JP2567137B2 - Composite film coated member having excellent wear resistance and molten metal resistance and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a composite coating member having excellent wear resistance and hot-dip metal resistance and a method for producing the same, and in particular, it is immersed in a continuous hot-dip galvanizing bath. It proposes the composition of a composite coating useful when used as a roll to be used or a bearing member thereof.

Such composite film coated members are typically applied to hot-dip tin plating, hot-dip zinc-aluminum alloy plating, rolls used in hot-dip aluminum baths and their bearing members. It is also useful as a wear member.

[Conventional technology]

By the way, most of the hot-dip galvanized steel sheets and hot-dip aluminum-plated steel sheets used as heat-resistant and food-resistant materials for automobile steel sheets, civil engineering and construction steel materials, home electric appliances, etc. are continuously fused as shown in Fig. 2. Manufactured by plating. The continuous hot dip galvanizing apparatus guides a sink roll 22 immersed in a hot dip zinc bath 21, a support roll 23 arranged near the surface of the hot dip zinc bath, and a plated steel plate 24 after passing through these rolls. A guide roll 25 and the like are provided. Reference numeral 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, or at positions where molten zinc is likely to be scattered and adhered, or at positions where this molten zinc is in contact with high-temperature steel plates,
(1) Erosion due to molten zinc is unlikely to occur, (2) Hard to wear even when it comes into contact with a strip material (steel plate), (3) Peeling of adhered molten zinc and maintenance and inspection are easy.
(4) Long roll life and low cost,
Then, (5) performance such as good resistance to thermal shock when immersed in a high temperature molten zinc bath is required.

By the way, the rolls currently used are (1) a roll whose surface is sprayed with a Co-based self-fluxing alloy established by JIS H8303 (1976), and (2) a roll disclosed in JP-A-61-117260. , ZrO ₂
And a roll on which a ceramic coating of Al ₂ O ₃ is formed by thermal spraying, (3) As disclosed in Japanese Patent Publication No. 58-37386, WC, Cr ₃ C
0.1 to 0.1 in which hot corrosion resistant metal such as Ni and Si or their oxides coexist with 1 or more of ₂ and TiC.
There are rolls, etc., in which a 2.4 mm thick film is formed mainly by the thermal spraying method.

Further, the parts constituting the bearing portion of the roll for the molten zinc bath as described above, such as bushes, bearings, collars and end balls, are gradually worn with use, resulting in defective rotation of the roll and the like. This may seriously hinder the production of plated steel sheets. From these facts, even those bearing members that come into contact with molten zinc have conventionally been
The molten metal material for rolls is often used as it is.

[Problems to be Solved by the Invention]

However, although the rolls of the prior arts (1) and (2) and the roll bearing member treated with the same kind of material have a longer life than untreated rolls and bearing members before that, In both cases, there is a phenomenon in which the film on the roll surface (self-fluxing alloy sprayed film or ceramics film) peels off locally after about 2 weeks of use. Then, the peeled film adheres to the surface of the steel plate to be plated, causing a discolored pattern. Therefore, there is a problem that the quality of the plated steel sheet is significantly deteriorated.

Further, the roll of the above-mentioned conventional technology (3) is composed of WC, Cr ₃ C ₂ , TiC
In terms of using a carbide such as, the corrosion resistance of the molten metal is excellent. However, since this carbide alone has poor adhesion to the roll, it is essential to add a metal to coexist with it. However, depending on the type of the added metal, there is a problem that it causes a metallurgical reaction with the molten metal and is extremely eroded.

Further, each of the above-mentioned rolls (1) to (3) is formed by a thermal spraying method. Therefore, the film is an aggregate of fine particles, and there is a problem that pinholes are easily generated microscopically.

Moreover, since the conventional rolls shown in and use the oxide or carbide ceramics, the expansion coefficient is significantly different from that of the metallic roll base material (ceramics are about 1/2 to 1/2 of metal). Therefore, when these rolls are immersed in a high temperature molten metal bath, a large thermal stress occurs due to the difference in expansion coefficient between the roll base material and the film,
Often, the film had cracks or peeled off. For this reason, even if a ceramic film excellent in molten metal resistance is formed on the roll surface, the function cannot be fully utilized.

As a countermeasure against this, it was considered that before the ceramics-coated roll is immersed in the molten metal, it is heated to raise the temperature of the roll itself in advance to reduce the temperature difference from the molten metal in the bath. However, preheating the carbide in the atmosphere may cause oxidation by oxygen (because the carbide changes to an oxide, the adhesion with the roll is reduced and peeling easily occurs), so that the ceramic film The drawback was that the life was rather shortened.

As described above, the prior art, particularly the molten zinc bath roll formed with a ceramic film is weak against thermal shock generated when it is immersed in hot molten zinc, and the film itself has excellent molten metal resistance. Even if they do, the reality is that they are not in a state where they can fully exercise their functions.

[Means for solving the problem]

According to the present invention, the surface of a steel roll or a bearing member is spray-coated with a carbide-based material that does not substantially react with molten metal, and then the obtained spray-coated film is subjected to a boriding treatment. By changing each part, especially each particle on the surface side, to boride, while maintaining excellent molten metal resistance as it is, it is possible to improve wear resistance by utilizing the high hardness possessed by boride. A composite coating that overcomes the various problems of conventional technology by improving the mutual bonding force, improving the adhesion between the thermal spray coating and steel members, and reducing the pores of the thermal spray coating. A covering member is provided.

That is, the present invention is characterized in that the carbide-based sprayed coating itself formed on the surface of the base material is a layer in which at least the outermost surface layer portion thereof is changed to a boride by a boriding treatment, which is characterized by wear resistance and melting resistance. A composite film-coated member excellent in metallicity and a carbide-based sprayed film coated on the surface of a steel base material are pure boride coating layers, boride conversion layers, boride-impregnated layers, and A composite film coating member having excellent wear resistance and molten metal resistance, characterized by comprising a boride alloy layer, and a carbide-based thermal spray coating on the surface of a steel base material by a thermal spraying method. Is formed, and the surface of the sprayed coating is covered with boride by subjecting this sprayed coating to boride treatment, and at the same time, a portion of the carbide and / or metal on the surface layer of the sprayed coating is converted to boride and the spray coating is performed. Of the film A boring alloy is impregnated and filled in the pores, and a boride treatment is further applied to a part of the surface of the base material through the pores to form a boride alloy layer thereat. Provided is a method for producing a composite film-coated member excellent in molten metal property.

[Work]

In the present invention, the most important boration treatment of the thermal spray coating is a treatment performed after forming the carbide thermal spray coating. Therefore, the process of forming a composite coating formed by borating the thermal spray coating and the characteristics of the composite coating will be described below.

In forming the composite film of the present invention, first,
On the surface of the steel member, a thermal spray coating mainly composed of carbide,
It is formed by a thermal spraying method using a combustion flame of hydrocarbon and oxygen or plasma as a heat source. As a thermal spray material for forming the matrix, that is, a carbide material, WC, WTiC, Cr ₃ C ₂ , TiC,
VC, B ₄ C, NbC, etc. can be used alone, or a carbide cermet obtained by adding a heat-resistant metal material such as Co, Ni—Cr, Ni to these can be used.

The thickness of the carbide spray coating formed on the substrate is 30 μm
The range of up to 3000 μm is preferable. If the thickness is less than 30 μm, the function of the composite coating of the present invention cannot be fully exerted, and if the thickness is more than 3000 μm, the function and effect of the boriding treatment described below becomes diminished and an expensive thermal spray material is used. The effect obtained is relatively small.

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

_{KCl (30wt%) - BaCl 2} (30wt%) - NaF (15wt%) -
A mixed salt of B ₂ O ₃ (2.4 wt%)-ferroboron (22.6 wt%) is raised to a temperature of 700 to 1000 ° C. to obtain a molten salt, and a steel member on which a carbide sprayed coating is formed is A molten salt method in which the material is immersed in and is borated for 0.5 to 5 hours.

B ₄ C (45%)-Al ₂ O ₃ (50%)-NH ₄ Cl (5%) mixed powder, the steel member on which the carbide sprayed coating was formed was buried and the temperature was 800 to 1100 ° C. Powder method of heating at 0.5-5 hours for boration.

When such a treatment is performed, at least a part of the carbide and the metal component contained in the thermal spray coating on the surface of the base material are changed to boride. Such a reaction of the carbide-based sprayed coating to boride starts from the outermost layer portion of the sprayed coating. That is, when there are pores or voids in the thermal spray coating, the boration reaction components gradually penetrate into the interior through these, so that the reaction of boration preferentially borates the defective portion of the thermal spray coating. Thought to happen. As a result, the sprayed coating after boration treatment is borided by the action of the boration reaction component that penetrates deeply inside the outermost layer as well as through the defective portion of the coating, thereby increasing the mutual bonding force of the sprayed particles. Not only improve
Further, a boride alloy layer is formed between the steel member and the steel member, and the state is changed to a metallurgical bonding state. Therefore, these films exhibit extremely strong adhesion.

FIG. 1 is a schematic view of the cross-sectional state of such a boride-based sprayed coating.

Reference numeral 1 is a base material, and the surface thereof is coated with a thermal spray coating C. This thermal sprayed coating C becomes a pure boride coating layer 4 having a thin outermost layer by the boration treatment, and a boride metamorphic layer 3 formed by boride of each carbide particle itself is formed inside the layer. A boride-impregnated layer (particle itself is a carbide) 5 is formed on the inside, and boride alloy layer 6 which is an alloy of a base metal and boron is formed on the inside. In this case, the composite film of the present invention is formed.

In the case of the molten salt method, such a composite coating structure can be changed by adjusting the temperature of the molten salt and the immersion time. Therefore, in the composite coating of the present invention, when the boride alloy layer 6 is not present, or when the boride conversion layer 3 and the boride impregnated layer 5 are
In some cases, they are indistinguishable from each other, and in any case, they can be said to have the same effect as the boride-forming sprayed coating in the present invention.

Regarding the constitution of the boride-forming thermal sprayed coating, in the case of the molten salt method, various film constitutions can be obtained by adjusting the temperature of the molten salt and the immersion time. Film thickness 120μm, temperature 800 ℃, immersion time 3
In time, as shown in FIG. 2, a thin pure boride layer 4 is formed on the surface layer of about 10 μm, a boride metamorphic layer 3 of 10 to 30 μm, a boride impregnated layer 5 of 10 to 20 μm, and some boride are formed. The alloy layer 6 is formed.

The composite film of the present invention thus obtained has the following features.

(1) The carbide type thermal spray coating alone is porous and its adhesion to the base material is relatively weak. Therefore, when used in molten metal, the molten metal penetrates into the interior from the pores and reacts with the base material. Although the film is peeled off by performing the boriding treatment, the porosity is filled with boride by the boriding treatment, and a part of the base metal is also firmly adhered by alloying by the metallurgical reaction. It also improves mechanical shock resistance.

(2) Borides (carbides of carbides) in the surface layer formed by the boriding treatment are hard and have excellent wear resistance, so they can be used for extending the life of rolls and bearing members used in molten metal. Great effect.

(3) Compared to the one in which the surface of the substrate is directly borated without forming a thermal spray coating on the base material, the borated layer can be made thicker, and the combination with the thermal spray coating causes both defects. You can make up for it and create strengths.

(4) Further, by performing the boriding treatment, the existence of porous voids, which is a fatal defect of the thermal spray coating, rather facilitates the intrusion of borides, so strict quality control is not required when forming the thermal spray coating. The film forming process can be performed by the most economical spraying method.

〔Example〕

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

Composite coating which is an application example of the present invention; WC-12Co sprayed coating, which is then subjected to boration treatment by a molten salt bath method, WC-20Co-7Ni sprayed coating, and then subjected to boration treatment by a molten salt bath method. which was, as the TiC-20Ni sprayed coating that has been subjected boride then processed by a molten salt bath method, a Cr ₃ C ₂ -20Ni-7Cr sprayed coating subjected to the boride then processed by the powder method, Comparative example and the composite coating film; WC-12Co that only alms sprayed coating that has been subjected only WC-20Co-7Cr sprayed coating that has been subjected only TiC-20Ni sprayed coating, Cr ₃ C ₂ -20Ni-7Cr sprayed coating Only those that have been subjected to JIS H8303 (1976) MSF Co2 self-fluxing alloy spray coating, the formation of the spray coating is SUS 304 (diameter 15 mm, length 2
00 mm) was obtained by spraying on a base material by a high-speed gas flame spraying method using propane as a fuel so that the film thickness was 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 was WC-12Co of No.5.
Except for the film, the adhesion of molten zinc was relatively strong. As a result of investigating the cause, it was found that the metal components of the coating, especially Cr and Ni, were the result of metallurgical reaction with molten zinc. Also in the No. 9 member using the self-fluxing alloy film, the adhesion of molten zinc was remarkable. However, the No. 5 member (WC-12Co only) had a weak adhesion to molten zinc and could be easily peeled from the coating surface. However, when observing the cross section of the coating of this No. 5 member with an optical microscope, it was found that the molten zinc had penetrated into the interior through the fine pores present in the coating. Therefore, it could be easily inferred that the film would penetrate if the immersion was continued for a longer period of time.

In contrast, the composite film coated on the member of the present invention is No.
Even with Cr, Ni, etc. such as 2,3,4 etc., the adhesion of molten zinc was extremely slight and the remaining zinc could be easily removed. In addition, no zinc was found to enter the film and it was sound. It was confirmed that these effects were due to the boration reaction after the formation of the sprayed coating, which resulted in the formation of a borated coating which was difficult to "wet" with molten zinc on the surface and in the pores of the sprayed coating.

Example 2 Next, the hot-dip galvanizing resistance of the composite film coated member of the present invention was investigated in an actual hot-dip galvanizing working environment. The temperature of the hot-dip galvanizing bath was 470 ° C., and the same kind of film (No. 1 to No. 1) as the film for the sink roll (SUS 304) 22, the support roll 23, and the guide roll 23 of the apparatus shown in FIG. 2 was used. The film of 9) was used for 2 weeks of operation to evaluate its performance.

Table 2 summarizes the results, and the sink roll, the support roll and the guide roll coated with the composite coating according to the present invention were sound without any change.

On the other hand, when the composite coating of the comparative example is coated, N
Except for the o.5 roll (WC-12Co), it is subject to erosion of molten zinc, and the molten zinc adheres strongly to the surface of the galvanized steel plate, causing scratches and degrading its quality. If such) occurs. However, the roll coated with the No. 5 film had relatively low zinc erosion and adhesion, but the performance seemed to be lower than that of the film of the roll of the invention.

[Effects of the Invention] As described above, the composite coating member of the present invention is
Since the surface layer and pores of the hard carbide cermet film and part of the film constituent particles are changed to boride, it prevents molten zinc from entering the inside of the film and has a large contact angle with zinc, which makes it wet. Since it is in a difficult state, its surface is always kept clean. Therefore, when such a member is used as each roll or bearing member of the hot dip galvanizing device, not only it is possible to manufacture a stable hot dip galvanized steel sheet for a long period of time, but also product quality and productivity are improved. It also has a great effect on reducing maintenance and inspection costs.

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

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view showing an example of a cross-sectional structure of a composite coating portion of a member of the present invention, and FIG. 2 is a schematic diagram showing an outline of a continuous galvanizing apparatus for steel plates. 1 ... Roll base material, 2 ... Carbide sprayed particles, 3 ... Boride coating, 4 ... Boride particles in which carbide cermet particles are changed, 5 ... Boride penetrated into boundaries of carbide particles, 6 ... … Metallurgical reaction part of base material and boride, 21 …… Molten zinc bath, 22 …… Sink roll, 23 …… Support roll, 24 …… Plated steel plate, 25 …… Guide roll, 26 …… Injection nozzle

 ─────────────────────────────────────────────────── --Continued from the front page (56) Reference JP-A-2-43352 (JP, A) JP-A-51-88441 (JP, A) JP-A-55-161063 (JP, A) JP-A-57- 156169 (JP, A) JP 57-42704 (JP, B2) JP 58-37386 (JP, B2) JP 58-55109 (JP, B2)

Claims (3)

(57) [Claims] 1. A wear resistance and melting resistance characterized in that a carbide-based thermal spray coating formed on a surface of a base material is formed as a layer in which at least the outermost surface layer thereof is converted into a boride by a boriding treatment. A composite film coated member with excellent metallic properties. 2. A carbide-based thermal spray coating coated on the surface of a steel base material is a pure boride coating layer from the surface layer toward the surface of the base material.
A composite film coated member having excellent wear resistance and molten metal resistance, which is characterized by comprising a boride metamorphic layer, a boride impregnated layer and a boride alloy layer. 3. A carbide-based thermal spray coating is formed on the surface of a steel base material by a thermal spraying method, and the thermal spray coating is borided to coat the surface of the thermal spray coating with boride. Part of the carbide and / or metal on the surface side of the sprayed coating is converted to boride, and the pores of the sprayed coating are impregnated and filled with boride. A method for producing a composite film-coated member having excellent wear resistance and molten metal resistance, characterized by forming a boride alloy layer thereover.