JP4483378B2 - High corrosion resistant steel - Google Patents
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- JP4483378B2 JP4483378B2 JP2004102245A JP2004102245A JP4483378B2 JP 4483378 B2 JP4483378 B2 JP 4483378B2 JP 2004102245 A JP2004102245 A JP 2004102245A JP 2004102245 A JP2004102245 A JP 2004102245A JP 4483378 B2 JP4483378 B2 JP 4483378B2
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- 239000010935 stainless steel Substances 0.000 title claims description 21
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 83
- 229910000831 Steel Inorganic materials 0.000 claims description 72
- 239000010959 steel Substances 0.000 claims description 72
- 238000005260 corrosion Methods 0.000 claims description 42
- 230000007797 corrosion Effects 0.000 claims description 42
- 229910052742 iron Inorganic materials 0.000 claims description 40
- 229910052759 nickel Inorganic materials 0.000 claims description 7
- 229910052698 phosphorus Inorganic materials 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 5
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 229910052782 aluminium Inorganic materials 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 3
- 229910052748 manganese Inorganic materials 0.000 claims description 3
- 229910052710 silicon Inorganic materials 0.000 claims description 3
- 229910052717 sulfur Inorganic materials 0.000 claims description 3
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 44
- 239000010410 layer Substances 0.000 description 38
- 238000000034 method Methods 0.000 description 17
- 239000000463 material Substances 0.000 description 13
- 229910000870 Weathering steel Inorganic materials 0.000 description 12
- 230000000694 effects Effects 0.000 description 11
- 238000005554 pickling Methods 0.000 description 10
- 230000001681 protective effect Effects 0.000 description 10
- 229910045601 alloy Inorganic materials 0.000 description 9
- 239000000956 alloy Substances 0.000 description 9
- 239000010949 copper Substances 0.000 description 9
- 239000007864 aqueous solution Substances 0.000 description 8
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 7
- 238000004519 manufacturing process Methods 0.000 description 6
- 229910052760 oxygen Inorganic materials 0.000 description 6
- 239000002994 raw material Substances 0.000 description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 5
- 238000005422 blasting Methods 0.000 description 5
- 239000001301 oxygen Substances 0.000 description 5
- 238000007670 refining Methods 0.000 description 5
- 239000000243 solution Substances 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 4
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 239000003973 paint Substances 0.000 description 4
- 230000003449 preventive effect Effects 0.000 description 4
- 239000013535 sea water Substances 0.000 description 4
- 229910052719 titanium Inorganic materials 0.000 description 4
- 229910052720 vanadium Inorganic materials 0.000 description 4
- 238000004458 analytical method Methods 0.000 description 3
- 229910052804 chromium Inorganic materials 0.000 description 3
- 239000011651 chromium Substances 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 239000003112 inhibitor Substances 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- 229910052758 niobium Inorganic materials 0.000 description 3
- 239000011347 resin Substances 0.000 description 3
- 229920005989 resin Polymers 0.000 description 3
- 150000003839 salts Chemical class 0.000 description 3
- 239000007921 spray Substances 0.000 description 3
- 238000004381 surface treatment Methods 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 239000012141 concentrate Substances 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000004453 electron probe microanalysis Methods 0.000 description 2
- 238000010828 elution Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000001771 impaired effect Effects 0.000 description 2
- 238000012423 maintenance Methods 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 238000003723 Smelting Methods 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000003321 atomic absorption spectrophotometry Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- GRWVQDDAKZFPFI-UHFFFAOYSA-H chromium(III) sulfate Chemical compound [Cr+3].[Cr+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O GRWVQDDAKZFPFI-UHFFFAOYSA-H 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 229910000365 copper sulfate Inorganic materials 0.000 description 1
- ARUVKPQLZAKDPS-UHFFFAOYSA-L copper(II) sulfate Chemical compound [Cu+2].[O-][S+2]([O-])([O-])[O-] ARUVKPQLZAKDPS-UHFFFAOYSA-L 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 238000007872 degassing Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- -1 molybdate ions Chemical class 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 239000012466 permeate Substances 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 238000009849 vacuum degassing Methods 0.000 description 1
- 230000037303 wrinkles Effects 0.000 description 1
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- Heat Treatment Of Steel (AREA)
- Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
Description
本発明は、屋外の鋼構造物に使用される耐候性鋼に関するものであり、特に耐食性を著しく向上して流れさびの発生を抑制する耐候性鋼（以下、高耐食鋼という）に関するものである。 The present invention relates to weathering steel used for outdoor steel structures, and particularly to weathering steel (hereinafter referred to as high corrosion resistance steel) that significantly improves corrosion resistance and suppresses the occurrence of flow rust. .
屋外の鋼構造物（たとえば橋梁等）に広く利用される耐候性鋼は、Ｐ，Cu，Cr，Ni等の合金元素を添加して、大気中での耐食性を改善している。屋外における鋼材の腐食の原因は、いうまでもなく酸素と水である。耐候性鋼は酸素や水を通し難いさび（以下、保護性さびという）を表面に形成し、鋼材が酸素や水に接触するのを抑制することによって、腐食の進行が抑えられる。保護性さびの形成には数年を要するが、保護性さびが形成された後は腐食の進行が顕著に鈍くなるので、耐候性鋼には防錆塗料を塗布する必要はない。 Weathering steel widely used for outdoor steel structures (for example, bridges) is improved in corrosion resistance in the atmosphere by adding alloy elements such as P, Cu, Cr, Ni and the like. Needless to say, the cause of corrosion of steel materials outdoors is oxygen and water. Weatherproof steel forms rust that is difficult to pass oxygen and water (hereinafter referred to as protective rust) on the surface, and suppresses the steel from coming into contact with oxygen and water, thereby suppressing the progress of corrosion. It takes several years to form the protective rust, but after the protective rust is formed, the progress of the corrosion is remarkably slowed. Therefore, it is not necessary to apply a rust preventive coating to the weather resistant steel.
一方、通常の鋼材を使用した鋼構造物では防錆塗料を塗布しなければならず、しかも風雨に曝されることによって防錆塗料の被膜が劣化するので、定期的に塗り替えを行なう必要がある。 On the other hand, a steel structure using ordinary steel materials must be coated with a rust preventive paint, and the coating of the rust preventive paint deteriorates when exposed to wind and rain, so it is necessary to repaint regularly. .
耐候性鋼を使用した鋼構造物では防錆塗料の塗布あるいは定期的な塗り替えは必要ないので、鋼構造物の維持コストを削減できる。 Since the steel structure using weathering steel does not require the application of a rust-preventive paint or periodic repainting, the maintenance cost of the steel structure can be reduced.
しかしながら、保護性さびが形成されるまでの数年間は腐食防止の効果が劣るので、耐候性鋼の表面や周囲に流れ落ちたような外観を呈するさび（以下、流れさびという）が現われる。流れさびは、鋼構造物としての景観を損ねるばかりでなく、環境汚染の原因にもなるという問題がある。そこで、流れさびの発生を抑制するための技術が種々検討されている。 However, since the effect of preventing corrosion is inferior for several years until the protective rust is formed, a rust (hereinafter referred to as a flow rust) that appears as if it has flowed down to the surface of the weather resistant steel or the surroundings appears. Flow rust not only impairs the landscape as a steel structure, but also causes environmental pollution. Therefore, various techniques for suppressing the occurrence of flow rust have been studied.
たとえば特開平6-136557号公報には、硫酸クロム水溶液あるいは硫酸銅水溶液を鋼材に塗布して乾燥させた後、さらに有機樹脂を被覆する表面処理法が提案されている。また特開平8-13158 号公報には、アルミニウムを含む水溶液を鋼材に塗布して乾燥させた後、さらに有機樹脂を被覆する表面処理法が提案されている。さらに特開2000-212682 号公報には、Ｐ，Cu，Ni，Cr，Mo，Ｂを１種以上含有させて流れさびを抑制する技術が提案されている。 For example, Japanese Patent Application Laid-Open No. 6-136557 proposes a surface treatment method in which a chromium sulfate aqueous solution or a copper sulfate aqueous solution is applied to a steel material and dried, and then further coated with an organic resin. Japanese Patent Application Laid-Open No. 8-13158 proposes a surface treatment method in which an aqueous solution containing aluminum is applied to a steel material and dried, and then coated with an organic resin. Furthermore, Japanese Patent Laid-Open No. 2000-212682 proposes a technique for suppressing flow rust by containing one or more of P, Cu, Ni, Cr, Mo, and B.
しかしながら、特開平6-136557号公報や特開平8-13158 号公報に開示された技術では、水溶液や樹脂を多量に消費するので、表面処理コストが上昇する。特開2000-212682 号公報に開示された技術では、比較的高価な合金元素を使用するので、鋼材の原料コストが上昇する。
本発明は、従来の技術が抱えている上記のような問題点に鑑み、耐候性鋼の耐食性をさらに向上して流れさびの発生を抑制できる安価な高耐食鋼を提供することを目的とする。 An object of the present invention is to provide an inexpensive high corrosion-resistant steel that can further improve the corrosion resistance of a weather-resistant steel and suppress the occurrence of flow rust in view of the above-described problems of conventional techniques. .
耐候性鋼の耐食性を一層向上させて流れさびの発生量を低減するためには、耐候性鋼に合金元素を適宜選択して添加することが有効である。しかしながら耐候性鋼に添加する合金元素は比較的高価であるから、その合金元素の添加量を増加すると原料コストの上昇を招く。 In order to further improve the corrosion resistance of the weathering steel and reduce the amount of flow rust, it is effective to select and add an alloy element to the weathering steel as appropriate. However, since the alloy elements added to the weathering steel are relatively expensive, increasing the amount of the alloy elements increases the raw material cost.
そこで本発明者らは、腐食現象が鋼材の金属相（以下、地鉄という）と酸素や水との化学反応であることに着目した。つまり、地鉄の表面で酸素や水と接触することによって腐食が進行することを考慮すると、地鉄の表面近傍にて合金元素を濃化させることによって、腐食の進行を抑制できる。しかも地鉄全体で合金元素を濃化するのではなく、表面近傍のみ濃化させるので、合金元素の使用量を削減（すなわち原料コストを削減）できる。 Therefore, the present inventors have paid attention to the fact that the corrosion phenomenon is a chemical reaction between a metal phase of steel material (hereinafter referred to as “steel”) and oxygen or water. That is, in consideration of the progress of corrosion due to contact with oxygen or water on the surface of the base iron, the progress of the corrosion can be suppressed by concentrating the alloy elements near the surface of the base iron. In addition, since the alloy element is not concentrated in the entire base iron but only in the vicinity of the surface, the amount of the alloy element used can be reduced (that is, the raw material cost can be reduced).
このような観点から本発明者らは、地鉄の表面近傍にて濃化させる合金元素として、鋼材の耐食性を高める作用を有するNiに着目し、そのNiを濃化させる技術について鋭意検討した。すなわち、通常の環境における流れさびの発生を抑制するためには、Niの他にも、Ｐ，Cu，Cr，Mo，Ｂが有効であるが、塩分が飛来する地域における耐食性を高めるためにはNiが最も有効である。 From such a point of view, the present inventors paid attention to Ni having an action of enhancing the corrosion resistance of steel as an alloy element to be concentrated near the surface of the ground iron, and intensively studied a technique for concentrating the Ni. In other words, in addition to Ni, P, Cu, Cr, Mo, and B are effective to suppress the occurrence of flow rust in a normal environment, but in order to increase the corrosion resistance in areas where salt comes in. Ni is the most effective.
そこで本発明者らは、Niを 2.9質量％含有する鋼スラブ（厚さ 210mm）を1120℃で２時間加熱した後、圧延して鋼板（厚さ20mm）とし、その鋼板の断面をＥＰＭＡ分析した。その結果の代表的な例を図１に示す。地鉄の表面近傍にはNiが濃化した領域（以下、Ni濃化層という）が認められる。このNi濃化層の厚さは５μｍ程度であり、Ni濃化層中の最大Ni濃度は地鉄の約５倍となっている。
Therefore, the present inventors heated a steel slab containing 2.9% by mass of Ni (thickness: 210 mm) at 1120 ° C. for 2 hours and then rolled it into a steel plate (
つまり、Niを含有する鋼材を加熱すると、表面にスケールと呼ばれるFe酸化物が生成する一方で、地鉄の表面近傍にNiが濃化する。その際、Niはスケールに濃化するのではなく、表面近傍の地鉄内に残留してNi濃化層を形成する。したがって耐候性鋼に添加されるNiを表面近傍で濃化させてNi濃化層を形成し、鋼構造物として使用するときにもNi濃化層を残存させることによって、耐候性鋼の耐食性を一層高めることができる。 That is, when a steel material containing Ni is heated, Fe oxide called scale is generated on the surface, while Ni is concentrated near the surface of the ground iron. At that time, Ni does not concentrate in the scale, but remains in the ground iron near the surface to form a Ni concentrated layer. Therefore, Ni added to the weathering steel is concentrated in the vicinity of the surface to form a Ni-enriched layer, and the Ni-enriched layer remains even when used as a steel structure, thereby improving the corrosion resistance of the weathering steel. It can be further enhanced.
なお、地鉄の表面近傍とは、地鉄表面から1000μｍ以内をいうものとする。あまり表面から離れても耐食性の向上に効果はない。また、Ni濃化層とは、母材内部のNi含有量の 1.2倍以上となる層をいうものとする。 In addition, the vicinity of the surface of the ground iron means within 1000 μm from the surface of the ground iron. Even if it is far away from the surface, there is no effect in improving the corrosion resistance. The Ni-enriched layer refers to a layer that is at least 1.2 times the Ni content inside the base material.
ところが従来の耐候性鋼は、その製造工程でショットブラスト処理を施し、表面のスケールを除去した耐候性鋼を使用している。これは、鋼構造物として使用する際に、表面に均一な保護性さびを形成するための処置である。ショットブラスト処理では、通常、直径約１mmの鋼球を吹き付けるので、スケールを除去した後の地鉄表面の粗度はＲmax で約60μｍとなる。したがって厚さ５μｍ程度のNi濃化層は、ショットブラスト処理によって、スケールとともに除去されてしまう。 However, the conventional weathering steel uses a weathering steel that has been subjected to shot blasting in the production process and from which the scale of the surface has been removed. This is a treatment for forming a uniform protective rust on the surface when used as a steel structure. In the shot blasting process, a steel ball having a diameter of about 1 mm is usually sprayed, so that the roughness of the surface of the steel after the scale is removed is about 60 μm in Rmax. Therefore, the Ni concentrated layer having a thickness of about 5 μm is removed together with the scale by the shot blasting process.
地鉄の表面近傍にNi濃化層を形成した本発明の高耐食鋼を製造するにあたって、スケールを除去する一方で、Ni濃化層を残存させる必要がある。ところが、ショットブラストや切削等の機械的な手段では、スケールとともにNi濃化層も取り除かれるのは避けられない。そこで化学的な手段を用いてスケールのみを除去する。すなわち、酸洗を施すことによって化学的にスケールのみを除去し、かつ地鉄の表面近傍にNi濃化層を残存させることが可能である。酸洗液は特定の成分濃度に限定する必要はないが、一般的に広く使用されている塩酸水溶液が好ましい。 In manufacturing the highly corrosion resistant steel of the present invention in which a Ni concentrated layer is formed in the vicinity of the surface of the base iron, it is necessary to remove the scale while leaving the Ni concentrated layer. However, it is inevitable that the Ni concentrated layer is removed together with the scale by mechanical means such as shot blasting or cutting. Therefore, only the scale is removed using chemical means. That is, it is possible to remove only the scale chemically by pickling and to leave the Ni concentrated layer in the vicinity of the surface of the base iron. Although it is not necessary to limit a pickling liquid to a specific component density | concentration, the hydrochloric acid aqueous solution generally used widely is preferable.
また、酸洗液にインヒビターを添加することによって、酸洗による地鉄の溶出を防止してNi濃化層を残存させることができる。 Further, by adding an inhibitor to the pickling solution, it is possible to prevent elution of the base iron by pickling and leave the Ni concentrated layer.
本発明は以上のような知見に基づいてなされたものである。 The present invention has been made based on the above findings.
すなわち本発明は、Ｃ：0.01〜0.20質量％，Si：0.05〜0.80質量％，Mn： 0.1〜3.0 質量％，Ｐ： 0.005〜0.1 質量％，Ｓ：0.01質量％以下，Al：0.08質量％以下，Ni：1.95〜4.0 質量％を含有し残部がFeおよび不可避的不純物からなる組成を有する地鉄の表面に厚さ３μｍ以上のNi濃化層を有する高耐食鋼である。 That is, the present invention includes C: 0.01 to 0.20 mass%, Si: 0.05 to 0.80 mass%, Mn: 0.1 to 3.0 mass%, P: 0.005 to 0.1 mass%, S: 0.01 mass% or less, Al: 0.08 mass% or less. , Ni: A high corrosion resistant steel having a Ni-concentrated layer of 3 μm or more in thickness on the surface of the base iron containing 1.95 to 4.0% by mass and the balance being composed of Fe and inevitable impurities.
本発明の高耐食鋼では、地鉄が、前記した組成に加えてCu： 0.1〜1.0 質量％およびMo：0.05〜0.5 質量％のうちの１種または２種を含有することが好ましい。さらに地鉄が、前記した組成に加えてNb： 0.005〜0.1 質量％，Ti： 0.005〜0.1 質量％以下およびＶ： 0.005〜0.1 質量％のうちの１種または２種以上を含有することが好ましい。 In the high corrosion resistance steel of the present invention, it is preferable that the ground iron contains one or two of Cu: 0.1 to 1.0 mass% and Mo: 0.05 to 0.5 mass% in addition to the above-described composition. In addition to the above-described composition, the ground iron preferably contains one or more of Nb: 0.005 to 0.1% by mass, Ti: 0.005 to 0.1% by mass and V: 0.005 to 0.1% by mass. .
本発明によれば、地鉄の表面近傍にNi濃化層を形成して耐食性を著しく向上させ、流れさびの発生を抑制できる安価な高耐食鋼を得ることができる。しかも本発明の高耐食鋼を使用した鋼構造物は、流れさびの発生を抑制して優れた景観を維持し、しかも防錆塗料を塗布する必要はないので、鋼構造物の維持コストを削減できる。 According to the present invention, it is possible to obtain an inexpensive high corrosion resistant steel that can form a Ni concentrated layer in the vicinity of the surface of the ground iron to remarkably improve the corrosion resistance and suppress the occurrence of flow rust. Moreover, the steel structure using the high corrosion resistance steel of the present invention suppresses the occurrence of flow rust, maintains an excellent landscape, and it is not necessary to apply a rust preventive paint, thus reducing the maintenance cost of the steel structure it can.
まず本発明の高耐食鋼の地鉄の成分を限定した理由について説明する。 First, the reason for limiting the components of the ground iron of the high corrosion resistance steel of the present invention will be described.
Ｃ：0.01〜0.20質量％
Ｃは、高耐食鋼の強度を増加させる元素であり、所望の強度を得るためには0.01質量％以上含有させる必要がある。一方、0.20質量％を超えると、高耐食鋼の靭性が劣化する。したがって地鉄中のＣは、0.01〜0.20質量％の範囲内を満足する必要がある。
C: 0.01-0.20% by mass
C is an element that increases the strength of the high corrosion-resistant steel. In order to obtain a desired strength, it is necessary to contain 0.01% by mass or more. On the other hand, if it exceeds 0.20% by mass, the toughness of the high corrosion resistant steel deteriorates. Therefore, C in the ground iron needs to satisfy the range of 0.01 to 0.20 mass%.
Si：0.05〜0.80質量％
Siは、溶鋼の溶製段階で脱酸剤として作用し、かつ高耐食鋼の強度を増加させる元素であり、所望の強度を得るためには0.05質量％以上含有させる必要がある。一方、0.80質量％を超えると、高耐食鋼の靭性および溶接性が劣化する。したがって地鉄中のSiは、0.05〜0.80質量％の範囲内を満足する必要がある。
Si: 0.05-0.80 mass%
Si is an element that acts as a deoxidizer in the melting stage of the molten steel and increases the strength of the high corrosion resistant steel. In order to obtain a desired strength, it is necessary to contain 0.05% by mass or more. On the other hand, if it exceeds 0.80% by mass, the toughness and weldability of the high corrosion resistance steel deteriorate. Therefore, Si in the ground iron needs to satisfy the range of 0.05 to 0.80 mass%.
Mn： 0.1〜3.0 質量％
Mnは、高耐食鋼の強度と靭性を増加させる元素であり、所望の強度を得るためには 0.1質量％以上含有させる必要がある。一方、 3.0質量％を超えると、高耐食鋼の靭性および溶接性が劣化する。したがって地鉄中のMnは、 0.1〜3.0 質量％の範囲内を満足する必要がある。
Mn: 0.1-3.0 mass%
Mn is an element that increases the strength and toughness of the high corrosion-resistant steel. In order to obtain a desired strength, it is necessary to contain 0.1% by mass or more. On the other hand, if it exceeds 3.0% by mass, the toughness and weldability of the high corrosion resistance steel deteriorate. Therefore, Mn in the ground iron needs to satisfy the range of 0.1 to 3.0 mass%.
Ｐ： 0.005〜0.1 質量％
Ｐは、保護性さびを緻密化し、高耐食鋼の耐食性を向上させる元素である。Ｐ含有量が 0.005質量％未満では、その効果は得られない。一方、 0.1質量％を超えると、高耐食鋼の靭性が劣化する。したがって地鉄中のＰは、 0.005〜0.1 質量％の範囲内を満足する必要がある。
P: 0.005 to 0.1% by mass
P is an element that densifies the protective rust and improves the corrosion resistance of the high corrosion resistant steel. If the P content is less than 0.005% by mass, the effect cannot be obtained. On the other hand, if it exceeds 0.1% by mass, the toughness of the high corrosion resistance steel deteriorates. Therefore, P in the ground iron needs to satisfy the range of 0.005 to 0.1% by mass.
Ｓ：0.01質量％以下
Ｓは、溶鋼の溶製段階で不可避的に混入する不純物であり、高耐食鋼の耐食性，靭性，溶接性を劣化させる元素である。そのため、地鉄中のＳは0.01質量％以下とする。
S: 0.01% by mass or less S is an impurity that is inevitably mixed in the melting stage of molten steel, and is an element that deteriorates the corrosion resistance, toughness, and weldability of high corrosion resistant steel. Therefore, S in the ground iron is set to 0.01% by mass or less.
Al：0.08質量％以下
Alは、溶鋼の溶製段階で脱酸剤として作用する元素であるが、高耐食鋼の靭性を劣化させるばかりでなく、溶接金属へも移行して溶接継手の靭性を劣化させる。そのため、地鉄中のAlは0.08質量％以下とする。
Al: 0.08 mass% or less
Al is an element that acts as a deoxidizer in the melting stage of molten steel, but not only deteriorates the toughness of high corrosion resistant steel, but also shifts to weld metal to deteriorate the toughness of welded joints. For this reason, Al in the ground iron is set to 0.08% by mass or less.
Ni：1.95〜4.0 質量％
Niは、本発明の高耐食鋼の添加元素のうちで最も重要な元素である。Niは、鋼電位を上昇させ、高耐食鋼の耐食性を向上させる。しかも保護性さび中にイオンとして溶出することによって、さび粒を微細にし、保護性さびの形成を促進する。そして塩化物イオンが保護性さびを透過して地鉄に到達するのを抑制する。その結果、鋼構造物として大気中に暴露された初期段階で、流れさびの発生を抑制する。しかも、塩分が飛来する地域における耐食性を高めることができる。この作用は、Ni含有量が増加するほど顕著に発揮される。しかしNiを過剰に（すなわち 4.0質量％を超えて）添加しても、流れさびの抑制効果の増大は期待できず、むしろNi消費量の増加による原料コストの上昇を招く。
Ni: 1.95 to 4.0 mass%
Ni is the most important element among the additive elements of the high corrosion resistance steel of the present invention. Ni increases the steel potential and improves the corrosion resistance of the high corrosion resistance steel. Moreover, by eluting it as ions in the protective rust, the rust grains are made finer and the formation of the protective rust is promoted. And it suppresses that a chloride ion permeate | transmits protective rust and reaches | attains a base iron. As a result, the generation of flow rust is suppressed at the initial stage when the steel structure is exposed to the atmosphere. Moreover, the corrosion resistance in the area where the salt content comes can be enhanced. This effect becomes more prominent as the Ni content increases. However, even if Ni is added excessively (ie, exceeding 4.0% by mass), the effect of suppressing flow rust cannot be expected, but rather the raw material cost increases due to an increase in Ni consumption.
既に説明した通り、Niを含有する耐候性鋼を加熱すると、地鉄の表面近傍にNi濃化層が形成される。Niは、スケールに濃化するのではなく、表面近傍の地鉄内に濃化する。このときNi濃化層のNi含有量は、地鉄のNi含有量の約５倍である。 As already explained, when the weathering steel containing Ni is heated, a Ni concentrated layer is formed in the vicinity of the surface of the base iron. Ni does not concentrate in the scale, but in the iron bar near the surface. At this time, the Ni content of the Ni concentrated layer is about 5 times the Ni content of the base iron.
本発明者らの研究によれば、Ni濃化層が流れさびの発生を抑制するためには、地鉄中のNiは、1.95〜4.0 質量％の範囲内を満足する必要がある。 According to the study of the present inventors, in order to suppress the occurrence of rust Ni-enriched layer flows, the Ni in the earth iron, it is necessary to satisfy the range of 1.95 to 4.0 wt%.
またNi濃化層の厚さは、３μｍ以上とする必要がある。その理由は、Ni濃化層が３μｍ未満では、鋼構造物を建設する際にNi濃化層に疵が生じて地鉄が暴露され、その結果、耐食性が低下するからである。一方、Ni濃化層の厚さが 500μｍを超えても、流れさびの抑制効果の増大は期待できず、むしろ加熱処理時間等の増加による製造コストの上昇を招く。したがってNi濃化層の厚さは、３〜500 μｍとするのが好ましい。 The thickness of the Ni concentrated layer needs to be 3 μm or more. The reason for this is that when the Ni concentrated layer is less than 3 μm, when the steel structure is constructed, wrinkles occur in the Ni concentrated layer and the steel is exposed, resulting in a decrease in corrosion resistance. On the other hand, even if the thickness of the Ni-concentrated layer exceeds 500 μm, an increase in the flow rust suppression effect cannot be expected, but rather an increase in manufacturing cost due to an increase in heat treatment time or the like is caused. Therefore, the thickness of the Ni concentrated layer is preferably 3 to 500 μm.
本発明の高耐食鋼では、Ｃ，Si，Mn，Ｐ，Ｓ，Niに加えて、必要に応じて下記の元素を添加しても良い。 In the high corrosion resistance steel of the present invention, the following elements may be added as needed in addition to C, Si, Mn, P, S, and Ni.
Cu： 0.1〜1.0 質量％
Cuは、さび粒を微細にすることによって保護性さびを早期に形成する。このことによって流れさびの発生を抑制する作用を有する元素である。地鉄中のCu含有量が 0.1質量％未満では、その効果は十分に得られない。一方、 1.0質量％を超えると、高耐食鋼の製造工程における熱間加工性が損なわれるばかりでなく、流れさびの抑制効果の増大は期待できず、むしろCu消費量の増加による原料コストの上昇を招く。したがって地鉄中にCuを添加する場合は、 0.1〜1.0 質量％の範囲内が好ましい。
Cu: 0.1 to 1.0 mass%
Cu forms protective rust early by making rust grains fine. This is an element having an action of suppressing the generation of flow rust. If the Cu content in the base iron is less than 0.1% by mass, the effect cannot be obtained sufficiently. On the other hand, if it exceeds 1.0 mass%, not only the hot workability in the production process of high corrosion resistant steel is impaired, but also the increase in flow rust control effect cannot be expected, but rather the increase in raw material cost due to the increase in Cu consumption Invite. Accordingly, when Cu is added to the ground iron, it is preferably in the range of 0.1 to 1.0 mass%.
Mo：0.05〜0.5 質量％
Moは、さび層中でモリブデン酸イオンを形成することによって、塩化物イオンがさび層を透過して地鉄に到達するのを防止する。その結果、鋼構造物として大気中に暴露された初期段階で、流れさびの発生を抑制する。しかも、塩分が飛来する地域における耐食性を一層高めることができる。地鉄中のMo含有量が0.05質量％未満では、その効果は十分に得られない。一方、 0.5質量％を超えると、高耐食鋼の製造工程における熱間加工性が損なわれるばかりでなく、流れさびの抑制効果の増大は期待できず、むしろMo消費量の増加による原料コストの上昇を招く。したがって地鉄中にMoを添加する場合は、0.05〜0.5 質量％の範囲内が好ましい。
Mo: 0.05-0.5 mass%
Mo forms molybdate ions in the rust layer, thereby preventing chloride ions from passing through the rust layer and reaching the base iron. As a result, the generation of flow rust is suppressed at the initial stage when the steel structure is exposed to the atmosphere. In addition, the corrosion resistance in areas where salt comes in can be further enhanced. If the Mo content in the ground iron is less than 0.05% by mass, the effect cannot be obtained sufficiently. On the other hand, if it exceeds 0.5% by mass, not only the hot workability in the production process of high corrosion resistant steel is impaired, but also the increase effect of flow rust can not be expected, but rather the raw material cost increases due to the increase in Mo consumption Invite. Therefore, when adding Mo to the ground iron, the range of 0.05 to 0.5 mass% is preferable.
Nb： 0.005〜0.1 質量％，Ti： 0.005〜0.1 質量％，Ｖ： 0.005〜0.1 質量％
Nb，Ti，Ｖは、鋼材の強度を増加させる元素であり、必要に応じ１種または２種以上を添加できる。Nb，Ti，Ｖは、いずれも 0.005質量％以上の含有で効果が認められるが、それぞれ 0.1質量％を超えて含有しても効果は飽和する。このためNb，Ti，Ｖのいずれも 0.005〜0.1 質量％とするのが好ましい。
Nb: 0.005 to 0.1 mass%, Ti: 0.005 to 0.1 mass%, V: 0.005 to 0.1 mass%
Nb, Ti, and V are elements that increase the strength of the steel material, and one or more of them can be added as necessary. Nb, Ti, and V are all effective when contained in an amount of 0.005% by mass or more, but the effect is saturated even if each content exceeds 0.1% by mass. For this reason, it is preferable that all of Nb, Ti, and V be 0.005 to 0.1% by mass.
次に、本発明の高耐食鋼の製造方法を説明する。 Next, the manufacturing method of the high corrosion resistance steel of this invention is demonstrated.
所定の組成を有する溶鋼を、転炉法，電気炉法等の従来から知られている技術で溶製した後、連続鋳造法あるいは造塊法で鋼スラブを製造する。なお溶鋼の溶製段階では、転炉法，電気炉法等の脱炭を主体とする精錬（いわゆる１次精錬）の後で、真空脱ガス法等の脱ガスを主体とする精錬技術（いわゆる２次精錬）を適宜組み合わせて使用しても良い。 A molten steel having a predetermined composition is melted by a conventionally known technique such as a converter method or an electric furnace method, and then a steel slab is manufactured by a continuous casting method or an ingot forming method. In addition, at the smelting stage of molten steel, refining technology (so-called primary refining) mainly using decarburization such as the converter method and electric furnace method, followed by refining technology mainly using degassing such as vacuum degassing method (so-called primary refining). Secondary refining) may be used in appropriate combination.
次いで、鋼スラブを 900〜1200℃に加熱し、さらに熱間圧延を施して所定の形状の鋼材（すなわち鋼板，形鋼等）とした後、空冷または加速冷却によって冷却する。 Next, the steel slab is heated to 900 to 1200 ° C. and further hot-rolled to obtain a steel material having a predetermined shape (ie, steel plate, section steel, etc.), and then cooled by air cooling or accelerated cooling.
このようにして製造した所定の形状を有する高耐食鋼は、表面にスケールが生成しているので、酸洗を施して化学的にスケールのみを除去する。酸洗液は、希塩酸（すなわち塩酸の水溶液），希硫酸（すなわち硫酸の水溶液），希リン酸（すなわちリン酸の水溶液）等の従来から知られているものが使用できる。ただし、酸洗の効率やスケールの溶解特性を考慮すると、希塩酸を使用するのが好ましい。 Since the high corrosion resistant steel having a predetermined shape produced in this way has a scale formed on its surface, it is pickled to remove only the scale chemically. As the pickling solution, conventionally known ones such as dilute hydrochloric acid (ie, an aqueous solution of hydrochloric acid), dilute sulfuric acid (ie, an aqueous solution of sulfuric acid), dilute phosphoric acid (ie, an aqueous solution of phosphoric acid) can be used. However, it is preferable to use dilute hydrochloric acid in consideration of pickling efficiency and dissolution characteristics of the scale.
また、酸洗液にインヒビターを添加することによって、酸洗による地鉄の溶出を防止してNi濃化層を残存させることができる。インヒビターは、地鉄の成分や酸洗液の種類等に応じて適宜選択して使用する。 Further, by adding an inhibitor to the pickling solution, it is possible to prevent elution of the base iron by pickling and leave the Ni concentrated layer. Inhibitors are appropriately selected and used according to the components of the base iron, the type of pickling solution, and the like.
転炉を用いて表１に示す成分の溶鋼を溶製し、さらに連続鋳造法によって厚さ 210mmの鋼スラブとした。表１の鋼番号３〜５，10，11は、本発明の高耐食鋼の成分を満足する。これらの鋼スラブを1120℃に加熱した後、熱間圧延によって厚さ20mm，幅2500mmの鋼板とした。こうして得られた高耐食鋼板に酸洗処理を施し、表面のスケールを除去した。酸洗液は希塩酸を使用した。これを発明例とする。Ni含有量が本発明の範囲を外れる鋼番号１，２，６〜９は参考例とする。 Using a converter, molten steel having the components shown in Table 1 was melted, and a steel slab having a thickness of 210 mm was obtained by continuous casting. Steel numbers 3 to 5, 10, and 11 in Table 1 satisfy the components of the high corrosion resistance steel of the present invention. These steel slabs were heated to 1120 ° C and then hot rolled to form steel plates with a thickness of 20 mm and a width of 2500 mm. The high corrosion-resistant steel plate thus obtained was pickled and the surface scale was removed. Dilute hydrochloric acid was used for the pickling solution. This is an invention example. Steel numbers 1, 2, 6 to 9 whose Ni content is outside the scope of the present invention are used as reference examples.
一方、比較例として、発明例，参考例と同様に製造した高耐食鋼板にショットブラスト処理を施し、表面のスケールを除去した。 On the other hand, as a comparative example, the high corrosion resistance steel plate manufactured in the same manner as the invention example and the reference example was subjected to shot blasting to remove the surface scale.
発明例，参考例と比較例について、Ni濃化層中のNi含有量（質量％），Ni濃化層の厚さ（μｍ），流れさびの発生量（μｇ／cm2 ）を調査した。 Regarding the inventive example , the reference example and the comparative example, the Ni content (% by mass) in the Ni concentrated layer, the thickness of the Ni concentrated layer (μm), and the amount of flow rust (μg / cm 2 ) were investigated.
Ni濃化層中のNi含有量，Ni濃化層の厚さを調査する際には、スケールを除去した各高耐食鋼板の表層部から分析試験片（10mm×10mm）を採取し、ＥＰＭＡ分析を行なった。Ni濃化層中のNi含有量の最大値を表２に示す。なおNi濃化層中のNi含有量の最大値は、母材内部のNi含有量（質量％）×Ni濃化層の最大Ni検出強度÷母材内部の平均Ni検出強度により算出した。また、Ni含有量が母材内部の 1.2倍以上の領域の厚さ（すなわちNi濃化層の厚さ）を表２に示す。 When investigating the Ni content in the Ni-enriched layer and the thickness of the Ni-enriched layer, an analytical test piece (10 mm x 10 mm) is taken from the surface layer of each highly corrosion-resistant steel plate from which scale has been removed, and EPMA analysis is performed. Was done. Table 2 shows the maximum Ni content in the Ni concentrated layer. The maximum value of the Ni content in the Ni-concentrated layer was calculated from the Ni content (mass%) inside the base material × the maximum Ni detected strength of the Ni-concentrated layer ÷ the average Ni detected strength inside the base material. In addition, Table 2 shows the thickness of the region in which the Ni content is 1.2 times or more of the inside of the base material (that is, the thickness of the Ni concentrated layer).
流れさびの発生量の調査にあたっては、各高耐食鋼板から鋼板表面を含む腐食試験片（厚さ５mm，幅50mm，長さ100mm ）を採取し、海水散布試験を行なった。海水散布試験は、腐食試験片に海水を１時間ずつ週２回散布する試験である。海水散布試験を１ケ月間行ない、腐食試験片から発生した流れさびをポリタンクに収容し、原子吸光光度法でFe2+の質量を測定した。表２には、腐食試験片１cm2 あたりの値に換算して示す。
In investigating the amount of flow rust, corrosion test pieces (thickness 5 mm,
表２から明らかなように、発明例（鋼板記号3B〜5B，10B，11B ）では、高耐食鋼板の表面近傍にNi濃化層が形成されている。一方、比較例（鋼板記号1A〜11A ）では、高耐食鋼板の表面近傍にNi濃化層は存在しない。
As apparent from Table 2, Inventive Example (steel plates symbols 3B ~ 5B, 10B, 11B) in, and Ni-enriched layer is formed near the surface of the high corrosion-resistant steel sheet. On the other hand, in Comparative Examples (steel plate symbol 1A～11A), no Ni-rich layer near the surface of the high corrosion-resistant steel sheet exists.
さらに各高耐食鋼板の流れさびの発生量について、鋼番号が同一の発明例と比較例を比較すると、同一成分の鋼板であるにも関わらず、発明例の方が流れさびの発生量が低減している。 Furthermore, regarding the amount of flow rust generated in each high corrosion resistance steel sheet, comparing the inventive example with the same steel number and the comparative example, the inventive example reduces the amount of flow rust even though it is a steel sheet of the same component. is doing.
このことから、Ni濃化層の存在が、流れさびの発生量を低減する上で、多大な効果を発揮することが分かる。 From this, it can be seen that the presence of the Ni concentrated layer exhibits a great effect in reducing the amount of flow rust generation.
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