Classifications

• • 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
  • B22F3/10—Sintering only
  • B22F3/1003—Use of special medium during sintering, e.g. sintering aid
• • 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
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling

Definitions

• the invention relates to a method for producing moldings, in particular for tools, machine parts, utensils or the like. with metals or metal alloys, preferably with at least one metal from the iron group, in particular high-alloy steels and / or Co-based alloys, with in particular powder-fine particles of the alloy constituents and / or master alloys and / or the alloy itself being mixed with at least one additive and at least below Heating to be compressed into a desired shaped body.
• Powder metallurgy is particularly well suited for the production of tools, machine parts and articles of daily use for economic reasons.
• Their advantage lies in the fact that, starting from metal powders, a porous body is produced by mechanical pressing, which is then compressed to the final shape during so-called sintering.
• Sintering is generally understood to mean the caking of powder particles under the action of heat in an oven. In many cases, the original air-filled pores in the powder compact are removed. However, this process is negatively influenced by the oxygen content of the powder.
• the oxygen content on the surface of the powder particles in particular has a sinter-inhibiting effect and leads to porosities and inadequate mechanical properties.
• GB-PS 2 084 612 describes e.g. a method for producing a workpiece from gas-atomized powder with low oxygen content, which is characterized in that the powder is ground. The ground powder is then mixed with a pressing aid, pressed into a shaped body, sintered and hot isostatically compressed. The disadvantage of this process is still the use of the expensive gas-atomized powder, which can only be ground with great effort into a uniformly compressible fine powder.
• Water atomized powders have the advantage that they have irregular shapes and can therefore be pressed well into preform bodies. However, they have the disadvantage that they contain a relatively large amount of oxide (700 to 1500 ppm) or are surrounded by an oxide layer which covers the sinter process hindered and caused porosity.
• the object of the invention is to design a method of the type mentioned in such a way that a shaped body is obtained in a labor and energy-saving manner, the sintering properties of which are optimal and whose porosity is minimal.
• this is achieved in that the particles, preferably in an inert atmosphere, are brought into contact with at least one compound of at least one metal as an additive at temperatures of 50 to 800 ° C., preferably 150 to 350 ° C, in particular around 250 ° C, at least one alloy-specific or alloy-compatible metal and / or an oxygen compound substoichiometric with respect to oxygen of such Metal releases, after which at least with heating, preferably with sintering, the final compression of the particles into the shaped body.
• This makes it possible to produce moldings that have practically no porosity and excellent mechanical properties.
• the additives used according to the invention have the effect that the ease of sintering of the shaped body components is increased; the additives bring about an improvement in diffusion at the particle boundaries, so that the achievable sintered composite is improved.
• the additives used according to the invention When heated as a result of decomposition, the additives used according to the invention release metal atoms or metal oxygen compounds whose oxygen content is substoichiometric, that is to say which contain oxygen in deficit, and which combine with the oxygen of oxides or oxide layers present on the particles or tear these layers apart. This creates metallic contact between the particles so that they can optimally sinter together. At the same time, the oxygen torn from the oxide compound reacts more easily to CO or CO2 with the carbon contained in the structure. The resulting metallic contact allows the sintering temperature to be lowered. Obtained from preforms with 700 to 1500 ppm O2 moldings with max. 50 to 100 ppm O2.
• the densities of sintered bodies achieved to date from about 99.5% to 99.8% based on the The maximum achievable density is increased and the densities of moldings produced by the process according to the invention are more than 99.8%.
• the temperatures for the compression of the preforms are somewhat below the temperatures currently customary for the respective metals of the alloys. In the method according to the invention, the use of temperatures about 5 to 10 ° lower is possible, which makes the sintering process much more manageable compared to temperature fluctuations in the sintering furnace; sintering is currently taking place just below the melting point of the respective eutectic compounds.
• particles obtained with water atomization optionally with an addition of up to max. 50% of gas atomized and / or ground particles, a metal, an alloy or pre-alloy with an irregular shape and size are used. Together with the irregularly shaped water-atomized particles, other particles can also be used, and a preform can be produced well and precisely due to the possible plastic deformation of the particles. Due to the addition of the additive, it is possible that particles or powders containing surface oxygen are also used. To form the preform body, it is expedient if the particles are subjected to a preform body formation after the addition of the additive with the application of pressure and / or temperature. The additive contributes to the cohesion of the particles.
• a durable preform and a structure with a good structure result if the particles with the connection of the metal by mixing, in particular special stirring, are brought into contact, preferably the entire surface of the particles being contacted, in particular wetted, with the compound of the metal.
• the particles can be intimately bonded over their entire surface during sintering. Mixing can take place in known mixing devices.
• the compound of the metal is brought into contact with the particles in a solid or fluid state at room temperature or in a state dissolved in a solvent.
• An addition of a gaseous compound of a metal to the particles can be carried out as well as an admixture of powdery particles of a compound of a metal to the particles to be sintered.
• the solvent of the compound of the metal is expediently evaporated off before the preform is formed.
• the sintering process or the compression to form the shaped body follows the production of the preform directly following the admixing of the connection of a metal or the evaporation of the solvent that may be necessary, without any further intermediate step; further reactive intermediate steps are also not required, which makes the procedure simple.
• particles of tool in particular Schnellar
• Schnellar are advantageously beitsteel ledeburitic cold work steels, high-temperature or sintered alloys on Ni and / or Co-based or the like. used. After sintering, the particles form the corresponding steels or alloys with a standardized composition.
• the released metal (s) or the oxygen compound (s) which is substoichiometric with respect to oxygen comprises metals or oxygen compounds of metals from the group Fe, Co, Ni, Cr , Mo, W, Ta, Nb, V, Ti Zr, Hf, Al, Si.
• the process becomes particularly simple with good results if, preferably in an organic solvent, dissolved complex, addition and / or coordination compounds of at least one alloy-specific or alloy-compatible metal, preferably with zero valence, are used.
• Such compounds of metals release the metal or the oxygen-sub-stoichiometric metal compound at a relatively low temperature and the compound residues leave the heated preform body relatively unhindered before the compression process begins. It is expedient if the residues of the compound of the metal after release of the metal or the oxygen-substoichiometric oxygen compound in the course of the temperature increase before reaching the compression temperature from the preform body e.g. be removed by applying a vacuum.
• Particles of at least one metal or a metal alloy are mixed with at least one compound of an alloy-specific or alloy-compatible metal which, when heated, releases a metal or a compound of the metal which is substoichiometric with respect to oxygen.
• the particles can be water-atomized metal powder, which to a certain extent, preferably 50%, is also gas-atomized or produced in another way or may contain pretreated powders. These particles are intimately mixed with the dissolved compound, for example by stirring, the particles being well wetted; after evaporation of the solvent, a layer of the compound should be deposited in molecular thickness on the particles. The particles are then pressed under pressure to form a preform.
• the preform is pressed in a press mold, which is also the sintered mold, and has a density of 80%.
• This preform is then heated to the compression temperature without further treatment, the connection being disassembled when heated.
• the metals released remain in the structure and the connection residues, in particular organic components, leave the preform body.
• the sintering temperature is reached, there is only the alloy structure that is sintered, since the organic components are selected such that they have left the structure before the main shrinkage process and have already released the reactive metal atoms and sub-stoichiometric oxygen compounds.
• Evaporation of the solvent is carried out by means of a vacuum or vacuum, if appropriate using protective gas, as is heating of the preform and compression or sintering.
• one or more compounds of one or more metals can be added to the particles to be compressed, which each give off one or more metal (s) or one or more oxygen substoichiometric oxygen compound (s) of a metal when heated.
• the particles to be compacted also have substances which improve the compression or sintering properties, for example, before, after or simultaneously with the addition of the compound of a metal. Paraffin or others can be added.
• a commercially available water-atomized high-speed steel powder with the material number 1.3343 and an oxygen content of 710 ppm was intimately mixed with 0.3% by weight of vanadyl acetylacetonate and with mineral spirits in a planetary mill. Then 1.5 wt .-% paraffin was added as a pressing or sintering aid and distributed homogeneously. After the solvent had been evaporated off, the powder was mechanically pressed into shaped bodies in a die at 5000 bar and then sintered under vacuum. The sintering conditions were 1235 ° C with a holding time of 30 minutes. The sintered density of the shaped body was 8.12 g / cm 3. The flexural strength was over 2000 N / mm2. The oxygen content was 20 ppm. The comparative body sintered without the additive according to the invention could only achieve a density of 8.00 g / cm 3 and a 20% lower bending strength.
• a commercially available water-atomized high-speed steel powder with the material number 1.3215 was mixed with the addition of 0.5% cobalt acetylacetonate, 1% molybdenyl Acetylacetonate and mixed with benzene in a planetary mill and then dried in a desiccator.
• the mechanical pressing was carried out at 5500 bar.
• the size of the moldings was 5 x 5 x 45 mm. Vacuum sintering of the pressed moldings took place at 1250 ° C., the holding time was 1 hour.
• the density of the sintered body, to which the additives according to the invention were fed, could be increased by 0.15 g / cm3 compared to the comparison body produced without additives.
• the flexural strength of the molded article produced according to the invention was 25% higher than that of the comparative article.
• a commercially available water-atomized high-speed steel powder with the material number 1.3343 was mixed according to the invention with 0.5% by weight molybdenyl acetylacetonate, 0.5% by weight vanadyl acetylacetonate and 0.3% by weight aluminum acetylacetonate and benzene. After the solvent had been evaporated off, the dry powder was pressed in a mechanical press at 5000 bar to form inserts with the ISO designation SPGN 120308. The green compacts were sintered at 1240 ° C. and in vacuo for 30 min. The carbon content of the sintered alloy after sintering was 0.91% by weight and the oxygen content was 20 ppm. The residual porosity was less than 0.1% by volume.
• the comparison body sintered without additives showed a lower carbon content and a residual porosity of 0.7% by volume.
• a wear test using the grinding wheel method gave the following results in specific weight loss (%): W.Nr. 1.3343 melt metallurgical 100% W.Nr. 1.3343 PM-without additives 60%
• the cutting inserts according to the invention showed a significant improvement in wear behavior.
• a mixture of a high-speed steel powder with the material number 1.3343 consisting of 50% water atomized and 50% gas atomized parts was produced and investigated in accordance with the conditions of Example 3.
• the following tool life was determined in the machining test at a cutting speed of 40 m / min, a cutting depth of 2 mm and a feed of 0.23 mm / rev on a tempering steel with material number 1.6582 and a hardness of 230 HB 30:
• Water-atomized powder based on cobalt (stellite 6) was mixed with 1% by weight of vanadyl acetylacetonate, 0.1 % By weight of aluminum acetylacetonate and 0.1% by weight of chromium acetylacetonate dissolved in acetone mixed in a stirrer.
• the dried powder was pressed into molds in a die at 6000 bar and sintered in a vacuum oven at 1290 ° C. with a holding time of 60 min.
• the residual porosity of the sintered body provided with the additive according to the invention was less than 0.1% by volume, while the comparison body produced without additive had a residual porosity of 12.1%.
• Water-atomized powder with the material number 1.2379 was mixed according to the invention with 0.3% by weight molybdenyl acetylacetonate, 1% by weight vanadyl acetylacetonate and benzene in a planetary mill and then dried under vacuum and mechanically pressed to give shaped bodies.
• the sintering took place at 1210 ° C. and a holding time of 1 hour.
• the residual porosity was below 0.2 vol%.
• the comparison body produced without additives showed a residual porosity of 3.8% by volume.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Powder Metallurgy (AREA)

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• 1986
  • 1986-11-28 AT AT317886A patent/AT388124B/de not_active IP Right Cessation
• 1987
  • 1987-11-26 EP EP19870890270 patent/EP0269612B1/fr not_active Expired - Lifetime
  • 1987-11-26 DE DE8787890270T patent/DE3782618D1/de not_active Expired - Lifetime

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