JPH0237401B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an alloy steel powder for powder metallurgy used for manufacturing various sintered parts and a method for manufacturing the same. [Prior Art] 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 and has the disadvantage that its uses are limited. Therefore, recently, in order to compensate for the above-mentioned drawbacks, a technique has been developed in which alloy steel powder is used in place 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 some extent, it may reduce formability, cause non-uniform structure due to powder segregation during compaction, and even cause uneven structure due to poor solid solution diffusion during sintering. There is a problem that uniformity may occur. Therefore, it is possible 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 alloy components with low diffusibility into iron powder, such as Mo, in a reducing atmosphere. A method has been disclosed in which Mo oxide is evaporated and reduced by heating at a temperature of 100 mL, and Mo oxide is precipitated and deposited as fine Mo on the surface of pure iron powder. This method complicates the Mo addition process, may reduce the Mo addition yield, and is difficult to apply to alloy components whose oxides, unlike Mo, 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. Needless to say, in addition to such cost problems, this prior art has the following essential problems. The problems with the prior art are as follows: First, the metal salt precipitates out of the solution mainly as plate-like or columnar crystals, so the precipitates are easily broken due to their shape, and the dried and deposited salt itself is fragile. Since iron powder is inherently brittle, it is easy to predict that the precipitated crystals will break and fall off the surface of the iron powder when the iron powder is handled after drying. Secondly, the crystals of these metal salts contain a large amount of non-metal elements such as C, N, O, and H compared to metal oxides, so as shown in Table 1, crystals form when heated. These crystals thermally decompose at a temperature much lower than that at which the metal elements inside are reduced and diffused and sintered on the surface of the iron powder. Therefore, voids are created between the surface of the iron powder and the attached crystals where C, N, O, H, etc. have escaped due to the decomposition of the crystals, from which the crystals peel off and fall off. The crystal itself also thermally decomposes at a temperature lower than that at which the reduction and diffusion sintering of the metal element occurs on the surface of the iron powder, releases the gasified components in the crystal, and collapses into a porous body. For this reason, crystals peel off and fall off from the surface of the iron powder during heating for reduction. Thirdly, these crystals have the property of releasing crystal water and melting when heated at a temperature that is lower than the temperature at which metal elements undergo reduction and diffusion sintering on the surface of iron powder. During heating, crystals peel off and fall off the surface of the iron powder.

[Problem that the invention seeks to solve]

The above-mentioned steel powder has excellent properties as mentioned above, but on the other hand, when the sintered body is carburized for the purpose of obtaining a high-strength sintered material using the steel powder, the steel As mentioned above, since the powder has excellent reactivity with C, the problem of poor impact toughness due to excessive carburization in the steel powder particles themselves constituting the sintered body and in the sintered necks between the steel powder particles can be avoided. had. The present invention was made in view of the above circumstances, and has high compressibility so as to obtain a high strength sintered material,
The object of the present invention is to provide an alloy steel powder for powder metallurgy that can provide high strength and high impact toughness even when the sintered body is carburized, and a method for producing the same. [Means for solving the problem] In other words, the alloy steel powder for powder metallurgy of the present invention contains alloy components such as Ni, Mo, and Cr that suppress and control the reaction between C and steel powder during carburizing treatment of a sintered body. in a minute form,
It is characterized by having a small amount of pre-alloy and being diffused and adhered to the surface of the steel powder, which has excellent compressibility. In addition, 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 adhering state to the above alloyed steel powder, or adding it in a mixed powder form. 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 uses Ni with an upper limit of 10.0% by weight and Mo with 0.1 to 0.4% by weight as alloying components that are diffused and adhered to the surface of the steel powder in the form of fine powder. . Further, Cu is used in an upper limit of 3.5% by weight as the second alloy component which can be diffused or mixed onto the surface of the steel powder in powder form without any restrictions on its adhesion state. The method for producing an alloy steel powder for powder metallurgy of the present invention first includes Ni and Mo, which are alloy components that suppress and control the reaction between the steel powder and C when carburizing the present alloy steel powder sintered body.
in the form of fine metal powders or their compounds,
Disperse them in a liquid that is insoluble in them. After sufficiently mixing this liquid and steel powder to adhere alloy components to the surface of the steel powder, a drying process is performed as necessary, and Ni, Mo is coated on the surface of the steel powder in a reducing atmosphere such as a hydrogen gas atmosphere. Diffuse and attach. Furthermore, if necessary, the function of suppressing and controlling the reaction with C during carburizing is also available.
Cu, which is smaller in amount than Ni and Mo, is added in the form of metal powder or compound to the surface of steel powder by diffusion or mixing. [Function] When the sintered body using the steel powder of the present invention is carburized, the reactivity between the steel 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 is slower to diffuse into the steel powder during sintering than Cu. Suppresses the diffusion of C into the joints and steel powder particles. Mo also has a positive affinity with C, and diffusion alloying into steel powder during sintering is slower than that of Cu.
By finely diffusing and adhering C to the surface of the steel powder, the diffusion of C into the steel powder particles during carburizing is suppressed. This action prevents embrittlement due to increased C concentration in the sintered neck 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 sufficiently perform this action, Ni and Mo are attached to the surface of the steel powder particles to suppress and control the diffusion of C into the sintering neck and into the steel powder particles. As mentioned above, you need to do this. In particular, its uniform adhesion is such that the concentration of fine particles with a particle diameter of 44 μm or less is in the range of 0.9 to 1.9 times the concentration of each alloy component relative to the entire steel powder. There is a need. If the adhesion is insufficient and fine Ni and Mo fall off the surface of the steel powder particles, and the concentration of Ni and Mo in the steel powder of 44 μm or less exceeds 1.9 times the concentration of each alloy component in the entire alloy steel powder. Ni and Mo
This is not preferable because carbon diffuses into the steel powder particles from the surface of the steel powder that has fallen off, reducing the toughness of the carburized material. On the other hand, if the diffusion adhesion concentration of alloy components is less than 0.9 times that of steel powder of 44 μm or less, there will be many fine steel powder whose surface is not sufficiently coated with Ni and Mo, and C will diffuse into this fine steel powder, resulting in carburization. This is not preferred because it reduces the toughness of the treated 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, when Mo is present on the surface of steel powder, Ni Mi due to its affinity with
Ni and Mo
must be attached to the surface of the steel powder at the same time. Next, the insoluble liquid in which the fine metal powders of Ni and Mo disperse these compounds is a liquid that does not react with these fine particles and has good wettability with the particles and steel powder.
It is not particularly limited as long as it can be removed by evaporation by a normal drying method, 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 powder form to the surface of the steel powder, fine alloy component powders such as Ni oxide and Mo oxide dispersed in the above-mentioned insoluble liquid are mixed with the steel powder. After mixing and drying if necessary, in a reducing atmosphere such as hydrogen gas atmosphere.
All you have to do is heat it to 700-1000℃. By doing so, the reduced Ni and Mo will partially diffuse into the steel powder at the contact surface with the steel powder, resulting in a state in which 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 sintered if necessary. In order to further enhance the properties of 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. Next, the difference from the conventional technology using soluble salts will be explained. Normal alloyed steel powder for powder metallurgy, which is the raw material for alloyed iron powder, contains about 30% of particles with a particle size of 44 μm or less. Therefore, if the concentration of the alloy component in particles with a particle size of 44 μm or less is 1.9 times or more of the total concentration, the concentration of the alloy component in particles with a particle size of more than 44 μm is 0.6 times or less of the total concentration. In this case, particles with a particle size of more than 44 μm have an insufficient amount of alloy with respect to the originally required alloy concentration, and a portion of the surface of the iron powder particles with a particle size of more than 44 μm is not coated with the alloy component. When a sintered body using this powder is carburized, the particles are excessively carburized from the portions not covered with the particle alloy component, reducing the impact value of the sintered body. Also a total of 70
The strength and hardness of the sintered body also decreases due to the insufficient amount of alloyed iron powder particles exceeding 44 μm, which account for 1% of the total. On the other hand, if the concentration of alloy components in particles with a particle size of 44 μm or less becomes 0.9 times or less of the total concentration, the particles with a particle size of 44 μm or less
Since it has a specific surface area about 8 times that of particles with a particle size of more than 44 μm, the degree of coverage of the surfaces of particles with a particle size of 44 μm or less with alloy components is about 1/8 compared to that of particles with a particle size of more than 44 μm. For this reason, a portion is formed on the surface of particles with a particle size of 44 μm or less that is not coated with the alloy component, and from this portion, the particles with a particle size of 44 μm or less are excessively carburized. Considering that particles with a particle size of 44 μm or less account for about 30% of the total, this excessive carburization cannot be ignored, and it not only reduces the impact value of the carburized material but also reduces its strength and hardness. From the above point of view, the method using soluble salts essentially results in extremely unstable and non-uniform deposition distribution of alloy components, and cannot achieve the original purpose of uniform deposition.
For example, when nickel formate (Ni(HCO ₂ ) ₂ ) is used, nickel formate starts to decompose at temperatures below 200°C, and further decomposes violently at 270°C. For this reason,
The degree of adhesion of Ni to particles with a particle size of 44 μm or less is 2.4 times the concentration of the entire iron powder, which is 0.9 to 1.
It is significantly inferior to 9 times. As described above, the prior art methods using soluble salts inherently have problems, and no matter which raw materials are used, it is impossible to obtain an excellent adhesion degree of alloy components of 1.9 times or less. In contrast, as in the present invention, the adhesion of alloy components is reduced.
Alloyed iron powder, which is 0.9 to 1.9 times, has never existed before. Such alloyed iron powder uses fine Ni powder and insoluble metals or oxides such as nickel oxide, so that the alloy components remain in a stable powder form without decomposing up to near the reduction, diffusion, and sintering temperatures. This can only be achieved by utilizing the property of drying and fixing the iron powder to follow the shape of the surface of the iron powder, which is extremely difficult to fall off from the surface of the iron powder both when handling it after drying and during reduction. By diffusing and adhering Ni and Mo, which have the function of suppressing and controlling the reaction between steel powder and C during carburizing, to the surface of the steel powder particles, the toughness of the carburized material of the sintered compact using the alloy steel powder of the present invention can be improved. As mentioned earlier, this improves performance. 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, since the adhesion is strong, there is less chance of alloy components falling off during the steel powder manufacturing process, improving the yield of alloy components. 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 there is no need for a waste liquid treatment process that does not generate waste liquid. The process of adding alloying components is simpler than that, and the cost of adding alloying components is lower. Further, according to the present invention, the elements obtained from fine particles of metal powder or compound powder that can be dispersed in an insoluble liquid can be used as all 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. Ni
Since Mo has poor diffusivity 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 and C
Enhances the reaction suppression effect of Diffused into steel powder
Ni improves toughness and hardenability, and particularly in the sintered neck part, it improves toughness along with the above-mentioned carburization suppressing effect. Mo has a low diffusivity into steel powder and a strong affinity with C, so it is 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 entering the steel powder. Prevents diffusion and improves toughness of carburized materials. In addition, Mo dissolved in steel powder increases the hardenability and hardness of steel powder, as in the case of ordinary steel materials. Cu increases the strength and toughness of the sintered body by releasing a liquid phase during sintering, and improves the hardness by forming a solid solution. Next, the reason why Ni and Mo were uniformly adhered to the surface of the steel powder and Cu was selected as an alloy component that does not require uniform adhesion is as follows. In other words, as mentioned earlier, Ni is an alloy component that suppresses and controls the reaction with C.
and Mo must be diffused and adhered to the surface of the steel powder to achieve that purpose. Ni and Mo diffuse slowly into steel powder, and it becomes even slower when Ni and Mo are used at the same time. Therefore, the solid solution in steel powder during steel powder production is small, and the compressibility of alloy steel powder is improved. Hard to degrade. 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 its ability to suppress the reaction with C is inferior to Ni and Mo. Therefore, rather than uniform adhesion, it is more advantageous to use coarse-grained 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 steel powder production. By being. Next, the upper limit of Ni is 10.0% by weight, the upper limit of Mo is 0.1 to 0.4% by weight, and the upper limit of 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 when the amount added exceeds 10.0% by weight, Ni is partially diffused and alloyed on the surface of the steel powder, causing compression to harden the surface of the steel powder. The upper limit was set at 10.0% by weight since the deterioration in properties would be significant. When Ni is used at the same time as Mo at 10.0% by weight or less, the diffusion of Ni into the steel powder is suppressed, so there is little decrease in compressibility. In addition, in order to demonstrate the effect of Ni, 0.5
It is desirable to add more than % by weight. Mo: Mo has the above-mentioned effect when added in an amount of 0.1% by weight or more. If the amount added exceeds 0.4%, Mo concentration on the surface of the steel powder will increase because Mo has poor diffusivity.
Since the hardening of the surface of the steel powder significantly reduces compressibility, the lower limit was set to 0.1% by weight and the upper limit to 0.4% by weight. Cu: The above-mentioned effect becomes greater as the amount of Cu added increases.The reason for this is that the above-mentioned effect of Cu increases as it diffuses into the steel powder, especially to the grain boundaries.
Even if Ni or Mo is attached to suppress the diffusion of Cu into the steel powder, if the concentration exceeds 3.5% by weight, the compressibility of the steel powder will decrease due to partially diffused Cu, so the upper limit should be set.
The content was 3.5% by weight. Further, in order to exhibit the effect of Cu, it is desirable to add 0.1% by weight or more. [Example] Next, the present invention will be described in more detail with reference to Examples. Example 1 After dispersing Ni oxide and Mo oxide in methyl alcohol containing 10% of the weight of the iron powder to be finally mixed, they were mixed with the iron powder for 10 minutes, and then heated and mixed at 80°C for 30 minutes in methyl alcohol. After drying, the steel powder A, which was reduced after reduction annealing at 1000℃ for 1 hour in a hydrogen gas atmosphere, was mixed with Ni oxide and Mo oxide in a dry process. Table 2 shows the alloy component concentration by particle size of steel powder B, which was obtained by removing agglomerated particles before mixing, and after mixing, reduction annealing in a hydrogen gas atmosphere under the same conditions as steel powder A, and then crushing. In steel powder A, fine-grained Ni with a steel powder particle size of 44 μm or less,
The Mo concentration is 1.40 times the value of the whole alloy steel powder, respectively.
1.47 times, both within the range of 0.9 times to 1.9 times, but for steel powder B, they are 2.45 times and 2.66 times, both more than double, and steel powder A according to the present invention is superior in terms of uniform adhesion of alloy components. It is clear that the steel powder B obtained by the conventional method is superior to the steel powder B produced by the conventional method.

[Table] Example 2 Using the same method as steel powder A in Example 1, however, three levels of Ni and a certain amount of Mo were finely diffused and adhered to the surface of the steel powder, and then a certain amount of Cu was mixed into the powder. Cu was diffused and adhered by annealing in a hydrogen atmosphere at 800°C for 1 hour, and 1.0% zinc steering acid was added to and mixed with the obtained alloy steel powder, followed by molding at a molding pressure of 7 t/cm ² . Table 3 shows the steel powder chemical composition, alloy component concentration and green powder density according to particle size in this example. From Table 3, a high green density of 7.15 g/cm ² was obtained at a compacting pressure of 7 t/cm ² when the Ni content was 4% by weight.
It is clear that when the amount of Ni exceeds 10.0% by weight, the amount of Ni diffused onto the surface of the steel powder increases, resulting in a sharp decrease in the green powder density.

[Table] Example 3 Using the same method as Example 2, but with three levels of Mo
By adding and mixing 1.0% zinc stearate to the alloy steel powder obtained by alloying a certain amount of Ni and Cu,
Molding was performed at a molding pressure of 7t/cm ² . Table 4 shows the steel powder chemical composition, alloy component concentration and green powder density according to particle size in this example.

[Table] From Table 4, a high green density of 7.15 g/cm ² was obtained at a molding pressure of 7 t/cm ² with a Mo content of 0.3% by weight.
It is clear that when the amount of Mo exceeds 0.4% by weight, the green density decreases rapidly. Example 4 Using the same method as Example 2, but with three levels of Cu
By adding and mixing 1.0% zinc stearate to the alloyed steel powder obtained by alloying a certain amount of Ni and Mo,
Molding was performed at a molding pressure of 7t/cm ² . Table 5 shows the steel powder chemical composition, alloy component concentration and green powder density according to particle size in this example.

[Table] From Table 5, a high green density of 7.15 g/cm ³ was obtained at a molding pressure of 7 t/cm ² with a Cu content of 2.5% by weight, but Cu
It is clear that when the amount 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 which was prepared by adding Cu to the steel powder A as a mixed powder, and the molding pressure was 7t/ ^cm2. Impact test specimens and tensile suspension test specimens were molded. This green compact was heated to 1200°C x 1 in an ammonia decomposition gas atmosphere.
After being sintered for an hour, it was carburized for 2.5 hours in a propane modified gas atmosphere with a carbon potential of 0.9%, quenched in oil, and tempered at 170°C. The chemical composition and green powder density of this example are shown in Table 6, and the impact value and tensile strength are shown in Table 7. According to Tables 6 and 7, it is clear that the steel powder according to the present invention can obtain high impact values and tensile strengths by carburizing, and that its properties are particularly improved by adding Cu.

【table】

[Table] Example 6 Same method as Example 2, except that Ni, Mo, Cu
Steel powders K and L according to the present invention were prepared by varying the mixing time of Ni and Mo while adding a constant amount. On the other hand, in order to make the final alloy content of the entire steel powder the same as K and L, the same alloying raw materials as steel powders K and L are used, but the alloying raw materials are dry-processed in the same way as steel powder B. They were mixed to obtain steel powder M. However, in Steel Powder M, like Steel Powder B, agglomerated particles of 44 μm or more in the alloy component raw materials were used without being removed before mixing. Further, steel powder N, like steel powder B, was used by removing agglomerated particles having a particle diameter of 44 μm or more from the alloy component raw materials before mixing. Further, the steel powder obtained by conventional dry mixing was N. These include 0.1% graphite and
7t/mix by adding 1.0% zinc stearate.
The compacts were molded into impact test pieces and tensile test pieces at a molding pressure of cm ² , and the compacts were sintered under the same conditions as in Example 5.
After carburizing and quenching, it was tempered. Table 8 shows the chemical composition and green density of each steel powder, and Table 9 shows the impact value and tensile strength.

【table】

[Table] From Tables 8 and 9, when Ni and Mo are uniformly deposited within the range of 0.9 to 1.9 times the concentration of each of the whole alloy steel powder in fine grain powder with a grain size of 44 μm or less is 2.18~2.21Kg・m/ ^cm2 , 98Kg
A high impact value and tensile strength of f/mm ² to 105 Kgf/mm ² were obtained, but it is clear that the impact value decreases rapidly when the ratio of alloy component adhesion is less than 0.9 times or exceeds 1.9 times. . Although there is not much difference in compressibility between Examples K and L and Comparative Examples M and N, there is a clear difference in impact value as shown in Table 8. The aim of the present invention is to achieve both high impact value and high compressibility. Example 7 Nickel formate and ammonium paramolybutate were dissolved in water containing 10% of the weight of the iron powder to be finally mixed, mixed with the iron powder for 10 minutes, and further heated at 100°C.
After drying the water while heating for 30 minutes, it was reduced annealed and crushed in the same manner as in Example A to obtain Comparative Example Steel Powder O. Table 10 shows the chemical composition of the steel powder in this comparative example, and the concentration of alloy components according to particle size. Steel powder O is a conventional method using soluble salts, so
For both Ni and Mo, the concentrations of Ni and Mo in the fine powder of alloy steel powder with a particle size of 44 μm or less are 2.42 times and 2.32 times the respective concentrations of the whole alloy steel powder, which is 1.9 times. The impact value and tensile strength of the carburized sintered material using this steel powder cannot be as excellent as those obtained when the steel powder according to the present invention is used.

〔Effect of the invention〕

As is clear from the above explanation, the alloy steel powder for powder metallurgy of the present invention has a carbon content during carburization of a sintered body.
The alloyed steel powder of the present invention has excellent compressibility, and is made by finely diffusing and adhering the alloy component that suppresses and controls the reaction with the present steel powder to the surface of the steel powder with a reduced amount of prealloy. When a sintered body made of powder is carburized, it has advantages such as high toughness.

Claims (1)

[Claims] 1. Ni and Mo are used as alloy components, and the two types of alloy components in powder form 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 An alloy steel powder for powder metallurgy, characterized in that the concentration range is 0.9 to 1.9 times the concentration of each alloy component diffused and adhered to the entire steel powder. 2. The alloy steel powder for powder metallurgy according to claim 1, wherein the upper limit of Ni is 10.0% by weight and the upper limit of Mo is 0.1 to 0.4% by weight. 3 Using Ni and Mo as the first alloy components,
Cu is used as the second alloy component, and the powdered first alloy component 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 that of the entire steel powder. The concentration range is 0.9 to 1.9 times the concentration of each alloy component diffused and deposited, and the second alloy component powder is diffused and deposited on the surface of the steel powder in an arbitrary state of adhesion, or is mixed and added in a powder state. Alloy steel powder for powder metallurgy. 4 The upper limit of alloy content for Ni is 10.0% by weight, and for Mo 0.1~
The alloy steel powder for powder metallurgy according to claim 3, wherein the content of Cu is 0.4% by weight, and the upper limit of Cu is 3.5% by weight.