JPH06212379A - Production of immersing member into hot dip galvanizing bath and its production - Google Patents

Abstract

PURPOSE:To provide an immersing member into a hot dip galvanizing bath in which corrosion from molten zinc or the precipitation of a zinc alloy on the member is prevented by forming a dense film on the surface of a base metal without using a metallic binder of Co or the like. CONSTITUTION:A coating layer constituted of MoB having 0.02 to 0.3mm thickness is formed on the surface of a member (base metal) made of iron steel by a thermal spraying method, and the porosity of the same coating layer is regulated to <2%. For example, in the case an MoB coating layer 3 is formed on a planar sample 1, and after that, zinc grains 4 are placed thereon and are held to 500 deg.C, the member in which the zinc grains 4 do not wet the coating layer at all even at the time of melting and having an excellent corrosion resistant coating layer not subjected to erosion from a bath even in a zinc bath immersing test by an other bar-shaped sample is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a member having excellent corrosion resistance for use in a zinc bath such as a hot dip galvanizing facility or in contact with hot dip zinc, and a method for producing the same.

[0002]

2. Description of the Related Art Molten zinc is highly corrosive to metals and has a low surface tension and a low viscosity, so that it also penetrates into minute gaps of a micrometer unit.

Therefore, for example, a stainless steel material such as SCH-13 is generally used as a material for a pot roll of a steel plate plating line, but aluminum which is significantly corroded by zinc and is usually added to a zinc bath. Further, since iron leached from the steel plate or the roll base material and the ternary intermetallic compound with zinc which is the main component of the bath are deposited, the surface of the roll body is roughened in a short period of time.
This surface roughness causes a flaw in the steel sheet and deteriorates the quality of the steel sheet.

Therefore, conventionally, the following techniques have been proposed in an attempt to improve the member itself or form a coating on the member to prevent corrosion of the metallic structural member by molten zinc or precipitation of a zinc alloy on the member. Has been done. (1) Improvement of roll base material (2) Self-fluxing alloy spraying (3) Cermet spraying and build-up

[0005]

As an example of the above (1), there is an iron-based alloy member disclosed in, for example, Japanese Patent Laid-Open No. 56-112447, but since it is a metal alloy, it is used as a molten zinc bath dipping member. For practical purposes, sufficient corrosion resistance is not obtained.

Regarding the above (2), for example, Japanese Patent Laid-Open No. 1-
Like the member disclosed in 108335, Co, N
There is one in which an i- or Fe-based self-fluxing alloy is sprayed on a base material, and then a densified corrosion-resistant coating is formed by welding heat treatment. In many cases of actual use, some improvement effects are recognized, but the member is Since it is basically a metal alloy, the corrosion resistance for the above-mentioned practical purpose is still insufficient.

Further, the above (3) is a thermal spray coating of an alloy of a metal and a carbide or boride or a mixed composition thereof. For example, like the member disclosed in Japanese Patent Laid-Open No. 1-225761, WC-Co. A member provided with a thermal spray coating layer of a cermet series, a member having a thermal spray coating layer of a cermet composed of a metal and a metal boride or a metal carbide, such as the member disclosed in JP-A-2-236266, or JP There is known a member such as the member disclosed in -94048 in which a carbide or boride-containing Co alloy is built up. However, in both cases, metal components such as Co added to obtain sufficient denseness are preferentially eroded by zinc, and thus it has not been possible to sufficiently exhibit the excellent corrosion resistance inherent to carbides and borides. . Conventionally,
It was an essential requirement to add a metal such as Co as a binder in the above-mentioned thermal spraying, because the boride or carbide of a certain metal has a high resistance to the molten metal. Although known,
Since all of them have a high melting point of 2,000 ° C. or more and are brittle, depending on the thermal spraying method often used for the surface treatment of relatively large-sized members such as hot-dip galvanizing bath members, only zinc boride or carbide is used for molten zinc. This is because it has been conventionally extremely difficult to form a coating having a sufficient density to prevent the invasion of the.

Therefore, an object of the present invention is to form a dense non-metal alloy coating on the surface of the base material without using a metal binder such as Co to prevent corrosion from molten zinc and to form a bath on the coating. To provide a zinc bath submerged member excellent in corrosion resistance, in which Al added therein, Fe eluted from a base material, and an intermetallic compound with zinc as a main component of the bath are not deposited, and a method for producing the same. is there.

[0009]

In order to achieve the above object, the inventors of the present invention proceeded with a test study of protective coatings made of various materials alone or in combination thereof, and did not contain any metal especially in various borides and carbides. Molybdenum boride (MoB) can be formed into a dense coating layer without a binder by a thermal spraying method, and by forming such a coating on a member, it exhibits sufficient corrosion resistance to molten zinc and wets with zinc. It has been found that a member having a small amount of metal (and therefore a small amount of intermetallic compound deposited thereon) can be obtained, and the present invention has been completed.

The dense coating layer of molybdenum boride is preferably formed by the explosive spraying method using the detonation of acetylene and oxygen, and the residual porosity is 1
It was also found that less than% could be achieved.

That is, the inventors of the present invention have mainly solved the above problems by developing the following members and methods.

(1) A molten zinc bath-immersed member comprising a steel member having a coating layer of molybdenum boride on the surface.

(2) The coating layer is a layer of molybdenum boride having a thickness in the range of 0.02 to 0.3 mm, and the porosity of the coating layer is less than 2%.
(1) A member for immersing in a molten zinc bath according to item (1).

(3) The molten zinc bath dipping member according to the above (1) or (2), wherein the coating layer is subjected to an inorganic sealing treatment with water glass or colloidal silica.

(4) A method for producing a molten zinc bath-immersed member coated with molybdenum boride, characterized in that a coating layer made of molybdenum boride is formed on the surface of the steel member by explosive spraying.

(5) A coating layer of molybdenum boride having a thickness of 0.02 to 0.3 mm is formed on the surface of a steel member by a thermal spraying method, and the coating layer is inorganic-sealed with water glass or colloidal silica. A method for manufacturing a molten zinc bath-immersed member, which comprises performing a hole treatment.

[0017]

In the present invention, the reason why the porosity of the coating layer formed by the thermal spraying method is less than 2% and the thickness is limited to the range of 0.02 to 0.3 mm is as follows.

Pure ceramic coatings without metal binders formed by conventional thermal spraying methods have porosities of 2% or more. In coatings with this level of porosity, molten zinc penetrates the pores through the pores, resulting in a strong adherence of the zinc to the coating. At the same time, the permeated zinc easily reaches the base metal and erodes the base metal,
The base material / coating interface becomes brittle, leading to peeling of the coating.

If the thickness of the coating is less than 0.02 mm, zinc is allowed to penetrate through the residual pores even if the coating is formed by explosive spraying, and if it exceeds 0.3 mm, cracks are generated in the coating due to residual stress during spraying. Occurs and significantly peels off during use.

[0020]

Example 1 FIGS. 1 and 2 are sketch diagrams showing the results of a test (reaction between a coating surface and zinc) on a member according to the present invention and a conventional member, and FIG. 3 is a plate subjected to the above test. FIG. 4 is a perspective view of a test sample, and FIG. 4 is a schematic cross-sectional view of a test apparatus used for a reaction test between a coating surface and zinc, which will be described below with reference to these figures.

A plate-like sample (30 × 30 × 10 mm) 1 as shown in FIG. 3, which has SUS103 having a coating layer 3 formed by spraying MoB on one side by explosive spraying as a base material 1
Nitrogen gas introduction hole 9 provided on furnace body 7 with zinc particles 4 placed thereon
In a furnace kept in a nitrogen atmosphere, the temperature was raised to 500 ° C., which is higher than the melting point of zinc, by the heater 6 and kept for 5 hours.

After the test, the zinc particles 4 were not wet with the coating layer 3 at all and remained in a droplet form as seen in the sketch of FIG. No evidence of reaction with zinc was observed on the coated surface.

[0023]

[Comparative Example 1] In the comparative material tested in the furnace at the same time as in Example 1, that is, in the WC-Co coated sample, a clear reaction between zinc and the coating layer was observed, and as shown in the sketch diagram of FIG. Moreover, the wetting angle was determined to be about 20 degrees from the shape of the zinc particles 4.

[0024]

[Embodiment 2] FIG. 5 is a schematic sectional view of a test apparatus used for a zinc bath immersion test using a rod-shaped sample, which will be described below with reference to this drawing.

With the apparatus shown in FIG. 5, a rod-shaped sample 2 having a diameter of 20 mm and having a base material of SUS403 having a semi-spherical tip is spray-coated with MoB to a thickness of 0.12 mm, and the furnace body 7
The graphite crucible 8 provided in the above was immersed in a zinc bath 5 kept at 470 ° C. by a heater 6 for 10 days.

Although zinc was thinly adhered to the sample 2 when it was pulled up from the bath, it could be easily removed, and after the removal, some oxidation was observed at the site exposed to the atmosphere from the bath surface. However, no change in appearance was observed at the site in the bath before the test.

The above results are summarized in Table 1 for comparison with the conventional material.

[0028]

Comparative Example 2 According to the procedure of Example 2, WC-C was formed on the base material.
A similar test was performed on the rod-shaped sample 2 coated with o. After the test, the entire surface of the sample was thickly covered with zinc, and its removal was difficult. The results are summarized in Table 1 for comparison with the examples.

[0029]

[Table 1]

[0030]

As described above, the zinc bath-immersed member obtained by the method of the present invention has a porosity of 2% on the base material.
Since the coating layer made of MoB having a film thickness of 0.02 to 0.3 mm is formed at a temperature of less than 100 mm, it is possible to completely prevent erosion by molten zinc or precipitation of a zinc alloy on a member. The strongly required effect on the surface quality of steel sheet will be significantly improved.

[Brief description of drawings]

FIG. 1 is a sketch diagram showing a test result of a member according to the present invention.

FIG. 2 is a sketch diagram showing a test result of a conventional member.

FIG. 3 is a perspective view showing a plate-shaped sample used for a reaction test between a coated surface and zinc.

FIG. 4 is a schematic cross-sectional view of a test device used for a reaction test between a coated surface and zinc.

FIG. 5 is a schematic cross-sectional view of a test apparatus used for a zinc bath immersion test using a rod-shaped sample.

[Explanation of symbols]

 1 plate-like sample 2 rod-like sample 3 coating layer 4 zinc particles 5 zinc bath 6 heater 7 furnace body 8 graphite crucible 9 nitrogen gas introduction hole

[Procedure amendment]

[Submission date] May 29, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

A plate-like sample (30 × 30 × 10 mm) as shown in FIG. 3 having SUS 403 having a coating layer 3 formed by spraying MoB on one surface by explosive spraying as a base material
1, the zinc particles 4 were placed on the furnace body 1, and a nitrogen gas introduction hole 9 provided in the furnace body 7 was used to heat the material in a furnace maintained in a nitrogen atmosphere to 500 ° C., which exceeds the melting point of zinc, by a heater 6, and then 5
Held for hours.

Claims (5)

[Claims] 1. A molten zinc bath immersion member comprising a steel member having a coating layer of molybdenum boride on its surface. 2. The coating layer is a layer of molybdenum boride having a thickness in the range of 0.02 to 0.3 mm,
The molten zinc bath dipping member according to claim 1, wherein the coating layer has a porosity of less than 2%. 3. The molten zinc bath dipping member according to claim 1, wherein the coating layer is subjected to an inorganic sealing treatment with water glass or colloidal silica. 4. A method for producing a molten zinc bath dipping member coated with molybdenum boride, which comprises forming a coating layer made of molybdenum boride on the surface of a steel member by explosive spraying. 5. A coating layer made of molybdenum boride is formed on the surface of a steel member by a thermal spraying method to a thickness of 0.02 to 0.3 mm, and the coating layer is provided with an inorganic pore-sealing material such as water glass or colloidal silica. A method for producing a molten zinc bath-immersed member, which is characterized by performing a treatment.