JP2009001882A - Powder mixture for powder metallurgy, and iron powder sintered body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a powder mixture for powder metallurgy by which an iron powder sintered body having excellent strength and impact value characteristics can be obtained and also to provide an iron powder sintered body. <P>SOLUTION: The powder mixture for powder metallurgy is obtained by mixing an alloy powder with a base powder composed of prealloy type steel powder. The base powder consists of Fe containing 0.2 to 1.5 mass% Mn and the balance inevitable impurities, and the alloy powder contains, in terms of mass percent in a whole powder mixture of this alloy powder and the above base powder, 0.5 to 3.5 mass% Cu, 0.4 to 1.5 mass% graphite (Gr) and 1.0 to 6.0 mass% Ni. The iron powder sintered body is obtained by sintering a green compact of the above powder mixture for powder metallurgy. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a mixed powder for powder metallurgy and an iron powder sintered body, and in particular, a mixed powder for powder metallurgy and an iron powder sintered body capable of obtaining an iron powder sintered body suitable as a high-strength sintered member for automobiles. Concerning union.

  At present, most sintered bodies manufactured by powder metallurgy are used as automotive parts, and iron-based sintered members are widely used. Various types of such iron-based sintered members are known. For example, for the purpose of improving strength, weather resistance, wear resistance, etc., the main component of iron powder is graphite. A mixture of fine powders such as copper and copper is known. In addition, from the viewpoint of expanding the application range of the sintered member, the sintered member is required to have higher strength, and as a means for achieving these, an alloying element such as Ni or Mo is added. Methods for alloying are also known.

  For example, in Patent Documents 1 and 2, powder metallurgy in which a prealloyed steel powder containing an alloy component in a range of 1.5 to 4.5 mass% is used as a mother powder, and alloyed fine powder or Ni powder is mixed with the mother powder. An iron-based sintered body is disclosed in which a powder mixture is mixed with graphite powder and then compacted and then compacted and sintered at 1050 to 1250 ° C.

  Patent Document 3 discloses a mixed powder in which Ni powder, Cu powder, and graphite powder (graphite) are mixed with alloy steel powder in which Ni and Mo are partially alloyed, and the mixed powder is partially alloyed Ni: 0.5-4 mass% and Mo: 0.5-5 mass%, Ni powder: 1-5 mass%, Cu powder: 0.5-4 mass% and graphite powder: 0.2-0.9 mass% And the mixed powder for high intensity | strength sintered parts characterized by the remainder consisting of Fe and an unavoidable impurity is disclosed.

In Patent Document 4, Ni: 3 to 5% by mass, Mo: 0.4 to 0.7% by mass, an alloy powder having a balance of Fe, 1-2% by mass of copper powder, and 1% of Ni powder. ~ 3 mass%, mixed powder blended so that the amount of C after sintering is 0.2-0.7 mass% is compression molded in the mold, and sintering of the green compact is non-oxidized A method for producing an iron-based sintered alloy is disclosed, which is performed in a temperature range of 1130 to 1230 ° C. in a neutral atmosphere and cooled in a sintering furnace at a rate of 5 ° C./min to 20 ° C./min. ing.
Japanese Patent Laid-Open No. 9-59740 Japanese Patent Laid-Open No. 2001-81501 JP 2000-640001 A JP-A-9-87794

However, the conventional mixed powder for powder metallurgy and the iron powder sintered body have the following problems.
Conventional mixed powders for powder metallurgy and iron powder sintered bodies are mainly intended to increase the strength of sintered parts, and the impact value characteristics (toughness) are reduced due to excessive attention to the increase in strength. There was a problem that it was easy. In addition, by making the mother powder highly alloyed, the mother powder has a higher hardness and the molding density (green compact density) does not increase, so that there is a problem that moldability and mechanical properties are lowered. Furthermore, depending on the alloy composition, a large amount of expensive metal (Mo, Ni, Cr, etc.) is used, resulting in a high cost.

  The present invention has been made in view of the above circumstances, and its purpose is to provide a mixed powder for powder metallurgy and iron powder sintering that can obtain an iron powder sintered body having excellent strength and impact value characteristics. To provide a body.

  The mixed powder for powder metallurgy according to claim 1 is a mixed powder for powder metallurgy in which a mother powder made of pre-alloyed steel powder and an alloy powder are mixed, and the mother powder has a Mn of 0.2 to 1.5. Fe containing mass%, the balance consists of inevitable impurities, and the alloy powder is Cu: 0.5 to 3.5 mass% as a blending mass% in the total mixed powder combined with the mother powder, graphite. (Gr): 0.4-1.5 mass%, Ni: 1.0-6.0 mass% is contained, It is characterized by the above-mentioned. Note that Cu as the alloy powder has the same role as CuP.

  If comprised in this way, mechanical characteristics, such as intensity | strength, improve by solid solution strengthening by containing Mn as a predetermined amount as an alloy component of mother powder. Further, when the alloy powder contains a predetermined amount of Cu, the sinterability and the strength and fatigue characteristics of the sintered body are improved, and when a predetermined amount of graphite is contained, the strength is improved by solid solution strengthening. . Further, when the alloy powder contains a predetermined amount of Ni, strength is improved and impact value characteristics (toughness) are improved.

  The mixed powder for powder metallurgy according to claim 2 is characterized in that the alloy powder further contains Mo: 0.3 to 3.5% by mass.

  If comprised in this way, when alloy powder contains Mo in a predetermined amount, hardenability will improve and intensity | strength will improve.

The iron powder sintered body according to claim 3 is obtained by sintering a green compact of the mixed powder for powder metallurgy according to claim 1 or claim 2.
If comprised in this way, since the iron powder sintered compact of this invention is obtained by sintering the green compact of the above-mentioned mixed powder for powder metallurgy, strength, impact value characteristics (toughness), fatigue characteristics, Excellent mechanical properties such as wear resistance.

  According to the mixed powder for powder metallurgy according to claim 1 of the present invention, it is possible to improve strength and impact value characteristics (toughness), and to improve mechanical characteristics such as fatigue characteristics and wear resistance. An excellent iron powder sintered body can be obtained. Furthermore, since the mother powder is not highly alloyed more than necessary, the formability and mechanical properties of the iron powder sintered body are not deteriorated, and the economic efficiency can be improved.

  According to the mixed powder for powder metallurgy according to claim 2 of the present invention, the strength and wear resistance of the iron powder sintered body are further improved. In addition, the mixed powder for powder metallurgy improves the fluidity at the time of shaping | molding by containing the organic substance as a lubrication agent.

  According to the iron powder sintered body according to claim 3 of the present invention, the strength of the sintered body can be improved, the impact value characteristics (toughness) can be improved, and fatigue characteristics, wear resistance, etc. can be improved. Mechanical properties can be improved. Furthermore, since the mother powder is not made higher in alloy than necessary, the moldability and mechanical properties are not deteriorated, and the economic efficiency can be improved.

Hereinafter, the mixed powder for powder metallurgy according to the present invention (hereinafter also referred to as a mixed powder as appropriate) and an iron powder sintered body (hereinafter also referred to as a sintered body as appropriate) will be described in detail.
≪Mixed powder for powder metallurgy≫
The mixed powder for powder metallurgy is a mixture of a mother powder made of prealloyed steel powder and an alloy powder. Each configuration will be described below.

<Mother powder>
The mother powder is composed of Fe containing 0.2 to 1.5% by mass of Mn and the remainder being inevitable impurities.
In the present invention, prealloyed steel powder obtained by prealloying a predetermined amount or less of an alloy component that does not deteriorate compressibility is used as the mother powder. When the content of the alloy component exceeds a predetermined amount, the compressibility is lowered, a sufficient sintered density cannot be obtained, and mechanical properties such as strength and impact value properties (toughness) are lowered. The pre-alloyed steel powder is alloyed steel powder in which an alloy component such as Mn is previously dissolved (alloyed) in iron. By using the pre-alloyed steel powder, the alloy components in the sintered body can be increased.

Further, in order to improve mechanical properties such as strength of the sintered body, it is necessary to strengthen the base of the mother powder, and for that purpose, the content of the alloy component needs to be a predetermined amount or more. When the content of the alloy component is less than a predetermined amount, the effect of increasing the alloy component in the sintered body as much as possible by not adding the alloy component to the mother powder in advance is not exhibited. In addition, when the alloy component is not contained at all, the strength is lowered. {If no alloy component is contained, the strength is lowered, but the toughness is improved. Therefore, as will be described later, Mn is added to the mother powder in a predetermined amount range (hardening to reduce toughness), and a predetermined amount of Ni is added as a whole mixed powder to improve toughness}. Therefore, the ratio of the alloy component contained in this prealloy type steel powder needs to be prescribed in a predetermined amount range.
Here, in the present invention, Mn is specifically used as an alloy component in the prealloy type steel powder used as the mother powder.

[Mn: 0.2 to 1.5% by mass]
Mn is an element that exhibits the effect of improving mechanical properties such as strength by solid solution strengthening. In order to exert such an effect, it is necessary to add 0.2% by mass or more. However, if much Mn is added to the steel powder, the steel powder is hardened and the compressibility is lowered. Moreover, since Mn is an element with poor reducibility, it is difficult to remove the oxide film during the production of steel powder, so the upper limit is 1.5% by mass. In addition, content of Mn becomes like this. Preferably it is 0.6-1.2 mass%.

[Balance: inevitable impurities]
The basic alloy components of the mother powder used in the present invention are as described above, and the balance consists of Fe and inevitable impurities. Here, it is desirable to suppress O, C, Si, etc. in the inevitable impurities to the following contents.

[O: 0.3% by mass or less]
An increase in the O content is not preferable because the compressibility is lowered. Further, when the content of O increases, it reacts with graphite powder (graphite) at the time of sintering to deteriorate the yield of C, increase the variation in the amount of C in the sintered body, and increase the amount of graphite powder to be added. Need to be expensive. From such a viewpoint, the O content is desirably suppressed to 0.3% by mass or less. A more desirable range of the O content is 0.15% by mass or less.

[C: 0.02 mass% or less]
C, like O, is an interstitial element for steel and has the effect of hardening ferrite. However, when the mixed powder is compression-molded, the softer the ferrite base, the higher the green compact density, so it is better to keep the C content as low as possible. Further, when the green compact density is increased, the strength of the molded body is improved and the handleability of the molded body is improved. From such a viewpoint, the C content is desirably suppressed to 0.02% by mass or less.

[Si: 0.1% by mass or less]
Since Si has a high binding force with oxygen, an oxide is formed on the surface of the steel powder when the molten steel is atomized. This oxide becomes difficult to reduce in the reduction step. Moreover, Si has a large effect of hardening the ferrite and impairs the compressibility of the mixed powder. From such a viewpoint, it is desirable to suppress the amount of Si to 0.1% by mass or less.

<Alloy powder>
The alloy powder is composed of Cu: 0.5 to 3.5% by mass, graphite (Gr): 0.4 to 1.5% by mass, and Ni: 1.0 to 6.0% by mass.

[Cu: 0.5 to 3.5% by mass]
Cu contributes effectively to the improvement of the sinterability and, consequently, the strength and fatigue characteristics of the sintered body. However, at least 0.5% by mass is required for this purpose. On the other hand, when it exceeds 3.5 mass%, strength and fatigue characteristics are lowered. Therefore, the Cu content is set to 0.5 to 3.5% by mass. The Cu content is preferably 1.0 to 2.5%. Furthermore, even if Cu is contained as CuP, it has an equivalent role.

[Graphite (Gr): 0.4 to 1.5% by mass]
Gr (graphite powder) is an element that easily diffuses into the mother powder (pre-alloyed steel powder) during sintering and increases the strength by solid solution strengthening. If the content of Gr is less than 0.4% by mass, the effect of improving the strength is not sufficient. On the other hand, if the content of Gr exceeds 1.5% by mass, the strength decreases due to the influence of proeutectoid cementite. Therefore, the content of Gr is set to 0.4 to 1.5% by mass. Note that the content of Gr is preferably 0.6 to 1.2%.

[Ni: 1.0 to 6.0% by mass]
Ni is an element that improves hardenability and improves impact value characteristics (toughness) by being alloyed, and is an element necessary for improving the strength of the sintered body. In order to exert such an effect, it is necessary to contain 1.0% by mass or more. However, if the amount is too large, the cost increases, so 6.0 mass% is the upper limit. The Ni content is preferably 2 to 5%.

  In addition to the above components, the alloy powder preferably further contains Mo: 0.3 to 3.5% by mass. Hereinafter, the reason for limitation of each component is demonstrated.

[Mo: 0.3 to 3.5% by mass]
Mo is an element that has the effect of improving the hardenability and increasing the strength. In order to exhibit this effect, the amount of Mo added is desirably 0.3% by mass or more. However, even if Mo is added excessively, the improvement effect is saturated and the cost is increased, so 3.5 mass% is made the upper limit.

  Further, the alloy powder may have a configuration in which an organic substance as a lubricant is mixed for molding other than the above-described mother powder and alloy powder. Examples of the organic substance include zinc stearate and ethylene bisstearyl amide. Moreover, when adding the organic substance as a lubrication agent, it is preferable that it is the range of 0.5-1.2 mass%. If the lower limit value of 0.5% is not reached, the function as a lubricant cannot be exhibited, and if the upper limit value of 1.2% is exceeded, the density decreases.

<Mixing method>
Next, a method for mixing the alloy powder into the mother powder will be described.
As a method for mixing the alloy powder, a premix method and a diffusion adhesion method are known, and either method may be used. The premix method is a method in which a mother powder and an alloy powder obtained by pre-alloying another metal powder or an alloy component are uniformly mixed, compacted, and then heated and sintered. This method has the advantage that the molding process is relatively simple. The diffusion adhesion method hardly reduces the compressibility and also prevents the problem of uneven strength and dimensional accuracy due to segregation to some extent. That is, in the diffusion adhesion method, Cu, Gr, Ni or the like is added to the mother powder and mixed uniformly, and then diffusion treatment is performed to diffuse and adhere the additive powder to the iron powder surface. Segregation does not occur.
In addition, when adding zinc stearate as a lubricant, the mother powder and the alloy powder are mixed together.

Next, the iron powder sintered body according to the present invention will be described in detail.
≪Sintered iron powder≫
The iron powder sintered body is obtained by sintering the green compact of the mixed powder for powder metallurgy described above.

As an example of a method for producing an iron powder sintered body, first, the above-described mother powder and alloy powder are mixed using a mixer or the like to obtain a mixed powder for powder metallurgy. In mixing, 0.75% by mass of zinc stearate may be added as a lubricant. Next, this mixed powder for powder metallurgy is molded at a molding pressure of, for example, 5 t / cm ² to obtain a green compact. Then, the green compact, RX gas is a weak oxidizing, _{N 2} gas, in an atmosphere such as AX gas, temperature: 1100 to 1250 ° C., time: by sintering at 15-60 minutes of conditions, An iron powder sintered body can be obtained.

As described above, according to the mixed powder for powder metallurgy according to the present invention, mechanical properties such as strength, impact value characteristics (toughness), fatigue characteristics, wear resistance, etc., suitable as a high-strength sintered member for automobiles. An iron powder sintered body having excellent characteristics and moldability can be obtained. In addition, economic efficiency can be improved.
According to the iron powder sintered body according to the present invention, by sintering the green compact of the powder metallurgy mixed powder having the alloy component, the strength, impact value characteristics (toughness), fatigue characteristics, Mechanical properties such as wear resistance and moldability can be improved.
In addition, when a lubricant is added, the iron powder sintered body can be easily taken out from the mold.

  Hereinafter, examples of the mixed powder for powder metallurgy and the iron powder sintered body according to the present invention will be specifically described in comparison with the comparative examples.

0.75% by mass of zinc stearate as a lubricant was added to the mother powder and alloy powder having the composition shown in Table 1 and mixed for 60 minutes with a V-type mixer to obtain a mixed powder for powder metallurgy. Next, this mixed powder for powder metallurgy is molded with a molding pressure of 5 t / cm ² , a cross-sectional length of 10 × 55 mm, and a depth of L10 mm (10 mm × 10 mm × 55 mm). The green compact was sintered at 1120 ° C. for 30 minutes in a nitrogen atmosphere containing 10% hydrogen. The sintered density of the iron powder sintered body thus obtained was measured, and the impact value and strength were examined.

≪Sintering density≫
The sintered density was measured by measuring the dimensions and weight and calculating.

≪Shock value≫
For Charpy impact value, Charpy absorbed energy was measured by an impact test according to MPIF STANDARD 40 at a hammer load of a testing machine of 5 kg and a test temperature of room temperature. However, there was no notch.
As the criteria for judging the impact value, those having Charpy absorbed energy of 15.0 J / cm ² or more were accepted.

≪Strength≫
The tensile test was performed according to MPIF STANDARD 10.
As a criterion for judging strength, those having a tensile strength of 500 MPa or more were accepted.
The test results are shown in Table 1.

Regarding the above results, the relationship between the content of the alloy component in the mother powder and the impact value is shown in FIG. 1, the relationship between the impact value of the mother powder and the tensile strength (TS) is shown in FIG. FIG. 3 shows the relationship between the alloy component content and the tensile strength (TS).
As shown in Table 1, Examples 1 to 13 were excellent in strength and impact value characteristics in order to satisfy the scope of the present invention.

  On the other hand, as shown in FIG. 2 and FIG. 3 together with Table 1, Comparative Example 1 was inferior in tensile strength and impact value because Mn was not contained in the mother powder. In Comparative Example 2, the tensile strength was inferior because the content of Mn in the mother powder was less than the lower limit. In Comparative Example 3, since the content of Mn in the mother powder exceeded the upper limit, the sintered density was lowered and the impact value was inferior. In Comparative Example 4, since the alloy component of the mother powder was added in combination (Mn, Ni), the sintered density was lowered and the impact value was inferior.

In combination with Table 1, as shown in FIG. 1 and FIG. 2, the test material in which the alloy powder is added to the mother powder containing 0.2 to 1.5 mass% of Mn as the alloy component has an impact value of 15.0 J / If it is as high as cm ² or more and Mn exceeds 1.5 mass%, the impact value is lowered. In addition, when the alloy component is added to the mother powder (Mn, Ni), the impact value is also lowered. In addition, when not containing Mn, since the intensity | strength is inferior about the case where 0.1 mass% of Mn is contained, description is abbreviate | omitted here.
In addition, in each point shown in FIG. 1 thru | or FIG. 3, Mn independent means the thing which added Mn by predetermined mass% to the mother powder of the mixed powder for powder metallurgy, and an alloy is for powder metallurgy As an alloy powder of the mixed powder, Mo is added at a predetermined mass%. Furthermore, the composite indicates a mixture of Fe-0.9Mn-0.6Ni as a mother powder of the mixed powder for powder metallurgy. Yes.

  As described above, the mixed powder for powder metallurgy and the iron powder sintered body according to the present invention have been described in detail by showing the best mode and examples, but the gist of the present invention is not limited to the above-described contents. . Needless to say, the contents of the present invention can be widely modified and changed based on the above description.

It is a graph which shows the content of the alloy component in mother powder, and the relationship of an impact value. It is a graph which shows the relationship between the impact value of mother powder, and the tensile strength (TS). It is a graph which shows the relationship between content of the alloy component in mother powder, and tensile strength (TS).

Claims (3)

A mixed powder for powder metallurgy in which a mother powder composed of prealloyed steel powder and an alloy powder are mixed,
The mother powder is Fe containing Mn: 0.2 to 1.5% by mass, and the balance consists of inevitable impurities,
As for the alloy powder, Cu: 0.5 to 3.5 mass%, graphite (Gr): 0.4 to 1.5 mass%, Ni: A mixed powder for powder metallurgy, characterized by containing 1.0 to 6.0% by mass.   The mixed powder for powder metallurgy according to claim 1, wherein the alloy powder further contains Mo: 0.3 to 3.5 mass%.   An iron powder sintered body obtained by sintering a green compact of the mixed powder for powder metallurgy according to claim 1 or 2.

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