EP3325194B1 - Tribological system comprising a valve seat insert (vsi) and a valve - Google Patents

Description

The invention relates to a tribological system comprising a valve seat ring made of sintered material and an untreated valve or a valve hardened and / or armored at least in the seat area.

In addition to increasing the power concentration, availability and extending the service life, the focus of the new development and downsizing of engines is on increasing the effectiveness of the engine while reducing emissions. To achieve these aspects, higher demands are often placed on the individual engine components with regard to durability and wear resistance than before.

An example of this are the intake and exhaust valve elements in the area of the combustion chamber of the engine, i.e. the valve and the associated valve seat ring, which together form a tribological system. They seal the combustion chamber and control the gas exchange in the engine. The surfaces interacting and interacting in this system are subject to extremely complex loads due to the load spectrum acting in an internal combustion engine, which is composed of mechanical, thermal, tribological and chemical loads.

Each partner in the tribological system mentioned above has to meet different requirements.

The valve seat ring must have a high strength, in particular a high resistance to deformation at medium temperatures (creep resistance), as well as a high degree of warm hardness, especially since the exhaust valves hit the valve seat more than 70 times per second. To ensure rapid heat transport in the cylinder head and a reduction in the valve temperature, valve seat rings must also have good thermal conductivity. Last but not least, high lubricity and wear resistance are imperative for valve seat rings.

Valve seat rings with the above-mentioned properties are usually obtainable by sintering a sintered material. The powder composition (Table 2) usually consists of a combination of a high-speed steel powder (e.g. the commercially widespread powders K3 or K1) and one or more hard phases based on Fe, possibly also based on Co, as well as other components , such as solid lubricants such as sulfides, e.g. B. MoS ₂ and / or graphite and / or copper and / or CaF ₂ . Often these valve seat rings are also infiltrated with copper in order to achieve higher thermal conductivity and better machinability. A disadvantage of these valve seat ring materials is that they are often relatively aggressive towards their counterparts and therefore also cause higher valve wear.

The valves, and in particular the valve plates, must have high heat resistance and high wear resistance due to temperatures of up to 1,000 ° C. For this purpose, it is customary to armor, harden and / or nitride the valves, in particular the valve disks, in order to improve the tribological properties of the system. There are also tribological systems in which the valve plates are not treated superficially.

The US6318327B1 describes a tribological system consisting of a valve seat ring and valve. The valve seat ring consists of an iron-based sintered material and fine deposits of 10 to 50% by weight of a CoMoCr-based intermetallic hard phase, for example T 800 and T 400. Solid lubricants (sulfides, nitrides, fluorides, graphite) are added; infiltration and impregnation with Cu are also described. Sintering takes place in a vacuum. This is very disadvantageous for a continuous sintering process of large quantities.

An austenitic steel is used as valve (SUH35 (JIS G 4311: 21% Cr-4% Ni-9% Mn-O.4% NO.5% C-Fe (rest)), which nitrides or with to improve wear resistance Stellite F, 6 or 12 or armored with K8, K10 to improve the tribological properties of the system.

It is disadvantageous that optimum properties are not achieved for specific tribological systems, especially since other valve materials are not taken into account. This is also relevant because not only the interaction between the valve plate and Valve seat ring determines the reliability of the system, but the valve guide must also be included in this consideration. In this respect, the restriction to only one group of valve materials leads to a restriction in the optimization of the material pairing.

The WO 2009 024 809 A1 discloses a material for a valve seat ring, in which an iron-based alloy with reduced contents of carbides of the elements Mo, W, V and Nb is used. This powder makes up the main part of the powder mixture to be processed. It also contains the usual additives for improving machining, sintering and solid lubricants, as well as hard phases and copper.

In addition to the individual properties of the valve and valve seat ring, it is important for a tribological system to keep the mechanical, physical and / or chemical interactions of the partners as low as possible. This is usually ensured by external lubrication using fuels, combustion products or engine oil. If this external lubrication is significantly reduced or if it is completely eliminated, the tribological system, which was previously exposed to liquid or mixed friction, is increasingly exposed to solid friction, which leads to higher overall wear.

Finally, the WO 2009 040 369 A1 a pre-alloyed powder made of water-atomized iron-based powder, which is suitable for the production of pressed and sintered components with high wear resistance. The iron-based powder comprises 10 to 18% by weight of Cr, each 0.5 to 5% by weight of at least one of Mo, W, V and Nb and 0.5 to 2%, preferably 0.7 to 2% and most preferably 1 to 2% by weight of C.

The object of the invention is to provide a tribological system comprising a valve seat ring and an untreated or a hardened and / or armored valve which avoids the disadvantages of the prior art and in particular has a higher wear resistance with reduced overall wear. We solved the problem with the tribological systems described in the patent claims.

The invention is defined in the claims. According to claim 1, the tribological system according to the invention comprises a first tribological partner, namely a valve seat ring made of a sintered material, which is characterized in that the sintered material is obtainable by pressing and sintering a mixture of individual powder components, the 5 to 45% by weight of one or more hard phases based on Fe and 0 to 2% by weight of graphite particles and / or 0 to 2% by weight of MnS and / or 0 to 2% by weight of MoS ₂ - and / or up to 2% by weight FeP and / or 0 to 7% by weight Cu and / or 0 to 4% by weight co-powder

and 0 to 1.0% by weight of a pressing aid and the remainder high-speed steel powder with a composition of 14 to 18% by weight of Cr, 1.2 to 1.9% by weight of C, 0.1 to 0.9% by weight % Si, 0.5 to 2.5% by weight V, 0.5 to 2.5% by weight W, 0.5 to 2.5% by weight Mo, and

contains the remainder Fe as well as production-related impurities, in particular by Ni, Cu, Co, Ca and / or Mn with proportions <1.5% by weight, one or more hard phases based on Fe having a composition of <0.2 % By weight C, 26 to 32% by weight Mo, 8 to 12% by weight Cr, 2.2 to 3% by weight Si. And a second tribological partner, namely a superficially untreated valve.

Alternatively, the second tribological partner is a valve hardened and / or armored and / or nitrided at least in the seating area. In addition to reduced wear in the tribological system, the armor or the nitriding also serves to achieve a better sealing effect of the valve during operation. The valves are therefore preferably nitrided and / or armored in the seat area with a material based on iron or Co.
According to claim 2, the tribological system according to the invention comprises a first tribological partner, namely a valve seat ring made of a sintered material, which is characterized in that the sintered material is obtainable by consolidating and sintering a mixture of individual powder components, which contains 5 to 45% by weight or several hard phases based on Fe with a composition of <0.3% by weight C, 26 to 32% by weight Mo, 14 to 20% by weight Cr, 2.9 to 4.2% by weight Si and 0 to 2% by weight of graphite particles and / or 0 to 2% by weight of MnS and / or 0 to 2% by weight of FeP and / or 0 to 2% by weight of MoS ₂ powder and / or 0 up to 7% by weight Cu and / or 0 to 4% by weight co-powder and
0.1 to 1.0% by weight of a pressing aid and the remainder,

a high-speed steel powder with a composition of 14 to 18 wt .-% Cr, 1.2 to 1.9 wt .-% C, 0.1 to 0.9 wt .-% Si, 0.5 to 2.5 wt. -% V, 0.5 to 2.5 wt% W, 0.5 to 2.5 wt% Mo and as
Remainder Fe as well as production-related impurities, in particular by Ni, Cu, Co, Ca and / or Mn with proportions <1.5% by weight.
And a second tribological partner, namely a superficially untreated valve.
Alternatively, the second tribological partner is a valve hardened and / or armored and / or nitrided at least in the seating area. In addition to reduced wear in the tribological system, the armor or the nitriding also serves to achieve a better sealing effect of the valve during operation. The valves are therefore preferably nitrided and / or armored in the seat area with a material based on iron or Co.
Compared to the known solution attempts, namely the optimization of the properties of the individual partners of a tribological system, the invention is based on the surprising finding that tribological partners are achieved through the material composition described in the valve seat ring, through the mixture of the selected starting powders, and through the clever choice of the valve , in which the solid friction in the valve seat ring - valve system is reduced and the total wear can be considerably reduced.

In general, in addition to the valve seat ring and valve with plate and stem, a tribological system also includes the valve guide. In particular, if the valve seat and valve stem are untreated, ie neither hardened, coated nor armored, the Adjustment of the valve guide should not be neglected. A corresponding material combination of valve stem and valve guide is also required here.

It was found that even compared to sintered materials that were alloyed with a high proportion of Co (see comparative example 2 below), reduced wear can be observed within the tribological system according to the invention. Compared to commercially available sintered materials (see comparative example 1 below, see comparative example 3 below), a significant reduction in wear can be observed. But it is only the skilful combination of the sintered material with untreated valves, or with valves that are nitrided and / or armored in the seating area with an iron or Co-based material, that leads to the tribological system according to the invention, which is characterized by significantly reduced wear of the individual tribological partners.

It was also found that the wear resistance of the tribological system according to the invention includes depends on the hardness and the thickness of a nitride diffusion layer formed at least in the seat area of the valve. The best results can be achieved with a hardness> 510 HV and a thickness> 19 µm. It has also been found that the wear resistance of the tribological system according to the invention includes depends on the type of layer and layer thickness of an armor formed at least in the seat area of the valve. The best results can be achieved with a layer thickness of the armor of> 400 µm and a Co content and / or Fe content of> 40%.

Furthermore, studies have shown that materials according to the invention for the valve seat ring in combination with the standard mixture Nireva 3015 (with the composition in% by weight: up to 0.08 C, up to 0.5 Si, up to 0.5 Mn, up to 0.015 P, to 0.01 S, 13.5 to 15.5 Cr, 30.0 to 33.5 Ni, 0.4 to 1.0 Mo, 1.6 to 2.2 Al, 2.3 to 2.9 Ti , 0.4 to 0.9 Nb and the balance Fe) or with the standard mixture Nimonic 80 (with the composition in% by weight: 0.04 to 0.1 C, to 1.0 Si, to 1.0 Mn , up to 0.02 P, up to 0.015 S, 18.0 to 21.0 Cr,> 65.0 Ni, up to 3.0 Fe, up to 2.0 Co, 1.0 to 1.8 AI and 1.8 up to 2.7 Ti) after optimal heat treatment even without superficial treatment, such as nitriding or armor, have reduced overall wear Hard phases based on Fe are cheaper than Ni and Co-based alloys and can be specifically adjusted to specific applications by heat treatment. Carbon hardens the matrix and also forms hard carbides that increase wear resistance.

In accordance with the different engine-specific requirements for wear resistance in various practical applications, it may also be advantageous to add a hard phase based on Fe as well as a hard phase based on Co to the sintered material. In a third embodiment of the tribological system according to the invention, a hard phase on a Co basis is therefore additionally mixed with the sintered material in a proportion of 0.5 to 9.9% by weight.

Preferred hard phases (Table 2) based on Fe are K11, K6, K7 and K4. K6 and K7 are particularly preferred. Preferred Co-based hard phases to be considered in the described tribosystem, K8, K9 and K10, with K8 and K9 being particularly preferred. The composition of the hard phases is explained below.
By selecting suitable sintering parameters, such as temperature, atmosphere or dew point, a structure can be set in the valve seat ring in which the special carbides in the sintered material are significantly coarser than, for example, in conventional high-speed steel. Despite the coarser carbides, the strength values, measured in the compression test between 25 and 300 ° C and described by the compression limit Rd 0.2 of the sintered material, are comparable. The hot hardness, however, is higher than that of the comparison materials.

The disclosure is explained in more detail below using examples and a reference.

example 1

Table 1 shows the compositions of a powder mixture "Reference" and a comparison mixture "Comparison 3". Manufacturing technology and application technology additives (eg sulfides) are contained in "Other". Some examples of mixture components used or can be used in the sense of the reference are summarized in Table 2 (starting powder). <b> Table 1: </b> Powder mixtures without solid lubricant, process-related additives and Cu-I nfiltrants K1 K2 graphite K12 Cu K6 Other Comparison 3 % By weight 84 0.3 0.3 5 10th 0.4 reference % By weight 84 0.3 0.3 5 10th 0.4 designation C. P Mn Si Cr Ni Mon Cu V W Co Fe rest K1 1.0 0.4 0.4 4.0 5.0 3.0 6.0 1.0 78.9 K2 1.5 0.5 16.0 1.5 1.0 1.5 60.3 K3 0.8 0.04 0.3 0.45 4.0 0.4 5.0 0.4 2.0 6.2 1.0 76.41 3rd K4 70 30th K5 4th 0.5 1.5 rest K6 0.1 2.6 8.5 28.5 50.8 K7 0.3 3.4 17.5 28.0 60.3 K8 0.1 2.6 8.5 28.5 60.3 K9 0.2 1.3 17.0 22.0 59.5 K10 3.4 17.5 28.0 51.1 K11 0.1 0.1 2.4 9.2 8.8 20.1 59 K12 15 85 K14 100

In a first step, the powders listed in Table 1 and specified in Table 2 are mixed in a tumble mixer for 30 min. Then these mixtures are pressed at a pressure of 700 MPa to valve seat rings (φa: 30 mm, φi: 23 mm; height: 6 mm). A part of the rings is sintered at a temperature of 1110 to 1125 ° C (approx. 30 min) under N ₂ -H ₂ (17 to 25% by volume H ₂ ) in a continuous furnace. Another portion is subjected to sintering at 1132 to 1145 ° C (approx. 30 min) under N ₂ -H ₂ (17 to 25% by volume H ₂ ).

The sintering conditions used and the sintered densities achieved are summarized in Table 3 (sintered densities). <b> Table 3 </b>: Sintering conditions for the powder mixture "reference" and the mixture to be compared "comparison 3 Sintering conditions and sintering density Tmax1 Duration Tmax2 Duration ° C min ° C min Comparison 3 1110-1125 20-33 1132-1145 20-33 reference 1110-1125 20-33 1132-1145 20-33 Atmosphere: N2-H2 (17-25 vol% H2) Mix for comparison Variants of heat treatment after sintem Start Reward T Duration cooling down T Duration cooling down Start Duration cooling down ° C H K / min ° C H ° C min K / min Comparison 3 620 2nd 5 - 10 880 2nd oil 580 40 5 - 10 reference 620 2nd 5 - 10 880 2nd oil 580 40 5 - 10

Due to the different sintering conditions and tempering, the average diameters shown in Table 1 for the special carbides formed (MoC, VC, Cr ₂ C ₃ ) result (see Table 4).

The maximum temperature during sintering was 1,132 to 1,145 ° C. The hold time was 20 to 33 minutes at the above temperature. A mixture of N ₂ -H ₂ with an H ₂ content of 17 to 25% was used as the atmosphere.

After the sintering, the sintered material was gem. Table 4 (heat treatment) heat treated. For this purpose, both simple tempering at temperatures between 550 and 620 ° C and tempering of the material, i.e. Hardening at 850 to 950 ° C - oil quenching - tempering at 510 to 610 ° C used. Since the differences in properties, especially wear behavior, machinability and creep behavior, are small, the tempered material is used.

A measurement of the special carbides showed an average diameter of 2.1 µm for conventional comparison material and 4.0 µm for the referenced sintered material. In addition to the mean values, the minimum and maximum values are given in Table 1. <b> Table 5 </b>: Average diameter of the special carbides in the sintered powder mixture "Reference" and in the mixture to be compared "Comparison 3" average diameter [µm] Min. MW Max. Comparison 3 0.5 2.1 5.1 reference 1.1 4.0 12.1

Table 6 shows both the hardness and the 0.2% compressive yield strength at room temperature and at 300 ° C. Surprisingly, despite the coarser carbides, the strength values of the referenced sintered material are comparable to those of conventional comparison material (e.g. comparison 3) <b> Table 6 </b>: Strength values and hardening after sintering / heat treatment of the powder mixture "reference" and the mixture to be compared "comparison 3" T [° C] Rd0.2 [MPa] Hardness [HV10] reference Comparison 3 reference Comparison 3 25th 1,400 1,813 415 391 300 1,328 1,195 372 349

Fig. 1:

(nicht grafisch dargestellt) Gesamtverschleiß - nach motorischer Erprobung im Tribosystem "Ventilsitzring - Ventilsitz", wobei neben dem hergestellten Ventilsitzring ("Referenz") Ventilsitzringe aus den Vergleichswerkstoffen "Vergleich 1", "Vergleich 2" und "Vergleich 3" betrachtet wurden

The performance is evaluated in a tribological system via the total wear on the valve seat ring and valve seat of a valve armored with Stellit F. 1, which is not shown graphically, shows the corresponding results for the sintered / heat-treated valve seat ring-valve combinations of the powder mixture "reference" and the mixture to be compared "comparison 3", and for two further mixtures which correspond to the prior art.

Fig. 1:

(not shown graphically) Total wear - after engine testing in the tribological system "valve seat ring - valve seat", whereby in addition to the valve seat ring manufactured ("reference"), valve seat rings made from the comparison materials "comparison 1", "comparison 2" and "comparison 3" were considered

1, which is not shown graphically, illustrates the improved performance of the tribological system “reference”. By skillful combination of manufacturing and Due to the composition of the referenced sintered material and combination with a valve armored with Stellite F at least in the seating area, the solid friction of the tribological partners is reduced and thus the wear is considerably reduced. The total wear measured is reduced in this case.

In the "Comparison 1" tribological system, the valve seat ring consists of in% by weight: C: 1.5; S: 0.6 Cr: 3; Mon: 5 to 15; Cu: 10 to 20; V: 2; Fe: rest; others: 4.

"Comparison 2" is a Co-containing material that contains high proportions of the refractory metals Mo and W in addition to this expensive raw material. In detail, the functional area consists of the elements in% by weight: C: 0.5 to 2; Mn: 1; Cr: 3 to 6; Mon: 8 to 15; Co: 16 to 22; W: 2 to 5; V: 1 to 3; Cu: 12 to 22; Fe: rest; others: 3.

In the "Comparison 3" tribological systems, the valve seat ring has the following composition in% by weight: 0.5 to 1.5; Si: 0.2 to 1.0; Cr: 2.5-5; Mon: 5 to 8; W: 3 to 6; V: 1 to 4; Cu: 10 to 20; Fe: rest; others: 3 and in "Reference" the VSR has the composition: C: 1 to 1.8; Si: 0.2 to 1.8; Mn: 0.6; Cr: 10 to 15; Mo: 2.5 to 4.5; V: 0.4 to 1.0; Cu: 0.8 to 1.5; Fe: rest; others: 3.

The "Comparison 1" to "Comparison 3" tribological systems are based on conventional valve seat ring materials, with "Comparison 1" being arbitrarily set to 100% in total wear.

In contrast to "Comparison 1" to "Comparison 3", the valve seat ring "Reference" contains significantly smaller proportions of expensive elements and achieves significantly less overall wear.

Example 2

Comparing the materials described in Example 1 (FIG. 1, not shown geaphically) (comparison 1, comparison 3 and reference) in a test in which armored (Stellite F) and nitrided X50 valves are used as tribo partners, is shown after a 100 h motor test, that the total wear (Fig. 2) with nitrided exhaust valve increases only slightly compared to that of an armored valve with referenced material. This tribo pairing is clearly superior to the standard comparison materials comparison 1 and comparison 3.

Example 3

The valve seat materials described in Example 1 (comparison 3 and reference) show in a motor test (500 h, cold-hot endurance test) with uncoated or untreated Nimonic 80 exhaust valves with very little overall wear. The wear on the valve seat ring and on the valve plate is so low that it cannot be measured. Original machining traces can still be seen in the material (reference). Since the referenced material is particularly cost-effective due to the use of small amounts of special carbides, a comparable technical (not measurable total wear) level results in a significant economic advantage over the comparative material "Comparison 3".

Claims (9)

1. Tribological system, comprising a valve seat ring produced from sintered material and a valve that is untreated or is hardened and/or plated at least in the seat region, characterised in that the sintered material can be obtained by pressing and sintering a powder mixture having a composition of:

   a) 5 to 45 wt% of one or more Fe-based hard phases,

   b) 0 to 2 wt% graphite particles, 0 to 2 wt% MnS powder, 0 to 2 wt% MoS₂ powder, 0 to 2 wt% FeP powder,

   c) 0 to 7 wt% Cu powder and 0 to 4 wt% Co powder,

   d) 0.1 to 1.0 wt% of a pressing aid, and a remainder of

   e) high-speed steel having a composition of 14 to 18 wt% Cr, 1.2 to 1.9 wt% C, 0.1 to 0.9 wt% Si, 0.5 to 2.5 wt% V, 0.5 to 2.5 wt% W, 0.5 to 2.5 wt% Mo and a remainder of Fe and production-related impurities, in particular of Ni, Cu, Co, Ca, and/or Mn having quantities of <1.5 wt%,
   characterised by one or more Fe-based hard phases having a composition of <0.2 wt% C, 26 to 32 wt% Mo, 8 to 12 wt% Cr, 2.2 to 3 wt% Si.
2. Tribological system, comprising a valve seat ring produced from a sintered material and a valve that is untreated or is hardened and/or plated at least in the seat region, characterised in that the sintered material can be obtained by pressing and sintering a powder mixture having a composition of:

   a) 5 to 45 wt% of one or more Fe-based hard phases,

   b) 0 to 2 wt% graphite particles, 0 to 2 wt% MnS powder, 0 to 2 wt% MoS₂ powder, 0 to 2 wt% FeP powder,

   c) 0 to 7 wt% Cu powder and 0 to 4 wt% Co powder,

   d) 0.1 to 1.0 wt% of a pressing aid, and a remainder of

   e) high-speed steel having a composition of 14 to 18 wt% Cr, 1.2 to 1.9 wt% C,

   0.1 to 0.9 wt% Si, 0.5 to 2.5 wt% V, 0.5 to 2.5 wt% W, 0.5 to 2.5 wt% Mo and a remainder of Fe and production-related impurities, in particular of Ni, Cu, Co, Ca, and/or Mn having quantities of <1.5 wt%.
   characterised by one or more Fe-based hard phases having a composition of <0.3 wt% C, 26 to 32 wt% Mo, 14 to 20 wt% Cr, 2.9 to 4.2 wt% Si.
3. Tribological system according to claim 1 or 2, characterised by 0 to 40 wt% of a pure Fe base powder and 0 to 40 wt% of a Fe base powder.
4. Tribological system, comprising a valve seat ring produced from a sintered material and a valve that is untreated or is hardened and/or plated at least in the seat region, characterised in that the sintered material can be obtained by pressing and sintering a powder mixture having a composition of:

   a) 5 to 45 wt% of one or more Fe-based hard phases,

   b) 0.5 to 9.9 wt% of a Co-based hard phase,

   c) 0 to 2 wt% graphite particles, 0 to 2 wt% MnS powder, 0 to 2 wt% MoS₂ powder, 0 to 2 wt% FeP powder,

   d) 0 to 7 wt% Cu powder and 0 to 4 wt% Co powder;

   e) 0.1 to 1.0 wt% of a pressing aid, and a remainder of

   f) high-speed steel having a composition including 14 to 18 wt% Cr, 1.2 to 1.9 wt% C, 0.1 to 0.9 wt% Si, 0.5 to 2.5 wt% V, 0.5 to 2.5 wt% W, 0.5 to 2.5 wt% Mo and a remainder of Fe and production-related impurities, in particular of Ni, Cu, Co, Ca, and/or Mn having quantities of <1.5 wt%.
5. Tribological system according to any of the preceding claims, characterised by a valve that is untreated in the seat region, wherein the valve consists of a mixture having a composition in wt% of 0.04 to 0.1 C, up to 1.0 Si, up to 1.0 Mn, up to 0.02 P, up to 0.015 S, 18.0 to 21.0 Cr, >65.0 Ni, up to 3.0 Fe, up to 2.0 Co, 1.0 to 1.8 AI and 1.8 to 2.7 Ti, or a mixture having a composition in wt% of up to 0.08 C, up to 0.5 Si, up to 0.5 Mn, up to 0.015 P, up to 0.01 S, 13.5 to 15.5 Cr, 30.0 to 33.5 Ni, 0.4 to 1.0 Mo, 1.6 to 2.2 AI, 2.3 to 2.9 Ti, 0.4 to 0.9 Nb and a remainder of Fe or another nickel-based alloy.
6. Tribological system according to any of claims 1 to 4, characterised in that the valve, at least in the seat region, is nitrided and/or plated with a material based on Fe or Co.
7. Tribological system according to any of claims 1 to 4 and 6, characterised by a nitriding layer formed at least in the seat region and having a thickness of >10 µm.
8. Tribological system according to any of claims 1 to 4, 6 and 7, characterised by a plating formed at least in the seat region and having a layer thickness of >200 µm and a Co content and/or Fe content of >40%.
9. Tribological system according to any of the preceding claims, characterised in that the sintered material has been infiltrated with a Cu-based infiltrant during the sintering process.