JP6287791B2 - Corrosion resistant steel for inner bottom plate of coal ship and coal / ore combined use hold - Google Patents
Corrosion resistant steel for inner bottom plate of coal ship and coal / ore combined use hold Download PDFInfo
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- 239000003245 coal Substances 0.000 title claims description 75
- 239000010935 stainless steel Substances 0.000 title claims description 13
- 229910000831 Steel Inorganic materials 0.000 claims description 77
- 239000010959 steel Substances 0.000 claims description 77
- 229910001563 bainite Inorganic materials 0.000 claims description 14
- 229910052720 vanadium Inorganic materials 0.000 claims description 6
- 229910000859 α-Fe Inorganic materials 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 3
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- 230000008520 organization Effects 0.000 claims 1
- 238000005260 corrosion Methods 0.000 description 39
- 230000007797 corrosion Effects 0.000 description 39
- 239000000463 material Substances 0.000 description 31
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 18
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 15
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- 238000001816 cooling Methods 0.000 description 11
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 10
- 229910052742 iron Inorganic materials 0.000 description 9
- 238000012360 testing method Methods 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 7
- 238000005098 hot rolling Methods 0.000 description 7
- 238000000034 method Methods 0.000 description 7
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- 230000015572 biosynthetic process Effects 0.000 description 4
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- 229910052750 molybdenum Inorganic materials 0.000 description 4
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- 238000007792 addition Methods 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
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- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 238000012423 maintenance Methods 0.000 description 2
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- 229920006395 saturated elastomer Polymers 0.000 description 2
- 229910052718 tin Inorganic materials 0.000 description 2
- 238000011282 treatment Methods 0.000 description 2
- 229910052725 zinc Inorganic materials 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N acrylic acid group Chemical group C(C=C)(=O)O NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 1
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Description
本発明は、石炭船および石炭・鉱石兼用船ホールド内底板に用いられる、耐食性に優れ、かつ荷役の影響による変形が小さい鋼材に関するものである。
本発明の鋼材は、厚鋼板をはじめとして、薄鋼板、形鋼および棒鋼等を含むものとする。
TECHNICAL FIELD The present invention relates to a steel material that is used for a coal ship and an inner bottom plate of a coal / ore combined ship hold and has excellent corrosion resistance and is less deformed by the influence of cargo handling.
The steel material of the present invention includes a thick steel plate, a thin steel plate, a shape steel, a bar steel, and the like.
エネルギー資源の運搬の多くに商船が用いられていて、その中でもばら積み貨物船は、その約30％の船腹量を占めている。このばら積み貨物船において、1990年代初頭に海難事故が相次いで発生し、国際問題となった。特に、石炭船や石炭・鉱石兼用船での事故が数多く報告されており、その原因の大部分は船倉（以下「ホールド」とも言う）内での損傷であった。 Merchant ships are used for the transportation of energy resources, and bulk cargo ships account for about 30% of the volume. In this bulk carrier, marine accidents occurred one after another in the early 1990s, which became an international issue. In particular, many accidents have been reported on coal ships and coal / ore combined ships, most of which were caused by damage in the hold (hereinafter also referred to as “hold”).
ばら積み貨物船では、積荷を直接ホールドに積載するため、腐食性の積荷の影響を受け易く、船倉内の腐食、特に石炭船や石炭・鉱石兼用船の船倉内の側壁部、肋骨部での孔食により、局所的に強度が減少することが問題と考えられている。実際、この孔食が著しく進行した事例や、船の強度を確保する肋骨部分の板厚が極端に減少している事例が報告されている。 Bulk cargo ships are loaded directly onto the hold, and are therefore susceptible to corrosive loads, and corrode in the hold, especially in the side walls and ribs in the hold of coal ships and coal / ore combined ships. It is considered that the strength is locally reduced by eating. In fact, there have been reports of cases in which this pitting corrosion has remarkably progressed and cases in which the plate thickness of the rib portion that ensures the strength of the ship has been extremely reduced.
上述したように孔食の発生するばら積み貨物船の側壁部、肋骨部では、結露水が生じ易い。こうした結露水が生じた場所に石炭の硫黄成分が溶け出し、結露水と反応して硫酸を生成するので、船倉内は硫酸腐食が生じ易い低ｐＨ環境となっている。さらに、生成した硫酸はホールド内底板に蓄積されるので、ホールド内底板は激しく腐食される。このため、ホールド内底板は船舶寿命25年において一度は全面的な補修が必要とされている。 As described above, dew condensation water is likely to occur at the side wall portion and rib portion of the bulk cargo ship where pitting corrosion occurs. Since the sulfur component of coal dissolves in the place where the condensed water is generated and reacts with the condensed water to generate sulfuric acid, the inside of the hold has a low pH environment in which sulfuric acid corrosion is likely to occur. Further, since the generated sulfuric acid is accumulated in the inner bottom plate of the hold, the inner bottom plate of the hold is severely corroded. For this reason, the inner bottom plate of the hold needs to be fully repaired once at a ship life of 25 years.
このような船倉内の腐食対策として、船倉内には変性エポキシ系塗装が被覆厚さ約150〜200μmで施されている。しかし、石炭や鉄鉱石によるメカニカルダメージや積荷搬出の際の重機による傷、磨耗により、塗装が剥がれる場合が多いため、十分な防食効果は得難かった。 As a countermeasure against such corrosion in the hold, a modified epoxy coating is applied in the hold with a coating thickness of about 150 to 200 μm. However, it is difficult to obtain a sufficient anticorrosion effect because the paint often peels off due to mechanical damage caused by coal or iron ore, and scratches and wear caused by heavy machinery during loading and unloading.
そのため、さらなる腐食対策として、定期的な再塗装あるいは一部補修するなどの方法が採られているが、このような方法は、非常に大きなコストがかかることから、船舶のメンテナンス費用を含め、ライフサイクルコストを低減させるために、新たな耐食鋼の開発が課題となっている。 Therefore, as a further countermeasure against corrosion, methods such as periodic repainting or partial repairs have been adopted, but such methods are very expensive, and therefore include life costs including ship maintenance costs. In order to reduce cycle costs, the development of new corrosion-resistant steel has become an issue.
ところで、船舶用の耐食鋼としては、カーゴオイルタンク用やバラストタンク用として開発された鋼が知られている。しかし、石炭船や石炭・鉱石兼用船のホールドの使用環境は、腐食環境（温度・湿度・腐食性物質など）および内容物によるメカニカルダメージの有無などの点で、カーゴオイルタンクやバラストタンクの使用環境と全く異なっている。このため、石炭船や石炭・鉱石兼用船ホールド用の鋼としては、独自の材料設計や特性評価が必要とされる。 By the way, steel developed for cargo oil tanks and ballast tanks is known as a corrosion-resistant steel for ships. However, the use environment of coal ships and coal / ore combined ships is the use of cargo oil tanks and ballast tanks in terms of the corrosive environment (temperature, humidity, corrosive substances, etc.) and the presence or absence of mechanical damage due to the contents. It is completely different from the environment. For this reason, original material design and characteristic evaluation are required for steel for coal ships and coal / ore combined ships.
一方で、石炭船および石炭・鉱石兼用船ホールドの内底板は、荷揚げの際におけるグラブバケット等の荷役装置との接触・衝突、または荷積みの際における石炭や鉱石との直接的な接触・衝突により、ロンジ間において変形し、へこみが形成されることが分かっている（図１参照）。内底板にへこみがある場合、このへこみ部に石炭・鉱石含有の水分や結露水が蓄積して水溜りが形成され、腐食性物質が濃縮するため、腐食による減厚が大きくなる。また、ホールド内底板がへこみ変形した場合、船体構造としての耐座屈性能が劣化し、重大事故の原因となる可能性がある。そのため、石炭船および石炭・鉱石兼用船ホールドの内底板には、へこみが形成されないようにある程度の強度を有した鋼板を適用する必要がある。 On the other hand, the inner bottom plate of coal ships and coal / ore combined ships hold contact / collision with grab buckets and other cargo handling equipment during unloading, or direct contact / collision with coal and ore during loading. Thus, it is known that deformation occurs between the longes and a dent is formed (see FIG. 1). When there is a dent in the inner bottom plate, water and condensation water containing coal and ore accumulates in the dent, forming a puddle, and corrosive substances are concentrated, resulting in a greater reduction in thickness due to corrosion. In addition, when the inner bottom plate of the hold is dented and deformed, the buckling resistance performance as a hull structure is deteriorated, which may cause a serious accident. Therefore, it is necessary to apply a steel plate having a certain degree of strength to the inner bottom plate of the coal ship and the coal / ore combined ship hold so that no dent is formed.
このような石炭船および石炭・鉱石兼用船ホールド用途に言及した従来技術としては、特許文献１〜４が知られている。特許文献１にはMgを必須成分とした鋼材が、また特許文献２および特許文献３にはSnを必須成分とした鋼材が開示されている。さらに、特許文献４には、Cu、Cr、Zn、Snを必須成分とした鋼材が開示されている。 Patent Documents 1 to 4 are known as conventional techniques referring to such coal ship and coal / ore combined ship hold applications. Patent Document 1 discloses a steel material containing Mg as an essential component, and Patent Documents 2 and 3 disclose a steel material containing Sn as an essential component. Furthermore, Patent Document 4 discloses a steel material containing Cu, Cr, Zn, and Sn as essential components.
しかしながら、特許文献１に示された鋼材は、船舶外板やバラストタンク、カーゴオイルタンク、鉱石船カーゴホールド等の共通的使用環境での耐食性の改善を目指しているためか、鋼材の耐食性の評価として、カーゴオイルタンクとバラストタンクの腐食試験の結果が良好であることは挙げられているものの、石炭船および石炭・鉱石兼用船のホールド使用環境を考慮した試験結果については示されていない。 However, the steel material disclosed in Patent Document 1 is intended to improve the corrosion resistance in common use environments such as ship outer plates, ballast tanks, cargo oil tanks, ore ship cargo hold, etc. Although it is mentioned that the results of the corrosion test of the cargo oil tank and the ballast tank are good, the test results in consideration of the holding use environment of coal ships and coal / ore combined ships are not shown.
また、特許文献２、３では、鋼材に耐食性を与える重要な元素としてSnが用いられているが、Snの添加は鋼材の靭性を著しく劣化させるため、母材・溶接継手靭性および熱間加工性について問題があった。 In Patent Documents 2 and 3, Sn is used as an important element for imparting corrosion resistance to steel materials. However, the addition of Sn significantly deteriorates the toughness of steel materials. There was a problem about.
さらに、特許文献４では、Cu、Cr、Zn、Snを複合添加することで耐食性を高めた鋼材が開示されているが、これらの添加は鋼材の靭性を著しく劣化させるため、母材・溶接継手靭性および熱間加工性について問題があった。 Furthermore, Patent Document 4 discloses a steel material whose corrosion resistance is improved by adding Cu, Cr, Zn, and Sn in combination. However, since these additions significantly deteriorate the toughness of the steel material, the base material and the welded joint are disclosed. There were problems with toughness and hot workability.
以上述べたとおり、石炭船および石炭・鉱石兼用船ホールドに用いられる耐食性に優れた鋼材の開発には、石炭船および石炭・鉱石兼用船ホールド特有の腐食環境を考慮すると同時に、耐食性を有しつつも造船用鋼材として必要な靭性を保持する成分設計が必要となるが、従来はこれらの点に対して考慮が払われていなかった。 As described above, the development of steel materials with excellent corrosion resistance for use in coal ships and coal / ore combined ships holds, while taking into account the corrosive environment unique to coal ships and coal / ore combined ships, while maintaining corrosion resistance. However, it is necessary to design a component that retains the toughness necessary for steel for shipbuilding. Conventionally, however, no consideration has been given to these points.
加えて、特許文献１〜４は、石炭船および石炭・鉱石兼用船ホールド用途に言及した従来技術であるが、上述したホールド内底板適用時における、荷役装置および積荷の接触・衝突による変形を低減するために必要な強度という点については、全く考慮されていなかった。 In addition, Patent Documents 1 to 4 are conventional technologies that mention coal ship and coal / ore combined ship hold applications, but reduce deformation due to contact / collision of cargo handling equipment and cargo when the above-mentioned hold inner bottom plate is applied. The point of strength required to do this was not taken into consideration at all.
本発明は、上記の現状に鑑み開発されたもので、石炭船および石炭・鉱石兼用船ホールドにおける腐食環境である、硫酸の生成した低ｐＨ環境下において、優れた耐食性を示し、かつ積荷の接触・衝突による変形を低減した石炭船および石炭・鉱石兼用船ホールド内底板用の耐食鋼を提供することを目的とする。 The present invention has been developed in view of the above situation, and shows excellent corrosion resistance in a low pH environment in which sulfuric acid is generated, which is a corrosive environment in a coal ship and a coal / ore combined ship hold, and is in contact with a load. -An object of the present invention is to provide a corrosion-resistant steel for the bottom plate of a coal ship and a coal / ore combined-use ship with reduced deformation caused by a collision.
一般に、船舶は、厚鋼板や薄鋼板、形鋼、棒鋼等の鋼材を溶接して建造されており、その鋼材の表面には防食塗膜が施されて使用される。しかし、石炭船や石炭・鉱石兼用船のホールド使用環境では、石炭や鉄鉱石のメカニカルダメージで塗装は剥がれやすい状況にあり、鋼材は腐食環境下に曝される。 Generally, a ship is constructed by welding steel materials such as thick steel plates, thin steel plates, shaped steels, and steel bars, and the surface of the steel materials is used with a corrosion-resistant coating film applied. However, in a hold use environment of a coal ship or a coal / ore combined ship, the coating is easily peeled off due to mechanical damage of the coal or iron ore, and the steel is exposed to a corrosive environment.
そこで、発明者らは、鋼材の表面の防食塗膜が剥離した後も耐食性を発揮できる鋼材の開発を試みた。すなわち、発明者らは、石炭船および石炭・鉱石兼用船ホールド内の環境を模擬した試験法により、各合金元素の影響を検討した。
その結果、Cu，Ni，Sb，ＷおよびNb等が、鋼材の耐食性の向上に有効に寄与することを見出した。
また、上述したように、石炭船および石炭・鉱石兼用船ホールド内底板のへこみ形成および水溜りの形成による腐食減厚の促進を抑制するには、鋼組織におけるベイナイトの体積分率を40％以上とすることが有効であることも併せて見出した。
本発明は、上記の知見に立脚して完成されたものである。
Therefore, the inventors have attempted to develop a steel material that can exhibit corrosion resistance even after the anticorrosion coating on the surface of the steel material is peeled off. That is, the inventors examined the influence of each alloy element by a test method simulating the environment in the coal ship and the coal / ore combined ship hold.
As a result, it has been found that Cu, Ni, Sb, W, Nb and the like effectively contribute to the improvement of the corrosion resistance of the steel material.
In addition, as described above, in order to suppress the promotion of corrosion thickness reduction due to the formation of dents and water pools in the bottom plate of coal ships and coal / ore combined-use ships, the volume fraction of bainite in the steel structure should be 40% or more. It was also found that it is effective.
The present invention has been completed based on the above findings.
すなわち、本発明の要旨構成は次のとおりである。
１．質量％で、
Ｃ：0.01〜0.25％、
Si：0.01〜0.50％、
Mn：0.1〜2.0％、
Ｐ：0.035％以下、
Ｓ：0.035％以下、
Al：0.003〜0.10％、
Cu：0.05〜0.35％、
Ni：0.02〜0.40％、
Sb：0.01〜0.2％、
Ｗ：0.005〜0.5％、
Nb：0.003〜0.025％および
Cr：0.1％以下
を含有し、残部はFeおよび不可避的不純物からなり、鋼組織がベイナイトを組織全体に対する体積分率で40％以上70％以下含むことを特徴とする石炭船および石炭・鉱石兼用船ホールド内底板用の耐食鋼。
That is, the gist configuration of the present invention is as follows.
1. % By mass
C: 0.01 to 0.25%
Si: 0.01 to 0.50%
Mn: 0.1-2.0%
P: 0.035% or less,
S: 0.035% or less,
Al: 0.003-0.10%,
Cu: 0.05 to 0.35%,
Ni: 0.02-0.40%,
Sb: 0.01-0.2%
W: 0.005-0.5%
Nb: 0.003-0.025% and
Cr: 0.1% or less, with the balance consisting of Fe and inevitable impurities, and steel structure containing bainite in a volume fraction of 40% to 70% with respect to the entire structure. Corrosion resistant steel for the bottom plate of ship hold.
２．前記鋼が、質量％で、さらに
Ti：0.001〜0.030％、
Zr：0.001〜0.030％および
Ｖ：0.002〜0.20％
のうちから選ばれる１種以上を含有することを特徴とする前記１に記載の石炭船および石炭・鉱石兼用船ホールド内底板用の耐食鋼。
2. The steel is in% by weight, and
Ti: 0.001 to 0.030%,
Zr: 0.001 to 0.030% and V: 0.002 to 0.20%
The corrosion resistant steel for the inner bottom plate of the coal ship and the coal / ore combined ship hold according to the above 1, which contains at least one selected from the above.
３．前記鋼が、質量％で、さらに
Ca：0.0002〜0.010％
を含有することを特徴とする前記１または２に記載の石炭船および石炭・鉱石兼用船ホールド内底板用の耐食鋼。
3. The steel is in% by weight, and
Ca: 0.0002 to 0.010%
The corrosion-resistant steel for a coal ship according to the above 1 or 2, and a coal / ore combined ship hold inner bottom plate, characterized by comprising:
４．前記鋼が、質量％で、さらに
Mo：0.01〜0.5％、
Co：0.01〜0.5％および
Ｂ：0.0002〜0.0050％
のうちから選ばれる少なくとも１種を含有することを特徴とする前記１〜３のいずれかに記載の石炭船および石炭・鉱石兼用船ホールド内底板用の耐食鋼。
4). The steel is in% by weight, and
Mo: 0.01-0.5%
Co: 0.01-0.5% and B: 0.0002-0.0050%
The corrosion-resistant steel for a coal ship according to any one of the above 1 to 3, and a coal / ore combined-use ship inner bottom plate, which contains at least one selected from the above.
本発明によれば、石炭船や石炭・鉱石兼用船ホールド内の硫酸が生成した低ｐＨ環境下において、優れた耐食性を示し、かつ積荷の接触・衝突による変形を低減した石炭船および石炭・鉱石兼用船ホールド内底板用の耐食鋼を得ることができる。 According to the present invention, a coal ship and a coal / ore exhibiting excellent corrosion resistance in a low pH environment where sulfuric acid is produced in a coal ship or a coal / ore combined ship hold and reducing deformation due to load contact / collision. Corrosion resistant steel for the bottom plate of the combined use ship hold can be obtained.
以下、本発明を具体的に説明する。
まず、本発明において、鋼材の成分組成を前記の範囲に限定した理由について説明する。なお、以下の成分組成を表す％は、特に断らない限り質量％を意味するものとする。
Ｃ：0.01〜0.25％
Ｃは、鋼の強度を上昇させるのに有効な元素であり、本発明では強度を確保するために0.01％以上含有させる。一方、Ｃを0.25％を超えて含有させると、溶接性および溶接熱影響部靭性を低下させる。よって、Ｃ量は0.01〜0.25％の範囲とする。好ましくは0.015〜0.18％の範囲である。
Hereinafter, the present invention will be specifically described.
First, the reason why the component composition of the steel material is limited to the above range in the present invention will be described. In addition,% showing the following component composition shall mean the mass% unless there is particular notice.
C: 0.01-0.25%
C is an element effective for increasing the strength of steel. In the present invention, C is contained in an amount of 0.01% or more in order to ensure the strength. On the other hand, when C is contained exceeding 0.25%, weldability and weld heat affected zone toughness are lowered. Therefore, the C content is in the range of 0.01 to 0.25%. Preferably it is 0.015 to 0.18% of range.
Si：0.01〜0.50％
Siは、脱酸剤として添加され、また鋼の強度を高める元素であるので、本発明では0.01％以上含有させる。しかしながら、Siを0.50％を超えて含有させると、鋼の靱性を劣化させるので、Si量の上限は0.50％とする。好ましくは0.05〜0.40％の範囲である。
Si: 0.01-0.50%
Si is added as a deoxidizer and is an element that enhances the strength of the steel. Therefore, in the present invention, Si is contained in an amount of 0.01% or more. However, if Si is contained in excess of 0.50%, the toughness of the steel is deteriorated, so the upper limit of Si content is 0.50%. Preferably it is 0.05 to 0.40% of range.
Mn：0.1〜2.0％
Mnは、鋼の強度を上げることができるため、0.1％以上含有させる。しかしながら、Mn を2.0％を超えて含有させると、鋼の靱性および溶接性を低下させるため、Mn量の上限は2.0％とする。好ましくは0.5〜1.6％の範囲である。
Mn: 0.1-2.0%
Mn can increase the strength of the steel, so 0.1% or more is contained. However, if Mn is contained in excess of 2.0%, the toughness and weldability of the steel are lowered, so the upper limit of the Mn content is 2.0%. Preferably it is 0.5 to 1.6% of range.
Ｐ：0.035％以下
Ｐは、鋼の母材靱性のみならず、溶接性および溶接部靱性を低下させる有害な元素であるので、極力低減することが望ましい。特にＰ量が0.035％を超えると、母材靭性および溶接部靭性の低下が大きくなる。よって、Ｐ量は0.035％以下とする。好ましくは0.025％以下である。
P: 0.035% or less P is a harmful element that deteriorates not only the base metal toughness of steel but also the weldability and weld zone toughness, so it is desirable to reduce it as much as possible. In particular, when the P content exceeds 0.035%, the deterioration of the base metal toughness and weld zone toughness increases. Therefore, the P content is 0.035% or less. Preferably it is 0.025% or less.
Ｓ：0.035％以下
Ｓは、鋼の靭性および溶接性を劣化させる有害な元素であるので、極力低減することが好ましく、本発明では0.035％以下とする。
S: 0.035% or less Since S is a harmful element that deteriorates the toughness and weldability of steel, it is preferably reduced as much as possible. In the present invention, it is 0.035% or less.
Al：0.003〜0.10％
Alは、脱酸剤として0.003％以上含有させるが、0.10％を超える含有は，溶接部靭性に悪影響を及ぼすので，Al量は0.003〜0.10％の範囲とする。
Al: 0.003-0.10%
Al is contained in an amount of 0.003% or more as a deoxidizer, but if it exceeds 0.10%, the toughness of the weld is adversely affected, so the Al content is in the range of 0.003 to 0.10%.
Cu：0.05〜0.35％
Cuは、腐食生成物を緻密にし、地鉄中へのH2O、O2、SO4 2-の拡散を抑制する。これにより、鋼の耐食性が向上する。この効果は、Cu量が0.05％以上になると発現するが、0.35％を超えて過剰に含有されると溶接性や母材靭性が低下する。そのため、Cu量は0.05〜0.35％の範囲とする。好ましくは0.10〜0.30％の範囲である。
Cu: 0.05-0.35%
Cu densifies corrosion products and suppresses the diffusion of H 2 O, O 2 , and SO 4 2− into the ground iron. Thereby, the corrosion resistance of steel improves. This effect is manifested when the Cu content is 0.05% or more, but when it exceeds 0.35% and is contained excessively, weldability and base metal toughness are lowered. Therefore, the amount of Cu is made 0.05 to 0.35% of range. Preferably it is 0.10 to 0.30% of range.
Ni：0.02〜0.40％
Niは、Cuと同様、腐食生成物を緻密にし、地鉄中へのH2O、O2、SO4 2-の拡散を抑制する。これにより、鋼の耐食性が向上する。この効果は、Ni量が0.02％以上になると発現するが、0.40％を超えると溶接性や母材靭性が低下する。そのため、Ni量は0.02〜0.40％の範囲とする。好ましくは0.04〜0.30％の範囲である。
Ni: 0.02-0.40%
Ni, like Cu, densifies corrosion products and suppresses diffusion of H 2 O, O 2 , and SO 4 2− into the ground iron. Thereby, the corrosion resistance of steel improves. This effect appears when the Ni content is 0.02% or more, but when it exceeds 0.40%, the weldability and the base metal toughness are lowered. Therefore, the Ni content is in the range of 0.02 to 0.40%. Preferably it is 0.04 to 0.30% of range.
Sb：0.01〜0.2％
Sbは、鋼材に合金元素として0.01％以上を含有させると、低ｐＨ環境において地鉄近傍に濃縮する。Sbは大きな水素過電圧を持つため、Sbが析出した部分では水素発生反応が抑制され、耐食性が向上する。また、Cuと金属間化合物であるCu2Sbを形成することで、さらに耐食性が向上する。一方、Sbは0.2％を超えて含有させると靭性を低下させる。よって、Sb量は0.01〜0.2％の範囲とする。好ましくは0.02〜0.15％の範囲である。
Sb: 0.01-0.2%
When the steel material contains 0.01% or more as an alloy element in the steel material, it is concentrated near the ground iron in a low pH environment. Since Sb has a large hydrogen overvoltage, the hydrogen generation reaction is suppressed in the portion where Sb is deposited, and the corrosion resistance is improved. Further, by forming the Cu 2 Sb is Cu intermetallic compound, to further improve the corrosion resistance. On the other hand, if the Sb content exceeds 0.2%, the toughness is lowered. Therefore, the Sb content is in the range of 0.01 to 0.2%. Preferably it is 0.02 to 0.15% of range.
Ｗ：0.005〜0.5％
Ｗは、WO4 2-の生成により、地鉄中へのSO4 2-の拡散を抑制すると共に、腐食生成物を緻密にして、地鉄中へのH2O、O2、SO4 2-の拡散を抑制する。これらの効果を得るためには、Ｗを0.005％以上含有させる必要がある。しかし、Ｗが0.5％を超えて含有されると効果が飽和するだけでなく、コストも上昇するので、Ｗ量は0.005〜0.5％の範囲とする。好ましくは0.02〜0.2％の範囲である。
W: 0.005-0.5%
W suppresses the diffusion of SO 4 2- into the ground iron due to the formation of WO 4 2- , and also densifies the corrosion products to form H 2 O, O 2 , SO 4 2 into the ground iron. - suppressing the diffusion of. In order to obtain these effects, it is necessary to contain 0.005% or more of W. However, if W is contained in excess of 0.5%, not only the effect is saturated but also the cost is increased, so the W amount is set in the range of 0.005 to 0.5%. Preferably it is 0.02 to 0.2% of range.
Nb：0.003〜0.025％
Nbは、腐食生成物を緻密にして、地鉄中へのH2O、O2、SO4 2-の拡散を抑制する。この効果を得るためにはNbを0.003％以上含有させる必要がある。一方、Nbを0.025％を超えて含有させても効果は飽和する。よって、Nb量は0.003〜0.025％の範囲とする。好ましくは0.005〜0.020％の範囲である。
Nb: 0.003-0.025%
Nb densifies the corrosion products and suppresses the diffusion of H 2 O, O 2 and SO 4 2− into the ground iron. In order to obtain this effect, it is necessary to contain 0.003% or more of Nb. On the other hand, even if Nb exceeds 0.025%, the effect is saturated. Therefore, the Nb content is in the range of 0.003 to 0.025%. Preferably it is 0.005 to 0.020% of range.
Cr：0.1％以下
Crは、低ｐＨ環境で加水分解を起こし、耐食性を低下させる元素であるので、極力低減することが好ましいが、0.1％以下であれば許容できる。
Cr: 0.1% or less
Cr is an element that causes hydrolysis in a low pH environment and lowers corrosion resistance. Therefore, Cr is preferably reduced as much as possible, but 0.1% or less is acceptable.
以上、基本成分について説明したが、本発明では、必要に応じて、以下に述べる元素を適宜含有させることができる。
Ti：0.001〜0.030％、Zr：0.001〜0.030％、Ｖ：0.002〜0.20％
Ti、ZrおよびＶはいずれも、鋼の強度を高める元素であり、必要とする強度に応じて選択して含有させることができる。このような効果を得るためには、TiおよびZrは0.001％以上、Ｖは0.002％以上含有させる必要がある。しかしながら、TiおよびZrはいずれも0.030％を超えて、またＶは0.20％を超えて含有させると靱性が低下するため、Ti，ZrおよびＶを含有させる場合には、それぞれ、上記の範囲で含有させることとする。
The basic components have been described above. In the present invention, the following elements can be appropriately contained as necessary.
Ti: 0.001 to 0.030%, Zr: 0.001 to 0.030%, V: 0.002 to 0.20%
Ti, Zr, and V are all elements that increase the strength of steel, and can be selected and contained according to the required strength. In order to obtain such an effect, it is necessary to contain Ti and Zr in an amount of 0.001% or more and V in an amount of 0.002% or more. However, if Ti and Zr both exceed 0.030% and V exceeds 0.20%, the toughness decreases. Therefore, when Ti, Zr and V are included, each content is within the above range. I will let you.
Ca：0.0002〜0.010％
Caは、介在物形態制御の効果があり、鋼の延性および靱性を高めることができる。この効果はCa量が0.0002％以上で発現する。一方、Caを0.010％を超えて含有させると、粗大な介在物を形成し、母材の靱性を劣化させる。そこで、Ca量は0.0002〜0.010％の範囲とする。好ましくは0.0005〜0.005％の範囲である。
Ca: 0.0002 to 0.010%
Ca has an effect of controlling the form of inclusions, and can increase the ductility and toughness of steel. This effect appears when the Ca content is 0.0002% or more. On the other hand, when Ca is contained in excess of 0.010%, coarse inclusions are formed and the toughness of the base material is deteriorated. Therefore, the Ca content is in the range of 0.0002 to 0.010%. Preferably it is 0.0005 to 0.005% of range.
Mo：0.01〜0.5％、Co：0.01〜0.5％、Ｂ：0.0002〜0.0050％
Mo、CoおよびＢはいずれも、鋼の強度を高める元素であり、必要とする強度に応じて選択して含有させることができる。このような効果は、Mo、Coは0.01％以上で、またＢは0.0002％以上で発現する。しかしながら、MoおよびCoはいずれも0.5％を超えて、またＢは0.0050％を超えて含有させるとそれぞれ靱性が低下するため、Mo，CoおよびＢを含有させる場合には、それぞれ、上記の範囲で含有させることとする。
Mo: 0.01-0.5%, Co: 0.01-0.5%, B: 0.0002-0.0050%
Mo, Co, and B are all elements that increase the strength of steel, and can be selected and contained according to the required strength. Such an effect appears when Mo and Co are 0.01% or more, and B is 0.0002% or more. However, if both Mo and Co exceed 0.5% and B exceeds 0.0050%, the toughness decreases. Therefore, when Mo, Co and B are included, It is supposed to be included.
本発明における成分組成のうち、上記以外の成分はFeおよび不可避的不純物である。ただし、本発明の効果を阻害しない範囲内であれば、上記以外の成分の含有を拒むものではない。 Among the component compositions in the present invention, components other than those described above are Fe and inevitable impurities. However, as long as the effects of the present invention are not impaired, the inclusion of components other than those described above is not rejected.
次に、本発明における鋼組織の限定理由を説明する。
組織全体に対するベイナイトの体積分率：40％以上70％以下
石炭船および石炭・鉱石兼用船ホールドの内底板は、荷揚げの際におけるグラブバケット等の荷役装置との接触・衝突、または荷積みの際における石炭や鉱石との直接的な接触・衝突により、ロンジ間において変形し、前掲図１に示したように、へこみが形成される。内底板にこのようなへこみが形成された場合、石炭・鉱石含有の水分や結露水の蓄積による水溜りが形成される結果、腐食減厚が大きくなる。また、ホールド内底板がへこみ変形した場合、船体構造としての耐座屈性能が劣化し、重大事故の原因となる可能性がある。そのため、石炭船および石炭・鉱石兼用船ホールドの内底板には、ある程度の降伏強度を有した鋼板を適用する必要がある。
ここに、降伏強度は鋼の組織に強く影響を受け、ベイナイトの組織全体に対する体積分率が40％未満になると、降伏強度が低下して、ホールド内底板がへこみ変形を防止することが困難となる。そのため、組織全体に対するベイナイトの体積分率は40％以上とする。
また、ベイナイトの組織全体に対する体積分率は、十分な降伏強度、具体的には390〜440MPaの降伏強度を確保しつつ、延性を高めてより良好な母材および溶接部靭性を得る観点から、組織全体に対するベイナイトの体積分率は70％以下とする。好ましくは60％以下である。
なお、ベイナイト以外の組織としてはフェライトやパーライト等が考えられるが、フェライトについては組織全体に対する体積分率50％以下、パーライトについては組織全体に対する体積分率で10％以下であれば許容できる。
Next, the reason for limiting the steel structure in the present invention will be described.
The volume fraction of bainite with respect to the entire structure: 40% or more and 70% or less The inner bottom plate of coal ships and coal / ore combined-use ships is in contact / collision with cargo handling equipment such as grab buckets during loading or loading. Due to direct contact / collision with coal or ore, deformation occurs between the longes, and dents are formed as shown in FIG. When such a dent is formed in the inner bottom plate, a puddle is formed due to accumulation of water and condensed water containing coal and ore, resulting in an increase in corrosion thickness. In addition, when the inner bottom plate of the hold is dented and deformed, the buckling resistance performance as a hull structure is deteriorated, which may cause a serious accident. Therefore, it is necessary to apply a steel plate having a certain yield strength to the inner bottom plate of the coal ship and the coal / ore combined ship hold.
Here, the yield strength is strongly influenced by the structure of the steel, and when the volume fraction of the entire bainite structure is less than 40%, the yield strength decreases and it is difficult to prevent the dent deformation in the hold inner bottom plate. Become. Therefore, the volume fraction of bainite relative to the entire structure is set to 40% or more.
In addition, the volume fraction of the bainite structure as a whole is from the viewpoint of obtaining a better base material and weld toughness by increasing the ductility while ensuring a sufficient yield strength, specifically a yield strength of 390 to 440 MPa. The volume fraction of bainite relative to the entire tissue is 70% or less. Preferably it is 60% or less.
As the structure other than bainite, ferrite, pearlite, and the like are conceivable. For ferrite, a volume fraction of 50% or less with respect to the entire structure is acceptable, and for pearlite, a volume fraction of 10% or less with respect to the entire structure is acceptable.
ここで、上記したベイナイトの体積分率は、以下のようにして求めることができる。
すなわち、鋼板のＬ断面（圧延方向に平行な垂直断面）を研磨後ナイタールで腐食させ、走査型電子顕微鏡にて倍率３０００倍の組織写真を１０視野撮影し、得られた組織写真データにおいてそれぞれベイナイト組織に相当する領域の画素数を計数し、写真全体の画素数に対する割合を算出することで体積率を求める。組織写真においては、針状あるいは羽毛状のフェライト中に炭化物が点列状に観察された領域をベイナイト組織とする。
Here, the volume fraction of bainite described above can be obtained as follows.
That is, the L cross-section (vertical cross-section parallel to the rolling direction) of the steel plate was polished and then corroded with nital, and 10 structural photographs with a magnification of 3000 times were taken with a scanning electron microscope. The number of pixels in the area corresponding to the tissue is counted, and the volume ratio is obtained by calculating the ratio to the number of pixels in the entire photograph. In the structure photograph, a region in which carbides are observed in a needle-like or feather-like ferrite in a dot sequence is defined as a bainite structure.
また、上記のような組織を有する鋼は、例えば、以下のようにして製造することができる。
上記した成分組成の溶鋼を、転炉、電気炉等の公知の方法で溶製し、連続鋳造法や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良いことは言うまでもない。
ついで、熱間圧延を施すのであるが、この熱間圧延においては、上記した鋼組織を得て、所望の降伏強度を確保するために、スラブの加熱温度、圧延終了温度および冷却条件を適正化することが好ましい。
すなわち、結晶粒粗大化防止の観点から、好ましくは1050〜1250℃の温度にスラブを加熱したのち、所望の寸法形状に熱間圧延するか、あるいは鋼素材の温度が熱間圧延可能な程度に高温である場合には加熱することなく、あるいは均熱する程度で直ちに所望の寸法形状の鋼材に熱間圧延することが好ましい。
また、熱間圧延時の圧延終了温度については、Ar3点以上の温度において熱間圧延を終了することが好ましい。
さらに、熱間圧延終了後の冷却条件については、熱間圧延終了後直ちにあるいは若干の放置時間の後、加速冷却を行えばよいが、上記した好適量のベイナイトを得るには、熱間圧延終了後に若干の時間放置し、開始温度を700〜780℃とする水冷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。
ただし、本発明の鋼を得るための製造方法は、これらに限定されるものではない。
Moreover, the steel which has the above structures can be manufactured as follows, for example.
The molten steel having the above component composition is melted by a known method such as a converter or an electric furnace, and is made into a steel material such as a slab or billet by a known method such as a continuous casting method or an ingot forming method. It goes without saying that treatments such as ladle refining and vacuum degassing may be added to the molten steel.
Next, hot rolling is performed. In this hot rolling, the slab heating temperature, rolling end temperature, and cooling conditions are optimized in order to obtain the above-described steel structure and ensure the desired yield strength. It is preferable to do.
That is, from the viewpoint of preventing the grain coarsening, the slab is preferably heated to a temperature of 1050 to 1250 ° C. and then hot-rolled to a desired dimensional shape, or the temperature of the steel material can be hot-rolled. When the temperature is high, it is preferable to immediately hot-roll to a steel material of a desired size and shape without heating or soaking.
As for the rolling end temperature at the time of hot rolling, it is preferable to end the hot rolling at a temperature not lower than the Ar 3 point.
Furthermore, as for the cooling conditions after the end of hot rolling, accelerated cooling may be performed immediately after the end of hot rolling or after some standing time, but in order to obtain the preferred amount of bainite, the end of hot rolling is completed. It is preferable to leave it for some time later and perform water cooling to a starting temperature of 700 to 780 ° C. Further, after cooling, a reheating treatment may be performed.
However, the production method for obtaining the steel of the present invention is not limited to these.
実施例１
表１に示す成分組成になる鋼を、真空溶解炉で溶製または転炉で溶製後、連続鋳造によりスラブとした。ついで、スラブを加熱炉に装入して、表２に示す条件で熱間圧延し、25mm厚の鋼板とした。その後、表１のNo.１〜25については表２に示す水冷開始温度から室温まで加速冷却（水冷）する一方、No.26〜32については930℃から空冷した。
これらの鋼板について、母材としての組織、引張特性および衝撃特性を調査した。また、溶接部靭性として、入熱量50kJ/cmで作製したFCB溶接継手の熱影響部１mm（ヒュージョンラインから母材側に１mm入った箇所）の熱履歴に相当する再現熱サイクル試験（最高加熱温度1400℃、保持時間１ｓ、800〜500℃の冷却時間40ｓ)を付与し、シャルピー衝撃試験により０℃での吸収エネルギーvＥ0を測定した。
Example 1
The steel having the composition shown in Table 1 was made into a slab by continuous casting after melting in a vacuum melting furnace or in a converter. Next, the slab was placed in a heating furnace and hot-rolled under the conditions shown in Table 2 to obtain a 25 mm thick steel plate. Thereafter, Nos. 1 to 25 in Table 1 were subjected to accelerated cooling (water cooling) from the water cooling start temperature shown in Table 2 to room temperature, while Nos. 26 to 32 were air cooled from 930 ° C.
About these steel plates, the structure | tissue as a base material, a tensile characteristic, and an impact characteristic were investigated. In addition, as the weld zone toughness, a reproducible thermal cycle test (maximum heating temperature) corresponding to the heat history of the heat affected zone of 1 mm (1 mm from the fusion line to the base metal side) of the FCB welded joint produced with a heat input of 50 kJ / cm The absorption energy vE 0 at 0 ° C. was measured by a Charpy impact test.
また、耐食性については、以下に示す条件で評価した。
前記鋼板から、5mmt×50mmW×75mmLの試験片を採取し、その表面をショットブラストして、表面のスケールや油分を除去した。この面を試験面として、塗膜剥離後の鋼材の耐食性を評価した。裏面と端面をシリコン系シールでコーティングした後、アクリル製の治具に嵌め込み、その上に石炭50ｇを敷き詰め、蒸留水を200ml加え、恒温恒湿器により、温度30℃、相対湿度95％の雰囲気を84日間与えた。
なお、石炭は、５ｇを秤量し、常温で100mlの蒸留水に２時間浸漬したのち、ろ過を行ない200mlに希釈した石炭浸出液のｐＨが3.0になるものを用いた。
本実施例では、上記の条件で試験を行うことにより、石炭船および石炭・鉱石兼用船のホールド内底板の腐食環境を模擬している。試験後、錆剥離液を用い、各試験片の錆を剥離し、鋼材の重量減少量を測定し腐食量とした。
表２に機械的特性調査結果および耐食性試験結果を示す。
Moreover, about corrosion resistance, it evaluated on the conditions shown below.
A test piece of 5 mmt × 50 mmW × 75 mmL was collected from the steel plate, and the surface was shot blasted to remove surface scale and oil. Using this surface as a test surface, the corrosion resistance of the steel material after peeling the coating film was evaluated. After coating the back and end surfaces with silicone seals, fit them in an acrylic jig, spread 50g of coal on top of them, add 200ml of distilled water, and maintain a temperature of 30 ° C and relative humidity of 95% with a constant temperature and humidity chamber. For 84 days.
In addition, 5 g of coal was weighed, immersed in 100 ml of distilled water at room temperature for 2 hours, filtered, and then the coal leachate diluted to 200 ml had a pH of 3.0 was used.
In this embodiment, the test is performed under the above conditions to simulate the corrosive environment of the bottom inner plate of the coal ship and the coal / ore combined ship. After the test, using a rust remover, the rust of each test piece was peeled off, and the weight loss of the steel material was measured to obtain the amount of corrosion.
Table 2 shows the results of the mechanical property investigation and the corrosion resistance test.
表２に示したとおり、機械的性質については、No.１〜25の発明例はいずれも良好な値を示しているが、No.26〜32の比較例は、目標値であるベイナイト分率が得られていない。これは、比較例No.26〜32の冷却条件が空冷であり、ベイナイト変態に必要な冷却速度が得られていないためであると考えられる。
一方、耐食性については、発明例の重量減は、ベース鋼である比較例No.26の70％以下であり、良好な耐食性を示したのに対し、比較例であるNo.27〜No.32の重量減はベース鋼No.26の90％以上であり、耐食性として不十分であった。
As shown in Table 2, regarding the mechanical properties, the inventive examples of Nos. 1 to 25 all show good values, but the comparative examples of Nos. 26 to 32 show the target value of bainite fraction. Is not obtained. This is considered to be because the cooling conditions of Comparative Examples No. 26 to 32 are air cooling, and the cooling rate necessary for bainite transformation is not obtained.
On the other hand, regarding the corrosion resistance, the weight loss of the inventive example is 70% or less of the comparative example No. 26 which is the base steel, and showed good corrosion resistance, whereas the comparative examples No. 27 to No. 32 The weight loss was 90% or more of the base steel No. 26, which was insufficient as corrosion resistance.
実施例２
表１に示した鋼板のうち、発明例No.１および比較例No.26を、実際の石炭船(小型ばら積み貨物船、載貨重量トン数：2400トン)ホールド内底板の一部に適用し、耐食性およびへこみ変形の程度について検証した。
以下にその方法を述べる。
Example 2
Of the steel sheets shown in Table 1, Invention Example No. 1 and Comparative Example No. 26 were applied to a part of an actual coal ship (small bulk cargo ship, cargo weight tonnage: 2400 tons) hold bottom plate, The corrosion resistance and the degree of dent deformation were verified.
The method is described below.
上述の鋼板より24mmt×320mmW×1600mmLの板を４枚ずつ採取し、図２に示すように、ホールド内底板中央付近のロンジ間に適用した。適用から５年後、平均板厚減少量および最大板厚減少量を計測し、加えて、最大へこみ深さの測定を行った。
平均板厚減少量については、図３に示す２点（図中×印の点）で板厚計測を行い、２点の平均値とした。
また、最大板厚減少量については、ロンジ間中央付近で３回板厚を計測し、測定された最大値とした。なお、板厚減少量は、次式から求めた。
板厚減少量(mm)＝図面初期板厚(mm)−計測板厚(mm)
さらに、最大へこみ深さについては、図３に示すように、ロンジ間に角柱を置いて基準面とし、最もへこんだ部位との距離をメジャーで計測して求めた。
表３に、平均板厚減少量、最大板厚減少量および最大へこみ深さについての調査結果を示す。
Four plates of 24 mmt × 320 mmW × 1600 mmL were sampled from the steel plates described above and applied between the longages near the center of the bottom plate in the hold as shown in FIG. Five years after application, the average plate thickness reduction amount and the maximum plate thickness reduction amount were measured, and in addition, the maximum dent depth was measured.
Regarding the average thickness reduction amount, the thickness was measured at the two points shown in FIG.
Moreover, about the maximum thickness reduction amount, plate thickness was measured 3 times near the center between longes, and it was set as the maximum value measured. In addition, the thickness reduction amount was calculated | required from following Formula.
Thickness reduction (mm) = Initial drawing thickness (mm)-Measurement thickness (mm)
Further, as shown in FIG. 3, the maximum dent depth was obtained by placing a prism between the longes as a reference plane and measuring the distance from the most dent portion with a measure.
Table 3 shows the results of the investigation on the average plate thickness reduction amount, the maximum plate thickness reduction amount, and the maximum dent depth.
表３に示したとおり、発明例No.１-1〜4は、比較例No.26-1〜4に比べて、平均板厚減少量、最大板厚減少量および最大へこみ深さのいずれについても低減できていることが分かる。
本発明例において、平均板厚減少量よりも最大板厚減少量を大きく低減できたのは、へこみ変形が抑制され、水溜りの形成による減厚の促進が抑制されたためと考えられる。
As shown in Table 3, Invention Examples Nos. 1-1 to 4 are any of the average sheet thickness reduction amount, the maximum sheet thickness reduction amount, and the maximum indentation depth as compared with Comparative Examples No. 26-1 to 4-4. It can be seen that the reduction is also possible.
In the example of the present invention, the reason why the maximum plate thickness reduction amount was able to be reduced more than the average plate thickness reduction amount is thought to be because the dent deformation was suppressed and the promotion of the thickness reduction due to the formation of the water pool was suppressed.
本発明に係る鋼材は、石炭船および石炭・鉱石兼用船ホールド内底板として使用した場合、優れた耐食性を発揮するだけでなく、優れた耐変形性能を示すので、荷役の影響によるへこみ変形を低減し、水溜りの形成による腐食減厚の促進を抑制することができ、鋼材切り替えを低減できるなどの効果を奏する。 The steel material according to the present invention not only exhibits excellent corrosion resistance when used as a coal ship and coal / ore combined ship hold inner bottom plate, but also exhibits excellent deformation resistance, thereby reducing dent deformation due to the effect of cargo handling. In addition, the promotion of corrosion thickness reduction due to the formation of a water pool can be suppressed, and the effect of reducing the steel material switching can be achieved.
Claims (4)
Ｃ：0.01〜0.25％、
Si：0.01〜0.50％、
Mn：0.1〜2.0％、
Ｐ：0.035％以下、
Ｓ：0.035％以下、
Al：0.003〜0.10％、
Cu：0.05〜0.35％、
Ni：0.02〜0.40％、
Sb：0.01〜0.2％、
Ｗ：0.005〜0.5％、
Nb：0.003〜0.025％および
Cr：0.1％以下
を含有し、残部はFeおよび不可避的不純物からなり、鋼組織がベイナイトを組織全体に対する体積分率で40％以上70％以下含み、かつ、フェライトおよびパーライトの組織全体に対する体積分率がそれぞれ50％以下および10％以下であることを特徴とする石炭船および石炭・鉱石兼用船ホールド内底板用の耐食鋼。 % By mass
C: 0.01 to 0.25%
Si: 0.01 to 0.50%
Mn: 0.1-2.0%
P: 0.035% or less,
S: 0.035% or less,
Al: 0.003-0.10%,
Cu: 0.05 to 0.35%,
Ni: 0.02-0.40%,
Sb: 0.01-0.2%
W: 0.005-0.5%
Nb: 0.003-0.025% and
Cr: containing 0.1% or less, the balance being Fe and unavoidable impurities, the volume fraction of the steel structure is a bainite for the entire organization seen contains 40% to 70%, and the volume for the entire structure of ferrite and pearlite Corrosion-resistant steel for the bottom plate of coal ships and coal / ore combined ships hold, characterized by fractions of 50% or less and 10% or less, respectively .
Ti：0.001〜0.030％、
Zr：0.001〜0.030％および
Ｖ：0.002〜0.20％
のうちから選ばれる１種以上を含有することを特徴とする請求項１に記載の石炭船および石炭・鉱石兼用船ホールド内底板用の耐食鋼。 The steel is in% by weight, and
Ti: 0.001 to 0.030%,
Zr: 0.001 to 0.030% and V: 0.002 to 0.20%
The corrosion resistant steel for a coal ship and a coal / ore combined ship hold inner bottom plate according to claim 1, comprising at least one selected from the group consisting of:
Ca：0.0002〜0.010％
を含有することを特徴とする請求項１または２に記載の石炭船および石炭・鉱石兼用船ホールド内底板用の耐食鋼。 The steel is in% by weight, and
Ca: 0.0002 to 0.010%
The corrosion-resistant steel for the inner bottom plate of a coal ship and a coal / ore combined ship hold according to claim 1 or 2, characterized in that
Mo：0.01〜0.5％、
Co：0.01〜0.5％および
Ｂ：0.0002〜0.0050％
のうちから選ばれる少なくとも１種を含有することを特徴とする請求項１〜３のいずれかに記載の石炭船および石炭・鉱石兼用船ホールド内底板用の耐食鋼。 The steel is in% by weight, and
Mo: 0.01-0.5%
Co: 0.01-0.5% and B: 0.0002-0.0050%
The corrosion-resistant steel for a coal ship and a coal / ore combined ship hold inner bottom plate according to any one of claims 1 to 3, characterized in that it contains at least one selected from among the above.
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