Iron based powder

Abstract

Disclosed is a new diffusion-bonded powder consisting of an iron powder having 1-5%, preferably 1.5-4% and most preferably 1.5-3.5% by weight of copper particles diffusion bonded to the surfaces of the iron powder particles. The new diffusion bonded powder is suitable for producing components having high sintered density and minimum variation in copper content.

Claims

1. A process for producing an iron-based powder comprising the following steps: providing an iron powder having a content of oxygen of 0.3-1.2% by weight, a content of carbon of 0.1-0.5% by weight, a maximum particle size of at most 250 μm and at most 30% by weight below 45 μm and providing a copper containing powder having a maximum particle size, X.sub.90, of at most 22 μm and a weight average particle size, X.sub.50, of at most 15 μm, mixing said iron powder and said copper containing powder, subjecting said mixture to a reduction annealing process in a reducing atmosphere at 800-980° C. for a period of 20 minutes to 2 hours to obtain a cake, and crushing the obtained cake and separating a resulting powder by desired particle size to form the iron-based powder.

2. The process according to claim 1, wherein the iron-based powder has a maximum particle size of 250 μm, at least 75% is below 150 μm and at most 30% is below 45 μm, wherein the iron-based powder has an apparent density of at least 2.70 g/cm3 and an oxygen content of at most 0.16% by weight, and wherein other impurities are at most 1% by weight of the iron-based powder.

3. The process according to claim 2, wherein the iron-based powder has a SSF-factor of at most 2.0, wherein the SSF-factor is defined as the quotient between the Cu content in weight % in the fraction of the iron-based powder which passes a 45 μm sieve and the Cu content in weight % in the fraction of the iron-based powder which does not pass a 45 μm sieve.

4. A process for forming a sintered component, the process comprising forming the iron-based powder according to claim 1 and forming the sintered component, wherein a maximum copper content in a cross section of the sintered component made from the iron-based powder is at most 100% higher than a nominal copper content, wherein the sintered component is produced by: mixing the iron-based powder with 0.5% of graphite, having a particle size, X90, of at most 15 μm measured with laser diffraction according to ISO 13320:1999, and 0.9% of lubricant; transferring the obtained mixture into a compaction die for production of tensile strength samples (TS-bars) according to ISO 2740: 2009 and subjecting the obtained mixture to a compaction pressure of 600 MPa; ejecting the compacted sample from the compaction die; and subjecting the compacted sample to a sintering process at 1120° C. for a period of 30 minutes in an atmosphere of 90% nitrogen/10% hydrogen at atmospheric pressure, wherein the maximum copper content is determined through lines scanning in a Scanning Electron Microscope (SEM) equipped with a system for Energy Dispersive Spectroscopy (EDS), wherein the magnification is 130×, working distance is 10 mm and the scanning time is 1 minute.

5. A process for forming a sintered component, the process comprising forming the iron-based powder according to claim 1 and forming the sintered component, wherein a largest pore area in a cross section of the sintered component made from the iron-based powder is at most 4000 μm.sup.2, wherein the sintered component is produced by: mixing the iron-based powder with 0.5% of graphite, having a particle size, X90, of at most 15 μm measured with laser diffraction according to ISO 13320:1999, and 0.9% of lubricant; transferring the obtained mixture into a compaction die for production of tensile strength samples (TS-bars) according to ISO 2740: 2009 and subjecting the obtained mixture to a compaction pressure of 600 MPa; ejecting the compacted sample from the compaction die; and subjecting the compacted sample to a sintering process at 1120° C. for a period of 30 minutes in an atmosphere of 90% nitrogen/10% hydrogen at atmospheric pressure, wherein the largest pore area is determined in a Light Optical Microscope (LOM) at a magnification of 100× with the aid of a digital video camera and a computer based software and the total measured area is 26.7 mm.sup.2.

6. A process for forming a composition, the process comprising forming the iron-based powder according to claim 1 and mixing the iron-based powder with graphite and lubricant to form a composition, the composition comprising: 10 to 99.8 weight % of the iron-based powder; graphite, in an amount of up to 1.5% weight %; lubricant, in an amount of 0.3-1.5 weight %; and optionally, at least one machinability enhancing additive, in an amount of up to 1.0 weight %.

7. The process according to claim 6, the composition comprising: 50 to 99.8 weight % of the iron-based powder; graphite, in an amount of up to 1.5% weight %; lubricant, in an amount of 0.3-1.5 weight %; and optionally, at least one machinability enhancing additive, in an amount of up to 1.0 weight %.

8. A process for forming a sintered component, the process comprising forming the composition according to claim 6, the process further comprising: subjecting the composition to a compaction process at a compaction pressure of at least 400 MPa to form a green component; ejecting the green component; sintering the green component in a neutral or reducing atmosphere at a temperature of about 1050-1300° C. for a period of 10 to 75 minutes; and optionally, hardening the sintered component in a hardening process, wherein the hardening process is a process selected from case hardening, through hardening, induction hardening, and a hardening process including gas or oil quenching.

9. The process according to claim 8, wherein a maximum copper content in a cross section of the sintered component is at most 100% higher than the nominal copper content, wherein the maximum copper content is determined through lines scanning in a Scanning Electron Microscope (SEM) equipped with a system for Energy Dispersive Spectroscopy (EDS), and wherein the magnification is 130×, working distance is 10 mm and the scanning time is 1 minute.

10. The process according to claim 8, wherein a largest pore area of the sintered component is at most 4000 μm.sup.2, wherein the largest pore area is determined in a Light Optical Microscope (LOM) at a magnification of 100× with the aid of a digital video camera and a computer based software and the total measured area is 26.7 mm.sup.2.

Description

FIGURE LEGENDS

(1) FIG. 1 shows variation in copper content for sample ac.

(2) FIG. 2 shows variation in copper content for sample bc.

(3) FIG. 3 shows variation in copper content for sample bd.

(4) FIG. 4 shows variation in copper content for sample be.

(5) FIG. 5 shows variation in copper content for sample ad.

EXAMPLES

Example 1

(6) Various diffusion-bonded powders were produced by mixing iron powders according to table 1 with copper containing powders according to table 2 in an amount sufficient to yield a content of 3% of copper in the subsequently obtained diffusion-bonded powder. The obtained mixtures were subjected to a reduction-annealing process at a temperature of 900° C. in a reducing atmosphere for a period of time 60 minutes. After the reduction-annealing process the obtained loosely sintered cake was gently crushed to a powder having a maximum particle size of 250 μm.

(7) The following tables show raw materials used.

(8) TABLE-US-00001 TABLE 1 Iron powder Iron powder O [%] C [%] D.sub.50 [μm] a) 1.02 0.41   98 b) 0.08 0.004 107

(9) TABLE-US-00002 TABLE 2 Copper containing powder Copper containing powder Cu [%] O [%] D.sub.50 [μm] D.sub.95 [μm] c) Cu.sub.2O 88.1 Not 15  22 measured d) Cu 100 99.5 0.18 85 160 e) Cu 200 99.6 0.15 60 100

(10) The obtained diffusion bonded powders were designated ac, bc, bd, be, ad and ae according to type of raw materials used.

(11) Determination of SSF-factors for the diffusion bonded powders according to the invention were performed according to the method described in the detailed description. The following results according to table 3 were obtained.

(12) TABLE-US-00003 TABLE 3 SSF-factor Sample SSF-factor ac 1.56 bc 1.97

(13) Samples for measuring maximum pore size, maximum pore area and copper variation were prepared according to the procedure in the detailed description.

(14) The maximum copper content was measured with the aid of a FEG-SEM, type Hitachi SU6600. The EDS system was manufactured by Bruker AXS.

(15) After inserting the specimen in the vacuum chamber and having adjusted the working distance to 10 mm, the electron ray was aligned to use the lowest possible magnification, 130×. The strait scanning line was chosen with as few pores as possible (deep pores could be capturing photons of importance). The scanning time was set to 1 min.

(16) The results are presented in FIGS. 1-6 and in table 4.

(17) The pore size analysis was carried out on a Light Optical Microscope (LOM) at a magnification of 100× with the aid of a digital video camera and a computer based software, Leica QWin. The module in the software called “Largest Pore Measurement” was used. The total measured area is 26.7 mm.sup.2 corresponding to 24 measure fields.

(18) All specimens were measured with a horizontal press orientation and a side way stepping of the cross section.

(19) The software was operating in black and white mode and detected pores using “detection of black area in measured area”, where black area is equal to pores.

(20) The following table 4 shows the results from the measurements.

(21) TABLE-US-00004 Maxi- Mini- Largest Largest mum % of mum Diffusion pore pore Cu nominal Cu bonded length area content Cu content powders [μm] [μm.sup.2] [%] content [%] ac Invention 144 3196 5.5 183 0.7 bc Invention 142 3130 5.9 197 0.0 bd Comparative 199 9034 8.1 270 0.0 be Comparative 160 5128 7.5 250 0.0 ad Comparative 178 8515 7.3 243 0.0 ae Comparative 162 5070

(22) From table 4 it can be concluded that components made from the diffusion bonded powders according to the invention show smaller largest pore areas and less variation in copper content compared to the comparative examples. It can further be concluded that when iron powder having higher oxygen content is used for producing the diffusion bonded powder according to the invention, the variation of copper content is less compared to when using iron powder having low oxygen content (ac-bc)

Example 2

(23) Four different iron-based powder compositions were prepared by mixing four different copper containing powders at an addition corresponding to 2 weight % copper in the metal powder composition with the atomized iron powder ASC 100.29, available from Höganäs AB, Sweden, 0.5% of synthetic graphite F10 from Imerys Graphite & Carbon, and 0.9% of the lubricant described in the patent publication WO2010-062250.

(24) The copper containing powders used were: The diffusion bonded powder ac according to Example 1. Distaloy®ACu, available from Höganäs AB Sweden. Distaoy®ACu is an iron powder having 10% of copper diffusion bonded on the surfaces if the iron powder. Cu-200, the elementary Cu powder described in table 2. Cu-100, the elementary Cu powder described in table 2.

(25) The following table 5 shows the copper containing powders used and the content of the ingredients in the metal powder compositions.

(26) TABLE-US-00005 TABLE 5 Iron based Copper powder Copper containing Lubri- composi- containing powder ASC100.29 Graphite cant tion No. powder [%] [%] [%] [%] 1 ac 66.7 31.9 0.5 0.9 2 Distaloy ® ACu 20 78.6 0.5 0.9 3 Cu-200 2 96.6 0.5 0.9 4 Cu-100 2 96.6 0.5 0.9

(27) The iron-based powder compositions were compacted into test bars at 700 MPa according to ISO3928. After compaction the ejected green test bars were sintered in an atmosphere of 90/10 N.sub.2/H.sub.2 at a temperature of 1120° C. during 30 minutes and cooled to ambient temperature. Thereafter the test bars were subjected to through hardening at 860° C. for 30 minutes at an atmosphere with a carbon potential of 0.5%, followed by quenching in oil.

(28) The heat treated test bars were tested for fatigue strength at R=−1 with a run out limit of 2×10.sup.6 cycles according to MPIF standard 56. The endurance limit was determined at 50% probability of survival.

(29) The following table 6 shows the results from the fatigue test.

(30) TABLE-US-00006 TABLE 6 Test bars made from Iron-based Fatigue strength 50% probability powder composition No. [MPa] 1 352 2 328 3 327 4 320

(31) Table 6 shows that samples made from an iron-based powder mixture containing the diffusion alloyed powder according to the invention exhibits increased fatigue strength compared to samples made from iron-based powder mixtures containing elemental copper powders or Known copper containing diffusion bonded powders.