KR20200018637A - Structural Steels and Structures - Google Patents

Abstract

The present invention is capable of reducing the coating frequency even when used in an air corrosive environment, particularly in a harsh corrosive environment such as at sea or near a coast where salt content is high, and also excellent in corrosion resistance and excellent primary rust resistance. An object of the present invention is to provide a structural steel material having excellent lamellar tier resistance when used in a large and complicated structure such as a bridge. The structural steel material of this invention has predetermined component composition, and makes Sn segregation degree 20 or less.

Description

Structural Steels and Structures

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to steel materials mainly applied to structures used on land such as bridges or outdoors and in outdoor corrosive environments, particularly in harsh corrosive environments such as seas and coasts where airborne salinity is high.

The steel structure used outdoors, such as a bridge, is normally used by performing some corrosion prevention treatment. For example, weathering steel is frequently used in an environment where the amount of salt in the fly is low.

Here, when the weathering steel is used in an air exposure environment, the surface is covered with a highly protective rust layer in which alloying elements such as Cu, P, Cr, and Ni are concentrated, thereby increasing the corrosion rate. It is the steel which greatly reduced. It is known that a bridge using such weathering steel can withstand decades of common use as it is no coating in an environment where the salt content of fly is low.

On the other hand, in an environment with a large amount of fly salt, such as in the sea or near the coast, it is difficult to form a highly protective rust layer in weathering steel, and it is difficult to use the weathering steel as it is without painting. For this reason, in the environment where the amount of adjuvant salts, such as the sea and the vicinity of a coast, are large, the steel material which gave anticorrosive treatment, such as painting to steel materials, is used normally.

However, in a coated steel material, regular recoating or the like is required due to deterioration of the coating film, generation of rust, swelling of the coating film, or the like over time. The painting work with recoating is often performed at a high place, and the work itself is difficult, and labor costs required for the work are also required. For this reason, when using a painted steel material, there exists a problem that the maintenance cost of a structure increases, and also the life cycle cost increases.

In addition, for the purpose of preventing corrosion from occurring during the period until fabrication of the structure and during the storage of the steel, in general, antirust treatment such as zinc-rich primer (primary antirust treatment) has been performed. All. However, when the storage period of steel material becomes long, or when the storage place of steel material is close to the sea, and there is a large amount of salt in the air, corrosion may advance even if said antirust process is performed.

In view of the above, steels having excellent corrosion resistance, in particular, coating corrosion resistance, which can extend the cycle of recoating coating, that is, reduce the coating frequency, can reduce the maintenance cost of the structure, and further improve the primary rust resistance. The development of this excellent structural steel is desired.

As a technique regarding steel materials excellent in corrosion resistance, Patent Document 1, for example,

"In mass%, C: 0.001-0.15%, Si: 2.5% or less, Mn: more than 0.5%, 2.5% or less, P: less than 0.03%, S: 0.005% or less, Cu: 0.05-1.0%, Ni: 0.01 -0.5%, Cr: 0.01-3.0%, Al: 0.003-2.5%, N: 0.001-0.1%, and Sn and / or Sb: 0.03-0.50% further, remainder consists of Fe and an impurity, , Having a composition having a Ni / Cu mass ratio of 0.5 or less.

Is disclosed.

In patent document 2,

"In mass%, C: 0.001-0.15%, Si: 2.5% or less, Mn: exceeding 0.5%, 2.5% or less, P: less than 0.03%, S: 0.005% or less, Cu: less than 0.05%, Ni: 0.05 A composition containing less than%, Cr: 0.01 to 3.0%, Al: 0.003 to 0.1%, N: 0.001 to 0.1%, and Sn: 0.03 to 0.50%, the balance consisting of Fe and impurities, and having a Cu / Sn ratio of 1 or less After heating the surface temperature of the slab which has to 1050-1200 degreeC, it carries out 70% or more of rolling reductions in the temperature range of 900 degreeC or more, and further cools after finishing rolling in the temperature range of 800 degreeC or more. A method for producing steel having excellent corrosion resistance and toughness in the Z direction.

Is disclosed.

In patent document 3,

"In mass%, C: 0.01-0.2%, Si: 0.01-1.0%, Mn: 0.05-3.0%, P: 0.05% or less, S: 0.01% or less, Sn: 0.01-0.5%, Cr: 1.0% 13.0% or less of Al, 0.1% or less of Al, and remainder Fe and impurities, and the ratio of solid solution Sn in Sn is 95.0% or more.

Is disclosed.

In patent document 4,

"In mass%, C: 0.01-0.2%, Si: 0.01-1.0%, Mn: 0.05-3.0%, P: 0.05% or less, S: 0.01% or less, Sn: 0.01-0.5%, Al: 0.1% or less And a residual Fe and impurities, and the ratio of solid solution Sn in Sn is 95.0% or more.

Is disclosed.

In patent document 5,

"Chemical composition is mass%, C: 0.01-0.20%, Si: 0.01-1.00%, Mn: 0.05-3.00%, Sn: 0.01-0.50%, O: 0.0001-0.0100%, Cu: 0-0.10% Less than Cr: 0 to 0.10%, Mo: less than 0 to 0.050%, W: less than 0 to 0.050%, Cu + Cr: less than 0 to 0.10%, Mo + W: less than 0 to 0.050%, Sb: less than 0 to 0.05%, Ni: 0% to 0.05%, Nb: 0% to 0.050%, V: 0% to 0.050%, Ti: 0% to 0.020%, Al: 0% to 0.100%, Ca: less than 0% to 0.0100%, Mg: 0% to 0.0100%, REM: 0-0.0100%, P: 0.05% or less, S: 0.01% or less, remainder: Fe and impurities; Soft tissues that are ferrite and hard tissues that are pearlite, bainite and martensite; A Sn concentration ratio that is a ratio of Sn concentration in the hard tissue to Sn concentration in the soft tissue is 1.2 or more and less than 6.0; Steel, characterized in that.

Is disclosed.

Japanese Laid-Open Patent Publication No. 2006-118011 Japanese Laid-Open Patent Publication No. 2010-7109 Japanese Laid-Open Patent Publication No. 2013-166992 Japanese Laid-open Patent Publication 2012-255184 Japanese Patent No. 5839151

 WES3008-1999

However, when a large amount of components for improving the corrosion resistance, such as Cr, is contained, performance other than the corrosion resistance may deteriorate.

For example, in the technique of Patent Documents 1 to 3, when the Cr content is increased, the alloy cost is increased and the toughness of the steel is deteriorated.

In recent years, the risk of lamellar tear has been pointed out in structures such as bridges. Here, lamellar tier is a welded joint subjected to tensile stress in a plate thickness direction such as a cross joint, a T joint, a corner joint, etc., in the direction parallel to the surface of the steel sheet by the tensile stress, cracking inside the steel. This is a phenomenon in which cracking occurs.

Regarding the generation of such lamellar tiers, for example, in Non-Patent Document 1, the relationship between the drawing value in the plate thickness direction and the amount of S in steel is shown, and the plate thickness is reduced by reducing the amount of S in the steel. It is disclosed that the drawing value in the direction improves, and furthermore, the lamellar tear resistance is improved.

However, with the increase in size and complexity of recent structures, in such a size and complexity of structure, a large number of cases are subjected to large tensile stress in the plate thickness direction by welding joints with strict constraint conditions in its constituent members. have.

In this case, only by reducing the amount of S in steel, sufficient lamella resistance cannot be obtained necessarily. Moreover, the influence which the various elements added for the purpose of improving corrosion resistance as disclosed in patent documents 1-5 on lamellar tier resistance is not revealed. For this reason, when applying the steel materials which improved the corrosion resistance disclosed by patent documents 1-5 to such a large and complicated structure, generation | occurrence | production of lamellar tier is feared.

The present invention was developed in view of the above-described phenomenon, and in the case of use in an air corrosive environment, particularly in a harsh corrosive environment such as a sea or a coast near a large salt content, it is possible to reduce the coating frequency, and 1 An object of the present invention is to provide a structural steel material having good anticorrosion resistance, excellent paint corrosion resistance, and excellent lamellar tear resistance when used for a large and complicated structure such as a bridge.

Moreover, an object of this invention is to provide the structure which uses said structural steel material.

Then, the inventors earnestly studied for the solution of the said subject, and acquired the following recognition.

(1) In order to improve corrosion resistance, especially coating corrosion resistance, it is effective to add 1 type, or 2 or more types selected from Cu, Ni, W, Sb, and Si together with Sn.

(2) On the other hand, from the viewpoint of the lamella tier resistance, it is effective to reduce the amount of S in the steel and to reduce Sn.

(3) Thus, although the addition of Sn is effective from the viewpoint of the improvement of coating corrosion resistance, it is effective to reduce Sn from the viewpoint of the lamella tier resistance. Therefore, the inventors made further studies based on the above recognition so as to make the corrosion resistance and the lamellae tier resistance compatible.

As a result,

(4) When the central segregation of Sn is suppressed and Sn is spread as much as possible throughout the steel material, even if it contains a predetermined amount of Sn, excellent lamellar tier resistance is obtained, that is, the amount of Sn is appropriately adjusted from the viewpoint of improving the coating corrosion resistance. By adjusting the central segregation of Sn and adjusting Sn to diffuse throughout the steel, the coating corrosion resistance and the lamellar tier resistance can be made compatible.

Got recognition.

(5) Furthermore, the lamella tier resistance is further improved by suppressing the thickness of the Sn segregation portion which becomes a predetermined or more concentration in the plate thickness direction as much as possible,

(6) Furthermore, the lamella tier resistance is further improved by strictly controlling the Sn amount in accordance with the S amount.

Got recognition.

The present invention is further completed based on the above recognition.

That is, the summary structure of this invention is as follows.

1.in mass%

C: 0.020% or more, 0.200% or less,

Mn: 0.20% or more, 2.00% or less,

P: 0.003% or more, 0.030% or less,

S: 0.0001% or more, 0.0100% or less,

Al: 0.001% or more, 0.100% or less and

Sn: 0.005% or more, 0.200% or less

With containing

Cu: 0.010% or more, 0.50% or less,

Ni: 0.010% or more, 0.50% or less,

W: 0.005% or more, 1.000% or less,

Sb: 0.005% or more, 0.200% or less and

Si: 0.05% or more, 1.00% or less

It contains 1 type or 2 or more types chosen from, and remainder has the component composition which consists of Fe and an unavoidable impurity,

Structural steel material with Sn segregation degree of 20 or less.

Here, Sn segregation degree is defined by following Formula (1).

[Sn Segregation Degree] = [Sn Segregation Part Sn Concentration] / [Mean Sn Concentration] --- (1)

2. Structural steel material as described in said 1 whose thickness of Sn segregation part is 50 micrometers or less in direction.

3. The structural steel according to the above 1 or 2, wherein the ST value defined by the following formula (2) is 1.50 or less.

ST = 10000 × [% S] × [% Sn] ² --- (2)

[% S] and [% Sn] are content (mass%) of S and Sn in the said component composition, respectively.

4. The said component composition is further in mass%,

Mo: 0.500% or less and

Co: 1.00% or less

Structural steel as described in any one of said 1-3 containing 1 type or 2 types chosen from.

5. The said component composition is further, by mass%,

Ti: 0.050% or less,

V: 0.200% or less,

Nb: 0.200% or less and

Zr: 0.100% or less,

The structural steel material in any one of said 1-4 containing 1 type or 2 or more types chosen from.

6. The said component composition is further, by mass%,

B: Structural steel according to any one of 1 to 5, containing 0.0050% or less.

7. The said component composition is further in mass%,

Ca: 0.0100% or less and

Mg: 0.0100% or less,

The structural steel material in any one of said 1-6 containing 1 type or 2 types chosen from.

8. Structural steel as described in any one of said 1-7 which has a coating film on the surface.

9. The coating has an anticorrosive base layer, an undercoat layer, an intermediate layer and a top coat layer,

The anticorrosive base layer is an inorganic zinc rich paint, the primary coating layer is an epoxy resin coating, the intermediate coating layer is an intermediate coating paint for a fluororesin top coat coating, and the finishing coating layer is a fluororesin finishing coating coating, respectively. The structural steel material described in 8 above.

10. The structural steel material according to any one of 1 to 7, wherein the surface has a zinc rich primer layer.

11. A structure comprising the structural steel material according to any one of 1 to 10 above.

12. The structure according to 11 above, which is a bridge.

According to the present invention, even when used in an air corrosive environment, especially in a harsh corrosive environment such as at sea or near a coast where salt content is high, it is possible to extend the recoating cycle to reduce the coating frequency and also to improve the lamella tier resistance. Excellent structural steels can be obtained.

The structural steel of the present invention is used in structures such as bridges used in outdoor corrosive environments such as bridges, particularly under severe corrosive environments such as at sea or near coasts where salt content is high. In addition, it is possible to reduce the life cycle cost, and furthermore, it is possible to effectively prevent the generation of lamellar tiers, and to ensure high safety even for large and complex structures.

(Form to carry out invention)

Hereinafter, the present invention will be described in detail. First, the component composition in one Embodiment of the structural steel material of this invention is demonstrated. In addition, although the unit of content of the element in a component composition is all "mass%", unless otherwise indicated, it shows simply as "%" below.

C: 0.020% or more and 0.200% or less

C is an element which raises the strength of steel materials. For this reason, it is necessary to contain C 0.020% or more in order to ensure the predetermined strength as structural steel. On the other hand, when C content exceeds 0.200%, weldability and toughness will deteriorate. Therefore, C content is made into 0.020% or more and 0.200% or less. Preferably, it is 0.040% or more. Moreover, preferably, it is 0.180% or less.

Mn: 0.20% or more, 2.00% or less

Mn is an element which raises the strength of steel materials. For this reason, Mn needs to be contained 0.20% or more in order to ensure the predetermined strength as structural steel. On the other hand, when Mn content exceeds 2.00%, toughness and weldability will deteriorate. Therefore, Mn content is made into 0.20% or more and 2.00% or less. Preferably it is 0.75% or more. Moreover, Preferably it is 1.80% or less.

P: 0.003% or more, 0.030% or less

P is an element which contributes to the improvement of the coating corrosion resistance of steel materials. In view of obtaining such an effect, it is necessary to contain P 0.003% or more. On the other hand, when P content exceeds 0.030%, weldability will deteriorate. Therefore, P content is made into 0.003% or more and 0.030% or less.

S: 0.0001% or more, 0.0100% or less

S is an important element involved in lamella tier resistance. In other words, when the amount of S increases, coarse MnS is formed, which is the starting point of the lamellar tier. For this reason, S content needs to be 0.0100% or less. However, when it is going to make S content less than 0.0001%, a production cost will increase. Therefore, S content is made into 0.0001% or more and 0.0100% or less. Preferably it is 0.0080% or less, More preferably, it is 0.0060% or less.

Al: 0.001% or more, 0.100% or less

Al is an element required for deoxidation during steelmaking. In order to acquire such an effect, Al needs to be contained 0.001% or more. On the other hand, when Al content exceeds 0.100%, it will adversely affect weldability. Therefore, Al content is made into 0.001% or more and 0.100% or less. Preferably it is 0.005% or more, More preferably, it is 0.010% or more. Moreover, Preferably it is less than 0.050%, More preferably, it is less than 0.030%.

Sn: 0.005% or more, 0.200% or less

Sn is an important element which has the effect of improving the durability of a coating film, and is an important element which participates in lamella tier resistance, in other words, an element which improves coating corrosion resistance and reduces lamella tier resistance.

That is, Sn exists in the rust layer near the surface of the steel substrate, and by miniaturizing the rust particles, the chloride ions, which are corrosion promoting factors, are prevented from reaching the rust layer. In addition, Sn suppresses the anode reaction on the steel material surface. In order to fully acquire these effects, it is necessary to make Sn content into 0.005% or more. Preferably it is 0.010% or more, More preferably, it is 0.020% or more.

However, Sn tends to segregate in the center of the plate thickness, and in such a Sn segregation portion, the hardness is high, embrittlement is formed, and the tissue is a starting point of destruction, thereby deteriorating the lamellar tier resistance. Therefore, from the viewpoint of ensuring the lamella tier resistance, the content of Sn is made 0.200% or less. Preferably it is 0.100% or less, More preferably, it is less than 0.050%.

In addition, from the viewpoint of improving the coating corrosion resistance of the steel, it is necessary to complexly add one or two or more selected from Cu, Ni, W, Sb, and Si together with Sn. That is, as mentioned above, Sn improves coating corrosion resistance, but cannot be contained in a large quantity from a lamellar tier viewpoint. For this reason, from the viewpoint of improving the coating corrosion resistance of steel materials while ensuring good lamellae resistance, it is necessary to complexly add one or two or more selected from Cu, Ni, W, Sb and Si together with Sn. Do.

Cu: 0.010% or more, 0.50% or less

Cu has an effect of forming a dense rust layer by miniaturizing rust particles of the rust layer, and suppressing the permeation of oxygen or chloride ions, which are corrosion promoting factors, into the iron. Such an effect is obtained in Cu content of 0.010% or more. On the other hand, when Cu content exceeds 0.50%, an alloy cost will rise. Therefore, content for obtaining the effect of Cu addition is 0.010% or more and 0.50% or less. Preferably it is 0.030% or more, More preferably, it is 0.040% or more, More preferably, it is 0.050% or more. Moreover, Preferably it is 0.40% or less, More preferably, it is 0.30% or less, More preferably, it is 0.25% or less.

Ni: 0.010% or more, 0.50% or less

Ni has the effect of forming a dense rust layer by miniaturizing the rust of the rust layer, and suppressing the permeation of oxygen and chloride ions, which are corrosion promoting factors, to the iron. Such an effect is obtained at 0.010% or more of Ni content. On the other hand, when Ni content exceeds 0.50%, an alloy cost will increase. Therefore, content for obtaining the effect of Ni addition is 0.010% or more and 0.50% or less. Preferably it is 0.030% or more, More preferably, it is 0.040% or more, More preferably, it is 0.050% or more. Moreover, Preferably it is less than 0.40%, More preferably, it is 0.30% or less, More preferably, it is 0.15% or less.

W: 0.005% or more, 1.000% or less

W elutes along with the anode reaction of the steel and is distributed as WO ₄ ²⁻ in the rust layer, thereby electrostatically preventing chloride ions of the corrosion promoting factor from penetrating the rust layer and reaching the base iron. Moreover, the compound containing W precipitates on the steel surface, and suppresses the anode reaction of steel materials. Such an effect is obtained at 0.005% or more of W content. On the other hand, when W content exceeds 1.000%, an alloy cost rises. Therefore, content for obtaining the effect of W addition is 0.005% or more and 1.000% or less. Preferably it is 0.010% or more, More preferably, it is 0.030% or more, More preferably, it is 0.050% or more. Moreover, Preferably it is 0.700% or less, More preferably, it is 0.500% or less, More preferably, it is 0.300% or less.

Sb: 0.005% or more, 0.200% or less

Sb exists in the rust layer in the vicinity of the surface of the iron, and by miniaturizing the rust particles, it is possible to suppress chloride ions, which are corrosion promoting factors, from penetrating the rust and reaching the iron. In addition, Sb suppresses an anode reaction on the steel material surface. Such an effect is obtained at 0.005% or more of Sb content. On the other hand, when Sb content exceeds 0.200%, deterioration of ductility and toughness of steel will be caused. Therefore, content for obtaining the effect of Sb addition is 0.005% or more and 0.200% or less. Preferably it is 0.010% or more, More preferably, it is 0.020% or more. Moreover, Preferably it is 0.150% or less, More preferably, it is 0.100% or less.

Si: 0.05% or more, 1.00% or less

Si has an effect which refine | miniaturizes the intrusion of the whole rust layer, forms a dense rust layer, and improves the coating corrosion resistance of steel materials. Si is an element necessary for deoxidation during steelmaking. Such an effect is obtained at 0.05% or more of Si content. On the other hand, when Si content exceeds 1.00%, toughness and weldability will remarkably deteriorate. Therefore, content for obtaining the effect of Si addition is 0.05% or more and 1.00% or less. Preferably it is 0.15% or more. Moreover, Preferably it is 0.80% or less.

Moreover, from a viewpoint of further improving the coating corrosion resistance of steel materials, it is more preferable to make Si content into 0.40% or more and 0.60% or less.

As mentioned above, although the basic component was demonstrated, the element described below can be contained suitably as needed.

Mo: 0.500% or less

Mo is eluted with the anode reaction of steel materials, and MoO ₄ ^2- is distributed in the rust layer, thereby suppressing chloride ions, which are corrosion promoting factors, from penetrating the rust layer and reaching ground iron. Moreover, the compound containing Mo precipitates on the steel surface, and suppresses the anode reaction of steel materials. However, when Mo content exceeds 0.500%, an alloy cost will rise. Therefore, Mo content is made into 0.500% or less when it contains Mo. Moreover, in order to acquire the said effect, Mo content becomes like this. Preferably it is 0.005% or more.

Co: 1.00% or less

Co is distributed throughout the rust layer, and finer rust is formed to form a dense rust layer, thereby improving the weather resistance of the steel. However, when Co content exceeds 1.00%, an alloy cost will rise. Therefore, when it contains Co, Co content is made into 1.00% or less. Preferably it is 0.50% or less, More preferably, it is 0.35% or less. Moreover, in order to acquire the said effect, Preferably Co content is 0.01% or more, More preferably, it is 0.03% or more, More preferably, it is 0.10% or more.

Ti: 0.050% or less

Ti is an element which raises strength. However, when Ti content exceeds 0.050%, there exists a possibility of causing toughness deterioration. Therefore, Ti content is made into 0.050% or less when it contains Ti. More preferably, it is 0.030% or less. Moreover, in order to acquire the said effect, Ti content becomes like this. Preferably it is 0.001% or more, More preferably, it is 0.005% or more.

V: 0.200% or less

V is an element which raises intensity. However, when V content exceeds 0.200%, the effect is saturated. Therefore, when it contains V, V content is made into 0.200% or less. Moreover, in order to acquire the said effect, V content becomes like this. Preferably it is 0.005% or more.

Nb: 0.200% or less

Nb is an element which increases strength. However, when Nb content exceeds 0.200%, there exists a possibility that it may cause deterioration of toughness. Therefore, when it contains Nb, Nb content is made into 0.200% or less. In addition, in order to acquire the said effect, Nb content becomes like this. Preferably it is 0.005% or more.

Zr: 0.100% or less

Zr is an element which raises strength. However, when Zr content exceeds 0.100%, the effect will be saturated. Therefore, when it contains Zr, Zr content is made into 0.100% or less. Moreover, in order to acquire the above effects, Zr content becomes like this. Preferably it is 0.005% or more.

B: 0.0050% or less

B is an element which raises strength. However, when B content exceeds 0.0050%, there exists a possibility of causing toughness deterioration. Therefore, when it contains B, B content is made into 0.0050% or less. In addition, in order to acquire the said effect, B content becomes like this. Preferably it is 0.0001% or more.

Ca: 0.0100% or less

Ca is an element which fixes S in steel and improves the toughness of a weld heat affected zone. However, when Ca content exceeds 0.0100%, the quantity of inclusions in steel will increase, but rather will cause toughness deterioration. Therefore, Ca content is made into 0.0100% or less when it contains Ca. Moreover, in order to acquire the said effect, Ca content becomes like this. Preferably it is 0.0001% or more.

Mg: 0.0100% or less

Mg is an element which fixes S in steel and improves the toughness of a weld heat affected zone. However, when the Mg content is more than 0.0100%, the amount of inclusions in the steel increases, which leads to deterioration of toughness. Therefore, Mg content is made into 0.0100% or less when it contains Mg. In addition, in order to acquire the said effect, Mg content becomes like this. Preferably it is 0.0001% or more.

Components other than the above are Fe and an unavoidable impurity. Moreover, as an unavoidable impurity, N and O (oxygen) are mentioned, It is acceptable if N: 0.010% or less and O: 0.010% or less.

In the structural steel material of the present invention, it is very important to control the Sn segregation degree as follows.

Sn segregation: 20 or less

As mentioned above, Sn tends to segregate in the plate thickness center part. In such a portion where Sn is segregated (hereinafter also referred to as Sn segregation), the hardness is high, and an embrittled structure is formed, and the structure becomes the starting point of fracture, and as a result, the lamella tier of the steel sheet Deteriorates the sex. Therefore, in order to secure the excellent lamella tier resistance, it is important to suppress the central segregation of Sn, in other words, to reduce the Sn segregation degree defined by the following formula (1). For this reason, Sn segregation shall be 20 or less. Preferably it is 18 or less. More preferably, it is 15 or less. More preferably, it is 12 or less. The lower limit of Sn segregation is preferable, but the lower limit is not particularly limited, but is preferably 1, more preferably 5.

[Sn Segregation Degree] = [Sn Segregation Part Sn Concentration] / [Mean Sn Concentration] --- (1)

Here, Sn segregation degree is more specifically, in the cross section (section perpendicular | vertical to the steel surface) cut | disconnected in parallel with the rolling direction of steel materials, of the electron beam microanalyzer (hereinafter referred to as EPMA). It is the ratio of the maximum Sn density | concentration of a Sn segregation part with respect to the average Sn concentration obtained by line analysis.

That is, when the thickness of the steel is t (mm) and the width (the direction perpendicular to the rolling direction and the thickness direction of the steel) is W (mm), first, the cross section cut in parallel with the rolling direction of the steel (on the steel surface In the thickness direction of the steel of the vertical cross section): (0.5 ± 0.1) × t, the rolling direction: the surface area of 15 mm (that is, the surface area including the center position in the thickness direction of the steel), the beam diameter: 20 μm , EPMA surface analysis of Sn is performed on the conditions of 20 micrometers of pitch. In addition, EPMA surface analysis of Sn is performed in three cross-sectional views of the position of 1 / 4xW, 1 / 2xW, and 3 / 4xW.

Next, the position where Sn concentration is highest in each cross-sectional view is selected from the said EPMA surface analysis, and EPMA of Sn is performed on the conditions of the beam diameter: 5 micrometers, and the pitch: 5 micrometers in the thickness direction of steel materials in the said position, respectively. Perform line analysis. In addition, in performing EPMA line | wire analysis, the area | region up to 25 micrometers is removed from the front and back surfaces of steel materials, respectively.

Next, the maximum value of Sn concentration (mass concentration) is calculated | required for every measurement line, and these average values are made into Sn concentration (mass concentration) of Sn segregation part. And the value obtained by dividing Sn concentration of this Sn segregation part by the average Sn concentration (mass concentration) which is an arithmetic mean value of all the measured values of a measurement line is taken as Sn segregation degree.

Thickness of plate | board thickness direction of Sn segregation part: 50 micrometers or less

In addition, the lamella tier resistance is further improved by suppressing the thickness in the plate thickness direction of the Sn segregation portion as much as possible. For this reason, it is preferable to set thickness of Sn segregation: 50 micrometers or less. More preferably, it is 40 micrometers or less, More preferably, it is 30 micrometers or less. In addition, a minimum is not specifically limited, 0 micrometer may be sufficient.

In addition, the Sn segregation part here is an area | region whose ratio of Sn density | concentration (mass concentration) with respect to average Sn density | concentration (mass concentration) obtained from said EPMA line | wire analysis is 5 or more.

In addition, the thickness of Sn segregation part is calculated | required by averaging the thickness of the plate thickness direction in the said area obtained for every said measurement line.

ST value: 1.50 or less

Moreover, lamellar tier resistance can be improved further by making ST value defined by following formula (2) into 1.50 or less. More preferably, it is 1.20 or less. The lower limit is not particularly limited, but is about 0.0000005.

ST = 10000 × [% S] × [% Sn] ² --- (2)

[% S] and [% Sn] are content (mass%) of S and Sn in the said component composition, respectively.

In addition, the structural steel material of one Embodiment of this invention coats and uses a steel material surface. Here, although it does not specifically limit as a coating film of the steel material surface, For example, the coating film which has an anticorrosive base layer, a primary coating layer, an intermediate coating layer, and a finishing coating layer in this order is mentioned.

In addition, the anticorrosive base layer is an inorganic zinc rich paint (e.g., SD zinc 1500), the primary layer is an epoxy resin paint (e.g., epomarin HB (K)), and the intermediate layer is an intermediate for fluororesin finishing paint. It is preferable to form a fill paint (for example, Celatect F intermediate paint) and a finish paint layer using a fluororesin finish paint (for example, Cellatect F (K) finish).

Moreover, at the time of product shipment, it is preferable to form a zinc rich primer layer on the surface of steel materials for the purpose of primary rust prevention.

In addition, a zinc rich primer layer is a primer layer formed using the zinc rich primer prescribed | regulated by JISK5552 (2002).

Next, the manufacturing method which concerns on one Embodiment of the said structural steel materials is demonstrated.

That is, the steel prepared by the above-mentioned component composition is melted using a well-known refining process, such as a converter, an electric furnace, and vacuum degassing, and a continuous casting method or an ingot-powder rolling method It is produced by steel sheet (slab) by (ingot casting-blooming), and then reheating the steel material as needed, followed by hot rolling to form a steel sheet or a shaped steel.

The thickness of the steel is not particularly limited, but is preferably 2 to 100 mm. More preferably, it is 3 mm or more, More preferably, it is 4 mm or more. More preferably, it is 80 mm or less, More preferably, it is 60 mm or less.

However, as mentioned above, in order to acquire the outstanding lamella tier characteristic, it is very important to suppress Sn segregation, specifically, to control Sn segregation to 20 or less. Here, Sn segregation degree changes greatly with manufacturing conditions, even if a component composition is the same. For this reason, in order to suppress the center segregation of Sn, it is important to appropriately control manufacturing conditions, especially casting conditions and hot rolling.

That is, in the case of continuous casting, the pressure reduction method of casting the slab at the end of the solidification with the non-solidified layer is gradually pressed down by the rolling roll group at a reduction total amount and a reduction speed corresponding to the sum of the solidification shrinkage amount and the heat shrinkage amount. It is preferable to carry out.

In this case, the casting speed (drawing speed) is preferably 0.50 to 2.80 m / min.

Here, when casting speed is less than 0.50 m / min, operating efficiency will worsen. In addition, solidification is completed before the cast steel reaches the light reduction rolling zone, and the reduction in the uncoagulated layer cannot be sufficiently performed, and the segregation suppression effect of Sn by the light reduction method is not sufficiently obtained. , Central segregation of Sn is promoted. More preferably, it is 0.70 m / min or more, More preferably, it is 0.80 m / min or more.

On the other hand, when the casting speed exceeds 2.80 m / min, surface temperature nonuniformity will arise, supply of molten steel to the inside of a slab will become insufficient, and center segregation of Sn will be promoted. In addition, the position where solidification is completely completed is a position past the low pressure zone, and the segregation suppression effect of Sn by the low pressure method is not sufficiently obtained, and the center segregation of Sn is promoted. More preferably, it is 2.50 m / min or less, More preferably, it is 1.20 m / min or less.

In addition, when hot rolling the said steel raw material to a desired dimension shape, it is preferable to heat at the temperature of 1000 degreeC-1350 degreeC. In other words, the higher the heating temperature, the more the diffusion of Sn in the central segregation portion is promoted, which is advantageous from the viewpoint of securing the lamella tier resistance. From such a viewpoint, it is preferable that heating temperature shall be 1000 degreeC or more. However, when the heating temperature exceeds 1350 ° C., surface scratches occur or scale loss or fuel consumption rate increases. Therefore, it is preferable that the upper limit of heating temperature shall be 1350 degreeC.

Moreover, it is preferable to soak so that the temperature difference of the steel material (slab) surface layer and center part may be 50 degrees C or less at the said heating temperature. Thereby, the diffusion of Sn in a center segregation part is fully promoted. For this reason, it is preferable to make the crack time in the said heating temperature 30 minutes or more. More preferably, it is 60 min or more. More preferably, it is 90 minutes or more. In addition, it is although it does not specifically limit about an upper limit, It is preferable to set it as 1000min.

In addition, when the temperature of a steel raw material is the case of the range of 1000-1350 degreeC originally, and was hold | maintained 30 minutes or more in the temperature range, you may provide for hot rolling as it is, without heating. In addition, the hot rolled sheet obtained after hot rolling may be subjected to reheating treatment, acid washing and cold rolling to obtain a cold rolled sheet having a predetermined plate thickness.

Moreover, in hot rolling, it is preferable to make a reduction ratio 3.0 or more. By setting the reduction ratio to 3.0 or more, the thickness of the Sn segregation portion in the plate thickness direction becomes thin. More preferably, it is 3.2 or more, More preferably, it is 4.0 or more. The upper limit of the reduction ratio is preferably about 60. In addition, it is preferable to make finish rolling finish temperature into 650 degreeC or more. If the finish rolling finish temperature is less than 650 ° C., the rolling load increases due to the increase in the deformation resistance, which makes the rolling difficult. The upper limit of the finish rolling finish temperature is preferably 950 ° C.

In addition, although the cooling after hot rolling may be any method of air cooling and accelerated cooling, when it is desired to obtain a higher strength, it is preferable to perform accelerated cooling.

Here, when performing accelerated cooling, it is preferable to make cooling rate 2-100 degreeC / s and cooling stop temperature 700-400 degreeC. That is, when the cooling rate is less than 2 ° C / s and / or the cooling stop temperature is more than 700 ° C, the effect of accelerated cooling is small, and sufficient high strength may not be achieved. In addition, it is preferable to make cooling rate into 100 degrees C / s or less from a viewpoint of a facility capability. Moreover, when cooling stop temperature is less than 400 degreeC, the toughness of steel materials may fall, or distortion may arise in the shape of steel materials. In addition, when cooling stop temperature is less than 400 degreeC, it is preferable to perform tempering heat processing in the temperature range of 400 degreeC-700 degreeC in a post process.

Example

The steel (residual residues are Fe and inevitable impurities) which becomes the component composition shown in Table 1 was melted, and it was set as the steel slab by continuous casting of the conditions shown in Table 2. In addition, continuous casting was performed by the low pressure method. Subsequently, these steel slabs were cracked after reheating under the conditions shown in Table 2, followed by hot rolling to obtain various steel sheets. In addition, cooling after hot rolling was made into air cooling to room temperature.

And the Sn segregation degree and the thickness of Sn segregation part were calculated | required in the steel plate obtained by the said method. The results are written together in Table 2.

In addition, when Sn segregation degree is less than 5, the description of the Sn segregation degree of Table 2 and the column of the thickness of Sn segregation part is made into "-".

(1) Evaluation of coating corrosion resistance

Moreover, about the steel plate obtained as mentioned above, the coating corrosion resistance was evaluated by the following methods.

That is, the test piece of 70 mm x 50 mm x 5 mm was extract | collected from the steel plate obtained as mentioned above. The surface of this test piece was shot blasted so that the rust removal degree Sa prescribed | regulated to JIS Z 0313 (2004) might be set to 2.5, ultrasonic degreasing in acetone was performed for 5 minutes, and it dried by the wind. Subsequently, one side of the test piece was used as a painted surface, and an inorganic zinc rich paint (SD zinc 1500A manufactured by Kansai Paint Co., Ltd., thickness: 75 µm) was applied as the anticorrosive base, and then an epoxy resin paint (Gansai Paint Co., Ltd.) was used as a mist coating. Kaisha Epomalin First Coating Mist Coating) was applied, and then epoxy resin paint (Epomalin HB (K), thickness: 120 μm manufactured by Kansai Paint Co., Ltd.) was applied as the first coating, followed by fluorine resin finishing as an intermediate coating. Coating intermediate paint (Seltec F Intermediate F Coating, thickness: 30 µm) for coating, followed by fluorine resin coating finish coating (Celatec F Finishing, manufactured by Kansai Paint Co., Ltd.) Paint, thickness: 25 탆), anticorrosive base layer, supercoat layer (including coating film formed by mist coating), medium To form a coating film made of a chilcheung and finishing chilcheung. In addition, the other single side | surface and the cross section of the test piece were sealed with the solvent-type epoxy resin paint, and were further coat | covered with the silicone type sealing agent.

After the coating, a straight cut having a width of 1 mm and a length of 40 mm was placed in the center of the coating film formed on the test piece so as to reach the base iron, and an initial defect was formed. Next, based on ISO 16539 2013, the corrosion test was done on condition shown below.

That is, a solution in which the artificial sea salt was diluted to a predetermined concentration with pure water was sprayed so that the artificial sea salt on the surface of the test piece became 6.0 g / m 2, and the artificial sea salt was attached to the test piece. Then, using this test piece, (condition 1. temperature: 60 degreeC, relative humidity: 35%, holding time: 3 hours), (condition 2. temperature: 40 degreeC, relative humidity: 95%, holding time: 3 hours) ), A corrosion test was performed in which a total of 8 hours of cycles, each of which has a transition time from condition 1 to condition 2 and condition 2 to condition 1 as 1 hour, was repeated 1 cycle, and this was repeated 1200 cycles. In addition, attachment of artificial sea salt was carried out once a week.

And after completion | finish of a corrosion test, the swelling width (henceforth a painting swelling width) from the initial-defect part in coating was measured, and the coating corrosion resistance was evaluated. Here, the coating swelling width is an average value of the coating swelling width (the swelling width of the sum of both sides) in the width direction of the initial defect, and specifically, the initial defect is 10 at equal intervals in the longitudinal direction. The coating swelling width (the swelling width of the total of both sides) in the width direction at the location is calculated | required, and these are averaged. Moreover, it was judged that coating corrosion resistance was excellent that the coating swelling width was 12.0 mm or less.

Here, the reason which judged that coating corrosion resistance was excellent when the coating swelling width is 12.0 mm or less is as follows.

That is, in general, when C5-based coating, which is a coating for newly formed bridges, is applied to ordinary steel, the life of the coating is about 50 years in a mild corrosion environment (general atmospheric corrosion environment). On the other hand, in harsh corrosive environments such as the sea and the coast, the paint life is about 30 years. Here, for example, in order to extend the life of the coating from 30 to 50 years in harsh corrosive environments such as the sea or the coast, it is necessary to suppress the swelling of the coating accompanying the corrosion of the steel through the coating defect. There is. Here, (a) the coating swelling area is shown as the first expression of the exposure period, and (b) the swelling shape is a circle or rectangle starting from a pinhole or the like, and the painting swelling area is 2 of the coating swelling width. Assuming that it is proportional to the power, 60% or less of the coating swelling area when the coating swelling area after exposing for a predetermined time in a predetermined environment is exposed to the same condition under ordinary conditions (speaking of the coating swelling width, 77.5% or less), and from the safety side, when it becomes 56.25% or less (about 75% or less in terms of coating swelling width), it can be considered that the life of the coating is extended from 30 years to 50 years.

When the above corrosion test was carried out by applying C5 coating to ordinary steel, the coating swelling width was 16.0 mm, so that the coating swelling width corresponding to 75% of the coating was 12.0 mm. I thought it was excellent.

In addition, the primary anticorrosiveness of each steel plate was evaluated by the following method.

That is, according to JIS K 5552 (2002): Salt-water sprayability test described in "Zink rich primer", the zinc rich primer (kansai paint Co., Ltd.) was made so that the dry film thickness might be set to 20 micrometers. Manufactured SD Zinc 1000) was applied, and after drying, a salt spray test was performed using these test pieces.

Then, the number of days until red rust was confirmed on the zinc rich primer layer by visual observation was measured, and the primary rust preventive property was evaluated by the following evaluation criteria.

In addition, in this evaluation, in order to evaluate the primary rust prevention property of the steel plate used as the base of a zinc rich primer layer, the test period was made longer than the test period prescribed by JISK5552 (2002).

A (passed, excellent): 120 days or more until red rust is identified

B (pass, especially excellent): 90 days or more and less than 120 days until red rust is identified

C (passed, excellent): 60 days or more and less than 90 days until red rust is confirmed

D (pass): 30 days or more and less than 60 days until red rust is confirmed

E (Failed): less than 30 days until red rust is confirmed

Furthermore, lamellar tear resistance evaluation was performed with the following tips.

(2) Evaluation of lamella tier resistance

In accordance with JIS G 3199, the tensile test of the steel plate obtained as mentioned above was performed in the plate | board thickness direction (Z direction) of the steel plate, and the drawing value was computed. And based on the calculated drawing value, lamellar tear resistance was evaluated on the following references | standards.

A (passed, very good): 85% or more

B (pass, especially excellent): 75% or more but less than 85%

C (pass, excellent): 65% or more and less than 75%

D (pass): 35% or more and less than 65%

E (failure): less than 35%

The evaluation results of (1) and (2) are written together in Table 2.

Table 1-1

Table 1-2

Table 2-1

Table 2-2

As shown in Table 2, all the invention examples have excellent coating corrosion resistance and lamella tier resistance.

On the other hand, in a comparative example, sufficient characteristic is not acquired about at least one of coating corrosion resistance and lamella tier resistance.

Claims (12)

In mass%,
C: 0.020% or more, 0.200% or less,
Mn: 0.20% or more, 2.00% or less,
P: 0.003% or more, 0.030% or less,
S: 0.0001% or more, 0.0100% or less,
Al: 0.001% or more, 0.100% or less and
Sn: 0.005% or more, 0.200% or less
With containing
Cu: 0.010% or more, 0.50% or less,
Ni: 0.010% or more, 0.50% or less,
W: 0.005% or more, 1.000% or less,
Sb: 0.005% or more, 0.200% or less and
Si: 0.05% or more, 1.00% or less
It contains 1 type or 2 or more types chosen from the remainder, and remainder has the component composition which consists of Fe and an unavoidable impurity,
Structural steel material with Sn segregation degree of 20 or less.
Here, Sn segregation degree is defined by following Formula (1).
[Sn Segregation Degree] = [Sn Segregation Part Sn Concentration] / [Mean Sn Concentration] --- (1) The method of claim 1,
The structural steel material whose thickness in the plate thickness direction of Sn segregation part is 50 micrometers or less. The method according to claim 1 or 2,
Structural steel material whose ST value defined by following formula (2) is 1.50 or less.
ST = 10000 × [% S] × [% Sn] ² --- (2)
[% S] and [% Sn] are content (mass%) of S and Sn in the said component composition, respectively. The method according to any one of claims 1 to 3,
The component composition is further, in mass%,
Mo: 0.500% or less and
Co: 1.00% or less
Structural steel containing 1 type or 2 types chosen from. The method according to any one of claims 1 to 4,
The component composition is further, in mass%,
Ti: 0.050% or less,
V: 0.200% or less,
Nb: 0.200% or less and
Zr: 0.100% or less,
Structural steel containing 1 type (s) or 2 or more types chosen from. The method according to any one of claims 1 to 5,
The component composition is further, in mass%,
B: Structural steel containing 0.0050% or less. The method according to any one of claims 1 to 6,
The component composition is further, in mass%,
Ca: 0.0100% or less and
Mg: 0.0100% or less,
Structural steel containing 1 type or 2 types chosen from. The method according to any one of claims 1 to 7,
Structural steel having a coating on its surface. The method of claim 8,
The coating film has an anticorrosive base layer, a rough coat layer, a middle coat layer and a finish coat layer,
Structural steel, wherein the anticorrosive base layer is an inorganic zinc rich paint, the primary coating layer is an epoxy resin coating, the intermediate coating layer is an intermediate coating paint for fluororesin finishing paint, and the finishing coating layer is a fluororesin finishing coating paint, respectively. . The method according to any one of claims 1 to 7,
Structural steel having a zinc rich primer layer on its surface. The structure formed using the structural steel material in any one of Claims 1-10. The method of claim 11,
Bridges, structures.