TW200902731A - Steel material having excellent corrosion resistance - Google Patents

Abstract

Disclosed is a steel material having excellent corrosion resistance, which is characterized by the following properties (A) to (C); (A) the steel material comprises the following components (by mass) as essential components: C: 0.02-0.15%, Si: 0.10-1.0%, Mn: 0.1-1.5%, S: 0.02-0.5%, Ti: 0.02-0.15%, Ca: 0.0001-0.01% and Al: 0.01-0.50%, and contains at least one component selected from Cu in an amount of 0.05-3.0% and Ni in an amount of 0.05-6.0%, with the remainder being Fe and unavoidable impurities, wherein the contents of Ni, Cu, S and Ti have the relationship represented by the following formula: [(Ni+4.5xCu)xSx2500xTi>5]; ; (B) the surface of the steel material is covered with a rust containing S in an amount of 0.3-5.0% by mass and further containing at least one element selected from Ti, Cu, Ni, Nb, Zr and V in the total amount of 0.5-10.0% by mass; and (C) a rust layer is formed on the surface of the steel material, wherein the crystallite size of a ss-FeOOH component in the rust layer is less than 50 nm as measured by the X-ray diffraction method, and the rust layer has a specific surface area of 10 m<2>/g or greater as measured by the molecular adsorption method.

Description

200902731 IX. INSTRUCTIONS OF THE INVENTION [Technical Fields According to the Invention] The present invention relates to a steel material excellent in uranium resistance, a material thereof, a building, an iron tower, a bridge, a construction machine, a steel pipe, and a material, and is particularly suitable for containing a large amount of sulfur oxides. A material for steel structures that require excellent corrosion resistance. [Prior Art] In general, in the heavy chemical industry, the environment is polluted by the atmosphere of burning coal and dust, and the weak acidic environment caused by the serious corrosion of steel due to sulfur and sulfur, volcanic zones, etc. As a suitable one, alloy steel has been used in the past. The steel is improved in corrosion resistance by containing Cr and Ni, and is put into practical use in various forms of stainless steel. Usually, the high-valent element has a Cr content of 13% by mass or more, which is very high, so it is rarely applied to a structure or a structural surface. Regarding a corrosion-resistant steel material, in addition to stainless steel, low-alloy steel which has been subjected to corrosion by corrosion is used. Low alloy steel: weather resistant steel of Cr, Cu, P, etc. and contains Cr, Cu, and steel. Weather-resistant steel and seawater-resistant steel exhibit excellent corrosion resistance in the atmosphere. These low-alloy steels are cheaper than stainless steel and resistant to corrosion, so they are often used as structural members. However, it is suitable for hot springs that produce a large amount of sulfur oxides as an atmospheric pollution environment of steel structures such as civil storage tanks. It is believed that the materials of corrosion-resistant materials of sulfur oxidation have long been mentioned, however, the cost of materials in stainless steel and many more. The other party knows that it is also protected by the protection &amp; division: the water-resistant environment containing Mo, the seawater energy is better than the ordinary steel in the acid rain environment or -5 - 200902731 sΟχ environment, and can not produce weather-resistant steel The unique protective rust does not provide the desired resistance to touch. In addition, there is a kind of "sulfur-resistant steel" which is one of low-alloy corrosion-resistant steels. It is made by adding Cu to steel and further adding a small amount of auxiliary elements (Sb, Sn, etc.). However, since 1975, the concentration of S02 in the atmosphere has been greatly reduced in Japan, and the above-mentioned sulfur oxides have caused severe corrosion, leaving only hot springs, etc., so no special materials have been developed. As described above, in order to improve the corrosion resistance of iron, a common method is to add a corrosion-improving element such as Cr, Cu, or Ni. In general, the higher the amount of addition, the higher the corrosion resistance is obtained. However, as the amount of addition increases, the cutting property, mechanical properties, and weldability are often deteriorated, and the material cost is also increased. Therefore, it is preferable to suppress the element as much as possible. The amount added. In this way, there is a contradiction between the improvement of corrosion resistance and the characteristics of steel and cost. In order to fully satisfy the two, although there are many discussions, they have to compromise at a certain balance point. On the other hand, equipment exposed to flue gas, chimneys, boiler air preheaters, etc., which are exposed to exhaust oil, coal, and garbage, can cause problems in the sulfuric acid dew point corrosive environment, using sulfuric acid dew point corrosion. steel. When a sulfur-containing fuel is burned, S〇X is generated in the exhaust gas, which is combined with water in the exhaust gas to produce sulfuric acid. When the exhaust gas temperature reaches a dew point of sulfuric acid, the sulfuric acid gas will condense and uranium steel. In the steel used in the sulfuric acid dew point corrosion environment, sulfuric acid dew point corrosion resistant steel which exhibits corrosion resistance in a sulfuric acid environment has been developed. Generally, it is a low-alloy steel which is formed by compounding sb and Cu which are resistant to sulfuric acid corrosion. In recent years, it has also been proposed to add low c-low S i - C U to the sulfuric acid dew point corrosion resistant steel (patent 200902731 document 1). However, in recent years, with the rapid economic development in East Asia, the demand for energy has increased rapidly. Especially in mainland China, the production and consumption of coal has increased sharply. The emission of sulfur dioxide (S 02 ) is estimated to be 20 million tons per year and more than 20 times that of Japan. The atmospheric pollution in mainland China is transported over long distances through the atmospheric circulation. In Japan, it has also been observed that the area where acid rain is reduced (below ρΗ4·5 or less due to SOx) is observed. However, the conventional steel material does not have excellent bare corrosion resistance in an air pollution environment in which a large amount of sulfur oxide is generated by lowering an acid rain of pH 4.5 or lower. It is not possible to exert sufficient high corrosion resistance in response to the use of steel structures such as civil engineering, buildings, iron towers, bridges, construction machinery, steel pipes, and storage tanks. In particular, steel materials used in Japan cannot be sufficiently resistant to these applications. In view of the above, an object of the present invention is to provide a steel material which exhibits excellent corrosion resistance even in an air pollution environment in which a large amount of sulfur oxide is generated by acid rain of ρΗ4·5 or less. In view of the foregoing, in order to solve the above problems, the present invention provides a steel material having excellent corrosion resistance as in the following 1 to 3. 1 - Steels that meet the following (A) (B) (C) corrosion resistance: (A) In terms of mass%, the necessary ingredients include c: 〇 . 〇 2~〇 . 1 5 %,

Si: 0.10 to 1.0%, Μη: 0.1 to 1.5%, S: 0·02 to 0.5%, Ti: 200902731 0.02 to 0.15 %, Ca: 0.0001 to 0.01%, and Al: 0.01 to 0.50 % Further containing a selected from Cu: At least one of 0.05 to 3.0% and Ni: 0.05 to 6.0%; the remainder is composed of Fe and unavoidable impurities; and the contents of Ni, Cu, S, and Ti have the following formula (1) [(Ni + 4.5xCu) xSx25 00xTi&gt;5] (1) The relationship represented by (1) The surface is covered with rust, and the rust contains S: 〇·3 to 5.0% by mass, and further contains a material selected from the group consisting of Ti, Cu, Ni, Nb, and Zr And at least one of V and V is a total of 0.5 to 10.0% by mass; (C) a rust layer having a grain size of less than 50 nm obtained by a ray-diffraction method of forming a point-F e Ο Ο Η component on the surface, Further, the specific surface area determined by the molecular adsorption method of the rust layer is l〇m 2 /g or more. 2. In the steel material excellent in corrosion resistance described in the above 1. 'More preferably selected from La: 0.0001 to 0.05% by mass, Ce: 0.0001 to 〇.〇5% by mass, Mg: 〇_〇〇〇1 〇 〇 〇 5 mass ° /. Mo: 0.05 to 3_0 mass %, Nb: 0.005 to 0.5 mass. /〇, V: 0.01 to 0_5 Mass %, Zr: 0.005 to 0.5% by mass, B: 0.0003 to 0.003% by mass, and W: 0.05 to 3.0% by mass. 3. In the steel material having excellent corrosion resistance as described in the above 1 or 2, the fraction of the amorphous component determined by the X-ray diffraction method of the rust generated on the surface is 30% by mass or more 'and; The fraction of the FeOOH component was 30% by mass or less, and the fraction of rust was a-FeOOH/y-FeOOH&gt; 200902731 The available Ni is not described or the lower 〇La can be used for the amount of the steel according to the above 1. In the air pollution environment, the content of Ni Cu, Ti and S has the formula (1). The specific relationship represented by 'forming a protective film composed of a unique insoluble sulfide film' gives good corrosion resistance. That is, in an atmospheric pollution ring containing a large amount of sulfur oxides, Ni, Cu, and Ti can be formed into rust in normal atmospheric corrosion (, Cu: stable amorphous rust generation promotion, α rust generation promotion; Ti : Stable/3 rust generation inhibition) control and formation of soluble sulfides in the S Ox environment to form a uranium-resistant lifting film. In addition, by conforming to the conditions of the former (B), the reproducibility is excellent in high corrosion resistance in a corrosive environment. Furthermore, by complying with the above-mentioned condition (C), even if the chloride environment contains a large amount of sulfur oxides and the atmosphere is polluted by the atmosphere, the flow rust and the stripping rust do not occur, and the rust can be excellent. Corrosion resistance According to the above-mentioned steel material, the uranium resistance is further improved by containing a specific amount of at least one selected from the group consisting of Ce, Mg, Mo, Nb, V, Zr, B and W. Among them, the action of L a, C e , and Mg can suppress the pH lowering of the corrosion front end portion and suppress the formation of MnS (which becomes the starting point of the etching and lowers the weather resistance). Furthermore, Nb, V, Zr Mo and B contribute to the promotion of protective rust formation, and Nb and V can be quenched and hardened, which contributes to the improvement of strength. B also has the purpose of improving hardenability. According to the steel of the above-mentioned item 3, the rust of the surface is rust, and the fraction of the amorphous rust which contributes to the improvement of the corrosion resistance is 30% by mass or more, and the crystalline rust (cold-FeOOH component) which is the starting point of the corrosion is The fraction is 30% by mass or less, and the rust fraction is in accordance with a -FeOOH / y-FeOOH &gt; 0.6. Since 200902731 can exhibit excellent corrosion resistance, it can maintain dense protective rust even in the s Ox environment. The steel material of the present invention exhibits excellent corrosion resistance even in an air pollution environment in which a large amount of sulfur oxide is generated by acid rain of pH 4 /5 or less. It is suitable for use as a material for steel structures such as civil engineering, buildings, iron towers, bridges, construction machinery, steel pipes, storage tanks, etc. It is especially suitable for materials of steel structures requiring excellent corrosion resistance in an air pollution environment containing a large amount of sulfur oxides. [Embodiment] Hereinafter, a steel material excellent in uranium resistance according to the present invention (hereinafter referred to as "steel material of the present invention") will be described in detail. In the present specification, all percentages defined by mass, etc., and percentages defined by weight respectively represent the same meaning. In the steel material of the present invention, C, S i , η η, S, Ti, Ca, and Α 1 are essential components, and at least one selected from the group consisting of Cu and Ni is contained in the balance of Fe and inevitable impurities. The composition has a specific relationship between the contents of Ni, Cu, S, and Ti. Hereinafter, the relationship between the range of the content of each component constituting the steel material of the present invention, the reason for limiting the range of the number, and the content of Ni, Cu, S, and Ti will be described. C is an element that contributes to the improvement of steel strength. It is an effective element for ensuring strength of 390 to 630 N/mm2 or higher. When the content of c exceeds 0.15 mass/〇, the weldability of steel and the weatherability of bare steel Will get worse. On the other hand, when the C content is less than 〇02% by mass, it is difficult to ensure that the above strength is -10-200902731. Based on this point of view, the C content is set to 〇 2 〇 2 i 5% by mass, preferably 0.04 to 0.10% by mass.

Si is an element which contributes to the deoxidation and solid-solution strengthening of molten steel, and promotes the formation of a dense and stable rust layer, and has an effect of improving the contact resistance such as bare weather resistance. However, when the Si content is less than 0.10% by mass, the equivalent is insufficient. Further, when the Si content exceeds 1% by mass, the weldability may be deteriorated. Based on this point of view, the Si content is set to o.io to ι·〇% by mass, preferably 0.2 to 0.8% by mass. Μη is an element which contributes to the improvement of the strength of the steel, and is an effective element which replaces c to ensure a strength of 390 to 630 N/mm2 or higher, but when the Μη content exceeds 1.5% by mass, a large amount of MnS is generated in the steel. It may cause deterioration of uranium resistance such as bare weather resistance. Further, when the Μη content is less than 0.1% by mass, it is difficult to secure the steel strength. From this viewpoint, the Μη content is set to 0.1 to 1.5% by mass, preferably 0.3 to 1.3% by mass. When the S content is too large, a large amount of corrosion starting points such as FeS and MnS are formed, and an element which is expected to reduce the content is conventionally used. However, in the steel material of the present invention, it can be formed in the SOx environment by coexisting with Cu, Ni, and Ti. Insoluble sulfides form a corrosion-resistant coating, which is an element that contributes to the improvement of corrosion resistance. However, when the content exceeds 〇·5 mass%, not only the mechanical properties will be deteriorated, but FeS, MnS, etc., which become the starting point of uranium, will be generated in the steel, which may hinder the formation of the aforementioned stable rust layer, and may cause deterioration of corrosion resistance. . Further, in the case where the content of Ni or the like is excessive, the N i S compound having a low melting point precipitates at the grain boundary of the welded metal by the reaction with S tends to deteriorate the ductility of the grain boundary of the solidified metal. Based on this point of view, as long as the S content is at most 5% by mass of 〇.5 -11 - 200902731, the above-mentioned low-melting-point NiS compound is not precipitated, and a larger amount of Ni can be contained. Therefore, the S content is set to 2 to 0.5% by mass, preferably 0.02 to 0.3% by mass.

Ti, like Cu and Ni, has an advantageous effect of promoting densification of rust formation to form a stable rust layer, and has excellent corrosion resistance, and therefore it is very important in the present invention to add an element. In particular, as a suppressing and forming element of lanthanum-FeOOH which is formed in the sea and the marine environment, it can exhibit excellent effects when added in combination with Cu and Ni. At the same time, it has the advantage of purifying steel. This effect is obtained by adding an amount of 0.02% by mass or more, and the effect is remarkably improved when the amount of addition of 〇.〇3 mass% is exceeded. However, when the excess is added, the effect tends to be saturated, resulting in poor economy. In the case of welding, the upper limit may be hindered, so the upper limit of Ti is set to 〇1.5 mass%. In addition, although the above-mentioned matter is a case of a corrosion product of steel, the effect of improving the compactness is also contained in the corrosion product of zinc by the inclusion of Ti. Therefore, it is also an important element based on the fact that the steel itself and the uranium-producing products of iron and zinc have an effect of improving corrosion resistance. Then, the Ti content is set to 〇_〇2 to 0.15 mass%, preferably 0.03 to 0.10 mass%.

Ca is an element that plays an important role in the corrosion of the defect portion of the coating film. That is, Ca has a function of buffering the pH drop in the coating film defect, and in the process of corrosion under the coating film, a slight melting is generated as the iron corrosion reaction is alkaline (the melt pH buffer of the anode melting end portion) effect). Therefore, Ca has an effect of suppressing crevice corrosion of the defect portion of the coating film, and raises the pH during melting to exhibit the effect of suppressing crevice corrosion. That is, in the front end portion of the corrosion -12-200902731, if there is a Ca which can raise the pH during the melting of iron, the crevice corrosion can be suppressed. From this viewpoint, the Ca content is set to 0.0001 to 0_01% by mass, preferably 0.0003 to 〇_〇〇5 mass%. The addition of A1' and Ti can further promote the formation of a stable rust layer, thereby further improving corrosion resistance. In addition, A1 also has the effect of improving the weldability. Furthermore, A1, as a deoxidizing element of molten steel, captures molten oxygen and prevents the occurrence of blowholes, which contribute to the toughness of the steel. Further, A1 forms an oxide on the surface layer, but the oxide particles of A1 are small and have few voids, and form a very stable dense scale, which contributes to laser cutting property. When the A1 content is less than 0.01% by mass, the effects cannot be sufficiently exerted. On the other hand, when the A1 content exceeds 0.5 mass%. In the case where the above-mentioned uranium-improving effect by the formation of the stable rust layer is saturated, the weldability is deteriorated, or the toughness of the steel is deteriorated due to an increase in the alumina-based inclusions. Based on this point of view, the A1 content is preferably from 0.01 to 5% by mass, more preferably from 0. 1 to 0.5% by mass. Further, the steel material of the present invention contains at least one selected from the group consisting of Cu and Ni in addition to C, Si, Mn, S, Ti, Ca, and A1, and is composed of Fe and unavoidable impurities. In the steel material of the present invention, Cu is an element which contributes to improvement in corrosion resistance and weldability. That is, in terms of electrochemistry, Cu is an element which is more noble than iron, and can densify rust generated on the steel surface, promotes formation of a stable rust layer, and improves corrosion resistance such as weather resistance. At the same time, it helps to improve the weldability. In addition, although some of the surface layer is an oxide, it is concentrated in a solid solution state, and the surface scale is densified and the adhesion is improved, which contributes to the improvement of the laser cutting property of -13-200902731. When the Cu content is less than 0.05% by mass, the effect of improving the corrosion resistance cannot be sufficiently exhibited. However, when the Cu content exceeds 3.0% by mass, the effect of improving the corrosion resistance is saturated, and when the steel material is produced and processed by hot rolling, it is possible. Causes embrittlement of the material (hereinafter also referred to as hot work embrittlement). In order to more reliably suppress the occurrence of the above-described hot work embrittlement, the Cu content is set to 〇_〇5 to 3.0% by mass, preferably 〇.3 to 1.5% by mass. N i is an element that contributes to corrosion resistance and weldability. n i is the same as in the case of C u , and it can densify the rust generated on the steel surface, promote the formation of a stable rust layer, improve the corrosion resistance such as weather resistance, and contribute to the improvement of the weldability. Further, 'Ni has the above-described effect of suppressing the hot work embrittlement. Therefore, the synergistic effect of both the effect of improving the corrosion resistance and the effect of suppressing the hot work embrittlement by the combination of Ni and Cu is expected. Ni is the same as Cu. Although some of the surface layer is an oxide, it is concentrated in a solid solution state, and the surface scale is densified and the adhesion is improved. This contributes to the laser cutting property. Improvement. When the content of N i is less than 0.05% by mass, the effect of improving the corrosion resistance cannot be sufficiently exerted. However, when the Ni content exceeds 6.0% by mass, the solid-liquid solidification temperature range of the complete Worthite iron structure becomes wider, which contributes to the low melting point impurity element. The segregation toward the dendritic grain boundary and the reaction with S precipitates a low-melting NiS compound at the grain boundary of the weld metal, which deteriorates the ductility of the grain boundary of the solidified metal, and further adversely affects the high-temperature crack resistance. Based on this point of view, in the case of containing Ni, the Ni content is set to 0.5 to 6.0% by mass, preferably 0.5 to 5.0% by mass, more preferably 1.0 to 3.0% by mass. -14- 200902731 In the steel material of the present invention, it is necessary to have a relationship represented by the formula (1) between the contents of N i , Cu , S i and T i . When the contents of Ni, Cu, Si and Ti are in accordance with the relationship of the formula (1), S and N i , C u and T i form an insoluble sulfide film in the environment of s Ο x to form a corrosion-resistant coating film. This achieves high corrosion resistance. (Ni+4.5xCu)xSx2500xTi&gt;5 (1) The steel material of the present invention can exhibit the following effects (a) to (d): (a): generation of amorphous rust having good protection Promotion, (b): promotion of the formation of α rust with good protective and thermodynamic stability, (c): inhibition of formation of rust which reduces corrosion resistance generated in a chloride environment' (d): oxidation of a large amount of sulfur Corrosion resistance that enhances corrosion resistance in the atmosphere and dust environment (SOx environment) promotes the formation of the film. Therefore, the inventors of the present application have repeatedly conducted various experiments to know that the amount of each element required for conforming to all items (a) to (d) must conform to the above formula (1). In the steel material of the present invention, Ni, Cu, and Ti can suppress the formation of rust under normal atmospheric corrosion (Ni, Cu: formation of stable amorphous rust, promotion of α rust generation; Ti: unstable; 8 suppression of rust formation), in the range of S content of 0.02 to 0.5% by mass, by coexistence with Ni, Cu and Ti, in the heavy chemical industry, the combustion of coal produces a large amount of sulfur oxides and dust air pollution In the environment (SOx environment), the corrosion-resistant coating film composed of insoluble sulfides can be formed to obtain excellent corrosion resistance. Further, in the steel material of the present invention, in order to further improve the corrosion resistance, it is preferable to contain at least one selected from the group consisting of La, Ce, Mg, Mo, Nb, V, Zr, B, and W -15-200902731. The result of the drop is the feed in the amount of B W

La, Ce, and Mg function to suppress the low pH of the corrosion front end portion and suppress the formation of MnS (which becomes the starting point of pore uranium and lowers weather resistance). Furthermore, in the early stage of uranium, Zn and Fe have the effect of stabilizing corrosion. Therefore, in the case of containing La, Ce, or Mg, the La content is preferably 0.0001 to 0.05% by mass, and the Ce content is preferably 0.0001 to 0.05% by mass. The Mg content is preferably 0.0001 to 〇.〇5 mass%.

Mo, Nb, V, Zr and B help to promote the formation of protective rust. - Nb and V can improve the hardenability and contribute to the improvement of strength. B also has the effect of improving the hardenability. Therefore, based on the improvement of corrosion resistance, in the case of containing Mo, Nb, V, Zr or B, the Mo content is preferably 0.05 3 〇 mass %, the Nb content is preferably 0.005 〜 0.5 mass %, and the V content is preferably 〇. 〇 1 The content of 0.5% by mass and Zr is preferably 〇_〇〇5 to 0.5% by mass, and the content of 6 is preferably 0.0003 to 0.003% by mass. Further, it is more preferable that the Mo content is 〇_1 to 1.0% by mass, the Nb content is 0.005 to 0.10% by mass, the V content is 0.01 to 0.20% by mass, and the Zr content is 0.005 to 0_10 by mass. /. , the content is 0.0003~0.0030 mass. /. . Further, W is also an element which contributes to an improvement in corrosion resistance. In the case of containing, the W content is preferably 〇. 〇 5 to 3.0% by mass. Further, in the steel material of the present invention, in order to obtain an insoluble sulfide film in the SO Ox environment in which acid rain is lowered, an effect of improving corrosion resistance is obtained, and it is preferably selected from the group consisting of Be, As, Sb, Bi, Ge, Sn, Pb, and Se ' Te At least one of Cd and Cd is 〇.〇〇2~o·2% by mass. These elements are believed to form a water-insoluble and acid-soluble sulfide (, -16-200902731, ruthenium, etc.) in the steel without replacing Μη, so that it is dissolved in a corrosive environment accompanied by corrosion to the steel surface. An insoluble sulfide film is formed. Further, the steel material of the present invention may contain P and Cr. P prevents chloride ions from invading the rust formed on the surface of the steel, and forms a dense and stable rust layer, which has an effect of improving corrosion resistance. Therefore, in the conventional weather-resistant steel, in order to exhibit the corrosion-improving effect, the content must be 0.05% by mass or more and 0.15% by mass or less. On the other hand, when P is contained in an excess amount of more than 0.15 mass%, the weldability is remarkably lowered. In contrast, in the present invention, a dense stable rust layer can be formed by containing T i or the like, so that it is not necessary to contain an excessive amount of P. Therefore, in consideration of the improvement in weldability, in the case of containing P, the P content is preferably 0.001 to 0.15 mass%. Here, in general, P must be reduced in the steel manufacturing process, but elements that are inevitably left in the steel. However, in the present invention, p is an element which contributes to an improvement in corrosion resistance. Therefore, in the production process of the steel material of the present invention, in order to increase the residual amount of p, the degree of reduction of p can be alleviated.

When Cr' is added to stainless steel or the like, it is generally an element which contributes to the improvement of corrosion resistance, but it adversely affects the chloride environment and the seaside environment in the atmosphere. In this environment, the puncture resistance can be improved by lowering the Cr content. Such an improvement in the perforation resistance, the local corrosion resistance, and the improvement in the corrosion resistance in a salt environment are particularly effective in reducing the Cr content. From this point of view, in the case where the steel material of the present invention contains Cr, the Cr content is preferably 0.1% by mass. the following. Although it is more preferably Cr-free (Cr content is 0), excessive reduction may cause economic deterioration. In addition, in the manufacturing process of steel, C r is an inevitable component of waste materials which are commonly used as raw materials. Therefore, in the invention of -17-200902731, it is not preferable to actively add Cr as in the weather-resistant steel specified by JIS-SMA. Therefore, the content thereof is preferably less than 0.02% by mass. As described above, the steel material of the present invention contains C, Si, Mn, S, Ti, Ca, and A1 as essential components, and further contains at least one selected from the group consisting of Cu and Ni, and the balance is Fe and unavoidable impurities. And the content of Ni, Cu, s, and Ti has a specific relationship represented by the above formula (1), or may be selected from the group consisting of La, Ce, Mg, Mo, Nb, V, Zr, B, and W as needed. At least one of them can form a protective film composed of a unique insoluble sulfide film to obtain good corrosion resistance. That is, in an atmospheric pollution environment containing a large amount of sulfur oxides, Ni, Cu, and Ti can generate rust in the usual atmospheric corrosion (Ni, Cu: stable amorphous rust formation promotion, and alpha rust generation promotion; Ti: Instability/3 rust generation inhibition is controlled, and an insoluble sulfide is formed in the S Ox environment to form a corrosion-resistant lifting film. Further, the steel structure of the present invention is basically a mixed structure of ferrite iron + wave iron, for example, a structural material such as a bridge or the like, in order to secure a necessary strength of 3 90 to 630 N/mm 2 or better. Strength and toughness' and excellent corrosion resistance, the amount of ferrite should be more than 90%. The more iron and iron in the ferrite, the closer the steel structure is to the single layer of the ferrite phase, the harder the steel structure itself is to form a microbattery, and the corrosion resistance such as bare weather resistance can be improved. Therefore, the steel structure is preferably more than 95% of the amount of ferrite. Next, the rust and rust layers on the surface of the steel material of the present invention will be described. The surface of the steel material of the present invention is covered with rust containing S and at least one selected from the group consisting of Ti, Cu, Ni, Nb, Zr and V. Therefore, in the corrosive environment of salt -18-200902731 or the atmospheric pollution environment containing a large amount of sulfur oxides, dense and fine a-FeOOH rust and amorphous rust can be formed, and the occurrence of 10,000-FeOOH can be suppressed as much as possible. , and good reproducibility can achieve high corrosion resistance. That is, in the steel surface or the steel rust layer, as long as the S is contained or present, and at least one selected from the group consisting of Ti, Cu, Ni, Nb, Zr, and V, the steel surface or the steel rust layer is in the atmosphere. The resulting rust, whereby the elements can form dense and fine a-FeOOH rust and amorphous rust even in a salt corrosion environment or an atmospheric pollution environment, and in this process, yS-FeOOH can be suppressed as much as possible. happened. The effects of such Ti, S, etc. on rust formation are presumed as follows. That is, in the stage of formation and growth of rust, fine compound particles or fine precipitates having ions or colloidal properties (hydrogen hydroxides or oxygen-containing hydroxides of Ti which are produced by oxidation or hydrolysis of Ti or Ti ions, The influence of the form of an oxide or a reactive product with other substance elements may destroy the crystal structure of the rust and suppress growth, and it may be prevented from becoming hunger or by forming defects such as rust and sulphide formation. The starting point of stripping. In the rust which coats the surface of the steel, the S content is from 0.3 to 5.0% by mass. If S is contained in the rust layer, the rust layer itself becomes dense and has high corrosion resistance. Although the mechanism is unclear, it is believed that the contact resistance can be further improved by the insoluble sulfur compounds on the surface of the steel and the synergistic effect of the fine and dense rust containing S and Ni, Cu, and Ti. When the S content in the recording layer on the surface is less than 0.3% by mass, the effect of improving the corrosion resistance is not exhibited. When it exceeds 5% by mass, the corrosion start point may become, and the corrosion resistance may be deteriorated. -19-200902731 The rust on the surface, the total content of at least one selected from the group consisting of Ti, Cu, Ni, Nb, Zr and V is 0.5 to 10.0% by mass. In the rust of the coated surface, the lower limit of the total content of at least one selected from the group consisting of Ti, Cu, Ni, Nb, Zr and V is preferably 2.0% by mass or more, and more preferably 3.0% by mass or more. In the rust layer formed on the surface of the steel material of the present invention, the grain size of the -FeOOH component determined by the X-ray diffraction method is less than 50 nm. Further, the specific surface area determined by the molecular adsorption method of the rust layer is l〇m2/g or more. Therefore, even in a harsh corrosive environment such as a chloride environment or an atmospheric pollution environment containing a large amount of sulfur oxides, flow rust and peeling rust do not occur, and excellent corrosion resistance can be exhibited and the appearance can be maintained. . Especially in the salt corrosion environment, the stabilization of the rust layer depends on the presence of 3-FeOOH rust, but the grain size of the --FeOOH rust and the specific surface area of the rust particles determine the corrosion resistance of the rust layer. The grain size of /3 -FeOOH rust exceeds 5 Onm, and since the peeling rust layer is easily formed, the grain size of the /3 rust is set to less than 50 nm. In other words, the grain size of the rust particles constituting the rust layer is reduced as a result of the rust-free type, and the corrosion resistance is not remarkably improved. Therefore, in particular, the grain size of the rust is lowered to reduce the size thereof, and the corrosion resistance is improved. The promotion is very important. In the present invention, the main component of rust is composed of α-FeOOH and/or amorphous rust. Among them, in particular, amorphous rust can form a finer and denser stable rust layer than crystalline rust, and even if the rust film forms "defective portion j, the amorphous rust portion has a "defect repair function". . Therefore, the higher the proportion (amorphous degree) of amorphous rust in rust, the higher the corrosion resistance of -20-200902731. Therefore, in the rust formed on the surface of the steel material, the fraction of the amorphous component determined by the x-ray diffraction method is preferably 30% by mass or more. On the other hand, rust other than this, in particular, crystalline rust such as /3 -FeOOH, even if the ratio of the amorphous or a-FeOOH in the rust is high, corrosion is caused by the rust as a starting point. Try to suppress. Therefore, in the rust formed on the surface of the steel material, the fraction of the yS-FeOOH component determined by the X-ray diffraction method is preferably 30% by mass or less. When the fraction of the amorphous component of the rust is less than 30% by mass and the fraction of the component of the arsenic-FeOOH component (stone rust) exceeds 30% by mass, the α-FeOOH, the -FeOOH, the γ-FeOOH, and the Fe304 are used. The crystalline rust component is increased, and the rust on the surface of the steel cannot form a dense and stable rust layer, and the high corrosion resistance of the steel may not be ensured. In addition, amorphous rust may not be formed depending on the environment. In this case, the rust protection can be evaluated by comparing ct rust (stability </ RTI> to acidity easily) and gamma rust (unstable, easy to generate in neutral). Therefore, in the steel material of the present invention, the fraction of rust is preferably a-FeOOH/y-FeOOH &gt; 0.6. In the present invention, the high uranium resistance of the rust generated on the surface of the steel refers to the corrosion resistance of the steel material in the s Ο X environment. Therefore, in order to ensure this high corrosion resistance, it is necessary to evaluate the corrosion resistance of the steel material based on the atmospheric exposure of the steel for half a year or the evaluation result of the acid rain spreading test in a simulated atmospheric environment. In the present invention, as a means for measuring the degree of amorphousness of rust, "Quantification of rust powder by powder X-ray diffraction method using corrosion corrosion prevention 95C-3 06 (34 1~3 44 pages) and its application can be used. The disclosed powder X-ray-21 - 200902731 line diffraction method. This document ' attempts to quantify the rust component on the steel surface by powder ray diffraction method for weather-resistant steel, and confirms that the ratio (amorphism) of amorphous embroidery in rust is higher. The barrel 'can form a denser and stable rust layer to improve corrosion resistance. The specific powder ray diffraction method, which is based on the internal standard, is a mixture of a certain mass ratio of CaF2 or ZnO and a rust sample taken from a steel material, and is powdered, and is identified by a usual X-ray diffraction method. The quantification of each crystalline rust component is performed based on the integrated intensity ratio of the respective diffraction peaks of the five types of rust and the calibration curve of each rust component obtained in advance, and each crystalline component is subtracted from the total amount of rust. The ratio of the amorphous component was calculated from the amount of the rust component. The reason is that the integrated intensity ratio of the diffraction peak of the amorphous component itself is not easily found, and it is difficult to quantify. Next, a method of producing the steel material of the present invention will be described. The steel material of the present invention can be produced by a usual method for producing a thick steel plate. That is, after the steel is melted by continuous casting or agglomeration, heat processing such as block rolling, hot forging, or thick plate rolling is performed to produce a predetermined product thickness. The hot working conditions, the cooling after hot working, and the heat treatment conditions are in accordance with the mechanical properties required for the steel (for example, the strength of the bridge material is 390 to 630 N/mm2 or higher) Specifications are determined appropriately. Therefore, in addition to the usual hot working, the method of ensuring the mechanical properties such as the aforementioned strength can be selected after the alloying is ensured to be low in alloying or low in carbon. For example, in order to make the amount of ferrite and iron in the steel structure of the present invention 90% or more, forced cooling such as accelerated cooling after hot working or controlled rolling can be performed. Further, regarding the heat treatment after the hot working, direct quenching on the rolling line, -22-200902731 fire (DQ), or off-line quenching annealing (QT), may be appropriately performed as needed. EXAMPLES The following is a detailed description of an embodiment consistent with the requirements of the present invention and a comparative example not meeting the requirements of the present invention. The following examples are merely representative and the invention is not limited to the examples. (Example N 〇 . 1 to 1 6 ) Steel blocks having the chemical compositions shown in Table 1 were each atmospheric melted at a laboratory scale. The mold was cast using a square mold of 45 k g f using a thin plate to produce an ingot having the chemical composition shown in Table 1. Next, the ingots were subjected to rough rolling. The heating condition is maintained at 1 100 ° C for 30 minutes, and the hot rolling roll process is not particularly limited, and is finished to a thickness of 25 mm x - a fixed width X length ("the certain width" herein means that the plate width is not limited but is calendered The resulting width is also the same for the length. The following are the same). Then, the gas was cut to prepare a sheet having a length of 300 mm. Next, the finishing is performed. The heat extension condition is heating 1 1 0 (TC x 2 hours, 5 times of roll making, finishing temperature is 90 0 °C ± 50 °C. Finishing size is 6mm thick X - fixed width X length, cooling rate is 70 °C / sec, the stop temperature is 65 〇 ° C. Then, the furnace is cooled at 600 ° C for 60 minutes to produce a steel plate. Each test piece is taken from the steel plates. -23- 200902731 Φ chain I 撇

Parameters 0.00 0.01 0.01 0.56 0.13 1.34 13.08 14.93 23.32 16.33 29.57 51.71 29.03 68.31 37.97 150.89 Other La+Ce: 0.05 Nb: 0.05 in ^ ^ Ο Ο Ο ο Ρ Ρ ο ο 〇 · · · · 0) σΰ 2 U Η ^ in X 9 ^ § ΐ ^ κ h-1 Β: 0_002 Mg: 0.008, wide inch 〇〇 ^ ο Ο Ρ ο ο 9&gt; ο ο ^ *d c3 ^ UJ Zr: 0.08 Mg:0.008 〇S ο ^ &gt; ¢ 3 | Not added | Not added | Not added 1 l Not added I 0.004 0.005 I 0.005 0.005 0.008 0.005 0.005 0.004 0.006 0.005 1 0.007 0.005 0.010 0.010 0.010 0.045 0.010 0.035 0.036" 0.035 0.045 0.035 0.045 0.045 0.045 0.045 lO.03 8 1 0.040 0.030 I 0.030 0.030 0.030 0.030 0.030 | 0.030 | | 0.030 | 0.070 0.030 0.070 0.060 0.070 0.070 [0.030 0.050 o.oi | 0.01 o.oi 1 0.55 1 | 0.01 [0.01 0.01 | 0.01 0.60 0.50 0.60 0.97 0.60 0.50 0.60 0.97 i o .oi | 0.01 1 0.04 1 0.32 ] | 0.30 j | 0.55 | 1 2.76 | 1.05 0.60 0.50 0.60 0.97 1.98 2.01 2.50 2.73 U [O.Olj 0.04 "0.01] 1 0.30 1 r 〇·3Μ [0.40 Γ 0.54 0.99] 0.99 0.98 0.99 S r—Η 0.50 1.02 1 0.95 1 0.99 cn | 0.003 I 0 .003 0.005] 0.003 1 0.003 0.028 J 0.028 | 0.03Π 0.041 0.038 0.052 0.082 0.061 0.092 j 0.059 1 0.21 pH 0.015 0.015 0.015 0.013 1 0.010 | o.oii | I 0.010 | 0.010 0.012 0.010 0.012 0.010 0.010 0.013 1 0.012 J 0.010 Μη 1-39 1.20 | i·21 1 1.20 1 !-2〇1 I.% 1 0.85 M8 1 Ο in Η 1.21 1.20 1.20 1.22 1.05 S m 0.32 0.32 0.31 0.32 0.32 0.32 j | 0.32] 0.33 ] 0.34 0.33 I 0.32 0.32 0.31 0.32 0.35 1 0.32 u | 0.08 I 0.08 | 0.08 1 0.08 1 丨 0.08 | "0.08 j [0.06 j 0.05 0.05 0.03 0.05 0.05 0.10 0.05 Γ〇·〇6 Π).05 Comparative Example Comparative Example 丨 Comparative Example 1 Comparative Example COMPARATIVE EXAMPLES "Inventive Example |" Inventive Example I Inventive Example Inventive Example Inventive Example Inventive Example Inventive Example Inventive Example Inventive Example Inventive Example d (N m inch 00 Os Ο 1 ^ (Ν cn inch in ^sO uxoos(nxsx9uxs·inch+ίΝ): Jude: ffi -24 - 200902731 Next, from the test piece taken, a test piece of 50 mm x 50 mm wide and 3 mm thick was produced and evaluated by the following test. Corrosion resistance. Corrosion resistance evaluation test A 7-day compound cycle type promotion laboratory test was conducted. The composite cycle test '1 cycle is included: spray with artificial acid rain of ρΗ = 3·5 for 2 hours, dry (temperature 60 °C, humidity 40%) for 2 hours, placed in a humid environment (temperature 40 °C 'humidity 9 5 % ) 2 hours; 4 days for 4 cycles. After the test, the rust was removed by liquid calendering, and the weight was measured to determine the corrosion loss. The corrosion reduction amount of No. 1 was set to 100, and the amount of rot of each test piece was standardized. Analysis of generated rust A rust sample was taken from the test material after the corrosion resistance evaluation test, and a grain size of /3 - F e Ο Η Η rust (Miller index 1 1 〇) was measured by a ray diffraction method. For a part of the sample, the grain size of Y-Fe0〇H (/3 rust) (020) or magnetite (220) was measured. In addition, 'the rust sample taken from the test material is identified by the above-mentioned χ ray diffraction method'. The diffraction is inherently based on the three kinds of rust of a_Fe0〇H, y3-Fe〇〇H, γ-FeOOH and Fe3〇4. The integrated intensity ratio of the peak and the calibration curve of each rust component obtained in advance are used to quantify each crystalline rust component. The amount of the rust component of each crystallinity is subtracted from the embroidering measurement to calculate the amorphous component. Proportion, and recording rate: a_Fe〇〇H/Y_Fe〇〇H. -25- 200902731 Specific surface area of rust layer The N2 isotherm is obtained at the liquid nitrogen temperature using an automatic volumetric adsorption device. The specific temperature is obtained by performing the bet mapping using the adsorption isotherm. Elemental analysis in the recording The test piece was cut, and the cross section was observed with a scanning electron microscope ( ) at a ratio of 100 to 2000 times, and the surface iron layer and the iron-adhered portion were arbitrarily taken out, and the electron beam probe micro analyzer was used. (ΕΡΜΑ) The degree (content) of the alloying elements (S, Ti, Cu, Ni, Nb, Zr ' V ) of the rust layer. Table 2 shows the results of the corrosion resistance evaluation test, the generated rust, the specific surface area of the rust layer, the pore diameter, and the elemental analysis in the rust. Adsorption surface SEM Matrix determination Concentration analysis, etc. -26- 200902731 Rust fraction («/r) 0.53 0.55 0.51 0.56 0.56 0.78 0.89 0.86 0.91 1- 丨0.95 1.05 1- ί 1.02 0.98 1 j 1.15 1.34 00 r·&quot;* (% by mass) in inch m as mm inch 1 — inch w _ inch inch »—Η l/Ί inch inch amorphous component (mass%) oo — called ON (N (N l〇-.H κη κη 5 CN IT) Specific surface area of rust layer (m2/g) 〇\ oo oo (N On oo 12.1 22.3 25.6 19.7 25.3 39.4 34.1 1- ί 53.9 45.3 1 52.8 /3 Recorded grain size (nm) g oo cn 00 5 t —&lt; ο cn οι 卜 m κη mm Elements in rust (% by mass) Total – ο 0.17 0.26 1.12 inches 1' ' i 1.13 4.68 j 3.93 3.72 I 3.35 5.22 1 4.82 1 4.53 1 6.44 6.16 6.58 &gt; 1 1 1 1 1 1 i 1 1 1 1 1 1 1 1 ! 0.08 N 1 1 1 1 1 1 1 1 1 1 1 1 1 | 0.12 1 I 1 1 1 1 1 ί tl 0.12 1 〇l ί ( l 1 0.09 0.01 0.01 0.03 0.34 0.31 0.61 2.98 1.31 0.78 0.54 0.68 1.09 2.31 1_ | 2.16 1 2.89 1 3.01 DU 0.02 0.06 0.01 0,62 0.69 0.09 m (N 1.89 00 On 2.13 3.35 2.46 1.21 2.98 2.34 κη 0.01 0.01 0.01 0.05 ! 0.01 0.04 0.05 0.04 0.06 0.04 0.06 ι i 0.06 0.05 | 0.05 0.04 ι 0.06 GO 0.11 0.09 0.21 y—io 0.13 0.39 0.42 0.69 0.78 0.64 SP·»· a &lt;N i-l 0.96 ,13 0.89 1.89 Corrosion resistance OB 00 s as s VO ON ί ΓΠ — VO ON ON ON ON ON ON 比较 VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT VT EMBODIMENT OF THE INVENTION EXAMPLES OF THE INVENTION The present invention is an example of the invention. The invention example No. (N inch in VO r- OO ON 〇τ-^ 1' Η 1 « CN m inch • · -27 - 200902731 as shown in Table 2 It is shown that compared with the comparative example (Ν ο · 1 to 5), N 〇. 6 to 1 6 ) shows superior corrosion resistance. The present invention is not limited, and the grain size of /3 -FeOOH rust is small and rust layer. In other words, in the example of the present invention, the corrosion resistance is excellent, and the fraction of the amorphous component determined by X-ray is 30% by mass or more, and the fraction of the component of the rust-removing component is 30% by mass or less, and the rust is divided. The rate / γ-FeOOH ) exceeds 0.6. On the other hand, the comparative examples have the same conditions, and therefore the corrosion resistance is poor. Further, in the inventive examples (Nos. 6 to 16), the rust layer contained effective elements such as Cu, Ni, Ti, etc., and the above results were confirmed. The above description of the present invention will be apparent to those skilled in the art of the present invention. In addition, this application is based on the application filed on January 31, 2007 (Japanese Patent Application No. 2007-020522) and the Japanese Invention Application No. 2007-303 3 3 3 of November 2007. in. Further, all of the references cited herein are the steel materials of the present invention, and can be excellent even in an air pollution environment in which a large amount of sulfur oxides having a pH of 4.5 or less is lowered. It is suitable for use as a material for steel structures such as civil engineering, buildings, iron towers, bridges, pipes, storage tanks, etc., and is particularly suitable for use in the present invention (only corrosion resistance excellent surface area large line diffraction method - FeOOH (β (a -FeOOH does not meet any S, and the concentration corrosion resistance test is clear, but it can be applied to the 22-inch application within the cooked range. Therefore, it uses all the acid rain to produce different corrosion resistance. Sulfur Oxygen-28- 200902731 Material of steel structure requiring excellent corrosion resistance under atmospheric pollution environment -29-

Claims (1)

200902731 X. Patent application scope 1 · A steel with excellent corrosion resistance conforms to the condition of ^ TCA) ( Β ) ( C): (A ) In mass %, the necessary components include c. Λ • 〇· 0 2 ～0 · 1 5 %, Si: 0.10 〜1.〇%, Μη: 0.1 〜1.5%, S: 〇.υ 2 ～0.5 %, T i ·· 0.02 ～0.15%, Ca: 0.0001 ～0.01 %, and Al and 1 0 . Ο 1 ～ 〇 _ 5 0 % » further containing at least one selected from the group consisting of Cu: 0.05 to 3.0% and Νι. 0·05 ～ 6.0%; the remainder being composed of Fe and unavoidable impurities; and Ni, The contents of Cu, S and Ti have the following formula (1) [(Ni+4.5xCu)xSx2500xTi&gt;5) ( { ^ represents the relationship; (B) the surface is covered with rust, the embroidery contains S: 〇 _3 〜5〇质量。 /β, and further containing at least one selected from the group consisting of Ti, Cu, Ni, Nb' Zr and ν is 〇. 5~1 0 . 〇 mass%; (C) surface forming its lun - The rust layer of the FeOOH component determined by the X-ray diffraction method has a grain size of less than 50 nm, and the specific surface area determined by the molecular adsorption method of the rust layer is 1 〇m 2 /g or more. Article 1 of the patent scope The steel material having excellent corrosion resistance further contains, for example, La: 0.0001 to 〇.〇5 mass%, Ce: 0.0001 to 0.05 mass%, Mg: 0.0001 〇·〇5 mass%, Mo: 0.05 to 3.0 mass%, Nb: 0.005 to 0.5% by mass, V: 0·01 to 0.5% by mass, /, Zr: 0.005 to 0_5 mass%, Β: 0.0003 to 0.003 mass% -30-200902731 and w: 0.05 to 3.0% by mass 1. A steel material having excellent corrosion resistance as described in claim 1 or 2, wherein the fraction of the amorphous component determined by the X-ray diffraction method of the rust generated on the surface is 30 masses. % or more, and the fraction of the cold _FeOOH component is 30% by mass or less, and the fraction of rust is α _Fe00H / Y_Fe 〇〇 H &gt; 〇. 6. -31 - 200902731 No clarification, no Jane eu.. The figure of the figure is replaced by the figure: the table pattern represents the book, and the standard refers to the CC. 8. If there is a chemical formula in this case, please reveal the chemical formula that best shows the characteristics of the invention: none