JP5413392B2 - Corrosion resistant steel for shipbuilding - Google Patents

Description

  The present invention relates to marine steel materials, and in particular, to improve the corrosion resistance of steel materials for ballast tanks used in a seawater corrosive environment from the viewpoint of extending the repair coating life and reducing the repair coating work.

  The ballast tank is in a severe corrosive environment because seawater enters and exits. Usually, the anticorrosion is combined with epoxy paint and cathodic protection. However, even if these anticorrosion measures are taken, the corrosion of the ballast tank is in a severe state. That is, when the ballast tank is filled with seawater, the portion that is completely immersed in seawater acts as an anticorrosion, and the progress of corrosion can be suppressed. However, the vicinity of the uppermost part of the ballast tank, particularly the back side of the upper deck, is not completely immersed in seawater and is in a state of splashing seawater. Therefore, in such a part, since the anticorrosion does not work and the steel plate is exposed to high temperature by sunlight, it becomes a severe corrosive environment and a severe corrosive state. Moreover, when there is no seawater in a ballast tank, it will be in a severe corrosion state by the effect | action of the residual adhering salt content of seawater.

  The coating film life of the ballast tank in such a severe corrosive environment is said to be about 10 years, which is half of the life of the ship (20 years). Therefore, for the remaining 10 years, safety must be maintained by repair painting. In ballast tanks, the severe corrosion caused by such a severe corrosive environment, and the work under adverse conditions of repair repainting in a narrow space resulting from this, is a serious problem. Development of corrosion-resistant steel that can achieve reduction in painting work is desired.

  On the other hand, the following have been proposed as countermeasures from the steel side regarding the corrosion resistance of the ballast tank.

  In Patent Document 1, P: 0.03 to 0.10%, Cu: 0.1 to 1.0%, Ni: 0.1 to 1.0%, steel material added with epoxy, pure epoxy, urethane resin The ballast tank which applied etc. is proposed. This is because the corrosion resistance of the base metal is improved, so that the adhesive deterioration life of the resin film is extended, and the ballast tank is made durable. And it has been proposed that maintenance can be made unnecessary for 20 to 30 years.

  Patent Document 2 adds Cr: 0.2 to 5%, and Patent Document 3 adds Cr: 0.5 to 3.5%, thereby improving corrosion resistance. A proposal has been made that it can contribute to maintenance-free.

  Patent Document 4 proposes that by adding Ni: 0.1 to 4.0%, the coating film damage resistance is improved, and maintenance costs such as repair coating can be significantly reduced.

Japanese Unexamined Patent Publication No. 7-34197 Japanese Patent Laid-Open No. 7-34196 JP-A-7-310141 JP 2002-266052 A

  However, in the technique of Patent Document 1, in order to improve the corrosion resistance of the base metal, the P content is relatively large as 0.03 to 0.10%, and there is a problem in weldability and weld toughness. Conceivable. Further, the technologies of Patent Documents 2 and 3 have a relatively high Cr content, and the technology of Patent Document 4 has a relatively high Ni content, both of which have the problem of high manufacturing costs.

  Therefore, the present invention has excellent corrosion resistance capable of avoiding the above-described deterioration of weldability, welded portion toughness and increase in manufacturing cost in order to contribute to the extension of the repair repaint life of the ship ballast tank and the reduction of the repair repaint work. It aims at providing the steel materials for ship ballast tanks.

  In order to find an effective element for improving corrosion resistance, the inventors melted and rolled steel materials added with various alloys, and collected 5 mm × 100 mm × 200 mm exposure test pieces from the respective steel plates. After shot blasting, zinc rich primer (about 15 μm) and tar epoxy resin paint (about 100 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 subjected to a dry and wet repeated test simulating the back of the upper deck of an actual ship's ballast tank, and the swelling of the coating film and the peeled area due to rust around the scratch were measured. The test period is 6 months.

  As a result, it has been found that the addition of W to steel significantly suppresses the formation of rust under the coating film, and is effective for coating film swelling and coating film peeling. Furthermore, it has been found that the effect can be further enhanced by addition of Ni and Mo and addition of Cu, Co, Sn and Sb. Furthermore, it has been found that optimization of the amounts of Ti and N is effective from the viewpoint of improving the toughness of the welded part in high heat input welding. The present invention was made by investigating the base metal mechanical properties and weld toughness of each alloy element, and further considering the cost.

  1. In the first invention, the component composition of steel is C: 0.03 to 0.25%, Si: 0.05 to 0.50%, Mn: 0.1 to 2.0%, P: in mass%. 0.025% or less, S: 0.01% or less, Al: 0.01 to 0.10%, W: 0.01 to 1.0%, comprising the remainder Fe and inevitable impurities Corrosion resistant steel for shipbuilding.

  2. The second invention is the corrosion-resistant steel for shipbuilding according to the first invention, further comprising Ni: 0.01 to 1.0% by mass% as a component composition of the steel.

  3. The third invention is a corrosion-resistant steel for shipbuilding according to the first invention or the second invention, characterized in that the composition of steel further includes Mo: 0.01 to 0.5% by mass. is there.

  4). 4th invention is Cu: 0.02-1.0% by mass% as a component composition of steel, Co: 0.02-1.0%, Sn: 0.001-0.3%, Sb: The corrosion-resistant steel for shipbuilding according to any one of the first to third inventions, further comprising one or more selected from 0.001 to 0.3%.

  5. According to a fifth aspect of the present invention, the component composition of steel is Nb: 0.002 to 0.05% in mass%, Ti: 0.002 to 0.05%, and V: 0.002 to 0.2%. The corrosion-resistant steel for shipbuilding according to any one of the first to fourth inventions, further comprising one or more selected.

  6). A sixth invention further includes B: 0.0003 to 0.003% by mass% as a component composition of steel, and is for shipbuilding according to any one of the first to fifth inventions Corrosion resistant steel.

  7). 7th invention contains further 1 type or 2 types chosen from Ca: 0.0002-0.01% and REM: 0.001-0.01% by mass% as a component composition of steel. A corrosion-resistant steel for shipbuilding according to any one of the first to sixth inventions.

  8). In the eighth invention, the component composition of steel is C: 0.03 to 0.25% in mass%, Si: 0.05 to 0.50%, Mn: 0.1 to 2.0%, P: 0.025% or less, S: 0.01% or less, Al: 0.01-0.10%, W: 0.01-1.0%, Ti: 0.005-0.025%, N: 0 It is a corrosion-resistant steel for shipbuilding excellent in high heat input welding toughness, characterized by comprising .0030-0.0065% and comprising the remainder Fe and inevitable impurities.

  9. The ninth invention is a corrosion resistance for shipbuilding excellent in high heat input welding toughness according to the eighth invention, wherein the composition of steel further includes Ni: 0.01 to 1.0% by mass%. It is steel.

  10. A tenth aspect of the present invention further includes Mo: 0.01 to 0.5% by mass% as a component composition of steel, and the large heat input welding toughness according to the eighth aspect or the ninth aspect of the invention Excellent corrosion resistant steel for shipbuilding.

  11. In the eleventh aspect of the present invention, the component composition of steel is Cu: 0.02 to 1.0%, Co: 0.02 to 1.0%, Sn: 0.001 to 0.3%, Sb in mass%. : Excellent in high heat input welding toughness according to any one of the eighth to tenth inventions, further comprising one or more selected from 0.001 to 0.3% Corrosion resistant steel for shipbuilding.

  12 The twelfth invention further includes one or two kinds selected from Nb: 0.002 to 0.05% and V: 0.002 to 0.2% by mass% as a component composition of steel. A shipbuilding corrosion-resistant steel excellent in high heat input welding toughness according to any one of the eighth to eleventh inventions.

  13. According to a thirteenth aspect of the invention, in any one of the eighth to twelfth aspects of the invention, wherein the composition of steel further includes B: 0.0003 to 0.003% by mass%. It is a corrosion-resistant steel for shipbuilding with excellent high heat input welding toughness.

  14 14th invention further contains 1 type or 2 types chosen from Ca: 0.0002-0.01% and REM: 0.001-0.01% by mass% as a component composition of steel. A shipbuilding corrosion-resistant steel excellent in high heat input welding toughness according to any one of the eighth to thirteenth inventions.

  According to the present invention, a relatively small amount of W added to the steel material exhibits excellent corrosion resistance in the corrosive environment of the ballast tank. Therefore, the ship ballast tank is suppressed while suppressing the increase in manufacturing cost and ensuring weldability and welded portion toughness. This greatly contributes to the extension of the repair and repaint life and the reduction of repair and repaint operations.

The component composition and manufacturing method of the steel material of the present invention will be specifically described below.
1. The reason why the component composition is limited will be described. In addition, all the content% of each element in a component composition means the mass%.

C: 0.03-0.25%
C is an element that increases the strength of the steel material. In the present invention, the content of 0.03% or more is required to obtain a desired strength. On the other hand, the content exceeding 0.25% deteriorates the toughness of HAZ (welding heat affected zone). For this reason, C was limited to the range of 0.03-0.25%. In addition, from a viewpoint of intensity | strength and toughness, Preferably it is 0.05 to 0.20%.

Si: 0.05 to 0.50%
Si is an element that acts as a deoxidizer and increases the strength of the steel material. In the present invention, it is preferably contained in an amount of 0.05% or more, but the content exceeding 0.50% deteriorates the toughness of the steel. Let For this reason, Si was limited to the range of 0.50% or less.

Mn: 0.1 to 2.0%
Mn is an element that increases the strength of the steel material, but the content exceeding 2.0% decreases the toughness and weldability of the steel. For this reason, Mn was limited to 2.0% or less. Preferably it is 0.5 to 1.6%.

P: 0.025% or less P deteriorates the base metal toughness of steel, and further the weldability and weld zone toughness. Therefore, it is preferable to reduce as much as possible, but up to 0.025% is acceptable. If the content exceeds 0.025%, the base metal toughness and the weld zone toughness are significantly reduced. For this reason, P was limited to 0.025% or less.

S: 0.01% or less Since S is a harmful element that deteriorates toughness and weldability, it must be reduced as much as possible. Therefore, it was limited to 0.01% or less.

Al: 0.01 to 0.10% or less Al is added as a deoxidizer and contains 0.01% or more, but if it exceeds 0.10%, the corrosion resistance is remarkably deteriorated. Therefore, 0.10% was made the upper limit.

W: 0.01 to 1.0%
W is the most important element in the steel of the present invention because it significantly suppresses rust formation under the coating film. The effect is that WO ₄ ²⁻ is formed in the rust as the steel sheet corrodes under the coating film, and the presence of this WO ₄ ²⁻ suppresses the entry of chloride ions to the steel sheet surface. Further, hardly soluble FeWO ₄ is formed at a site where the pH is lowered, such as the anode portion on the surface of the steel plate, and the presence of this FeWO ₄ suppresses the penetration of chloride ions into the steel plate surface. By suppressing the penetration of chloride ions into the steel sheet surface, corrosion of the steel sheet is suppressed and rust formation is suppressed. The above effect becomes remarkable when the content of W is 0.01% or more, and when 1.0% or more, the effect is saturated. For this reason, W content was limited to 0.01 to 1.0% of range.

Ni: 0.01 to 1.0%
Ni is an important element in the steel of the present invention because it suppresses the formation of rust under the coating film.
This effect densifies rust particles and suppresses the penetration of water, oxygen, and chloride ions into the steel plate surface. By suppressing the penetration of the above corrosion factors into the steel sheet surface, corrosion of the steel sheet is suppressed and rust formation is suppressed. This effect is exhibited when the content of Ni is 0.01% or more, and the effect is saturated when the content is 1.0% or more. For this reason, Ni content was limited to the range of 0.01 to 1.0%.

Mo: 0.01 to 0.5%
Mo can be used supplementarily because it has the same effect as W and slightly suppresses the formation of rust under the coating film. The effect is that MoO ₄ ²⁻ is formed in the rust as the steel sheet corrodes under the coating film, and the presence of MoO ₄ ²⁻ suppresses the entry of chloride ions to the steel sheet surface. This effect is manifested when Mo: 0.01% or more is contained, and the effect is saturated at 0.5% or more. For this reason, Mo content was limited to 0.01 to 0.5% of range.

One or two of Cu: 0.02-1.0%, Co: 0.02-1.0%, Sn: 0.001-0.3%, Sb: 0.001-0.3% More than seed Cu, Co, Sn, Sb suppresses the formation of rust under the coating film, but the effect is not as great as the above W, Ni, Mo. However, it can be used supplementarily from the viewpoint of suppressing rust formation.
Cu and Co have an effect of inhibiting rust formation in the range of 0.02 to 1.0% from the action of inhibiting chloride ion intrusion due to rust grain refinement. The mechanism of action of Sn and Sb is not clear, but 0.001% or more can be contained to suppress rust formation by adding 0.001% or more. However, if it exceeds 0.3%, the base metal toughness and the HAZ toughness are remarkably deteriorated. Therefore, it was set as 0.001 to 0.3% of range, respectively.

One or more of Nb: 0.002 to 0.05%, Ti: 0.002 to 0.05%, V: 0.002 to 0.2% Nb, Ti, and V are all It is an element that increases the strength of the steel material, and can be selected and contained as necessary. In order to acquire such an effect, it is preferable to contain Nb: 0.002%, Ti: 0.002%, V: 0.002%, respectively. On the other hand, if Nb: 0.05%, Ti: 0.05%, and V: 0.2% are contained, the toughness deteriorates. For this reason, it is good to set it as Nb: 0.05% or less, Ti: 0.05% or less, and V: 0.2% or less.

B: 0.0003 to 0.003%
B is an element that increases the strength of the steel material and can be contained as required. In order to acquire such an effect, it is preferable to contain 0.0003% or more. On the other hand, if the content exceeds 0.003%, the toughness deteriorates. For this reason, B is preferably 0.0003 to 0.003%.

Ca: 0.0002 to 0.01%, REM: One or two of 0.001 to 0.01% Ca and REM are both elements that contribute to the improvement of HAZ toughness, as needed Can be selected and contained. Such an effect becomes remarkable when Ca is contained at 0.0002% and REM: 0.001% or more, but when it is contained exceeding Ca: 0.01% and REM: 0.01%, toughness deteriorates. . For this reason, it is good to set it as the range of Ca: 0.01% and REM: 0.01% or less.

Ti: 0.005-0.025%, N: 0.0030-0.0065%
Ti and N form TiN during solidification of molten steel. TiN prevents austenite grains from coarsening due to heating during welding, and generates a large amount of fine ferrite. This action improves the toughness of the high heat input weld heat affected zone. When Ti is less than 0.005% and N is less than 0.0030%, the amount of TiN formed during solidification of molten steel is small, and most of TiN is dissolved by heating during high heat input welding. Cannot be obtained. On the other hand, if Ti exceeds 0.025%, the base material toughness is adversely affected. If the N content exceeds 0.0065%, continuous casting cracks occur, toughness deteriorates due to the formation of island martensite in the heat affected zone, and the toughness of the weld metal due to dilution from the base metal to the weld metal. Causes deterioration. Therefore, Ti: 0.005 to 0.025%, N: 0.0030 to 0.0065% range.
In the steel material of the present invention, the balance other than the above components is Fe and inevitable impurities.

2. About a manufacturing method Below, the preferable manufacturing method of the steel materials of this invention is demonstrated. First, it is preferable that molten steel having the above-described component composition is melted by an ordinary melting method such as a converter or an electric furnace, and is made into a steel material by an ordinary known casting method such as a continuous casting method or an ingot-making method. It goes without saying that treatments such as ladle refining and vacuum degassing may be added to the molten steel.

  Next, the obtained steel material is preferably heated to a temperature of 1050 to 1250 ° C. from the viewpoint of preventing grain coarsening, and then hot-rolled to a desired size or shape, or the temperature of the steel material is hot-rolled. When the temperature is as high as possible, it can be immediately hot-rolled into a steel material having a desired size and shape without heating or with a level of soaking.

  In the present invention, from the viewpoint of securing strength, in hot rolling, it is preferable to set the hot finish rolling end temperature and the cooling rate after the hot finish rolling end to an appropriate range. Here, the finish temperature of hot finish rolling is preferably 700 ° C. or higher, and after the finish of hot finish rolling, air cooling or accelerated cooling at a cooling rate of 100 ° C./less can be performed. In addition, a reheating treatment can be performed after cooling.

  Steel of the chemical composition shown in Table 1 was melted in a converter and made into a slab by a continuous casting method. This slab was inserted into a heating furnace and heated to 1150 ° C., and then hot-rolled to a thick steel plate (25 mm thick × 2500 mm width). The base material tensile characteristics and impact characteristics of the steel sheets thus obtained were investigated. Moreover, the impact characteristics (reproduced HAZ impact characteristics) of HAZ reproduced by applying a thermal cycle corresponding to heat input of 150 kJ / cm in submerged arc welding were evaluated. As a result, as shown in Table 2, the steel No. In No. 20, the base metal impact characteristics and the reproduced HAZ impact characteristics deteriorated.

  Next, an exposure test piece of 5 mm × 100 mm × 200 mm was taken from each steel plate. After shot blasting to these test pieces, a zinc rich primer (about 15 μm) and a tar epoxy resin paint (about 200 μm) were applied. Thereafter, a 80 mm long scratch reaching the surface of the test piece was added with a cutter knife. These test pieces were mounted on the back of the ballast tank upper deck of an actual ship and subjected to an exposure test. The exposure period is 2 years, and the environment in this ballast tank is one cycle: the period when seawater is in the ballast tank: about 20 days, the period when seawater is not in the ballast tank: about 20 days It was an environment. After the exposure test, the swelling of the coating film and the peeled area due to rust around the scratch were measured. And the ratio with respect to base steel (steel No. 18) was computed. The results are shown in Table 2.

  The area ratio of (steel No. 1-17) of this invention steel is 60% or less, and it turns out that the steel material of this invention has the outstanding corrosion resistance. On the other hand, the area ratios of the comparative examples (steel Nos. 19, 21, and 22) that are out of the scope of the present invention are larger than those of the present invention examples. In the comparative example (steel No. 20), since the W amount is within the range of the present invention, the area ratio shows a small value of 43%, but as described above, the base metal impact characteristics and the reproduced HAZ impact characteristics are deteriorated. .

  In addition, from the viewpoint of improving high heat input welding toughness, steels having chemical components shown in Table 3 with optimized amounts of Ti and N are melted and rolled in the same manner as in Example 1 to obtain thick steel plates (25 mm thickness × 2500 mm width). The tensile properties and impact properties of the base metal were investigated, and the impact properties (reproduced HAZ impact properties) of the HAZ reproduced by applying a heat cycle equivalent to a heat input of 150 kJ / cm in submerged arc welding were also evaluated.

  Furthermore, 5 mm × 100 mm × 200 mm exposed test pieces were collected from each steel plate, and after being shot blasted to these test pieces, zinc rich primer (about 15 μm) and tar epoxy resin paint (about 200 μm) were applied. Then, the test piece which added the scratch of 80 mm length which reaches to the ground-iron surface of a test piece with a cutter knife was attached to the back of the ballast tank upper deck of the actual ship, and used for the exposure test. The results are shown in Table 4.

  Steel No. which is the steel of the present invention. Nos. 23 to 31 showed extremely excellent values for the reproduced HAZ impact characteristics and also showed excellent corrosion resistance in the exposure test.

  Since the corrosion-resistant steel for shipbuilding of the present invention has excellent paint damage resistance, it can be applied to a ballast tank of a ship which is a severe corrosive environment. It can also be used in wet environments similar to ballast tanks.

Claims (7)

The component composition of steel is C: 0.03 to 0.25%, Si: 0.05 to 0.50%, Mn: 0.1 to 2.0%, P: 0.025% or less in mass%. S: 0.01% or less, Al: 0.01 to 0.10%, W: 0.06 to 1.0%, Ti: 0.011 to 0.025%, N: 0.0045 to 0.0065 A corrosion-resistant steel for shipbuilding excellent in high heat input welding toughness, characterized by comprising the remaining Fe and inevitable impurities.   The corrosion resistant steel for shipbuilding excellent in high heat input welding toughness according to claim 1, further comprising Ni: 0.01 to 1.0% by mass as a component composition of the steel.   The corrosion resistant steel for shipbuilding excellent in high heat input weld toughness according to claim 1 or 2, further comprising Mo: 0.01 to 0.5% by mass% as a component composition of the steel.   As a component composition of steel, Cu: 0.02-1.0%, Co: 0.02-1.0%, Sn: 0.001-0.3%, Sb: 0.001-0. The corrosion resistant steel for shipbuilding excellent in high heat input welding toughness according to any one of claims 1 to 3, further comprising one or more selected from 3%.   The steel composition further comprises one or two selected from Nb: 0.002 to 0.05% and V: 0.002 to 0.2% by mass% as a component composition of steel. Item 5. A corrosion-resistant steel for shipbuilding excellent in high heat input weld toughness according to any one of Items 1 to 4.   The corrosion resistance for shipbuilding excellent in high heat input toughness according to any one of claims 1 to 5, further comprising B: 0.0003 to 0.003% by mass% as a component composition of steel. steel.   The steel composition further includes one or two kinds selected from Ca: 0.0002 to 0.01% and REM: 0.001 to 0.01% by mass%. Item 7. A corrosion-resistant steel for shipbuilding excellent in high heat input welding toughness according to any one of Items 1 to 6.