JPH04350154A - Member for hot-dip metal bath - Google Patents

Abstract

PURPOSE:To form deposit capable of preventing the peeling of ceramics material deposit formed on a member for a hot-dip metal bath over a long period. CONSTITUTION:The surface of a steel member is provided, as an underlaying layer, with a thermal-spray-coating layer of carbide of one or more kinds selected from Cr3C2, NbC, TiC, WC, WTiC, ZrC and SiC or carbide cermet contg., >=50wt.% above carbide and the balance one or more of hot corrosion resistant metals selected from Co, Ni, Cr and Mo. The surface of the underlaying layer is provided, as an overlaying layer, with an oxide ceramics thermal- spray coating layer contg. 10 to 40wt.% SiO2, and, as the balance, contg. at least one kind selected from MgO, CaO, ZrO2, Al2O3, Y2O3 and TiO2. This is a member for a hot-dip metal bath obtd. by providing the surface of a base metal with sprayed deposit with the above two layer structure.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to members for molten metal baths, and in particular, to members having excellent properties as bath members for hot-dip aluminum plating baths and hot-dip galvanizing baths, such as excellent hot corrosion resistance, thermal shock resistance, and peeling resistance. This is a proposal for a molten metal bath member provided with a multilayer thermal spray coating. Also,
The present invention is applicable not only to rolls and various parts (such as bearings) that are immersed in molten aluminum or hot-dip galvanizing baths, but also to various parts attached to hot-dip plating baths where these molten metals are scattered and adhered. It is something that will be done.

0002

BACKGROUND OF THE INVENTION 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.

[0003] The continuous plating processing equipment includes a dipping roll immersed in the molten metal, a plating roll installed near the surface of the molten metal, or a plated steel plate for guiding the plated steel sheet after passing through these rolls. Guide rolls etc. are provided. These rolls are immersed in molten metal, and because they come into contact with a high-temperature steel plate coated with molten metal, they are required to have the following performance. (1) Less likely to be eroded by molten metal; (2)
) It is resistant to wear even when it comes into contact with the steel plate being threaded, (3
) It is easy to remove adhering molten metal and maintain and inspect it, (4) It has a long life as a roll, (5)
Must be low cost.

[0004] Conventional technologies aimed at providing rolls that meet these demands, that is, members for plating baths, include: (1) a roll surface coated with a self-fluxing alloy specified in JIS H8303 (1976); -1172
A ceramic coating layer consisting of ZrO2 and Al2O3 as disclosed in Publication No. 60, ■Special Publication No. 57-1
SiO2 15 to 4 as disclosed in Japanese Patent No. 74440
5% by weight, MgO 5 - 40% by weight, balance ZrO2
A ceramic coating layer made of
WC, CrC, as disclosed in Publication No.-37386,
Roll with a surface coating layer of 0.1 to 2.4 mm thick consisting of one or more types of TiC and the remainder being a hot corrosion resistant metal or its oxide, ■ Japanese Patent Publication No. 1-22
A thermal spray coating of WC-Co cermet with a porosity of 1.8% or less as disclosed in Japanese Patent No. 5761 has been proposed.

[0005]

[Problems to be Solved by the Invention] Regarding each of the above-mentioned conventional technologies, in the case of technology (2), although the lifespan is longer than that of the previous untreated rolls, the self-fluxing alloy film is corroded by molten metal. The roll surface becomes uneven even after about two weeks of use, which has the disadvantage of causing scratches on the surface of the threaded material.

In addition, in the case of the technique (2), although the ceramic film itself is not subject to corrosion, it is prone to through cracks and local peeling due to the difference in thermal expansion between the ceramic film and the material, and the molten film that enters from that part is likely to occur. Metals corrode the metal spray layer and material of the undercoat. As a result, the ceramic film peels off, making it difficult to use repeatedly over a long period of time.

[0007] In addition, in the case of technology (①), SiO2 is
Since the ceramic coating containing 45% by weight is used, fine vertical cracks suitable for absorbing thermal stress are present in the thermal sprayed layer, so it has excellent thermal shock resistance. However, when used in a hot-dip galvanizing bath or a molten aluminum bath for a long period of time, molten metal is easily penetrated and diffused through the above-mentioned fine vertical cracks and pores in the ceramic coating, resulting in thermal expansion of the ceramic and the material. It severely corrodes the intermediate metal layer or material provided for the purpose of alleviating the difference. As a result, the ceramic film peels off, the rolls must be replaced relatively frequently, and productivity is inevitably lowered due to line stoppages, making the method impractical.

[0008] Furthermore, in the case of the technique (3) disclosed in Japanese Patent Publication No. 57-174440, in order to alleviate the difference in thermal expansion between the ceramic coating layer and the base material, one layer or It is made up of two or more intermediate layers, but even if a Ni-Cr alloy or a Co alloy is used as the intermediate layer for the purpose of mitigating such a difference in thermal expansion, this intermediate layer is not covered by a ceramic coating. It has been confirmed through experiments by the present inventors that corrosion occurs due to penetration and diffusion of molten metal through the grain boundaries, resulting in peeling of the ceramic coating layer.

On the other hand, in the case of each of the prior art techniques listed in (1) and (2), since carbide and carbide cermet coating layers are used,
Although it exhibits relatively excellent corrosion resistance against molten metal, if it is used in a hot-dip plating bath for a long period of time, the surface becomes minutely uneven due to penetration of molten metal from the grain boundaries of the coating, which causes discoloration on the surface of the plated steel sheet. This has the disadvantage that it is transferred as a pattern, resulting in a significant reduction in commercial value.

[0010] As explained above, each of the above-mentioned conventional techniques:
Although each of them had the effect of improving, it is still insufficient when considering the recent strict operating conditions and quality requirements. It has not been shown to have a sufficient effect on the reduction of For this reason, there has been a strong desire to develop bath members that have excellent corrosion resistance against molten metal and that do not cause coating defects such as peeling even when applied to steel members that are the base material of molten metal bath members.

An object of the present invention is to provide a molten metal bath member, particularly a molten metal bath member that overcomes the above-mentioned drawbacks of conventional bath members whose surfaces are thermally spray coated with a ceramic material, and that meets the demands of the industry. Our goal is to provide the following.

0012

[Means for Solving the Problems] As a result of intensive research aimed at overcoming the drawbacks of conventional techniques coated with oxide ceramic materials, the present inventors have obtained the following knowledge regarding the oxide ceramic film peeling phenomenon. . That is, this peeling phenomenon of the ceramic film is caused by (1) the difference in thermal expansion coefficient between the coating layer and the material when the oxide ceramic coating layer is immersed in or pulled up from a molten metal bath; ■Those caused by penetration of molten metal through through cracks caused by the above-mentioned thermal expansion difference between the oxide ceramic coating layer and the material, resulting in corrosion of the underlying metal coating layer and the material. During use for a period of time, it is possible that molten metal invades through the grain boundaries of minute particles that make up the sprayed coating, or that molten metal corrodes the underlying metal coating layer or material due to diffusion and penetration. It became clear.

Therefore, in order to achieve the above-mentioned object of the present invention, the surface structure of the molten metal bath member should have excellent thermal shock resistance, and the molten metal in the oxide ceramic layer should be It was found that an underlay layer with excellent corrosion resistance against penetration and diffusion penetration is necessary.

[0014] Therefore, the present invention is based on the use of an oxide ceramic as the overlay layer, which exhibits excellent properties of molten metal corrosion resistance and thermal shock resistance. During use, a base layer is provided to maintain corrosion resistance even if molten metal diffuses into the oxide ceramic coating, thereby suppressing corrosion of the molten metal. A member for a molten metal bath that can be repeatedly and stably used for a long period of time by preventing the above-mentioned oxide ceramic from peeling has been completed.

[0015] The present invention, which was developed based on such knowledge, consists of a base layer consisting of a carbide or a carbide cermet coating layer of a hot corrosion resistant metal on the surface of a steel member, and a top layer consisting of 10 to 40% by weight. The basic structure is a molten metal bath member provided with a two-layer thermal spray coating composed of an oxide ceramic coating layer containing SiO2, and furthermore, as an underlay layer, Cr3C2, NbC, TiC, WC is applied to the surface of the steel member. ，
One or more carbides selected from WTiC, ZrC, and SiC, or one or more hot corrosion-resistant metals containing 50% or more of these carbides, with the balance being selected from Co, Ni, Cr, and Mo. It has a thermally sprayed coating layer of carbide cermet consisting of
Contains 0 to 40% by weight of SiO2, the balance being MgO,
This is a member for a molten metal bath provided with a two-layer sprayed coating composed of an oxide ceramic sprayed coating layer containing at least one selected from CaO, ZrO2, Al2O3, Y2O3 and TiO2.

[0016]

[Operation] In the present invention, as the oxide ceramic constituting the overlay layer, an oxide ceramic containing 10 to 40% by weight of SiO2 is used. Originally, oxide ceramics are materials that do not react with molten metal and have extremely low wettability. In particular, when SiO2 is contained in an amount of 10% by weight or more, fine vertical cracks occur in the thermally sprayed coating layer, which act to absorb thermal stress and significantly improve thermal shock resistance. However, this SiO2 content is 4
If it exceeds 0% by weight, such an oxide ceramic film becomes porous, and penetration of molten metal becomes noticeable.
Even if the underlay layer has corrosion resistance against molten metal, it is susceptible to corrosion and peeling. That is, the oxide ceramic used for the overlay layer in the present invention needs to contain 10 to 40% by weight of SiO2. In the present invention, other ceramic components added in addition to SiO2 include MgO, CaO, ZrO2,
At least one of Al2O3, Y2O3 and TiO2 is used.

On the other hand, the underlay layer in the present invention is made of Cr3C
2, NbC, TiC, WC, WTiC, Zr
one or more carbides selected from C and SiC,
or contains 50% by weight or more of such carbides, with the balance being C.
A carbide cermet made of a mixture with one or more hot corrosion resistant metals selected from O, Ni, Cr, and Mo is used by thermal spraying. Cr3C2, NbC, TiC
Carbide ceramics such as , WC, WTiC, ZrC and SiC are difficult to wet with molten metal;
Furthermore, it is a material that does not react with molten metal and exhibits excellent adhesion to steel materials, making it ideal as an undercoat material for ceramic overlay layers.

In particular, carbide cermets made by mixing heat-resistant metals such as Co, Ni, Cr, and Mo have high adhesion to steel materials, and furthermore, they can reduce the difference in thermal expansion between steel materials and oxide ceramics. Since it also has the effect of a film structure that gradually relaxes, it exhibits an extremely excellent effect as a base layer for an oxide ceramic coating layer. However, in order to prevent peeling of the oxide ceramic layer due to erosion of the underlying layer by molten metal penetrating through the oxide ceramic coating layer, the carbide cermet should contain 50% by weight or more of carbide. It is necessary.

[0019]

【Example】

Example 1 As explained above, the main causes of peeling of the oxide ceramic layer in a molten metal member are cracks caused by thermal stress due to the difference in coefficient of thermal expansion between the steel material and the ceramic layer, and metal cracking due to diffusion and penetration of the molten metal. It is thought that this is due to erosion of the sprayed layer or steel material. Therefore, in order to confirm these points below, we used S as a material with a large coefficient of thermal expansion.
A test piece was prepared using US 304 steel and sprayed with several thermal spraying materials, and was subjected to a test by immersing it in a molten aluminum bath and a thermal cycle test.

That is, a test was repeated 50 times in which the spray-coated test piece was immersed in a molten aluminum bath at 700°C, taken out after 30 minutes, cooled, and then washed with alkali. In this test, a SUS 304 steel base material with a diameter of 30 mm and a length of 300 mm was blasted with alumina abrasive grains, and then an underlay layer of 100 μm each as shown in Table 1 was thermally sprayed, and various oxide ceramic coatings were further applied on top of the underlay layer shown in Table 1. A test piece with a plasma sprayed layer of 300 μm was used. The results are shown in Table 1.

[0021]

As is clear from the results shown in Table 1, the underlay layer is a carbide coating layer or a carbide coating layer containing 50% by weight or more of carbide, with the balance being one or more hot-coating layers selected from Co, Ni, Cr, and Mo. Thermal sprayed coating has a carbide cermet coating layer made of a corrosion-resistant metal, and an oxide ceramic coating layer containing 10 to 40% by weight of SiO2 as an overlay layer on top of the carbide cermet coating layer has excellent peeling resistance and reaction resistance. , it was found to have outstanding durability.

Example 2 Next, 80 μm of WC-12Co, which is the coating of the present invention, was applied to the immersion roll and support roll of a continuous galvanizing device.
The bottom layer is sprayed and the top layer is 250μm of 30wt% SiO.
A 2-65% by weight CaO-5% by weight ZrO2 thermal spray coating was applied by plasma spraying, and a hot-dip galvanizing treatment test was carried out by passing it through a structural steel plate using a conventional method. This thermal spray roll was repeatedly removed from the molten zinc bath every 10 days (1 charge) for maintenance and inspection of the galvanizing bath equipment, and then used again. It could be used successfully without peeling or cracking, and of course, there was no reaction with molten zinc. In this point,
In the case of conventional thermal spray coatings, reactions with hot-dip zinc and local peeling occurred after 3 to 4 charges, but the coating of the present invention not only extends the service life several times, but also improves the lifespan of hot-dip galvanized steel sheets. improved the quality of steel, making it possible to manufacture high-grade steel sheets.

Example 3 A 100 μm thick underlay layer of Cr3C2-20% by weight NiCr was thermally sprayed on the surface of the roll base material, and a 300 μm layer was coated on top of it.
A pot roll (immersion roll) on which an ultra-high-speed gas flame sprayed coating of oxide ceramic consisting of 10% by weight SiO2-70% by weight MgO-20% by weight ZrO2 was formed was installed in the aluminum bath of a continuous hot-dip aluminum plating machine. I used it. The hot-dip aluminum plating equipment was removed from the plating bath every 7 days (1 charge) for maintenance and inspection, and then reused.
During 0 days (10 charges), there was no local peeling or cracking, and there was no reaction with molten aluminum or wear, and it could be used satisfactorily. In this regard, since conventional thermal spray coated rolls were replaced after 1 to 3 charges due to reaction with molten aluminum or peeling, it was found that the coated bath member of the present invention has several times the durability.

Example 4 The support roll of a continuous zinc-55% by weight aluminum alloy plating device was coated with Cr, which is the coated bath member of the present invention.
After spraying 70 μm of 3C2 on the bottom layer, 250 μm was applied to the top layer.
μm 35 wt% SiO2-45 wt% MgO-20
A hot-dip zinc-45% by weight aluminum alloy plating test was conducted by applying a ZrO2 material using a plasma spraying method and passing it through a structural steel plate using a conventional method. This thermal spray roll was removed from the hot-dip plating bath every 7 days (1 charge) and used again for maintenance and inspection of the zinc-aluminum alloy plating bath equipment, for a total of 77 days (11 charges). During that time, it could be used satisfactorily, with no local peeling or cracking, and no reaction with molten metal. In this regard, conventional thermal spray coatings and SUS 316L stainless steel rolls caused local peeling or reaction with molten metal after 2 to 4 charges, so the bath member of the present invention can extend the life span several times. It became.

[0026]

Effects of the Invention As is clear from the above description and the verification results in the examples, a carbide underlay coating layer or a carbide cermet underlayer consisting of 50% by weight or more of carbide and a hot corrosion resistant metal, The molten metal component of the present invention, which has a thermally sprayed coating composed of an overlay of an oxide ceramic coating layer containing ~40% by weight of SiO2, is corrosion resistant not only in galvanizing baths but also in aluminum baths at high processing temperatures. It has excellent performance and a satisfactory lifespan. Furthermore, the bath member of the present invention exhibits effects on stable hot-dip metal plating, high productivity, and quality improvement of plated steel sheets.

Claims (4)

[Claims] [Claim 1] On the surface of a steel member, the base layer is composed of a carbide or a carbide cermet coating layer of a hot corrosion-resistant metal, and the top layer is composed of an oxide ceramic coating layer containing 10 to 40% by weight of SiO2. A molten metal bath member provided with a two-layer thermal sprayed coating. [Claim 2] The underlay layer is made of Cr3C2, NbC
, TiC, WC, WTiC, ZrC and S
2. The molten metal bath member according to claim 1, comprising a sprayed layer made of one or more carbides selected from iC. 3. The underlay layer is made of Cr3C2, NbC
, TiC, WC, WTiC, ZrC and S
50% by weight of one or more carbides selected from iC
2. A thermally sprayed layer of carbide cermet which is a hot corrosion resistant metal containing the above and the remainder being a metal or alloy of one or more of Co, Ni, Cr, and Mo. Components for molten metal baths. 4. The upper layer contains 10 to 40% by weight of S.
In addition to iO2, MgO, CaO, ZrO2, Al
Any one of 2O3, Y2O3 and TiO2
2. The member for a molten metal bath according to claim 1, comprising a sprayed layer of a composite material containing at least one kind of oxide ceramic.