EP0881958A1

EP0881958A1 - Material for the powder-metallurgical production of shaped parts, in particular valve seat rings or valve guides with high resistance to wear

Info

Publication number: EP0881958A1
Application number: EP97905071A
Authority: EP
Inventors: Ekkehard KÖHLER; Kirit Dalal; Anil V. Nadkarni
Original assignee: Bleistahl Produktions-GmbH and Co KG; SCM Metal Products Inc
Current assignee: Bleistahl Produktions-GmbH and Co KG; SCM Metal Products Inc
Priority date: 1996-02-21
Filing date: 1997-02-21
Publication date: 1998-12-09
Anticipated expiration: 2017-02-21
Also published as: US6039785A; JP2001500567A; JP4272706B2; DE19606270A1; DE59703672D1; EP0881958B1; WO1997030808A1

Abstract

The invention concerns a material for the powder-metallurgical production from a powder mixture containing at least approximately 50 wt.% copper in particular of valve seat rings or valve guides with high resistance to wear and corrosion and high heat conductivity. The starting powder mixture consists of between 50 and 90 wt.% of a basic powder, containing the copper portion, and between 10 and 50 wt.% of a powdery molybdenum-containing alloy flux. The basic powder is a copper powder which is dispersion-hardened by Al2O3, has an Al2O3 content of between 0.1 and 1.1 wt.%, and is produced by pulverizing a Cu-Al melt followed by heating in an oxidizing atmosphere. The invention further concerns the use of a dispersion-hardened powder of this type for the powder-metallurgical production in particular of wear and corrosion-resistant valve seat rings or valve guides with high heat conductivity. Finally, the invention concerns a method of producing such valve seat rings or valve guides.

Description

MATERIAL FOR POWDER METALLURGICAL PRODUCTION OF MOLDED PARTS, IN PART. VALVE SEAT RINGS OR VALVE GUIDES WITH HIGH WEAR RESISTANCE

The invention relates to a material for the powder-metallurgical production of molded parts with high thermal conductivity and high wear and corrosion resistance by pressing, sintering and optionally post-compression of a powder mixture with a copper content of at least about 50% by weight.

Sintered materials of this type are required for molded parts which are exposed to hot gases or gas mixtures, for example for the production of valve seat rings and valve guides for internal combustion engines which are exposed to high mechanical loads on the one hand and at the same time to the action of hot combustion gases. They must therefore be made from materials that are not only wear and corrosion resistant, but also have a high thermal conductivity. Thermal conductivity is becoming increasingly important, as the temperature level at the valves increases due to the expansion of the stoichiometric mixture required for emission reasons, and a continuing trend towards more powerful engines can be seen. It is known to reduce the temperature difference between the head of the valve and the cylinder head into which the valve seat ring is incorporated by transporting heat in the valve. For this purpose, the valve stem is provided with a hollow bore and cooled. For cost and weight reasons, the diameters of the valve stems have been reduced in recent years to such an extent that in most cases it is no longer possible to provide them with a hollow bore, so that the use of hollow-bore valves, for example filled with sodium, in Future will no longer be possible. The aim is therefore to improve the thermal conductivity of the material from which the valve seat, in particular the valve seat ring, is made, in order in this way to dissipate the heat more quickly, to lower the temperature level, in order to improve the tribological conditions and the system technologically and improve in cost.

Powder-metallurgically produced molded parts made of sintered materials based on iron with infiltrated copper are known which have sufficient wear resistance for use as a valve seat ring or valve guide, the thermal conductivity of which is not high enough compared to sintered materials without a copper content. For example, a sintered material is known from DE-PS 21 14 160, which consists of an iron-based material to which carbon and lead and other alloy components have been added. Valve seat rings made from this material do have sufficient heat and wear resistance, but their thermal conductivity is not sufficient to overcome the problem in particular in the outlet area of a modern one

Solve internal combustion engine.

PCT-EP 89/01343 discloses a sintered material for the powder metallurgical production of valve seat rings which are said to have increased thermal conductivity with high wear resistance. The sintered material consists of a base metal powder with a copper content of approximately 70 to 100% by weight of copper and an alloy content. The alloy fraction can consist, for example, of 1 to 3% by weight of cobalt or a high-alloy additional metal powder which is mixed into the basic metal powder as a hard phase, the proportion of which then amounts to a maximum of 30% by weight.

Tests carried out with such a material have shown that the material has a wear resistance which is insufficient for the manufacture of valve seats, in particular for the exhaust area of internal combustion engines. This is due to the fact that the hardness of the material could be increased by solidifying the matrix by embedding hard materials with a maximum particle size of 150 μm and thus the wear resistance of the valve seat, but on the other hand by the relatively large and sharp-edged embedments the counter body was worn out more. The wear on the valve seat ring was therefore low, while the overall wear, which is important for the permanent functioning of the system, was worsened.

The invention has for its object to provide a sintered material for powder metallurgical production, in particular of valve seats or valve guides, the wear resistance of which is very high and which at the same time has a significantly high thermal conductivity compared to known sintered materials used for this purpose.

Starting from a material for the powder metallurgical production of molded parts with high wear and corrosion resistance and high thermal conductivity, in particular for the production of valve seats or valve guides for internal combustion engines, by pressing, sintering and, if necessary, post-compression of a starting powder mixture with a copper content of at least about 50% by weight. %, the invention consists in that the starting powder mixture consists of a base powder containing the Cu content in an amount of 50 to 90% by weight and a powdery alloy additive containing molybdenum in an amount of 10 to 50% by weight and that the base powder is a dispersion-strengthened copper powder. The dispersion-strengthened copper powder is preferably solidified by Al2O3, contains from 0.1 to 1.1% by weight of Al2O3 and less than 0.5% by weight of impurities and 97/30808 PC17EP97 / 00837

is produced by atomizing a Cu-Al melt and then heating in an oxidizing atmosphere for the selective oxidation of the aluminum.

The invention is based on the surprising finding that the use of a Cu-Al∑Os powder, preferably dispersion-strengthened by means of Al2O3, as a material for the powder-metallurgical production of moldings leads to products which, on the one hand, have high wear and corrosion resistance and, on the other hand, high thermal conductivity have, so that they are particularly suitable for the production of valve seat rings or valve guides for internal combustion engines.

For the present purpose, only those with Al2O3 dispersion-strengthened Cu powder are suitable, which after the z. B. from US-PS 37 79 714 or DE-PS 23 55 1 22 known processes by internal oxidation and subsequent heating of Cu-Al alloy powder, made from atomizers of a Cu-Al melt, in an oxidizing atmosphere, while dispersion-strengthened metal powders produced by another method according to GB-A-2 083 500, in which internal oxidation is expressly to be excluded, are unsuitable. The applicant attributes this to the fact that the distance between the dispersed AbO 3 particles in the copper matrix in the Cu-Al 2 O 3 powder produced by means of internal oxidation is of the order of 3 to 12 nm, whereas it is approximately the same in the case of the powder produced without internal oxidation Is 40 μm. There is no reference in these publications to the use according to the invention of dispersion-strengthened metals as base powder for the powder-metallurgical production of molded parts, in particular valve seat rings or valve guides.

A preferred embodiment of the invention provides that the alloy surcharge consists of a powdery, preferably water-thinned, intermetallic hard phase of 28 to 32, preferably 30,% by weight.

Molybdenum, 9 to 1 1, preferably 10% by weight of chromium, 2.5 to 3.5, pre- preferably 3% by weight silicon, the rest cobalt, the intermetallic hard phase being present in the powder mixture in an amount of about 10% by weight and the base powder in an amount of about 90% by weight.

In another embodiment of the invention, the intermetallic hard phase consists of 28 to 32, preferably 30% by weight molybdenum, 9 to 11, preferably 10% by weight chromium, 2.5 to 3.5, preferably 3% by weight. % Silicon, balance iron, the intermetallic phase being present in the powder mixture in an amount of about 10% by weight and the base powder in an amount of about 90% by weight.

According to the invention, the alloy surcharge can also consist of a hard phase consisting of a high-speed steel powder of approximately 6% by weight of tungsten, approximately 5% by weight of molybdenum, approximately 2% by weight of vanadium, approximately 4% by weight of chromium, the rest being iron Hard phase is present in the powder mixture in an amount of up to about 30% by weight and the base powder in an amount of about 70% by weight or higher.

The alloy surcharge can also consist of a hard phase from a Mo-PC powder composed of approximately 11% by weight molybdenum, approximately 0.6% by weight phosphorus, approximately 1.2% by weight carbon, the rest being iron, the Hard phase and the base powder are present in the powder mixture in an amount of approximately 50% by weight.

The invention further relates to a material which consists of a starting powder mixture of approximately 80% by weight of base powder, approximately 10% by weight of molybdenum powder and approximately 10% by weight of copper powder or approximately 79% by weight of base powder, approximately 10% by weight of molybdenum powder, approximately 10% by weight of copper powder and approximately 1% by weight of powdered molybdenum trioxide.

The invention further provides that the base powder additionally molybdenum disulfide (M0S2) and / or manganese sulfide (MnS) and / or tungsten disulfide (WS2) and / or calcium fluoride (CaF2) and / or tellurium (Te) and / or calcium carbonate (CaC03 > in a total amount of at least 1% by weight to a maximum of 3% by weight based on the amount of the base powder. The invention further relates to a process for the powder-metallurgical production of molded parts with high wear and corrosion resistance and high thermal conductivity, in particular for the production of valve seat rings or valve guides for internal combustion engines, in which an initial powder mixture having one of the compositions described above with about 0.3% by weight of a pressure-relieving agent, e.g. B. wax, mixed, molded and pressed into a molded part with a density of about 8.0 g / cm ³ and subjected to a subsequent sintering under protective gas; the sintering is preferably carried out under a protective gas atmosphere of approximately 80% by weight of nitrogen and approximately 20% by weight of hydrogen for a period of approximately 45 minutes at a temperature of approximately 1,040 ° C. If necessary, the sintered molded part can be subjected to post-compression to a density of approximately 8.8 g / cm ³ .

An alternative embodiment of the invention provides that the starting puiver according to claim 1 contains one or more of the substances or substance mixtures listed below:

a) 5 - 30% by weight tool steel type M35 or type T15,

Ni-Cr-Si-Fe-B-Cu-Mo;

b) 5-10% by weight of W, Mo, Nb, WC, TiC, B ₄ C, TiN, c-BN, TiB ₂ ;

c) 0.5-5% by weight of Ti, Cr, Zr, Cr + Zr, Be, Ni + P.

The materials of group a) alloy with the copper matrix of the dispersion-strengthened copper by diffusing these additives into the copper and thereby significantly reducing the electrical and thermal conductivity. In order to keep the thermal conductivity above 100 W / m ^• k, the proportion should not exceed 5-20% by weight, typically 10% by weight.

The materials of group b) do not alloy with the copper matrix and therefore have no noticeable influence on the thermal conductivity. they are however relatively expensive. However, it has been found that a proportion of 5-10% by weight is sufficient.

The additions of group c) cause the intermetallic components to be excreted and in this way superimpose the hardness effect in addition to the hardening by the Al2O3 particles in the dispersion-strengthened copper. While the aluminum oxide particles effectively harden the copper matrix at high temperatures (> 500 ° C), the precipitation phases result in more effective hardening in the medium temperature range (200 - 500 ° C), which are the typical operating temperatures to which the valve seat rings are concerned are exposed. The higher warm hardness generally leads to higher wear resistance.

The wear of the valve seat rings is also caused by the addition of solid lubricants such as graphite, M0S2, MnS, h-BN, CaF∑ and the like, as well as metal additives such as Mo, Co, W or the like, which form oxide skins at the operating temperatures, which have a smear effect.

The fact that the starting powder according to one or more of the substances listed below:

5-20% by weight of Zn, 0.1-5% by weight of one of the elements Al, Be, Si, Mg, Sn

contains, the oxidation resistance, i. H. Corrosion resistance in operation, significantly increased. With a view to reducing the thermal conductivity as little as possible, Zn is the preferred alloy component. In this regard, an addition of 5-30% by weight is not critical.

The starting powder preferably contains one or more of the following powdery substances with an irregular particle shape: 5 - 25 wt .-% Cu high green strength, electrolyte Cu, oxide-reduced Cu, Mo, or the like.

Because the dispersion-strengthened copper used has round, smooth particles, the unsintered, green parts made of this material have only a low strength. The green strength can be increased considerably by adding the aforementioned components. The "Cu of high green strength" is powder with long, thin, fiber-like particles that intertwine when pressed together and in this way bring about a high strength of the green body. The addition of pure Cu does not increase the thermal conductivity touched so that 5-25% by weight can be added, the preferred range being 10-15% by weight.

The machinability, in particular the machinability, of dispersion-strengthened copper is improved by adding one or more of the substances mentioned below:

a). 0.2-2% by weight of chemical elements such as C (graphite), Te, Se; b). 0.5-5 wt% sulfides such as M0S2, MnS, etc .; c). 0.5-5% by weight of oxides such as M0O3, WÜ3, C03O4, etc .; d). 0.5 - 5 wt .-% compounds such as hexagonal BN, CaF∑.

The radial breaking strength of the valve seat rings, which must be given in particular when pressed into the cylinder head, is increased by adding one or more of the following substances:

a) 5-20% by weight of Zn, 0.1-1% by weight of Al or Sn, etc .; b) 5 - 30% by weight tool steel type M35 or type T1 5, Ni-Cr-Si-Fe-B-Cu-Mo

The starting powder mixture can be optimally coordinated with regard to the properties required for the valve seat ring by a corresponding combination of the aforementioned alloy additives. The main advantage with regard to the production of valve seat rings in all of the aforementioned starting powder mixtures according to the invention is that the thermal conductivity is particularly high, ie at least 100 W / m ^• k.

embodiments

example 1

A medium-internal oxidation-strengthened Cu-Al∑Os powder with a content of 0.5% by weight of Al2O3 was mixed with 0.3% by weight of a conventional press-serifying agent and with a press pressure of 800 MN / mm ² to form valve seat rings the dimensions 36.6 x 30, 1 x 9 mm pressed. The green compacts, which had a pressed density of 8.4 g / cm ³ , were then sintered for 45 minutes at a temperature of 1,040 ° C. under a protective gas atmosphere of 80% N2 and 20% hydrogen. The sintered density was 8.4 g / cm ³ . The sintered rings were then subjected to post-compression to a density of 8.8 g / cm ³ at a pressure of 1,600 MN / mm ² .

Table 1 shows the measured densities and hardness values, Table 2 the thermal conductivity values, which were determined by the laser flash method.

Table 1 :

Table 2:

Example 2

90% by weight of a dispersion-strengthened Cu-Al2θ3 powder produced by means of internal oxidation with a content of 0.5% by weight of Al2O3 was mixed with 10% by weight of a water-soluble, powdery, intermetallic hard phase and 0.3% by weight. % of a conventional press-relieving agent mixed. The intermetallic hard phase consisted of 60% by weight of cobalt, 30% by weight of molybdenum, 10% by weight of chromium and 3% by weight of silicon. The powder mixture was pressed at a pressure of 800 MN / mm ² into molds to form valve seat rings with the dimensions 36.6 x 30, 1 x 9 mm. The green compacts had a compression density of 8.2 g / cm ³ . The rings were then sintered for 45 minutes at a temperature of 1,040 ° C. in a protective gas atmosphere composed of 80% N2 and 20% H2; the sintered density was 8.2 g / cm ³ . The densification to a density of 8.7 g / cm ^{3 was} carried out with a pressure of 1,600 MN / mm ² . Table 3 shows the density and hardness values, Table 4 the thermal conductivity values determined by the laser flash method.

Table 3:

Table 4:

The valve seat rings produced according to Examples 1 and 2 showed an unexpected improvement in thermal conductivity compared to commercially available valve seat rings based on Fe with and without copper infiltration. This is shown in Figure 1. Curve 1 shows the Thermal conductivity values of a valve seat ring according to Example 1, curve 2 the values for a ring according to Example 2, curve 3 the values of a valve seat ring based on Fe with copper infiltration and curve 4 the values of a commercially available valve seat ring from the applicant.

The rings produced according to Example 1 have a hardness which permits their use in the inlet area of an internal combustion engine, while the valve seat rings according to Example 2 can be used in the outlet area and have excellent running behavior here. This was determined by tests, the conditions of which are summarized in Table 5.

Table 5:

The results of the engine test are summarized in Table 6 and shown graphically in Figure 2. The sinking depth is the sum of the wear of the valve and the valve seat ring. The valve seat ring according to the invention according to Example 2 was compared with the Series material Como1 2 by the applicant, which is used on a large scale.

Table 6:

It can be seen that the sinking depth of the valve seat ring according to the invention with a significantly increased thermal conductivity of the material is less than that of a commercially available valve seat ring.

Claims

Patent claims

1. Material for the powder-metallurgical manufacture of molded parts with high wear and corrosion resistance and high thermal conductivity, in particular for the manufacture of valve seat rings or valve guides for internal combustion engines by pressing, sintering and, if necessary, re-compression of a starting powder mixture with a copper content of at least about 50% by weight. , characterized in that the starting powder mixture consists of a base powder containing the Cu content in an amount of 50 to 90% by weight and a powdery alloy additive containing molybdenum in an amount of 10 to 50% by weight and that Base powder is a dispersion-strengthened copper powder.

5 2. Material according to claim 1, characterized in that the dispersion-strengthened copper powder is solidified by AI2O3, contains 0.1 to 1.1 wt .-% AI2O3 and less than 0.5 wt .-% impurities and by spraying a Cu -Al melt and subsequent heating in an oxidizing atmosphere for selective oxidation of the aluminum 0 is produced.

3. Material according to claim 1 and 2, characterized in that the alloy surcharge consists of a powdery, preferably water-evaporated intermetallic hard phase.

4. Material according to claims 1 to 3, characterized gekennzeich¬ net that the intermetallic hard phase has the following composition:

28 to 32, preferably 30% by weight of molybdenum, 9 to 11, preferably 10% by weight of chromium, 2.5 to 3.5, preferably 3% by weight of silicon,

Rest cobalt.

5. Material according to claim 4, characterized in that the intermetallic hard phase in the powder mixture in an amount of about 10 wt .-% and the base powder are present in an amount of about 90 wt .-%.

6. Material according to claims 1 and 3, characterized gekennzeich¬ net that the intermetallic hard phase has the following composition:

Rest of iron.

7. Material according to claim 6, characterized in that the intermetallic phase in the powder mixture in an amount of about 10 wt .-% and the base powder are present in an amount of about 90 wt .-%.

8. Material according to claims 1 and 2, characterized gekenn¬ characterized in that the alloy surcharge consists of a hard phase from a high-speed steel powder (AISI type M2; DIN S-6-5-2) with the following composition:

about 6% by weight of tungsten, about 5% by weight of molybdenum, about 2% by weight of vanadium, about 4% by weight chromium, balance iron.

9. Material according to claim 8, characterized in that the hard phase in the powder mixture in an amount of up to 30 wt .-% and the base powder in an amount of about 70 wt .-% or higher.

10. Material according to claims 1 and 2, characterized gekenn¬ characterized in that the alloy surcharge consists of a hard phase from a Mo-P-C powder with the following composition:

about 11% by weight molybdenum, about 0.6% by weight phosphorus, about 1.2% by weight carbon, balance iron.

1 1. Material according to claim 10, characterized in that the hard phase and the base powder are each present in the powder mixture in an amount of approximately 50% by weight.

12. Material according to claim 1, characterized by the following composition of the starting powder mixture:

about 80% by weight base powder, about 10% by weight molybdenum powder, about 10% by weight copper powder.

13. Material according to claim 1, characterized by the following composition of the starting powder mixture:

about 79% by weight base powder, about 10% by weight molybdenum powder, about 10% by weight copper powder and about 1% by weight molybdenum trioxide.

14. Material according to one of the preceding claims, characterized in that the base powder additionally molybdenum disulfide (M0S2) and / or manganese sulfide (MnS) and / or tungsten disulfide (WS2) and / or calcium fluoride (CaF2) and / or tellurium (Te) and / or calcium carbonate (CaCO3) in a total amount of at least 1% by weight to a maximum of 3% by weight based on the amount of the base powder.

1 5. A method for powder metallurgical production of molded parts with high wear and corrosion resistance and high thermal conductivity, in particular for the manufacture of valve seat rings or valve guides for internal combustion engines, characterized in that an initial powder mixture according to one of the preceding claims with about 0.3 wt. % of a pressure-relieving agent, e.g. B. wax, mixed, deformed and pressed into a molded part with a density of approximately 8.0 g / cm ³ and subjected to a subsequent sintering under protective gas.

1 6. The method according to claim 1 5, characterized in that the sintering under a protective gas atmosphere of about 80 wt .-% nitrogen and about 20 wt .-% hydrogen for a period of about 45 minutes at a temperature of about 1 .040 ° C is done.

17. The method according to claims 15 and 1 6, characterized gekenn¬ characterized in that the sintered molded body is subjected to post-compression to a density of about 8.8 g / cm ³ .

18. Use of a Cu-Al2θ3 powder which has been dispersion-strengthened by means of AI2O3 and has a content of AI2O3 of between 0.3 and 1.1% by weight, which is produced by atomizing a Cu-Al melt and then heating in an oxidizing atmosphere Powder metallurgical production of wear and corrosion resistant molded parts with high thermal conductivity, especially for the production of valve seat rings or valve guides.

1 9. Materials according to claim 1, characterized in that the starting powder mixture contains one or more of the substances or substance mixtures listed below:

a) 5 - 30% by weight tool steel type M35 or type T15, Ni-Cr-Si-Fe-B-Cu-Mo;

b) 5-10% by weight of W, Mo, Nb, WC, TiC, B ₄ C, TiN, c-BN, TiB∑;

c) 0.5-5% by weight of Ti, Cr, Zr, Cr + Zr, Be, Ni + P.

20. Materials according to claim 1, characterized in that the starting powder mixture contains one or more of the substances listed below:

5 - 10% by weight Co, W.

21. Material according to claim 1, characterized in that the starting powder mixture contains one or more of the substances listed below:

5-20% by weight of Zn, 0.1-5% by weight of one of the elements Al, Be, Si, Mg, Sn.

22. Material according to claim 1, characterized in that the starting powder mixture contains one or more of the powdery substances listed below with an irregular particle shape:

5 - 25 wt .-% Cu high green strength, electrolyte Cu, oxide-reduced Cu, Mo.

23. Material according to claim 1, characterized in that the starting powder mixture one or more of the following under a). Tenz to d). Tenz listed substances contains: a). 0.2 - ^■ 2% by weight of chemical elements such as C (graphite), Te, Se; b). 0.5-5% by weight sulfides such as M0S2, MnS, etc .; c). 0.5 - 5% by weight oxides such as M0O3, WO3, C03O4, etc .; d). 0.5 - 5 wt .-% compounds such as hexagonal BN, CaF∑.

24. Material according to claim 1, characterized in that the

Starting powder mixture contains one or more of the substances listed below:

a) 5-20% by weight of Zn, 0.1-1% by weight of Al or Sn, etc .; b) 5 - 30% by weight tool steel type M35 or type T1 5, Ni-Cr-Si-Fe-B-Cu-Mo.

25. Material according to claim 1 and one or more of claims 18-23, characterized in that the starting powder mixture contains combinations of the substances or the substance mixtures of claims 18-23:

26. Use of a material according to claim 1 and one or more of claims 19-24 for the production of a valve seat ring or valve guides, the thermal conductivity of which is at least 100 W / m ^• k.