JPWO2016092756A1 - Structural steel with excellent weather resistance - Google Patents

Abstract

To provide a structural steel material with excellent weather resistance at low cost. In mass%, C: 0.01% or more and less than 0.20%, Si: 0.05% or more and 1.00% or less, Mn: 0.20% or more and 2.00% or less, P: 0.001% or more 0.050% or less, S: 0.0001% to 0.0200%, Al: 0.005% to 0.050%, Cu: 0.010% to 0.500%, Nb: 0.005 %, 0.100% or less, Sn: 0.005% or more and 0.300% or less, and the solid solution Nb content is 0.002% or more and 0.080% or less, with the balance being iron and inevitable Structural steel with excellent weather resistance consisting of impurities.

Description

  The present invention relates to a structural steel material. In particular, the present invention relates to a structural steel material that is suitable as a member that requires weather resistance in an environment where the amount of flying salt is relatively small and the corrosivity is not so high.

  Conventionally, weathering steel is used for steel structures used outdoors such as bridges. Weather-resistant steel is a steel material whose corrosion rate is significantly reduced by covering the surface with a highly protective rust layer enriched with alloy elements such as Cu, P, Cr, and Ni in an atmospheric corrosion environment. Due to its excellent weather resistance, it is known that bridges using weather-resistant steel can withstand service for decades without being painted.

  Weathering steel was developed in the United States in the 1930s and applied to structures such as buildings. Later, it was also introduced in Japan, and weatherproof steel was manufactured and applied to bridges. In this way, weather resistant steel has been developed in the United States and has been introduced in large quantities in various countries. In countries with remarkable economic development represented by BRICS, infrastructure is currently being developed, and in particular, an increase in maintenance costs is regarded as a problem. For example, unpainted bridges using weathering steel can keep maintenance costs low compared to painted bridges, and therefore, in such countries, application of weathering steel is desired. Considering use in these countries with remarkable economic development, it is considered essential to reduce the cost of steel. For example, a requirement for being a low-cost steel material is a low alloy cost. In addition, these countries have a relatively large land area, and it is considered that there are many areas far from the coastline, that is, an environment where the amount of incoming salt is small. Therefore, a steel material that can be used without coating in an environment where the amount of flying salt is relatively small and the corrosivity is not so high is desired.

  Until now, as a technique for improving the weather resistance of steel materials, for example, Patent Document 1 discloses a high weather resistance steel material to which Cu and Ni of 1 mass% or more are added. Patent Document 2 discloses a steel material excellent in weather resistance to which 1 mass% or more of Ni and Mo are added. Patent Document 3 discloses a steel material excellent in weather resistance in which Cu and Ti are added in addition to Ni. Patent Document 4 discloses a steel material for welded structure containing a large amount of Ni and additionally containing Cu, Mo, Sn, Sb, P and the like. Further, Patent Document 5 discloses a steel material excellent in corrosion resistance to which Sn is added.

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

  However, when the Ni content is increased as in Patent Documents 1, 2, and 3, there is a problem that the price of the steel material increases due to an increase in alloy cost. Further, as in Patent Document 4, in the steel material containing the contents of Ni and P and containing Cu, Mo, Sn, Sb, etc., the price of the steel material increases due to an increase in alloy cost, and the P content is further increased. High weldability is lowered due to its high value. Further, when the Sn content is increased as in Patent Document 5, there is a problem that the price of the steel material increases due to an increase in the alloy cost and further promotes hot brittleness.

  This invention is made | formed in view of this situation, Comprising: It aims at providing the structural steel material excellent in the weather resistance at low cost.

  In order to solve the above-mentioned problems, the component composition of the steel material was intensively studied from the viewpoint of weather resistance. As a result, it was found that the weather resistance of the steel material is improved by containing Cu, further containing trace amounts of Nb and Sn, and further strictly controlling the solid solution amount of Nb. Thus, although the detailed reason which shows the outstanding weather resistance is unknown, it estimates as follows. Cu refines the rust layer by refining the rust particles, and not only prevents corrosion and oxygen and chloride ions from passing through the rust layer and reaching the iron, but also the surface of the iron Concentration in the vicinity suppresses the anode reaction of the steel material. Nb is concentrated in the vicinity of the surface of the iron core to suppress the anode reaction and cathode reaction of the steel material. In particular, in order to improve the weather resistance, it is important that Nb exists in a solid solution state in the steel. Further, Sn, like Nb, is concentrated near the surface of the ground iron to suppress the anode reaction and cathode reaction of the steel material. However, these effects are insufficient when contained alone, and it is presumed that the corrosion resistance is remarkably improved by the combined inclusion of Cu, Nb and Sn.

  The gist of the present invention is as follows.

  [1] By mass%, C: 0.01% to less than 0.20%, Si: 0.05% to 1.00%, Mn: 0.20% to 2.00%, P: 0.00. 001% to 0.050%, S: 0.0001% to 0.0200%, Al: 0.005% to 0.050%, Cu: 0.010% to 0.500%, Nb: 0.005% or more and 0.100% or less, Sn: 0.005% or more and 0.300% or less, further, the amount of solid solution Nb is 0.002% or more and 0.080% or less, and the balance is iron Structural steel with excellent weather resistance consisting of inevitable impurities.

  [2] The structural steel material having excellent weather resistance according to [1], further containing Ge: 0.0005% to 0.0100% by mass.

  [3] The structural steel material having excellent weather resistance according to [1] or [2], further containing Ta: 0.001% or more and 0.100% or less by mass%.

  [4] The structural steel material having excellent weather resistance according to any one of [1] to [3], further containing Ni: 0.01% to 0.50% by mass%.

  [5] Further, by mass, Mo: 0.005% to 0.500%, Co: 0.01% to 0.50%, W: 0.005% to 0.500%, Sb: From 0.005% to 0.200%, Sc: 0.001% to 0.200%, Sr: 0.001% to 0.200%, Se: 0.001% to 0.200% Structural steel material excellent in weather resistance according to any one of [1] to [4], which contains one or more selected.

  [6] Further, in terms of mass%, V is selected from 0.005% to 0.200%, Zr: 0.005% to 0.200%, and B: 0.0001% to 0.0050%. Structural steel material excellent in weather resistance according to any one of [1] to [5], which contains one or more.

  [7] Further, by mass%, REM: 0.0001% to 0.0100%, Ca: 0.0001% to 0.0100%, Mg: 0.0001% to 0.0100% or less Structural steel material excellent in weather resistance according to any one of [1] to [6], which contains one or more.

  In the present invention, excellent weather resistance means that the average thickness reduction amount is 20.0 μm or less in the weather resistance evaluation in the examples described later.

  According to the present invention, a structural steel material having excellent weather resistance can be obtained. The structural steel material of the present invention has excellent weather resistance at a low cost by compounding elements effective for improving weather resistance.

  The present invention is described in detail below. In the following description, the unit of the content of each element of the steel component composition is “mass%”, and is simply “%” unless otherwise specified.

C: 0.01% or more and less than 0.20% C is an element that improves the strength of the structural steel material, and it is necessary to contain 0.01% or more in order to ensure a predetermined strength. On the other hand, if it is 0.20% or more, weldability and toughness deteriorate. Therefore, the C content is 0.01% or more and less than 0.20%.

Si: 0.05% or more and 1.00% or less Si has an effect of reducing the rust grains of the rust layer to form a dense rust layer and improving the weather resistance of the steel material. Moreover, it has the effect of preventing cracks on the surface of the steel material during hot rolling. In order to acquire these effects, it is necessary to contain 0.05% or more. The content is preferably 0.10% or more, and more preferably 0.15% or more. On the other hand, when it contains excessively exceeding 1.00%, toughness and weldability will deteriorate remarkably. Therefore, the Si content is 1.00% or less. The content is preferably 0.80% or less, more preferably 0.60% or less.

Mn: 0.20% or more and 2.00% or less Mn is an element that improves the strength of the structural steel material, and it is necessary to contain 0.20% or more in order to ensure a predetermined strength. The content is preferably 0.40% or more. On the other hand, when it contains excessively exceeding 2.00%, toughness and weldability will deteriorate. Therefore, the Mn content is 2.00% or less. Preferably it is 1.70% or less.

P: 0.001% to 0.050% P is an element that improves the weather resistance of the structural steel material. In order to acquire such an effect, it is necessary to contain 0.001% or more. The content is preferably 0.003% or more, and more preferably 0.005% or more. On the other hand, if it exceeds 0.050%, 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 exceeds 0.0200%, weldability and toughness deteriorate. The content is preferably 0.0100% or less, more preferably 0.0050% or less. On the other hand, when the content is reduced to less than 0.0001%, the production cost increases. The content is preferably 0.0003% or more, more preferably 0.0005% or more.

Al: 0.005% to 0.050% Al is an element necessary for deoxidation during steelmaking. In order to acquire such an effect, it is necessary to contain 0.005% or more as Al content. Preferably it is 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: 0.010% or more and 0.500% or less Cu is an important requirement in the present invention, and has the effect of remarkably improving the weather resistance of steel by coexisting with Nb and Sn. Cu suppresses the anode reaction of the steel material by concentrating near the rust layer-steel interface. In addition, a fine rust layer is formed by refining the rust grains of the rust layer, and has an effect of suppressing the permeation of chloride ions, which are corrosion promoting factors, to the ground iron. These effects are obtained when the content is 0.010% or more. The content is preferably 0.020% or more, more preferably more than 0.035%. On the other hand, if it exceeds 0.500%, a cost increase accompanying an increase in the amount of Cu used is caused. Therefore, the Cu content is 0.500% or less. Preferably it is 0.300% or less, More preferably, it is 0.200% or less, More preferably, it is 0.150% or less.

Nb: 0.005% or more and 0.100% or less Nb is an important requirement in the present invention, and coexistence with Cu and Sn has an effect of significantly improving the weather resistance of the steel material. Nb is concentrated near the interface between the rust layer and the ground iron in the anode part to suppress the anode reaction and the cathode reaction. In order to obtain these effects sufficiently, it is necessary to contain 0.005% or more. The content is preferably 0.008% or more, and more preferably 0.010% or more. On the other hand, if it exceeds 0.100%, the toughness is reduced. Therefore, the Nb content is 0.100% or less. Preferably, it is 0.050% or less, More preferably, it is 0.030% or less.

Solid solution Nb amount: 0.002% or more and 0.080% or less In order to improve the weather resistance by adding Nb, the content should be within the above range, and the solid solution amount of Nb in steel should be appropriate. It is important to set the range. In order for Nb in steel to exhibit the above-described effect of improving weather resistance, it is necessary that Nb elutes into the rust layer in the form of oxygen acid or oxide as the steel material corrodes. On the other hand, Nb carbonitride is generally known as a hardly soluble substance, and it is difficult to elute into the rust layer in the above-described form. Therefore, when Nb forms carbonitride, the effect of improving weather resistance is reduced by reducing the amount of solid solution Nb around the Nb. If the amount of dissolved Nb is less than 0.002%, the effect of improving weather resistance cannot be obtained sufficiently. Therefore, the solid solution Nb amount is 0.002% or more. The amount of solid solution Nb is preferably 0.005% or more, and more preferably 0.008%. On the other hand, when the amount of solute Nb exceeds 0.080%, the manufacturing cost increases. Therefore, the solid solution Nb amount is set to 0.080% or less. Preferably it is 0.040% or less, More preferably, it is 0.025% or less.

Sn: 0.005% or more and 0.300% or less Sn is an important requirement in the present invention, and has the effect of remarkably improving the weather resistance of the steel by coexisting with Cu and Nb. Sn is concentrated in the vicinity of the interface between the rust layer and the ground iron, and suppresses the anode reaction and cathode reaction of the steel material. Further, by reducing the size of the rust grains in the rust layer, transmission of chloride ions, which are corrosion promoting factors, is suppressed. In order to obtain these effects sufficiently, it is necessary to contain 0.005% or more. The content is preferably 0.010% or more, and more preferably 0.020% or more. On the other hand, if it exceeds 0.300%, the ductility and toughness of the steel are deteriorated. Moreover, the cost rise accompanying the increase in Sn consumption is caused. Therefore, the Sn content is 0.300% or less. Preferably it is 0.100% or less, More preferably, it is 0.045% or less, More preferably, it is 0.035% or less.

  The balance is Fe and inevitable impurities. Here, for example, N: 0.010% or less and O: 0.010% or less are acceptable as inevitable impurities.

  With the above essential elements, the steel material of the present invention has the desired characteristics. In addition to the above essential elements, the present invention can contain the following elements as necessary.

Ge: 0.0005% or more and 0.0100% or less Ge has the effect of remarkably improving the weather resistance of steel by coexisting with Cu, Nb and Sn. Ge is concentrated near the interface between the rust layer and the ground iron in the anode portion, and suppresses the anode reaction and the cathode reaction. In order to obtain these effects sufficiently, 0.0005% or more is contained. 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 0.0100% or less. The content is preferably 0.0050% or less.

Ta: 0.001% or more and 0.100% or less Ta has the effect of remarkably improving the weather resistance of the steel by coexisting with Cu, Nb and Sn, and (optionally, further Ge). Ta is concentrated near the interface between the rust layer and the ground iron in the anode portion, and suppresses the anode reaction and the cathode reaction. In order to sufficiently obtain these effects, 0.001% or more is contained. 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 0.100% or less. Preferably it is 0.050% or less, More preferably, it is 0.014% or less.

Ni: 0.01% or more and 0.50% or less Ni has the effect of remarkably improving the weather resistance of the steel material by coexisting with Cu, Nb, Sn, and (optionally, Ge, Ta). Ni refines the rust grains to form a dense rust layer and has the effect of improving the weather resistance of the structural steel. In order to sufficiently obtain this effect, the content is 0.01% or more. The content is preferably 0.02% or more, and more preferably 0.03% or more. On the other hand, if the content exceeds 0.50%, the cost increases due to an increase in Ni consumption. Therefore, the Ni content is 0.50% or less. Preferably it is less than 0.10%, More preferably, it is 0.08% or less.

  In this invention, 1 or more types chosen from Mo, Co, W, Sb, Sc, Sr, and Se can be contained for the following reasons.

Mo: 0.005% or more and 0.500% or less Mo is a corrosion-promoting factor chloride because MoO ₄ ²⁻ is eluted with the anode reaction of the steel material and MoO ₄ ²⁻ is distributed in the rust layer. It prevents ions from penetrating the rust layer and reaching the ground iron. Moreover, the anode reaction of steel materials is suppressed because the compound containing Mo precipitates on the steel material surface. In order to sufficiently obtain these effects, 0.005% or more is contained. The content is preferably 0.010% or more, and more preferably 0.020% or more. On the other hand, if it exceeds 0.500%, a cost increase accompanying an increase in Mo consumption is caused. Therefore, when it contains, Mo content shall be 0.500% or less. Preferably it is 0.100% or less, More preferably, it is 0.080% or less.

Co: 0.01% or more and 0.50% or less Co is distributed in the rust layer, and by forming fine rust layers by refining rust grains, it has the effect of improving the weather resistance of the steel material. In order to sufficiently obtain such an effect, the content is 0.01% or more. On the other hand, if it exceeds 0.50%, a cost increase accompanying an increase in Co consumption will be caused. Therefore, when it contains, Co content shall be 0.50% or less.

W: 0.005% or more and 0.500% or less W is eluted as WO ₄ ^2- with the anodic reaction of the steel material, and is distributed in the rust layer, so that chloride ions as corrosion promoting factors permeate the rust layer. To prevent it from reaching the railway. Moreover, the anode reaction of steel materials is suppressed because the compound containing W precipitates on the steel material surface. In order to sufficiently obtain these effects of improving corrosion resistance, 0.005% or more is contained. The content is preferably 0.050% or more. On the other hand, if it exceeds 0.500%, a cost increase accompanying an increase in W consumption is caused. Therefore, when it contains, W content shall be 0.500% or less. Preferably it is 0.200% or less.

Sb: 0.005% or more and 0.200% or less Sb is an element that improves the weather resistance of the steel material by suppressing the anode reaction of the steel material and suppressing the hydrogen generation reaction that is a cathode reaction. In order to sufficiently obtain such an effect, the content is 0.005% or more. The content is preferably 0.010% or more. On the other hand, when Sb is contained excessively, the toughness may be deteriorated. Therefore, when it contains Sb, content is made into 0.200% or less. Preferably it is 0.080% or less.

Sc: 0.001% or more and 0.200% or less Sc is distributed in the rust layer, forming a dense rust layer by refining the rust grains, and suppressing the penetration of the corrosion promoting factor to the rust layer. It is an element that improves corrosion resistance. In order to sufficiently obtain such effects, the content is 0.001% or more. The content is preferably 0.005% or more. On the other hand, when Sc is contained excessively, the toughness may be deteriorated. Therefore, when it contains Sc, content is made into 0.200% or less. Preferably it is 0.100% or less.

Sr: 0.001% or more and 0.200% or less Sr is an element that elutes with the anode reaction of the steel material and reduces the anode reaction rate of the steel material by exhibiting a pH buffering action in the vicinity of the interface of the steel. In order to sufficiently obtain such effects, the content is 0.001% or more. The content is preferably 0.005% or more. On the other hand, if Sr is contained excessively, the toughness may be deteriorated. Therefore, when it contains Sr, content is made into 0.200% or less. Preferably it is 0.100% or less.

Se: 0.001% or more and 0.200% or less Se elutes as oxygen acid with the anode reaction of the steel material, and distributes in the rust layer, so that chloride ions of the corrosion promoting factor permeate the rust layer. Prevent reaching the railway. In order to sufficiently obtain such effects, the content is 0.001% or more. The content is preferably 0.005% or more. On the other hand, when Se is contained excessively, the toughness may be deteriorated. Therefore, when it contains Se, the content is set to 0.200% or less. Preferably it is 0.100% or less.

  In this invention, 1 or more types chosen from V, Zr, and B can be included for the following reasons.

V: 0.005% or more and 0.200% or less V is an element useful for increasing the strength. In order to obtain this effect sufficiently, the content is 0.005% or more. On the other hand, if it exceeds 0.200%, the effect is saturated. Therefore, when it contains, V content shall be 0.200% or less.

Zr: 0.005% or more and 0.200% or less Zr is an element useful for increasing the strength. In order to obtain this effect sufficiently, the content is 0.005% or more. On the other hand, if it exceeds 0.200%, the effect is saturated. Therefore, when it contains, Zr content shall be 0.200% or less.

B: 0.0001% or more and 0.0050% or less B is an element useful for increasing the strength. In order to sufficiently obtain this effect, the content is 0.0001% or more. On the other hand, if it exceeds 0.0050%, the toughness may be deteriorated. Therefore, when it contains, B content shall be 0.0050% or less.

  In this invention, 1 or more types chosen from REM, Ca, and Mg can be contained for the following reasons.

REM: 0.0001% or more and 0.0100% or less REM is distributed in the rust layer, and by forming fine rust layers by refining rust grains, it has the effect of improving the weather resistance of the steel material. In order to sufficiently obtain this effect, the content is 0.0001% or more. On the other hand, when it exceeds 0.0100%, the effect is saturated. Therefore, when it contains, REM content shall be 0.0100% or less.

Ca: 0.0001% or more and 0.0100% or less Ca is an element effective for fixing S in steel and improving the toughness of the heat affected zone. In order to obtain this effect sufficiently, the content is 0.0001% or more. On the other hand, if it exceeds 0.0100%, the amount of inclusions in the steel increases, which may lead to deterioration of toughness. Therefore, when it contains, Ca content shall be 0.0100% or less.

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

  The structural steel material of the present invention can be applied to structures. Examples of such structures include bridges, steel towers, lighting poles, construction / mine / agricultural / industrial machinery, tanks, elevated water tanks, vehicles, containers, and the like.

  The structural steel material having excellent weather resistance according to the present invention is a steel plate having the above composition, by hot rolling a slab obtained by ordinary continuous casting or a block method, a thick plate, a shape steel, a thin steel plate, a steel bar. It is manufactured and obtained in steel materials such as. Hereinafter, the preferable manufacturing method of this invention steel material is demonstrated. In the following description, the temperature is the surface temperature of a slab or a steel plate.

  The heating temperature of the slab has a correlation with the solid solution amount of Nb in steel. By setting the slab heating temperature to 1000 ° C. or higher, a necessary amount of Nb solid solution in steel can be secured, and as a result, corrosion resistance can be improved. However, if the slab is heated above 1200 ° C., there is a risk that yield will decrease due to excessive scale generation and energy consumption will increase. Therefore, the slab heating temperature is set to 1000 ° C. or more and 1200 ° C. or less. Preferably, it is 1050 degreeC or more and less than 1150 degreeC.

  The heated slab is then subjected to hot rolling which is finished at a temperature of 700 ° C. or higher to obtain a steel plate having a desired size and shape. When the rolling finishing temperature is less than 700 ° C., the precipitation amount of Nb carbonitride increases due to strain-induced precipitation, and the Nb solid solution amount in the steel may decrease. Accordingly, the rolling finishing temperature is 700 ° C. or higher. Preferably it is 800 degreeC or more, More preferably, it is 900 degreeC or more.

  The cooling conditions after the hot rolling is finished may be appropriately determined according to the required material, and air cooling or accelerated cooling may be performed. Moreover, when performing reheating heat processing, it is preferable that reheating temperature shall be 850 degreeC-950 degreeC or more, and in-furnace time shall be 5 minutes or more and 120 minutes or less. The cooling rate of quenching after reheating is not particularly limited. Moreover, when performing a tempering process, it is preferable that tempering temperature shall be 450 to 680 degreeC.

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

  The amount of solute Nb was evaluated by taking the difference between the Nb content (total Nb amount) in steel and the amount of precipitated Nb. The amount of precipitated Nb was determined by constant-current decomposition of the sample in a 10 vol% acetylacetone-1 mass% tetramethylammonium chloride-methanol solution. .

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

  A steel having a chemical composition shown in Table 1 is melted, the slab is heated to 1000 ° C. or more and 1200 ° C. or less, hot rolled at a rolling finish temperature of 800 to 950 ° C., cooled to room temperature, and a steel plate having a thickness of 12 mm is obtained. Prototype.

  Steel No. For No. 83, the slab was heated to 950 ° C., hot-rolled at a rolling finish temperature of 680 ° C., air-cooled to room temperature, and a steel plate having a thickness of 12 mm was prototyped.

  Next, a test piece of 35 mm × 35 mm × 5 mm was collected from the obtained steel plate. The test piece was ground so that the surface roughness Ra was 1.6 μm or less, the end surface and the back surface were tape-sealed, and the surface was also tape-sealed so that the area of the exposed surface portion was 25 mm × 25 mm.

The test pieces obtained as described above were subjected to repeated wet and dry corrosion tests to evaluate the weather resistance.
As a weather resistance evaluation test, a corrosion test was performed that simulates the environment inside a girder without rain, which is considered to be the most severe environment in structures such as actual bridges. The conditions of the corrosion test are as follows. Drying process at a temperature of 40 ° C and relative humidity of 40% RH for 1 hour, then a transition time of 1 hour, then a temperature of 25 ° C and a humidity process of 95% RH for 3 hours, then a transition to 1 hour Time was taken to make one cycle for a total of 6 hours. Moreover, the artificial sea water solution adjusted so that the amount of salt adhering to the test piece surface might be 0.3 mdd was apply | coated to the surface of the test piece once a week during the drying process. The test of 224 cycles was done on the above conditions.

  After the corrosion test is completed, the test piece is immersed in an aqueous solution of hexamethylenetetramine in hydrochloric acid and derusted, and then the weight is measured. The difference between the obtained weight and the initial weight is determined to reduce the average thickness on one side. The amount (μm) was determined. If this average thickness reduction amount was 20.0 μm or less, it was evaluated that the weather resistance was excellent.

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

  As shown in Table 2, steel No. 1 of the present invention. It can be seen that 1-28 and 32-82 have excellent weather resistance with an average thickness reduction of 20.0 μm or less. On the other hand, Comparative Steel No. Nos. 29 to 31 and 83 to 84 have an average reduction in thickness exceeding 20.0 μm, which is inferior in weather resistance to the steel of the present invention.

Claims (7)

% By mass
C: 0.01% or more and less than 0.20%,
Si: 0.05% or more and 1.00% or less,
Mn: 0.20% or more and 2.00% or less,
P: 0.001% to 0.050%,
S: 0.0001% or more and 0.0200% or less,
Al: 0.005% to 0.050%,
Cu: 0.010% to 0.500%,
Nb: 0.005% or more and 0.100% or less,
Sn: 0.005% or more and 0.300% or less,
Furthermore, the amount of solid solution Nb is 0.002% or more and 0.080% or less,
Structural steel with excellent weather resistance, with the balance being iron and inevitable impurities. Furthermore, in mass%,
The structural steel material excellent in weather resistance according to claim 1, containing Ge: 0.0005% or more and 0.0100% or less. Furthermore, in mass%,
Ta: Structural steel material excellent in weather resistance according to claim 1 or 2 containing 0.001% or more and 0.100% or less. Furthermore, in mass%,
The structural steel material excellent in weather resistance according to any one of claims 1 to 3, containing Ni: 0.01% or more and 0.50% or less. Furthermore, in mass%,
Mo: 0.005% to 0.500%,
Co: 0.01% or more and 0.50% or less,
W: 0.005% to 0.500%,
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: The structural steel material excellent in the weather resistance in any one of Claims 1-4 containing 1 or more types chosen from 0.001% or more and 0.200% or less. Furthermore, in mass%,
V: 0.005% or more and 0.200% or less,
Zr: 0.005% or more and 0.200% or less,
B: The structural steel material excellent in the weather resistance in any one of Claims 1-5 containing 1 or more types chosen from 0.0001% or more and 0.0050% or less. Furthermore, in mass%,
REM: 0.0001% or more and 0.0100% or less,
Ca: 0.0001% or more and 0.0100% or less,
Mg: Structural steel material excellent in weather resistance according to any one of claims 1 to 6, comprising one or more selected from 0.0001% to 0.0100%.