JPH06240303A - Treatment of surface layer of alloy powder - Google Patents

Abstract

PURPOSE:To improve the wear resistance and durability of the alloy powder by micronizing the structure close to the surface of the alloy powder to increase the density between green compacts, and reduce the deposition of a binder in the surface layer of the powder. CONSTITUTION:The alloy powder consists of plural various green compacts just like a sintered hard alloy consists of the green compacts of high-hardness WC and the green compact of Co as the binder. Shots of 40-200mum size having a hardness higher than that of the green compacts are shotted at a high speed of >=50m/sec over the surface of the alloy powder product by shot peening to heat the shotted surface of the alloy powder to a temp. above recrystallization temp. of the binder, hence the surface of the green compact is smoothed by the impact force of the succeeding shots, and the density between the green compacts is increased. The binder is not deposited on the surface of alloy powder even when the powder surface is coated by CVD.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating the surface layer of products such as tools and machine parts made of powdered alloys such as cemented carbide, cermet and ceramics. More specifically, in sandblasting or shot peening The shot itself raises the temperature of the surface layer of the powder alloy to soften the powder compact of the binder among the various powder compacts that make up the powder alloy and strengthen the bond of the various powder compacts by the impact force of the shot. The present invention relates to a method for treating a surface layer of a powdered alloy,

[0002]

2. Description of the Related Art Powder alloys are produced by compressing and compacting metal powders and powder compacts of carbides, nitrides and oxides at temperatures below the melting point of the respective powder compacts and sintering. It has high hardness and strength up to high temperatures, has excellent wear resistance, and is formed into cutting tools, plastic working tools, etc. Typical examples of powder alloys include cemented carbide, cermet, and ceramics, which exhibit excellent performance in high-speed machinability because hardness decreases less with temperature than alloy steel and high-speed steel.

Cemented carbide has a powder compact of tungsten carbide (WC) which is a hard refractory metal as its main component, to which a powder compact of cobalt (Co) powder is added as a binder and compressed. It is formed and then sintered at high temperature. In addition to WC as the main component, a powder compact such as titanium carbide (TiC) or tantalum carbide (TaC) is blended according to the purpose, and this is burned with a binder such as Ti, Co, C or TiN. Some are tied.

Cermet is a combination of ceramics (refractory material) and metal (metal), which is an intermediate material having both characteristics of ceramics and cemented carbide, and TiC-N.
There are i-Mo ₂ C based cermets and Al ₂ O ₃ based cermets. TiC-Ni-Mo ₂ C-based cermet, the powder compact of titanium carbide having excellent high temperature strength (TiC), Mo-
There are two types, one of which is sintered by adding a green compact of Ni alloy, and the other of which is sintered by adding titanium nitride (TiN) to give toughness and heat resistance. Ni of the body serves as a binder. The TiC-Ni-Mo ₂ C cermet is used as a cutting tool material, inferior toughness than WC cemented carbide, but hardness, wear resistance is large, suitable for high-speed cutting.

Products such as tools and machine parts made of powder alloy are coated with CVD (chemical vapor deposition) or PV.
By D coating (physical vapor deposition), a hard film of several μ is formed on the surface of the product to further improve the wear resistance. For example, by CVD or PVD coating, a hard film of a composite ceramic mainly composed of alumina (Al ₂ O ₃ ) and a high-strength special ceramic having excellent heat resistance is formed on the surface of the powder alloy, and the carbide phase becomes finer. Ultrafine alloys have been developed. This ultra-fine particle alloy has better wear resistance than the above-mentioned powder alloy without CVD coating or PVD coating in cutting at low speed range or in cutting difficult-to-cut materials such as Inconel. Also, as another example of the aforementioned coating on the powder alloy,
A hard film of titanium nitride (TiN) with a thickness of several μm is formed on the surface of the powder alloy to further improve wear resistance and fracture resistance.

The PVD coating is 380 to
With a low temperature coating of 600 ° C, the CVD coating is a high temperature coating of 800-1000 ° C.

[0007]

In the conventional products such as tools and machine parts made of powder alloy, since the powder alloy itself is formed by compression molding various green compacts and sintering at high temperature, A minute space is created between the green compacts. For example, in the cemented carbide, the binder such as Ti, Co, C, and TiN is not completely melted and bonded to the WC, but the contact portion between the WC and the binder is pressed at a high temperature. WC
Calculating from the respective specific gravities and mixing ratios of the binder and the density of the cemented carbide, about 2 to 5% of the total volume of the powder alloy is occupied by minute spaces between the WC and the individual particles of the binder. Cermet, which is another typical powder alloy, also has a minute space between the green compacts as in the cemented carbide described above. There is a problem in that this minute space causes the settling of the edge of the tools made of the powder alloy (for example, the bite and the tip of the milling cutter) and chipping, and the durability of the product made of the powder alloy is deteriorated.

In addition, when a high temperature CVD coating is performed on the surface of a conventional powder alloy product, a low hardness binder is deposited on the surface layer of the product, which reduces the effect of the CVD coating. there were.

For example, the surface of a conventional cemented carbide is 800 to
When performing CVD coating at a high temperature of 1000 ° C, the temperature is considerably lower than the melting point (1495 ° C) of Co, which is a binder, at a temperature of about 700 ° C or higher, which is lower than the hardness of WC on the surface layer of the cemented carbide. A phenomenon that hardness Co precipitates occurs.

The reason why Co precipitates on the surface of the cemented carbide is as follows.
Since the coefficient of thermal expansion of Co is as large as 2.4 times the coefficient of thermal expansion of WC, the expansion of the volume of Co at a temperature of about 700 ° C is larger than that of WC as shown below. Therefore, C expanded near the surface layer of the cemented carbide
It is considered that this is because o escapes from the surface of the cemented carbide where there is an escape.

To explain this in more detail, the respective volumes of WC and Co at 700 ° C (t ₁ ° C) and 1000 ° C (t ₂ ° C) with respect to room temperature of 20 ° C (t ₀ ° C). The expansion rate of is shown below. However, α is a thermal expansion coefficient, and Co has a thermal expansion coefficient α of 12.3 / 10 ⁶ , W
The thermal expansion coefficient α of C is 5.1 / 10 ⁶ .

At 700 ° C. , Co volume expansion = [1 + α (t ₁ −t ₀ )] ³ = [1+ (12.3 / 10 ⁶ ) × (700-20)] ³ = 1.025 WC Expansion of volume of [= 1 + α (t ₁ −t ₀ )] ³ = [1+ (5.1 / 10 ⁶ ) x (700−20)] ³ = 1.01 Therefore, Co at room temperature of 20 ° C. and For each volume of WC, at 700 ° C the volume of WC is 1
%, But the volume of Co expands by 2.5%.

At 1000 ° C., expansion of Co volume = [1 + α (t ₂ −t ₀ )] ³ = [1+ (12.3 / 10 ⁶ ) × (1000-20)] ³ = 1.037 WC Expansion of the volume of [= 1 + α (t ₂ −t ₀ )] ³ = [1+ (5.1 / 10 ⁶ ) × (1000−20)] ³ = 1.015 Therefore, Co at room temperature of 20 ° C. and For each volume of WC, at 1000 ° C., the volume of WC expands by 1.5%, but the volume of Co expands by 3.7%.

As described above, since the expansion of the volume of Co of the binder is larger than that of WC at 700 to 1000 ° C, the surface of the cemented carbide is subjected to high temperature CVD coating at 800 to 1000 ° C. When Co. is applied, Co, which has a lower hardness than the hardness of WC, is deposited on the surface of the cemented carbide, so that the hardness of the surface layer of the cemented carbide is reduced and the original wear resistance of the CVD coating is improved. There was a problem in that

When cermet, which is another typical powder alloy, is subjected to high temperature CVD coating at 800 to 1000 ° C., it is lower than TiC as in the case of the cemented carbide described above. Ni, which is a hardness binder, is deposited on the surface of the cermet.

That is, high hardness TiC has a melting point of 32.
Whereas the binder Ni has a melting point of 1455 ° C and a thermal expansion coefficient α of 13.3 / 10 ⁶ , while the thermal expansion coefficient α is 00 ° C and the thermal expansion coefficient α is 7.6 / 10 ⁶ , For the same reason as in the case of the above cemented carbide, a phenomenon in which Ni precipitates on the surface layer of the cermet in the temperature range of the CVD coating considerably lower than the melting point of Ni (1455 ° C) occurs, and the hardness of the surface layer of the cermet increases. There is a problem in that the effect of improving the original wear resistance by the CVD coating is reduced.

The present invention was developed in order to solve the above-mentioned problems, and the structure near the surface of the powder alloy is changed and the structure between the respective powder compacts is made fine so that the powder compacts The purpose of the present invention is to improve the adhesion of the powder alloy and further improve the wear resistance and durability of the powder alloy. Further, in the case where the powder alloy is subjected to the CVD or PVD coating, the precipitation phenomenon of the binder in the surface layer of the powder alloy is reduced to improve the CVD.
Alternatively, the purpose is to improve the original effect of the PVD coating.

[0018]

In order to achieve the above object, in the method for treating the surface layer of the powder alloy of the present invention, when shots are jetted at high speed in sand blasting or shot peening, the product to be processed becomes Heat was generated on the injection surface, and it was made based on the fact that the injection surface temperature of the product rises with the increase in the injection speed of the shot, and on the surface of the product of the powder alloy consisting of multiple various powder compacts, Among the various powder compacts, a 40 to 200μ shot having a hardness equal to or higher than that of the powder compact with the highest hardness is sprayed at a spraying speed of 50 m / sec or more, and the temperature near the surface of the powder alloy is adjusted to various powder compacts. It is characterized in that the temperature rises above the recrystallization temperature of the green compact that serves as a binder in the body, and the arrangement state of the high hardness green compact near the surface of the powder alloy is changed by the pressing force of the subsequent shot. . Then P on the surface of this powder alloy
VD coating or CVD coating is applied.

[0019]

The operation will be described below by taking a cemented carbide, which is a typical powder alloy, as an example.

When the impact force of the shot raises the temperature of the surface layer of the cemented carbide and reaches the recrystallization temperature of Co, which is the powder compact of the crystallizing agent, Co of the binder is significantly softened. The individual particles of WC, which is a high-hardness green compact mixed with the softened Co, are relatively much smaller than the shot particle size, and are therefore pressed on the almost smooth surface by the impact force of the shot. And the flat surfaces of the individual particles of WC in the surface layer are aligned with the surface of the cemented carbide, and at the same time WC and C
A change in the structure of the surface layer occurs in which the space between individual particles of o is reduced and the adhesion is improved. For this reason, individual particles of WC are less likely to delaminate from the surface of the cemented carbide.

Further, CVD or PV is applied to the surface of the cemented carbide which has been sandblasted or shot peened.
Even when D coating is performed, expanded Co does not precipitate on the surface of the cemented carbide because the surface of each particle of WC in the surface layer is smoothed and the structure between the WCs is in close contact.

[0022]

EXAMPLE A typical cemented carbide powder alloy will be described below with reference to the drawings, and other powder alloys such as cermet will be omitted.

Cemented carbide tips for milling (hereinafter,
The surface of the "carbide chip") was subjected to a blasting treatment using a gravity blasting apparatus 30 (hereinafter referred to as "gravity apparatus") as shown in FIG. A direct pressure type blasting machine may be used as the blasting machine.

In the gravity type device 30, a nozzle 32 for ejecting an abrasive 36 such as shot is provided in a cabinet 31 having an entrance / exit 35 for taking in / out a workpiece W, and a pipe 44 is connected to the nozzle 32. The pipe 44 communicates with a compressor (not shown), and compressed air is supplied from the compressor. A hopper 38 is provided in the lower part of the cabinet 31, and the lowermost end of the hopper 38 communicates with the upper side surface of a recovery tank 33 installed above the cabinet 31 via a conduit 43, and the lower end of the recovery tank 33 connects a pipe 41. It is communicated with the nozzle 32 via the. The abrasive in the recovery tank 33 receives gravity or a predetermined pressure, falls from the recovery tank 33, and is injected into the cabinet 31 together with the compressed air supplied to the nozzle 32 through the pipe 44.

In the recovery tank 33, the abrasive material 36 has a hardness H _RC 65 which is higher than the hardness of the green compact of WC of the cemented carbide of the base material of the cemented carbide chip as the workpiece W and the shot grain size. Is a 44 μm hard bead. In this example, the shot uses spherical ceramic beads made of glass and ceramic. However, spherical glass beads having a hardness of WC or higher, which is a high hardness green compact of cemented carbide, or spherical glass beads or Other materials such as stainless steel may be used.

A workpiece W, a cemented carbide chip, is put into the cabinet 31 through the inlet / outlet 35, and the shot is jetted from the nozzle 32 at a jetting pressure of 6 kg / cm ² , a jetting speed of 80 m / sec, and a jetting distance of 100 mm. It is jetted for 10 to 20 seconds. In particular, 5 to the corner of the tip of the carbide tip
It is jetted for 6 seconds.

The sprayed abrasive 36 and the dust 37 generated at this time are transferred to the hopper 38 at the bottom of the cabinet 31.
And then rises by the ascending air current generated in the conduit 43 and is sent into the recovery tank, where the abrasive 36 in the recovery tank is recovered. The dust 37 in the recovery tank 33 is guided by the air flow in the recovery tank 33 from the upper end of the recovery tank 33 to the dust collector 34 through the pipe 42 and accumulated at the bottom of the dust collector 34, so that normal air is collected in the dust collector 34. It is discharged from the blower 39 provided at the upper part.

The above blasting processing conditions are summarized in the table below.

[0029]

Table 1 Example 1

The temperature in the vicinity of the surface of the cemented carbide chip blasted under the above conditions rises, the structure of the surface layer of the cemented carbide changes, and a cemented carbide chip having more excellent durability and wear resistance is obtained. The result was reached.

FIG. 2 is an enlarged view of an enlarged corner portion of the tip of the cemented carbide tip for milling after the blasting treatment under the above-mentioned conditions of this embodiment. Compared with the enlarged view of the corner portion of the tip of the cemented carbide tip, that is, the tip of the cemented carbide tip before the blasting treatment, the surface roughness of the corner portion of the tip of the cemented carbide tip of this example is obviously smaller, There is a marked difference compared to the carbide tip. In FIGS. 1 and 2, the white portion near the tip of each cemented carbide tip is caused by the reflection of light on the surface of the cemented carbide tip when a micrograph is taken.

Further, FIG. 3 is a vertical cross-sectional metallographic view of the corner portion of the tip of the conventional cemented carbide tip, and FIG. 3 is a vertical metallographic view of the corner portion of the tip of the cemented carbide tip of this embodiment. Comparing with No. 4, a large difference is seen in the surface roughness and texture of the surface layer. In the cemented carbide tip of the present example, the surface roughness is remarkably small as compared with the conventional cemented carbide tip, and the texture in the vicinity of the surface layer is such that each particle is miniaturized and the arrangement of the particles is uniform. There is.

Further, using the above-mentioned cemented carbide tip obtained in this embodiment, Inconel, which is a typical hard metal material having excellent heat resistance and wear resistance and which is extremely hard and difficult to cut, is used as a milling object. When processed, the following good results were obtained.

The cutting speed of the object to be cut is 1
If the milling process of cutting at a cutting length of 500 mm and a reciprocating time of 10 minutes at 00 mm / min is defined as one pass, the conventional cemented carbide tip cannot be used in one pass. The hard tip was usable up to 5 passes.

That is, the cemented carbide tip of this embodiment has a life of 5 times that of the conventional cemented carbide tip, and the durability of the cemented carbide tip itself is significantly improved.

Further, the cemented carbide tip of this example had better machinability than the conventional cemented carbide tip. As a result, the surface roughness and the variation in the size of the processed surface of the work piece cut by the carbide tip of the present example are smaller than those of the conventional work piece by the carbide tip, and the work piece of good quality is cut. You can get things.

As an example, using a cemented carbide bit having the cemented carbide tip of the present embodiment and a cemented carbide bite having a conventional cemented carbide tip, the diameter of the material of S45C is 75-
120 objects to be cut by a lathe at 750 rpm. When the lathe was rotated under the same machining conditions with a cutting depth of 2 mm from the outer periphery of the object to be cut, the following remarkable differences were observed. In addition, this example is an example of an experiment conducted to see the difference in machinability between this embodiment and the conventional cemented carbide tip. When the dimension of the object to be cut was measured after continuously cutting the object to be cut for 30 minutes, the variation in the dimension of the object to be cut was 15μ in the conventional cemented carbide tool, but in the cemented carbide tool of this example. It was 5μ.

When the dimension of the object to be cut was measured after continuously cutting the object to be cut for 60 minutes, the variation in the dimension of the object to be cut was 38 μ in the conventional cemented carbide bite. For the hard bite, it was 22μ.

From the above, the cemented carbide tip of the present embodiment has improved wear resistance, effect of suppressing the constituent cutting edge, chipping resistance, etc., and the quality of the cemented carbide tip itself has been improved as a whole. As a result, it is considered that the excellent effect that the quality of the object to be cut by the carbide tip of the present example is improved was obtained.

Further, the reason why the above-described good result is obtained in this embodiment will be described below. First, the temperature rise when the shot is sprayed on the surface of the workpiece W made of a metallic object will be described. The change in velocity before and after the collision of the shot depends on the hardness of the workpiece W and the shot. However, the speed decreases after the collision. Due to the law of energy invariance, most of this speed change is converted into thermal energy in addition to sound. The thermal energy is considered to be internal friction due to the deformation of the collision portion at the time of collision, but heat is exchanged only at the deformed portion where the shot has collided, so the temperature becomes high locally.

That is, the weight of the portion which is deformed by the shot and rises in temperature increases in proportion to the velocity of the shot before the collision, but the ratio to the total weight of the workpiece W is small, so that the temperature rises. Occurs locally near the surface of the workpiece W.

Incidentally, the coefficient of restitution e is close to 1 in a collision when the surface hardness of both the shot and the workpiece W is high, but in this case the deformed portion is small and the temperature becomes higher locally.

Since the temperature rise is proportional to the speed of the shot before the collision, it is necessary to increase the shot injection speed, and the smaller shot diameter of 40 μ to 200 μ is 5.
It can be jetted at a high speed of 0 m / sec or more, and the temperature rise on the surface of the workpiece W can be made uniform.

However, if the workpiece W is a metal object having a hardening effect such as carbon tool steel, the surface layer of the base material of the carbon tool steel is locally hardened by the temperature rise due to the impact force of the shot. Although it is possible to increase the surface hardness, it was not always possible to expect a treatment effect on a metal object such as a powder alloy having a high hardness and no quenching effect. However, the inventor of the present application has repeatedly conducted an experiment in which a metal object made of a powder alloy is subjected to blasting, and has obtained the favorable result as described above.

When the surface of the cemented carbide is blasted under the above conditions, the temperature of the surface layer of the cemented carbide rises due to the impact force of the shot, and the temperature at which Co of the binder is significantly softened, that is, the recrystallization temperature of Co. The temperature reached above 700 ° C and this C
Only when o becomes a softened state, the impact force of the shot further changes the arrangement state of the green compacts of WC and Co of the surface layer, and other than the temperature rise of the surface layer of the cemented carbide. Be effective.

The approximate size of tungsten carbide (WC) is 1
.About.2 μ or less, which is much smaller than the shot grain size of 44 μ, so that W mixed with softened Co is mixed.
C becomes almost the same as the state of being pressed on a smooth surface.
That is, since a shot having a volume of 10,000 times or more of the WC collides with the WC at a high speed, the impact force per unit area of each WC particle becomes very large, and therefore the surface layer of the cemented carbide is formed. When the temperature rises to reach the recrystallization temperature of Co and the Co is softened, the impact force of the shot changes the orientation of the individual particles of WC in the surface layer, and
The flat surface of the C particles is aligned with the surface of the cemented carbide. At the same time, the individual particles of WC receive a large impact force (per unit area) due to a shot of a relatively large volume, and the binder is miniaturized. It decreases and the texture between the individual particles of WC and Co adheres.

Therefore, in the cemented carbide tip of the present embodiment, the surface of the WC particles is smoothed as described above, and each green compact W
Since the structure between the individual particles of C and Co adheres and the individual particles of WC are less likely to separate from the surface of the cemented carbide, the WC falling off during cutting is reduced and the durability of the cemented carbide tip is reduced. It is considered that the sex has increased.

In fact, as described above, comparing the texture states of the surface layers of the conventional and the cemented carbide chips of the present embodiment with reference to FIGS. It can be seen that the tissues between the particles are in close contact.

When the blast-processed cemented carbide was subjected to high temperature CVD coating at 800 to 1000 ° C., almost no precipitation of Co was observed in the surface layer of the cemented carbide. Therefore, unlike the conventional cemented carbide having CVD coating, the cemented carbide chip of the present embodiment reduces the original effect of CVD coating, that is, the effect of improving the wear resistance of the powder alloy by CVD coating. Good results were obtained.

As an example, CVD and TiC and TiN having a thickness of 3 .mu.
After the coating, the crankshafts of automobile parts were cut using these carbide tips, respectively, and it was possible to produce 60 crankshafts with the conventional carbide tips. Carbide chips could produce 120 crankshafts.

Also in terms of the surface roughness and dimensional accuracy of the crankshaft of the object to be cut, the carbide tip of this example provided an object of better quality than the conventional carbide tips.

As described above, the reason why good results were obtained with the carbide coating of this embodiment coated with CVD is that, as described above, the temperature of the surface layer of the carbide tip is changed by the impact force of the shot. When the recrystallization temperature of the binder Co is reached, the surface of the individual particles of WC in the surface layer is smoothed and
Since the microstructure of Co adheres as the structure between the two adheres to each other, even if Co intervening between WC of the surface layer is expanded by applying CVD coating to the surface of this cemented carbide chip, It is considered that this is because the effect of suppressing the precipitation of Co was obtained.

Even when products such as tools and machine parts made of cermet are shot peened under the above-mentioned conditions, the same effect is recognized for the same reason as for the cemented carbide.

[0054]

Since the present invention is constructed as described above, it has the following effects.

(1) The binder in the vicinity of the surface of the powder alloy can be changed so as to be fine and the minute space between the green compacts can be reduced to improve the adhesion of the structure between the green compacts. ,
It was possible to further improve the wear resistance and durability of the powder alloy.

(2) During the cutting process, the surface of the high hardness green compact of the surface layer of the powder alloy is precisely smoothed so that the flat surface of the high hardness green compact is aligned with the surface of the powder alloy. It was possible to reduce the possibility of the high-hardness green compact falling off and further improve the wear resistance and durability of the powder alloy.

(3) Further, in the cutting tool of the powder alloy subjected to the blasting treatment by the treatment method of the surface layer of the powder alloy, the mechanical properties such as wear resistance, the effect of suppressing the constituent cutting edge, and the chipping resistance are Since it is improved as a whole, it is possible to improve the quality characteristics such as the dimensional accuracy and surface roughness of the work to be cut by the cutting tool.

(4) Because of the reason described in (2) above, the texture between the high hardness green compacts of the surface layer of the powder alloy is brought into close contact with each other, so that even if high temperature CVD coating is applied to the surface of the powder alloy. , The precipitation phenomenon of the binder existing between the high hardness green compacts on the surface of the powder alloy can be reduced, and the CVD
It was possible to further improve the wear resistance and durability of the powder alloy without impairing the effect of the coating.

[Brief description of drawings]

FIG. 1 is an enlarged view based on a micrograph (× 105) of a surface of a corner portion at a tip of a cemented carbide chip before blasting treatment of the present invention.

FIG. 2 is an enlarged view based on a micrograph (× 105) of the surface of the corner portion at the tip of the cemented carbide tip after the blasting treatment of the present invention.

FIG. 3 is a structural diagram based on a micrograph (× 1400) of a metal structure of a vertical cross section near the surface of a corner portion at the tip of a carbide tip before blasting treatment of the present invention.

FIG. 4 is a structural diagram based on a micrograph (× 1400) of a metal structure of a vertical cross section near the surface of a corner portion at the tip of a cemented carbide chip after the blasting treatment of the present invention.

FIG. 5 is an overall view of a gravity type blasting apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 30 Gravity Blasting Machine 31 Cabinet 32 Nozzle 33 Collection Tank 34 Dust Collector 35 Inlet / Outlet 36 Abrasive 38 Hopper 39 Blower 41 Pipe 42 Pipe 43 Pipe 44 Pipe

Claims (6)

[Claims] 1. A jet speed of 40 to 200 .mu.m having a hardness equal to or higher than that of a green compact having the highest hardness among various green compacts is sprayed on the surface of a powder alloy product composed of a plurality of various green compacts. Spraying at 50 m / sec or more to raise the temperature near the surface of the powder alloy to a temperature higher than the recrystallization temperature of the green compact as a binder among various green compacts. Processing method. 2. A shot of 40 to 200 .mu. Having a hardness equal to or higher than the hardness of the high hardness green compact is sprayed on the surface of a powder alloy product comprising a high hardness green compact and a binder green compact. Spraying at a speed of 50 m / sec or more to raise the temperature near the surface of the powder alloy above the recrystallization temperature of the powder compact of the binder, and the high hardness near the surface of the powder alloy by the pressing force of the subsequent shot. A method for treating a surface layer of a powder alloy, characterized in that the arrangement state of the green compact is changed. 3. The method for treating a surface layer of a powder alloy according to claim 1, wherein the injection speed is preferably 80 m / sec or more, and the shot has a shot grain size of 44 μ and a shot hardness of H _RC 65. 4. The method for treating a surface layer of a powder alloy according to claim 1, 2 or 3, wherein the powder alloy is cemented carbide or cermet. 5. A jet speed of 40 to 200 μ having a hardness equal to or higher than the hardness of the green compact having the highest hardness among various green compacts is sprayed on the surface of a powder alloy product composed of a plurality of various green compacts. Spraying at 50 m / sec or more to raise the temperature in the vicinity of the surface of the powder alloy above the recrystallization temperature of the green compact as a binder among various green compacts, and then PVD coating or A method for treating a surface layer of a powder alloy, which comprises applying a CVD coating. 6. A shot of 40 to 200 μ having a hardness equal to or higher than the hardness of the high hardness green compact is sprayed on the surface of a powder alloy product comprising a high hardness green compact and a binder green compact. Spraying at a speed of 50 m / sec or more to raise the temperature near the surface of the powder alloy above the recrystallization temperature of the powder compact of the binder, and the high hardness near the surface of the powder alloy by the pressing force of the subsequent shot. 2. A method for treating a surface layer of a powder alloy, which comprises changing the arrangement state of the green compact and then applying PVD coating or CVD coating to the surface of the powder alloy.