JP2758707B2 - Thermal spray coating for hot dip galvanizing bath - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a hot-dip galvanizing bath member, in particular, a sink roll or a support roll used by dipping in a galvanizing bath of a continuous hot-dip galvanizing apparatus, and a jet in contact with hot-dip zinc. The present invention relates to a thermal spray coating member used for a nozzle or a bearing.

[Conventional technology]

Most of the hot-dip galvanized steel sheets used as heat-resistant and corrosion-resistant materials for automobile steel sheets, civil engineering, construction steel materials, and home electric appliances, etc., use the continuous hot-dip galvanizing equipment shown in Fig. 1. Being manufactured. The hot-dip galvanizing apparatus guides a sink roll 2 immersed in a plating bath 1, a support roll 3 disposed near the surface in the plating bath, or a galvanized steel sheet 4 after passing through these rolls. There are provided members such as a guide roll 5 and a spray nozzle 6 for blowing off excess zinc attached to the steel plate with nitrogen gas.

Since these members are immersed in a plating bath, installed in places where molten zinc is liable to scatter and adhere, or used in contact with hot steel sheets to which molten zinc adheres, (1) molten zinc Erosion is unlikely to occur,
(2) It is hard to wear even when it comes in contact with the threading material (steel plate),
(3) easy removal and maintenance inspection of the adhered molten zinc, (4) excellent service life, and (5) good resistance to thermal shock when immersed in a high-temperature molten zinc bath; Such performance is required.

By the way, conventionally used components such as sink rolls and bearing components, such as bushes, bearings, collars, and end balls, which are immersed in a hot-dip galvanizing bath, are as follows: (1) Coatings specified by JIS H8303 (1976) (2) ZrO ₂ as disclosed in JP-A-61-117260.
And Al ₂ that O ₃ with ceramic coating consisting of thermally sprayed formed, as disclosed in (3) JP-B 58-37386 discloses, WC, Cr
_A hot corrosion resistant metal such as Ni or Si or an oxide thereof is allowed to coexist with one or more of ₃ C ₂ and TiC.
Up to 2.4 mm thick film mainly formed by thermal spraying.

[Problems to be solved by the invention]

As can be seen from the above examples, the conventional components used in hot-dip galvanizing equipment mainly consist of the development of coating components with excellent hot-dip galvanizing resistance, improved coating adhesion, improved coating density, and improved coating surface roughness. Control, etc. was the subject of research.

However, according to the study of the inventors, in order to improve the life of the member, especially the sprayed coating coated on the surface thereof, the components of the sprayed coating itself coated on the surface of the member and the adhesion of the coating are required. It turns out that there is a limit just to improving. In particular, it is necessary to study how the film deteriorates when it comes into contact with the molten zinc in the plating bath on the environment side. From this viewpoint, it is necessary to develop technologies to prevent the film from deteriorating. Was determined to be necessary.

An object of the present invention is to propose a thermal spray-coated member for a hot-dip galvanizing bath having a long life by improving the hot-dip galvanizing property of a thermal-sprayed film coated on the member surface.

[Means for solving the problem]

According to the study of the present inventors, the cause of the deterioration of the melter film coated on the member surface is that the metal component in the melter film, that is, the free metal component in the cermet is molten zinc in the plating bath (hereinafter, referred to as “ (Indicated by "Zn"). Then, the elution of the free metal component is caused by zinc-free coating on the surface of the cermet sprayed coating.
The inventors of the present invention have found out that it can be prevented by forming an aluminum alloy layer, and arrived at the present invention.

Such a finding is that, when such a spray-coated member is used in a hot-dip galvanizing treatment facility, aluminum (hereinafter, referred to as “Al”) is added to the plating bath at a predetermined ratio, and the cermet spray-coated film is used. The present inventors have found out a phenomenon that, when an alloy layer of Zn and Al is formed on the surface of the alloy, the life of the sprayed coating is improved by orders of magnitude, and invented based on this finding.

The present invention, which has been developed based on such novel findings, is a hot-dip galvanizing bath having a cermet spray-coated film on the surface of a base material, in which the cermet spray-coated film is made of Cr ₂ C ₃ , TiC, ZrC, WC, WTiC, B ₄ C and either one or more carbides and Co, Ni, carbide cermet thermal spray coating consisting of either one or more metal components of the Ni-Cr of NbC, the carbide cermet A spray-coated member for a hot-dip galvanizing bath, characterized in that a Zn-Al alloy layer having an aluminum content of 0.1 to 10 wt% is formed on the surface of the sprayed coating.

In other words, when the cermet spray-coated member is immersed in an Al-containing molten zinc bath, Zn and Al in the molten zinc are adsorbed on the surface of the cermet spray-coated film, and the content of Al adsorbed on the film surface is particularly high in the bath. Concentrate so that it reaches several times to several hundred times. And the surface of the thermal spray coating is the Zn-Al
As a result of being coated with the alloy, the penetration of molten zinc into the thermal spray coating on the member surface during the plating process is prevented, and the molten zinc resistance of the cermet thermal spray coating is significantly improved.

In the above alloy layer formed on the cermet sprayed coating surface
The reason why the Al% is higher (concentrate) than the Al in the bath is not clearly understood, but the inventors imagine that it is due to the difference in chemical activity between Zn and Al.

(Operation)

In the present invention, a cermet containing non-oxide-based ceramics as a main component is used as the thermal spray coating covering the member surface. The effects of the present invention are not sufficient for oxide ceramics and cermets thereof, and metal (alloy) sprayed coatings exhibit some effects when used in a hot dip galvanizing bath with a low Al content. This does not extend the life of the molten coating significantly. In the present invention, as the thermal spray coating to be coated on the substrate surface, Cr ₂ C ₃ , TiC, ZrC, WC, W
TiC, B ₄ C and at least one carbide and Co selected from among NbC, Ni, is sprayed carbide cermet thermal spray coating obtained by a mixture of Ni-Cr are suitable.

Here, in the present invention, the reason why carbide cermet was particularly selected is that, in the case of this material, it is strong against erosion of molten Zn, excellent in wear resistance, and resistant to thermal shock when immersed in a molten zinc bath. This is because it has a feature that it is strong and can be formed by a thermal spraying method.

Thermal spray coating of such carbide cermet, for example, WC
When a member spray-coated with Co-cermet is immersed in a molten zinc bath, the molten zinc diffuses and penetrates into the sprayed WC-Co coating. In this case, if there is a through hole in the thermal spray coating,
Zn penetrates through the through-holes and diffuses with Co, which is a cermet metal component, to elute the Co. Therefore, the Co surrounding the WC particles in the cermet spray coating
The WC particles become unstable to the extent that (matrix) elutes, leading to deterioration of the film.

In the present invention, it is a precondition that the thermal spray coating is a dense coating having no through holes. The penetration of the molten Zn into the dense coating is caused by the fine particles (W
Selectively proceeds through the grain boundary of C), but at a speed of about 480 ° C
Is several microns per day in a hot-dip galvanizing bath.

However, this cermet melt-coated member is
It was found that, when immersed in a molten zinc bath containing 0.1 to 10% Al, the penetration rate of Zn into the thermal spray coating was extremely low.

In order to confirm this, the surface of the sprayed coating immersed in the Al-containing molten zinc bath was observed in detail, and the surface of the sprayed coating was covered with a Zn-Al alloy layer containing a large amount of Al. It turned out that it became. Moreover, the Al content in the Zn-Al alloy layer is higher than the Al content in the bath, and the penetration rate of zinc into the thermal spray coating coated on such an alloy is 1 at 480 ° C. 0.01 ~ per day
It was found to be about 1 μm, and almost no erosion. That is, the thermal spray coating is in a state protected by the Zn-Al alloy.

Incidentally, when the Zn-Al alloy layer is formed on the thermal spray coating surface,
It is not clear why the sprayed coating is no longer eroded, but the Zn-Al alloy generated on the coating surface has a high melting point and the viscosity increases accordingly, so the penetration rate of Zn diffusing in this alloy coating layer. Is thought to be due to the extreme decrease of the interdiffusion between Zn and the cermet metal component. That is, it is considered that the presence of the Zn—Al alloy layer serves as a barrier for the penetration of the molten zinc into the thermal spray coating.

In order to protect the thermal spray coating by forming the Zn-Al alloy layer on the surface of the thermal spray coating as described above, the member is appropriately placed in a molten zinc bath containing 0.1 to 10% by weight of Al. It is effective to form a Zn-Al alloy layer having an Al content of 0.1 to 10% by weight on the surface of the base material by immersion for a time. If the Al content in this bath is less than 0.1%,
If the effect is not sufficient, and if it is 10% or more, the melting point itself of the molten zinc bath rises, so that it becomes difficult to form a uniform Zn-Al alloy layer on the surface of the sprayed coating, and in addition to the general molten zinc Operating temperature conditions of 440 to 500 ° C., which is the temperature of the plating bath, make it difficult to produce high quality hot-dip galvanized steel sheets. More preferably, the range is 0.5 to 10%.

In the present invention, as a method for forming a cermet sprayed coating on the surface of a member, combustion gas flames (including explosive spraying) such as hydrocarbon-oxygen and hydrogen-oxygen, and argon,
A thermal spraying method using a gas plasma using nitrogen, helium, hydrogen, or the like as a heat source can be used, but it is important that the formed thermal spray coating has no through pores.

According to such a thermal spraying method, for example, when thermal spraying WC-Co cermet powder, WC itself does not completely melt because of its high melting point, but Co melts in a heat source, and a part thereof melts.
While reacting with WC to generate intermetallic compounds such as Co ₃ W ₃
The object collides with the surface of the object. As a result, on the surface of the object to be treated, Co became an extremely large flat body compared to the initial particle diameter and was fixed to the surface to form a matrix, and the WC powder was laminated in a state where WC powder was dispersed in the Co matrix. A thermal spray coating can be formed.

As described above, the thermal spray coating of the member is formed by spraying a carbide cermet, and these thermal spray coating materials are subjected to a thermal history such as a sintering reaction in the manufacturing process, and Since it is also placed in a high-temperature environment during thermal spraying, it is expected that a part of the carbide will be oxidized to an oxide, or will react with a metal component to form an intermetallic compound. For example, it is known that the reaction between WC and Co produces Co ₃ W ₃ C and W ₆ C _2.54. It goes without saying that these compounds also contain these intermetallic compounds which are produced by reaction in the environment.

〔Example〕

Example 1 In order to confirm the effects of the plating bath member according to the present invention, the following experiment was performed.

(1) Aluminum concentration of zinc bath: 0.1%, 1%, 10%, 15
% (Wt%) (2) temperature and immersion time in the zinc bath: 480 ° C., 240 h (3) Type :( numbers of test試溶morphism coatings are by weight%) carbide _{cermet: WC-12Co Cr 3 C 2} - 20Cr-7Ni TiC-20Ni (4) Thermal spraying method: Carbide cermet ~, oxygen: 0.25 ~ 0.98MP
a, acetylene: 0.06 to 0.12 MPa, hydrogen: 0.14 to 0.30 MPa, kerosene gas: 0.7 to 0.98 MPa, using a high-speed gas flame spraying method with a combustion flame as a heat source, made of SUS 304 stainless steel with a diameter of 15 mm and a length of 200 mm Was sprayed to a thickness of 200 μm.

The comparative example is an example in which the above-described test piece was immersed in a pure zinc bath (JIS H2107 ordinary zinc ingot 99.97% or more, 480 ° C.) for 240 hours.

After completion of the test, the sprayed coating was cut, and the cross-section of the sprayed coating was observed with an optical microscope and an X-ray microanalyzer to observe the state of penetration of zinc into the coating.

Table 1 shows the observation results. In other words, the evaluation of molten zinc resistance is based on the penetration rate of Zn into the sprayed coating in a pure zinc bath (Comparative Example), and is compared with the penetration rate of Zn when an Al-added molten zinc bath is used. It is shown.

[Notes] In this table, the molten zinc resistance was measured by measuring the depth of penetration of Zn into each coating when each member was immersed in an Al-added zinc bath for 240 hours. The depth of penetration of Zn into the film when immersed in a pure zinc bath
侵入, を indicate that the penetration depth was 1/10 or less and 1/100 or less.

○: 1/10 or less of zinc penetration depth when immersed in pure zinc bath ◎: 1/100 or less zinc penetration depth when immersed in pure zinc bath The △ mark shows that the viscosity of the molten zinc increases at 480 ° C and it is difficult to form a uniform Zn-Al alloy layer on the surface of the sprayed coating. When Al is added, the penetration rate of Zn into the sprayed coating becomes 1/10 or less of the penetration rate of the comparative example (a member having no Zn-Al alloy layer on the surface of the sprayed coating). 1.
It was found that the Zn-Al alloy layer formed on the surface of the film by immersing the member in a molten zinc bath containing 0% or more of Zn further reduced the penetration rate of Zn into the film. In particular, WC-12
In the case of the Co film, the penetration rate of Zn was 1/100 or less as compared with a member having no Zn-Al alloy layer on the film surface, and a remarkable effect was recognized.

Example 2 Even when a test piece prepared under the same thermal spraying conditions as in Example 1 was immersed in a hot dip galvanizing bath at 500 ° C. for 240 hours, a member with a cermet thermal spray coating formed with a Zn—Al alloy layer was used. However, it was confirmed that the zinc penetration rate into the coating was 1/10 or less as compared with a member having a thermal spray coating having no alloy layer.

Example 3 Using the continuous hot-dip galvanizing bath shown in FIG. 1, the effect of improving the roll obtained by forming the following cermet sprayed coating on the surface of the base material with and without the formation of the Zn-Al alloy layer investigated.

(1) Thermal spray coating roll: sink roll, support roll (2) Cermet thermal spray coating: WC-6Co, WC-12Co, WC-17
Co (3) Thickness of sprayed coating: 200 μm (4) Spraying method: high-speed gas flame spraying method (5) Al content added to hot-dip galvanizing bath: 0%,
0.2% (6) Hot-dip galvanizing bath temperature: 480 ° C. A galvanized sheet (JIS G3302 SPGC) was produced under the above conditions, and the state of erosion of the hot-dip coating when hot-dip galvanizing was applied was observed. As a result, most of the coating was eroded by Zn in a pure zinc plating bath having an Al content of 0% after 3 weeks of use, but the roll was immersed in a hot dip galvanizing bath containing 0.2% Al. In the case where the Zn-Al alloy layer is formed on the surface of the cermet spray coating, the erosion of the Zn into the spray coating is 1
It was in the range of ３3 μm, and excellent molten zinc resistance was observed. In addition, no abnormalities were observed in the manufactured zinc iron plate, which was favorable.

The molten zinc used in this example was JIS H2
107 Normal zinc ingot, Pb 0.02% or less as impurities, F
The aluminum contained in the zinc bath is JIS H2102 Class 1 metal, containing 0.01% or less and Cd 0.005% or less, including Si 0.15% or less, Fe 0.20% or less, and Cu 0.0
It contains impurities such as 1% or less, Ti 2.02% or less, and Mn 0.02% or less. Therefore, Al in the hot dip galvanizing bath
And elements other than Zn are those inevitably contained during the production of the metal as described above, and the content of such an extent would reduce the effects of the present invention. is not.

〔The invention's effect〕

As is clear from the above description and the results of the examples,
According to the present invention, the thermal spray coating member for the hot-dip galvanizing bath, the cermet thermal spray coating formed on the surface of the substrate and a carbide-based thermal spray coating, by coating the surface with a Zn-Al alloy layer, the coating. Life is dramatically improved. Therefore, a stable hot-dip galvanizing operation can be continued for a long period of time, and a great effect is exhibited in terms of reduction of maintenance and inspection costs and reduction of manufacturing costs.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an outline of a continuous hot-dip galvanizing apparatus for steel sheets. 1 ... molten zinc bath 2 ... sink roll 3 ... support roll 4 ... plated steel sheet 5 ... guide roll 6 ... injection nozzle

Claims (1)

(57) [Claims] 1. A sprayed coating member for a hot-dip galvanizing bath having a cermet sprayed coating on the surface of a substrate, wherein the cermet sprayed coating is formed of Cr ₂ C ₃ , TiC, ZrC, WC, WTiC, B ₄ C and NbC. One or more of carbides and Co, Ni, Ni-C
r is a carbide cermet sprayed coating composed of at least one metal component, and a zinc-aluminum alloy layer having an aluminum content of 0.1 to 10 wt% is formed on the surface of the carbide cermet sprayed coating. A spray-coated member for a hot dip galvanizing bath.