JP6641699B2 - Welded H-section steel - Google Patents

Description

  The present invention relates to a welded H-section steel used for building materials of houses and the like, which has both corrosion resistance and appearance.

  The welded H-section steel manufactured by welding the steel strip has the same degree of freedom in the thickness and width of the web and the flange as compared with the rolled H-section steel manufactured by hot rolling, and thus is the same as the rolled H-section steel. When obtaining the cross-sectional performance of, the thickness of the plate can be reduced. Therefore, the welded H-section steel is used as a member of a house, a warehouse, a highway, etc. as a lightweight H-section steel having excellent sectional rigidity (such as a general structural welded lightweight H-section steel of JIS G 3353). .

  The welded H-section steel is manufactured by welding a flange material to both sides of a web material, and continuously manufactured by joining steel strips as raw materials by a high-frequency resistance welding machine. When corrosion resistance (rust resistance) is required for a welded H-section steel, a welded H-section steel is manufactured using a hot-dip galvanized steel strip as a material (see Patent Document 1).

  However, when welding a hot-dip galvanized steel strip, particularly a hot-dip galvanized steel strip whose plating layer contains Al, Mg, or the like, the appearance of the welded portion may deteriorate. In order to solve such a problem, a method of manufacturing a welded H-section steel in which high frequency resistance welding is performed after removing a plating layer in a region of a flange material to be joined to a web material and a region in contact with a power supply tip before welding is proposed. (For example, see Patent Documents 2 and 3).

JP-A-7-9151 JP 2012-200774 A JP 2012-200775 A

  In recent years, the need for longer life of a structure and a reduction in maintenance costs has led to a demand for even better corrosion resistance in welded H-section steels. Conventionally, when corrosion resistance is required for welded H-section steel for building materials, hot-dip galvanizing has been applied. However, by adding aluminum or magnesium to the plating layer, corrosion resistance can be improved. Are being considered. Further, in order to prevent white rust caused by corrosion of the plating, a chemical conversion coating may be formed on the surface of the hot-dip galvanizing.

  The present inventors studied the addition of aluminum or magnesium to the plating layer in order to obtain a welded H-section steel having excellent corrosion resistance. However, unlike the conventional hot-dip galvanized steel strip, when aluminum or magnesium is contained in the plating layer, when a chemical conversion coating is formed and continuously joined by a high-frequency resistance welding machine, sparks are generated and the welded H-shape is formed. There was a problem that the appearance of the steel was poor. When a steel strip provided with a plating layer and a chemical conversion coating containing aluminum and magnesium is subjected to high frequency resistance welding as a web material and a flange material, the plating layer and the chemical conversion coating at the welded portion of the obtained welded H-section steel disappear. ing.

  In a welded H-section steel, a web material and a flange material are welded to each other by high-frequency resistance welding (hereinafter, sometimes simply referred to as “high-frequency welding”). Electric current is supplied, and a spark may be generated from the contact portion. The occurrence of such sparks was observed only when a steel strip containing aluminum or magnesium which is an easily oxidizable element in a plating layer and further provided with a chemical conversion coating was used.

  That is, when the plating layer does not contain aluminum or magnesium, even if the chemical conversion treatment film is provided, appearance defects such as darkening are not seen, and even if the plating layer contains aluminum or magnesium, the chemical conversion treatment film is provided. If not, it was found that poor appearance such as darkening was not observed. The present invention has been made in view of the above circumstances, even if a high corrosion-resistant steel strip is used as the material of the welded H-section steel, without causing appearance defects due to sparks during high-frequency resistance welding, An object of the present invention is to provide a welded H-section steel having both corrosion resistance and appearance.

  The present inventors have presumed that the corrosion resistance of a welded H-section steel is improved by increasing the content of aluminum and magnesium in the plating layer, and a chemical conversion applicable when such a plating layer is used. To provide an H-section steel having an excellent appearance by suppressing the occurrence of welding defects and darkening even when a web material and a flange material are joined by high-frequency welding by suitably controlling the thickness of a treatment film. That we can do it. The gist of the present invention is as follows.

[1] A welded H-section steel including a web and a pair of flanges connected to both ends of the web by welding,
Both the web and the flange are a base material and a Zn-Al-Mg-Si based alloy plating, a Zn-Al-Mg based alloy plating, and a Zn-Al based alloy plating laminated on the base material. Any one of a plating layer and a chemical conversion treatment film containing an organic substance laminated on the plating layer,
From the surface of the chemical conversion film, the thickness of the chemical conversion film determined as the distance from the surface to the position where the carbon amount in the depth direction measured by glow discharge emission analysis becomes 1/10 of the maximum value is 0.1 to A welded H-section steel having a diameter of 0.7 μm.

[2] The base material is in mass%,
C: 0.01-0.3%,
Si: 0.01 to 2.0%,
Mn: 0.1-3.0%,
S: 0.015% or less,
P: 0.030% or less,
Al: 0.001 to 0.5%,
Ti 0.001-0.5%,
N: 0.0005 to 0.006%
Wherein the balance comprises Fe and inevitable impurities.

  [3] The welded H-section steel according to the above [1] or [2], wherein the base material further contains B: 0.0003 to 0.0040% by mass%.

  [4] The Zn-Al-Mg-Si based alloy plating contains Al: 2 to 19%, Mg: 1 to 10%, Si: 0.01 to 2% by mass%, with the balance being Zn and The welded H-section steel according to any one of the above [1] to [3], which is an unavoidable impurity.

  [5] The Zn—Al—Mg based alloy plating contains Al: 2 to 19% and Mg: 0.5 to 10% by mass%, with the balance being Zn and unavoidable impurities. The welded H-section steel according to any one of the above [1] to [3].

[6] The Zn—Al-based alloy plating is 0.18 to 5% by mass Al.
And Mg: 0.01 to 0.5%;
La: 0.001 to 0.5%,
Ce: 0.001 to 0.5%
The welded H-section steel according to any one of the above [1] to [3], comprising one or more of the above, and the balance is Zn and inevitable impurities.

  In the welded H-section steel according to the present invention, the thickness of the chemical conversion coating is particularly improved on the premise that the composition of the plating layer is adjusted. As a result, according to the welded H-section steel of the present invention, both corrosion resistance (rust resistance) and appearance can be achieved.

It is a graph which shows the relationship between the spark generation number and the carbon thickness of the steel plate surface by GDS. It is a graph which shows the relationship between the white rust generation rate and the number of sparks generated, and the carbon thickness of the steel sheet surface by GDS. It is a schematic diagram which shows an example of the welding H-section steel of this invention. It is a flowchart which shows the manufacturing method of the welding H-section steel of this invention.

  The present inventors have found that when a welded H-section steel is manufactured using a hot-dip galvanized steel strip formed with a plating layer containing aluminum and magnesium and a chemical conversion coating, sparks are generated in a power supply part used for high-frequency welding. A method for suppressing the occurrence of defects that occur was studied. First, when an easily oxidizable element such as aluminum or magnesium is contained in the plating layer, a spark occurs due to ignition. In addition, since the chemical conversion coating contains an organic substance, carbon also causes sparks.

  It is considered that when sparks are generated, the carbide contained in the chemical conversion coating becomes soot, and when the amount of soot increases, defects (darkening) occur. Since the amount of soot adhering to the welded H-section steel is considered to depend particularly on the thickness of the chemical conversion treatment film, it is considered that the occurrence of defects can be suppressed by properly managing the thickness of the chemical conversion treatment film. Was done.

  The components of the chemical conversion coating are selected according to the purpose and the type of plating, but the organic acid is always contained as a binder. Since the organic acid contains carbon as a main component, the film thickness can be controlled by obtaining the distribution of carbon in the depth direction on the surface of the steel sheet. Furthermore, when manufacturing a welded H-section steel, since soot generated due to spark generation is considered to be derived from carbon contained in the chemical conversion coating, the thickness of the chemical conversion coating is determined by the distribution of carbon in the depth direction. It is considered that the occurrence of defects can be effectively suppressed by proper management.

Here, a method of measuring the thickness of the chemical conversion treatment film will be described. The thickness of the chemical conversion coating was set to a region where the carbon content distribution in the coating in the depth direction from the surface determined by a glow discharge optical emission spectrometer (GDS) was 1/10 of its peak value. When the measurement result of the film thickness by GDS was made to correspond to the film adhesion amount, when the film adhesion amount was 80 mg / m ² , the film thickness was 0.2 μm, and the film adhesion amount was 400 mg / m ^2. In the case of m ² , the film thickness was 1.1 μm, and it was confirmed that the film adhesion amount and the film thickness had a roughly proportional relationship.

  Using the thickness of the chemical conversion coating thus measured as an index, the state of spark generation after welding was evaluated. FIG. 1 is a graph showing the relationship between the number of sparks generated and the carbon thickness of the steel sheet surface by GDS, and particularly compares the case of high corrosion resistance plating with the case of hot dip galvanizing. The number of sparks generated was the number of darkening marks per 4 m of welded H-section steel (pieces / 4 m). According to FIG. 4, it can be seen that the number of sparks of the high corrosion resistant zinc plating is larger than that of the hot dip galvanization. In the case of hot-dip galvanizing, the number of sparks was 1/4 m or less in the range of the normal film thickness of 0.8 to 1.4 μm, whereas in the case of high corrosion resistance plating, the number of sparks increased to 2 to 6/4 m.

  This is considered to be a result of aluminum and magnesium added to the highly corrosion resistant plating to induce spark generation. On the other hand, it can be seen that spark generation can be suppressed by reducing the film thickness to 0.7 μm or less even in highly corrosion resistant plating. However, when the coating amount is too small, there is a concern that primary rust prevention is insufficient and white rust is likely to occur.

  Therefore, the relationship between the state of spark generation and the state of white rust generation during high-frequency welding was determined using a high corrosion-resistant plated steel sheet in which the thickness of the chemical conversion coating was changed. The result is shown in FIG. FIG. 2 is a graph showing the relationship between the white rust occurrence rate and the number of sparks generated and the carbon thickness of the steel sheet surface by GDS. As described above, the number of sparks was the number of dark spots per 4 m of the welded H-section steel, and the white rust occurrence was the ratio of white rust on the flange surface of the welded H-section steel exposed outdoors for 2 months. When the number of darkening marks is 1 / 4m or less, there is almost no decrease in productivity even when the part is repair-painted, so that the number of darkening marks is 1 / 4m or less is preferred. When the white rust occurrence rate was 5% or less, almost no change in appearance was observed. Therefore, a white rust occurrence rate of 5% or less was regarded as good.

According to FIG. 2, when the film thickness is less than 0.1 μm, the generation of white rust is remarkable, and when the film thickness exceeds 0.7 μm, the number of sparks becomes 1/4 m or more. That is, it is understood that spark suppression can be achieved if the film thickness is 0.1 to 0.7 μm. When the film thickness was represented by the film adhesion amount, the proper range was 30 to 150 mg / m ² .

  Based on the above findings, embodiments of the present invention will be described below with reference to the drawings. In the present specification, the vertical direction of the H-beam refers to a direction connecting a pair of flanges, and the horizontal direction of the H-beam refers to a direction perpendicular to both the vertical direction and the longitudinal direction of the H-beam. Say. Hereinafter, the vertical direction of the H-section steel, the longitudinal direction of the H-section steel, and the horizontal direction of the H-section steel may be referred to as a vertical direction, a longitudinal direction, and a horizontal direction, respectively. Further, in the present specification, all ratios (%) of each element mean mass%.

<Welded H-section steel>
FIG. 3 is a schematic diagram showing an example of a welded H-section steel according to the present invention (when the flange has a vertical thickness of 4.5 mm) (the longitudinal direction is a direction perpendicular to the paper surface). In FIG. 3, the dimensional ratio of each layer is not shown accurately. As shown in FIG. 1, the H-section steel 10 includes a web 12 and a pair of flanges 14 connected to both ends of the web 12 in the vertical direction by welding. In the figure, the boundary (dotted line) between the web 12 and the flange 14 is welded.

  The web 12 is made of a base material 12a and any one of Zn-Al-Mg-Si based alloy plating, Zn-Al-Mg based alloy plating, and Zn-Al based alloy plating laminated on the surface of the base material 12a. It includes a seed plating layer 12b and a chemical conversion coating 12c that is laminated on at least a part (all in FIG. 3) of the plating layer 12b and contains an organic substance.

  Further, the flange 14 is made of a base material 14a and any one of Zn-Al-Mg-Si based alloy plating, Zn-Al-Mg based alloy plating, and Zn-Al based alloy plating laminated on the surface of the base material 14a. It includes one type of plating layer 14b and a chemical conversion coating 14c that is laminated on at least a part (all in FIG. 3) of the plating layer 14b and contains an organic substance.

(Base material)
As the base materials 12a and 14a, a low-carbon steel is mainly used, but a medium-carbon steel, a high-carbon steel, an alloy steel, or the like can be used as needed. The components of the low carbon steel used for the base material are preferably as follows. The balance of the components shown below is Fe and unavoidable impurities. The unavoidable impurities are components contained in the raw materials or components mixed in the manufacturing process, and are intentionally contained in the base material. Refers to components that are not components.

  C: The lower limit is preferably set to 0.01% in order to secure a predetermined tensile strength. Excessive addition of C hardens the welded HAZ and leads to a decrease in bending performance and delayed cracking, so the upper limit of the C content is preferably set to 0.3%.

  Si: Si is necessary for deoxidizing the base material, and the lower limit of the content is preferably 0.01%. Further, Si has a solid solution strengthening action and can be used for adjusting the strength of the base material together with the following Mn. In addition, since excessive addition of Si leads to an increase in oxide scale at the time of steel production, the upper limit of the content is preferably 2.0%.

  Mn: Mn is preferably fixed to a lower limit of 0.1% in order to fix S, which is an unavoidable impurity in the steel that causes hot brittleness of the steel material, as MnS and render it harmless. On the other hand, excessive addition of Mn hardens the welded HAZ and leads to a decrease in bending performance and the occurrence of delayed cracking. Therefore, the upper limit of the content is preferably set to 3.0%.

  S: S is an element that lowers the hot workability of the steel material, and preferably has an upper limit of 0.015%.

  P: Like P, S is an element that reduces hot workability, and its upper limit is preferably set to 0.03%.

  Al: Al is preferably added at 0.001% or more as a deoxidizing element of steel. On the other hand, if added in excess, coarse non-metallic inclusions may be generated and the performance such as the toughness of the steel material may be reduced, so the upper limit is preferably 0.5%.

  Ti: Ti has an effect of fixing N in steel as nitride and preventing B from being precipitated as nitride. The lower limit is preferably 0.001%. On the other hand, if the content exceeds 0.5%, the effect is saturated, so the upper limit is preferably 0.5%.

  N: While N increases the strength of the steel, a large addition of N lowers the toughness of the steel and precipitates B as a nitride, which may impair the effect of B to reduce cracking. 0.006% is preferred. The smaller the N, the better, but if it is 0.0005% or less, the cost will increase, so the lower limit may be 0.0005%.

  Further, when welding the welded H-section steel to another member or when welding the welded H-section steels together, it is preferable to add B to the base material in addition to the above components.

  B: B has the effect of segregating and enriching the grain boundaries in the austenitic region of 800 ° C. or higher during welding to prevent the zinc-based alloy plating in the molten state from entering the grain boundaries, and has a tensile stress due to thermal shrinkage in a low temperature region When this occurs, there is an effect of reducing the plastic strain in the stress concentrated portion by strengthening the grain boundary of the weld HAZ. To obtain the effect, it is preferable to add 0.0003% or more. On the other hand, excessive addition may cause deterioration of the toughness of the welded portion, so the upper limit is preferably 0.0040%.

  The thickness of the base materials 12a and 14a (horizontal dimension for the base material 12a and vertical vertical dimension for the base material 14a) is not particularly limited, but the base material forming the web 12 is for the purpose of improving the sectional rigidity. It is preferable to make the thickness of the base material 14a constituting the flange 14 larger than the thickness of the base material 12a.

(Plating layer)
As the plating layers 12b and 14b, any one of Zn-Al-Mg-Si-based alloy plating, Zn-Al-Mg-based alloy plating, and Zn-Al-based alloy plating is used from the viewpoint of improving corrosion resistance. Used.

  The Zn-Al-Mg-Si based alloy plating preferably contains Al: 2 to 19%, Mg: 1 to 10%, Si: 0.01 to 2% by mass%, with the balance being Zn and inevitable. Use what is a target impurity.

  The reason for setting the Al content to 2 to 19% is that if the Al content is less than 2%, excellent corrosion resistance may not be realized and excellent adhesion to the base material may not be realized. If the content exceeds 19%, the effect of improving the corrosion resistance may not be recognized.

  The reason why the content of Mg is set to 1 to 10% is that if it is less than 1%, it may not be possible to realize excellent corrosion resistance. On the other hand, if it exceeds 10%, the plating layer becomes brittle and may be inferior to the base material. This is because excellent adhesion may not be realized in some cases.

  The reason why the content of Si is set to 0.01 to 2% is that if the content is less than 0.01%, Al in the plating layer and Fe in the base material react with each other, and the plating layer becomes brittle and becomes incompatible with the base material. This is because excellent adhesion may not be achieved in some cases, and if it exceeds 2%, the effect of improving the adhesion may not be recognized in some cases.

  Next, the Zn—Al—Mg based alloy plating preferably contains, by mass%, Al: 2 to 19% and Mg: 0.5 to 10%, with the balance being Zn and unavoidable impurities. Used. The reasons for limiting the contents of Al and Mg are the same as in the case of the above-described Zn-Al-Mg-Si alloy plating.

  Further, the Zn—Al-based alloy plating preferably contains Al: 0.18 to 5% by mass%, further Mg: 0.01 to 0.5%, La: 0.001 to 0.5%. %, Ce: one or two or more of 0.001 to 0.5%, with the balance being Zn and unavoidable impurities. The reason for limiting the Al content is the same as in the case of the above-described Zn-Al-Mg-Si alloy plating. Mg, La, and Ce are elements that enhance both the protective action of the plating due to aluminum and the sacrificial anticorrosion action of the zinc, and in order to further improve the corrosion resistance, set the lower limit as described above. Is preferred. On the other hand, even if Mg, La, and Ce are excessively contained, the corrosion resistance cannot be improved, so the upper limit may be set as described above.

  In the plating layer, In: 0.01 to 1%, Bi: 0.01 to 1%, Sn: 1 to 10%, Ca: 0.01 to 0.5%, Be: 0 by mass%. 0.01 to 0.2%, Ti: 0.01 to 0.2%, Cu: 0.1 to 1.0%, Ni: 0.01 to 1.0%, Co: 0.01 to 0.3 %, Cr: 0.01 to 0.2%, Mn: 0.01 to 0.5%, Fe: 0.01 to 3.0%, Sr: 0.01 to 0.5% It can be contained.

  In, Bi, and Sn are respectively contained in order to improve the corrosion resistance, but if contained excessively, the appearance after plating may become coarse, so that the lower limit and upper limit as described above, respectively. Is preferably set.

  On the other hand, Ca, Be, Ti, Cu, Ni, Co, Cr, Mn, Fe, and Sr are used to enhance the corrosion resistance after coating. However, when excessively contained, the appearance after plating becomes coarse. Therefore, it is preferable to set the lower limit and the upper limit as described above.

  In addition, it is preferable to limit the total amount of inevitable impurities such as Fe, Pb, Sn, and Sb to 0.5% or less, and to limit Pb to 0.1% or less and Sb to 0.1% or less. The reason for limiting the total amount of impurities to 0.5% or less is that if the total amount exceeds 0.5%, the adhesion of the plating is not sufficiently exhibited. From such a viewpoint, it is particularly preferable to set the respective upper limits of the Pb content and the Sb content as described above.

The thickness of the plating layers 12b and 14b (horizontal dimension for the plating layer 12b and vertical vertical dimension for the plating layer 14b) is controlled as the amount of plating per unit area on one side, and is 60 g / m ² or more and 270 g / m ² or less. When the thickness is 60 g / m ² or more, the original effect (corrosion protection) of the plating layer can be sufficiently obtained. On the other hand, when the thickness is 270 g / m ² or less, buildings such as welded H-beams are used. Workability such as arc welding performed when assembling the components can be improved.

  In the example shown in FIG. 3, the plating layer 12b of the web 12 is laminated on both end surfaces in the horizontal direction (regions excluding both end portions in the vertical direction) of the base material 12a. On the other hand, in the flange 14, the plating layers 14b are stacked at both ends in the vertical direction (regions excluding both ends in the horizontal direction).

(Chemical conversion coating)
The chemical conversion coatings 12c and 14c are not particularly limited as long as they are so-called chromate-free coatings used for the purpose of improving corrosion resistance, furthermore, blackening resistance and coating adhesion. For example, a chemical conversion treatment film formed by applying a treatment solution containing a basic zirconium compound, a vanadyl-containing compound, a phosphate compound, a cobalt compound, an organic acid, and water can be suitably used.

The basic zirconium compound is, for example, a zirconium carbonate compound having [Zr (CO ₃ ) ₂ (OH) ₂ ] ^2- or [Zr (CO ₃ ) ₂ (OH) ₂ ] ^2- as a cation, or a zirconium carbonate compound having these cations. The contained ammonium salt, potassium salt, sodium salt and the like may be used. The vanadyl (VO ²⁺ ) -containing compound is, for example, a salt of an oxovanadium cation with an inorganic acid anion such as hydrochloric acid, nitric acid, phosphoric acid or sulfuric acid, or an organic acid anion such as formic acid, acetic acid, propionic acid, butyric acid or oxalic acid. There may be. Further, a chelate of a vanadyl compound with an organic acid such as vanadyl glycolate or vanadyl dehydroascorbate may be used.

  Phosphoric acid compounds include phosphoric acid and its ammonium salts, such as orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid, phytic acid, phosphonic acid, ammonium phosphate, ammonium dihydrogen phosphate, and hydrogen phosphate. Ammonium, sodium phosphate, potassium phosphate and the like may be used. The cobalt compound may be cobalt carbonate, cobalt nitrate, cobalt acetate and the like.

  The organic acid may be, for example, glycolic acid, malic acid, tartaric acid, oxalic acid, citric acid, ascorbic acid, lactic acid, dehydrobenzoic acid, dehydroascorbic acid, gallic acid, tannic acid, phytic acid, and the like. It may be an ammonium salt of an acid.

  The chemical conversion treatment film is formed by applying a treatment liquid containing a basic zirconium compound, a vanadyl-containing compound, a phosphate compound, a cobalt compound, an organic acid, and water, followed by drying. The method for applying the treatment liquid is not particularly limited, and for example, a spray method, a dipping method, a roll coating method, a shower ringer method, an air knife method, or the like may be employed. A surfactant, an organic solvent and an antifoaming agent can be added to the treatment liquid. Further, a lubricant or a filler may be added to the treatment liquid. After applying the treatment liquid, it may be heated to 50 to 200 ° C. for drying.

  The thickness of the chemical conversion coatings 12c and 14c can be 0.1 μm or more and 0.7 μm or less. When the thickness is 0.1 μm or more, the original effect (corrosion protection) of the chemical conversion treatment film can be sufficiently obtained. On the other hand, when the thickness is 0.7 μm or less, the occurrence of darkening due to spark generation is suppressed. be able to.

  In the example shown in FIG. 3, the chemical conversion coating 12 c is laminated on the plating layer 12 b of the web 12. Similarly, regarding the flange 14, the chemical conversion treatment film 14c is laminated on the plating layer 14b. The thickness of the chemical conversion coating can be determined from the carbon content distribution in the depth direction obtained by a glow discharge optical emission spectrometer, and is defined as a region from the surface until the carbon content becomes 1/10 of the peak value.

  In the H-section steel of the present embodiment, the thickness of the chemical conversion coating is set to 0.1 μm or more on the assumption that the corrosion resistance is increased by relatively increasing the content of aluminum and magnesium in the plating layer. Thereby, the original effect (corrosion prevention action) of the chemical conversion treatment film can be exhibited, and the excellent corrosion resistance (rust resistance) of the H-section steel can be realized. In addition, it is preferable that the thickness of the chemical conversion coating be 0.2 μm or more, since the corrosion resistance of the H-section steel is realized at a higher level.

  On the other hand, by setting the thickness of the chemical conversion coating to 0.7 μm or less, regardless of the presence or absence of sparks, even if the web material and the flange material are joined by high-frequency welding in the process of manufacturing the H-section steel, It is possible to prevent the occurrence of darkening at the welding location and its surroundings, and as a result, it is possible to maintain a good appearance. In addition, it is preferable that the thickness of the chemical conversion coating be 0.6 μm or less, since the appearance of the H-section steel is realized at a higher level.

  As described above, in the welded H-section steel according to the present embodiment, the carbon content in the chemical conversion coating is particularly improved on the assumption that the composition of the plating layer is adjusted. As a result, according to the H-shaped steel, both excellent corrosion resistance (rust resistance) and appearance can be achieved.

(Coating)
In the present embodiment, the coating film 16 is further laminated on at least a part of the plating layer and the chemical conversion coating (in the example shown in FIG. 3, a part of the chemical conversion coating 12 c and a part of the chemical conversion coating 14 c). Preferably, the coating 16 covers the weld bead 18. The coating film 16 may be a coating film containing at least one organic resin.

  Examples of the organic resin include polyolefin resin, acrylic resin, urethane resin, epoxy resin, polyester resin, vinyl chloride resin, fluorine resin, butyral resin, polycarbonate resin, phenol resin, and the like. In addition, as the coating film, a mixture or a copolymer thereof can also be used. Further, an isocyanate resin, an amino resin, a silane coupling agent, a titanium coupling agent, or the like can be used in combination as an auxiliary component. In many cases, the H-section steel of the present embodiment is used as it is without any repair after processing. Therefore, in applications where severe processing is performed, resin systems that crosslink polyester resins with melamine, resin systems that crosslink polyester resins with urethane resins (isocyanates, isocyanate resins), vinyl chloride resins, and fluororesins (solvent-based) It is preferable to use a solution type or a dispersion mixed type with an acrylic resin.

  As will be described later, the H-section steel of the present embodiment is obtained by joining a web material and a flange material by high-frequency welding, and by this welding, as shown in FIG. 3, both the base materials 12a and 14a are formed. , A weld bead 18 having a component equivalent to the base metal component is formed. Even if the plating layer and the chemical conversion treatment film are sequentially laminated on the entire surface of both the base material of the web material and the flange material, the plating layer and the chemical conversion treatment film disappear at the place where the weld bead 18 is formed at the time of welding. Therefore, the weld bead 18 is exposed.

  However, for example, as shown in FIG. 3, by coating the coating film 16 so as to cover the weld bead 18, the corrosion resistance of the welded H-section steel can be further enhanced without leaving the weld bead 18 in a bare state. it can. It is preferable to use a metallic coloring pigment such as an aluminum pigment as the coating film 16 so that the welded H-section steel does not have a locally different hue portion. In the present embodiment, a paint in which aluminum phosphate is added as an anticorrosive pigment to an epoxy resin is applied by spraying the weld bead portion by air spraying, but the type of paint and the spraying method are not limited to this method.

<Production method of welded H-section steel>
Next, a method for manufacturing the H steel sheet described above will be described in detail. The method for producing a welded H-section steel of the present invention is characterized by the dilution of the resin contained in the chemical conversion coating in step 1-2 described below. The welded H-section steel of the present invention is manufactured, for example, by the following method.

  FIG. 4 is a flowchart showing a method for producing a welded H-section steel according to the present invention. The method for manufacturing a welded H-section steel according to the present invention includes 1) a step of preparing a web material and a flange material (step 1), 2) a high-frequency welding step (step 2), and 3) a coating step of a weld bead (step 3). . Steps 1 and 2 are essential steps, but step 3 is an optional step. Hereinafter, each step will be described.

1) Step 1
In step 1, a web material and a flange material are prepared. Step 1 includes a plating layer laminating step (step 1-1) and a chemical conversion coating layer laminating step (step 1-2).

  In step 1-1, for each of the web material and the flange material, a plating layer (Zn-Al-Mg-Si alloy plating, Zn-based alloy plating) is applied to a base material (low-carbon steel, medium-carbon steel, high-carbon steel, alloy steel). -Al-Mg based alloy plating and Zn-Al based alloy plating, for example, containing Al: 2 to 19%, Mg: 1 to 10%, Si: 0.01 to 2%, and the balance is Zn). As a lamination method, hot-dip plating, which is excellent in productivity and can thicken a plating layer, is preferable. For example, it is manufactured by controlling a plating thickness with an air knife after passing a steel sheet through a hot-dip plating bath.

  In step 1-2, a chemical conversion coating containing an organic substance is laminated on the plating layer for the web material and the flange material. For example, in the case of manufacturing the H-section steel shown in FIG. 3, a chemical conversion coating is laminated on the plating layer for both the web material and the flange material.

  As a method of laminating a chemical conversion treatment film, an aqueous coating composition containing coating film components (organic substance, if necessary, silica, silane coupling agent, etc.) in an aqueous solvent is applied on a plating layer, and heated and dried. To form the film. Here, the aqueous solvent means a solvent in which water is a main component of the solvent. Examples of the solvent other than water include an organic solvent. As a result, the thickness of the chemical conversion coating measured using a glow discharge optical emission analyzer becomes 0.1 μm or more and 0.7 μm or less, and both excellent corrosion resistance and appearance of the welded H-section steel are achieved.

2) Step 2
In step 2, the web material and the flange material are welded by high frequency. The high-frequency welding can be performed in a known manner, that is, via a power supply unit provided near the joint of each of the web material and the flange material.

3) Step 3
In step 3, a color matching coating is applied to the welded H-section steel, and a coating film containing at least one organic resin is laminated. For example, as shown in FIG. 3, the coating film 16 can be laminated so as to cover the weld bead 18.

  In the method for producing a welded H-section steel according to the present invention described above, on the assumption that the composition of the plating layer is adjusted in step 1-1, in particular, the organic substance (particularly, carbon) contained in the chemical conversion coating in step 1-2. By the dilution of (amount), it is possible to suppress the occurrence of darkening at the welding location and its surroundings due to spark generation. As a result, according to the welded H-section steel obtained by the production method of the present invention, both excellent corrosion resistance and appearance can be achieved.

  Hereinafter, the effects of the present invention will be specifically described with reference to the invention examples. Note that the present invention is not limited to the conditions used in the following invention examples. Test Nos. 1 to 7 are welded H-sections within the scope of the present invention, and Test Nos. 8 to 10 are welded H-sections outside the scope of the present invention.

  A welded H-section steel of the type shown in FIG. 3 was produced through the web material and flange material preparation step, high-frequency welding step, and color matching coating step as described above. The high-frequency welding was performed using a copper power supply, the frequency of the high-frequency power supply was set to 360 kHz, and the size of the contact portion between the power supply and the steel strip was set to 15 mm × 20 mm so that the heating temperature of the joint was 1300 ° C. .

  In addition, the base material component, the plating component, and the chemical conversion coating component of each test example (test numbers 1 to 10) are as shown in Tables 1 to 3, respectively. Also, regarding the dimensions of the welded H-section steel in each test example, the vertical dimension of the web was 200 mm, the horizontal dimension of both flanges was 100 mm, the horizontal dimension (thickness) of the web was 3.2 mm, and the vertical direction of both flanges was The size (thickness) was 4.5 mm.

  Next, each test example was evaluated for corrosion resistance and appearance.

(Evaluation on corrosion resistance)
The welded portion of the welded H-section steel was subjected to a coating in which a paint obtained by adding aluminum phosphate as an anticorrosive pigment to an epoxy resin was sprayed on a weld bead portion by air spray, and the corrosion resistance was evaluated. The welded H-section steel was exposed outdoors for 2 months, and the test was judged as acceptable if the ratio of white rust on the upper surface of the flange was 5% or less. The results are shown in Table 4.

(Evaluation on appearance)
The weld and its surroundings were visually observed, and the number of black marks around 4 m of the welded H-section steel was counted. The results are shown in Table 4.

  According to Table 4, the welded H-section steels of the invention belong to the technical range of the present invention (high corrosion resistance plating containing Al or Mg as a plating component and the film thickness is 0.1 to 0.7 μm). Shows that the corrosion resistance and the appearance are both compatible at a high level with respect to the welded H-section steel of the comparative example, which does not belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Welded H-section steel 12 Web 14 Flange 12a, 14a Base material 12b, 14b Plating layer 12c, 14c Chemical conversion treatment film 16 Coating film 18 Weld bead

Claims (3)

A high frequency resistance welded H-beam including a web and a pair of flanges connected to both ends of the web by welding,
The web and the flange are both a base material and a Zn-Al-Mg-Si based alloy plating, a Zn-Al-Mg based alloy plating, and a Zn-Al based alloy plating laminated on the base material. Any one of a plating layer and a chemical conversion treatment film containing an organic substance laminated on the plating layer,
From the surface of the chemical conversion treatment film, the thickness of the chemical conversion treatment film determined as the distance to the position where the carbon amount in the depth direction measured by glow discharge emission spectrometry becomes 1/10 of the maximum value is 0.1 to 0.3 μm,
The Zn-Al-Mg-Si based alloy plating contains, by mass%, Al: 2 to 19%, Mg: 1 to 10%, and Si: 0.01 to 2%, with the balance being Zn and inevitable impurities. And
The Zn—Al—Mg based alloy plating contains, by mass%, Al: 2 to 19% and Mg: 0.5 to 10%, with the balance being Zn and unavoidable impurities,
The Zn—Al-based alloy plating contains, by mass%, Al: 0.18 to 5%, and further Mg: 0.01 to 0.5%,
La: 0.001 to 0.5%,
Ce: 0.001 to 0.5%
H-shaped steel of contact type high frequency resistance welding, characterized in that it contains any one or more of the above, and the balance is Zn and inevitable impurities. The base material is represented by mass%,
C: 0.01 to 0.3%,
Si: 0.01 to 2.0%,
Mn: 0.1-3.0%,
S: 0.015% or less,
P: 0.030% or less,
Al: 0.001 to 0.5%,
Ti 0.001-0.5%,
N: 0.0005 to 0.006%
The contact type high frequency resistance welded H-section steel according to claim 1, wherein the H-shaped steel comprises Fe and inevitable impurities. The base material further contains, by mass%, B: according to claim 1 or 2, characterized in that it contains 0.0003 to 0.0040 percent contactless high frequency resistance welding H-shaped steel.

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