Powder for molding, lubricant-concentrated powder and method for producing metal member

Abstract

A powder for molding is a mixture of first constituent particles, which are made up of first metal base particles, and second constituent particles, which are made up of second metal base particles. A first lubricant concentration that is a mass proportion of a first internal lubricant adhered to the surface of the first metal base particles with respect to the total of the first constituent particles, is greater than a second lubricant concentration that is a mass proportion of a second internal lubricant that is adhered to the surface of the second metal base particles with respect to the total of the second constituent particles.

Claims

1. A powder for molding, comprising: first constituent particles including first metal base particles and a first internal lubricant adhered to a surface of the first metal base particles, the first internal lubricant is a composite of at least two types of lubricant; and second constituent particles including second metal base particles and a second internal lubricant that is adhered to a surface of the second metal base particles, the second internal lubricant is a composite of at least two types of lubricant, the composite of the second internal lubricant is different than the composite of the first internal lubricant; wherein the first constituent particles are different than the second constituent particles, the first constituent particles and the second constituent particles are mixed, and a first lubricant concentration is a mass proportion of the first internal lubricant adhered to the surface of the first metal base particles with respect to a total of the first constituent particles, a second lubricant concentration is a mass proportion of the second internal lubricant that is adhered to the surface of the second metal base particles with respect to the total of the second constituent particles, and the first lubricant concentration is greater than the second lubricant concentration, wherein a total amount of internal lubricant is 0.35 mass % or less with respect to 100% as the whole powder.

2. The powder for molding according to claim 1, wherein the first metal base particles have a first average particle diameter and the second metal base particles have a second average particle diameter, the first average particle diameter is greater than the second average particle diameter.

3. The powder for molding according to claim 1, wherein a lubricant concentration ratio (Lr=L2/L1) of the second lubricant concentration (L2) with respect to the first lubricant concentration (L1) ranges from 0.01 to 0.5.

4. The powder for molding according to claim 1, wherein the first lubricant concentration ranges from 0.4 to 5 mass %, and the second lubricant concentration is 0.2 mass % or less.

5. The powder for molding according to claim 1, wherein the first metal base particles are different than the second metal base particles.

6. The powder for molding according to claim 1, wherein the content of the first constituent particles is 3 to 30 mass % with respect to 100% as the whole powder.

7. The powder for molding according to claim 1, wherein the first metal base particles and the second metal base particles include iron base particles; and the composite of the first internal lubricant includes one or more from among fatty acid amides, higher alcohols, ester waxes, amide waxes and metal soaps.

8. A method for producing a metal member, comprising: warm-molding a molded compact by pressing the powder for molding according to claim 1 inside a heated die.

9. The method for producing a metal member according to claim 8, further comprising: sintering a sintered compact by heating the molded compact.

10. A lubricant-concentrated powder, comprising: metal base particles, wherein a concentrated internal lubricant is adhered to a surface of the metal base particles; a lubricant concentration, which is a mass proportion of the internal lubricant with respect to the metal base particles, ranges from 1 to 5 mass %; and the lubricant-concentrated powder constitutes a supply source of the first constituent particles according to claim 1.

11. The lubricant-concentrated powder according to claim 10, wherein the lubricant-concentrated powder is obtained by mixing of a metal powder of the metal base particles and the internal lubricant fully melted.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

(2) FIG. 1A is a scanning electron microscope (SEM) micrograph of a constituent particle of a ML2 powder;

(3) FIG. 1B is a SEM micrograph of a constituent particle of a standard powder;

(4) FIG. 2A is a SEM micrograph of the surface of a molded compact resulting from molding using a MLG2 powder;

(5) FIG. 2B is a SEM micrograph of the surface of a molded compact resulting from molding using a standard powder; and

(6) FIG. 3 is a graph illustrating a relationship between lubricant concentration ratio and ejection force.

DETAILED DESCRIPTION OF EMBODIMENTS

(7) The content of the explanation in the specification applies suitably not only to the powder for molding and the lubricant-concentrated powder of the invention, but also to a molded compact or sintered compact (metal member) that is produced using the powder for molding, and to a method for producing that metal member. The description relating to the method, when understood as product-by-process, applies likewise to constituent elements relating to that product. Any one or more features selected from the specification may be freely added to the abovementioned invention. The intended purpose and required performance, among other factors, will determine whether any given embodiment is optimal or not.

(8) Starting Material Powder

(9) (1) Metal Base Particles (Metal Powder)

(10) The metal base particles according to the invention have no preferred composition, form, or type, but are typically iron base particles having iron (Fe) as a main component. The composition of the iron base particles may include pure iron or iron alloys. The metal base particles (or powder thereof) may be made up of a powder of a single type, or may be a combination of two or more types of simple powders having dissimilar compositions, production methods, particle shape distributions and the like. For instance, an iron-based powder made up of iron base particles may be a mixed powder of pure iron powder and an alloy powder made up of an iron alloy or a non-iron alloy, or may be a mixed powder of two or more atomized powders (for instance, water-atomized powders or gas-atomized powders) obtained through dissimilar production methods and having dissimilar particle shapes (grain shapes).

(11) (2) Strengthening Powder, Modifying Powder

(12) The metal member of the invention may be a molded compact such as a powder magnetic core, or a sintered compact that constitutes a structural member or the like. In a case where the metal member of the invention is a sintered compact, the starting powder may include strengthening elements and/or modifying elements. Characteristics amenable to strengthening include, for instance, strength, elongation and toughness, while characteristics amenable to modification include, for instance, sinterability, dimensional stability and machinability. Examples of such elements include, for instance, C, Cu, Ni, Cr, Mn, Si, V, Mo, P, S, W and the like. These elements may be incorporated into a powder of metal base particles; alternatively, a composition may be prepared through mixing of the foregoing, in the form of a separate powder (strengthening powder or modifying powder), into the starting powder. Examples of such powders include, for instance, graphite (Gr) powders, Cu powders, Cu alloy powders, Fe—Cr-alloy powders, Fe—Mo alloy powders, Fe—Mn—Si alloy powders, Fe—P powders and the like.

(13) The powder for molding of the invention may contain a CB powder, separately from a modifying powder such as graphite. A small amount of CB may enhance the fillability of the powder for molding in the die cavity. The content of CB may range from 0.005 to 0.05%, or yet 0.01 to 0.04%, with respect to 100% as the powder for molding as a whole.

(14) (3) Particle Size Distribution

(15) In the powder for molding of the invention, particles of large particle diameter may be used as the first metal base particles or the first constituent particles, while particles of small particle diameter may be used as the second metal base particles or the second constituent particles. These particle diameters are defined by particle sizes worked out through sieving according to JIS Z 8801 described above. Particle size is expressed herein as “−a μm”, “+b μm” or “−a μm/b μm”, where “−a μm” indicates that particles or a powder pass through a sieve of nominal opening a μm, and “+b μm” indicates that particles or a powder do not pass through a sieve of nominal opening b μm. Further, “−a μm/(+)b μm” indicates that particles or a powder pass through a sieve of nominal opening a μm, but not through a sieve of finer nominal opening b μm.

(16) Internal Lubricant

(17) The internal lubricant according to the invention has no preferred type, composition and so forth, and may be not only a single internal lubricant, but also a composite lubricant resulting from mixing two or more types. For instance, the internal lubricant according to the invention may be made up of a composite lubricant of one or more types of lubricant from among fatty acid amides, saturated fatty acids, higher alcohols, ester waxes, amide waxes and metal soaps. Examples of fatty acid amides include, for instance, one or more types from among stearic acid amide, ethylene-bis-oleamide, ethylene-bis-stearic acid amide, oleic acid amide, erucic acid amide, ethylene-bis-erucic acid amide and the like. Examples of saturated fatty acids include, for instance, palmitic acid, stearic acid, alginic acid, behenic acid and the like. Examples of higher alcohols include, for instance, one or more types from among behenyl alcohol, cetyl alcohol, stearyl alcohol, lignoceryl alcohol and the like. The content of higher alcohol may be set to range from 15 to 60%, or yet 5 to 45%, with respect to 100% as the total composite lubricant.

(18) Examples of ester waxes include, for instance, one or more types from among fatty acid alkyl esters, pentaerythritol fatty acid esters and the like. Examples of metal soaps include, for instance, one or more types from among zinc stearate, lithium stearate, calcium stearate, magnesium stearate and the like.

(19) Incidentally, the internal lubricant at the surface of the constituent particles plays also a role in preventing scattering of various modifying particles, CB particles and the like, through adhesion of these particles to the surface of the constituent particles. In this respect, the internal lubricant may be adhered, in small amounts, not only to the first constituent particles at which the internal lubricant is concentrated, but also to the second constituent particles. The internal lubricant that is adhered to the surface of the first constituent particles and the internal lubricant that is adhered to the surface of the second constituent particles may be of dissimilar type, composition and so forth, and may be adhered in accordance with dissimilar adhesion methods. The internal lubricant is not limited only to instances where the internal lubricant is supplied through adhesion to the surface of the metal base particles. For instance, the powder for molding of the invention may include very small amounts of a granular internal lubricant that has been separately mixed into the powder for molding.

(20) Molding and Sintering

(21) No preferred molding conditions apply to the powder for molding of the invention. The powder may be cold-molded or warm-molded, the molding pressure that is applied may range ordinarily from 400 to 850 MPa, although ultra-high pressure beyond these ranges may also be resorted to. The molding pressure depends also on the melting point of the lubricant that is used. Herein, the density of the molded compact and, accordingly, of the sintered compact, is increased by performing warm molding with a die temperature set to a range of 60 to 100° C. The use of the powder for molding of the invention for die-lubricated molding is not ruled out, although that is ordinarily not necessary, inasmuch as the powder for molding of the invention has an internal lubricant.

(22) There are no preferred sintering conditions, but sintering involves ordinarily furnace heating or high-frequency heating in an antioxidant atmosphere such as a nitrogen atmosphere, at a temperature range of 1050 to 1250° C., for 1 to 120 minutes. The sintered compact may be subjected, as appropriate, to various thermal treatments such as annealing, normalizing, aging, thermal refining (quenching, tempering), carburizing, nitriding and the like.

(23) Applications

(24) No particular restrictions apply to the forms and uses of the molded compact and sintered compact obtained from the powder for molding of the invention. Examples of the use of the sintered compact include, for instance, various types of pulleys, synchronizer hubs in transmissions, engine connecting rods, hub sleeves, sprockets, ring gears, parking gears, pinion gears and the like, in the automotive field. Other uses include, for instance, sun Gears drive gears, driven gears, reduction gears and the like.

FIRST EXAMPLE

(25) Preparation of a Sample Powder

(26) (1) Starting materials

(27) There were prepared a pure iron powder (ASC100.29/−212 μm, by Hoganas AB) made up of pure iron base particles, a graphite powder (Gr) (J-CPB/average particle diameter: 5 μm, by Nippon Graphite Industries), as a modifying powder, as well as the internal lubricants given in Table 1. The pure iron powder (metal powder) above was water-atomized in all instances.

(28) TABLE-US-00001 TABLE 1 Lubricant Generic Melting point denomination term Name (° C.) Product name Manufacturer kal Higher Behenyl alcohol 70 KALCOL Kao alcohol 220-80 Corporation S10 Fatty acid Stearic acid 102 ALFLOW NOF amide mono-amide S10 Corporation kenolub — — — Kenolub Hoganas AB

(29) (2) Master Lubricant

(30) Powder Preparation

(31) The pure iron powder above or a powder resulting from classifying the foregoing according to particle size, as well as the internal lubricants given in Table 1, were subjected to a complete melt mixing process, to prepare thereby a plurality of master lubricant powders (lubricant-concentrated powders) made up of particles (first constituent particles) on the surface whereof the internal lubricant was adhered at a high concentration. More specifically, there were prepared a pure iron powder, as procured (pure iron powder I), a pure iron powder resulting from sieving the procured pure iron powder to a particle size of −212 μm/+106 μm (pure iron powder II), and a pure iron powder similarly obtained, to a particle size of −106 μm (pure iron powder III). The lubricant kal and the lubricant S10 in Table 1 were each added, in an amount of 1%, to the powders (addition amount to a total 2% with respect to the powder as a whole after adjustment), followed by a full melt-mixing process.

(32) Three master lubricant powders were obtained as a result (also referred to as “ML powders”), namely a ML1 powder (pure iron powder I+1% kal+1% S10), a ML2 powder (pure iron powder II+1% kal+1% S10) and a ML3 powder (pure iron powder III+1% kal+1% S10). Unless otherwise indicated, the addition amount of internal lubricants, Gr and so forth in the specification refer to mass % (expressed simply as “%”) with respect to the powder as a whole after preparation.

(33) The full melt-mixing process was performed as described next. Firstly, the whole was mixed using a heat mixing apparatus (High-speed mixer LFS-SG-2J by Fukae Powtech) for 5 minutes, at 150 rpm agitator revolutions, and at a temperature of 150° C., at which all the internal lubricants melt completely. The obtained mixture was then cooled down to a temperature (room temperature) not higher than the melting point of the internal lubricants, and the resulting solidified product was crushed. Respective master lubricant powders were prepared in this manner.

(34) (3) Preparation of a Sample Powder (Powder for Molding)

(35) A base powder to be mixed with each of the master lubricant powders was prepared first. The base powder was prepared by subjecting the above-described pure iron powder (powder as procured, particle size: −212 μm), 0.88% of Gr, 0.05% of kal and 0.05% of S10, to the above-described full melt-mixing process. The total amount of internal lubricants in the base powder (hereafter also referred to as “BG powder”) was 0.1% with respect to the powder as a whole.

(36) Any one of the above-described ML powders was added, in an amount of 10%, to the BG powder, and the whole was mixed for 30 minutes in a ball mill. Three sample powders (MLG1 powder to MLG3 powder) were prepared that way. These were ML1 powder: BG powder+10% ML1 powder, ML2 powder: BG powder+10% ML2 powder, and ML3 powder: BG powder+10% ML3 powder. The total amount of internal lubricant in each powder was 0.3% with respect to the powder as a whole, in all cases.

(37) Further, a standard powder (Fe-0.8%+0.15% kal+0.15% S10) having a greater internal lubricant amount than that of the BG powder (Fe-0.88%+0.05% kal+0.05% S10) was also prepared by carrying out the above-described full melt-mixing process.

(38) A comparative powder (Fe-0.8%+0.3% kenolub) was further prepared through simple mixing, for 30 minutes in a ball mill, of the above-described pure iron powder (powder as procured, particle size: −212 μm), 0.8% of Gr and 0.3% of kenolub.

(39) Molding and Sintering

(40) (1) Molded compacts were produced using the sample powders described above, and respective sintered compacts (metal members) were produced through sintering of the molded compacts. Each molded compact was obtained by filling the cavity of a die, heated at 60° C., with 30 g of the respective sample powder, followed by pressing at 686 MPa (warm molding process). The die was made of an ultra-hard alloy. The cavity of the die was cylindrical, with ϕ23 mm. The surface roughness Ra (JIS) of the inner wall surface of the die was 0.1 μm.

(41) The flow rate (FR) and apparent density (AD) of each sample powder were measured in accordance with JIS Z 2502, 2504. The load (ejection force) necessary to eject the molded compact out of the die, after pressure molding of each sample powder, was measured using a load cell of a compression molding machine. The mass and dimensions of the molded compacts were measured to calculate the respective molded compact densities (G.D.). The results are summarized in Table 2.

(42) TABLE-US-00002 TABLE 2 Moldability Sinterability Molded Sintered dimensional compact density Ejection compact density change Powder FR AD G.D. force S.D. ΔD name (sec/50 g) (g/cm.sup.3) (g/cm.sup.3) (MPa) (g/cm.sup.3) (%) MLG1 25.3 3.28 7.32 12.8 7.27 0.16 MLG2 23.8 3.31 7.32 11.8 7.27 0.15 MLG3 24.6 3.26 7.32 13.1 7.27 0.16 Standard 23.6 3.28 7.33 14.3 7.27 0.16 Comparative 26.2 3.33 7.31 18.2 7.27 0.09

(43) The total amount of internal lubricant with respect to the powder as a whole is 0.3 mass % in all instances

(44) (2) The obtained molded compacts were heated in a nitrogen atmosphere at 1150° C. for 30 minutes, to yield a respective sintered compact. The mass and dimensions of each sintered compact were measured, to calculate respective sintered compact densities (S.D.) and dimensional changes (ΔD). These results as well are summarized in Table 2.

(45) Evaluation

(46) (1) Moldability

(47) A comparison between the standard powder and the comparative powder and the MLG1 to MLG3 powders in Table 2 reveals that the ejection force can be significantly reduced by using a powder having mixed thereinto constituent particles of dissimilar lubricant concentration. The reduction in ejection force was particularly significant in the ML2 powder, where a ML powder of large particle size was added to, and mixed with, the BG powder.

(48) The MLG1 to MLG3 powders (in particular, the MLG2 powder) exhibited also excellent powder fillability, as made apparent by the FR and AD.

(49) (2) Surface Observation

(50) FIG. 1A and FIG. 1B illustrate SEM images of observations of the surface of respective constituent particles of the ML2 powder and the standard powder. The portions visible as black in the micrographs are internal lubricant that is adhered to the particle surface. As FIG. 1A shows, the constituent particles of the ML2 powder have internal lubricant adhered thereon at a high concentration, so as to fill the recesses of the pure iron base particles. In the constituent particles of the standard powder, by contrast, a small amount of internal lubricant is adhered thinly and substantially uniformly over the surface of the pure iron base particles, as can be seen in FIG. 1B.

(51) The surfaces of respective molded compacts, obtained through warm molding of the standard powder and the MLG2 powder, in which the ML2 powder was added to the BG powder, were likewise observed. FIG. 2A and FIG. 2B illustrate the resulting SEM micrographs. The portions that appear black in the micrographs are internal lubricant. A comparison between the two micrographs reveals that, although the total amount of internal lubricant is identical in both instances, the molded compact in which the MLG2 powder is used exhibits more internal lubricant in the vicinity of the surface of the molded compact, and fewer portions at which the pure iron base particle is exposed (white portions). This indicates that a greater amount of lubricant seeps to the vicinity of the surface of the molded compact (boundary with the inner wall surface of the die) when molding is performed using the MLG2 powder.

SECOND EXAMPLE

(52) Preparation of a Sample Powder

(53) The first example showed that remarkable moldability is enhanced (in particular, in terms of reduction of ejection force) by using a powder for molding that includes coarse particles of high lubricant concentration (L1) (high-concentration coarse particles). Such being the case, an assessment was performed, as described below, on the influence exerted on moldability (in particular, ejection force) by a lubricant concentration ratio (Lr=L2/L1) in a powder for molding resulting from mixing a powder (low-concentration fine particles) made up of fine particles of low lubricant concentration (L2) and a powder (high-concentration coarse powder) made up of high-concentration coarse particles.

(54) Firstly, the pure iron powder (particle size: −212 μm) was classified, by sieving, into a coarse iron powder having a particle size: −150 μm/+106 μm and into a fine iron powder having a particle size: −106 μm. For reference, the particle size distribution of the pure iron powder (−212 μm) before particle size classification was ascertained for three lots. The results are given in Table 3. As the particle size distributions illustrated in Table 3 indicate, particles having a particle size: +150 μm and which constitute about 7 to 8%, are cut off as a result of the above-described particle size classification, such that about 17 to 20% is used as coarse iron powder, and the balance is used as fine iron powder.

(55) TABLE-US-00003 TABLE 3 Particle size distribution (mass %) −212 μm/ −180 pm/ −150 μm/ −106 μm/ −75 μm/ −63 μm/ Lot. No. +180 μm +150 μm +106 μm +75 μm +63 μm +45 μm −45 μm 1 1.2 6.0 16.6 20.9 12.5 18.8 23.9 2 1.1 6.4 18.9 22.5 12.6 18.2 20.3 3 1.0 6.9 19.5 22.7 12.2 17.8 19.8

(56) Respective sample powders illustrated in Table 4 were prepared using the coarse iron powders and fine iron powders described above, as well as Gr and the internal lubricants (kal and S10) described above. In each sample powder, the coarse iron powder and the fine iron powder were blended at a ratio (mass ratio) of 1:4. Herein, Gr was added in a proportion of 0.8% with respect to the total coarse iron powder or the total fine iron powder (Gr constitutes about 0.8% of the total sample powder).

(57) TABLE-US-00004 TABLE 4 Internal lubricant Lubricant concentration by powder Moldability Coarse Lubricant Molded iron Fine iron concentration compact powder powder ratio Total density Ejection Sample L1 L2 Lr lubricant FR AD G.D. force powder (%) (%) (L2/L1) (%) (sec/50 g) (g/cm.sup.3) (g/cm.sup.3) (MPa) 11 1.0 0.0 0.0 0.2 26.4 2.89 7.31 16.7 12 0.8 0.05 0.06 0.2 24.1 3.26 7.31 14.0 13 0.6 0.1 0.17 0.2 22.9 3.25 7.32 14.9 14 0.4 0.15 0.38 0.2 22.1 3.27 7.34 15.9 C1 0.2 1.0 0.2 21.5 3.28 7.34 17.3 C2 0.3 1.0 0.3 21.3 3.29 7.33 13.5 C3 0.4 1.0 0.4 21.1 3.27 7.32 11.3
Overall composition of sample powders: Fe-0.8% Gr+a % kal+a % S10 (a=t/2)
Coarse iron powder: fine iron powder=1:4 (mass proportion)

(58) The internal lubricants in each powder were kal:S10 of 1:1 (mass ratio). The internal lubricants were caused to be adhered to the particles by performing the above-described full melt-mixing process. The lubricant concentration or total amount of internal lubricant was set to vary for each sample powder. For a lubricant concentration of coarse iron powder of 0.8% in sample powder 12, for instance, kal and S10 adhered to the coarse iron powder in the sample powder 12 are each worked out as 0.8×(⅕)×(½)=0.08%, and the total amount of both lubricants adhered to the coarse iron powder in sample powder 12 is 0.16%. The lubricant concentration in the fine iron powder is 0.05%, and hence kal and S10 adhered to the fine iron powder in sample powder 12 are each worked out as 0.05×(⅘)×(½)=0.02%, and the total amount of both lubricants adhered to the fine iron powder in sample powder 12 is 0.04%. The total of internal lubricant adhered to the particles is 0.16+0.04=0.2%, when considering the sample powder 12 as a whole.

(59) Sample powders 11 to 14 result from mixing in a ball mill, for 30 minutes, coarse iron powders and fine iron powders having the internal lubricants separately adhered thereon as a result of the above-described full melt mixing. Sample powders C1 to C3, by contrast, result from performing the above-described full melt mixing on mixed powders that are obtained by mixing beforehand coarse iron powders and fine iron powders.

(60) Molding

(61) (1) The above-described sample powders were warm-molded in the same way as in the first example, to produce cylindrical molded compacts. The moldability of each sample powder at the time of molding was measured in the same way as in the first example. The obtained results are summarized in Table 4.

(62) (2) On the basis of the results in Table 4, FIG. 3 illustrates the relationship between lubricant concentration ratio and ejection force for sample powders 11 to 14 and sample powder C1, where the total amount of internal lubricant is 0.2%.

(63) Evaluation

(64) The density of the molded compacts exhibited no large differences, irrespective of the sample powder that was used. AD dropped significantly in sample powder 11, where no internal lubricant was adhered to the fine iron powder, but other powders exhibited no large difference in AD. FR and ejection force improved as the total amount of internal lubricant increased. For a given total amount of internal lubricant, a higher lubricant concentration in the low-concentration fine powder translated into higher fluidity.

(65) As FIG. 3 shows, a comparison between sample powders 11 to 14 and sample powder C1, all of which have the same total amount of internal lubricant, reveals that ejection force is further reduced when the lubricant concentration ratio (Lr=L2/L1), which is the ratio of the lubricant concentration (L2) of the fine iron powder with respect to the lubricant concentration (L1) of the coarse iron powder, lies within a specific range (for instance, 0.01 to 0.5). The total amount of internal lubricant in sample powder 12 is small, of 0.2%, but the powder exhibits an ejection force similar to that of sample powder C2, where the total amount of internal lubricant is 0.3%.

(66) Accordingly, it is found that the use amount of internal lubricant is reduced, and moldability is secured or enhanced, by combining powders that have dissimilar lubricant concentrations and/or particle sizes, and by using a high-concentration coarse powder and a low-concentration fine powder.