MXPA05004256A

MXPA05004256A - Method of preparing iron-based components by compaction with elevated pressures.

Info

Publication number: MXPA05004256A
Application number: MXPA05004256A
Authority: MX
Inventors: Hilmar Vidarsson
Original assignee: Ganaes Ab H
Priority date: 2002-10-22
Filing date: 2003-10-22
Publication date: 2005-07-05
Also published as: RU2005115474A; TW200417433A; EP1554071B1; ZA200501296B; PL375094A1; RU2333075C2; TW201127521A; AU2003269786B2; KR101179725B1; WO2004037468A1; JP4909514B2; JP2010189769A; CN1705533A; CA2495697C; BR0314079B1; ES2357741T3; CA2495697A1; AU2003269786A1; KR20050059285A; JP2006503983A

Abstract

The present invention concerns a process for the preparation of high density green compacts comprising the steps of providing an iron-based powder essentially free from fine particles; optionally mixing said powder with graphite and other additives; uniaxially compacting the powder in a die at a compaction pressure of at least about 800 MPa and ejecting the green body. The invention also concerns the powder used in the method.

Description

METHOD OF PREPARING IRON-BASED COMPONENTS BY HIGH PRESSURE COMPACTING FIELD OF THE INVENTION The present invention relates to metal powder compositions within the powder metallurgical industry. More specifically, the invention relates to a method for the preparation of components having high density, by the use of these compositions. There are several advantages to using powder metallurgical methods to produce structural parts, compared to conventional methods of adaptation of fully compact steel. Thus, the energy consumption is much lower and the use of material is much higher. Another important factor in favor of the powder metallurgical routine is that the components can be produced with exact form or almost exact form, directly after the sintering process without expensive forming procedures, such as turning, milling, drilling or burnishing. However, normally a completely compact material has superior mechanical properties, compared to the powder metallurgical (PM) components. This is mainly due to the presence of porosity in the PM components. Therefore, efforts have been made to increase the density of the PM components in order to achieve values as close as possible to the density value of a fully compact steel. Among the methods used in order to achieve a greater density than the PM components, the powder forging method has the advantage that completely compact components can be obtained. The process is however expensive and is mainly used for mass production of heavier components, such as connecting rods. Completely compact materials can also be obtained at high pressures and high temperatures, such as in hot isostatic pressing (HIP), but this method is also expensive. By the use of moderately hot compaction, a process in which compaction is performed at an elevated temperature typically at 120 and 250 ° C, the density can be increased by approximately 0.2 g / cm 3, which results in a considerable improvement of the mechanical properties. An advantage is however that the method of moderately hot compaction involves additional investment and processing. Other methods, such as double pressing, double sintering, sintering at elevated temperatures, etc., can further increase the density. Also these methods will add additional production costs, thereby reducing the joint costability. In order to extend the market for the powder metallurgical components and to utilize the advantages of the powder metallurgical technique, there is therefore a need for a simple, less expensive method of obtaining high density compacted products with improved static and dynamic mechanical strength.

BRIEF DESCRIPTION OF THE INVENTION It has now been found that high density components can be obtained by the use of high compaction pressures in combination with coarse powders. In view of the general knowledge that conventionally used powders, ie powders that include fine particles, can not be compacted at high densities without problems, for example with the damaged or deteriorated surfaces of the compacted products, this finding is quite unexpected. Specifically, the method according to the present invention includes the steps of providing an iron-based powder, essentially free of fine particles; optionally mixing said powder with graphite or other additives; uniaxially compact the mold powder and expel the uncooked body, which can be subsequently sintered.

DETAILED DESCRIPTION OF THE INVENTION The term "high density" means compacted products having a density of at least about 7.3 g / cm 3. Components with lower densities may 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 atomized iron powder, sponge iron powder, reduced iron powder; steel powder partially alloyed by diffusion; and steel powder completely alloyed. Partially alloyed steel powder by diffusion is preferably a steel powder partially alloyed with one or more 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 shape, it is preferred that the particles have an irregular shape, such as that obtained by atomization with water. Sponge iron powders having irregularly shaped particles may also be of interest. A critical feature of the invention is that the powder used has coarse particles, ie the powder is essentially free of fine particles. The term "essentially without fine particles" implies that less than about 5% of the powder particles have a size of less than 45 μp ?, measured by the method described in SS-EN 24 497. Until now, they have been achieved the most interesting results with powders consisting essentially of particles greater than about 106 μ? t? and particularly greater than about 212 μ? t ?. The term "essentially consists" implies that at least 50%, preferably at least 60% and most preferably at least 70% of the particles have a particle size greater than 106 and 212 μ ??, respectively. The maximum particle size can be about 2 mm. The particle size distribution for the iron-based powders used in the PM production is normally distributed, with a Gaussian distribution with an average particle diameter in the range of 30 to 100 μ? and approximately 10-30% less than 45 μ? t ?. Iron-based powders essentially free of fine particles can be obtained by removing the finer fractions of the powder or by making a powder having the desired particle size distribution. The influence of the particle size distribution and the influence of the particle shape on the compaction properties and the properties of the compacted body have been subjected to intense studies. Thus, the patent of E. U. A. No. 5,594,186 discloses a method of producing PM components with a density greater than 95% of the theoretical density, by the use of substantially linear, needle-shaped metal particles having a triangular cross-section. Such particles are produced suitably, by a machining or milling process. Dusts having coarse particles are also used for the manufacture of easily magnetizable / demagnetizable components. Thus, the patent of E. U. A. No. 6,309,748 discloses a ferromagnetic powder, whose particles have a diameter size of between 40 and 600 μ? T ?. In contrast to the iron-based powder particles according to the present invention, these powder particles are provided with a coating.

In the patent of E. U. A. No. 4,190,441, a powder composition is exposed for the production of easily magnetizable / demagnetizable, sintered components. In this patent, iron powder includes particles less than 5% that exceed 417 μ? T? and less than about 20% of the dust particles have a size smaller than 147 μ? t ?. This patent teaches that, because of the very low content of particles smaller than 147 μ ??, the mechanical properties of the components manufactured in this coarse, highly pure powder are very low. In addition, the patent teaches that, if greater strength is desired, it is not possible to increase the content of particles having a size smaller than 147 μ? without simultaneously deteriorating the properties of easy magnetization / demagnetization. Thus, this powder is mixed with specific amounts of ferrophosphorus. Graphite that can be used in the compositions according to the present invention is not mentioned in the patent and, moreover, the presence of graphite would deteriorate the magnetic properties. Powder mixtures including coarse particles are also disclosed in the patent of US Pat. No. 5,225,459 (EP 554 009) which also relates to mixtures of powders for the preparation of easily magnetizable / demagnetizable components. These powder mixtures also do not include graphite. Within the field of powder forging, it is also known that previously allied iron-based powders with coarse particles can be used. The patent of E. U. A. No. 3,901, 661 discloses such powders. Such a patent discloses that a lubricant can be included and specifically that the amount of lubricant should be 1% by weight (example 1). If the powders according to the present invention were mixed with such a high amount of lubricant, it would not be possible however to achieve high densities. In order to obtain compacted products having satisfactory mechanical properties of sintering the sintered part according to the present invention, it is necessary to add certain amounts of graphite of the powder mixture to be compacted. Thus, graphite could be added in amounts between 0.1-1, preferably 0.2-1.0 and most preferably 0.2-0.8% by weight of the total mixture, before compaction. Other additives can 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. These alloying elements can be added in amounts of up to 10% by weight. Other additives are compounds that enhance the machinability, tubular phase material and flow agents. The iron-based powder can also be combined with a lubricant, before it is transferred to the mold (internal lubrication). The lubricant is added to minimize friction between the metal powder particles and between the mold particles during a compaction or pressing step. Some examples of suitable lubricants are v. gr. stearates, waxes, fatty acids and derivatives thereof, oligomers, polymers and other organic substances with lubricating effect. The lubricants are preferably added in the form of particles, but they can be bound and / or applied to the particles as well. According to the present invention, the amount of lubricant added to the iron-based powder can vary between 0.05 and 0.6%, preferably between 0.1-0.5% by weight of the mixture. The method according to the invention can also be realized by the use of external lubrication (lubrication of the mold walls) in which a lubricant is provided to the walls of the mold, before the compaction is carried out. A combination of external and internal lubrication can also be used. The term "at high compaction pressure" means pressures of at least about 800 MPa. More interesting results are obtained at higher pressures, such as pressures greater than 900, preferably greater than 1000, more preferably higher than 100 MPa. Conventional compaction at high pressures, ie pressures in excess of about 800 MPa with conventionally used powders that include finer particles, in admixture with small amounts of lubricants (less than 0.6% by weight), is generally considered inadequate due to the large forces required in order to expel the compacted products, the great concomitant wear of the mold and the fact that the surfaces of the components tend to be less bright and deteriorate. By using the powders according to the present invention, it has unexpectedly been found that the ejection force at high pressures is reduced, to about 1000 MPa, and that components having acceptable and even perfect surfaces can also be obtained, when the lubrication of the mold walls is not used. Compaction can be done with ordinary equipment, which means that the new method can be carried out without expensive investments. The compaction is carried out uniaxially in a single step at room or elevated temperature. Alternatively, compaction may be performed with the aid of a percussion machine (Hydropulsor Model HYP 35-4), as described in patent publication WO 02/38315. Sintering can be performed at temperatures normally used within the PM field, for example at ordinary temperatures between 1080 and 1160 ° C or at higher temperatures above 1160 ° C and in conventionally used atmospheres. Other treatments of the sintered or uncooked component, such as machining, hardening of the surface layer, densification of the surface or other methods used in the PM technology, can also be applied. In summary, the advantages obtained by using the method according to the present invention are that it is possible to produce compacted non-sintered high-density products, in a cost-effective manner. The new method also allows the production of higher quality components that are difficult to produce by using the conventional technique. Additionally, ordinary compaction equipment can be used to produce high density compacted products having an acceptable or even perfect surface finish. Some examples of products that can be adequately manufactured by the new method are rods, sprockets and other structural parts subjected to large loads. Through the use of stainless steel powders, flanges are of special interest. The invention is illustrated in more detail by the following examples.

EXAMPLE 1 Two different iron-based powder compositions according to the present invention were compared with an ordinary iron-based powder composition. The three compositions were produced with Astaloy Mo obtainable from Hoganás AB, Sweden. 0.2% by weight of graphite and 0.4% by weight of a lubricant were added to the compositions. In one of the iron-based powder compositions according to the invention, the particles of Astaloy Mo with diameter less than 45 μ were removed ?? and, in the other composition according to the invention, the Astaloy Mo particles smaller than 212 μ? t ?. The compaction was carried out at room temperature and the ordinary equipment. As can be seen in Figure 1A, a clear density increase is obtained at all compaction pressures with the powder having a particle size greater than 200 μ? T ?.

Figure 1B shows that, in order to obtain component without deteriorated surfaces, the most important factor is the reduction or elimination of the smallest particles, ie particles less than 45 μ ??. Furthermore, in the figure it can be seen that the force that is needed for the expulsion of the compacted products produced by the iron-based powder composition without particles smaller than 212 μ? it was reduced considerably compared to the ejection force needed for compacted products produced with the ordinary iron-based powder composition, which have approximately 20% of the particles less than 45 μ ??. The ejection force needed for compacted products produced with the iron-based powder composition according to the invention with particles smaller than μ? T ?, is reduced in comparison with ordinary powder. A notable phenomenon is that the ejection force for compacted products produced in accordance with the present invention decreases with the increasing ejection pressure, while the opposite is valid for the ordinary composition. It was also observed that the compacted products that were obtained, when the ordinary powder was compacted at a pressure higher than 700 MPa, had deteriorated surfaces and were therefore not acceptable. The compacted products, which obtained when the powder was essentially compacted without particles, less than 45 μ ??, at a pressure higher than 700 MPa, had a less bright surface, which is acceptable at least in certain circumstances.

EXAMPLE 2 Example 1 was repeated, but as a lubricant 0.5% EBS (ethylenebistearamide) was used and the compaction was performed with the help of a percussion machine (Model HYP 35-4 of Hydropulsor, Sweden) In figures 2 A and 2 B, respectively, it can be seen that higher uncooked densities and lower ejection forces were obtained with the powder composition according to the invention, compared to the powder composition with the ordinary powder. It can also be noted that the components produced with the ordinary powder had deteriorated surfaces at all compaction pressures.

Claims

NOVELTY OF THE INVENTION CLAIMS 1. - A process for the preparation of compacted, uncooked, high density products, characterized in that it comprises the following steps: providing an iron or iron-based powder, in which less than about 5% of the iron-based powder particles have a size less than 45 μ ??; optionally mixing said powder with graphite and other additives; compacting the powder uniaxially in a mold at a compaction pressure of at least about 800 MPa; and eject the uncooked body from the mold. 2. - The method according to claim 1, further characterized in that the compaction is carried out in a single step. 3. The process according to claim 1 or 2, further characterized in that at least 50%, preferably at least 60% and most preferably at least 70% of the iron-based powder consists of particles having a size of particle greater than about 106 μ? t ?. 4. The process according to any one of claims 1-3, further characterized in that at least 50%, preferably at least 60% and most preferably at least 70% of the iron-based powder consists of particles that have a particle size greater than about 212 μ? t ?. 5. The method according to claim 4, further characterized in that the maximum particle size is about 2 mm. 6 - The method according to any of claims 2-5, further characterized in that the graphite is present in an amount of 0.1-1.0%. 7. - The method according to any of claims 1-6, further characterized in that the iron-based powder is combined with a lubricant in an amount between 0.05 and 0.6% by weight before compaction. 8. - The method according to any of claims 1-6, further characterized in that the compaction is carried out in a lubricated mold. 9. - The method according to any of claims 7-8, further characterized in that the compaction is performed by using a combination of internal and external lubrication. 10. - The method according to any of claims 1-9, further characterized in that additives are selected from the group consisting of alloying elements, such as Mn, Cu, Ni, Cr, Mo, V, Co, W, Nb, Ti, Al, P, S and B, agents that enhance the machinability, hard phase materials and flow agents. 11. The process according to any of claims 1-10, further characterized in that the compaction is carried out at a pressure of at least 900 MPa, more preferably at least 1000 and most preferably greater than 1 100 MPa. 12. The process according to any of claims 1-11, further characterized in that the compaction is carried out at room temperature. 13. - The method according to any of claims 1-11, further characterized in that the compaction is carried out at elevated temperature. 14. - The method according to any of claims 1 - 13, further characterized in that, for preparing said sintered products, said process additionally includes a single step of sterilization at a temperature higher than 1 100 ° C. 15. A powder composition, characterized in that it comprises an iron or iron-based powder in which less than about 5% of the powder particles have a size of less than 45 μ ??; and 0.1-1.0% by weight of graphite. 16. - The powder composition according to claim 15, further characterized in that it additionally includes 0.05- 0.6% by weight of a lubricant. 17. The composition according to claim 15 or 16, further characterized in that at least 50%, preferably at least 60% and most preferably at least 70% of the iron-based powder has an approximately higher particle size. at 106 μp ?. 18. - The composition according to claim 17, further characterized in that at least 50% of the iron-based powder particles have a particle size greater than about 212 μ? t ?. 19. - The composition according to any one of claims 15-18, further characterized in that it additionally includes additives selected from the group consisting of alloying elements, such as Mn, Cu, Ni, Cr, Mo, V, Co, W , Nb, Ti, Al, P, S and B, agents that enhance the machinability, hard phase materials and flow agents.