JPH06145936A - Immersion member for molten metal bath and its production - Google Patents

Abstract

PURPOSE:To provide the immersion member for a molten metal bath which has excellent erosion peeling resistance and wear resistance to molten metal, a long life, low wettability with the molten metal and less metal pickup. CONSTITUTION:A thermally sprayed film contg. 1 to 50wt.% tungsten boride, contg. 3 to 40wt.% one or >=2 kinds among Cr, Mo and W and consisting of the balance tungsten carbide with inevitable impurities is formed on the surface of the body of the immersion member for the molten metal bath. The member is thereafter subjected to an impregnation treatment by any of chromic acid (H2CrO4 and H2Cr2O7), sodium molybdate and/or ammonium molybdate soln, water-soluble inorg. sealing liquid or metal alkoxy alcohol soln. The member is then subjected to a calcination treatment, by which the immersion member for the molten metal bath is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten metal bath dipping member which is used by being immersed in a high temperature molten metal bath of molten zinc, molten aluminum, molten tin or the like for a long period of time, and a method for producing the same. Is a dipping member for a molten metal bath in a hot dip galvanizing line, hot dip aluminum coating line, hot dip tin plating line, etc. The present invention relates to a dipping member and a manufacturing method thereof.

[0002]

2. Description of the Related Art Immersion members used for a long time in a high temperature molten metal bath such as molten zinc, molten aluminum, molten tin, etc. are naturally required to be resistant to corrosion by molten metal. In particular, in the sink roll and the support roll, not only erosion due to molten metal is unlikely to occur, but the roll is less likely to be abraded even by contact with the substrate to be plated of the steel sheet that is immersed in the bath, that metal adhesion is unlikely to occur, Is also required.

When metal deposits occur on the dipping rolls such as sink rolls and support rolls, the substrate to be plated such as a steel plate or the plating surface which is guided by these rolls and immersed in the bath is flawed. Therefore, there is a problem that the dipping rolls such as the sink roll and the support roll cannot be used.

[0004]

Conventionally, dipping members formed by spraying various cermet materials have been developed and used in response to such various demands, but they are still not sufficient. For example, as a dipping member for a molten metal bath, WC-Co
Cermet spray coating is used, but it is not sufficient in terms of molten metal erosion. Further, the above-mentioned demands are increasing more and more with the demand for higher quality of plated products, the demand for manufacturing cost reduction, and the demand for longer life of dipping rolls.

In response to such demands, the present inventors have already found that the surface layer of the body of the immersion member is immersed in a molten zinc bath or the like containing one or more of tungsten carbide, tungsten boride, molybdenum boride and Co. A member was invented and filed (Japanese Patent Laid-Open No. 3-94048).

According to the invention of the above application, the corrosion resistance of the immersion member to the molten metal bath was successfully improved, but there was still a problem that erosion and peeling occurred in long-term use. Generally, the sprayed coating has cracks and small holes. When the immersion member is used for a long time in the molten metal, the molten metal penetrates into the thermal spray coating through these cracks and small holes, destroys the thermal spray coating, or erodes the thermal spray coating from the underlayer. The film peels off.

The present invention solves the conventional problems described above, and a dipping member for a molten metal bath which is used by being dipped in a molten metal bath of high temperature such as molten zinc, molten aluminum, molten tin for a long period of time, and a method for producing the same. Is intended to provide.

[0008]

[Means for Solving the Problems] In order to solve the above-mentioned object, the inventors of the present invention have conducted extensive studies and found that it is extremely effective to seal cracks and small holes in the sprayed coating. Then, the present invention has been completed.

That is, according to the present invention, the surface of the molten metal bath dipping member body contains 1 to 50 wt% of tungsten boride and 3 to 40 wt% of one or more of Cr, Mo and W as a metal phase. %, And the summary is a molten metal bath dipping member having a thermal spray coating composed of the balance tungsten carbide and unavoidable impurities. Chromic acid (H ₂ CrO ₄ And H ₂ Cr ₂ O ₇ ) as a main component, or a treatment liquid containing a water-soluble inorganic sealing liquid or a metal alkoxide alcohol solution as a main component, impregnation treatment is performed, and then firing treatment is performed. A method of manufacturing a dipping member for a molten metal bath is also the gist thereof.

[0010]

The structure and operation of the present invention will be described. Conventionally, a WC-Co cermet has been used as a dipping member for a molten metal bath. First, the present inventors found that in addition to WC, W
It was recognized that B is excellent in molten metal erosion resistance.
Also, boride produces B ₂ O ₃ on the surface in an oxidizing atmosphere,
It was confirmed that this partially volatilized at high temperature but remained on the surface.

Further, the present inventors have established that WC + WB is C
One or two or more of r, Mo and W are cermetized and WC and WB are encapsulated and coated with Cr, Mo and W, or finely pulverized and granulated and sintered in a neutral atmosphere. It was confirmed that the sprayed material was sprayed by a high speed gas spraying method or a plasma spraying method to obtain a good coating.

It has also been found that WB-WC is superior to WC in wettability of molten metal and is less likely to adhere even when immersed in molten zinc, for example. However, it has been found that if a large amount of WB is added, good thermal spraying in the atmosphere becomes difficult.

Therefore, the limit of the content of WB in the thermal spray coating is% by weight, and it is desirable to set it to 50% by weight or less.
If the amount is too small, the effect will not be obtained. Therefore, WB is 1 to 5
0 wt% is contained. More preferable content is 10-4
It is 0 wt%.

The inclusion of one or more of Cr, Mo and W as the metal phase is to enhance the peeling resistance and altitude and to obtain a good film. The content of one kind or two or more kinds of Cr, Mo and W is 3 to 40 wt%. 3 wt%
If less than, there is no effect as a cermet. If the metal phase exceeds 40 wt%, the effect of adding ceramics such as WC and WB is lost. Addition of one or more of Cr, Mo and W in an amount of 25 wt% or less provides the effect of improving the molten metal erosion resistance of the metal phase. However, in this case, Cr, M
The total amount of o and W must be 40 wt% or less.

The dipping member for molten metal bath may be subjected to polishing finish after thermal spraying, but in the production method of the present invention, polishing may be performed after forming the thermal spray coating, before impregnating the treatment liquid, or after firing treatment. As the treatment liquid, a strong acid solution containing chromic acid as a main component, a metal alkoxide-based alcohol solution, or a water-soluble inorganic sealing agent treatment liquid is used.

In order to impregnate the thermal spray coating with the treatment liquid, the molten metal bath member having the thermal spray coating formed thereon is immersed in the treatment liquid, or the thermal spray coating formed on the surface of the molten metal bath member main body is subjected to the treatment. It can be performed by brushing the liquid. By the impregnation treatment, the treatment liquid permeates and fills cracks (micro cracks) and small holes.

In the case of chromic acid treatment, chromic acid (H ₂ CrO ₄ and H ₂ Cr
₂ O ₇ ) becomes CrO ₃ by the initial heating during firing, and first exhibits the effect of filling cracks and small holes.
The chromic acid solution is dried by heating to remove water, but if heating is continued, molten Cr will melt around 200 ° C.
It becomes O ₃ (chromic anhydride), and the sprayed coating can be subjected to CrO ₃ molten salt treatment. Then, the thermal spray coating in contact with this is oxidized and CrO ₃ is densely bonded to the thermal spray coating.

That is, due to the reaction with CrO ₃ , the inner surfaces of the cracks and small holes are chemically bonded to the generated Cr ₂ O ₃ to form a dense ceramics sprayed coating. The firing temperature is 400 ° C at which Cr ₂ O ₃ is sufficiently converted.
As described above, the temperature is preferably 500 ° C. or lower, and almost all of CrO ₃ is converted into Cr ₂ O ₃ at this temperature.

In the case of a metal alkoxide-based alcohol solution, a metal element such as Si, Al, Ti, or Zr dissolved in alcohol penetrates into the small holes, and S is added by the subsequent baking treatment.
It becomes an oxide such as iO ₂ , Al ₂ O ₃ , TiO ₂ , and ZrO ₂ . And the spray coating is made dense and strong. The same applies to the case of the water-soluble inorganic pore-sealing agent solution, and the inorganic component that has penetrated by the impregnation treatment becomes an inorganic oxide by the subsequent firing treatment, and exhibits a pore-sealing effect.

Further, the reason why the dipping member manufactured according to the present invention exhibits excellent corrosion resistance to molten metal is that the WB etc. boride in the thermal spray coating is Cr ₂ O ₃ or It has been found that this is because it is closely and strongly bonded to SiO _{2 and the} like.

Particularly in the present invention, there is a vitrification reaction between B ₂ O ₃ produced by the oxidation of the boride in the thermal spray coating and CrO ₃ or SiO ₂ . That is, B ₂ O ₃ is about 30 when heated.
Vitrification begins at 0 ° C, but from that temperature Cr ₂ O ₃ ,
The adhesion of SiO ₂ begins. Further heating, 400
Above ₂ ° C, B ₂ O ₃ is softened further, and some is C
It reacts with r ₂ O ₃ and SiO ₂ and more closely bonds to fill cracks and small holes. By the way, the melting point of B ₂ O ₃ is about 450 ° C.

Therefore, the combination of the thermal spray coating and the treatment of the present invention should be called glass sealing, in which the fusion bonding phenomenon and the sealing phenomenon are synergistic, and a strong and complete crack / small hole filling action is achieved. It also exerts a film densification action. Further, heating to a temperature exceeding 500 ° C. is not preferable because distortion or residual stress is generated in the molten metal bath immersion member. From the above, it is recommended that the heating temperature during the firing treatment be 400 ° C. or higher and about 500 ° C.

When the impregnation treatment of the present invention is carried out with chromic acid, salts containing Na ⁺ and K ⁺ ions are added in order to improve its permeability and to impart the solubility of the metal oxide on the film surface to B ₂ O _3. You may add a small amount. Further, ammonium molybdate can be added to the treatment liquid. As a result, vitrification as described above can be assisted, and a denser and stronger filling and densifying action due to the coexistence of MoO ₃ can be obtained. Further, in order to further ensure the effect of modifying / strengthening the thermal spray coating by the production method of the present invention, the cycle of the treatment liquid impregnation treatment and the firing treatment can be repeated twice or more.

[0024]

EXAMPLES The present invention will be specifically described with reference to Examples.
This does not limit the invention. Example 1 JIS standard S having a thickness of 5 mm, a length of 30 mm, and a width of 100 mm
A large number of US316 metal plates were prepared, and a spray coating was formed on one surface of each of the metal plates by a high-speed gas spraying method, and as shown in Table 1, each composition of a to k, o, p, q, and r. A metal plate having a thermal sprayed coating formed thereon was prepared.

[0025]

[Table 1]

Table 1 shows the component composition of the thermal spray coating formed on the surface of the sample metal plate. The compositions represented by symbols a to k are compositions within the condition range of the present invention. The compositions of symbols o and p are compositions outside the condition range of the present invention and are comparative examples. The sample metal plates with symbols q and r are conventional examples corresponding to conventional standard products, and are WC-Co based cermet thermal spray coatings.

Next, as shown in Tables 2 to 4, the sample metal plate prepared as described above was subjected to thermal spraying as it was, and was impregnated with the treatment liquid and fired, and immersed in a molten zinc bath. Tested.

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

The plating bath used for the test is a zinc aluminum (Zn-Al) plating bath having an Al content of 3%. In the test, each sample metal plate was continuously immersed in this plating bath, the bath temperature was maintained at 500 ° C., and the state of the sprayed coating of each sample metal plate was observed and evaluated. Evaluation is ◎ if no erosion and peeling is observed even after continuous immersion for 30 days, ◎ no erosion and peeling is observed after continuous immersion for 10 days, but if erosion and peeling is observed after 15 days of continuous immersion ○ after 10 days of continuous immersion Those in which erosion and peeling were observed are represented by Δ.

In Tables 2 to 4, Example No. 1 to 39 are Examples of the present invention, and Comparative Example No. Nos. 40 to 43 are examples in which the thermal spray coatings other than the components of the present invention were impregnated with the treatment liquid and fired. As is clear from these results, in the examples of the present invention, the results of the immersion test are good, and it is understood that a longer life can be obtained by further performing the impregnation treatment with the treatment liquid and the firing treatment.

Further, the immersion member having the WC-Co cermet sprayed coating of the conventional example does not give good results as in Comparative Examples 44 and 45, even if the treatment liquid is impregnated and fired. Further, as can be seen from Comparative Examples 40 and 41, when the metal phase of the sprayed coating is 2 wt% and 45 wt%, WB is 1
Despite being contained in 0 wt%, it was not good. It was found that when the amount of the metal phase was too small, the ceramic material was easily separated from the thermal spray coating, and when the amount of the metal phase was too large, the metal phase was eroded by the molten metal. It can be seen that the effects of the present invention are greater than those of the above Examples, Comparative Examples and Conventional Examples.

[0034]

EFFECTS OF THE INVENTION Since the present invention is constituted as described above, it is excellent in erosion resistance to molten metal, erosion and peeling resistance, and also excellent in abrasion resistance, has a long life, and has a long life. Since it is possible to manufacture a dipping member for a molten metal bath which has a low wettability and a low metal adhesion, it is extremely useful industrially.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kiyohiro Tarumi 46, Nakahara, Tobata-ku, Kitakyushu, Fukuoka Prefecture New Nippon Steel Co., Ltd. Yawata Works Tobata Campus Nippon Steel Hard Co., Ltd. Tobata Works

Claims (5)

[Claims] 1. A surface of a molten metal bath dipping member body contains 1 to 50 wt% of tungsten boride, and 3 to 3 kinds of one or more of Cr, Mo and W as a metal phase.
A dipping member for a molten metal bath, which contains 40 wt% and has a thermal spray coating composed of the balance tungsten carbide and unavoidable impurities. 2. The surface of the molten metal bath dipping member body contains 1 to 49 wt% of tungsten boride, and one or more of chromium boride, molybdenum boride, zirconium boride and titanium boride. 1 to 30 wt%
And the total amount of these metal borides is 50 wt%
1 or less of Cr, Mo, and W as the metal phase
A dipping member for a molten metal bath, which contains 3 to 40 wt% of one kind or two or more kinds, and has a thermal spray coating formed of the balance tungsten carbide and unavoidable impurities. 3. A process according to claim 1 or 2 to form a thermal spray coating according molten metal bath immersion member chromic acid spray coating (H ₂
A method for producing a dipping member for a molten metal bath, which comprises performing impregnation with a treatment liquid containing CrO ₄ and H ₂ Cr ₂ O ₇ ) as main components, and then performing firing treatment. 4. The method for producing a dipping member for a molten metal bath according to claim 3, wherein the treatment liquid with which the thermal spray coating is impregnated contains sodium molybdate and / or ammonium molybdate. 5. The impregnation treatment of the thermal spray coating of the molten metal bath dipping member having the thermal spray coating according to claim 1 or 2 with a treatment liquid containing a water-soluble inorganic sealing solution or a metal alkoxide alcohol solution as a main component. A method of manufacturing a dipping member for a molten metal bath, which comprises performing a firing treatment and then performing a firing treatment.