JPS59113902A - Production of steel plate having high corrosion resistance for preventing biological contamination - Google Patents

Abstract

PURPOSE:To obtain a steel plate for preventing corrosion and sticking of living things having >=20 years maintenance interval by blasting the steel plate then melt spraying a metal electrically baser than Fe thereon and further melt spraying Cu or its alloy thereon and rolling the steel plate at the draft equivalent to the specific value of the total film thickness or above. CONSTITUTION:A base material 3 which is a steel plate is subjected to blasting on its surface in a blasting stage (A) and is fed to a preheating stage (B) where the material 3 is preheating with a heater 6. The material 3 is fed to a melt spraying stage (C1) for melt spraying a lower layer, wherein a metallic layer of, for example, Zn, Al, Zn-Al alloy or the like electrically baser than Fe is formed thereon by a melt spraying torch 7. A Cu or its alloy layer 1 is formed thereon as an upper layer by the torch 7 in a stage (C2). Such steel plate is rolled down at >=20% of the total coating thickness by rolls 8 in a rolling stage (D) and is delivered as a product (D).

Description

[Detailed Description of the Invention] The present invention relates to a method for manufacturing steel plates, more specifically, steel plates for ship outer plates, seawater intake pipes, or steel plates for offshore structures such as oil drilling platforms and sea berths. The present invention relates to a novel method for producing steel sheets that are highly corrosion resistant and intended to prevent biofouling.

Corrosion protection for structures used in seawater involves cutting, welding, and assembling steel plates coated with rolled black scale or shop primer, and then applying anticorrosion paint and then applying a plasting process. Antifouling paint is applied as necessary to prevent corrosion and biofouling.

However, the effect of antifouling coatings on preventing biofouling can be expected for at most 2 years, but in general, the effect can only be expected for about 1 year. Needs to be reapplied. In addition, especially for ships, recently developed antifouling coatings for ships with a service life of 2 years have the disadvantage that they have little effect on preventing biological fouling when the ship is moored.

For this reason, there has been a strong desire from the petroleum, shipping, and shipbuilding industries to develop a steel plate for corrosion protection and biofouling prevention that can be used in areas submerged in seawater and has a long maintenance interval.

If we consider the anti-corrosion measures conventionally used for steel structures, ships, etc., we find that the aforementioned coatings, organic linings, inorganic linings, highly corrosion-resistant metal linings, metal spraying, or plating are used. .

First, since metal spraying technology was developed in 7970, it has been mainly applied to land structures such as bridges, water gates, chimneys, and steel buildings, and has an excellent track record in terms of corrosion protection.

These thermal spray coatings are formed by product thermal spraying, and the welding material is mainly Zn with a low melting point, and other materials A7. Alternatively, a metal electrically less noble than Fe, such as Zn-A1 alloy, is used.

However, the durability of thermally sprayed coatings on submerged parts of offshore structures such as oil drilling platforms and sea berths is not necessarily sufficient, and therefore composite corrosion protection systems with a single thermally sprayed coating are sometimes used. However, this coos also causes early coating defects such as coating blistering and coating peeling, followed by elution of sprayed metal and generation of red rust, and lacks reliability in terms of durability. That is, it has been conventionally believed that thermal spray coatings cannot withstand use in areas submerged in seawater.

The reasons for this are that the anti-corrosion sprayed metal is active and its oxide easily dissolves in seawater, that the sprayed coating has quite a few voids and that the sprayed coating alone does not have water-stopping properties, and that the sprayed coating alone has no water-stopping properties. Examples include poor adhesion between the sprayed coating and the secondary adhesion between the thermally sprayed coating and the top coat.

Particularly in the case of ships, it has long been well known that in addition to the antifouling paint mentioned above as a means of preventing biofouling, the outer skin of the ship is lined with Cu or Cu alloy. There are also examples of this being implemented on ships.

However, this lining construction requires special skills and
It requires a long working time and is actually difficult to apply to large ships and offshore structures.

Therefore, instead of providing such a Cu lining, it is conceivable to use the thermal spraying method described above as a means of coating a high melting point metal such as Cu or a Cu alloy. However, if thermal spraying is used, the workability will be significantly improved, but the thermal spray coating itself has problems. ; Since there are 96 voids, long-term durability cannot be expected in terms of corrosion prevention due to the problem of waterproofing as mentioned above, and the surface roughness is also maximum /θθ~3θθμ,
Very large.

The large surface roughness is inconvenient when applied to a ship because it receives wave resistance during navigation and increases fuel consumption. In other words, for ships, the roughness of the outer skin surface is required to be 5θμ or less for the above reasons.
Therefore, the above-mentioned surface roughness cannot satisfy this requirement.

As a result of various studies, the inventors of the present invention have found that it is possible to obtain a thermally sprayed steel sheet with water-stopping properties and a surface roughness of jθμ or less by rolling the thermally sprayed steel sheet at a reduction rate of at least βθchi of the coating thickness. I discovered something.

That is, in the present invention, after plasting a steel plate, electrically
A steel plate with high corrosion resistance and biological contamination prevention, characterized in that the steel plate is thermally sprayed with a metal less base than e, further thermally sprayed with Cu or an alloy thereof, and rolled at a reduction rate of 2θ or more of the total coating thickness. This is a manufacturing method that makes it possible to manufacture steel plates for corrosion protection and biofouling prevention that have a maintenance interval of 2θ years or more.

The present invention will be explained in detail below.

First, in the present invention, metals electrically more base than Fe include Zn, At% Zn-At alloy, or Zn-Mn, A
t-Mn.

It refers to an alloy such as At-8t, which prevents corrosion of Fe by preferentially dissolving it than Fe in corrosive environments such as seawater, which is what is called electrochemical corrosion protection. The thickness is not particularly limited, but from a practical standpoint, it is appropriate to be around 7θ~jθθμ; if it is too thin, it will not have an anti-corrosion effect, and if it is too thick, it will cause cohesive cracking of the coating, which also reduces the anti-corrosion effect. will be halved.

In addition, in the present invention (Cu1 or its alloy refers to Cu alone, Cu-8n alloy, Cu-Mn-At alloy, Cu-
Ni alloy, Cu-Ni-Mn-Al-Fe%Cu-
Refers to Ni-Mn alloy, etc., and when submerged in seawater,
A small amount of Cu ions are dissolved from Cu and Cu alloys, and this serves to prevent the attachment of living organisms. The thickness is not particularly limited, but from a practical point of view, /θ~3θθμ is appropriate; if it is too thin, cracks will form in the coating during rolling of the steel plate, and the water-stopping effect will be lost. If it is too thick, it will not be economical.

In the present invention, the reason why the above-mentioned electrically less base metal layer than Fe is provided as the lower layer and the above-mentioned Cu or its alloy layer is provided as the upper layer is that the synergistic effect of these two layers prevents submersion in seawater. This is because it exhibits an excellent synergistic effect of long-term durability and long-term biofouling prevention. In other words, in the case of a plain lower layer, the coating easily dissolves in seawater, and in the case of a plain upper layer, when the coating layer is broken, Fe to be protected is selectively dissolved ((
However, by providing both layers, this risk is eliminated.

The ratio of the thickness of these two layers is not particularly limited, but for practical purposes, it is appropriate that the ratio of lower layer: upper layer = jθ: / ~ 7:3θ, and if it is outside this range, the water-stopping property may be lost or the water-proofing property may be lost. The stain resistance may be reduced, the anti-corrosion durability may be reduced,
This causes inconveniences such as a decrease in economic efficiency.

Furthermore, in the present invention, thermal spraying is used as a means for forming these two layers. The reasons for using thermal spraying are that it is easy to work with, allows combinations of low-melting point metals and high-melting point metals, does not cause any thermal distortion to the steel plate, and can be processed in large quantities with high efficiency. This is because it has many advantages in such points. In this case, as a specific means of spraying, any of gas spraying such as oxygen-propane, oxygen-acetylene, arc spraying, gas plasma spraying, water plasma spraying, etc. may be used.

In the present invention, the two layers are formed by thermal spraying on a steel plate in this way, but the most important point in the present invention is that the steel plate that has been thermally sprayed in this way is
When rolled at the upper rolling rate, the relationship ρθ of the total coating thickness is as follows.

In other words, by performing such rolling, the essential problems of thermal spray coatings, such as improving the adhesion of the coating layer and improving the water-stopping rate, as well as reducing the actual surface area due to the reduction of surface roughness, can be improved. .

Alternatively, it becomes an excellent coating that reduces the dissolution rate of Cu alloy. In this case, if the rolling reduction ratio is less than βθ, voids will remain in the coating, and the surface roughness will also exceed jθμ, which is unsatisfactory.

On the other hand, although the upper limit is not particularly limited, if the reduction rate is too high, the coating may break or the coating may be too thin to provide sufficient corrosion resistance, and the surface of the steel sheet may also become deformed. , the upper limit of the rolling reduction ratio is practically the total coating thickness j.
It is preferable that the angle is around θ. Also, the total film thickness after rolling is not particularly stipulated, but from a practical point of view it is gθ~7θ.
The degree of θμ is good; if it is too thin, long-term durability cannot be expected in terms of corrosion protection, and if it is too thick, there is a risk of cohesive failure of the coating, and it is not economical.

Next, the steps of the present invention will be explained based on the drawings.

FIG. 7 shows an example of the final steps for carrying out the method of the present invention. The base material 3, which is a steel plate, is subjected to a plast process (A)
The surface is then plastered, scale and foreign matter adhering to the surface are removed, the metal surface is exposed, and appropriate irregularities are added to the surface. Plasting the surface with this
The purpose is to improve the adhesion of the sprayed layer, and the plast method can be either the commonly used pressure-feed type or impeller type, and the abrasive material can be sand or steel grid;
Any material such as corundum can be used. Next, the base material 3 is sent to a preheating process (B)K. Part B is a heater. The purpose of preheating is to improve the adhesion of the sprayed film.

Note that as the heater 6, any heating means such as electricity, infrared rays, or gas may be used. Next, the preheated base material 3 is sent to a thermal spraying step (cl) in which a lower layer is thermally sprayed. 7 is a thermal spraying torch, and 2 is a layer of a metal electrically less noble than Fe, and the thermal spraying means can be appropriately selected from those described above. Next, in step (C2) K, Cu,
Alternatively, the alloy layer is thermally sprayed as an upper layer by a thermal spraying torch 7.

In the rolling process (D)K, the base material 3 on which the two layers/and 2 have been formed is subjected to a rolling reduction of 2θ or more of the total coating thickness and sent out as a product (E). In this case, although not shown, a bonding coat step (described later) is performed between step (A) and step (B), a post-heating step is performed between step (C2) and step Q), and a post-heating step is performed between step (C1) and step (C1). and process (C
A coating process can be provided as necessary between 2) and 3) Furthermore, during the adhesion process of the sprayed coating, a preheating process (
It is also possible to omit B).

Some embodiments of steel plates manufactured by such a process are shown in FIGS. 1 to 6. FIG. 1 is an example of a steel plate obtained by the process shown in FIG. 7. Fig. 2 shows a steel plate in which a metal layer 2, which is more base than electrical KFe, is also formed on the side opposite to the side with the three layers, and is used when both sides of the steel plate are exposed to a severe corrosive environment. It is. Further, in FIG. 3, a bonding coat is provided on the surface of the plasted base material 3 prior to providing the two layers. This bonding coat is called 5teel.
, Ni-A4 It means to spray a thin layer of metal such as Ni or Mo, and it is carried out for the purpose of improving the adhesion of the sprayed layer 2. Next, FIG. 7 shows the case of FIG. 3 in which a bonding coat or an organic coating j is further applied between layer 2 and layer 2.

This coating means a resin such as epoxy, urethane, silicone, cyanoacrylate, vinyl, etc., and is used to improve the impact resistance and processability of the sprayed layer 2. Figure 5 is a combination of Figures 2 and 3, and Figure 6 is a combination of Figures 2 and 3.
The figure shows an example of the combination of FIG. 2 and FIG. 7, each of which is used for the purpose of improving anti-corrosion durability depending on the usage situation of the steel plate.

Although some examples of steel plates obtained by the method of the present invention have been shown above, it is needless to say that the invention is not limited to these, and that steel plates of any type can be manufactured within the scope of the present invention. Needless to say.

The effects of the present invention will be explained in more detail with reference to Examples below.

Table 1 shows the types of coatings and test results. The test piece is /j
The entire surface was coated using SM'l/ for θ×3θθ×/, and 2 layers. Sample numbers 73 to 7 in the table are examples of the present invention, and both the anticorrosive properties and the antifouling properties are satisfactory.

As mentioned above, according to the method of the present invention, the adhesion of the coating is 5 to 70 times higher than that of conventional product spraying, and therefore has sufficient bending workability and resistance to rolling, and has an extremely low porosity. Therefore, the water-stopping property of the coating is sufficient, and its surface roughness is also less than Sθμ. Moreover, by using the outermost thermal sprayed metal KCu or Cu alloy, it has both the function of preventing biofouling due to Cu ions and long-term corrosion protection due to the metal layer baser than electrical KFe on the inner surface, which is a demand in the industry. It becomes possible to provide technology that fully satisfies the following.

[Brief explanation of the drawing]

FIGS. 1 to 3 are cross-sectional views showing several embodiments of steel plates obtained by the method of the present invention, and FIG. 7 is a process diagram showing one embodiment of the method of the present invention. /...Cu or Cu alloy layer 2...Metal layer 3, which is less electrically sensitive than Fe, Base material...Bonden coat J...Bonden coat or organic coating B...Heater 7... To the thermal spray torch...Roll Fig. 1 Fig. 3 Fig. 5 Fig. 2 Fig. 4

Claims (1)

[Claims] After plasting the steel plate, spraying with a metal less base than electrical KFe, then spraying 1 ccu or an alloy thereof,
A method for producing a steel plate with high corrosion resistance and for preventing biological contamination, the method comprising rolling the steel plate at a reduction rate of 2θ% or more of the total coating thickness.