JP7192824B2 - Structural steel materials and structures with excellent fire resistance and paint corrosion resistance - Google Patents

Description

The present invention relates to a steel material with a coating film on its surface, which is mainly used on land and outdoors such as bridges in atmospheric corrosive environments, and in particular structures used in severe corrosive environments such as seas and coasts where there is a large amount of airborne salt. It relates to steel materials for use and structures.

Steel structures used outdoors, such as bridges, are usually used after being subjected to some kind of anticorrosion treatment. For example, weathering steel is often used in environments with a small amount of airborne salt.

Here, when the weathering steel is used in an atmospheric exposure environment, the surface is covered with a highly protective rust layer in which alloy elements such as Cu, P, Cr, and Ni are concentrated. It is a steel material that has been greatly reduced. It is known that bridges using such weather-resistant steel can withstand several decades of service without painting in an environment with a small amount of airborne salt.

On the other hand, it is difficult to form a highly protective rust layer on weathering steel in an environment with a large amount of airborne salt, such as at sea or near the coast, and it is difficult to use weathering steel without coating. For this reason, in environments where there is a large amount of airborne salt such as in the sea or near the coast, steel materials that have undergone anticorrosion treatment such as painting are usually used.

However, such a coated steel material requires periodic repair such as repainting due to degradation of the coating film, generation of rust, blistering of the coating film, etc. over time. The painting work associated with repainting is often done at high places, and the work itself is difficult, and labor costs for the work are also required. For this reason, when using coated steel, there is a problem that the maintenance cost of the structure increases, and thus the life cycle cost increases.

From the above, it is desired to develop steel materials with excellent corrosion resistance, especially structural steel materials with excellent paint corrosion resistance, that can extend the repainting cycle, that is, reduce the frequency of painting, and reduce the maintenance cost of structures. ing.

As a technique related to steel materials with excellent corrosion resistance, for example, Patent Document 1 discloses, in mass %, C: 0.001 to 0.15%, Si: 2.5% or less, Mn: more than 0.5% to 2.0%. 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 to 2.5%, N: 0.001 to 0.1%, Sn and/or Sb: 0.03 to 0.50%, the balance being Fe and impurities and having a composition in which the Ni/Cu mass ratio is 0.5 or less, a steel material excellent in seashore weather resistance is disclosed.

In Patent Document 2, in mass%, C: 0.001 to 0.15%, Si: 2.5% or less, Mn: more than 0.5% and 2.5% or less, P: less than 0.03% , S: 0.005% or less, Cu: less than 0.05%, Ni: less than 0.05%, 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 being Fe and impurities, and the surface temperature of the slab having a composition in which the Cu/Sn ratio is 1 or less. After heating to ° C., rolling is performed in a temperature range of 900 ° C. or higher by 70% or more of the total reduction amount, and after rolling is completed in a temperature range of 800 ° C. or higher, cooling is performed. Disclosed is a method for producing a steel having excellent Z-direction toughness.

In Patent Document 3, in mass%, C: 0.01 to 0.2%, Si: 0.01 to 1.0%, Mn: 0.05 to 3.0%, P: 0.05% or less , S: 0.01% or less, Sn: 0.01 to 0.5%, Cr: more than 1.0% and 13.0% or less, Al: 0.1% or less, the balance being Fe and impurities A steel material having excellent corrosion resistance is disclosed, which is characterized in that the ratio of solid-soluted Sn in Sn is 95.0% or more.

In Patent Document 4, in mass%, C: 0.01 to 0.2%, Si: 0.01 to 1.0%, Mn: 0.05 to 3.0%, P: 0.05% or less , S: 0.01% or less, Sn: 0.01 to 0.5%, Al: 0.1% or less, the balance being Fe and impurities, and the ratio of solid solution Sn in Sn is 95 A steel material with excellent corrosion resistance is disclosed, which is characterized by .0% or more.

In Patent Document 5, in mass%, C: 0.020% or more and 0.200% or less, Si: 0.05% or more and 1.00% or less, Mn: 0.20% or more and 2.00% or less, P : 0.003% or more and 0.030% or less, S: 0.0001% or more and 0.0100% or less, Al: 0.001% or more and 0.100% or less, Cu: 0.01% or more and 0.50% or less , Ni: 0.01% to 0.50% and W: 0.005% to 1.000%, Sn: 0.005% to 0.200% and Sb: 0.005% A steel material having a chemical composition containing one or two selected from the group consisting of 0.200% or less and the balance being iron and unavoidable impurities is disclosed.

On the other hand, in recent years, cases of steel structures such as bridges being damaged by fire have been reported. In the event of a fire, it is necessary for the structure to endure without collapsing until the users of the structure evacuate . Therefore, there is a need for a steel material that does not significantly deteriorate the strength characteristics of the steel member due to heat reception.

Regarding steel materials having such fire resistance performance, for example, Non-Patent Document 1 proposes an estimation formula using Mn, Si, Nb, Mo, Cr, and V regarding high temperature strength at 600 ° C., and these alloys The addition of elements is disclosed to increase the high temperature strength.

Japanese Patent Application Laid-Open No. 2006-118011 JP-A-2010-7109 JP 2013-166992 A JP 2012-255184 A JP 2018-40031 A

Fire Resistance Guidebook for Structural Materials 2017, Architectural Institute of Japan

However, the effects of various elements added for the purpose of improving corrosion resistance, as disclosed in Patent Documents 1 to 5, on fire resistance have not been clarified. For this reason, when the steel materials disclosed in Patent Documents 1 to 5 are applied to structures that may be damaged by fire as described above, there is a concern that the strength will decrease due to heat reception. In addition, if a large amount of a component such as Cr that improves corrosion resistance is contained, performance other than corrosion resistance may deteriorate. increases, the toughness of the steel material deteriorates.

In addition, it has not been clarified how the alloying elements added to increase the high-temperature strength as disclosed in Non-Patent Document 1 affect the corrosion resistance. For this reason, when applying the steel material using the technology disclosed in Non-Patent Document 1 to a structure that is provided by painting for the purpose of preventing corrosion, the increase in the frequency of painting will increase the life cycle cost. Concerned.

The present invention was developed in view of the above-mentioned current situation, and reduces the frequency of painting even when used in an atmospheric corrosive environment, especially in a severe corrosive environment such as the sea or near the coast where there is a large amount of airborne salt. It is an object of the present invention to provide a structural steel material and a structure having excellent corrosion resistance and excellent fire resistance.

The present inventors have made intensive studies to solve the above problems, and have obtained the following findings.
(1) In order to improve corrosion resistance, especially paint corrosion resistance, it is effective to add one or two selected from Mo, Sn and Sb together with W, Cu and Ni. Although the reason why the combined addition of these elements provides excellent corrosion resistance is unknown, it is presumed as follows.
W is eluted with the anode reaction and distributed in the rust layer as WO ₄ ^2- , thereby electrostatically preventing chloride ions, which are corrosion-promoting factors, from penetrating the rust layer and reaching the steel substrate. do. Furthermore, precipitation of compounds containing W on the surface of the steel suppresses the anodic reaction of the steel. Furthermore, the finer rust particles suppress permeation of corrosion-promoting factors such as chloride ions, thereby preventing anodic and cathodic reactions. Cu and Ni densify the rust layer and prevent chloride ions, which are corrosion-promoting factors, from penetrating the rust layer and reaching the steel substrate. Sn and Sb are present in the rust layer in the vicinity of the surface of the base iron, and by miniaturizing the rust particles, prevent chloride ions, which are corrosion-promoting factors, from penetrating the rust layer and reaching the base iron. In addition, it suppresses the anode reaction on the surface of the steel material. However, these effects are insufficient when contained alone, and the synergistic effect of containing these elements in combination greatly improves the corrosion inhibitory effect.
(2) Furthermore, from the viewpoint of fire resistance, it is effective to add one or more selected from Sn, Sb, and Mo together with W, Cu, and Ni.
(3) Based on the knowledge of (1) and (2), we further studied the effects of these elements on corrosion resistance and fire resistance, and found the F value that indicates fire resistance and the R value that indicates corrosion resistance. Then, the contents of W, Cu, Ni, Sn, and Sb are adjusted so that the R value is 0.75 or more, and the W, Cu, Ni, By adjusting the component contents of Sn, Sb, and Mo in steel, a steel material with excellent fire resistance and corrosion resistance can be obtained.

The present invention has been completed through further studies based on the above findings. That is, the gist and configuration of the present invention are as follows.
[1] % by mass,
C: more than 0.030% and 0.200% or less,
Si: 0.05% or more and 1.00% or less Mn: 0.20% or more and 2.00% or less,
P: 0.003% or more and 0.030% or less,
S: 0.0001% or more and 0.0100% or less,
Al: 0.001% or more and 0.100% or less,
W: 0.03% or more and 2.00% or less,
Cu: 0.03% or more and 0.50% or less,
Ni: containing 0.03% or more and 0.50% or less,
Sn: 0.005% or more and 0.200% or less,
Sb: 0.005% or more and 0.200% or less,
Mo: containing one or more selected from 0.01% or more and 1.00% or less,
Furthermore, the F value defined by formula (1) is 1.00 or more,
Furthermore, the R value defined by formula (2) is 0.75 or more,
A structural steel material having excellent fire resistance and paint corrosion resistance, the balance being composed of Fe and unavoidable impurities.
F=0.2×Cu+0.05×Ni+0.65×W+0.5×Sn+0.5×Sb+1.9×Mo (1)
R=3.5×Cu+4.5×Ni+8×W+4×(Sn+Sb) (2)
Here, Cu, Ni, W, Sn, Sb, and Mo are contents (% by mass) of each element.
[2] Furthermore, in % by mass,
The structural steel material having excellent fire resistance and paint corrosion resistance according to [1], characterized by containing Co: 0.010% or more and 1.000% or less.
[3] Furthermore, in % by mass,
Ti: 0.001% or more and 0.050% or less,
V: 0.005% or more and 0.200% or less,
Nb: 0.005% or more and 0.200% or less,
Zr: The structural steel material excellent in fire resistance and paint corrosion resistance according to [1] or [2], characterized by containing one or more selected from 0.005% or more and 0.200% or less.
[4] Furthermore, in % by mass,
B: The structural steel material having excellent fire resistance and paint corrosion resistance according to any one of [1] to [3], characterized by containing 0.0001% or more and 0.0050% or less.
[5] Furthermore, in % by mass,
Ca: 0.0001% or more and 0.0100% or less,
Mg: The structural use excellent in fire resistance and paint corrosion resistance according to any one of [1] to [4], characterized by containing one or more selected from 0.0001% or more and 0.0100% or less steel.
[6] The structural steel material having excellent fire resistance and paint corrosion resistance according to any one of [1] to [5], characterized by having a coating film on the surface of the structural steel material.
[7] The coating film has an inorganic zinc-rich paint as an anticorrosion base, an epoxy resin paint as an undercoat, an intermediate coat for a fluororesin topcoat as an intermediate coat, and a fluororesin topcoat as a top coat. The structural steel material having excellent fire resistance and paint corrosion resistance according to [6], characterized by:
[8] A structure having excellent fire resistance and paint corrosion resistance using the structural steel material according to any one of [1] to [7].
[9] The structure having excellent fire resistance and paint corrosion resistance according to [8], wherein the structure is a bridge.

According to the present invention, it is possible to extend the repainting cycle and reduce the painting frequency even when used in an atmospheric corrosive environment, particularly in a severely corrosive environment such as the sea or near the coast where a large amount of airborne salt content is present. It is possible to obtain a structural steel material that is possible and has excellent fire resistance. By using the structural steel material of the present invention for structures such as bridges that are used in outdoor atmospheric corrosive environments such as bridges, particularly in severe corrosive environments such as the sea or near the coast where there is a large amount of airborne salt, It is possible to reduce the maintenance cost of such a structure, and eventually the life cycle cost, and furthermore, it is possible to prevent deterioration of strength characteristics in the event of a fire and ensure high safety.

The present invention will be specifically described below.

First, the reason why the composition of the base material is limited in the present invention will be explained. Although the unit of content of elements in the chemical composition of steel is "% by mass", hereinafter, it is indicated simply as "%" unless otherwise specified.

C: more than 0.030% and 0.200% or less C is an element that increases the strength of the steel material. Therefore, in order to secure a predetermined strength as structural steel, C needs to be contained in an amount exceeding 0.030%. On the other hand, when the C content exceeds 0.200%, weldability and toughness deteriorate. Therefore, the C content should be more than 0.030% and 0.200% or less. Preferably, it is 0.040% or more. Moreover, it is preferably 0.180% or less.

Si: 0.05% to 1.00% Si is an element necessary for deoxidation during steelmaking. Such an effect is obtained when the Si content is 0.05% or more. On the other hand, when the Si content exceeds 1.00%, the toughness and weldability deteriorate significantly. Therefore, the Si content is 0.05% or more and 1.00% or less. Preferably it is 0.10% or more. Moreover, it is preferably 0.65% or less. More preferably, it is 0.55% or less.

Mn: 0.20% to 2.00% Mn is an element that increases the strength of steel materials. Therefore, Mn must be contained in an amount of 0.20% or more in order to secure a predetermined strength as structural steel. On the other hand, if the Mn content exceeds 2.00%, the toughness and weldability deteriorate and the alloy cost increases. Therefore, the Mn content should be 0.20% or more and 2.00% or less. Preferably it is 0.50% or more. Moreover, it is preferably 1.75% or less.

P: 0.003% or more and 0.030% or less P is an element that contributes to the improvement of the paint corrosion resistance of steel materials. From the viewpoint of obtaining such effects, it is necessary to contain 0.003% or more of P. On the other hand, when the P content exceeds 0.030%, the weldability deteriorates. Therefore, the P content should be 0.003% or more and 0.030% or less.

S: 0.0001% to 0.0100% S is an element that deteriorates weldability and toughness. Therefore, the S content should be 0.0100% or less. However, an attempt to reduce the S content to less than 0.0001% increases production costs. Therefore, the S content should be 0.0001% or more and 0.0100% or less.

Al: 0.001% or more and 0.100% or less Al is an element necessary for deoxidation during steelmaking. In order to obtain such effects, it is necessary to contain 0.001% or more of Al. On the other hand, if the Al content exceeds 0.100%, the weldability is adversely affected. Therefore, the Al content should be 0.001% or more and 0.100% or less. It is preferably 0.005% or more, more preferably 0.010% or more. Also, it is preferably less than 0.050%, more preferably less than 0.030%.

W: 0.03% or more and 2.00% or less W is an important element in the steel material of the present invention. By adding W in combination with Cu, Ni, Sn, Sb, and Mo, the synergistic effect with these elements significantly increases the fire resistance of the steel material. In addition, it is eluted with the anode reaction and distributed as WO ₄ ^2- in the rust layer, thereby electrostatically preventing chloride ions, which are corrosion-promoting factors, from penetrating the rust layer and reaching the base iron. do. Furthermore, precipitation of compounds containing W on the surface of the steel suppresses the anodic reaction of the steel. Furthermore, the finer rust particles suppress permeation of corrosion-promoting factors such as chloride ions, thereby preventing anodic and cathodic reactions. Furthermore, by adding W in combination with Cu, Ni, Sn, and Sb, the synergistic effect with these elements greatly improves the paint corrosion resistance of the steel material. In order to sufficiently obtain these effects, it is necessary to contain 0.03% or more of W. On the other hand, if the W content exceeds 2.00%, the alloy cost will increase. Therefore, the W content should be 0.03% or more and 2.00% or less. It is preferably 0.04% or more and 1.00% or less, more preferably 0.05% or more and 0.75% or less.

Cu: 0.03% or more and 0.50% or less Cu is an important element in the steel material of the present invention, and increases the room-temperature strength and high-temperature strength of the base material by solid-solution strengthening. In addition, it has the effect of forming a dense rust layer by making the rust grains of the rust layer finer, and suppressing permeation of oxygen and chloride ions, which are factors that promote corrosion, into the base iron. These effects are obtained when the Cu content is 0.03% or more. On the other hand, when the Cu content exceeds 0.50%, the alloy cost increases. Therefore, the Cu content should be 0.03% or more and 0.50% or less. It is preferably 0.04% or more and 0.40% or less, more preferably 0.05% or more and 0.30% or less.

Ni: 0.03% or more and 0.50% or less Ni is an important element in the steel material of the present invention, and increases the room-temperature strength and high-temperature strength of the base material by solid-solution strengthening. In addition, Ni forms a fine rust layer by refining the rust grains of the rust layer, and has the effect of suppressing permeation of oxygen and chloride ions, which are factors that promote corrosion, into the base steel. These effects are obtained when the Ni content is 0.03% or more. On the other hand, when the Ni content exceeds 0.50%, the alloy cost increases. Therefore, the Ni content should be 0.03% or more and 0.50% or less. It is preferably 0.04% or more and 0.40% or less, more preferably 0.05% or more and 0.30% or less.

The present invention contains the above components and one or more selected from the following components.

Sn: 0.005% or more and 0.200% or less Sn is an important element in the steel material of the present invention, and increases the room-temperature strength and high-temperature strength of the base material by solid-solution strengthening. In addition, it is present in the rust layer near the surface of the base iron, and by miniaturizing the rust particles, it prevents chloride ions, which are corrosion-promoting factors, from penetrating the rust layer and reaching the base iron. In addition, Sn suppresses the anode reaction on the surface of the steel material. In order to sufficiently obtain these effects, the Sn content should be 0.005% or more. On the other hand, when the Sn content exceeds 0.200%, the ductility and toughness of the steel deteriorate. Therefore, the Sn content should be 0.005% or more and 0.200% or less. It is preferably 0.010% or more and 0.100% or less, more preferably 0.020% or more and less than 0.050%.

Sb: 0.005% or more and 0.200% or less Sb is an important element in the steel material of the present invention, and increases the room-temperature strength and high-temperature strength of the base material by solid-solution strengthening. In addition, it is present in the rust layer near the surface of the base iron, and by miniaturizing the rust particles, it prevents chloride ions, which are corrosion-promoting factors, from penetrating the rust layer and reaching the base iron. Moreover, Sb suppresses the anode reaction on the surface of the steel material. In order to sufficiently obtain these effects, the Sb content should be 0.005% or more. On the other hand, when the Sb content exceeds 0.200%, the ductility and toughness of the steel deteriorate. Therefore, the Sb content should be 0.005% or more and 0.200% or less. It is preferably 0.010% or more and 0.100% or less, more preferably 0.020% or more and less than 0.050%.

Mo: 0.01% or more and 1.00% or less Mo is an important element in the steel material of the present invention. Furthermore, high-temperature strength is increased by forming carbonitrides at high temperatures. In addition, MoO ₄ ^2- is eluted with the anodic reaction of the steel material and distributed in the rust layer, thereby suppressing chloride ions, which are corrosion-promoting factors, from penetrating the rust layer and reaching the base iron. . In addition, a compound containing Mo precipitates on the surface of the steel material, thereby suppressing the anode reaction of the steel material. In order to sufficiently obtain these effects, it is necessary to contain Mo at 0.01% or more. However, when the Mo content exceeds 1.00%, the alloy cost increases. Therefore, Mo content shall be 0.01% or more and 1.00% or less. It is preferably 0.05% or more and 1.00% or less, more preferably 0.10% or more and 0.75% or less.

Moreover, in the present invention, it is important to control the F value defined by the following formula (1) to 1.00 or more.
F=0.2×Cu+0.05×Ni+0.65×W+0.5×Sn+0.5×Sb+1.9×Mo (1)
Here, Cu, Ni, W, Sn, Sb, and Mo are contents (% by mass) of each element.
However, an element whose content analysis value is below the detection limit shall be 0 (zero)%.
The F value represented by the above formula (1) is an index indicating the fire resistance of steel materials, and is set to 1.00 or more in order to obtain excellent fire resistance. The upper limit is not limited, and the larger the value, the better the fire resistance. 00 to 1.40 is preferred.

Also, in the present invention, it is important to control the R value defined by the following formula (2) to 0.75 or more.
R=3.5×Cu+4.5×Ni+8×W+4×(Sn+Sb) (2)
Here, Cu, Ni, W, Sn, and Sb are contents (% by mass) of each element.
However, an element whose content analysis value is below the detection limit shall be 0 (zero)%.
The R value represented by the above formula (2) is an index indicating the corrosion resistance of steel materials, and in order to obtain excellent corrosion resistance, the R value should be 0.75 or more. The upper limit is not limited, and the larger the value, the better the corrosion resistance, and it may be set appropriately according to the desired corrosion resistance. 20.0 is preferred.
In addition, the F value and R value were calculated by the formulas (1) and (2) by investigating the relationship between the amount of each component and the fire resistance and corrosion resistance.

Although the basic components have been described above, the elements described below can be appropriately contained as necessary.

Co: 0.010% or more and 1.000% or less Co is distributed throughout the rust layer and forms a dense rust layer by refining the rust grains, thereby improving the weather resistance of the steel material. have. In order to obtain these effects, it is necessary to contain 0.010% or more of Co. However, if the Co content exceeds 1.000%, the alloy cost will increase. Therefore, when Co is contained, the Co content should be 0.010% or more and 1.000% or less. It is preferably 0.030% or more and 0.500% or less, more preferably 0.100% or more and 0.350% or less.

Ti: 0.001% or more and 0.050% or less Ti is an element that increases room-temperature strength and high-temperature strength when added in a small amount. In order to obtain these effects, it is necessary to contain 0.001% or more of Ti. However, if the Ti content exceeds 0.050%, there is a risk of deterioration in toughness. Therefore, when Ti is contained, the Ti content should be 0.001% or more and 0.050% or less. Preferably, it is 0.005% or more and 0.030% or less.

V: 0.005% or more and 0.200% or less V is an element that increases room-temperature strength and high-temperature strength when added in a very small amount. In order to obtain these effects, it is necessary to contain 0.005% or more of V. However, when the V content exceeds 0.200%, the effect is saturated. Therefore, when V is contained, the V content should be 0.050% or more and 0.200% or less. It is preferably 0.010% or more and 0.100%.

Nb: 0.005% or more and 0.200% or less Nb is an element that increases room-temperature strength and high-temperature strength when added in a very small amount. In order to obtain these effects, it is necessary to contain 0.005% or more of Nb. However, if the Nb content exceeds 0.200%, there is a risk of deterioration in toughness. Therefore, when Nb is contained, the Nb content should be 0.005% or more and 0.200% or less. Preferably, it is 0.010% or more and 0.050% or less.

Zr: 0.005% or more and 0.200% or less Zr is an element that increases room-temperature strength and high-temperature strength when added in a very small amount. In order to obtain these effects, it is necessary to contain 0.005% or more of Zr. However, when the Zr content exceeds 0.200%, the effect is saturated. Therefore, when Zr is contained, the Zr content should be 0.005% or more and 0.200% or less. It is preferably 0.010% or more and 0.200% or less.

B: 0.0001% or more and 0.0050% or less B is an element that increases strength. In order to obtain this effect, it is necessary to contain 0.0001% or more. However, if the B content exceeds 0.0050%, there is a risk of deterioration in toughness. Therefore, when B is contained, the B content should be 0.0001% or more and 0.0050% or less. It is preferably 0.0005% or more and 0.0025% or less.

Ca: 0.0001% or more and 0.0100% or less Ca is an element that fixes S in steel and improves the toughness of the weld heat affected zone. In order to obtain this effect, the content should be 0.0001% or more. However, when the Ca content exceeds 0.0100%, the amount of inclusions in the steel increases, rather causing deterioration of toughness. Therefore, when Ca is contained, the Ca content should be 0.0001% or more and 0.0100% or less. In addition, Ca content is preferably 0.0005% or more and 0.0080% or less.

Mg: 0.0001% to 0.0100% Mg is an element that fixes S in steel and improves the toughness of the weld heat affected zone. In order to obtain this effect, the content should be 0.0001% or more. However, when the Mg content exceeds 0.0100%, the amount of inclusions in the steel increases, resulting in deterioration of toughness. Therefore, when Mg is contained, the Mg content should be 0.0001% or more and 0.0100% or less. In addition, it is preferably 0.0005% or more and 00080% or less.

Components other than the above are Fe and unavoidable impurities. Inevitable impurities include N and O (oxygen), and N: 0.010% or less and O: 0.010% or less are permissible.

Further, the structural steel material of the present invention is used after coating the surface of the steel material. Here, the coating film on the surface of the steel material is not particularly limited, but for example, a coating film having an anticorrosive base layer, an undercoat layer, an intermediate coating layer and a top coating layer in this order, an undercoat layer, an intermediate coating layer and a top coating A coating film having coating layers in this order can be mentioned.

In addition, for example, in the case of a coating film having an anticorrosion base layer, an undercoat layer, an intermediate coat layer and a topcoat layer in this order, the anticorrosion base layer is an inorganic zinc-rich paint (e.g., SD Zinc 1500), and the undercoat layer is an epoxy resin paint ( For example, EPOMARINE HB (K)), an intermediate coating for a fluororesin top coating (e.g., Ceratect F intermediate coating) for the intermediate layer, and a fluororesin top coating (e.g., Ceratect F (K) top coating) for the top coating layer. preferably formed.

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

The zinc-rich primer layer is a primer layer formed using a zinc-rich primer specified in JIS K 5552 (2002). The functional primer layer is a primer layer formed by using a functional primer whose zinc content is reduced to about 50% compared to the zinc-rich primer to improve weldability and fusibility.

Next, a manufacturing method according to one embodiment of the structural steel material described above will be described. The production method is not particularly limited, but the following method is preferred.

That is, the steel prepared to the above composition is melted using a known refining process such as a converter, electric furnace, vacuum degassing, etc., and the steel material (slab ), and then hot-rolled after reheating the steel material as necessary to produce a steel plate or shaped steel.

Although the thickness of the steel material is not particularly limited, it is preferably 2 to 100 mm. It is more preferably 3 mm or more, still more preferably 4 mm or more. Also, it is more preferably 80 mm or less, and still more preferably 60 mm or less.

When hot-rolling the above steel material into a desired size and shape, it is preferable to heat it to a temperature of 1000°C to 1350°C. If the heating temperature is lower than 1000° C., the deformation resistance increases, and rolling may become difficult due to the increased rolling load in the subsequent rolling step. On the other hand, if the heating temperature exceeds 1350° C., surface marks may occur, or excessive scale formation may reduce the yield and increase the fuel consumption rate. Therefore, the heating temperature is preferably 1000°C to 1350°C. More preferably, it is in the range of 1050°C to 1300°C. When the temperature of the steel material is originally in the range of 1000 to 1350° C., the steel material may be directly subjected to hot rolling without heating. Alternatively, the hot-rolled sheet obtained after hot rolling may be reheated, acid-rolled, and cold-rolled to obtain a cold-rolled sheet having a predetermined thickness.

The heated slab is then subjected to hot rolling, ending at temperatures above 600° C., to form steel sheets of desired dimensions. If the rolling finishing temperature is less than 650°C, the deformation resistance of the steel sheet increases, and rolling becomes difficult due to the increased rolling load. Therefore, the rolling finishing temperature is set to 600° C. or higher. It is preferably 650° C. or higher.

The cooling conditions after the hot rolling is completed may be appropriately determined depending on the required material, and air cooling or accelerated cooling may be performed. Moreover, you may perform tempering heat processing after that.

As described above, according to the present invention, even when used in an atmospheric corrosive environment, especially in a severe corrosive environment such as the sea or near the coast where there is a large amount of airborne salt, the repainting cycle is extended to reduce the painting frequency. It is possible to obtain a structural steel material that can be used and has excellent fire resistance.

In addition, by using the structural steel material of the present invention in structures such as bridges that are used in outdoor atmospheric corrosive environments such as bridges, particularly in severe corrosive environments such as the sea or near the coast where there is a large amount of airborne salt. , it becomes possible to reduce the maintenance cost of such a structure, and eventually the life cycle cost, and furthermore, it is possible to prevent the deterioration of strength characteristics in the event of a fire and ensure a high degree of safety.

Steel having the chemical composition shown in Table 1 (the balance being Fe and unavoidable impurities) was melted, heated to 1120 ° C., hot rolled at a finishing temperature of 800 ° C., and air-cooled to a thickness of 15 mm. of steel sheets were obtained. Then, fire resistance and coating corrosion resistance were evaluated in the following manner.

(1) Evaluation of fire resistance A JIS No. 4 tensile test piece (round bar) was taken from the 1/4 position of the plate thickness of each steel plate so that the tensile direction was parallel to the direction perpendicular to the rolling direction, and the yield strength at room temperature The strength YS, tensile strength TS and yield strength YS at a high temperature of 600° C. were determined. In addition, if the yield strength YS at a high temperature of 600° C. is 2/3 or more of the YS standard value at room temperature, it is considered to be excellent in fire resistance. Here, the normal temperature YS standard value is based on the required standard, for example, JIS G 3106 for rolled steel for welded structures.

(2) Evaluation of Paint Corrosion Resistance A test piece of 70 mm×50 mm×5 mm was taken from a steel plate. The surface of this test piece was shot-blasted so that the degree of rust removal Sa specified in JIS Z 0313 (2004) was 2.5, ultrasonically degreased in acetone for 5 minutes, and air-dried. Next, 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 an anticorrosive base, and then an epoxy resin paint (manufactured by Kansai Paint Co., Ltd.) was applied as a mist coat. Epomarine undercoat for mist coat) is applied, then epoxy resin paint (Epomarine HB (K) manufactured by Kansai Paint Co., Ltd., thickness: 120 μm) is applied as an undercoat, and then an intermediate coat for fluororesin topcoat as an intermediate coat. (Kansai Paint Co., Ltd. Ceratect F intermediate paint, thickness: 30 μm) is applied, and then a fluororesin topcoat paint (Kansai Paint Co., Ltd. Ceratect F top paint, thickness: 25 μm) is applied as a topcoat to prevent corrosion. A coating film consisting of a base layer, an undercoat layer (including a coating film formed by mist coating), an intermediate coating layer and a top coating layer was formed. The other side and the end face of the test piece were sealed with a solvent type epoxy resin paint and further coated with a silicon-based sealing agent. After coating, a linear cut with a width of 1 mm and a length of 40 mm was made in the central part of the coating film formed on the test piece so as to reach the steel base, thereby forming an initial defect. Then, in accordance with ISO 16539 2013, a corrosion test was carried out under the conditions shown below.
That is, a solution obtained by diluting artificial sea salt with pure water to a predetermined concentration was sprayed so that the amount of artificial sea salt adhered to the surface of the test piece was 6.0 g/m ² , and the artificial sea salt adhered to the test piece. let me Then, using this test piece, from condition 1 (temperature: 60 ° C., relative humidity: 35%, holding time: 3 hours) to condition 2 (temperature: 40 ° C., relative humidity: 95%, holding time: 3 hours) A corrosion test was carried out by repeating 1200 cycles of a total of 8 hours, with each transition time from Condition 2 to Condition 1 being 1 hour. The artificial sea salt was applied once a week. After the corrosion test was completed, the area of blistering from the initial defect in the coating (hereinafter referred to as blistering area of coating) was measured to evaluate the corrosion resistance of the coating. In addition, it was judged that the coating corrosion resistance was excellent if the coating bulging area was 548 mm ² or less.

Table 2 shows the evaluation results.

As shown in Table 2, all invention examples have both excellent fire resistance and paint corrosion resistance.

In contrast, in the comparative examples, sufficient properties were not obtained with respect to at least one of fire resistance and paint corrosion resistance.

Claims (9)

in % by mass,
C: more than 0.030% and 0.200% or less,
Si: 0.05% or more and 1.00% or less Mn: 0.20% or more and 2.00% or less,
P: 0.003% or more and 0.030% or less,
S: 0.0001% or more and 0.0100% or less,
Al: 0.001% or more and 0.100% or less,
W: 0.03% or more and 2.00% or less,
Cu: 0.03% or more and 0.50% or less,
Ni: containing 0.03% or more and 0.50% or less,
Sn: 0.005% or more and 0.200% or less,
Sb: 0.005% or more and 0.200% or less,
Mo: containing one or more selected from 0.01% or more and 1.00% or less,
Furthermore, the F value defined by formula (1) is 1.00 or more,
Furthermore, the R value defined by formula (2) is 0.75 or more,
A structural steel material having excellent fire resistance and paint corrosion resistance, the balance being composed of Fe and unavoidable impurities.
F=0.2×Cu+0.05×Ni+0.65×W+0.5×Sn+0.5×Sb+1.9×Mo (1)
R=3.5×Cu+4.5×Ni+8×W+4×(Sn+Sb) (2)
Here, Cu, Ni, W, Sn, Sb, and Mo are contents (% by mass) of each element. Furthermore, in mass %,
The structural steel material according to claim 1, characterized by containing Co: 0.010% or more and 1.000% or less. Furthermore, in mass %,
Ti: 0.001% or more and 0.050% or less,
V: 0.005% or more and 0.200% or less,
Nb: 0.005% or more and 0.200% or less,
Zr: The structural steel material excellent in fire resistance and paint corrosion resistance according to claim 1 or 2, characterized by containing one or more selected from 0.005% or more and 0.200% or less. Furthermore, in mass %,
B: The structural steel material having excellent fire resistance and paint corrosion resistance according to any one of claims 1 to 3, characterized by containing 0.0001% or more and 0.0050% or less. Furthermore, in mass %,
Ca: 0.0001% or more and 0.0100% or less,
Mg: 0.0001% or more, 0.0100% or less for structure excellent in fire resistance and paint corrosion resistance according to any one of claims 1 to 4, characterized by containing one or more selected from 0.0100% or less steel. The structural steel material having excellent fire resistance and paint corrosion resistance according to any one of claims 1 to 5, characterized by having a coating film on the surface of the structural steel material. The coating film has an inorganic zinc-rich paint as an anticorrosion base, an epoxy resin paint as an undercoat, an intermediate coat for a fluororesin topcoat as an intermediate coat, and a fluororesin topcoat as a topcoat. Structural steel material excellent in fire resistance and paint corrosion resistance according to claim 6. A structure having excellent fire resistance and paint corrosion resistance, using the structural steel material according to any one of claims 1 to 7. 9. The structure having excellent fire resistance and paint corrosion resistance according to claim 8, wherein the structure is a bridge.