Method for producing a powder-metallurgical product

Abstract

A method for producing a powder-metallurgical product, in particular a bearing element or a motor component, is provided. According to the method, a metal powder, typically with a grain size between 2 μm and 15 μm, is melt-metallurgically produced and agglomerated into a powder mixture having a grain size smaller than 400 μm by organic binders and waxes. Subsequently, the agglomerated powder mixture is formed into a green body typically by way of uniaxial pressing and the formed green body thermally debindered. Finally, the debindered green body is sintered typically at temperatures of 1000° C. to 1300° C. and the sintered body reworked into the powder-metallurgical product.

Claims

1. A method for producing a powder-metallurgical product comprising the steps of: a) melt-metallurgical producing a metal powder with a mean granulate size between 2 μm and 15 μm; b) agglomerating the metal powder produced in step a) by organic binders and waxes into a powder mixture containing 1 to 1.4% by weight of carbon, 27 to 39% by weight of chromium, 0.1 to 0.5% by weight of manganese, 3.1 to 4.0% by weight of nickel, 2.6 to 5.0% by weight of molybdenum, 2.1 to 3.5% by weight of silicon, 2.1 to 3.5% by weight of tungsten, 2.1 to 3.5% by weight of vanadium, 0.1 to 3.5% by weight of copper, and 0.0 to 3.5% by weight each of cobalt and niobium, with the mean granulate size of less than 400 μm; c) forming the powder mixture agglomerated in step b) into a green body by uniaxial pressing; d) thermal debindering the green body formed in step c); e) sintering the green body debindered in step d) at temperatures of 1000° C. to 1300° C.; and f) reworking the green body sintered in step e) into the powder-metallurgical product.

2. The method according to claim 1, wherein the metal powder produced in step a) is iron based and/or contains more than 20% by weight of chromium and more than 1% by weight of carbon.

3. The method according to claim 1, further comprising: in step b) admixing further metal powders with proportions smaller than or equal to 5% each and/or solid lubricants and/or hard phases and/or further metal powders on iron base.

4. The method according to claim 1, further comprising: in step c), forming the powder mixture agglomerated in step b) into the green body under a pressure of 400 MPa to 1500 MPa.

5. The method according to claim 1, further comprising: in step d), debindering the green body formed in step c) at temperatures from 45° C. to 820° C.

6. The method according to claim 1, further comprising: in step e), sintering the green body debindered in step d) at a temperature between 1115° C. and 1275° C.

7. The method according to claim 1, further comprising: in step a), producing the metal powder by water atomization.

8. The method according to claim 1, further comprising: in step b), agglomerating the metal powder by spray drying.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described with reference to the drawings wherein:

(2) FIG. 1 shows a schematic illustration of a tribological system according to an exemplary embodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

(3) An exemplary embodiment of the invention is shown in FIG. 1 and is explained in more detail in the following description.

(4) FIG. 1 illustrates a simplified example of a tribological system 10 according to the invention, which is used in an internal combustion engine of a motor vehicle or an electric power machine of a motor vehicle. The tribological system 10 comprises a bearing element 1 which is arranged in a bearing housing 4, a shaft 3 and a shaft journal 2 connected to a shaft 3. In the tribological system 10, friction is created between the bearing element 1 and the shaft journal 2 and, alternatively or additionally, between the bearing element 1 and the shaft 3 because the shaft journal 2 together with the shaft 3 rotates relative to the bearing element 1 about an axis A.

(5) Apart from this, the surface of the bearing element 1 can be in mechanical contact with a product which contains 0 to 0.1% by weight of carbon, 0 to 0.5% by weight of silicon, 0 to 0.5% by weight of manganese, 0 to 0.015% by weight of phosphorous and sulphur each, 13.5 to 15.5% by weight of chromium, 30 to 33.5% by weight of nickel, 0.4 to 1.4% by weight of molybdenum, 1.6 to 2.2% by weight of aluminium, 2.3 to 2.9% by weight of titanium, 0.4 to 1% by weight of niobium and the remaining proportion of the total weight is formed by iron and production-related contaminations.

(6) The bearing element 1 can for a predominant part have a ferritic structure.

(7) In addition, the bearing element 1 can additionally contain 2.8% by weight of carbon, 20 to 39% by weight of chromium, 0.1 to 1.8% by weight of manganese, 0 to 4% by weight of nickel, 0.5 to 5% by weight of molybdenum, 0.5 to 3.5% by weight of silicon, 0 to 3.5% by weight each of vanadium, tungsten, cobalt, niobium, copper as well as production-related contaminations.

(8) The powder-metallurgical product can contain 1.8 to 2.5% by weight of carbon, 29 to 36% by weight of chromium, 0.2 to 1.2% by weight of manganese, 0 to 1% by weight of nickel, 1 to 5% by weight of molybdenum, 0.8 to 3.5% by weight of silicon as well as production-related contaminations.

(9) The bearing element 1 can have a relative density of greater than 95% and, alternatively or additionally, the carbides in the ferritic structure of the bearing element 1 can have a size of less than 50 μm. Here, “relative density” means the ratio of the absolute density relative to the density of pure water in the standard state at 3.98° C.

(10) The bearing element 1 was produced by the method according to the invention, i.e., powder-metallurgically.

(11) In the method for producing the bearing element 1 according to the invention, a metal powder with a mean granulate size between 2 μm and 15 μm is melt-metallurgically produced and agglomerated into a powder mixture, typically with a mean granulate size of less than 400 μm, by organic binders and waxes. Mean granulate size as part of the present invention means the arithmetic mean of the granulate diameter of a quantity of powder granulates. The agglomerated powder mixture is formed into a green body preferentially by way of uniaxial pressing. The formed green body is subsequently thermally debindered to remove the organic binders and waxes and the debindered green body is then sintered typically at temperatures between 1000° C. and 1300° C. Here, sintering can take place in the vacuum or in a nitrogen-hydrogen atmosphere. Finally, the sintered green body is reworked into the bearing element.

(12) Here, the produced metal powder can be based on iron and, alternatively or additionally, contain more than 20% by weight of chromium and more than 1% by weight of carbon.

(13) Apart from this, further metal powders with proportions in each case smaller than or equal to 5% by weight and, alternatively or additionally, solid lubricants and, alternatively or additionally, hard phases and, alternatively or additionally, further metal powders on iron bases can be admixed during the agglomeration of the powder mixture.

(14) The agglomerated powder mixture can contain 1 to 2.8% by weight of carbon, 20 to 39% by weight of chromium, 0.1 to 1.8% by weight of manganese, 0 to 4% by weight of nickel, 0.5 to 5% by weight of molybdenum, 0.5 to 3.5% by weight of silicon and 0 to 3.5% by weight each of vanadium, cobalt, copper, tungsten, and niobium.

(15) In addition to this, the agglomerated powder mixture can be formed into a green body with a pressure of 400 MPa to 1,500 MPa.

(16) Furthermore, the formed green body can be debindered at temperatures of 45° C. to 820° C. The debindered green body in turn can be sintered at a temperature between 1115° C. and 1275° C.

(17) The metal powder can be produced by water atomization and, alternatively or additionally, agglomerated by spray drying.

(18) In the manner shown above, other powder-metallurgical products in particular sealing or sliding elements, valve drive and turbocharger components, valve components, valve guides, bearing bushes, camshafts, running and guide bushes, shaft sealing rings, valve bodies, valve seat rings or components in emission control or exhaust gas recirculation systems can likewise be produced.