JP6772942B2 - Corrosion resistant steel for ballast tanks - Google Patents
Corrosion resistant steel for ballast tanks Download PDFInfo
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- JP6772942B2 JP6772942B2 JP2017082128A JP2017082128A JP6772942B2 JP 6772942 B2 JP6772942 B2 JP 6772942B2 JP 2017082128 A JP2017082128 A JP 2017082128A JP 2017082128 A JP2017082128 A JP 2017082128A JP 6772942 B2 JP6772942 B2 JP 6772942B2
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- 239000010935 stainless steel Substances 0.000 title claims description 36
- 239000000463 material Substances 0.000 claims description 57
- 239000011248 coating agent Substances 0.000 claims description 50
- 238000000576 coating method Methods 0.000 claims description 50
- 239000004593 Epoxy Substances 0.000 claims description 18
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 10
- 239000002987 primer (paints) Substances 0.000 claims description 10
- 239000011701 zinc Substances 0.000 claims description 10
- 229910052725 zinc Inorganic materials 0.000 claims description 10
- 239000012535 impurity Substances 0.000 claims description 5
- 229910000831 Steel Inorganic materials 0.000 description 50
- 239000010959 steel Substances 0.000 description 50
- 230000007797 corrosion Effects 0.000 description 43
- 238000005260 corrosion Methods 0.000 description 43
- 230000007547 defect Effects 0.000 description 17
- 229910052787 antimony Inorganic materials 0.000 description 14
- 229910052749 magnesium Inorganic materials 0.000 description 14
- 229910052718 tin Inorganic materials 0.000 description 14
- 230000008961 swelling Effects 0.000 description 13
- 238000003466 welding Methods 0.000 description 13
- 239000003973 paint Substances 0.000 description 11
- 239000010953 base metal Substances 0.000 description 9
- 229910052748 manganese Inorganic materials 0.000 description 9
- 229910052750 molybdenum Inorganic materials 0.000 description 9
- 239000002245 particle Substances 0.000 description 9
- 239000013535 sea water Substances 0.000 description 9
- 230000000694 effects Effects 0.000 description 8
- 229910052721 tungsten Inorganic materials 0.000 description 8
- 229910052804 chromium Inorganic materials 0.000 description 7
- 238000001816 cooling Methods 0.000 description 7
- 229910052802 copper Inorganic materials 0.000 description 7
- 230000007423 decrease Effects 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- 229910052726 zirconium Inorganic materials 0.000 description 6
- 229910052758 niobium Inorganic materials 0.000 description 5
- 229910052715 tantalum Inorganic materials 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 4
- 238000001035 drying Methods 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- 238000005096 rolling process Methods 0.000 description 4
- 229910052719 titanium Inorganic materials 0.000 description 4
- 229910052720 vanadium Inorganic materials 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 3
- 230000001965 increasing effect Effects 0.000 description 3
- 229910001369 Brass Inorganic materials 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 239000010951 brass Substances 0.000 description 2
- 239000003245 coal Substances 0.000 description 2
- 230000002950 deficient Effects 0.000 description 2
- 229920006334 epoxy coating Polymers 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- 238000009863 impact test Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 238000010422 painting Methods 0.000 description 2
- 238000005507 spraying Methods 0.000 description 2
- 238000011282 treatment Methods 0.000 description 2
- 238000009736 wetting Methods 0.000 description 2
- 235000019738 Limestone Nutrition 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 238000005422 blasting Methods 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 239000010779 crude oil Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000004070 electrodeposition Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 239000003822 epoxy resin Substances 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 239000006028 limestone Substances 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 238000003032 molecular docking Methods 0.000 description 1
- 230000008520 organization Effects 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 229920000647 polyepoxide Polymers 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000003303 reheating Methods 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 238000009849 vacuum degassing Methods 0.000 description 1
- 239000002023 wood Substances 0.000 description 1
Landscapes
- Laminated Bodies (AREA)
- Heat Treatment Of Steel (AREA)
Description
本発明は、特に海水による厳しい腐食環境下にあるバラストタンク等に用いられる耐食鋼材であって、表面にエポキシ系塗膜を有するバラストタンク用耐食鋼材に関するものである。 The present invention relates to a corrosion-resistant steel material used for a ballast tank or the like in a severe corrosion environment due to seawater, and relates to a corrosion-resistant steel material for a ballast tank having an epoxy-based coating film on the surface.
タンカー等の貨物船は、空荷であると航行中に船体が浮いて横風や横波に対して不安定になるため、積荷がない時には、喫水が下がらないように、バラストタンクに海水を積載している。バラストタンクは、貨物の積み下ろしに応じて海水の注入、排出が繰り返されるため、厳しい腐食環境に曝される。そのため、バラストタンクに使用される鋼材の表面には、エポキシ系塗料による防食が施される。 When a cargo ship such as a tanker is empty, the hull floats during navigation and becomes unstable against crosswinds and waves. Therefore, when there is no load, seawater is loaded in the ballast tank so that the draft does not drop. ing. Ballast tanks are exposed to severe corrosive environments because seawater is repeatedly injected and discharged according to the loading and unloading of cargo. Therefore, the surface of the steel material used for the ballast tank is protected against corrosion with an epoxy-based paint.
バラストタンクの最上部付近、特に上甲板の裏側は、海水の飛沫が付着した状態で、日中の温度上昇と夜間の温度低下が繰り返されるため、非常に厳しい腐食環境となる。また、バラストタンクに電気防食を施しても、貨物積載時には海水が注入されないため機能せず、残留付着塩分の作用によって激しい腐食を受ける。 Near the top of the ballast tank, especially on the back side of the upper deck, the temperature rises repeatedly during the day and the temperature drops at night with seawater droplets attached, resulting in a very severe corrosive environment. In addition, even if the ballast tank is provided with anticorrosion, it does not function because seawater is not injected when the cargo is loaded, and it is severely corroded by the action of residual salt.
バラストタンクは塗装が義務付けられているが、非常に厳しい腐食環境下での塗膜の寿命は15年程度といわれている。一方、船舶の寿命は25年であるため、塗装補修や鋼板の切替えが必要となる。バラストタンクの補修は、ドック時の修繕費用や期間を増加させるため、塗装の劣化後も10年程度は孔空き腐食に至らないような、耐食性に優れた鋼材の開発が望まれている。 The ballast tank is obliged to be painted, but it is said that the life of the coating film in a very severe corrosive environment is about 15 years. On the other hand, since the life of the ship is 25 years, it is necessary to repair the paint and switch the steel plate. Since the repair of the ballast tank increases the repair cost and period at the time of docking, it is desired to develop a steel material having excellent corrosion resistance so that the perforated corrosion does not occur for about 10 years even after the deterioration of the coating.
このような要求に対して、優れた塗装耐食性を発揮する耐食鋼材が提案されている(例えば、特許文献1〜4、参照)。これらは、Cu、Ni、W、Mo、Sn、Sbなどを含有させた鋼材に、ジンクリッチプライマーやエポキシ樹脂などの塗膜を形成した耐食鋼材である。また、耐食性を向上させるため、Cu、Mgを含有させた鋼材が提案されている(例えば、特許文献5、参照)。 Corrosion-resistant steel materials that exhibit excellent coating corrosion resistance have been proposed in response to such demands (see, for example, Patent Documents 1 to 4). These are corrosion-resistant steel materials in which a coating film such as a zinc rich primer or an epoxy resin is formed on a steel material containing Cu, Ni, W, Mo, Sn, Sb or the like. Further, in order to improve the corrosion resistance, a steel material containing Cu and Mg has been proposed (see, for example, Patent Document 5).
更に、バラストタンクに塗装を施す場合、塗膜下腐食が問題になる場合がある。本発明者らの一部は、塗装下腐食の原因の一つと考えられる、鋼中のMnSの生成を抑制したバラストタンク用耐食鋼材を提案している(例えば、特許文献6、7、参照)。特許文献6は、Mnの含有量と、Sの含有量とを考慮したものであり、特許文献7は、Caを利用してMnSの生成を抑制したものである。 Further, when painting the ballast tank, corrosion under the coating film may become a problem. Some of the present inventors have proposed corrosion-resistant steel materials for ballast tanks that suppress the formation of MnS in steel, which is considered to be one of the causes of corrosion under painting (see, for example, Patent Documents 6 and 7). .. Patent Document 6 considers the content of Mn and the content of S, and Patent Document 7 suppresses the production of MnS by utilizing Ca.
本発明者らは、バラストタンクに塗装を施した場合の塗膜欠陥部の耐食性を向上させる手段の検討を進め、Mgが有効な元素であることを知見した。一方、塗装欠陥部の腐食を抑制するために、Cuと、Sn、Sbの一方又は両方と、Mgとを同時に含有させる場合、Mgの含有量が過剰であると、大入熱の溶接によって熱影響部の靱性が低下することがわかった。 The present inventors have proceeded with the study of means for improving the corrosion resistance of the coating film defect portion when the ballast tank is coated, and have found that Mg is an effective element. On the other hand, when Cu, one or both of Sn and Sb, and Mg are simultaneously contained in order to suppress corrosion of the coating defect portion, if the Mg content is excessive, heat is generated by welding with a large heat input. It was found that the toughness of the affected area decreased.
本発明は、このような実情に鑑み、バラストタンク内の腐食環境下における塗装耐食性に優れ、大入熱による溶接が行われた場合においても、優れた溶接熱影響部(Heat Affected Zone:HAZ)の靭性を有するバラストタンク用耐食鋼材を提供するものである。 In view of such circumstances, the present invention has excellent coating corrosion resistance in a corrosive environment in a ballast tank, and even when welding is performed by a large heat input, the heat-affected zone (HAZ) is excellent. Provided is a corrosion resistant steel material for a ballast tank having the toughness of.
本発明者らは、Cuと、Sn、Sbの一方又は両方を同時に含有する耐食鋼材の塗装欠陥部の耐食性を向上させ、かつ、大入熱での溶接が行われた場合においても、優れた継手靭性(特にHAZの靭性)を確保するための手段について検討を行った。
その結果、まず、塗装欠陥部の耐食性を劣化させる要因であった粗大なMnSを微細な(Mg、Mn)S粒子として分散させるMgを含有させると、塗装欠陥部の耐食性の劣化を低減できることが判明した。
また、微細な(Mg、Mn)S粒子はHAZの靭性の向上にも有効であるが、大入熱での溶接においても優れた継手靭性を得るためには、Mg含有量とCu含有量とのバランスが重要であることを見出した。
The present inventors have improved the corrosion resistance of the coating defect portion of the corrosion-resistant steel material containing Cu and one or both of Sn and Sb at the same time, and are excellent even when welding is performed with a large heat input. The means for ensuring joint toughness (particularly HAZ toughness) was examined.
As a result, first, if Mg is contained in which coarse MnS, which has been a factor of deteriorating the corrosion resistance of the coating defect portion, is dispersed as fine (Mg, Mn) S particles, the deterioration of the corrosion resistance of the coating defect portion can be reduced. found.
Further, fine (Mg, Mn) S particles are also effective in improving the toughness of HAZ, but in order to obtain excellent joint toughness even in welding with a large heat input, the Mg content and Cu content are required. I found that the balance of is important.
本発明は上記の知見に基づいてなされたものであり、その要旨は以下のとおりである。
(1)質量%で、
C :0.03〜0.25%、
Si:0.05〜0.50%、
Mn:0.10〜2.50%、
S :0.001〜0.020%、
Cu:0.10〜0.060%、
Ni:0.03〜1.00%、
Al:0.001〜0.100%、
Mg:0.0012〜0.0030%、及び、
O :0.0007〜0.0020%
を含有し、更に、
Sn:0.010〜0.300%、及び、
Sb:0.010〜0.300%
の少なくとも一方を含有し、
P :0.025%以下
N :0.0080%以下
に制限し、残部がFe及び不可避的不純物からなり、
前記Cuの含有量と前記Mgの含有量とが、
70<Cu/Mg<220
を満足し、
表面にエポキシ系塗膜を有することを特徴とするバラストタンク用耐食鋼材。
(2)更に、質量%で、
Cr:1.00%以下、
Mo:0.90%以下、及び、
W :1.00%以下
の1種又は2種以上を含有することを特徴とする上記(1)に記載のバラストタンク用耐食鋼材。
(3)更に、質量%で、
Ti:0.100%以下、
Zr:0.10%以下、
Ta:0.100%以下、
Nb:0.200%以下、及び、
V :0.20%以下
の1種又は2種以上を含有することを特徴とする上記(1)又は(2)に記載のバラストタンク用耐食鋼材。
(4)更に、質量%で、
B :0.0030%以下
を含有することを特徴とする上記(1)〜(3)の何れかに記載のバラストタンク用耐食鋼材。
(5)更に、質量%で、
Ca:0.0050%以下、
REM:0.005%以下、及び
Y :0.100%以下
の1種又は2種以上を含有することを特徴とする上記(1)〜(4)の何れかに記載のバラストタンク用耐食鋼材。
(6)前記エポキシ系塗膜の下地にジンクプライマー塗膜を有することを特徴とする上記(1)〜(5)の何れかに記載のバラストタンク用耐食。
The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) By mass%
C: 0.03 to 0.25%,
Si: 0.05 to 0.50%,
Mn: 0.10-2.50%,
S: 0.001 to 0.020%,
Cu: 0.10 to 0.060%,
Ni: 0.03 to 1.00%,
Al: 0.001 to 0.100%,
Mg: 0.0012 to 0.0030%, and
O: 0.0007 to 0.0020%
Containing,
Sn: 0.010 to 0.300% and
Sb: 0.010 to 0.300%
Contains at least one of
P: 0.025% or less N: Limit to 0.0080% or less, the balance consists of Fe and unavoidable impurities,
The content of Cu and the content of Mg are
70 <Cu / Mg <220
Satisfied,
A corrosion-resistant steel material for ballast tanks, which has an epoxy-based coating film on its surface.
(2) Furthermore, by mass%,
Cr: 1.00% or less,
Mo: 0.90% or less, and
W: The corrosion-resistant steel material for ballast tanks according to (1) above, which contains one type or two or more types of 1.00% or less.
(3) Furthermore, by mass%,
Ti: 0.100% or less,
Zr: 0.10% or less,
Ta: 0.100% or less,
Nb: 0.200% or less, and
V: The corrosion-resistant steel material for ballast tanks according to (1) or (2) above, which contains one type or two or more types of 0.20% or less.
(4) Furthermore, by mass%,
B: The corrosion-resistant steel material for a ballast tank according to any one of (1) to (3) above, which contains 0.0030% or less.
(5) Furthermore, by mass%,
Ca: 0.0050% or less,
The corrosion-resistant steel material for a ballast tank according to any one of (1) to (4) above, which contains one or more of REM: 0.005% or less and Y: 0.100% or less. ..
(6) The corrosion resistance for a ballast tank according to any one of (1) to (5) above, which comprises having a zinc primer coating film as a base of the epoxy-based coating film.
本発明のバラストタンク用耐食鋼材は、バラストタンク内の腐食環境下で優れた塗装耐食性を示し、大入熱による溶接が行われた場合においても優れた溶接継手部靭性を有する。したがって、本発明は、過酷な腐食環境に曝されるバラストタンクヘ適用した場合、初期コスト及び補修再塗装等の保守費用を大幅に削減することができるなど、産業上の貢献が極めて顕著である。 The corrosion-resistant steel material for a ballast tank of the present invention exhibits excellent coating corrosion resistance in a corrosive environment inside the ballast tank, and has excellent welded joint toughness even when welding is performed by a large amount of heat input. Therefore, when the present invention is applied to a ballast tank exposed to a harsh corrosive environment, the initial cost and maintenance cost such as repair and repainting can be significantly reduced, and the industrial contribution is extremely remarkable. ..
本発明者らは、エポキシ系塗料を塗布した種々の耐食鋼材を用いて、エポキシ系塗膜の欠陥部の腐食について、以下の検討を行った。 The present inventors have conducted the following studies on the corrosion of defective portions of the epoxy-based coating film using various corrosion-resistant steel materials coated with the epoxy-based paint.
種々の合金元素を含有させた鋼を溶製し、熱間圧延して板厚が5mmの鋼板を作製し、長さ150mm、幅70mmの試験片を採取した。試験片の表面のスケールをショットブラスによって除去し、塗膜厚が300〜400μmになるようにエポキシ系塗料を2回塗布した。その後、塗膜の欠陥部の耐食性を評価するため、試験片の中央に、幅2mmのエンドミルで地鉄表面まで達する50mm長さの疵を一文字状に付与した。 Steel containing various alloying elements was melted and hot-rolled to prepare a steel plate having a plate thickness of 5 mm, and a test piece having a length of 150 mm and a width of 70 mm was collected. The scale on the surface of the test piece was removed by shot brass, and the epoxy paint was applied twice so that the coating film thickness was 300 to 400 μm. Then, in order to evaluate the corrosion resistance of the defective portion of the coating film, a flaw having a length of 50 mm reaching the surface of the base metal was formed in a single letter in the center of the test piece by an end mill having a width of 2 mm.
耐食性は、複合サイクル試験によって評価した。バラストタンクの環境に合わせるために、腐食液には、5%NaCl水溶液ではなく、人工海水を用いた。サイクル条件は、腐食液噴霧(温度35℃)1時間、乾燥(60℃、湿度20〜30%)2時間、湿潤(50℃、湿度95%以上)1時間とした。このサイクルを300サイクル行った後、付与した疵部の塗装膨れの最大長さを測定した。 Corrosion resistance was evaluated by a combined cycle test. In order to match the environment of the ballast tank, artificial seawater was used as the corrosive solution instead of the 5% NaCl aqueous solution. The cycle conditions were 1 hour for spraying a corrosive liquid (temperature 35 ° C.), 2 hours for drying (60 ° C., humidity 20 to 30%), and 1 hour for wetting (50 ° C., humidity 95% or more). After performing this cycle for 300 cycles, the maximum length of the paint swelling of the applied flaw was measured.
その結果、Sn、Sbの一方又は両方を含有させた場合、塗装欠陥部の塗膜膨れや腐食が抑制されている試験片と、抑制されていない試験片が見られることがわかった。これらを詳細に調査した結果、塗装欠陥部の膨れが抑制されていないものには、MnSが多く生成していることが判明した。 As a result, it was found that when one or both of Sn and Sb were contained, a test piece in which the coating film swelling and corrosion of the coating defect portion were suppressed and a test piece in which the coating film swelling and corrosion were not suppressed were observed. As a result of investigating these in detail, it was found that a large amount of MnS was generated in the one in which the swelling of the coating defect portion was not suppressed.
次に、表面を鏡面研磨し、観察されたMnSの周囲にビッカース硬度計でマーキングを施して、その位置に疵を入れた試験片を用いて耐食性評価を行った。その結果、塗膜膨れは抑制されず、MnSが塗装欠陥部の耐食性に悪影響を及ぼしていることが明らかになった。SnやSbを含む耐食鋼材であっても、MnSが多く生成している場合、塗膜欠陥部の腐食が抑制されない理由は、MnSの加水分解によって硫酸が生じ、pHが大きく低下したためではないかと推定している。 Next, the surface was mirror-polished, the observed MnS was marked with a Vickers hardness tester, and the corrosion resistance was evaluated using a test piece having a flaw at that position. As a result, it was clarified that the swelling of the coating film was not suppressed and MnS had an adverse effect on the corrosion resistance of the coating defect portion. Even in a corrosion-resistant steel material containing Sn and Sb, when a large amount of MnS is produced, the reason why the corrosion of the coating film defect portion is not suppressed may be that sulfuric acid is generated by the hydrolysis of MnS and the pH is greatly lowered. I'm estimating.
一方、Sn、Sbの一方又は両方を含有させた耐食鋼材のうち、Mgを含有させたものの一部は、塗装欠陥部の塗膜膨れや腐食が著しく抑制されていることが判明した。Mgを含有させた鋼材では(Mg、Mn)S粒子が微細に分散しており、(Mg、Mn)Sが加水分解した場合でもpHの低下が抑制されるだけでなく,溶け出したMgによってMg化合物が形成され、いわゆるエレクトロコーティングによって腐食の進展が著しく抑制されたのではないかと推定している。 On the other hand, among the corrosion-resistant steel materials containing one or both of Sn and Sb, it was found that some of the corrosion-resistant steel materials containing Mg were remarkably suppressed from swelling and corrosion of the coating film in the coating defect portion. In the steel material containing Mg, (Mg, Mn) S particles are finely dispersed, and even when (Mg, Mn) S is hydrolyzed, not only the decrease in pH is suppressed but also the dissolved Mg causes It is presumed that the Mg compound was formed and the progress of corrosion was significantly suppressed by the so-called electrocoating.
次に、本発明者らは、鋼材に板厚20mmから30mmの板を1パスで溶接する、入熱の非常に高い溶接での溶接継手部の靭性を向上させる手段の検討を行った。高い入熱での溶接を行った場合、熱影響を受ける部分の靭性が大幅に低下する。その理由は、この溶接熱影響部の金属組織が溶接の際に高温に曝される時間が長くなるためで、高温時に現れるγ粒が粗大化することによって冷却後の金属組織が粗大化するためである。 Next, the present inventors have studied a means for improving the toughness of a welded joint portion in welding with extremely high heat input, in which a plate having a plate thickness of 20 mm to 30 mm is welded to a steel material in one pass. When welding is performed with high heat input, the toughness of the heat-affected zone is significantly reduced. The reason is that the metal structure of the weld heat-affected zone is exposed to high temperature for a long time during welding, and the γ grains appearing at high temperature become coarse, so that the metal structure after cooling becomes coarse. Is.
そこで、(Mg、Mn)S粒子の微細分散によるピン止め効果によってγ粒の粗大化抑制を検討した。その結果、微細な(Mg、Mn)S粒子は、溶接熱影響部の靭性向上に有効であることがわかった。しかし、Mgを過剰に含有させると粗大な介在物が形成され、熱影響部の靱性を低下させるため、Mg含有量を0.0030%以下にする必要がある。 また、CuとMgとを同時に含有させる場合、Cuの含有量に対してMgの含有量が適正でないと、大入熱溶接によって熱影響部の靱性が低下することが判明した。 Therefore, the suppression of coarsening of γ particles was examined by the pinning effect due to the fine dispersion of (Mg, Mn) S particles. As a result, it was found that the fine (Mg, Mn) S particles are effective in improving the toughness of the weld heat affected zone. However, if Mg is excessively contained, coarse inclusions are formed and the toughness of the heat-affected zone is lowered. Therefore, the Mg content needs to be 0.0030% or less. Further, it was found that when Cu and Mg are contained at the same time, if the Mg content is not appropriate for the Cu content, the toughness of the heat-affected zone is lowered by the large heat input welding.
Cuの含有量に対してMgの含有量が過剰である場合、(Mg、Mn)S粒子を形成しない過剰なMgが粗大な介在物を形成し、HAZの靱性を低下させると考えられる。一方、Cuの含有量に対してMgの含有量が不足する場合、鋼中にCuSが形成されて、(Mg、Mn)S粒子の生成が不十分になり、HAZの靱性が向上しないと考えられる。本発明者らの検討の結果、大入熱溶接を行う場合、HAZの靱性の低下を抑制するためには、Cu含有量との関係が70<Cu/Mg<220を満足する必要があることがわかった。 When the content of Mg is excessive with respect to the content of Cu, it is considered that the excess Mg that does not form (Mg, Mn) S particles forms coarse inclusions and reduces the toughness of HAZ. On the other hand, when the Mg content is insufficient with respect to the Cu content, CuS is formed in the steel, the generation of (Mg, Mn) S particles becomes insufficient, and the toughness of HAZ is not improved. Be done. As a result of the study by the present inventors, it is necessary that the relationship with the Cu content satisfies 70 <Cu / Mg <220 in order to suppress the decrease in the toughness of HAZ when performing large heat-affected welding. I found out.
このような検討結果に基づいて、本発明のバラストタンク用耐食鋼材(以下、「本発明の耐食鋼材」という)では、Cu及びNiを含有させた上で、Sn、及び、Sbの一方又は両方を含有し、Mgの上限を0.0030%として含有させ、さらにCu量との関係が70<Cu/Mg<220とすることとした。また、必要に応じて、Cr、Mo、及び、Wの1種又は2種以上を含有させると、さらに優れた耐食性が得られる。 Based on the results of such studies, the corrosion-resistant steel material for ballast tanks of the present invention (hereinafter referred to as "corrosion-resistant steel material of the present invention") contains Cu and Ni, and then one or both of Sn and Sb. The upper limit of Mg was set to 0.0030%, and the relationship with the amount of Cu was set to 70 <Cu / Mg <220. Further, when one or more of Cr, Mo, and W are contained, if necessary, further excellent corrosion resistance can be obtained.
次以下に、本発明の耐食鋼材の成分組成について具体的に説明する。なお、特に断りのない限り、「%」は、「質量%」を示す。 Next, the component composition of the corrosion-resistant steel material of the present invention will be specifically described below. Unless otherwise specified, "%" indicates "mass%".
(C:0.03〜0.25%)
Cは、鋼材強度を上昇させるのに有効な元素であり、所望の強度を得るために0.03%以上の含有を必要とする。好ましくは0.05%以上、より好ましくは0.08%以上とする。一方、0.25%を超えてCを含有させると、溶接熱影響部の靭性を低下させるため、Cの含有量を0.25%以下とする。好ましくは0.20%以下、より好ましくは0.17%以下とする。
(C: 0.03 to 0.25%)
C is an element effective for increasing the strength of the steel material, and needs to be contained in an amount of 0.03% or more in order to obtain the desired strength. It is preferably 0.05% or more, more preferably 0.08% or more. On the other hand, if C is contained in excess of 0.25%, the toughness of the weld heat affected zone is lowered, so the C content is set to 0.25% or less. It is preferably 0.20% or less, more preferably 0.17% or less.
(Si:0.05〜0.50%)
Siは、脱酸剤として、また、鋼材の強度を高めるために有効な元素であり、0.05%以上を含有させる。好ましくは0.10%以上、より好ましくは0.15%以上のSiを含有させる。しかし、0.50%を超えて含有させると、鋼の靭性を劣化させるので、0.50%以下とする。好ましくは0.40%以下、より好ましくは0.30%以下とする。
(Si: 0.05 to 0.50%)
Si is an element effective as a deoxidizer and for increasing the strength of steel materials, and contains 0.05% or more. It preferably contains 0.10% or more, more preferably 0.15% or more of Si. However, if it is contained in excess of 0.50%, the toughness of the steel is deteriorated, so the content is set to 0.50% or less. It is preferably 0.40% or less, more preferably 0.30% or less.
(Mn:0.10〜2.50%)
Mnは、鋼材の強度を高める元素であり、0.10%以上のMnを含有させる。好ましくは0.60%以上、より好ましくは1.00%以上とする。しかし、2.50%を超えてMnを含有させると、MnSを増加させて塗膜欠陥部の耐食性を低下させるため、2.50%以下とする。好ましくは2.00%以下、より好ましくは1.60%以下とする。
(Mn: 0.10-2.50%)
Mn is an element that enhances the strength of the steel material, and contains 0.10% or more of Mn. It is preferably 0.60% or more, more preferably 1.00% or more. However, if Mn is contained in excess of 2.50%, MnS is increased and the corrosion resistance of the coating film defect portion is lowered, so the content is set to 2.50% or less. It is preferably 2.00% or less, more preferably 1.60% or less.
(S:0.001〜0.020%)
Sは、MnSを生成させて塗膜欠陥部の耐食性を低下させるため、Sの含有量を0.020%以下とする。好ましくは0.015%以下、より好ましくは0.010%以下含有させる。Sの含有量は、耐食性の観点からは低減することが好ましいが、0.001%未満にするに製鋼上の負荷が大きくコストが高くなるため、下限を0.001%とする。より好ましくはSの含有量を0.003%以上とする。
(S: 0.001 to 0.020%)
Since S produces MnS and lowers the corrosion resistance of the coating film defect portion, the content of S is set to 0.020% or less. It is preferably contained in an amount of 0.015% or less, more preferably 0.010% or less. The content of S is preferably reduced from the viewpoint of corrosion resistance, but if it is less than 0.001%, the load on steelmaking is large and the cost is high, so the lower limit is set to 0.001%. More preferably, the S content is 0.003% or more.
(Cu:0.10〜0.60%)
Cuは、Niとともに含有させた上で、Sn、及び、Sbの一方又は両方を含有し、Mgを含有させて耐食性を向上させるために必要であるため、0.10%以上を含有させる。好ましくは0.15%以上を含有させる。一方、0.60%以上のCuを含有させると溶接熱影響部の脆化を生じることからCu量を0.50%以下とする。好ましくは、0.40%以下、より好ましくは0.30%以下とする。
(Cu: 0.10 to 0.60%)
Cu is contained together with Ni, and then one or both of Sn and Sb are contained, and since it is necessary to contain Mg to improve corrosion resistance, 0.10% or more is contained. It preferably contains 0.15% or more. On the other hand, if 0.60% or more of Cu is contained, embrittlement of the weld heat affected zone occurs, so the amount of Cu is set to 0.50% or less. It is preferably 0.40% or less, more preferably 0.30% or less.
(Ni:0.03〜1.00%)
Niは、Cuともに含有させた上で、Sn、及び、Sbの一方又は両方を含有し、Mgを含有させて耐食性を向上させるために必要であるため、0.03%以上を含有させる。CuとNiとを同時に含有させると鋼材の表面性状の劣化を抑制することもできる。一方、Niは高価な元素であり、1.00%を超えて含有させるとはコストが高くになることからNi量を1.00%以下とする。好ましくは、0.50%以下、より好ましくは0.30%以下とする。
(Ni: 0.03 to 1.00%)
Ni contains one or both of Sn and Sb after being contained together with Cu, and since it is necessary to contain Mg to improve corrosion resistance, 0.03% or more is contained. When Cu and Ni are contained at the same time, deterioration of the surface texture of the steel material can be suppressed. On the other hand, Ni is an expensive element, and if it is contained in excess of 1.00%, the cost will be high, so the amount of Ni is set to 1.00% or less. It is preferably 0.50% or less, more preferably 0.30% or less.
(Al:0.001〜0.100%)
Alは、脱酸剤であり、0.001%以上のAlを含有させる。好ましくはAlの含有量を0.005%以上、より好ましくは0.010%以上とする。しかし、0.100%を超えてAlを含有させると、靭性が低下するため、0.100%以下とする。好ましくは0.080%以下、より好ましくは0.060%以下とする。
(Al: 0.001 to 0.100%)
Al is a deoxidizing agent and contains 0.001% or more of Al. The Al content is preferably 0.005% or more, more preferably 0.010% or more. However, if Al is contained in an amount of more than 0.100%, the toughness is lowered, so the content is set to 0.100% or less. It is preferably 0.080% or less, more preferably 0.060% or less.
(Mg:0.0012〜0.0030%)
Mgは、本発明の耐食鋼材の塗装欠陥部の塗膜膨れや腐食を抑制するため、また、大入熱溶接での溶接熱影響部の靭性劣化を抑制するために必要な元素であり、0.0012%以上を含有させる。好ましくは0.0015%以上、より好ましくは0.0020%以上とする。しかし、耐食性を向上させるためにCuを含有させた場合、Mgの含有量が0.0030%を超えると溶接熱影響部の靭性が低下するため、Mgの含有量を0.0030%以下とする。好ましくは0.0025%以下とする。
(Mg: 0.0012 to 0.0030%)
Mg is an element necessary for suppressing the coating swelling and corrosion of the coating defect portion of the corrosion-resistant steel material of the present invention and for suppressing the toughness deterioration of the welding heat-affected zone in the large heat input welding. Contains 0012% or more. It is preferably 0.0015% or more, more preferably 0.0020% or more. However, when Cu is contained in order to improve the corrosion resistance, if the Mg content exceeds 0.0030%, the toughness of the weld heat affected zone decreases, so the Mg content is set to 0.0030% or less. .. It is preferably 0.0025% or less.
(O:0.0007〜0.0020%)
Oは、溶接熱影響部の靭性低下や母材の機械特性の低下を引き起こす粗大な酸化物の形成を抑制するため制限することが好ましいが、コストの観点から、O量の下限値を0.0007%とする。特にO量が0.0020%を超えると、粗大な酸化物の形成にするため、0.0020%以下とする。好ましくは0.0018%以下、より好ましくは0.0015%以下とする。
(O: 0.0007 to 0.0020%)
It is preferable to limit O in order to suppress the formation of coarse oxides that cause a decrease in toughness of the weld heat affected zone and a decrease in mechanical properties of the base metal, but from the viewpoint of cost, the lower limit of the amount of O is set to 0. It shall be 0007%. In particular, when the amount of O exceeds 0.0020%, it is set to 0.0020% or less in order to form a coarse oxide. It is preferably 0.0018% or less, more preferably 0.0015% or less.
(Sn:0.010〜0.300%)
(Sb:0.010〜0.300%)
Sn、Sbは、塗膜欠陥部の耐食性を向上させる効果があり、一方又は両方を含有させる。効果を得るには、Sn、Sbとも0.010%以上の含有が必要であり、好ましくは0.020%以上、より好ましくは0.030%以上を含有させる。一方、Sn、Sbとも含有量が0.300%を超えると、母材及びHAZの靭性を劣化させる。したがって、Sn及びSbの含有量を、0.300%以下とし、好ましくは0.200%以下、より好ましくは0.150%以下とする。
(Sn: 0.010 to 0.300%)
(Sb: 0.010 to 0.300%)
Sn and Sb have the effect of improving the corrosion resistance of the coating film defect portion, and include one or both of them. In order to obtain the effect, both Sn and Sb need to be contained in an amount of 0.010% or more, preferably 0.020% or more, and more preferably 0.030% or more. On the other hand, when the contents of both Sn and Sb exceed 0.300%, the toughness of the base metal and HAZ is deteriorated. Therefore, the contents of Sn and Sb are set to 0.300% or less, preferably 0.200% or less, and more preferably 0.150% or less.
(P:0.025%以下)
Pは、不純物であり、鋼の母材靭性や溶接性、溶接部靭性を劣化させるため、できるだけ低減するのが好ましい。特に、Pの含有量が0.025%を超えると、母材靭性及び溶接部靭性の低下が大きくなるので、0.025%以下に制限する。好ましくはPの含有量を0.020%以下、より好ましくは0.015%以下とする。
(P: 0.025% or less)
P is an impurity and deteriorates the toughness of the base metal, the toughness of the weld, and the toughness of the welded portion of the steel. In particular, if the P content exceeds 0.025%, the toughness of the base metal and the toughness of the weld will be significantly reduced, so the content is limited to 0.025% or less. The P content is preferably 0.020% or less, more preferably 0.015% or less.
(N:0.0080%以下)
Nは、不純物であり、鋼の母材靭性や溶接性、溶接部靭性を劣化させるため、できるだけ低減するのが好ましい。特に、Nの含有量が0.0080%を超えると、母材靭性及び溶接部靭性の低下が大きくなるので、0.0080%以下に制限する。好ましくはNの含有量を0.0050%以下、より好ましくは0.0040%以下、より一層好ましくは0.0035%以下とする。
(N: 0.0080% or less)
N is an impurity and deteriorates the toughness of the base metal, the toughness of the weld, and the toughness of the welded portion of the steel. In particular, if the N content exceeds 0.0080%, the toughness of the base metal and the toughness of the welded portion will be significantly reduced, so the content is limited to 0.0080% or less. The N content is preferably 0.0050% or less, more preferably 0.0040% or less, and even more preferably 0.0035% or less.
本発明の耐食鋼材は、上述された基本成分(必須元素)に加え、更に、塗装欠陥部の耐食性を高めるために、Cr、Mo、及び、Wの1種又は2種以上を選択元素として含有させてもよい。 In addition to the above-mentioned basic components (essential elements), the corrosion-resistant steel material of the present invention further contains one or more of Cr, Mo, and W as selective elements in order to enhance the corrosion resistance of coating defects. You may let me.
(Cr:1.00%以下)
(Mo:0.90%以下)
(W :1.00%以下)
Cr、Mo、及び、Wは、1種又は2種以上を、Cu、Ni、Mgを含有させた上で、Sn、及び、Sbの一方又は両方と同時に含有させると、塗装欠陥部の耐食性を更に高める効果が発現する。塗装欠陥部の耐食性を向上させる効果を得るには、Cr、Mo、Wとも、0.01%以上の添加が好ましい。ただし、Cr、Mo、Wを過剰に含有させると、HAZ靭性が劣化する場合がある。Crは1.00%以下、Moは0.90%以下、Wは1.00%以下とすることが好ましい。より好ましくは、Cr、Mo、Wの含有量を0.50%以下、より一層好ましくはCr、Mo、Wの含有量を0.30%以下とする。
(Cr: 1.00% or less)
(Mo: 0.90% or less)
(W: 1.00% or less)
When one or more of Cr, Mo, and W are contained in Cu, Ni, and Mg, and then one or both of Sn and Sb are contained at the same time, the corrosion resistance of the coating defect portion is improved. The effect of further enhancing is exhibited. In order to obtain the effect of improving the corrosion resistance of the coating defect portion, it is preferable to add 0.01% or more of Cr, Mo, and W. However, if Cr, Mo, and W are excessively contained, the HAZ toughness may deteriorate. It is preferable that Cr is 1.00% or less, Mo is 0.90% or less, and W is 1.00% or less. More preferably, the content of Cr, Mo, W is 0.50% or less, and even more preferably, the content of Cr, Mo, W is 0.30% or less.
本発明の耐食鋼材は、上述された必須元素に加え、更に、母材の機械特性を向上させるために、Ti、Zr、Ta、Nb、V、B、Ca、REM、及び、Yの1種又は2種以上を含有させてもよい。 In addition to the above-mentioned essential elements, the corrosion-resistant steel material of the present invention is one of Ti, Zr, Ta, Nb, V, B, Ca, REM, and Y in order to further improve the mechanical properties of the base material. Alternatively, two or more kinds may be contained.
(Ti:0.100%以下)
(Zr:0.10%以下)
(Ta:0.100%以下)
(Nb:0.200%以下)
(V :0.20%以下)
Ti、Zr、Ta、Nb、Vは、いずれも、析出物を生じて鋼材の強度を高める元素であり、必要に応じて含有することができる。Ti、Zr、Ta、Nb、Vは、0.001%以上を含有させることが好ましい。一方、Ti、Zr、Ta、Nb、Vを過剰に含有させると靭性が低下することがあるため、Tiは0.100%以下、Zrは0.10%以下、Taは0.100%以下、Nbは0.200%以下、Vは0.20%以下として含有させるのが好ましい。より好ましくは、Tiは0.020%以下、Zrは0.02%以下、Taは0.010%以下、Nbは0.030%以下、Vは0.10%以下とする。
(Ti: 0.100% or less)
(Zr: 0.10% or less)
(Ta: 0.100% or less)
(Nb: 0.200% or less)
(V: 0.20% or less)
Ti, Zr, Ta, Nb, and V are all elements that generate precipitates and increase the strength of the steel material, and can be contained as needed. Ti, Zr, Ta, Nb, and V are preferably contained in an amount of 0.001% or more. On the other hand, if Ti, Zr, Ta, Nb, and V are excessively contained, the toughness may decrease. Therefore, Ti is 0.100% or less, Zr is 0.10% or less, and Ta is 0.100% or less. It is preferable that Nb is contained in an amount of 0.200% or less and V is contained in an amount of 0.20% or less. More preferably, Ti is 0.020% or less, Zr is 0.02% or less, Ta is 0.010% or less, Nb is 0.030% or less, and V is 0.10% or less.
(B:0.0030%以下)
Bは、微量の添加で鋼材の強度を高める元素であり、必要に応じて含有させることができる。B量は0.0003%以上が好ましい。より好ましくは0.0005%以上とする。一方、0.0030%を超えて含有させると、靭性が劣化することがあるため、Bの含有量は0.0030%以下が好ましい。より好ましくは0.0020%以下とする。
(B: 0.0030% or less)
B is an element that increases the strength of the steel material by adding a small amount, and can be contained as needed. The amount of B is preferably 0.0003% or more. More preferably, it is 0.0005% or more. On the other hand, if the content exceeds 0.0030%, the toughness may deteriorate. Therefore, the content of B is preferably 0.0030% or less. More preferably, it is 0.0020% or less.
(Ca:0.0050%以下)
(REM:0.005%以下)
(Y :0.100%以下)
Ca、REM、及び、Yは、いずれも、母材の機械特性の向上に効果のある元素であり、必要に応じて選択して含有することができる。Ca、REM、及び、Yは、それぞれ、0.0001%以上を含有させることが好ましい。より好ましくは、Mg、REM、及び、Yの含有量を、それぞれ、0.0005%以上とする。一方、これらを過剰に含有させると母材靭性を低下させることがあるため、Ca及びREMは0.005%以下、Yは0.100%以下が好ましい。より好ましくは、Mg、REM、及び、Yの含有量を、それぞれ、0.0030%以下、0.005%以下、及び、0.05%以下とする。
(Ca: 0.0050% or less)
(REM: 0.005% or less)
(Y: 0.100% or less)
Ca, REM, and Y are all elements that are effective in improving the mechanical properties of the base material, and can be selected and contained as necessary. It is preferable that Ca, REM, and Y each contain 0.0001% or more. More preferably, the contents of Mg, REM, and Y are 0.0005% or more, respectively. On the other hand, if these are excessively contained, the toughness of the base metal may be lowered, so Ca and REM are preferably 0.005% or less, and Y is 0.100% or less. More preferably, the contents of Mg, REM, and Y are 0.0030% or less, 0.005% or less, and 0.05% or less, respectively.
本発明の耐食鋼材において、上記以外の成分は、Fe及び不可避的不純物であるが、本発明の効果を害しない範囲内であれば、上記以外の成分の含有は許容される。 In the corrosion-resistant steel material of the present invention, components other than the above are Fe and unavoidable impurities, but the inclusion of components other than the above is permitted as long as the effects of the present invention are not impaired.
(70<Cu/Mg<220)
CuとMgとを同時に含有させる場合、Cu含有量とMg含有量とが、70<Cu/Mg<220を満足することが必要である。Mg含有量がCu含有量に対して過剰であると、粗大な介在物が形成されてHAZ靭性が低下するため、Cu/Mgを220未満とする。好ましくは180以下、より好ましくは150以下とする。一方、Mg含有量がCu含有量に対して不足すると、CuSの形成により(Mg、Mn)S粒子の形成が不十分になり、HAZ靭性が低下するため、Cu/Mgを70超とする。好ましくは75以上、より好ましくは80以上とする。
(70 <Cu / Mg <220)
When Cu and Mg are contained at the same time, it is necessary that the Cu content and the Mg content satisfy 70 <Cu / Mg <220. If the Mg content is excessive with respect to the Cu content, coarse inclusions are formed and the HAZ toughness is lowered, so that Cu / Mg is set to less than 220. It is preferably 180 or less, more preferably 150 or less. On the other hand, if the Mg content is insufficient with respect to the Cu content, the formation of (Mg, Mn) S particles becomes insufficient due to the formation of CuS, and the HAZ toughness is lowered. Therefore, Cu / Mg is set to more than 70. It is preferably 75 or more, more preferably 80 or more.
本発明の耐食鋼材は、上記組成からなる下地鋼材の表面に、表面にエポキシ系塗膜を有する。エポキシ系塗膜は、国際海事機関(International Maritime Organization、IMO)が定めた塗装性能基準を満たすものであれば、特に制限されるものではなく、エポキシ系塗料を塗布し、乾燥させて形成すればよい。 The corrosion-resistant steel material of the present invention has an epoxy-based coating film on the surface of the base steel material having the above composition. The epoxy coating film is not particularly limited as long as it meets the coating performance standards set by the International Maritime Organization (IMO), and may be formed by applying an epoxy coating film and drying it. Good.
また、上記組成からなる下地鋼材の表面に、ジンクリッチプライマー塗膜を形成してから、エポキシ系塗膜を設けることができる。ジンクリッチプライマー塗膜は、特に制限されるものではなく、ジンクリッチプライマーを塗布し、乾燥させて形成すればよい。 Further, an epoxy-based coating film can be provided after forming a zinc-rich primer coating film on the surface of the base steel material having the above composition. The zinc rich primer coating film is not particularly limited, and may be formed by applying a zinc rich primer and drying it.
本発明の耐食鋼材は、常法で製造することができる。
例えば、溶鋼を転炉、電気炉等の公知の方法で溶製し、連続鋳造法、造塊法等の公知の方法でスラブやビレット等の鋼素材とし、熱間圧延に供する。なお、溶鋼に、取鍋精錬や真空脱ガス等の処理を付加してもよい。
The corrosion-resistant steel material of the present invention can be produced by a conventional method.
For example, molten steel is melted by a known method such as a converter or an electric furnace to make a steel material such as a slab or a billet by a known method such as a continuous casting method or an ingot forming method, and is used for hot rolling. The molten steel may be subjected to treatments such as ladle refining and vacuum degassing.
そして、鋼素材を、好ましくは1050〜1250℃の温度に加熱し、所望の寸法形状に熱間圧延する。鋳造や造塊後の鋼材をそのまま熱間圧延してもよい。なお、熱間圧延では、強度を確保するために、熱間仕上圧延終了温度及び熱間仕上圧延終了後の冷却速度を適正化することが好ましく、熱間仕上圧延終了温度は、700℃以上、熱間仕上圧延終了後の冷却は、空冷又は冷却速度100℃/s以下の加速冷却を行うことが好ましい。また、冷却後、再加熱処理を施してもよい。 Then, the steel material is heated to a temperature of preferably 1050 to 1250 ° C. and hot-rolled to a desired size and shape. The steel material after casting or ingot may be hot-rolled as it is. In hot rolling, in order to ensure strength, it is preferable to optimize the hot finish rolling end temperature and the cooling rate after hot finish rolling, and the hot finish rolling end temperature is 700 ° C. or higher. For cooling after the completion of hot finish rolling, it is preferable to perform air cooling or accelerated cooling at a cooling rate of 100 ° C./s or less. Further, after cooling, reheating treatment may be performed.
そして、鋼材の表面にエポキシ系塗料を塗布し、乾燥させてエポキシ系塗膜を形成させる。エポキシ系塗料を塗布する前にジンクリッチプライマー塗膜を形成してもよい。また、エポキシ系塗料やジンクリッチプライマーを塗布する前に、ショットブラストを施してもよく、酸洗を行ってもよい。 Then, an epoxy-based paint is applied to the surface of the steel material and dried to form an epoxy-based coating film. A zinc rich primer coating may be formed before applying the epoxy paint. Further, shot blasting may be performed or pickling may be performed before applying the epoxy-based paint or zinc rich primer.
以下、実施例により本発明をさらに詳細に説明するが、実施例での条件は、本発明の実施可能性及び効果を確認するために採用した一条件例であり、本発明は、この一条件例に限定されるものではない。本発明は、本発明の要旨を逸脱せず、本発明の目的を達成する限りにおいて、種々の条件を採用し得るものである。 Hereinafter, the present invention will be described in more detail by way of examples. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is the one condition. It is not limited to the example. In the present invention, various conditions can be adopted as long as the gist of the present invention is not deviated and the object of the present invention is achieved.
表1に示した成分組成を有する鋼を真空溶解炉又は転炉で溶製して、鋳塊又は鋼スラブとし、これらを加熱炉で1150℃に加熱し、熱間圧延して25mm厚の厚鋼板とした。得られた厚鋼板に大入熱溶接での熱影響部を想定した熱履歴を付与し、シャルピー試験を行った。熱履歴は、昇温速度100℃/秒で1400℃まで加熱後15秒保持し、その後1℃/秒で室温まで冷却した。シャルピー衝撃試験はJIS Z 2242に準拠して−20℃で行い、6本の平均値で評価した。 Steels having the composition shown in Table 1 are melted in a vacuum melting furnace or converter to form ingots or steel slabs, which are heated to 1150 ° C. in a heating furnace and hot-rolled to a thickness of 25 mm. It was made of steel plate. The obtained thick steel sheet was given a heat history assuming a heat-affected zone in large heat input welding, and a Charpy test was conducted. The heat history was maintained for 15 seconds after heating to 1400 ° C. at a heating rate of 100 ° C./sec, and then cooled to room temperature at 1 ° C./sec. The Charpy impact test was performed at −20 ° C. in accordance with JIS Z 2242, and was evaluated by the average value of 6 pieces.
次に、それぞれの厚鋼板から、長さ150mm、幅70mm、厚さ5mmの試験片を採取し、試験片の表面のスケールをショットブラスによって除去した後、エポキシ塗料を2回塗布して塗膜厚が300〜400μmとなる試験片を作製した。また、いくつかの鋼板についてはエポキシ塗料による塗布の前にジンクプライマーを10μm塗布したものも用意した。 Next, test pieces having a length of 150 mm, a width of 70 mm, and a thickness of 5 mm were collected from each thick steel plate, the scale on the surface of the test pieces was removed by shot brass, and then epoxy paint was applied twice to coat the coating. A test piece having a thickness of 300 to 400 μm was prepared. In addition, for some steel sheets, those coated with zinc primer by 10 μm before coating with the epoxy paint were also prepared.
これらの試験片の中央を幅2mmのエンドミルで、地鉄表面まで達する50mm長さの疵を横方向に一文字状に付与し、人工海水を用いて複合サイクル試験を行った。サイクル条件は、腐食液噴霧(温度35℃)1時間、乾燥(60℃、湿度20〜30%)2時間、湿潤(50℃、湿度95%以上)1時間とした。このサイクルを300サイクル行った後、付与した疵部の塗装膨れの最大長さを測定した。耐食性は、耐食性向上元素を特に含まないNo.27の鋼をベース鋼(100)として塗装膨れの最大長さの比率を算出し、評価した。 A composite cycle test was carried out using artificial seawater by using an end mill with a width of 2 mm at the center of these test pieces to give a flaw with a length of 50 mm reaching the surface of the base metal in a single letter in the horizontal direction. The cycle conditions were 1 hour for spraying a corrosive liquid (temperature 35 ° C.), 2 hours for drying (60 ° C., humidity 20 to 30%), and 1 hour for wetting (50 ° C., humidity 95% or more). After performing this cycle for 300 cycles, the maximum length of the paint swelling of the applied flaw was measured. Corrosion resistance is No. 1 which does not contain any corrosion-improving element. Using 27 steels as the base steel (100), the ratio of the maximum length of the coating swelling was calculated and evaluated.
表2に腐食試験及びHAZ靭性の指標となる衝撃試験の結果を示す。本発明の成分組成を満たす発明例のNo.1〜26の鋼は、ベース鋼(No.27)に対する塗装膨れの最大長さの比率が50%以下であり、良好な耐食性を有していることがわかる。また、発明例にジンクプライマーを塗布した鋼材は、ベース鋼(No.27)に対する塗装膨れの最大長さの比率が25%以下であり、良好な耐食性を有していることがわかる。 Table 2 shows the results of the corrosion test and the impact test, which is an index of HAZ toughness. No. 1 of the invention example satisfying the component composition of the present invention. It can be seen that the steels 1 to 26 have a ratio of the maximum length of the coating swelling to the base steel (No. 27) of 50% or less, and have good corrosion resistance. Further, it can be seen that the steel material coated with the zinc primer in the invention example has a ratio of the maximum length of the coating swelling to the base steel (No. 27) of 25% or less, and has good corrosion resistance.
これに対して、本発明の成分組成の条件を満たさないNo.28〜33の鋼は、ベース鋼(No.27)に対する塗装膨れの最大長さの比率がいずれも50%を超えている。No.34〜36の鋼は、ベース鋼(No.27)に対する塗装膨れの最大長さの比率が50%以下であるが、No.34鋼はOが過剰に含まれるため、No.35〜36鋼は、Cu/Mgの値が本発明の条件を満たさないため、それぞれHAZ靭性が低くなっている。 On the other hand, No. which does not satisfy the condition of the component composition of the present invention. In the steels 28 to 33, the ratio of the maximum length of the coating swelling to the base steel (No. 27) exceeds 50%. No. In the steels 34 to 36, the ratio of the maximum length of the coating swelling to the base steel (No. 27) is 50% or less. No. 34 steel contains O in excess. Since the Cu / Mg values of the 35-36 steels do not satisfy the conditions of the present invention, the HAZ toughness of each of them is low.
本発明は、表面にエポキシ系塗膜を有するバラストタンク用耐食鋼材であって、厚鋼板、薄鋼板、形鋼や棒鋼を含むものである。本発明のバラストタンク用耐食鋼材は、例えば 、石炭船や鉱石船、鉱炭兼用船、原油タンカー、LPG船、LNG船、ケミカルタンカー、コンテナ船、ばら積み船、木材専用船、チップ専用船、冷凍運搬船、自動車専用船、重量物船、RORO船、石灰石専用船、セメント専用船等のバラストタンク等の素材として、好適に使用することができる。なお、本発明の耐食鋼材は、海水による腐食環境下で優れた塗装耐食性を示すので、船舶のバラストタンクだけでなく、他の類似の海水による腐食環境で使用される用途にも用いることができる。よって、本発明は、産業上の利用可能性が高いものである。 The present invention is a corrosion-resistant steel material for ballast tanks having an epoxy-based coating film on its surface, and includes thick steel plates, thin steel plates, shaped steels, and steel bars. The corrosion-resistant steel material for ballast tanks of the present invention is, for example, a coal ship, an ore ship, a ship for both mining and coal, a crude oil tanker, an LPG ship, an LNG ship, a chemical tanker, a container ship, a bulk carrier, a wood ship, a chip ship, and a freezer. It can be suitably used as a material for ballast tanks of transport ships, automobile ships, heavy lift ships, RORO ships, limestone ships, cement ships, etc. Since the corrosion-resistant steel material of the present invention exhibits excellent coating corrosion resistance in a corrosive environment due to seawater, it can be used not only for ballast tanks of ships but also for applications used in other similar corrosive environments due to seawater. .. Therefore, the present invention has high industrial applicability.
Claims (6)
C :0.03〜0.25%、
Si:0.05〜0.50%、
Mn:0.10〜2.50%、
S :0.001〜0.020%、
Cu:0.10〜0.60%、
Ni:0.03〜1.00%、
Al:0.001〜0.100%、
Mg:0.0012〜0.0030%、及び、
O :0.0007〜0.0020%
を含有し、更に、
Sn:0.010〜0.300%、及び、
Sb:0.010〜0.300%
の少なくとも一方を含有し、
P :0.025%以下
N :0.0080%以下
に制限し、残部がFe及び不可避的不純物からなり、
前記Cuの含有量と前記Mgの含有量とが、
70<Cu/Mg<220
を満足し、
表面にエポキシ系塗膜を有することを特徴とするバラストタンク用耐食鋼材。 By mass%
C: 0.03 to 0.25%,
Si: 0.05 to 0.50%,
Mn: 0.10-2.50%,
S: 0.001 to 0.020%,
Cu: 0.10 to 0.60%,
Ni: 0.03 to 1.00%,
Al: 0.001 to 0.100%,
Mg: 0.0012 to 0.0030%, and
O: 0.0007 to 0.0020%
Containing,
Sn: 0.010 to 0.300% and
Sb: 0.010 to 0.300%
Contains at least one of
P: 0.025% or less N: Limit to 0.0080% or less, the balance consists of Fe and unavoidable impurities,
The content of Cu and the content of Mg are
70 <Cu / Mg <220
Satisfied,
A corrosion-resistant steel material for ballast tanks, which has an epoxy-based coating film on its surface.
Cr:1.00%以下、
Mo:0.90%以下、及び、
W :1.00%以下
の1種又は2種以上を含有することを特徴とする請求項1に記載のバラストタンク用耐食鋼材。 Furthermore, in% by mass,
Cr: 1.00% or less,
Mo: 0.90% or less, and
W: The corrosion-resistant steel material for a ballast tank according to claim 1, which contains one type or two or more types of 1.00% or less.
Ti:0.100%以下、
Zr:0.10%以下、
Ta:0.100%以下、
Nb:0.200%以下、及び、
V :0.20%以下
の1種又は2種以上を含有することを特徴とする請求項1又は2に記載のバラストタンク用耐食鋼材。 Furthermore, in% by mass,
Ti: 0.100% or less,
Zr: 0.10% or less,
Ta: 0.100% or less,
Nb: 0.200% or less, and
V: The corrosion-resistant steel material for a ballast tank according to claim 1 or 2, which contains one type or two or more types of 0.20% or less.
B :0.0030%以下
を含有することを特徴とする請求項1〜3の何れか1項に記載のバラストタンク用耐食鋼材。 Furthermore, in% by mass,
B: The corrosion-resistant steel material for ballast tanks according to any one of claims 1 to 3, which contains 0.0030% or less.
Ca:0.0050%以下、
REM:0.005%以下、及び
Y :0.100%以下
の1種又は2種以上を含有することを特徴とする請求項1〜4の何れか1項に記載のバラストタンク用耐食鋼材。 Furthermore, in% by mass,
Ca: 0.0050% or less,
The corrosion-resistant steel material for a ballast tank according to any one of claims 1 to 4, wherein REM: 0.005% or less and Y: 0.100% or less are contained in one or more.
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