellent coating durability.
Moreover, zinc-rich paint (zinc-rich primer) can be given as a preferred form of coating in which the steel sheet according to the embodiment of the present invention exhibits high coating durability.
３．製造方法
本発明の実施形態に係る鋼板は、上述の化学成分を満足する限り、橋梁用の鋼板を含む通常の鋼板の製造方法を用いて得ることができる。
なお、上述の好ましい実施形態である板厚ｔ／４位置における金属組織がフェライトおよびベイナイトの一方または両方を含み、残部がパーライトおよび島状マルテンサイトの一方または両方であり、フェライトおよびベイナイトにおいて最大結晶粒径が３０μｍ以下である鋼板については、熱間圧延の条件（圧延後の冷却条件を含む）を以下に示す条件で行うことにより製造可能である。すなわち以下に示す圧延条件は好適な圧延条件である。
3. Manufacturing Method The steel plate according to the embodiment of the present invention can be obtained using a normal manufacturing method for steel plates including steel plates for bridges, as long as the above-described chemical composition is satisfied.
In addition, the metal structure at the plate thickness t / 4 position, which is the preferred embodiment described above, contains one or both of ferrite and bainite, and the remainder is one or both of pearlite and island martensite, and the maximum crystal in ferrite and bainite A steel sheet having a grain size of 30 μm or less can be produced by performing hot rolling conditions (including cooling conditions after rolling) under the following conditions. That is, the rolling conditions shown below are suitable rolling conditions.
・鋳片加熱温度：８５０℃～１３００℃
加熱温度が低いほど旧オーステナイト粒径は微細化し高靱化するが、再結晶温度域での圧延が製造上困難になることから加熱温度は８５０℃以上としてよい。しかし、加熱温度が１３００℃以上になると旧オーステナイト粒径が粗大化し低靱化を招くことから加熱温度は１３００℃以下としてよい。
・Slab heating temperature: 850°C to 1300°C
The lower the heating temperature, the finer the grain size of prior austenite and the higher the toughness. However, if the heating temperature is 1300° C. or higher, the grain size of the prior austenite is coarsened and the toughness is lowered, so the heating temperature may be 1300° C. or lower.
・再結晶温度域圧下率：４０％以上
鋳片加熱後の圧延において、再結晶温度域での圧下は旧オーステナイト粒径を微細化し高靱化に寄与する。ただし、その効果は４０％以上の圧下率で飽和する。このため、生産性の観点から再結晶温度域での圧下率を４０％以上とした。
なお、再結晶温度域圧下率は（ｔ１－ｔ２）／ｔ１×１００（％）と定義する。ここで、ｔ１は再結晶温度域での圧下前の板厚であり、ｔ２は再結晶温度域での圧下完了時の板厚である。
Recrystallization temperature range reduction rate: 40% or more In rolling after heating the slab, reduction in the recrystallization temperature range refines the prior austenite grain size and contributes to high toughness. However, the effect saturates at a rolling reduction of 40% or more. Therefore, from the viewpoint of productivity, the rolling reduction in the recrystallization temperature range is set to 40% or more.
The recrystallization temperature range reduction ratio is defined as (t1-t2)/t1×100(%). Here, t1 is the plate thickness before reduction in the recrystallization temperature range, and t2 is the plate thickness after completion of the reduction in the recrystallization temperature range.
・未再結晶温度域圧下率パラメータＲ：２４未満
未再結晶温度域での圧下率が高いほど組織微細化により高靱化に寄与する。圧延によるｔ／４位置への導入ひずみを考慮するとその効果は板厚が薄いほど大きくなり、また、焼入れ性が高いほど変態温度が低温化することで組織が微細となることから、板厚および焼き入れ性指数ＤＩを変数とするパラメータＲを導入する。安定して高靱性を実現するための条件としてパラメータＲは２４未満（Ｒ＜２４）としてよい。
なお、Ｒは次式にて定義される。
Ｒ＝４２．１８－１．７５×（未再結晶温度域圧下率）０．５－１２４．５９÷板厚－９．４３×ＤＩ
上式のうち、「板厚」は、圧延完了時点での鋼板の板厚であり、従って下記のｔ４と同じである。
上式のうち、「未再結晶温度域圧下率」は（ｔ３－ｔ４）／ｔ３×１００（％）と定義する。ｔ３は未再結晶温度域での圧下前の板厚であり、ｔ４は未再結晶温度域での圧下完了時の板厚である。
またＤＩは成分指標であり、ＤＩ＝１．１６×（Ｃ／１０）０．５×（５．１×（Ｍｎ－１．２）＋５）×（０．３５Ｃｕ＋１）×（０．３６Ｎｉ＋１）×（２．１６Ｃｒ＋１）×（３．０Ｍｏ＋１）×（１．７５Ｖ ＋１）×（２００Ｂ ＋１）である。元素記号は対応する各元素の含有量（質量％）を意味する。また、当該元素が含まれていない場合は値をゼロとして計算する。
Non-recrystallization temperature range reduction rate parameter R: less than 24 The higher the reduction rate in the non-recrystallization temperature range, the finer the structure, contributing to higher toughness. Considering the strain introduced to the t/4 position by rolling, the effect becomes greater as the sheet thickness becomes thinner. A parameter R is introduced with the hardenability index DI as a variable. As a condition for stably achieving high toughness, the parameter R may be less than 24 (R<24).
Note that R is defined by the following formula.
R = 42.18 - 1.75 x (unrecrystallized temperature range reduction rate) 0.5 - 124.59 ÷ plate thickness - 9.43 x DI
In the above formula, "thickness" is the thickness of the steel sheet at the time of completion of rolling, and is therefore the same as t4 below.
In the above formula, the "non-recrystallization temperature range reduction ratio" is defined as (t3-t4)/t3×100(%). t3 is the plate thickness before reduction in the non-recrystallization temperature range, and t4 is the plate thickness after completion of the reduction in the non-recrystallization temperature range.
DI is a component index, DI = 1.16 × (C / 10) 0.5 × (5.1 × (Mn-1.2) + 5) × (0.35Cu + 1) × (0.36Ni + 1) × (2.16Cr+1)*(3.0Mo+1)*(1.75V+1)*(200B+1). An element symbol means the content (mass %) of each corresponding element. If the element is not included, the value is calculated as zero.
・圧延完了温度：６００℃以上
圧延完了温度（最終圧延ロール出口温度）は生産性の観点から６００℃以上としてよい。
- Rolling completion temperature: 600°C or higher The rolling completion temperature (final roll exit temperature) may be 600°C or higher from the viewpoint of productivity.
・圧延後冷却
圧延後の冷却については冷却速度が遅いほど変態が高温となり組織が粗大化し靱性劣化を招く。このため、圧延完了温度から４００℃までの温度域での平均冷却速度を０．１℃／秒以上としてよい。
- Cooling after rolling As for the cooling after rolling, the slower the cooling rate, the higher the temperature of the transformation, which causes coarsening of the structure and deterioration of toughness. Therefore, the average cooling rate in the temperature range from the rolling completion temperature to 400° C. may be 0.1° C./second or more.
なお、以上に示した圧延条件を満足することで、十分な靭性を確保できるが、強度調整のために追加で熱処理を施してもよい。ただし、過度に高い温度で熱処理を施すと粗大組織となり靱性が劣化する。このため、熱処理温度を９６０℃以下としてよい。 By satisfying the rolling conditions described above, sufficient toughness can be ensured, but additional heat treatment may be performed to adjust the strength. However, if the heat treatment is performed at an excessively high temperature, the structure becomes coarse and the toughness deteriorates. Therefore, the heat treatment temperature may be 960° C. or lower.
１．実施例１
表１に示す化学組成を有する供試材を通常の溶製法で溶製した後、鋳造材を得た。得られた鋳造材を表２に示す圧延条件で圧延して鋼板サンプルを得た。また組成から計算した焼き入れ性指数ＤＩを表１に示し、パラメータＲを表２に示す。サンプル１-７は橋梁等に広く用いられている従来鋼ＳMであり、後述の耐食性評価の基準となるサンプルである。
表２の「冷却速度」は圧延完了温度から４００℃までの温度域での平均冷却速度を意味する。
1. Example 1
After the test material having the chemical composition shown in Table 1 was melted by a normal melting method, a cast material was obtained. The obtained cast materials were rolled under the rolling conditions shown in Table 2 to obtain steel plate samples. Table 1 shows the hardenability index DI calculated from the composition, and Table 2 shows the parameter R. Sample 1-7 is a conventional steel SM that is widely used for bridges and the like, and serves as a standard for evaluating corrosion resistance, which will be described later.
"Cooling rate" in Table 2 means the average cooling rate in the temperature range from the rolling completion temperature to 400°C.
（耐食性評価）
得られたサンプルの耐食性を評価した。評価には、ＪＩＳ－Ｋ－５６００－７－９：２００６ サイクルＤ法から湿潤時間を増加させ、乾燥時間を減少させた、上述のより厳しい腐食促進試験方法を用いた。以下に具体的に説明する。
(Corrosion resistance evaluation)
The corrosion resistance of the obtained samples was evaluated. The evaluation used the more stringent accelerated corrosion test method described above with increased wet time and decreased dry time from the JIS-K-5600-7-9:2006 Cycle D method. A specific description will be given below.
各サンプルのｔ／４あるいは３／４ｔ位置から３ｍｍt×５０ｍｍW×１５０ｍｍLの板材を切り出し、この鋼材の表面に鋼材側から順に防食下地塗装として厚さ３５μｍのジンクリッチプライマ（ジンクリッチペイント）層、中塗り塗装として厚さ２０μｍのエポキシ系樹脂層、上塗り塗装として厚さ２０μｍのフッ素系樹脂層を設けた。次いで、供試材の表面にカッターナイフでクロスカット式の人工塗膜欠陥を入れて腐食促進試験用サンプルを得た。 A plate material of 3 mmt × 50 mm W × 150 mm L was cut from the t/4 or 3/4t position of each sample, and on the surface of this steel material, a zinc-rich primer (zinc-rich paint) layer with a thickness of 35 µm as an anticorrosive undercoating from the steel material side. An epoxy resin layer with a thickness of 20 μm was provided as a coating, and a fluorine-based resin layer with a thickness of 20 μm was provided as a top coating. Then, a cross-cut type artificial coating film defect was made on the surface of the test material with a cutter knife to obtain a sample for corrosion acceleration test.
得られた腐食促進試験用サンプルを用いて、表３に示す工程１～４を１サイクルとして、２２４サイクル終了後に塗膜下で発生した赤錆面積を画像解析にて算出する腐食促進試験（ＣＣＴ）を行った。従来鋼ＳMサンプル（サンプルＮｏ．１－７）の赤錆面積に対する各サンプルの赤錆面積の比を求めた。各腐食促進試験用サンプルの得られた赤錆面積の比を表２の「耐食性」の欄に示す。この赤錆面積の比が０．６０以下であれば耐食性に優れると判断した。
なお表３から分かるように、腐食促進試験の１サイクルにおける塩水噴霧時間＋湿潤時間は３時間であり、塩水噴霧時間＋乾燥（熱風乾燥＋温風乾燥）時間＋修正湿潤時間が６時間であるため、Ｗｅｔ率は３÷６×１００＝５０％となる。
Using the obtained samples for accelerated corrosion test, processes 1 to 4 shown in Table 3 are regarded as one cycle, and after 224 cycles, the area of red rust generated under the coating film is calculated by image analysis. Corrosion accelerated test (CCT) did The ratio of the red rust area of each sample to the red rust area of the conventional steel SM sample (sample No. 1-7) was obtained. The ratio of the red rust area obtained for each sample for accelerated corrosion test is shown in the column of "corrosion resistance" in Table 2. It was judged that the corrosion resistance was excellent when the ratio of the red rust areas was 0.60 or less.
As can be seen from Table 3, the salt spray time + wetting time in one cycle of the accelerated corrosion test was 3 hours, and the salt spray time + drying (hot air drying + hot air drying) time + corrected wetting time was 6 hours. Therefore, the wet rate is 3/6×100=50%.
表２の耐食性の結果から分かるように、本発明の実施形態に係るサンプルＮｏ．１-２～１－６は何れも優れた耐食性を示した。一方、所定量のＴａを含まず（サンプルＮｏ．１－１はＴａが過剰）且つ所定量のＭｇおよび所定量のＲＥＭ量の一方または両方を含有しないサンプルＮｏ．１－１と１－７は耐食性が劣っていた。 As can be seen from the corrosion resistance results in Table 2, Sample No. 1 according to the embodiment of the present invention. All of 1-2 to 1-6 exhibited excellent corrosion resistance. On the other hand, sample No. 1 does not contain a predetermined amount of Ta (Sample No. 1-1 has excess Ta) and does not contain either or both of a predetermined amount of Mg and a predetermined amount of REM. 1-1 and 1-7 were inferior in corrosion resistance.
２．実施例２
表４に示す化学組成を有する供試材を通常の溶製法で溶製した後、鋳造材を得た。得られた鋳造材を表５に示す圧延条件で圧延して鋼板サンプルを得た。また組成から計算した焼き入れ性指数ＤＩを表４に示し、パラメータＲを表５に示す。
表５の「冷却速度」は圧延完了温度から４００℃までの温度域での平均冷却速度を意味する。
2. Example 2
After the test material having the chemical composition shown in Table 4 was melted by a normal melting method, a cast material was obtained. The obtained cast materials were rolled under the rolling conditions shown in Table 5 to obtain steel plate samples. Table 4 shows the hardenability index DI calculated from the composition, and Table 5 shows the parameter R.
"Cooling rate" in Table 5 means the average cooling rate in the temperature range from the rolling completion temperature to 400°C.
（耐食性評価）
表４および表５に記載の鋼種A、Ｂ、ＣおよびDは何れも本発明の実施形態に係る組成の条件を満足するため、上記の実施例を含む記載より明らかなように優れた耐食性を有する。念のため、サンプルＮｏ．２－５（鋼種D）について耐食性の評価を行った。サンプルＮｏ．２－５および比較用の従来鋼ＳMサンプル（サンプルＮｏ．１－７）とも腐食促進試験のサイクルが１１２であったこと以外は、実施例１に示した耐食性評価方法と同じ方法を用いた。得られた結果を表６に示す。優れた耐食性を示すことが確認できた。
(Corrosion resistance evaluation)
Steel grades A, B, C and D listed in Tables 4 and 5 all satisfy the conditions of composition according to the embodiments of the present invention, and therefore exhibit excellent corrosion resistance as is clear from the description including the above examples. have. Just in case, sample no. 2-5 (steel type D) was evaluated for corrosion resistance. Sample no. 2-5 and the comparative conventional steel SM sample (Sample No. 1-7), the same method as the corrosion resistance evaluation method shown in Example 1 was used except that the cycle of the corrosion acceleration test was 112. Table 6 shows the results obtained. It was confirmed that excellent corrosion resistance was exhibited.
（金属組織観察）
後述する衝撃試験片採取位置と同じ板厚ｔ／４位置において、光学顕微鏡を用い倍率１００倍で、視野が６００μｍ×８００μｍの領域を組織観察した。認められた組織を表６に示す。また、画像解析ソフトを用いて、視野内の最大結晶粒径を測定した。具体的にはフェライトおよびベイナイトのうち（フェライトおよびベイナイトの一方しか存在しない場合は存在している方）最大の結晶粒の面積を測定し、その円相当径を最大結晶粒径とした。得られた最大結晶粒径を表６に示す。
(Metal structure observation)
At the plate thickness t/4 position, which is the same as the impact test piece sampling position described later, the structure of the region with a field of view of 600 μm×800 μm was observed with an optical microscope at a magnification of 100 times. Tissues observed are shown in Table 6. Also, using image analysis software, the maximum crystal grain size within the field of view was measured. Specifically, the area of the largest crystal grain of ferrite and bainite (if only one of ferrite and bainite is present, the one that is present) was measured, and its equivalent circle diameter was taken as the maximum crystal grain size. Table 6 shows the obtained maximum grain size.
（靭性評価）
各サンプルの板厚ｔ／４位置から試験片の長手方向が圧延方向と平行となるように、フルサイズのシャルピー衝撃試験片（ＪＩＳ Ｚ ２２０２のＶノッチ試験片）を３本ずつ採取した。得られたシャルピー衝撃試験片について－２０℃でシャルピー衝撃試験を行い、吸収エネルギー（ＶＥ－２０）を測定した。これら各３本ずつのシャルピー衝撃試験測定結果の平均値を表６に示す。吸収エネルギー（ＶＥ－２０）が４７Ｊ以上を靭性良好とした。また、参考のため各サンプルの降伏強さ（ＹＰ）と引張強さ（ＴＳ）も表６に示した。
(Toughness evaluation)
Three full-size Charpy impact test pieces (JIS Z 2202 V-notch test pieces) were taken from each sample at the thickness t/4 position so that the longitudinal direction of the test piece was parallel to the rolling direction. The obtained Charpy impact test piece was subjected to a Charpy impact test at -20°C to measure the absorbed energy (VE -20 ). Table 6 shows the average values of the Charpy impact test measurement results for each of these three pieces. Absorbed energy (VE −20 ) of 47 J or more was defined as good toughness. Table 6 also shows the yield strength (YP) and tensile strength (TS) of each sample for reference.
圧延条件が上述した好適な圧延条件を満足しているサンプルＮｏ．２－２～２－５の金属組織はフェライトおよびベイナイトの一方または両方を含み、残部がパーライトである。また、フェライトおよびベイナイトの最大結晶粒径が３０μｍ以下となっている。そして、優れた靭性を有している。 Sample No. 1 satisfies the preferred rolling conditions described above. The metallographic structure of 2-2 to 2-5 contains one or both of ferrite and bainite, with the balance being pearlite. Also, the maximum crystal grain size of ferrite and bainite is 30 μm or less. And it has excellent toughness.
Claims (5)
Ｓｉ：０．１０質量％以上、０．５０質量％以下、
Ｍｎ：０．３０質量％以上、２．００質量％以下、
Ｃｕ：０．４０質量％以上、１．００質量％以下、
Ｎｉ：０．４０質量％以上、１．００質量％以下、
Ｓ ：０．０１０質量％以下（０質量％を含む）、
Ｐ ：０．０３０質量％以下（０質量％を含む）、
Ｃｒ：４．００質量％以下（０質量％を含む）、
Ｔｉ：０．０２質量％以上、０．０７質量％以下、
Ａｌ：０．０１０質量％以上、０．０７０質量％以下、
Ｂ ：０．０００５質量％以上、０．００３０質量％以下、
Ｎ ：０．００１０質量％以上、０．０１００質量％以下、
Ｃａ：０．００５０質量％以下（０質量％を含む）、
Ｔａ：０．０１質量％以上、０．２０質量％以下、ならびに
Ｍｇ：０．０５質量％以下（０質量％を含まず）およびＲＥＭ：０．０５質量％以下（０質量％を含まず）の一方または両方、
を含み、残部がＦｅおよび不可避不純物からなる鋼板。 C: 0.02% by mass or more and 0.10% by mass or less,
Si: 0.10% by mass or more and 0.50% by mass or less,
Mn: 0.30% by mass or more and 2.00% by mass or less,
Cu: 0.40% by mass or more and 1.00% by mass or less,
Ni: 0.40% by mass or more and 1.00% by mass or less,
S: 0.010% by mass or less (including 0% by mass),
P: 0.030% by mass or less (including 0% by mass),
Cr: 4.00% by mass or less (including 0% by mass),
Ti: 0.02% by mass or more and 0.07% by mass or less,
Al: 0.010% by mass or more and 0.070% by mass or less,
B: 0.0005% by mass or more and 0.0030% by mass or less,
N: 0.0010% by mass or more and 0.0100% by mass or less,
Ca: 0.0050% by mass or less (including 0% by mass),
Ta: 0.01% by mass or more and 0.20% by mass or less, and Mg: 0.05% by mass or less (excluding 0% by mass) and REM: 0.05% by mass or less (excluding 0% by mass) one or both of
A steel sheet containing Fe and the balance consisting of unavoidable impurities.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2003129133A (en) * | 2001-10-24 | 2003-05-08 | Nippon Steel Corp | Method for manufacturing thick steel plate with high strength and high toughness |
| JP2005305471A (en) * | 2004-04-19 | 2005-11-04 | Nippon Steel Corp | Method of electroslag welding for giving excellent toughness to weld metal |
| JP2008303424A (en) * | 2007-06-07 | 2008-12-18 | Nippon Steel Corp | Method for producing high-tension steel excellent in weld-cracking resistance |
| JP2009019244A (en) * | 2007-07-12 | 2009-01-29 | Kobe Steel Ltd | Thick steel plate for high heat input welding having excellent brittle fracture propagation stop characteristic |
| WO2019050010A1 (en) * | 2017-09-08 | 2019-03-14 | Ｊｆｅスチール株式会社 | Steel sheet and method for producing same |
| WO2020208711A1 (en) * | 2019-04-09 | 2020-10-15 | 日本製鉄株式会社 | Steel material |
| JP2022013657A (en) * | 2020-06-30 | 2022-01-18 | 株式会社神戸製鋼所 | Thick steel plate and method for manufacturing the same |
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