JP3294980B2 - Alloy steel powder for high-strength sintered materials with excellent machinability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron powder for powder metallurgy, and more particularly to a sintering method capable of straightening (sizing) after sintering, excellent in machinability of a sintered body, and obtaining high strength after quenching. It relates to alloy steel powder for materials.

[0002]

2. Description of the Related Art Iron powder for powder metallurgy is obtained by adding and mixing Cu powder, graphite powder, etc. with iron powder, compacting in a mold and sintering.
It is used for manufacturing sintered machine parts having a density of 5.0 to 7.2 g / cm ³ . Although powder metallurgy can produce sintered bodies with complicated dimensions and good dimensional accuracy, cutting parts after sintering or drilling may be necessary when manufacturing parts with strict dimensional accuracy. is there.

[0003] Powder metallurgy products are generally inferior in machinability and have a problem that tool life is shorter than that of ingots, so that the cost of machining is high. It is said that the deterioration of the machinability of the powder metallurgy product is caused by intermittent cutting due to pores contained in the powder metallurgy product or an increase in cutting temperature due to a decrease in thermal conductivity. In order to improve the machinability, free cutting components such as S and MnS are often mixed with iron powder. These S and MnS are said to have the effect of facilitating the breakage of chips or to form a thin cutting edge of S and MnS on the tool, thereby improving the machinability by the lubricating action on the rake face of the tool.

In Japanese Patent Publication No. 3-25481, some Mn
(0.1-0.5%) and pure iron powder containing Si, C, etc.
Iron powder for powder metallurgy has been proposed, which is produced by spraying molten metal containing 0.03 to 0.07% of water with water or gas. In this method, the machinability has been improved only less than twice that of the conventional material, and further improvement is required. Also, a technique for containing B in powdered metallurgy iron powder for the purpose of improving the moldability is disclosed in
No. 61-253301. In the present invention, C: 0.10% or less, Mn: 2.0% or less, oxygen content is 0.30%
And Cr: 0.10 to 5.0%, Ni: 0.10 to 5.0
%, Si: 2.0% or less, Cu: 0.1 to 10.0%, Mo: 0.01 to 3.
0%, W: 0.01 to 3.0%, V: 0.01 to 2.0%, Ti: 0.005
~ 0.50%, Zr: 0.005 ~ 0.50%, Nb: 0.005 ~ 0.50%,
One or more of the group consisting of P: 0.03-1.0% and B: 0.0005-1.0%, and if necessary, S:
An alloy steel powder containing 1.0% or less and the balance substantially consisting of Fe has been proposed.

However, alloy steel powder of this composition is
Is higher than 0.10% and iron ore,
Water atomized mother alloy powder pre-alloyed to powder obtained by roughly reducing iron oxide such as mill scale with a reducing agent such as coke breeze,
That is, C: 0.50% or less, Mn: 5.0% or less, and oxygen content is 1.
5% or less, Cr: 0.10 to 20.0%, Ni: 0.15 to
20.0%, Si: 5.0% or less, Cu: 0.15 to 20.0%, Mo: 0.01
5 to 15.0%, W: 0.015 to 15.0%, V: 0.015 to 5.0
%, Ti: 0.01 to 2.0%, Zr: 0.01 to 2.0%, Nb: 0.01 to
2.0%, P: 0.04 to 2.0%, and B: 0.0010 to 2.0%
And one or more of the group consisting of: and, if necessary, S: 4% or less, with the balance being substantially Fe
It is necessary to mix and adjust the water-sprayed master alloy powder consisting of the alloy elements after the finish reduction to the above-mentioned desired amount, and then to finish-reduce the mixed powder in a reducing atmosphere. Complex and costly manufacturing methods must be adopted.

[0006] In particular, gears and the like as automobile parts are required to have high strength and high fatigue characteristics. When these parts are manufactured by a powder metallurgy method, a method of adding an alloy component in order to improve strength and fatigue characteristics is generally used. For example, in Japanese Patent Publication No. 45-9649, pure iron powder contains N
Powders such as i, Cu, and Mo are added as alloying components by diffusing and adhering. However, although the steel powder produced by this method is excellent in compressibility and strength of the sintered body, since the hardness of the sintered body is high, straightening after sintering is almost impossible and the cutability is poor. there were.

Further, using iron powder produced by the method disclosed in the above-mentioned Japanese Patent Publication No. 3-25481, Ni,
Even when alloying component powders such as Cu and Mo are diffused and adhered, the cutability is not improved only by the effect of S because the sintered body is hard.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the prior art, the present invention provides a sintered body which can be straightened after sintering, has excellent machinability, and has high strength after bright quenching or carburizing. It is an object of the present invention to provide an alloy steel powder for powder metallurgy that can be obtained.

[0009]

Means for Solving the Problems The present inventors have filed Japanese Patent Application No.
No. 208949, Japanese Patent Application No. 6-235025, when sintering powdered metallurgy iron powder containing a predetermined amount of S, Cr, Mn produced by spraying method using water, residual graphite remains in the pores of the sintered steel. It has been proposed that MnS within 5 μm is present in iron particles and in grain boundaries, and that a sintered steel excellent in machinability can be easily obtained.

[0010] The iron powder for powder metallurgy according to Japanese Patent Application No. 6-208949 was quenched during sintering in a pure nitrogen atmosphere, and the residual graphite was analyzed. As a result, carburization of the residual graphite was inhibited during sintering. As a result, it was found to be generated. Further, it has been found that FeS present in the surface layer of iron powder is effective in inhibiting the carburization of graphite, and that the amount of residual graphite is further increased by adding Cr in combination.

In addition to S, investigations were made on alloying elements that inhibit carburization during sintering and increase the amount of residual graphite. As a result, the smelting material has low solubility in iron and segregates at crystal grain boundaries. Se and Te, which are easy to produce, have the effect of producing residual graphite as in the case of S. Separately, when atomizing molten steel containing B with water, a part of B is easily oxidized by water and a B-based oxide precipitates on the surface of iron powder, and this B-based oxide is burned. In order to suppress the carburization of graphite into iron powder during sintering, it has been found that there is an effect of increasing the amount of residual graphite in the sintered body and improving machinability. In addition, since the content of ferrite in the sintered body increases, straightening is possible. After bright quenching and carburizing heat treatment, the residual graphite is re-dissolved in the iron particles to form a structure mainly composed of bainite and martensite, and high strength is obtained.

Based on these findings, intensive experiments were conducted and examined. As a result, Cr: 0.02 to 0.07%, Mn: 0.1% by weight%
And the balance is Fe and atomized iron powder, which is an unavoidable impurity, and iron powder containing 0.001 to 0.3% of B. Ni: 0.5 to 7%, Cu: 0.5 to 3%, and Mo: 0.05
The sintered material obtained by using partially alloyed steel powder to which at least one selected from ~ 3.5% is diffused and attached becomes a structure mainly composed of bainite and martensite after carburizing treatment and bright quenching, resulting in a high strength material. Not only can be obtained, but also it can be straightened as it is and shows excellent cutting properties.

Further, by adding a total of 0.03 to 0.15% of one or more kinds selected from S, Se and Te to the atomized iron powder containing B, Ni: 0.5 to 7%, Cu:
It has been found that a sintered material obtained by using a partially alloyed steel powder to which at least one selected from 0.5 to 3% and Mo: 0.05 to 3.5% is diffused and adhered exhibits more excellent machinability.
That is, in the present invention, B: 0.001 to 0.3% by weight, Cr:
0.02 to 0.07%, Mn: less than 0.1%, and if necessary, one or more selected from S, Se and Te in a total amount of 0.03 to 0.03%.
To 0.15%, the balance being Fe and iron powder, which is an inevitable impurity, by weight: Ni: 0.5 to 7%, Cu: 0.5 to 3% and M
o: Alloy steel powder for a high-strength sintered material excellent in machinability, characterized in that at least one selected from 0.05 to 3.5% is partially alloyed.

The element source for partial alloying is Ni.
In the case of Cu and Cu, those metal powders can be suitably used, and in the case of Mo, not only metal powder but also MoO ₃ powder can be suitably used.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention improves the machinability of a sintered alloy steel by the action of residual graphite generated in the pores of the sintered alloy steel by the carburization preventing action of B-based oxide and S, Se and Te. It is to let. In addition, since any one or more of Ni, Cu, and Mo are partially alloyed by diffusion adhesion, forming and sintering with a normal Fe-Cu-C-based or Fe-C-based compound will produce a residual alloy. A high-strength sintered alloy steel having graphite and excellent machinability can be easily obtained.

Hereinafter, each of the important functions in the present invention will be described.
The action and the limited range of the element will be described in detail. B: 0.001 to 0.3% As mentioned above, molten steel containing B is atomized by water.
When mist, a part of B is easily oxidized by water,
B-based oxide precipitates on the surface, and this B-based oxide
In order to suppress the carburization of graphite in the powder, the residual black
Increased lead content, resulting in improved machinability of sintered alloy steel
And at the same time correct after sintering. B-based acid
Is very stable and H_TwoRarely reacts with
So H _TwoEven when heat treated in an atmosphere containing
It does not decline.

If B is less than 0.001%, no improvement in machinability due to the addition of B is observed. If B exceeds 0.3%, the hardness of the sintered alloy steel increases due to solid solution hardening, and the machinability is reduced. A preferable range is 0.005 to 0.03% in consideration of the machinability and the manufacturing cost. Also,
Although the reason is not clear, after bright quenching after sintering or carburizing heat treatment, the remaining graphite forms a solid solution to form martensite or bainite, and high strength is obtained in combination with Ni and Mo.

Since the improvement in the machinability is due to the residual graphite, the machinability is not improved even if the Fe-B alloy powder is mixed and added to the iron powder containing no B. Cr: 0.02 to 0.07% Cr in the iron powder has an effect of increasing residual graphite generated during sintering. If Cr is less than 0.02%, no improvement in machinability due to the addition of Cr is observed. If the Cr content exceeds 0.07%, the hardness of the sintered alloy steel increases due to carbides, and the machinability decreases. With the balance between machinability and manufacturing cost,
A preferred range is from 0.04 to 0.06%.

Mn: less than 0.1% Mn is less than 0.1%. When Mn is 0.1% or more, the residual graphite in the sintered steel is small and the machinability is poor. The reason for this is that Mn itself is an alloying element that reduces residual graphite, and when iron powder contains S, Se or Te, Mn in the powder is S, Se, Te.
This is because S, Se, and Te, which are effective in increasing the residual graphite in the sintered steel, tend to be reduced. From the viewpoint of refining cost and Mn reduction for Mn reduction in the converter,
The preferred range of Mn is 0.04 to 0.08%.

Ni: 0.5 to 7%, Cu: 0.5 to 3%, Mo: 0.
Any one or more of 05 to 3.5% Ni, Cu, and Mo are added to increase the strength. The addition amounts of Ni: 0.5 to 7%, Cu: 0.5 to 3%, Mo: 0.05 to respectively
Limited to 3.5%. If each element is less than the lower limit, no improvement in strength due to the addition is observed. When each element exceeds the upper limit, the machinability sharply decreases.

The sum of at least one of S, Se and Te: 0.03
、 0.15% S, Se and Te of powdered iron for powder metallurgy produced by a spraying method using water are added to generate residual graphite in sintered steel. The total amount of the addition is limited to 0.03 to 0.15%. If it is less than 0.03%, there is no effect of improving machinability due to the generation of residual graphite. If it exceeds 0.15%, soot is easily generated during sintering, and there is a concern that the sintering furnace may be damaged. The preferred range is 0.08-0.13% for reasons of machinability and alloy cost.
As described above, B, S, Se, and Te each independently have an effect of generating residual graphite during sintering. When B is used in combination with one or more of S, Se, and Te, a combined effect that is equal to or greater than the sum of the effects obtained when each is added alone is exhibited.

[0022]

【Example】

(Example 1) Table 1 shows the chemical composition of the iron powder as the base powder and the content of the diffusion-adhering component in the alloy steel powder which is diffused and adhered. These alloy steel powders are obtained by spraying raw powder obtained by spraying molten steel with an oxygen content of 150 ppm or less in water at 140 ° C for 60 minutes in a nitrogen atmosphere, reducing it in a pure hydrogen atmosphere at 930 ° C for 20 minutes, and then pulverizing. Carbonyl Ni powder, Mo trioxide powder, and Cu powder were mixed at a predetermined ratio with the classified iron powder, and annealed at 875 ° C. for 60 minutes in H ₂ gas to cause diffusion adhesion.

[0023]

[Table 1]

After mixing 1 part by weight of zinc stearate with 100 parts by weight of alloy steel powder mixed with 0.6% of graphite powder, the mixture was molded so as to have a green density of 7.0 g / cm ^3.
After sintering at 60 ° C. for 60 minutes, the as-sintered material was evaluated for its machinability and its potential for correction. Evaluation of machinability is outer diameter 60φ, height 10mm
After sintering under the above conditions, the average number of holes (three drills) processed using a high-speed steel drill with a diameter of 1 mmφ until it became impossible to process at 10,000 rpm and 0.012 mm / rev The average value of the tool life was evaluated as the tool life. As for the possibility of straightening, the material was pressed as sintered at 5 t / cm ² , and the deformed one was acceptable, and the one with small deformation was not acceptable.

The amount of graphite remaining in the sintered steel was quantified by filtering the residue dissolved in nitric acid through a glass filter and using an infrared absorption method. In addition, the sintered body has a car phone potential of 0.8% and 850 ° C x 30
After heating for one minute, bright quenching was performed in oil at 160 ° C., and the tensile strength was measured. Table 1 summarizes the residual graphite content, tool life, and tensile strength after bright quenching of the sintered body. As can be seen from the examples in Table 1, B: 0.001 to 0.3%, Cr: 0.02 to 0.07
%, Mn: less than 0.1%, and Ni: 0.
Residual graphite of sintered steel obtained from iron powder for powder metallurgy obtained by diffusing and adhering at least one of 5 to 7%, Cu: 0.5 to 3% and Mo: 0.05 to 3.5% to the surface of iron powder The tool life was more than 0.2% and the tool life was more than 60 pieces. On the other hand, the tensile strength increased to 960 to 3030 MPa with increasing amounts of Ni, Cu and Mo. In all the examples, the correction was possible.

In Comparative Example 1, B was not contained, the residual graphite of the sintered body was 0.02%, and the tool life was one piece, which was uncorrectable.
It can be seen from the comparison with the examples that the addition of B improved the machinability. As shown in Comparative Examples 2 and 5, the content of B was
If the content exceeds 0.3% or the content of Ni exceeds 7%, the machinability deteriorates. Further, as shown in Comparative Examples 3 and 4, when the Cr content exceeds 0.07% or the Mn content exceeds 0.1%, the machinability is deteriorated. Further, as shown in Comparative Examples 5, 6, and 7, when the amount of Ni, Cu, and Mo adhered is large, improvement in machinability cannot be expected. In addition, straightening after sintering was impossible in all comparative examples. (Example 2) Table 2 shows the chemical composition of the iron powder as the base powder and the content of the diffusion-adhered component in the alloy steel powder which was diffuse-adhered. These alloy steel powders are obtained by drying raw powder obtained by spraying molten steel with water at 140 ° C for 60 minutes in a nitrogen atmosphere, reducing it at 930 ° C for 20 minutes in a pure hydrogen atmosphere, and then pulverizing and classifying the iron powder. , Carbonyl Ni powder, Mo trioxide powder, and Cu powder were mixed at a predetermined ratio, and annealed at 875 ° C. for 60 minutes in H ₂ gas to cause diffusion adhesion.

[0027]

[Table 2]

After mixing 1 part by weight of zinc stearate with 100 parts by weight of alloy steel powder mixed with 0.6% of graphite powder, the mixture was molded to a green compact density of 7.0 g / cm ³ , and mixed in a nitrogen stream at 1250 parts by weight.
After sintering at 60 ° C for 60 minutes, the amount of residual graphite, machinability and correctability were evaluated. The evaluation of the machinability was made into a disk shape with an outer diameter of 60φ and a height of 10mm, and after sintering under the above conditions, it became impossible to machine with a 1mmφ high-speed drill at 10,000rpm and 0.012mm / rev. The average number of holes processed up to (the average value of three drills) was evaluated as the tool life.

The residual graphite content of the sintered steel was quantified by filtering the residue dissolved in nitric acid through a glass filter and using an infrared absorption method. Table 2 summarizes the residual graphite content after sintering, the tool life, and the tensile strength after bright quenching. The sintered body was bright quenched under the same conditions as in Example 1 and the tensile strength was measured. As can be seen from the examples of Table 2, B: 0.001 to 0.3%, Cr: 0.02
0.07%, Mn: less than 0.1%, the total of one or more of S, Se, and Te is 0.03 to 0.15%, and Ni: 0.5 instead of part of Fe.
-7%, Cu: 0.5-3%, and Mo: 0.05-3.5%, and the residual graphite of the sintered steel obtained from the iron powder for powder metallurgy obtained by diffusing and adhering at least one of them to the surface of the iron powder is 0.2 % And the tool life was 60 pieces or more. On the other hand, the tensile strength after bright quenching increased to 950 to 5050 MPa with increasing amounts of Ni, Cu and Mo added. In all the examples, the correction of the sintered body was possible.

Comparative Example 8 did not contain B, and the residual graphite was 0.02.
%, And the tool life was 10, and it can be seen from the comparison with the examples that the addition of B improved the machinability. Comparative Examples 9 and 19
As shown in Fig. 5, when the content of B exceeds 0.3% or the content of Ni exceeds 7%, the machinability deteriorates. Comparative Examples 10 to
When the total of one or more of S, Se, and Te is less than 0.03% as shown in FIG. 13, the machinability is poor, and as shown in Comparative Examples 14 to 17, S, S
If the total of one or more of e and Te exceeds 0.15%, the tensile strength decreased, and soot was generated during sintering. Further, as shown in Comparative Example 18, when the content of Mn is 0.1% or more, the machinability is deteriorated. Further, as shown in Comparative Examples 19, 20, and 21, when the amount of Ni, Cu, and Mo adhered is large, improvement in machinability cannot be expected.

[0031]

According to the present invention, in the case of sintering alloy steel powder obtained by diffusing and adhering Ni, Cu and Mo to powdered metallurgy iron powder produced by a spraying method using water, straightening after sintering is performed. Thus, a sintered body excellent in machinability can be obtained, and a sintered steel having high strength and toughness after quenching can be easily produced without generating soot.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Kuniaki Ogura, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Engineering Co., Ltd. (72) Inventor Sekiaki Yang 3-10 Koganecho, Niigata, Niigata Mitsubishi Materi Al Niigata Works (58) Fields surveyed (Int. Cl. ⁷ , DB name) B22F 1/00 B22F 1/02

Claims (2)

(57) [Claims] 1. A weight ratio of B: 0.001 to 0.3%, Cr: 0.02
0.00.07%, Mn: less than 0.1%, the balance being Fe and iron powder which is an unavoidable impurity, Ni: 0.5Ni7%, Cu: 0.
Alloy steel powder for high-strength sintered materials excellent in machinability, characterized in that at least one selected from 5 to 3% and Mo: 0.05 to 3.5% is partially alloyed. 2. B: 0.001 to 0.3% by weight, Cr: 0.02 by weight ratio
0.00.07%, Mn: contains less than 0.1%, and further contains S, Se and T
e containing at least one selected from the group consisting of 0.03 to 0.15%, the balance being Fe and iron powder, which is an inevitable impurity, in a weight ratio of Ni: 0.
Alloy steel powder for high-strength sintered material excellent in machinability, characterized in that at least one selected from 5 to 7%, Cu: 0.5 to 3% and Mo: 0.05 to 3.5% is partially alloyed. .