JPH01301802A - Low alloy steel powder for sintering - Google Patents

Abstract

PURPOSE:To produce the low alloy steel powder having an excellent press characteristic, etc., by specifying the average grain size and S content of the fine iron alloy powder of the powder consisting of iron and steel powder contg. a specific ratio of iron, a specific ratio of iron, a proper ratio of a solid soln. intensifying element and the fine low alloy steel powder contg. S. CONSTITUTION:The low alloy steel powder for sintering is prepd. from the iron and steel powder contg. >=98wt.% iron, >=30wt.% iron, 1 or >=2 kinds of the solid soln. intensifying elements and the fine iron alloy powder contg. a proper ratio of the S. The average grain size of the fine iron alloy powder is specified to <=1/5 the average grain size of the iron and steel powder at this time and the S content in the state of mixing 5 to 20wt.% iron alloy powder with the iron and steel powder is specified to 0.03 to 0.7wt.%. the total content of the solid soln. intensifying elements is specified to >=0.5wt.% of the weight of the low alloy steel powder for sintering. One or more kinds selected from Ni and Cr are preferably used for the solid soln. intensifying elements. The low alloy steel powder which forms a high-strength sintered body having improved machinability is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a low alloy steel powder for vine sintering that has excellent press properties and improves the machinability of sintered bodies.

(Prior Art) Along with casting methods, forging methods, and the like, powder metallurgy is widely known as a method for manufacturing final products or mechanical structural parts having a shape similar to the final product. The raw material powder used in the powder metallurgy method is, for example, a low alloy steel powder made by blending various additive elements with steel in order to improve the strength of sintered parts.

This low-alloy steel powder is made by adding small amounts of elemental powders such as Ni, Cr, and Mo to iron powder, and its manufacturing method involves spraying an alloy powder in which additional elements are dissolved in iron powder. method, and a master alloy mixing method in which elemental powders of predetermined components are added and mixed with iron powder are known.

However, in the former injection method, the added elements harden as a solid solution in the iron powder, reducing the compressibility of the iron powder and making it impossible to obtain a high-density sintered body.As a result, the strength of the sintered body deteriorates. There is an inconvenience of damage. On the other hand, in the latter method of mixing the master alloy, the elemental powder is only attached around the iron powder and the compressibility is relatively good, but under normal sintering conditions, the diffusion reaction of the added element into the iron powder is difficult. If it is insufficient, the structure of the obtained sintered body will be non-uniform, and the strength, particularly the ductility, will tend to decrease.

Therefore, as an improvement method of this master alloy mixing method,
-9649, JP-A-59-215401, JP-A-6
Patent publications No. 1-130401 disclose a method for producing low-alloy steel powder for vine sintering, in which fine elemental powder is used to promote diffusion alloying into iron powder during sintering. There is.

On the other hand, the present inventors have found that if the elements to be added to the steel powder are attached in advance in the form of iron alloy fine powder, diffusion alloying during sintering becomes easier, and furthermore, when the added elements are Cr, Mn, etc. We found that these additive elements are less likely to be oxidized during sintering when they are active metals, and based on this knowledge, we have developed a low alloy for sintering consisting of steel powder and fine iron alloy powder with a smaller particle size. Applied for a patent on steel powder (patent application filed in 1989)
1-258583, patent application No. 62-234797).

(Problem to be solved by the invention) However, as the shapes of sintered parts have become more complex in recent years, cutting processes such as drilling and turning are increasingly performed after sintering. Since there is a tendency to combine machining processes to produce final products, there is a strong demand for improving the machinability of sintered bodies.In particular, low alloy steel sintered bodies containing Ni, Cr, etc. are hard and hard to bake. Since it is easy to cut, there is a demand for further improvement in machinability.

Therefore, the present inventors added an appropriate amount of S to iron alloy fine powder, and mixed and adhered the iron alloy fine powder containing S to steel powder and sintered it, thereby impairing the inherent compressibility of iron powder. Basic experiments were repeated to see if a low-alloy steel sintered body with improved machinability could be obtained. The present inventors focused on the fact that the existence form and occupancy rate of S in the sintered body are important factors for improving machinability, and added an appropriate amount of S to the fine iron alloy powder attached to the steel powder. It has been found that the machinability of the sintered body can be improved by containing concentrated S and dispersing S as a sulfide in the state of the low alloy steel powder sintered body.

(Means for Solving the Problems) The low alloy steel powder for sintering according to the present invention completed by the present inventors is configured as follows.

That is, the low alloy steel powder for sintering of the present invention contains a steel powder containing 98% by weight or more of iron, 30% or more of iron and 1% by weight.
a fine iron alloy powder containing a suitable amount of a seed or two or more solid solution strengthening elements and S, the average particle size of the fine iron alloy powder being one-fifth or less of the average particle size of the steel powder, ,
The iron alloy fine powder is contained in an amount of 5 to 20% by weight based on the steel powder.
In the mixed state, S is contained in an amount of 0.03 to 0.7% by weight.

The total amount of the solid solution strengthening elements is desirably set to account for 0.5% or more by weight of the low alloy powder for sintering. Further, it is preferable that the solid solution strengthening element is at least one selected from Ni and Cr.

In the low alloy powder for sintering of the present invention, the steel powder contains 98% by weight or more of Fe and has good compressibility. The average particle size is, for example, 50~looLL
Although it is set to m, the present invention is not limited to this value.

The iron alloy fine powder contains 30% by weight or more of Fe, and component elements other than Fe include, for example, Ni, Cu, Cr, and Mo.
, contains solid solution strengthening elements such as Mn, and an appropriate amount of S. this is,
This is because if the Fe content in the iron alloy fine powder is less than 30% by weight, the diffusion reaction of each solid solution strengthening element described above into the steel powder becomes difficult to occur during sintering. In addition, when active metals such as Mn and Cr are contained as solid solution strengthening elements, Mn, Cr, etc. are likely to be present in the form of oxides during sintering.
This is because the strength of the sintered body deteriorates (see Japanese Patent Application No. 61-258583).

The reason why the average particle size of the iron alloy fine powder is set to be one-fifth or less of the average particle size of the steel powder is because if the average particle size exceeds one-fifth, the iron alloy fine powder will be uniformly dispersed in the intergranular spaces of the steel powder. This is because the compressibility of the low-alloy steel powder is impaired.

The blending ratio of the iron and steel powder and the iron alloy fine powder is set in a range of 5 to 20% by weight of the iron alloy fine powder to the steel powder. If the iron alloy fine powder is less than 5% by weight, the F
This is because component elements other than e will be concentrated, making it impossible to obtain a sufficient uniform diffusion effect of the solid solution strengthening element. On the other hand, if the iron alloy fine powder exceeds 20 weight 1%, the coordination of the iron alloy fine powder in the gaps between the steel powder becomes supersaturated, which impairs the compressibility of the low alloy steel powder. (Patent Application No. 61-258583).

The proportion of the solid solution strengthening element in the low alloy steel powder for sintering is desirably 0.5% by weight or more. This is because the addition of solid solution strengthening elements improves the compressive strength and Charpy impact value of the sintered body.

In particular, when Ni and Cr are added, the effect of improving hardening becomes remarkable.

Regarding the machinability improving element S, the content of S in the iron alloy fine powder is adjusted so that it falls within the range of 0.03 to 0.7% by weight in the final sintered body state.

This means that if the S content in the sintered body is less than 0.033% by weight,
The improvement effect on machinability becomes smaller, and on the contrary, S is 0.7% by weight.
This is because, if it exceeds this value, the deterioration of the mechanical properties, particularly the Charpy impact value, will be significant, and the practical value of the sintered steel component will be impaired.

(Example) Examples of the present invention will be described.

Iron alloy fine powder produced by water spray method (average particle size: lo
-13 μm) and ore reduced iron powder (-100 mesh, average particle size near 3 μm) were mixed and calcined at a blending ratio of 1:9, and further 0.3% by weight of carbon powder and lubricant were mixed uniformly. . The obtained mixed powder was press-molded at 6 tons/cm' and passed J S P M 42 standard 2-65. IOX
A prismatic column with an IOX size of 55 mm and a cylinder with an outer diameter of 33 mm were produced, and these were hydrogen-sintered at 1230° C. for 1 hour. The composition and green density of the sintered body are shown in Table 1.

A tensile strength test, a Charpy impact test, and a drill cutting test were conducted on each of the sintered bodies of Examples.

The cutting test conditions are as follows.

Cutting test conditions Tool: 5KH51 (5D) Feed: O, I Omm/rev Cutting speed = 43 to 55 m/min (Tool life):
30 m/min (Cutting resistance) Cutting curve/no tool life judgment: Melt damage The results obtained are shown in Table 1 and Figure 1.

As is clear from the comparison of sample numbers 1 and 2 in Table 1, S
When the content is 0.02% by weight or less, there is no difference in the cutting resistance (thrust load) of the sintered body, and as shown in FIG. 1, no effect on extending tool life is observed. However, when the S content becomes 0.04% by weight, the effect of improving both machinability and tool life becomes noticeable as in sample number 3.4.5.

As a result, as the amount of S is increased from 0.03% by weight, both properties are improved, but on the contrary, the slag-like properties are slightly decreased, especially when S exceeds 0.7% by weight, as in sample number 6. ,
The Charpy impact value decreases significantly.

Three types of iron alloy fine powders (average particle size, 8 to 10 μm) produced by the water spray method and ore-reduced iron powder (-100 mesh,
A sintered body was prepared in the same manner as in Example 1 using a mixture of 1:9 (1:9) carbon powder with an average particle size of 3 μm, and a uniform mixture of 0.3% by weight of carbon powder and a lubricant. Tests, Charpy impact tests and drill cutting tests were conducted.

The obtained results are shown in Table 1 and FIG. 2 together with the composition and green density.

As is clear from Table 1 and Figure 2, N1-Mo system (sample numbers 7 to 81 alloy amount: 2.5% by weight),
Mo-based (sample number 9 ~ lO1 alloy amount: 2.O weight ffi%
) Tomo, about 0.3 heavy ffi % 1iij The addition of S after the cutting force has a remarkable effect of reducing cutting force and extending the tool life (sample number 8.10), and sample numbers 7, 8, and 9. The amount of change in mechanical properties between 10 and 10% is relatively small. However, a sintered body similar to carbon steel (sample numbers 11-12, N
i: around 0.36 wt%), the decrease in cutting force due to the addition of S is relatively small, and the improvement effect is not very noticeable, especially in terms of tool life, because the basic steel type (sample number 11) itself has a high life level. do not have.

In the examples of the present invention, S was used as the machinability element, but elements such as Pb, Bi, Te, and composite additives that combine these elements can also have a lubricity effect due to the low melting point element. It goes without saying that the machinability of the sintered body can be improved by the machinability improvement effect.

(Effects of the Invention) As explained above, according to the low alloy steel powder for sintering of the present invention, it is possible to produce a high-strength sintered body because the powder has excellent press properties, especially compressibility, and Since S as a free machining element is present in the form of sulfide in the sintered body, the pH resistance of the sintered body can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing the relationship between cutting speed and tool life for an example of the present invention and a comparative example, respectively.

Claims (3)

[Claims] (1) Steel powder containing 98% by weight or more of iron and 3% iron
0% by weight or more, one or more solid solution strengthening elements, and an iron alloy fine powder containing an appropriate amount of S, and the average particle size of the iron alloy fine powder is 5 minutes of the average particle size of the steel powder. 1 or less, and S is 0.03 to 0.7 when 5 to 20% by weight of the fine iron alloy powder is mixed with the steel powder.
Low alloy steel powder for sintering characterized by containing % by weight. (2) The low alloy steel powder for sintering according to claim 1, wherein the total amount of the solid solution strengthening elements is 0.5% by weight or more based on the low alloy powder for sintering. (3) The low alloy steel powder for sintering according to claim 1 or 2, wherein the solid solution strengthening element is at least one selected from Ni and Cr.