JP2000144358A - Roll member for hot-dip metal coating bath, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a roll which has a surface structure hardly causing adhesion of plating dross to roll surface and having the ease of its peeling from roll surface, and also to provide a method for forming a film on the roll surface. SOLUTION: The surface of a base material made of steel is coated with a WC-(metal boride)-Co cermet by thermal spraying. Then, the surface of the resultant sprayed deposit composed of the WC-(metal boride)-Co cermet is coated with slurry consisting of a mixture of chromium-oxide-containing aqueous solution and nitride, followed by heating and burning. By this method, the inside of micropores existing in the surface of the sprayed deposit of WC-(metal boride)-Co cermet and in the vicinity of the surface layer of the sprayed deposit is coated and filled with the resultant burned mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roll member for a molten metal plating bath, which is used for guiding and running a material to be plated in a plating bath among devices in a bath provided in a continuous molten metal plating apparatus. And its manufacturing method.
The present invention particularly relates to the surface of a sink roll or a support roll used by dipping in a plating bath of a non-ferrous metal hot-dip coating apparatus such as hot-dip galvanizing, hot-dip aluminum plating, hot-dip zinc-aluminum alloy plating, and hot-dip tin plating. It is a reforming technology.

[0002]

2. Description of the Related Art As shown in FIG. 1, a sink roll 2 and a support roll 3 used in a hot-dip galvanizing apparatus 1 and a hot-dip aluminum plating apparatus for performing metal plating on a steel strip surface are, as shown in FIG. It is used by immersion. For example, since the sink roll 2 is constantly immersed and used in a molten metal such as zinc or aluminum, the use conditions are severe, and it is basically required to have the following functions. I have. The roll surface is not easily eroded by molten metal,
The surface is hardly worn even when it comes into contact with the passing steel strip, the initial shape accuracy can be maintained for a long time, and although it is a consumable material, its life is long and the equipment cost can be suppressed. Moreover, since the sink roll 2 is used by winding the steel strip in the plating bath for the direction change at the same time as the guide running of the steel strip, the following performance is also required. Foreign matter suspended in the plating bath ("dross", mainly Fe
-Particles such as Zn alloys or particles that are mechanically bonded to the plating metal component, and have a melting point higher than that of metallic Zn and, when this adheres to the steel strip surface, cause shape defects in the plating layer). In general, spiral grooves 4, 4 'for discharging the dross are engraved on the outer peripheral surface of the sink roll. In addition, the surface should be less likely to become a non-uniform portion of the plating, and to cause plating surface defects (called so-called “groove marks”) such as uneven color tone and uneven gloss.

Conventional sink rolls 2 that can meet these requirements include: a. A roll outer peripheral surface provided with a coating layer having excellent resistance to molten metal erosion, b. There is one in which the groove shape formed on the outer peripheral surface of the roll is improved. As the former roll, for example, a WC-Co cermet coated by using a high-speed gas spraying method as disclosed in Japanese Patent Application Laid-Open No. 1-225761, a thermal spray coating as disclosed in Japanese Utility Model Application Laid-Open No. 3-63565, and the like. CrO ₃ by chemical densification for coating layer
And the like, in which fine pores of the thermal spray coating are impregnated with Cr ₂ O ₃ fine particles. In addition, the latter roll is obtained by engraving grooves 4, 4 'as shown in FIGS.
As disclosed in Japanese Utility Model Laid-Open No. 3-74654, the roll body has a depth of 0.05 to 0.5 mm, a width of 0.05 to 1.6 mm, and a pitch of 0.5 to 10 mm.
mm with continuous or discontinuous grooves,
As disclosed in Japanese Patent Publication No. -301057, a sink roll in which a conveyed material and a roll outer peripheral surface are not directly in surface contact with each other by forming an uneven surface having a height difference of 0.5 to 5 mm on the peripheral surface of the roll body. Proposed.

[0004]

Each of these prior arts is for long-term stabilization of the roll surface shape and for the Zn-Al
-It has been significantly effective in preventing the adhesion of Fe intermetallic compounds, preventing growth, and reducing the unevenness of the color tone or luster of the plating caused by the contact of the spiral groove for dross discharge with the steel plate. However, the quality of galvanized steel sheets required for automotive anti-corrosion steel sheets in recent years is becoming increasingly sophisticated, and conventional improvement techniques are not always satisfactory. In other words, not only the mechanical properties of the plated steel sheet, but also in the field of undercoat coating to which the present invention belongs, the demand for surface quality, for example, for point defects or pattern defects of plating, has further increased. It is a fact.

[0005] Under such technical background, the inventors of the present invention proceeded with research to further improve the plating quality, and found that defects on the surface of the coated steel sheet were inferior to the contact surface between the steel sheet and the roll, especially the roll surface. Tiny shape defects (surfaces, lines,
Point). In addition, it was found that the shape defect was caused not by the shape defect of the surface film itself but by a component (dross or the like) in the plating bath attached to the surface of the film. It was also found that the components in the plating bath were fine Fe-Al or Fe-Al-Zn intermetallic compounds.

[0006] The WC-Co cermet sprayed coating disclosed in the above-mentioned Japanese Patent Application Laid-Open No. Hei 1-222561 is a material having a resistance to molten metal, and is therefore effective for protecting the roll base material. . However, a minute amount of the metal Co phase that cannot be identified by the X-ray diffraction method is present in the sprayed coating, and since this Co phase has an affinity for molten Zn-Al, Fe-Al or Fe-Al It is considered to be a nucleus for adhesion of the -Al-Zn intermetallic compound and promote the adhesion. In addition, Cr ₂ O ₃ disclosed in Japanese Utility Model Publication No.
In the part of the roll surface that comes into contact with molten Zn-Al,
Al reduces Cr ₂ O ₃ to generate metallic Cr. Therefore, the durability in a hot-dip galvanizing bath containing both Al in the plating bath is thermodynamically unstable with Cr ₂ O ₃ , deterioration of the film occurs early, and the intermetallic compound of There was a problem that adhesion was promoted.

As described above, in the conventional methods, although the roll substrate surface can be protected to some extent, the adhesion and growth of Fe—Al or Fe—Al—Zn intermetallic compound from a microscopic viewpoint can be ensured. The fact is that it has not reached the point where it will be stopped. Accordingly, a main object of the present invention is to propose a roll member effective for preventing the occurrence of plating surface defects caused by roll surface properties, particularly a surface film structure thereof and a method of manufacturing the same. Another object of the present invention is to propose a roll having a surface structure in which plating dross does not easily adhere to the roll surface and easily peels off, and a method for forming a film on the roll surface.

[0008]

Means for Solving the Problems The present inventors have studied the microscopic structure of the WC-Co sprayed film formed on the roll surface in order to realize the above-mentioned object, and are generally called "dross". As a result of intensive studies to eliminate the adverse effect of Fe-Al or Fe-Al-Zn intermetallic compound adhering to and growing on the roll surface, the present inventors have conceived the present invention having the following gist configuration. That is, the present invention relates to a roll comprising a steel substrate surface coated with a WC-metal boride-Co cermet sprayed coating, wherein the WC
A metal boride-Co based cermet thermal spray coating, on the surface of the chromium oxide and nitride formed a fired film of a mixture of chromium oxide and nitride, and in the fine pores present near the surface layer of the thermal spray coating, the chromium oxide and the We propose a roll member for a molten metal plating bath, which is filled with fine particles of a mixture with a nitride.

Next, the present invention provides a method of spray-coating a WC-metal boride-Co cermet on the surface of a steel substrate, and then coating the surface of the sprayed WC-metal boride-Co cermet coating with a chromium oxide-containing aqueous solution. After coating with a slurry made of a mixture of a WC-metal boride-Co-based cermet sprayed coating and the micropores existing near the surface of the coating, the fired mixture is coated with a slurry made of a mixture of And a method for producing a roll member for a hot-dip metal plating bath characterized by filling and filling.

In the present invention, TiB ₂ , ZrB ₂ , HfB ₂ , VB ₂ , Ta
It is preferable to use at least one selected from B ₂ , NbB ₂ , NiB ₂ , W ₂ B ₅ (or may be WB) and CrB ₂ . In the present invention, as the nitride, TiN, Zr
N, VN, TaN, AlN, BN, NbN, it is preferable to use any one or more selected from among the Si ₃ N ₄ and SiO ₂ -AlN.

In the present invention, the WC-metal boride-
Co-based cermet powder is prepared by first baking a mixed powder of WC and Co to form an intermetallic compound or a modified WC compound of both, and then adding a metal boride to the WC-Co intermetallic compound, It is preferable to use a granulated one having a size of 5 to 50 μm via a binder. Further, in the present invention, the mixed slurry preferably has a concentration obtained by mixing the nitride with the aqueous chromic acid solution 1 at a volume ratio of 0.1 to 0.5. The present invention is particularly effectively applied particularly to a use as a roll member for a hot-dip zinc alloy plating bath containing Al as a plating bath component.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hot-dip metal plating bath, especially hot-dip Zn
Known materials exhibiting durability against an Al alloy include carbides, oxides, nitrides, borides, and the like. According to the study of the present inventors, it has been found that it is desirable to spray a mixture of these materials, for example, a WC-metal boride-Co cermet, onto a roll member for a hot-dip metal plating bath. However, this is not enough, and a surface treatment for sealing the pores of the sprayed coating is required. That is, in the present invention, it has been found that it is desirable to coat and fill a mixture of chromium oxide and nitride as an effective method for the sealing. Hereinafter, this will be described in more detail.

Now, a hot-dip metal plating process, for example, Zn-
In Al alloy plating, molten metal Al is an extremely active component, and when coexisting with other metal oxides, often reduces the partner metal oxide to change to a metal state, and becomes more stable aluminum oxide ( It is well known that it is going to change to Al ₂ O ₃ ). This phenomenon is also taught by the relationship between the standard free energy of formation of oxides in metal thermodynamics and temperature. That is, according to this relationship,
For example, Cr ₂ O _3, which is well known as a sealing material for WC-Co sprayed coatings, is thermodynamically more unstable than Al ₂ O _{3 at} the level of the plating temperature (about 460 ° C), and has an equilibrium theory. In the presence of Al, coexistence of metal may cause reduction to generate metal Cr.

[0014] Under these circumstances, the present inventors have first replaced WC-Co cermet with WC-boride, which is more stable against molten metal and excellent in heat resistance.
On the assumption that the use of Co cermet, as a further or sealing material as an overcoat on top of the sprayed coating, as a supplementary material for redeeming the Cr ₂ O _3, the Cr ₂ O ₃ in the molten zinc We focused on the use of nitrides that are thermodynamically more stable. That is, in the present invention, a mixture of chromium oxide and nitride is used as an overcoat and a pore sealing material. Here, the nitride is a compound that has a contact angle of 90 ° C. or more with the molten metal Zn—Al alloy and is extremely hard to wet. Moreover,
This nitride has lower thermodynamic reactivity with molten Al than Cr oxide. Therefore, if such nitride particles are present in the vicinity of Cr ₂ O ₃ particles, even if Cr ₂ O ₃ is reduced by molten Al in the plating bath to generate metal Cr, the fine metal Cr sites The probability of contact with the plating bath is low. As a result, the metal Cr reduced and generated by the molten Al in the microscopic region shows an affinity with the plating bath component itself, and Fe-Al, Fe-Al-Zn intermetallic compound on the sink roll surface immersed in the plating bath. It is thought that the action of inhibiting the adhesion and growth of uranium occurs.

Therefore, in the present invention, a mixture of chromium oxide and nitride, for example, chromium oxide-containing, is coated on the WC-metal boride-Co sprayed coating to reinforce and seal the sprayed coating. It was applied in the form of a slurry of a mixture of aqueous solution and nitride, dried and fired. That is, the mixed slurry is applied on the thermal spray coating, hydration reaction, hydrolysis, polycondensation reaction and the like are caused to occur, and then by heating and firing, mixed fired particles of Cr ₂ O ₃ and nitride Is coated on the surface of the thermal spray coating, and is impregnated into the pores through the pores in the surface layer of the coating.

In the present invention, the mixed slurry is replaced with an aqueous solution of ammonium chromate (N) instead of the aqueous solution of chromate (CrO ₃ ).
Aqueous solutions such as H ₄ ) ₂ CrO ₄ and ammonium bichromate (NH ₄ ) ₂ Cr ₂ O ₇ can be used alone or in combination. These aqueous solutions of chromic acid and chromate compounds are decomposed by heating and calcining, and all of them are characterized in that fine Cr ₂ O ₃ particles are produced as final products. As described above, if the compound generates Cr ₂ O ₃ as a final product, it is chromium chloride CrCl ₂ , chromium sulfate CrSO ₄ ,
Chromium carbonate CrCO ₃ , chromium nitrate Cr (NO ₃ ) ₃ , chromium hydroxide Cr (OH) _{3 and the} like can also be used. Therefore, in the present invention, such various chromium compounds are collectively referred to as chromium oxide-containing compounds for convenience.

In the present invention, the chromic acid aqueous solution, that is, the nitride used by being mixed with the chromium oxide is titanium nitride (TiN), zirconium nitride (ZrN), vanadium nitride (VN), tantalum nitride ( TaN), aluminum nitride (AlN), boron nitride (BN), niobium nitride (NbN), silicon nitride (Si ₃ N _4), a fine powder, such as sialon (SiO ₂ -AlN), dissolved as it is or in water Can be added afterwards.

The mixed slurry of the chromic acid aqueous solution and the nitride is prepared by mixing the above-mentioned nitride powder adjusted to an average particle size of 0.5 to 1.0 μm with the chromic acid aqueous solution, and furthermore, it is necessary. Accordingly, chromium oxide powder may be added as an aggregate. The mixed slurry thus adjusted is
It is coated on the WC-metal boride-Co thermal spray coating coated on the surface of the steel substrate by coating or spraying means. Then 550 ±
By heating and sintering at a temperature of 10 ° C., the sintering fine particles cover the sprayed coating and penetrate into and impregnate into micropores near the surface layer.

On the other hand, titanium boride (TiB ₂ ) and zirconium boride are used as metal borides in the thermal spray coating covering the surface of the substrate.
(ZrB ₂ ), hafnium boride (HfB ₂ ), vanadium boride (VB
₂ ), tantalum boride (TaB ₂ ), niobium boride (NbB ₂ ), tungsten boride (W ₂ B ₅ , WB), chromium boride (CrB ₂ ) and the like are preferable. These metal borides are added so as to be contained at a ratio of 5 to 60% by weight. The reason for this is that if the amount of boride is less than 5 wt%, the wettability to molten zinc as a boride is difficult to exhibit, while if it exceeds 60 wt%, the characteristics are not particularly improved.

The Co mixed in the thermal spray coating is 5
It is added in the range of 2020 wt%. The reason is that if the content is less than 5 wt%, the mutual bonding force of the WC and metal boride particles constituting the thermal spray coating becomes weak, causing cracks and adhesion to the steel base material. It is not preferable because it decreases. On the other hand, if the Co content is more than 20% by weight, the diffusion reaction of the molten metal into the inside of the film becomes large, and the dross component adhesion phenomenon increases, which is not preferable.

Next, the manufacturing method of the present invention will be described. Formation of lower cermet thermal spray coating; High-speed flame spraying of WC-metal boride-Co cermet on steel substrate (roll substrate) that has been subjected to predetermined surface treatment such as degreasing, cleaning, and surface roughening. Cover. Here, as the cermet powder used for the thermal spraying, a mixed powder of raw material powders such as WC, metal boride, and Co is used. The mixed powder is initially WC
By sintering Co and Co, first of all, an intermetallic compound of both, such as Co ₃ W ₃ C or W ₆ C _2.54 or W ₂ C generated by partial decomposition of WC, is used. Then, the WC-Co
It is preferable that the metal boride is directly mixed with the intermetallic compound powder or mixed with an organic binder to granulate to an average particle size of 5 to 50 μm. By adopting such a method, metals Co, TiB ₂ , Ni
B ₂ , CrB _{2 and the} like can be evenly mixed. Regarding the formation of the upper mixture fired film; WC described above
- on the metal boride -Co cermet sprayed coating, an aqueous solution of chromic acid and Ni ₃ N ₄ solution, mixed a mixed slurry and nitride-containing aqueous solution such as BN aqueous solution or AlN solution,
Coating is performed by application or spraying under normal pressure or pressure, and then baked at 540 to 560 ° C. By this treatment, the particles of chromium oxide and nitride in the mixed slurry are coated (thickness: 5 to 20 μm), and at the same time, penetrate into the pores of the cermet sprayed coating and are degassed by subsequent heating. In the form, which is effectively filled
Covers the surface of the cermet spray coating.

Table 1 shows a 25 mmφ × 300 mml carbon steel material coated with a 90 μm-thick boride-Co cermet sprayed coating. These were mixed slurry of chromic acid aqueous solution and Si ₃ N ₄ , chromic acid aqueous solution. And BN mixed slurry, chromic acid aqueous solution and AlN mixed slurry, and, as a comparative example, chromic acid aqueous solution only, were coated, covered, impregnated, and fired at 550 ° C x 1 hr. And Then, these samples were subjected to Zn-0.1%
Al Attach to the end of sink roll in 460 ℃ plating bath, 30
After fluidized immersion for 0 hours, the degree of adhesion of crystalline Fe-Al or Fe-Al-Zn intermetallic compound on the surface was compared and observed. As a result, conforming examples No., No., No.
In Comparative Example, the adhesion amount of the intermetallic compound was smaller than that of Comparative Example No. and the superiority was recognized.

Further, the above sample was cut into pieces and the SEM characteristics X
When the presence of Al on the film surface was semi-quantified by a line image, as shown in Table 1, the No. of the conforming example of the present invention was compared with the No. of the comparative example.
The superiority of was recognized. This means that in the baked film of the mixture of chromium oxide and nitride impregnated and fired in the WC-metal boride-Co-based cermet sprayed film, and in the portion of the filled layer, part of the chromium oxide is formed by molten Al. It is presumed that although the metal component was reduced and microscopically formed a metal Cr component, the effect of reducing the contact of the bath component due to the adjacent coexisting nitride appeared. Further, it is considered that nitrides such as BN have solid lubricating ability by themselves, and this is because the contact / adhesion of the plated metal fluid bath was reduced in the boundary region.

[0024]

[Table 1]

[0025]

Example 1 This example uses a test material having a diameter of 250 mm and a surface length of 1800 mm.
Roll (13Cr stainless steel), WC-25wt
% W ₂ B ₅ −5 wt% TiB ₂ −12 wt% Co cermet spray coating
After coating with a thickness of 08 to 0.09 mm, a slurry having the following composition is further applied on the WC-metal boride-Co cermet sprayed coating and dried, and then subjected to a condition of 550 ° C. ± 10 ° C. × 2 hours in an air atmosphere. This roll was rolled with 0.12% Al
Support roll 3 in bath of hot-dip galvanizing equipment 1 containing
(See FIG. 1). Composition of mixed slurry for coating; this slurry has a specific gravity of 1.60
Chromic acid aqueous solution and a nitride-containing aqueous solution having a specific gravity of 1.9 to 2.1 obtained by adding Si ₃ N ₄ having a particle size range of 5 to 10 μm to purified water and adjusting the mixture ratio (volume ratio) to 1: 1. It is.

The above-described support roll 3 thus obtained was actually used in a hot-dip galvanizing bath at 460 ° C. for a galvanized steel sheet. As a result, a plated steel sheet with stable surface quality was obtained without problems for 20 days after the operation. Thereafter, the support roll 3 was once pulled up from the plating bath, and the roll surface was inspected.
Almost no precipitation or adhesion of the intermetallic compound of -Al-Zn was observed. In addition, in order to remove the metal Zn attached to the roll surface, the support roll was immersed in a 5% H ₂ SO ₄ aqueous solution for 15 minutes to remove the metal Zn. Then, it was mounted again on the hot-dip galvanizing apparatus and used, but the operating life was almost the same as the initial use. According to this embodiment, the service life of the conventional support roll 3 was 5 to 15 days, but the life of the support roll 3 was extended about 2.5 times by using the support roll 2 twice, and the surface quality of the plated steel sheet was remarkably improved. I was able to.

Example 2 As a test material, a roll having a diameter of 700 mm and a surface length of 1800 mm (13
Made of Cr stainless steel, but the depth of this roll surface
A 0.25-0.35mm, 2.5mm pitch threaded dross discharge groove is pre-formed. ) On the surface of WC-30
wt% CrB ₂ -12wt% Co cermet sprayed coating 0.08 ~ 0.09mm
WC-Co sprayed coating on the surface of the roll, a slurry having the following composition was applied, dried, and then fired at 550 ° C. for 2 hours in an air atmosphere. Composition of mixed slurry; This slurry is composed of a chromic acid aqueous solution having a specific gravity of 1.60, and a nitride-containing aqueous solution adjusted to a specific gravity of 1.30 by adding BN particles having a particle size range of 0.5 to 1.0 μm to purified water.
The mixing ratio (volume ratio) was 1: 2.

The roll treated as described above was used in Example 1.
This was put to practical use as a sink roll of the same hot-dip galvanizing apparatus 1. As a result, in the prior art, fine surface defects on the plated steel sheet gradually increased due to the adhesion of the fine dross on the surface of the sink roll, and the roll was replaced almost every five days to exceed the allowable limit of the plating surface quality. . However, with the sink roll in the above example, a plated steel sheet having a stable surface quality was obtained for two consecutive weeks after the operation. Then, once the sink roll was pulled out of the bath and the roll surface was inspected, no deposits such as Fe-Al, Fe-Al-Zn intermetallic compounds were observed so as to cause indentation on the plated steel sheet. However, it has been found that such a method is effective in stabilizing the surface quality of the plated steel sheet.

[0029]

As described above, according to the present invention,
A slurry consisting of a nitride and a chromic acid aqueous solution is coated, sprayed or dipped on the surface of a steel sheet guide roll for a hot-dip metal plating bath, which is spray-coated with a WC-metal boride-Co cermet, and then fired. Thus, a thermodynamically stable protective layer can be formed with respect to the molten metal plating bath, so that Fe-Al, Fe-Al-Zn
It is possible to manufacture a high-quality steel sheet which is hardly adhered to and grown by intermetallic compound particles, has excellent durability, and has few plating surface defects.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a general hot-dip galvanizing apparatus.

FIG. 2 is a schematic diagram of a conventional plating bath roll having a dross discharge groove.

Continued on the front page F term (reference) 4K027 AA02 AA22 AB42 AB44 AB46 AB48 AD17 4K031 AA02 AA08 CB21 CB44 CB45 FA01 FA07

Claims (8)

[Claims] A roll comprising a steel substrate surface coated with a WC-metal boride-Co cermet sprayed coating, wherein the WC
A metal boride-Co based cermet thermal spray coating, on the surface of the chromium oxide and nitride formed a fired film of a mixture of chromium oxide and nitride, and in the fine pores present near the surface layer of the thermal spray coating, the chromium oxide and the A roll member for a hot-dip metal plating bath, which is filled with fine particles of a mixture with a nitride. 2. The WC-metal boride-Co-based cermet sprayed coating comprises TiB ₂ , ZrB ₂ , HfB ₂ , VB ₂ , TaB ₂ , NbB ₂ , NiB ₂ ,
W ₂ B ₅ and 5～60Wt% metal boride consisting of one or more selected from among CrB _2, the Co containing 5 to 20 wt%, claim the balance being a composition of WC 1 4. The roll member according to 1. 3. The method according to claim 2, wherein the nitride is TiN, ZrN, VN, TaN, Al.
_{N, BN, NbN, Si 3} N 4 and the roll member according to claim 1, wherein the chosen from among SiO ₂ -AlN either 1 or more. 4. A WC-metal boride-Co cermet powder is spray-coated on the surface of a steel substrate, and then a chromium oxide-containing aqueous solution and a nitride are coated on the surface of the WC-metal boride-Co cermet sprayed coating. After coating with the mixed slurry consisting of: and baking under heating, the firing mixture is coated and filled in the WC-metal boride-Co-based cermet sprayed coating and in the micropores present near the coating surface layer. A method for producing a roll member for a hot-dip metal plating bath, comprising: 5. The WC-metal boride-Co-based cermet spray coating comprises TiB ₂ , ZrB ₂ , HfB ₂ , VB ₂ , TaB ₂ , NbB ₂ , NiB ₂ ,
Claims W ₂ B ₅ and CrB 5~60wt% of metal boride consisting of one or more selected from among _2, a Co containing 5 to 20 wt%, and wherein the balance of the composition of WC 5. The production method according to 4. 6. The WC-metal boride-Co cermet powder is prepared by first baking a mixed powder of WC and Co to form an intermetallic compound or a WC composite compound of the two, and then forming the WC-Co metal. 6. The method according to claim 4, wherein a metal boride is added and mixed to the inter-compound or the WC composite compound, or the mixture is granulated to a size of 5 to 50 [mu] m via a binder. 7. TiN, ZrN, VN, TaN, AlN, BN, NbN, Si ₃ N ₄ are nitrides added to the chromium oxide-containing aqueous solution.
And the manufacturing method according to claim 4, characterized in that use one or more one selected from among SiO ₂ -AlN. 8. The method according to claim 4, wherein the mixed slurry has a concentration obtained by mixing the nitride with the chromic acid aqueous solution 1 at a volume ratio of 0.1 to 0.5.