TWI282372B - Corrosion resistance excellent steel for ship - Google Patents

Abstract

This invention is to provide steel for shipbuilding having excellent corrosion resistance which can be put to practical use even without applying coating and electrolytic protection, particularly, steel for shipbuilding in which the improvement of durability to crevice corrosion can be attained, and which exhibits excellent durability even to corrosion owing to the sticking of salt caused by seawater and owing to a wetting environment. The corrosion resistant steel for shipbuilding has a composition comprising 0.01 to 0.30% C, 0.01 to 1.50% Si, 0.01 to 2.0% Mn and 0.005 to 0.10% Al, and further comprising 0.01 to 5.00% Co and 0.0005 to 0.020% Mg, and the balance Fe with inevitable impurities.

Description

(1) 1282372 _ IX. OBJECTS OF THE INVENTION ^ Technical Field of the Invention The present invention relates to corrosion-resistant steel for ships used as main structural materials in ships such as oil tankers, cargo ships, passenger ships, warships, and the like, particularly regarding exposure to seawater. A ship steel material excellent in salt resistance and uranium resistance in a constant temperature and humidity environment. ^ [Prior Art] In each of the above ships, steel materials used as main structural materials (for example, outer plates, ballast tanks, oil tanks, etc.) are often exposed to salt formed in seawater and in a constant temperature and humidity environment. Suffering from uranium damage. Such corrosion can lead to shipwrecks such as flooding or sinking, so it is necessary to implement certain anti-corrosion measures for steel. As a method of preserving uranium which has been carried out to date, conventionally known methods include (a) painting treatment or (b) electrical corrosion treatment. Among them, in the painting treatment typified by multiple paintings, there is a high possibility that the coating film is defective, and the coating film may be damaged by the collision in the manufacturing process, so that the base steel material is often exposed. In such a steel exposed portion, the steel is locally or concentratedly corroded, resulting in an early leakage of the stored petroleum liquid fuel. In addition, in the electric corrosion-preventing treatment, it is very effective for a part that is completely immersed in seawater. However, in a place where the seawater is splashed in the atmosphere, sometimes a circuit required for corrosion prevention cannot be formed, and an anti-corrosion effect cannot be sufficiently exhibited. In addition, the galvanic anode for corrosion prevention is abnormally consumed or dropped, and when it disappears, the accelerated corrosion may start immediately. (2) 1282372 ^ In addition to the above-described technique, as a technique for improving the tamper resistance of the steel material itself, for example, the technique of Patent Document 1 has been proposed. In this technique, a ship-resistant steel for shipbuilding which can be used by appropriately adjusting the chemical composition of the steel material to improve corrosion resistance and can be used without painting treatment is disclosed. Further, in Patent Document 2, a ship steel material for improving the life of a coating film is disclosed by appropriately designing a chemical composition of a steel material. In the above technique, it can be said that it is possible to ensure a certain degree of corrosion resistance as compared with the prior art. Φ However, for corrosion resistance in a more severe corrosive environment, it is still not very good, and it is required to improve corrosion resistance. In particular, corrosion (that is, crevice corrosion) at the "fracture" portion formed at the contact portion of the foreign matter with the steel material, at the structural part or the damaged portion of the anti-corrosion coating film, is remarkable, sometimes lowering the life, but in In the previously proposed technology, the uranium resistance is insufficient in this part. [Patent Document 1] Japanese Patent Laid-Open Publication No. JP-A No. JP-A No. JP-A No. JP-A No. JP-A No. JP-A No. JP-A No. JP-A No. JP-A No. JP-A No. JP-A----- [Problem to be Solved] The present invention has been made in view of the above circumstances, and an object of the invention is to provide a shipbuilding steel which is excellent in corrosion resistance and can be put into practical use even if it is not necessary to carry out painting or electrical uranium treatment. Steel for shipbuilding can improve the durability against crevice corrosion, and at the same time, it exhibits excellent durability (the means to solve the problem) even if the seawater causes the salt adhesion of -6-(3) 1282372 and the corrosion caused by the wet environment. The shipbuilding steel material of the present invention which can achieve the above object contains C: 0.0 1 to 0.3 0% (indicating mass %, the same below), Si: 〇·〇1 to 1.5 0%, Μη ··0.0 1 to 2.0, respectively. %, A1 : 0.0 05 to 0.10%, in addition, Co: 0.01 to 5.00 % and Mg: 0.0005 to 0.020%, and the balance is composed of Fe and unavoidable impurities. In the steel material for shipbuilding, it is preferred to adjust the ratio 〔 ([ Co ] / [Mg]) of the content of Co [Co] to the content of Mg [Mg] in the range of 2 to 350. Further, in the steel material for ship of the present invention, (1) is composed of Cu: 0.01 to 5.0%, Cr: 0.01 to 5.0%, Ni: 0.01 to 5.0%, and Ti: 0.005 to 0.20%, if necessary. Select one or more of the groups, (2) Ca: 0.0005 to 0.020%, (3) Mo: 0.01 to 5.0% and / or W: 〇·〇1 to 2.0%, (4) from B: 0.0001 ~ 0.010%, V: 0.01 to 0.50%, and Nb: 0.003 to 0.5% of 0% of the selected groups, and (5) Zn: 0.001 to 0.10%, which is also effective, and can be further depending on the type of the components contained. Improve the characteristics of steel for shipbuilding. [Effect of the Invention] In the steel material for shipbuilding of the present invention, by containing a predetermined amount of Co and Mg and appropriately adjusting the chemical composition, it is possible to realize practical corrosion resistance even without performing painting or electrical corrosion treatment. In particular, it is possible to achieve a steel material for shipbuilding, which can improve the durability against cracks, and exhibit excellent durability even in the case of salt adhesion and wet corrosion caused by seawater. Such ship steel is only used as an outer plate in ships such as oil tankers, cargo ships, passenger ships, warships, etc., and can be used as a base material for ballast tanks, oil tanks, and the like. [Embodiment] φ In order to solve the above problems, the inventors of the present invention have found that it is possible to realize shipbuilding that can solve the above problems by including a predetermined amount of Co and Mg and a suitable chemical composition. Thus, the present invention has been completed. In the steel material of the present invention, it is important that the Co spear does not contain any of the above-mentioned components, and various effects of the components of the present invention are not described later, but it is recognized by the reason why the corrosion resistance is used. As follows. • Mg is an element that suppresses the decrease in pH on the corrosion portion, suppresses it, and improves the corrosion resistance. Such a function, in the classification of the material (e.g., Si-Μη steel), due to the generated 'hole', the dissolved Mg does not stay near the surface of the steel sheet, and the vertical portion (for example, in seawater) diffuses. Therefore, if the corrosion resistance alone is contained, the effect of improvement is small. However, it is possible to suppress the formation of Mg to the outside by forming a fine surface rust film with the same content of Mg, and it is considered that the corrosion resistance can be greatly improved by the reaction with the hydrolysis of dissolved Co. Corrosive environmental materials are not, and they are not. When the adjustment is made with steel]Mg, purpose. To increase the corrosion of the steel rust is much more outward, Mg, ξ Co 9 diffusion. Synergistic effect-8-(5) 1282372 ^ Such an effect can be achieved by controlling the appropriate amount to be described later, 'but it is preferable to appropriately control the ratio of their contents ([Co]/[Mg]: mass ratio). That is, if the 値([Co]/[Mg]) is less than 2, the suppression of local corrosion is likely to be insufficient, and if it exceeds 305, the suppression of general corrosion is insufficient. The oxime of [Co]/[Mg] is preferably in the range of 10 to 3 50, more preferably in the range of 20 to 60. In the steel material of the present invention, in order to conform to the basic characteristics φ of the steel material, it is necessary to appropriately adjust basic components such as c, Si, Μη, and A1. The reason for limiting the range of these components will be described below together with the effects of the above-mentioned elements of Co and Mg. C : 0 · 0 1 ～ 0 · 3 0 % C, which is the element required to ensure the strength of the material. To obtain the minimum strength of the structural member of the ship, it is generally about 400 MPa (but also depending on the thickness of the steel used), and it needs to contain 0.01% or more. However, if # exceeds 0.30%, the toughness will deteriorate. Therefore, the range of the C content is specified to be from 0.01 to 0.30%. Further, a preferred lower limit of the C content is 0.02%, and more preferably 〇.〇4% or more. Further, the upper limit of the C content is preferably 0.28%, and more preferably 0.26% or less. S i : 0.0 1 〜1. 5 0 % S i is an element required for deoxidation and strength, and if it is less than 0.01%, the lowest strength as a structural member cannot be ensured. However, if it exceeds 1.50%, the weldability deteriorates. Further, the preferred (6) 1282372 lower limit of the Si content is 0.02%, and more preferably 0.15% or more. Further, a preferred upper limit of the Si content is 1.25%, and more preferably 1.00% or less. Μη ·· 0·0 1 ～2.0% Μη, also like Si, is an element required for deoxidation and strength, and if it is less than 0.01%, the lowest strength as a structural member cannot be ensured. However, if it exceeds 2.0%, the toughness deteriorates. Further, a preferred lower limit of the Μη content φ is 〇 · 〇 5 %, and more preferably 〇 1 〇 % or more. Further, a preferred upper limit of the Μη content is 1.80%, and more preferably 1.75% or less. Α1 : 0.005 ～0· 1 0% Α1, also like Si and Μη, is the element required for deoxidation and ensuring strength. If it is less than 0.005%, deoxidation has no effect. However, if it is added in excess of 0.10%, the range of the amount of Α1 added is set to 〇·〇〇5 to 0.10% due to impaired weldability. Further, a preferred lower limit of the content of cerium 1 is 0 · 0 1 0 %, and more preferably 0. 0 1 5 % or more. Further, a preferred upper limit of the Α1 content is 0.040%, and more preferably 〇.〇 50% or less. C 0 : 0 · 〇 1 〜5 · 0 %

Co is an indispensable element for forming a dense surface rust film which is highly conducive to the corrosion resistance of steel in a high-salt environment. In order to exert such an effect, the Co content needs to be specified to be 0.01% or more. However, if it exceeds 5.0%, the weldability deteriorates. Therefore, the Co content is specified in -10- 1282372 (7) 0.01 to 5.0%. Further, a preferred lower limit of the Co content is 〇·015%, and more preferably, it is specified at 0·0 2 0% or more. Further, a preferred upper limit of the C 〇 content is 4 · 5 %, and more preferably 4.0 % or less.

Mg: 0.0005 to 0.020%

Since Mg exhibits an action of increasing the pH by dissolution, it has a function of suppressing the pH lowering caused by the hydrolysis reaction on the local anode due to the dissolution of iron, and suppressing the corrosion reaction and improving the corrosion resistance. In order to exhibit such an effect, the Mg needs to be contained in an amount of 0.0005% or more. However, if it is excessively contained in excess of 0.020%, workability and weldability are deteriorated. Therefore, a Mg content of from 0.0005 to 0.020% is suitable. A preferred lower limit of the Mg content is 0.007%, and more preferably 〇.〇〇1% or more. Further, a preferred upper limit of the Mg content is 0.018%, and more preferably 0.015% or less. The basic components in the steel material for ship of the present invention are as described above, and the rest are composed of iron and unavoidable impurities (for example, P, S, bismuth, etc.), but in addition to these, components which do not hinder the degree of steel properties are also allowed (for example, , Zr, N, etc.). However, if the content of these allowable components is too large, the toughness is deteriorated, so the degree should be controlled to 0.1% or less. Further, in the steel material for ship of the present invention, in addition to the above components, the root 'as needed' contains (1) one or more selected from the group consisting of Cu, Ni, Ti, and Cr, and (2) Ca, (3) Mo and/or W, (4) One or more selected from the group consisting of B, V, and Nb, (5) Zn, etc. are also effective, and shipbuilding can be further improved depending on the type of the contained component. Use the characteristics of steel. -11 - (8) 1282372 'Selected from the group consisting of Cu: 0.01 to 5.0%, Cr: 0.01 to 5·0%, Ni: 0·5.0%, and Ti: 〇·〇〇5 to 0.20% One of C u, C r, N i and τ i is an effective element for improving uranium resistance. Cu and Cr, like Co, form a dense surface rust film which is highly resistant to uranium. Is a valid element. In order to achieve this, it is preferable to contain 〇·〇1% or more. However, since φ bondability or hot workability is deteriorated in excess, it is preferable to set it at 5 00% to contain Cu and Cr. A preferred lower limit is 0.05%, more preferably 4.50%.

Ni is an effective element for rusting a dense surface that contributes to the improvement of uranium resistance. To achieve such an effect, it is preferably 0.0 1 ° /. the above. However, if the Ni content is excessive, the weldability or workability is deteriorated, so it is preferably set at 5.0%. The lower limit when Ni is contained is 0.05%, and the upper limit is more preferably 4.50%. Φ Ti is an element which densifies the surface rust film which contributes to the improvement of uranium resistance, high environmental resistance, and suppresses corrosion inside the crack, and also improves the crevice corrosion. In order to ensure the corrosion resistance required in such an environment, it is preferable to contain 0.005% or more, but if it exceeds 0.20%, it contains 'processability and weldability deterioration. Therefore, it is better to have a lower price of 0.008%, and a higher upper limit is 0.15%.

Ca: 0.0005 to 0.020%

Ca, like Mg, shows that the pH is increased by dissolution to 01~. Its effect is improved, under welding. It is limited to the film containing heat and better, and it is resistant to cracking. The heat limit is -12-1282372. (9) It is effective to suppress the ρ 造成 caused by the hydrolysis reaction on the local anode caused by iron dissolution, inhibit the corrosion reaction, and improve the corrosion resistance. element. With 0.0005. /. The above-mentioned Ca can effectively exhibit the effect of Ca formation, and if it exceeds 0.020%, it is excessively contained, and the workability and weldability are deteriorated. A lower limit of C a is preferably 〇·〇〇1 〇%, and a more preferable upper limit is 〇. φ Mo : 0.01 to 5.0% and / or W : 0.01 to 2.0%

Mo and W have the effect of improving the uniformity of corrosion and suppressing the perforation of local corrosion. In particular, by being contained together with Co, it is possible to enhance the effect of uniform rot. In order to exhibit such an effect, it is more than 0. 01% or more. However, if it is excessively contained, Mo is preferably made 5.0% or less, and W is preferably 2.0% or less. A more preferred lower limit for Mo is 0.02%, and a more preferred upper limit is 4.50%. The lower limit of the case where W is contained is 〇. 〇 2 %, and the upper limit is preferably from the group consisting of B: 0.0001 to 0·010%, V: 0.01 to 0.50%, and Nb: (~0.5 0%) One or more of the steel materials selected for ships are sometimes required to be used depending on the site to be applied, and these elements are essential elements for improving strength. Among them, B contains 0.000 1% or more, improves hardenability, and improves strength. Yes, if it is more than 0 · 0 1 0%, it is not preferable because of the toughness of the base material. V, by containing 0.01% or more, increases the strength and reduces the content, but contains 15% of the etched wave. Excellent inclusions contain 1.8% 1.003 high strength, and the deterioration of the effect is -13- (10) 1282372. However, if it exceeds 〇·50% excess, it will be worse due to the deterioration of steel toughness. N b is effective for improving strength by containing 〇· 〇0 3 °/ or more, but if it is excessively contained in excess of 0.50%, the toughness of the steel is deteriorated. Further, a lower limit of these elements, B 0.000 3 ° /, V is 0.02%, Nb is 0.00 5 / .. Further, the upper limit more preferably, B is 0.0090%, V of 0.45%, Nb of 0.45% • Zn:. 0.001- 0.10%

Zn has a precipitation film which reacts with salt or sulfur to form zinc chloride or zinc sulfide on the surface of the steel material, and separates the steel substrate from the water of the environment to suppress the effect of corrosion. In the coating film or the crack portion where the substance is restricted from moving, since zinc chloride or zinc sulfide is easily deposited on the surface of the steel material without splashing at sea, the corrosion inhibiting effect under the coating film or the crack portion is particularly good. In order to achieve such an effect, the required corrosion resistance is ensured, and the Zn content needs to be 0.001% or more. However, if it exceeds 0.10%, the workability and weldability deteriorate. Therefore, the Zn content is specified to be 0.001 to 0.10%. Further, a more preferable lower limit of the Zn content is 0.03%, more preferably 0.005% or more. Further, a preferred upper limit of the Zn content is 0.09%, and more preferably 〇.〇 8 % or less. ^ In the case of forming a welded structure by welding the steel material of the present invention, if normal welding conditions or welding materials are used, since the concentration of the above-mentioned effective element varies at the welded joint, corrosion resistance is sometimes not found in the welded portion. . In particular, in the case where the ratio of Mg and Co to the deposited metal and the base material (the content of the deposited metal/the content of the base material) is less than 0.3, -14-(11) 1282372 • No formation of these elements is added. The synergistic effect of the improved corrosion resistance 'melting' of the metallized portion is insufficient. Further, if the ratio is more than 3 · 0 ' because the toughness of the welded portion is deteriorated, it is not preferable from the viewpoint of mechanical strength. Therefore, it is recommended to adjust the ratio within the range of 〜. 3 to 3 · 0, preferably within the range of 0.5 to 2.0. In addition, in the case of an effective element for improving corrosion resistance other than Mg or Co, that is, Cu, Cr, Ni, Ti, Ca, Mo, W, and Zn' are also added to these elements of φ, it is recommended to be 0.3 to 3.0. The content ratio of the deposited metal to the base material (the content of the deposited metal / the content of the base material) is adjusted within the range, and it is more preferably adjusted within the range of 0.5 to 2.0. In the steel material for shipbuilding of the present invention, the corrosion resistance of the steel material body can be exhibited substantially without performing the painting treatment. However, the tar epoxy resin paint shown in the examples below may be used as needed or other than Representative multiple anti-corrosion paints, zinc-rich paints, shop prime coatings, electrical corrosion protection and other anti-corrosion methods. In the case of performing such an anti-corrosion paint, the corrosion resistance (painting corrosion resistance) of the paint film itself is also good as shown in the examples described later. Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to the following examples, and of course, it may be implemented in a modified manner within the scope of the present invention, and these are included in the present invention. Within the technical scope. [Examples] Example 1 -15- (12) 1282372 A steel material having a chemical composition shown in the following Tables 1 to 3 was melted in a converter, and various steel sheets were produced by continuous casting and hot rolling. The obtained steel sheet was cut and subjected to surface honing to finally obtain a test piece (test piece A) having a size of 1 00 x 1 00 x 25 (mm). Fig. 1 shows the appearance of the test piece A.

-16- 1282372

ί [Co]/[Mg] 0.71 733.3 CD 337.5 CD 218.3 164.1 186.4 334.2 175.6 166.7 16.7 14.7 69.3 92.1 75.9 10.0 Chemical composition of the sample (% by mass) Others 1 IIIIIIB: 0.0008 Nb: 0.015 IB: 0.0002, Nb: 0.498 IIIV: 0.14 IIB: 0.0010, V: 0.012 II 5 1 IIIIIIIIIIIIIIIIIII 〇 1 III ! IIIIIIIIIIIIIII (5 1 IIIIIIIIIIIII i 0.009 4 III 0.004 9 ! IIIIIIIIIIIII 0.026 III 0.006 I 〇1 IIIIIIIIIIIIIIIIIII 少1 IIIIIIIIIIII 0.28 II 0.34 0.18 II 3 〇1 IIIIIIIIIII 0.35 III 0.29 0.39 1.36 0.78 Ο) 1 0.0068 I 0.0112 0.0003 0.0015 0.0032 0.0198 0.0115 0.0064 0.0125 0.0149 0.0041 0.0039 0.0048 0.0102 0.0075 § od 0.0029 0.0050 〇Ο 1 I 0.11 0.008 ί 0.22 0.01 1.08 0.15 2.51 1.05 2.33 4.98 0.72 0.65 0.08 0.15 0.52 0.82 0.22 0.05 < 0.016 0.014 0.015 0.015 0.009 0.017 0.016 0.012 0.025 0.014 0.015 0.005 0.016 0.014 0.011 0.012 0.011 0.010 0.012 0.011 C 0.98 0.98 q T— 0.95 1.20 1.59 1.32 0.94 0.96 0.97 0.95 0.90 0.95 0.92 1.49 1.55 0.92 0.93 0.92 1.35 ω 0.20 0.21 0.20 0.25 0.21 0.24 0.20 0.22 0.99 0.21 0.50 0.10 0.19 0.12 0.31 1.32 0.21 0.18 0.20 0.48 〇0.18 0.18 0.18 0.17 0.18 0.18 0.16 0.23 0.18 0.17 0.18 0.18 0.18 0.20 0.19 0.19 0.09 0.16 0.12 0.18 1 τ— CM CO Inch l〇CD 00 O) 〇τ- τ— τ— CM CO 寸 r—i〇τ— 卜τ— 00 O) -17- 1282372

CNI«

i [Co]/[Mg] 81.8 79.2 150.0 144.4 63.6 65.9 81.5 41.9 49.2 46.4 38.2 59.6 42.0 46.9 57.1 20.8 35.7 36.4 43,2 Chemical composition of the sample (% by mass) Other IIIIIIIIIIIIII i IIB: 0.0011, Nb: 0.010, V: 0.011 V: 0.497 5 IIIIIIIIIII 0.99 I 0.02 0.11 1.97 0.35 I 0.55 〇IIIIIIIII 1.02 ! 0.08 0.29 0.01 5.00 I 3.23 CO I 0.0196 0.0028 I 0.0006 0.0027 0.0020 0.0012 I 0.0035 II 0.0016 0.0006 0.0015 0.0016 I 0.0015 0.0047 - 0.019 I 0.012 0.015 I 0.196 0.018 0.052 I 0.012 0.005 III 0.009 I 0.012 0.014 I Ο IIIIIIII 1.12 0.15 II 4.95 I 0.03 0.35 0.81 0.09 0.92 Depleted 4.98 2.06 I 0.38 0.34 0.98 0.32 0.38 I 0.33 I 1.02 0.30 0.49 0.01 0.12 0.89 0.31 1.29 (3 III 0.35 0.02 I 0.30 0.36 4.97 0.28 I 0.02 0.23 II 0.19 0.09 0.24 1.25 0.0011 0.0024 0.0032 0.0009 0.0033 0.0044 0.0054 0.0129 0.0063 0.0028 0.0055 0.0099 0.0188 0.0049 0.0021 0.0048 0.0028 0.0022 0.0088 〇〇0.09 0.19 0.48 0.13 0.21 0.29 0.44 0.54 0.31 0.13 0.21 0.59 0.79 0.23 0.12 0.10 0. 10 0.08 0.38 < 0.011 0.012 0.036 0.020 I_________ -____ 0.009 0.012 0.013 0.018 0.029 0.024 0.011 0.010 0.015 0.016 0.014 0.016 0.015 0.009 0.014 C 0.95 0.90 0.95 0.90 0.92 0.95 0.98 1.42 0.90 0.92 1.55 1.28 1.01 0.91 0.90 0.91 0.90 1.24 σ> T- 〇5 0.29 0.11 0.09 0.20 0.48 0.18 0.33 0.20 0.21 0.34 0.20 0.19 0.45 0.21 0.20 0.22 0.25 0.19 0.20 〇0.09 0.05 0.08 0.08 0.18 0.18 0.18 0.17 0.15 0.15 0.11 0.13 0.09 0.15 0.18 0.15 0.14 ! 0.10 0.12 1 c5 csi η CO -18- 1282372

(%sseE )φ^^Λ3>δ_Με*

Co/Mg 360.0 166.7 45.5 28.6 97.7 76.3 80.5 159.4 104.5 295.1 221.6 Other Ζη:0.015 Ζη:0.099 Ζη:0.005 Ζη:0.001 Ζη:0.056 Ζη:0.020 Ζη:0.032 CM δ Ο Ο ώ cvf ο ο β Ζη:0.018 Ζη: 0·028 ο δ ο J6 ζ in' τ- Ο ο r5 σ) 0.0005 0.0012 I 0.0011 0.0049 0.0043 0.0038 0.0041 0.0032 0.0022 0.0041 0.0037 ca Ο IIII 0.0031 0.0012 II 0.0022 0.0021 0.0007 - III 0.020 0.011 0.009 II 0.015 I 0.089 ο Ο 0.18 0.20 0.05 0.14 0.42 0.29 0.33 0.51 0.23 τ—Csl τ—0.82 5 IIIIIII 1.05 I 0.09 -1 0.12 ο IIIIII 0.05 0.03 0.11 II Ο IIIIIII 0.49 I 0.18 1.08 Lack II 0.29 0.33 0.22 ο τ — I 0.54 0.30 I 1.05 3 I ! 0.25 0.30 0.19 III 0.32 I 1.26 < 0.011 0.015 0.013 0.015 0.021 0.006 0.016 0.013 0.015 0.016 0.010 C Έ 1.21 1.02 0.99 0.95 1.09 1.11 -1 1.20 i 0.99 1.03 1.02 1.05 U) 0.19 0.21 0.18 0.25 0.20 0.26 0.24 0.23 0.25 0.19 0.18 Ο 0.15 0.14 0.20 0.19 0.15 0.16 0.20 0.11 0.21 0.20 0.11 6 2 ο 5 5 JO (Ό S -19- (16) 1282372 In addition, As shown in FIG. 2, so that four 20x20x5 (mm) of the small test piece with 1 00x 1 00x2 5 (mm) of a large test piece (the same as the test piece A) contacting 'prepared test piece was fractured portion B. The small test piece for forming the crack and the large test piece are steel materials having the same chemical composition, and the surface finish is also the same as the above test piece A, and is defined as surface honing. Further, a hole of φ 5 mm was opened at the center of the small test piece, and a screw hole was opened on the substrate side (large test piece side), and bolted with M4 plastic. p In addition, a test piece c of tar epoxy resin coating (base coating: zinc-rich coating) with an average thickness of 25 // m is also used (Fig. 3). Also, in order to investigate the exposed base steel due to damage to the corrosion-resistant coating film At the time of the progress of the corrosion, on the one side of the test piece C, the cut portion reaching the base body (length: 100 mm, width: about 〇. 5 mm) was formed with a dicing blade. For each sample ' of each chemical composition shown in Tables 1 to 3, five test pieces A, one test piece B, and test piece C were used for the corrosion test. The corrosion test method at this time is as follows. [Test method for uranium uranium] First, simulate the marine environment, conduct a seawater spray test and repeat the combined cycle corrosion test of constant temperature and humidity formation. In the seawater spray test, '60 from the level. The sample (each test piece A to C) was sprayed obliquely in the test tank. The artificial seawater (saline) of the mist spray 3 5 X:. The spray of brine is usually carried out continuously. At this time, in the test tank, artificial seawater of 1 · 5 ± 〇 · 3 πιί was taken at an arbitrary position in a horizontally-arranged container of 80 cm 2 in an horizontal position, so that the amount of spray was adjusted in advance. The constant temperature and humidity test was carried out by setting the sample ground * at a temperature of 60 -20 - (17) 1282372 ' ° C and a humidity of 95% from the horizontal. The seawater spray test was carried out for 4 hours as one cycle, and the constant temperature and humidity test was carried out for 4 hours as one cycle, and the above test was alternately performed to promote corrosion of the sample. The total test time was set at 6 months. (1) With respect to the test piece A, the weight change before and after the test was converted into an average thickness reduction amount D-ave (mm), and the average enthalpy of the five test pieces was calculated, and the overall corrosion property of each sample was evaluated. In addition, the maximum uranium depth D-max (mm) of the test piece A is obtained by a stylus type three-dimensional shape φ measuring device, and normalized by the average thickness reduction amount [D-ave (mm)] (that is, calculated!) -max/D-ave), evaluation of corrosion uniformity. In addition, the weight measurement and the thickness measurement after the test were carried out by removing the rust-resistant product such as rust by a cathodic electrolysis method [JIS K8 2 84] in an aqueous solution of diammonium hydrogen citrate. (2) For the test piece B, visual observation of the cracked portion (contact surface) was carried out to investigate the occurrence of crevice corrosion. When the uranium was found to be cracked, the cathodic electrolysis method was used to remove the corrosion product, and the stylus type was used. * Dimensional shape measuring device, measuring the maximum crevice corrosion depth D-crev (mm) ο (3) About the test piece C (with cut portion) for performing the painting treatment, and measuring the coating drum on the face formed after the test. Ratio of area (* bulging area ratio). The bulging area ratio was obtained by the lattice point method (grid spacing 1 mm). In other words, the enthalpy obtained by dividing the total number of grid points by the number of plaques to be confirmed is defined as the blasting area ratio, and the average enthalpy of the five test pieces is obtained. Further, the caliper is used to measure the vertical direction of the cut portion. The film bulging width defines the maximum enthalpy of the five test pieces as the maximum bulging amplitude. -21 - (18) 1282372 The comprehensive corrosion resistance (D-ave), corrosion uniformity (D-max / D-ave), crevice corrosion resistance (D-crev), paint corrosion resistance (drum The evaluation criteria for the area and the maximum bulging amplitude are shown in Table 4 below. Tables 5 to 7 below show the results of the uranium test.

-22- 1282372 • · Inch 撇 judgment ◎ Below 〇. 〇5mm t Below 1·5 Below 〇.〇5mm Below 〇·1% Below 1 mm 〇0.05mm or more 丨Lower than CUOmm 1.5 or less 2.0 0. 05mm or more is less than 〇.1〇_ 0.1% or less is less than 0-5% 1mm or more is less than 2mm <1 0.10mm or more is less than 0, 50mm 2.0 or more is less than 2.5 0.10mm or more is less than 〇.50mm 0.5% or more | Less than 5% 2mm or more and less than 5mm X 0.50mm or more and 2.5 or more 0: 50mm or more and 5% or more and 5mm or more Measurement items D-ave (mm) D-max/D-ave -1 D-crev (mm ) Area ratio of bulging (%) Maximum bulging amplitude (mm) Evaluation characteristics Resistance to general corrosion Corrosion uniformity Resistance to crack corrosion Corrosion resistance test piece < ω 〇-23 1282372

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Remarks i The present invention comprehensively judges ◎~◎ 〇~◎ 〇~◎ 〇~◎ 〇◎ ◎ ◎ ◎ ◎ ◎ Test piece C Maximum bulging range 〇〇 ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ 鼓 面积 area ratio 〇 ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ Test piece B Corrosion resistance 〇〇〇〇 ◎ ◎ ◎ ◎ ◎ ◎ Test piece A Corrosion uniformity 〇〇〇〇〇〇 ◎ ◎ ◎ ◎ ◎ General corrosion resistance 〇〇 ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ 1 〇T-inch ΙΛ (D CO -26- (23) 1282372 ^ According to the above results, the following is considered. No Co or Mg is included. No. 2, 3 The samples of No. 4 and 5 in which the content of Co or Mg is less than the lower limit specified in the present invention, the effect of addition of Co or Mg is slightly more resistant to general corrosion than the conventional steel (No. 1). There was an improvement. However, in the sample No. 2 containing no Co and the No. 4 sample having insufficient Co amount, no improvement effect was observed in terms of corrosion uniformity and bulging area ratio. .3 sample and the amount of Mg in the No. 5 sample, in the resistance to φ cracked uranium The improvement effect was not found in the maximum bulging range. The corrosion resistance of the steel material for ships was insufficient. In this case, it was found that the sample (No. 6 to 50) containing Co and Mg in an appropriate amount was added by use. The synergistic effect of Co and Mg, all the corrosion resistance is superior to that of traditional steel (No. 1), and it is preferably used as a steel for shipbuilding. In particular, in addition to Co and Mg, it additionally contains Cu and Cr. , Ni, Ti, Ca, Mo, W, Zn and other uranium-improving elements, further improve the corrosion resistance of steel. # Among them, in the addition of Cu, Cr, Ni or Ti samples, found that especially the paint test The effect of the maximum bulging amplitude (Νο·13~15, etc.), it is judged that the rust densification of these elements is used for the rust stabilization of the cut portion, and the result of the corrosion progress is made. In addition, the Ca is confirmed. Improve the effect of crevice corrosion (Νο·16, 20, 22, etc.), and consider that Ca enhances the effect of reducing the pH in the crack and reduces corrosion. In addition, it is known that adding Mo or W improves the corrosion uniformity. Sexual or paint bulging is very effective (No. 3 1 to 33, etc.). In addition, No. 30, The results of 33, 34, 35, etc. show that by appropriately adjusting the ([C 〇] / [M g]) enthalpy, it has various effects of increasing the corrosion resistance of -27-(24) 1282372. In addition, Zn is added. The samples (Ν ο. 4 Ο, 4 1 , '42, etc.) also have the effect of improving paint corrosion resistance or crevice corrosion resistance. For example, in addition to the use of Mg and Co, a sample No. 41 in which an appropriate amount of Zn was added was used, and the blasting area ratio of the test piece C was lowered as compared with No. 6 in which only Mg and Co were used. As a result of the improvement of the corrosion resistance by the addition of Zn, it is estimated that a deposition film of zinc chloride or zinc sulfide is formed on the surface of the steel material to exhibit the effect of suppressing corrosion by separating the steel substrate from the water in the environment. Example 2 A steel material having a chemical composition shown in the following Table 8 was melted in a converter. Various steel sheets were produced by continuous casting and hot rolling. The obtained steel sheet was subjected to surface honing to finally obtain a test piece D' having a size of 300 x 150 x 25 (mm). The solder joint material of the chemical composition shown in Table 9 was used for the recessed arc welding, and the joint test piece D (Fig. 4) shown in the figure was produced using two D'. In addition, the Φ has a wire diameter of 4 · 8 mm and the groove shape is V-shaped. The heat input is suitably adjusted within the range of 1 to 10 kJ / mm. Further, two small test pieces '6 0 X 6 0 X 5 (m m ) were brought into contact with the welded portion of the test piece 'D to prepare a test piece E (Fig. 5) which forms a slit portion. The chemical composition of the small test piece for forming the crack was the same as that of the test piece D, and the surface finishing was also the same as that of the test piece D described above as the surface honing. Further, a hole of Φ 10 mm was opened in the center of the small test piece, and a screw hole was opened on the substrate side (large test piece side), and was fixed with a M 8 plastic bolt. In addition, a test piece F (Fig. 6) of tar epoxy -28-(25) 1282372* resin coating (base coating: zinc-rich coating) with an average thickness of 25 Å/Zm was also used. Further, in order to understand the degree of corrosion progress when the base steel material is exposed by the damage of the anti-corrosion coating film, a cut portion that reaches the substrate is formed on the single surface of the test piece F by a dicing blade in the vertical and horizontal directions with the weld line (length: 200mm, width · about 0.5mm). For the joint test piece prepared using the base material and the welding material shown in Tables 8 and 9, the test piece eu, the test piece e and the test piece φ F were respectively used for the uranium test. The corrosion test method (solid ship exposure test) at this time is as follows. [Corrosion test method] Five samples of each of the test specimens and each of the test pieces D to F were placed on the bottom plate of the inner surface of the inner surface of the VLCC crude oil tank, and each sample was investigated after normal shipping for five years. Corrosion conditions. After the exposure for 5 years, the test piece D was subjected to cathodic electrolysis (jis • K82 84) in an aqueous solution of diammonium hydrogen citrate to remove a corrosion product such as rust. Further, on the test piece E, a small test piece for forming a crack was taken, and the corrosion product was removed in the same manner. " (1) For the test piece D, the weight change before and after the test was converted into the average plate thickness reduction D-ave (mm), and the average enthalpy of the five test pieces was calculated, and the overall rot properties of each sample were evaluated. In addition, the maximum erosion depth D-max (mm) of the test piece D is obtained by using a stylus type three-dimensional shape measuring device, and normalized by the average thickness reduction amount [D_ave (mm)] (that is, D-max/D- is calculated). Ave), evaluation of corrosion uniformity. -29- (26) 1282372 ^ (2) For the test piece E, the maximum crack corrosion depth D-crev (mm) on the side of the large test piece was measured using a stylus type three-dimensional shape measuring device*. (3) For the test piece F (having a cut portion) for performing the painting treatment, the bulging amplitude (mm) of the coating film in the direction perpendicular to the cut portion was measured with a caliper, and the maximum 値 of the five test pieces was defined as the maximum bulging amplitude. . The general corrosion resistance (average plate reduction: D-ave), uranium uniformity (D-max/D-ave), crevice corrosion resistance (D-crev), φ paint corrosion resistance (maximum drum The evaluation criteria of the amplitude range are shown in Table 10 below. Table 1 1 below shows the results of the corrosion test. However, in Table 11, I (Co) represents the Co content of the deposited metal / Co content of the base material, and I (Mg) represents the Mg content of the deposited metal / the Mg content of the base material. The Mg and Co contents on the welded portion do not conform to the relationship (1) or (2), and are excellent in general corrosion resistance, but they are not compatible with other aspects such as crack resistance. This is the result of corrosion spreading over the portion of the weld metal. In this case, in the corrosion resistant steel (Νο·2~4) of the ratio ®ο·53~58 which is in accordance with the relationship (1) and (2), corrosion resistance is improved in all corrosion characteristics, and the result is 'displayed'. Preferred as the corrosion resistance of the welded structure. Further, in the present embodiment, the welded portion using the hidden arc welding method is used for evaluation, but the same effect can be obtained by other welding methods such as the coating electric welding method or the electroslag welding method. In addition, the welding materials used are not limited to Table 9. -30- 1282372

-0^owSE - « * Co/Mg 55.6 I_ 75.0 80.0 30.8 186.7 107.6 Other IIB: 0.0013 I Ζη:0·022 Zn:0.051 Ο) 0.0009 0.0012 0.0020 0.0026 LO δ Ο d 0.0092 <3 II 0.0050 -1 0.0029 III 0.020 I 0.009 II 〇〇0.05 I 0.09 0.16 0.08 0.28 0.99 IIII 1.05 I 〇III 0.12 0.03 0.54 〇IIII 0.49 丨I Lack I 0.51 0.38 0.22 0.54 ID 〇II 0.33 0.19 0.39 I < 0.014 0.013 0.012 0.018 0.014 I 0.014 C 0.99 〇T—0.98 1.19 0.99 1.05 j 〇5 0.25 0.18 0.28 0.21 0.18 0.20 〇0.11 0.12 0.18 0.15 0.18 0.12 6 Z τ— CM CO inch in CD CO E Φ Trace ω I rest | I rest | remaining rest I rest II rest | 1 remaining | rest | 0.0033 I 0.0005 | 0.0011 | 0.0082 0.0081 0.0056 | 0.0039 1 | 0.052 I 〇Ο 1 I 0.08 | I 0.05 I 0.06 I 0.49 I | 0.05 I 1 0.19 I | 2.08 I 琅 昍 11 11 匚 1 1.56 II 139 I 1.58 1.44 1.33 1.37 1.72 1.08 I 酲琅〇> 嗽C0 0.20 I 0.18 I 0.22 II 0.20 I | 0.21 II 0.22 I 0.23 I 0.22 I 〇0.15 0.14 | 0.12 I 0.11 I 0.12 0,12 012 0.11 ό Ζ I W2 C0 W4 W5 1 00 -31 - 1282372

Judgment ◎ lower than 〇·ι〇I lower than 1. 5 lower than 0.10 lower than 1 〇 om or more lower than 〇 · 50 1.5 or more lower than 2_0 0. 10 or more lower than 0.50 1 or more lower than 2 < Less than 3_00 2.0 or more im 5.0 0.50 or more is less than 3_00 2 or more is less than 10 X j- 3.00 or more 5.0 or more 3.00 or more 10 or more Measurement items D-ave (mm) D-max/D-ave D-crev (mm) Maximum Blowing amplitude (mm) Evaluation characteristics General corrosion resistance i_ Corrosion uniformity Rift resistance Corrosion resistance Paint resistance test piece Q LU LL ^11 -3⁄4 Comparative example - Comprehensive judgment of the present invention 〇X~〇〇〇~◎ 〇~ ◎ ◎ ◎ 〇 ~ ◎ Paint corrosion resistance 1 X < 〇〇〇 ◎ ◎ ◎ Rust resistance XX 〇 ◎ ◎ ◎ ◎ ◎ Corrosion uniformity << 〇〇〇 ◎ ◎ 〇 Resistant to comprehensive i corrosive 〇 ◎ ◎ ◎ ◎ ◎ 1 (Mg) 0.88 0.29 0.30 0.82 I 0·79 I 1.28 0.54 2.89 1 (C〇) 0.28 1.09 0.69 1 °-51 I 2.99 0.82 | 0.77 I 1.92 Welding material W2 00 W4 W5 1 00 Base material τ- CNI CN C0 00 inch ΙΟ 1 CM ID CO 1〇LO ΙΩ ί8 LO 00 in -32 - (29) 1282372 [Simplified description of the drawings] Fig. 1 is an explanatory view showing the appearance of the test piece A used in the corrosion resistance test. Fig. 2 is an explanatory view showing the appearance of the test piece B used for the corrosion resistance test. Fig. 3 is an explanatory view showing the appearance of the test piece C used for the corrosion resistance test. Fig. 4 is an explanatory view showing the appearance of the test piece D used in the corrosion resistance test. Fig. 5 is an explanatory view showing the appearance of the test piece E used for the corrosion resistance test. Fig. 6 is an explanatory view showing the appearance of the test piece F used for the corrosion resistance test.

-33-

Claims (1)

X. Application for Patent Scope Patent Application No. 94 1 20995 Patent Revision of Chinese Patent Application Revision of the Republic of China on February 2, 1996 1 · A ship steel with excellent corrosion resistance, characterized by Each includes: C: 0.01 to 0.30% (indicating mass %, the same below), Si: 0.01 to 1.50%, Μη: 0.01 to 2.0%, A1: 0.005 to 0.10%, and further containing Co: 0.01 to 5.00% And Mg: 0.0005~ 0· 02 0%, the rest consists of Fe and unavoidable impurities. 2. For the steel material for ships of the first application of the patent scope, the ratio [Co]/[Mg] of the Co content [Co] and the Mg content [Mg] is 2 to 3 50 〇3. Or 2 items of steel for ships, wherein ^ also contains one selected from the group consisting of Cu: 0.01 to 5.0%, Cr: 0.01 to 5.0%, Ni: 0.01 to 5.0%, and Ti: 0.005 to 0.20%. the above. * 4. For shipbuilding steels in the scope of patent application No. 1 or 2, where - also contains Ca: 0.0005 to 0.020% ° 5. For shipbuilding steels of claim 1 or 2, which also contains Mo: 0.01 ~5.0% and / or W: 0.01 ~ 2.0%. 6. The steel material for ships of claim 1 or 2, further comprising a group consisting of B: 0.0001 to 0.010%, V: 0.01 to 0.50%, and Nb: 1282372 (2) • 0.003 to 0.50%. More than one of the choices. 7. For the steel material for ships of the first or second patent application, it also contains Zn·· 〇_〇〇1~〇·1〇% by mass. 8. A welded structure for a ship having excellent corrosion resistance, characterized by: welding a steel material for a ship according to any one of claims 1 to 7, wherein the deposited metal and the mother are welded. The relationship between Co and Mg φ contained in the steel material is in accordance with the following formulas (1) and (2), and the Co content of the 〇·30 S deposited metal/the Co content of the base material S 3.0 (1) 0.30S melting The Mg content of the metallization/the Mg content of the base material S 3.0 (2). -2 -