JP2009209410A - Mixed powder for powder metallurgy, and iron powder sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide mixed powder for powder metallurgy which solves the conventional problems, and can obtain an iron powder sintered compact having excellent strength and toughness, and to provide the iron powder sintered compact. <P>SOLUTION: Disclosed is mixed powder for powder metallurgy obtained by mixing mother powder composed of prealloy type steel powder and powder for alloying. The mother powder is composed of iron powder comprising W and/or V by 0.05 to 1.0 mass% in total, and the balance inevitable impurities, and, in the powder for alloying, regarding the blending mass% in the total mixed powder together with the mother powder, graphite is 0.4 to 1.5 mass%, and Cu powder and/or Ni powder is 1.0 to 8.0 mass% in total. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention compacts a mixed powder for powder metallurgy capable of obtaining an iron powder sintered body that can be suitably used as a high-strength sintered member for automobiles, and the powder mixed for powder metallurgy. The present invention relates to an iron powder sintered body obtained by sintering.

  Conventionally, the iron powder sintered body obtained by compacting and sintering a powder mainly composed of iron powder has a feature that it is easy to mold. However, the strength, weather resistance, wear resistance, and the like are not necessarily superior to steel materials manufactured by forging or rolling. In addition, in order to obtain an iron powder sintered body having improved strength, weather resistance, wear resistance, etc., a powder such as graphite (C) or Cu is mixed with the iron powder, and further, Ni or Mo is alloyed. Conventionally, the strength has been improved.

  For example, in Patent Documents 1 and 2, prealloy-type steel powder containing an alloy component in the range of 1.5 to 4.5% by weight is used as a mother powder, and alloyed fine powder and further nickel powder are mixed with this mother powder. An iron-based sintered body made of a powdered metallurgical mixed powder and a powder compacted sintered body of the powdered metallurgical mixed powder and graphite powder is disclosed.

  Patent Document 3 discloses a mixed powder in which Ni powder, Cu powder and graphite powder 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 wt%, Ni powder: 1-5 wt%, Cu powder: 0.5-4 wt%, and graphite powder: 0.2-0.9 wt%, and the balance of Fe and inevitable impurities A mixed powder is disclosed.

  Furthermore, Patent Document 4 discloses that, by weight ratio, Ni: 3 to 5%, Mo: 0.4 to 0.7%, and an alloy powder composed of the remaining Fe, copper powder 1 to 2%, Ni The green compact obtained by compression-molding a mixed powder containing 1 to 3% of powder and 0.2 to 0.7% of C after sintering is sintered to iron. A method for producing an iron-based sintered alloy for obtaining an iron-based sintered alloy is disclosed.

  However, both of these conventional powder metallurgy mixed powders and iron powder sintered bodies have been developed with a focus on increasing the strength of the obtained iron powder sintered bodies. There was a problem that the impact resistance (toughness) was likely to deteriorate. Further, by using a mother powder containing a large amount of alloy components, it has been difficult to increase the strength of the compact in press molding, resulting in a problem that strength and toughness are not improved. Furthermore, since a large amount of expensive metals such as Mo and Ni are used, there is a problem that the cost is increased.

Japanese Patent Laid-Open No. 9-59740 JP 2001-81501 A JP 2000-640001 A JP-A-9-87794

  The present invention has been made as a solution to the above-described conventional problems, and is a mixed powder for powder metallurgy capable of obtaining an iron powder sintered body having excellent strength and impact resistance (toughness), and its iron An object of the present invention is to provide a powder sintered body.

  The invention 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 is 0.05 to 1. The iron powder containing 0% by mass, the balance being inevitable impurities, and the alloying powder, the compounding mass% in the total mixed powder combined with the mother powder is graphite: 0.4-1.5 mass %, Cu powder and / or Ni powder is 1.0 to 8.0% by mass, and is a mixed powder for powder metallurgy.

  The invention according to claim 2 is characterized in that, as the alloy powder, the blending mass% in the total mixed powder further includes 0.3 to 3.5 mass% of Mo powder. It is a mixed powder for powder metallurgy.

  The invention described in claim 3 is an iron powder sintered body obtained by sintering a green compact obtained by compression molding the powder mixture for powder metallurgy described in claim 1 or 2. .

  According to the mixed powder for powder metallurgy according to claim 1 of the present invention, by containing a predetermined amount of W and / or V in the prealloy type steel powder, the W and V are inevitable impurities in the prealloy type steel powder. By combining with certain C or N to produce carbide or nitride, compressibility is improved. Furthermore, these carbides and nitrides can suppress the coarsening of the crystal grain size during sintering and refine the structure, and the strength and impact resistance (toughness) of the resulting iron powder sintered body. ) Will improve. Moreover, since Cu powder and / or Ni powder are mix | blended, the balance of intensity | strength and toughness can be improved. Furthermore, when a predetermined amount of Cu powder is contained, the strength and toughness can be improved without performing heat treatment such as quenching and tempering of the iron powder sintered body. That is, according to the mixed powder for powder metallurgy according to claim 1 of the present invention, an iron powder sintered body having excellent strength and impact resistance (toughness) can be obtained.

  According to the mixed powder for powder metallurgy according to claim 2 of the present invention, the strength of the iron powder sintered body obtained by improving the hardenability is further improved.

  According to the iron powder sintered body of claim 3 of the present invention, an iron powder sintered body having excellent strength and toughness can be obtained.

  Hereinafter, the present invention will be described in more detail based on embodiments.

  The mixed powder for powder metallurgy of the present invention is a mixture of a mother powder made of prealloyed steel powder and an alloy powder. Hereinafter, the detailed configuration such as the composition of the mother powder and the alloy powder will be described.

  The mother powder is an iron powder containing 0.05 to 1.0% by mass of W and / or V, and the balance is inevitable impurities. In the present invention, prealloyed steel powder obtained by pre-alloying a small amount of alloy components such as W and V that do not deteriorate compressibility is used as the mother powder. When the alloy component such as W or V exceeds a predetermined amount, the compressibility is lowered, a sufficient sintered density cannot be obtained, and mechanical properties such as strength and toughness are lowered. The pre-alloyed steel powder refers to alloyed steel powder inside the iron powder in which the alloy components are previously dissolved (alloyed) in iron. By using this pre-alloy type steel powder, the alloy components in the iron powder sintered body can be increased more uniformly, and the strength of the iron powder can be increased.

  In order to improve the mechanical properties such as strength and toughness of the iron powder sintered body, it is necessary to strengthen the base of the mother powder. For this reason, it is necessary to contain an alloy component in a predetermined amount or more although it is a trace amount. is there. If the alloy component is less than a predetermined amount, the above-described effect that the alloy component in the iron powder in the iron powder sintered body can be increased by adding the alloy component in the mother powder in advance can be achieved. become unable. In the case where no alloy component is contained, the strength is lowered. Therefore, the ratio of the alloy component contained in the pre-alloy type steel powder needs to be specified in a predetermined amount range.

  In the present invention, the alloy components contained in the pre-alloyed steel powder used as the mother powder are W and V. W and V are dissolved in iron to improve strength, and by reacting with unavoidable impurities C and N to generate carbides and nitrides, the grain size is refined, and strength and toughness It is an element that expresses the effect of improving. However, when there is too much content of them, the compressibility of iron powder will fall and it will become difficult to raise a density of a forming object, and intensity and toughness will fall. Moreover, when there is too little content of them, the effect of high strength and high toughness cannot be produced. Therefore, the content of W and / or V is set in the range of 0.05 to 1.0% by mass. More preferably, it is the range of 0.1-0.7 mass%.

  Inevitable impurities contained in the pre-alloyed steel powder used as the mother powder include O, C, Si and the like. About O, C, and Si, it is desirable to suppress below the following content.

  An increase in the O content is not preferable because the compressibility is lowered. Further, when the content of O increases, the yield of C reacts with graphite during sintering, and the variation in the amount of C in the iron powder sintered body increases. Further, the amount of graphite added increases. It is necessary to do this, and the cost becomes high. Therefore, the O content is preferably suppressed to 0.3% by mass or less. More preferably, it is 0.15 mass% or less.

  C is an element that dissolves and lowers compressibility. Moreover, although it combines with W and V of the alloy component contained in the prealloy type | mold steel powder used as mother powder, a fine carbide | carbonized_material is formed, The carbide | carbonized_material also reduces compressibility. Therefore, the C content is preferably as low as possible. Therefore, the C content is preferably suppressed to 0.02% by mass or less.

  Si is an element that easily binds to oxygen, and when its content increases, an oxide film is formed on the surface of the iron powder, and it becomes very difficult to remove. Therefore, the content of Si should be as low as possible. Therefore, the Si content is preferably suppressed to 0.1% by mass or less.

  Next, the alloy powder will be described. The alloy powder is composed of graphite (graphite powder), Cu powder, and Ni powder. The blending mass% in the total mixed powder including the mother powder is 0.4 to 1.5 mass% for graphite, and 1.0 to 8.0 mass% for Cu powder and / or Ni powder in total. In addition, although the powder for alloys shown below and the mass% of the lubricant are not particularly specified, they are all the mixed mass% in the total mixed powder including the mother powder.

  Graphite (graphite powder) is an essential powder that diffuses into the iron powder during sintering to form a structure with high hardness such as pearlite, bainite, martensite, and the like, thereby improving the strength of the iron powder sintered body. Moreover, in this invention, since it couple | bonds with W and V and produces | generates a carbide | carbonized_material, it contributes to high intensity | strength, It is necessary to prescribe | regulate the range of the compounding quantity according to content of W or V. If the blending amount is less than 0.4% by mass, sufficient strength cannot be obtained. Conversely, if the blending amount exceeds 1.5% by mass, coarse cementite is precipitated during sintering, leading to a decrease in toughness. Therefore, the compounding quantity of graphite shall be 0.4-1.5 mass%.

  Both the Cu powder and the Ni powder are effective for improving the strength. In the present invention, either one or both may be blended in the alloy powder.

  Cu powder becomes liquid at the time of sintering, thereby promoting the sintering of iron powders and improving the strength of the iron powder sintered body. In addition, the strength can be improved without performing heat treatment such as quenching and tempering after sintering. The effect of blending this Cu powder begins to appear at 0.5% by mass or more, and when it exceeds 3.5% by mass, conversely, the sintered density decreases and the strength begins to decrease.

  Ni powder has the effect of improving the toughness by forming a residual γ phase rich in Ni at the interface of the iron powder particles in addition to the effect of increasing the hardenability and improving the strength by diffusing into the iron powder. The effect of the Ni powder blending begins to appear at 0.5% by mass or more, and when it exceeds 6.0% by mass, the strength begins to decrease.

  As described above, although the mechanism in which the Cu powder and the Ni powder act is different, in order to improve the strength and toughness level to a satisfactory level, the Cu powder and / or the Ni powder are combined to 1.0 to 8. It is necessary to mix 0% by mass.

  In addition, it is desirable that the alloy powder further contains 0.3 to 3.5% by mass of Mo powder. Mo powder diffuses into iron powder during sintering to improve hardenability and improve strength. In order to acquire the effect, it is necessary to mix | blend 0.3 mass% or more, and since the effect will be saturated when it exceeds 3.5 mass%, the compounding quantity was prescribed | regulated as mentioned above.

  Furthermore, in addition to the above-mentioned mother powder and alloy powder, a lubricant such as zinc stearate and ethylene bisstearyl amide is usually mixed in order to reduce friction with the mold during the production of the iron powder sintered body. To do. The mixing amount of the lubricant is preferably in the range of 0.05 to 1.2% by mass. If it is less than 0.05% by mass, the function as a lubricant cannot be exhibited, and if it exceeds 1.2% by mass, the density of the molded product will be reduced.

  Next, a method for mixing the alloy powder with the mother powder to obtain a mixed powder for powder metallurgy will be described. As a method of mixing the alloy powder into the mother powder in producing the iron powder sintered body of the present invention, a premix method in which the mother powder and the alloy powder are simply mixed, the alloy powder is added to the mother powder by an organic substance. Any mixing method generally known to those skilled in the art, such as a deposition method, can be employed. Further, by mixing pre-mix method powders for alloys such as Cu powder, Ni powder, Mo powder and the like, the mixed powder is heated to form a partially diffused steel powder in which the mother powder and the alloy powder are diffused and adhered, A method of mixing with graphite or a lubricant may be employed.

The iron powder sintered body is obtained by sintering a green compact obtained by compression-molding the powder metallurgy mixed powder described above. An example of the manufacturing method will be described. First, using a V-type mixer, the mother powder, the alloy powder, and the lubricant are mixed by the above-described method to obtain a mixed powder for powder metallurgy. As the lubricant, for example, zinc stearate: 0.75% by mass may be mixed. Next, the mixed powder for powder metallurgy is filled into a mold for a Charpy test piece or a tensile test piece, and compression molded at a molding pressure of 6 t / cm ² to obtain a green compact. By sintering the obtained green compact in an atmosphere such as RX gas, N ₂ gas, AX gas, etc. under conditions of temperature: 1100 to 1260 ° C. and time: 15 to 90 minutes, iron powder sintering You can get a body.

  This iron powder sintered body can be further strengthened by heat treatment after sintering. For example, a method of heating and oil quenching under conditions of temperature: 860 ° C. and time: 20 minutes and tempering under conditions of temperature: 180 ° C. and time: 60 minutes can be employed.

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 30 minutes with a V-type mixer to obtain a mixed powder for powder metallurgy. Next, this mixed powder for powder metallurgy is filled in a mold having a cross-sectional length and width of 10 mm × 55 mm and a depth of 10 mm (10 mm × 55 mm × 10 mm), and compression-molded with a molding pressure of 6 t / cm ^2. Got the body. This green compact was sintered in a nitrogen atmosphere containing 10% hydrogen at 1120 ° C. for 30 minutes to obtain an iron powder sintered body. In this example, the sintered density of the iron powder sintered body thus obtained was measured, and the impact value (toughness) and tensile strength (strength) were examined. The results are shown in Table 1.

  The sintered density was measured by measuring the size and weight of the obtained iron powder sintered body and calculating it.

The impact value was determined by a Charpy impact test. In accordance with MPIF STANDARD 40, Charpy absorbed energy was measured as an impact value under the conditions of a hammer load of the testing machine: 5 kg, notch: none, test temperature: room temperature. As for the impact value, those having Charpy absorbed energy of 18.0 J / cm ² or more were regarded as acceptable.

  Furthermore, the tensile strength was determined by a tensile test according to MPIF STANDARD 10. Regarding the strength, those having a tensile strength of 550 MPa or more were regarded as acceptable.

  Example 1 contains W in the mother powder, but the content is 0.05% by mass of the lower limit defined in claim 1, and Example 2 contains V in the mother powder, but the content is The lower limit of 0.05% by mass as defined in claim 1. Conversely, Example 5 contains W and V in the mother powder, but the total content is 1.0% by mass of the upper limit defined in claim 1, and Example 6 contains W in the mother powder. However, the content is 1.0% by mass of the upper limit defined in claim 1. In Examples 3 and 4, the contents of W and V are intermediate between them.

  Example 7 has a graphite content of 0.4% by mass as defined in claim 1, and Example 8 has an graphite content of 1.5% by mass as defined in claim 1. %belongs to. In Example 9, the total amount of Cu powder and Ni powder is 7.8% by mass, which is close to the upper limit defined in Claim 1, and in Example 10, the total amount of Cu powder and Ni powder is Claim 1. The lower limit of 1.0% by mass as defined in. In Example 11, only Cu powder was blended and Ni powder was not blended.

All of Examples 1 to 11 satisfy the conditions described in claim 1 and satisfy both the impact value of the acceptance criterion: 18.0 J / cm ² or more and the tensile strength: 550 MPa or more. is doing.

  Examples 12 to 14 are provided with the conditions described in claim 2 in which Mo powder is blended, and in Example 12, the blending amount of Mo powder is 0.3% by mass of the lower limit defined in claim 2 In Example 14, the compounding amount of Mo powder is 3.0% by mass close to the upper limit defined in claim 2, and in Example 13, the compounding amount of Mo powder is 0.8 mass in between them. %belongs to.

As described above, each of Examples 12 to 14 has the conditions described in claim 2. Impact value of acceptance criteria: 18.0 J / cm ² or more, tensile strength: Both 550 MPa or more are satisfied. In Examples 12 to 14, the content of W in the mother powder and the amount of graphite, Cu powder, and Ni powder are the same as in Example 4 except that Mo powder is blended. The impact value and the tensile strength are further improved according to the blending amount.

  Comparative Example 1 has a graphite blending amount of 0.3% by mass less than the lower limit defined in claim 1, and Comparative Example 2 has a graphite blending amount of 1.7% exceeding the upper limit defined in claim 1. %belongs to. Comparative Example 3 contains W in the mother powder, but its content is less than the lower limit defined in claim 1 of 0.02% by mass, and Comparative Example 4 contains W and V in the mother powder. The total content is 1.5% by mass exceeding the upper limit defined in claim 1. In Comparative Example 5, the total amount of Cu powder and Ni powder is 0.7% by mass less than the lower limit defined in Claim 1, and in Comparative Example 6, the total amount of Cu powder and Ni powder is Claim 1. It is 8.5 mass% exceeding the upper limit determined in.

As described above, Comparative Examples 1 to 6 do not satisfy any of the conditions described in claim 1, so that the impact value of the acceptance criterion: 18.0 J / cm ² or more, and the tensile strength: 550 MPa or more, Not satisfied with at least one.

Claims (3)

A mixed powder for powder metallurgy in which a base powder made of pre-alloyed steel powder and an alloy powder are mixed,
The mother powder is an iron powder containing 0.05 to 1.0% by mass of W and / or V together with the balance being inevitable impurities,
In the alloy powder, the blending mass% in the total mixed powder in which the mother powder is combined is graphite: 0.4 to 1.5 mass%, and the Cu powder and / or Ni powder is 1.0 to 8. A mixed powder for powder metallurgy characterized by being 0% by mass.   2. The mixed powder for powder metallurgy according to claim 1, wherein the alloying powder further contains 0.3 to 3.5% by mass of Mo powder in the total mixed powder.   An iron powder sintered body obtained by sintering a green compact obtained by compression-molding the mixed powder for powder metallurgy according to claim 1 or 2.