DK166219B - VALVE WITH HAIR PILOT - Google Patents

Description

in

DK 166219 B

The invention relates to a valve, in particular an exhaust valve for an internal combustion engine, comprising a movable valve body with a valve seat region of a nickel-based metallic alloy.

5 The selected material composition of the valve seat area in the exhaust valves for internal combustion engines has for many years played a major role in the safety of the engine concerned and in the service life of the exhaust valves and thus the extent of the necessary maintenance work.

In an internal combustion engine, the combustion in the working cylinder produces coking residues consisting of hard particles which must be discharged through the exhaust valve, the particles occasionally intersecting between the closing valve seats, whereby in the seat surfaces there may be impression marks which may appear at first. a local leak, and then a greater reburning with corrosive degradation of the seat surfaces.

It is desirable that the valve seat material have sufficient hardness to reduce or prevent the formation of impression marks. In the case of large heavy-duty diesel engines, in recent years, the valve seat area of the nickel-based hard coating material Alloy 50 has been attempted, which, as the main alloys 25, contains approximately 12% Cr, 3.9% Si, 2.9% Pe, 2.25% B and 0.5% C. In addition to the desired hardness, Alloy 50 exhibits heat corrosion resistance to the highly corrosive environment to which an exhaust valve in a heavy-oil diesel engine is exposed. In engines with large cylinder bores, such as 600-900 mm, where, in addition to good corrosion resistance, high demands are made on the mechanical strength of the materials used, operating experience has shown that in the Alloy 50 hard coating material in some cases radial cracks are formed, which can lead to 35 bursting of the seat or breeding ground for dangerous circumferential cracks. To avoid the risk of accidents,

DK 166219B

2, therefore, for these engine sizes, the more fabric-hardening material Stellite 6, which is a cobalt-based alloy, which in the current environment has been found to have a lower heat corrosion resistance than 5 Alloy 50, necessitates shorter operating intervals between each valve condition inspection .

It is well known that the hardness of the coating material decreases with increasing temperature. Thus, Stellite 6 has a hardness of approx. 370 HB at room temperature 10 and approx. 298 HB at a temperature of 500 ° C and at similar temperatures the hardness of the Alloy 50 drops from approx.

530 HB to 420 HB.

It is also well known that especially the previously known Ni-base hard coating materials of high hardness usually have little or no ductility and thus poor fatigue strength properties.

In the previously known Ni-base alloys, the desired hardness is preferably obtained by the additions of B, Si and C. In particular, the metal borides in the structure of these alloys have, due to their size and shape, a very low ductility of the hard coating. with the risk of cracking already during welding or after shorter or longer operating periods.

In cases where the B content is reduced 25 or completely omitted in the assay, it has been necessary to increase the C content in order to increase the hardness of the alloy by means of extensive carbide separations, with the result that the excreted carbide network also significantly reduces ductility. .

It is a common feature of said known nickel base alloys that it is necessary to give the alloy extremely high hardness and thus brittleness at room temperature to achieve a high hardness at operating temperatures of about 500 ° C.

From Japanese Publication No. 59-9146, a valve is known by a nickel alloy wherein

DK 166219 B

3 it is less than 4.5% to allow welding of the alloy. The alloy content of Ti, W and Mo in combination with a C content of more than 0.55% allows the alloy hardness to be increased by carbide excretion.

In addition, the stated B content of up to 2% can significantly contribute to an increase in hardness. However, there will be variation in the microhardness of the alloy as the very hard carbides and borides are secreted into a relatively soft base matrix, just as the carbide network, as mentioned above, can reduce ductility.

From US-A-3 795 510 a nickel alloy with 20% Cr, 5.5% Al, 2.5% Ti, 7.5% Fe and 0.15% C. is known. The valve itself is manufactured by frictionally welding a finished nickel alloy blank. on the remaining 15 valve part consisting of carbon steel. The alloy is not weldable in the conventional manner and the hardness is less than the hardness of the present invention.

The object of the invention is to provide a valve with a hard coating material that can be used for all engine sizes combining good heat corrosion resistance to the combustion products with high hardness at temperatures up to 500 ° C while maintaining sufficient ductility to allow application to mechanically high loads , cyclically operated 25 valves.

To this end, the valve according to the invention is characterized in that the nickel-based alloy indicated in weight percent and other than common impurities comprises 20-24% 30 Cr, 0-8% W, 4-7% Al, 0.2- 0.55% C, 0-1.8% Hf, 0-1.5% Nb, 0-8.0% Mo, 0-1.2% Si and 0-15% Fe, where the W and Mo content together not more than 10%.

Surprisingly, it has been found that an alloy of this kind possesses the desired properties. In the past, it has been 35 times believed that a welded nickel alloy with said high content of Al will exhibit a pronounced

DK 166219B

4 heat crack tendency in the weld metal as well as cracking in the heat affected area by multilayer welding. Ni-Cr alloys with more than 3-4% Al are thus described in the literature as weldable.

The weldability of the Ni-Cr-Al-C alloy of the invention with said Al content permits the utilization of the secretion cure mechanism in this type of alloy, thereby separating the intermetallic Ni3Al (y1) as a coherent hardness-increasing phase in the ductile nickel-ma trix (y) . The γ 'phase can be separated into a 15-25% structural portion of the γ basic structure to obtain a material of the desired high strength and hardness which is substantially constant in the temperature range of 20-600 ° C, which covers the temperature range to which a normal 15 working exhaust valve is exposed.

The Cr content of the alloy contributes significantly to the requirement that the alloy be high corrosion resistant in the current environment where sulfur compounds play a significant role. The alloy 20 of Al leads to the formation of a combined Al 2 O 3 and Cr 2 O 3 surface layer on the valve seat, which provides increased corrosion resistance, which is especially improved at temperatures of 750 ° C and above. This improved corrosion resistance, in particular, prevents rapid degradation of the valve seat in the event of a leakage over the seat due to the appearance of impression marks, such leakage locally may cause surface temperatures substantially higher than the usual operating temperature of the valve.

The 30 Cr content further has a dissolving enhancing effect which helps to increase the strength of the alloy. The solution enhancing effect can be further enhanced by the addition of Mo and w, which can be exchanged with each other. The total content of W and Mo must not exceed 35%, otherwise the alloy carbide configuration is adversely affected.

DK 166219B

5

The final determination of the alloy hardness is done by adjusting the C content, thereby affecting the amount and configuration of the carbide secretions.

Furthermore, in contrast to the commercially available 5 Ni, Cr, B, Si hard alloys, it has been found possible to use the alloy of the invention in the manufacture of Hot Isostatic Pressure (HIP) compound exhaust valves, the solidus temperature of the alloy being close to the solidus-10 temperature of the valve base material. , which is a prerequisite for using the HIP process.

The ductility of the alloy is greatly affected by the carbide configuration, and especially needle and plate shaped carbide separations adversely affect ductility. It is found in the current alloy that the tendency to form unfortunate carbide configurations of the type called "Chinese script" is increasing with increasing C content, which is why the C content should be kept below 0.6%.

It has been found that the carbide configuration can be positively affected by the addition of Hf in amounts of 1-2%. By the addition of Hf, the carbide form is changed from flake and needle-shaped carbides to more rounded forms which do not to the same extent impair the alloy ductility. Unexpectedly, however, it has been found that if the carbon content exceeds 0.5%, the carbide excretion is only affected to a limited extent by the addition of Hf, which is why the C content in this case can conveniently be adjusted to 0.35-0.50%.

Furthermore, it has surprisingly been found that the structure of the alloy, especially at slow solidifying melts, exhibits increased hardness if up to 1.5% Nb is added, which is probably due to the fact that Nb increases the amount of carbide secretions and / or alters the carbide composition. 35 the sentence. At the same time, with the addition of Nb to the alloy, a changed carbide configuration in

DK 166219 B

6 form of finely separated metal carbides, which is believed to have a positive influence on the ductility of the alloy.

When the valve seat area is applied by welding, the alloy can be added Si to improve the welding properties due to the deoxidizing effect of silicon. The Si content may conveniently be set at 0.8-1.2%. However, it has surprisingly been found that at said Si content, an Al, Si, Cr and presumably C rich eutectic are formed when the Al content exceeds 10 to 5.5%. Since it has been unexpectedly found that this eutectic is substantially less corrosion-resistant than the other structural elements of the alloy, it is desirable to limit the phase proportion of this eutectic to a maximum of approx.

5%.

The valve body itself, which carries the valve seat area, is usually made of an austenitic stainless steel alloy. When the valve seat area is applied by welding, a minor mixing of the steel alloy will occur in the nickel-based additive so that up to 15% Fe can be mixed in the first applied welding layer.

Fe in amounts of up to 20% can increase the strength of the γ phase, but at the same time the corrosion resistance is reduced. Already at a Fe content of 5% there is a risk of 25 cows for deteriorating corrosion properties, so it should be sought that the Fe content in the last welded layer is · at most 5%.

Next, various exemplary embodiments of the invention are described in detail, partly with reference to the drawing, in which fig. 1-4 shows images in 320 times magnification of ground and polished samples of four different alloys according to the invention.

EXAMPLE 1

In order to obtain a comparative basis 35 between the alloy according to the invention and previously known valve seat alloys, 4 pcs.

DK 166219B

7 geometrically identical valve stem elements in the form of austenitic stainless steel valve plate with a diameter of D = 250 mm. After preheating the spindle elements, the four different alloys were welded to each of the workpieces by means of plasma arc with transferred arc and the following welding parameters:

Grain Powder Grain Size: 50-150 pm

Sales performance: 1.7 kg / hour

10 Welding current: 120 A

Welding speed: approx. 60 mm / hour

The weld was made up of three layers and was 8 mm deep and 25 mm wide with 60e joints.

The approximate analysis of the manufactured alloys is shown in Table 1, where the Stellite 6 and Alloy 50 alloys are discussed previously and the alloy labeled BW1-50 is also a commercially available nickel alloy, while the alloy labeled 1-1 is an alloy of the invention. .

TABLE 1

Ingredient by weight c Si B Cr Fe Ni W Mo Al Other

Stellite 6 1.14 1.06 - 28.5 0.43 - 4.65 - - the rest Co

Alloy 50 0.46 3.9 2.25 10.78 2.88 residue - - - - 25 BW 1-50 0.49 6.99 0.92 19.30 3.5 residue, 75- - - 1- 1 0.51 1.02 - 23.05 0.23 residue7.1 - 5.63 0.43ϊ

After welding, the welded sealing surfaces were turned off and checked for capillary test errors.

The blanks were then placed in an oven and heated to 250 ° C, after which they were quenched in a water bath at a temperature of approx. 40eC. The items were checked visually and by capillary testing and no cracks were found in the seat materials.

35 All items were again placed in the oven and heated to 350 ° C, after which they were first quenched in

DK 166219B

8 is a water bath having a temperature of ca. 70 ° C and then checked visually and by capillary testing, whereby in the Alloy 50 alloy there were 3 radial cracks and single crackings, while the other three blanks were 5 faultless.

The temperature shock test was repeated for the three faultless blanks which were heated to 450 ° C. After quenching in water at approx. In the BW 1-50 alloy, a crack pattern was found in the form of a coarse-mesh cracking, while the two remaining blanks were undamaged in the actual valve seat area.

These two blanks were then heated to 520 ° C and quenched in water at ca. 70 ° C, after which, visually and with capillary testing, a large number of 15 radial small cracks in the Stellite 6 alloy and a radial crack in the actual valve seat area of the I-1 alloy showed. In contrast to the cracks in the three other alloys, the crack in the I-1 alloy showed clear signs of plastic deformation in the form of rounded 20 crack edges.

Thus, the nickel-based alloy of the invention has a surprisingly good weldability and a ductility and crack resistance that is fully at par with Stellite 6 and is significantly better than the nickel alloys Alloy 50 and BW 1-50.

From the seat region of each valve stem member, a radial section was taken, of which approx. in the middle of the weld on a line perpendicular to the seat surface, hardness measurements (HV 20) were made at room temperature at varying distances from the seat surface. The result is shown in Table 2.

DK 166219B

9

Table 2

Alloy Stellite 6 Alloy 50 BW 1-50 1-1

Weld layer thickness in mm 8.8_9 ^ 5_8_ £ 0_8.5 5 Measured hardness (HV20) The location of the measuring point in mm below the seat surface 0.5 426 473 490 457 10 1.5 441 473 509 412 2.5 441 473 509 426 3.5 426 490 509 426 4.5 386 473 374 441 5.5 412 374 412 362 15 6.5 412 374 374 374 7.5 399 386 278 286 8.5 412 271 232 303 9.5 257 271 - 226 10.5 - 232 20 It is seen that the hardness of the nickel-based games rings is sensitive to mixing of the valve stem material into the seat material, and that the hardness of the outer half of the seat material varies within the limits to be expected due to the fastening of the melt bath 25 preventing a complete equalization of the alloy composition.

EXAMPLE 2

In order to investigate the alloy hardness at elevated temperature, a powder blank with a diameter of 30 mm and a length of 160 mm was cut from powdered starting material by a so-called Hot Isostatic Pressure (HIP) process. 8 mm thick washers for use in hardness measurement. The blanks were prepared in the alloy Stellite 6 and in a nickel-based alloy with an assay corresponding to 1-1

DK 166219B

10 Table 1. The measured hardnesses (HB 10/3000/15) are shown in Table 3, which shows that the heat hardness at 500 ° C shows a marked decrease (28%) for Stellite 6, while the hardness of the alloy according to the invention has only decreased quite a bit 5 (3%).

Table 3

Stellite 6 1-1

Temperature Hardness HB

20 ° C 415 406 10 500 ° C 298 393

In order to compare the hardnesses with those in Table 2, three slices of Stellite 6 and 1-1, respectively, were made hardness measurement (HV20) at room temperature with the following result: Table 4 _Stellite 6_1 ^ 1_ abc abc HV (20) 441 441 438 426 426 426

The hardness of 473 HV of the Alloy 20 50 seat material measured in Table 2 at about 20 ° C decreases by about 20% at the operating temperature of the seat material to a hardness of 378 HV, whereas the hardness of the 1-1 alloy decreases only by approx. 3% to a hardness at operating temperature of approx. 413 HV.

EXAMPLE 3

With the help of manual TIG welding, different alloys according to the invention were welded on austenitic stainless steel pieces with a diameter of 80 mm and a thickness of 20 mm. The approximate analysis of the alloys is presented in Table 5.

Hardness measurements (HB 10/3000/15) of each alloy were made at both 20 ° C and at approx.

500eC.

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11

Table 5

C Si Cr W Nb MO Al Ni 208C 500CC

1-2 0.55 1.14 23.3 6.53 - - 6.04 residue 438 429 1-3 0.5 1.05 23 5.88 0.35 0.9 5.44 residue 435 415 5 1 -4 0.44 0.95 23 5.22 0.7 1.8 4.83 residue 420 388 1-5 0.4 0.86 23 4.57 1.05 2.7 4.22 residue 415 385

It is seen that the decrease in hardness by heating from room temperature to approx. 500 ° C grows from approx. 2% for the alloy 1-2 to approx. 7% for the alloy 1-5.

10 A grinded and polished sample of each alloy was further made, and in the drawing, FIG. 1-4 shows the samples for the alloys 1-2 to 1-5.

In FIG. 1 shows in the alloy 1-2 spherical dark deposits, presumably consisting of the aluminum-containing carbide Perovskite, as well as elongated light excretions of aluminum-free metal carbides. An alloy with greater ductility can be produced by reducing the carbide separations.

In FIG. 2, alloys 1-3 show a distinct detrital structure with cells where the material has a crystal lattice-like orientation. There are some secretions of Perovskite as well as secretions of metal carbides between the dentite arms. This alloy presumably has good ductility at the same time as high heat hardness.

25 Alloy 1-4 in FIG. 3 has a dendrite structure which is slightly less regular and exhibits only a few secretions of Perovskite, and in the alloy 1-5 in FIG. 4, the Perovskite excretions have largely disappeared.

If the Cr content of the alloy becomes less than 20%, the corrosion resistance becomes too low at high temperature, and if the Cr content exceeds 24%, the strength properties of the alloy appear to be adversely affected and, in addition, the weldability deteriorates.

35 At Al content of less than 4%, the heat hardness appears to be too low, and at Al content at

Claims (12)

Alloys comprising 22.5-23.5% Cr, 4.5-5.75% Al, 0.45-0.55% C and 5.5-6% W and / or Mo appear to be applicable in cases by placing very high demands on crack resistance. If the alloys are prepared by HIP, it is possible to include Y in the assay, whereby the high temperature resistance can be positively affected. A valve, in particular an exhaust valve for a combustion engine, comprising a movable valve body having a valve seat region of a nickel-based metallic alloy, characterized in that the nickel-based alloy, expressed in weight percent and other than 30 common impurities, comprises 20-24% Cr, 0 -8% W, 4-7% Al, 0.2-0.55% C, 0-2% Hf, 0-1.5% Nb, 0-8% Mo, 0-1.2% Si and 0 -15% Fe, with the W and Mo content together not exceeding 10%. Valve according to claim 1, characterized in that the alloy comprises 20-23% Cr, 4-5.5% Al, 0-5% Fe, 0.3-0.5% C and from 5-7.5 % W and / or Mo. DK 166219B Valve according to claim i, characterized in that the alloy comprises 22.5-23.5% Cr, 4.5-5.75% Al, 0.45-0.55% C and 5.5-6% W and / or Mo. Valve according to one of claims 1-3, characterized in that the alloy comprises 1-2% Hf and preferably 0.35-0.5% C. Valve according to one of claims 1-4, characterized in that the alloy comprises 0.3-1.5% Nb, preferably 0.5-1.4% Nb. Valve according to one of claims 1-5, characterized in that the alloy comprises 0.6 -4.0% of Mo and W. Valve according to one of claims 1-6, characterized in that the content of the alloy of at least one of the components Hf, Nb and Mo is substantially 0%. Valve according to one of claims 1-6, characterized in that the alloy comprises 0.6-1.2%, preferably 0.8-1.2% Si. Valve according to one of claims 1-6, characterized in that the alloy near the surface of the valve seat area contains a maximum of 5% Fe. Process for the manufacture of a valve according to any one of claims 1-8, wherein a valve seat region is applied to a valve body 25 by means of a valve seat region, characterized in that a welding material is added in the form of a nickel alloy, except for ordinary welding. occurring impurities include 20-23% Cr, 4-5.5% Al, 0.3-0.5% C, 0.8-1.2% 30 Si, 5-7.5% W and / or Mo and the remainder Ni.