JP4483107B2 - Marine steel with excellent coating life - Google Patents

Description

【００２９】
【表２】

【００３０】
表２に示したとおり、発明例（鋼No.1〜10）の塗膜膨れ面積は68〜527 mm² であり、比較例に比べて格段に小さく、優れた耐塗膜損傷性を有していることが分かる。。
一方、比較例のうち、No.11, 14 はCu量が、No.12 はNi量が、No.15 はＣ量とCu量とNi量が、それぞれこの発明の適正範囲を逸脱しているため、塗膜膨れ面積は極めて大きかった。また、No.13 は、Ｐ量がこの発明の上限を超えているため、塗膜膨れ面積は発明例と同程度であるが、母材靱性および溶接部靱性が劣化している。
なお、No.1〜４の結果から、Ni量を増加させることが塗膜膨れ面積の減少には極めて有効であることが分かる。
【００３１】
【発明の効果】
この発明の船舶用鋼材は、優れた耐塗膜損傷性を有し、苛酷な腐食環境であるバラストタンクへ適用した場合に、補修塗装や再塗装といった保守費用を大幅に削減することができ、産業上その貢献度は極めて大である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to marine steel materials with excellent coating film life, and particularly for marine steel materials such as ballast tanks used under severe environments such as high temperature and high humidity, from the viewpoint of preventing corrosion, the coating film life is advantageous. It is intended to make extension possible.
[0002]
[Prior art]
Since the ballast tank is used in a particularly severe environment of high temperature and high humidity, various countermeasures have been conventionally taken for its anticorrosion.
Usually, the anti-corrosion of the ballast tank uses a tar epoxy resin paint and an electric anti-corrosion, but since the seawater enters and exits the ballast tank, it is in a severe corrosive environment. In other words, when the ballast tank is full of seawater, the part immersed in seawater is hardly corroded by the effect of electrocorrosion protection, but the top of the ballast tank not immersed in seawater or the back side of the upper deck is In addition to high temperature, it is in a severe corrosive environment called a splash zone. On the other hand, when there is no seawater in the ballast tank, it becomes a high-temperature and high-humidity environment. In this case, the anticorrosive effect cannot be expected, and only the tar epoxy resin paint is anticorrosive.
In addition, when filling the ballast tank with seawater, pebbles and dust contained in the seawater also enter the ballast tank, causing scratches on the paint film, so corrosion progresses from the scratch part. To do.
[0003]
The life of such a ballast tank is said to be about 10 years, which is half the life of a ship (20 years). Therefore, for the remaining 10 years, safety must be maintained by repair painting.
Ballast tanks have the serious problem of requiring painting under such severe corrosive conditions and adverse conditions, so it is hoped to develop marine steel that can improve the steel surface, that is, extend the life of the paint film. It is rare.
[0004]
By the way, seawater-resistant steel intended for use in the marine environment is supplemented with Cr, Ni, Mo, Cu, etc. to improve corrosion resistance. Seawater resistant steel for welded structures has been developed. These are used for sluices, steel sheet piles, buoys, piers, and the like.
As such seawater-resistant steel, steel materials disclosed in Japanese Patent Application Laid-Open No. 51-25420 are known, but the applications of these steel materials are the above-described marine structures and port facilities, and the usage environment is as follows. It is seawater at the atmospheric temperature. Japanese Laid-Open Patent Publication No. 63-255341 proposes a corrosion-resistant steel sheet for welded structures with improved salt damage in the atmospheric environment.
[0005]
As described above, the environment considered as the conventional seawater-resistant steel material problem is greatly different from the environment in question in this invention, that is, the environment in the ballast tank where seawater enters and exits and becomes hot and humid.
That is, the corrosive environment of the ballast tank is a high-temperature and high-humidity environment in which seawater enters and exits as described above, and the corrosive environment when assuming a tanker is as follows.
When transporting crude oil from the Middle East to Japan, the cargo oil tank is empty on the outbound route from Japan to the Middle East, so the ballast tank is almost full of seawater to maintain the balance of the ship and ensure navigation safety. To. The corrosive environment at this time is such that the middle to lower part of the ballast tank is in seawater and the upper part of the ballast tank is close to a splash zone. On the other hand, on the return route from the Middle East to Japan, the ballast tanks are filled with seawater and emptied. The inside of the ballast tank at this time becomes a hot and humid environment due to the seawater remaining on the bottom of the ship and the heat from the deck. One cycle in which the ballast tank is exposed to these corrosive environments is about 80 days.
[0006]
[Problems to be solved by the invention]
Currently, steel materials used in ships are manufactured by component design and process design that take strength, toughness, and weldability into account, but currently there are few measures for corrosion resistance and corrosion resistance. .
This invention was developed in view of the above-mentioned present situation, and by adding alloying elements, the coating film life can be effectively extended even in severe corrosive environments, particularly in high temperature and high humidity environments. The purpose is to propose an excellent marine steel.
[0007]
The coating film life means the life until repair coating or full repainting is performed. The judgment index for the timing of repair painting or full repainting is not clear, but it is generally judged that repainting is necessary when the paint film is damaged due to corrosion and the rust area is expanded to some extent.
Therefore, if the damage to the coating film due to rust is reduced, the coating film life is extended, that is, the coating film life is improved.
[0008]
[Means for Solving the Problems]
Now, the inventors made many exposure test pieces containing various alloy elements in various proportions, and used these test pieces for an exposure test for two years in an actual ballast tank.
As a result, it was found that paint bulging due to rust from paint film scratches was remarkably reduced with test pieces mainly made of Cu-less and added with Ni. For example, a steel material in which Ni is added by 1 mass% and Cu is reduced to 0.02 mass% has a swollen area reduced to 1/10 compared to a conventional steel material. It was also found that the test piece to which Mo, Co, Sb, and W were added also suppressed the swelling of the coating film due to rust. That is, it has been found that these alloy elements have an effect of suppressing the progress of corrosion from the scratch portion and reducing coating film damage.
The present invention is based on the above findings.
[0009]
That is, the gist configuration of the present invention is as follows.
1. % By mass
C: 0.001 to 0.025%,
Si: 0.60% or less,
Mn: 0.10 to 3.0%,
P: 0.030% or less,
S: 0.01% or less,
Al: 0.10% or less,
Ni: 0.1-4.0% and
Cu: A marine steel material with excellent coating life, characterized by containing 0.1% or less and the balance being Fe and inevitable impurities.
[0010]
2. In the above 1, the steel material is further in mass%,
Mo: 0.05-0.5%,
Co: 0.05-0.5%
W: 0.05-0.5% and
Sb: 0.05-0.5%
A marine steel material excellent in coating film life which has a composition containing one or more selected from among them.
[0011]
3. In said 1 or 2, steel materials are further mass%,
Nb: 0.005 to 0.20%,
V: 0.005 to 0.20%,
Ti: 0.005 to 0.20%,
REM: 0.02% or less,
Ca: 0.005% or less and B: 0.0003 to 0.0050%
A marine steel material excellent in coating film life which has a composition containing one or more selected from among them.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described below.
First, the reason why the component composition of the steel material is limited to the above range in the present invention will be described. In addition, the% display of the component composition shown below is "mass%".
C: 0.001 to 0.025%
C is an element effective in improving the strength. However, if the content is less than 0.001%, the effect of addition is poor. On the other hand, if it exceeds 0.025%, the toughness of the base metal and the welded portion are deteriorated. It was limited to the range of 0.001 to 0.025%.
[0013]
Si: 0.60% or less
Si is not only useful as a deoxidizer, but is also an element useful in improving the strength of steel. However, Si is 0.60% because the base metal toughness and weld toughness deteriorate when contained in too large amounts. Limited to: Preferably it is 0.15 to 0.50% of range.
[0014]
Mn: 0.10 to 3.0%
Mn is an element that greatly affects not only the strength of steel but also the base metal toughness and weld zone toughness. In the present invention, Mn is contained in an amount of 0.10% or more in order to ensure a desired strength. However, if the content exceeds 3.0%, the base metal toughness and weld zone toughness are adversely affected, so Mn is limited to the range of 0.10 to 3.0%. Preferably it is 0.10 to 2.0% of range.
[0015]
P: 0.030% or less P is limited to 0.03% or less because P deteriorates the base metal toughness and weld toughness.
[0016]
S: 0.01% or less S, like P, deteriorates the base metal toughness and weld zone toughness, so it was limited to 0.01% or less.
[0017]
Al: 0.10% or less
Al is added as a deoxidizer, but if the content exceeds 0.10%, the toughness of the weld is adversely affected.
[0018]
Ni: 0.1 to 4.0%
Ni is the most important element in the present invention as an element that significantly suppresses blistering. The effect is exhibited by densifying the rust particles and blocking the penetration of corrosion factors such as water, oxygen, and Cl into the ground iron. Thus, after a certain amount of rust is formed, this rust layer prevents the penetration of corrosion factors, thereby suppressing the subsequent corrosion of the ground iron. If corrosion is suppressed, the occurrence of rust is reduced and the swelling of the coating film due to rust is also suppressed. This effect is small when the Ni content is less than 0.1%. On the other hand, when the Ni content exceeds 4.0%, the effect is saturated and rather disadvantageous economically. Therefore, the Ni content is limited to the range of 0.1 to 4.0%.
[0019]
Cu: 0.1% or less
Cu is generally an element for improving corrosion resistance, and is added to weathering steel used in an atmospheric environment such as a bridge. However, the internal environment of the ballast tank that is the subject of the present invention is hot and humid and almost wet. However, in such an environment, Cu does not work effectively but acts adversely.
This is because Cu has two actions of promoting rust densification and activating the dissolution of steel. That is, the wet time is relatively short in the atmospheric environment, so that the steel melting time is short. Therefore, in this case, the protective rust layer formed by the Cu rust densification promoting action suppresses the corrosion reaction of steel due to Cu dissolution activation. On the other hand, in the always wet state, the corrosion reaction of the steel due to the activation of dissolution of Cu becomes larger than the protective action of the rust layer due to the accelerating action of densification of Cu rust, so that the corrosion of the steel proceeds. If the corrosion of steel progresses, the swelling of the coating also progresses.
Here, if the amount of Cu exceeds 0.1%, the corrosion of the steel and thus the swelling of the coating film proceeds, so the amount of Cu is limited to 0.1% or less.
[0020]
Although the essential components have been described above, in the present invention, in addition to the essential components described above, the following components can be appropriately contained.
Mo, Co, W, Sb: 0.05-0.5%
Mo, Co, W, and Sb all have the effect of suppressing the swelling of the coating film. However, when the content is less than 0.05%, the effect is small, whereas when the content exceeds 0.5%, the effect is saturated, which is rather economically disadvantageous. Therefore, these elements are contained in the range of 0.05 to 0.5% in either case of single addition or composite addition.
[0021]
Nb, Ti, V: 0.005 to 0.20%
Nb, Ti, and V are all elements that increase the strength of steel materials. However, if the content is less than 0.005%, the effect of addition is poor, while if it exceeds 0.20%, the effect is saturated. In either case of single addition or combined addition, 0.005 to 0.20% is included.
[0022]
REM: 0.02% or less
REM contributes effectively to improving the toughness of the weld zone. However, if the content exceeds 0.02%, the cleanliness of the steel deteriorates. Therefore, REM was added at 0.02% or less.
[0023]
Ca: 0.005% or less
Ca, as well as REM, effectively contributes to improving the toughness of the weld zone. However, if the content exceeds 0.005%, the cleanliness of the steel material deteriorates, so it was determined to be contained at 0.005% or less.
[0024]
B: 0.0003-0.0050%
B is an element advantageous for improving the strength. However, when the content is less than 0.0003%, the effect of addition is poor. On the other hand, when it exceeds 0.0050%, the base metal toughness and weld toughness are deteriorated. It was made to contain in -0.0050% of range.
[0025]
Next, the manufacturing method of this invention steel material is demonstrated.
The method for producing the steel material of the present invention is not particularly limited, and may be produced by a conventionally known method.
That is, after melting by a normal method such as a converter or an electric furnace, a raw material is obtained by a continuous casting method or an ingot forming method. In addition, vacuum melting may be performed in the melting process.
Then, these materials are rolled into a desired shape by hot rolling after heating in a heating furnace or the like or directly without heating.
[0026]
【Example】
Steels having the composition shown in Table 1 were melted in a converter and made into slabs by a continuous casting method. Subsequently, these slabs were heated and then hot rolled to form a steel plate having a plate thickness of 25 mm and a plate width of 2500 mm.
The tensile properties and impact properties of these steel plates were investigated.
Further, as the weld zone toughness, a heat input of 50 kJ / cm and a heat cycle affected by the weld heat affected zone of 1 mm were applied, and the absorbed energy vE ₀ at 0 ° C. was measured by a Charpy impact test.
[0027]
Furthermore, 5 mm x 100 mm x 200 mm exposure test pieces were collected from these steel plates, and after zinc blasting, zinc rich primer (about 15 μm) and tar epoxy resin paint (about 200 μm) were applied to these test pieces. . Thereafter, a 80 mm long scratch reaching the surface of the test piece was added with a cutter knife. These test pieces were mounted in a ballast tank of an actual ship and subjected to an exposure test. The exposure period is 2 years. The environment in the ballast tank was a dry and wet repetitive environment where one cycle was a period in which the seawater was in the ballast tank: about 40 days, and a period in which the seawater was not in the ballast tank: about 40 days. After the exposure test, the swollen area of the coating film due to rust around the scratch was measured.
The above survey results are shown in Table 2.
[0028]
[Table 1]

[0029]
[Table 2]

[0030]
As shown in Table 2, the coating film blister area of the inventive example (steel No. 1 to No. 10) is 68 to 527 mm ^2, much smaller than that of Comparative Example, has excellent耐塗film damaging I understand that .
On the other hand, among the comparative examples, Nos. 11 and 14 have a Cu content, No. 12 has a Ni content, and No. 15 has a C content, a Cu content, and a Ni content deviating from the appropriate ranges of the present invention. Therefore, the swollen area of the coating film was extremely large. In No. 13, since the amount of P exceeds the upper limit of the present invention, the swollen area of the coating film is similar to that of the inventive example, but the base material toughness and welded portion toughness are deteriorated.
From the results of Nos. 1 to 4, it can be seen that increasing the amount of Ni is extremely effective in reducing the film swelling area.
[0031]
【The invention's effect】
The marine steel material of the present invention has excellent coating film damage resistance, and when applied to a ballast tank that is a severely corrosive environment, can greatly reduce maintenance costs such as repair coating and repainting, The industrial contribution is extremely large.

Claims (3)

% By mass
C: 0.001 to 0.025%,
Si: 0.60% or less,
Mn: 0.10 to 3.0%,
P: 0.030% or less,
S: 0.01% or less,
Al: 0.10% or less,
Ni: 0.1-4.0% and
Cu: A marine steel material with excellent coating life, characterized by containing 0.1% or less and the balance being Fe and inevitable impurities. In Claim 1, steel materials are further mass%,
Mo: 0.05-0.5%,
Co: 0.05-0.5%
W: 0.05-0.5% and
Sb: 0.05-0.5%
A marine steel material excellent in coating film life, having a composition containing one or more selected from the above. In Claim 1 or 2, steel materials are further mass%,
Nb: 0.005 to 0.20%,
V: 0.005 to 0.20%,
Ti: 0.005 to 0.20%,
REM: 0.02% or less,
Ca: 0.005% or less and B: 0.0003 to 0.0050%
A marine steel material excellent in coating film life which has a composition containing one or more selected from among them.