Steel materials

Abstract

To provide a steel that exhibits excellent corrosion resistance in a dry-wet repeated environment including chloride.SOLUTION: A steel has a chemical composition comprising, in mass%, C: 0.01-0.20%, Si: 0.01-1.0%, Mn: 0.05-3.00%, P: 0.150% or less, S: 0.030% or less, Al: 1.500% or less, N: 0.001-0.010%, Sn: 0.01-0.50%, In: 0.001-0.20%, Cu: 1.0% or less, Ni: 5.00% or less, Cr: 9.00% or less, and the balance being Fe and impurities, the steel comprising at least one selected from P: more than 0.050%, Al: more than 0.100%, Ni: more than 1.00%, and Cr: more than 1.00%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to steel materials.

Background Art

[0002] As a factor accelerating the corrosion of steel materials, the influence of chlorides is well known to be extremely large. For example, in coastal areas, although there are no sea spray droplets, corrosion is promoted by the influx of sea salt particles. Also, even in inland areas, corrosion due to chlorides is a problem everywhere, such as when spreading a freezing inhibitor containing chlorides in winter to prevent road surface freezing.

[0003] In outdoor areas where the amount of chlorides is relatively low compared to coastal areas, etc., weathering steel is used. Weathering steel is a steel material in which, during the process of being corroded by exposure to the atmosphere, the corrosion rate is significantly reduced by forming a highly protective rust layer that suppresses the permeation of corrosion factors on the surface of the steel material. Due to the protectiveness of this rust layer, which has the characteristic of significantly reducing the corrosion rate, it is known that bridges, etc. using weathering steel can withstand decades of use without painting. Also, when weathering steel is painted, it is known to have excellent corrosion resistance after painting.

[0004] For example, Patent Document 1 discloses a weathering steel containing Cu, Ni, and Cr in combination. Patent Document 2 discloses a weathering steel containing Cu, Nb, and Sn in combination.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the weathering steels described in Patent Documents 1 and 2, the rust layer is gradually formed over several years to several decades. That is, until a rust layer that can sufficiently prevent the permeation of corrosive factors such as chloride ions into the base material is formed, the corrosion of the base material progresses. Regarding the corrosion resistance of the base material before the rust layer is formed in the weathering steels described in Patent Documents 1 and 2, there remains room for study.

[0007] An object of the present invention is to solve the above problems and provide a steel material that exhibits excellent corrosion resistance in a dry-wet repeated environment containing chlorides.

Means for Solving the Problems

[0008] The present invention has been made to solve the above problems, and its gist is the following steel material.

[0009] (1) The chemical composition is, by mass%, C: 0.01 to 0.20%, Si: 0.01 to 1.0%, Mn: 0.05 to 3.00%, P: 0.150% or less, S: 0.030% or less, Al: 1.500% or less, N: 0.001 to 0.010%, Sn: 0.01 to 0.50%, In: 0.001 to 0.20%, Cu: 1.0% or less, Ni: 5.00% or less, Cr: 9.00% or less, The balance: Fe and impurities, P: more than 0.050%, Al: more than 0.100%, Ni: more than 1.00%, and, Cr: more than 1.00%, and contains one or more selected from Steel material.

[0010] (2) The chemical composition contains, in mass %, one or more selected from the following in place of a part of the Fe: Mo: 1.0% or less, and W: 1.0% or less, and is the steel material according to (1) above.

[0011] (3) The chemical composition contains, in mass %, one or more selected from the following in place of a part of the Fe: Sb: 0.30% or less, Co: 1.0% or less, As: 0.30% or less, Ce: 0.50% or less, Bi: 0.10% or less, Se: 0.50% or less, Pb: 0.50% or less, Hf: 0.20% or less, Zn: 0.10% or less, Ga: 0.10% or less, Sr: 0.020% or less, Ba: 0.020% or less, Ge: 0.10% or less, Sc: 0.010% or less, and Sm: 0.010% or less, and is the steel material according to (1) or (2) above.

[0012] (4) The chemical composition contains, in mass %, one or more selected from the following in place of a part of the Fe: Ti: 0.20% or less, Zr: 0.20% or less, Nb: 0.10% or less, V: 0.50% or less, B: 0.010% or less, Ta: 0.10% or less, Te: 0.50% or less, Y: 0.10% or less, La: 0.10% or less, Nd: 0.010% or less, Ca: 0.010% or less, Mg: 0.010% or less, and REM: Below 0.0150%, containing one or more selected from the following,[[]] the steel material according to any one of (1) to (3) above.[[]]

[0013] (5) At least a part of the surface of the steel material is subjected to anticorrosion treatment,[[]] the steel material according to any one of (1) to (4) above.[[]]

Effect of the Invention

[0014] According to the present invention, a steel material exhibiting excellent corrosion resistance in a dry-wet repeated environment containing chlorides can be obtained.[[]]

Mode for Carrying Out the Invention

[0015] By containing one or more selected from P, Al, Ni, and Cr in a steel material in a certain amount or more, a protective rust and / or a passive film are formed on the surface of the steel material as the steel material is used. As a result, the corrosion resistance of the steel material can be improved. Although the thickness on the surface of the steel material is different between the protective rust and the passive film, both can improve the corrosion resistance of the steel material by covering the surface of the steel material with an oxide.[[]]

[0016] However, if the steel material is exposed to a dry-wet repeated environment containing chlorides before a sufficient protective rust and / or passive film is formed to suppress the corrosion of the steel material, dry-wet repetition of the FeCl3 solution occurs, and the pH at the corrosion interface decreases due to the hydrolysis of Fe 3+ and corrosion accelerates due to the action of Fe 3+ as an oxidizing agent.[[]]

[0017] The corrosion reaction at this time is as follows.[[]] Cathode reaction: Fe 3+ +e - →Fe 2+ (Reduction reaction of Fe 3+ )[[]] Anode reaction: Fe → Fe 2+ +2e - (Dissolution reaction of Fe)[[]]

[0018] Therefore, the overall corrosion reaction is as shown in the following equation (i). 2Fe 3+ +Fe→3Fe 2+ ···(i)

[0019] The Fe generated by the reaction of the above equation (i) 2+ is oxidized to Fe 3+ by air oxidation, and the generated Fe 3+ accelerates corrosion as an oxidant again. At this time, the reaction rate of the air oxidation of Fe 2+ is generally slow in a low pH environment, but Fe 3+ is likely to be generated in a chloride solution. Due to such cyclic reactions, the corrosion resistance of steel deteriorates significantly in an environment containing chloride.

[0020] The pH of the acidified corrosion interface is neutralized by rainwater adhering to the steel surface, etc., but it decreases again due to the above reaction. Thus, in a dry-wet repeated environment, the pH of the corrosion interface continuously changes in the region from acidic to neutral.

[0021] Furthermore, in a low pH environment, the following reduction reaction of hydrogen ions proceeds, and the anodic reaction of Fe dissolution is promoted. 2H + +2e - →H2

[0022] To suppress the anodic dissolution reaction, it is effective to contain Sn in steel. Sn dissolves as a cation Sn 2+ in the corrosion environment and has an effect of suppressing corrosion by an inhibitor action in an acidic chloride solution. Furthermore, Sn can also suppress the corrosion promotion action of Fe 3+ by quickly reducing Fe 3+ and reducing the concentration of Fe 3+ as an oxidant.

[0023] Also, it is known that the progress rate of the hydrogen generation reaction on the Sn surface is smaller compared to the Fe surface. Therefore, by forming an Sn layer on the steel surface, the hydrogen generation reaction can be suppressed, and as a result, the anodic dissolution reaction of the steel can be suppressed.

[0024] Specifically, by the underpotential deposition (UPD) of Sn 2+ it is possible to form an extremely thin metallic Sn layer on the surface of the steel material in the usage environment, thereby improving the corrosion resistance.

[0025] Thus, Sn can suppress the anodic dissolution reaction and improve the corrosion resistance. However, while Sn is very effective in a strongly acidic environment with a pH of less than 2, there is still room for improvement in suppressing the anodic dissolution reaction in a weakly acidic environment.

[0026] Based on the effect of Sn in such a saline environment, the inventors have conducted a detailed study on the relationship between various metal elements and the anodic dissolution reaction in order to further improve the corrosion resistance in an environment where the pH fluctuates. As a result, the findings shown in the following (a) to (c) were obtained.

[0027] (a) In becomes a cation In 3+ in the corrosion environment and suppresses corrosion by its inhibitor action in the acid chloride solution.

[0028] (b) The progress rate of the hydrogen generation reaction on the In surface is smaller compared to the Fe surface. Therefore, by the underpotential deposition (UPD) of In 3+ it is possible to form an extremely thin metallic In layer on the surface of the steel material in the usage environment, thereby significantly suppressing the anodic dissolution reaction of Fe. Thereby, even a trace amount of In can significantly improve the corrosion resistance.

[0029] (c) The UPD of Sn 2+ occurs in a strongly acidic environment with a pH of less than 2, whereas In 3+The UPD occurs in a weakly acidic environment with a pH of 3 to 5. Therefore, by simultaneously containing Sn and In, a corrosion inhibition effect superior to that obtained by separately containing each of them can be achieved against changes in pH caused by repeated wet and dry cycles.

[0030] The present invention has been made based on the above findings. Hereinafter, each requirement of the present invention will be described in detail.

[0031] (A) Chemical composition The reasons for limiting each element are as follows. In the following description, "%" regarding the content means "mass %".

[0032] C: 0.01 to 0.20% C is an element necessary to ensure the strength of the material. However, if it is contained in excess, the weldability will be significantly reduced. Also, as the C content increases, the amount of cementite that becomes the cathode and promotes corrosion increases in an environment where the pH decreases, so the corrosion resistance decreases. Therefore, the C content is set to 0.01 to 0.20%. The C content is preferably 0.02% or more, more preferably 0.03% or more. Also, the C content is preferably 0.18% or less, more preferably 0.16% or less.

[0033] Si: 0.01 to 1.0% Si is an element necessary for deoxidation. However, if it is contained in excess, the toughness of the base material and the welded joint will be impaired. Therefore, the Si content is set to 0.01 to 1.0%. The Si content is preferably 0.03% or more, more preferably 0.05% or more. Also, the Si content is preferably 0.80% or less, more preferably 0.60% or less.

[0034] Mn: 0.05 to 3.00% Mn is an element that has the effect of increasing the strength of steel at low cost. However, if it is contained in excess, the weldability deteriorates and the joint toughness also deteriorates. Therefore, the Mn content is set to 0.05 - 3.00%. The Mn content is preferably 0.20% or more, and more preferably 0.40% or more. Also, the Mn content is preferably 2.50% or less, and more preferably 2.00% or less.

[0035] P: 0.150% or less If P is contained in excess, the mechanical properties and manufacturability of the steel material deteriorate. Therefore, the P content is set to 0.150% or less. The P content is preferably 0.100% or less. The lower limit of the P content does not need to be particularly specified, that is, the P content may be 0%, but extreme reduction leads to an increase in steelmaking cost. Therefore, the P content may be 0.0001% or more.

[0036] S: 0.030% or less S is an element that exists as an impurity in the steel material. S forms MnS which becomes the starting point of corrosion in the steel, and when its content is excessive, the decrease in corrosion resistance becomes remarkable. Therefore, the S content is set to 0.030% or less. The S content is preferably 0.025% or less, and more preferably 0.020% or less. The lower limit of the S content does not need to be particularly specified, that is, the S content may be 0%, but extreme reduction leads to an increase in steelmaking cost. Therefore, the S content may be 0.0001% or more.

[0037] Al: 1.500% or less If Al is contained in excess, the temperature range of the ferrite phase transformation becomes extremely wide, causing problems such as slab cracking during the manufacturing process. Therefore, the Al content is set to 1.500% or less. Considering the workability, the Al content is preferably 1.300% or less. Also, considering the balance of corrosion resistance, manufacturability and cost, the Al content is more preferably 1.200% or less.

[0038] Al is an element effective for deoxidizing steel. Therefore, the Al content may be 0.005% or more. To stably obtain the deoxidation effect by Al, it is preferable that the Al content is 0.010% or more, and more preferably 0.030% or more.

[0039] N: 0.001 - 0.010% N is an element that forms nitrides and contributes to improving mechanical properties such as refining crystal grains. However, if it is contained in excess, the mechanical properties deteriorate due to nitrides. Therefore, the N content is set to 0.001 - 0.010%. To suppress the formation of coarse ferrite, it is preferable that the N content is 0.002% or more, and more preferably 0.003% or more. Also, it is preferable that the N content is 0.008% or less, and more preferably 0.006% or less.

[0040] Sn: 0.01 - 0.50% Sn dissolves as Sn 2+ in a corrosive environment and has an effect of suppressing corrosion by an inhibitor action in an acidic chloride solution. Furthermore, since Sn 2+ has an effect of significantly suppressing the anodic dissolution reaction of steel by underpotential deposition (UPD), the corrosion resistance can be significantly improved even in trace amounts. However, if it is contained in excess, not only does the above effect saturate, but the toughness of the base material and large heat input welded joints deteriorates. Therefore, the Sn content is set to 0.01 - 0.50%. It is preferable that the Sn content is 0.05% or more, and more preferably 0.10% or more. Also, it is preferable that the Sn content is 0.40% or less, and more preferably 0.30% or less.

[0041] In: 0.001 - 0.20% In dissolves as In 3+ in a corrosive environment and has an effect of suppressing corrosion by an inhibitor action in an acidic chloride solution. Furthermore, In 3+Since it has the effect of significantly suppressing the anodic dissolution reaction of steel by UPD, it can greatly improve the corrosion resistance even in trace amounts. However, even if it is contained in excess, not only does the above effect saturate, but the toughness of the base material deteriorates. Therefore, the In content is set to 0.001 to 0.20%. The In content is preferably 0.010% or more, more preferably 0.020% or more. Also, the In content is preferably 0.15% or less, more preferably 0.10% or less.

[0042] Here, the reason for being able to obtain excellent corrosion resistance in a dry-wet repeated environment containing chlorides by simultaneously containing In and Sn will be explained. As described above, in a dry-wet repeated environment containing chlorides, the pH at the corrosion interface continuously changes in the region from acidic to neutral.

[0043] When the steel material is exposed to an environment where the pH at the corrosion interface is less than 2, Sn in the steel is more stable as Sn 2+ ions, so Sn elutes from the base material as Sn 2+ ions. Then, when it reaches a specific potential range, Sn deposits as a single atomic layer on the steel material surface by UPD, suppressing the anodic dissolution reaction of the steel material. And when the pH at the corrosion interface rises to about 3, Sn 2+ can no longer exist stably, so part of Sn becomes an oxide. As a result, a single atomic layer of Sn and / or a Sn oxide layer is formed on the steel material surface. Since the Sn oxide layer also has a corrosion suppression effect on the steel material, the steel material exhibits excellent corrosion resistance even in a corrosive environment from acidic to neutral.

[0044] On the other hand, when the steel material is exposed to an environment where the pH at the corrosion interface is 3 to 5, no elution of Sn 2+ ions occurs. However, since In can stably exist as In 3+ ions, In elutes from the base material as In 3+ ions, and when it reaches a specific potential range, In deposits as a single atomic layer on the steel material surface by UPD, suppressing the anodic dissolution reaction of the steel material. Then, when the pH at the corrosion interface drops below 2, In dissolves, but Sn becomes Sn 2+It elutes as such, forms a single atomic layer on the surface of the steel material, and suppresses the anodic dissolution reaction of the steel material.

[0045] As described above, by simultaneously containing In and Sn, in a dry-wet repeated environment containing chlorides, In and / or Sn form a single atomic layer on the surface of the steel material in accordance with the pH fluctuation. As a result, the corrosion resistance of the steel material can be effectively improved.

[0046] Cu: 1.0% or less Since Cu has the effect of improving corrosion resistance by suppressing the anodic dissolution of steel in a low pH environment, it can be contained as necessary. However, if it is contained in excess, not only does the effect saturate, but it also causes embrittlement. Therefore, the Cu content is set to 1.0% or less. The Cu content is preferably 0.80% or less. Cu may not be contained, and the lower limit is 0%. However, in order to stably obtain the above effects, the Cu content is preferably 0.02% or more, and more preferably 0.03% or more.

[0047] Ni: 5.00% or less Similar to Cu, Ni has the effect of improving corrosion resistance by suppressing the anodic dissolution of steel in a low pH environment, so it can be contained as necessary. However, if it is contained in excess, not only does the effect saturate, but it also leads to a significant increase in cost. Therefore, the Ni content is set to 5.00% or less. The Ni content is preferably 3.50% or less. Ni may not be contained, and the lower limit is 0%.

[0048] Cr: 9.00% or less Since Cr has the effect of improving corrosion resistance, it can be contained as necessary. However, if it is contained in excess, coarse ferrite crystal grains are formed, impairing the manufacturability and mechanical properties. Therefore, the Cr content is set to 9.00% or less. The Cr content is preferably 8.00% or less, and more preferably 7.50% or less. Cr may not be contained, and the lower limit is 0%.

[0049] One or more selected from P, Al, Ni, and Cr P, Al, Ni, and Cr are elements that have the effect of forming a protective rust and / or passive film on the surface of the steel material and improving the corrosion resistance of the steel material. Therefore, one or more selected from these elements are contained within the ranges shown below. The reasons for limiting the content of each element will be explained.

[0050] P: More than 0.050% P is an element that has the effect of promoting the formation of protective rust. Therefore, when it is desired to obtain this effect, the P content should be more than 0.050%. The P content is preferably 0.060% or more, and more preferably 0.070% or more.

[0051] Al: More than 0.100% Al is an element that has the effect of improving the corrosion resistance of the steel material by forming a passive film. Therefore, when it is desired to obtain this effect, the Al content should be more than 0.100%. Considering workability, the Al content is preferably 0.500% or more. Also, considering the balance of corrosion resistance, manufacturability, and cost, it is more preferably 0.850% or more.

[0052] Ni: More than 1.00% Ni is an element that has the effect of improving corrosion resistance by forming protective rust. Also, Ni is an element that has the property of suppressing the permeation of substances by being contained in X-ray amorphous rust or α-FeOOH, becoming finer, and improving the denseness of the protective rust. Therefore, when it is desired to obtain this effect, the Ni content should be more than 1.00%. The Ni content is preferably 2.00% or more.

[0053] Cr: More than 1.00% Cr is an element that has the effect of improving the corrosion resistance of steel by forming a passive film. In particular, when Cr and Al are contained simultaneously, the above effect is remarkably manifested. Therefore, when it is desired to obtain this effect, the Cr content should be more than 1.00%. The Cr content is preferably 1.30% or more, more preferably more than 2.00%, and even more preferably 3.00% or more, 4.00% or more.

[0054] The steel material according to the present invention has the above chemical composition, and the balance consists of Fe and impurities. Here, the impurities are components that are mixed in due to various factors in the manufacturing process, including raw materials such as ore and scrap when the steel material is industrially manufactured, and are allowed within a range that does not adversely affect the present invention.

[0055] In the chemical composition of the steel material of the present invention, instead of a part of Fe, one or more selected from the following elements may be contained within the following ranges. The reasons for limiting each element will be explained.

[0056] Mo: 1.0% or less Mo dissolves and adsorbs on rust in the form of oxygen acid ion MoO4 2- Since it is an element having the effect of suppressing the permeation of chloride ions in the rust layer, it can be contained as necessary. However, if it is contained in excess, not only does the effect saturate, but the cost of the steel material significantly increases. Therefore, the Mo content is set to 1.0% or less. The Mo content is preferably 0.70% or less. In order to stably obtain the above effect, the Mo content is preferably 0.01% or more, and more preferably 0.02% or more.

[0057] W: 1.0% or less W, like Mo, dissolves and forms oxygen acid ion WO4 2-It exists in the form of and has the effect of suppressing the permeation of chloride ions in the rust layer, so it can be contained as needed. However, if it is contained in excess, not only will the effect saturate, but the cost of the steel material will increase significantly. Therefore, the W content should be 1.0% or less. The W content is preferably 0.70% or less. In order to stably obtain the above effect, the W content is preferably 0.01% or more, and more preferably 0.02% or more.

[0058] Sb: 0.30% or less Sb is an element that has the effect of improving corrosion resistance in an acidic environment. It suppresses the anodic dissolution reaction of steel in a low pH environment, and improves corrosion resistance in a chloride environment by suppressing the hydrogen gas generation reaction and the reduction reaction of Fe 3+ so it can be contained as needed. However, if it is contained in excess, the toughness will deteriorate significantly. Therefore, the Sb content should be 0.30% or less. The Sb content is preferably 0.15% or less. In order to stably obtain the above effect, the Sb content is preferably 0.05% or more, and more preferably 0.08% or more.

[0059] Co: 1.0% or less Co is an element that improves corrosion resistance in an acidic environment, so it can be contained as needed. However, if it is contained in excess, not only will the effect saturate, but the cost of the steel material will increase significantly. Therefore, the Co content should be 1.0% or less. The Co content is preferably 0.70% or less. In order to stably obtain the above effect, the Co content is preferably 0.01% or more, and more preferably 0.02% or more.

[0060] As: 0.30% or less Although the effect of As is not as remarkable as that of Sb and Sn, it is an effective element for improving corrosion resistance in an acidic environment, and therefore may be added as necessary. However, excessive addition of As reduces hot workability. Therefore, the As content is set to 0.30% or less. The As content is preferably set to 0.20% or less. In order to stably obtain the above effects, the As content is preferably set to 0.02% or more, and more preferably set to 0.05% or more.

[0061] Ce: 0.50% or less Ce is in a corrosive environment. 3+ Ce is an element that dissolves as a cation and acts as an inhibitor in chloride solutions to suppress the anodic dissolution reaction of steel, so it can be included as necessary. However, excessive Ce content can cause rolling cracks. Therefore, the Ce content is set to 0.50% or less. The Ce content is preferably set to 0.15% or less. To stably obtain the above effects, the Ce content is preferably set to 0.005% or more, and more preferably set to 0.010% or more.

[0062] Bi:0.10% or less Although the effect of Bi is not as remarkable as that of Sb and Sn, it is an element that improves corrosion resistance in an acidic environment, so it can be contained as necessary. However, if it is contained in excess, hot workability decreases. Therefore, the Bi content is set to 0.10% or less. The Bi content is preferably set to 0.050% or less. In order to stably obtain the above effect, the Bi content is preferably set to 0.002% or more, and more preferably set to 0.005% or more.

[0063] Se: 0.50% or less Pb: 0.50% or less Since Se and Pb are elements effective in improving corrosion resistance in an acidic environment, they can be contained as needed. However, if contained in excess, the hot workability deteriorates. Therefore, the contents of Se and Pb are each set to 0.50% or less. The contents of Se and Pb are preferably each 0.15% or less. In order to stably obtain the above effects, the contents of Se and Pb are preferably each 0.005% or more, and more preferably each 0.010% or more.

[0064] Hf: 0.20% or less Since Hf is an element that densifies the rust layer formed on the surface of the steel material and improves corrosion resistance, it can be contained as needed. Therefore, the Hf content is set to 0.20% or less. The Hf content is preferably 0.10% or less. In order to stably obtain the above effects, the Hf content is preferably 0.002% or more, and more preferably 0.005% or more.

[0065] Zn: 0.10% or less Ga: 0.10% or less Since Zn and Ga are elements that suppress the cathodic reaction on the surface of the steel material in an acidic environment and improve corrosion resistance, they can be contained as needed. However, if contained in excess, the toughness and weldability of the base material deteriorate. Therefore, the contents of Zn and Ga are each set to 0.10% or less. The contents of Zn and Ga are preferably each 0.080% or less. In order to stably obtain the above effects, the contents of Zn and Ga are preferably each 0.002% or more, and more preferably each 0.005% or more.

[0066] Sr: 0.020% or less Ba: 0.020% or less Since Sr and Ba have the effect of suppressing the decrease in the pH of the interface in the corrosion reaction part and suppressing the promotion of corrosion, they can be contained as necessary. However, excessive inclusion may reduce the toughness of the base material. Therefore, the content of Sr and Ba is set to 0.020% or less, respectively. The content of Sr and Ba is preferably 0.010% or less, respectively. In order to stably obtain the above effects, the content of Sr and Ba is preferably 0.0005% or more, respectively, and more preferably 0.0010% or more.

[0067] Ge: 0.10% or less Since Ge has the effect of improving corrosion resistance, it can be contained as necessary. However, excessive inclusion may reduce the mechanical properties of the base material. Therefore, the Ge content is set to 0.10% or less. The Ge content is preferably 0.080% or less. In order to stably obtain the above effects, the Ge content is preferably 0.002% or more, and more preferably 0.005% or more.

[0068] Sc: 0.010% or less Sc is an element that is incorporated into the rust layer formed by corrosion and has the effect of forming a dense rust layer and suppressing the overall corrosion of the steel material, so it can be contained as necessary. However, excessive inclusion is not preferable because it causes a decrease in low-temperature toughness. Therefore, the Sc content is set to 0.010% or less. In order to stably obtain the above effects, the Sc content is preferably 0.0001% or more.

[0069] Sm: 0.010% or less Since Sm has the effect of improving corrosion resistance, it can be contained as necessary. However, excessive inclusion may reduce the mechanical properties of the base material. Therefore, the Sm content is set to 0.010% or less. The Sm content is preferably 0.0060% or less. In order to stably obtain the above effects, the Sm content is preferably 0.0002% or more, and more preferably 0.0005% or more.

[0070] Ti: Below 0.20% Since Ti has the effect of suppressing the formation of MnS, which is the starting point of corrosion, by forming sulfides, it can be contained as necessary. However, if it is contained in excess, not only does the effect saturate, but the cost of the steel material increases. Therefore, the Ti content should be 0.20% or less. Preferably, the Ti content is 0.15% or less. In order to stably obtain the above effect, it is preferable that the Ti content is 0.001% or more, and more preferably 0.005% or more.

[0071] Zr: Below 0.20% Similar to Ti, Zr has the effect of suppressing the formation of MnS, which is the starting point of corrosion, by forming sulfides, so it can be contained as necessary. However, if it is contained in excess, not only does the effect saturate, but the cost of the steel material increases. Therefore, the Zr content should be 0.20% or less. Preferably, the Zr content is 0.15% or less. In order to stably obtain the above effect, it is preferable that the Zr content is 0.001% or more, and more preferably 0.005% or more.

[0072] Nb: Below 0.10% Since Nb is an element that increases the strength of the steel material, it can be contained as necessary. However, if it is contained in excess, not only does the effect saturate, but the toughness of the HAZ decreases. Therefore, the Nb content should be 0.10% or less. Preferably, the Nb content is 0.050% or less. In order to stably obtain the above effect, it is preferable that the Nb content is 0.001% or more, and more preferably 0.003% or more.

[0073] V: Below 0.50% V is an element that increases the strength of steel materials similar to Nb. Also, like Mo and W, it dissolves and exists in the form of oxygen acid ions, and has the effect of suppressing the permeation of chloride ions in the rust layer, so it can be contained as needed. However, if it is contained in excess, not only does the effect saturate, but the cost also increases significantly. Therefore, the V content should be 0.50% or less. The V content is preferably 0.30% or less. In order to stably obtain the above effects, the V content is preferably 0.005% or more, and more preferably 0.010% or more.

[0074] B: 0.010% or less B is an element that improves hardenability and increases strength, so it can be contained as needed. However, if it is contained in excess, the effect of increasing strength saturates, and the tendency of toughness deterioration becomes significant in both the base material and the HAZ. Therefore, the B content should be 0.010% or less. In order to stably obtain the above effects, the B content is preferably 0.0003% or more.

[0075] Ta: 0.10% or less Ta is an element that contributes to the improvement of the strength of steel materials and can be contained as needed. Also, although the mechanism is not always clear, it has been found that Ta also contributes to the improvement of corrosion resistance. However, if it is contained in excess, not only does the effect saturate, but the cost also increases. Therefore, the Ta content should be 0.10% or less. The Ta content is preferably 0.060% or less. In order to stably obtain the above effects, the Ta content is preferably 0.001% or more, and more preferably 0.005% or more.

[0076] Te: 0.50% or less Te is an element that contributes to the improvement of the strength of steel materials and can be contained as needed. However, if it is contained in excess, the toughness and weldability decrease. Therefore, the Te content should be 0.50% or less. The Te content is preferably 0.40% or less. In order to stably obtain the above effects, the Te content is preferably 0.0005% or more, and more preferably 0.0010% or more.

[0077] Y: Below 0.10% La: Below 0.10% Y and La are effective in controlling the form of inclusions, effective in improving ductility characteristics, and also effective in improving the toughness of the HAZ of large heat input welded joints. Therefore, they can be contained as necessary. However, if contained in excess, the inclusions will coarsen, adversely affecting the mechanical properties, especially ductility and toughness. Therefore, the content of Y and La is set to 0.10% or less respectively. Preferably, the content of Y and La is 0.060% or less respectively. In order to stably obtain the above effects, preferably, the content of Y and La is 0.0001% or more respectively, and more preferably 0.0050% or more respectively.

[0078] Nd: Below 0.010% Nd is an element that contributes to toughness improvement through refinement of the structure and can be contained as necessary. Also, although the mechanism is not necessarily clear, it has been found that Nd also contributes to improvement of corrosion resistance. However, if contained in excess, not only does the effect saturate, but the cost also increases. Therefore, the Nd content is set to 0.010% or less. Preferably, the Nd content is 0.0080% or less. In order to stably obtain the above effects, preferably, the Nd content is 0.0001% or more, and more preferably 0.0005% or more.

[0079] Ca: Below 0.010% Ca is an element mainly used for controlling the form of sulfides and can be contained as necessary. It also has the effect of suppressing a decrease in the pH of the interface in the corrosion reaction part and suppressing the promotion of corrosion. However, if contained in excess, the mechanical properties may be impaired. Therefore, the Ca content is set to 0.010% or less. Preferably, the Ca content is 0.0050% or less. In order to stably obtain the above effects, preferably, the Ca content is 0.0002% or more, and more preferably 0.0005% or more.

[0080] Mg: Below 0.010% Similar to Ca, Mg can suppress the decrease in the pH of the interface in the corrosion reaction part, so it can be contained as needed. However, if it is contained in excess, the effect will saturate. Therefore, the Mg content should be 0.010% or less. Preferably, the Mg content is 0.0050% or less. In order to stably obtain the above effect, it is preferable that the Mg content is 0.0002% or more, and more preferably 0.0005% or more.

[0081] REM: 0.0150% or less REM (rare earth elements), except for Y, Sc, La, Ce, Nd, and Sm, has the effect of improving the weldability of steel, so it can be contained as needed. However, if it is contained in excess, the effect will saturate, so the REM content should be 0.0150% or less. Preferably, the REM content is 0.0100% or less. In order to stably obtain the above effect, it is preferable that the REM content is 0.0002% or more, and more preferably 0.0005% or more.

[0082] Here, REM is the general term for 17 elements including Y and Sc in addition to the 15 elements of lanthanoids. However, in the present invention, since Y, Sc, La, Ce, Nd, and Sm are separately defined as described above, the content of one kind or the total content of two or more kinds of elements excluding Y, Sc, La, Ce, Nd, and Sm from REM is called the REM content.

[0083] (B) Anticorrosion coating The steel material of the present invention described above shows good corrosion resistance even when used as it is. However, when an anticorrosion treatment is performed on its surface, specifically, when the surface is coated with an anticorrosion coating made of an organic resin or a metal, the durability of the anticorrosion coating is improved compared to conventional steel materials, and the corrosion resistance is further improved.

[0084] Here, examples of the anticorrosive coating made of an organic resin include resin coatings such as vinyl butyral-based, epoxy-based, urethane-based, and phthalic acid-based coatings. Examples of the anticorrosive coating made of a metal include plating coatings such as Zn, Al, and Zn-Al coatings or thermal spraying coatings such as Zn, Al, and Al-Mg coatings.

[0085] It is considered that the durability of the anticorrosive coating is improved because the corrosion of the base steel material of the present invention is significantly suppressed, and as a result, the swelling or peeling of the anticorrosive coating due to the corrosion of the base steel material from the defective part of the anticorrosive coating is suppressed.

[0086] (C) Manufacturing method There is no particular limitation on the manufacturing method of the steel material according to the present invention. For example, it includes steel plates, steel pipes, etc. that are manufactured by subjecting an ingot having the above-described chemical composition to hot rolling and further subjecting it to cold rolling if necessary. There is no particular limitation on the heating conditions for performing hot rolling, and normal conditions may be adopted.

[0087] When manufacturing a steel material, steel is melted by a conventional method, and after adjusting the components, the steel slab obtained by casting is hot rolled, and further cold rolled if necessary. After hot rolling, it may be directly water-cooled, or air-cooled and then reheated for quenching. After hot rolling, it may be wound into a coil shape. After hot rolling, it may be cold rolled and further heat treated.

[0088] When manufacturing a steel pipe, a steel plate may be formed into a tubular shape and welded, and it can be made into a UO steel pipe, an electric resistance welded steel pipe, a forged welded steel pipe, a spiral steel pipe, etc. A seamless steel pipe manufactured by subjecting a steel slab to hot extrusion or piercing rolling is also included in the steel material of the present invention.

[0089] Also, the treatment of covering with the above-described anticorrosive coating may be performed by a normal method. Also, it is not always necessary to apply the anticorrosive coating to the entire surface of the steel material, and it is sufficient to perform anticorrosion treatment on only one side of the steel material as the surface exposed to the corrosive environment, or only the outer surface or the inner surface in the case of a steel pipe, that is, at least a part of the surface of the steel material.

[0090] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples.

Example

[0091] Steel having the chemical composition shown in Table 1 was melted and made into a 50 kg ingot, and then hot forged by a usual method to produce a block with a thickness of 60 mm. Next, the block was heated at 1120 °C for 1 hour and then hot rolled, finished to a thickness of 20 mm at 850 °C, and then air-cooled to room temperature in the atmosphere to obtain a steel plate.

[0092]

Table 1

[0093]

Table 2

[0094]

Table 3

[0095] Then, two test pieces with a width of 60 mm, a length of 100 mm, and a thickness of 3 mm were taken from each steel plate. One test piece was subjected to the following corrosion test that simulated a chloride environment. For the other test piece, an anticorrosive coating with a thickness of about 200 μm was formed on the entire surface of the test piece by spray coating with a modified epoxy-based paint, and cross scratches were made on the anticorrosive coating to expose a part of the base metal, and then it was subjected to the same corrosion test.

[0096] The corrosion test was carried out by an accelerated atmospheric exposure test in which an aqueous solution obtained by diluting artificial seawater solution to 1 / 10 was applied to the front and back surfaces of the test piece once a week. The exposure test was carried out in Amagasaki City, Hyogo Prefecture, which is an industrial area, for 6 months.

[0097] After the accelerated atmospheric exposure test, the rust layer on the surface of each test piece was removed, and the reduction in plate thickness was measured. For the anticorrosion-treated steel, the maximum corrosion depth at the scratch part of the anticorrosive coating was measured.

[0098] The test results are shown in Table 4. The "corrosion weight loss" in the table is the average thickness reduction amount of the test piece, which is calculated using the weight reduction before and after the test and the surface area of the test piece. Also, the "corrosion depth" is the maximum value of the depth from the surface of the steel material at the coating defect part.

[0099] [Table 4]

[0100] As is clear from the results in Table 4, since the steel materials of Test Specimens No. 4 and 5, which are comparative examples, contain only one of Sn and In, the corrosion weight loss and corrosion depth are larger than those of the steel materials containing both Sn and In.

[0101] On the other hand, in the steel materials of Test Specimens No. 1 to 3 and 6 to 33, which are examples of the present invention, since all satisfy the component content specified in the present invention, the corrosion weight loss was 0.09 mm or less and the corrosion depth was 0.08 mm or less, which were small.

Industrial Applicability

[0102] The steel material according to the present invention can be used as a corrosion-resistant steel having excellent corrosion resistance, which is used in a dry-wet repeated environment containing chlorides.

Claims

1. The chemical composition is, by mass%, C: 0.01 to 0.20%, Si: 0.01 to 1.0%, Mn: 0.05 to 3.00%, P: 0.150% or less, S: 0.030% or less, Al: 1.500% or less, N: 0.001 to 0.010%, Sn: 0.01 to 0.50%, In: 0.001 to 0.20%, Cu: 1.0% or less, Ni: 5.00% or less, Cr: 9.00% or less, The balance: Fe and impurities, P: more than 0.050%, Al: more than 0.100%, Ni: more than 1.00%, and Cr: more than 1.00%, containing one or more selected from steel material.

2. The chemical composition contains, by mass%, one or more selected from the following in place of a part of the Fe: Mo: 1.0% or less, and W: 1.0% or less, The steel material according to Claim 1.

3. The chemical composition contains, by mass%, one or more selected from the following in place of a part of the Fe: Sb: 0.30% or less, Co: 1.0% or less, As: 0.30% or less, Ce: 0.50% or less, Bi: 0.10% or less, Se: 0.50% or less, Pb: 0.50% or less, Hf: 0.20% or less, Zn: 0.10% or less, Ga: 0.10% or less, Sr: 0.020% or less, Ba: 0.020% or less, Ge: 0.10% or less, Sc: 0.010% or less, and Sm: 0.010% or less, The steel material according to Claim 1 or Claim 2.

4. The chemical composition contains, by mass%, one or more selected from the following in place of a part of the Fe: Ti: 0.20% or less, Zr: 0.20% or less, Nb: 0.10% or less, V: 0.50% or less, B: 0.010% or less, Ta: 0.10% or less, Te: 0.50% or less, Y: 0.10% or less, La: 0.10% or less, Nd: 0.010% or less, Ca: 0.010% or less, Mg: 0.010% or less, and REM: 0.0150% or less, The steel material according to any one of Claims 1 to 3.

5. The steel material according to any one of Claims 1 to 4, wherein at least a part of the surface of the steel material is subjected to an anticorrosion treatment.

6. The steel material according to any one of Claims 1 to 5, wherein the anticorrosion treatment is a galvanizing treatment.

7. The steel material according to any one of Claims 1 to 6, wherein the galvanizing treatment is a hot-dip galvanizing treatment.

8. The steel material according to any one of Claims 1 to 7, wherein the hot-dip galvanizing treatment is performed in a molten zinc bath containing aluminum.

9. The steel material according to any one of Claims 1 to 8, wherein the chemical composition contains, by mass%, one or more selected from the following in place of a part of the Fe: Mo: 1.0% or less, W: 1.0% or less, Sb: 0.30% or less, Co: 1.0% or less, As: 0.30% or less, Ce: 0.50% or less, Bi: 0.10% or less, Se: 0.50% or less, Pb: 0.50% or less, Hf: 0.20% or less, Zn: 0.10% or less, Ga: 0.10% or less, Sr: 0.020% or less, Ba: 0.020% or less, Ge: 0.10% or less, Sc: 0.010% or less, Sm: 0.010% or less, Ti: 0.20% or less, Zr: 0.20% or less, Nb: 0.10% or less, V: 0.50% or less, B: 0.010% or less, Ta: 0.10% or less, Te: 0.50% or less, Y: 0.10% or less, La: 0.10% or less, Nd: 0.010% or less, Ca: 0.010% or less, Mg: 0.010% or less, REM: 0.0150% or less.

10. The steel material according to any one of Claims 1 to 9, wherein the steel material has a tensile strength of 400 MPa or more and a yield strength of 250 MPa or more.

11. The steel material according to any one of Claims 1 to 10, wherein the steel material has a thickness of 0.1 mm to 10 mm.

12. The steel material according to any one of Claims 1 to 11, wherein the steel material is used for a building material.

13. The steel material according to any one of Claims 1 to 12, wherein the steel material is used for a structural member.

14. The steel material according to any one of Claims 1 to 13, wherein the steel material is used for a roofing material.

15. The steel material according to any one of Claims 1 to 14, wherein the steel material is used for a siding material.

16. The steel material according to any one of Claims 1 to 15, wherein the steel material is used for a fencing material.

17. The steel material according to any one of Claims 1 to 16, wherein the steel material is used for a pipe.

18. The steel material according to any one of Claims 1 to 17, wherein the steel material is used for a sheet pile.

19. The steel material according to any one of Claims 1 to 18, wherein the steel material is used for a reinforcing bar.

20. The steel material according to any one of Claims 1 to 19, wherein the steel material is used for a wire rope.

21. The steel material according to any one of Claims 1 to 20, wherein the steel material is used for a chain.

22. The steel material according to any one of Claims 1 to 21, wherein the steel material is used for a spring.

23. The steel material according to any one of Claims 1 to 22, wherein the steel material is used for a bolt.

24. The steel material according to any one of Claims 1 to 23, wherein the steel material is used for a nut.

25. The steel material according to any one of Claims 1 to 24, wherein the steel material is used for a washer.

26. The steel material according to any one of Claims 1 to 25, wherein the steel material is used for a rivet.

27. The steel material according to any one of Claims 1 to 26, wherein the steel material is used for a nail.

28. The steel material according to any one of Claims 1 to 27, wherein the steel material is used for a screw.

29. The steel material according to any one of Claims 1 to 28, wherein the steel material is used for a gear.

30. The steel material according to any one of Claims 1 to 29, wherein the steel material is used for a shaft.

31. The steel material according to any one of Claims 1 to 30, wherein the steel material is used for a bearing.

32. The steel material according to any one of Claims 1 to 31, wherein the steel material is used for a bushing.

33. The steel material according to any one of Claims 1 to 32, wherein the steel material is used for a valve.

34. The steel material according to any one of Claims 1 to 33, wherein the steel material is used for a pump.

35. The steel material according to any one of Claims 1 to 34, wherein the steel material is used for a compressor.

36. The steel material according to any one of Claims 1 to 35, wherein the steel material is used for a turbine.

37. The steel material according to any one of Claims 1 to 36, wherein the steel material is used for an engine.

38. The steel material according to any one of Claims 1 to 37, wherein the steel material is used for a ship.

39. The steel material according to any one of Claims 1 to 38, wherein the steel material is used for an aircraft.

40. The steel material according to any one of Claims 1 to 39, wherein the steel material is used for a bridge.

41. The steel material according to any one of Claims 1 to 40, wherein the steel material is used for a building.

42. The steel material according to any one of Claims 1 to 41, wherein the steel material is used for a tower.

43. The steel material according to any one of Claims 1 to 42, wherein the steel material is used for a container. 【Claim 44

Images