JPH08209202A - Alloy steel powder for high strength sintered material excellent in machinability - Google Patents

Abstract

PURPOSE: To produce alloy steel powder for powder metallurgy capable of obtaining a sintered body excellent in machinability arid having high strength. CONSTITUTION: Iron powder having a compsn. contg., by weight, 0.001 to 0.3% B, 0.02 to 0.07% Cr and <0.1%. Mn, furthermore contg., at need, total 0.03 to 0.15% of one or more kinds selected from S, Se and Te, and the balance Fe with inevitable impurities is partially alloyed with one or more kinds selected from 0.5 to 7% Ni, 0.5 to 3% Cu and 0.05 to 3.5% Mo.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Iron powder for powder metallurgy is usually manufactured by adding Cu powder, graphite powder, etc. to iron powder, compacting it in a mold and sintering it.
It is used for producing sintered machine parts and the like having a density of 5.0 to 7.2 g / cm ³ . The powder metallurgy method can produce a sintered body with a good dimensional accuracy and a complicated shape, but when manufacturing a component with a strict dimensional accuracy, cutting or drilling after sintering may be necessary. is there.

Generally, powder metallurgy products have inferior machinability and short tool life as compared with ingots, and therefore have a drawback that the cost during machining is high. It is said that the deterioration of the machinability of the powder metallurgy product is caused by the intermittent cutting due to the pores contained in the powder metallurgy product or the increase of the cutting temperature due to the decrease of the thermal conductivity. In order to improve machinability, free-cutting components such as S and MnS are often mixed with iron powder. These S and MnS are said to bring about the effect of facilitating the breakage of chips, or to form a thin cutting edge of S and MnS on the tool to improve the cutting performance 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 a molten metal added with 0.03 to 0.07% with water or gas. In this method, the machinability was improved only slightly less than twice that of the conventional material, and further improvement was required. Further, a technique of incorporating B into iron powder for powder metallurgy for the purpose of improving moldability is disclosed in Japanese Patent Application Laid-Open
61-253301. In the present invention, C: 0.10% or less, Mn: 2.0% or less, oxygen amount is 0.30%
Below: Cr: 0.10 to 5.0%, Ni: 0.10 to 5.0
%, Si: 2.0% or less, Cu: 0.10 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%,
P: 0.03 to 1.0% and B: 0.0005 to 1.0%, containing 1 or 2 or more of the group consisting of S:
Alloy steel powders containing 1.0% or less and the balance being substantially Fe have been proposed.

However, the alloy steel powder of this composition contains Cr
Is higher than 0.10%, iron ore to obtain this composition,
Powder of iron oxide such as mill scale roughly reduced with a reducing agent such as powder coke, pre-alloyed water spray mother alloy powder,
That is, C: 0.50% or less, Mn: 5.0% or less, 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%
1 or 2 or more of the group consisting of, and optionally S: 4% or less, with the balance being substantially Fe.
It is necessary to mix and adjust the water-sprayed mother alloy powder consisting of so that the amount of alloying elements after finish reduction becomes the above-mentioned desired amount, and then finish-reduce the mixed powder in a reducing atmosphere. A complicated and costly manufacturing method must be taken.

By the way, in particular, gears as automobile parts are required to have high strength and high fatigue characteristics. When these parts are manufactured by the powder metallurgy method, a method of adding an alloy component in order to improve strength and fatigue properties is common. For example, in Japanese Patent Publication No. 45-9649, pure iron powder has N
It is added as an alloying component by diffusing and adhering powders of i, Cu, Mo and the like. However, the steel powder produced by this method is excellent in compressibility and sintered body strength, but since the hardness of the sintered body is high, there is a problem that straightening after sintering is almost impossible and machinability is poor. there were.

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

[0008]

In view of such 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 intended to provide an alloy steel powder for powder metallurgy that can be obtained.

[0009]

[Means for Solving the Problems]
In 208949 and Japanese Patent Application No. 6-235025, when iron powder for powder metallurgy containing a predetermined amount of S, Cr, and Mn produced by a spraying method using water is sintered, residual graphite is left in the pores of the sintered steel. It has been proposed that MnS of 5 μm or less exists in iron particles and in grain boundaries, and a sintered steel having excellent machinability can be easily obtained.

Iron powder for powder metallurgy according to Japanese Patent Application No. 6-208949 was rapidly cooled during sintering in a pure nitrogen atmosphere, and residual graphite was analyzed. As a result, residual graphite was found to inhibit carburization during sintering. It turns out that it produces as a result. Further, it was discovered that FeS existing in the surface layer of iron powder is effective for inhibiting the carburization of graphite, and that the addition of Cr in combination further increases the amount of residual graphite.

Further, as a result of investigating alloy elements other than S, which inhibit carburization during sintering and increase the amount of residual graphite, the melted material has a low solubility in iron and segregates at grain boundaries. Like Se, easy Se and Te had the effect of forming residual graphite. Separately from this, when molten steel containing B is atomized and sprayed with water, part of B is easily oxidized by water to deposit B-based oxide on the iron powder surface, and this B-based oxide is burned. It has been found that there is an effect of increasing the amount of residual graphite in the sintered body and improving the machinability in order to suppress the carburization of graphite in the iron powder during binding. Further, since the content of ferrite in the sintered body is increased, it is possible to correct it. Further, after the bright quenching and the 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.

[0012] Based on these findings, a diligent experiment was conducted, and as a result, a study was made. As a result, Cr: 0.02 to 0.07% and Mn: 0.1% by weight.
If the content is less than Fe, the balance is Fe and atomized iron powder which is an unavoidable impurity, and iron powder containing 0.001 to 0.3% of B is added to Ni: 0.5 to 7%, Cu: 0.5 to 3% and Mo: by weight. 0.05
Sintered materials obtained by using partially alloyed steel powder with one or more kinds selected from ~ 3.5% diffused and adhered have a structure mainly composed of bainite and martensite after carburizing and bright quenching, and are high strength materials. It has been found that not only is it obtained, but also it can be straightened as it is and exhibits excellent machinability.

Further, by adding 0.03 to 0.15% in total 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 the sintered material obtained by using the partially alloyed steel powder in which one or more kinds selected from 0.5 to 3% and Mo: 0.05 to 3.5% are diffusion-adhered and exhibits further excellent machinability.
That is, in the present invention, the weight ratio of B: 0.001 to 0.3% and Cr:
0.02 to 0.07%, Mn: less than 0.1%, and if necessary, one or more selected from S, Se and Te in total of 0.03
~ 0.15%, with the balance being Fe and inevitable impurities in iron powder, Ni: 0.5 to 7%, Cu: 0.5 to 3% and M by weight ratio.
o: One or more selected from 0.05 to 3.5% is partially alloyed, which is an alloy steel powder for a high-strength sintered material having excellent machinability.

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 the 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 the B-based oxide and S, Se and Te. It is what makes me. In addition, since at least one of Ni, Cu, and Mo is partially alloyed by diffusion adhesion, it can be retained by molding and sintering with a usual Fe-Cu-C-based or Fe-C-based composition. It is possible to easily obtain a high-strength sintered alloy steel having graphite and having excellent machinability.

Each of the following has an important function in the present invention.
The action and limiting range of the element will be described in detail. B: 0.001 to 0.3% As described above, molten steel containing B is atomized with water.
When atomized, part of B is easily oxidized by water and iron powder surface
B-type oxides are deposited on the surface, and these B-type oxides become
In order to suppress the carburization of graphite into the powder, the black residue remaining in the sintered body
Increased lead content, resulting in improved machinability of sintered alloy steel
In addition to making it possible to correct after sintering. B-type acid
Compound is very stable and H₂Rarely reacts with
So H ₂Even if heat-treated in an atmosphere containing
It never drops.

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

Since the improvement of 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 not containing B. Cr: 0.02 to 0.07% Cr in iron powder has the effect of increasing the amount of 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 becomes high due to the carbide, and the machinability deteriorates. With the balance of machinability and manufacturing cost,
A preferred range is 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 the 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 amount of residual graphite in the sintered steel, are easily bonded to S, Se, and Te. From the viewpoint of refining cost and machinability for reducing Mn in the converter,
The preferable 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 enhance the strength. The addition amounts are Ni: 0.5-7%, Cu: 0.5-3%, Mo: 0.05-, respectively.
Limited to 3.5%. If each element is less than the lower limit, no improvement in strength due to addition is observed. Further, when the content of each element exceeds the upper limit, the machinability sharply decreases.

Sum of at least one of S, Se and Te: 0.03
Iron powders for powder metallurgy produced by a spraying method using 0.15% water, S, Se and Te are added to form residual graphite in the sintered steel. The total amount of addition is limited to 0.03 to 0.15%. If it is less than 0.03%, there is no effect of improving the machinability due to the generation of residual graphite. If it exceeds 0.15%, soot is likely to be generated during sintering, which may damage the sintering furnace. For reasons of machinability and alloy cost, the preferred range is 0.08-0.13%.
As described above, B, S, Se, and Te each independently have the effect of producing residual graphite during sintering. When one or more of B, S, Se, and Te are used in combination, a combined effect equal to or more than the sum of the effects when each is added alone is exhibited.

[0022]

【Example】

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

[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 to have a compacted density of 7.0 g / cm ^3, and the temperature was 1250 in a nitrogen stream.
After sintering at 60 ° C for 60 minutes, the machinability of the as-sintered material and the possibility of straightening were evaluated. The machinability is evaluated with an outer diameter of 60φ and a height of 10 mm.
Disc shape, and after sintering under the above conditions, using a HSS drill with a diameter of 1 mmφ, the average number of holes (3 drills) machined under the conditions of 10,000 rpm and 0.012 mm / rev Was evaluated as the tool life. Whether or not straightening was possible was determined by pressing the material as it was sintered at 5 t / cm ² and allowing it to be deformed, and not allowing it to be slightly deformed.

The residual graphite content of the sintered steel was quantified by infrared absorption method after filtering the nitric acid-dissolved residue through a glass filter. Also, the sintered body is made into a carphone potential of 0.8%, 850 ° C x 30
After minute heating, bright quenching was performed in oil at 160 ° C., and tensile strength was measured. Table 1 collectively shows the residual graphite amount of the sintered body, the tool life, and the tensile strength after bright quenching. As can be seen from the examples of Table 1, B: 0.001 to 0.3%, Cr: 0.02 to 0.07
%, Mn: less than 0.1%, and Ni: 0 in place of part of Fe.
The residual graphite of the sintered steel obtained from the iron powder for powder metallurgy in which at least one of 5 to 7%, Cu: 0.5 to 3% and Mo: 0.05 to 3.5% is diffused and adhered to the surface of the iron powder is The tool life was over 0.2% and the tool life was over 60. On the other hand, the tensile strength increased to 960 to 1030 MPa with increasing amounts of Ni, Cu and Mo added. Moreover, the correction was possible in all the examples.

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, and it was impossible to correct.
Comparison with the examples shows that the addition of B improved the machinability. As shown in Comparative Examples 2 and 5, the content of B was
If it exceeds 0.3% or the Ni content 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 deteriorates. Further, as shown in Comparative Examples 5, 6, and 7, if the amount of Ni, Cu, and Mo deposited 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 that is the base powder and the content of the diffusion adhesion component in the alloy steel powder that is diffusion adhered. These alloy steel powders are raw powders obtained by spraying molten steel with water, dried in a nitrogen atmosphere at 140 ° C for 60 minutes, then reduced in a pure hydrogen atmosphere at 930 ° C for 20 minutes, and then crushed and classified into iron powders. Carbonyl Ni powder, Mo trioxide powder, and Cu powder were mixed at a predetermined ratio and annealed in H ₂ gas at 875 ° C. for 60 minutes to diffuse and adhere.

[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 have a green compact density of 7.0 g / cm ^3, and the temperature was 1250 in a nitrogen stream.
After sintering at 60 ° C for 60 minutes, the amount of residual graphite, machinability, and correctability were evaluated. For the evaluation of machinability, a disk shape with an outer diameter of 60φ and a height of 10mm was used. After sintering under the above conditions, using a HSS drill with a diameter of 1mmφ, processing becomes impossible under the conditions of 10000rpm and 0.012mm / rev. The average number of holes machined 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 infrared absorption method after filtering the nitric acid-dissolved residue through a glass filter. Table 2 collectively shows the amount of residual graphite after sintering, tool life, and 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%, at least one of which is diffused and adhered to the surface of the iron powder, the residual graphite of the sintered steel obtained from the iron powder for powder metallurgy is 0.2. %, The tool life was 60 or more. On the other hand, the tensile strength after bright quenching increased to 950 to 1050 MPa with the addition of Ni, Cu and Mo. Further, in all the examples, it was possible to correct the sintered body.

Comparative Example 8 does not contain B and the residual graphite is 0.02.
%, The tool life was 10, and it was found from the comparison with the examples that the addition of B improved the machinability. Comparative Examples 9 and 19
As shown in (3), if the B content exceeds 0.3% or the Ni content exceeds 7%, the machinability deteriorates. In addition, Comparative Example 10 ~
As shown in 13, when the sum of one or more of S, Se and Te is less than 0.03%, the machinability is poor, and as shown in Comparative Examples 14 to 17, S, S
When the sum of one or more of e and Te exceeds 0.15%, the tensile strength is lowered and soot is generated during sintering. Further, as shown in Comparative Example 18, the machinability deteriorates when the Mn content is 0.1% or more. Further, as shown in Comparative Examples 19, 20, and 21, if the adhered amounts of Ni, Cu, and Mo are large, improvement in machinability cannot be expected.

[0031]

According to the present invention, when the alloy steel powder having Ni, Cu, Mo diffused and adhered to the iron powder for powder metallurgy produced by the spraying method using water is sintered, the straightening after the sintering is performed. It is possible to obtain a sintered body having excellent machinability and capable of easily producing a sintered steel having high strength and toughness after quenching without causing soot.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Kaminozono 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Technical Research Institute, Kawasaki Steel Co., Ltd. (72) Kuniaki Ogura 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Address: Kawasaki Iron and Steel Co., Ltd., Technical Research Institute (72) Inventor, Yang Sakaki, 3-10 Koganecho, Niigata City, Niigata Prefecture Mitsubishi Material Co., Ltd., Niigata Works

Claims (2)

[Claims] 1. A weight ratio of B: 0.001 to 0.3% and Cr: 0.02.
~ 0.07%, Mn: less than 0.1%, the balance is iron and iron powder which is an unavoidable impurity, Ni: 0.5 to 7% by weight, Cu: 0.
Alloy steel powder for high-strength sintered materials with excellent machinability, characterized in that at least one selected from 5 to 3% and Mo: 0.05 to 3.5% is partially alloyed. 2. A weight ratio of B: 0.001 to 0.3% and Cr: 0.02.
~ 0.07%, Mn: less than 0.1%, S, Se and T
Iron powder containing 0.03 to 0.15% in total of at least one selected from e, and the balance being Fe and inevitable impurities, Ni: 0.
Alloy steel powder for high-strength sintered materials with excellent 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. .