JP6772942B2 - Corrosion resistant steel for ballast tanks - Google Patents

Description

The present invention relates to a corrosion-resistant steel material used for a ballast tank or the like in a severe corrosion environment due to seawater, and relates to a corrosion-resistant steel material for a ballast tank having an epoxy-based coating film on the surface.

When a cargo ship such as a tanker is empty, the hull floats during navigation and becomes unstable against crosswinds and waves. Therefore, when there is no load, seawater is loaded in the ballast tank so that the draft does not drop. ing. Ballast tanks are exposed to severe corrosive environments because seawater is repeatedly injected and discharged according to the loading and unloading of cargo. Therefore, the surface of the steel material used for the ballast tank is protected against corrosion with an epoxy-based paint.

Near the top of the ballast tank, especially on the back side of the upper deck, the temperature rises repeatedly during the day and the temperature drops at night with seawater droplets attached, resulting in a very severe corrosive environment. In addition, even if the ballast tank is provided with anticorrosion, it does not function because seawater is not injected when the cargo is loaded, and it is severely corroded by the action of residual salt.

The ballast tank is obliged to be painted, but it is said that the life of the coating film in a very severe corrosive environment is about 15 years. On the other hand, since the life of the ship is 25 years, it is necessary to repair the paint and switch the steel plate. Since the repair of the ballast tank increases the repair cost and period at the time of docking, it is desired to develop a steel material having excellent corrosion resistance so that the perforated corrosion does not occur for about 10 years even after the deterioration of the coating.

Corrosion-resistant steel materials that exhibit excellent coating corrosion resistance have been proposed in response to such demands (see, for example, Patent Documents 1 to 4). These are corrosion-resistant steel materials in which a coating film such as a zinc rich primer or an epoxy resin is formed on a steel material containing Cu, Ni, W, Mo, Sn, Sb or the like. Further, in order to improve the corrosion resistance, a steel material containing Cu and Mg has been proposed (see, for example, Patent Document 5).

Further, when painting the ballast tank, corrosion under the coating film may become a problem. Some of the present inventors have proposed corrosion-resistant steel materials for ballast tanks that suppress the formation of MnS in steel, which is considered to be one of the causes of corrosion under painting (see, for example, Patent Documents 6 and 7). .. Patent Document 6 considers the content of Mn and the content of S, and Patent Document 7 suppresses the production of MnS by utilizing Ca.

Japanese Unexamined Patent Publication No. 2010-138454 Japanese Unexamined Patent Publication No. 2012-177168 Japanese Unexamined Patent Publication No. 2014-199008 Japanese Unexamined Patent Publication No. 2015-151571 Japanese Unexamined Patent Publication No. 2000-17381 Japanese Unexamined Patent Publication No. 2016-141819 Japanese Unexamined Patent Publication No. 2017-14554

The present inventors have proceeded with the study of means for improving the corrosion resistance of the coating film defect portion when the ballast tank is coated, and have found that Mg is an effective element. On the other hand, when Cu, one or both of Sn and Sb, and Mg are simultaneously contained in order to suppress corrosion of the coating defect portion, if the Mg content is excessive, heat is generated by welding with a large heat input. It was found that the toughness of the affected area decreased.

In view of such circumstances, the present invention has excellent coating corrosion resistance in a corrosive environment in a ballast tank, and even when welding is performed by a large heat input, the heat-affected zone (HAZ) is excellent. Provided is a corrosion resistant steel material for a ballast tank having the toughness of.

The present inventors have improved the corrosion resistance of the coating defect portion of the corrosion-resistant steel material containing Cu and one or both of Sn and Sb at the same time, and are excellent even when welding is performed with a large heat input. The means for ensuring joint toughness (particularly HAZ toughness) was examined.
As a result, first, if Mg is contained in which coarse MnS, which has been a factor of deteriorating the corrosion resistance of the coating defect portion, is dispersed as fine (Mg, Mn) S particles, the deterioration of the corrosion resistance of the coating defect portion can be reduced. found.
Further, fine (Mg, Mn) S particles are also effective in improving the toughness of HAZ, but in order to obtain excellent joint toughness even in welding with a large heat input, the Mg content and Cu content are required. I found that the balance of is important.

The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) By mass%
C: 0.03 to 0.25%,
Si: 0.05 to 0.50%,
Mn: 0.10-2.50%,
S: 0.001 to 0.020%,
Cu: 0.10 to 0.060%,
Ni: 0.03 to 1.00%,
Al: 0.001 to 0.100%,
Mg: 0.0012 to 0.0030%, and
O: 0.0007 to 0.0020%
Containing,
Sn: 0.010 to 0.300% and
Sb: 0.010 to 0.300%
Contains at least one of
P: 0.025% or less N: Limit to 0.0080% or less, the balance consists of Fe and unavoidable impurities,
The content of Cu and the content of Mg are
70 <Cu / Mg <220
Satisfied,
A corrosion-resistant steel material for ballast tanks, which has an epoxy-based coating film on its surface.
(2) Furthermore, by mass%,
Cr: 1.00% or less,
Mo: 0.90% or less, and
W: The corrosion-resistant steel material for ballast tanks according to (1) above, which contains one type or two or more types of 1.00% or less.
(3) Furthermore, by mass%,
Ti: 0.100% or less,
Zr: 0.10% or less,
Ta: 0.100% or less,
Nb: 0.200% or less, and
V: The corrosion-resistant steel material for ballast tanks according to (1) or (2) above, which contains one type or two or more types of 0.20% or less.
(4) Furthermore, by mass%,
B: The corrosion-resistant steel material for a ballast tank according to any one of (1) to (3) above, which contains 0.0030% or less.
(5) Furthermore, by mass%,
Ca: 0.0050% or less,
The corrosion-resistant steel material for a ballast tank according to any one of (1) to (4) above, which contains one or more of REM: 0.005% or less and Y: 0.100% or less. ..
(6) The corrosion resistance for a ballast tank according to any one of (1) to (5) above, which comprises having a zinc primer coating film as a base of the epoxy-based coating film.

The corrosion-resistant steel material for a ballast tank of the present invention exhibits excellent coating corrosion resistance in a corrosive environment inside the ballast tank, and has excellent welded joint toughness even when welding is performed by a large amount of heat input. Therefore, when the present invention is applied to a ballast tank exposed to a harsh corrosive environment, the initial cost and maintenance cost such as repair and repainting can be significantly reduced, and the industrial contribution is extremely remarkable. ..

The present inventors have conducted the following studies on the corrosion of defective portions of the epoxy-based coating film using various corrosion-resistant steel materials coated with the epoxy-based paint.

Steel containing various alloying elements was melted and hot-rolled to prepare a steel plate having a plate thickness of 5 mm, and a test piece having a length of 150 mm and a width of 70 mm was collected. The scale on the surface of the test piece was removed by shot brass, and the epoxy paint was applied twice so that the coating film thickness was 300 to 400 μm. Then, in order to evaluate the corrosion resistance of the defective portion of the coating film, a flaw having a length of 50 mm reaching the surface of the base metal was formed in a single letter in the center of the test piece by an end mill having a width of 2 mm.

Corrosion resistance was evaluated by a combined cycle test. In order to match the environment of the ballast tank, artificial seawater was used as the corrosive solution instead of the 5% NaCl aqueous solution. The cycle conditions were 1 hour for spraying a corrosive liquid (temperature 35 ° C.), 2 hours for drying (60 ° C., humidity 20 to 30%), and 1 hour for wetting (50 ° C., humidity 95% or more). After performing this cycle for 300 cycles, the maximum length of the paint swelling of the applied flaw was measured.

As a result, it was found that when one or both of Sn and Sb were contained, a test piece in which the coating film swelling and corrosion of the coating defect portion were suppressed and a test piece in which the coating film swelling and corrosion were not suppressed were observed. As a result of investigating these in detail, it was found that a large amount of MnS was generated in the one in which the swelling of the coating defect portion was not suppressed.

Next, the surface was mirror-polished, the observed MnS was marked with a Vickers hardness tester, and the corrosion resistance was evaluated using a test piece having a flaw at that position. As a result, it was clarified that the swelling of the coating film was not suppressed and MnS had an adverse effect on the corrosion resistance of the coating defect portion. Even in a corrosion-resistant steel material containing Sn and Sb, when a large amount of MnS is produced, the reason why the corrosion of the coating film defect portion is not suppressed may be that sulfuric acid is generated by the hydrolysis of MnS and the pH is greatly lowered. I'm estimating.

On the other hand, among the corrosion-resistant steel materials containing one or both of Sn and Sb, it was found that some of the corrosion-resistant steel materials containing Mg were remarkably suppressed from swelling and corrosion of the coating film in the coating defect portion. In the steel material containing Mg, (Mg, Mn) S particles are finely dispersed, and even when (Mg, Mn) S is hydrolyzed, not only the decrease in pH is suppressed but also the dissolved Mg causes It is presumed that the Mg compound was formed and the progress of corrosion was significantly suppressed by the so-called electrocoating.

Next, the present inventors have studied a means for improving the toughness of a welded joint portion in welding with extremely high heat input, in which a plate having a plate thickness of 20 mm to 30 mm is welded to a steel material in one pass. When welding is performed with high heat input, the toughness of the heat-affected zone is significantly reduced. The reason is that the metal structure of the weld heat-affected zone is exposed to high temperature for a long time during welding, and the γ grains appearing at high temperature become coarse, so that the metal structure after cooling becomes coarse. Is.

Therefore, the suppression of coarsening of γ particles was examined by the pinning effect due to the fine dispersion of (Mg, Mn) S particles. As a result, it was found that the fine (Mg, Mn) S particles are effective in improving the toughness of the weld heat affected zone. However, if Mg is excessively contained, coarse inclusions are formed and the toughness of the heat-affected zone is lowered. Therefore, the Mg content needs to be 0.0030% or less. Further, it was found that when Cu and Mg are contained at the same time, if the Mg content is not appropriate for the Cu content, the toughness of the heat-affected zone is lowered by the large heat input welding.

When the content of Mg is excessive with respect to the content of Cu, it is considered that the excess Mg that does not form (Mg, Mn) S particles forms coarse inclusions and reduces the toughness of HAZ. On the other hand, when the Mg content is insufficient with respect to the Cu content, CuS is formed in the steel, the generation of (Mg, Mn) S particles becomes insufficient, and the toughness of HAZ is not improved. Be done. As a result of the study by the present inventors, it is necessary that the relationship with the Cu content satisfies 70 <Cu / Mg <220 in order to suppress the decrease in the toughness of HAZ when performing large heat-affected welding. I found out.

Based on the results of such studies, the corrosion-resistant steel material for ballast tanks of the present invention (hereinafter referred to as "corrosion-resistant steel material of the present invention") contains Cu and Ni, and then one or both of Sn and Sb. The upper limit of Mg was set to 0.0030%, and the relationship with the amount of Cu was set to 70 <Cu / Mg <220. Further, when one or more of Cr, Mo, and W are contained, if necessary, further excellent corrosion resistance can be obtained.

Next, the component composition of the corrosion-resistant steel material of the present invention will be specifically described below. Unless otherwise specified, "%" indicates "mass%".

(C: 0.03 to 0.25%)
C is an element effective for increasing the strength of the steel material, and needs to be contained in an amount of 0.03% or more in order to obtain the desired strength. It is preferably 0.05% or more, more preferably 0.08% or more. On the other hand, if C is contained in excess of 0.25%, the toughness of the weld heat affected zone is lowered, so the C content is set to 0.25% or less. It is preferably 0.20% or less, more preferably 0.17% or less.

(Si: 0.05 to 0.50%)
Si is an element effective as a deoxidizer and for increasing the strength of steel materials, and contains 0.05% or more. It preferably contains 0.10% or more, more preferably 0.15% or more of Si. However, if it is contained in excess of 0.50%, the toughness of the steel is deteriorated, so the content is set to 0.50% or less. It is preferably 0.40% or less, more preferably 0.30% or less.

(Mn: 0.10-2.50%)
Mn is an element that enhances the strength of the steel material, and contains 0.10% or more of Mn. It is preferably 0.60% or more, more preferably 1.00% or more. However, if Mn is contained in excess of 2.50%, MnS is increased and the corrosion resistance of the coating film defect portion is lowered, so the content is set to 2.50% or less. It is preferably 2.00% or less, more preferably 1.60% or less.

(S: 0.001 to 0.020%)
Since S produces MnS and lowers the corrosion resistance of the coating film defect portion, the content of S is set to 0.020% or less. It is preferably contained in an amount of 0.015% or less, more preferably 0.010% or less. The content of S is preferably reduced from the viewpoint of corrosion resistance, but if it is less than 0.001%, the load on steelmaking is large and the cost is high, so the lower limit is set to 0.001%. More preferably, the S content is 0.003% or more.

(Cu: 0.10 to 0.60%)
Cu is contained together with Ni, and then one or both of Sn and Sb are contained, and since it is necessary to contain Mg to improve corrosion resistance, 0.10% or more is contained. It preferably contains 0.15% or more. On the other hand, if 0.60% or more of Cu is contained, embrittlement of the weld heat affected zone occurs, so the amount of Cu is set to 0.50% or less. It is preferably 0.40% or less, more preferably 0.30% or less.

(Ni: 0.03 to 1.00%)
Ni contains one or both of Sn and Sb after being contained together with Cu, and since it is necessary to contain Mg to improve corrosion resistance, 0.03% or more is contained. When Cu and Ni are contained at the same time, deterioration of the surface texture of the steel material can be suppressed. On the other hand, Ni is an expensive element, and if it is contained in excess of 1.00%, the cost will be high, so the amount of Ni is set to 1.00% or less. It is preferably 0.50% or less, more preferably 0.30% or less.

(Al: 0.001 to 0.100%)
Al is a deoxidizing agent and contains 0.001% or more of Al. The Al content is preferably 0.005% or more, more preferably 0.010% or more. However, if Al is contained in an amount of more than 0.100%, the toughness is lowered, so the content is set to 0.100% or less. It is preferably 0.080% or less, more preferably 0.060% or less.

(Mg: 0.0012 to 0.0030%)
Mg is an element necessary for suppressing the coating swelling and corrosion of the coating defect portion of the corrosion-resistant steel material of the present invention and for suppressing the toughness deterioration of the welding heat-affected zone in the large heat input welding. Contains 0012% or more. It is preferably 0.0015% or more, more preferably 0.0020% or more. However, when Cu is contained in order to improve the corrosion resistance, if the Mg content exceeds 0.0030%, the toughness of the weld heat affected zone decreases, so the Mg content is set to 0.0030% or less. .. It is preferably 0.0025% or less.

(O: 0.0007 to 0.0020%)
It is preferable to limit O in order to suppress the formation of coarse oxides that cause a decrease in toughness of the weld heat affected zone and a decrease in mechanical properties of the base metal, but from the viewpoint of cost, the lower limit of the amount of O is set to 0. It shall be 0007%. In particular, when the amount of O exceeds 0.0020%, it is set to 0.0020% or less in order to form a coarse oxide. It is preferably 0.0018% or less, more preferably 0.0015% or less.

(Sn: 0.010 to 0.300%)
(Sb: 0.010 to 0.300%)
Sn and Sb have the effect of improving the corrosion resistance of the coating film defect portion, and include one or both of them. In order to obtain the effect, both Sn and Sb need to be contained in an amount of 0.010% or more, preferably 0.020% or more, and more preferably 0.030% or more. On the other hand, when the contents of both Sn and Sb exceed 0.300%, the toughness of the base metal and HAZ is deteriorated. Therefore, the contents of Sn and Sb are set to 0.300% or less, preferably 0.200% or less, and more preferably 0.150% or less.

(P: 0.025% or less)
P is an impurity and deteriorates the toughness of the base metal, the toughness of the weld, and the toughness of the welded portion of the steel. In particular, if the P content exceeds 0.025%, the toughness of the base metal and the toughness of the weld will be significantly reduced, so the content is limited to 0.025% or less. The P content is preferably 0.020% or less, more preferably 0.015% or less.

(N: 0.0080% or less)
N is an impurity and deteriorates the toughness of the base metal, the toughness of the weld, and the toughness of the welded portion of the steel. In particular, if the N content exceeds 0.0080%, the toughness of the base metal and the toughness of the welded portion will be significantly reduced, so the content is limited to 0.0080% or less. The N content is preferably 0.0050% or less, more preferably 0.0040% or less, and even more preferably 0.0035% or less.

In addition to the above-mentioned basic components (essential elements), the corrosion-resistant steel material of the present invention further contains one or more of Cr, Mo, and W as selective elements in order to enhance the corrosion resistance of coating defects. You may let me.

(Cr: 1.00% or less)
(Mo: 0.90% or less)
(W: 1.00% or less)
When one or more of Cr, Mo, and W are contained in Cu, Ni, and Mg, and then one or both of Sn and Sb are contained at the same time, the corrosion resistance of the coating defect portion is improved. The effect of further enhancing is exhibited. In order to obtain the effect of improving the corrosion resistance of the coating defect portion, it is preferable to add 0.01% or more of Cr, Mo, and W. However, if Cr, Mo, and W are excessively contained, the HAZ toughness may deteriorate. It is preferable that Cr is 1.00% or less, Mo is 0.90% or less, and W is 1.00% or less. More preferably, the content of Cr, Mo, W is 0.50% or less, and even more preferably, the content of Cr, Mo, W is 0.30% or less.

In addition to the above-mentioned essential elements, the corrosion-resistant steel material of the present invention is one of Ti, Zr, Ta, Nb, V, B, Ca, REM, and Y in order to further improve the mechanical properties of the base material. Alternatively, two or more kinds may be contained.

(Ti: 0.100% or less)
(Zr: 0.10% or less)
(Ta: 0.100% or less)
(Nb: 0.200% or less)
(V: 0.20% or less)
Ti, Zr, Ta, Nb, and V are all elements that generate precipitates and increase the strength of the steel material, and can be contained as needed. Ti, Zr, Ta, Nb, and V are preferably contained in an amount of 0.001% or more. On the other hand, if Ti, Zr, Ta, Nb, and V are excessively contained, the toughness may decrease. Therefore, Ti is 0.100% or less, Zr is 0.10% or less, and Ta is 0.100% or less. It is preferable that Nb is contained in an amount of 0.200% or less and V is contained in an amount of 0.20% or less. More preferably, Ti is 0.020% or less, Zr is 0.02% or less, Ta is 0.010% or less, Nb is 0.030% or less, and V is 0.10% or less.

(B: 0.0030% or less)
B is an element that increases the strength of the steel material by adding a small amount, and can be contained as needed. The amount of B is preferably 0.0003% or more. More preferably, it is 0.0005% or more. On the other hand, if the content exceeds 0.0030%, the toughness may deteriorate. Therefore, the content of B is preferably 0.0030% or less. More preferably, it is 0.0020% or less.

(Ca: 0.0050% or less)
(REM: 0.005% or less)
(Y: 0.100% or less)
Ca, REM, and Y are all elements that are effective in improving the mechanical properties of the base material, and can be selected and contained as necessary. It is preferable that Ca, REM, and Y each contain 0.0001% or more. More preferably, the contents of Mg, REM, and Y are 0.0005% or more, respectively. On the other hand, if these are excessively contained, the toughness of the base metal may be lowered, so Ca and REM are preferably 0.005% or less, and Y is 0.100% or less. More preferably, the contents of Mg, REM, and Y are 0.0030% or less, 0.005% or less, and 0.05% or less, respectively.

In the corrosion-resistant steel material of the present invention, components other than the above are Fe and unavoidable impurities, but the inclusion of components other than the above is permitted as long as the effects of the present invention are not impaired.

(70 <Cu / Mg <220)
When Cu and Mg are contained at the same time, it is necessary that the Cu content and the Mg content satisfy 70 <Cu / Mg <220. If the Mg content is excessive with respect to the Cu content, coarse inclusions are formed and the HAZ toughness is lowered, so that Cu / Mg is set to less than 220. It is preferably 180 or less, more preferably 150 or less. On the other hand, if the Mg content is insufficient with respect to the Cu content, the formation of (Mg, Mn) S particles becomes insufficient due to the formation of CuS, and the HAZ toughness is lowered. Therefore, Cu / Mg is set to more than 70. It is preferably 75 or more, more preferably 80 or more.

The corrosion-resistant steel material of the present invention has an epoxy-based coating film on the surface of the base steel material having the above composition. The epoxy coating film is not particularly limited as long as it meets the coating performance standards set by the International Maritime Organization (IMO), and may be formed by applying an epoxy coating film and drying it. Good.

Further, an epoxy-based coating film can be provided after forming a zinc-rich primer coating film on the surface of the base steel material having the above composition. The zinc rich primer coating film is not particularly limited, and may be formed by applying a zinc rich primer and drying it.

The corrosion-resistant steel material of the present invention can be produced by a conventional method.
For example, molten steel is melted by a known method such as a converter or an electric furnace to make a steel material such as a slab or a billet by a known method such as a continuous casting method or an ingot forming method, and is used for hot rolling. The molten steel may be subjected to treatments such as ladle refining and vacuum degassing.

Then, the steel material is heated to a temperature of preferably 1050 to 1250 ° C. and hot-rolled to a desired size and shape. The steel material after casting or ingot may be hot-rolled as it is. In hot rolling, in order to ensure strength, it is preferable to optimize the hot finish rolling end temperature and the cooling rate after hot finish rolling, and the hot finish rolling end temperature is 700 ° C. or higher. For cooling after the completion of hot finish rolling, it is preferable to perform air cooling or accelerated cooling at a cooling rate of 100 ° C./s or less. Further, after cooling, reheating treatment may be performed.

Then, an epoxy-based paint is applied to the surface of the steel material and dried to form an epoxy-based coating film. A zinc rich primer coating may be formed before applying the epoxy paint. Further, shot blasting may be performed or pickling may be performed before applying the epoxy-based paint or zinc rich primer.

Hereinafter, the present invention will be described in more detail by way of examples. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is the one condition. It is not limited to the example. In the present invention, various conditions can be adopted as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

Steels having the composition shown in Table 1 are melted in a vacuum melting furnace or converter to form ingots or steel slabs, which are heated to 1150 ° C. in a heating furnace and hot-rolled to a thickness of 25 mm. It was made of steel plate. The obtained thick steel sheet was given a heat history assuming a heat-affected zone in large heat input welding, and a Charpy test was conducted. The heat history was maintained for 15 seconds after heating to 1400 ° C. at a heating rate of 100 ° C./sec, and then cooled to room temperature at 1 ° C./sec. The Charpy impact test was performed at −20 ° C. in accordance with JIS Z 2242, and was evaluated by the average value of 6 pieces.

Next, test pieces having a length of 150 mm, a width of 70 mm, and a thickness of 5 mm were collected from each thick steel plate, the scale on the surface of the test pieces was removed by shot brass, and then epoxy paint was applied twice to coat the coating. A test piece having a thickness of 300 to 400 μm was prepared. In addition, for some steel sheets, those coated with zinc primer by 10 μm before coating with the epoxy paint were also prepared.

A composite cycle test was carried out using artificial seawater by using an end mill with a width of 2 mm at the center of these test pieces to give a flaw with a length of 50 mm reaching the surface of the base metal in a single letter in the horizontal direction. The cycle conditions were 1 hour for spraying a corrosive liquid (temperature 35 ° C.), 2 hours for drying (60 ° C., humidity 20 to 30%), and 1 hour for wetting (50 ° C., humidity 95% or more). After performing this cycle for 300 cycles, the maximum length of the paint swelling of the applied flaw was measured. Corrosion resistance is No. 1 which does not contain any corrosion-improving element. Using 27 steels as the base steel (100), the ratio of the maximum length of the coating swelling was calculated and evaluated.

Table 2 shows the results of the corrosion test and the impact test, which is an index of HAZ toughness. No. 1 of the invention example satisfying the component composition of the present invention. It can be seen that the steels 1 to 26 have a ratio of the maximum length of the coating swelling to the base steel (No. 27) of 50% or less, and have good corrosion resistance. Further, it can be seen that the steel material coated with the zinc primer in the invention example has a ratio of the maximum length of the coating swelling to the base steel (No. 27) of 25% or less, and has good corrosion resistance.

On the other hand, No. which does not satisfy the condition of the component composition of the present invention. In the steels 28 to 33, the ratio of the maximum length of the coating swelling to the base steel (No. 27) exceeds 50%. No. In the steels 34 to 36, the ratio of the maximum length of the coating swelling to the base steel (No. 27) is 50% or less. No. 34 steel contains O in excess. Since the Cu / Mg values of the 35-36 steels do not satisfy the conditions of the present invention, the HAZ toughness of each of them is low.

The present invention is a corrosion-resistant steel material for ballast tanks having an epoxy-based coating film on its surface, and includes thick steel plates, thin steel plates, shaped steels, and steel bars. The corrosion-resistant steel material for ballast tanks of the present invention is, for example, a coal ship, an ore ship, a ship for both mining and coal, a crude oil tanker, an LPG ship, an LNG ship, a chemical tanker, a container ship, a bulk carrier, a wood ship, a chip ship, and a freezer. It can be suitably used as a material for ballast tanks of transport ships, automobile ships, heavy lift ships, RORO ships, limestone ships, cement ships, etc. Since the corrosion-resistant steel material of the present invention exhibits excellent coating corrosion resistance in a corrosive environment due to seawater, it can be used not only for ballast tanks of ships but also for applications used in other similar corrosive environments due to seawater. .. Therefore, the present invention has high industrial applicability.

Claims (6)

By mass%
C: 0.03 to 0.25%,
Si: 0.05 to 0.50%,
Mn: 0.10-2.50%,
S: 0.001 to 0.020%,
Cu: 0.10 to 0.60%,
Ni: 0.03 to 1.00%,
Al: 0.001 to 0.100%,
Mg: 0.0012 to 0.0030%, and
O: 0.0007 to 0.0020%
Containing,
Sn: 0.010 to 0.300% and
Sb: 0.010 to 0.300%
Contains at least one of
P: 0.025% or less N: Limit to 0.0080% or less, the balance consists of Fe and unavoidable impurities,
The content of Cu and the content of Mg are
70 <Cu / Mg <220
Satisfied,
A corrosion-resistant steel material for ballast tanks, which has an epoxy-based coating film on its surface. Furthermore, in% by mass,
Cr: 1.00% or less,
Mo: 0.90% or less, and
W: The corrosion-resistant steel material for a ballast tank according to claim 1, which contains one type or two or more types of 1.00% or less. Furthermore, in% by mass,
Ti: 0.100% or less,
Zr: 0.10% or less,
Ta: 0.100% or less,
Nb: 0.200% or less, and
V: The corrosion-resistant steel material for a ballast tank according to claim 1 or 2, which contains one type or two or more types of 0.20% or less. Furthermore, in% by mass,
B: The corrosion-resistant steel material for ballast tanks according to any one of claims 1 to 3, which contains 0.0030% or less. Furthermore, in% by mass,
Ca: 0.0050% or less,
The corrosion-resistant steel material for a ballast tank according to any one of claims 1 to 4, wherein REM: 0.005% or less and Y: 0.100% or less are contained in one or more. The corrosion-resistant steel material for a ballast tank according to any one of claims 1 to 5, wherein a zinc primer coating film is provided as a base of the epoxy-based coating film.