JP4997808B2 - Sulfuric acid dew-point corrosion steel with excellent hydrochloric acid resistance - Google Patents
Sulfuric acid dew-point corrosion steel with excellent hydrochloric acid resistance Download PDFInfo
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- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 title claims description 130
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 title claims description 98
- 229910000831 Steel Inorganic materials 0.000 title claims description 89
- 239000010959 steel Substances 0.000 title claims description 89
- 230000007797 corrosion Effects 0.000 title claims description 86
- 238000005260 corrosion Methods 0.000 title claims description 86
- 229910052787 antimony Inorganic materials 0.000 claims description 31
- 229910052721 tungsten Inorganic materials 0.000 claims description 29
- 239000000203 mixture Substances 0.000 claims description 17
- 229910052718 tin Inorganic materials 0.000 claims description 16
- 239000000463 material Substances 0.000 claims description 15
- 229910052799 carbon Inorganic materials 0.000 claims description 14
- 229910052802 copper Inorganic materials 0.000 claims description 13
- 229910052717 sulfur Inorganic materials 0.000 claims description 11
- 229910052710 silicon Inorganic materials 0.000 claims description 10
- 239000010935 stainless steel Substances 0.000 claims description 7
- 229910052748 manganese Inorganic materials 0.000 claims description 6
- 229910052698 phosphorus Inorganic materials 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052758 niobium Inorganic materials 0.000 claims description 2
- 229910052720 vanadium Inorganic materials 0.000 claims description 2
- 229940032330 sulfuric acid Drugs 0.000 description 60
- 239000002253 acid Substances 0.000 description 41
- 230000000694 effects Effects 0.000 description 35
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- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- 229910052777 Praseodymium Inorganic materials 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- -1 chloride ions Chemical class 0.000 description 1
- 239000000460 chlorine Substances 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
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- 229910052746 lanthanum Inorganic materials 0.000 description 1
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- 239000011593 sulfur Substances 0.000 description 1
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical class S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 1
- 229910052815 sulfur oxide Inorganic materials 0.000 description 1
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Description
本発明は、塩酸や硫酸などの酸に接する環境下で、あるいは塩酸露点や硫酸露点などの酸露点が生じる環境下で使用されるタンクやプラント等の構成材料として用いられる耐硫酸露点腐食鋼に関し、特に、耐硫酸露点腐食性に優れるだけでなく、耐塩酸露点腐食性（以降、「耐塩酸性」と称する）にも優れる耐硫酸露点腐食鋼に関するものである。 The present invention relates to a sulfuric acid dew-point corrosion steel used as a constituent material for tanks, plants, etc. used in an environment in contact with an acid such as hydrochloric acid or sulfuric acid, or in an environment where an acid dew point such as hydrochloric acid dew point or sulfuric acid dew point is generated. In particular, the present invention relates to a sulfuric acid dew point corrosion resistant steel that not only has excellent sulfuric acid dew point corrosion resistance but also excellent hydrochloric acid dew point corrosion resistance (hereinafter referred to as “hydrochloric acid resistance”).
硫黄を含む重油や石炭等の燃料を燃焼させるボイラーや火力発電所等の煙道では、排気ガス中に含まれる硫黄酸化物が、温度の低下とともに結露して硫酸となり、激しい腐食を生じる、いわゆる「硫酸露点腐食」が問題となっている。この硫酸露点腐食問題に対しては、優れた耐食性を有する「耐硫酸露点腐食鋼」が開発され、実用化されている。 In the flue of boilers and thermal power plants that burn fuels such as heavy oil and coal containing sulfur, sulfur oxides contained in the exhaust gas condense into sulfuric acid as the temperature decreases, causing severe corrosion. “Sulfuric acid dew point corrosion” is a problem. With respect to this sulfuric acid dew point corrosion problem, “sulfuric acid dew point corrosion steel” having excellent corrosion resistance has been developed and put into practical use.
一方、ごみ焼却炉の煙道や電気炉の排気ダクトでは、被燃焼物への塩素を含むプラスチック類の混入により、やはり塩酸が結露して起こる「塩酸露点腐食」が問題となっている。塩酸露点は、硫酸露点よりも低い温度で起こるため、塩酸露点腐食が起こる場合、実際には、硫酸と塩酸との混酸による腐食である場合が多いのが特徴である。また、塩酸酸洗設備等の塩酸を使用する設備の構造材料としても、耐塩酸性に優れる鋼への要求が高まっている。 On the other hand, in the flue of a waste incinerator and the exhaust duct of an electric furnace, “hydrochloric acid dew point corrosion” caused by the condensation of hydrochloric acid due to the mixing of plastics containing chlorine into the combusted material is a problem. Since the hydrochloric acid dew point occurs at a temperature lower than the sulfuric acid dew point, when hydrochloric acid dew point corrosion occurs, it is actually characterized by many cases of corrosion caused by a mixed acid of sulfuric acid and hydrochloric acid. In addition, as a structural material of equipment using hydrochloric acid such as hydrochloric acid pickling equipment, there is an increasing demand for steel having excellent hydrochloric acid resistance.
ところで、上述した耐硫酸露点腐食鋼は、一般鋼材と比較すれば、それなりに耐塩酸性にも優れている。しかし、そのレベルは十分とは言えないものである。そこで、耐塩酸性を有する耐硫酸露点腐食鋼が幾つか提案されている。例えば、特許文献１には、Ｃ：０．００１〜０．２ｍａｓｓ％の鋼にＳｉ，Ｍｎ，Ｐ，Ｓを適正量添加し、さらにＣｕ：０．１〜１ｍａｓｓ％、Ｍｏ：０．００１〜１ｍａｓｓ％、Ｓｂ：０．０１〜０．２ｍａｓｓ％を含有させた上で、Ｓｂ，ＣおよびＭｏがある特定の関係を満たすよう制御することにより耐塩酸性に優れる耐硫酸露点腐食鋼が得られることが開示されている。
しかしながら、上記耐塩酸性に優れる耐硫酸露点腐食鋼を実際の設備に適用した場合には、耐塩酸性に関しては、従来の耐硫酸露点腐食鋼よりも優れた耐食性を示すものの、本来有すべき耐硫酸露点腐食性そのものが、従来の耐硫酸露点腐食鋼よりも劣ってしまうという根本的な問題があった。 However, when the above-mentioned sulfuric acid dew point corrosion steel having excellent hydrochloric acid resistance is applied to actual equipment, the hydrochloric acid resistance is superior to that of the conventional sulfuric acid dew point corrosion steel, but the sulfuric acid resistance that should be inherently present. There is a fundamental problem that the dew point corrosion itself is inferior to the conventional sulfuric acid dew point corrosion resistant steel.
そこで、本発明の目的は、耐硫酸露点腐食性を劣化させることなく耐塩酸性を向上させた耐硫酸露点腐食鋼を提供することにある。 Accordingly, an object of the present invention is to provide a sulfuric acid dew point corrosion resistant steel having improved hydrochloric acid resistance without deteriorating the sulfuric acid dew point corrosion resistance.
発明者らは、上記問題点を解決するために、まず、硫酸露点および塩酸露点の腐食環境における各添加元素の影響を調査し、その単独添加の効果を詳細に検討した。また、添加元素の複合効果にも着目し、硫酸露点および塩酸露点腐食環境において有効な添加元素の組み合わせを検討した。 In order to solve the above problems, the inventors first investigated the influence of each additive element in the corrosive environment of sulfuric acid dew point and hydrochloric acid dew point, and examined the effect of the single addition in detail. In addition, paying attention to the combined effect of additive elements, we examined combinations of additive elements that are effective in a sulfuric acid dew point and hydrochloric acid dew point corrosion environment.
その結果、硫酸露点および塩酸露点腐食環境における腐食支配因子および腐食機構について以下のような知見を得た。
１）従来のＣｕおよびＳｂを複合添加した耐硫酸露点腐食鋼の耐硫酸露点腐食性は、ＣｕおよびＳｂが鋼材表面に濃化し、鋼材の全面腐食と粒界腐食を抑制することによって得られる。
２）耐塩酸性を向上すると言われているＭｏの耐硫酸露点腐食鋼への添加は、耐塩酸性を向上するものの、耐硫酸露点腐食性を、従来鋼よりも低下させる。
３）耐硫酸露点腐食鋼にＷを添加すると、このＷが鋼材表面に濃化するとともに、徴密な酸化皮膜を形成して表面を保護し、耐硫酸露点腐食性を損ねることなく、耐塩酸性を向上させることができる。
４）上記Ｗの効果は、Ｓｎの添加によりさらに高められ、耐塩酸性および耐硫酸露点腐食性が一段と向上する。
５）上記ＷおよびＳｎの効果は、鋼材表面の最外層に形成されたＳ，Ｃｕ，Ｓｂ，Ｗ濃化層およびその内層に形成されたＳｉ，Ｓｎ濃化層に起因している。
本発明は、上記知見に、さらに検討を加えて完成したものである。
As a result, the following knowledge about the corrosion controlling factor and the corrosion mechanism in sulfuric acid dew point and hydrochloric acid dew point corrosive environment was obtained.
1) The sulfuric acid dew point corrosion resistance of conventional sulfuric acid dew point corrosion steel combined with Cu and Sb is obtained by concentrating Cu and Sb on the surface of the steel material and suppressing the overall corrosion and intergranular corrosion of the steel material.
2) Addition of Mo to sulfuric acid dew point corrosion steel, which is said to improve hydrochloric acid resistance, improves hydrochloric acid resistance, but lowers sulfuric acid dew point corrosion resistance compared to conventional steels.
3) When W is added to sulfuric acid dew-point corrosion steel, this W concentrates on the steel surface and forms a dense oxide film to protect the surface. Can be improved.
4) The effect of W is further enhanced by the addition of Sn, and hydrochloric acid resistance and sulfuric acid dew point corrosion resistance are further improved.
5) The effect of W and Sn is due to the S, Cu, Sb, W concentrated layer formed in the outermost layer on the steel material surface and the Si, Sn concentrated layer formed in the inner layer.
The present invention has been completed by further studying the above findings.
すなわち、本発明は、Ｃ：０．０１〜０．１２ｍａｓｓ％、Ｓｉ：０．０１〜１．５ｍａｓｓ％、Ｍｎ：０．１〜２．５ｍａｓｓ％、Ｐ：０．０５ｍａｓｓ％以下、Ｓ：０．００５〜０．０３ｍａｓｓ％、Ｃｕ：０．０３〜１．０ｍａｓｓ％、Ｓｂ：０．００２〜０．７ｍａｓｓ％、Ｗ：０．００３〜０．５ｍａｓｓ％およびＡｌ：０．００５〜０．５ｍａｓｓ％を含有し、残部がＦｅおよび不可避的不純物からなり、Ｃ，ＳｂおよびＷが下記（１）式；
２．５≦（Ｗ＋Ｓｂ）／Ｃ ・・・（１）
ここで、上記Ｗ，ＳｂおよびＣは、各成分の含有量（ｍａｓｓ％）
の関係を満たすことを特徴とする耐硫酸露点腐食鋼である。
That is, the present invention is C: 0.01-0.12 mass%, Si: 0.01-1.5 mass%, Mn: 0.1-2.5 mass%, P: 0.05 mass% or less, S: 0 0.005-0.03 mass%, Cu: 0.03-1.0 mass%, Sb: 0.002-0.7 mass%, W: 0.003-0.5 mass%, and Al: 0.005-0.5 mass %, The balance is Fe and inevitable impurities, and C, Sb and W are represented by the following formula (1):
2.5 ≦ (W + Sb) / C (1)
Here, the above W, Sb and C are the contents of each component (mass%).
It is a sulfuric acid dew-point corrosion steel characterized by satisfying the following relationship.
本発明の耐硫酸露点腐食鋼は、上記成分組成に加えてさらに、Ｓｎ：０．００５〜０．５ｍａｓｓ％を含有し、Ｃ，Ｓｂ，ＷおよびＳｎが下記（２）式；
２．５≦（Ｗ＋Ｓｂ＋３×Ｓｎ）／Ｃ ・・・（２）
ここで、上記Ｗ，Ｓｂ，ＳｎおよびＣは、各成分の含有量（ｍａｓｓ％）
の関係を満たすことを特徴とする。
In addition to the above component composition, the sulfuric acid dew point corrosion steel of the present invention further contains Sn: 0.005 to 0.5 mass%, and C, Sb, W and Sn are represented by the following formula (2):
2.5 ≦ (W + Sb + 3 × Sn) / C (2)
Here, the above W, Sb, Sn and C are the contents of each component (mass%).
It is characterized by satisfying the relationship.
また、本発明の耐硫酸露点腐食鋼は、上記成分組成に加えてさらに、Ｃｒ：０．０１〜１ｍａｓｓ％、ＲＥＭ：０．０００５〜０．０５ｍａｓｓ％およびＣａ：０．０００２〜０．００５ｍａｓｓ％のうちから選ばれる１種または２種以上を含有することを特徴とする。 In addition to the above component composition, the sulfuric acid dew-point corrosion steel of the present invention further includes Cr: 0.01 to 1 mass%, REM: 0.0005 to 0.05 mass%, and Ca: 0.0002 to 0.005 mass%. 1 type or 2 types or more chosen from among these are contained.
また、本発明の耐硫酸露点腐食鋼は、上記成分組成に加えてさらに、Ｎｉ：０．０１〜０．５ｍａｓｓ％、Ｎｂ：０．００５〜０．１ｍａｓｓ％、Ｖ：０．００５〜０．１ｍａｓｓ％、Ｔｉ：０．００５〜０．１ｍａｓｓ％およびＢ：０．０１ｍａｓｓ％以下のうちから選ばれる１種または２種以上を含有することを特徴とする。 Moreover, in addition to the said component composition, the sulfuric-acid dew point corrosion steel of this invention is further Ni: 0.01-0.5mass%, Nb: 0.005-0.1mass%, V: 0.005-0. It is characterized by containing 1 type (s) or 2 or more types chosen from 1 mass%, Ti: 0.005-0.1 mass%, and B: 0.01 mass% or less.
また、本発明の耐硫酸露点腐食鋼は、塩酸露点腐食環境において鋼材表面に形成される皮膜の最外層がＳ，Ｃｕ，Ｓｂ，Ｗ濃化層であり、その内層がＳｉ，Ｓｎ濃化層であることを特徴とする。 In the sulfuric acid dew-point corrosion steel of the present invention, the outermost layer of the film formed on the steel surface in the hydrochloric acid dew point corrosion environment is an S, Cu, Sb, W concentrated layer, and the inner layer is an Si, Sn concentrated layer. It is characterized by being.
本発明によれば、耐硫酸露点腐食性に優れるだけでなく、塩酸あるいは塩酸と硫酸との混酸に対しても優れた耐食性を有する耐硫酸露点腐食鋼を提供することができる。したがって、本発明の耐硫酸露点腐食鋼は、硫酸露点腐食環境下および塩酸露点腐食環境下で使用される容器や設備、プラント等の鋼材に好適に用いることができる。 According to the present invention, it is possible to provide a sulfuric acid dew point corrosion-resistant steel having not only excellent sulfuric acid dew point corrosion resistance but also excellent corrosion resistance against hydrochloric acid or a mixed acid of hydrochloric acid and sulfuric acid. Therefore, the sulfuric acid dew point corrosion steel of the present invention can be suitably used for steel materials such as containers, equipment, and plants used in a sulfuric acid dew point corrosion environment and a hydrochloric acid dew point corrosion environment.
本発明の耐塩酸性に優れた耐硫酸露点腐食鋼が有すべき成分組成について説明する。
Ｃ：０．０１〜０．１２ｍａｓｓ％
Ｃは、鋼の強度を高める元素であり、本発明では、所望の強度を得るために、０．０１ｍａｓｓ％以上添加する。一方、０．１２ｍａｓｓ％を超える添加は、耐塩酸性および耐硫酸露点腐食性（以降、これらを総称して「耐酸性」と称する）を劣化させるとともに、溶接性および溶接熱影響部の靭性をも劣化させる。よって、本発明では、Ｃは０．０１〜０．１２ｍａｓｓ％の範囲とする。好ましくは０．０１〜０．１ｍａｓｓ％の範囲である。
The component composition that the sulfuric acid dew-point corrosion steel excellent in hydrochloric acid resistance should have is described.
C: 0.01-0.12 mass%
C is an element that increases the strength of steel. In the present invention, C is added in an amount of 0.01 mass% or more in order to obtain a desired strength. On the other hand, addition exceeding 0.12 mass% deteriorates hydrochloric acid resistance and sulfuric acid dew point corrosion resistance (hereinafter collectively referred to as “acid resistance”), and also improves the weldability and toughness of the heat affected zone. Deteriorate. Therefore, in the present invention, C is in the range of 0.01 to 0.12 mass%. Preferably it is the range of 0.01-0.1 mass%.
Ｓｉ：０．０１〜１．５ｍａｓｓ％
Ｓｉは、脱酸剤として添加される成分であり、また、鋼の強度を高める効果があるので、本発明では０．０１ｍａｓｓ％以上含有させる。しかし、１．５ｍａｓｓ％を超える添加は、鋼の靭性を劣化させる。よって、Ｓｉは０．０１〜１．５ｍａｓｓ％の範囲とする。なお、Ｓｉは、酸性環境では、防食皮膜を形成して耐酸性の向上に寄与する。この耐酸性向上効果を得るためには、０．２ｍａｓｓ％以上添加することが好ましい。
Si: 0.01-1.5 mass%
Si is a component added as a deoxidizer and has the effect of increasing the strength of steel. Therefore, in the present invention, Si is contained in an amount of 0.01 mass% or more. However, addition exceeding 1.5 mass% deteriorates the toughness of steel. Therefore, Si is set to a range of 0.01 to 1.5 mass%. In addition, Si contributes to the improvement of acid resistance by forming an anticorrosion film in an acidic environment. In order to obtain this acid resistance improving effect, 0.2 mass% or more is preferably added.
Ｍｎ：０．１〜２．５ｍａｓｓ％
Ｍｎは、鋼の強度を高める元素であり、本発明では所望の強度を得るために、０．１ｍａｓｓ％以上の含有を必要とする。一方、２．５ｍａｓｓ％を超えるＭｎの含有は、鋼の靭性および溶接性を低下させる。よって、本発明では、Ｍｎは０．１〜２．５ｍａｓｓ％の範囲とする。なお、強度の維持および耐酸性を劣化させる介在物形成を抑制する観点からは、０．３〜１．６ｍａｓｓ％の範囲が好ましく、より好ましくは０．３〜１ｍａｓｓ％の範囲である。
Mn: 0.1 to 2.5 mass%
Mn is an element that increases the strength of steel. In the present invention, it is necessary to contain 0.1 mass% or more in order to obtain a desired strength. On the other hand, the content of Mn exceeding 2.5 mass% decreases the toughness and weldability of steel. Therefore, in the present invention, Mn is in the range of 0.1 to 2.5 mass%. In addition, from the viewpoint of maintaining strength and suppressing inclusion formation that degrades acid resistance, a range of 0.3 to 1.6 mass% is preferable, and a range of 0.3 to 1 mass% is more preferable.
Ｐ：０．０５ｍａｓｓ％以下
Ｐは、粒界に偏析して、鋼の靭性を低下させる有害な元素であり、特に、０．０５ｍａｓｓ％を超えて含有すると、靭性が顕著に低下するため、Ｐは、０．０５ｍａｓｓ％以下とする。なお、Ｐはできるだけ低減するのが望ましいが、０．００５ｍａｓｓ％未満への低減は、製造コストの上昇を招くので、Ｐの下限は０．００５程度とするのが好ましい。
P: 0.05 mass% or less P is a harmful element that segregates at the grain boundaries and lowers the toughness of the steel. In particular, if it exceeds 0.05 mass%, the toughness is significantly reduced. Is 0.05 mass% or less. Note that it is desirable to reduce P as much as possible. However, since reduction to less than 0.005 mass% causes an increase in manufacturing cost, the lower limit of P is preferably about 0.005.
Ｓ：０．００５〜０．０３ｍａｓｓ％
Ｓは、非金属介在物であるＭｎＳを形成し、これが局部腐食の起点となって耐局部腐食性を低下させる有害な元素であり、低減するのが望ましいが、一方で、Ｃｕの存在下では、Ｃｕ２Ｓ皮膜の形成に寄与し、鋼表面における腐食反応を抑制し、耐硫酸露点腐食性を向上させる元素でもある。そこで、本発明では、耐局部腐食性の低下を回避するために、Ｓの上限を０．０３ｍａｓｓ％とするとともに、耐硫酸露点腐食性を確保する観点からＳの下限を０．００５ｍａｓｓ％とする。
S: 0.005-0.03 mass%
S is a harmful element that forms MnS, which is a non-metallic inclusion, which is a starting point for local corrosion and reduces local corrosion resistance, and it is desirable to reduce it, but in the presence of Cu, It is also an element that contributes to the formation of a Cu 2 S film, suppresses the corrosion reaction on the steel surface, and improves the resistance to sulfuric acid dew point corrosion. Therefore, in the present invention, in order to avoid a decrease in local corrosion resistance, the upper limit of S is set to 0.03 mass%, and the lower limit of S is set to 0.005 mass% from the viewpoint of ensuring sulfuric acid dew point corrosion resistance. .
Ｃｕ：０．０３〜１．０ｍａｓｓ％
Ｃｕは、酸による腐食環境において耐酸性を向上する元素であり、本発明では、耐酸性を向上させるために必須の元素である。しかし、０．０３ｍａｓｓ％未満の添加では、その効果が小さく、一方、１．０ｍａｓｓ％を超える過度の添加は、熱間加工性の劣化を招く。よって、Ｃｕは０．０３〜１．０ｍａｓｓ％とする。
Cu: 0.03-1.0 mass%
Cu is an element that improves acid resistance in an acid corrosive environment. In the present invention, Cu is an essential element for improving acid resistance. However, when the addition is less than 0.03 mass%, the effect is small. On the other hand, when the addition exceeds 1.0 mass%, hot workability is deteriorated. Therefore, Cu is set to 0.03 to 1.0 mass%.
Ｓｂ：０．００２〜０．７ｍａｓｓ％
Ｓｂは、Ｃｕとの複合効果により鋼板表面に濃化し、耐酸性を向上する元素であり、必須の添加成分である。しかし、０．００２ｍａｓｓ％未満では、その効果が小さく、一方、０．７ｍａｓｓ％を超える添加は、効果が飽和するとともに、加工性が劣化する。よって、Ｓｂは０．００２〜０．７ｍａｓｓ％の範囲で添加する。好ましくは、０．０２〜０．３ｍａｓｓ％の範囲である。
Sb: 0.002 to 0.7 mass%
Sb is an element that concentrates on the surface of the steel sheet due to the combined effect with Cu and improves acid resistance, and is an essential additive component. However, if it is less than 0.002 mass%, the effect is small. On the other hand, if it exceeds 0.7 mass%, the effect is saturated and workability deteriorates. Therefore, Sb is added in the range of 0.002 to 0.7 mass%. Preferably, it is the range of 0.02-0.3 mass%.
Ｗ：０．００３〜０．５ｍａｓｓ％
Ｗは、耐硫酸露点腐食性を維持したまま、耐塩酸性を向上させる効果があり、本発明では、必須の添加元素である。上記Ｗの添加は、腐食環境で形成されるＷＯ４ ２−イオンが、塩化物イオン等の陰イオンに対するバリア効果を発揮するとともに、不溶性のＦｅＷＯ４を形成して腐食の進行を抑制すること、さらに、鋼板表面に形成される錆層は、Ｗを含むことにより非常に緻密化されることによるものである。すなわち、Ｗの添加は、化学的および物理的な作用によって、酸環境における腐食を抑制する。上記の効果は、０．００３ｍａｓｓ％よりも少ないと、効果が十分に得られず、一方、０．５ｍａｓｓ％を超えると、耐塩酸性が徐々に低下するとともに、コストの上昇を招く。よって、本発明では、Ｗは０．００３〜０．５ｍａｓｓ％の範囲で添加する。
W: 0.003-0.5 mass%
W has an effect of improving hydrochloric acid resistance while maintaining sulfuric acid dew point corrosion resistance, and is an essential additive element in the present invention. The addition of W allows WO 4 2- ions formed in a corrosive environment to exert a barrier effect against anions such as chloride ions, and form insoluble FeWO 4 to suppress the progress of corrosion. Furthermore, the rust layer formed on the steel plate surface is due to being highly densified by containing W. That is, the addition of W suppresses corrosion in an acid environment by chemical and physical action. If the above effect is less than 0.003 mass%, the effect is not sufficiently obtained. On the other hand, if it exceeds 0.5 mass%, the hydrochloric acid resistance is gradually lowered and the cost is increased. Therefore, in the present invention, W is added in the range of 0.003 to 0.5 mass%.
Ａｌ：０．００５〜０．５ｍａｓｓ％
Ａｌは、脱酸剤として添加される成分であり、本発明では０．００５ｍａｓｓ％以上の添加が必要である。一方、０．５ｍａｓｓ％を超えて添加すると、鋼の靭性が低下する。よって、Ａｌは０．００５〜０．５ｍａｓｓ％の範囲とする。好ましくは０．０１〜０．０５ｍａｓｓ％の範囲である。
Al: 0.005-0.5 mass%
Al is a component added as a deoxidizer, and in the present invention, addition of 0.005 mass% or more is necessary. On the other hand, if added in excess of 0.5 mass%, the toughness of the steel decreases. Therefore, Al is set to a range of 0.005 to 0.5 mass%. Preferably it is the range of 0.01-0.05 mass%.
Ｎ：０．００１〜０．０１ｍａｓｓ％
Ｎは、固溶状態で、鋼の靭性を劣化させる不可避的不純物であり、低いほど好ましい。靭性を確保する観点からは、０．０１ｍａｓｓ％以下であれば許容できる。一方、Ｎを完全に除去することは技術的に難しく、また、必要以上の低減は、製鋼コストの上昇を招くだけなので、Ｎの下限は０．００１ｍａｓｓ％とする。
N: 0.001 to 0.01 mass%
N is an unavoidable impurity that degrades the toughness of steel in a solid solution state, and is preferably as low as possible. From the viewpoint of ensuring toughness, 0.01 mass% or less is acceptable. On the other hand, it is technically difficult to completely remove N, and more than necessary reduction only increases the steelmaking cost, so the lower limit of N is set to 0.001 mass%.
本発明の耐硫酸露点腐食鋼は、上記基本成分の他に、耐酸性に対する要求レベルに応じて、下記の成分を添加することができる。
Ｓｎ：０．００５〜０．５ｍａｓｓ％
Ｓｎは、Ｗと複合効果されることにより、緻密な錆層を形成して酸環境における腐食を抑制する作用があり、特に、耐塩酸性の向上が求められた時の、耐硫酸露点腐食性の維持、向上に大きな効果を発揮する。しかし、上記効果は、０．００５ｍａｓｓ％未満の添加では十分ではなく、一方、０．５ｍａｓｓ％を超える添加は、熱間加工性および靭性の劣化を招く。よって、Ｓｎは、添加する場合には、０．００５〜０．５ｍａｓｓ％の範囲で添加するのが好ましい。
In addition to the above basic components, the sulfuric acid dew point corrosion steel of the present invention can contain the following components according to the required level for acid resistance.
Sn: 0.005-0.5 mass%
Sn has a combined effect with W, thereby forming a dense rust layer and suppressing corrosion in an acid environment. Particularly, when the improvement of hydrochloric acid resistance is required, the resistance to sulfuric acid dew point corrosion resistance Great effect on maintenance and improvement. However, the addition of less than 0.005 mass% is not sufficient for the above effect. On the other hand, addition of more than 0.5 mass% leads to deterioration of hot workability and toughness. Therefore, when adding Sn, it is preferable to add in 0.005-0.5 mass%.
Ｃｒ：０．０１〜１ｍａｓｓ％
Ｃｒは、常温における耐酸性の向上効果は少ないが、使用環境が１２０℃以上の高温となる場合には、耐酸性を維持、向上するとともに、鋼の機械的強度をも向上する効果がある。しかし、０．０１ｍａｓｓ％未満では、添加効果がなく、一方、１ｍａｓｓ％超えの添加では、その効果が飽和するとともに、コストの上昇を招く。よって、Ｃｒは、添加する場合には、０．０１〜１ｍａｓｓ％の範囲とするのが好ましい。特に、高温における耐酸性が要求される場合には、０．５〜１．０ｍａｓｓ％の範囲が望ましい。
Cr: 0.01-1 mass%
Cr has little effect of improving acid resistance at room temperature, but has an effect of maintaining and improving acid resistance and improving the mechanical strength of steel when the use environment is a high temperature of 120 ° C. or higher. However, if it is less than 0.01 mass%, there is no effect of addition, while if it exceeds 1 mass%, the effect is saturated and the cost is increased. Therefore, when Cr is added, the content is preferably in the range of 0.01 to 1 mass%. In particular, when acid resistance at high temperatures is required, the range of 0.5 to 1.0 mass% is desirable.
ＲＥＭ：０．０００５〜０．０５ｍａｓｓ％
ＲＥＭは、レアアース成分の組成が、Ｃe：５０±５ｍａｓｓ％、Ｌａ：２５±５ｍａｓｓ％、Ｎｄ：１５±５ｍａｓｓ％、Ｐｒ：１０±５ｍａｓｓ％であるものを指し、各元素が複合した硫化物および酸化物を形成することによって、耐酸性を向上する効果がある。また、ＲＥＭは、介在物の形態制御によって延性および靭性を向上させる作用も有する。これらの効果は、０．０００５ｍａｓｓ％未満では得られず、一方、０．０５ｍａｓｓ％超えでは、靭性が劣化するため、添加する場合は、０．０００５〜０．０５ｍａｓｓ％の範囲とするのが好ましい。十分な耐酸性を確保する観点からは、０．００５〜０．０５ｍａｓｓ％の範囲がより好ましい。
REM: 0.0005 to 0.05 mass%
REM indicates that the composition of the rare earth component is Ce: 50 ± 5 mass%, La: 25 ± 5 mass%, Nd: 15 ± 5 mass%, Pr: 10 ± 5 mass%, By forming an oxide, there is an effect of improving acid resistance. REM also has the effect of improving ductility and toughness by controlling the form of inclusions. These effects cannot be obtained if the content is less than 0.0005 mass%. On the other hand, if the content exceeds 0.05 mass%, the toughness deteriorates. Therefore, when added, the content is preferably in the range of 0.0005 to 0.05 mass%. . From the viewpoint of ensuring sufficient acid resistance, a range of 0.005 to 0.05 mass% is more preferable.
Ｃａ：０．０００２〜０．００５ｍａｓｓ％
Ｃａは、ＲＥＭと同様、介在物の形態制御によって延性および靭性を向上するとともに、耐酸性を向上する作用がある。上記効果は、０．０００２ｍａｓｓ％未満では得られず、一方、０．００５ｍａｓｓ％以上では靭性の低下を招くため、添加する場合には、０．０００２〜０．００５ｍａｓｓ％の範囲とするのが好ましい。より耐酸性を向上するためには、０．００１〜０．００５ｍａｓｓ％の範囲が望ましい。
Ca: 0.0002 to 0.005 mass%
Ca, like REM, has the effect of improving acidity while improving ductility and toughness by controlling the form of inclusions. The above effect cannot be obtained if it is less than 0.0002 mass%. On the other hand, if it is 0.005 mass% or more, the toughness is lowered. Therefore, when added, the content is preferably in the range of 0.0002 to 0.005 mass%. . In order to further improve acid resistance, a range of 0.001 to 0.005 mass% is desirable.
本発明の耐硫酸露点腐食鋼は、上記成分の他に、熱間加工性や強度、靭性向上を目的として、下記の成分を添加することができる。
Ｎｉ：０．０１〜０．５ｍａｓｓ％
Ｎｉは、ＣｕやＳｎの添加による熱間加工性の劣化を抑制する働きがあるため、添加することができる。しかし、０．０１ｍａｓｓ％未満では、その効果がなく、一方、０．５ｍａｓｓ％を超える添加は、効果が飽和し、コストの上昇を招く。よって、添加する場合は０．０１〜０．５ｍａｓｓ％の範囲とするのが好ましい。
In addition to the above components, the sulfuric acid dew-point corrosion steel of the present invention may contain the following components for the purpose of improving hot workability, strength, and toughness.
Ni: 0.01-0.5 mass%
Ni can be added because it has a function of suppressing deterioration of hot workability due to the addition of Cu or Sn. However, if it is less than 0.01 mass%, the effect is not obtained. On the other hand, if it exceeds 0.5 mass%, the effect is saturated and the cost is increased. Therefore, when adding, it is preferable to set it as the range of 0.01-0.5 mass%.
Ｎｂ：０．００５〜０．１ｍａｓｓ％
Ｎｂは、鋼の強度向上を目的として添加する元素であるが、０．００５ｍａｓｓ％未満では、強度向上効果が小さく、一方、０．１ｍａｓｓ％超えでは、靭性が劣化するため、添加する場合は、０．００５〜０．１ｍａｓｓ％の範囲とするのが好ましい。
Nb: 0.005 to 0.1 mass%
Nb is an element added for the purpose of improving the strength of steel. However, if it is less than 0.005 mass%, the effect of improving the strength is small, whereas if it exceeds 0.1 mass%, the toughness deteriorates. A range of 0.005 to 0.1 mass% is preferable.
Ｖ：０．００５〜０．１ｍａｓｓ％
Ｖは、鋼の強度向上を目的として添加する元素であるが、０．００５ｍａｓｓ％未満では強度向上効果が得られず、一方、０．１ｍａｓｓ％超えでは、靭性が劣化するため、添加する場合は、０．００５〜０．１ｍａｓｓ％の範囲とするのが好ましい。
V: 0.005-0.1 mass%
V is an element added for the purpose of improving the strength of steel. However, if it is less than 0.005 mass%, the effect of improving the strength cannot be obtained. On the other hand, if it exceeds 0.1 mass%, the toughness deteriorates. , 0.005 to 0.1 mass% is preferable.
Ｔｉ：０．００５〜０．１ｍａｓｓ％
Ｔｉは、鋼の強度向上および靭性向上を目的に添加する元素であるが、０．００５ｍａｓｓ％未満では、その効果が得られず、一方、０．１ｍａｓｓ％超えでは、効果が飽和するため、添加する場合は、０．００５〜０．１ｍａｓｓ％の範囲とするのが好ましい。
Ti: 0.005 to 0.1 mass%
Ti is an element added for the purpose of improving the strength and toughness of steel. However, if it is less than 0.005 mass%, the effect cannot be obtained. On the other hand, if it exceeds 0.1 mass%, the effect is saturated. When it does, it is preferable to set it as the range of 0.005-0.1 mass%.
Ｂ：０．０１ｍａｓｓ％以下
Ｂは、鋼の強度向上を目的に添加する元素であるが、０．０１ｍａｓｓ％超えでは靭性が劣化するため、添加する場合は、０．０１ｍａｓｓ％以下とするのが好ましい。
B: 0.01 mass% or less B is an element added for the purpose of improving the strength of steel. However, if it exceeds 0.01 mass%, the toughness deteriorates, so when added, the content should be 0.01 mass% or less. preferable.
次に、上記に説明したＣ，ＳｂおよびＷが満たすべき関係式（１）およびＣ，Ｓｂ，ＷおよびＳｎが満たすべき関係式（２）について説明する。
２．５≦（Ｗ＋Ｓｂ）／Ｃ
発明者らは、成分組成を種々に変化させた鋼を対象として、後述する実施例と同じ塩酸浸漬腐食試験を行い、腐食減量を測定し、回帰式を得て、各成分の耐塩酸性への寄与を定量的に求めた。同様にして、硫酸浸漬腐食試験も行い、耐硫酸露点腐食性への各成分の寄与についても定量的に求めた。その結果、Ｃｕを有意に含有している鋼においては、ＳｂおよびＷの添加は、耐酸性の向上に優れた効果を示すこと、そして、それら成分の耐酸性に対する有効性は、（Ｗ＋Ｓｂ（ここで、上記各元素記号は、それら成分の含有量（ｍａｓｓ％））の値の大きさで表すことができることを見出した。この式は、各成分の許容組成範囲内においては、ＳｂおよびＷの添加量が増えるほど、耐酸性が向上することを示している。一方、Ｃは、耐酸性を劣化させる元素であることも見出したが、実用的なＣの範囲である０．０１〜０．１２ｍａｓｓ％においては、上記式で得られる値が、Ｃ含有量に対して、一定量以上存在していれば、具体的には、ＳｂおよびＷが下記（１）式；
２．５≦（Ｗ＋Ｓｂ）／Ｃ ・・・（１）
ここで、上記各元素記号は、それら成分の含有量（ｍａｓｓ％）
を満たして含有していれば、耐酸性を高いレベルに保持できることを見出した。よって、本発明においては、高い耐酸性を確保するためには、上記（１）式を、満たすようＳｂおよびＷを添加する。
Next, the relational expression (1) to be satisfied by C, Sb and W described above and the relational expression (2) to be satisfied by C, Sb, W and Sn will be described.
2.5 ≦ (W + Sb) / C
The inventors conducted the same hydrochloric acid immersion corrosion test as in the examples described later for steels with various composition changes, measured corrosion weight loss, obtained regression equations, and improved the resistance to hydrochloric acid resistance of each component. The contribution was determined quantitatively. Similarly, a sulfuric acid immersion corrosion test was also performed, and the contribution of each component to the sulfuric acid dew point corrosion resistance was quantitatively determined. As a result, in steels containing significantly Cu, the addition of Sb and W shows an excellent effect in improving acid resistance, and the effectiveness of these components against acid resistance is (W + Sb (here It was found that the above element symbols can be expressed by the magnitude of the content (mass%) of these components, within the allowable composition range of each component. It shows that acid resistance improves as the amount added increases, while C has also been found to be an element that degrades acid resistance, but is in the practical range of C 0.01 to 0.00. At 12 mass%, if the value obtained by the above formula is present in a certain amount or more with respect to the C content, specifically, Sb and W are represented by the following formula (1);
2.5 ≦ (W + Sb) / C (1)
Here, each said element symbol is content (mass%) of those components.
It was found that the acid resistance can be maintained at a high level as long as the content is satisfied. Therefore, in this invention, in order to ensure high acid resistance, Sb and W are added so that the said (1) Formula may be satisfy | filled.
２．５≦（Ｗ＋Ｓｂ＋３×Ｓｎ）／Ｃ
さらに、発明者らは、Ｃｕを有意に含有している鋼においては、ＳｂおよびＷの他に、特にＳｎの添加が、耐酸性の向上に対して著しい効果を示すことを見出した。その各成分の耐酸性に対する有効性は、（Ｗ＋Ｓｂ＋３×Ｓｎ（ここで、上記各元素記号は、それら成分の含有量（ｍａｓｓ％））の値の大きさで表すことができる。この式は、各成分の許容組成範囲内においては、Ｓｎ，ＳｂおよびＷの添加量が増えるほど、耐酸性が向上し、Ｓｎの効果は、ＳｂおよびＷの３倍であることを示している。そして、実用的なＣの範囲である０．０１〜０．１２ｍａｓｓ％においては、上記式で得られる値が、Ｃ含有量に対して、一定量以上存在していれば、具体的には、Ｓｂ，ＷおよびＳｎが下記（２）式；
２．５≦（Ｗ＋Ｓｂ＋３×Ｓｎ）／Ｃ ・・・（２）
ここで、上記各元素記号は、それら成分の含有量（ｍａｓｓ％）
を満たして含有していれば、耐酸性を非常に高いレベルに保持できることを見出した。よって、本発明においては、高い耐酸性を確保するためには、上記（２）式を、満たすようＳｂ，ＷおよびＳｎを添加することが好ましい。
2.5 ≦ (W + Sb + 3 × Sn) / C
Furthermore, the inventors have found that in steel containing significantly Cu, in addition to Sb and W, the addition of Sn in particular has a significant effect on the improvement of acid resistance. The effectiveness of each component with respect to acid resistance can be expressed by the magnitude of the value of (W + Sb + 3 × Sn (where each element symbol is the content (mass%) of those components). Within the allowable composition range of each component, the acid resistance improves as the added amount of Sn, Sb and W increases, and the effect of Sn is three times that of Sb and W. In the range of 0.01 to 0.12 mass%, which is a typical C range, if the value obtained by the above formula is more than a certain amount with respect to the C content, specifically, Sb, W And Sn is the following formula (2);
2.5 ≦ (W + Sb + 3 × Sn) / C (2)
Here, each said element symbol is content (mass%) of those components.
It was found that the acid resistance can be maintained at a very high level if the content is satisfied. Therefore, in the present invention, in order to ensure high acid resistance, it is preferable to add Sb, W and Sn so as to satisfy the above formula (2).
本発明の耐硫酸露点腐食鋼は、上記成分以外の残部は、Ｆｅおよび不可避的不純物である。ただし、本発明の効果を害さない範囲であれば、上記以外の成分の添加を拒むものではない。 In the sulfuric acid dew-point corrosion steel of the present invention, the balance other than the above components is Fe and inevitable impurities. However, addition of components other than those described above is not rejected as long as the effects of the present invention are not impaired.
次に、本発明の耐硫酸露点腐食鋼が、塩酸露点腐食環境において、鋼材表面の形成する皮膜構造について説明する。
本発明の成分組成に適合するＳｎを含有する鋼Ａ（Ｃ：０．０３ｍａｓｓ％、Ｓｉ：０．４５ｍａｓｓ％、Ｍｎ：０．９ｍａｓｓ％、Ｐ：０．０１ｍａｓｓ％、Ｓ：０．０１０ｍａｓｓ％、Ｃｕ：０．２９ｍａｓｓ％、Ｓｂ：０．１１ｍａｓｓ％、Ｗ：０．０５５ｍａｓｓ％、Ａｌ：０．０３２ｍａｓｓ％、Ｓｎ：０．０２ｍａｓｓ％、残部：実質的にＦｅ）と本発明の成分組成に適合するがＳｎを含有しない鋼Ｂ（Ｃ：０．０３ｍａｓｓ％、Ｓｉ：０．２６ｍａｓｓ％、Ｍｎ：１．０ｍａｓｓ％、Ｐ：０．０１ｍａｓｓ％、Ｓ：０．００６ｍａｓｓ％、Ｃｕ：０．３１ｍａｓｓ％、Ｓｂ：０．１０ｍａｓｓ％、Ｗ：０．０５１ｍａｓｓ％、Ａｌ：０．０３７ｍａｓｓ％、残部：実質的にＦｅ）の２種類の鋼材を、８０℃に保持された５ｍａｓｓ％ＨＣｌ中に２４時間浸漬し、鋼材表面に形成された皮膜をＧＤＳで解析した。その結果、鋼Ａの皮膜では、最外層にＳ，Ｃｕ，Ｓｂ，Ｗの濃化層が形成されており、その内層にＳｉ，Ｓｎの濃化層が形成されているが、鋼Ｂの皮膜では、上記のような内層の濃化層の形成は認められなかった。また、鋼Ａの皮膜は、上記のようなの成分濃化層が形成される結果、鋼Ｂの皮膜よりも薄く、しかも、緻密であることも判った。その結果、Ｓｎの添加により、耐酸性が向上したものと考えられる。
Next, the coating structure formed on the surface of the steel material in the sulfuric acid dew-point corrosion steel of the present invention in a hydrochloric acid dew-point corrosion environment will be described.
Steel A containing Sn suitable for the composition of the present invention (C: 0.03 mass%, Si: 0.45 mass%, Mn: 0.9 mass%, P: 0.01 mass%, S: 0.010 mass%, Cu: 0.29 mass%, Sb: 0.11 mass%, W: 0.055 mass%, Al: 0.032 mass%, Sn: 0.02 mass%, balance: substantially Fe) and conforms to the component composition of the present invention Steel B that does not contain Sn (C: 0.03 mass%, Si: 0.26 mass%, Mn: 1.0 mass%, P: 0.01 mass%, S: 0.006 mass%, Cu: 0.31 mass%) , Sb: 0.10 mass%, W: 0.051 mass%, Al: 0.037 mass%, balance: substantially Fe), 5 ma, maintained at 80 ° C. s% HCl was immersed for 24 hours in, and analyzed the formed film on the steel material surface by GDS. As a result, in the coating of steel A, a concentrated layer of S, Cu, Sb, W is formed in the outermost layer, and a concentrated layer of Si, Sn is formed in the inner layer, but the coating of steel B Then, the formation of the inner thickening layer as described above was not recognized. It was also found that the steel A film was thinner and denser than the steel B film as a result of the formation of the above-described component concentrated layer. As a result, it is considered that the acid resistance is improved by the addition of Sn.
次に、本発明の鋼材の好ましい製造方法について説明する。
本発明の鋼材は、上記成分組成に調整した鋼を、通常の鋼と同様の方法で、厚鋼板、薄鋼板および形鋼などの種々の形状に仕上げたものである。例えば、本発明の鋼は、転炉や電気炉、真空脱ガス装置等の通常公知の方法で、主要５元素（Ｃ，Ｓｉ，Ｍｎ，Ｐ，Ｓ）を本発明範囲に調整するとともに、その他の合金元素を要求特性に応じて添加して溶製し、その後、上記鋼は、連続鋳造法等で鋼スラブとし、この鋼スラブは、その後直ちに、あるいは冷却後、再加熱して熱間圧延し、製品とするのが好ましい。
Next, the preferable manufacturing method of the steel material of this invention is demonstrated.
The steel material of the present invention is obtained by finishing steel adjusted to the above component composition into various shapes such as a thick steel plate, a thin steel plate, and a shaped steel by a method similar to that of ordinary steel. For example, in the steel of the present invention, the main five elements (C, Si, Mn, P, S) are adjusted to the scope of the present invention by a generally known method such as a converter, electric furnace, vacuum degassing apparatus, etc. The alloy element is added according to the required characteristics and melted, and then the steel is made into a steel slab by a continuous casting method or the like, and this steel slab is hot-rolled by reheating immediately or after cooling. And preferably a product.
熱間圧延条件については、耐食鋼としては、特に条件を付さないが、鋼材として要求される機械的特性を確保する観点からは、適切な熱延温度や圧下比等に制御するのが望ましい。熱間圧延後は、所望する機械的特性に応じて、冷却速度を制御することが望ましい。例えば、引張強さ４９０Ｎ／ｍｍ２級以上の高強度鋼材とする場合には、熱間圧延の仕上温度を７５０℃以上とし、その後２℃／ｓｅｃ以上の冷却速度で７００℃以下まで冷却するのが好ましい。仕上げ温度が７５０℃未満では、変形抵抗が大きくなり、形状制御が難しくなる。また、冷却速度が２℃／ｓｅｃ未満もしくは冷却停止温度が７００℃を超える場合には、４９０Ｎ／ｍｍ２級以上の引張強さが得難いからである。 As for the hot rolling conditions, there is no particular condition for the corrosion resistant steel, but from the viewpoint of ensuring the mechanical properties required as a steel material, it is desirable to control to an appropriate hot rolling temperature, reduction ratio, etc. . After hot rolling, it is desirable to control the cooling rate according to the desired mechanical properties. For example, when a high strength steel material having a tensile strength of 490 N / mm grade 2 or higher is used, the hot rolling finish temperature is set to 750 ° C. or higher, and then cooled to 700 ° C. or lower at a cooling rate of 2 ° C./sec or higher. Is preferred. When the finishing temperature is less than 750 ° C., the deformation resistance increases and the shape control becomes difficult. Further, when the cooling rate is less than 2 ° C./sec or the cooling stop temperature exceeds 700 ° C., it is difficult to obtain a tensile strength of 490 N / mm class 2 or higher.
上記のようにして得られる本発明の鋼は、硫酸および塩酸あるいはそれらの混酸環境で使用される容器や設備、プラントに用いて好適な、優れた耐硫酸露点腐食性および耐塩酸性を有する。 The steel of the present invention obtained as described above has excellent sulfuric acid dew point corrosion resistance and hydrochloric acid resistance suitable for use in vessels, equipment, and plants used in sulfuric acid and hydrochloric acid or mixed acid environments thereof.
表１−１および表１−２に示したＮｏ．１〜４４の成分組成を有する鋼を転炉で溶製し、連続鋳造法により厚さ２００ｍｍの鋼スラブとし、この鋼スラブを１２００℃に再加熱後、仕上終了温度を８００℃とする熱間圧延し、板厚が８ｍｍの熱延鋼板とした。このようにして得た熱延鋼板から、幅２０ｍｍ×長さ３０ｍｍ×厚さ５ｍｍの直方体の腐食試験片を切り出し、これらの腐食試験片を、塩酸（５ｍａｓｓ％ＨＣｌ，８０℃）に２４時間浸漬する塩酸浸漬腐食試験および硫酸（２０ｍａｓｓ％Ｈ２ＳＯ４，４０℃）に６時間浸漬する硫酸浸漬腐食試験の２種類の腐食試験に供して、各試験片の腐食速度（腐食減量）を測定した。 No. shown in Table 1-1 and Table 1-2. A steel having a component composition of 1 to 44 is melted in a converter and made into a steel slab having a thickness of 200 mm by a continuous casting method. The steel slab is reheated to 1200 ° C., and the finish finish temperature is 800 ° C. It rolled and it was set as the hot rolled steel plate whose plate | board thickness is 8 mm. A rectangular parallelepiped corrosion test piece having a width of 20 mm, a length of 30 mm and a thickness of 5 mm was cut out from the hot-rolled steel sheet thus obtained, and these corrosion test pieces were immersed in hydrochloric acid (5 mass% HCl, 80 ° C.) for 24 hours. The corrosion rate (corrosion loss) of each test piece was measured by two types of corrosion tests: a hydrochloric acid immersion corrosion test and a sulfuric acid immersion corrosion test immersed in sulfuric acid (20 mass% H 2 SO 4 , 40 ° C.) for 6 hours. .
耐酸性の評価は、塩酸浸漬腐食試験における腐食速度が５０ｇ／ｍ２・ｈｒ以下かつ硫酸浸漬腐食試験における腐食速度が３０ｇ／ｍ２・ｈｒ以下のものを合格（○）とし、中でも、塩酸浸漬腐食試験における腐食速度が３０ｇ／ｍ２・ｈｒ以下のものは、特に耐塩酸性が優れているもの（◎）と評価した。一方、両腐食試験において、いずれか一方でも腐食速度が上記値を超えるものは不合格（×）と評価した。 The evaluation of acid resistance is a pass (○) when the corrosion rate in the hydrochloric acid immersion corrosion test is 50 g / m 2 · hr or less and the corrosion rate in the sulfuric acid immersion corrosion test is 30 g / m 2 · hr or less. Those having a corrosion rate of 30 g / m 2 · hr or less in the corrosion test were evaluated as being particularly excellent in hydrochloric acid resistance (◎). On the other hand, in both corrosion tests, any one of which the corrosion rate exceeded the above value was evaluated as rejected (x).
上記測定結果および評価結果を表２に示した。表２から、本発明の成分組成に適合する鋼板（Ｎｏ．１〜１９）は、いずれも、耐酸性（耐塩酸性、耐硫酸露点腐食性）に優れている。一方、本発明の成分組成から外れる比較例の鋼板（Ｎｏ．２０〜４４）は、耐塩酸性あるいは耐硫酸露点腐食性のいずれか一方が優れているものはあるものの、両方の耐酸性に優れるものはないことがわかる。 The measurement results and evaluation results are shown in Table 2. From Table 2, all the steel plates (No. 1 to 19) conforming to the component composition of the present invention are excellent in acid resistance (hydrochloric acid resistance, sulfuric acid dew point corrosion resistance). On the other hand, comparative steel plates (Nos. 20 to 44) deviating from the component composition of the present invention are excellent in both acid resistance, although some of them are excellent in hydrochloric acid resistance or sulfuric acid dew point corrosion resistance. I understand that there is no.
図１は、Ｓｎを含有していないＮｏ．１〜６およびＮｏ．２０〜２３の鋼について、Ｃ含有量と（Ｗ＋Ｓｂ）の値が、表２に示した耐酸性の総合評価に及ぼす影響を示したものである。この図から、本発明の（１）式；
２．５≦（Ｗ＋Ｓｂ）／Ｃ
を満たして、Ｃ，ＳｂおよびＷを添加した場合には、耐塩酸性、耐硫酸露点腐食性のいずれにも優れた鋼を得ることができることがわかる。
FIG. 1 shows No. 1 containing no Sn. 1-6 and no. The effects of the C content and the value of (W + Sb) on the comprehensive evaluation of acid resistance shown in Table 2 for steels 20 to 23 are shown. From this figure, the formula (1) of the present invention;
2.5 ≦ (W + Sb) / C
When C, Sb and W are added while satisfying the above, it can be seen that a steel excellent in both hydrochloric acid resistance and sulfuric acid dew point corrosion resistance can be obtained.
また、図２は、Ｓｎを含有するＮｏ．７〜１９およびＮｏ．２４〜２８の鋼について、Ｃ含有量と（Ｗ＋Ｓｂ＋３×Ｓｎ）の値が、表２に示した耐酸性の総合評価に及ぼす影響を示したものである。この図から、本発明の（２）式；
２．５≦（Ｗ＋Ｓｂ＋３×Ｓｎ）／Ｃ
を満たして、Ｃ，Ｓｂ，ＷおよびＳｎを添加した場合には、耐塩酸性、耐硫酸露点腐食性のいずれにも優れた鋼を得ることができることがわかる。
Moreover, FIG. 7-19 and no. The effects of the C content and the value of (W + Sb + 3 × Sn) on the overall evaluation of acid resistance shown in Table 2 are shown for 24-28 steels. From this figure, the formula (2) of the present invention;
2.5 ≦ (W + Sb + 3 × Sn) / C
When C, Sb, W and Sn are added while satisfying the above, it can be seen that a steel excellent in both hydrochloric acid resistance and sulfuric acid dew point corrosion resistance can be obtained.
Claims (5)
記
２．５≦（Ｗ＋Ｓｂ）／Ｃ ・・・（１）
ここで、上記Ｗ，ＳｂおよびＣは、各成分の含有量（ｍａｓｓ％） C: 0.01-0.12 mass%, Si: 0.01-1.5 mass%, Mn: 0.1-2.5 mass%, P: 0.05 mass% or less, S: 0.005-0.03 mass %, Cu: 0.03-1.0 mass%, Sb: 0.002-0.7 mass%, W: 0.003-0.5 mass% and Al: 0.005-0.5 mass%, the balance Is composed of Fe and inevitable impurities, and C, Sb and W satisfy the relationship of the following formula (1).
2.5 ≦ (W + Sb) / C (1)
Here, the above W, Sb and C are the contents of each component (mass%).
記
２．５≦（Ｗ＋Ｓｂ＋３×Ｓｎ）／Ｃ ・・・（２）
ここで、上記Ｗ，Ｓｂ，ＳｎおよびＣは、各成分の含有量（ｍａｓｓ％） In addition to the said component composition, Sn: 0.005-0.5mass% is contained, C, Sb, W, and Sn satisfy | fill the relationship of following (2) Formula, It is characterized by the above-mentioned. Sulfuric acid dew point corrosion steel.
2.5 ≦ (W + Sb + 3 × Sn) / C (2)
Here, the above W, Sb, Sn and C are the contents of each component (mass%).
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