JPH0751721B2 - Low alloy iron powder for sintering - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a low-alloy iron powder for sintering suitable for producing a high-strength sintered material used for structural machine parts and the like.

[Conventional technology]

Conventionally, as a method of using the sintered material, a method of using the sintered material has been mainly used for the purpose of reducing the manufacturing cost by taking advantage of the high yield of the sintering process and the feature that cutting can be largely omitted. However, in recent years, it is often used as a functional material. For example, adoption in mechanical parts used in parts requiring strength is also under study, and some have already been used. The demand for higher strength of sintered materials is increasing year by year, but few materials meet this requirement.

In order to obtain a high-strength sintered material, various strengthening methods such as alloying, homogenization and densification have been studied. A prealloying method in which copper (Cu), nickel (Ni), molybdenum (Mo), manganese (Mn), chromium (Cr), etc. are solid-dissolved in iron and strengthened in order to improve strength by alloying. Alternatively, a mixing method is known, but each has its own problems and there are many points to be solved.

That is, in the mixing method, it is necessary to heat the added alloy elements at a high temperature for a long time in order to diffuse into the iron, and the active metals such as Cr and Mn are oxidized unless the sintering atmosphere is strictly controlled. It prevents the diffusion.
Therefore, it is difficult to obtain a homogeneous material, and the strength is not improved despite the addition of alloying elements.

On the other hand, in the pre-alloying method, the hardness of the powder increases due to the solid solution hardening due to alloying, and the compressibility decreases, which is disadvantageous for increasing the strength. Therefore, it is necessary to further increase the density by a method such as recompression.

As described above, the method for improving strength by alloying is considered to be the most advantageous method as compared with other strengthening methods although it involves problems, and therefore various studies have been made. For example, in the specification of JP-B-45-9649, "Production Method of Low-Alloy Powder Iron", alloying elements such as Mo, Ni, and Cu that can be easily reduced are attached to the surface of iron powder by a special reduction method to pre-alloy A method of making a pulverized powder is disclosed. This is an improvement of compressibility deterioration due to oxidation during prealloying,
The compressibility is similar to that of pure iron powder, but there is a problem with the diffusion of alloying elements and it is not sufficiently homogenized. Also, the hardenability is
It is slightly inferior to the material charge containing Cr and Mn.

Cr and Mn have a large contribution to the hardenability and are alloying elements effective for strengthening, but they have not been used so far because of their poor reducibility. However, due to the improvement of the atomization method in pulverization and the improvement of the reduction method after atomization, low-alloy powders containing Cr and Mn as the main components have been commercially available.

[Problems to be solved by the invention]

However, it is necessary to sinter the powder containing Cr and Mn in an atmosphere having a high reducing property, for example, in expensive hydrogen or vacuum, and strictly controlling the state of the reducing furnace.
All of the low alloy powders currently on the market have problems such as high powder cost and high cost at the time of sintering, and there are problems in manufacturing difficulty and economical aspect.

The present invention is intended to solve the above problems in the prior art, and an object of the present invention is excellent in compressibility, high strength after sintering, easy to manufacture, and lower cost than conventional ones. To provide a low alloy iron powder for use.

[Means for solving problems]

That is, the low alloy iron powder for sintering of the present invention contains molybdenum (Mo) 0.2 to 1.5% and manganese (Mn) 0.05 to 0.25% by weight.
Containing 0.1% or less of carbon (C) as impurities and 0.3% or less of oxygen (O), and the balance substantially iron (Fe)
And is manufactured by a water atomization method. Mo has the effect of bainite the sintered structure, improving the strength, and improving the hardenability during heat treatment, but if the weight ratio is less than 0.2%, the effect is small, and if it exceeds 1.5%, the compressibility decreases. In addition, since the effect of improving the hardenability is not so great and the cost is high, 0.2
% -1.5% range is preferred. Mn has an effect similar to that of Mo, but if less than 0.05% by weight, no effect can be expected, and
If it exceeds 25%, the compressibility and the strength may be deteriorated, so the range of 0.05% to 0.25% is preferable. C is the weight ratio
If it exceeds 0.1%, the compressibility is lowered, so 0.1% or less is preferable. Also, if O exceeds 0.3%, the compressibility decreases,
It has a considerable adverse effect on the properties of the sintered body.
0.3% or less is preferable.

The low alloy iron powder for sintering of the present invention is produced from molten metal by using a water spray method. Properties such as average particle size and particle size distribution can be changed by selecting manufacturing conditions or by classifying means depending on the intended use of the obtained powder.

〔Example〕

The present invention will be described in more detail in the following examples and comparative examples. The present invention is not limited to the examples below.

Example 1: A molten metal adjusted to a target component ratio was prepared in a melting furnace, the molten metal was allowed to flow out of a tundish, and then powdered by a water spray method in which high-pressure water was acted as a spray medium on the molten metal flow. The water spray method powder produced by the grinding the solidified mass was subjected to 1800 seconds reduced at 1203K in H ₂ -N ₂ mixed atmosphere and then classified with a standard sieve JIS80 mesh, 80 mesh or less powder Was collected.

Examples 2-3: Powders of 80 mesh or less were collected by the same method as in Example 1 except that the addition ratio of each alloy component was changed.

Comparative Example 1: A commercially available alloy powder in which Ni, Mo, and Cu were attached to and diffused on the surface of iron powder was used.

Comparative Examples 2 to 4: Preparation was performed in the same manner as in Examples 1 to 3 except that the composition of each alloy component was changed.

The compositions of the low alloy iron powders for sintering of Examples 1 to 3 and Comparative Examples 1 to 4 are summarized in Table 1 below.

Physical property comparison test: As a raw material powder for high-strength sintered materials, it is required to have good compressibility and good mechanical properties when made into a sintered body or when a heat treatment is applied to the sintered body. ing.

The compressibility of each material shown in Table 1 was measured in accordance with the JSPM standard 1-64 metal powder compressibility test method. The test piece was molded at a pressure of 588 MPa. The results are shown in Fig. 1. Also, the tensile strength was measured. That is, 0.6% by weight of graphite powder and 0.8% by weight of lubricant were added to each powder of Examples and Comparative Examples, and after mixing, a tensile test piece having a green compact density of 6.9 Mg / m ³ (JS
A PM2-64 tensile test piece for sintered metal) was molded and then sintered in a decomposed ammonia gas atmosphere at 1423K for 3600 seconds, and this test piece was further vacuumed at 1143K for 2400 seconds.
After heating for 2 seconds, oil quenching is performed, and then test pieces are tempered at 443K for 4800 seconds, and a tensile test is performed on both test pieces at a crosshead speed of 3.3 × 10 ^-5 m / s to obtain tensile strength. I asked. The results are summarized in FIG.

As is clear from FIG. 1, Examples 1 to 3 have a density of 7.07 to
It shows a good compressibility of 7.12 Mg / m ³ . This value is comparable to Comparative Example 1 which is said to have the highest compressibility among commercially available low alloy irons. Comparative Example 2 is a powder in which Mn is increased as compared with Example 2, but the compressibility is considerably lower than that of Example 2. Comparative Example 3 is a powder obtained by adding 0.4% by weight of Cr to Example 2, and it can be seen that the compressibility is significantly lowered by Cr. Comparative Example 4 is a powder in which the amount of Mn is reduced to 0.03% by weight, and the compressibility is slightly higher than that of Example 2.

Further, from FIG. 2, the tensile strength of the sintered body is about 530M in Example 1.
It is Pa, and comparing Examples 1 to 3, it can be seen that the tensile strength increases as the amount of Mo increases. Comparing Example 1 and Comparative Example 1, the tensile strength of the sintered body showed the same value,
Comparative Example 1 contains a large amount of expensive Cu and Ni, which are not contained in Example 1, so that Example 1 is particularly advantageous in terms of cost. This is because the material of the present invention completely pre-alloys Mo, whereas the comparative material 1 has an incomplete pre-alloying of alloying elements, and therefore the alloying elements are not sufficiently diffused into iron. It is estimated that this is due to the difference in the amount of solid solution due to this. Example 2 and Comparative Example 2 have almost the same composition except that the amount of Mn is different, but Example 2 containing 0.2% by weight of Mn has Mn0.0.
It shows a higher tensile strength than Comparative Example 2 containing 3% by weight. It is presumed that this is due to the magnitude of the effect of solid solution strengthening by Mn.

Next, the tensile strength after heat treatment is compared. Comparing Example 1 and Comparative Example 1 in which the tensile strengths of the sintered bodies were the same, Example 1 showed a tensile strength as high as about 60 MPa, and Mo and Mn contained in Example 1 were It can be seen that the effect of improving the hardenability is fully exhibited. On the other hand, in Comparative Example 1, Mo and C
It is considered that since u and Ni were not completely prealloyed, the solid solution strengthening ability of the alloy elements was not sufficiently exerted and the value was lower than that in Example 1. Example 2 and Comparative Example 2
And 4 have different Mn contents. In Comparative Example 4, the Mn content was 0.03% by weight, and it was not possible to expect the improvement of the hardenability by Mn, so the tensile strength was lower than that of Example 2. on the other hand,
Comparative Example 2 contains 0.8% by weight of Mn, but the tensile strength is lower than that of Example 2. It is considered that this is because the oxide of Mn is present in a larger amount than in Example 2, and indicates that Mn has an appropriate addition range.

〔The invention's effect〕

As described above, the low alloy iron powder for sintering of the present invention is Mo, Mn,
Since each component element of C and O is contained in iron in a predetermined ratio, when used as a raw material for machine component parts, it is possible to obtain a high-density molded product because of its good compressibility, and to improve the mechanical properties such as tensile strength. It is possible to obtain parts having excellent properties.

Further, the low alloy iron powder for sintering of the present invention is easily manufactured by a water atomization method and does not contain expensive components such as Cr and Ni, so that it is cost-effective and widely used for various applications. You can

[Brief description of drawings]

FIG. 1 is a graph showing the density of compacts under the same molding conditions when the low alloy iron powder for sintering of the examples and comparative examples of the present invention is used, and FIG. 2 shows the examples of the present invention and comparative examples. It is a graph which shows the tensile test result of the sintered compact produced using the low alloy iron powder for sintering.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuntaro Sudo 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Corporation (56) References JP-A-57-73154 (JP, A) JP-A-57-164901 (JP, A)

Claims (1)

[Claims] 1. A weight ratio of molybdenum (Mo) is 0.2 to 1.5% and manganese (Mn) is 0.05 to 0.25%. Carbon (C) as impurities is 0.1% or less and oxygen (O) is 0.3% or less. A low alloy iron powder for sintering characterized in that it is regulated and the balance consists essentially of iron (Fe), and is produced by a water atomization method.