JPS635441B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an alloy steel powder used for manufacturing a high-density, wear-resistant sintered alloy having a fine sintered structure. Conventionally, wear-resistant chilled cast iron, heat-treated steel, etc. have been used for parts with sliding surfaces that are subject to large surface pressure, such as valve locker arms, cams, and tappets of internal combustion engines, or parts that have such parts. Nowadays, even greater durability is required. Therefore, attempts have been made to use high carbon sintered alloys containing Cr etc. obtained by powder metallurgy. In other words, according to the powder metallurgy method, a powder with a predetermined composition or a mixture of multiple types of powder is molded in a mold and sintered in a reducing or neutral atmosphere or in a vacuum to cause sufficient shrinkage. , it is possible to obtain a high-density, wear-resistant sintered alloy in which carbides are dispersed. The metal powder used to produce such a sintered alloy is made by spraying molten alloy steel containing alloying elements such as Cr that are difficult to diffuse into Fe in the form of a pre-alloy during the sintering process. In this method, an element such as C, which is easily diffused, is added to alloyed steel powder using a mixed powder method. The atomization process, in which a stream of molten steel is splashed and solidified into powder by a jet of water or other liquid stream, yields alloyed steel powder of irregular shape that allows molding. Further, the particle size of the alloy steel powder used in the production of the above-mentioned conventional wear-resistant sintered alloy is usually adjusted according to the conventional atomized pure iron powder or atomized stainless steel powder. The wear-resistant sintered alloy using the above-mentioned alloy steel powder is
It has high hardness due to the inclusion of carbide, but if the carbide becomes coarse, impact resistance will be impaired, so it must have a fine structure. Also,
Since the presence of pores significantly deteriorates pitting resistance, a low porosity, that is, a low true density and a low sintered density are required. However, when sintering is performed using conventional alloy steel powder for wear-resistant sintered alloys, it is extremely difficult to simultaneously satisfy these conditions. In other words, if the carbide is sintered to the extent that it does not become coarse, high density cannot be obtained; on the other hand, if the sintering conditions are such that the carbide becomes coarse, the carbide will become coarse and shrinkage during sintering will not occur. There was a problem that the sintered body tends to become uniform, causing distortion in the sintered body. To overcome this problem, it is possible to manufacture wear-resistant sintered alloy products with a high density and fine structure using the sinter forging method or hot isostatic pressing method, but the process is complicated and productivity is low. The problem was that it was inferior and expensive. An object of the present invention is to solve the problems caused by the conventional methods described above and to provide a spray alloyed steel powder for producing a sintered alloy with high density, low shape distortion, and a fine structure. . Therefore, the steel powder for wear-resistant sintered alloys according to the present invention has a weight ratio of 3 to 20% Cr, 0.3 to 2% Si, and 0.3% C.
Contains N0.2% or less and has an average particle size of 30
It is characterized by being an atomized steel powder in the range of ~50μm. In addition, the steel powder for wear-resistant sintered alloys according to the present invention may contain a total of 50% Ni and Cu as required.
% or less, and the total content of one or more of V, Mo, and W is preferably 5% or less. The average particle size of the alloy steel powder according to the present invention is JISR600
+100 mesh with the value specified using the particle size distribution results from sieve analysis in accordance with 1956.
161μm, -100/+150 mesh to 126μm, -150/
+200 mesh is 89μm, -200/+250 mesh is
It was calculated based on the assumption that 68 μm, −250/+325 mesh is 52 μm, and −325 mesh is 22 μm. The method of making the alloy steel powder according to the present invention have the above average particle size of 30 to 50 μm is by adjusting the spray jet during spraying, or, if necessary, by annealing the powder after spraying. However, it can be obtained by crushing particles that have been sintered and agglomerated during annealing and adjusting them to a predetermined particle size. Further, the spraying method may be any method in which molten steel is sprayed with a jet of liquid such as water or oil, and there are no restrictions on the equipment. For example, special public service in Showa 52-
The method described in Publication No. 19540 can be adopted. The reason for limiting the composition range of the steel powder of the present invention will be explained below. In the sintered body, Cr dissolves in Fe to strengthen the matrix, and also combines with added C during sintering to form carbides, increasing the hardness of the sintered body and improving wear resistance. improve. It also has the effect of reducing the surface energy of molten steel during spraying, improving spray efficiency and making it easier to obtain fine-grained steel powder. If the Cr content is less than 3%, these effects will be small, and if the Cr content exceeds 20%, no further effects will be obtained. In the sintered body, Si dissolves in Fe to strengthen the matrix and also has the effect of preventing oxidation of molten steel during spraying. If it is less than 0.3%, no anti-oxidation effect is observed, and if it exceeds 2%, the hardness of the sintered body decreases.
Impairs wear resistance. C and N in the steel powder must be kept low because they increase the hardness of the steel powder and impair compressibility and formability. If C exceeds 0.3% and N exceeds 0.2%, 6t/cm ²
When compacted at ^a pressure of Even if the density is obtained, the amount of shrinkage due to sintering is large, resulting in large distortion of the sintered body. In order to incorporate C into the wear-resistant sintered alloy using the steel powder according to the present invention, it is necessary to add it to the spray alloyed steel powder by a mixing method. Further, as mentioned above, depending on the purpose, the alloy steel powder according to the present invention may contain 5% or less of Ni and Cu in total.
Ni within a range of 5% or less in total for V, Mo and W,
Cu, V, Mo, and W can be contained. It is difficult for any of these elements to be added to steel powder by a mixing method and sufficiently diffused during sintering, and therefore it is desirable to include them as a pre-alloy when producing alloy steel powder by a spraying method. Ni and Cu are dissolved in Fe in the sintered body to strengthen the matrix and make carbides finer, but even if the total amount exceeds 5%, there is no further effect. I can't get it. V, Mo and W form a solid solution in Fe in the sintered body to strengthen the matrix, and also combine with added C to form carbides and improve wear resistance, but the total amount is 5%. Exceeding this will actually impair toughness. Unavoidable impurities are mixed in from dissolved materials.
These include Mn, P, S, Al, etc., and O, which is mainly captured by the oxidation of steel powder during spraying or annealing, and improves the formability and compressibility of steel powder and the wear resistance of sintered alloys. In order not to impair performance, it is necessary to limit the total amount of these to 2% or less. Next, the reason for limiting the average particle size of steel powder to 30 to 50 μm will be explained. A spraying method using a liquid such as water or oil as a spraying medium is an advantageous steel powder manufacturing technique because it allows relatively free selection of the alloy composition of the powder and the process is simple. Therefore, it is widely used for powder metallurgy, but all ordinary steel powders for powder metallurgy have an average particle size exceeding 50 μm as determined from particle size distribution by sieve analysis. However, in order to obtain a high-density sintered alloy with carbide dispersion heat, a sufficient effect cannot be obtained with such comparatively coarse-grained steel powder. In other words, if the particle size of the powder is coarse, sintering properties are poor, making it difficult to obtain a high-density sintered alloy, and since the crystal grains of the alloy during sintering are also large, carbides formed at the grain boundaries will grow and become coarse. Cheap. Furthermore, since large pores are present in the green compact, shrinkage that occurs during sintering is difficult to progress uniformly, resulting in large distortions in the shape of the sintered compact. Furthermore, large pores remain in the sintered body, which deteriorates pitting resistance. Moreover, especially when mixing and adding powders containing P, B, etc. to alloy steel powder to easily generate a liquid phase during sintering and sintering at a relatively low temperature, it is necessary to mix and add powders containing P, B, etc. It is difficult to eliminate the large pores that exist, and the effects of adding P, B, etc. are not sufficiently exerted, so it is difficult to obtain a high sintered density. These problems reduce the average particle size of the atomized steel powder.
This problem can only be solved by setting the diameter to 50 μm or less, resulting in small shape distortion and a
It is possible to obtain a sintered alloy in which the average particle size of carbides identified by light microscopy observation at a magnification of about 600 times is 10 μm or less, and the density ratio is 95% or more. On the other hand, if the average particle size of steel powder is set to 30 μm or less, the amount of fine powder of several μm or less increases, causing problems such as mold galling during molding, and it is difficult to manufacture with a good yield using normal spray equipment. Therefore, the lower limit of the average particle size
Defined as 30μm. Examples will be described below. Using the water spray device described in Japanese Patent Publication No. 52-19540, the molten steel nozzle diameter is 6 to 14 mm, and the water pressure is 80 to 150.
Kg/cm ² and a water/molten steel ratio of 3 to 6/Kg to produce atomized raw steel powder with a predetermined composition, annealed in ammonia decomposition gas at 700 to 950°C, and crushed in a mortar to determine the particle size structure. However, alloy steel powder according to the present invention and steel powder for comparison, each having a mesh size of 80 or less, were obtained as shown in Table 1.

【table】

[Table] Next, 1% zinc stearate, a predetermined amount of natural graphite powder, and some ferrophosphor powder (27wt.%P) were added to these alloy steel powders,
At a pressure of 6t/ ^cm2 , width 10.0mm, length 35.1mm, thickness 6.5
600 mm specimens were molded in ammonia decomposition gas.
After dewaxing at ℃ for 30 minutes, the temperature in the same gas was 1200℃ without phosphorus added, and 1150℃ with phosphorus added.
Each was sintered for 60 minutes. Table 2 summarizes the green powder density, sintered density ratio, sintered body shape distortion, and average carbide particle size when using the steel powder according to the present invention and the steel powder for comparison. Here, the sintered density ratio is expressed as the ratio to the true density, and the shape distortion of the sintered body is defined as the distortion when the measured width of the same specimen differs by a maximum of 0.02 mm depending on the measurement position. It was determined that there was. Further, the average grain size of carbides is the average grain size of carbides observed in a light micrograph of a sintered alloy cross section magnified 600 times, converted into the diameter of a circle having the same area.

[Table] Test numbers 1 to 6 using steel powders A, B, C, D, and E according to the present invention all had green powder density.
It has a preferable value of 6 g/cm ³ or more and a sintered density ratio of 95% or more, has no shape distortion of the sintered body, and has a microstructure with a carbide grain size of 10 μm or less, and has excellent properties as a wear-resistant sintered alloy. We are prepared. On the other hand, test numbers 7 to 11 all used steel powder for comparison. Test numbers 7 and 8 are
Compared to test numbers 1 and 4, respectively, steel powders (F and G) with higher C and N contents than the range according to the present invention are used, so the green density is low, and as a result, the green powder In addition to insufficient body strength, it is not possible to obtain a sintered density ratio of 95% or more due to shrinkage during sintering. Moreover, since the shrinkage does not proceed uniformly, the shape of the sintered body is distorted. Test numbers 9 to 11 use steel powder (H, I, and J) whose average particle size is larger than the range according to the present invention compared to test numbers 4 to 6, so the carbide particle size is 10 μm in all cases. exceeds
This is not preferred from the viewpoint of impact resistance of the sintered alloy. Test number 6 (using the steel powder of the present invention) and test number 11 (using the comparative steel powder) are shown in Figures 1 and 2, respectively.
A comparison of light microscopic microstructure photographs of cross-sections is shown. The matrix is bainite (black) and martensite (white), and the carbides (white) are finely scattered and relatively spherical in test number 6, while in test number 11 they are found along the grain boundaries of the matrix. It can be seen that the growth is becoming coarser. In addition, in test numbers 9 and 11, large pores existed in the compact due to the coarse grain size of the steel powder, and as a result, shrinkage during sintering tended to be uneven, and the sintered compact Large shape distortion. Furthermore, in Test No. 10 in which P was added, the effect of P could not be exhibited because the steel powder grain size was coarse, and the sintered density was lower than in Test No. 5 in which steel powder according to the present invention was used. As mentioned above. As described above, according to the present invention, by limiting the components and particle size of the atomized steel powder within a predetermined range, the sintered alloy steel powder according to the present invention can be used to produce high density, low shape distortion, The effect is that a wear-resistant sintered alloy having a fine texture can be produced.

[Brief explanation of the drawing]

Figure 1 is a light micrograph (600x) of a cross section of a sintered alloy using the steel powder of the present invention, and Figure 2 is a light micrograph (600x) of a cross section of a sintered alloy using comparative steel powder.
shows.

Claims (1)

[Scope of Claims] 1 Contains 3 to 20% Cr, 0.3 to 2% Si, 0.3% or less of C, and 0.2% or less of N, the balance being Fe and 2% or less of unavoidable impurities, A steel powder for wear-resistant sintered alloys, characterized in that the average particle size determined from the particle size distribution by sieve analysis is 30 to 50 μm. 2 Contains 3 to 20% Cr, 0.3 to 2% Si, 0.3% or less C, 0.2% or less N, 5% or less of one or both of Ni and Cu, the balance being Fe and 2% or less by weight. A steel powder for use in wear-resistant sintered alloys, which contains unavoidable impurities and has an average particle size of 30 to 50 μm as determined from particle size distribution by sieve analysis. 3 Contains 3 to 20% of Cr, 0.3 to 2% of Si, 0.3% or less of C, 0.2% or less of N, 5% or less of one or more of V, Mo, and W, and the balance is Fe and 2%
A steel powder for wear-resistant sintered alloys, comprising the following unavoidable impurities and having an average particle size of 30 to 50 μm as determined from particle size distribution by sieve analysis. 4 Weight ratio: Cr3-20%, Si0.3-2%, C0.3% or less, N0.2% or less, 5% or less of one or both of Ni and Cu, one of V, Mo and W Or a wear-resistant sintered alloy containing 5% or less of two or more types, the balance being Fe and 2% or less of unavoidable impurities, and having an average particle size of 30 to 50 μm as determined from the particle size distribution by sieve analysis. Steel powder for use.