IRON-BASED POWDER COMBINATION

Description

FIELD OF THE INVENTION

[0001] The present invention refers to iron-based powder metallurgical combinations and to methods for preparing sintered powder metallurgical components therefrom. More specifically the invention refers to the production of sintered components including copper, nickel and molybdenum by using these combinations.

BACKGROUND OF THE INVENTION

[0002] Within the powder metallurgical field, copper, nickel and molybdenum has since long been used as alloying elements in the production of high strength sintered components.

[0003] Sintered iron-based components can be produced by mixing alloying elements with the pure iron powders. However, this may cause problems with dust and segregation which may lead to variations in size and mechanical properties of the sintered component. In order to avoid segregation the alloying elements may be pre-alloyed or diffusion alloyed with the iron powder. In one method molybdenum is pre-alloyed with iron powder and this pre-alloyed iron powder is subsequently diffusion alloyed with copper and nickel for production of sintered components from iron-based powder compositions containing molybdenum, nickel and copper.

[0004] It is however obvious that, when producing a sintered iron-based component, from a powder wherein molybdenum is pre-alloyed and wherein copper and nickel are diffusion alloyed, the content of the alloying elements in the sintered iron-based component will be substantially identical with the content of alloying elements in the used diffusion alloyed powder. In order to reach different contents of the alloying elements in the sintered component, yielding different properties, iron-based powders having different contents of the alloying elements have to be used.

[0005] US 5082433 disclose moulded articles, particularly cams for camshafts of internal combustion engines, subjected to high wear conditions. In order to make them resistant to wear, they are produced from a sintered alloy which has been fabricated by powder metallurgical means. The alloy has a hardened matrix with interstitial copper and consists of 0.5 to 16% by weight of molybdenum, 1 to 20% by weight of copper, 0.1 to 1.5% by weight of carbon and, optionally, of admixtures of chromium, manganese, silicon and nickel totalling, at most, 5% by weight, the remainder being iron.

[0006] US 5567890 disclose an iron-based powder for producing highly resistant components having a small local variation in dimensional change by powder compacting and sintering. The powder contains - in addition to Fe - 0.5-4.5% by weight Ni, 0.65-2.25% by weight Mo and 0.35-0.65% by weight C, and optionally a lubricant and impurities. The maximum variation in dimensional change is 0.07% for a minimum density of 6.7 g/cm³.

[0007] WO 2004/038054 disclose a method of controlling the dimensional change to a predetermined value including the steps of providing a first powder (A) consisting of an iron based powder (1) and copper in the form of elemental copper (2), or copper diffusion bonded to said iron-based powder (3). Providing a second powder (B) consisting of said iron-based powder (1) and a pre-alloyed iron-copper powder (4); mixing said first and second powder mixtures (A) and (B) in proportions resulting in the desired dimensional change adding graphite and lubricant and optionally hard phase materials and other alloying elements to the obtained mixture. At last compacting the obtained mixture and sintering the compacted body.

[0008] The article "New high performance ferrous P/M material for demanding automotive applications" by James, W.B,, Baran, M.C., Semel, F.J., Causton, R.J., Narasimhan, K.S., Murphy, T.F., presented at Euro2000, Munich, 18th-20th October 2000, discloses that engineered binder-treated premixes have been developed as alternatives to diffusion-alloyed powders including those based on a pre-alloyed powder (1.5 w/o molybdenum). The engineered binder-treated materials are compacted with their diffusion-alloyed counterparts.

[0009] The present invention provides a method of eliminating the need of producing a specific powder for each desired chemical composition of the sintered iron-based component having alloying elements from molybdenum, copper and nickel. The invention also offers the advantage of providing a method for controlling the dimensional change and the tensile strength to predetermined values. In a specific embodiment the dimensional change is independent of the carbon content and the density.

SUMMARY OF THE INVENTION

[0010] In brief the invention concerns a powder metallurgical combination of three different iron-based powders as defined in claim 1. The first of these iron-based powders consisting of core particles of iron, pre-alloyed with molybdenum, which is additionally diffusion alloyed with copper and the second iron-based powder consisting of core particles of iron, pre-alloyed with molybdenum, which is diffusion alloyed with nickel. The third iron-based powder essentially consists of particles of iron pre-alloyed with molybdenum.

[0011] A method according to the invention is defined in claim 6 and comprises the steps of combining these three iron-based powders in predetermined amounts, mixing the combination with graphite, compacting the obtained mixture and sintering the obtained green body to provide a sintered component having a predetermined strength and a predetermined dimensional change during sintering.

DESCRIPTION OF THE DRAWINGS

[0012] Figs 1-4 illustrate diagrams for determining the copper and nickel content in the powder metallurgical combination for a predetermined strength and dimensional change.

DETAILED DESCRIPTION OF THE INVENTION

[0013] Specifically the iron-based powder metallurgical combination according to the invention comprises:

• an iron-based powder A essentially consisting of core particles of iron pre-alloyed with molybdenum, whereby 6-15%, preferably 8-12% by weight of copper, is diffusion alloyed to the core particles.
• an iron-based powder B essentially consisting of core particles of iron pre-alloyed with molybdenum, whereby 4.5-8%, preferably 5-7% by weight of nickel, is diffusion alloyed to the core particles, and
• an iron-based powder C, essentially consisting of particles of iron pre-alloyed with molybdenum and the relation between powders A, B and C is chosen so that the copper content of the powder metallurgical combination is 0.2 - 2 % by weight, the nickel content of the powder metallurgical combination is 0.1 - 4 % by weight and the molybdenum content of the powder metallurgical combination is 0.3 - 2 % by weight, and the graphite content of the powder metallurgical combination is 0.3-0.7% by weight,
• wherein the amount of molybdenum in each of powder A, B or C is 0.3-2%, preferably 0.5-1.5%, by weight, and the amount of molybdenum is essentially the same in each of powder A, B or C. Amounts above 2% of Mo do not give an increase of the strength justifying the increase of the costs. Amounts of Mo below 0.3% do not give a significant effect of the strength.

[0014] The amount of copper and nickel which is diffusion alloyed to the core particles is limited in the upper range to 15% copper and 12% nickel. The lower limit of copper and nickel which is diffusion alloyed to the core particles should be substantially higher than the amount required in the sintered component to achieve the advantages of the invention. Thus, for practical reasons an iron-based powder essentially consisting of core particles pre-alloyed with molybdenum and comprising at least 6% copper diffusion alloyed to the core particles and an iron-based powder having core particles pre-alloyed with molybdenum and comprising at least 4.5% nickel diffusion alloyed to the core particles are of special interest.

[0015] The powders A, B and C, respectively, essentially consist of particles of iron pre-alloyed with molybdenum, but other elements, except unavoidable impurities, may be pre-alloyed to the particles. Such elements may be nickel, copper, chromium and manganese.

[0016] In order to produce a sintered component from the powder combination according to the present invention, the respective amounts of powder A, B and C are determined and mixed with graphite in the amount required for the predetermined strength. The obtained mixture may be mixed with other additives before compaction and sintering. The amount of graphite which is mixed in the powder combination is 0.3-0.7%.

[0017] Other additives are selected from the group consisting of lubricants, binders, other alloying elements, hard phase materials, machinability enhancing agents.

[0018] In accordance with one embodiment of the powder metallurgical combination, powder C is essentially free from Cu and Ni.

[0019] The relation between powder A, B and C is chosen so that the copper content will be 0.2-2% by weight, the nickel content will be 0.1-4% by weight and the molybdenum content is preferably 0.5-1.5% by weight of the sintered component.

[0020] When the copper content is 0.2-2%, preferably 0.4-0.8% and the nickel content is 0.1-4%, it has been unexpectedly been found that the dimensional change during sintering is independent of the carbon content and sintered density.

[0021] In order to produce a sintered component with a predetermined dimensional change and strength, the amounts of copper, nickel and carbon, respectively, in the sintered component is determined by means of diagrams, e.g. from fig 1-4. The required amounts of powder A, B and C, respectively, may then be determined by a person skilled in the art.

[0022] The powders are mixed with graphite to obtain the final desired carbon content. The powder combination is compacted at a compaction pressure between 400-1000 MPa and the obtained green body is sintered at 1100-1300°C for 10-60 minutes in a protective atmosphere. The sintered body may be subjected to further post treatments, such as heat treatment, surface densification, machining etc.

[0023] The exemplifying diagrams in fig 1-4 are valid at a compaction pressure of 600 MPa, sintered at 1120°C for 30 minutes in an atmosphere of 90% nitrogen and 10% of hydrogen.

[0024] According to the present invention sintered components containing various amounts of molybdenum, copper and nickel may be produced. This is achieved by using a combination of three different powders, which are mixed in different proportions to achieve a powder having the required chemical composition for the actual sintered component.

[0025] To summarize a particular advantage of the invention is that the dimensional change during sintering as well as the strength of the sintered component can be controlled. The advantage of being able to control the dimensional change will facilitate the use of existing pressing tools. When producing sintered parts a certain scatter in carbon content and density may be unavoidable. By utilising the combinations having a dimensional change independent of the density and carbon content the scatter in dimensions after sintering will be reduced hence subsequent machining and machining costs can be decreased.

[0026] The invention is illustrated by the following nonlimiting examples:

Example 1

[0027] This example demonstrates how to choose an alloying composition having a desired strength of about 600 MPa and three levels of dimensional change (-0.1%, 0.0% and +0.1%). This was done for two carbon levels, 0.5% C and 0.3% C, respectively, in the powder combinations according to table 1, where the lower carbon content yields better ductility as can be seen in table 2.

[0028] The powder combinations according to the present invention were prepared from a powder A with 10% of copper diffusion alloyed to the surface of an iron-based powder pre-alloyed with 0.85% of molybdenum, a powder B with 5% of nickel diffusion alloyed to the surface of an iron-based powder pre-alloyed with 0.85% of molybdenum and a powder C of an iron-based powder pre-alloyed with 0.85% of molybdenum.

[0029] The powder combinations were mixed with 0.8% amide wax as a lubricant and graphite, to yield a sintered carbon content of 0.3 % and 0.5 %, respectively. The obtained mixtures were compacted to tensile test specimen according to ISO 2740.

[0030] The compaction pressure was 600 MPa and the sintering conditions were: 1120°C, 30 min, 90% N₂/10% H₂. In table 2 other mechanical properties from the powder combinations according to the invention are presented. It can be clearly seen that the powder combinations according to the invention have the predetermined dimensional change according to fig 3.

Table 1

	Cu (%)	Ni (%)	Mo (%)	C (%)	Sintered density (g/cm3)	Dimensional change (%)
Powder combination (1)	0.6	1.3	0.83	0.5	7.08	-0.104
Powder combination (2)	1.15	0.8	0.83	0.5	7.06	0.004
Powder combination (3)	1.55	0.4	0.83	0.5	7.04	0.096
Powder combination (4)	0.9	2.3	0.83	0.3	7.11	-0.096
Powder combination (5)	1.3	2	0.83	0.3	7.09	0.007
Powder combination (6)	1.6	1.7	0.83	0.3	7.07	0.095

Table 2

	Hardness HV10	Tensile strength (MPa)	Yield strength (MPa)	Young's modulus (GPa)	Elongation (%)
Powder combination (1)	219	599	413	139	2.0
Powder combination (2)	223	601	429	139	1.8
Powder combination (3)	219	602	447	139	1.6
Powder combination (4)	207	601	397	138	2.4
Powder combination (5)	209	604	408	137	2.2
Powder combination (6)	206	602	417	137	2.1

Example 2

[0031] This example illustrates powder combinations according to the invention, comprising 0.6% Cu and 2% Ni and a specific embodiment having dimensional change independent of carbon content and sintered density as shown in table 3. The results obtained with these combinations are compared with the results obtained with Distaloy AB (available from Höganäs AB, Sweden) as well as with a powder having the same chemical composition as the powder combination according to the invention but wherein iron-based powder pre-alloyed with molybdenum has both copper and nickel diffusion alloyed to the surface, in table 3 designated as "fixed composition".

[0032] The powder combinations according to the present invention were prepared from a powder A with 10% of copper diffusion alloyed to the surface of an iron-based powder pre-alloyed with 0.85% of molybdenum, a powder B with 5% of nickel diffusion alloyed to the surface of an iron-based powder pre-alloyed with 0.85% of molybdenum and a powder C consisting of an iron-based powder pre-alloyed with 0.85% of molybdenum.

[0033] Table 3 shows a specific example where a mixture of powder A, powder B and powder C having a total content of 0.6% copper, 2% of nickel and 0.83% of molybdenum is compared with a known powder, Distaloy AB, and an iron-based powder having 0.83% of pre-alloyed molybdenum, 0.6% of copper and 2% of nickel diffusion alloyed to the surface of the iron-based powder. As disclosed in table 3 the dimensional change of sintered samples, produced from the powder combination according to the invention, is essentially independent of the carbon content and density compared with the known powder Distaloy AB or the iron-based powder diffusion alloyed with both copper and nickel.

[0034] The powder combinations were mixed with 0.8% amide wax as a lubricant and graphite, to yield a sintered carbon content according to table 3. The obtained mixtures were compacted to tensile test specimen according to ISO 2740 at different compaction pressures according to table 3. The tensile test specimens were sintered at 1120°C for 30 minutes in an atmosphere of 90 % nitrogen and 10 % of hydrogen. In table 4 further mechanical properties are presented.

Table 3

	Cu (%)	Ni (% )	Mo (%)	C (%)	Compacting pressure (MPa)	Sintered density (g/cm3)	Dimensional change (%)
Powder combination (7)*	0.6	%		0.38	600	7.11	-0.117
Powder combination (8)*	0.6	2		0.54	600	7.09	-0.118
Powder combination (9)*	0.6	2		0.74	600	7.06	-0.117
Powder combination (10)*	0.6	2		0.55	400	6.77	-0.114
Powder combination (11)*	0.6	2		0.53	800	7.22	-0.129
Fixed composition (1)	0.6	2		0.21	600	7.16	-0.155
Fixed composition (2)	0.6	2		0.50	600	7.12	-0.147
Fixed composition (3)	0.6	2		0.78	600	7.08	-0.118
Fixed composition (4)	0.6	2		0.21	400	6.79	-0.134
Fixed composition (5)	0.6	2		0.49	800	7.26	-0.163
Distaloy AB (2)	1.5	1.75	0.5 0.35	0.35	600	7.06	-0.012
Distaloy AB (3)	1.5	1.75	0.5	0.54	600	7.05	-0.034
Distaloy AB (4)	1.5	1.75	0.5	0.73	600	7.04	-0.056
Distaloy AB (5)	1.5	1.75	0.5	0.54	400	6.73	-0.048
Distaloy AB (6)	1.5	1.75	0.5	0.53	800	7.19	-0.027

(*) Powder combination according to the invention

Table 4

	Hardness HV10	Tensile strength (MPa)	Yield strength (MPa)	Young's modulus (GPa)	Elongation (%)
Powder combination (7)*	183	570	391	137	2.6
Powder combination (8)*	206	632	433	135	1.8
Powder combination (9)*	244	669	485	138	1.1
Powder combination (10)*	171	507	363	114	1.3
Powder combination (11)*	234	672	450	143	2.1
Fixed composition (1)	-	-	-	-	-
Fixed composition (2)	213	649	437	133	2.2
Fixed composition (3)	-	-	-	-	-
Fixed composition (4)	-	-	-	-	-
Fixed composition (5)	-	-	-	-	-
Distaloy AB (2)	160	562	333	133	3.8
Distaloy AB (3)	189	618	392	136	2.2
Distaloy AB (4)	218	626	437	139	1.1
Distaloy AB (5)	160	523	344	115	1.0
Distaloy AB (6)	200	658	411	145	2.8

(*) Powder combination according to the invention

Claims

1. A powder metallurgical combination comprising:

- an iron-based powder A, consisting of core particles of iron pre-alloyed with molybdenum, whereby 6-15% by weight of powder A is copper being diffusion alloyed to the core particles,

- an iron-based powder B, consisting of core particles of iron pre-alloyed with molybdenum, whereby 4.5-8% by weight of powder B is nickel being diffusion alloyed to the core particles, and

- an iron-based powder C, consisting of particles of iron pre-alloyed with molybdenum

- the relation between powder A, B and C is chosen so that the copper content of the powder metallurgical combination is 0.2 - 2 % by weight, the nickel content of the powder metallurgical combination is 0.1 - 4 % by weight, the molybdenum content of the powder metallurgical combination is 0.3 - 2 % by weight, and the graphite content of the powder metallurgical combination is 0.3-0.7% by weight,

- wherein the amount of molybdenum in each of powder A, B or C is 0.3-2%, preferably 0.5-1.5%, by weight, and the amount of molybdenum is essentially the same in each of powder A, B or C.

2. The powder metallurgical combination according to claim 1, wherein the amount of copper in powder A is 8-12% by weight.

3. The powder metallurgical combination according to claim 1 or 2, wherein the amount of nickel in powder B is 5-7% by weight.

4. The powder metallurgical combination according to any one of claims 1 to 3, comprising other additives selected from the group consisting of lubricants, binders, other alloying elements, hard phase materials, machinability enhancing agents.

5. The powder metallurgical combination according to any one of claims 1 to 4, wherein powder C is essentially free from Cu and Ni.

6. A method to obtain a sintered component, having a predetermined strength and a predetermined dimensional change during sintering, including the steps of :

- determining the required amounts of copper, nickel, molybdenum and carbon in the sintered component needed for obtaining the predetermined strength and dimensional change,

- determining the respective amounts of powder A, B and C as defined in any one of claims 1-5,

- mixing the determined amounts of powders A, B and C with graphite and optional other additives ,

- compacting the mixture to form a powder compact; and

- sintering the powder compact,
wherein the mixture is compacted at a compaction pressure between 400-1000 MPa and the sintering is done at 1100-1300°C for 10-60 minutes.

Ansprüche

1. Pulvermetallurgische Kombination umfassend:

- ein eisenbasiertes Pulver A, bestehend aus Kernpartikeln von mit Molybdän vorlegiertem Eisen, wobei 6-15 Gew.-% von Pulver A Kupfer ist, das zu den Kernpartikeln diffusionslegiert ist,

- ein eisenbasiertes Pulver B, bestehend aus Kernpartikeln von mit Molybdän vorlegiertem Eisen, wobei 4,5-8 % Gew.-% von Pulver B Nickel ist, das zu den Kernpartikeln diffusionslegiert ist, und

- ein eisenbasiertes Pulver C, bestehend aus Partikeln von mit Molybdän vorlegiertem Eisen

- das Verhältnis zwischen dem Pulver A, B und C so gewählt ist, dass der Kupferinhalt der pulvermetallurgischen Kombination 0,2-2 Gew.-%, der Nickelinhalt der pulvermetallurgischen Kombination 0,1-4 Gew.-%, der Molybdäninhalt der pulvermetallurgischen Kombination 0,3-2 Gew.-%, und der Graphitinhalt der pulvermetallurgischen Kombination 0,3-0,7 Gew.-% beträgt,

- wobei die Menge von Molybdän in jedem der Pulver A, B und C 0,3-2 Gew.-%, vorzugsweise 0,5-1,5 Gew.-%, beträgt, und die Menge von Molybdän in jedem der Pulvers A, B und C im Wesentlichen die gleiche ist.

2. Pulvermetallurgische Kombination nach Anspruch 1, wobei die Kupfermenge des Pulvers A 8-12 Gew.-% beträgt.

3. Pulvermetallurgische Kombination nach Anspruch 1 oder 2, wobei die Nickelmenge des Pulvers B 5-7 Gew.-% beträgt.

4. Pulvermetallurgische Kombination nach einem der vorgehenden Ansprüche 1 bis 3, umfassend übrige Additive, die aus der Gruppe bestehend aus Gleitmitteln, Bindemitteln, übrigen Legierungsbestandteilen, Hartphasenwerkstoffen und die Verarbeitbarkeit verbessernden Mitteln ausgewählt sind.

5. Pulvermetallurgische Kombination nach einem der Ansprüche 1 bis 4, wobei das Pulver C im Wesentlichen frei von Cu und Ni ist.

6. Verfahren zum Erhalten einer gesinterten Komponente, die während der Sinterung eine vorgegebene Festigkeit und eine vorgegebene Dimensionsänderung aufweist, umfassend die folgenden Schritte:

- Bestimmen der zum Erhalten der vorgegebenen Festigkeit und Dimensionsänderung erforderlichen Mengen von Kupfer, Nickel, Molybdän und Kohlenstoff in der gesinterten Komponente,

- Bestimmen der jeweiligen Mengen von Pulver A, B und C wie in einem der Ansprüche 1-5 definiert,

- Mischen der bestimmten Mengen von Pulvern A, B und C mit Graphit und eventuellen anderen Additiven,

- Verdichten der Mischung zum Bilden eines Pulverpresskörpers; und

- Sinterung des Pulverpresskörpers,
wobei die Mischung bei einem Kompaktierungsdruck von 400-1000 MPa verdichtet wird, und die Sinterung bei 1100-1300 °C für 10-60 Minuten durchgeführt wird.

Revendications

1. Combinaison de poudre métallurgique comprenant :

- une poudre à base de fer A, constituée de particules de noyau de fer pré-alliées au molybdène, 6 à 15% en poids de la poudre A étant du cuivre étant allié par diffusion aux particules de noyau,

- une poudre à base de fer B, constituée de particules de noyau de fer pré-alliées au molybdène, 4,5 à 8% en poids de la poudre B étant du nickel allié par diffusion aux particules de noyau, et

- une poudre à base de fer C, constituée de particules de fer pré-alliées au molybdène

- le rapport entre les poudres A, B et C est choisi si bien que le contenu en cuivre de la combinaison de poudre métallurgique est 0,2 - 2 % en poids, le contenu en nickel de la combinaison de poudre métallurgique est 0,1 -4 % en poids, le contenu en molybdène de la combinaison de poudre métallurgique est 0,3 - 2 % en poids, et le contenu en graphite de la combinaison de poudre métallurgique est 0,3-0,7% en poids,

- dans laquelle la quantité de molybdène dans chacune des poudres A, B ou C est de 0,3 à 2%, de préférence de 0,5 à 1,5% en poids, et la quantité de molybdène est essentiellement la même dans chacune des poudres A, B ou C.

2. Combinaison de poudre métallurgique selon la revendication 1, dans laquelle la quantité de cuivre dans la poudre A est 8 à 12 % en poids.

3. Combinaison de poudre métallurgique selon la revendication 1 ou 2, dans laquelle la quantité de nickel dans la poudre B est 5 à 7 % en poids.

4. Combinaison de poudre métallurgique selon l'une quelconque des revendications 1 à 3, comprenant des additifs sélectionnés parmi le groupe composé de lubrifiants, de liants, d'autres éléments d'alliage, de matériaux en phase dure et d'agents d'amélioration d'usinabilité.

5. Combinaison de poudre métallurgique selon l'une quelconque des revendications 1 à 4, la poudre C est essentiellement dépourvue de Cu et de Ni.

6. Procédé de préparation d'un composant fritté, ayant une résistance prédéterminée et un changement dimensionnel prédéterminé pendant le frittage, comprenant les étapes consistant à :

- déterminer les quantités requises de cuivre, de nickel, de molybdène et de carbone dans le composant fritté nécessaire pour obtenir la résistance prédéterminée et le changement dimensionnel prédéterminé,

- déterminer les quantités respectives de poudre A, B et C telles que définies dans l'une quelconque des revendications 1 à 5,

- mélanger des quantités déterminées de poudres A, B et C avec du graphite et d'autres additifs éventuels,

- compacter le mélange pour former un compact de poudre ; et

- fritter le compact de poudre,
dans lequel le mélange est compacté à une pression de compactage entre 400-1000 MPa et le frittage est réalisé à 1100-1300°C pendant 10-60 minutes.

Drawing