JP3351844B2 - Alloy steel powder for iron-based sintered material and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloy steel for an iron-based sintering heat treatment material, which is suitable for manufacturing parts requiring high precision, high strength and high fatigue characteristics, among various sintered parts. The present invention relates to a powder and a production method thereof. Here, iron
Sintered heat treatment materials are carburized and then quenched after sintering.
Iron-based sintered materials subjected to heat treatment such as tempering
means.

[0002]

2. Description of the Related Art When manufacturing iron-based parts, such as automobile gears, which require high strength and high fatigue properties by powder metallurgy, alloy elements are added to improve strength and fatigue properties.
In addition to carburizing and nitriding, quenching and tempering are performed thereafter.

[0003] In pre-alloyed steel powder produced by dissolving alloy components in pure iron powder to produce alloyed steel powder, the dimensional accuracy of the sintered body after heat treatment is high, but the compressibility of the steel powder is impaired. In such a case, a high sintering density cannot be obtained, and as a result, improvement in fatigue characteristics cannot be expected. In this regard, for example,
In Japanese Patent Application Laid-Open No. 45-9649, the above-mentioned problem is solved by diffusing and attaching an alloy component powder such as Ni, Cu, and Mo to pure iron powder (hereinafter, referred to as composite alloying).

[0004] However, the alloy steel powder produced by the above-described composite alloying method is excellent in compressibility, but is mixed by mixing different kinds of metal powder and then heated to cause diffusion to partially alloy. Therefore, as compared with pre-alloyed steel powder from which a completely uniform composition can be obtained, the uniformity of the structure is low and the dimensional accuracy of the product varies. As described above, the above-described composite alloy steel powder has high compressibility and can improve the strength and fatigue characteristics of the sintered body, but it is hardly sufficient in terms of dimensional accuracy.

On the other hand, in Japanese Patent Application Laid-Open No. 1-215904,
A steel powder that not only has high compressibility but also has excellent dimensional accuracy after heat treatment of the sintered body has been proposed together with its manufacturing method. This steel powder contains Ni at 5.0 wt% (hereinafter simply referred to as%). ), It is not only economically disadvantageous but also leaves a problem that it cannot sufficiently meet recent demands for strict dimensional accuracy and high fatigue properties.

[0006]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems, and provides a sintered material having not only high dimensional accuracy after heat treatment of a sintered body but also excellent strength and fatigue characteristics. It is an object of the present invention to propose an alloy steel powder for an iron-based sintering heat treatment material that can be obtained more economically than in the past, together with its advantageous production method.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to achieve the above-mentioned object, and as a result, have found that a stable reduction in a steel alloy powder for sintering that does not cause reduction and oxidation reactions during heat treatment. It has been found that the addition and mixing of a small amount of a fine powder is extremely effective in achieving the intended purpose. The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows. 1. At least one selected from Ni, Cu, Mo, and Cr in pure iron powder: 0.5 to 7 wt% as a solid solution. Prealloyed alloy steel powder: 100 parts by weight, average particle size: 1 μm or less One or more selected from fine SiO ₂ , Al ₂ O ₃ , TiO ₂ , CaO and MgO powder: 0.01 to 1 part by weight of the alloy steel powder
Carburizing characterized by adding and blending to cover the surface
An alloy steel powder for an iron-based sintered material to be subsequently quenched and tempered (first invention).

[0009] 2. Mo and / or Cr: 0.5 to 7 in pure iron powder
wt% as a solid solution and pre-alloyed, and Ni and / or C
u: alloy steel powder obtained by diffusing and adhering 0.5 to 7 wt% to form a composite alloy: 100 parts by weight of fine SiO ₂ , Al ₂ O ₃ , TiO ₂ , CaO and MgO powder having an average particle size of 1 μm or less. One or more selected from among: 0.01 to 1 part by weight of the alloy steel powder
After carburizing , characterized by being added and blended in a form that covers the surface ,
Alloy steel powder for ferrous sintered material to perform quenching and tempering (second invention).

[0010] 3. At least one selected from Ni, Cu and Mo on pure iron powder: 0.5 to 7 wt% is diffused and adhered to form a composite alloy. Alloy steel powder: 100 parts by weight, average particle diameter:
One or more selected from fine SiO ₂ , Al ₂ O ₃ , TiO ₂ , CaO and MgO powders of 1 μm or less: 0.01 to 1 part by weight is added and mixed in a form covering the surface of the alloy steel powder For iron-based sintered materials that are quenched and tempered after carburizing
Alloy steel powder (third invention).

4. Pure iron powder pre-alloyed to solid solution alloy components and / or pure iron powder in alloy steel powder was combined alloying diffusing deposited alloy components: 100 parts by weight, average particle diameter:
One or more selected from fine SiO ₂ , Al ₂ O ₃ , TiO ₂ , CaO and MgO powder of 1 μm or less: 0.01 to 1 part by weight, and binder mixed with 0.5 to 1.5 parts by weight A method for producing an alloy steel powder for an iron-based sintered material, wherein the powder is heated and mixed at a temperature equal to or higher than the melting point of the binder and equal to or lower than the thermal decomposition point , followed by quenching and tempering after carburizing (fourth invention).

[0012]

[Action] Ni, Cu, Mo and Cr are all elements that improve the strength of steel by improving hardenability and solid solution strengthening.
In addition, Ni contributes to the improvement of toughness, and Cr has the effect of increasing hardness after heat treatment and improving wear resistance. As an alloying method of these strength improving elements, as described above,
Pre-alloying method (for example, water atomizing method) in which alloying elements are added simultaneously when melting, or composite alloying method in which powder containing alloying elements is attached to pure iron powder or pre-alloyed steel powder by heat treatment or using a binder There is.

In the present invention, the method of alloying such strength-improving elements is not particularly limited. However, regardless of the alloying method, if the total content of these elements is less than 0.5%, the effect is not limited. On the other hand, if it exceeds 7%, the strength, toughness and fatigue properties are reduced. Therefore, the total content of these elements was limited to the range of 0.5 to 7%.

According to the present invention, a small amount of a stable fine powder that does not cause a reduction reaction or an oxidation reaction during the heat treatment such as sintering, quenching or tempering is added to such alloy steel powder and mixed, so that the heat treatment during the carburizing heat treatment is performed. The dimensional variation is reduced and the surface pressure fatigue strength is improved. That is, by covering the surface of the base steel powder with the stable fine powder, the rate of diffusion of carbon from the surface of the sintered body during carburization is suppressed, and the diffusion of carbon becomes uniform, so that in the martensitic transformation during quenching, Expansion occurs uniformly inside the sintered body,
As a result, the dimensional variation is reduced, and the surface pressure fatigue strength is improved due to the uniformity of the sample.

The finer the powder, the finer the particle, the better the average particle diameter is to cover the base powder having a diameter of 60 to 100 μm. Average particle size is 1
If it exceeds μm, the effect of reducing the dimensional variation is reduced.
Therefore, the average particle size of the fine powder is set to 1 μm or less. As such fine powders, SiO ₂ , Al ₂ O ₃ , TiO ₂ , CaO and MgO powders are advantageously suitable.

If the amount of the fine powder is more than 1 part by weight with respect to 100 parts by weight of the base powder, the sintering of the base powder is hindered. And the effect of reducing dimensional variation during heat treatment is small. Therefore, the blending amount of the fine powder is set to 0.01 to 1 part by weight.

The alloy steel powder can be obtained by adding and blending the fine powder of the base powder, and then heating and mixing the powder at a temperature not lower than the melting point of the binder and not higher than the thermal decomposition point. In addition, variations in dimensions during the heat treatment can be significantly reduced.

In the above production method, if the amount of the binder is less than 0.5 part by weight with respect to 100 parts by weight of the base powder, the binding effect is small, while if it exceeds 1.5 parts by weight, the fluidity of the powder is reduced. . Therefore, the amount of binder was limited to the range of 0.5 to 1.5 parts by weight. Suitable examples of the binder include metal soaps such as zinc stearate and tin stearate, fatty acids such as capric acid and stearic acid, fatty acid amides such as stearic acid amide and oleic acid amide, and low molecular weight polyethylene.

By forming and sintering the alloy steel powder as described above, the dimensional accuracy of the sintered body after the heat treatment can be improved. Very good. Incidentally, the molding referred to here, the sintering generally means a method of making a powdered metal part, for example after compression molding by 4 to 8 t / cm ² pressure of about, N ₂ at 1100 to 1300 ° C., AX, Sintering in RX gas is preferred. If necessary, graphite can be added prior to molding for the purpose of improving strength.
About 0.05 to 0.4% is preferable.

[0020]

【Example】

Example 1 As shown in Table 1, 0.1 parts by weight of graphite and 1 part by weight of zinc stearate were used for 100 parts by weight of alloy steel powder obtained by pre-alloying or compounding alloys of Mo, Ni, Cu and Cr. Parts by weight and 0.1 parts by weight of silicon dioxide powder having an average particle size of 0.01 μm were added and mixed by heating at 140 ° C. for 10 minutes. Subsequently, from the obtained alloy steel powder, compacts having a density of 7.0 g / cm ³ were prepared by compression molding, and then these compacts were placed in a nitrogen atmosphere for 1150 g.
After sintering at 30 ° C for 30 minutes, carburizing treatment (carbon potential 0.9%) at 900 ° C for 60 minutes, followed by oil quenching, and then tempering at 150 ° C for 60 minutes. In this experiment, the composite alloy steel powder was crushed and classified after mixing a prescribed amount of carbonyl Ni powder, Cu powder and Mo trioxide powder with the base powder, diffusion annealing in hydrogen at 700 ° C for 60 min. It was obtained. The heating and mixing treatment is for melting zinc stearate to form an adhesive.

Table 1 also shows the results obtained by examining the dimensional accuracy of the sintered heat-treated body thus obtained and the endurance fatigue strength by the forest-type surface pressure fatigue test. The dimensional accuracy is 78m outside diameter.
m, inner diameter: 35 mm, height: 12 mm The ring-shaped test piece was evaluated by the standard deviation of the variation in strain between the sintered body and the tempered body (10 test pieces), which was obtained as shown in FIG. .

[0022]

[Table 1]

As is clear from the table, according to the present invention, it was possible to obtain a sintered heat-treated body having excellent dimensional accuracy and fatigue characteristics.

Example 2 As shown in Table 2, 0.1 part by weight of graphite, 0.1 part by weight of stearic acid and 100 parts by weight of alloy steel powder obtained by pre-alloying or complex-alloying Mo, Ni, Cu and Cr, respectively. 1 part by weight of zinc, SiO ₂ , Al ₂ O ₃ , TiO ₂ , Ca
O and MgO powders were added and mixed by heating at 140 ° C. for 10 minutes. Then, from the obtained alloy steel powder, a density of 7.0 was obtained by compression molding.
After preparing a molded body of g / cm ^3, these moldings, 1150 ° C. in a nitrogen atmosphere, and sintered under the conditions of 30 minutes, followed
Carburizing treatment at 900 ° C for 60 minutes (carbon potential 0.9
%), Followed by oil quenching and then tempering at 150 ° C. for 60 minutes. Table 3 shows the results obtained by examining the dimensional accuracy of the heat-treated sintered body thus obtained and the endurance fatigue strength by a forest-type surface pressure fatigue test.

[0025]

[Table 2]

[0026]

[Table 3]

As is clear from Table 3, according to the present invention, it was possible to obtain a sintered heat-treated body having excellent dimensional accuracy and fatigue characteristics.

[0028]

The alloy steel powder of the present invention not only has excellent fatigue characteristics after sintering and heat treatment, but also can maintain extremely high dimensional accuracy. For example, the alloy steel powder has high fatigue characteristics such as cam gears of automobiles. It is effective as a raw material powder for sintered parts that require high dimensional accuracy.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a procedure for evaluating dimensional accuracy.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI C22C 38/08 C22C 38/08 38/42 38/42 C23C 8/22 C23C 8/22 (72) Inventor Eiji Hatsutani Chiba, Chiba No. 1, Kawasaki-cho, Chuo-ku, Kawasaki-shi Inside the Chiba Works of Kawasaki Steel Corporation (56) References JP-A-6-65693 (JP, A) JP-A-2-25502 (JP, A) JP-A-59-215401 (JP, A) A) JP-A-2-97602 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22F 1 / 00,1 / 02 C22C 33/02 C22C 38/00-38/60 C23C 8/22

Claims (4)

(57) [Claims] 1. An alloy steel powder obtained by dissolving at least one selected from Ni, Cu, Mo and Cr in a pure iron powder in a solid solution of 0.5 to 7 wt%, and prealloying the alloy steel powder. Diameter: 1μ
m or less fine _{SiO 2, Al 2 O 3,} TiO 2, CaO and selected one or two or more from among MgO powder: 0.01 to 1 part by weight, the
An alloy steel powder for an iron-based sintered material that is quenched and tempered after carburization , characterized by being added and blended so as to cover the surface of the alloy steel powder. 2. Pure iron powder, Mo and / or Cr: 0.5 to 7 wt.
% As a solid solution and pre-alloyed, and Ni and / or Cu:
Alloy steel powder which is made into a composite alloy by diffusing and adhering 0.5 to 7 wt% to 100 parts by weight, and having an average particle size of 1 μm or less for 100 parts by weight.
One or more selected from among SiO ₂ , Al ₂ O ₃ , TiO ₂ , CaO and MgO powder: 0.01 to 1 part by weight of the surface of the alloy steel powder
Characterized in that the addition formulated in the form of a cover, after carburization, baked
Alloy steel powder for ferrous sintered material to perform tempering placed. 3. An alloy steel powder obtained by diffusing and adhering 0.5 to 7% by weight of at least one selected from Ni, Cu and Mo to pure iron powder to form a composite alloy: 100 parts by weight, an average particle diameter is: 1
One or more selected from among fine SiO ₂ , Al ₂ O ₃ , TiO ₂ , CaO and MgO powder of μm or less: 0.01 to 1 part by weight ,
Characterized in that the addition formulated so as to cover the surface of the alloy steel powder, after carburization, if <br/> alloy steel powder for ferrous sintered material to perform quenching and tempering. 4. A pure iron powder pre-alloyed to solid solution alloy components and / or pure iron powder in alloy steel powder was combined alloying diffusing deposited alloy components: 100 parts by weight, average particle diameter : 1
One or more selected from among fine SiO ₂ , Al ₂ O ₃ , TiO ₂ , CaO and MgO powder of μm or less: 0.01 to 1 part by weight,
Binder: The powder mixture was added with 0.5-1.5 parts by weight, higher than the melting point of the binder, heated in the following thermal decomposition point, characterized by mixing, after carburization, for iron-based sintered material for performing quenching and tempering Manufacturing method of alloy steel powder.