METHOD OF PRODUCING A DIFFUSION ALLOYED IRON OR IRON-BASED POWDER, A DIFFUSION ALLOYED POWDER, A COMPOSITION INCLUDING THE DIFFUSION ALLOYED POWDER, AND A COMPACTED AND SINTERED PART PRODUCED FROM THE COMPOSITION

Abstract

A method of producing a diffusion alloyed powder having an iron or iron-based core powder having particles of an alloying powder containing Cu and Ni bonded to the surface of the core particles, including providing a unitary alloying powder capable of forming particles of a Cu and Ni containing alloy, mixing the unitary alloying powder with the core powder, and heating the mixed powders in a non-oxidizing or reducing atmosphere to a temperature of 500-1000 C. during a period of 10-120 minutes to convert the alloying powder into a Cu and Ni containing alloy, so as to diffusion bond particles of the Cu and Ni alloy to the surface of the iron or iron-based core powder.

Claims

1. A method of producing a diffusion alloyed powder comprising a total content of copper and nickel of at most 20% by weight, wherein the copper content is above 4.0 wt % and the ratio between copper and nickel is between 9/1 and 3/1, said powder consisting of an iron or iron-based core powder having particles of an alloying powder containing copper and nickel bonded to the surface of the core powder particles, comprising providing a unitary alloying powder comprising copper and nickel, said unitary alloying powder having a particle size distribution such that D.sub.50 is less than 15 m, mixing the unitary alloying powder with the core powder, and heating the mixed powders in a non-oxidizing or reducing atmosphere to a temperature of 500-1000 C. during a period of 10-120 minutes to convert the alloying powder into a copper and nickel containing alloy, by diffusion bonding particles of the copper and nickel alloying powder to the surface of the iron or iron-based core powder.

2. The method as claimed in claim 1, wherein the unitary alloying powder is an alloy consisting essentially of copper and nickel.

3. The method as claimed in claim 1, wherein the unitary alloying powder essentially is a metal alloy, an oxide, carbonate, or other suitable compound of copper and nickel.

4. The method as claimed in claim 1, wherein the diffusion bonding of particles of copper and nickel alloying powder to the surface of the iron or iron-based core powder results in a weakly sintered cake, which is then crushed gently and sieved to a particle size essentially below 150 m.

5. The method as claimed in claim 1, wherein the diffusion alloyed powder comprises a content of copper in the range of 5-15 wt % and a content of nickel is in the range of 0.5-5 wt %.

6. The method as claimed in claim 1, wherein the diffusion alloyed powder comprises a total content of copper and nickel between 4% and 16% by weight.

7. A diffusion alloyed powder, comprising a total content of copper and nickel of at most 20% by weight, wherein the copper content of the diffusion powder is between 8-15 wt % and the ratio between copper and nickel is between 9/1 and 3/1, wherein the content of nickel is between 0.5-5 wt %, said powder consisting of an iron or iron-based core powder having particles of an average size less than 15 m of a unitary alloying powder containing copper and nickel, bonded to the surface of the core particles.

8. The diffusion alloyed powder as claimed in claim 7, wherein the diffusion alloyed powder has a particle size essentially below 150 m.

9. The diffusion alloyed powder as claimed in claim 7, wherein the content of copper is between 8-12 wt % and the content of nickel is between 1-4.5 wt %.

10. The diffusion alloyed iron or iron-based powder composition, comprising the diffusion alloyed powder as claimed in claim 7, and in addition graphite and optionally at least one additive selected from the group consisting of organic lubricants, hard phase materials, solid lubricants and other alloying substances.

11. An iron based powder composition consisting of: an iron or iron-based powder a diffusion alloyed powder as claimed in claim 7, up to 1% by weight of graphite, and optionally at least one additive selected from the group consisting of organic lubricants, hard phase materials, solid lubricants and other alloying substances.

12. The composition according to claim 11, wherein the iron or iron-based powder consists of essentially pure iron.

13. The composition according to claim 11, wherein the total copper and nickel content does not exceed 5% by weight of the composition.

14. (canceled)

15. A compacted and sintered part produced from a powder composition as claimed in claim 10.

16. The diffusion alloyed powder as claimed in claim 8, wherein the content of copper is between 8-12 wt % and the content of nickel is between 1-4.5 wt %.

17. An iron based powder composition consisting of: an iron or iron-based powder a diffusion alloyed powder as claimed in claim 8, up to 1% by weight of graphite, and optionally at least one additive selected from the group consisting of organic lubricants, hard phase materials, solid lubricants and other alloying substances.

18. An iron based powder composition consisting of: an iron or iron-based powder a diffusion alloyed powder as claimed in claim 9, up to 1% by weight of graphite, and optionally at least one additive selected from the group consisting of organic lubricants, hard phase materials, solid lubricants and other alloying substances.

19. The composition according to claim 12, wherein the total copper and nickel content does not exceed 5% by weight of the composition.

20. The diffusion alloyed powder as claimed in claim 7, wherein the content of copper is between 12-15 wt % and the content of nickel is between 0.5-5 wt %.

21. The diffusion alloyed powder as claimed in claim 8, wherein the content of copper is between 12-15 wt % and the content of nickel is between 0.5-5 wt %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In the following, the invention will be described in more detail with reference to preferred embodiments and the appended drawings.

[0035] FIG. 1 is a diagram showing the hardness HV10 of pressed and sintered samples as a function of the Cu to Ni ratio at various mean particle sizes D.sub.50 of the alloying powders.

[0036] FIG. 2 is a diagram showing the tensile strength (MPa) of pressed and sintered samples as a function of the Cu to Ni ratio at various mean particle sizes D.sub.50 of the alloying powders.

[0037] FIG. 3 is a diagram showing the scatter of dimensional change of the samples during sintering as a function of the Cu to Ni ratio at various mean particle sizes D.sub.50 of the alloying powders.

DETAILED DESCRIPTION

Base Powder for Producing the Diffusion Alloyed Powder

[0038] The base powder is preferably a pure iron-based powder such as AHC100.29, ASC100.29 and ABC100.30 all available from Hgans AB, Sweden. However, other pre-alloyed iron-based powders may also be used.

Particle Size of the Base Powder

[0039] There are no restrictions as to the particle size of the base powder and, consequently, nor to the diffusion alloyed iron-based powder. However, it is preferred to use powder a particle size normally used within the PM industry.

Copper and Nickel Containing Unitary Alloying Powder

[0040] The copper and nickel containing alloying substance to be adhered to the surface of the iron-based powder can be in the form of a metal alloy, an oxide or a carbonate or in any other form resulting in an iron-based powder according to the present invention. The relation between copper and nickel, Ni (% by weight)/Cu (% by weight) is preferably between 1/3 and 1/9 in the copper and nickel containing alloying substance. If the weight ratio between Ni and Cu is above 1/3, the effect on hardness and yield strength will be unacceptable and if the ratio is below 1/9 the scatter of the dimensional change due to varying carbon content and sintering temperature will be too high, above about 0.035 wt % according to the methodology described herein.

[0041] The particle size of the copper and nickel containing alloying powder preferably is such that D.sub.50, meaning that 50% by weight of the powder has particle size less than the D.sub.50 value, preferably is below 15 m, more preferably below 13 m, most preferably below 10 m.

Production of the New Powder

[0042] The base powder and the copper and nickel containing alloying powder are mixed in such proportions that the total content of copper and nickel in the new powder will be at most 20% by weight, preferably between 1% and 20% by weight, and more preferably between 4% and 16% by weight. Preferably the content of Cu is above 4.0 wt %. In a preferred embodiment the content of Cu is between 5-15 wt % and the content of Ni is between 0.5-5%, such as Cu 8-12 wt % and Ni 1-4.5 wt %.

[0043] A low content, such as a content below 1% by weight is believed to be too low in order to obtain desired mechanical properties of the sintered component. If the content of the copper and nickel containing alloying powder exceeds 20%, bonding of the alloying powder to the base powder will be insufficient and increase the risk for segregation.

[0044] The homogeneous mix is then subjected to a diffusion annealing process, wherein the powder is heated in a reducing atmosphere up to a temperature of 500-1000 C. during period of 10-120 minutes. The obtained diffusion bonded powder, in the form of a weakly sintered cake, is then crushed gently.

Production of Sintered Components

[0045] Before compaction, the new powder is mixed with graphite, up to 1% by weight depending on the intended use of the finished component, organic lubricants up to 2% by weight, preferably between 0.05 to 1% by weight, optionally other alloying substances, hard phase materials and inorganic solid lubricants rendering lubricating properties of the finished component.

[0046] The organic lubricant reduces interparticular friction between the individual particles and also the friction between the wall of the mould and the compressed powder or ejected compressed body during compaction and ejection.

[0047] The solid lubricants may be chosen from the group of stearates, such as zinc sterate, amides or bis-amides such as ethylene-bis-stearamide, fatty acids such as stearic acid, Kenolube, other organic substances or combinations thereof, having suitable lubricating properties.

[0048] The new powder may be diluted with a pure iron powder or an iron-based powder in order to obtain a iron-based powder composition wherein the total copper and nickel content does not exceed 5% by weight of the composition, such as between 0.5% and 4.5% by weight or between 1.0% and 4.0% by weight, since a content above 5% by weight may not cost-effectively contribute to improved desired properties. The relation between copper and nickel in the diluted alloy, Ni (% by weight)/Cu (% by weight) is preferably between 1/3 and 1/9.

[0049] The obtained iron powder composition is transferred to a compaction mould and compacted at ambient or elevated temperature to a compacted green body at a compaction pressure up to 2000 MPa, preferably between 400-1000 MPa.

[0050] Sintering of the green body is performed in a non-oxidizing atmosphere, at a temperature of between 1000 to 1300 C., preferably between 1050-1250 C.

EXAMPLES

[0051] The following examples illustrate embodiments of the invention.

Example 1

[0052] Three samples of diffusion bonded iron-based powders were produced by first blending different alloying powders, cuprous oxide Cu.sub.2O, Cu.sub.2O+Ni powder and a Cu and Ni containing powder with a iron powder, ASC100.29.

[0053] The homogenous blended powder mixes were diffusion annealed at 800 C. for 60 minutes in an atmosphere of 75% hydrogen/25% nitrogen. After diffusion annealing, the weakly sintered powder cakes were gently crushed and sieved to a particle size substantially below 150 m.

TABLE-US-00001 TABLE 1 Cu content in Ni content in diff. diff. Diffusion Alloying Cu/Ni ratio D50 alloying annealed annealed annealed iron- powder of alloying powder powder powder based powder used powder [m] [%] [%] 1 (reference) Cu.sub.2O 100/0 8.8 10 0 2 (reference) Cu.sub.2O + 100/0 8.8 Ni 0/100 8.5 9 1 3 (invention) CuNi alloy 9/1 8.5 9 1 powder

[0054] Table 1 shows particle size, D.sub.50, and ratio of Cu and Ni of the alloying powders as well as Cu and Ni content of the diffusion annealed powders. The mean particle size, D.sub.50, was analyzed by laser diffraction in a Sympatec instrument.

[0055] Three iron-based powder compositions consisting of 20% by weight of the diffusion annealed iron-based powders 1, 2 and 3 respectively, 0.5% by weight of graphite C-UF4 and 0.8% by weight of Amide Wax PM balanced by ASC100.29, were produced by homogenously mixing the components.

[0056] The different compositions were compacted at 600 MPa into seven tensile strength samples, from each composition, according to ISO 2740. The samples were sintered at 1120 C. for 30 minutes in an atmosphere of 90% nitrogen/10% hydrogen. Dimensional change was measured as well as mechanical properties according to ISO 4492 and EN 10 002-1. Hardness, HV10, according to ISO 4498 was measured.

TABLE-US-00002 TABLE 2 Diff annealed Dimensional iron-based Dimensional change, powder used in change, standard iron-based mean deviation Tensile Elon- Hard- powder value of 7 of 7 strength gation ness composition samples [%] samples [%] [MPa] [%] [HV10] 1 (reference) 0.34 0.007 437 3.2 135 2 (reference) 0.29 0.006 436 3.6 139 3 (invention) 0.22 0.004 424 3.8 135

[0057] Table 2 shows that a substantial reduction of the dimensional change between compacted and sintered part, as well as variation of dimensional change between different parts, are obtained when using diffusion the annealed iron-based powder of the invention.

[0058] Reference 2 shows that when cuprous oxide and nickel powder are used for making the diffusion bonded powder, the swelling during sintering was reduced. Sample 3 according to the invention has the same copper and nickel contents as reference 2, but shows a much more pronounced reduction of the swelling and scatter.

Example 2

[0059] Various types of copper/nickel containing alloying powder according to Table 3, having different ratios of copper and nickel as well as different particle size distribution, were used as copper and nickel containing alloying powder. As reference a cuprous oxide powder, Cu.sub.2O, available from American Chemet was used. The particle size distribution was analyzed by laser diffraction in a Sympatec instrument. In order to simplify the evaluation, powders having D.sub.50 less than 8.5 m was designated as fine, between 8.5 m and less than 15.1 m was designated as medium and above 15.1 as coarse.

TABLE-US-00003 TABLE 3 Iron-based diffusion annealed powder No. Ratio Cu/Ni D.sub.50 m 1 (reference) 8.8 (medium) 2 19 7.1 (fine) 3 19 9.9 (medium) 4 19 15.5 (coarse) 5 9 4.7 (fine) 6 9 10.1 (medium) 7 9 21.1 (coarse) 8 4 4.2 (fine) 9 4 8.5 (medium) 10 4 15.1 (coarse) 11 1 6.4 (fine)

[0060] As base powder, a pure iron powder, ASC100.29 available from Hgans AB, was used.

[0061] Various samples having a weight of 2 kg of diffusion bonded powder were prepared by mixing ASC100.29 with the copper and nickel containing alloying powder in proportions giving a total content of copper and nickel in the diffusion bonded annealed powder of 10% by weight.

[0062] The reference sample was prepared by mixing the iron powder with the cuprous oxide giving a total content of copper in the diffusion bonded annealed powder of 10% by weight.

[0063] The mixed powder samples were annealed in a laboratory furnace at 800 C. for 60 minutes in an atmosphere of 75% hydrogen/25% nitrogen. After cooling, the obtained weakly sintered powder cakes were gently milled and sieved to a particle size substantially below 150 m.

[0064] Thirty-three iron-based powder compositions consisting of 20% by weight of the diffusion annealed iron-based powders 1-11, 0.4, 0.6 and 0.8% by weight of graphite C-UF4 respectively, 0.8% by weight of Amide Wax PM, balanced by ASC100.29 were produced by homogenously mixing the components.

[0065] The different compositions were compacted at 600 MPa into tensile strength samples according to Example 1.

[0066] Tensile tests samples made from compositions having 0.6% graphite added, were sintered at three different temperatures, 1090 C., 1120 C. and 1150 C. for 30 minutes, respectively, in an atmosphere of 90% nitrogen/10% hydrogen, seven samples for each sintering run.

[0067] Samples made from compositions containing 0.4% added graphite and samples made from compositions containing 0.8% added graphite were sintered at 1120 C. for 30 minutes in an atmosphere of 90% nitrogen/10% hydrogen, also seven samples per sintering run. Dimensional change was measured as well as mechanical properties including hardness according to the procedures described in Example 1.

[0068] The following Table 4 describes the test series.

TABLE-US-00004 TABLE 4 Graphite added to compositions 1-11 Sintering temp Test series [% by weight] [ C.] A 0.4 1120 B1 0.6 1120 B2 0.6 1150 B3 0.6 1190 C 0.8 1120

Test Series

[0069] The following Table 5 shows the results from measurements of dimensional change during sintering as well as results from analysis of C, Cu and Ni content of sintered samples.

TABLE-US-00005 TABLE 5 diffusion Stand. deviation annealed Graphite Sintering Dimensional between Test powder addition temperature change A, B1, B2, Analyzed Analyzed Analyzed series No. (%) ( C.) DC (%) B3, C (%) C (%) Cu (%) Ni (%) A 1 0.4 1120 0.37 0.37 2.12 0.02 B1 1 0.6 1090 0.33 0.56 2.04 0.02 B2 1 0.6 1120 0.31 0.56 2.02 0.02 B3 1 0.6 1150 0.24 0.55 2.03 0.02 C 1 0.8 1120 0.19 0.072 0.75 2.10 0.02 A 2 0.4 1120 0.31 0.38 1.95 0.12 B1 2 0.6 1090 0.27 0.55 1.89 0.11 B2 2 0.6 1120 0.26 0.55 1.88 0.11 B3 2 0.6 1150 0.21 0.55 1.90 0.11 C 2 0.8 1120 0.19 0.049 0.74 1.97 0.12 A 3 0.4 1120 0.32 0.36 1.95 0.12 B1 3 0.6 1090 0.28 0.54 1.88 0.12 B2 3 0.6 1120 0.27 0.56 1.83 0.12 B3 3 0.6 1150 0.22 0.56 1.88 0.12 C 3 0.8 1120 0.19 0.052 0.76 1.96 0.12 A 4 0.4 1120 0.32 0.35 1.92 0.14 B1 4 0.6 1090 0.29 0.54 1.88 0.14 B2 4 0.6 1120 0.27 0.54 1.86 0.14 B3 4 0.6 1150 0.23 0.54 1.87 0.14 C 4 0.8 1120 0.19 0.051 0.76 2.00 0.15 A 5 0.4 1120 0.20 0.36 1.66 0.27 B1 5 0.6 1090 0.17 0.54 1.59 0.25 B2 5 0.6 1120 0.16 0.55 1.58 0.25 B3 5 0.6 1150 0.14 0.55 1.61 0.25 C 5 0.8 1120 0.15 0.025 0.74 1.67 0.27 A 6 0.4 1120 0.22 0.38 1.75 0.29 B1 6 0.6 1090 0.19 0.55 1.71 0.28 B2 6 0.6 1120 0.19 0.54 1.72 0.28 B3 6 0.6 1150 0.17 0.55 1.72 0.28 C 6 0.8 1120 0.16 0.025 0.74 1.79 0.29 A 7 0.4 1120 0.27 0.35 1.82 0.30 B1 7 0.6 1090 0.20 0.55 1.71 0.27 B2 7 0.6 1120 0.21 0.54 1.67 0.27 B3 7 0.6 1150 0.18 0.55 1.71 0.28 C 7 0.8 1120 0.19 0.034 0.73 1.89 0.31 A 8 0.4 1120 0.17 0.38 1.67 0.40 B1 8 0.6 1090 0.14 0.54 1.67 0.40 B2 8 0.6 1120 0.16 0.54 1.66 0.39 B3 8 0.6 1150 0.13 0.54 1.67 0.39 C 8 0.8 1120 0.14 0.019 0.76 1.69 0.41 A 9 0.4 1120 0.17 0.38 1.66 0.41 B1 9 0.6 1090 0.13 0.55 1.57 0.40 B2 9 0.6 1120 0.15 0.55 1.58 0.39 B3 9 0.6 1150 0.12 0.55 1.59 0.40 C 9 0.8 1120 0.13 0.020 0.74 1.65 0.41 A 10 0.4 1120 0.19 0.38 1.64 0.44 B1 10 0.6 1090 0.13 0.54 1.55 0.42 B2 10 0.6 1120 0.15 0.57 1.55 0.42 B3 10 0.6 1150 0.12 0.53 1.56 0.42 C 10 0.8 1120 0.14 0.023 0.71 1.72 0.46 A 11 0.4 1120 0.01 0.37 1.05 1.01 B1 11 0.6 1090 0.01 0.56 1.04 1.00 B2 11 0.6 1120 0.03 0.55 1.02 0.99 B3 11 0.6 1150 0.06 0.55 1.01 1.98 C 11 0.8 1120 0.02 0.020 0.74 1.04 1.01

[0070] The following Table 6 shows the result from mechanical testing of samples made from pressed and sintered compositions consisting of 20% by weight of different iron-based diffusion annealed powders, 0.8% by weight of Amide Wax PM, 0.6% of graphite, balanced by ASC100.29.

[0071] Sintering was conducted 1120 C. for 30 minutes in an atmosphere of 90% nitrogen/10% hydrogen.

TABLE-US-00006 TABLE 6 Iron-based D.sub.50 m of iron- Tensile diffusion annealed Ratio based diffusion strength Hardness powder No. Cu/Ni annealed powder [MPa] HV10 1 (reference) 8.8 (medium) 504 150 2 19 7.1 (fine) 500 148 3 19 9.9 (medium) 507 154 4 19 15.5 (coarse) 506 144 5 9 4.7 (fine) 479 141 6 9 10.1 (medium) 498 146 7 9 21.1 (coarse) 492 133 8 4 4.2 (fine) 481 139 9 4 8.5 (medium) 488 141 10 4 15.1 (coarse) 489 134 11 1 6.4 (fine) 445 127

[0072] Diagrams 1 and 2, presenting the compiled test results, show that when the ratio Cu/Ni in the iron-based diffusion annealed powder is below 3/1 (above 30% of Ni) the hardness and tensile strength will be unacceptably affected.

[0073] Furthermore, diagram 3 shows that when the ratio Cu/Ni exceeds 9/1 (less than 10% Ni), the scatter of the dimensional change during sintering, related to variations in the carbon content and sintering temperature, will be unacceptably high.

INDUSTRIAL APPLICABILITY

[0074] The present invention is applicable in powder metallurgical processes, where components produced from the new powder presents a minimum of variation of dimensional change from component to component.