Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/05—Metallic powder characterised by the size or surface area of the particles
  • B22F1/052—Metallic powder characterised by the size or surface area of the particles characterised by a mixture of particles of different sizes or by the particle size distribution
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/02—Compacting only
  • B22F2003/023—Lubricant mixed with the metal powder

Definitions

• the present invention relates to new metal powder compositions useful within the powder metallurgical industry.
• the invention also concerns a method for the preparation of high density metal components by using these compositions.
• the powder forging process has the advantage that full dense components may be obtained.
• the process is however costly and is utilised mainly for mass production of heavier components, such as connection rods.
• Full dense materials can also be obtained by elevated pressures at high temperatures, such as in hot isostatic pressing, HIP, but also this method is costly.
• warm compaction a process where the compaction is performed at an elevated temperature, typically at 120 to 250 °C, the density can be increased with about 0,2 g/cm 3 , which results in a considerable improvement of the mechanical properties.
• a disadvantage is however that the warm compaction method involves additional investment and processing. Other processes, such as double pressing, double sintering, sintering at elevated temperatures etc, may further increase the density. Also these methods will add further production costs hence reducing the overall cost effectiveness. In order to expand the market for powder metallurgical components and utilise the advantages with the powder metallurgical technique there is thus a need for a simple, less expensive method of achieving high density compacts with improved mechanical properties.
• compositions can be obtained by using high compaction pressures in combination with a new type of powder compositions. Distinguishing features of these compositions are that less than about 5 % of the particles of the iron or iron-based powder have a size below 45 ⁇ m and that the compositions include a lubricating amount of an alkylalkoxy or polyetheralkoxy silane.
• the present invention also includes a method of preparing green and optionally sintered compacts from these compositions.
• This method comprises the steps of providing the composition, optionally mixing said composition with graphite and other additives such as alloying elements, machinability improving agents etc; uniaxially compacting the composition in a die at high pressure and ejecting the green body, which may subsequently be sintered.
• compositions with this type of silanes in combination with iron or iron based powders irrespective of particle size i.e. in combination with powders conventionally used. Also in this case quite high densites may be obtained.
• high density is intended to mean compacts having a density of about at least 7.3 g/cm 3 . "High density” is not an absolute value.
• a typical achievable density according to the state of the art for single pressed, single sintered components is about 7,1 g/cm . By using warm compaction an increase of about 0,2 g/cm may be reached.
• high density is intended to mean compacts having a density of about 7.35-7.65 g/cm 3 and above, depending of type and amount of additives used, and type of iron- based powder used. Components having lower densities can of course also be produced but are believed to be of less interest.
• the iron-based powder according to the present invention includes pure iron powder, such as water or gas atomised iron powder, sponge iron powders, reduced iron powder; partially diffusion-alloyed steel powder; and completely alloyed steel powder.
• the partially diffusion- alloyed steel powder is preferably a steel powder alloyed partially with one or more of Cu, Ni, Mo,.
• the completely alloyed steel powder is preferably a steel powder alloyed with Mn, Cu, Ni, Cr, Mo, V, Co, W, Nb, Ti, Al, P, S and B. Also stainless steel powders are of interest.
• the particles have an irregular form as is obtained by water atomisation.
• sponge iron powders have irregularly shaped particles and may be of interest.
• the powder used have coarse particles i.e. the powder is essentially without fine particles.
• the term "essentially without fine particles” is intended to mean that less than about 5 % of the iron or iron-based powder particles have size below 45 ⁇ m as measured by the method described in SS-EN 24 497. So far the most interesting results have been achieved with powders essentially consisting of particles above about 106 ⁇ m and particularly above about 212 ⁇ m.
• the term "essentially consisting” is intended to mean that at least 40 %, preferably at least 60 % of the particles have a particle size above 106 and 212 ⁇ m, respectively.
• the maximum particle size may be about 2 mm.
• the particle size distribution for iron-based powders used at PM manufacturing is normally distributed with a gaussian distribution with a average particle diameter in the region of 30 to 100 ⁇ m and about 10-30 % less than 45 ⁇ m.
• Iron based powders essentially free from fine particles may be obtained by removing the finer fractions of the powder or by manufacturing a powder having the desired particle size distribution.
• a critical feature according to the invention in order to obtain the high density products is the type and amount of lubricant. It has thus been found that a specific type of lubricants which has previously not been used in connection with metal powders give very promising results. These lubricants belongs to the group of alkylalkoxy or polyether silanes and more specifically alkylalkoxy or polyether silanes wherein at least one substituent on the Si atom is an alkyl group having at least 8 carbon atoms, wherein the alkyl group may be interrupted by one or more O atoms.
• the compounds wherein the alkyl group includes one or more oxygen atoms used according to the present invention are called polyether silans
• the chain length of the alkyl or polyether group is an important feature of the silanes used according to the present invention and have an influence on the lubricating properties of the silane. So far it has been found that the most interesting results are obtained with alkyl or polyether chains having between 8 and 30, preferably between 10 and 24 carbon atoms.
• the silane is selected form the group consisting of octyl-tri-metoxy silane, hexadecyl-tri-metoxy silane and polyethyleneether-trimetoxy silane with 10 ethyleneether groups.
• the organosilane with lubricating effect used according to the present invention is preferably used in such a way that it is dissolved or dispersed in a suitable solvent, e.g. an organic solvent, such as acetone or ethanol.
• a suitable solvent e.g. an organic solvent, such as acetone or ethanol.
• the obtained solution or dispersion is subsequently added to the iron based powder during mixing and optionally heating.
• the solvent is finally evaporated optionally in vacuum.
• the iron or iron based powder must not be mixed with a separate (conventional) lubricant before it is transferred to the die.
• a separate (conventional) lubricant nor is it necessary to use external lubrication (die wall lubrication) where the walls of the die are provided with a lubricant before the compaction is performed.
• the invention does not exclude the possibility of, when it is of interest ,to utilise conventional internal lubrication (in an amount up to 0.5 % by weight), external lubrication or a combination of both.
• graphite in amounts between 0.1 - 1.0, preferably 0.2 - 1,0 and most preferably 0.3-0.8 % by weight of the total mixture to be compacted should be added before the compaction.
• additives which may be added to the iron-based powder before compaction such as alloying elements comprising Mn, Cu, Ni, Cr, Mo, V, Co, W, Nb, Ti, Al, P, S and B ma- chinability enhancing compounds, hard phase material and flow agents.
• At high compaction pressure is intended to mean at pressures of about at least 800 MPa. More interesting results are obtained with higher pressures such as pressures above 900, preferably above 1000, more preferably above 1100 MPa.
• Conventional compaction at high pressures i.e. pressures above about 800 MPa with conventionally used powders including finer particles, are generally considered unsuitable due to the high forces required in order to eject the compacts from the die, the accompanying high wear of the die and the fact that the surfaces of the components tend to be less shiny or deteriorated.
• the powders according to the present invention it has unexpectedly been found that the ejection force is reduced at high pressures, about 1000 MPa, and that components having acceptable or even perfect surfaces may be obtained.
• the compaction may be performed with standard equipment, which means that the new method may be performed without expensive investments.
• the compaction is performed uni- axially and preferably in a single step at ambient or elevated temperature.
• the compaction may be performed with the aid of a percussion machine (Model HYP 35-4 from Hydropulsor) as described in patent publication WO 02/38315.
• the sintering may be performed at the temperatures normally used within the PM field, e.g. at low temperature such as 1100-1140°C or higher temperatures such as 1200-1300°C and in conventionally used atmospheres or vacuum.
• the advantages obtained by using the method according to the present invention are that high density green compacts can be cost effectively produced.
• the new method also permits production of higher components which are difficult to produce by using the conventional technique.
• standard compaction equipment can be used for producing high density compacts having acceptable or even perfect surface finish.
• silanes having lubricating effect have been described particularly in connection with coarse powders. It has however also been found that these silanes may also be used in combination with powder including higher amounts of fine particles i.e. the type of powders which are conventionally used in the PM industry today.
• Example 4 below illustrates the effect of the silanes according to the present invention on both conventional powders and coarse powders. As can be seen very high densities are obtained also with a conventional powder including higher amounts of fine particles.
• Compositions including iron or iron-based powders with the usual particle size distributions and the silanes according to the present invention may be of special interest for certain applications and are also within the scope of the invention.
• Iron-based powder composition prepared from AstaloyMo which is a prelloyed iron based powder alloyed with 1.5 % by weight of molybdenum available from Hoganas AB, Sweden, and where particles less than 212 ⁇ m had been eliminated was mixed with 0.1 and 0.15 %, respectively, of hexadecyl trimethoxy silane.
• the mixing process was performed as follows: hexadecyl trimethoxy silane was diluted in ethanol to a 20 % solution, by weight, and the solution was stirred during 60 minutes. An amount of this solution corresponding to 0.1 and 0.15 % by weight, respectively, was added during mixing to the iron based powder mixtures, which had previously been heated to 75 °C in the mixer. An intensive mixing was carried out in the same mixer during 3 minutes followed by mixing at a lower speed during 30 minutes and during vacuum in order to evaporate the solvent. The obtained mixture was sieved with a 500 ⁇ m sieve.
• Rings with an inner diameter of 35 mm and an outer diameter of 14 mm and a height of 10 mm were uniaxially compacted in a single step at different compaction pressures.
• green densities of 7.67 g/cm were obtained at a pressure of 1100 MPa for both compositions.
• the total energy needed for ejection is somewhat lower for the compacts prepared from the composition with 0.15 % of silane than for ejection of the compacts prepared from the powder which had been treated with 0.1 % by weight of silane, see figure 1-2.
• Example 2 The same powder and the same procedure as in Example 1 was used except that the powder was mixed with 0.2 % by weight of hexadecyl trimethoxy silane. Two compositions were prepared, one with. 0.2 % by weight of graphite and the other with 0.6 % by weight of graphite. The green density and the green strength were measured.
• Figure 2-1 shows that the green strength increases with increasing compaction pressure and that the green strength is high enough to allow handling of the green components.
• This example shows the effect of the eliminating different fractions of the iron based powder, four different iron based powder compositions were tested.
• Three of the iron based powder compositions contained Astaloy Mo including 0.2 % hexadecyl trimethoxy silane and the mixing procedure in example 1 was used.
• the first composition contained Astaloy Mo coarser than 45 ⁇ m
• the second composition contained Astaloy Mo coarser than 106 ⁇ m
• the third composition contained Astaloy Mo coarser than 212 ⁇ m.
• the fourth composition contained Astaloy Mo having particles coarser than 212 ⁇ m.
• the particles of this composition were mixed with 0.1 % by weight of hexadecyl trimethoxysilane.
• all compositions contained 0.2 % of graphite. All compositions were uniaxially compacted in a single step in a die forming rings with an outer diameter of 35 mm, inner diameter of 14 mm and a height of 10 mm.
• Figure 3-1 shows that the green densities increased and the ejection forces decreased with increasing particles sizes.
• Figure 3-2 shows that the ejection forces decrease when the amount of silane is increased from 0.1 to 0.2 % by weight.
• This example demonstrates the effect of the chain length of the alkyl or polyether group, the particle size distribution and the added amount off silanes on the lubricating properties at ejection after compaction with high pressures.
• Two kinds of powder were used, namely a standard 100 mesh iron- based powder, Astaloy 85 Mo with about 20 % of the particles less than 45 ⁇ m (S- powder) and a powder having the same chemical composition without fine particles and a weight average particle size of about 212 ⁇ m, (C-powder).
• a chain length of at least 8 atoms in the alkylene chain is needed in order to successfully eject the component for an added amount of silanes of 0,05- 0,5 %. Added amounts above 0,5 % is believed to be of less interest as the density of the green component while be negatively influenced.
• the table also shows that when the silane content is less than 0,05 % ejection without damaging the component and the surface of the die is not possible for silanes with a chain length of 30 atoms.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Powder Metallurgy (AREA)
• Lubricants (AREA)

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• 2002
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• 2003
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