ES2357741T3 - METHOD OF PREPARATION OF IRON-BASED COMPONENTS THROUGH COMPACTION WITH HIGH PRESSURES. - Google Patents

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 components based on iron by compaction with high pressures.

Field of the Invention

The present invention relates to a method for the preparation of components that have high density using metal powder compositions useful within the industry metallurgical powder. The invention is defined in the claims. 1-10.

There are several advantages to using methods powder metallurgists to produce structural parts in comparison with conventional steel alignment procedures full density Thus, energy consumption is much lower and the use of much higher material. Another important factor to favor of the powder metallurgical route is that they can occur network shaped components or almost network form directly after the sintering process without expensive conformation processes such as turning, milling, drilling or grinding. Without But material typically has full dense steel superior mechanical properties compared to components of P.M. This is mainly due to the appearance of porosity in the PM components. Therefore, the effort has been to increase the density of PM components in order to reach values closest possible to the density value of a density steel complete.

Among the methods used in order to achieve a higher density of PM components, the forging process of dust has the advantage that components of full density However, this process is expensive and is used. mainly for mass production of components more heavy, such as connecting rods. Materials can also be obtained from full density through high pressures at high temperatures, such as hot isostatic pressing, HIP, but also this method is expensive.

Using hot compaction, a process in which the compaction is performed at an elevated temperature, normally at 120 to 250 ° C, the density can be increased by approximately 0.2 g / cm3, which results in an improvement considerable mechanical properties. However, a disadvantage is that the hot compaction method implies Additional processing and investment. Other procedures, such as double pressing, double sintering, sintering to high temperatures, etc., can further increase the density. These methods will also add production costs. additional, thus reducing the overall cost effectiveness.

In order to expand the market for powder metallurgical components and use the advantages with the powder metallurgical technique, there is therefore a need for a simple, less expensive method to achieve high tablets density with mechanical, dynamic and static resistance, improved

SUMMARY OF THE INVENTION

It has now been found that they can be obtained high density components using high pressures of compaction in combination with thick powders. In view of the general knowledge, which conventionally used powders, that is, powders that included fine particles, which cannot be compacted up to high densities without problems with, for example, surfaces damaged or damaged tablets, 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 mix said powder with graphite and other additives; uniaxially compact the powder in a high pressure mold and extract the raw body, which subsequently sintered.

Detailed description of the invention

The term "high density" is intended mean tablets having a density of approximately at minus 7.3 g / cm3. Of course, they can also occur components with lower densities but are believed to be less interest.

The iron-based powder according to the present invention includes pure iron powder, such as iron powder atomized, spongy iron powder, reduced iron powder; partially alloyed diffusion steel powder; and steel powder completely alloyed. The steel alloy partially alloyed by diffusion is preferably a partially alloyed steel powder with one or more of Cu, Ni and Mo. The fully alloyed steel powder It is preferably an alloy steel powder with Mn, Cu, Ni, Cr, Mo, V, Co, W, Nb, Ti, Al, P, S and B. Also of interest are powders of stainless steel.

Regarding the shape of the particles, it is preferred that the particles have an irregular shape, such as It is obtained by atomization with water. They can also be from interest spongy iron powders that have shape particles irregular.

A critical feature of the invention is that the dust used has coarse particles, that is, the dust does not It has essentially fine particles. The expression "has no essentially fine particles "is meant to mean that less than approximately 5% of the dust particles have a size less than 45 µm, measured by the method described in the standard SS-EN24 497. To date, the results more interesting have been achieved with powders that consist essentially in particles above about 106 µm and particularly above about 212 µm. The expression "consisting essentially of" is meant that the minus 50%, preferably at least 60% and most preferably at least 70% of the particles have a size of particle greater than 106 and 212 µm, respectively. The size Maximum particle can be approximately 2 mm. The particle size distribution for iron-based powders used in the manufacture of PM is normally distributed with a Gaussian distribution with an average particle diameter in the region 30 to 100 \ m and about 10-30% less than 45 µm. Powders can be obtained Iron-based essentially free of fine particles by removing the finest dust fractions or making a powder that has the desired particle size distribution.

The influence of the size distribution of particle and the influence of the shape of the particles on the compaction properties and compacted body properties They have been the subject of intensive studies. Thus, the US patent 5,594,186 reveals a method of producing PM components with a density greater than 95% of the theoretical density using acicular, substantially linear metal particles that have a triangular cross section. Such particles are produced from proper way through a machining or milling process.

Powders that have particles are also used thick for the manufacture of soft magnetic components. So, U.S. Patent 6,309,748 discloses a powder ferromagnetic, whose particles have a diameter size of between 40 and 600 µm. Unlike dust particles a iron base according to the present invention, these particles powder are provided with a coating.

In US Patent 4,190,441 it is given to know a powder composition for component production soft magnetic sintered. In this patent, iron powder includes particles with less than 5% exceeding 417 µm, and less than approximately 20% of the dust particles have a size less than 147 µm. This patent teaches that due to the very low content less than 147 \ mum particle properties Mechanical components manufactured from this coarse powder, extremely pure, they are very low. In addition, this patent teaches that if For a superior resistance, it is not possible to increase the content in particles smaller than 147 µm without deteriorating Simultaneously soft magnetic properties. Therefore this powder is mixed with specific amounts of ferrophosphorus. I dont know mentions graphite in this patent, which can be used in compositions according to the present invention, and also the presence of Graphite would deteriorate the magnetic properties.

Disclosed also powder mixtures include coarse particles in U.S. Patent 5225459 (EP 554 009) which also refers to powder mixtures for the preparation of soft magnetic components. None of These powder mixtures include graphite.

Within the field of powder forging, it is known in addition that previously alloyed iron-based powders can be used with thick particles. U.S. Patent 3 901 661 gives Know such powders. This patent discloses that it can be included a lubricant and specifically that the amount of lubricant should be 1% by weight (example 1). If the powders according to the present invention will be mixed with such a high amount of this type of lubricant, it would not be possible however to achieve high densities

In order to get tablets that have satisfactory mechanical sintered properties of the part sintered according to the present invention, it is necessary to add certain quantities of graphite to the powder mixture to be compacted. By therefore, before compaction graphite could be added in amounts between 0.1-1, preferably the 0.2-1.0 and most preferably the 0.2-0.8% by weight of the total mixture that is going to compacting

Other additives can be added to the powder based iron before compaction, such as alloy elements comprising Mn, Cu, Ni, Cr, Mo, V, Co, W, Nb, Ti, Al, P, S and B. These alloy elements can be added in amounts of up to 10% by weight. Additional additives are enhancer compounds of Machinability, hard phase material and flow agents.

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 dust particles and between the particles and the mold during a compaction or pressing stage. Examples of suitable lubricants are, for example, stearates, waxes, fatty acids and derivatives thereof, oligomers, polymers and other organic substances with lubrication effect. The lubricants are preferably added in the form of particles but can also be attached to and / or coated with the particles. According to the present invention, the amount of lubricant added to the iron-based powder may 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 be carried out. also with the use of external lubrication (lubrication of mold walls), in which the mold walls are provides a lubricant before compaction is performed. A combination of external lubrication and internal

The expression "at high pressure of compaction "is intended to mean at pressures of approximately at least 800 MPa. More interesting results are obtained with higher pressures such as pressures above 900, preferably above 1000, more preferably above of 1100 MPa.

Conventional compaction at high pressures, that is, pressures above about 800 MPa with powders conventionally used that include finer particles, in mixture with low amounts of lubricants (less than 0.6% in weight), is generally considered inappropriate due to high forces required in order to extract the tablets from the mold, the consequent high wear of the mold and the fact that component surfaces tend to be less bright or to deteriorate. Using the powders according to the present invention, it has been unexpectedly found that the extraction force is reduced to high pressures, approximately 1000 MPa, and which can be obtained components that have acceptable or even perfect surfaces also when no lubrication of the mold walls is used.

Compaction can be done with equipment conventional, which means that the new method can be performed No expensive investments. Compaction is performed uniaxially in a single stage at room or elevated temperature. Alternatively, compaction can be done with the help of a machine percussion (HYP 35-4 Hydropulsor model) such as It is described in patent publication WO 02/38315.

Sintering can be done at temperatures normally used within the PM field, for example at temperature conventional between 1080 and 1160 ° C or at higher temperatures by above 1160 ° C and in conventionally used atmospheres.

Other treatments of the raw or sintered component, such as machining, surface hardening, surface densification or others methods used in PM technology.

In summary, the advantages obtained using the method according to the present invention are that they can be produced Raw high density tablets cost-effectively. The new method also allows the production of superior components that They are difficult to produce using conventional technique. Additionally, conventional compaction equipment can be used to produce high density tablets that have a finish Superficial acceptable or even perfect.

Examples of products that can be manufactured properly using the new method are connecting rods, gears and other structural parts subjected to high loads. Using powders stainless steel are especially interesting flanges

The invention is further illustrated by The following examples.

Example one

two powder compositions were compared based of different iron according to the present invention with a composition of conventional iron-based powder. The three occurred compositions with Astaloy Mo available from Höganäs AB, Sweden. Be added 0.2% by weight of graphite and 0.4% by weight of a lubricant (Kenolube ™) to the compositions. In one of the iron-based powder compositions according to the invention, are removed particles of Astaloy Mo with a diameter less than 45 um and in the other composition according to the invention were removed Astaloy Mo particles less than 212 µm. The compacting at room temperature and in conventional equipment. Such as can be seen from figure 1-1, it obtains a clear increase in density at all pressures of compaction, the powder having a particle size greater than 212 µm.

Figure 1-2 shows that, in order to obtain components without damaged surfaces, the most important factor is the reduction or elimination of smaller particles, that is, particles below 45 µm. Furthermore, it can be seen from this figure that the force necessary for the extraction of the tablets produced by the iron-based powder composition without particles smaller than 212 µm was considerably reduced compared to the extraction force necessary for tablets produced from the conventional iron-based powder composition having approximately 20% of the particles less than 45 µm. The necessary extraction force for tablets produced from the iron-based powder composition according to the invention without particles smaller than 45 µm is also reduced compared to the conventional powder.
tional

A notable phenomenon is that the strength of extraction for tablets produced according to the present invention decreases with increasing extraction pressure while the opposite is true for the conventional composition.

It was also observed that the tablets obtained when the conventional powder was compacted at a pressure greater than 700 MPa had deteriorated surfaces and therefore were not acceptable. The tablets that were obtained when the powder essentially without particles less than 45 µm at a pressure greater than 700 MPa had a less shiny surface which, at least in certain circumstances, is acceptable.

Example 2

Example 1 was repeated but as a lubricant used 0.5% EBS (ethylene bisestearamide) and the compaction with the help of a percussion machine (HYP model 35-4 from Hydropulsor, Sweden).

From Figure 2-1 and 2-2, respectively, it may be noted that obtained higher crude densities and extraction forces lower with the powder composition according to the invention in Comparison with the powder composition with conventional powder. It can also be seen that the components produced from the Conventional powder have deteriorated surfaces at all compaction pressures.

Claims (10)

1. Procedure for the preparation of high density raw tablets comprising the following stages:

provide a atomized iron-based powder, optionally comprising Mn, Cu, Ni, Cr, Mo, V, Co, W, Nb, Ti, Al, P, S and B, in which less than 5% of the iron-based dust particles have a size less than 45 µm;

mix said powder with 0.1-1.0% by weight of graphite and a lubricant in an amount between 0.05 and 0.6% by weight, optionally machinability enhancing agents, materials hard phase and flow agents;

compact uniaxially the powder in a mold at a compaction pressure of at least 800 MPa; and extract the raw body from the mold.

2. Method according to claim 1, in which the compaction is done in a single stage. 3. Method according to claim 1 or 2, in which at least 50%, preferably at least 60% and most preferably at least 70% of the iron-based powder consists in particles that have a particle size greater than 106 \ mum. 4. Procedure according to any one of the claims 1-3, wherein 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 212 µm. 5. Method according to claim 4, in The maximum particle size is 2 mm. 6. Procedure according to any one of the claims 1-5, wherein the compaction is performed in a lubricated mold. 7. Procedure according to any one of the claims 1-6, wherein the compaction is performs at a pressure of at least 900 MPa, more preferably at minus 1000 MPa and most preferably greater than 1100 MPa. 8. Procedure according to any one of the claims 1-7, wherein the compaction is performed at room temperature. 9. Procedure according to any one of the claims 1-8, wherein the compaction is performed at elevated temperature. 10. Procedure according to any one of the claims 1-9 for preparing products sintered, said procedure also including a single stage of sintering at a temperature above 1100 ° C.