JPH075923B2 - High alloy steel powder for powder metallurgy with excellent compressibility and formability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a high alloy steel powder containing Co, which is used when a heat-resistant sintered alloy steel part or the like is manufactured by powder metallurgy. It has improved moldability.

<Prior Art> Sintered alloy steel is widely used for automobile parts and the like, and recently, parts having a high alloy composition have been increasing. Heat-resistant parts are an important application, and exhaust valve seat rings for automobile engines are being put to practical use. These heat-resistant parts often use Co as an alloying element, for example 6.5%.
(Wt%, the same applies below) Alloy steel powder containing Co is used as a raw material. In order to improve heat resistance, it is often necessary to add a larger amount of Co, and a sintered alloy steel containing 7 to 25% Co has been studied. When the Co content is 7% or more, the steel particles of the pre-alloyed steel powder up to now become hard, so that the compressibility and the formability of the steel powder are deteriorated, which is a serious problem in the production of parts.
On the other hand, if iron powder and alloy element powder, for example, Co powder, are mixed to produce a component by the so-called mixed powder method, there is no problem in the compressibility of the powder, but it is aimed at uniform diffusion alloying during sintering. If fine Co powder is used, the flowability of the powder is poor, the formability is extremely deteriorated, and defects of the green compact frequently occur.

In order to solve these points, a method called a mother alloy method, in which a Fe-Co alloy powder having a higher Co content is mixed with pure iron powder, etc., is considered, and a similar technique is disclosed in Japanese Patent Publication No. Sho 61-36043. As can be seen in No. 6, there is no master alloy method with an excellent composition including additive elements other than Co until now.

By the way, the element used in the heat-resisting alloy steel is C
O, Cr, Ni, Mo, V, etc., but in the case of powder metallurgy, if a non-reducible oxide is formed in the process up to sintering, the quality of parts will be deteriorated without being reduced. However, elements such as Co, Ni, and Mo, which are easily reducing elements, are preferred over oxides of Fe and are often used. Here, part of Ni is equal weight Cu and part of Mo is 2
It can be replaced with double weight W. Currently, the composition of sintered steel is often studied as Co: 3 to 25%, Ni:
0.2-10%, Mo: 0.2-15%. Ni when Cu or W is included
Can be replaced by Ni + Cu (the sum of Ni content and Cu content. The same applies below), and Mo can be replaced by Mo + 1 / 2W (Mo
The sum of the content and 1/2 of the W content is shown. The same applies below).

<Problems to be Solved by the Invention> In view of such a situation, the present invention includes an alloy element having such a composition range and a Co content of 3 to 25%, which is excellent in compressibility and formability. It provides steel powder.

<Means for Solving the Problems> In the present invention, by weight ratio, Co: 10 to 36%, Ni + Cu: 0.2 to 20
%, Mo + 1 / 2W: 0.15% or less, with the balance being alloy steel powder with a composition range consisting of Fe and unavoidable impurities, and Mo + 1 / 2W:
0.2 to 19%, Co + Ni + Cu: 2% or less, the balance is a mixed powder with alloy steel powder with a composition range consisting of Fe and unavoidable impurities, and pure iron powder for powder metallurgy can be mixed if necessary. Average composition: Co: 3-25%, Ni + Cu: 0.2-10%, Mo + 1 / 2W: 0.2
It is a high alloy steel powder for powder metallurgy having excellent compressibility and formability, characterized by being in the range of up to 15% and the balance being Fe and inevitable impurities. However, Ni + Cu is the sum of the contents of Ni and Cu, Mo + 1 / 2W is the sum of the contents of Mo and half of the content of W, and Co + Ni + Cu is the sum of the contents of Co, Ni and Cu.

<Operation> The grounds for the limited scope of the present invention will be described in detail below.

First, the Co content of the first steel powder is set to 10 to 36%. This is because the compressibility and formability of the mixed alloy steel powder are optimal when the final composition is constant, as shown in the examples described later. Has been selected. When the final composition is given, the Co of the first steel powder is 10
If it is less than%, the blending ratio of the second steel powder, which is softer than that of the first steel powder, is inevitably small, and overall compressibility and formability deteriorate. On the other hand, when Co exceeds 36%, the first steel powder itself becomes too hard, which also causes deterioration of compressibility and formability. A suitable range is 10-36%.

The Ni + Cu content of the first steel powder is 0.2 to 20%.

The lower limit of the amount of Ni + Cu is automatically determined to secure the lower limit of Ni + Cu in the final sintered material. The upper limit is the same as Co
It is defined as the range in which the compressibility and the moldability are improved.

Basically, it is desirable that the first steel powder does not contain Mo or W. This is based on the findings of the study conducted by the present inventors and is an important point of the present invention. That is, Mo and W do not impair the compressibility and formability even if they are alloyed with iron powder themselves, but when Co, Ni, or Cu is alloyed, their deterioration is markedly increased due to a synergistic effect. It will be remarkable. In the examples described later, the proper range is specifically shown as data, but the upper limit of Mo + 1 / 2W of the first steel powder is 0.
15%. When it exceeds this, the compressibility and the moldability are significantly deteriorated.

In the present invention, the contents of Mo and W in the first steel powder are thus limited as much as possible, and Mo and W are contained in the second steel powder. Mo + 1 / 2W in the second steel powder is 0.2 to 19%. This lower limit is necessarily established to ensure the lower limit of the final composition. Similar to Co and Ni + Cu of the first steel powder, the upper limit is given as a condition that does not deteriorate the compressibility and formability of the entire mixed alloy steel powder. These are supported by concrete data in the examples described later.

The second steel powder basically does not contain Co, Ni, and Cu, but the reason is the same as the reason for limiting Mo and W of the first steel powder. However, if Co + Ni + Cu is up to 2%, the adverse effect is small, so that it is acceptable.

The second embodiment of the present invention is a case where pure iron powder for powder metallurgy is further mixed in addition to the first steel powder and the second steel powder. The advantage in this case is that by mixing pure iron powder with the first and second steel powders having a limited composition range, mixed alloy steel powders with various final compositions can be obtained, and Table 2 ( Example of 2)
As shown in 15,16,18, the compressibility and moldability are improved.

This pure iron powder for powder metallurgy is obtained by the atomization method or reduction of oxide scale.

Further, both the first steel powder and the second steel powder do not have to be one kind of steel powder, and two or more kinds of steel powder may be mixed and used within the respective composition ranges. That is, for example, the final steel powder can be obtained by mixing the first steel powder with a mixture of two types of steel powder and the second steel powder with a combination of three types of steel powder.

It should be noted that stainless steel powder, graphite powder usually used in powder metallurgy, and mixed powder obtained by adding zinc stearate, stearic acid or the like as a lubricant to these alloy steel mixed powders are also included in the scope of the present invention.

<Example> As for the steel powder used in the examples, all molten steel having a predetermined composition was pulverized by water atomization, subjected to finish reduction in H ₂ gas at 980 ° C. for 30 minutes, and used as −80 # grain size. As impurities, all steel powders are C: 0.002-0.016%, Si: 0.01-0.03%, Mn: 0.05-0.32%, P: 0.003-0.029%, S: 0.006-0.026%, O: 0.06-0.23% Was included.

The pure iron powder used as the third powder in the method of the present invention was similarly used as -80 # after water atomizing and finish reduction. Impurities are C: 0.003%, Si: 0.01%, Mn: 0.06%, P: 0.008%, S: 0.010%,
O was 0.07%.

Prealloy steel powder for comparison was also procured by the same manufacturing method. Further, in the comparative example by the conventional mixed powder method, the same atomized powder as described above was used as the pure iron powder, Ni had an average particle size of 7 μ, and Cu had an average particle size.
13 μ, Co had an average particle size of 5 μ, Mo had an average particle size of 10 μ, and W had an average particle size of 9 μ.

Table 1 shows the compositions of the steel powder of the example and the steel powder of the comparative example.

These steel powders were prepared by mixing 0.8% zinc stearate and 0.5% graphite powder (average particle size 19μ) at a molding pressure of 7t / cm ² and a diameter of 1
It was molded into a cylindrical shape having a height of 1.3 mm and a height of 11.3 mm, and the compressibility was evaluated by the density of the green compact, and the moldability was evaluated by the Ratler value. The results are summarized in Table 2 together with the composition of the steel powder after compounding.

In Comparative Example 1, Examples 1 to 4, and Comparative Examples 2 to 4, the final composition was Co: 7.
%, Ni: 1.4%, Mo: 1.4%. This result is summarized and shown in FIG. When Co in the first steel powder is in the range of 10 to 36%, the compressibility is better (high green compact density) and the formability is better (low ratler value) than the conventional pre-alloy method. There is. Further, the moldability is remarkably improved as compared with the mixed powder method.

In Examples 5 and 6, Comparative Examples 5 to 7, the final compositions were Co: 8%, Ni: 6%,
Mo: 2%. As shown in FIG. 2, in the first steel powder
It can be seen that when the amount of Ni is 0.2 to 20% within the range of the present invention, excellent moldability and compressibility are obtained.

Examples 7, 8 and Comparative Examples 8, 9 have a final composition of Co: 10%, Ni: 3%, Mo: 1.
% Is the case. As shown in FIG. 3, Mo in the first steel powder
When the content is 0.15% or less, excellent compressibility and moldability are obtained.

Examples 9 and 10, Comparative Examples 10 and 11, the final composition is Co: 8%, Ni: 4%,
Mo: 8%. As shown in FIG. 4, when the Mo content in the second steel powder is 0.2 to 19%, the one having excellent compressibility and moldability can be obtained.

Examples 11 to 13 and Comparative Examples 12 to 15 have a final composition of Co: 22%, Ni:
This is the case when 9.5% and Mo: 2.5%. As shown in FIG. 5, when the amount of Co + Ni + Cu in the second steel powder is kept within 2%, the overall characteristics of compressibility and formability are improved as compared with the conventional pre-alloy method and the mixed powder method.

Examples 14 and 15, Comparative Examples 16 and 17, the final composition is Co: 8%, Ni: 1.5
%, Cu: 0.5%, Mo: 1.5%, W: 2%. As is clear from Table 2, even when a part of Ni is replaced by Cu and a part of Mo is replaced by W, the method of the present invention provides superior compressibility and moldability as compared with the conventional method. In Example 15, 20% of pure iron powder was blended as the third powder, and this also shows very excellent characteristics.

In Example 16 and Comparative Examples 18 and 19, the final composition was Co: 3%, Cu: 1%, W:
It is the case of 2%. Thus, even when the amount of Co is low, the effect of the method of the present invention can be sufficiently seen, as can be seen from Table 2.

Example 17 and Example 18, the final composition is the same as Examples 14 and 15, Comparative Examples 16 and 17, the final composition is Co: 8%, Ni: 1.5%, Cu: 0.
5%, Mo: 1.5%, W: 2%, but this is the case where there are multiple first steel powders and second steel powders. In any case, the effect of the present invention is achieved.

In Example 19 and Comparative Examples 20 and 21, the final composition was Co: 4.5%, Ni: 1.5.
%, Mo: 14.5%, when the Mo content is high. By setting the Mo of the second steel powder within 19%, high compressibility and formability can be obtained.

<Effects of the Invention> As described above, according to the present invention, according to the present invention, not only in the high Co composition of 7% or more, but also in the Co composition of 3% or more, the compressibility and the formability of the conventional prealloy method, Significantly improved by the mixed powder method, Co: 3-25%, Ni + Cu: 0.2-10
%, Mo + 1 / 2W: It is clear that a very useful alloy steel powder is provided for a final composition of 0.2 to 15%.

[Brief description of drawings]

1 to 5 show Co content in the first steel powder, Ni content in the first steel powder, Mo content in the first steel powder, and Mo content in the second steel powder, respectively.
It shows the influence of the amount and the amount of Co + Ni + Cu in the second steel powder on the compressibility and formability of the mixed alloy steel powder.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Ota 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor Osamu Furu-kun 1 Kawasaki-cho, Chiba-shi Kawasaki Steel Co., Ltd. Technical Research Division

Claims (2)

[Claims] 1. An alloy steel powder containing Co: 10 to 36% Ni + Cu: 0.2 to 20% Mo + 1 / 2W: 0.15% or less by weight, the balance being Fe and inevitable impurities, and Mo + 1. / 2W: 0.2 to 19% Co + Ni + Cu: 2% or less, the balance is a mixed powder with alloy steel powder in the composition range consisting of Fe and inevitable impurities, and the average composition is Co: 3 to 25% Ni + Cu: 0.2 ~ 10% Mo + 1 / 2W: 0.2 to 15%, the balance being Fe and inevitable impurities, and high alloy steel powder for powder metallurgy with excellent compressibility and formability. However, Ni + Cu is the sum of the contents of Ni and Cu, Mo + 1 / 2W is the sum of the contents of Mo and half of the content of W, and Co + Ni + Cu is the sum of the contents of Co, Ni and Cu. 2. An alloy steel powder containing Co: 10 to 36% Ni + Cu: 0.2-20% Mo + 1 / 2W: 0.15% or less by weight, the balance being Fe and inevitable impurities, and Mo + 1. / 2W: 0.2 to 19% Co + Ni + Cu: 2% or less, a mixed powder of alloy steel powder with a balance of Fe and inevitable impurities, and pure iron powder for powder metallurgy. : 3 to 25% Ni + Cu: 0.2 to 10% Mo + 1 / 2W: 0.2 to 15%, the balance being Fe and unavoidable impurities, the balance being Fe and unavoidable impurities. Steel powder. However, Ni + Cu is the sum of the contents of Ni and Cu, Mo + 1 / 2W is the sum of the contents of Mo and half of the content of W, and Co + Ni + Cu is the sum of the contents of Co, Ni and Cu.