JP3879581B2 - Marine steel with excellent coating film peel resistance and high heat input weld toughness, and method for producing the same - Google Patents

Description

【００３５】
【表２】

【００３６】
【発明の効果】
本発明の船舶用鋼材は、優れた耐塗膜剥離性および大入熱溶接部靭性を有し、苛酷な腐食環境に置かれるバラストタンクへ適用した場合に、溶接施工の高能率化に加え、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るという効果を奏し、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 a marine steel material excellent in coating film peeling resistance and large heat input weld toughness, and a method for producing the same, and in particular, used as a constituent material for ballast tanks and the like used in severe environments such as high temperature and high humidity. The present invention relates to a marine steel material excellent in coating film peeling resistance and high heat input weld toughness, and a method for producing the same.
〔Definition of terms〕
In the present invention, the steel material is a general term for steel plates (generic terms for thick steel plates and thin steel plates) and shape steels, and large heat input welding is welding with a heat input of 60 kJ / cm or more, and also contains components. % and ppm are, respectively it mass percentage according to the amount, means mass per million, also, REM means rare earth elements.
[0002]
[Prior art]
Normally, the anti-corrosion of the ballast tank uses a tar epoxy resin paint and an anti-corrosion in combination. However, the ballast tank is exposed to a severe corrosive environment because seawater enters and exits the tank. Especially in tankers, the following periodic corrosive environment occurs.
[0003]
When transporting crude oil from the Middle East to Japan, the ballast tank is almost full of water in order to maintain the balance of the ship and ensure navigation safety on the outbound route toward the Middle East with emptying the oil tank. The corrosive environment at this time is that the middle to lower part of the ballast tank is in seawater, and the upper part is in a state close to a splash zone. On the other hand, on the return trip to Japan where the oil tank is filled with crude oil, the ballast tank is emptied by emptying the seawater. At this time, the inside of the ballast tank becomes a high temperature (about 40 ° C) and high humidity environment by the seawater remaining on the bottom of the ship and the heat from the deck. Since a tanker takes about 80 days to make one round trip, the ballast tank is exposed to a severe corrosive environment due to the entry and exit of seawater at intervals of about 80 days.
[0004]
When the ballast tank is filled with seawater, the seawater immersion part is hardly corroded by the anti-corrosion effect, but the non-immersion parts such as the top of the ballast tank and the back side of the upper deck are severely called splash zones in addition to the high temperature. Under corrosive environment. On the other hand, when there is no seawater in the ballast tank, it becomes a hot and humid environment, and the anticorrosive effect cannot be expected, and only the tar epoxy resin paint is protected. Further, when the ballast tank is filled with seawater, pebbles, dust, etc. contained in the seawater also enter together, and scratches (scratches) are generated in the coating film, so that corrosion progresses from the scratch portion.
[0005]
For this reason, the paint film life of the ballast tank is about 10 years, which is about half of the ship life (20 years), and the remaining about 10 years need to be maintained by repair painting. However, the repair coating not only requires a corresponding cost, but also has a problem that it is difficult to secure workers because the interior of the ballast tank is in a poor painting work environment.
[0006]
Since the ballast tank has such a problem, it is desired to develop a marine steel material capable of improving from the steel surface, that is, extending the life of the coating film.
By the way, in the field of seawater-resistant steel intended for use in the marine environment, Cr, Ni, Mo, Cu, etc. are added to improve the corrosion resistance. Various seawater-resistant steels for welded structures have been developed. These are used for sluices, steel sheet piles, buoys, piers, and the like.
[0007]
As such seawater-resistant steel, steel materials described in Japanese Patent Application Laid-Open No. 51-25420 are known, but the use of these steel materials is the above-mentioned marine structures and port facilities, and the usage environment is as follows. Seawater at room temperature (about 25 ° C) or lower. Japanese Laid-Open Patent Publication No. 63-255341 proposes a corrosion-resistant steel sheet for welded structures with improved salt damage resistance in the atmospheric environment. The same applies to this.
[0008]
Therefore, in a severe corrosive environment where the temperature and humidity are high, such as in a ballast tank, it cannot be used without a paint film, and the life of the paint film is also different from that of ordinary ship steels. It will only be comparable.
On the other hand, steel structures in the fields of shipbuilding, architecture, and civil engineering are generally often assembled by joining steel materials by welding. Steel materials used in such welded structures are required to have excellent weld toughness as well as base metal toughness from the viewpoint of ensuring safety.
[0009]
However, in recent years, with the increase in the size of welded structures, improvement in welding efficiency has been demanded from the viewpoint of improving the construction efficiency of the structure and reducing the construction cost, and an increase in welding heat input has been aimed at. It is the toughness of the weld bond. The weld bond portion is exposed to a high temperature just below the melting point during welding, the crystal grains are most likely to be coarsened, and the cooling rate is lowered as the welding heat input increases, and a fragile upper bainite structure is likely to be formed. Further, in the weld bond portion, an embrittled structure such as a Widmann-Stätten structure or an island martensite is easily generated, and the toughness is likely to be lowered.
[0010]
In order to solve this problem, the following proposals have been made as means for improving the toughness of the welded heat affected zone or the welded heat affected zone in the vicinity thereof.
・ TiN is finely dispersed in steel and combined with MnS or REM oxysulfide to suppress austenite grain coarsening (JP-A-2-250917, JP-A-2-254118, JP-B-3-53367) No.)
・ Combined addition of REM and Ti to disperse fine particles in steel to suppress austenite grain growth (JP-A-60-184663)
・ Ti oxide is finely dispersed and used as a nucleation site for ferrite transformation (JP 60-245768, JP 61-79745)
・ Using BN precipitated on TiN during the cooling process during welding as the core of ferrite transformation (Japanese Patent Laid-Open No. 61-253344)
・ Including Ti and a sufficient amount (0.05 to 0.10%) of Al to thoroughly reduce solid solution N, and using Ca oxide as finely dispersed particles (Japanese Patent Laid-Open No. 2000-107177)
· Addition of Ca or REM to control sulfide morphology (Japanese Patent Laid-Open No. 60-204863, Japanese Patent Publication No. 4-14180)
[0011]
[Problems to be solved by the invention]
As mentioned above, conventional seawater-resistant steel only exhibits corrosion resistance and corrosion resistance comparable to those of ordinary marine steels in a severely corrosive environment that is hot and humid, such as in a ballast tank. There are no material properties that can be used.
On the other hand, regarding the toughness of the welded part, although various improvement means have been proposed as described above, there are the following problems.
-With the means using Ti oxide, it is quite difficult to disperse the oxide uniformly and finely, and the variation in weld toughness becomes large.
・ With TiN-based means, TiN dissolves and loses grain refinement under heat input conditions in which the vicinity of the weld bond is exposed to high temperatures for a long time, and the weld grain toughness is not improved. An embrittlement structure is generated due to the increase in solid solution Ti and solid solution N, and the toughness of the welded portion is remarkably lowered.
-In the means using Al and Ca, since the amount of addition increases, the oxides cluster, and the toughness may be lowered as a starting point of fracture.
-The means for controlling sulfide morphology with Ca and REM has the problem that it is difficult to ensure high toughness at high heat input welds with welding heat input exceeding 60kJ / cm2.
[0012]
In view of the current state of the prior art described above, the present invention is resistant to peeling of the coating film even in severe corrosive environments, particularly in a high temperature and high humidity environment, and has a high heat input weld toughness that is stable at a high level and has a high heat input resistance. An object of the present invention is to provide a marine steel material having excellent weld toughness and a method for producing the same.
[0013]
[Means for Solving the Problems]
In order to improve the peel resistance of the coating film, the present inventors produced a large number of exposed test pieces containing various alloy elements at various ratios, and these test pieces were stored in an actual ballast tank for 2 years. The following findings were obtained in the exposure test.
1-1) This test piece is mainly Cu-less and Ni is added, and the swelling of the paint film due to rust from paint film scratch is remarkably reduced. For example, a steel material containing 1.0% Ni and Cu reduced to 0.02% has a swollen area reduced to 1/10 of the conventional steel.
[0014]
1-2) 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, these alloy elements have an effect of suppressing the progress of corrosion from the scratch portion and reducing the damage to the coating film.
On the other hand, in order to stabilize the toughness of high heat input welds, various factors affecting the toughness were studied and studied, and the following knowledge was obtained.
[0015]
2-1) The toughness of high heat input welds, especially welded bonds, is greatly influenced by the presence or absence of embrittlement.
2-2) Formation of the embrittled structure can be prevented by suppressing the coarsening of austenite in the region heated to a high temperature and by finely dispersing ferrite-forming nuclei that promote ferrite transformation during cooling. Conventionally, since these were insufficient, it was not possible to achieve high level stabilization of weld zone toughness.
[0016]
2-3) In order to finely disperse ferrite-forming nuclei, it is effective to use Ca, which plays a role in sulfide morphology control, to crystallize CaS during solidification. Since CaS crystallizes at a lower temperature than oxides, fine and uniform dispersion in the solidified steel is possible.
2-4) In order to crystallize CaS, it is necessary to adjust the dissolved oxygen content in the molten steel immediately before Ca addition to 30 ppm or less.
[0017]
2-5) Ca (or S) is added to the molten steel adjusted to below 30ppm of dissolved oxygen.
ACR = (Ca-(0.18 + 130 x Ca) x O) / ( 1.25 x S )
(Ca, O, and S are the contents of each alloy element ( mass %))
By adding in an amount of 0.00 to 1.00, a solid solution S amount can be ensured after CaS crystallization, and a composite sulfide in which MnS is precipitated on the surface of CaS can be formed. MnS has the ability to form ferrite nuclei, and further, a Mn dilute band is formed around it, so that the ferrite transformation is further promoted.
[0018]
2-6) Ferrite transformation is further promoted by precipitation of ferrite-forming nuclei such as TiN, BN and AlN on MnS. The present invention has been made on the basis of the above findings and further studied, and the gist thereof is as follows.
[1] By mass%, C: 0.001 to 0.025%, Si: 0.60% or less, Mn: 0.10 to 3.0%, P: 0.005 to 0.030%, S: 0.0005 to 0.01%, Al: 0.10% or less, Cu: 0.10 %: Ni: 0.10 to 4.0%, Ti: 0.005 to 0.030%, N: 0.0030 to 0.0070%, O: 0.0030% or less, Ca: 0.0005 to 0.0030%, comprising the balance Fe and inevitable impurities, and A marine steel with excellent coating peel resistance and high heat input weld toughness characterized by the following ACR exceeding 0.00 and less than 1.00.
[0019]
Record
ACR = (Ca-(0.18 + 130 x Ca) x O) / ( 1.25 x S )
However, Ca, O, and S are component contents of each element ( mass %)
[2] Further, by mass%, one or more selected from Mo: 0.05 to 0.50%, Co: 0.05 to 0.50%, W: 0.05 to 0.50%, Sb: 0.05 to 0.50% [1] A marine steel material excellent in coating film peeling resistance and high heat input weld zone toughness.
[3] The coating film peel resistance and large heat input according to [1] or [2], further comprising one or more of the following (a) to (c) by mass%: Marine steel with excellent weld toughness.
[0020]
(A) Nb: 0.005 to 0.20%, V: One or two selected from 0.005 to 0.20% (b) REM: 0.004 to 0.02%
(C) B: 0.0003 to 0.0050%
[4] By mass%, C: 0.001 to 0.025%, Si: 0.60% or less, Mn: 0.10 to 3.0%, P: 0.005 to 0.030%, S: 0.0005 to 0.01%, Al: 0.10% or less, Cu: 0.10 %: Ni: 0.10 to 4.0%, Ti: 0.005 to 0.030%, N: 0.0030 to 0.0070%, O: 0.0030% or less, Ca: 0.0005 to 0.0030%, or, in addition, (A) to (D In the method of manufacturing a steel material in which a steel material that has been melted and solidified to a component composition containing one or more of the above is hot-rolled, Ca is added to the molten steel immediately after the dissolved oxygen content is adjusted to 30 ppm or less. A method for producing marine steel having excellent coating film peeling resistance and high heat input weld toughness, characterized by adding an amount of less than 1.00.
[0021]
(A) Mo: 0.05 to 0.50%, Co: 0.05 to 0.50%, W: 0.05 to 0.50%, Sb: One or more selected from 0.05 to 0.50% (B) Nb: 0.005 to 0.20% V: One or two selected from 0.005 to 0.20% (C) REM: 0.004 to 0.02%
(D) B: 0.0003 to 0.0050%
ACR = (Ca-(0.18 + 130 x Ca) x O) / ( 1.25 x S )
However, Ca, O, and S are component contents of each element ( mass %)
[0022]
DETAILED DESCRIPTION OF THE INVENTION
First, the reasons for limiting the composition of the steel of the present invention will be described.
C: 0.001 to 0.025%
C is an element effective for improving the strength. However, if the content is less than 0.001%, the effect is poor. On the other hand, if it exceeds 0.025%, the base metal toughness and weld toughness are deteriorated. The range was 0.025%.
Si: 0.60% or less
Si is an element useful not only as a deoxidizer but also in terms of improving the strength of the steel. However, if excessively contained, the base metal toughness and weld zone toughness deteriorate, so the content was made 0.60% or less. . Preferably it is 0.15 to 0.50% of range.
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 the desired strength. However, if the content exceeds 3.0%, the base material toughness and weld zone toughness are adversely affected, so the range was made 0.10 to 3.0%. Preferably it is 0.10 to 2.0% of range.
P: 0.005 to 0.030%
P needs to be contained in an amount of 0.005% or more in order to form a dense rust, but an excessive content deteriorates the base metal toughness and weld zone toughness, so it was made 0.005 to 0.03%.
S: 0.0005-0.01%
S needs to be contained in an amount of 0.0005% or more in order to cause CaS to crystallize in a finely dispersed state during solidification of molten steel and to precipitate MnS or TiN or the like thereon to function as ferrite nuclei. Further, since excessive inclusion deteriorates the base metal toughness and the welded portion toughness, it is set to 0.0005 to 0.01%. In addition, Preferably it is 0.0010 to 0.0050% of range.
Al: 0.10% or less
Al is added as a deoxidizer, but if it exceeds 0.01%, the weld toughness is adversely affected, so it was limited to 0.10% or less.
Cu: 0.10% 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, which is the application target in the present invention, is in a state of being almost wet with high temperature and humidity, and in such an environment, Cu does not work effectively but acts adversely.
[0023]
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 the steel due to the dissolution activation of Cu. On the other hand, in a constantly wet state, the corrosion reaction of the steel due to Cu dissolution activation is greater than the protective effect of the rust layer due to the Cu rust densification promoting action, and thus the corrosion of the steel proceeds. If the corrosion of steel progresses, the swelling of the coating also progresses.
[0024]
Here, when the Cu content exceeds 0.10%, the corrosion of the steel, and thus the swelling of the coating film proceeds, so the Cu content is limited to 0.10% or less.
Ni: 0.10 to 4.0%
Ni is the most important element in the present invention as an element that remarkably suppresses blistering. The effect is exhibited by densifying the rust particles and preventing the penetration of corrosion factors such as water, oxygen, and chlorine into the ground iron. Thus, after a certain amount of rust is formed, this rust layer prevents the penetration of corrosion factors, thereby suppressing 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 0.10%. On the other hand, when the Ni content exceeds 4.0%, the effect is saturated and rather disadvantageous economically, so the Ni content is limited to 0.1 to 4.0%.
Ti: 0.005 to 0.030%
Ti has a strong affinity with N and precipitates as TiN, thereby suppressing the coarsening of austenite grains in the weld heat affected zone, or contributes to increasing the toughness of the weld heat affected zone as a ferrite nucleus. Such an effect is recognized when the content is 0.005% or more. However, if the content exceeds 0.030%, the TiN particles are coarsened and the effect cannot be expected. For this reason, Ti was limited to the range of 0.005 to 0.030%.
N: 0.0030-0.0070%
N combines with Ti and precipitates as TiN to suppress the coarsening of austenite grains in the weld heat affected zone, or contributes to increasing the toughness of the weld heat affected zone as a ferrite transformation nucleus. In order to secure the necessary amount of TIN having such an effect, N needs to be contained in an amount of 0.0030% or more. On the other hand, if the content exceeds 0.0070%, the amount of solute N increases in the region heated to a temperature at which TIN is melted by welding heat, and the toughness is significantly reduced. For this reason, N was limited to the range of 0.0030 to 0.0070%.
O: 0.0030% or less O is contained as an unavoidable impurity, exists as an oxide in steel, and lowers cleanliness. Therefore, it is preferably reduced as much as possible in the present invention. If the O content exceeds 0.0030%, CaO inclusions are coarsened, which adversely affects toughness. Further, in the present invention, in order to crystallize Ca as CaS, O having a strong binding force with Ca is strengthened in degassing or added with a deoxidizing agent before adding Ca. It is preferable to reduce O to 0.0030% or less.
Ca: 0.0005 to 0.0030%
Ca is an element that contributes to improving the toughness of steel by controlling the form of sulfide. In order to exert such an effect, it is necessary to contain at least 0.0005%, but even if it exceeds 0.0030%, the effect is saturated. For this reason, the Ca content is limited to a range of 0.0005 to 0.0030%.
[0025]
Further, according to the production method of the present invention, which will be described later, Ca is finely and uniformly dispersed in the steel as CaS and combined with MnS to act as ferrite nuclei, contributing to the improvement of weld toughness.
ACR: More than 0.00 and less than 1.00
ACR = (Ca- (0.18 + 130 × Ca) × O) / (1.25 × S); however, Ca, O, S component content of each element (mass%)
When the ACR is 0.00 or less, CaS does not crystallize at the melting stage, so MnS does not become a composite sulfide with CaS but precipitates alone and is present in the steel material in a form stretched by rolling. As a result, the toughness of the welded heat-affected zone is not improved. On the other hand, when the ACR is 1.00 or more, S is completely fixed by Ca, and MnS acting as a ferrite nuclei does not precipitate on CaS, so that the improvement of the weld heat affected zone toughness cannot be achieved. The fine dispersion state of composite sulfide in which MnS is deposited on CaS is realized only when the ACR is more than 0.00 and less than 1.00. This composite sulfide functions as a ferrite formation nucleus, the structure of the weld heat affected zone is refined, and the weld heat affected zone toughness is improved.
[0026]
Although the essential components have been described above, in the present invention, in addition to these essential components, the following components can be appropriately contained.
Mo, Co, W, Sb: 0.05-0.50%
Mo, Co, W, and Sb all have the effect of suppressing the swelling of the coating film, but the effect is small when the content is less than 0.05%, while the effect is saturated when the content exceeds 0.50%, which is rather economically disadvantageous. Therefore, it is preferable to contain these elements in the range of 0.05 to 0.50% regardless of whether they are added alone or in combination.
Nb, V: 0.005 to 0.20%
Nb and V are elements that increase the strength of the steel material. 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. Even if it is added in any of the composites, it is preferably contained in the range of 0.005 to 0.20%.
REM: 0.004 to 0.02%
REM contributes to the improvement of weld toughness, but if the content is less than 0.004%, the effect of addition is poor. On the other hand, if it exceeds 0.02%, the cleanliness of the steel deteriorates, so the range of 0.004 to 0.02% It is preferable to contain.
B: 0.0003-0.0050%
B is an element advantageous for improving the strength. However, if the content is less than 0.0003%, the effect of addition is poor. On the other hand, if it exceeds 0.0050%, the base metal toughness and weld toughness are deteriorated, so 0.0003 to 0.0050 It is preferable to make it contain in the range of%.
[0027]
Next, the manufacturing method of this invention steel material is demonstrated.
In this manufacturing method, steel is melted by the usual method such as a converter or an electric furnace so as to have the above component composition, and then a slab material such as a slab is formed by a continuous casting method or an ingot forming method. Moreover, you may implement vacuum degassing smelting etc. in the case of melting.
There are two points to keep in mind when melting.
[0028]
The first point is to adjust the dissolved oxygen content in the molten steel immediately before Ca addition to 0.0030% or less. Thereby, the formation of Ca oxide is suppressed and the crystallization of CaS is promoted. Since CaS crystallizes in molten steel at a lower temperature than oxides, it can be finely and uniformly dispersed in the slab after solidification. Such finely dispersed CaS particles are combined with MnS to act as ferrite nuclei during welding and contribute to improving weld toughness.
[0029]
The second point is that, after satisfying the first point, Ca is added to the molten steel in such an amount that the ACR is more than 0.00 and less than 1.00. By carrying out like this, the structure | tissue of a welding heat affected zone can be refined | miniaturized for the reason mentioned above, and a weld heat affected zone toughness can be improved. In addition, in addition of Ca, what is necessary is just to monitor S content in molten steel and to determine Ca addition amount according to it. Moreover, when S runs short in molten steel, you may add this shortage of S.
[0030]
About the molten steel component adjustment method other than these two points to keep in mind, a normal steel refining method may be used.
Next, the obtained slab material is hot-rolled to obtain a steel material having a desired shape. The material heated in a heating furnace or the like may be rolled, or the heating may be omitted and the hot piece being cooled after solidification may be rolled as it is. The hot rolling method is not particularly limited in the present invention, and an appropriate method may be selected from normal methods.
[0031]
【Example】
Steels having the composition shown in Table 1 were melted in a converter and made into slabs by a continuous casting method. Next, these slabs were heated to 1150 ° C. and then hot rolled to form steel plates (thick steel plates) 25 mm thick × 2500 mm wide.
JISZ2201 No. 4 test piece and JISZ2202 V-notch test piece were sampled from the C direction at the thickness 1/4 position of these steel plates, and the tensile properties and impact properties were investigated.
[0032]
In addition, as a high heat input weld zone toughness, a reproducible thermal cycle equivalent to 1 mm of weld heat affected zone with a heat input of 100 kJ / cm (1 mm from the fusion line on the base metal side) was given, and at 0 ° C by Charpy impact test The absorption energy vE _{0 of} was measured.
In addition, 5 mm x 100 mm x 200 mm exposure test specimens were collected from these steel sheets, and after shot blasting, a zinc rich primer was applied to a coating thickness of about 15 μm, and then a tar epoxy resin paint was applied. Was applied to a coating thickness of about 200 μm. Thereafter, a scratch having a length of 80 mm reaching the surface of the test piece with a cutter knife was put into the coating film. These test pieces were mounted in an actual ship's ballast tank and subjected to a two-year exposure test. The environment in this ballast tank was a wet and dry environment with one cycle of about 40 days of wet season with seawater and about 40 days of dry season without seawater. After the exposure test, the swollen area of the coating film due to rust around the scratch was measured.
[0033]
The survey results are shown in Table 2.
From Table 2, the comparative example shows that the swollen area of the paint film is as large as about 1000 mm ^{2 for} No. 9 and 10, and vE ₀ is as low as about 30 J or less for No. ₇ , 8, and 11-16. Either the heat resistance or the weld zone toughness is insufficient. On the other hand, in Invention Example No. 1-6, the swollen area of the coating film was 187 to 295 mm ² and the weld zone toughness was vE ₀ 97J or more, and both the coating film peeling resistance and the weld zone toughness were excellent. It has become.
[0034]
[Table 1]

[0035]
[Table 2]

[0036]
【The invention's effect】
The marine steel of the present invention has excellent coating film peeling resistance and large heat input weld toughness, and when applied to a ballast tank placed in a severe corrosive environment, in addition to improving the efficiency of welding construction, The maintenance cost such as repair painting and repainting can be greatly reduced, and the contribution to the industry is extremely large.

Claims (4)

In mass%, C: 0.001 to 0.025%, Si: 0.60% or less, Mn: 0.10 to 3.0%, P: 0.005 to 0.030%, S: 0.0005 to 0.01%, Al: 0.10% or less, Cu: 0.10% or less, Ni: 0.10 to 4.0%, Ti: 0.005 to 0.030%, N: 0.0030 to 0.0070%, O: 0.0030% or less, Ca: 0.0005 to 0.0030%, consisting of the balance Fe and unavoidable impurities, and the following ACR: A marine steel with excellent film peeling resistance and high heat input weld toughness characterized by exceeding 0.00 and less than 1.00.
Record
ACR = (Ca-(0.18 + 130 x Ca) x O) / ( 1.25 x S )
However, Ca, O, and S are component contents of each element ( mass %) Furthermore, it is characterized by containing one or more selected from Mo: 0.05 to 0.50%, Co: 0.05 to 0.50%, W: 0.05 to 0.50%, Sb: 0.05 to 0.50% by mass%. The marine steel material excellent in coating film peeling resistance and high heat input weld toughness according to claim 1. Furthermore, it is excellent in coating film peeling resistance and large heat input weld toughness according to claim 1 or 2, characterized by containing one or more of the following (a) to (c) in mass%. Marine steel.
(A) Nb: 0.005 to 0.20%, V: One or two selected from 0.005 to 0.20% (b) REM: 0.004 to 0.02%
(C) B: 0.0003 to 0.0050% In mass%, C: 0.001 to 0.025%, Si: 0.60% or less, Mn: 0.10 to 3.0%, P: 0.005 to 0.030%, S: 0.0005 to 0.01%, Al: 0.10% or less, Cu: 0.10% or less, Ni: 0.10 to 4.0%, Ti: 0.005 to 0.030%, N: 0.0030 to 0.0070%, O: 0.0030% or less, Ca: 0.0005 to 0.0030%, or further, among the following (A) to (D) In a method of manufacturing a steel material that hot-rolls a steel material that has been solidified after melting to a target composition containing one or more, Ca is added to the molten steel immediately after the dissolved oxygen content is adjusted to 30 ppm or less, and the following ACR is less than 0.00 and less than 1.00 A method for producing a marine steel material excellent in coating film peeling resistance and high heat input weld toughness, characterized by adding an amount of
(A) Mo: 0.05 to 0.50%, Co: 0.05 to 0.50%, W: 0.05 to 0.50%, Sb: One or more selected from 0.05 to 0.50% (B) Nb: 0.005 to 0.20% V: One or two selected from 0.005 to 0.20% (C) REM: 0.004 to 0.02%
(D) B: 0.0003 to 0.0050%
ACR = (Ca-(0.18 + 130 x Ca) x O) / ( 1.25 x S )
However, Ca, O, and S are component contents of each element ( mass %)