JPH09268361A - Powder for boride cermet thermal spraying - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form sprayed coating having high hardness and excellent in wear resistance, corrosion resistance, heat resistance, thermal impact resistance and toughness by specifying the elemental compsn. SOLUTION: This powder contains, by weight, 5.0 to 8.0% B, 15.0 to 30.0% Co, 5.0 to 15.0% Cr, 3.0 to 9.0% W, and the balance Mo with inevitable impurities. Each element works as the following manner by their incorporation in the above range. B is needed for the formation of combined boride phases and imparts sufficient hardness, strength and wear resistance to the obtd. sprayed coating layer. Mo is needed also for the formation of combined boride phases and contributes to the improvement of sufficient hardness, strength, wear resistance, corrosion resistance and the yield at the time of thermal spraying similarly to B. Co is needed also for the formation of combined boride phases and imparts high temp. strength and oxidation resistance to the sprayed coating layer. Cr contributes to the improvement of its corrosion resistance, heat resistance, oxidation resistance and toughness. W forms metallic bonding phases with Co and Cr to further increase its corrosion resistance and strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cermet material for thermal spraying, which has hardness and wear resistance comparable to those of a tungsten carbide-cobalt (WC-Co) -based thermal spray coating layer, and chromium carbide nickel chrome ( Cr ₃ C
_2- NiCr) -based thermal spray coating layer having heat resistance and oxidation resistance superior to those of the above-mentioned WC-Co-based and Cr ₃ C ₂
The present invention relates to a thermal spraying powder for producing a cermet thermal sprayed coating having high thermal shock resistance and toughness not found in a NiCr thermal spray coating.

[0002]

2. Description of the Related Art In recent years, as industrial machinery and the like have become higher in performance, higher in precision, more diversified and energy costs have been reduced in recent years, a material containing metal and ceramics as a thermal spray material. The required performance for the cermet thermal spray coating layer, which forms a cermet composite coating by thermal spraying with, is becoming more and more severe, and it is now required to have even better performance than before. Typical cermet thermal spray coating layers (hereinafter, also simply referred to as coating layers or coating layers) conventionally have different usage characteristics depending on the temperature, and in the temperature range from room temperature to about 500 ° C. Is a WC-Co type or a WC-Ni type, and Cr ₃ C ₂ in a higher temperature range up to 900 ° C.
Those -NiCr system or _Cr 3 _C 2 -Ni system is used,
Each of these coating layers has hardness, heat resistance, wear resistance, oxidation resistance, etc. according to the purpose.

However, as described above, as the use environment of cermet has diversified with the recent industrial development, it is desired that the cermet has these excellent properties. Development of a coating material having both toughness and toughness is desired. To give an example, it is immersed in a hot-dip galvanizing bath (450 to 500 ° C) or a hot-dip aluminum plating bath (700 to 800 ° C) for producing a surface-treated steel sheet for automobiles, etc., and continuously. The coating layer that coats the sink rolls, support rolls, etc. used to support and guide the passing steel sheet and apply uniform zinc plating to the surface of the steel sheet simply has high hardness, simple heat resistance, and resistance to heat. Not only wear resistance but also corrosion resistance to molten metal, thermal shock resistance and excellent toughness are required.

Among the conventional cermet coatings mentioned above,
The WC-Co type is excellent in hardness and wear resistance in a dry atmosphere up to 500 ° C, but has low corrosion resistance and heat resistance, and has a problem in heat resistance and corrosion resistance particularly in an oxidizing atmosphere of 500 ° C or higher. is there. In addition, Cr ₃ C ₂ -NiCr
The materials of the system maintain corrosion resistance, heat resistance, and oxidation resistance up to a high temperature region of 900 ° C., but have poor hardness and wear resistance. Further, these coatings generally have low thermal shock resistance and poor toughness, so that the coating layer is easily peeled off and the application range is limited.

As described above, the conventional coatings are
Even if it has high hardness and excellent wear resistance, it has poor corrosion resistance and heat resistance. Even if it has excellent heat resistance and corrosion resistance, it has insufficient wear resistance and hardness. The current situation is that a cermet sprayed coating that is low and has poor toughness and that can simultaneously satisfy all of these required properties has not been obtained.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems in the conventional cermet sprayed coating, and has high hardness, excellent wear resistance, corrosion resistance, and heat resistance, and further has a thermal shock resistance. An object of the present invention is to provide a powder for thermal spraying for forming a cermet thermal spray coating having properties and toughness.

[0007]

As a result of intensive studies to solve the above-mentioned problems, the present invention has revealed that Mo-Co type compound borides represented by Mo ₂ CoB ₂ have high hardness and wear resistance. Not only exhibiting excellent thermal shock resistance and toughness, but also combining the double boride with a Co--Cr--W alloy phase having excellent heat resistance as a metal bonding phase to form a cermet. It has been found that a cermet sprayed coating having high hardness and wear resistance, and having both heat resistance, oxidation resistance and thermal shock resistance can be obtained. Further, in order to form an appropriate amount of the double boride phase in the cermet coating in a dense and uniform manner, B has an optimum addition range, and Co, Cr, and W, which are the metal binding phases, are present. It was found that it is appropriate to add each as a single metal, not in the state of alloy.

That is, in the present invention, B5.0 to 8.0%, Co15.0 to 30.0%, and C in terms of weight ratio.
It is a boride-based cermet thermal spraying powder comprising a composite powder composition containing r5.0 to 15.0% and W3.0 to 9.0% and the balance Mo and inevitable impurities.

The preferred particle size of the powder constituting the thermal spraying powder depends on the thermal spraying method, but is 15 to 53 μm when the atmospheric or reduced pressure plasma thermal spraying method is adopted.
Is suitable, and in the case of the high-speed gas flame spraying method, the range is preferably 5 to 45 μm or 15 to 53 μm. Further, in the composite powder composition, the total of Mo and B is preferably 50.0 to 70.0%, and the total of Co and Cr is preferably 25.0 to 45.0%.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The constituent components of the cermet thermal spraying powder for obtaining the boride-based cermet thermal spray coating layer according to the present invention are as described above. The reasons for limiting the respective components will be explained below.

B is an element necessary to combine with Mo and Co to form a double boride phase, and if the content of B in the cermet thermal spraying powder is less than 5.0% by weight, the thermal spray coating is performed. The amount of B in the thermal spray coating layer is 3.
Since the amount is reduced to less than 0% by weight, the obtained sprayed coating layer cannot have sufficient hardness and abrasion resistance. On the other hand, if it exceeds 8.0% by weight, the hardness becomes high, but the strength (toughness and thermal shock resistance) of the thermal spray coating layer remarkably decreases. Therefore, the B content in the thermal spraying powder is appropriately in the range of 5.0 to 8.0%.

Mo is an element necessary for forming a double boride phase, similar to B, and the double boride phase is Mo ₂ Co.
As represented by B ₂ , if the Mo content in the cermet sprayed powder is less than 45.0% by weight, the formation of the complex boride phase will be insufficient, and the sprayed coating layer will have a desired hardness and wear resistance. I can't get it. On the other hand, if it exceeds 65.0% by weight, hardness, wear resistance and corrosion resistance to molten zinc and molten aluminum are improved, and toughness and thermal shock resistance, and further, the efficiency of thermal spray adhesion of powder (yield during thermal spraying) is significantly reduced. Therefore, the Mo content in the thermal spraying powder is preferably in the range of 45.0 to 65.0%.

[0013] Co is an element that is the main constituent of the metal bonded phase formation, but on the other hand, it is also an essential element for the formation of the double boride phase, and the obtained thermal spray coating layer has high temperature strength and oxidation resistance. Has the effect of imparting. When the Co content is less than 15.0% by weight, the mutual solid solution amount of the metal binding phase and the double boride phase formed is small, so that the binding force is lowered and defects such as pores are easily generated. Become. On the other hand, 30.0% by weight
If it exceeds, the corrosion resistance in the metallic binder phase is lowered, and a large amount of brittle boride such as CoB is formed in the double boride, so that the toughness of the thermal spray coating layer is lowered. Therefore, the Co content in the powder for thermal spraying is 1
A range of 5.0 to 30.0% by weight is suitable.

Cr is an element that contributes to corrosion resistance, heat resistance and oxidation resistance, and has an effect of combining with Co to form a metal bonding phase and improving toughness. The Cr content is 5.
If it is less than 0% by weight, the above-mentioned effects are not sufficiently obtained, and if it exceeds 15.0% by weight, the toughness is reduced although the corrosion resistance, heat resistance and oxidation resistance of the obtained thermal spray coating layer are further improved. It is not preferable because it causes. Therefore,
Cr content in the powder for thermal spraying is 5.0 to 15.0% by weight.
Is appropriate.

W combines with Co and Cr forming a metal binder phase to further enhance the corrosion resistance and strength of the metal binder phase, and further to form a complex boride represented by W ₂ CoB _2. It is an element necessary for this. W content is 3.0
If it is less than 10% by weight, the above effect cannot be obtained, and if it exceeds 9.0% by weight, the strength of the metallic binder phase is rather lowered. Therefore, the W content in the powder for thermal spraying is 3.0 to
A range of 9.0% by weight is suitable.

Further, in the thermal spraying powder composition of the present invention, the total amount of Mo and B is further 50.0 to 70.0.
%, And the total amount of Co, Cr, and W is 25.0 to 4
By restricting the content to 5.0% by weight, embrittlement and peeling phenomenon of the obtained thermal spray coating layer can be suppressed. Further, when producing the above-mentioned thermal spray powder of the present invention, Co, C
It is important to use r and W as a single metal powder. This is the form of alloy powder of these elements,
For example, when used in the form of stellite alloy powder,
Co in the alloy powder is difficult to combine with boride such as MoB, and Mo
_This is because it is difficult to form ₂ CoB ₂ complex boride.

As a method for cermet thermal spray coating on a substrate using the thermal spray powder of the present invention, a conventional method, that is, an atmosphere using a thermal spray gun, a low pressure plasma thermal spraying method or a high speed gas flame thermal spraying method is applied. Usually, a thermal spraying powder having a particle diameter of 15 to 53 μm is used in the plasma spraying method, and a thermal spraying powder having a particle diameter of 5 to 45 μm or 15 to 53 μm is used in the high speed gas flame spraying method. When these powders are coarser than the above-mentioned particle size range, it is difficult to form a dense thermal spray coating layer, and therefore only a thermal spray coating layer having low hardness can be obtained. Further, when the particle size is smaller than the above range, the fluidity of the powder is lowered, and the fine powder having high heat receiving efficiency is melted and deposited on the inner surface of the nozzle of the spray gun, resulting in remarkable workability of spraying. Be damaged.

[0018]

EXAMPLES Examples of the present invention will be described below in comparison with conventional examples. The present invention is not limited to the following examples.

Example 1: M containing 10.1% by weight of B
70% by weight, 18% by weight, 8% by weight and 4% by weight of oB powder, Co powder, Cr powder and W powder, respectively, were sampled and placed in a stainless steel container for 2 in a vibrating ball mill.
It was pulverized and mixed for 4 hours in a wet manner. The slurry taken out from the container was spray-dried in a non-oxidizing atmosphere for granulation, and then the powder obtained by sintering in a vacuum was recovered, and the powder was sized to a powder of 5 to 45 μm by an air classifier. Then, a powder for thermal spraying was prepared.

The chemical composition of the resulting thermal spray powder is shown in Table 1. Next, by using this powder, a high-speed gas flame spraying method (fuel is hydrogen-oxygen) was applied to the SS400 substrate to form
A sprayed coating layer of thickness was formed. After that, the unevenness on the surface of the coating layer was removed by machining and surface polishing to obtain a test piece having a smoothness of ∇∇.

As a result of identifying the thermal spray coating layer formed on the substrate surface by the Cu-κα X-ray diffraction method, mainly M
A ternary compound boride phase of o ₂ CoB ₂ was observed. Also E
Table 2 shows the results of composition analysis of the coating layer by PMA quantitative analysis. The Vickers hardness (load:
0.3 kgf) is 1,250. Using a reciprocating motion abrasion tester, according to the test method specified in JIS H 8503 Item 9, SiC abrasive paper No. 320 is used, and the test load is 3. 0kgf, the number of reciprocating loads is 1,6
As a result of performing the wear resistance test of the test piece as 00 times, the loss on wear was 0.50 mg / cm ² .

On the other hand, the test piece was placed in an electric furnace at 600 ° C. for 30 minutes.
After holding for a minute, a thermal cycle of rapid cooling in water was repeated 20 times, and each time, the presence or absence of cracks or peeling in the coating layer was observed visually and by color check to evaluate the thermal shock resistance. No abnormality was observed during the heat cycle, and it was found to have high thermal shock resistance. next,
The test piece was kept in an electric furnace at 900 ° C. for 2 hours to measure the increase in oxidation of the coating layer. The value was 1.7 mg /
It was cm ² and was confirmed to have high oxidation resistance. The results of the above various characteristic tests are summarized in Table 3. From the above results, the cermet sprayed coating according to the present invention has a hardness,
It is excellent in various properties such as abrasion resistance, high temperature oxidation resistance, thermal shock resistance, and high temperature hardness (heat resistance), and it can be said that the effectiveness of the present invention has been sufficiently proved.

Examples 2-4 and Conventional Examples 1-3: Example 1 except that the amount of powder to be mixed and the classification particle size range were changed.
The same raw material powder was used, and a predetermined amount thereof was pulverized and mixed, granulated and then sintered to obtain the thermal spraying powders of Examples 2 to 4. Also,
W powder, Co powder and C powder and Cr powder, Ni
Using a predetermined amount of powder and C powder, WC-Co cermet thermal sprayed coating formed powder by the respective conventional method (conventional example 1-2) and _Cr 3 _C 2 -NiCr cermet sprayed coating forming powder (Conventional Example 3 )created. Table 1 also shows the chemical compositions of these powder compositions.

Next, using these thermal spraying powders, in the same manner as in Example 1, test pieces having a thermal spray coating layer formed on the SS substrate by the high-speed gas flame spraying method were obtained. Similarly, the composition analysis and the characteristic test of the thermal spray coating layer were performed, and shown in Table 2 and Table 3, respectively.

[0025]

[Table 1] Actual chemical composition Grain number No. MoBCoCrCrWCNi Range ──────────────────────────── ─────── Example 1 61.4 7.5 17.7 7.5 4.3 − − 5 to 45 Example 2 49.3 5.8 27.2 12.3 5.1 − − 15 to 53 Example 3 53.4 6.4 22.6 10.1 6.4 − − 15 to 53 Example 4 57.9 7.0 19.8 5.5 8.5 − − 5 to 45 Conventional example 1 − − 12.0 − bal 5.3 − 5 to 45 Conventional example 2 − − 18.9 − bal 5.0 − 15 to 53 Conventional example 3 − − − 68.2 − 10.4 20.8 5 to 45 ── ──────────────────────────────────

[0026]

[Table 2] Actual chemical composition No. Mo B Co Cr W C Ni ────────────────────────────── Example 1 62.1 4.5 17.1 7.4 4.0 − − Example 2 48.9 3.3 27.3 12.5 5.0 − − Example 3 53.5 3.7 21.9 9.9 6.1 − − Example 4 56.5 4.0 19.6 5.4 8.7 − − Conventional example 1 − − 9.2 − 81.9 4.9 − Conventional example 2 − − 14.8 − 77.7 4.5 − Conventional example 3 − − − 62.5 − 9.8 18.4 ───────────────────────────────

[0027]

[Table 3] Actual compounding hardness Hv Abrasion resistance Thermal shock resistance High temperature oxidation High temperature hardness No. phase (0.3kg) mg / cm ² Number of times mg / cm ² Hv (900 ℃) ─────── ─────────────────────────── Example 1 Mo2CoB2 1250 0.50> 20 1.7 645 Example 2 Mo2CoB2 1150 0.61> 20 1.3 575 Example 3 Mo2CoB2 1175 0.54> 20 1.5 570 Example 4 Mo2CoB2 1220 0.55> 20 1.7 615 Conventional Example 1 WC 1150 0.75 6 90 290 Conventional Example 2 WC 1100 0.89 10 72 245 Conventional Example 3 Cr3C2 850 1.28 11 3.1 380 ────── ─────────────────────────────

The above results show that the boride-based cermet spray coating obtained by using the spray powder according to the present invention has hardness and abrasion resistance comparable to those of the conventionally used WC-Co cermet spray coating. And has Cr ₃ C ₂ −
It can be seen that it has oxidation resistance and heat resistance superior to that of the NiCr-based cermet thermal spray coating, and has significantly higher thermal shock resistance than these conventional cermet thermal spray coatings. Zn-0.15% Al melted at 470 ° C
When an immersion test was performed for 120 hours (5 days), the corrosion weight loss of Example 1 was 121 mg / cm ² and the film residual rate was 78.6%. Similarly, in Conventional Example 1, the corrosion weight loss was 282 mg / cm ² , and the film residual rate was 33.9.
According to the results of the immersion test in the molten zinc and the molten aluminum, it was confirmed that the corrosion resistance of the cermet sprayed coating of the present invention to these molten metals is far superior to that of the conventional cermet sprayed coating. It was

[0029]

As described above, the boride-based cermet thermal sprayed coating obtained by using the thermal spraying powder of the present invention is excellent in hardness, wear resistance, corrosion resistance, and heat resistance, and also has a thermal shock resistance and Since it also has toughness, it can be used in a wide range of applications and can be said to be an extremely useful invention in industry.

Claims (4)

[Claims] 1. A weight ratio of B5.0 to 8.0% and Co1.
5.0 to 30.0%, Cr 5.0 to 15.0%, W3.
A boride-based cermet thermal spraying powder comprising a composite powder composition containing 0 to 9.0% and the balance Mo and unavoidable impurities. 2. The boride-based cermet thermal spraying powder according to claim 1, which has a particle size of 5 to 45 μm. 3. The boride-based cermet thermal spraying powder according to claim 1, which has a particle size of 15 to 53 μm. 4. The total amount of Mo and B is 50.
0 to 70.0%, the total amount of Co, Cr and W is 25.0
It is -45.0%, The boride type cermet thermal spraying powder of any one of Claims 1-3.