KR101943240B1 - Structural steel material having excellent atmospheric corrosion resistance - Google Patents

Abstract

Providing structural steel having excellent weather resistance at low cost. At least 0.01% to less than 0.20% of Si, at least 0.05% of at least 1.00% of Mn, at least 0.20% of Mn, up to 2.00% of P, 0.001% to 0.050% : 0.005% to 0.050%, Cu: 0.010% to 0.500%, Nb: 0.005% to 0.100%, Sn: 0.005% to 0.300% , And the balance of iron and inevitable impurities.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a structural steel material having excellent weather resistance,

The present invention relates to a structural steel material. Particularly, the present invention relates to a structural steel which is desirable as a member which requires weatherability under an environment in which the amount of fly ash is relatively small and the corrosion resistance is not so high.

BACKGROUND ART [0002] Weathering steels are conventionally used for steel structures used in outdoor applications such as bridges. Weathering steel is a steel material whose corrosion rate is remarkably reduced by covering the surface with a highly protective green layer in which alloying elements such as Cu, P, Cr and Ni are concentrated in an atmospheric corrosive environment. Due to its excellent weatherability, bridges using weather-resistant steel are known to withstand decades of common use without being painted.

Weathering steels were developed in the United States in the 1930s and applied to structures such as buildings. After that, it was introduced in Japan, and weather-resistant steel was produced and applied to bridges and so on. As such, the weather-resistant steel has been widely introduced in various countries after its development in the United States. In countries with significant economic development represented by BRICS, the maintenance of infrastructure is currently being carried out, and in particular, the increase in maintenance costs is questionable. For example, in a non-painted bridge using weather-resistant steel, it is possible to suppress the maintenance cost to a lower level as compared with the coating bridges, and application of the weather-resistant steel is also desired in such countries. Considering that these economic developments are used in countries with remarkable economies, it is considered necessary to lower the cost of steel. For example, as a low cost steel, a low alloy cost can be cited. In addition, these countries are considered to have a relatively large land area and a region distant from the shoreline, that is, an environment with low salinity. Therefore, there is a demand for a steel material that can be used in unprepared areas in an environment where the amount of salinity is relatively small and the corrosion resistance is not so high.

As a method for improving the weatherability of a steel so far, for example, Patent Document 1 discloses a high-weatherability steel containing Cu and at least 1% by mass of Ni added thereto. Patent Document 2 discloses a steel material excellent in weather resistance to which 1 mass% or more of Ni and Mo is added. Patent Document 3 discloses a steel material excellent in weather resistance to which Cu and Ti are added in addition to Ni. Patent Document 4 discloses a steel for welded structure containing a large amount of Ni and further containing Cu, Mo, Sn, Sb, P and the like. Patent Document 5 discloses a steel material excellent in corrosion resistance added with Sn.

Japanese Laid-Open Patent Publication No. 11-172370 Japanese Laid-Open Patent Publication No. 2002-309340 Japanese Patent Application Laid-Open No. 11-71632 Japanese Patent Application Laid-Open No. 10-251797 Japanese Laid-Open Patent Publication No. 2012-255184

However, when the content of Ni is increased as in Patent Documents 1, 2 and 3, there is a problem that the cost of the steel increases due to an increase in the alloy cost. In addition, as in Patent Document 4, the steel material containing Cu, Mo, Sn, Sb, or the like increases the content of Ni and P and increases the cost of the steel due to an increase in alloy cost, The weldability is lowered. Also, when the content of Sn is increased as in Patent Document 5, there is a problem that the cost of the steel increases due to an increase in the alloy cost and promotes hot brittleness.

The present invention has been made in view of such circumstances, and an object thereof is to provide a structural steel material having excellent weather resistance at a low cost.

In order to solve the above problems, the composition of the steel material has been studied extensively from the viewpoint of weatherability. As a result, it has been found that the weatherability of the steel material is improved by containing Cu, further containing trace amounts of Nb and Sn, and strictly controlling the solid content of Nb. As described above, the reason for the excellent weatherability is unclear, but is estimated as follows. Cu makes the green layer densified by finely granulating the green particles to prevent oxygen or chloride ions, which are corrosion promoting factors, from penetrating through the green layer to reach the steel, and by being concentrated in the vicinity of the steel surface, . Nb is concentrated in the vicinity of the steel surface, thereby suppressing the anode reaction and the cathode reaction of the steel. Particularly, in order to improve the weather resistance, it is important that Nb exists in a solid state in the steel. Sn, like Nb, is concentrated in the vicinity of the steel surface, thereby suppressing the anode reaction and the cathode reaction of the steel. However, it is presumed that these effects are insufficient in the solids content, and the corrosion resistance is remarkably improved by the inclusion of Cu, Nb and Sn.

The gist of the present invention is as follows.

The steel sheet according to any one of the above items [1] to [6], wherein C: 0.01 to 0.20%, Si: 0.05 to 1.00%, Mn: 0.20 to 2.00%, P: 0.001 to 0.050% 0.005% or more and 0.300% or less of Sn; Nb in an amount of 0.005% or more and 0.300% or less in terms of Nb; 0.002% or more and 0.080% or more in solid content of Nb; % Or less, and the balance of iron and inevitable impurities.

[2] The structural steel according to [1], further comprising, in mass%, Ge: 0.0005% or more and 0.0100% or less.

[3] The structural steel according to [1] or [2], further comprising, by mass%, Ta: 0.001% or more and 0.100% or less.

[4] The structural steel according to any one of [1] to [3], further comprising Ni in an amount of 0.01% or more and 0.50% or less in terms of mass%.

Co: 0.01% or more and 0.50% or less, W: 0.005% or more and 0.500% or less, Sb: 0.005% or more and 0.200% or less, Sc: 0.001% or less, Of at least one selected from the group consisting of Sr, Sr, and Ca at 0.001% or more and 0.200% or less, Sr, 0.001% or more and 0.200% or less,

[6] The steel sheet according to any one of [1] to [6], further comprising at least one selected from the group consisting of 0.005 to 0.200% of V, 0.005 to 0.200% of Zr, and 0.0001 to 0.0050% 5], wherein the structural steel has excellent weather resistance.

[7] The steel sheet according to any one of [1] to [5], further comprising at least one member selected from the group consisting of 0.0001% to 0.0100% of REM, 0.0001% to 0.0100% of Ca and 0.0001% 6]. ≪ / RTI >

The excellent weather resistance in the present invention means that the average plate thickness reduction amount is not more than 20.0 占 퐉 in the weather resistance evaluation in Examples described later.

According to the present invention, a structural steel material excellent in weather resistance can be obtained. INDUSTRIAL APPLICABILITY The structural steel according to the present invention has a low cost and excellent weather resistance by compounding elements effective for improving weather resistance.

Hereinafter, the present invention will be described in detail. In the following description, the units of the content of each element of the steel component composition are "% by mass ", and are simply expressed as "% "

C: 0.01% or more and less than 0.20%

C is an element for improving the strength of the structural steel, and it is necessary to contain at least 0.01% in order to secure a predetermined strength. On the other hand, if it is 0.20% or more, the weldability and toughness are deteriorated. Therefore, the C content is set to be not less than 0.01% and not more than 0.20%.

Si: not less than 0.05% and not more than 1.00%

Si has an effect of improving the weatherability of the steel material by forming a dense green layer by making the green layer fine-grained. It also has an effect of preventing the surface of the steel material from cracking during hot rolling. In order to obtain these effects, it is necessary to contain not less than 0.05%. The content is preferably 0.10% or more, more preferably 0.15% or more. On the other hand, if it is contained in excess of 1.00%, the toughness and weldability are remarkably deteriorated. Therefore, the Si content is 1.00% or less. The content is preferably 0.80% or less, more preferably 0.60% or less.

Mn: not less than 0.20% and not more than 2.00%

Mn is an element which improves the strength of the structural steel and is required to contain 0.20% or more in order to secure a predetermined strength. The content is preferably 0.40% or more. On the other hand, if it exceeds 2.00%, the toughness and weldability deteriorate. Therefore, the Mn content should be 2.00% or less. Preferably, it is 1.70% or less.

P: not less than 0.001% and not more than 0.050%

P is an element that improves the weatherability of the structural steel. In order to obtain such an effect, it is necessary to contain 0.001% or more. The content is preferably 0.003% or more, more preferably 0.005% or more. On the other hand, if it exceeds 0.050%, the weldability deteriorates. The content is preferably 0.030% or less, more preferably 0.020% or less.

S: 0.0001% or more and 0.0200% or less

If S is contained in excess of 0.0200%, weldability and toughness are deteriorated. The content is preferably 0.0100% or less, and more preferably 0.0050% or less. On the other hand, if the content is lowered to less than 0.0001%, the production cost is increased. The content is preferably 0.0003% or more, and more preferably 0.0005% or more.

Al: 0.005% or more and 0.050% or less

Al is an element necessary for deoxidation in steelmaking. In order to obtain such an effect, it is necessary to contain Al in an amount of 0.005% or more. It is preferably 0.010% or more. On the other hand, if it exceeds 0.050%, the weldability is adversely affected. The content is preferably 0.040% or less.

Cu: not less than 0.010% and not more than 0.500%

Cu is an important requirement in the present invention, and coexists with Nb and Sn, thereby remarkably improving the weatherability of the steel. Cu is enriched near the green layer-steel interface to inhibit the anode reaction of the steel. In addition, it has an effect of forming a dense green layer by making the green layer fine-grained and suppressing the permeation of chloride ions, which are corrosion-promoting factors, into the substrate. These effects are obtained at a content of 0.010% or more. The content is preferably 0.020% or more, more preferably 0.035% or more. On the other hand, if it exceeds 0.500%, the increase in the cost of Cu increases. Therefore, the Cu content is 0.500% or less. Preferably 0.300% or less, more preferably 0.200% or less, and further preferably 0.150% or less.

Nb: 0.005% or more and 0.100% or less

Nb is an important requirement in the present invention, and coexisting with Cu and Sn has the effect of remarkably improving the weatherability of the steel material. Nb is concentrated in the vicinity of the interface between the green layer and the base iron in the anode portion, thereby suppressing the anode reaction and the cathode reaction. In order to sufficiently obtain these effects, it is necessary to contain 0.005% or more. The content is preferably 0.008% or more, more preferably 0.010% or more. On the other hand, if it exceeds 0.100%, the toughness is lowered. Therefore, the content of Nb is 0.100% or less. , Preferably not more than 0.050%, and more preferably not more than 0.030%.

Emulsified Nb amount: 0.002% or more and 0.080% or less

In order to improve the weatherability by the addition of Nb, it is important to set the content in the above range and to further set the amount of Nb in the steel to a suitable amount. In order for Nb in the steel to exhibit the above-described weathering-improving effect, it is necessary that Nb is eluted into the green layer in the form of oxygen acid or oxide with corrosion of the steel material. On the other hand, Nb carbonitride is generally known as a poorly soluble substance, and it is difficult to elute it into the green layer in the above form. Therefore, when Nb forms carbonitride, the amount of dissolved Nb in the periphery thereof decreases, so that the effect of improving the weatherability is reduced. When the amount of solute Nb is less than 0.002%, the effect of improving the weatherability is not sufficiently obtained. Therefore, the solid content of Nb is 0.002% or more. The amount of dissolved Nb is preferably 0.005% or more, more preferably 0.008%. On the other hand, if the amount of solid solution Nb exceeds 0.080%, the manufacturing cost is increased. Therefore, the amount of dissolved Nb is 0.080% or less. Preferably 0.040% or less, and more preferably 0.025% or less.

Sn: not less than 0.005% and not more than 0.300%

Sn is an important requirement in the present invention, and coexisting with Cu and Nb has the effect of remarkably improving the weatherability of the steel material. Sn is concentrated in the vicinity of the interface between the green layer and the base metal to suppress the anode reaction and the cathode reaction of the steel. In addition, the penetration of chloride ions, which is a corrosion promoting factor, is suppressed by making the green layer thinner. In order to sufficiently obtain these effects, it is necessary to contain 0.005% or more. The content is preferably 0.010% or more, more preferably 0.020% or more. On the other hand, if it exceeds 0.300%, the ductility and toughness of the steel are deteriorated. In addition, the increase in the consumption of Sn leads to an increase in cost. Therefore, the Sn content is 0.300% or less. , Preferably not more than 0.100%, more preferably not more than 0.045%, and still more preferably not more than 0.035%.

The remainder is Fe and inevitable impurities. Herein, as an inevitable impurity, for example, 0.010% or less of N and 0.010% or less of O can be allowed.

With the indispensable element described above, the steel of the present invention has desired properties. In addition to the above essential elements, the present invention may contain the following elements as necessary.

Ge: 0.0005% or more and 0.0100% or less

Ge coexists with Cu, Nb and Sn, thereby remarkably improving the weatherability of the steel. Ge is concentrated in the vicinity of the interface between the green layer and the base metal in the anode portion, thereby suppressing the anode reaction and the cathode reaction. In order to sufficiently obtain these effects, the content is 0.0005% or more. The content is preferably 0.0010% or more. On the other hand, if it exceeds 0.0100%, the toughness of the steel may be deteriorated. Therefore, the Ge content is set to 0.0100% or less. The content is preferably 0.0050% or less.

Ta: 0.001% or more and 0.100% or less

Ta has an effect of remarkably improving the weatherability of the steel material by coexisting with Cu, Nb and Sn (and optionally Ge). Ta is concentrated in the vicinity of the interface between the green layer and the base metal in the anode portion, thereby suppressing the anode reaction and the cathode reaction. In order to sufficiently obtain these effects, the content is 0.001% or more. The content is preferably 0.002% or more. On the other hand, if it exceeds 0.100%, the toughness of the steel may be deteriorated. Therefore, the Ta content is set to 0.100% or less. Preferably 0.050% or less, and more preferably 0.014% or less.

Ni: 0.01% or more and 0.50% or less

Ni coexists with Cu, Nb, Sn (and, in some cases, further, Ge, Ta), thereby remarkably improving the weatherability of the steel material. Ni has the effect of improving the weatherability of the structural steel by forming a dense green layer by making the green grain fine. In order to obtain this effect sufficiently, it is contained at 0.01% or more. The content is preferably 0.02% or more, more preferably 0.03% or more. On the other hand, if it is contained in an amount exceeding 0.50%, the cost associated with an increase in Ni consumption is increased. Therefore, the Ni content is 0.50% or less. , Preferably less than 0.10%, and more preferably 0.08% or less.

The present invention may contain at least one kind selected from Mo, Co, W, Sb, Sc, Sr and Se for the following reasons.

Mo: 0.005% or more and 0.500% or less

Mo dissolves MoO ₄ ^2- along with the anode reaction of the steel, and MoO ₄ ^2- is distributed in the green layer, thereby preventing the chloride ions of the corrosion promoting factor from penetrating through the green layer to reach the substrate. Further, the compound containing Mo is precipitated on the surface of the steel to suppress the anode reaction of the steel. In order to sufficiently obtain these effects, it is contained in an amount of 0.005% or more. The content is preferably 0.010% or more, more preferably 0.020% or more. On the other hand, if the Mo content exceeds 0.500%, the increase in the cost of Mo increases. Therefore, when contained, the Mo content is 0.500% or less. Preferably 0.100% or less, and more preferably 0.080% or less.

Co: 0.01% or more and 0.50% or less

Co is distributed in the green layer, and it has an effect of improving the weatherability of the steel material by forming a dense green layer by making the green grain fine. In order to sufficiently obtain such an effect, it is contained at 0.01% or more. On the other hand, if it exceeds 0.50%, the cost increase accompanying the increase of Co consumption is caused. Therefore, if contained, the content of Co should be 0.50% or less.

W: 0.005% or more and 0.500% or less

W is eluted as WO ₄ ^2- along with the anode reaction of the steel, and is distributed in the green layer, thereby preventing the chloride ions of the corrosion promoting factor from penetrating the green layer to reach the substrate. Further, the compound containing W is precipitated on the surface of the steel to suppress the anode reaction of the steel. In order to sufficiently obtain these corrosion resistance improving effects, it is contained in an amount of 0.005% or more. The content is preferably 0.050% or more. On the other hand, if it exceeds 0.500%, the increase in the consumption of W causes an increase in cost. Therefore, if contained, the W content should be 0.500% or less. And preferably 0.200% or less.

Sb: 0.005% or more and 0.200% or less

Sb is an element that suppresses the anode reaction of the steel and suppresses the hydrogen generation reaction as the cathode reaction, thereby improving the weatherability of the steel material. In order to obtain such an effect sufficiently, it is contained in an amount of 0.005% or more. The content is preferably 0.010% or more. On the other hand, if Sb is excessively contained, the toughness may be deteriorated. Therefore, when Sb is contained, the content is 0.200% or less. And preferably 0.080% or less.

Sc: 0.001% or more and 0.200% or less

Sc is distributed in the green layer, and it is an element which improves the corrosion resistance of the steel by forming a dense green layer by microwaving and suppressing permeation of the green layer of the corrosion promoting factor. In order to obtain such an effect sufficiently, it is contained in an amount of 0.001% or more. The content is preferably 0.005% or more. On the other hand, if Sc is excessively contained, the toughness may be deteriorated. Therefore, when Sc is contained, the content is 0.200% or less. And preferably 0.100% or less.

Sr: 0.001% or more and 0.200% or less

Sr is an element that elutes along with the anode reaction of the steel and exhibits a buffering action of pH near the steel interface, thereby lowering the anode reaction rate of the steel. In order to obtain such an effect sufficiently, it is contained in an amount of 0.001% or more. The content is preferably 0.005% or more. On the other hand, if Sr is excessively contained, the toughness may be deteriorated. Therefore, when Sr is contained, the content is 0.200% or less. And preferably 0.100% or less.

Se: 0.001% or more and 0.200% or less

Se is eluted as an oxygen acid with the anode reaction of the steel and distributed in the green layer, thereby preventing the chloride ions of the corrosion promoting factor from penetrating the green layer to reach the substrate. In order to obtain such an effect sufficiently, it is contained in an amount of 0.001% or more. The content is preferably 0.005% or more. On the other hand, if Se is contained excessively, the toughness may be deteriorated. Therefore, in the case of containing Se, the content is 0.200% or less. And preferably 0.100% or less.

In the present invention, at least one selected from V, Zr and B may be contained for the following reasons.

V: not less than 0.005% and not more than 0.200%

V is a useful element for increasing strength. In order to obtain this effect sufficiently, it is contained in an amount of 0.005% or more. On the other hand, if it exceeds 0.200%, the effect becomes saturated. Therefore, when contained, the V content should be 0.200% or less.

Zr: 0.005% or more and 0.200% or less

Zr is a useful element for increasing strength. In order to obtain this effect sufficiently, it is contained in an amount of 0.005% or more. On the other hand, if it exceeds 0.200%, the effect becomes saturated. Therefore, when contained, the Zr content is 0.200% or less.

B: 0.0001% or more and 0.0050% or less

B is a useful element for increasing strength. In order to obtain this effect sufficiently, it is contained at 0.0001% or more. On the other hand, if it exceeds 0.0050%, the toughness may be deteriorated. Therefore, if contained, the content of B should be 0.0050% or less.

In the present invention, at least one selected from REM, Ca, and Mg may be contained for the following reasons.

REM: 0.0001% or more and 0.0100% or less

REM is distributed in the green layer, and it has the effect of improving the weatherability of the steel material by forming a dense green layer by making the green grain fine. In order to obtain this effect sufficiently, it is contained at 0.0001% or more. On the other hand, if it exceeds 0.0100%, the effect becomes saturated. Therefore, when contained, the REM content should be 0.0100% or less.

Ca: 0.0001% or more and 0.0100% or less

Ca is an element effective for improving the toughness of the weld heat affected zone by fixing S in the steel. In order to obtain this effect sufficiently, it is contained at 0.0001% or more. On the other hand, if it exceeds 0.0100%, the amount of inclusions in the steel increases, which may result in deterioration of toughness. Therefore, if contained, the content of Ca should be 0.0100% or less.

Mg: 0.0001% or more and 0.0100% or less

Mg is an element effective for fixing the S in the steel and improving the toughness of the weld heat affected zone. In order to obtain this effect sufficiently, it is contained at 0.0001% or more. On the other hand, if it exceeds 0.0100%, the amount of inclusions in the steel increases, which may result in deterioration of toughness. Therefore, when contained, the Mg content is set to 0.0100% or less.

The structural steel of the present invention can be applied to a structure. For example, there are bridges, steel towers, lighting poles, construction machinery, mining, agriculture, industrial machinery, tanks, high-priced water tanks, vehicles, containers and the like.

The structural steel material having excellent weather resistance of the present invention can be obtained by subjecting a steel having the above-mentioned composition composition to a hot rolling of a slab obtained by a typical continuous casting or crushing method to form a steel material such as a thick plate, a thin steel plate, ≪ / RTI > Hereinafter, a preferable production method of the steel material of the present invention will be described. In the following description, the temperature is the surface temperature of the slab or steel plate.

The heating temperature of the slab has a correlation with the high capacity of the Nb steel. By setting the slab heating temperature at 1000 占 폚 or higher, it is possible to secure a required large amount of Nb among the steels, and as a result, the corrosion resistance can be improved. However, if the slab is heated to a temperature exceeding 1200 deg. C, there is a fear that the yield is lowered due to excessive scale generation and the energy consumption is increased. Therefore, the slab heating temperature is set to 1000 deg. C or higher and 1200 deg. C or lower. Preferably 1050 DEG C or more and less than 1150 DEG C or less.

The heated slab is then subjected to hot rolling at a temperature of 700 DEG C or higher to obtain a steel sheet having a desired dimensional shape. When the rolling finishing temperature is less than 700 캜, the precipitation amount of the Nb carbonitride is increased due to the transformation strain precipitation, and there is a possibility that the Nb high capacity in the steel is lowered. Therefore, the rolling finishing temperature is 700 ° C or higher. Preferably 800 DEG C or higher, and more preferably 900 DEG C or higher.

The cooling conditions after completion of the hot rolling may be suitably determined according to the required material, and may be subjected to air cooling or accelerated cooling. When the reheating heat treatment is performed, the reheating temperature is preferably 850 to 950 DEG C and the time in the furnace is preferably 5 to 120 minutes. The cooling rate after reheating is not particularly limited. When the tempering treatment is carried out, the tempering temperature is preferably 450 to 680 占 폚.

The content of each element can be determined by spark discharge emission spectroscopy, fluorescent X-ray analysis, ICP emission spectroscopy, ICP mass spectrometry, and combustion method. In particular, the content of Ge, Sc, and Sr is preferably measured by ICP mass spectrometry.

The amount of dissolved Nb was evaluated by taking the difference between the Nb content (total Nb content) in the steel and the precipitated Nb amount. The amount of precipitated Nb was determined by ICP emission spectroscopy after the sample was subjected to constant current flow in a 10 vol% acetylacetone-1 mass% tetramethylammonium chloride-methanol solution and alkali melt and acid decomposition of the extracted residue .

Example 1

Examples are shown below. The technical scope of the present invention is not limited to the following embodiments. In the following examples, Table 1-1 and Table 1-2 are shown in Table 1, and Table 2-1 and Table 2-2 are shown in Table 2.

The steel having the chemical composition shown in Table 1 was melted and the slab was heated to not less than 1000 ° C and not more than 1,200 ° C and then subjected to hot rolling at a rolling finishing temperature of 800 to 950 ° C and then cooled to room temperature to start a steel sheet having a thickness of 12 mm Trial production).

For Steel No. 83, the slab was heated to 950 占 폚, hot-rolled at a rolling finish temperature of 680 占 폚, and cooled to room temperature to start a steel sheet having a thickness of 12 mm.

Then, test pieces of 35 mm x 35 mm x 5 mm were obtained from the obtained steel sheet. The test piece was subjected to grinding so that its surface had a surface roughness Ra of 1.6 占 퐉 or less and the surface was also tape-sealed so that the area of the surface exposed portion was 25 mm 占 25 mm.

[Table 1-1]

[Table 1-2]

The test pieces thus obtained were subjected to dry and wet repeated corrosion test to evaluate the weather resistance.

In the evaluation test of weatherability, a corrosion test simulating the environment inside the trench without rain shield, which is considered to be the most severe environment in a structure such as an actual bridge, was carried out. The conditions of the corrosion test are as follows. The drying step at a temperature of 40 DEG C and a relative humidity of 40% RH for 1 hour, and then a transition time of 1 hour, followed by a wetting step at 25 DEG C and a relative humidity of 95% RH for 3 hours, The time to transit time was taken to be one cycle, totaling 6 hours. The artificial seawater solution adjusted to have a salt content of 0.3 m dd adhered to the surface of the test piece was coated once a week on the surface of the test piece during the drying process. Tests of 224 cycles were conducted under the above conditions.

After completion of the corrosion test, the test piece was immersed in an aqueous solution containing hexamethylenetetramine added to hydrochloric acid to remove the rust, and then the weight was measured. The difference between the weight and the initial weight was determined to obtain the average plate thickness reduction (mu m) . When the average plate thickness reduction amount was 20.0 탆 or less, it was evaluated that the weather resistance was excellent.

Table 2 shows the corrosion amount (average plate thickness reduction).

[Table 2-1]

[Table 2-2]

As shown in Table 2, the steels Nos. 1 to 28 and 32 to 82 according to the present invention had an average thickness reduction of 20.0 占 퐉 or less and excellent weatherability. On the other hand, the comparative steels Nos. 29 to 31 and 83 to 84 had an average plate thickness reduction amount exceeding 20.0 占 퐉, so that the weather resistance was lower than that of the steels according to the present invention.

Claims (20)

In terms of% by mass,
C: not less than 0.01% and not more than 0.20%
Si: not less than 0.05% and not more than 1.00%
Mn: not less than 0.20% and not more than 2.00%
P: not less than 0.001% and not more than 0.050%
S: not less than 0.0001% and not more than 0.0200%
Al: 0.005% or more and 0.050% or less,
Cu: not less than 0.010% and not more than 0.500%
Nb: 0.005% or more and 0.100% or less,
Sn: not less than 0.005% and not more than 0.300%
The amount of solid solution Nb is 0.002% or more and 0.080% or less,
The balance being iron and inevitable impurities,
Further, in terms of% by mass,
Ge: 0.0005% or more and 0.0100% or less. In terms of% by mass,
C: not less than 0.01% and not more than 0.20%
Si: not less than 0.05% and not more than 1.00%
Mn: not less than 0.20% and not more than 2.00%
P: not less than 0.001% and not more than 0.050%
S: not less than 0.0001% and not more than 0.0200%
Al: 0.005% or more and 0.050% or less,
Cu: not less than 0.010% and not more than 0.500%
Nb: 0.005% or more and 0.100% or less,
Sn: not less than 0.005% and not more than 0.300%
The amount of solid solution Nb is 0.002% or more and 0.080% or less,
The balance being iron and inevitable impurities,
Further, in terms of% by mass,
Ta: 0.001% or more and 0.100% or less. The method according to claim 1,
Further, in terms of% by mass,
Ni: 0.01% or more and 0.50% or less. 3. The method of claim 2,
Further, in terms of% by mass,
Ni: 0.01% or more and 0.50% or less. The method according to claim 1,
Further, in terms of% by mass,
Mo: 0.005% or more and 0.500% or less,
Co: 0.01% or more and 0.50% or less,
W: 0.005% or more and 0.500% or less,
Sb: 0.005% or more and 0.200% or less,
Sc: 0.001% or more and 0.200% or less,
Sr: 0.001% or more and 0.200% or less,
Se: 0.001% or more and 0.200% or less
By weight of at least one kind of structural steel. 3. The method of claim 2,
Further, in terms of% by mass,
Mo: 0.005% or more and 0.500% or less,
Co: 0.01% or more and 0.50% or less,
W: 0.005% or more and 0.500% or less,
Sb: 0.005% or more and 0.200% or less,
Sc: 0.001% or more and 0.200% or less,
Sr: 0.001% or more and 0.200% or less,
Se: 0.001% or more and 0.200% or less
By weight of at least one kind of structural steel. The method of claim 3,
Further, in terms of% by mass,
Mo: 0.005% or more and 0.500% or less,
Co: 0.01% or more and 0.50% or less,
W: 0.005% or more and 0.500% or less,
Sb: 0.005% or more and 0.200% or less,
Sc: 0.001% or more and 0.200% or less,
Sr: 0.001% or more and 0.200% or less,
Se: 0.001% or more and 0.200% or less
By weight of at least one kind of structural steel. 5. The method of claim 4,
Further, in terms of% by mass,
Mo: 0.005% or more and 0.500% or less,
Co: 0.01% or more and 0.50% or less,
W: 0.005% or more and 0.500% or less,
Sb: 0.005% or more and 0.200% or less,
Sc: 0.001% or more and 0.200% or less,
Sr: 0.001% or more and 0.200% or less,
Se: 0.001% or more and 0.200% or less
By weight of at least one kind of structural steel. The method according to claim 1,
Further, in terms of% by mass,
V: not less than 0.005% and not more than 0.200%
Zr: 0.005% or more and 0.200% or less,
B: 0.0001% or more and 0.0050% or less
By weight of at least one kind of structural steel. 3. The method of claim 2,
Further, in terms of% by mass,
V: not less than 0.005% and not more than 0.200%
Zr: 0.005% or more and 0.200% or less,
B: 0.0001% or more and 0.0050% or less
By weight of at least one kind of structural steel. The method of claim 3,
Further, in terms of% by mass,
V: not less than 0.005% and not more than 0.200%
Zr: 0.005% or more and 0.200% or less,
B: 0.0001% or more and 0.0050% or less
By weight of at least one kind of structural steel. 5. The method of claim 4,
Further, in terms of% by mass,
V: not less than 0.005% and not more than 0.200%
Zr: 0.005% or more and 0.200% or less,
B: 0.0001% or more and 0.0050% or less
By weight of at least one kind of structural steel. 6. The method of claim 5,
Further, in terms of% by mass,
V: not less than 0.005% and not more than 0.200%
Zr: 0.005% or more and 0.200% or less,
B: 0.0001% or more and 0.0050% or less
By weight of at least one kind of structural steel. The method according to claim 6,
Further, in terms of% by mass,
V: not less than 0.005% and not more than 0.200%
Zr: 0.005% or more and 0.200% or less,
B: 0.0001% or more and 0.0050% or less
By weight of at least one kind of structural steel. 8. The method of claim 7,
Further, in terms of% by mass,
V: not less than 0.005% and not more than 0.200%
Zr: 0.005% or more and 0.200% or less,
B: 0.0001% or more and 0.0050% or less
By weight of at least one kind of structural steel. 9. The method of claim 8,
Further, in terms of% by mass,
V: not less than 0.005% and not more than 0.200%
Zr: 0.005% or more and 0.200% or less,
B: 0.0001% or more and 0.0050% or less
By weight of at least one kind of structural steel. 17. The method according to any one of claims 1 to 16,
Further, in terms of% by mass,
REM: 0.0001% or more and 0.0100% or less,
Ca: not less than 0.0001% and not more than 0.0100%
Mg: 0.0001% or more and 0.0100% or less
By weight of at least one kind of structural steel. 5. The method of claim 4,
Further, in terms of% by mass,
Ge: 0.0005% or more and 0.0100% or less. 9. The method of claim 8,
Further, in terms of% by mass,
Ge: 0.0005% or more and 0.0100% or less. 13. The method of claim 12,
Further, in terms of% by mass,
Ge: 0.0005% or more and 0.0100% or less.