JPH0711007B2 - Iron-based mixed powder for powder metallurgy with excellent machinability and mechanical properties after sintering - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an iron-based mixed powder for powder metallurgy as a raw material for a sintered machine part, etc., and particularly aims to improve machinability and mechanical properties after sintering advantageously. It proposes the results of development research on this and aims to utilize it in the field of technology to which powder metallurgy belongs.

Sintered machine parts, whose usage in automobiles, precision machinery, and household appliances have increased significantly in recent years, originally had a feature that cutting could be omitted, but when the shape was complicated. Since it has been applied to cases where high dimensional accuracy is required, it is necessary to perform drilling and boring after sintering, cutting of peripheral surfaces and end surfaces, and cutting such as grooving.

By the way, the sintered steel material, unlike the molten steel material, becomes an intermittent cutting during the above processing because of the holes that remain inside, and in addition, the holes serve as a heat retention and prevent heat conduction,
As a result, the cutting edge temperature of the cutting tool rises,
This is the reason why the cutting tool life tends to be shortened and the machinability is desired to be improved, and it goes without saying that compatibility with mechanical properties is desired here.

(Prior Art) As a method for improving the machinability of a sintered steel material, S, Pb, Se and Te, which have long been known as free-cutting components, and their compounds such as TaS ₂ , TaSe ₂ , TiSe ₂ And MoSe ₂
Etc. (JP-A-48-80409), BaSO ₄ , BaS
(Japanese Patent Publication No. 46-39564), CaS or CaSO
It has already been disclosed that ₄ is added (Japanese Patent Publication No. 52-16684).

(Problems to be solved by the invention) Of the free-cutting components, when S is applied to sintered steel, it combines with hydrogen in the atmosphere during sintering to generate hydrogen sulfide. In addition to damaging the heating element and the heating element, the size of the sintered body tends to expand, and the mechanical strength significantly decreases, which is not preferable.

Similarly, since Pb has a low melting point of 330 ° C and does not form a solid solution in iron at all, it is difficult to disperse it uniformly in the sintered steel material, and there is a problem of pollution in the sintering environment. Is also unfavorable.

Next, Se and TaSe _2, etc., like S, have the disadvantage that hydrogen selenide is generated during sintering and damages the bricks in the furnace and the heating element.

Next, BaS and CaS have hygroscopicity, and even if BaSO ₄ or CaSO ₄ is used, it changes to BaS or CaS during sintering and becomes hygroscopic.
It has the disadvantage of causing rust in sintered steel.

By advantageously solving the above problems, the machinability is advantageously improved without deteriorating the mechanical properties of the sintered mechanical parts, and at the same time, the in-furnace brick and the heating element are not damaged during sintering. Another object of the present invention is to propose an iron-based mixed powder for powder metallurgy that does not cause rusting of sintered products.

(Means for Solving the Problem) In order to solve the above-mentioned conventional problems, the inventors have
As a result of studying various additives other than sulfides, it was found that MgO-SiO ₂ system oxides have an extremely large effect to improve machinability. And MgO
Among the —SiO ₂ -based oxides, it has come to the attention that talc is easy to obtain and suitable in terms of cost.

However, if the powder of talc is simply mixed with the iron-based powder, the sintered body can be easily cut, but the mechanical strength is inevitably lowered. As a result of a detailed investigation by the inventors of the cause of this decrease in strength, it was found that the water of crystallization contained in the tank had a great adverse effect. That is, talc generally has a chemical formula of 3MgO / 4SiO ₂ H ₂
As represented by O, it contains about 5% by weight (same below) of water of crystallization, and this water of crystallization decomposes and desorbs at around 600 to 1000 ° C. when the temperature is raised for sintering. , This temperature range is an area where iron powder starts to react with graphite added as a carbon source, and due to the presence or absence of water of crystallization, a partial loss of carbon or an increase in vacancies due to gas generation. It is considered that the above causes, and as a result, the strength of the sintered body decreases.

In order to prevent such adverse effects, the inventors of the present invention have diligently studied, and even a MgO / SiO ₂ composite oxide having a MgO / SiO ₂ molar ratio of about the same as talc, a composition having no water of crystallization, that is, anhydrous It has been found that the above problems can be solved with talc. Furthermore, by adjusting the particle size of this anhydrous talc, it has been found that the mechanical properties of the sintered body are hardly deteriorated even when the machinability improving additive is added.

Based on the above findings, the above-mentioned object can be advantageously achieved by the structure having the following points as the main points.

1. 0.1 to 1.5 wt% of a powder of MgO-SiO ₂ composite oxide having a molar ratio of MgO / SiO _{2 in} the range of 0.5 or more and less than 1.0 and having no water of crystallization to an iron-based raw material powder. An iron-based mixed powder for powder metallurgy, which is excellent in machinability and mechanical properties after sintering, characterized in that it has a composition blended in the following ratio.

2. An iron-based raw material is a powder of MgO / SiO ₂ having a molar ratio of 0.5 to less than 1.0 and having an average particle size of 8 to 20 μm, which is made of a MgO-SiO ₂ -based composite oxide having no crystallization water. 0.1 to powder
An iron-based mixed powder for powder metallurgy having excellent machinability and mechanical properties after sintering, characterized by having a composition blended at a ratio of up to 1.5 wt%.

3. A powder having an average particle size of 8 to 20 μm, which is made of a MgO-SiO ₂ composite oxide having a molar ratio of MgO / SiO ₂ of 0.5 or more and less than 1.0 and having no water of crystallization, is used as an alloy component powder. In addition, the powder is excellent in machinability and mechanical properties after sintering, characterized by being adhered to the particle surface of the iron-based raw material powder by using a mixed heating body of an oil bond and a lubricant. Iron-based mixed powder for metallurgy.

4. A powder having a molar ratio of MgO / SiO ₂ of 0.5 or more and less than 1.0 and having an average particle size of 8 to 20 μm, which is made of a MgO-SiO ₂ composite oxide having no water of crystallization, and a glass powder. An iron-based mixed powder for powder metallurgy, which is excellent in machinability and mechanical properties after sintering, characterized by being added to an iron-based raw material powder.

5. A powder having a molar ratio of MgO / SiO _{2 in} the range of 0.5 or more and less than 1.0 and having an average particle size of 8 to 20 μm, which is made of a MgO-SiO ₂ composite oxide having no crystal water, and a glass powder With the alloy component powder, to the particle surface of the iron-based raw material powder, by using a mixed heating body of an oil binder and a lubricant, is adhered, the machinability after sintering, and Iron-based mixed powder for powder metallurgy with excellent mechanical properties.

That is all.

By the way, the methods classified into the following three types are known for improving machinability in molten steel.

(1) Embrittlement ..... Additive components S, P, N (2) Tool lubrication ..... Additive components Pb, Bi (3) Tool protection ... Additive component Ca Actually each of the above elements alone In addition to the case where it is used in the above, it is often used in combination with other components. Among these actions, the method of improving machinability by embrittlement action is It causes a marked decrease in strength, and especially P and N harden the iron powder particles to make them less likely to be deformed, so it is obvious that they are not suitable in terms of the decrease in compressibility of the raw material powder.

However, as already mentioned, sintered steel has poorer thermal conductivity than molten steel, so the cutting edge temperature during cutting is 60% higher than that of molten steel, although it depends on the cutting speed.
As the machinability-improving method, an additive component exhibiting a tool lubrication action and a tool protection action is preferable because it is about 150 ° C. higher. However, the conventional additive components aiming at these effects have the above-mentioned disadvantages and are not suitable in the case of sintered steel.

Therefore, the inventors examined various components as a machinability-improving additive that is stable to the sintering atmosphere even during sintering, and as a result, the above-mentioned anhydrous MgO and SiO ₂ composite oxide powder, and this and glass It was found that the mixed powder with the powder is excellent.

(Operation) As mentioned above, the sintered steel material causes the cutting tool to have a shorter life because the cutting edge temperature of the tool becomes 60 to 150 ° C higher during cutting than the molten steel material, but the MgO-SiO ₂ system of the above composition is used. the addition of compound oxide, the MgO-SiO ₂ composite oxide reacts with Fe, to produce a composite oxide of MgO-SiO ₂ -FeO system, melted at a cutting temperature for a relatively low melting point , Which protects and lubricates the surface of the cutting tool during cutting, and also prevents the composition change of the cutting tool by preventing the diffusion reaction of C between the cutting tool and the sintered steel, thereby prolonging the life of the cutting tool. It is presumed that.

Moreover, since the MgO-SiO ₂ -based composite oxide is originally relatively soft (Mohs hardness of 1 to 4) and has a rich anti-friction and lubrication function, it also functions as a lubricant during iron powder molding, There is also an advantage that adverse effects such as reduction of powder compressibility and dimensional change during sintering are small.

Among the MgO-SiO ₂ composite oxides, talc represented by the chemical formula 3MgO · 4SiO ₂ · H ₂ O, which has a MgO / SiO ₂ molar ratio of 0.75, is particularly easy to obtain and advantageous in terms of cost. .
On the other hand, however, as described above, since water of crystallization adversely affects sintering, anhydrous talc having no water of crystallization is used.

To obtain anhydrous talc, it is advisable to bake talc in the air at about 1200 ° C. for about 1 hour. In this way, if the water of crystallization is dehydrated to about 2 wt%, there is virtually no harm.

This anhydrous talc is stoichiometrically 3MgO.4SiO ₂ ,
The molar ratio MgO / SiO ₂ is 0.75, but considering that natural talc is used as the raw material, and considering the variation in this composition, the value of the molar ratio MgO / SiO ₂ is 0.5 or more and less than 1.0. Make it within the applicable range.

A sufficient effect within this range will be demonstrated in later examples. Incidentally, since anhydrous talc tends to absorb moisture and have water of crystallization again, anhydrous talc powder or mixed powder using it is stored in a deep-separated N ₂ or the like so as not to absorb moisture. Care must be taken in storage in inert gas or dehumidified air, storage in a heated state, etc.

Next, the reason why the average particle size of the composite oxide needs to be 8 to 20 μm will be described.

As the average particle diameter, for example, a median diameter according to the Microtrac method is used. If the average particle diameter is too finer than 8 μm, it easily absorbs moisture and crystal water recovers, resulting in deterioration of mechanical properties during sintering. On the other hand, if the average particle size exceeds 20 μm, it will not be uniformly and finely dispersed in the sintered body, so the machinability improvement effect will decrease and it will become a large inclusion.
It is not preferable in terms of fatigue strength of the sintered body. Therefore, the average particle size of the composite oxide is 8 to 20 μm.

When mixing the complex oxide powder for improving machinability described above with the iron-based raw material powder, in order to prevent large inclusions from remaining in the sintered body due to segregation and causing defects, segregation using a binder It is useful to apply preventive treatment. That is, it is the use of a mixed heating body of an oil binder and a lubricant, where the oil binder is vegetable oil or resin acid, such as soybean oil, rice bran oil, spindle oil, oleic acid. Including those prepared by mixing more than one kind, the lubricant refers to a commonly used lubricant for powder metallurgy such as metal soap such as zinc stearate, higher fatty acid such as stearic acid or wax powder.

The mixed heating body refers to the one in which the lubricant and the oil binder are heated and integrated.

With this mixed heating body, the added oxide powder is well dispersed and fixed on the surface of the raw material iron powder particles, so that adverse effects such as large inclusions in the sintered body and the origin of fatigue fracture can be avoided. , The mechanical properties are improved.

Further, since this mixed heating body covers a part of the anhydrous MgO—SiO ₂ type oxide, it contributes to the solution of the problem that the oxide recovers water of crystallization due to moisture absorption.

Furthermore, as an additive powder for improving the machinability, the previously mentioned Mg
In addition to the O—SiO ₂ composite oxide powder, glass powder is further used to further improve the machinability.

Here, the glass powder refers to powder of soda lime glass, borosilicate glass, lead glass and the like. So-called glass such as soda lime glass, borosilicate glass, lead glass, etc. also has a melting temperature of 1350 to 1800 ° C depending on the type, but since it begins to soften gradually below the melting temperature, MgO-SiO ₂ composite Like oxides, glass adheres to the cutting tool surface during cutting, protects and lubricates the cutting tool, and prevents the diffusion reaction of carbon between the cutting tool and the sintered steel to significantly improve the cutting tool life. I think that the.

Further, by simultaneously adding MgO-SiO ₂ -based composite oxide powder and glass powder, the number of types of oxide liquid phases adhering to the cutting tool is increased, and the life of the cutting tool is improved over a wide range of cutting conditions. You can

As described above, the MgO-SiO ₂ -based composite oxide and the glass have a common face in terms of action and effect, so when these are used together, the total amount is the same as in the case of the MgO-SiO ₂ -based composite oxide alone. 0.1 wt% to 1.5 wt%

All of the above free-cutting components are thermally stable MgO during sintering.
Since it contains oxides such as SiO ₂ and SiO ₂ as a main component, it does not generate harmful gas during sintering, and does not damage the bricks in the furnace of the sintering furnace, the heating element, or the pipes.

Even in the case of such combined use, it is useful to prevent the segregation of the composite oxide and the glass powder by the binder as mentioned above.

In any of the above cases, the composite oxide powder, and further, the mixed powder of this and the glass powder requires a range of 0.1 to 1.5 wt% in the weight ratio in the mixture with the iron-based raw material powder. When the mixed heating body is used, the blending amount is preferably 0.1 wt% to 1.5 wt%.

(Example) Example 1 Talc powder D having a composition of 31.7% MgO-61.8% SiO _{2 by} weight.
In addition, MgO or SiO ₂ as a reagent is mixed at various ratios and sintered at 1200 ° C. for 1 hour in the air, and four kinds of MgO-SiO ₂ composites having the compositions shown in Table 1 (symbols A to D) are obtained. Prepare the oxide M
The effect of the gO / SiO ₂ molar ratio was investigated.

These MgO-SiO ₂ composite oxides were crushed and classified by air to obtain an average particle diameter (median diameter by Microtrac method;
The same shall apply hereinafter) 11 to 15 μm, and 0.5 wt% was added to each atomized iron powder (-80 mesh). Furthermore, 0.5 wt% of natural graphite powder and 2.0 wt% of electrolytic Cu powder were added and mixed, and then zinc stearate as a solid lubricant was added in an amount of 1.0 w
t% was added and mixed.

From such mixed powder, each of the JSPM with a green density of 6.9 g / cm ³
Test piece for standard tensile test and inner diameter 20 mm for cutting test,
A ring test piece with an outer diameter of 60 mm and a height of 30 mm was prepared, and then 600 ° C, 30 m in a decomposed ammonia gas atmosphere with a flow rate of 4 / min.
After dewaxing in, sintering was performed at 1250 ° C. for 60 minutes. All of the above tests were performed within one day to prevent the sintered oxide powder from absorbing moisture.

For comparison, D: Ordinary talc powder with water of crystallization instead of the above oxides (MgO 31.7%, SiO ₂ 61.8%, Al ₂ O ₃ 0.2%, CaO 0.2%, F
Tests were also conducted with an average particle size of 12 μm, eO 0.9%; MgO / SiO ₂ molar ratio 0.76), with 0.5% addition and with E: no oxide addition.

Table 2 shows the results of examining the tensile strength of each of the thus obtained sintered bodies, the lateral flank wear amount of the cutting tool, and the surface roughness of the sintered body.

The cutting conditions of the cutting test in which the amount of lateral flank wear and the surface roughness are examined are as follows.

Depth of cut ‥‥‥‥‥‥‥‥‥‥‥‥‥ 0.10mm / rev Cutting speed ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ From Table 2, Samples A to D to which the complex oxide powder was added have improved tool wear amount and surface roughness as compared with E not added, while the strength is higher than that of E. Contrary to the favorable results of A to C according to (4), which is preferable, D of talc having water of crystallization was considerably decreased.

MgO-SiO ₂ system of Example 2 Example 1 oxide powder B (MgO / SiO ₂ molar ratio
0.76, average particle size 12 μm) was used as a machinability improving additive, and the same test was performed with the same iron powder, copper powder, and lubricant as in Example 1, but the addition amount of powder B was changed. Then, the effect of the added amount was investigated.

The results are shown in Table 3.

As is clear from Table 3, the addition amount is required to be 0.1 to 1.5 wt% because of the balance between machinability and strength.

MgO-SiO ₂ system of Example 3 Example 1 oxide powder B (MgO / SiO ₂ molar ratio
0.76) was used as a machinability improving additive, but the average particle size was changed by crushing and selecting air classification. The test was conducted in the same manner as in Example 1 to evaluate the effect of particle size. The results are shown in Table 4.

From the viewpoint of the strength of the sintered body, good results have been obtained in the range of the average particle size of 8 to 20 μm.

MgO-SiO ₂ system of Example 4 Example 1 oxide powder B (MgO / SiO ₂ molar ratio
0.76, average grain size 12 μm), 73% SiO ₂ -13% Na ₂ O
Soda glass powder with -10% CaO-4% MgO composition (average grain size)
(17 μm) as a machinability improving additive, and the same test as in Example 1 was conducted with the same iron powder, copper powder and lubricant, but the addition amount of powder B was 0.5% and soda glass was used. The effect of glass composite addition was investigated by changing the amount of powder added.
The results are shown in Table 5.

Obviously, the combined addition of MgO-SiO ₂ based oxides and glass, are grave is further machinability improvement. However,
If the total amount added exceeds 1.5%, the mechanical strength deteriorates significantly.

Example 5 In order to examine the effect of adding a binder, the case of adding no soda glass in Example 4 and 0.5 soda glass
As a standard, a test under the same conditions as in the case of addition of% was made standard, and each of them was subjected to segregation prevention treatment by addition of a binder in the state of mixed powder, and its effect was confirmed. That is, the mixed powder (iron powder,
Copper powder, graphite powder, machinability-improving powder and zinc stearate), 0.3% of oleic acid was further added and mixed.
Heated to ° C and cooled. Then, a test piece was prepared and sintered in the same manner as in Example 1. The results are shown in Table 6.

As shown in Table 6, addition of the binder improves both machinability and mechanical strength, which is a preferred embodiment.

(Effects of the Invention) As described above, the iron-based mixed powder for powder metallurgy according to the present invention does not cause damage to the brick and the heating element in the sintering furnace at the time of sintering, and the dimensional change after sintering and mechanical It is possible to obtain a sintered machine part having excellent machinability while maintaining the same mechanical properties as conventional iron powder, and the effect is great.

Claims (5)

[Claims] 1. A powder of an MgO-SiO ₂ composite oxide having a molar ratio of MgO / SiO ₂ of 0.5 or more and less than 1.0 and having no water of crystallization is added to an iron-based raw material powder in an amount of 0.1 to An iron-based mixed powder for powder metallurgy, which has a composition blended at a ratio of 1.5 wt% and is excellent in machinability and mechanical properties after sintering. 2. A powder having a molar ratio of MgO / SiO _{2 in} the range of 0.5 or more and less than 1.0 and having an average particle size of 8 to 20 μm, which is made of a MgO—SiO ₂ composite oxide having no water of crystallization, An iron-based mixed powder for powder metallurgy having excellent machinability after sintering and mechanical properties, characterized by having a composition of 0.1 to 1.5 wt% mixed with iron-based raw material powder. 3. A powder having a molar ratio of MgO / SiO _{2 in} the range of 0.5 or more and less than 1.0 and having an average particle size of 8 to 20 μm, which is made of a MgO—SiO ₂ composite oxide having no water of crystallization, Machinability and mechanical properties after sintering, characterized by being adhered to the particle surface of the iron-based raw material powder together with the alloy component powder by using a mixed heating body of an oil binder and a lubricant. Excellent iron-based mixed powder for powder metallurgy. Value of 4. The MgO / SiO ₂ molar ratio is in the range of less than 0.5 and less than 1.0, and a powder having an average particle size of 8~20μm consisting MgO-SiO ₂ composite oxide having no water of crystallization, A glass powder and an iron-based raw material powder, characterized by comprising,
Iron-based mixed powder for powder metallurgy that excels in machinability and mechanical properties after sintering. Value of 5. The MgO / SiO ₂ molar ratio is in the range of less than 0.5 and less than 1.0, and a powder having an average particle size of 8~20μm consisting MgO-SiO ₂ composite oxide having no water of crystallization, Glass powder and alloy component powder are adhered to the particle surface of the iron-based raw material powder by using a mixed heating body of an oil binder and a lubricant, and are machined after sintering. Iron-based mixed powder for powder metallurgy with excellent properties and mechanical properties.