JPS61130401A - Alloy steel powder for powder metallurgy and its production - Google Patents

Abstract

PURPOSE:To obtain alloy steel powder for powder metallurgy having excellent compressibility by diffusing and sticking a powder alloy consisting of plural components to the surface of iron or steel powder and specifying the concn. of the respective alloys diffused and stuck to the iron or steel powder having a prescribed grain size. CONSTITUTION:Ni and Mo which are the alloy components to suppress and control the reaction of steel powder and C are dispersed in the form of fine metallic powder or the compd. thereof into a liquid (methyl alcohol, etc.) which does not dissolve such components. The liquid and the iron or steel powder are thoroughly mixed to stick the alloy components to the surface of the iron or steel powder than the powder is dried. The iron or steel powder is then treated in a reducing atmosphere to diffuse the Ni and Mo to the surface thereof. The concn. of the Ni and Mo diffused and stuck to the iron or steel powder having <=44mu grain size is maintained within the concn. range of 0.8-1.9 times the concn. of the Ni and Mo diffused and stuck to the entire iron or steel powder. The upper limit of the Ni is specified to 10.0wt% and the upper limit of the Mo to 0.1-0.4wt%. High toughness is obtd. if the sintered body for which such iron powder is used is subjected to a carburization treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an alloy steel powder for powder metallurgy used in the production of various sintered parts and a method for producing the same.

[Conventional technology]

Sintered parts using pure iron powder as the main raw material have been known for some time, but this type of sintered part has a low strength level, which limits its uses. Therefore, recently, in order to compensate for the above-mentioned drawbacks, a technique has been developed in which alloy steel powder is used instead of pure iron powder.

However, when an excessive amount of alloy components are dissolved in pure iron powder, the compressibility of the steel powder is often impaired, and in that case, it becomes impossible to obtain high sintered density, resulting in the problem that no improvement in strength can be expected. be.

On the other hand, a method of mixing alloy components with pure iron powder and causing the alloy components to react and form a solid solution during sintering has also been widely adopted.

However, although this method secures compressibility to a certain extent, formability may deteriorate, the structure may become non-uniform due to powder segregation during compaction, and furthermore, the structure may become non-uniform due to poor solid solution diffusion during sintering. There are some problems that may occur.

Therefore, it is conceivable to overcome the above-mentioned problem by diffusing and adhering alloy component powder to pure iron powder, as proposed in, for example, Japanese Patent Publication No. 45-9649. In the above proposal, a specific method for diffusing alloy component powder into pure iron powder is to mix Mo oxide with pure iron powder for an alloy component with low diffusibility into iron powder, such as Mo, in a reducing atmosphere. A method is disclosed in which the Mo oxide is evaporated and reduced by heating at a temperature of 100 nm to deposit and deposit fine Mo on the surface of the pure iron powder. This method complicates the Mo addition process and may reduce the Mo addition yield. Furthermore, unlike Mo, it is difficult to apply this method to alloy components whose oxides do not evaporate at relatively low temperatures. There are some problems.

In addition, in the above proposal, pure iron powder is soaked in a solution of soluble salts of alloy components such as Mo, dried and heated to precipitate fine alloy components such as Mo on the surface of the pure iron powder, and the alloy components are dissolved in the iron powder. A method of diffusing the liquid into a liquid is also disclosed, but in this case, a drying process and treatment of waste liquid are required, which complicates the process and increases manufacturing costs.

In addition, in view of this situation, Japanese Patent Application No. 58-088498 states that during copper powder sintering, alloy components that have poor diffusivity into copper powder, such as Mo, are contained within a composition range that does not adversely affect compressibility. An alloy steel powder is disclosed in which the remaining alloy components are diffused and adhered in the form of powder to the surface of an atomized alloy steel powder that has been prealloyed, and a method for producing the same. According to this method, since Mo, which has a relatively high affinity with C, is prealloyed, the copper powder itself has excellent reactivity with C compared to the conventional mixed powder method, and the uniformity of the sintered body structure is improved. As a result, the tensile strength of the sintered body is approximately 5 kg/mm'' higher than that of the conventional mixed powder method.

[Problem that the invention seeks to solve]

The above steel powder has excellent properties as mentioned above, but
On the other hand, when the sintered body is carburized using the copper powder for the purpose of obtaining a high-strength sintered material, the sintered body is The steel powder particles themselves and the sintered neck portions of the steel powder particles are excessively carburized, resulting in poor impact toughness.

The present invention was made in view of the above circumstances, and it has high compressibility so as to obtain a high strength sintered material, and even when the sintered body is carburized, it has high strength and high impact. The object of the present invention is to provide an alloy steel powder for powder metallurgy that has good toughness and a method for producing the same.

[Means for solving problems]

In other words, the alloy steel powder for powder metallurgy of the present invention contains alloy components such as Ni, Mo, and C in a fine form in a pre-alloyed amount in a small amount to suppress and control the reaction between C and copper powder during carburizing treatment of a sintered body. It is characterized by being diffused and adhered to the surface of the steel powder, which is less compressible and crushed.

Further, the alloyed steel powder for powder metallurgy of the present invention is obtained by diffusing and adhering a second alloying component powder such as Cu or P to the surface of the steel powder in an arbitrary adhesion state or mixing and adding it in powder form to the above-mentioned alloyed steel powder. It is characterized by

In the present invention, "diffusion adhesion" means that the alloy components are not completely dissolved in the steel powder, but some of the alloy components from the alloy component powder are diffused into the steel powder, and other parts of the alloy component powder are dispersed. This means that the steel powder is bonded and adhered to the steel powder.

In addition, the alloy steel powder for powder metallurgy of the present invention has an upper limit of 10
．． 0% by weight of Ni and 0.1-0.4% by weight of M
This uses o.

Further, as the second alloy component, which is diffused or mixed onto the surface of the steel powder in the form of a powder without being restricted in its adhesion state, Cu is used with an upper limit of 3.5% by weight.

The method for producing alloyed steel powder for powder metallurgy of the present invention involves first adding Ni and Mo, which are alloying ingredients that suppress and control the reaction between the steel powder and C, to fine metal powder when carburizing the present alloyed steel powder sintered body. or disperse them in the form of their compounds in a liquid in which they are insoluble.

After sufficiently mixing this liquid and the steel powder to deposit alloy components on the surface of the steel powder, a drying process is performed as necessary, and Ni, Ni,
Mo is diffused and attached. Furthermore, if necessary, Cu is added to the surface of the steel powder in the form of a metal powder or compound, either before being diffused or as a mixed powder, in the form of a metal powder or a compound, which has a lower function of suppressing and controlling the reaction with C during carburizing than Ni or Mo.

[Effect]

When the sintered body using the steel powder of the present invention is carburized, the reactivity between the copper powder and C is suppressed and controlled. This is achieved by finely adhering Ni to the surface of the steel powder, which has a negative affinity with C and which diffuses into the steel powder at a slower rate than Cu during sintering.
Suppresses the diffusion of C into the sintering neck between steel powder particles and into the steel powder particles during carburizing. It also has a positive affinity with C,
Diffusion alloying into steel powder during sintering is slower than Cu.
By finely diffusing and adhering C to the surface of the steel powder, the spread of C into the steel powder particles during carburizing is suppressed. This action prevents embrittlement due to increased C concentration in the sintered neck portion and inside the steel powder particles, and improves the toughness of the carburized material.

[Specific structure of the invention]

In order for Ni and Mo to fully perform this action, it is first necessary to attach Ni and Mo to the surface of the steel powder particles and to suppress and control the diffusion of C into the sintering neck and into the steel powder particles. As stated above. The uniform adhesion to steel powder is such that the concentration of diffusion and adhesion to fine powder with a particle size of 44 gm or less is within the range of 0.9 to 1.9 times the concentration of diffusion and adhesion of each alloy component to the entire steel powder. It is necessary to diffusely adhere to the surface. Due to insufficient adhesion, fine Ni and Mo fall off from the surface of the steel powder particles, and the concentration of Ni and Mo for steel powder of 44 g, m or less is 1.9 times the concentration of each alloy component in the entire alloy steel powder. If it exceeds the carbon content, C diffuses into the steel powder particles from the surface of the steel powder where Ni and Mo have fallen off.
This is not preferable because it lowers the tenacity of the carburized material.

On the other hand, if the concentration of diffusion and adhesion of alloy components is 0.9 times or less than the steel powder of 444 m or less, the surface becomes Nt or M.

This is not preferable because the amount of fine iron and steel powder that is not sufficiently covered with carbon increases, and carbon diffuses into the fine iron and steel powder, which also reduces the toughness of the carburized material.

In addition, as mentioned earlier, when Mo exists on the surface of steel powder, it has the function of suppressing and controlling the reaction of steel powder with C, but in addition, Mo has the function of suppressing and controlling the reaction with C of steel powder when it exists on the surface of steel powder. Ni and Mo need to be attached to the surface of the steel powder at the same time in order to suppress the diffusion of Ni into the steel powder due to their affinity with the iron and steel powder, and to enhance the effect of Ni on suppressing the reaction between the steel powder and C.

Next, the insoluble liquid in which fine metal powders such as Ni and Mo and their compounds are dispersed is a liquid that does not react with these fine particles and has good wettability with the particles and steel powder (1) and can be removed by evaporation using normal drying methods. It is not particularly limited as long as it can be used, and examples thereof include alcohols such as methyl alcohol and ethyl alcohol, and aqueous solutions thereof.

In order to finely diffuse and adhere the alloy components in the form of powder to the surface of the steel powder, a fine alloy component powder, such as NiI# compound or Mo oxide, dispersed in the above-mentioned insoluble liquid and the steel powder are mixed. After mixing and drying if necessary, it may be heated to 700 to 1000°C in a reducing atmosphere such as a hydrogen gas atmosphere. Then, the reduced Ni and Mo will be absorbed into the steel powder at the contact surface with the steel powder. Ni and Mo are diffused and adhered to the steel powder. When the diffusion adhesion treatment is performed in this manner, the entire powder is usually in a solidified state, so it is crushed to the required particle size and further annealed as necessary.

Further, in order to further enhance the characteristics of the steel powder, Cu powder is added by diffusion or as a mixed powder.

The alloy steel powder of the present invention can be clearly distinguished from conventional steel powder by comparing the alloy component concentration for each grain size with the overall alloy component concentration.

N acts to suppress and control the reaction between steel powder and C during carburizing.
By diffusing and adhering i and Mo to the surface of steel powder particles,
As mentioned above, the toughness of the carburized sintered material using the alloy steel powder of the present invention is improved. Furthermore, since the adhesion of the alloy components is strong and uniform, macroscopic segregation of the alloy components is reduced, the uniformity of the sintered body structure is improved, and variations in the properties of the sintered body are reduced. Furthermore, because the adhesion is strong, there is less chance of alloy components falling off during the steel powder manufacturing process.

The yield of alloy components is improved. In addition, by using an insoluble liquid as the dispersion medium for wet mixing, it is possible to use ordinary water atomized raw powder drying equipment, and since no waste liquid is generated, there is no need for a waste liquid treatment process. Compared to the case, the process of adding alloying components becomes simpler and the cost of adding alloying components becomes cheaper. Furthermore, according to the present invention, all elements from which fine particles of metal powder or compound powder that can be dispersed in an insoluble liquid can be used as alloy components.

The reason why Ni, Mo, and Cu were selected as alloy components is as follows.

Ni suppresses and controls the reaction of steel powder with C.

Since Ni has poor diffusibility into steel powder, it suppresses the reaction between steel powder and C, as mentioned above, and when used simultaneously with Mo, its diffusivity becomes even slower, increasing the reaction suppression effect of C. . Ni diffused into the steel powder improves toughness and hardenability, and particularly in the sintered neck, it improves toughness along with the above-mentioned carburization suppressing effect.

Mo has a low diffusivity into steel powder and has a strong affinity with C, so it is present on the surface of the steel powder and prevents C from diffusing into the steel powder.Mo also has a strong affinity with Ni, so it prevents Ni from diffusing into the steel powder. and improves the toughness of carburized materials. Further, Mo dissolved in steel powder improves the hardenability and hardness of copper powder, as in the case of ordinary steel materials.

Cu increases the strength and toughness of the sintered body by temporarily producing a liquid phase during sintering, and improves the hardness by forming a solid solution.

Next, Ni and Mo are uniformly adhered to the surface of the steel powder, and Cu
The reason why is selected as an alloy component that does not require uniform adhesion is as follows. That is, as mentioned earlier, Ni and Mo, which are alloy components that suppress and control the reaction with C, need to be diffused and attached to the surface of the steel powder in order to achieve that purpose.
Nl and M.

Diffusion into steel powder is slow, especially when Ni and Mo are used at the same time, which makes it even slower, so it is less likely to be solid dissolved in steel powder during the production of copper powder, making it difficult to reduce the compressibility of alloyed steel powder. .

Cu also has the function of suppressing the reaction between C and steel powder.
However, Cu diffuses into the steel powder during sintering to a greater extent than Ni and Mo, and the ability to suppress the reaction with g
Inferior. Therefore, rather than uniform adhesion, it is more advantageous to use coarse powder to reduce the contact area with the steel powder, or to use mixed powder to prevent the compressibility of the steel powder from decreasing due to diffusion into the steel powder during production of copper powder. Depends on something.

Next, the upper limit of Ni is 10.0% by weight, and the upper limit of Mo is 0.1-0.
4% by weight, and the upper limit for Cu is 3.5% by weight, but the reason for limiting the range of these components is as follows.

Ni: The aforementioned effect increases as the amount of Ni added increases, but if the amount added exceeds 10.0% by weight, the surface of the copper powder will harden due to the Ni partially diffused and alloyed on the surface of the steel powder. Since the decrease in compressibility becomes large, the upper limit was set at 10.0% by weight. If it is 10.0% by weight or less, when it is used simultaneously with Mo, the diffusion of Ni into the steel powder is suppressed, so there is little decrease in compressibility, and in order to exhibit the effect of N1, it is necessary to use 0.5% by weight or more. It is desirable to add

Mo: Mo has the above-mentioned effect when added in an amount of 0.1% by weight or more, and if the amount added exceeds 0.4%, Mo concentration on the steel powder surface increases because Mo has poor diffusivity. The lower limit is set to 0.1 because the decrease in compressibility due to hardening of
The upper limit was set to 0.4% by weight.

Cu: The above-mentioned effect of Cu increases as the amount added increases, but since Cu has excellent diffusion into steel powder, especially to grain boundaries, it is better to attach the aforementioned Ni and Mo to the surface of steel powder. Even if the diffusion of Cu into the steel powder is suppressed, if the content exceeds 3.5% by weight, the compressibility of the copper powder will decrease due to partially diffused Cu, so the upper limit was set at 3.5% by weight. Also, Cu
In order to exhibit this effect, it is desirable to add O, 11% or more.

〔Example〕

Next, this invention will be explained in more detail according to examples.

Example I Ni oxide and Mo oxide were dispersed in methyl alcohol, mixed with iron powder, dried, reductively annealed in a hydrogen gas atmosphere at 100°C for 1 hour, and then crushed into steel powder A. ,
Table 1 shows the alloy component concentration by particle size of steel powder B, which was dry mixed with iron powder and subjected to reduction annealing in a hydrogen gas atmosphere under the same conditions as steel powder A, and then crushed. It was shown to.

In steel powder A, fine powder Ni and Mo with a steel powder particle size of 44 meters or less are used.
5 degrees is 1.40 times the value of the entire alloy steel powder, and 1.
47 times, which is within the range of 0.9 times to 1.9 times, but for steel powder B, it is 2.45 times and 2.66 times, both more than twice, and the uniform adhesion of alloy components is It is clear that the steel powder A according to the invention is superior to the steel powder B produced by the conventional method.

Example 2 Same method as steel powder A of Example 1, but with 3 levels of Ni
After finely diffusing and adhering a certain amount of Mo to the surface of the steel powder, a certain amount of Cu was mixed into the powder and annealed in a hydrogen atmosphere at 800°C for one hour to diffuse and adhere Cu to the obtained alloy steel powder. 1.
7t/cr by adding and mixing 0% zinc steering acid
Molding was performed at a molding pressure of n'. The copper powder chemical composition and green powder density in this example are shown in Table 5112.

From Table 2, when the Ni content is 4% by weight, a high green density of 7.15 g/crn' was obtained at a compacting pressure of 7L/crn', but if the Ni content exceeds 10.0% by weight, the steel powder It is clear that the density of green powder decreases rapidly because the amount of Ni diffused into the surface increases.

Table 2 Example 3 Same method as in Example 2, but with 3 levels of M.

1.0% zinc stearate was added to alloyed steel powder obtained by alloying a certain amount of Ni and Cu, and 7t/
The steel powder chemical composition and green powder density in this example are shown in Table 3.

Table 3 From Table 3, Mo amount 0.3fE maximum% is 7t/crn'c
7) Although a high green density of 7.15 g/cmj was obtained under the molding pressure, it is clear that the green density sharply decreases if Mofl exceeds 0.4 fi%.

Example 4 An alloyed steel powder obtained by alloying three levels of Cu with a certain amount of Ni and Mo in the same manner as in Example 2, except that 1.0
% of zinc stearate was added and mixed and molded at a molding pressure of 7 t/cm''. Table 4 shows the chemical composition of the steel powder and the density of the green powder in this example.

4th surface (2) ■ Powder density steel Powder Ni Mo Cu (g/crrOC3,940,
341,457,15 H3,940,342,517,16 From Table 4, with a Cu content of 2.5% by weight, a high green density of 7.15g/crn' was obtained at a molding pressure of 7t/cm''. It is clear that when the amount of Cu exceeds 3.5% by weight, the green density decreases rapidly.

Example 5 0.1% graphite and 1.0% zinc stearate were added and mixed to the steel powder A of Example 1 and the steel powder J obtained by adding Cu to the steel powder A as a mixed powder. Impact test pieces and tensile test pieces were molded at a molding pressure of cr rn'. This compact was sintered in an ammonia decomposition gas atmosphere at 1200°C for 1 hour, then carburized for 2.5 hours in a propane converted gas atmosphere with a carbon potential of 0.9%, then quenched in oil and heated to 170°C.
Tempering was performed. Table 5 shows the copper powder chemical composition and green density of this example, and Table 6 shows the impact value and tensile strength.

According to Tables 5 and 6, the copper powder according to the present invention can obtain high impact value and tensile strength by carburizing, but especially C
It is clear that the properties are further improved by adding u.

Table 5 Table 6 1) 10mm square x 55mmL impact test piece 2 without notch
) JSPM standard tensile test piece Example 6 Same method as Example 2, except for Ni and Mo.

Steel powders K and Lt according to the present invention were adjusted in which the amount of Cu added was constant but the mixing time was varied for Ni and Mo. To this steel powder K, fine iron powder whose surface was not coated with Ni and Mo and whose particle size was 447 zm or less was added to obtain steel powder M.

In addition, N was used as the copper powder obtained by conventional dry mixing. 0 for these
．． 1% graphite and 1.0% zinc stearate were added and mixed and molded into impact test pieces and tensile test pieces at a molding pressure of 7 t/cm'', and this green compact was subjected to the same conditions as in Example 5. After sintering and carburizing and quenching, it was tempered.The chemical composition and green density of these steel powders by particle size are shown in Table 7, and the impact value and tensile strength are shown in Table 8.
Shown in the table.

Table 8 1) 10mm square x 55mmL impact test piece without notch 2) J
From Tables 7 and 8 of SPM standard tensile test specimens, it is found that in fine-grained alloy steel powder with a grain size of 44 Bm or less, Ni and Mo are within the aiIi range of 0.9 to 1.9 times the concentration of each of the whole alloy steel powder. 2.18 to 2.21 kg・m/cm" if it is evenly deposited,
A high impact value and tensile strength of 98 kgf/mrn' to 105 kgf/mrn' were obtained, but when the ratio of 1-alloy acid adhesion is less than 0.9 times or exceeds 1.9 times, the impact value decreases rapidly. That is clear.

〔Effect of the invention〕

As is clear from the above explanation, the alloyed steel powder for powder metallurgy of the present invention contains an alloy component that suppresses and controls the reaction with C during carburizing of a sintered body on the surface of the steel powder with a reduced amount of pre-alloy. In addition, since the alloy steel powder of the present invention is made by diffusion and adhesion, it has excellent compressibility, and in particular, when a sintered body using this copper powder is carburized, high toughness can be obtained. has advantages.

Claims (1)

[Scope of Claims] 1. Two or more powdered alloy components are diffused and adhered to the surface of the steel powder, and the concentration of each alloy component diffused and adhered to the steel powder with a particle size of 44 μm or less is the same as the concentration of each of the alloy components relative to the entire steel powder. An alloy steel powder for powder metallurgy, characterized in that the concentration range is 0.9 to 1.9 times the diffusion and adhesion concentration of. 2. The alloy steel powder for powder metallurgy according to claim 1, which uses Ni and Mo as alloy components. 3 The upper limit of Ni is 10.0% by weight, and the upper limit of Mo is 0.1-0.
The alloy steel powder for powder metallurgy according to claim 2, wherein the content is 4% by weight. 4. A first alloy component consisting of two or more types of powder is diffused and adhered to the surface of the steel powder, and the concentration of each of the alloy components diffused and adhered to the steel powder with a particle size of 44 μm or less is the same as the concentration of each of the alloy components to the entire steel powder. The second alloy component powder, which has a concentration range of 0.9 to 1.9 times the concentration of diffused deposit and is composed of one or more types, is diffused and deposited on the surface of the steel powder in any desired state, or mixed and added in powder form. An alloy steel powder for powder metallurgy characterized by the following. 5 Using Ni and Mo as the first alloy components, the second
The alloy steel powder for powder metallurgy according to claim 4, wherein Cu is used as the alloy component. 6 The upper limit of alloy content is 10.0% by weight for Ni and 0.1% for Mo.
The alloy steel powder for powder metallurgy according to claim 5, wherein the upper limit of Cu is 3.5% by weight. 7 An alloy component consisting of a fine powder of metal powder or a metal compound is dispersed in a liquid that is insoluble therein, mixed with steel powder, and then reduced annealed to coat the surface of the steel powder with the alloy component. A method for producing alloy steel powder for powder metallurgy, characterized by diffusion adhesion.