JP2014019908A - Anticorrosion coated steel material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anticorrosion coated steel material usable as a minimum maintenance material even under an environment in which the amount of flying salt is high.SOLUTION: The anticorrosion coated steel sheet is obtained by coating a steel material having a composition comprising, by mass, 0.001 to 0.20% C, 2.5% or lower of Si, above 0.5% to 2.5% or lower of Mn, below 0.03% of P, 0.005% or lower of S, 0.05 to 0.6% Cu, below 0.5% Ni, 0.01 to 4.0% Cr, 0.003 to 0.5% Al, 0.001 to 0.1% N and 0.03 to 0.50% Sn, and the balance Fe with impurities, and in which a Cu/Sn ratio is 3.5% or lower, and also, CP value defined by the following formula (A) satisfies 0.98% or lower is coated with a zinc-containing film. The steel material may comprise one or two or more kinds selected from B, Ti, Nb, Mo, W, V, ca, Mg and REM: CP=3Cu-2Ni+Sn-Al-100B (A); in which the element symbols in the formula (A)denote the contents (mass%) of the respective elements.

Description

  The present invention relates to an anticorrosion-coated steel material that can be used as a minimum maintenance material even in an environment in which salt such as seawater is flying or scattered.

  Generally, in civil engineering steel structures such as bridges and ships, it is known that extremely severe corrosion proceeds in an environment in which salt such as seawater flies or scatters. For example, bridges are a problem not only in coastal areas, but also in inland areas where the amount of incoming salt is high, such as areas where snowmelt salt and antifreeze are sprayed, and for harbor steel structures and ships, As a matter of course, corrosion becomes a big problem because seawater droplets adhere to the steel material surface.

  Therefore, in order to prevent corrosion, a method of forming a corrosion-resistant coating layer on the surface of the steel material by painting or spraying, etc., and widely suppressing the permeation of water, oxygen, and chloride, which cause corrosion, is widely used. However, even if such an anticorrosion coating layer is formed, it cannot be completely shielded from the corrosive environment. For example, in the case of coating, corrosion progresses from minute defects, or the coating peels off and corrosion progresses due to flaws (defects) on the anticorrosion coating layer such as painting and spraying during construction or use. There is a problem of doing.

  For bridges, anti-corrosion coatings have been applied according to the environment to solve these problems. In recent years, as a heavy coating system, the corrosion resistance of steel materials has been improved by multilayer coating of zinc rich paint, epoxy resin paint and fluororesin paint (referred to as “C-based coating”). In other words, after the surface of the steel material is blasted (ISO Sa2 1/2) to prepare a secondary substrate, a primer coating is applied with an inorganic zinc-rich paint as an anticorrosive base, and a multilayer of epoxy resin paint and fluororesin paint is applied on it. Painted. The coating specifications are as described in Non-Patent Document 1. The “C-5 coating” is shown in Table 1 below.

  Thus, in the C-based coating of bridges, zinc rich paint that becomes a zinc-containing coating is used as a primer (undercoat layer). Steel with a primer coating formed of inorganic zinc rich paint has a sacrificial anticorrosive action when the coating on the surface of the steel is defective. Has the effect of suppressing the corrosion of. Further, an anticorrosion method in which the zinc-containing coating is coated on a steel material by thermal spraying instead of painting, for example, zinc aluminum alloy thermal spraying or zinc aluminum pseudoalloy thermal spraying has been proposed. The anticorrosion method using these zincs as a primer has extremely high anticorrosion properties compared to conventional general coating. Even if wrinkles (defects) occur in the surface coating film, peeling and swelling of the coating film are remarkably suppressed.

  Further, in recent years, focusing on the sacrificial anticorrosive action of zinc, it has been proposed to improve the anticorrosion property by forming a zinc-containing coating on the steel material surface as a marine steel material. For example, Patent Document 1 discloses a steel material obtained by applying a zinc rich primer containing W or Mo and further containing Sn or Sb. Patent Document 2 discloses that a steel material to which Sn is added can suppress corrosion due to surface flaws even in an environment in which salt such as seawater flies or scatters. It is disclosed that this steel material can be subjected to galvanized coating, zinc spray coating, resin coating, and C-based coating.

JP 2011-21247 A JP 2008-163374 A

"Steel Road Bridge Painting and Anticorrosion Handbook" issued on December 26, 2005

  However, in recent years, it has gradually been found that corrosion progresses in some environments even in C-based coating using zinc as a primer. Despite the fact that zinc is used as a primer, a phenomenon that deep corrosion holes (called abnormal corrosion) are formed has been confirmed ("Steel Road Bridge Painting and Anticorrosion Handbook II-25" Japan) (See Road Association, published September 2010). In addition, despite the fact that paint film peeling on the paint ridges is small, the phenomenon that corrosion progresses under the paint film and the corrosion progresses locally, that is, the phenomenon that the thickness of the steel structure is reduced by pitting corrosion is also confirmed. (Refer to Makoto Tanaka, “Steel Bridge Painting” 38 (2), 18-25 (2010)).

  For steel structures, a local reduction in plate thickness may concentrate the force on the part and lead to extremely severe damage by losing the originally planned strength. In addition, during maintenance, whether or not corrosion has progressed and repairs need to be performed is determined based on the appearance of the paint peeling of the steel material. There is a danger of not being aware of the ongoing corrosion because it is not visible. Under these backgrounds, there is a demand for a steel material that not only suppresses peeling, but also prevents corrosion of the steel material from progressing pitting corrosion. Long-term durability is also required after repair.

  In the ship field, for example, in tankers and cargo transport ships, seawater is injected and loaded into ballast tanks so that the hull is stable even when empty. Corrosion of the steel materials that make up this ballast tank is not so much at the tank inner wall where the seawater injected and loaded into the ballast tank is in direct contact, but at the part of the ballast tank that is in contact with the space (gas phase) on the seawater surface It is known to be intense. This is because the tank inner wall of the space portion on the seawater surface in the ballast tank is always in a wet state, and oxygen causing corrosion (promoting) is continuously supplied from the air. As a countermeasure for inhibiting the corrosion of the inner wall surface of the ballast tank, it has been made to coat the inner wall surface of the ballast tank with a relatively thick film of about 300 μm to prevent corrosion. However, in this method, since the corrosive environment is severe, the life of the coating film is as short as about 10 years, and there is a drawback that repair coating is necessary. Although the steel material formed by applying the zinc rich primer disclosed in Patent Document 1 has a longer life of the coating film, there are cases in which pitting corrosion occurs in the coating defect portion as in the bridge field.

  Furthermore, in an environment where salt content such as seawater flies or scatters, it is necessary to repaint the paint every few to a dozen years because the paint peels off early and the corrosion proceeds. . In order to perform repainting, it is necessary to build a scaffold on a once corroded bridge or ship, and to reblast the steel material, which is very expensive. And even if it re-blasts, a rust cannot be removed completely, and even if it repaints on the steel material which has not removed rust completely, a coating life will become remarkably short.

  Therefore, it has been strongly desired to extend the service life of the coating and greatly extend the interval between repair coatings. In other words, even in the ship and bridge fields where painting is required, there is a high demand for minimizing the life cycle cost. It becomes very important.

  An object of the present invention is to provide an anticorrosion-coated steel material that is excellent in pitting corrosion resistance even in an environment in which a salt content such as seawater is scattered or scattered, using a zinc-containing coating as a primer.

  As a result of intensive studies to improve the pitting corrosion resistance of a steel material using a zinc-containing coating as a primer, the present inventors have found the following findings (a) to (g).

(a) In the coating film defect portion, zinc that should protect the exposed steel material by sacrificial anodic action is chloride or suspended matter contained in the atmosphere, such as SO _x , NO _x , CO _2, etc. As a result of forming a potential noble coating on the zinc surface under the influence of the effect, a large-area cathode is formed at the flange (defect) where the steel is exposed, and the exposed steel is locally corroded. It has been found that pitting corrosion occurs. This phenomenon is a potential reversal phenomenon often discussed in soil such as galvanized pipes and submerged environments, but this phenomenon may also occur in the atmosphere.

(b) Then, locally exposed steel parts, wet and dry repetition of FeCl ₃ solution is an essential condition of corrosion, while pH is lowered by hydrolysis of Fe ^3+, and Fe ³⁺ action as an oxidizing agent This accelerates corrosion.

  The corrosion reaction at this time is as follows.

As the cathode reaction, the following reaction mainly occurs.
Fe ³⁺ + e ⁻ → Fe ²⁺ (reduction reaction of Fe ³⁺ )
In addition to this reaction, the following cathode reaction also occurs.
2H ₂ O + O ₂ + 2e ⁻ → 4OH ⁻ ,
2H ⁺ + 2e ⁻ → H ₂
On the other hand, the following anodic reaction occurs with respect to the above Fe ³⁺ reduction reaction.
Anode reaction: Fe → Fe ²⁺ + 2e ⁻ (Fe dissolution reaction)
Therefore, the overall reaction of corrosion is as shown in the following equation (1).
2Fe ³⁺ + Fe → 3Fe ²⁺ (1)

Fe ²⁺ generated by the reaction of the above formula (1) is oxidized to Fe ³⁺ by air oxidation, and the generated Fe ³⁺ acts again as an oxidant to accelerate corrosion. At this time, the reaction rate of air oxidation of Fe ²⁺ is generally slow in a low pH environment, but is accelerated in a concentrated chloride solution, and Fe ³⁺ is easily generated. Due to such a cyclic reaction, in an environment where the amount of incoming salt is very large, Fe ³⁺ is always supplied, the corrosion of the steel is accelerated, and the corrosion resistance is significantly deteriorated.

(c) On the other hand, when a small amount of Sn is added to the steel material, Sn is dissolved as Sn ²⁺ , and the concentration of Fe ³⁺ is reduced by the reaction of 2Fe ³⁺ + Sn ²⁺ → 2Fe ²⁺ + Sn ⁴⁺ (1) Suppresses the reaction of the formula. Sn further has an effect of suppressing anodic dissolution.

(d) If Sn is present, the details are unknown, but the eluted Sn ²⁺ or oxidized Sn ⁴⁺ alleviates the potential noble phenomenon of zinc or zinc oxide and reduces the potential difference from steel. As a result, pitting corrosion is suppressed.

  (e) When Cu coexists, pitting corrosion is further suppressed. However, if Cu and Sn coexist, cracking occurs during rolling. This crack can be prevented by adding Ni and Al.

  (f) Furthermore, if a small amount of B is present in the presence of Sn, the potential noble phenomenon of zinc or zinc oxide is alleviated and the potential difference with steel is reduced, thereby suppressing pitting corrosion. Is done. In addition, when Cu and Sn coexist, further cracking during rolling can be further prevented by further coexisting B in addition to Ni and Al.

  (g) These zinc-coated steel materials are less likely to undergo pitting corrosion even in an environment where salt such as seawater flies or scatters. And if coating films, such as resin, are further coated on this steel material, the anticorrosion coating steel material which was excellent in the coating-peeling-proof property and the durability after repainting can be obtained.

  The present invention has been made on the basis of the above findings, and the gist thereof lies in the following anticorrosion coated steel materials (1) to (7). Hereinafter, the present invention may be collectively referred to as the present invention.

(1) By mass%, C: 0.001 to 0.20%, Si: 2.5% or less, Mn: more than 0.5% and 2.5% or less, P: less than 0.03%, S: 0.005% or less, Cu: 0.05 to 0.6%, Ni: less than 0.5%, Cr: 0.01 to 4.0%, Al: 0.003 to 0.5%, N: 0 0.001 to 0.1% and Sn: 0.03 to 0.50%, the balance is Fe and impurities, the Cu / Sn ratio is 3.5 or less, and the following formula (A) An anticorrosion-coated steel material obtained by coating a steel material having a composition satisfying that the CP value defined by the above is 0.98 or less with a zinc-containing coating.
CP = 3Cu-2Ni + Sn-Al-100B (A)
However, the element symbol in the formula (A) means the content (% by mass) of each element.

  (2) The anticorrosion-coated steel material according to (1) above, further containing, by mass%, B: 0.010% or less.

  (3) The above (1) or further comprising, in mass%, one or two selected from the group consisting of Ti: 0.3% or less and Nb: 0.1% or less (2) Anticorrosion coated steel material.

  (4) Further, by mass%, it contains one or more selected from the group consisting of Mo: 1.0% or less, W: 1.0% or less, and V: 1.0% or less. The anticorrosion-coated steel material according to any one of (1) to (3) above.

  (5) The above (1) to (1), further comprising one or two selected from the group consisting of Ca: 0.1% or less and Mg: 0.1% or less by mass% (4) Any of the anticorrosion coated steel materials.

  (6) The anticorrosion-coated steel material according to any one of (1) to (5) above, further containing 0.02% or less of REM in mass%.

  (7) The anticorrosion-coated steel material according to any one of (1) to (6) above, wherein at least a part of the surface is coated.

  The anticorrosion-coated steel material of the present invention is a minimum maintenance material used for structures such as bridges in beach areas and structures such as bridges in areas where snowmelt salt and anti-freezing agents are sprayed. It can be widely applied to marine steel materials exposed to the corrosive environment of seawater. It can be widely applied as a material that contributes to maintenance minimization because it has excellent pitting corrosion resistance under coating coating defects, especially under zinc coating.

  Below, the effect of the alloy element contained in the anticorrosion coating steel material of this invention is demonstrated with the reason for limitation of the content. The alloy element content “%” means “mass%”.

C: 0.001 to 0.20%
C is an alloying element necessary for ensuring the strength of steel, but if contained in a large amount, the weldability of the steel material deteriorates. Therefore, the upper limit of the C content is 0.20%. Further, if the content is less than 0.001%, a predetermined strength cannot be secured, so the lower limit is made 0.001%. A desirable range is 0.005% to 0.15%.

Si: 2.5% or less Si is an alloy element necessary for deoxidation during steelmaking. Similarly, when Al is included which acts as a deoxidizer, it is not particularly necessary to add it. However, when the Al content is less than 0.005%, it is necessary to contain 0.4% or more. desirable. On the other hand, if the Si content exceeds 2.5%, the toughness of the steel is impaired. Therefore, the Si content is 2.5% or less. Si also has the effect of improving weather resistance. In order to obtain this effect, it is preferable to add 0.1% or more.

Mn: more than 0.5% and not more than 2.5% Mn is an element that has the effect of increasing the strength of steel at low cost. When the content of S in steel is low, it is generally a high-flying salinity environment. Has the effect of improving the weather resistance. However, it combines with S in steel to form MnS, and this MnS becomes a starting point of corrosion, which deteriorates the corrosion resistance and consequently the weather resistance. Further, the mechanism is unknown, but when it coexists with Ni, the weather resistance deteriorates when the Mn content exceeds 2.5%. Therefore, the Mn content is 2.5% or less. Desirably, it is 1.5% or less. In addition, in order to maintain the strength as structural steel, it is necessary to contain Mn exceeding 0.5%.

P: Less than 0.03% P is contained as an impurity, but excessive P content in a concentrated chloride environment deteriorates the weather resistance, so it is necessary to reduce it as much as possible. Therefore, the content is made less than 0.03%.

S: 0.005% or less Although S is contained as an impurity, when it is combined with Mn, it forms MnS of non-metallic inclusions, which tends to be a starting point of corrosion, and deteriorates weather resistance. Accordingly, the S content needs to be as small as possible, so the upper limit is made 0.005%.

Cu: 0.05 to 0.6%
Cu has the effect of enhancing pitting corrosion resistance under a zinc-based coating. For this reason, it is necessary to contain Cu 0.05% or more. However, if it is contained in a large amount exceeding 0.6%, the corrosion resistance may be lowered in a relatively dry environment. Therefore, the Cu content is set to 0.05 to 0.6%. Moreover, when it coexists with Sn, the crack at the time of rolling may be induced, and it is preferable that Cu content shall be less than 0.5%.

Ni: Less than 0.5% Ni is conventionally added to steel as an element that significantly improves beach weather resistance in environments with a large amount of incoming salt, and has been developed and put into practical use as Ni-based weather-resistant steel. It is coming. However, although the reason is not clear, when it is added in combination with Sn, there is not only an effect of improving the corrosion resistance but also an adverse effect of reducing the effect of improving the weather resistance by Sn. In particular, when Sn coexists, if the Ni content is 0.5% or more, deep corrosion holes are formed under the zinc-based coating, so even if the Ni content is contained as an impurity, it is 0.5. Must be less than%. Note that Ni is also effective in preventing cracking during rolling when Cu and Sn coexist.

Cr: 0.01-4.0%
In general, Cr can be expected to improve the corrosion resistance due to the formation of protective rust in an environment where the amount of flying salt is not so high, but it is considered that the anodic dissolution reaction of steel is accelerated and the weather resistance is deteriorated in an environment where the amount of flying salt is large. I came.

  However, when coexisting with Sn, the effect of improving weather resistance due to the Cr content is exhibited even in an environment where the amount of incoming salt is large. This effect is exhibited when the content is 0.01% or more. However, if the content exceeds 4.0%, the local corrosion sensitivity increases and the weldability deteriorates. Therefore, the Cr content needs to be 0.01 to 4.0%. In addition, the minimum with preferable Cr content is 0.05%, and a preferable upper limit is 1.0%.

Al: 0.003 to 0.5%
When Al is contained in an amount of 0.003% or more, the weather resistance is improved. Moreover, since there exists an effect which suppresses the crack of the rolling surface at the time of Cu-Sn coexistence, it contains 0.003% or more. However, if the Al content exceeds 0.5%, the local corrosion susceptibility increases as in the case of Cr. Therefore, the upper limit of the Al content is 0.5%. More preferably, it is 0.2% or less.

N: 0.001 to 0.1%
N dissolves as ammonia and has an effect of improving the weather resistance in a salt environment by suppressing the pH drop due to the hydrolysis of Fe ^{3+ in} an environment with a large amount of incoming salt. This effect is obtained by containing 0.001% or more of N, and is saturated when it exceeds 0.1%. Therefore, the N content is set to 0.001 to 0.1%. The minimum with preferable content of N is 0.002%, and a preferable upper limit is 0.08%.

Sn: 0.03 to 0.50%
Sn dissolves as Sn ²⁺ and has an action of inhibiting corrosion by an inhibitor action in an acidic chloride solution. Further, rapidly to reduce the Fe ^3+, by having an effect of reducing Fe ³⁺ concentration as oxidizing agent, since inhibit corrosion promoting effect of Fe ^3+, thereby improving the weather resistance in high airborne salt environments.

  Moreover, Sn has the effect | action which suppresses the anodic dissolution reaction of steel and improves corrosion resistance. Furthermore, by containing Sn, the effect of improving the weather resistance of Cr is exhibited even in an environment with a large amount of incoming salt. These effects are obtained by containing 0.03% or more of Sn, and are saturated when it exceeds 0.50%. Therefore, the Sn content is 0.03 to 0.50%. The minimum with preferable content of Sn is 0.03%, and a preferable upper limit is 0.20%.

Cu / Sn ratio: 3.5 or less In the case of steel containing Sn as in the present invention, the deterioration of corrosion resistance due to the coexistence of Cu is remarkable. Moreover, when manufacturing the steel material containing Sn, it becomes a cause of the rolling crack by coexistence of Cu. For this reason, the Cu / Sn ratio, that is, the ratio of the Cu content to the Si content needs to be 3.5 or less.

CP value: 0.98 or less When a method of suppressing surface cracking during rolling due to red hot brittleness of steel containing Cu and Sn was examined, red hot brittleness was evaluated by the CP value defined by the following equation (A). I understood that I could do it. That is, red hot brittleness is related to the formation of a liquid phase with high Cu and Sn concentrations during heating and the penetration of the liquid phase into the austenite grain boundary. It has been found that by appropriately containing Al, Ni, and B, generation of the liquid phase or entry into the austenite grain boundary can be suppressed. And in addition to prescribing each element in the steel material, when the CP value defined by the formula (A) is set to 0.98 or less, it is found that the surface properties after hot rolling are improved. It was. The CP value is more preferably 0.66 or less, and further preferably 0.20 or less. When the steel material does not contain B, the term B in the formula (A) is “0”.
CP = 3Cu-2Ni + Sn-Al-100B (A)
However, the element symbol in the formula (A) means the content (% by mass) of each element.

  The anticorrosion-coated steel material of the present invention further contains one or more selected from the group consisting of B, Ti, Nb, Mo, W, V, Ca, Mg, and REM, in addition to the above alloy elements. May be. The reason why these elements may be contained and the contents at that time are as follows.

B: 0.010% or less B is an element effective for improving the strength of the steel material, and suppresses entry of the liquid phase into the austenite grain boundary, thereby preventing red hot brittleness and suppressing cracking during rolling. Contribute. Furthermore, when a small amount of B is added together with Sn, the potential noble phenomenon of zinc or zinc oxide is alleviated, and the potential difference with steel is reduced, thereby suppressing pitting corrosion. Therefore, B can be contained as necessary. However, if the B content exceeds 0.010%, toughness reduction and weld cracking are likely to occur. Therefore, when B is contained, the upper limit of the B content is set to 0.010%. A preferable upper limit of B is 0.003%. A more preferred upper limit is 0.002%. In addition, in order to acquire the effect by B, it is preferable to contain B 0.0001% or more, and it is more preferable to contain 0.0005% or more.

Ti: 0.3% or less Ti forms TiC and fixes C, thereby suppressing the formation of chromium carbide and improving weather resistance. Further, by fixing S by forming TiS, formation of MnS that becomes a starting point of corrosion is suppressed. Therefore, Ti can be contained as necessary. However, if the Ti content exceeds 0.3%, not only this effect is saturated, but also the cost of the steel material increases, so the upper limit of the content is 0.3%. In addition, in order to acquire the effect by Ti, it is preferable to contain Ti 0.01% or more.

Nb: 0.1% or less Nb, like Ti, has the effect of suppressing the formation of chromium carbide and improving the weather resistance by forming NbC. Therefore, Nb can be contained as necessary. However, if the Nb content exceeds 0.1%, this effect is not only saturated, but the cost of the steel material increases, so the upper limit of the content is 0.1%. In addition, in order to acquire the effect by Ti, it is preferable to contain Nb 0.01% or more.

Mo: 1.0% or less Mo dissolves and is adsorbed on rust in the form of oxyacid ions MoO ₄ ²⁻ , and suppresses transmission of chloride ions in the rust layer, thereby improving the corrosion resistance. Therefore, Mo can be contained as necessary. However, if the Mo content exceeds 1.0%, not only this effect is saturated, but also the cost of the steel material increases, so the upper limit of the content is 1.0%. In addition, in order to acquire the effect by Mo, it is preferable to contain Mo 0.01% or more.

W: 1.0% or less W, like Mo, dissolves and adsorbs to rust in the form of oxyacid ions WO ₄ ²⁻ , suppresses transmission of chloride ions in the rust layer, and improves corrosion resistance. There is. Therefore, W can be contained as necessary. However, if the W content exceeds 1.0%, this effect is saturated, and the cost of the steel material increases, so the upper limit of the content is 1.0%. In addition, in order to acquire the effect by W, it is preferable to contain 0.01% or more of W.

V: 1.0% or less V, like Mo and W, dissolves and adsorbs to rust in the form of oxyacid ion VO ₃ ^2- , suppresses permeation of chloride ions in the rust layer, and improves corrosion resistance. There is an effect to make. Therefore, V can be contained as necessary. However, if the V content exceeds 1.0%, not only this effect is saturated, but also the cost of the steel material increases, so the upper limit of the content is 1.0%. In addition, in order to acquire the effect by V, it is preferable to contain V 0.01% or more.

Ca: 0.1% or less Ca is present in the form of oxide in steel, and has an effect of suppressing the promotion of corrosion by suppressing the decrease in pH at the interface in the corrosion reaction part. Therefore, Ca can be contained as necessary. However, when the Ca content exceeds 0.1%, not only this effect is saturated, but also the cost of the steel material increases, so the upper limit of the content is set to 0.1%. In addition, in order to acquire the effect by Ca, it is preferable to contain Ca 0.0001% or more.

Mg: 0.1% or less Mg, like Ca, has the effect of suppressing the decrease in pH at the interface in the corrosion reaction part and improving the corrosion resistance. Therefore, Mg can be contained as necessary. However, if the Mg content exceeds 0.1%, this effect is not only saturated, but the cost of the steel material increases, so the upper limit of the content is 0.1%. In addition, in order to acquire the effect by Mg, it is preferable to contain 0.0001% or more of Mg.

REM: 0.02% or less REM has the effect of improving the weldability of steel. Therefore, REM can be contained as needed. However, if the content of REM exceeds 0.02%, this effect is not only saturated, but the cost of the steel material increases, so the upper limit of the content is 0.02%. In addition, in order to acquire the effect by REM, it is preferable to contain REM 0.0001% or more. Here, REM is a general term for 17 elements in which Y and Sc are combined with 15 elements of lanthanoid, and one or more of these elements can be contained. Note that the content of REM means the total content of these elements.

  The anticorrosion-coated steel material of the present invention is a steel material that contains the above essential elements or the above optional elements, with the balance being Fe and impurities. In addition, steel in which inclusions such as oxide are finely dispersed in steel is also included in the anticorrosion coated steel material of the present invention.

  Next, a film containing zinc (zinc-based coating) will be described.

  Examples of the zinc-based coating include so-called zinc rich primer and zinc rich paint. The steel material according to the present invention is a steel material that suppresses pitting corrosion under a zinc-based coating, and when zinc is added to the zinc rich primer and zinc rich paint in a weight ratio of 25% or more to cover the steel material, the sacrificial corrosion prevention of zinc The effect is demonstrated. The steel material according to the present invention is particularly effective in suppressing pitting corrosion.

  As the color developing agent (resin component), any of organic epoxy, polyamide, polyamine, butyral, etc. may be used, and alkali silicate, ethyl silicate, etc. may be used as inorganic. In addition, known rust preventive pigments and additives can be added, which is suitable for improving the corrosion resistance.

  Furthermore, it is also possible to carry out known paints such as epoxy, urethane and fluorine coatings on these zinc-based coatings, which is suitable for improving corrosion resistance and aesthetics.

  Further, as other zinc-based coatings, zinc plating and thermal spraying including zinc, for example, zinc aluminum thermal spraying and zinc aluminum pseudoalloy thermal spraying can be exemplified, and a known sealing treatment can be performed after thermal spraying.

  The anticorrosion-coated steel material of the present invention can have various shapes including deformed materials such as a plate material, a pipe material, a bar material, and an H-shaped steel. In general, the thickness is preferably 3 mm or more.

  The anticorrosion-coated steel material of the present invention is effective even in a situation where rusted steel material, that is, surface rust cannot be completely removed during repair. If rust cannot be completely removed with keren or the like, the life can be significantly extended even if the above zinc-based paint, especially organic zinc rich paint, is applied as a base treatment with an electric tool or wire brush. .

  Steel Nos. 1 to 26 having the chemical compositions shown in Table 2 were melted in a 150 kg vacuum melting furnace, forged into an ingot, heated to 1100 ° C., rolled, and 9 mm thick. X A steel material having dimensions of 150 mm in width and 1000 mm in length was produced.

The surface after rolling was observed, cracks after rolling, in particular, end portions were observed, and evaluation was performed in the following four stages. The results are shown in Table 3.
3: Very good (smooth)
2: Good (wrinkles are observed, but there is no problem)
1: Slightly poor (Partial cracks such as fine streaks are observed, but there are no practical problems.)
0: Defect (a crack that can be visually confirmed is observed. There is a problem in practical use.)

  Next, the front and back surfaces of these steel materials were mechanically ground, and test pieces having a thickness of 6 mm × width of 70 mm × length of 150 mm were cut out and subjected to shot blasting. The oxygen content of the steel material produced in this example was in the range of 0.0001 to 0.005%.

  The obtained test piece was subjected to surface coating or thermal spraying under the conditions shown in Table 4. Specification A (surface coating) was spray coated in accordance with “Steel Road Bridge Painting and Anticorrosion Handbook II-25” (Japan Road Association, published in September 2010). In the specification B (surface coating), an inorganic zinc rich primer (Cerabond Gray S manufactured by China Paint Co., Ltd.) was applied, and then a modified epoxy resin paint (Banno 200 manufactured by China Paint Co., Ltd.) was spray applied. Specification C (pseudoalloy spray) formed a composite metal sprayed coating (pseudoalloy) consisting of fine particles of zinc and aluminum melted.

  The coating or sprayed test piece obtained in this way was provided with a 70 mm long scratch with a vinyl chloride cutter (P cutter) in the longitudinal direction. These test pieces were evaluated by SAE (Society of Automotive Engineers) J2334 test. The SAE J2334 test is an accelerated test performed under the following conditions, and the corrosion form is said to be similar to the outdoor exposure test (Hiroo Nagano, Masato Yamashita, Hitoshi Uchida: Environmental Materials Science, Kyoritsu Shuppan (2004) , P.74). This test is a test that simulates a severe corrosive environment in which the amount of incoming salt exceeds 1 mdd and an environment in which salt from a ship or the like adheres and repeats drying and drying. The SAE J2334 test is carried out with the test piece tilted by about 10 to 15 °. However, since the corrosive environment on the back side (to the ground) is severe, the back side was set as the evaluation target.

<Contents of SAE J2334 test>
Wet: 50 ° C., 100% RH, 6 hours,
Adherence of salt: 0.5 mass% NaCl, 0.1 mass% CaCl ₂ , 0.075 mass% NaHCO ₃ aqueous solution immersion, 0.25 hours,
Drying: 60 ° C., 50% RH,
17.75 hours was defined as one cycle (24 hours in total).

  After 250 cycles of SAE J2334 test, the coating or sprayed coating on the surface of each test piece was peeled off to the part where peeling progressed, the appearance was photographed with a digital camera, binarized image processing was performed, and the peeling area ratio was determined It was measured. Moreover, after removing rust, the maximum corrosion depth in the heel portion was measured using a point micrometer. The test results are shown in Table 3.

In addition, in order to simulate a relatively dry environment with salt attached, a salt adhesion wet and dry test was conducted. The test piece was cut into a thickness of 6 mm, a width of 50 mm, and a length of 50 mm, and salt water was applied in advance so that the amount of adhered salt was 1 mg / cm ^2, and placed in a constant temperature and humidity chamber at 40 ° C. % RH, repeated 4 hours 80% RH as one cycle, every 30 cycles, a test for applying a water to become more 1 mg / cm ^2. In this example, 3 mL of a 0.171 mol / L NaCl aqueous solution was applied to the entire surface of the steel material to deposit salt. This test was carried out for 200 cycles, the rust layer on the surface of each test piece was removed, and the maximum corrosion depth at the heel was measured using a point micrometer. In the case of the salt adhesion test, since the peeling of the coating film was very slight, only the maximum corrosion depth of the buttocks was measured. The test results are shown in Table 3.

As is clear from the results of test numbers 1 to 20 in Table 3, the steel materials (steel Nos. 1 to 20) according to the examples of the present invention all satisfy the chemical composition content defined in the present invention. , SAE
From the results of the J2334 test, the coated part is excellent in corrosion resistance, and also exhibits excellent corrosion resistance in a salt-attached dry and wet environment. Moreover, cracks after rolling, which are practical problems, were not observed.

  On the other hand, as is clear from the results of test numbers 21 to 23, the steel No. 1 according to the comparative example. In No. 21, since the amount of Sn is insufficient, the maximum corrosion depth is large in both the SAE J2334 test and the salt adhesion wet / dry test. Further, as shown in Test No. 21, peeling itself was suppressed by the effect of zinc rich paint, but it was found that the maximum corrosion depth was extremely deep. Further, when the pseudoalloy was sprayed (test number 23), the entire surface was peeled in the SAE J2334 test.

  In the test number 24, the steel No. according to the comparative example. No. 22 is used, and since the amount of Cu is too large, the tendency to increase the maximum corrosion depth is clearly observed in the salt-attached wet-dry test. Moreover, the crack of the steel material after rolling was also remarkable.

  In the test number 25, the steel No. according to the comparative example. 23 is used, and since the amount of Ni is too large, a tendency to increase the maximum corrosion depth after the SAE J2334 test and after the salt adhesion wet / dry test is observed.

  In the test number 26, the steel No. according to the comparative example. No. 24 was used, and the Sn content was low and the Cu content was large. Therefore, not only the maximum corrosion depth after the SAE J2334 test and the salt adhesion wet / dry test was large, but also the steel material after rolling was prominent.

  In test No. 27, steel No. according to the comparative example. 25 was used, and the amount of Cu was small, so that the maximum corrosion depth after the SAE J2334 test and after the salt adhesion wet / dry test was increased.

  In Test No. 28, although the corrosion resistance is good, the steel No. according to the comparative example. No. 26 was used, and the CP value was not satisfied, so that cracking of the steel material after rolling was significant.

  The anticorrosion-coated steel material of the present invention is a minimum maintenance material used for structures such as bridges in beach areas and structures such as bridges in areas where snowmelt salt and anti-freezing agents are sprayed. It can be widely applied to marine steel materials exposed to the corrosive environment of seawater. It can be widely applied as a material that contributes to maintenance minimization because it has excellent pitting corrosion resistance under coating coating defects, especially under zinc coating.

Claims (7)

In mass%, C: 0.001 to 0.20%, Si: 2.5% or less, Mn: more than 0.5% to 2.5% or less, P: less than 0.03%, S: 0.005 %: Cu: 0.05-0.6%, Ni: less than 0.5%, Cr: 0.01-4.0%, Al: 0.003-0.5%, N: 0.001 0.1% and Sn: 0.03 to 0.50%, the balance is Fe and impurities, the Cu / Sn ratio is 3.5 or less, and is defined by the following formula (A) An anticorrosion-coated steel material obtained by coating a steel material having a composition satisfying a CP value of 0.98 or less with a zinc-containing coating.
CP = 3Cu-2Ni + Sn-Al-100B (A)
However, the element symbol in the formula (A) means the content (% by mass) of each element.   Furthermore, it contains B: 0.010% or less by the mass%, The anticorrosion coating steel material of Claim 1 characterized by the above-mentioned.   Furthermore, it contains the 1 type (s) or 2 types chosen from the group which consists of Ti: 0.3% or less and Nb: 0.1% or less in the mass%, The Claim 1 or 2 characterized by the above-mentioned. Anticorrosion coated steel.   Furthermore, it is characterized by containing one or more selected from the group consisting of Mo: 1.0% or less, W: 1.0% or less, and V: 1.0% or less by mass%. The anticorrosion-coated steel material according to any one of claims 1 to 3.   Furthermore, it contains 1 type or 2 types chosen from the group which consists of Ca: 0.1% or less and Mg: 0.1% or less by mass%, Any of Claim 1 to 4 characterized by the above-mentioned. The anticorrosion-coated steel material according to crab.   Furthermore, 0.02% or less of REM is contained by mass%, The anticorrosion coating steel material in any one of Claim 1-5 characterized by the above-mentioned.   The anticorrosion-coated steel material according to any one of claims 1 to 6, wherein at least a part of the surface is coated.