KR101064429B1 - Iron-based powder composition including a silane lubricant - Google Patents

Abstract

The invention concerns a powder composition including an iron or iron based powder and a lubricating amount of an alkylalkoxy or polyetheralkoxy silane, wherein the alkyl or polyether group has between 8 and 30 carbon atoms and the alkoxi group includes 1-3 carbon atoms.

Description

Iron-based powder composition comprising a silane lubricant {IRON-BASED POWDER COMPOSITION INCLUDING A SILANE LUBRICANT}

The present invention relates to novel metal powder compositions useful in the powder metallurgy industry. The present invention also relates to a method for producing a component having a high density by using these compositions.

Compared with the corresponding conventional full dense steel process, several advantages exist by using powder metallurgical methods to manufacture structural parts. Therefore, energy consumption is much smaller and material utilization is much greater. Another important factor when using powder metallurgical routes is that the net or nearly net shaped parts are sintered without expensive molding processes such as turning, milling, boring or grinding. It can be produced immediately. In general, however, fully dense steel materials have good mechanical properties compared to PM parts. This is mainly because voids occur in PM parts. Therefore, efforts have been made to increase the density of PM components in order to reach values as close as possible to the density values of fully dense steels.

Among the methods used to obtain higher density PM parts, the powder forging process has the advantage that a completely dense part may be obtained. However, the process is mainly used for mass production of expensive and heavier parts such as connecting rods. Fully dense material can be obtained by high pressure at high temperatures, such as in hot isostatic molding (HIP), but this method is expensive.

By using warm compaction, a process in which the molding is carried out at high temperatures, generally from 120 to 250 ° C., the density can be increased to about 0.2 g / cm 3, which leads to a significant improvement in mechanical properties. However, a disadvantage is that the warm forming method involves additional investment costs and processes. Other processes such as double pressing, double sintering, sintering at high temperature, etc. may also increase the density. These methods will also incur additional manufacturing costs and reduce the overall cost efficiency.

There is a need for a simple and inexpensive method of achieving high density compacts with improved mechanical properties to expand the marketability of powder metallurgical parts and to take advantage of powder metallurgy techniques.

It has now been found that high density parts can be obtained unexpectedly using high molding pressures with novel forms of powder compositions. A distinguishing feature of these compositions is that up to about 5% of the particles of iron or iron-based powder have a size of 45 μm or less and the composition comprises a predetermined amount of a lubricant of alkylalkoxy or polyetheralkoxy silane. The invention also relates to a process for producing green and optionally sintered green compacts from these compositions. The method comprises providing a composition; Optionally mixing the composition with other additives such as graphite and alloying elements, machinability enhancers, and the like; Molding the composition uniaxially at high pressure in a die and injecting a green body, which may be subsequently sintered.

Another aspect of the invention relates to a composition having a silane form in combination with iron or iron-based powders, ie in combination with powders conventionally used, regardless of particle size. Also in this case a fairly high density may be obtained.

The term "high density" means a green compact having a density of at least about 7.3 g / cm 3. "High density" is not an absolute value. The density that can generally be achieved according to the prior art for a single pressed, single sintered part is about 7.1 g / cm 3. An increase of about 0.2 g / cm 3 may be achieved by using warm forming.

The term “high density” herein means a green compact having a density of about 7.35-7.65 g / cm 3, depending on the type and amount of additive used and the type of iron-based powder used. Also parts with lower densities can be made but that is not of interest here.

Iron-based powders according to the present invention include pure iron powders such as water or gas atomized iron powder, spongy iron powder, reduced iron powder; Partially diffused alloy steel powder; And fully alloyed steel powders. The partially diffusion alloy steel powder is preferably a steel powder partially alloyed with at least one of Cu, Ni and Mo. The fully 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. Stainless steel powders are also of interest.

With regard to the particle morphology, the particles preferably have an irregular shape as obtained by water atomisation. Spongy iron also has irregularly shaped particles and may be of interest.

One feature of the present invention is that the powder used has granulated particles, ie the powder is essentially free of fine particles. The expression “basically free of particles” means that about 5% or less of the iron or iron-based powder particles have a size of 45 μm or less, as measured by the method described in SS-EN 24 497. The most interesting results so far have been achieved with powders consisting essentially of particles of at least about 106 μm and in particular at least about 212 μm. The expression “consist essentially of” means that at least 40%, preferably at least 60%, of the particles have a particle size of at least 106 and 212 μm, respectively. So far the best results have been obtained with powders having an average particle size of about 212 μm or more and only 212 μm or less. The maximum particle size may be about 2 mm. The particle size distribution in the iron-based powders used for PM production is generally a Gaussian distribution with an average particle diameter in the range of 30 to 100 μm and about 10-30% below 45 μm. Basically iron-based powder free of fine particles may be obtained by removing finer portions of the powder or by preparing a powder having a desired particle size distribution.

The influence of particle size distribution and the shape of particles on the molding properties and the properties of the molded body have been extensively studied. U. S. Patent No. 5,594, 186 discloses a method for producing PM parts having a density of at least 95% of theoretical density by using a substantially linear, acicular metal powder having a triangular cross section. Powders with granulated particles are also used in the manufacture of soft magnetic components as disclosed, for example, in US Pat. Nos. 6,309,748 and 4,190,441.

An important feature according to the present invention for obtaining high density products is the type and amount of lubricant. A special type of lubricant that has not been used previously with regard to metal powders gives very promising results.

These lubricants belong to the group of alkylalkoxy or polyether silanes and more specifically alkylalkoxy or polyether silanes wherein at least one substituent to the Si atom is an alkyl group having at least 8 carbon atoms, the alkyl group being at least one O atom It may be interrupted. Compounds containing at least one oxygen atom in which an alkyl group is used according to the invention are referred to as polyether silanes. The chain length of the alkyl or polyether groups is an important feature of the silanes used according to the invention and affects the lubricating properties of the silanes. It is known that by far the most interesting results have been obtained with alkyl or polyether chains having carbon atoms in the range of 8 to 30, preferably in the range of 10 to 24. Preferably the silane is selected from the group consisting of octyl-tri-methoxy silane, hexadecyl-tri-methoxy silane and polyethyleneether-trimethoxy silane having ten ethyleneether groups.

Herein very small amounts of the total composition formed in U.S. Pat. It is mentioned that it may be used as a surface treatment agent for powders. In the first four US patents the following silane compounds, γ-methacryloxypropyl trimethoxy silane, γ-glycidoxypropyl trimethoxy silane, N-beta (aminoethyl) -γ-trimethoxy silane, methyl Trimethoxy silane, phenyl trimethoxy silane and diphenyl dimethoxy silane were tested. In US Pat. No. 6,451,082, compounds triphenylmethoxysilane, diphenyldimethoxysilane, phenyltrimethoxysilane, isobutyltrimethoxysilane, and methyltriethoxysilane were used. The organosilane forms with lubricating effect used according to the invention are not mentioned or tested.

Organosilanes with a lubricating effect used according to the invention are preferably used in such a way that they are dissolved or dispersed in a suitable solvent, for example an organic solvent such as acetone or ethanol. The solution or dispersion obtained is subsequently added to the iron-based powder during mixing and optionally heating. The solvent is optionally finally evaporated in vacuo.

In accordance with a preferred embodiment of the present invention and with conventional practice in powder metallurgy, where conventional PM lubricants are used in iron powder mixtures, or when lubricants are used in combination with binders and / or surface treatment agents as mentioned in the aforementioned US patents; In contrast, the iron or iron based powder should not be mixed with a separate (typical) lubricant before being delivered to the die. External lubrication (die wall lubrication) need not be used, where lubricant is provided to the walls of the die before molding is performed. However, the present invention does not exclude the possibility of using conventional internal lubrication (in amounts up to 0.5% by weight), external lubrication, or combinations thereof, if of interest.

In certain applications trace amounts of graphite need to be added to the powder mixture to be shaped. Therefore, graphite in the range of 0.1-1.0, preferably 0.2-1.0 and most preferably 0.3-0.8% by weight of the total mixture to be molded should be added before molding.

Alloying elements, machinability enhancing compounds, hard phase materials and flow agents, including Mn, Cu, Ni, Cr, Mo, V, Co, W, Nb, Ti, Al, P, S, and B; Other additives such as may also be added to the iron-based powder prior to molding.

The expression "high molding pressure" means a pressure of about 800 MPa or more. More interesting results are obtained with higher pressures, such as at least 900, preferably at least 1000, more preferably at least 1100 MPa. Conventional molding of conventionally used powders containing particulates at high pressures, ie pressures above about 800 MPa, is generally considered inadequate because of the large forces required to inject the green compacts from the dies, resulting in large wear of the dies and This is due to the fact that the surface of the part tends to be shiny or degraded. By using the powders according to the invention unexpectedly the injection force is reduced at high pressure, about 1000 MPa, and parts with acceptable or even perfect surfaces may be obtained.

Molding may be carried out with standard equipment, which means that the new process may be carried out without expensive costs. Molding is performed monoaxially and preferably in a single step at ambient or elevated temperatures. Alternatively molding may be carried out with the aid of a percussion machine (model HYP 35-4 made from Hydropulsor) disclosed in patent publication WO 02/38315.

Sintering may be carried out at temperatures generally used in the PM field, for example at low temperatures in the range of 1100 to 1140 ° C or high temperatures of 1200-1300 ° C and conventionally used atmospheres or vacuums.

Other treatments of green or sintered parts may also be applied, such as green machining, surface treatment, surface densification, steam treatment.

Briefly, the advantage obtained by using the process according to the invention is that high density green compacts can be produced at low cost. The novel method also allows the manufacture of larger parts that are difficult to manufacture by using conventional techniques. Additionally standard molding equipment can be used to produce high density green compacts with acceptable or even perfect surface finish.

Examples of products that can be properly manufactured by the novel method are connecting rods, cam lobes, gears and other structural parts subjected to high loads. By using stainless steel powder, the flange is of particular interest.

Silanes with a lubricating effect have been disclosed, particularly with regard to granulated powder, since the main object of the present invention is to achieve high density products. However, it is known that these silanes can also be used in combination with the form of powders containing higher amounts of particulates, ie, powders commonly used in the PM industry today. Example 4 below describes the effect of silanes according to the invention on conventional powders and granulated powders. As can be seen here very high densities are obtained with conventional powders containing higher amounts of particulates. Compositions comprising iron or iron-based powders having a general particle size distribution and silanes according to the invention are of particular interest in the field and are also within the scope of the invention.

The invention is illustrated in more detail by the following examples.

1-1 is a graph depicting green density versus molding pressure in two compositions,

1-2 are graphs showing injection force versus molding pressure in two compositions,

2-1 is a graph depicting green intensity versus green density in two compositions,

2-2 are graphs showing green strength versus molding pressure in two compositions,

3-1 is a graph showing particle size versus injection force and green density,

3-2 is a graph depicting% silane versus injection force and green density.

Example 1

0.1 and 0.15% of an iron-based powder composition made from Astalloy Mo, a prealloyed iron-based powder alloyed with molybdenum at 1.5% by weight, available from Hoganas Avessa, Sweden, with no particles below 212 μm. Were mixed with hexadecyl trimethoxy silane of. The mixing process was carried out as follows: hexadecyl trimethoxy silane was diluted in ethanol to form a 20% by weight solution and the solution was stirred for 60 minutes. An amount of the solution corresponding to 0.1 and 0.15% by weight, respectively, was added to the iron-based powder mixture during mixing, and the iron-based powder mixture was already heated to 75 ° C. in the mixer. Strong mixing is carried out for 3 minutes in the same mixer, followed by slow mixing for 30 minutes and in vacuum to evaporate the solvent. The resulting mixture was filtered through a 500 μm sieve.

Rings with an inner diameter of 35 mm and an outer diameter of 14 mm and a height of 10 mm were molded uniaxially in a single step at different molding pressures. As can be seen from Fig. 1-1, a green density of 7.67 g / cm 3 was obtained at a pressure of 1100 MPa for both compositions. The total energy required for injection in green compacts prepared from a composition having 0.15% silane is slightly less than the total energy required for injection of green compacts prepared from powder treated with 0.1 wt% silane, which is shown in FIG. This can be seen in 2.

Example 2

The same powders and procedures as in Example 1 were used except that the powder was mixed with 0.2% by weight of hexadecyl trimethoxy silane. Two compositions were prepared, one having 0.2 wt% graphite and the other having 0.6 wt% graphite. Green density and green strength were measured.

As can be seen from FIGS. 2-2, a green density of at least 7.65 g / cm 3 was obtained for green parts molded at 1200 MPa and containing 0.2% graphite. A green density of 7.58 g / cm 3 was obtained for green parts containing 0.6% graphite.

2-1 shows that the green strength increases with increasing molding pressure and the green strength is high enough to allow processing of the green part.

Example 3

This example has the effect of removing different portions of the iron-based powder. Four different iron-based powder compositions were tested. The three iron based powder compositions contained Astaloy Mo containing 0.2% hexadecyl trimethoxy silane and the mixing procedure of Example 1 was used. The first composition contained granules of ataloidal Mo than 45 μm, the second composition contained moles of granules of acetone than 106 μm and the third composition contained granules of atalloy Mo. The fourth composition contained Astalloy Mo with particles of granulation more than 212 μm. Particles of the composition were mixed with 0.1 wt% hexadecyl trimethoxy silane. Moreover, all compositions contained 0.2% graphite. All compositions were molded uniaxially in a single step in the die to form a ring having an outer diameter of 35 mm, an inner diameter of 14 mm and a height of 10 mm.

3-1 shows that as the particle size increases, the green density increases and the injection force decreases.

3-2 shows that the injection force decreases when the amount of silane is increased from 0.1% by weight to 0.2% by weight.

Example 4

This example illustrates the effect of the amount of silane addition, particle size distribution and chain length of alkyl or polyether groups on lubrication properties during injection after molding at high pressure. Two types of powder, i.e., standard 100 mesh iron-based powder (S-powder), which is an Asterloy 85 Mo with about 20% of particles smaller than 45 μm, have a weight average particle size of about 212 μm with the same chemical composition without particulates. Powder having (C-powder) was used. Five different kinds of silanes were used according to Table a.

A methyl-trimethoxy silane

B propyl-trimethoxy silane

C octyl-trimethoxy silane

D hexadecyl-trimethoxy silane

E polyethyleneether-trimethoxy silane having 10 ethylene ether groups.

Different amounts of silane were added to the iron-based powder and the resulting mixture was molded at 1100 MPa with uniaxial press movement in slugs having a diameter of 25 mm and a height of 12 mm. Dynamic injection force was measured during injection as indicated in Table a above and green surface finish after injection was evaluated and density was measured.

As can be seen from Table a, a chain length of 8 or more atoms in the alkylene chain is necessary for successful injection of the part for the amount of added silane of 0.05 to 0.5%. Addition amounts of 0.5% or more are not of interest because the density of the green parts is adversely affected. Table a also indicates that injection is impossible for silanes having a chain length of 30 atoms without damaging the surface of the part and die when the silane content is 0.05% or less.

Assuming that the amount of silane added from Table a is 0.5% or less and the length of the alkylene or polyethyleneether chain is at least 8 atoms, a powder with a standard particle size distribution is molded to a high density of at least 7.60 g / cm 3, and successfully Can be concluded.

Claims (21)

A powder composition comprising iron or iron-based powder having a size of greater than 0 wt% and less than or equal to 5 wt% of the powder particles and an alkylalkoxy or polyetheralkoxy silane which is a lubricant, Wherein the alkyl group of the alkylalkoxy silane and the polyether chain of the polyetheralkoxy silane comprise 8 to 30 carbon atoms, and the alkoxy group comprises 1 to 3 carbon atoms, Powder composition. The method of claim 1, Wherein said alkyl group and polyether chain of said alkylalkoxy or polyetheralkoxy silane have from 10 to 24 carbon atoms, Powder composition. The method according to claim 1 or 2, The silane is selected from the group consisting of octyl-trimethoxy silane, hexadecyl-trimethoxy silane, polyethyleneether-trimethoxy silane having ten ethylene ether groups, Powder composition. The method of claim 3, wherein The alkoxy silane is present in an amount in the range of 0.05-0.5 wt%, Powder composition. The method of claim 4, wherein At least 40% of the iron or iron-based powder is composed of particles having a particle size of 106 ㎛ or more, Powder composition. The method of claim 5, At least 40% of the iron-based powder is composed of particles having a particle size of 212㎛ or more, Powder composition. The method of claim 6, Further comprising up to 1% by weight graphite, Powder composition. The method of claim 7, wherein Further comprising up to 10% by weight of alloying elements, Powder composition. The method of claim 8, The alloying element is selected from the group consisting of Mn, Cu, Ni, Cr, Mo, V, Co, W, Nb, Ti, Al, P, S and B, Powder composition. As a method for producing a high density green compact, Providing an iron-based powder composition according to claim 9; Optionally mixing the composition with graphite and other additives; Compacting the powder on a single axis at a compression pressure of at least 800 MPa in the die; And Injecting said powder into a living body, Method for producing high density green compacts. delete delete delete delete delete delete delete The method of claim 3, wherein The alkoxy silane is present in an amount in the range of from 0.1 to 0.4% by weight, Powder composition. The method of claim 3, wherein The alkoxy silane is present in an amount ranging from 0.15 to 0.3 wt% Powder composition. delete delete

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