JPH01225761A - Member for metal hot dipping bath tank - Google Patents

Abstract

PURPOSE:To manufacture a member for metal hot dipping bath tank excellent in erosion resistance by forming a thermally sprayed layer of a specific porosity on the surface of a member by using a WC-Co-type cermet material in which specific percentage of Co is mixed. CONSTITUTION:A thermally sprayed layer of <=1.8% porosity is formed on the surface of a member for plating bath tank to 0.040-<0.10mm thickness by a thermal spraying method by using a WC-Co-type cermet material in which Co is mixed by 5-28wt.%. Since this thermally sprayed layer has about 1,100-1,300 hardness HV and has superior wear resistance, the inexpensive member for plating bath tank free from wear even if brought into contact with hot dipped steel sheets and excellent in erosion resistance can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a member for a molten metal plating bath, and particularly to a member for a molten metal plating bath that exhibits excellent corrosion resistance against molten aluminum, molten zinc, or molten alloys thereof. This is a proposal regarding parts.

[Conventional technology]

Molten aluminum and hot-dip galvanized steel sheets are used as heat-resistant and corrosion-resistant members for automobiles and construction materials, but these are mainly manufactured by continuous plating.

The continuous plating processing equipment is equipped with immersion rolls immersed in molten metal, plating rolls installed near the molten metal surface, and guide rolls that guide the plated steel sheet after passing through these rolls. It is.

These rolls are either immersed in molten metal or
Since it comes into contact with a high-temperature steel plate coated with molten metal, the following performance is required.

[1] Less likely to be eroded by molten metal, (
2) Resistant to wear even if it comes into contact with the steel plate being passed; (3)
) Easy separation of adhering molten metal and easy maintenance and inspection; (4) Long life as a roll; (5) Low cost. Providing a roll that meets these requirements, that is, a member for plating bath. Conventional techniques aimed at this include: (1) thermal spraying of a self-fluxing alloy specified by JIS H8303 (1976) on the roll surface; (2) ZrO□ and A1.0. (1) One or more of WC, CrC, and Tic as disclosed in Japanese Patent Publication No. 58-37386, with the remainder being a hot corrosion-resistant metal or its oxide.
, a roll having a surface coating layer formed with a thickness of 1 to 2.4 fi has been proposed.

[Problem to be solved by the invention]

Regarding each of the above conventional technologies, for example, in the case of ■ and ■, although the lifespan is longer than that of previous untreated rolls, the self-fusing alloy coating and ceramic coating may peel off locally after about two weeks of use. However, as a result of this being transferred to the surface of the plated steel plate as a discolored pattern, there was a drawback that the commercial value was significantly reduced. In addition, in the case of ■, WC,
Although carbides such as CrC and TiC exhibit excellent corrosion resistance that meets the requirements, carbides alone cannot form a coating layer, so depending on the type of metal coexisting with the carbide, the performance may deteriorate significantly, making it impossible to put it to practical use. There were drawbacks. That is, in this prior art, Ni and S are added to the carbide.
If i is used in combination, even if a coating layer is formed by thermal spraying, it will have no effect on the molten metal.

However, it has been reported that cermet materials made by mixing carbide with Co can withstand molten metal relatively well, but still require a film thickness of 0.1 or more, and that the coating is not effective below this. are doing.

However, since WC, Co, etc. are very expensive materials, forming such a thick film inevitably increases the cost. Moreover, this type of cermet material consisting of carbide and metal has a different coefficient of expansion from that of the base steel material, so in high-temperature molten metal, it will expand.

There is a concern that the film may peel off from the base material due to internal stress due to the difference in thermal expansion between the two.From this point of view as well, the thick film used in the prior art is disadvantageous; There is a strong demand for the development of coated members.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned drawbacks of the prior art of thermally spray coating a plating bath member with a cermet material, particularly a WC-Co cermet material. That is, the technique disclosed in JP-A No. 58-37386 involves thermally spraying a coating material made of carbide and metal onto the surface of a member immersed in a hot-dip metal plating bath to a thickness of 0.1 to 2.4 mm. However, the purpose is to solve the problem of the fact that the coating is not effective unless the coating thickness is 0.1f1 or more.

In short, in a thick film coating such as 0.1 to 2.4 Tsuru,
Due to thermal changes when immersed in or pulled up from a high-temperature molten metal bath, internal stress is likely to occur due to the difference in expansion coefficient between the coating layer and the base material, and this value is particularly If the adhesion is greater than that of the base material, the coating will peel off. Generally, it is well known that as the thickness of the coating layer increases, the expansion difference between them increases and the adhesion to the base material tends to decrease.

[Means to solve the problem]

The present invention uses the following means to solve the above-mentioned drawbacks of the prior art. In other words, WC as a carbide and C as a metal to be mixed are added to the surface of the plating bath member.
When forming a coating using a thermal spraying method using a cermet material made using
．． The coating layer should be 8% or less. Such a coating layer (hereinafter referred to as "film") is a thin film with a thickness of 0.11 mm or less, which was considered impossible with conventional technology, but according to the findings of the present inventors, it has excellent melting resistance. It was found that it exhibited metal performance. In the present invention, the thickness of the film is preferably controlled within the range of 0.040 to less than 0.10 m, and the amount of Co to be mixed in the WC is 5 to 28 m.
It is preferable to set it as wt%.

[For production]

In the present invention, WC-C is formed on the surface of a member that is immersed in a molten metal plating bath and comes into contact with molten or softened metal.
o The cermet material thermal spray coating has a hardness Hv of 1100 to 1
It has excellent wear resistance at about 300, and does not wear out even when it comes into contact with hot-dip plated steel sheets. Such cermet thermal spray materials are composed of highly hard WC particles and metal (Co
), and the film obtained by plasma spraying has a Mi weave in which WC particles are surrounded by metal particles (Co). However, since WC particles are hard and do not undergo plastic deformation, they can be destroyed by collisions during thermal spraying, or the impact energy can cause cranks in the already formed film, so that pores are likely to occur in the thermal sprayed coating.

On the other hand, if pores exist in the thermal spray coating, molten metal enters the interior through the pores, causes a metallurgical reaction with the base steel material, expands the volume, and causes the thermal spray coating to peel off from the bottom. Furthermore, even if the pores do not penetrate through the pores, molten metal may accumulate inside and repeatedly expand and contract as the temperature changes in the environment, thereby destroying the sprayed coating.

Therefore, the present inventors first studied the thermal spraying conditions for obtaining a dense thermal sprayed coating, and found that (1) the thermal spray particles become softer due to an increase in the ambient temperature, and (2) the impact energy on the surface of the object to be thermally sprayed increases. , we focused on However, in the method (1), the high temperature changes the WC into an oxide, making it impossible to utilize the high hardness of the carbide. Therefore, the present inventors further investigated method (2).

Specifically, by using oxygen-hydrogen gas as a heat source and increasing the supply pressure to the thermal spray gun, the injection velocity of combustion gas (fuel gas supply pressure was used as a variable factor. In this case,
The higher the supply pressure, the faster the combustion gas injection speed, and the aim was to reduce the air and porosity of the sprayed coating. ) was increased to increase the collision energy of sprayed particles. FIG. 1 shows the relationship between the supply pressure of oxygen-hydrogen gas to the thermal spray gun and the porosity of the obtained thermal spray coating. As is clear from the results shown in FIG. 1, it was found that the higher the fuel gas supply pressure, the more a sprayed coating with a lower porosity could be obtained.

Therefore, by adjusting the supply pressure of fuel gas, the thickness of 0.094 to 0.098 dragon (
average 0.096 fins) and 1.80-1.90 (average 1.8
5tm) with a WC-Co cermet thermal spray coating formed on the diameter 3. Q crane.

A cylindrical test piece made of mild steel with a length of 100 mm is prepared, and one step is to immerse it in a 480°C molten zinc bath for 1 hour, then pull it out and cool it to room temperature. By repeating this process, the thermal spray coating is formed. The state of destruction was observed.

FIG. 2 shows the relationship between the porosity of the WC-Co cermet sprayed coating and the number of immersions at which the coating was destroyed. As is clear from these results, it was confirmed that even if the thermal sprayed coating is thick but has a high porosity, it will break after a small number of immersions, and conversely, even if the coating is thin but has a low porosity, it can withstand many immersions. . Moreover, as shown in FIG. 2, it is clear that the coating exhibits excellent erosion resistance up to a porosity of 1.8%, and from this fact, in the present invention, the thermal sprayed coating is The porosity was increased to 1.8% or less. With such a porosity, good resistance to molten zinc is exhibited. The thermal spray material used in this test was W C
(88%)-Co (12%) weight ratio, and the porosity of the sprayed coating was determined by photographing the cross section of the coating using an optical microscope.
After the pores were colored, the area occupied by the colored portions was determined using an image analysis device.

Next, in the present invention, the amount of Co mixed in the cermet material to be thermally sprayed onto the surface of the member is set at 5 to 28 wt%.The reason for this is that if it is less than 5 wt%, the bonding force between the WC particles constituting the film will be reduced. This is because as the amount decreases, the adhesion between the coating and the object to be thermally sprayed becomes weaker.On the other hand, if it exceeds 28-L%, even though Co is strong against molten metal, it is more easily corroded than WC, so the melting resistance of the coating decreases. This is because the metallicity decreases.

Furthermore, in the present invention, the thickness of the thermal spray coating is 0.04
0 to 0.1 (bm) It is desirable to have no grooves, but the reason for this is that if it is less than 0.040 w, the porosity in the film will be high and the molten metal resistance will be poor; This is because if the thickness increases, the internal stress in the sprayed coating becomes high, making it easy to peel off, and it is not economically advisable.

〔Example〕

Example-1 In this example, the immersion roll, plating roll, and guide roll (materials are JIS G
3445 (1983) STKM13A), a WC-Co cermet material as shown in the margin of Table 1 was added to a thickness of 0.
．． 096-0.098 Tsuru, porosity 0.6.1.0.1.
8.2.2゜2.8% thermal spray coating, using this thermal spray coated roll, a steel plate with a width of 900 mm and a thickness of 0.35 mm,
Molten zinc maintained at 470-480°C (JIS H21
07 (1957) (equivalent to a special type of distilled zinc) was passed through a plating bath to undergo continuous hot-dip plating treatment, and the characteristics of the sprayed coating were investigated.

Table 1 shows the observation results of the thermal spray coatings treated on the surfaces of each roll after the hot-dip Zn plating treatment was carried out for 20 consecutive days. As is clear from the results shown in Table 1, the thermal sprayed coating according to the present invention has a porosity of 1°8 regardless of the Co content and even if it is a thin film of less than 0.1 mm. % or less, it was confirmed that excellent corrosion resistance against molten zinc can be exhibited over a long period of time. On the other hand, for the comparative examples with high porosity (2.2%, 2.8%), more than 30% of the thermal sprayed coating had fallen off, and it is clear that the molten zinc resistance was inferior. .

Table 1〈Remarks〉 Thermal spray material G) WC(95Z)-Co(5X) ■ WC(
887:) -Co (127:)■ WC (82Z)
-Co (18Z) ■ WC (72Z) -Co
(2B7:) Evaluation ○ Thermal spray coating soundness × Example of peeling off 30% or more of the coating -
2 Using a roll with the same thermal spraying material, thermal spray coating thickness, and porosity as in Example-1, a steel plate (width 9001mm x thickness 0.22m) was continuously coated in a hot-dip aluminum plating bath maintained at 700 to 710°C. Plating treatment was performed. JIS H2102 (196B) aluminum type 1 was used as the hot-dip plating metal.

Table 2 shows the results of the visual inspection of the thermal spray rolls after continuous hot-dip Al plating for 15 days.

From this result, the thermal spray roll of the present invention maintained a healthy state in all of the dipping roll, plating roll, and guide roll, but in the roll of the comparative example, most of the thermal spray coating peeled off on the dipping roll, and 50% on the plating roll. As mentioned above, peeling of 35% or more was observed even with the guide roll.

Table 2 <Remarks> Thermal spray material G) WC (95 Ri-Co (5z)) ■ WC (8
8Z) -Co (12Z)■WC(82Z)-Co(
18Z) ■ WC (72z) -Co (28Z)
Evaluation ○ Thermal spray coating soundness × Example of peeling of 35% or more of the coating -
3 In this example, when manufacturing a thermal spray roll according to the procedure of Example 1, the thickness of the thermal spray coating was varied within the range of 0.020 to 0.100 mm, and the coating was applied to an immersion roll in a hot-dip zinc and hot-dip aluminum plating machine. The properties of the material were tested. Hot-dip galvanizing temperature is 470-480℃ for 20 days.
Hot-dip aluminum plating temperature is 700-710℃, 15
After continuous plating treatment for each day, the immersion roll was pulled up and inspected.

Table 3 shows the results of the immersion rolls used in the molten zinc bath, and it can be seen that the lower the porosity of the sprayed coating, the better the erosion resistance, but the porosity is 1.8%.
It has been found that a coating thickness of at least 0.040 mm is sufficient to withstand daily work. On the other hand, all the films of Comparative Examples were peeled off regardless of the film thickness.

Table 4 shows the results for immersion rolls used in a molten aluminum bath. Even in this case, the smaller the porosity of the sprayed coating, the better the erosion resistance, and the porosity is 1.8% or less. It was confirmed that if the film thickness was 0.040 mm or more, it could withstand use for 15 days. In addition, all the films of the comparative examples were peeled off, and no corrosion resistance was observed at all.

〔Effect of the invention〕

As explained above, in the present invention, as a result of forming a WC-Co cermet spray coating with a porosity of 1.8% or less and a thin film of less than 0.04 to 0.10x on the surface of a plating bath member, molten zinc It is possible to provide an inexpensive plating bath member that exhibits excellent corrosion resistance against aluminum and molten aluminum. Moreover, by using such a member, stable hot-dip plating work, high productivity, and improvement in the quality of plated steel sheets can be guaranteed.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the supply pressure of the fuel gas for thermal spray heat source to the spray gun and the porosity in the coating formed by the combustion gas. Figure 2 is the graph showing the relationship between the porosity in the sprayed coating and the melting It is a graph showing the relationship between the number of times a film is peeled off due to repeated immersion in a zinc bath, followed by pulling up and cooling.

Claims (1)

[Claims] 1. A member having a cermet coating layer on its surface,
The above coating layer is made of WC mixed with 5 to 28 wt% of Co.
- A member for a hot-dip metal plating bath, comprising a thermal spray coating layer made of a Co-based cermet material and having a porosity of 1.8% or less. 2. The thickness of the thermal spray coating layer is 0.040-0.10mm.
The member for a molten metal plating bath according to claim 1, wherein the member is less than or equal to