JP3127050B2 - Structural steel plate with excellent corrosion resistance after painting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structural steel plate having excellent corrosion resistance after painting and used in marine environments such as ships, bridges and marine structures.

[0002]

2. Description of the Related Art Steel structures such as ships, bridges, and marine structures have been exposed to an atmosphere containing chlorides for many years, and are required to have high durability in such environments. Most steel sheets used for this type of application are milled to remove black scales on the surface of the rolled steel material by a maker for primary rust prevention, and then coated with a primary primer (wash primer or zinc-rich primer) to fabricate the fabric. Delivered to the caterer.

In a fabricator, a block is manufactured by gas cutting, welding, or the like, and after a base coat is applied, the block is transported to the site, assembled, installed, and finally subjected to a middle / top coat and used. I have. During the service period, repainting is repeatedly performed according to the degree of rusting and blistering.

[0004]

Many primers applied for primary rust prevention impair gas cutting properties and weldability. Therefore, primers near gas cutting lines and welding lines must be coated in advance with primers. It has to be removed, requiring a great deal of labor and cost. In addition, when a block is manufactured, transported, or installed at a site, the coating is easily damaged by conventional coating, and a scratch is made on a steel base, so that a partial repair such as touch-up is required. Further, there is a problem that leakage of partial repair due to oversight of damage significantly deteriorates corrosion resistance.

[0005] During the service period, the rust-preventing life of the paint does not reach the service life of the steel structure at present, so that repainting must be repeatedly performed for the purpose of maintaining rust-prevention. In the case of bridges, members located on the lower flange lower surface where water is apt to accumulate and the splash zone where wet and wet and dry conditions are repeated are more likely to corrode earlier than other parts and are applied in submerged parts Often, cathodic protection is also ineffective. For this reason, the interval between the entire repainting has to be shortened due to the control of the corrosion of these members.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a primary primer can be omitted by forming a thin and hard plating layer of a Co or Ni alloy on the surface of a steel sheet. It is an object of the present invention to provide a structural steel plate which is hard to be damaged in a steel base and has excellent corrosion resistance after painting.

[0007]

Means for Solving the Problems The gist of the present invention, a thickness of the steel sheet surface is 4 to 100 [mu] m, and hardness of HV225 or more Ni
It is a structural steel plate with excellent corrosion resistance after coating, in which one of the alloy and Co plating layers is formed.

[0008]

[Function] The plating layer formed on the steel sheet surface is Ni alloy or Co
These are metals whose corrosion potential is more noble than steel, but are limited to those whose potential difference from steel is smaller than that of Ni. The reason is that if the interface is exposed to a corrosive environment, if the interface is exposed to a corrosive environment, the steel part will preferentially corrode and its speed will increase if the corrosion potential is higher than the steel, which will make the durability worse. It is.

The inventors conducted a corrosion test to investigate the effect of the thickness of the plating layer on the corrosion resistance. The corrosion test piece was prepared by applying electroplating of the metal to the surface of the steel sheet, applying the coating specification a shown in Table 2 to the surface of the plating layer, and then applying a cross cut through the coating film and the plating layer. .

[0010] The corrosion test was a repeated cycle corrosion test in which wet → salt spray → dry was one cycle. The wet condition is 50 ° C x 6hr, 95% or more RH, and the salt spray condition is
5% NaCl aqueous solution, 35 ℃ × 2hr, drying condition is 50 ℃ × 16hr
It is.

[0011] As shown in Table 1 of the examples,
When the thickness of the plating layer is 1 μm, compared to the material without plating layer,
Almost no improvement in corrosion resistance can be expected. But Ni
It can be seen that when the thickness of the plating layer made of an alloy or Co is 4 μm , the effect of improving corrosion resistance is exhibited.

In the plating layer, the formation of pinholes is not avoided industrially. When the thickness of the plating layer is less than 4 μm , the effect of improving corrosion resistance is small due to the pinholes.
When the thickness of the plating layer exceeds 100 μm, not only does the economic efficiency deteriorate, but also the gas cutting property and the weldability deteriorate due to the presence of the plating layer. Therefore, the plating layer thickness is limited to the range of 4 to 100 μm.

The hardness of the plating layer is preferably such that the harder the steel, the less likely it is for the steel base to be scratched, and it is preferable that the scratches due to abrasion or impact during block production, transportation, installation on site, or service are minimized. According to the present invention, the hardness of the plating layer is limited to HV225 or more so as not to reach the substrate.

[0014]

Embodiments of the present invention will be described below.
The thick steel plate used was JIS standard SM490A, 12 mm thick. The test piece was a steel plate having a width of 70 mm and a length of 150 mm. The black scale was removed by shot blasting, and then degreased. After that, the surface of the plating layer is coated according to the coating specifications shown in Table 2, and after the coating film is dried, a crosscut that penetrates only the coating film on the coating surface, and a crosscut that penetrates the coating film and the plating layer and reaches the steel base. And subjected to a corrosion test.

The corrosion test conditions are as follows: a combined cycle corrosion test in which the above-described wet → salt spray → dry cycles are defined as one cycle.
Repeated times. After the corrosion test, the corrosion length in the horizontal direction and the corrosion length in the thickness direction at the boundary between the plating layer and the steel were measured. Table 1 shows the results.

As apparent from Table 1, No of the present invention .1～
6 shows that even under the above-mentioned severe corrosion test conditions, when a cross cut that penetrates only the paint film is inserted, no rust is generated, and a cross cut that penetrates the paint film and plating layer and reaches the steel base Even in the case where it is inserted, the corrosion generated at the boundary between the plating layer and the steel is slight, and it can be seen that the so-called blistering is suppressed from progressing. That is, it can be seen that the presence of the plating layer significantly improves the corrosion resistance.

On the other hand, in Comparative Example No. 7, the plating layer was Ni and
Since the thickness is as thin as 1.0 μm, the effect of corrosion resistance has not appeared. Nos. 8 and 9 of the comparative examples are materials without a plating layer, but when a cross cut penetrating only the coating film was made, that is, when the coating film had a flaw reaching the steel base, corrosion of the steel part was observed. Is extremely large compared to the present invention, indicating that an early repainting is necessary.

The gas cutting properties and weldability of Nos. 1 to 6 of the present invention were examined, and it was confirmed that all of them had the same performance as the material without a plating layer.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

According to the present invention, the thickness of the steel sheet is 4 to 100 μm.
m, and a steel plate having excellent corrosion resistance after painting, characterized by forming a plating layer of any one of Ni alloy and Co having a hardness of HV225 or more, wherein the structural thickness plate of the present invention is provided. By using a steel plate, the primary primer can be omitted, so that it is not necessary to remove the primer near the gas cutting line or the welding line in advance. Further, since the steel base material is less likely to have flaws, the corrosion resistance after painting is improved, and the interval between repainting during operation can be lengthened. That is, the structural steel plate of the present invention is easy to construct,
This has an excellent effect that the maintenance itself can be reduced.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 30/00

Claims (1)

(57) [Claims] An excellent corrosion resistance after coating, characterized in that a plated layer of any one of Ni alloy and Co having a thickness of 4 to 100 μm and a hardness of HV 225 or more is formed on the surface of a steel sheet. Structural steel plate.