KR101389160B1 - Steel material for structural member having excellent corrosion resistance - Google Patents

Abstract

단, [S], [P], [Mn], [Ti], [Ca], [Cu], [Ni] 및 [Cr]은, 각각 S, P, Mn, Ti, Ca, Cu, Ni 및 Cr의 함유량(질량％)을 나타낸다.In a severe corrosive environment, there is provided a structural member steel that exhibits excellent long-term corrosion resistance without requiring other anticorrosive means such as painting or lining. The steel material for structural members of this invention satisfy | fills a predetermined chemical component composition, and A value prescribed | regulated by following formula (1) is -2.0 or more and 2.0 or less.
[Equation 1]

However, [S], [P], [Mn], [Ti], [Ca], [Cu], [Ni] and [Cr] are S, P, Mn, Ti, Ca, Cu, Ni, and Content (mass%) of Cr is shown.

Description

Steel for structural members with excellent corrosion resistance {STEEL MATERIAL FOR STRUCTURAL MEMBER HAVING EXCELLENT CORROSION RESISTANCE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to steel for structural members useful as structural members of offshore structures such as bridges, in addition to ships such as crude oil tankers, cargo ships, ships, ships, and the like. It is about. In addition, although the steel for structural members of this invention is applicable as a structural member of offshore structures, such as a bridge, etc. other than various ships, it demonstrates centering on the case where it is used for ship as a typical thing below.

Steel materials used as major structural members in various ships are exposed to severe corrosive environments by corrosive gas components, in addition to salts from sea water, high temperature and high humidity, and water contained in crude oil. In particular, in oil tanks (crude oil tanks) of crude oil tankers, night and day other than the inert gas (exhaust gas of exhaust engine) sent to oil tank for volatile components, mixed seawater, salt in oilfield brine, and explosion-proof in crude oil Due to condensation due to temperature fluctuations, the corrosion environment becomes a unique corrosion environment, and thus, the corrosion thickness of the steel (particularly, steel sheet) decreases (plate thickness phenomenon due to corrosion).

For this reason, the plate thickness design which considered the corrosion margin is performed, and it is a countermeasure against whole surface corrosion and local corrosion. In the case where it is difficult to maintain the desired member strength due to the reduction of the corrosion thickness as described above, the corroded member is cut and welded to a new member, or so-called conversion of the steel sheet is required, which leads to enormous cost. In view of this, it is desired to develop a copper member for a structural member that is excellent in corrosion resistance that can reduce corrosion zones and prevent cost increase.

As a technique for preventing corrosion of steel materials, a method of coating (coating method) by coating or a method of lining zinc or aluminum by thermal spraying on the surface of steel materials (lining method) is common. However, in this technique, in addition to the economic problem that the construction cost increases, in addition, there is a micro defect in the construction in the layer (corrosive layer) for the corrosion protection or corrosion due to the deterioration of the corrosion protection layer over time. This inevitably progresses. Therefore, there exists a problem that regular inspection and maintenance are indispensable also by the coating method or the lining method.

In addition to the above technology, many corrosion resistant steels which have improved the corrosion resistance of the copper material itself by adjustment of chemical components or the like have been proposed so far. For example, in patent document 1, the shipbuilding corrosion resistant steel which suitably controlled content of Mg, Cu, etc. is proposed, and in patent document 2, shipbuilding corrosion resistant steel which suitably controlled the content of W is proposed. In these techniques, even if it is unpainted, what exhibits excellent corrosion resistance is disclosed. In addition, Patent Document 3 discloses having an excellent corrosion resistance by appropriately controlling the content of Sn and coating the surface.

However, in the above technique, the corrosion resistance under severe corrosive environment is not all sufficient. In particular, even in severe corrosive environments in contact with crude oil, it is actually desired to further improve the corrosion resistance of steel for structural members in order to ensure excellent corrosion resistance over a long period of time.

Japanese Patent Application Publication No. 2000-17381 Japanese Patent Application Publication No. 2009-97083 Japanese Patent Application Publication No. 2009-127076

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a structural member steel material exhibiting excellent long-term corrosion resistance even in the case of severe corrosive environment without requiring other anticorrosive means such as coating or lining.

With the steel for structural members of the present invention which can achieve the above object, C: 0.05 to 0.20% (the meaning of mass%, hereinafter the same), Si: 0.1 to 0.3%, Mn: 0.50 to 1.20%, P: 0.005 to 0.020%, S: 0.005% or less (not including 0%), Al: 0.01 to 0.08%, Cu: 0.15 to 0.50%, Ni: 0.15 to 0.50%, Cr: 0.02 to 0.20%, Ti: 0.005 to 0.020 % And Ca: 0.001 to 0.010%, respectively, the remainder being made of iron and unavoidable impurities, and having a summary that the A value defined by the following formula (1) is -2.0 or more and 2.0 or less.

[Equation 1]

However, [S], [P], [Mn], [Ti], [Ca], [Cu], [Ni] and [Cr] are S, P, Mn, Ti, Ca, Cu, Ni, and Content (mass%) of Cr is shown.

In the steel for structural members of the present invention, if necessary, (a) Mg: 0.005% or less (not including 0%), (b) Co: 1% or less (not containing 0%), ( c) It is also effective to contain Mo: 1% or less (not containing 0%) and the like, and by including them, the characteristics of the copper member for structural members are further improved.

In the present invention, the chemical composition is strictly defined, and the A value specified according to the content of S, P, Ti, Mn, Ca, Cu, Ni and Cr is controlled in an appropriate range, thereby being excellent even in severe corrosive environments. The steel material for structural members which exhibits corrosion resistance and can ensure favorable corrosion resistance over a long time can be realized, and such structural member steel materials are very useful as a raw material of ships or offshore structures.

BRIEF DESCRIPTION OF THE DRAWINGS The graph which shows the relationship between A value and corrosion rate prescribed | regulated by Formula (1).

MEANS TO SOLVE THE PROBLEM The present inventors earnestly researched in order to solve the said subject. As a result, while precisely adjusting elements such as C, Si, Mn, P, S, Al, Cu, Ni, Cr, Ti, Ca and the like, the following A value (Equation 1) determined by the component is- When it controlled in the range of 2.0 or more and 2.0 or less, it discovered that the steel material for structural members excellent in corrosion resistance was obtained, and completed this invention.

[Equation 1]

However, [S], [P], [Mn], [Ti], [Ca], [Cu], [Ni] and [Cr] are S, P, Mn, Ti, Ca, Cu, Ni, and Content (mass%) of Cr is shown.

The value A is a parameter for expressing a uniform and stable surface rust coating, which is an index showing long-term corrosion resistance even under severe corrosive environments. The coefficient for each element in the above formula (1) is determined by the present inventors by regression analysis. If the sign of the coefficient is positive, the element acts in the direction of deteriorating corrosion resistance, and if negative, it is an element acting in the direction of improving corrosion resistance. In addition, since the corrosion resistance deteriorates when the A value prescribed | regulated to the said Formula (1) exceeds 2.0, it is necessary to make A value 2.0 or less. In addition, when A value is less than -2.0, it will inhibit uniform rust formation reaction of steel materials. The minimum with preferable A value is -1.8, and a preferable upper limit is 1.8.

In the steel of the present invention, in order to satisfy the basic characteristics and corrosion resistance as the steel, it is necessary to appropriately adjust components such as C, Si, Mn, P, S, Al, Cu, Ni, Cr, Ti, and Ca. The reason for range limitation of these components is as follows.

[C: 0.05 to 0.20%]

C is an element necessary for securing the strength of the steel. In order to obtain the intensity | strength (about 300 Mpa or more) calculated | required as steel for structural members, it is necessary to contain 0.05% or more. However, when it contains exceeding 0.20% excessively, the toughness of steel materials will deteriorate. In this respect, the range of C content was 0.05 to 0.20%. Moreover, the minimum with preferable C content is 0.06%, More preferably, it is good to set it as 0.07% or more. The upper limit of the C content is preferably 0.18%, more preferably 0.16% or less.

[Si: 0.1 to 0.3%]

Si is an element necessary for deoxidation and ensuring strength, and if it does not satisfy 0.1%, the strength required as a structural member cannot be secured. However, when it contains exceeding 0.3% excessively, weldability will deteriorate.

[Mn: 0.50 to 1.20%]

Mn is an element effective for improving corrosion resistance by trapping S as MnS. In addition, like Si, it is necessary for deoxidation and securing strength, and if it does not satisfy 0.50%, the strength required as a structural member cannot be secured. However, when it contains excessively more than 1.20%, MnS will coarsen and corrosion resistance will worsen, and toughness will also deteriorate. Therefore, the range of Mn content was made into 0.50 to 1.20%. Moreover, the minimum with preferable Mn content is 0.55%, More preferably, it is good to set it as 0.6% or more. Moreover, the upper limit with preferable Mn content is 1.15%, More preferably, it is good to set it as 1.10% or less.

[P: 0.005 to 0.020%]

In addition to being harmful to corrosion resistance, P also degrades toughness and weldability. If the P content is up to about 0.020%, there is no actually harm. However, since huge cost is required for P reduction, P content was made into 0.005% or more.

[S: 0.005% or less (not including 0%)]

S is an element harmful to corrosion resistance, toughness and weldability, and the amount thereof is preferably as small as possible. In this regard, the S content is set at 0.005% or less. In addition, the upper limit with preferable S content is 0.004% (more preferably, 0.003% or less).

[Al: 0.01 to 0.08%]

Al, like Si and Mn, is also an element necessary for deoxidation and ensuring strength. If the content does not satisfy 0.01%, the effect of deoxidation is not exhibited. However, when it contains exceeding 0.08% excessively, weldability will be impaired. In this regard, Al content was 0.01 to 0.08%. Moreover, the minimum with preferable Al content is 0.015%, More preferably, it is good to set it as 0.02% or more. Moreover, the upper limit with preferable Al content is 0.075%, More preferably, it is good to set it as 0.065% or less.

[Cu: 0.15 to 0.50%]

Cu is an element effective for improving corrosion resistance. Cu has an effect which improves the densification of a surface rust film, and is an element effective in improving environmental barrier property and improving corrosion resistance. In order to exhibit such an effect, it is necessary to contain Cu 0.15% or more, but when it contains excessively, weldability and hot workability deteriorate, and it is necessary to be 0.50% or less. Moreover, the minimum with preferable Cu content is 0.2%, and a preferable upper limit is 0.4%.

[Ni: 0.15 to 0.50%]

Ni is an element effective for improving corrosion resistance. In particular, Ni has an effect of forming a dense surface rust coating in a corrosive environment, and Ni is an element expressing a corrosion inhibiting effect by the surface rust coating. Moreover, Ni also exhibits the effect of preventing the red light brittleness by containing Cu. In order to exhibit such an effect, it is necessary to contain Ni 0.15% or more, but when it contains excessively, weldability and hot workability will deteriorate, and it is necessary to be 0.50% or less. Moreover, the minimum with preferable Ni content is 0.2%, and a preferable upper limit is 0.4%.

[Cr: 0.02 to 0.20%]

Cr is an element effective for improving corrosion resistance. In particular, Cr, like Cu, has the effect of improving the densification of the surface rust coating, and is an effective element for improving the environmental barrier properties and improving the corrosion resistance. In addition, an appropriate amount of Cr is effective for improving the toughness and is also an element necessary for obtaining the mechanical properties required as steel materials for structural members. In order to exhibit such an effect, it is necessary to contain Cr 0.02% or more, but when it contains excessively, weldability and hot workability will deteriorate, It is necessary to be 0.20% or less. Moreover, the minimum with preferable Cr content is 0.05%, and a preferable upper limit is 0.15%.

[Ti: 0.005 to 0.020%]

Ti is an element effective for improving corrosion resistance. In particular, Ti has an effect of stabilizing the surface rust film formed in a corrosive environment, and is an element effective for expressing the corrosion inhibitory effect by the surface rust film for a long time. In order to exhibit such an effect, it is necessary to contain Ti 0.005% or more, but when it contains excessively, weldability and hot workability deteriorate, and it is necessary to make it 0.020% or less. In addition, the minimum with preferable Ti content is 0.008%, and a preferable upper limit is 0.018%.

[Ca: 0.001 to 0.010%]

Ca is an element effective for improving corrosion resistance. In particular, it has the effect | action which suppresses pH fall by the hydrolysis of the Fe melt | dissolved by corrosion. By this action, in the structural gap portion where hydrogen ion diffusion to the outside is unlikely to occur, the pH decrease can be suppressed to suppress corrosion, and in particular, the gap corrosion resistance can be improved. In order to exhibit such an effect, it is necessary to contain Ca 0.001% or more, but when it contains exceeding 0.010% excessively, weldability and workability will deteriorate. In addition, the upper limit with preferable Ca content is 0.005%.

The basic component in the steel for structural members of this invention is as above-mentioned, and remainder consists of iron and an unavoidable impurity. As an unavoidable impurity, O, H, W, etc. are mentioned, for example, You may contain these elements to the extent which does not impair the characteristic of steel materials.

In addition, in the steel for structural members of the present invention, (a) Mg: 0.005% or less (does not contain 0%), (b) Co: 1% or less (0%) by other needs of the above components. And (c) Mo: 1% or less (not containing 0%) and the like are effective, and the properties of the steel for structural members are further improved depending on the components to be contained.

[Mg: 0.005% or less (not including 0%)]

Mg is an element effective for improving corrosion resistance similarly to Ca, and can be included as necessary. Although such an effect increases as its content increases, it is preferable to set it as 0.005% or less because it will deteriorate weldability and workability when it contains excessively. In addition, the minimum with preferable Mg is 0.0005% or more.

[Co: 1% or less (not including 0%)]

Co is an element effective for improving corrosion resistance and can be contained as needed. Co, like Ni, has a function of forming a dense surface rust coating in a corrosive environment and exhibits a corrosion inhibiting effect by the surface rust coating. In particular, a significant corrosion effect is obtained by coexisting with Mg. Although such an effect increases as its content increases, it is preferable to set it as 1% or less because it will deteriorate weldability and workability when it contains excessively. Moreover, the minimum with preferable Co at the time of containing Co is 0.01% or more (more preferably 0.02% or more).

[Mo: 1% or less (not including 0%)]

Mo is an element effective for improving corrosion resistance and can be contained as needed. Mo is an element which exhibits the corrosion inhibitory effect by surface rust film. Although such an effect increases as the content increases, the weldability deteriorates when it is excessively contained, so it is preferably 1% or less. In addition, the minimum with preferable Mo when it contains Mo is 0.01% or more (more preferably 0.03% or more).

The steel for structural members of the present invention basically exhibits excellent corrosion resistance even when the steel coating itself or the lining coating is not applied. However, if necessary, a tar epoxy resin coating or other heavy coating or zinc represented by other applications is required. It is also possible to use together with other methods such as rich paint and shop primer.

Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not restrict | limited by the following example from the original, It is also possible to implement by changing suitably in the range which may be suitable for the meaning of the previous and the later. Of course, they are possible and they are all included in the technical scope of this invention.

<Examples>

Steel materials (tests N0.1 to 68) having chemical composition shown in the following Tables 1 to 3 were dissolved, hot rolled, and subjected to heat treatment as necessary to obtain a plate thickness of 20 mm. The corrosion test piece of dimension: 5 * 30 * 30 (mm) was cut out from this movable plate, and was used for the corrosion test.

At this time, the corrosion environment (simulation environment) was carried out for 72 hours using a hydrochloric acid aqueous solution of 0.14 mol / L. Moreover, aqueous solution temperature was 30 degreeC.

After the corrosion test in the simulation environment, the corrosion rate (mm / year) was calculated and compared with the A value. The result (corrosion test result) is shown to the said Tables 1-3 with A value. The test N0.1-31 is an example (example) which satisfy | fills the requirements (chemical composition and A value) prescribed | regulated by this invention. On the other hand, the test N0.32 to 52 are those in which the chemical composition is outside the range defined by the present invention, and the test N0.53 to 67 are in the range where the A value is defined in the present invention, although the chemical composition is satisfied. It is beyond. The thing of test N0.68 is a chemical component composition degree and A value out of the range prescribed | regulated by this invention.

Although the relationship of the A value prescribed | regulated by Formula (1) and corrosion rate is shown in FIG. 1 among the thing of the test N0.1-31 and the thing of the test N0.53-68 among what is shown in Tables 1-3, it is shown in FIG. Indicates that corrosion resistance is improved by controlling the A value within an appropriate range.

Claims (2)

C: 0.05 to 0.20% (meaning of mass%, the same below), Si: 0.1 to 0.3%, Mn: 0.50 to 1.20%, P: 0.005 to 0.020%, S: 0.005% or less (not including 0%) , Al: 0.01 to 0.08%, Cu: 0.15 to 0.50%, Ni: 0.15 to 0.50%, Cr: 0.02 to 0.20%, Ti: 0.005% to 0.020%, and Ca: 0.001 to 0.010%, respectively, and the remaining amount The steel material for structural members excellent in corrosion resistance which consists of addition iron and an unavoidable impurity, and A value prescribed | regulated by following formula (1) is -2.0 or more and 2.0 or less.
[Equation 1]

However, [S], [P], [Mn], [Ti], [Ca], [Cu], [Ni] and [Cr] are S, P, Mn, Ti, Ca, Cu, Ni, and Content (mass%) of Cr is shown. The method of claim 1 wherein Mg is selected from 0.005% or less (does not contain 0%), Co: 1% or less (does not contain 0%), Mo: 1% or less (does not contain 0%) The steel for structural members which further contains 1 or more types and is excellent in corrosion resistance.

Images