DE112009002701B4 - Process for producing a sintered iron alloy - Google Patents

Abstract

A method of producing a sintered iron alloy, the method being characterized in that it is a method for producing a sintered iron alloy, comprising: a compacting step in which a raw material powder is compacted under pressure, in which an Fe system powder, pure iron and / or having an iron (Fe) alloy mixed with a reinforcing powder containing an alloying element which is not Fe, whereby the raw material powder is transformed into a powder compact; and a sintering step in which the powder compact is heated in an oxidation-resistant atmosphere, thereby sintering the powder compact; and wherein the reinforcing powder is an Fe-Mn-Si-C powder comprising a Fe alloy or an Fe compound containing manganese (Mn) in an amount of 58 to 70 mass% (hereinafter, simply by "%"). " designated); Silicon (Si) in an amount to have a composition ratio of Mn to Si (i.e., Mn / Si) of 3.3 to 4.6; and carbon (C) in an amount of 1.5 to 3%; based on a total of 100%.

Description

FIELD OF TECHNOLOGY

The present invention relates to a method for producing a sintered iron alloy, which exhibits good properties in terms of strength and dimensional stability and which makes it possible to dispense with Cu or Ni and which is inexpensive.

TECHNICAL BACKGROUND

In order to lower the cost of manufacturing articles such as mechanical parts, it may be considered to use a sintered ferrous alloy article for which a powder compact made by compressing a raw material powder mainly consisting of iron under pressure is heated to sinter him. When a sintered iron alloy article is used, it is also possible to obtain products (or sintered bodies) which approximate the final shapes, and therefore, the manufacturing cost and the material cost of the articles can be tried based on the shortening of the machining processes to lower the increase in material yields, etc. In view of this, the strength of the sintered ferrous alloy article and its dimensional stability before and after sintering are important.

• Patentdokument Nr. 1: US 6,346,133 ;
• Patentdokument Nr. 2: US 6,364,927 ;
• Patentdokument Nr. 3: japanische Patent Gazette Nr. 3,309,970 ;
• Patentdokument Nr. 4: japanische ungeprüfte Patent-Offenlegungsschrift (KOKAI) Gazette Nr. 58-2 10,147 ;
• Patentdokument Nr. 5: veröffentlichte japanische Übersetzung PCT Application Gazette Nr. 10-510,007 ;
• Patentdokument Nr. 6: japanische ungeprüfte Patent-Offenlegungsschrift (KOKAI) Gazette Nr. 2005-336,608 ;
• Patentdokument Nr. 7: japanische ungeprüfte Patent-Offenlegungsschrift (KOKAI) Gazette Nr. 2005-336,609 ;
• nicht auf ein Patent bezogenes Dokument Nr. 1: High Strength Si-Mn-Alloyed Sintered Steels, P. M. Int., Bd. 17, Nr. 1 (1985);
• nicht auf ein Patent bezogenes Dokument Nr. 2: ”Effect of Sinter-Hardening on the Properties of High Temperature Sintered PM Steels”, Advances in Powder Metallurgy & Particulate Materials, MPIF, 2002, Teil 13, S. 1–13; und
• nicht auf ein Patent bezogenes Dokument Nr. 3: ”New focus an chromium alloy may sidestep alloy cost increases”, MPR. September (2004), S. 16–19.

From this viewpoint, Fe-Cu-C sintered iron alloys for which powder compacts containing raw material powders containing Fe-Cu-C compositions have been sintered have been widely used in component applications. The reason for this is that Cu is an element effective to increase the strength of a sintered iron alloy and to stabilize the dimensional accuracy before and after sintering. Therefore, in the case of sintered iron alloys, it has been considered that Cu is indeed the most important element unlike in conventional iron and steel materials.

• Patent Document No. 1: US 6,346,133 ;
• Patent Document No. 2: US 6,364,927 ;
• Patent Document No. 3: Japanese Patent Gazette No. 3,309,970 ;
• Patent Document No. 4: Japanese Unexamined Patent Publication (KOKAI) Gazette No. 58-2 10,147 ;
• Patent Document No. 5: published Japanese Translation PCT Application Gazette No. 10-510,007 ;
• Patent Document No. 6: Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2005-336,608 ;
• Patent Document No. 7: Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2005-336,609 ;
• Non-Patent Document No. 1: High Strength Si-Mn Alloyed Sintered Steels, PM Int., Vol. 17, No. 1 (1985);
• Non-Patent Document 2: "Effect of Sintering Hardening on the Properties of High Temperature Sintered PM Steels", Advances in Powder Metallurgy & Particulate Materials, MPIF, 2002, Part 13, pp. 1-13; and
• Non-Patent Document 3: "New focus on chromium alloy may sidestep alloy cost increases", MPR. September (2004), p. 16-19.

DISCLOSURE OF THE INVENTION

Task to be solved by the invention

However, Cu powders have higher unit prices, and they are used in sintered iron alloys in relatively higher proportions. Thus, in and of itself they increase the production costs for sintered iron alloys. Further, although Cu is an element which causes hot brittleness in iron and steel materials, it is also an element which is difficult to remove by, for example, smelting. As a result, sintered iron alloys containing Cu are unpopular because they can inadvertently end up in the scrap and are difficult to recycle. Therefore, the use of sintered ferrous alloys containing Cu is not necessarily preferred from an environmental point of view for the efficient use of resources.

Besides Cu, Ni is available as an element widely used in sintered iron alloys. Similar to Cu, Ni is also an element effective, among others, to increase the strength of a sintered iron alloy. However, Ni powders are also expensive and thus increase the Production costs of sintered iron alloys. In addition, since Ni is an allergenic element, its use may be unfavorable.

In the above-mentioned patent documents Nos. 1 and 2 and non-patent document Nos. 1, there are disclosed sintered iron alloys in which, inter alia, it has been attempted to increase strength by adding Mn or Si thereto without Cu use. However, they have by no means come beyond the laboratory stage and they are different from the present invention described below even with regard to the proportions of Mn and Si in the composition and with regard to the addition methods and so forth.

Patent Document No. 3 discloses a method of ultrahigh-density compacting powder compacts.

In Patent Documents Nos. 4 to 7, a sintered iron alloy is described in which a powder mixture of a powder of a Si-Mn-Fe powdered master alloy and an iron powder is compacted and sintered under pressure. However, when the sintered iron alloy disclosed in these patent documents is compared with a sintered iron alloy according to the present invention described below, the former differs from the latter in the following: composition ratio of Mn and Si (ie Mn / Si); whether or not C is appreciably contained per se in view of the composition of the reinforcing powder used, and so on.

Moreover, Patent Document No. 5 even discloses a sintered iron alloy in which Mo is contained as a substitute for Ni. However, their strength is not necessarily sufficient, and therefore, it needs a heat treatment such as a hardening or tempering treatment to increase its strength. It is obvious that such a heat treatment increases the production costs for the sintered iron alloy, since it requires a considerable amount of time and man-hours.

On the other hand, in the non-patent document No. 2 or 3, a description is disclosed according to which an iron alloy (or a sintering hardening steel) having a high strength can be obtained even if heat treatments are omitted after the sintering step. However, non-patent document No. 2 differs from the present invention and does not disclose a sintered iron alloy containing Mn and Si. Non-patent document No. 3 discloses a sintering-hardening steel containing Cr, Mn, Si and Mo. However, unlike a sintered iron alloy according to the present invention which will be described below, it is not one prepared by using a reinforcing powder such as Fe-Mn-Si-C powder.

The present invention has been accomplished in view of these circumstances; and it is an object of it to provide a production method with which it is possible to lower cost sintered iron alloys, sintered iron alloys with which mechanical properties such as strength, and dimensional stability before and after sintering can be ensured, even under exclusion to obtain a use of Cu or Ni.

Means of solving the task

The object of the invention is achieved by the method of claim 1. Advantageous embodiments are the subject of dependent claims 2 to 11. The inventors have made intensive studies to solve this problem; as a result of repeated trial and error they have made the new discovery that it is possible to obtain sintered iron alloys which have good mechanical properties such as strength and dimensional stability at a lower cost using reinforcing powders (eg Fe-Mn). Si-C powders) whose compositions differ from the conventional ones, and then achieved the completion of the present invention.

<< Process for producing sintered iron alloys >>

• (1) A sintered iron alloy according to the present invention is a method for producing a sintered iron alloy characterized in that it comprises: a compacting step in the raw material powder in which an Fe system powder containing pure iron (Fe) and or containing an iron alloy, is compacted with a reinforcing powder containing an alloying element other than Fe, thereby forming the raw material powder into a powder compact; and a sintering step in which the powder compact is heated in an oxidation-inhibiting atmosphere, whereby the powder compact is sintered; and the reinforcing powder is an Fe-Mn-Si-C powder containing a Fe alloy or an Fe compound comprising manganese (Mn) in an amount of 58 to 70 mass% (hereinafter simply referred to as%) ; Silicon (Si) in an amount giving a composition ratio of Mn to Si (ie, Mn / Si) of 3.3 to 4.6; and carbon (C) in an amount of 1.5 to 3%; based on a total of 100%.
• (2) In the method of producing a sintered iron alloy according to the present invention, a reinforcing powder constituting a raw material powder comprises an Fe alloy or Fe compound containing not only Mn and Si but also C. In addition, a sintered iron alloy obtained by using a reinforcing powder (e.g., a Fe-Mn-Si-C powder) in which the contents of Mn, Si and C are in the above specific ranges is also exhibited without The use of Cu powder or Ni powder has good properties such as mechanical properties (strength, elongation, hardness and the like) and dimensional stability.

Further, raw materials for this Fe-Mn-Si-C powder are much better in terms of, for example, their mullability (or collapsibility) than, for example, conventional Fe-Mn-Si powders. Thus, a Fe-Mn-Si-C powder which is homogeneous and has a fine grain size can be obtained in a relatively simple manner. By using such a Fe-Mn-Si-C powder which is finely grained and uniform, dimensional accuracy and mechanical properties of sintered iron alloys can be improved to a much greater extent. In addition, Fe-Mn-Si-C powders having the above composition ranges or their raw materials can be procured relatively inexpensively since they are widely used as a deoxidizer (for example, silicon manganese) used during steelmaking.

Therefore, according to the manufacturing method of the present invention, it is possible to use a Fe-Mn-Si-C powder that is easy and inexpensive to procure or its raw materials without ever having to use a Cu powder that is relatively expensive , In addition, its raw materials can be relatively easily used as fine, homogeneous powders because they can be pulverized well. Therefore, at the stage of obtaining or preparing a powder raw material, a greater cost saving may be sought. In addition, the resulting sintered iron alloy not only has good mechanical properties but also good dimensional stability. Therefore, not only the lowering of heat treatment costs for articles having the sintered iron alloy but also, for example, the reduction of the cost of their processing can be aimed at.

Thus, according to the manufacturing method according to the present invention, the production cost of a sintered iron alloy or a sintered iron alloy article can be remarkably lowered throughout the whole manufacturing step starting from a raw material step and ending at the finished product stage.

• (3) Übrigens sind im Falle der Verwendung des oben genannten Verstärkungspulvers (z. B. eines Fe-Mn-Si-C-Pulvers) unter anderem die folgenden Gründe oder Mechanismen nicht unbedingt klar: warm dieses Pulver oder diese Rohmaterialien sich gut pulverisieren lassen; oder warum die jeweiligen Eigenschaften der gesinterten Eisenlegierungen, die unter Verwendung dieses Pulvers erhalten werden, stärker verbessert werden können als diejenigen von herkömmlichen Eisenlegierungen. Gemäß intensiven Studien, die von den Erfindern durchgeführt wurden, wird Folgendes angenommen: Erstens wird angenommen, dass außer den Zusammensetzungen von Mn und Si (wozu das Mn/Si-Verhältnis gehört) ein Merkmal, nämlich dass ein Fe-Mn-Si-C-Pulver, das auf die vorliegende Erfindung gerichtet ist, C in relativ größerer Menge enthält, ein Grund dafür ist, dass es sich leichter pulverisieren lässt als herkömmliche Fe-Mn-Si-Pulver. Genauer wird angenommen, dass dies deswegen der Fall ist, weil außer den intermetallischen Verbindungen von Mangan und Silicium (z. B. MnSi₃ und Mn₅Si₃) auch die Carbide von Mangan (z. B. Mn₂₃C₆, Mn₇C₃ und dergleichen) vorhanden sind.

Further, the sintered iron alloy obtained by the present invention outperforms conventional sintered iron alloys, among others, in view of mechanical properties. Thus, if the levels of required specifications for a sintered ferrous alloy component are comparable to conventional levels, the following also becomes possible: a reduction in the amount of reinforcing powder used per se; a replacement of an Fe system powder by a much cheaper powder in which the alloy element quantities are lower; and so on. If this is the case, the cost of manufacturing a sintered iron alloy or an article having the same can be further reduced.

• (3) Incidentally, in the case of using the above-mentioned reinforcing powder (eg, Fe-Mn-Si-C powder), among others, the following reasons or mechanisms are not necessarily clear: warm this powder or these raw materials can be well pulverized ; or why the respective properties of the sintered iron alloys obtained by using this powder can be more improved than those of conventional iron alloys. According to intensive studies conducted by the inventors, it is considered that: First, it is considered that apart from the compositions of Mn and Si (to which the Mn / Si ratio belongs), a feature that Fe-Mn-Si-C Powder, which is directed to the present invention contains C in relatively larger amount, one reason is that it is easier to pulverize than conventional Fe-Mn-Si powder. More specifically, this is considered to be the case because, besides the intermetallic compounds of manganese and silicon (eg, MnSi ₃ and Mn ₅ Si ₃ ), the carbides of manganese (eg, Mn ₂₃ C ₆ , Mn ₇ C ₃ and the like) are present.

Further, it is believed that the reasons that the sintered iron alloy obtained by using a Fe-Mn-Si-C powder has good mechanical properties or good dimensional stability are as follows:
First, Mn, Si and C contained in an Fe-Mn-Si-C powder, besides phosphorus (P) and sulfur (S), are referred to as the five steel elements, and they are common reinforcing elements in iron and steel materials to be cast or melted.

However, Mn and Si have not hitherto been used to any significant extent in the field of sintered iron alloys. Since Mn and Si cause the formation of oxides whose affinity to oxygen is extremely high, it has been generally believed that they produce sintered iron alloys in which the oxides have been arranged within the metal structure. This is particularly noticeable in a case where Mn and Si in the form of powders other than Fe system powder are added to a raw material powder. While it would be possible to use an Fe system powder in which Mn and Si were preliminarily alloyed, the resultant Fe system powder is very hard in this case, so that densification of a powder compact per se becomes difficult.

Thus, in the manufacturing method according to the present invention, Mn and Si are mixed in a powder raw material to be present as reinforcing powders different from Fe system powder. In addition, sintering of a powder compact containing Mn and Si is conducted in an atmosphere which prevents oxidation, so that oxidation of Mn and Si can be sufficiently limited (i.e., in a sintering step).

In any case, the inventors succeeded in obtaining, using a Fe-Mn-Si-C powder as a reinforcing powder, a sintered iron alloy superior to conventional Fe-Cu (-C) system-based sintered iron alloys and exhibiting mechanical properties which are equivalent to those of carbon steel for machine components without ever using Cu or Ni.

Note that a composition ratio of Mn to Si (i.e., Mn / Si) as described above is limited for the following reasons: the strength should be improved with the least possible addition; and the dimensional changes (or the extent of expansion) should be reduced.

<< Sintered iron alloy and sintered iron alloy object >>

• (1) Geeigneterweise kann diese gesinterte Eisenlegierung (nachstehend die jeweiligen „Gegenstände aus gesinterter Eisenlegierung”) beispielsweise aufweisen: Mn in einer Menge von 0,1 bis 2,1%; Si in einer Menge von 0,05 bis 0,6%; C in einer Menge von 0,1 bis 0,9% und zu übrigen Teilen Fe und unvermeidbare Verunreinigungen und/oder ein modifizierendes Element; bezogen auf insgesamt 100% dieser Legierung
• (2) Außerdem kann die gesinterte Eisenlegierung vorzugsweise ein Legierungselement aufweisen, das unter anderem seine mechanischen Eigenschaften verbessert. Ein solches Legierungselement wird von Cr oder Mo dargestellt. Wenn die Menge an Cr oder Mo zunimmt, ist eine starke Zunahme der Festigkeit zu erwarten, ohne dass irgendeine besondere Wärmebehandlung durchgeführt werden muss. Da unter anderem die Härtbarkeit verbessert wird, wird es natürlich auch möglich, die Festigkeit, die Zähigkeit, die Duktilität und so weiter in höherem Maße zu harmonisieren.

By means of the manufacturing method described above, a sintered iron alloy and various articles including the sintered iron alloy (or ferritic iron alloy articles) can be obtained, although they are not the subject matter of the claims.

• (1) Conveniently, this sintered iron alloy (hereinafter the respective "sintered ferrous alloy articles") may include, for example: Mn in an amount of 0.1 to 2.1%; Si in an amount of 0.05 to 0.6%; C in an amount of 0.1 to 0.9% and in other parts Fe and unavoidable impurities and / or a modifying element; based on a total of 100% of this alloy
• (2) In addition, the sintered iron alloy may preferably have an alloying element which, inter alia, improves its mechanical properties. Such an alloying element is represented by Cr or Mo. As the amount of Cr or Mo increases, a large increase in strength is expected without any special heat treatment being required. Of course, since the hardenability is improved, it also becomes possible to harmonize the strength, the toughness, the ductility and so on to a greater extent.

As an example, the sintered iron alloy may suitably comprise:
Mn in an amount of 0.1 to 1.4%;
Si in an amount of 0.05 to 0.4%;
C in an amount of 0.1 to 0.9%;
Cr in an amount of 0.1 to 5% and / or Mo in an amount of 0.1 to 2%; and
to remaining parts Fe and unavoidable impurities and / or a modifying element;
based on a total of 100% of this alloy.

Here, Mn is an element that is particularly effective for improving the strength of sintered iron alloys. If too little Mn is present, its beneficial effect is impaired. Depending on However, in the case of the type of alloying elements contained in the raw material powder, a sintered iron alloy having sufficient strength can be obtained even if Mn is present in trace amounts. On the other hand, if too much Mn is present, the elongation of the resulting sintered iron alloy decreases, so that the ductility becomes worse, and then dimensional changes also increase, so that the dimensional stability is impaired. Thus, with respect to a total of 100% sintered iron alloy, although the upper and lower limit values of Mn are arbitrarily selectable within the above numerical range, it is particularly preferable that numerical values are selected at will from the group consisting of 0.1%, 0.3%, 1.2%, 1.5%, 1.8% and 2.1%, which can form upper and lower limits.

In particular, although Si contributes to the improvement of the strength of a sintered iron alloy, it contributes greatly to the dimensional stability of sintered iron alloys. This effect is particularly pronounced in a case where Si and Mn coexist. While Mn acts to increase the size of a sintered iron alloy, Si acts to reduce the size of a sintered iron alloy. It is believed that both elements, which are present side by side, compensate each other for these effects and thus ensure the dimensional stability of a sintered iron alloy. Too little Si is not preferred because it affects dimensional stability; Too much Si is not preferred because it increases the amount of dimensional shrinkage. Thus, with respect to a total of 100% sintered iron alloy, although the upper and lower limit values of Si are arbitrary within the above-mentioned numerical range, it is particularly preferable that numerical values are selected at will from the group consisting of 0.05%. , 0.1%, 0.4%, 0.5% and 0.6%, which form upper and lower limits.

C is one of the important reinforcing elements in a sintered iron alloy. It goes without saying that C diffuses during sintering, so that the sintered iron alloy undergoes solid solution hardening; and by adding C in an appropriate amount, heat treatments such as hardening and tempering of sintered iron alloys are also possible; thereby, the mechanical properties of sintered iron alloys can be improved to a much greater extent. If too little C is present, its beneficial effect is greatly impaired, if too much C is present, the resulting ductility decreases. Thus, with respect to a total of 100% sintered iron alloy, although the upper and lower limit values of C within the above-mentioned numerical range may be arbitrarily selected, it is particularly preferable that numerical values which are arbitrarily selected from the group consisting of 0.1 %, 0.2%, 0.3%, 0.8% and 0.9%, which can form upper and lower limits.

• (3) Das „modifizierende Element”, das in der vorliegenden Beschreibung erwähnt wird, ist ein Element, bei dem es sich nicht um Fe, Mn, Si oder C (zusätzlich dazu Cr und/oder Mo) handelt, und ist ein Element, das wirksam ist, um die Eigenschaften einer gesinterten Eisenlegierung zu verbessern. Obwohl die Arten der Eigenschaften, die verbessert werden sollen, nicht beschränkt sind, sind die folgenden möglich: Festigkeit, Zähigkeit, Duktilität, Maßhaltigkeit, Bearbeitbarkeit usw. In einem spezifischen Beispiel für das modifizierende Element sind 0,1 bis 0,3 Massenprozent V usw. möglich. Darüber hinaus ist es sogar empfehlenswert, eine modifizierende Verbindung, wie MnS, für die Einführung eines modifizierenden Elements zu verwenden. In diesem Fall ist es beispielsweise bevorzugt, eine MnS-Menge auf 0,1 bis 0,5 Massenprozent einzustellen.

Further, in the case of the present invention, it may be desired to make high-strength sintered iron alloys stronger with a smaller amount of C as compared with conventional carbon steel. Although the reason is not clear, it is believed that Mn and Si are strongly involved. More specifically, it is considered that the yield strength of C is improved by the addition of Mn and Si, and the hardenability is also further improved. In any case, a high toughness can be secured while striving to strengthen sintered iron alloys because their strength can be increased with less carbon than heretofore. In other words, there can be obtained a sintered iron alloy whose strength and toughness, which are generally considered as opposing properties, are compatible with each other.

• (3) The "modifying element" mentioned in the present specification is an element other than Fe, Mn, Si or C (in addition to Cr and / or Mo), and is an element which is effective to improve the properties of a sintered iron alloy. Although the kinds of the properties to be improved are not limited, the following are possible: strength, toughness, ductility, dimensional stability, workability, etc. In a specific example of the modifying element, 0.1 to 0.3 mass% V, etc possible. In addition, it is even advisable to use a modifying compound, such as MnS, for the introduction of a modifying element. In this case, it is preferable, for example, to adjust an amount of MnS to 0.1 to 0.5 mass%.

The respective elements can be combined with each other as desired. The proportions of these modifying elements are not limited to the specified example ranges. In addition, they are usually present in trace amounts.

• (4) Für die „gesinterte Eisenlegierung” oder den „Gegenstand aus einer gesinterten Eisenlegierung”, die bzw. der in der vorliegenden Erfindung genannt wird und die nicht Gegenstand der Ansprüche sind, ist die Form nicht beschränkt. Genauer ist es sogar zulässig, dass die gesinterte Eisenlegierung ein Werkstück sein kann, das beispielsweise eine massive Form, eine Stabform, eine Röhrenform oder eine Plattenform und dergleichen hat, oder es ist auch zulässig, dass es eine endgültige Form aufweisen kann oder sogar ein Bauteil sein kann, das dieser nahe kommt. In der Praxis jedoch werden gesinterte Werkstoffe üblicherweise unter anderem deshalb verwendet, weil die Herstellungskosten gesenkt werden sollen, und daher kann die Form einer gesinterten Eisenlegierung (oder eines Gegenstands) mittels (Nahe-)Nettoformgebung der Form eines fertigen Produkts angenähert werden.
• (5) Obwohl die Arten der Legierungselemente, die in der gesinterten Eisenlegierung enthalten sind, nicht besonders beschränkt sind, ist es bevorzugter, dass Cu oder Ni nicht enthalten sind als dass sie enthalten sind. Der Grund dafür ist, dass Cu-freie gesinterte Legierungen, die im Wesentlichen kein Cu enthalten, und Ni-freie gesinterte Legierungen, die überhaupt kein Ni enthalten, wegen der Verbesserung der Recycling-Fähigkeit bevorzugt sind.

The "unavoidable impurities" are impurities contained in a raw material powder, and are, for example, impurities which are inadvertently mixed during the respective steps; and are elements that, for example, for cost reasons or for technical reasons difficult to remove. In the case of a sintered iron alloy directed to the present invention, these are, for example, P, S, Al, Mg, Ca, etc. Note that the modifying element compositions and inevitable impurities are not particularly limited, of course.

• (4) For the "sintered ferrous alloy" or "sintered ferrous alloy article" mentioned in the present invention, which are not the subject matter of the claims, the shape is not limited. More specifically, it is even permissible that the sintered iron alloy may be a workpiece having, for example, a solid shape, a rod shape, a tube shape or a plate shape and the like, or it is also permissible that it may have a final shape or even a component that can come close to it. In practice, however, sintered materials are commonly used inter alia because manufacturing costs are to be lowered, and therefore, the shape of a sintered iron alloy (or article) can be approximated by (near) net molding to the shape of a finished product.
• (5) Although the kinds of alloying elements contained in the sintered iron alloy are not particularly limited, it is more preferable that Cu or Ni is not contained than they are contained. The reason for this is that Cu-free sintered alloys containing substantially no Cu and Ni-free sintered alloys containing no Ni at all are preferable because of the improvement in recycling ability.

However, the present invention does not exclude cases where Cu and Ni are contained in the sintered iron alloy. The cases where Cu or Ni in addition to the Mn or Si described above are contained in appropriate amounts are also within the scope of the present invention.

• (6) Solange nichts anderes angegeben ist, schließen die Bezeichnungen, das heißt „von ,x' bis ,y'”, die in der vorliegenden Erfindung genannt werden, den unteren Grenzwert ,x' und den oberen Grenzwert ,y' ein. Darüber hinaus können die oberen und unteren Grenzwerte, die in der vorliegenden Beschreibung genannt werden, beliebig kombiniert werden, und können daher einen Bereich wie „von ,a' bis ,b'” umfassen.

The "mechanical properties" and "dimensional stability" mentioned in the present invention depend, among others, on the composition of a raw material, the compression pressure, the sintering conditions (eg, temperature, duration, atmosphere, and the like) , Therefore, it is not always possible to unconditionally specify these "mechanical properties" and "dimensional accuracy". Roughly speaking, it is preferable that the tensile strength, one of the mechanical properties, in sintered iron alloy articles for universal applications is 550 MPa or more, 600 MPa or more, and further 650 MPa or more; and for high-sintered iron alloy articles, is 850 MPa or more, 900 MPa or more, 950 MPa or more. In addition, it is preferable that the dimensional accuracy before and after sintering is ± 0.5%, ± 0.3%, ± 0.1%, and further ± 0.05% based on the dimensional change before and after sintering , Also, in terms of elongation, it is preferable that the elongation is 0.5% or more, 1% or more, 1.5% or more, 2% or more, and further 3% or more.

• (6) Unless otherwise specified, the terms, that is, 'from' x 'to' y '' referred to in the present invention include the lower limit value, x 'and the upper limit value, y'. In addition, the upper and lower limit values mentioned in the present specification may be arbitrarily combined, and therefore may include a range such as "from, a 'to, b'".

BRIEF DESCRIPTION OF THE DRAWINGS

1 FIG. 12 is a diagram showing a structure of a tensile test specimen to be described later. FIG.

2 FIG. 15 is a graph showing relationships between amounts of reinforcing powder and dimensional changes for sintered iron alloys with respect to Experimental Example No. 1 described below.

3 FIG. 12 is a graph showing relations between amounts of reinforcing powder and hardness values for sintered iron alloys with respect to Experimental Example No. 1. FIG.

4 FIG. 12 is a graph showing relationships between amounts of reinforcing powder and tensile strength values for sintered iron alloys with respect to Experimental Example No. 1.

5 Fig. 14 is a graph showing relationships between amounts of reinforcing powder and elongation values for sintered iron alloys with respect to Experimental Example No. 1;

6 Fig. 12 is a graph indicating relationships between FeMS IV powder amounts and dimensional changes for sintered iron alloys with respect to Experimental Example 2 described below.

7 FIG. 12 is a graph showing relationships between FeMS IV powder amounts and hardness values for sintered iron alloys with respect to Experimental Example No. 2.

8th Fig. 10 is a graph showing relationships between FeMS IV powder amounts and tensile strength values for sintered iron alloys with respect to Experimental Example No. 2.

9 Fig. 10 is a graph showing relationships between FeMS IV powder amounts and elongation values for sintered iron alloys with respect to Experimental Example No. 2.

10 FIG. 10 is a graph showing relationships between FeMS IV powder amounts and dimensional changes for sintered iron alloys with respect to Experimental Example No. 3 described below.

11 FIG. 12 is a graph showing relationships between FeMS IV powder amounts and hardness values for sintered iron alloys with respect to Experimental Example No. 3.

12 10 is a graph showing relationships between FeMS IV powder amounts and tensile strength values for sintered iron alloys with respect to Experimental Example No. 3.

13 FIG. 12 is a graph showing relationships between FeMS IV powder amounts and elongation values for sintered iron alloys with respect to Experimental Example No. 3.

14 Fig. 12 is a graph showing relations between sintering temperatures and tensile strength values for sintered iron alloys with respect to Experimental Example No. 4 described below; and

15 FIG. 12 is a graph showing relationships between sintering temperatures and elongation values for sintered iron alloys with respect to Experimental Example No. 4. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be explained in more detail by giving some embodiments of the invention. Note that, in the following embodiments, contents explained in the present specification apply not only to an application to the method of producing sintered iron alloys according to the present invention, but also to the sintered iron alloy itself (which also includes articles of sintered iron alloys) Iron alloy) may be suitable, even if they are not the subject of the claims. More specifically, in addition to the above-described means, one or two or more other agents which can be arbitrarily selected from the below-described agents, the production method according to the present invention, and a sintered iron alloy obtained by this method can also be to be added. The means selected from those listed below may be added to any aspect of the invention and may also be imposed across categories or added as desired. For example, it is obvious that, among other things, an agent that is related to a composition of the sintered iron alloy may also be important for its production process. Moreover, an agent that is related at first glance to the "manufacturing process" may also become an agent related to a "sintered iron alloy" when considered as a product resulting from the process. Note that it depends on the objects, the required properties, and so on, whether one of the embodiments is considered the best one or not.

<< raw material powder >>

A raw material powder includes Fe system powder, one of the main components of the sintered iron alloy, and a reinforcing powder (eg, an Fe-Mn-Si-C powder) having Mn, Si, and C. Note that the Fe-Mn-Si-C powder is hereinafter referred to as "FeMS powder".

(1) Fe system powder

It is permissible that the Fe system powder is either a pure iron powder or an iron alloy powder, and it may even be a mixture of these powders. It is not critical which alloying elements are contained in the iron alloy powder. These alloying elements may be primarily C, Mn, Si, P, S and the like. Although Mn, Si and C are also added as reinforcing elements, they may be present in the Fe system powder each in a small amount. If the proportions of C, Mn, Si and so on, however, the resulting Fe system powder becomes so hard that the compactability decreases. Thus, in a case where the Fe system powder is an iron alloy powder, a following setting is allowed: C in an amount of 0.02 mass% or less; Mn in an amount of 0.2 mass% or less and Si in an amount of 0.1 mass% or less.

Other alloying elements that may be included in the Fe system powder are Mo, Cr, Ni, V, Co, Nb, W, and the like. Since these alloying elements improve the heat treatment suitability of a sintered iron alloy, they are effective elements for increasing the strength of the sintered iron alloy.

In particular, it is favorable that the raw material powder can be prepared so that Mo is 0.1 to 2 mass% and / or Cr is 0.1 to 5 mass%, based on 100 mass% of raw material powder (hereinafter, if necessary, simply "%"). Although the upper and lower limits for Cr may be selected at will within their range of numbers, it is particularly preferred that numerical values selected at will from the group consisting of 0.1%, 0.3%, 0, In addition, although the upper and lower limits of Mo can be arbitrarily selected within their range of numbers, it is particularly preferred that numerical values, which are selected at will from the group consisting of 0.1%, 0.5%, 0.6%, 0.8%, 1%, 1.5% and 2%, which can form upper and lower limits Note that these alloying elements are also used as amplifiers Although it is preferred that the Fe system powder be handled well and be homogeneous when contained therein, it can be added to powder powders separate from the Fe system powder.

(2) FeMS powder

A FeMS powder directed to the present invention comprises an Fe alloy or Fe compound which, based on a total of 100% FeMS powder, Mn in an amount of 58 to 70%, Si in an amount which gives an Mn / Si ratio of 3.3 to 4.6, contains C in an amount of 1.5 to 3%, and Fe in the remaining parts. By using this FeMS powder, the sintered iron alloy having good mechanical properties and good dimensional stability can be produced at a lower cost.

When the amounts of Mn, Si and C are too small, the resulting raw material for the FeMS powder (or the FeMS raw material) becomes a ductile alloy, and therefore it becomes difficult to pulverize it into a fine powder. Moreover, an addition amount of the FeMS powder in the raw material powder becomes large, and thus the cost of the sintered iron alloy increases. On the other hand, a FeMS powder or raw material with too much Mn, Si or C is not preferable because the procurement cost is higher. Note that when the pulverization suitability of this FeMS powder is addressed, the presence of C is particularly important.

Therefore, although the upper and lower limit values of Mn in the FeMS powder can be arbitrarily set within the above-mentioned numerical range, it is particularly preferable that numerical values arbitrarily selected from the group consisting of 58%, 60%, 65 %, 68% and 70%, which can form upper and lower limits, based on a total of 100% FeMS powder. Moreover, although the upper and lower limits of C in the FeMS powder can be arbitrarily selected within the above-mentioned numerical range, it is particularly preferable that the numerical values selected at will from the group consisting of 1.5%, 2%, 2.5% and 3%, which can form upper and lower limits. And although the upper and lower limits of Mn / Si in the FeMS powder can be arbitrarily selected within the above-mentioned numerical range, it is particularly preferable that numerical values arbitrarily selected from the group consisting of 3,3,3 , 6, 3, 8, 4, 4, 4, 4, 4, which may form upper and lower limits.

• (3) Obwohl das Verhältnis, in dem das FeMS-Pulver in das Rohmaterialpulver gemischt wird, abhängig von einer Zusammensetzung des FeMS-Pulvers oder einer gewünschten Eigenschaft der gesinterten Eisenlegierung (oder einer Zusammensetzung der gesinterten Eisenlegierung) verschieden sein kann, ist es zulässig, eine Menge von 0,05 bis 3% einzumischen, bezogen auf 100 Massenprozent Rohmaterialpulver.

In the FeMS powder, it is preferable that an amount of O contained therein is 1.5% or less, 1.2% or less, 1% or less, and further 0.8% or less. When the amount of O in the raw material powder increases, the reinforcing effect resulting from Mn and Si can not be sufficiently exhibited. Further, in a case where a powder compact whose density is so high that a green compact density ratio (or ρ / ρ ₀ ), that is, a ratio of a bulk density (ρ) of the powder compact relative to one theoretical density (ρ ₀ ) exceeds 96%, not preferred that O is present in its interior, this may become the cause of puffing (or bubbles) in the resulting sintered body.

• (3) Although the ratio in which the FeMS powder is mixed in the raw material powder may be different depending on a composition of the FeMS powder or a desired property of the sintered iron alloy (or a composition of the sintered iron alloy), it is permissible to Mix in an amount of 0.05 to 3%, based on 100 mass percent raw material powder.

• (4) Je kleiner der Teilchendurchmesser des FeMS-Pulvers ist, desto besser werden nicht nur das Grünlings-Dichteverhältnis und ein Sinterkörper-Dichteverhältnis (ρ'/ρ'₀), das heißt, ein Verhältnis eines Schüttgewichts (ρ') eines Sinterkörpers in Bezug auf dessen theoretische Dichte (ρ'₀), sondern desto besser werden auch die Maßhaltigkeit und verschiedene mechanische Eigenschaften usw. Die Gründe dafür scheinen die Folgenden zu sein: Es werden wahrscheinlich homogene gesinterte Eisenlegierungen erhalten, in denen Variationen der Zusammensetzung oder Segregationen seltener vorkommen; jedoch ist dieser Grund derzeit nicht endgültig bestätigt.

When a blending amount of the FeMS powder is too small, the properties of the resulting sintered iron alloy can not be improved, while a too large amount is not preferable because the dimensional accuracy or the elongation of the resulting sintered iron alloy may be deteriorated. Although the upper and lower limits for the amount of FeMS powder admixed may be arbitrarily chosen within this range of numbers, it is particularly preferred that numerical values selected at will from the group consisting of 0.05%, 0.1%, 0 , 2%, 0.3%, 2.1%, 2.5% and 3%, which may form upper and lower limits, based on a total of 100% by mass of raw material powder.

• (4) The smaller the particle diameter of the FeMS powder, the better not only the green compact density ratio and a sintered compact density ratio (ρ '/ ρ' ₀ ), that is, a ratio of a bulk density (ρ ') of a sintered body in FIG Regarding its theoretical density (ρ ' ₀ ), but also the dimensional stability and various mechanical properties, etc. become better. The reasons for this seem to be the following: Homogeneous sintered iron alloys are likely to be obtained in which variations in composition or segregations occur less frequently ; however, this reason is not finally confirmed at present.

Incidentally, it is difficult to produce a powder having a smaller particle diameter, or its production is more expensive. However, the FeMS powder of the present invention can be produced inexpensively since it can be relatively easily formed into a fine powder. For example, even if FeMS raw materials such as pulverized are used, this FeMS powder can be reformed into a powder whose particle diameter is approximately 45 μm or less (or -45 μm). This is a sufficient particle diameter, also in comparison with conventional reinforcing powders.

In practice, however, it is more preferable to limit a variation in particle diameter, and then to use a fine powder having a much finer grain to improve the properties of the sintered iron alloy or to stabilize the quality. Thus, it is recommended to use a FeMS powder which has been classified by sieving and the like. More specifically, for example, it is recommended to use a FeMS powder not only 45 μm or less, but 30 μm or less, 20 μm or less, 10 μm or less, 8 μm or less, and even 6 μm or less etc. was classified. Although the lower limit of the particle diameter of a FeMS powder is not necessarily critical, it is preferably 1 μm or more in view of handleability and production cost and further 3 μm or more.

• (5) Geeigneterweise kann das Rohmaterialpulver als ein weiteres Verstärkungspulver ein C-Systempulver zum FeMS-Pulver enthalten. Obwohl C in der gesinterten Eisenlegierung auch von einem Fe-Systempulver oder einem FeMS-Pulver kommen kann, ist es bevorzugt, wenn ein C-Systempulver durch separates oder unabhängiges Zumischen in das Rohmaterialpulver vorhanden ist, um das Härten der Fe-Systempulver zu vermeiden, oder um die Steuerung der C-Menge in der Zusammensetzung zu erleichtern. Als ein solches C-Systempulver eignet sich ein Graphitpulver (oder „Gr”-Pulver), in dem C praktisch 100% ausmacht, obwohl es auch möglich ist, Fe-C-Legierungspulver (oder Zementitpulver), verschiedene Carbidpulver und dergleichen zu verwenden.

Note that in addition to the indexing by the above classification, among others, an average particle diameter and a grain size distribution can be used as an index for evaluating the particle size of a FeMS powder. However, in practice, it is convenient, and from an industrial point of view, it is preferable to describe the particle size in a FeMS powder with an upper limit of the particles. Therefore, in the present specification, the particle size in a FeMS powder is determined by means of an upper limit of the particles. For example, "a particle diameter of 45 μm or less" indicates that a maximum particle diameter is 45 μm or less, which may be represented as "-45 μm".

• (5) Suitably, the raw material powder may contain as a further reinforcing powder a C-system powder to the FeMS powder. Although C in the sintered iron alloy may also come from an Fe system powder or a FeMS powder, it is preferred that a C system powder be present in the raw material powder by separate or independent admixing to avoid hardening of the Fe system powders. or to facilitate the control of the amount of C in the composition. As such a C system powder, a graphite powder (or "Gr" powder) in which C is almost 100% is suitable although it is also possible to use Fe-C alloy powder (or cementite powder), various carbide powders and the like.

In any case, the raw material powder can be suitably prepared so that, in the end, Mn is 0.5 to 1.5%, Si is 0.15 to 0.6%, and C is 0.2 to 0.9%, based on a total of 100%. iron alloy.

<< manufacturing steps >>

Since the method for producing a sintered iron alloy according to the present invention primarily comprises a compacting step and a sintering step, these steps are explained in this order.

<Compaction step>

• (1) The compacting step is a step in which the above-described raw material powder in which an Fe system powder is mixed with a reinforcing powder is compressed under pressure, whereby the raw material powder is formed into a powder compact. A compression pressure on this occasion, a density of the resulting powder compact (or a green compact density ratio), a shape of the resulting powder compact and the like are not limited in any way.

• (2) Wie im oben genannten Patentdokument Nr. 3 offenbart, haben die Erfinder ein Verdichtungsverfahren für einen Pulverpresskörper geschaffen, wobei dieses Verdichtungsverfahren eine Verdichtung unter ultrahohem Druck, der allgemeine Verdichtungsdrücke übertrifft, möglich macht. Gemäß diesem Verdichtungsverfahren ist eine Pulververdichtung bei ultrahohen Drücken wie 750 MPa oder mehr, 800 MPa oder mehr, 900 MPa oder mehr, 1000 MPa oder mehr, 1200 MPa oder mehr, 1500 MPa oder mehr und ferner etwa 2000 MPa möglich. Die Dichte eines Pulverpresskörpers, die dadurch erhalten werden kann, kann 96% oder mehr, 97% oder mehr, 98% oder mehr und ferner bis zu 99% erreichen. Dieses Verdichtungsverfahren (im Folgenden gegebenenfalls als das „Formwandschmierung/Warmdruck-Verdichtungsverfahren” bezeichnet) kann wie folgt zusammengefasst werden.

However, it is permissible to set the compression pressure and the green density ratio at least so far that the resultant powder compact does not easily collapse. For example, the compression pressure is preferably 350 MPa or more, 400 MPa or more, 500 MPa or more, and further 550 MPa or more. As for the green density ratio, it may preferably be 80% or more, 85% or more, and further 90% or more. The higher the compression pressure and the green density ratio, the more likely it is that the sintered iron alloy has higher strength can be obtained; however, it is permissible to select an optimal compaction pressure or green compact density ratio according to the applications and specifications for the sintered ferrous alloy. Moreover, it is also permissible that the compacting step is carried out by either cold compacting or hot compacting, and it is also permissible to add an internal lubricant to the raw material powder. In case of adding internal lubricant, the raw material powder containing the internal lubricant is regarded as raw material powder.

• (2) As disclosed in the above-mentioned Patent Document No. 3, the inventors have provided a compacting method for a powder compact, which compacting method makes possible ultra-high-pressure compression exceeding general compression pressures. According to this compacting method, powder compression at ultra-high pressures such as 750 MPa or more, 800 MPa or more, 900 MPa or more, 1000 MPa or more, 1200 MPa or more, 1500 MPa or more and further about 2000 MPa is possible. The density of a powder compact which can be obtained thereby can reach 96% or more, 97% or more, 98% or more, and further up to 99%. This densification process (hereinafter optionally referred to as the "mold wall lubrication / hot pressure densification process") may be summarized as follows.

The mold wall lubrication / hot pressure compacting method (ie, a compacting step) includes a filling step in which the raw material powder is filled into a mold on the inner surface of which a lubricant of a higher fatty acid system has been applied, and a hot pressure compacting step in which of heat and pressure, a metal soap film is formed on the surface of the raw material powder put into this mold, which is in contact with the inner surface of the mold.

According to this compression method, even if the compression pressure is increased substantially, the disadvantages associated with general compression methods are not exhibited. Specifically, the seizure between the raw material powder and the inner surface of the mold, the excessively increasing ejection force, the shortening of the life of the mold and the like can be limited. In the following, the filling step and the hot pressure compacting step will be explained in more detail.

(a) filling step

Before the raw material powder is filled into a mold (i.e., a cavity), a lubricant of a higher fatty acid system is applied to the inner surface of a mold (i.e., an application step). The higher fatty acid system lubricant used herein may be, in addition to a higher fatty acid per se, also higher fatty acid metallic salts. As for the metallic salts of higher fatty acids, these may include lithium salts, calcium salts or zinc salts. In particular, lithium stearate, calcium stearate, zinc stearate, etc. are preferable. In addition to these, barium stearate, lithium palmitate, lithium oleate, calcium palmitate, calcium oleate, etc. may also be used.

The applying step may be performed, for example, by spraying a lubricant of a higher fatty acid system dispersed in, for example, water, an aqueous solution or an alcoholic solution into a heated form. When a lubricant of a higher fatty acid system is dispersed in water, etc., the lubricant of the higher fatty acid system is likely to be uniformly sprayed on the inner surface of a mold. When sprayed into a heated mold, the contained water, etc. evaporates rapidly, and thus the lubricant of the higher fatty acid system adheres evenly to the inner surface of the mold. As for the heating temperature of the mold, it is preferable to set it with respect to the temperature in the hot pressure compacting step described below, but preliminary heating to 100 ° C or more is sufficient, for example. In order to form a uniform coating of a lubricant from a higher fatty acid system, however, it is preferred in practice to set the heating temperature below the melting point of the lubricant from the higher fatty acid system. For example, in a case where lithium stearate is used as a lubricant of a higher fatty acid system, the heating temperature can be set below 220 ° C.

Note that in dispersing a lubricant of a higher fatty acid system in water and the like, it is preferable to use the lubricant of the higher fatty acid system in a proportion of 0.1 to 5 mass%, and more preferably 0.5 to 2 mass percent, based on a total of 100 mass percent of the aqueous solution, as a uniform lubricant coating is formed on the inner surface of a mold.

In dispersing a lubricant from a higher fatty acid system in water and the like, it may also be desirable to evenly distribute the lubricant from the higher fatty acid system when a surfactant is added in advance to the water. As for this surfactant, for example, lubricants of an alkylphenol system, polyoxyethylene nonylphenyl ether (EO) 6, polyoxyethylene nonylphenol ether (EO) 10, anionic / nonionic type lubricants, emulsifier T-80 of a boric acid ester system and the like can be used. You can also use two or more of them in combination. For example, when lithium stearate is used as the lubricant of a higher fatty acid system, preferably three of the surfactants, namely, polyoxyethylene nonylphenyl ether (EO) 6, polyoxyethylene nonylphenol ether (EO) 10, and emulsulum T80 from the boric acid ester system are used simultaneously. The reason for this is that in this case, the dispersibility of lithium stearate in water and the like is even better activated as compared with a case where only one of these surfactants is added.

In order to obtain an aqueous solution of a lubricant from a higher fatty acid system whose viscosity is suitable for spraying, the proportion of a surfactant is preferably from 1.5 to 15% by volume, based on a total of 100% by volume of the aqueous solution, adjusted.

In addition, a small amount of antifoaming agent (for example, an antifoaming agent of a silicon system and the like) may be added. The reason for this is that, when bubbling in an aqueous solution is severe, a uniform coating of a lubricant of a higher fatty acid system on the inner surface of a mold is less likely to be formed as it is sprayed. It is recommended that a proportion in which an antifoaming agent is added is, for example, about 0.1 to 1% by volume, based on a total of 100% by volume of the aqueous solution.

Suitably, the particles of a higher fatty acid system lubricant dispersed in water and the like may have a maximum particle diameter of less than 30 microns. The reason for this is that when the maximum particle diameter is 30 μm or more, the particles of a lubricant from a higher fatty acid system precipitate more easily in an aqueous solution, so that it becomes difficult to remove the lubricant from the higher fatty acid system evenly applied to the inner surface of a mold.

The application of an aqueous solution in which a lubricant of a higher fatty acid system is dispersed can be carried out, for example, by using spray guns, electrostatic spray guns, and the like. Note that the inventors have found, from investigations of the relationship between the application amount of higher fatty acid lubricant and the ejection force for powder compact, that a lubricant of a higher fatty acid system is preferably in a thickness of about 0.5 should adhere to 1, 5 microns on the inner surface of a mold.

(b) Warm pressure compacting step

It is believed that when a raw material powder filled in a mold has a higher fatty acid lubricant applied to the inner surface thereof under heat and pressure, a metal soap layer is formed on the surface of the raw material powder (or the powder compact) ), which is in contact with the inner surface of the mold, is formed, so that ultra-high pressure industrial-level compaction is possible because of the presence of this metal soap film. This metal soap layer strongly bonds to the surface of the powder compact and exhibits a much better lubricating effect than the lubricant from the higher fatty acid system which has adhered to the inner surface of the mold. As a result, the frictional force between the contact surface of the inner surface of the mold and the contact surface of the outer surface of the powder compact is greatly reduced, and seizure and the like are not caused despite high pressure compression. In addition, the resulting powder compact can be retrieved from the mold with a very low ejection force, and thus the excessively shortening of the life is eliminated.

The metal soap layer is, for example, an iron salt layer of a higher fatty acid formed by a mechanochemical reaction which has passed between a lubricant of a higher fatty acid system and Fe in a raw material powder under heat and high pressure. A representative example of this is an iron stearate layer formed when lithium stearate or zinc stearate, that is, a lubricant of a higher fatty acid system, reacts with Fe.

"Heat" referred to in the present step may be a degree of heating that facilitates the reaction between a raw material powder and a higher fatty acid system lubricant. Roughly speaking, it is permissible to set the compression temperature to 100 ° C or more. However, from the viewpoint that the degenerative change of a lubricant of a higher fatty acid system should be prevented, the compression temperature should be set to 200 ° C or less. Even more suitable is a densification temperature which is in a range of 120 to 180 ° C.

"Pressure" referred to in the present step may be suitably determined in consideration of the specifications of the sintered iron alloy in a region where a metal soap layer is formed. From the viewpoint of mold life and productivity, the upper limit of the compression pressure is preferably set to 2000 MPa. When the compaction pressure reaches about 1500, the density of the powder compact obtained also approaches the absolute density (reaches 98 to 99% to a green density ratio), and even when a pressure of 2,000 MPa or more is applied, no even higher densification is to be expected ,

Note that using this hot pressure compression method using a wall lubricant, no internal lubricant needs to be used, and therefore, a much higher density powder compact can be obtained. Moreover, when this powder compact is sintered, it does not cause the inside of a furnace to be contaminated with the decay, emission, etc. of an internal lubricant. It should be understood, however, that in the present invention, the use of an internal lubricant is nevertheless not excluded.

<Sintering>

The sintering step is a step in which a powder compact obtained in the compacting step is sintered by heating in an oxidation-resistant atmosphere. The sintering temperature and the sintering time are suitably adjusted in consideration of, among other things, the desired properties and the productivity of the sintered iron alloy. The higher the sintering temperature, the shorter the time, high-strength sintered iron alloy can be obtained. In practice, however, liquid phases or shrinkage increases when the sintering temperature is too high, which is undesirable. If the sintering temperature is too low, the diffusion of the alloying elements is insufficient, which is undesirable. In addition, the sintering takes longer, and thus the productivity of the sintered iron alloys decreases. As a result, the sintering temperature is preferably 900 ° C or more, and more preferably 950 ° C or more; and it is preferably 1400 ° C or less, and more preferably 1350 ° C or less.

More specifically, to obtain a sintered ferrous alloy having higher strength, the sintering temperature can be set to 1000 ° C or more, 1100 ° C or more, and especially 1150 ° C or more. If a FeMS powder having a smaller grain size (more specifically, a fine powder, the however, the higher strength sintered iron alloy can be obtained at a sintering temperature of 1025 ° C or more, and more preferably 1075 ° C or more. When using a powder of a Fe system having a smaller grain size (more specifically, a fine powder classified to 70 μm or less, and more preferably to 65 μm or less) together with the FeMS powder having the smaller grain size, the sintered Iron alloy with the higher strength at a sintering temperature of 950 ° C or more, and especially of 1050 ° C or more can be obtained.

• (2) Als Sinterungsatmosphäre ist eine Atmosphäre zulässig, die eine Oxidation verhindert bzw. die oxidationsfeindlich ist. Mn und Si, die Legierungselemente, weisen eine äußerst starke Affinität zu O auf, und daher können diese Elemente sehr leicht oxidiert werden. Da ein FeMS-Pulver wie das der vorliegenden Erfindung eine geringere freie Energie für eine Oxidbildung braucht als die einfachen Stoffe Mn und Si, besteht die Sorge, dass es in einem Wärmeofen sogar mit wenig vorhandenem O reagiert, um die Oxide von Mn und Si im gesinterten Körper zu bilden. Die Einlagerung solcher Oxide ist ungünstig, da sie die mechanischen Eigenschaften der gesinterten Eisenlegierung verschlechtern. Somit ist die Sinterungsatmosphäre vorzugsweise eine Atmosphäre, die eine Oxidation verhindert, wie eine Vakuumatmosphäre, eine Inertgasatmosphäre oder eine Stickstoffgasatmosphäre.

The sintering time can be set to 0.1 to 3 hours, and more preferably to 0.1 to 2 hours, taking into consideration, for example, the sintering temperature, specifications, productivity and cost of the sintered iron alloy.

• (2) As the sintering atmosphere, an atmosphere is permissible which prevents oxidation or which is hostile to oxidation. Mn and Si, the alloying elements, have an extremely strong affinity for O, and therefore these elements can be easily oxidized. Since a FeMS powder like that of the present invention requires less free energy for oxide formation than the simple materials Mn and Si, there is a concern that it will react even in a heating furnace with little O present to produce the oxides of Mn and Si in the to form sintered body. The incorporation of such oxides is unfavorable because they degrade the mechanical properties of the sintered iron alloy. Thus, the sintering atmosphere is preferably an atmosphere that prevents oxidation, such as a vacuum atmosphere, an inert gas atmosphere, or a nitrogen gas atmosphere.

If remaining oxygen (or an oxygen partial pressure) is important in such an atmosphere, a reducing atmosphere in which a hydrogen gas (high-purity hydrogen gas purified to a low dew point (for example, -30 ° C or less) may be used) in an amount of a few vol% (for example, 2 to 10 vol%, based on a total of 100 vol%) mixed with a nitrogen gas.

• (3) Es ist sogar empfehlenswert, eine Sinterungshärtung durchzuführen, um eine Härtung anhand einer Kühlung durchzuführen, die auf eine Erwärmung im Sinterungsschritt folgt. Im Sinterungsschritt wird ein Pulverpresskörper üblicherweise auf eine hohe Sinterungstemperatur (beispielsweise von 1050 bis 1350°C, und insbesondere von 1100 bis 1300°C) erwärmt, die höher ist als die A1-Übergangstemperatur (etwa 730°C oder mehr) (d. h. ein Erwärmungsschritt). Dann wird eine Sinterungshärtung durch Abschrecken eines Sinterkörpers, der hierbei erwärmt wurde, von der Sinterungstemperatur auf ungefähr Raumtemperatur (oder bis auf oder unter den Ms-Punkt) durchgeführt (d. h. ein Abkühlungsschritt). Vorzugsweise liegt eine Abkühlungsgeschwindigkeit bzw. Kühlrate in diesem Fall bei 0,5 bis 3°C/Sekunde. Die oberen und unteren Grenzwerte dieser Geschwindigkeit können nach Belieben innerhalb dieses Zahlenbereichs ausgewählt werden, besonders bevorzugt ist es, wenn Zahlenwerte, die nach Belieben aus der Gruppe ausgewählt sind, die aus 0,5°C/Sekunde, 0,7°C/Sekunde, 2°C/Sekunde und 2,5°C/Sekunde besteht, die oberen und unteren Grenzwerte bilden können. Eine höhere Abkühlungsgeschwindigkeit ist bevorzugt, da das Härten umso zuverlässiger abläuft, je schneller es vor sich geht; jedoch kann gemäß dem Herstellungsverfahren der vorliegenden Erfindung ein ausreichendes Härten auch dann durchgeführt werden, wenn die Abkühlungsgeschwindigkeit niedriger ist. Infolgedessen ist gemäß der vorliegenden Erfindung eine Zwangskühlungsvorrichtung, die ein Abschrecken durchführt, nicht unbedingt notwendig, und daher können auch die Anlagekosten gesenkt werden. Man beachte, dass diese Wirkung besonders ausgeprägt ist, wenn die gesinterte Eisenlegierung außer C, Mn und Si auch Cr und Mo enthält.

In a case where the use of a hydrogen gas is unfavorable, it is advisable to carry out the sintering step according to the present invention in an inert gas atmosphere having an ultra-low partial pressure of oxygen, wherein the partial pressure of oxygen is 10 ^-19 or lower (CO concentration of 100 ppm or less). In such an inert gas atmosphere having an ultra-low oxygen partial pressure, even if, for example, a FeMS powder reacts with O adhering to a raw material powder to form oxide compounds and the like, these oxide compounds are further decomposed. As a result, a sintered iron alloy having a healthy structure in which no oxides and the like are incorporated can be obtained. Note that a continuous sintering furnace realizing an inert gas atmosphere under ultra-low oxygen partial pressure (or N ₂ gas) is commercially available (OXYNON furnace, manufactured by KANTO YAKIN KOGYO Co., Ltd.).

• (3) It is even recommended to perform a sintering hardening to perform hardening by means of cooling following heating in the sintering step. In the sintering step, a powder compact is usually heated to a high sintering temperature (for example, from 1050 to 1350 ° C, and more preferably from 1100 to 1300 ° C) higher than the A1 transition temperature (about 730 ° C or more) (ie, a heating step ). Then, sintering hardening is performed by quenching a sintered body, which has been heated thereby, from the sintering temperature to about room temperature (or to or below the Ms point) (ie, a cooling step). Preferably, a cooling rate or cooling rate in this case is 0.5 to 3 ° C / second. The upper and lower limits of this speed may be selected at will within this range of numbers, and it is particularly preferred if numerical values selected at will from the group consisting of 0.5 ° C / second, 0.7 ° C / second , 2 ° C / second and 2.5 ° C / second, which can form upper and lower limits. A higher cooling rate is preferred since curing is all the more reliable the faster it is going; however, according to the production method of the present invention, sufficient curing can be performed even if the cooling rate is lower. As a result, according to the present invention, a forced cooling device which performs quenching is not absolutely necessary, and hence the equipment cost can be lowered. Note that this effect is particularly pronounced when the sintered iron alloy contains Cr and Mo besides C, Mn and Si.

<< Sintered iron alloy >>

• (1) In the sintered iron alloy according to the present invention, it is not critical whether the density is high or low. That is, as with the conventional sintered iron alloys, it may also be a sintered low-density iron alloy prepared by sintering a powder compact compacted with a general-purpose compaction pressure, or it may also be a high-density sintered iron alloy which is prepared by sintering a high density sintered powder compact subjected to high pressure densification using the above-described hot pressure compacting method using a mold wall lubricant. In any case, improvement of mechanical properties and dimensional stability of the sintered iron alloy using a FeMS powder can be desired.

• (2) Wie im oben angegebenen Patentdokument Nr. 7 beschrieben, haben die Erfinder bereits entdeckt, dass es im Fall eines Pulverpresskörpers mit ultrahoher Dichte (dessen Grünlings-Dichteverhältnis beispielsweise 96% oder mehr beträgt) zu einer Blasenbildung (oder zu Blasen) kommt. Insbesondere kommt es in einem Fall, wo in einem Rohmaterialpulver C, beispielsweise „Gr”-Pulver, enthalten ist, leicht zu einer solchen Blasenbildung. Wenn es zu einer solchen Blasenbildung kommt, ist es jedoch nur natürlich, dass die Maßhaltigkeit zwischen vor und nach dem Sintern stark nachlässt.

In particular, a green density ratio or a sintered body density ratio which becomes 92% or more, 95% or more, 96% or more and especially 97% or more is preferable because the resulting strength is high strength, that of sintered bodies , which can be obtained by means of a double pressing and a double sintering (or 2P2S), which equals those of forged sintered bodies and further those of die-cast materials.

• (2) As described in the above-mentioned Patent Document No. 7, the inventors have already discovered that in the case of an ultrahigh-density powder compact (whose green density ratio is, for example, 96% or more) blistering (or blistering) occurs. In particular, in a case where C is contained in a raw material powder, for example, "Gr" powder, such blistering tends to occur. However, when such blistering occurs, it is only natural that the dimensional stability between before and after sintering decreases greatly.

Such blistering is caused by various gases such as H ₂ O, CO and CO ₂ , which are generated when moisture or oxides and the like adhering to the particle surface of a raw material powder are reduced or decomposed during heating in the sintering step. That is, it is believed that these gases are enclosed in sealed cavities within the resulting sintered body in which the particles of the respective constituents are in a state of being closely adhered to each other, and that these gases then become heated during the sintering step expand, so that it comes to blistering in the resulting sintered body. Of course, if a powder compact whose density is at a conventional level is used, blistering as described above does not easily occur because the generated gases can escape to the outside through voids formed between the particles of raw material powder.

In practice, however, in a case where a FeMS powder is used as the reinforcing powder as in the present invention, Mn and Si (especially Si) in the FeMS powder each act as oxygen scavengers and thus prevent blistering in the resulting sintered body. The reason for this is that Mn and Si show a stronger affinity for O than for C, so they need less free energy for oxide formation.

• (3) Eine Metallstruktur der gesinterten Eisenlegierung gemäß der vorliegenden Erfindung ist nicht beschränkt. Es ist empfehlenswert, sie durch Steuern einer Abkühlgeschwindigkeit nach dem Sinterungsschritt oder durch Ausführen von Wärmebehandlungen, die unabhängig sind vom Sinterungsschritt, gemäß benötigten Spezifikationen für die gesinterte Eisenlegierung in Martensit-Strukturen, Bainit-Strukturen, Perlit-Strukturen, Ferrit-Strukturen und deren Mischstrukturen umzuwandeln. Abhängig von Spezifikationen und Zusammensetzungen der gesinterten Eisenlegierung ist es auch zulässig, die gesinterte Eisenlegierung ferner Wärmebehandlungsschritten, wie Ausheilen, Normalglühen, Wärmealtern, Umschmelzen (z. B. Härten und Tempern) zu unterziehen.
• (4) Eine Form der gesinterten Eisenlegierung gemäß der vorliegenden Erfindung und ihr Verwendungszweck sind nicht beschränkt. Als Beispiele aus dem Automobilbereich für die Gegenstände aus gesinterter Eisenlegierung, welche die gesinterte Eisenlegierung gemäß der vorliegenden Erfindung aufweisen, können die folgenden genannt werden: verschiedene Riemenscheiben, Synchronisationsnaben für Getriebe, Pleuel für Verbrennungsmotoren, Nabenhülsen, Kettenräder, Zahnkränze, Parksperrenräder, Ritzel usw. Außerdem gibt es noch die folgenden: Sonnenräder, Antriebszahnräder, Untersetzungszahnräder usw.

Thus, by using a FeMS powder as in the present invention, a sintered iron alloy having a good dimensional stability can be obtained even in a case where it has been densely densified.

• (3) A metal structure of the sintered iron alloy according to the present invention is not limited. It is advisable to control them by controlling a cooling rate after the sintering step or by performing heat treatments that are independent of the sintering step according to required sintered iron alloy specifications in martensite structures, bainite structures, pearlitic structures, ferrite structures, and their composite structures convert. Depending on the specifications and compositions of the sintered iron alloy, it is also permissible to further subject the sintered iron alloy to heat treatment steps such as annealing, normalizing, heat aging, remelting (eg, hardening and tempering).
• (4) A form of the sintered iron alloy according to the present invention and its use are not limited. As examples of the automotive field for the sintered iron alloy articles having the sintered iron alloy according to the present invention, there may be mentioned various pulleys, transmission gear hubs, internal combustion engine connecting rods, hub shells, sprockets, sprockets, parking lock gears, pinions, etc. In addition, there are the following: sun gears, drive gears, reduction gears, etc.

EXAMPLES

In the following, the present invention will be explained in more detail by giving specific examples.

<< Production of Reinforcing Powder >>

As the reinforcing powder to be mixed in Fe system powder, the following were prepared: two kinds of FeMS powder having different compositions shown in Table 1; and a Cu powder ("DistaloyACu" (or Fe-10% Cu) having particle diameters of 20 to 180 μm, a product of HOEGANAES AB Corp.).

First, a FeMS II powder (or a Fe-Mn-Si powder) of FeMS powder was prepared by pulverizing a green body (or a solidified metal body) which had been die cast in an Ar gas atmosphere and whose compound composition was Fe-50Mn -30-Si (units: mass%) was prepared in air. Then, a FeMS IV powder (or F-Mn-Si-C powder), the other FeMS powder, was prepared by pulverizing silicon manganese (e.g., JIS No. 3) manufactured by NIHON DENKO Corp. in air ,

• (2) Wie aus Tabelle 1 hervorgeht, war eine Mn/Si-Zusammensetzung im FeMS II-Pulver 1,5, während eine Mn/Si-Zusammensetzung im FeMS IV-Pulver 4 wurde.

Each of the powders was pulverized by pulverizing for 30 minutes by means of a vibration mill manufactured by CHUO KAKOKI Co., Ltd. Those whose state corresponds to that after their pulverization processing are referred to as "as pulverized" in the present specification and in tables and diagrams attached to the present specification. These pulverized powders were further sieved, thereby adequately dispersed in FeMS. Powders were classified, which had different particle sizes and whose particle diameter, for example, less than 5 microns (or - 5 microns) was. For comparison, as shown in Table 2 described below, particle diameter "as pulverized" was smaller than 45 μm (or -45 μm).

• (2) As shown in Table 1, an Mn / Si composition in the FeMS II powder was 1.5 while an Mn / Si composition in the FeMS IV powder became 4.

In addition, measurement results of the grain size distributions of the "as-pulverized" FeMS II and FeMS IV powders subjected to the same pulverization treatment are shown in Table 2. In the measurement, these grain size distributions were measured by a laser diffraction scattering method using "MT3000II", a micro-track grain size distribution measuring apparatus, manufactured by NIKKI-SO Co., Ltd. In Table 2, the numerical values corresponding to D10, D50 and D90 are maximum values of particle diameters exhibited by 10%, 50% and 90% of the measured powder particles. Considering the FeMS IV powder, the grain size at D90 was 11.5 (μm), that is, 90% of all particles had particle diameters of 11.5 μm or less. As a result of comparing the D90 value of the FeMS II powder with that of the FeMS IV powder, the grain size of the FeMS IV powder as a whole was much smaller than the grain size of the FeMS II powder although they had been subjected to the same pulverization treatment and thus it is clear that the FeMS IV powder was better pulverized (or more easily collapsed) than the FeMS II powder.

Based on a total of 100 mass% FeMS powder, an Fe amount in the FeMS II powder was about 16.5%, while a FeMS amount in the FeMS IV powder was about 22.7%. Therefore, the Fe content was higher in the FeMS IV powder than in the FeMS II powder. Nevertheless, it appears that the FeMS IV powder was better pulverized than the FeMS II powder, because C was present in the FeMS IV powder in contrast to the FeMS II powder in an amount of at least about 2.3%.

<< Production of test specimens >>

<Experimental Example No. 1: Sample Nos. E493 to E502, C1 and C2>

In addition to the above reinforcing powders, pure iron powder (e.g., a pure iron powder / "ASC100.29" with diameters of 20 to 180 μm, a product of HOEGANAES Corp.), one of Fe system powders, and a graphite ( or "Gr") powder (eg, "JCPB", manufactured by NIHON KOKUEN Co., Ltd., having particle diameters of 45 μm or less), one of the C system powders. These powders were mixed with zinc stearate ("ZnSt."), One of the internal lubricants, in various manners as shown in Table 3, and then subjected to centrifugal mixing with a ball mill to prepare a series of powder mixtures (or raw material powders).

Using various types of powder mixtures, the following were prepared: test piece (or base test piece: ⌀ 23 mm × 10 mm thick) for measuring densities and dimensional changes before and after sintering; and test specimens (or tensile test specimens) having a shape in 1 which should be subjected to a tensile test.

Specifically, first, various kinds of powder mixtures were compacted under pressure at 588 MPa using dies, thereby obtaining powder compacts having two kinds of specimen molds (ie, compacting step). These powder compacts were each sintered at 1150 ° C in a nitrogen gas atmosphere using a continuous sintering furnace ("OXYNON FURNACE", manufactured by KANTO YAKIN KOGYOU Co., Ltd.) (ie, a sintering step). An equalization hold time was set to 30 minutes, and a re-sintering cooling rate was set to 30 ° C / min. (Or 0.5 ° C / sec.). Note that a CO concentration within the sintering furnace was set so as to obtain an ultra-low oxygen partial pressure atmosphere of 50 to 100 ppm (which corresponds to 10 ^-19 to 10 ^-21 when converted to an oxygen partial pressure).

<Experimental Example No. 2: Sample Nos. E503 to E520>

• (1) Using an iron alloy powder (for example, a "CrL" powder / "AstaloyCrL" having particle diameters of 20 to 180 μm, a product of HOEGANAES Corp.) whose constituent composition is Fe-1.5% Cr. 0.2% Mo (units: mass%), instead of the pure iron powder in Experimental Example 1, raw material powders were prepared. In this case, the respective powders were mixed in a different manner without using an internal lubricant as shown in Table 4, and then subjected to centrifugal mixing with a ball mill to prepare a series of powder mixtures (or raw material powders). Using these raw material powders, powder compacts and sintered bodies were prepared, and these powder compacts and sintered bodies had the same shapes as those of the two types of test specimens specified in Experimental Example No. 1.
• (2) However, in the present experimental example, the powder compacts were densified by the following hot pressure compacting method performed using a mold wall lubricant (i.e., a compaction step).

TiN coating treatment had previously been performed on the inner circumferential surface of each mold, and then its surface roughness was set to 0.4 Z. The respective molds had previously been heated to 150 ° C with a heating tape. Then, an aqueous solution in which lithium stearate (or "LiSt."), One of the lubricants of a higher fatty acid system was dispersed, was uniformly applied to an inner peripheral surface of the heated molds with a spray gun (i.e., a coating step). Thus, an LiSt film of about 1 μm was formed on the inner circumferential surface of the respective molds.

The aqueous solution used here is one in which LiSt. in water to which a surfactant and antifoaming agent had been added. As the surfactant, polyoxyethylene nonylphenyl ether (EO) 6 and (EO) 10 and boric acid ester Emulbon T-80 were used, which were added in an amount of 1% by volume based on the total aqueous solution (ie, 100% by volume) were. As the anti-foaming agent, FS Antifoam 80 was used which was added in an amount of 0.2% by volume based on the total aqueous solution (ie, 100% by volume). As LiSt. For example, one having a melting point of about 225 ° C and a particle diameter of about 20 μm was used. Its dispersion amount was adjusted to 25 g per 100 cm ^{3 of} the above aqueous solution. The aqueous solution in which LiSt was dispersed was further subjected to microfeining treatment with a ball mill pulverizer (e.g., Teflon-coated steel balls (Teflon ^™ is a registered trademark)) for 100 hours. The stock solution thus obtained was diluted 20 times, and an aqueous solution having a final concentration of 1% was provided for the above-mentioned coating step.

Into the cavities of the respective molds on the inner surfaces of which the uniform LiSt.-film was formed, various kinds of the above-described raw material powders were naturally charged (i.e., a filling step). The raw material powders had been previously heated to 150 ° C with a dryer, which corresponded to the temperature of the molds.

• (3) Die so erhaltenen Pulverpresskörper wurden auf die gleiche Weise wie im Versuchsbeispiel Nr. 1 gesintert. Was die jeweiligen Sinterkörper betrifft, so wurde ferner eine Stunde lang eine Wärmevergütungsbehandlung bei 200°C durchgeführt.

The respective raw material powders filled in the molds were compacted at 784 MPa, whereby powder compacts were obtained (ie, a hot pressure compacting step). Everyone who Powder compact could be removed from the molds with less ejection force without seizure or the like on the inner surfaces of the molds.

• (3) The powder compacts thus obtained were sintered in the same manner as in Experimental Example No. 1. As for the respective sintered bodies, heat-treatment treatment at 200 ° C was further carried out for one hour.

<Experimental Example No. 3: Sample Nos. E521 to E529>

Using an iron alloy powder (for example, a "CrM" powder / "AstaloyCrM" having particle diameters of 20 to 180 μm, a product of HOEGANAES Corp.) whose constituent composition is Fe-3% Cr-0.5% Mo (Units: mass%), instead of the iron alloy powder (ie, CrL powder) in Experimental Example No. 2, raw material powders were prepared. Also in this case, the respective powders were compacted completely without using an internal lubricant, by the same hot pressure compression method using a mold wall lubrication as in Experimental Example No. 2, using powder raw materials in which the respective powders were mixed in various manners. as shown in Table 5 (ie, a densification step). Further, the same sintering and heat-aging steps were carried out as in Experimental Example No. 2. Thus, various types of powder compacts and sintered bodies shown in Table 5 were prepared.

<< measurements >>

• (1) Using the base test specimens each prepared in the above experimental examples, the following were determined: densities (or G.D.) of the powder compacts; Densities (or S.D.) of the sintered bodies; and dimensional changes between before and after sintering (eg changes in outside diameter: ΔD).
• (2) Using the tensile strength test specimens each made in the above-mentioned experimental examples, a tensile test was conducted to determine tensile strengths, 0.2% elongation resistances and elongation values. In addition, a hardness in one of the side surfaces of the tensile test specimen having a load of 30 kg was measured by a Vickers hardness meter.

The results obtained for the respective test specimens are shown in Table 3 and in 2 to 5 for Experimental Example No. 1; in Table 4 and 6 to 9 for Experimental Example No. 2; and in Table 5 and 10 to 13 for Experimental Example No. 3.

<< >> evaluations

<Experimental Example No. 1>

(1) dimensional change

As shown in Table 3 and 2 As a result, the smaller the amount of FeMS powder and the finer the grain size, the smaller the dimensional change was. In particular, in a case where the fine FeMS IV powder whose particle diameter was 5 μm or less was used, the dimensional changes were comparable to those of cases where the conventional Cu powder or FeMS II powder was used.

(2) hardness

As shown in Table 3 and 3 As a result, the greater the amount of FeMS powder, the greater the hardness, but the grain made almost no difference. Moreover, in cases where the FeMS IV powder was used, the hardness increased more in comparison with cases where the conventional Cu powder or FeMS II powder was used.

(3) tensile strength

As shown in Table 3 and 4 As a result, the larger the amount of the FeMS powder, the finer the tensile strength was, and the finer the grain was. In addition, with identical blending amounts, the FeMS powder caused higher tensile strength than the Cu powder. In particular, in a case where the FeMS IV powder (eg, 5 μm) was used, the tensile strength was improved by about 20% over a case where the Cu powder was used.

In addition, in the samples in which the FeMS powder was used, the tensile strength sharply increased when the amount of FeMS powder was in a range of 1.5 to 2 mass%. On the other hand, when the amount of FeMS powder was 2.5 mass% or above, the increase in tensile strength was weakened.

(4) stretching

• (5) Aus den obigen Ergebnissen wurde deutlich, dass in einem Fall, wo das FeMS IV-Pulver, insbesondere dessen feines Pulver (z. B. – 5 μm) verwendet wurde, Maßänderungen, Härte- und Dehnungswerte gezeigt wurden, die mit denen eines Falles vergleichbar waren, wo das herkömmliche Cu-Pulver oder dergleichen verwendet wurde, während die Zugfestigkeitswerte erheblich zunahmen.

As shown in Table 3 and 5 As a result, the smaller the amount of FeMS powder and the finer the grain size, the larger the elongation became. In addition, the FeMS powder caused a greater elongation than the Cu powder at identical blending amounts. In addition, in the samples in which the finely pulverized (-5 μm) FeMS powder was used, the elongation increased sharply when the amount of the FeMS powder was in the range of 1.5 to 2 mass%. In contrast, the elongation decreased when the amount of the FeMS powder was 2 mass% or above.

• (5) From the above results, it became clear that in a case where the FeMS IV powder, especially its fine powder (eg, 5 μm) was used, dimensional changes, hardness and elongation values were shown to be consistent with those of a case where the conventional Cu powder or the like was used while the tensile strength values significantly increased.

In other words, even when the blending amount of the FeMS IV powder was decreased from the blending amount of the conventional Cu powder, it became clear that high strength could be obtained, which high strength is higher than in a case where a Cu powder is used. Incidentally, in such a case, it was confirmed that although the hardness scarcely changed, the dimensional changes became much smaller and the elongation values became much larger, resulting in very pleasing results.

Thus, in fact, the FeMS IV powder causes substantially less raw material cost than the Cu powder and the Fe-MS II powder. In addition, since good properties similar to or better than those of conventional sintered iron alloys can be obtained, the manufacturing cost of the present sintered iron alloys can be significantly lowered.

<Experimental Example No. 2>

(1) dimensional change

As shown in Table 4 and 6 As a result, the dimensional change did not depend on the particle diameter of the FeMS powder nor on the "Gr" amount, and was stable with a fluctuation of about ± 0.1. In particular, in a case where the fine FeMS IV powder (for example, -5 μm was used), the dimensional change was very stable regardless of the "Gr" amount with a fluctuation of about ± 0.05.

(2) hardness

As shown in Table 4 and 7 As a result, the larger the FeMS powder amount, the more the hardness increased, but the grain made almost no difference.

(3) tensile strength

As shown in Table 4 and 8th As a result, as the FeMS IV powder amount is increased to 1.5 mass%, the larger the FeMS powder amount becomes, the larger the tensile strength becomes. However, the tensile strength showed a downward trend as the FeMS IV powder amount increased to 1.5 mass% or more. In addition, the tensile strength showed an upward tendency the finer the grain of the FeMS IV powder was. In addition, the tensile strength of the sintered iron alloys exceeded 1,000 MPa in each case when the FeMS IV powder amount exceeded 1.0 mass%.

(4) stretching

As shown in Table 4 and 9 As a result, the smaller the FeMS IV powder amount, the larger the elongation values became. In addition, the larger the "Gr" amount, the larger the elongation values became. However, the grain size of the FeMS IV powder had virtually no influence.

(5) From the above results, it became clear that the sintered iron alloys in which the fine powder (eg, 5 μm) of the FeMS IV powder used, which is directed to the present experimental example, scarcely caused dimensional changes and after sintering; they had sufficient hardness; and they showed very high tensile strength and high elongation values at the same time.

Since the sintered iron alloys whose respective properties were so much better were obtained by admixing the FeMS IV powder in an amount of about 1 to 1.5 mass%, it became clear that it is possible to suppress sintered iron alloys both by using densification To produce ultra-high pressure as well as to significantly reduce production costs, as well as in the case of Experimental Example No. 1.

<Experimental Example No. 3>

(1) dimensional change

As shown in Table 5 and 10 The change in size was not dependent on the amount of FeMS powder added nor on the particle diameter and was very stable with a fluctuation of about ± 0.1.

(2) hardness

As shown in Table 5 and 11 As a result, the larger the FeMS powder amount, the larger the hardness, but the hardness scarcely increased when the amount of the FeMS IV powder exceeded 1 mass%. In addition, the grain made virtually no difference in hardness.

(3) tensile strength

As shown in Table 5 and 12 As can be seen, the tensile strength showed a very similar tendency as the hardness. That is, the larger the amount of FeMS powder, the higher the tensile strength became, but the tensile strength hardly increased when the amount of FeMS IV powder exceeded 1 mass%.

In contrast to the hardness, however, the smaller the grain size, the greater the tensile strength became. And although the tensile strength in each case exceeded 1000 MPa, the tensile strength particularly in cases where a fine powder of the FeMS IV powder was used became ultra-high in strength exceeding 1300 MPa.

(4) stretching

• (5) Aus den obigen Ergebnissen wurde Folgendes klar: Die gesinterten Eisenlegierungen, in denen das FeMS IV-Pulver verwendet wurde, das auf das vorliegende Versuchsergebnis gerichtet ist, bewirkten kaum eine Maßänderung vor und nach dem Sintern; sie besaßen eine ausreichende Harte; und sie zeigten gleichzeitig eine sehr große Zugfestigkeit. Insbesondere ergaben in den gesinterten Eisenlegierungen, in denen das feine Pulver des FeMS IV-Pulvers verwendet wurde (z. B. – 5 μm) sämtliche Eigenschaften auch gute Ergebnisse. Daher können auch in dem vorliegenden Versuchsbeispiel die gesinterten Eisenlegierungen durch Durchführen einer Verdichtung unter ultrahohem Druck hergestellt werden, wodurch die Herstellungskosten erheblich gesenkt werden, ebenso wie im Falle des Versuchsbeispiels Nr. 2.

(Tabelle 1) Chemische Bestandteile eines Verstärkungspulvers (Fe-Mn-Si-C-Pulver) (Massenprozent) Mn/Si-Verhältnis Mn Si C O N S P Fe FeMS II 50,2 32,8 0,06 0,42 < 0,001 < 0,003 0,016 Rest 1,5 FeMS IV 59,3 14,8 2,3 0,75 0,01 0,031 0,1 Rest 4,0 (Tabelle 2) Körnungsverteilung im Verstärkungspulver nach Pulverisierungsbehandlung D10 D50 D90 FeMS II 1,0 3,8 18,5 FeMS IV 0,8 3,3 11,5 As shown in Table 5 and 13 As a result, the smaller the FeMS powder amount, the larger the elongation values became, but the elongation values were almost stable with a fluctuation of about 1%. And the finer grade FeMS IV powder resulted in higher elongation values, albeit only to a small extent.

• (5) From the above results, it became clear that: the sintered iron alloys in which the FeMS IV powder was used, which is directed to the present experimental result, scarcely effected dimensional change before and after sintering; they possessed a sufficient hardness; and they also showed very high tensile strength. In particular, in the sintered iron alloys in which the fine powder of the FeMS IV powder was used (for example, -5 μm), all the properties also gave good results. Therefore, also in the present experimental example, the sintered iron alloys can be produced by performing ultra-high-pressure compacting, thereby remarkably lowering the production cost, as well as in the case of Experimental Example No. 2.

(Table 1) Chemical constituents of a reinforcing powder (Fe-Mn-Si-C powder) (mass percentage) Mn / Si ratio Mn Si C O N S P Fe FeMS II 50.2 32.8 0.06 0.42 <0.001 <0.003 0.016 rest 1.5 FeMS IV 59.3 14.8 2.3 0.75 0.01 0.031 0.1 rest 4.0 (Table 2) Grain distribution in the reinforcing powder after pulverization treatment D10 D50 D90 FeMS II 1.0 3.8 18.5 FeMS IV 0.8 3.3 11.5

<< Production of Reinforcing Powder >>

• (1) As a reinforcing powder blended in an Fe system powder, a FeMS powder (eg, FeMSC II powder) shown in Table 6 and a Cu powder ("DistaloyACu") (or Fe-10% Cu) with particle diameters of 20 to 180 μm, a product of HOEGANAES AB Corp.).

The FeMSC II powder (or Fe-Mn-Si-C powder) was one prepared by pulverizing silicon manganese (e.g., JIS No. 1) in air, wherein the silicon manganese was obtained from NIHON DENKO Corp. had been made. As compared with the FeMS IV powder shown in Table 1, the contents of Mn, Si and O were high, but the content of C was low in this FeMSC powder. In addition, the Mn / Si composition became 4.

• (2) Die Ergebnisse aus der Messung der Korngrößenverteilungen für das „wie pulverisierte” FeMSC II-Pulver, das der gleichen Pulverisierungsbehandlung unterzogen worden war, sind in Tabelle 7 dargestellt. Eine Körnung des FeMSC II-Pulvers bei D90 von 7,9 (μm), gibt an, dass insgesamt 90% der Teilchen Teilchendurchmesser von 7,9 μm oder weniger hatten. Das heißt, das FeMSC II-Pulver hatte eine erheblich kleine Körnung, und somit ist klar, dass das FeMSC II-Pulver in Bezug auf Pulverisierbarkeit (oder Kollabierbarkeit) gut war. Dies scheint ein Ergebnis des Folgenden zu sein: eine Fe-Menge im FeMSC II-Pulver betrug nur 15,2%; und darüber hinaus lag C in einer Menge von immerhin 2% vor.

Each of the powders was treated by pulverizing for 30 minutes using a vibrating mill manufactured by CHUO KAKOKI Co. Ltd. Those which are in a state to which they have been pulverized are referred to in the present specification and in the tables attached to the present specification as "as pulverized" or as "as R". These pulverized powders were further sieved, thereby appropriately classified as FeMS powder having grains as different as less than 5 μm (or -5 μm) or so. As apparent from Table 7 described below, the particle diameter "as pulverized" was smaller than 45 μm (or -45 μm).

• (2) The results from the measurement of the grain size distributions for the "as-pulverized" FeMSC II powder subjected to the same pulverization treatment are shown in Table 7. A grain size of the FeMSC II powder at D90 of 7.9 (μm) indicates that a total of 90% of the particles had particle diameters of 7.9 μm or less. That is, the FeMSC II powder had a considerably small grain size, and thus it is clear that the FeMSC II powder was good in terms of pulverizability (or collapsibility). This appears to be a result of the following: an Fe amount in FeMSC II powder was only 15.2%; and moreover, C was at least 2%.

<< Production of test specimens >>

<Experimental Example No. 4: Sample Nos. E599, E610, E657, E607 and E609>

In addition to the above reinforcing powders (ie, FeMSC II powder or Cu powder), pure iron powder (ie, pure Fe powder / "ASC100.29" having particle diameters of 20 to 180 μm, a product of HOEGANAES Corp.) was used. ), one of the Fe system powders, and a graphite (or "Gr") powder (e.g., "JCPB", manufactured by NIHON KOKUEN Co., Ltd., having particle diameters of 45 μm or less), one of C System powder, prepared. These powders were mixed in various manners as shown in Tables 8A and 8B, and then were subjected to centrifugal mixing with a ball mill to prepare a series of mixed powders (or raw material powders). No internal lubricant was used.

Using various kinds of mixed powders, the following were prepared: test piece (or base test piece: ⌀ 23 mm × 100 mm thick) for measuring densities and dimensional changes before and after sintering; and specimens (or tensile specimens) with an in 1 shown form, which are subjected to a tensile test.

More specifically, various types of the powder mixtures were first pressure-compacted at 150 ° C with a pressure of 588 MPa by a forging wall hot-compacting method described in the <Experimental Example No. 2> section, thereby obtaining powder compacts containing two kinds of the sample pieces -Forms (ie, a hot pressure densification step). These powder compacts were each sintered at a predetermined temperature selected from a range of 900 to 1150 ° C in a nitrogen gas atmosphere using a continuous sintering furnace ("OXYNON FURNACE", manufactured by KANTO YAKIN KOGYOU Co., Ltd.) ( ie a sintering step). An equalization hold time was set to 30 minutes, and a re-sintering cooling rate was set to 30 ° C / min (0.5 ° C / sec). Note that a CO concentration inside the sintering furnace was adjusted to be an atmosphere having an ultra-low oxygen partial pressure of 50 to 100 ppm (equivalent to 10 ^-19 to 10 ^-21 Pa after conversion to partial pressure of oxygen).

<Experimental Example No. 5: Sample Nos. E628 to E634, E640, E641, E643 and E645>

Raw material powders were prepared using a series of Fe system powders having different constituent compositions. In this case, the respective powders were mixed in a different manner as shown in Table 9 without the use of an internal lubricant, and then they were subjected to centrifugal mixing with a ball mill to prepare a series of powder mixtures (or raw material powders). The constituent compositions (units: mass%) of Fe system powders used are shown below in sequence.

"DistaloyAE": Fe-4Ni-1.5% Cu-0.5% Mo (with particle diameters of 20 to 180 μm); "DistaloyHP-1": Fe-4Ni-2% Cu-1.5% Mo (with particle diameters of 20 to 180 μm); "AstaloyCrL": Fe-1.5% Cu-0.2% Mo (with particle diameters of 20 to 180 μm); "AstaloyCrM": Fe-3% Cu-0.5% Mo (with particle diameters of 20 to 180 μm); and "ASC100.29": pure iron (with particle diameters of 20 to 180 μm, alternatively, classified to -63 μm). Manufacturer was HOEGANAES Corp. respectively.

Using various types of powder mixtures, the following were prepared: test piece (or base test piece: ⌀ 23 mm × 10 mm thick) for measuring densities and dimensional changes before and after sintering; and specimens (or tensile specimens with an in 1 form subjected to a tensile test.

More specifically, various kinds of the powder mixtures were first compacted under pressure by the forging wall hot-compacting method described in the <Experimental Example No. 2> section, thereby obtaining powder compacts having two kinds of the test piece molds (i.e., a hot pressure compacting step). The pressure compression was carried out at 150 ° C at a pressure of 392 MPa, 588 MPa, 784 MPa or 1176 MPa.

These powder compacts were each sintered at 1180 ° C (ie, a sintering step). At this time, the equalization hold time was set to 45 minutes, and a cooling rate after sintering was set to 100 ° C / min. Note that the inside of a sintering furnace was adjusted to have a reducing atmosphere in which a hydrogen gas was mixed with a nitrogen gas (for example, a mixing ratio: N ₂ - 10 vol% H ₂ , and a dew point : -30 ° C or below).

Each of the sintered bodies was further subjected to a tempering treatment at 200 ° C in air for 1 hour (i.e., a tempering step).

<Experimental Example No. 6: Samples Nos. E877, E879 and E881>

In addition to the above-mentioned reinforcing powders (ie, FeMSC II powder or Cu powder), a pure iron powder (eg, a pure Fe powder / "ASC100.29" having particle diameters of 20 to 180 μm, a product of U.S. Pat HOEGANAES Corp.), one of the Fe system powders, and a graphite (or "Gr") powder (e.g., "JCPB", manufactured by NIHON KOKUEN Co., Ltd., having particle diameters of 45 μm or less) the C system powder, prepared. The FeMSC II powder was classified for use at -5 μm. These powders were mixed with zinc stearate ("ZnSt."), One of the internal lubricants, in various manners as shown in Table 10, and then subjected to centrifugal mixing with a ball mill to prepare a series of powder mixtures (or raw material powders).

Using various kinds of mixed powders, the following were prepared: test piece (or base test piece: ⌀ 23 mm × 10 mm thick) for measuring densities and dimensional changes before and after sintering; and specimens (or tensile specimens) with an in 1 form subjected to a tensile test.

Specifically, various kinds of powder mixtures were first compacted under pressure at predetermined compression pressures using dies, thereby obtaining powder compacts having two kinds of test piece shapes (ie, a compacting step). Here, for the raw material powders in which the amount of internal lubricant was 0.4 mass%, the press molds were heated to 80 ° C, and then hot densification was carried out; whereas for the 0.8 mass percent raw material powders, densification was performed at room temperature. These powder compacts were each sintered at 1150 ° C (ie, a sintering step). An equalization hold time was set to 15 minutes, and a cooling rate after sintering was set to 30 ° C / min. (Or 0.5 ° C / sec.). Note that the inside of a sintering furnace has been adjusted to fit a reducing atmosphere in which a hydrogen gas was mixed with a nitrogen gas (for example, mixing ratio: N ₂ - 3 vol% H ₂ , and dew point: -30 ° C or below).

<< measurements >>

Using the base test specimens prepared in Experimental Examples 4 to 6, the following were determined: densities (or G.D.) of the powder compacts; Densities (or S.D.) of the sintered bodies; and dimensional changes between before and after sintering (eg changes in outside diameter: ΔD). In addition, using the tensile test specimens prepared in Experimental Examples No. 4 to No. 6, a tensile test was conducted to find tensile strengths and elongation values. In addition, a hardness was measured in one of the side surfaces of the tensile test specimen having a load of 30 kg by means of a Vickers hardness meter.

The measurement results thus obtained for the respective test pieces are shown in Table 8A and Table 8B (which are collectively referred to as "Table 8") and in 14 and 15 reproduced with reference to Experimental Example No. 8; they are shown in Table 9 with reference to Experimental Example No. 5; and they are shown in Table 10 with reference to Experimental Example No.6.

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<Experimental Example No. 4>

(1) dimensional change

As shown in Table 8, the dimensional changes scarcely became much worse even when sintering was carried out at temperatures below 1150 ° C. It was found that it is possible to inhibit dimensional changes by selecting an optimum sintering temperature in accordance with the grain of a raw material powder used.

(2) hardness and tensile strength

In each of the test pieces, the higher the sintering temperature, the higher the hardness and tensile strength of the sintered body.

How out 14 As can be seen, the use of the FeMSC II powder as the reinforcing powder resulted in the sintered bodies having sufficient strength being obtained even at low sintering temperatures. In a Fe-Cu-C system such as "E610", a sintered body having sufficient strength, that is, a sintered body whose tensile strength exceeded 500 MPa could not be obtained if the sintering temperature was not at or above the melting point of copper (ie, for example at 1085 ° C or above). However, when the FeMSC II powder was used as the reinforcing powder, high-strength sintered bodies were obtained even by sintering at temperatures as low as 950 ° C, depending on the particle diameters of the raw material powders.

More specifically, Sample No. E657 prepared by using the FeMSC II powder classified to -45 μm was converted into a sintered body exhibiting a tensile strength at 1050 ° C or higher by performing sintering, which exceeded 500 MPa. In the sample No. E607 prepared by using the FeMSC II powder classified to -5 μm, it was predicted that a sintered body exhibiting a tensile strength exceeding 500 MPa would undergo sintering a temperature of over 1000 ° C could be obtained. Further, the sample No. E609 prepared by using the FeMSC II powder classified to -5 μm together with the iron system powder classified to -63 μm was prepared by carrying out sintering at 950 ° C or more converted into a sintered body showing a tensile strength exceeding 500 MPa.

(3) stretching

• (4) Aus den obigen Ergebnissen wurde klar, dass es möglich ist, die Sintertemperatur durch Verfeinern der Körnung eines vorgegebenen Verstärkungspulvers zu senken. In diesem Fall wurde festgestellt, dass ein hochfester gesinterter Eisenkörper dadurch erhalten werden kann, dass die Körnung des Eisensystempulvers ebenfalls verfeinert wird, auch wenn das Sintern bei einer niedrigeren Temperatur durchgeführt wird.

How out 15 each of the specimens showed an elongation value of 2% or more. In cases where the FeMSC II powder was used as the reinforcing powder, the elongation values became lowest around 1050 ° C and were about 2 to 2.5% in each of the sample pieces. The more the temperatures at which sintering was performed were above or below this temperature, the better the strain values. However, the smaller the grain size of the iron system powder and the FeMSC II powder, the more the elongation values tended to increase.

• (4) From the above results, it became clear that it is possible to lower the sintering temperature by refining the grain of a given reinforcing powder. In this case, it has been found that a high-strength sintered iron body can be obtained by also refining the grain of the iron system powder, even if the sintering is carried out at a lower temperature.

In addition, it became clear that other properties such as dimensional change and elongation scarcely deteriorated even if the sintering temperature is set to a lower temperature.

<Experimental Example No. 5>

(1) dimensional change

It was possible to produce high density materials with densities of about 7.6 g / cm ³ by setting the compaction pressure to 1176 MPa.

In addition, as shown in Table 9, the dimensional changes in cases where the specimens were made by using the FeMSC II powder were stable with an increase in the compaction pressure with a fluctuation of about ± 0.2%, even though they were Raw material powder traded whose ΔD values tend to increase with low compaction pressures.

(2) hardness and tensile strength

As shown in Table 9, even when the test pieces did not contain Cu, hardness and tensile strength values comparable to those of the sample pieces containing Cu and Ni could be obtained. Specifically, the test piece No. E634 showed hardness and tensile strength superior to those of samples containing Cu and Ni.

(3) stretching

• (4) Aus den obigen Ergebnissen wurde klar, dass es auch im Hinblick auf gesinterte Eisenlegierungen, die durch Verdichten von Rohmaterialpulvern, die vorgegebene Verstärkungspulver enthielten, unter ultrahohen Drücken hergestellt wurden, möglich war, die gesinterten Eisenlegierungen mittels einer Sinterhärtungsbehandlung erheblich zu festigen. Und es wird klar, dass Sinterkörper, die Festigkeiten aufweisen, die denen von gesinterten Eisenlegierungen, die Cu und Ni enthalten, vergleichbar sind, zu geringeren Kosten erzeugt werden können.

As shown in Table 9, the higher the compression pressure, the larger the elongation became.

• (4) From the above results, it became clear that also with respect to sintered iron alloys prepared by compacting raw material powders containing predetermined reinforcing powders under ultra-high pressures, it was possible to considerably strengthen the sintered iron alloys by means of a sintering hardening treatment. And, it becomes clear that sintered bodies having strengths comparable to those of sintered iron alloys containing Cu and Ni can be produced at a lower cost.

<Experimental Example No. 6>

In Experimental Example No. 6, sintered iron alloys (ie, "E877" and "E879") according to the present invention were produced while the composition of raw material powders, densification conditions, sintering temperature, sintering atmosphere, and the like were set to more practical production conditions aimed at: increase efficiency, reduce costs, etc.

In each of the samples, the dimensional change was stable with a fluctuation of about ± 0.2%. Moreover, in a case where the samples obtained by performing the compaction with a compaction pressure of 588 MPa were compared with each other, "E877" and "E879" containing no Cu showed better hardness values Tensile strength and elongation as "E881" containing Cu. The samples according to "E877" and "E879" became considerably stronger by further increasing their compaction pressures.

Note that from the respective evaluations based on Experimental Examples Nos. 1 to 5, it is understood that lowering the sintering temperatures within a reasonable range under the production conditions of Experimental Example No. 6 or further carrying out sintering hardening results in: The following can be realized: an energy saving in the manufacturing steps, an even better strength of the sintered iron alloys; and the same.

In other words, it has become clear that high-strength sintered iron alloys can be obtained even if they are produced under practical production conditions. (Table 6) Chemical constituents of a reinforcing powder (eg Fe-Mn-Si-C powder) (mass percentage) Mn / Si ratio Mn Si C O N P Fe FeMSC II 65.4 16.4 1.93 1.05 0.01 0,022 rest 4.0 (Table 7) Grain distribution in the reinforcing powder after pulverization treatment FeMSC II D10 D50 D90 1.3 3.6 7.9

Claims (11)

A method of producing a sintered iron alloy, the method being characterized in that it is a method of producing a sintered iron alloy comprising: a compacting step in which a raw material powder is compacted under pressure in which an Fe system powder comprising pure iron and / or an iron (Fe) alloy is mixed with a reinforcing powder containing an alloying element which it does not is Fe, whereby the raw material powder is transformed into a powder compact; and a sintering step in which the powder compact is heated in an oxidation-inhibiting atmosphere, whereby the powder compact is sintered; and wherein the reinforcing powder is an Fe-Mn-Si-C powder comprising a Fe alloy or an Fe compound containing: Manganese (Mn) in an amount of 58 to 70 mass% (hereinafter simply referred to as "%"); Silicon (Si) in an amount to have a composition ratio of Mn to Si (i.e., Mn / Si) of 3.3 to 4.6; and Carbon (C) in an amount of 1.5 to 3%; based on a total of 100%. A method of producing a sintered iron alloy according to claim 1, wherein a particle diameter of the Fe-Mn-Si-C powder is 45 μm or less. A method of producing a sintered iron alloy according to claim 1, wherein an amount in which the Fe-Mn-Si-C powder is mixed in the raw material powder is 0.05 to 3% based on a total of 100% of raw material powder. The method for producing a sintered iron alloy according to claim 1, wherein the raw material powder further comprises a graphite (or "Gr") powder. A method of producing a sintered iron alloy according to claim 1, wherein the Fe-Mn-Si-C powder has oxygen (O) in an amount of 1.5% or less, based on a total of 100 mass%. The method for producing a sintered iron alloy according to claim 1, wherein the raw material powder is prepared so that: Mn is 0.1 to 2.1%; Si is 0.05 to 0.6%; and C represents 0.1 to 0.9%; based on a total of 100% sintered iron alloy. The method for producing a sintered iron alloy according to claim 1, wherein the oxidation-resistant atmosphere of the sintering step is a reducing atmosphere in which a hydrogen gas in an amount of 2 to 20% by volume is mixed in a nitrogen gas, totaling 100% by volume. The method for producing a sintered iron alloy according to claim 1, wherein the oxidation-resistant atmosphere is an inert gas atmosphere having such a low partial pressure of oxygen that the partial pressure of oxygen corresponds to 10 ^-19 Pa or less. The method for producing a sintered iron alloy according to claim 1, wherein the sintering step comprises: a heating step in which the powder compact is heated to a temperature of 900 to 1400 ° C, whereby the powder compact is converted into a sintered body; and a cooling step in which the sintered body is cooled after heating at a cooling rate of 0.1 to 3 ° C / second. The method for producing a sintered iron alloy according to claim 1, wherein the raw material powder has chromium (Cr) in an amount of 0.3 to 5% and / or molybdenum (Mo) in an amount of 0.1 to 2% based on 100 in total %. A method of producing a sintered iron alloy according to claim 10, wherein the Cr and / or Mo is contained in the Fe system powder.

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