JPH0488159A - Composite film coated member excellent in wear resistance and molten metal resistance and its manufacture - Google Patents

Abstract

PURPOSE:To improve the wear resistance of a composite film coated member while its excellent molten metal resistance is maintained as it is by coating the surface of a roll and a bearing member made of steel with a carbide material by thermal spraying and thereafter subjecting the thermal-sprayed film to boriding treatment to convert a part of carbides, particularly each particle on the side of the surface into borides. CONSTITUTION:A thermal-sprayed film essentially consisting of carbides is formed on the surface of a member made of steel by a thermal spraying method with the combustion flame or plasma of hydrocarbon and oxygen as a heat source. Next, the carbide thermal-sprayed film is subjected to boriding treatment. At least a part of the carbides constituting the thermal- sprayed film on the surface of a substrate and metallic components included in the above is converted into borides. In the case pores and voids are present on the thermal-sprayed film, through these, the components subjected to the boriding reaction are gradually infiltrated into the inside, so that the reaction of the boriding occurs in such a manner that the defective part in the thermal-sprayed film is preferentially borided. As a result, the thermal-sprayed film after the boriding treatment is borided by the effect of the components subjected to the boriding reaction not only on the outermost layer but also the ones infiltrated into the depth of the inside through the defective part in the film, by which the bonding strength of thermal-spray particles each other is improved. Furthermore, they form a borided alloy layer with the member made of steel, and their state is formed into a metallurgical bonding one.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a composite film-coated member having excellent wear resistance and molten metal resistance, and a method for manufacturing the same. This paper proposes the structure of a composite film that is useful when used as a roll or its bearing member.

Such composite film-coated members are coated with hot-dip tin plating, hot-dip zinc plating, etc.
Typical applications include aluminum alloy plating, rolls used in molten aluminum baths, and their bearing members, and other examples include use as wear-resistant members for boat fishing.

[Prior Art] Most of the hot-dip galvanized steel sheets and hot-dip aluminized steel sheets that are used as heat-resistant materials such as automotive steel sheets, civil engineering and construction steel materials, and home appliances are shown in Figure 2. Manufactured by continuous hot-dip plating process as shown. The continuous hot-dip plating processing equipment includes a zinc roll 22 immersed in a hot-dip zinc bath 21, a support roll 23 disposed near the surface of the hot-dip zinc bath, and a plated steel sheet 24 guided after passing through these rolls. A guide roll 25 and the like are disposed. Note that 26 is an injection nozzle for blowing off excess zinc adhering to the steel plate with nitrogen gas.

These rolls are immersed in a molten zinc bath, are in locations where molten zinc is likely to scatter, or are in contact with hot steel sheets to which molten zinc has adhered (
1) It is difficult to be eroded by molten zinc, (2) it is not easily abraded even when it comes into contact with the running material (steel plate), (3) it is easy to remove adhering molten zinc and maintain and inspect it, (4)
) It must have a long life as a roll and be low cost; and (5) it must have good resistance to thermal shock when immersed in a high-temperature molten zinc bath.

By the way, the roles currently in use are (1)
A roll whose surface is thermally sprayed with a Co-based self-fluxing alloy established by JTS 88303 (1976), (2) A roll whose surface is thermally sprayed with a ceramic coating consisting of ZrO2 and Al2O2 as disclosed in JP-A-61-117260, ( 3) As disclosed in Japanese Patent Publication No. 58-37386, -
For one or more of CCr3C and TiC, Ni
.

There are rolls in which a coating of 0.1 to 2.4 m thick made of hot corrosion-resistant metals such as Si or oxides thereof is formed mainly by thermal spraying.

Also, parts constituting the bearing portion of the roll for molten zinc bath as described above, such as bushings and bearings.

The collars and end balls gradually wear out with use, which can result in roll rotation failure, which can seriously impede the production of hot-dip galvanized steel sheets.

For this reason, conventionally, the above-mentioned molten metal material for rolls is often used as is for these bearing members that come into contact with molten zinc.

Furthermore, as another example, it has been proposed to use carbon that does not react with molten zinc for bearing members and the like, and to pressurize and impregnate this with SiC.

[Problem to be solved by the invention]

However, although the rolls of prior art (1) and (2) and roll bearing members treated with the same type of material have a longer lifespan than previous untreated rolls and bearing members, After about two weeks of use, there is a phenomenon in which the coating on the roll surface (self-fluxing alloy sprayed coating or ceramic coating) peels off locally. This peeled film then adheres to the surface of the steel plate to be plated, producing a discolored pattern.

Therefore, there was a problem in that the quality of the plated steel sheet deteriorated considerably.

Moreover, the roll of the above conventional technology (3) is a card + CrzC
Since carbide such as z+TiC is used, it has excellent corrosion resistance of molten metal. However, since this carbide alone has poor adhesion to the roll, it is essential to add a metal to coexist with this carbide. However, depending on the type of added metal, metallurgical reactions may occur with the molten metal, resulting in severe corrosion.

Furthermore, each of the doffing rolls (1) to (2) had a coating formed by a thermal spraying method. Therefore, the film is an aggregate of fine particles, and microscopically, there is a problem in that pinholes are easily generated.

Further, since the conventional rolls shown in (1) and (2) use oxide or carbide ceramics, their expansion coefficients are significantly different from those of the metallic roll base material (ceramics are about 172 to 173 of metals). Therefore, when these rolls are immersed in a high-temperature molten metal bath, large thermal stress occurs due to the difference in expansion coefficient between the roll base material and the coating, which often causes cracks in the coating. There was a phenomenon of peeling. For this reason, even if a ceramic film with excellent molten metal resistance is formed on the roll surface, the actual situation is that its function cannot be fully utilized.

As a countermeasure to this problem, we considered heating the Ceraminox-coated roll before immersing it in the molten metal to raise the temperature of the roll itself to reduce the temperature difference between it and the molten metal in the bath. However, preheating carbide in the air may cause oxidation due to oxygen (carbide changes to oxide, resulting in reduced adhesion to the roll and easy peeling), so the ceramic film There were some drawbacks that actually shortened the lifespan.

As explained above, conventional technology, especially rolls for molten zinc baths with ceramic coatings, are vulnerable to thermal shock that occurs when immersed in high-temperature molten zinc, and the coating itself has excellent molten metal resistance. Even if there are, the reality is that they are not in a state where they can fully demonstrate their functions.

[Means to solve the problem]

In the present invention, after coating the surfaces of steel rolls and bearing members by thermal spraying with a carbide-based material that does not essentially react with molten metal,
Furthermore, by boronizing the obtained thermal spray coating,
By changing some of the carbides, especially the particles on the surface side, to borides, 1) maintaining excellent molten metal resistance, and 2) improving wear resistance by taking advantage of the high hardness possessed by borides. In order to: ■ improve the mutual bonding force of the sprayed particles, ■ improve the adhesion between the sprayed coating and the prepared parts,
Furthermore, (2) the present invention provides a composite film-coated member that can overcome the various problems faced by the prior art by reducing the pores of the thermally sprayed film.

That is, the present invention provides a composite film-coated member with excellent wear resistance and molten metal resistance, which is obtained by converting a part of a carbide sprayed film formed on the surface of a base material into a boride through boriding treatment, and The carbide sprayed coating coated on the surface of the base material is composed of a pure boride film layer, a boride modified layer, a boride impregnated layer, and a boride alloy layer from the surface layer to the base material surface. A composite coated member with excellent wear resistance and molten metal resistance, and a carbide-based sprayed coating is formed on the surface of a steel base material by a thermal spraying method, and this sprayed coating is boronized. By this, the surface of the thermal spray coating is coated with boride, and at the same time,
A part of the carbide and/or metal on the surface layer side of the thermal sprayed coating is changed into boride, and the boride is impregnated and filled into the pores of the thermal sprayed coating, and the boron treatment is applied to the surface of the base material through the pores. We propose a method for manufacturing a composite film-coated member with excellent wear resistance and molten metal resistance, which is characterized by forming a boride alloy layer thereon.

[Function] Now, the most important boronizing treatment of the thermal sprayed coating in the present invention is the treatment performed after the formation of the carbide-based thermal sprayed coating. Therefore,
Below, a process for forming a composite coating obtained by boronizing the thermal spray coating and the characteristics of this composite coating will be explained.

In forming such a composite coating of the present invention, first, a thermal spray coating containing carbide as a main component is formed on the surface of a steel member by a thermal spraying method using a combustion flame of hydrocarbon and oxygen or plasma as a heat source. Thermal spray materials for forming the base, that is, carbide materials, include WC, WTiC, and Cr.
+Cz+ Tic, V CB4C, NbC, etc. alone, or carbide cermets in which heat-resistant metal materials such as Co, NiCr, and Ni are added can be used.

The thickness of the carbide sprayed coating formed on the base material is 30um.
A range of 3,000 μm to 3,000 μm is preferable. Its thickness is 30
If the thickness is less than μm, the function of the composite coating of the present invention cannot be fully demonstrated, and if the thickness is more than 3000 μm, the effect of the boriding treatment described below will be weakened, and it may be difficult to use an expensive thermal spray material. Fewer effects can be obtained.

Next, the carbide sprayed coating formed as described above is then subjected to a boriding treatment. In the case of the present invention, the following method is suitable for this boriding treatment, for example.

■KCI (30wt%) BaC1z (30wt%
) NaF (15tmt%) Bz(h(2,4wt%
)-ferropolone (22.6 wt%) mixed salt, 70
A steel member that has been raised to a temperature of 0 to 1000°C to form a molten salt and has a carbide sprayed coating formed thereon is immersed in the molten salt and held for about 0.5 to 5 hours to undergo boriding treatment. Molten salt method.

■B, C (45%) -4120: + (50%) -NH
A powder method in which a steel member on which a carbide spray coating has been formed is buried in a mixed powder of 2Cl (5%) and heated at a temperature of 800 to 1100°C for 0.5 to 5 hours to undergo boronization treatment.

When such a treatment is performed, at least a portion of the carbide and the metal component contained therein that constitute the sprayed coating on the surface of the base material are changed into borides. The reaction of such a carbide sprayed coating to boride starts from the outermost layer of the sprayed coating. That is, if there are pores or voids in the thermal sprayed coating, the boriding reaction components will gradually penetrate into the interior through these, so that the boriding reaction will preferentially boronize the defective parts of the thermal sprayed coating. It is thought that it will happen. As a result, the thermal sprayed coating after boriding becomes boride due to the action of the boriding reaction components that have penetrated deep into the interior through the defective parts of the coating, not only in the outermost layer, but as a result, the mutual bonding force of the thermal sprayed particles is reduced. In addition to this, a boride alloy layer is created between the steel members and the bond changes to a metallurgical state, and therefore, these coatings exhibit extremely strong adhesion.

FIG. 1 schematically shows the cross-sectional state of such a boride sprayed coating.

1 in the figure is a base material, the surface of which is coated with a thermally sprayed coating C. This thermal sprayed coating C has the outermost layer turned into a thin pure boride coating layer 4 by the boriding treatment, and a boride metamorphic layer 3 consisting of each carbide particle itself converted into boride is formed inside the pure boride coating layer 4. On the inside, a boride-impregnated layer 5 (the particles themselves are carbide) is formed in which boride has penetrated through pores, and further on the inside there is a boron alloy layer 6, which is an alloy of the base metal and boron. In this case, the composite film of the present invention is formed.

Such a composite film structure can be changed by adjusting the temperature of the molten salt and the immersion time, for example, in the case of a molten salt method. Therefore, the composite coating of the present invention has the above-mentioned boride alloy layer 6
In some cases, the boride-modified layer 3 and the boride-impregnated layer 5 are virtually indistinguishable; in any case, these are equivalent to the boride sprayed coating in the present invention. You can say that.

Regarding the structure of the boride thermal spray coating, in the case of the molten salt method, various film structures can be obtained by adjusting the temperature of the molten salt and the immersion time.
When the sprayed coating has a thickness of 120 am and is immersed at a temperature of 800°C for 3 hours, as shown in Figure 2, a thin pure boride layer 4 is formed on the surface layer of approximately 10 am, and a boride modified layer 3 of 10 to 30 μm is formed. A boride impregnated layer 5 of 10 to 20 μm and some boride alloy layer 6 are formed.

The composite film of the present invention obtained in this manner has the following characteristics.

(1) Carbide sprayed coatings alone are porous and have relatively weak adhesion to the base material, so if used in molten metal, the molten metal will enter through the pores and react with the base material. However, the boride treatment fills the pores with boride, and some of the material also adheres strongly to the base material through metallurgical reaction, resulting in poor molten metal resistance. , mechanical impact resistance is also improved.

(2) The boride (boronized carbide) in the surface layer produced by the boriding treatment is hard and has excellent wear resistance, so it is useful for extending the life of rolls and bearing parts used in molten metal. It has a great effect.

(3) Compared to the method in which boriding treatment is applied directly to the surface of the base material without forming a thermal spray coating on the base material, the boriding layer can be made thicker, and by combining with the thermal spray coating, the disadvantages of both can be avoided. You can complement them and create strengths.

(4) Furthermore, by performing the boriding treatment, the existence of porous voids, which are a fatal defect in thermal spray coatings, actually makes it easier for boride to penetrate, so strict quality control is no longer necessary when forming thermal spray coatings. , the film can be formed using the most economical thermal spraying method.

[Example] Example 1 In order to investigate the performance of the composite film of the present invention, a member coated with the desired film was placed in a molten zinc bath maintained at 480°C for 3 hours.
The molten zinc resistance was evaluated by immersing it for a week, then pulling it out and observing the film surface.

Composite coatings that are application examples of the present invention; (1) -C-12Co thermal sprayed coating, which was then borated by a molten salt bath method; (2) -C-20Co -7Ni thermal sprayed coating, which was then borated by a molten salt bath method; ■ TiC-2ONi thermal spray coating, which was then borided by the molten salt bath method; ■ Cr, Cz-2ONi -7Cr thermal sprayed coating, which was then boridized by the powder method. Composite coating as a comparative example; ■ -C-12Co sprayed coating only, ■ -
C-20Co -7Cr sprayed coating only,■
Ti C-2ONi sprayed coating only,■
Cr+Cz 2ONi 7 Cr thermal sprayed coating only, ■ JIS H8303 (1976) MSFCo2 self-fluxing alloy thermal sprayed coating. The thermal sprayed coating is formed using SO5304 (diameter 15mm).
, length 200 mm) was sprayed onto a substrate by high-velocity gas flame spraying using propane as fuel to a film thickness of 120 μm.

Table 1 shows the appearance of each film coated on the test member after immersion and the adhesion of molten zinc. As is clear from this result, the composite film of the comparative member has -C-
Except for the 12co film, the adhesion of molten zinc was relatively strong. When we investigated the cause of this, we found that it was the result of a metallurgical reaction between the metal components that make up the film, especially Cr and Ni, and molten zinc. In addition, adhesion of molten zinc was also noticeable in the Nα9 member using the self-fluxing alloy film. However, the No. 5 member (WC-12Co only) had weak adhesion to molten zinc and could be easily peeled off from the coating surface. However, when the cross section of the film of this Nα5 member was observed using an optical microscope, it was found that molten zinc had penetrated into the film through the fine pores present in the film. Therefore, if you continue soaking for a longer period of time,
It was easy to guess that it would penetrate the film.

On the other hand, the composite film coated on the member of the present invention has Nα2
, 3.4, etc., even if they contained Cr and Ni, the adhesion of molten zinc was extremely slight, and the remaining zinc could be easily removed. Further, no penetration of zinc was observed in the film, which was healthy. It was confirmed that these effects were due to the formation of a boride film on the surface and in the pores of the sprayed coating that was difficult to wet with molten zinc due to the boriding reaction that was carried out after the sprayed coating was formed.

Table 1 [Notes] l O Δ × N20 △ × Almost no zinc adhesion 10% Zinc adhesion is observed on 5 to 10% of the film surface
Example 2: Zinc adhesion, no zinc corrosion, healthy zinc corrosion, light zinc corrosion, large corrosion Example 2 Next, the resistance to molten zinc of the composite film-coated member of the present invention was investigated under an actual hot-dip galvanizing working environment.

The temperature of the hot-dip galvanizing bath was 470°C, and the zinc roll <SUS 304) of the apparatus shown in Fig. 2 was 22. Support roll 23. As the coating for the guide roll 25, coatings of the same species i (Nα1 to Nα9) as in Example 1 were used and operated for two weeks to evaluate their performance.

Table 2 summarizes the results and shows that the zinc rolls, support rolls, and guide rolls coated with the composite film of the present invention were sound with no change observed at all.

On the other hand, the one coated with the composite film of the comparative example had a distance of 5
With the exception of 0-roll (WC-12Co), the galvanized steel sheet may be eroded by molten zinc, or the molten zinc may adhere firmly and cause scratches on the surface of the galvanized steel sheet, reducing its quality (in the case of guide rolls). ) and other phenomena occurred. However, no
Although the roll coated with .

[Remarks] O Zinc corrosion and adhesion not observed △ Slight zinc corrosion × Zinc corrosion and adhesion large Since the surface layer, pores, and some of the film constituent particles are changed to boride, it prevents molten zinc from entering the film, and the contact angle with zinc is large, making it difficult to wet. The effect is that the surface is always kept clean. Therefore, if such parts are used as rolls and bearing parts in hot-dip galvanizing equipment, it will not only be possible to manufacture hot-dip galvanized steel sheets stably over a long period of time, but also improve product quality and productivity. It also has a great effect on reducing maintenance and inspection costs.

According to the present invention, such a composite coating having excellent wear resistance and molten metal resistance can be easily produced.

[Brief Description of the Drawings] Fig. 1 is an enlarged cross-sectional view showing an example of the cross-sectional structure of the member of the present invention, especially the composite coating portion, and Fig. 2 is a route diagram showing an outline of a continuous galvanizing apparatus for steel sheets. . DESCRIPTION OF SYMBOLS 1... Roll base material, 2... Carbide thermal spray particles, 3...
・Boride film,

Claims (3)

[Claims] 1. A composite film coated member with excellent wear resistance and molten metal resistance, which is obtained by converting a part of the carbide thermal sprayed film formed on the surface of a base material into a boride through boriding treatment. 2. The carbide sprayed coating coated on the surface of a steel base material is composed of a pure boride film layer, a boride metamorphic layer, a boride impregnated layer, and a boride alloy layer from the surface layer to the base material surface. Composite film-coated parts with excellent wear resistance and molten metal resistance. 3. A carbide-based sprayed coating is formed on the surface of a steel base material by a thermal spraying method, and this sprayed coating is boronized to coat the surface of the sprayed coating with boride, and at the same time, the surface side of the sprayed coating is coated with boride. In addition to converting part of the carbide and/or metal into boride, the boride is impregnated and filled into the pores of the thermal spray coating, and the boride treatment is further applied to a part of the surface of the base material through the pores. A method for producing a composite film-coated member having excellent wear resistance and molten metal resistance, the method comprising forming a boride alloy layer on the material.