JPH0398765A - Manufacture of metal bonded tool - Google Patents

Abstract

PURPOSE:To disperse a micro deposit of carbon uniformly in alloy powder by melting iron base alloy powder forming a matrix and powdering the obtained molten metal as well as cooling it at the same time rapidly at the cooling speed of over 10 deg.C per second so as to prepare the iron base alloy powder. CONSTITUTION:At the time of manufacturing a metal bonded tool provided with an abrasive grain layer formed of a sintered body of iron base alloy powder containing carbon and abrasive grain, an iron base alloy is melted, and the obtained molten metal is powdered and at the same time cooled down to the temperature of 200 deg.C or less at the cooling speed of over 10 deg.C per second. The mixture of the obtained iron base alloy powder and abrasive grain is integrally sintered so as to form the abrasive grain layer, thus obtaining the desired metal bonded tool.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides a metal having an abrasive grain layer consisting of a sintered body of an iron-based alloy containing carbon and abrasive grains having high hardness. Regarding the manufacturing method of bond tools, in particular, it is possible to uniformly disperse microscopic carbon in the material, which improves lubricity during grinding, improves matrix strength, and extends life. It relates to a method for manufacturing tools.

(Prior technology) Metal pound diamond tools that use diamond abrasive grains are conventionally used as grinding tools for grinding and finishing high-hardness fine ceramics such as aluminum oxide, silicon nitride, aluminum nitride, and silicon carbide. more widely used.

In addition, cubic boron nitride (hereinafter referred to as rCBN) is used as an abrasive grain in grinding and finishing of difficult-to-cut alloy materials such as high-speed steel and martensitic stainless steel containing vanadium (V).
It is abbreviated as J. ) dispersed in a matrix have been used.

Among the above-mentioned metal bond tools, for example, metal bond diamond tools that use diamond powder as abrasive grains are generally made by mixing diamond powder abrasive grains with metal powder and metal powder containing a metal compound if necessary, and then sintering the abrasive grains. It is formed. This sintering operation improves the bonding force and mechanical strength between the matrix and the diamond powder abrasive grains, and the resulting metal bonded diamond tool is
It is used as a polishing and grinding tool while regenerating the surface of the whetstone by dressing it appropriately.

By the way, in the case of metal-bonded diamond tools that are suitable for heavy-duty grinding with large depths of cut, the raw material for the matrix is powder obtained by pulverizing chips of iron-based alloy casting material with a high carbon content using a ball mill or stamping method. is used. Diamond abrasive grains are uniformly mixed with this high carbon iron-based alloy powder, and the mixture is heated to a temperature of 800 to 900' in a vacuum or in a protected atmosphere with an inert gas such as argon.
C. Hot pressing is performed at a pressure of about 200 to 400 kg/cfl to form an abrasive layer. Carbon particles are fixed and dispersed around the abrasive grains. The carbon particles act as a lubricant that reduces grinding resistance with the object to be ground, while the matrix acts as a holding material that supports and fixes the diamond abrasive grains.

(Problems to be Solved by the Invention) However, iron-based alloy powder obtained by crushing chips of alloy casting materials using conventional manufacturing methods has a low cooling rate during casting, so the size of carbon precipitates is small. is several tens of μm to several hundred μm
It is larger than the average particle size of the abrasive grains (several μm to 100 μm), and is non-uniform in shape, and does not have a finely dispersed structure in the matrix.

Therefore, the carbon particles held in the powder are likely to fall off during the crushing operation, resulting in uneven distribution and shape of carbon in the powder. In tool materials whose matrix is formed from this iron-based alloy powder, the diameter of carbon precipitates is large, so carbon precipitates tend to fall off during grinding, and shavings and polishing debris are deposited in the depressions formed by the falling off. This builds up and causes clogging, which further causes damage to the matrix and plastic deformation due to seizure.

In addition, due to the formation of depressions near the abrasive grains, the retention strength of the abrasive grains rapidly decreases, and diamond abrasive grains rapidly fall off, leading to a decrease in grinding and polishing efficiency, and furthermore, high finishing accuracy cannot be obtained. was there.

In addition, in the conventional manufacturing process for metal-bonded diamond tools, carbon particles such as graphite are added, compression molded, and then sintered to disperse carbon particles in the sintered body. However, it has been difficult to uniformly disperse fine carbon grains throughout the abrasive grain layer. As a result, many carbon precipitates and abrasive grains fall off, which reduces the efficiency of grinding and polishing processes, making it impossible to obtain high finishing accuracy, and posing the fundamental problem that the life of the grinding wheel itself is short.

The present invention was made to solve the above-mentioned problems, and by uniformly dispersing fine carbon particles in the material, it improves lubricity during grinding, increases the strength of the matrix, and improves the abrasive grains and lubricant. The purpose of the present invention is to provide a method for manufacturing a metal bond tool that can produce an economical metal bond tool that has a long lifespan, has less carbon particles falling off, and can perform grinding and polishing processes with high efficiency. shall be.

[Structure of the invention]

(Means and effects for solving the problem) The inventors of the present application discovered that the conventional problem was caused by the form of carbon in the matrix. Aiming to obtain a metal-bonded tool, a method of dispersing fine carbon particles in the matrix material was investigated, and the influence of the type of grinding wheel on the polishing properties of the abrasive layer was also studied.

As a result, the iron-based alloy that is the raw material is melted, the resulting molten metal is powdered, and at the same time the cooling rate is 200°C or higher at a cooling rate of 10°C or more per second.
When the resulting mixture of iron-based alloy powder and abrasive grains is cooled to a temperature below ℃ and then sintered together to form an abrasive layer, the grinding properties are significantly improved compared to conventional methods. We were able to obtain a metal bond tool with excellent long life.

In addition, the blending amount of silicon content (Awt%) and carbon content (Bwj%) in the iron-based alloy powder should be adjusted to satisfy the following relational expressions: 2.5≦B≦4.5 3≦B+A/3≦5 When the setting was set to

The present invention has been made based on the above findings. As the iron-based alloy powder used in the method of the present invention, an alloy material is used in which Fe is used as a base material and elements such as carbon, which serves as a lubricant, and silicon, which promotes the precipitation of carbon, are added.

Iron-based alloy powder is prepared by heating and melting an iron-based alloy, pulverizing it, and cooling it at the same time.

Generally, there are methods for powdering and cooling iron-based alloys, such as dropping molten metal into water and turning it into powder, or heating it to a semi-molten state and rapidly stirring it, but the raw material powder obtained by the above method is Since the particles are large, about 250 μm in size, have a complicated shape, and contain a large amount of oxide, it is desirable to use the molten metal spraying method (atomization method) described below.

In this molten metal spraying method, molten metal of iron-based alloy is pulverized by blowing compressed air of 2 to 10 atm, inert gas, or other pulverizing gas through an alumina injection nozzle, and the molten metal is pulverized into a water tank located below the nozzle. It is a method of accumulating in the nozzle opening amount,
By adjusting the injection rate of the molten metal, the pressure and temperature of the powdering gas, etc., it is possible to change the particle size, particle size distribution, and cooling rate of the powder, allowing raw material powder with the desired particle size and crystal structure to be produced. This is the way to get it.

In the method of the present invention, the iron-based alloy is pulverized and simultaneously cooled rapidly to a temperature of 200°C or less at a cooling rate of 10°C or more per second. Slow cooling at a cooling rate of less than 10 degrees Celsius per second will cause carbon precipitates to become coarser, reducing its function as a lubricant when used as a tool, while abrasive grains will frequently fall off, reducing grinding and polishing efficiency. In addition, high finishing accuracy cannot be obtained.

On the other hand, when rapidly cooled at 10°C or more per second, minute carbon precipitates are evenly dispersed within the alloy powder, making it possible to form a tool with a long life without reducing the retention strength of the abrasive grains. .

Further, the alloy powder after being sprayed with the molten metal needs to be sufficiently cooled to a temperature of 200° C. or lower. This is because, in a high temperature state where the powder is cooled to a temperature exceeding 200° C., the elements within the powder are still actively diffusing and moving, and the coarsening of carbon precipitates progresses.

Further, the average particle size of the alloy powder to be prepared is preferably 150 μm or less and 1/3 or less of the average particle size of the abrasive grains.

The average particle size exceeds 150 μm, and the average particle size of the abrasive grains exceeds 150 μm.
This is because if it exceeds /3, the distribution of abrasive grains in the matrix becomes uniform, the retention strength of the abrasive grains also decreases, and the grinding and polishing ability of the tool tends to decrease.

Further, in the present invention, the carbon content in the iron-based alloy powder forming the matrix is set at 2.5% by weight or more and 4.5% by weight or less. This is because if the carbon content is less than 2.5%, self-lubricating properties will be reduced, the strength as a matrix metal will be reduced, and diamond, which is an abrasive grain, will be eluted into the iron base material.

On the other hand, if the carbon content exceeds 4.5% by weight, the strength as a tool decreases, so the carbon content (Bwj%) is
．． It is set in the range of 5≦B≦4.5.

As described above, the iron-based alloy used in the present invention may be one containing carbon within the range described above. The effects of the present invention can be obtained by controlling the size, and as long as it is an iron-based alloy that is used for the matrix of ordinary tools, it may contain inevitable impurities such as Mn and Mg. Its composition does not matter.

However, when silicon is used as the alloy composition, and silicon is added in a weight ratio of A% and carbon is B% in the matrix, if it is added in the range of 3≦(B+A/3)≦5, silicon will absorb the cementite matrix. It is destabilized to facilitate the formation of carbon (graphite), forming finer carbon precipitates, which can increase the strength and lubricity of the matrix.

If it is less than the range of the above relational expression, the effect of carbon precipitation will be small and the substrate will be likely to become cementite.

Moreover, if it exceeds this range, sinterability will deteriorate.

This amount of silicon is 1.Owl% to 3.0%. 5wj% is preferable. If the amount of silicon is less than 1.0%, carbon precipitation and grain size become non-uniform, and at the same time, it is difficult to obtain sufficient strength as a tool. On the other hand, if the amount of silicon exceeds 3.5%, the ferrite phase that occupies the main part of the matrix metal is transformed and hardened, resulting in a decrease in sinterability and a tendency to reduce strength.

Further, as the abrasive grains, CBN may be mixed in addition to diamond powder. diamond and cb
The Knoop hardness of N is 850 0. 5 1
All have extremely high hardness of 0.0 kg/mtA or more, and are useful as abrasive grains for processing difficult-to-grind materials. Especially CB
Since N abrasive grains have excellent heat resistance, their use is rapidly expanding as abrasive grains for dry machining that do not use a coolant.

As mentioned above, an abrasive grain layer is formed by sintering a mixture of an iron-based alloy powder in which fine carbon is uniformly precipitated and diamond and/or CBN used as abrasive grains. , a metal bond tool is manufactured by joining the abrasive grain layer and the alloy part.

The sintering operation is preferably carried out in a non-oxidizing atmosphere at about 1000-180°C. F when the sintering temperature is less than 1000℃
It takes a long time to diffuse Si and C in e, making it difficult to obtain an abrasive grain layer with sufficient strength. On the other hand, if the temperature exceeds 1180°C, a liquid phase is generated, which causes an interfacial reaction with the abrasive grains, which tends to cause a decrease in the strength of the abrasive grain layer.

From this point of view, when pressure sintering is used, low-temperature sintering at 850° C. or higher is possible, and interfacial reactions are less likely to occur, compared to the above-mentioned normal pressure sintering. Furthermore, there is little dimensional change in the sintered body,
Truing can be simplified.

The pressing force is set to 50 kg/c/ or more in order to promote formability and mutual diffusion during sintering. However, even when pressure sintering is performed, the sintering temperature is 850°C.
If it is less than 0.degree. C., it takes a long time to diffuse silicon and carbon into the iron base material, making it difficult to obtain sufficient strength. Therefore, the pressure sintering temperature is set in the range of 850 to 11,800C.

As described above, according to the method for manufacturing a metal bond tool according to the present invention, the iron-based alloy powder forming the matrix is once melted, and the resulting molten metal is pulverized at a rate of 10°C per second.
Iron-based alloy powder is prepared by rapid cooling at the above cooling rate. Therefore, fine carbon precipitates can be uniformly dispersed within the alloy powder. Therefore, there is no reduction in the retention strength of the abrasive grains by the matrix, and it is possible to maintain sufficient lubricity, and the life of the tool can be significantly extended.

Further, since the temperature of the alloy powder after rapid cooling is set to 200° C. or lower, diffusion of alloy constituent elements after cooling is small, and coarsening of carbon precipitates can be prevented.

Additionally, by adding silicon, which destabilizes cementite and makes graphite precipitates more likely to form, it becomes possible to uniformly form more stable and fine carbon precipitates in the alloy powder, increasing the strength of the bond material. The interfacial bonding force with the abrasive grains can be improved.

In addition, the metal powder that forms the matrix and the highly hard abrasive grains made of at least one of diamond and CBN are firmly bonded by sintering to form the abrasive grain layer, so the retention force of the abrasive grains is large. , it is possible to obtain a good ground surface and extend the life of the tool. Note that by using diamond and CBN together as abrasive grains, the range to be ground can be widened.

In addition, since fine carbon precipitates are uniformly dispersed in advance in the iron-based alloy powder that forms the matrix, even after sintering, the carbon grains as a lubricant are uniformly distributed around the abrasive grains. be able to.

Therefore, the lubrication function during grinding is fully demonstrated, the strength of the matrix as a supporting material is ensured sufficiently, and abrasive grains are prevented from falling off. As a result, it is possible to maintain high grinding efficiency at all times, and the abrasive grain layer The lifespan of can be significantly extended.

(Examples) Next, the present invention will be described in more detail with reference to the following examples.

Examples 1 to 3 and Comparative Examples 4 to 6 First, as Examples 1 to 3, an iron-based alloy was heated to form a molten metal, and this molten metal was jetted together with compressed air for powdering from an injection nozzle of a molten metal spray device. At the same time, the powder was pulverized and rapidly cooled to 200°C to obtain an iron-based alloy powder consisting of 3.0% by weight of carbon, 1.5% by weight of silicon, and the balance iron, with an average particle size of 30 μm, as shown in Table 1. . At this time, the cooling rate is 10
,20,30°C/see.

Next, iron-based alloy powder 8 obtained by the above molten metal spraying treatment
20% by weight of diamond abrasive grains having an average particle diameter of 100 μm were uniformly mixed with 0% by weight.

Furthermore, a mold space having an outer diameter of 80 mm and an inner diameter of 15 mm was filled with the mixture having the above composition, and sintering was performed in a vacuum by a hot press method. In the sintering operation, the temperature was raised to 900° C. while applying a pressure of 400 kg/ctl, and after holding for 30 minutes, processing was performed to form a diamond tool with a width of 10 mm.

Also, Comparative Example 4. 5. As for 6, raw materials having the same alloy structure as in Examples 1 to 3 were used, the molten metal spraying device was operated, and the cooling rate was set to 3°C/sec and 7°C/s, respectively.
The temperature was rapidly cooled to 200°C at a cooling rate of 20°C/sec (Comparative Examples 4 and 5), and the
The material rapidly cooled to ℃ (Comparative Example 6) was mixed with diamond abrasive grains, sintered, and processed into a diamond tool with an outer diameter of 80 mm, an inner diameter of 15 mm, and a width of 10 mm.

Using the diamond tools of Examples 1 to 3 and Comparative Examples 4 to 6 thus obtained, Vickers hardness machining of 700 S
Grinding of i3N4 was performed.

Grinding conditions are rotation speed 300 rpm, feed speed 5 m.
/min, grinding width 10mm, cutting depth 0.25m
It was set to m.

The grinding test results obtained in this way are shown in Examples 1 to 3 in Table t.
, shown in the right column corresponding to Comparative Examples 4 to 6.

The grinding ratio shown in Table ↑ is expressed as the ratio of the amount of material removed to the amount of wear on the grinding wheel.

As can be seen from the results in Table 1, in the molten metal spraying process,
The precipitated carbon in the iron-based alloy powder prepared by setting the cooling rate to 10°C/sec or higher is extremely fine and is uniformly dispersed in the matrix. Diamond whetstone has a cooling rate of 10℃
It can be seen that the grinding ratios are higher in all cases than in Comparative Example 4.5, which was processed at less than /sec, indicating that the grinding ratios are longer.

On the other hand, since the alloy powders shown in Comparative Examples 4 and 5 have a slow cooling rate, it is observed that the carbon precipitates tend to become coarser and the grinding ratio decreases.

In addition, as shown in Comparative Example 6, the cooling rate was set to 20°C/see.
It can be seen that even if the temperature after cooling is set to a high value of 300°C, the diffusion of elements inside the powder will continue even after cooling, and the precipitated carbon will become coarser, resulting in a slight decrease in the grinding ratio. .

Examples 7-10 and Comparative Examples 11-14 Next, Examples 7-10
10 and Comparative Examples 11 to 14, an iron-based alloy was melted, and the obtained molten metal was subjected to a molten metal spraying device to be powdered, and at the same time, the temperature was adjusted to 1. It was rapidly cooled to 80'C. The cooling rate at this time was 20° (::/secC).

By this molten metal spraying treatment, an iron-based alloy powder having a composition shown in the left column of Table 1 and having an average particle size of 30 μm was obtained.

Next, 20% by weight of CBN with an average particle size of 100 μm was added to 80% by weight of the obtained iron-based alloy powder, and the uniformly mixed mixture was sintered under the same conditions as in Examples 1 to 3. Sintered, outer diameter 80mm, inner diameter ↓5mm, width 10mm
A CBN grinding wheel was formed.

Using the CBN grindstones obtained in Examples 7 to 10 and Comparative Examples 11 to 14, grinding of cemented carbide was carried out under the same processing conditions as in Examples 1 to 3, and the grinding ratio was measured. The influence of the amount of carbon and silicon added on the grinding properties was investigated. The grinding test results are shown in the corresponding right column of Table 1.

As can be understood from the results shown in Table 1, even when CBN abrasive grains are used, the carbon content is 2.5 to 4.5% by weight.
, Examples 7 to 10 using iron-based alloy powder containing silicon in the range of 1.0 to 3.5% by weight have better grinding ratios than Comparative Examples 11 to 14, which are outside the above range. . In Comparative Examples 11 to 14, the iron-based alloy powder was adjusted by rapid cooling, so the particle size of the precipitated carbon in the alloy was fine, but the strength of the matrix decreased due to excess or deficiency of carbon or silicon. Therefore, there is a tendency for the grinding ratio to decrease.

Example 15 and Comparative Example 16 Next, in Example 15, an iron-based alloy consisting of 3.6% carbon, 1.1% silicon, and the balance iron was heated and melted, and the resulting molten metal was injected into a molten metal spraying device. It is ejected from the injection nozzle together with compressed air, and at the same time it is pulverized and cooled at a cooling rate of 40°C/sec.
It was rapidly cooled to 50°C.

The obtained iron-based alloy powder has carbon 3.5 as shown in Table 1.
%, silicon 1.0%, balance iron, average grain size 28μ
It was m.

Diamond abrasive grains (average particle size 100 μm) and CBN abrasive grains (average particle size 100 μm) were added as abrasive grains at a weight ratio of 9=1 to 75% by weight of the thus obtained iron-based alloy powder.
The proportions of 22.5% by weight and 2.5% by weight were mixed, and the obtained mixed powder was subjected to the same sintering process as in Examples 1 to 3 to form a diamond CBN composite grindstone. .

In Comparative Example 16, an alloy powder obtained by crushing a cast material having the same composition as the iron-based alloy powder obtained in Example 15 to 28 μm by a stamping method was used, and a similar sintered body composition,
A diamond CBN composite grindstone was formed under sintering conditions.

Diamond C obtained in Example 15 and Comparative Example 16
When a Si3N4 grinding test was carried out using a BN composite grindstone under the same processing conditions as in Examples 1 to 3, the results shown in the right column of Table 1 below were obtained.

[Margin below]

As can be seen from the results in Table I, diamond abrasive grains and CB
Example 1 using iron-based alloy powder formed by molten metal spraying even when mixed abrasive grains with N abrasive grains are used
In tool No. 5, the grain size of precipitated carbon in the alloy is fine. Therefore, the roughness of the ground surface is small, it is possible to perform a good finish, and it is possible to ensure a particularly high grinding ratio.

On the other hand, even though the alloy and powder have the same composition as Example 15, the cooling rate was slow in Comparative Example 16, which used iron-based alloy powder obtained by crushing a conventionally cast material by stamping. It can be seen that the carbon particle size becomes coarse and a sufficient grinding ratio cannot be obtained.

〔Effect of the invention〕

As explained above, according to the method for manufacturing a metal bonded tool according to the present invention, the iron-based alloy powder forming the matrix is once melted, and the resulting molten metal is powdered and at the same time
Iron-based alloy powder is prepared by rapid cooling at a cooling rate of 0° C. or higher. Therefore, fine carbon precipitates can be uniformly dispersed within the alloy powder. Therefore, there is no reduction in the retention strength of the abrasive grains due to the matrix, it is possible to maintain sufficient lubricity, and the grinding ratio is large, making it possible to significantly extend the life of the tool.

Further, since the temperature of the alloy powder after rapid cooling is set to 200° C. or lower, diffusion of alloy constituent elements after cooling is small, and coarsening of carbon precipitates can be prevented.

Furthermore, by adding silicon, which destabilizes cementite and facilitates the formation of graphite precipitates, it becomes possible to uniformly form more stable and fine carbon precipitates in the alloy powder, improving the strength of the bond material. The interfacial bonding force with the abrasive grains can be improved.

In addition, since the abrasive layer is formed by firmly bonding the metal powder that forms the matrix and the highly hard abrasive grains made of at least one of diamond and CBN through sintering, the retention force of the abrasive grains is increased. A large and good ground surface can be obtained, and the life of the tool can be extended. Note that by using diamond and CBN together as abrasive grains, the range to be ground can be widened.

In addition, since fine carbon precipitates are uniformly dispersed in advance in the iron-based alloy powder that forms the matrix, even after sintering, the carbon grains as a lubricant can be uniformly distributed around the abrasive grains. I can do it.

Therefore, the lubrication function during grinding is fully demonstrated, the strength of the matrix as a support material is ensured, and the falling off of abrasive grains is suppressed, resulting in a significantly higher grinding ratio compared to conventional methods. Because of this increase, the life of the abrasive layer can be significantly extended.

Claims (1)

[Claims] 1. In a method for manufacturing a metal bond tool having an abrasive grain layer made of a sintered body of carbon-containing iron-based alloy powder and abrasive grains, At the same time as the molten metal is powdered, it is cooled to a temperature of 200°C or less at a cooling rate of 10°C or more per second, and then the resulting mixture of iron-based alloy powder and abrasive grains is sintered together to form an abrasive grain layer. A method for manufacturing a metal bond tool, characterized by: 2. When silicon content (A weight %) and carbon content (B weight %) in iron-based alloy powder, satisfy the following relationships: 2.5≦B≦4.5 3≦B+A/3≦5 The method for manufacturing a metal bond tool according to claim 1. 3. The method for manufacturing a metal bond tool according to claim 1, wherein at least one of diamond and cubic boron nitride is used as the abrasive grain.