HK1168391B - Nickel based alloy useful for valve seat inserts - Google Patents

Description

Nickel-based alloy for valve seat inserts

Technical Field

The present invention relates to nickel-base alloys having high hardness and compressive yield strength. Such alloys are particularly useful for engine components such as valve seat inserts.

Background

Nickel-based valve seat insert alloys generally have wear, heat and corrosion resistance superior to high alloy steels and are therefore commonly used as materials for structural members, such as valve seat inserts, that are in service under severe conditions. Known nickel-based alloys for exhaust valve seat inserts, such as those identified as J96 and marketed by the company l.e. jones, have relatively good properties, including good hardness and compressive yield strength. Another alloy marketed by the company l.e. jones is J89, the details of which are provided in U.S. patent No.6,482,275, the disclosure of which is incorporated herein by reference. Typically, the J89 alloy contains, in weight percent ("percent" and "%" as used herein mean percent by weight, unless otherwise specified): 2.25-2.6% of C, at most 0.5% of Mn, at most 0.6% of Si, 34.5-36.5% of Cr, 4.00-4.95% of Mo, 14.5-15.5% of W, 5.25-6.25% of Fe, and the balance of Ni and incidental impurities.

Disclosure of Invention

Disclosed herein is a nickel-based alloy comprising (in weight percent): carbon from about 0.5 to about 1.5, chromium from about 25 to about 35, tungsten from about 12 to about 18, iron from about 3.5 to about 8.5, molybdenum from about 1 to about 8, manganese up to about 0.50, silicon up to about 1.0; and the balance nickel and incidental impurities. The alloy is suitable for valve seat insert applications in internal combustion engines.

Drawings

FIG. 1 is an OLM micrograph of J91 at 500 Xmagnification in as-cast condition.

FIG. 2 is an SEM micrograph of J91 at 500 times in the as-cast condition.

FIG. 3 is a wear graph at elevated temperatures for the J3, J130, J160, and J91 alloys.

Detailed Description

The nickel-based alloys described herein (referred to as "J91 alloys") are specified to improve machinability and maintain desired hardness and wear resistance at elevated temperatures. By adjusting the carbon, chromium, nickel and tungsten contents, a matrix material can be provided that is free of coarse primary carbides and yet exhibits desirable wear resistance properties. The microstructure of the J91 alloy may be characterized by spherical or egg-shaped eutectic domains (domains) interspersed with a Ni-rich FCC phase, and thus provides the desired wear resistance properties without relying on coarse primary carbides.

In addition to improved machinability and desired hardness, the J91 alloy may also exhibit high compressive yield strength, good corrosion resistance, and good oxidation resistance.

Before the embodiments are explained in detail, it is to be understood that the J91 alloy is not limited in its application to the details of composition and concentration of components set forth in the following description. The J91 alloy can be implemented in other embodiments and can be practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. As used herein, the term "about" is meant to include values up to 10% higher and up to 10% lower than the recited value or range.

While the design J91 alloy is specifically designed for use in an internal combustion engine valve seat shim plate, other applications are possible. Compared with the J89 alloy, the J91 alloy is based on the following experimental findings: the hardness and compressive yield strength of nickel-base alloys can be achieved by removing coarse primary carbides and creating a uniformly distributed face-centered cubic (FCC) nickel-solid solution phase in a eutectic reaction phase matrix into which other strengthening solutes can be introduced.

Carbon (C) is present in the J91 alloy in an amount of from about 0.5 to about 1.5 weight percent of the total alloy; preferably, from about 0.95 to about 1.3 weight percent. Surprisingly, the J91 alloy exhibits the same wear resistance properties as the J89 alloy, but with a lower carbon content. Whereas the J89 alloy relies on the presence of coarse primary carbides to achieve wear resistance, the desired wear resistance is achieved in the as-cast condition by an improved wear resistant matrix microstructure, preferably the J91 alloy without coarse primary carbides. By selecting the Ni, Cr and W contents, the amount of eutectic structure can be increased by a ternary eutectic reaction that produces spherical or egg-shaped eutectic domains interspersed with a Ni-rich FCC phase.

Chromium (Cr) is present in the alloy in an amount of about 25 to about 35 weight percent, preferably 27 to 33 weight percent, and more preferably about 28.5 to about 31.5 weight percent of the total alloy. The chromium content may be selected such that the relative amounts of Cr, Ni and W move the J91 alloy closer to the eutectic center point of the Ni-W-Cr ternary diagram, thereby promoting a tendency for intermetallic phase(s) to form between W and Ni. By increasing the amount of eutectic structures that are evenly distributed, the matrix material can be made very wear resistant.

Tungsten (W) is present in the alloy in an amount of about 12 to about 18 weight percent of the total alloy. Preferably, the tungsten content is at least about 14 weight percent and at most about 16 weight percent. More preferably, the W content is from about 14.5% to about 15.5%.

Iron (Fe) is present in the alloy in an amount of about 3.5 to about 8.5 weight percent of the total alloy; preferably, at least about 5 wt% and at most about 7 wt%. The preferred Fe content is about 5.25% to about 8.25%.

Molybdenum (Mo) is present in the alloy in an amount of about 1 to about 8 weight percent of the total alloy. Generally, more molybdenum increases alloy hardness and reduces carbide size; however, too much molybdenum can lead to brittle products. The weight percent of molybdenum is preferably at least about 2 weight percent and at most about 6.25 weight percent. More preferably, the alloy contains about 4 to 5 weight percent Mo, most preferably the Mo content is about 4.35% to about 4.95%.

Manganese (Mn) may be added or present in an amount up to about 0.5 wt.% of the total alloy. The preferred Mn content is from about 0.25% to about 0.5%.

Silicon (Si) is added or present in the alloy at a level of up to about 1.0 wt.% of the total alloy. The preferred level of S i is from about 0.15% to about 0.60%.

The alloy may contain other intentionally added elements in a total amount of up to 1.5 wt.%. Such elements include cobalt (Co), vanadium (V), titanium (Ti), niobium (Nb), hafnium (Hf), zirconium (Zr), tantalum (Ta), rare earth elements, yttrium (Y), copper (Cu), sulfur (S), phosphorus (P), nitrogen (N), or other elements. For example, the alloy may contain up to 0.5% V, up to 0.5% Co, up to 0.03% P, up to 0.03% S.

The balance of the alloy is nickel (Ni) and incidental impurities. Typically, the alloy contains at least about 30 wt.% nickel. The preferred Ni content is about 35 to about 45%. Thus, the alloy preferably consists essentially of C, Cr, W, Mo, Fe, Ni, Mn, and S i. As used herein, "consisting essentially of" excludes additives that adversely affect machinability and wear properties of the alloy.

At 800 ℃, the matrix material between the carbides preferably comprises a three-phase eutectic composition of the elements Cr-Ni-W, which provides improved strength. The relative concentrations of Cr-Ni-W required to form a three-phase eutectic composition can be determined by reference to a Cr-Ni-W ternary phase diagram. Such phases are illustrated, for example, on pages 3-48 of ASM Handbook, Copyright 1992, Volume 3, which is incorporated herein by reference.

In a highly preferred embodiment, the alloy comprises:

element(s)	Weight percentage range
		C	0.95-1.3
Cr	28.5-31.5
		Mo	4.35-4.95
W	14.5-15.5
		Fe	5.25-8.25
Si	0.15-0.6
		Mn	0.25-0.50
V	At most 0.5
		Co	At most 0.5
S	At most 0.03
		P	At most 0.03
Ni	Balance of
		Other elements	At most 1.5

Metal parts may be made from the alloy by casting or by molding from powder and sintering, or the alloy may be used as a coating for hard-face (hardface) parts. Preferably, the alloy is prepared by casting. Casting is a conventional method of adding raw materials together and melting them to a liquid state, followed by pouring them into a mold.

Preferably, the metal component is a valve seat insert for use in an internal combustion engine made by casting or powder metallurgy.

Although the J91 alloy is nickel-based, the coefficient of thermal expansion of the alloy tends to be closer to that of iron than nickel. (the cast iron has a coefficient of thermal expansion of about 11.5X 10 at a temperature of 25-600 ℃ C.)^-6mm/mm deg.C. This is advantageous because the valve seat insert tends to be much hotter than the surrounding material when the engine is running. This enables the gasket and cylinder head to expand at the same rate if the coefficient of thermal expansion of the valve gasket alloy is closely matched to the cylinder head alloy, thereby improving the retention properties of the gasket.

The J91 alloy has good high temperature compressive yield strength, which improves wear resistance and reduces material yield during operation. The reduced yield serves to improve the retention of the tie plate. Preferably, the alloy has a compressive yield strength of at least about 110 kilopounds per square inch (KSI) at room temperature; more preferably, at least about 130KSI at room temperature.

The increased hot hardness contributes to improved wear resistance and provides a safety factor for tie plates operating above the nominal operating temperature.

Examples

Comparative properties of the J91 and J89 alloys are given in the tables and discussion below.

Typical microstructure

The J91 alloy has a matrix composed of a eutectic reaction connected with a small amount of a randomly distributed FCC nickel solid solution phase. The nickel solid solution phase is distributed along the grain boundaries of the eutectic phase. An optical microscope (OLM) micrograph and a Scanning Electron Microscope (SEM) micrograph showing a typical J91 microstructure are depicted in fig. 1 and 2, respectively. For microstructure characterization by optical microscopy, J89 smelt (heat) (smelt No.7K17K) and J91 smelt (smelt No.8L15XA) were used. In addition, for microstructure characterization by scanning microscopy, smelt J91 (smelt No.7G10XA) and J89 smelt (7K17K) were used. The composition of the three smelt materials referred to above is summarized in table 1.

TABLE 1 characterization of the microstructure the compositions of the applied J89 and J91 heats

Alloy/smelt No.	C	Si	Mn	Cr	Mo	W	Fe	Ni
									J89/7K17K	2.25	0.20	0.39	35.12	4.48	15.00	5.69	36.49
J91/8L15XA	1.19	0.20	0.52	30.51	4.44	14.92	7.19	40.72
									J91/7G10XA	1.21	0.16	0.02	30.54	4.88	14.20	4.47	41.32

Sample for hot hardness measurement

The compositions of the heats used to prepare the hot hardness measurement samples (for alloys J89 and J91) are summarized in table 2.

TABLE 2 composition of alloy/smelt grades for J89 and J91 used for hot hardness testing

Alloy/smelt No.	C	Si	Mn	Cr	Mo	W	Fe	Ni
									J89/4E18D	2.40	0.39	0.26	34.92	4.38	14.90	5.93	36.64
J91/8D02Q	0.98	0.46	0.22	30.55	4.36	15.25	6.95	41.06

Properties of the Material

Alloy J91 typically has a bulk Hardness of Rockwell C (HRC)48-52, preferably about 49-51. Thus, alloy J91 has a bulk hardness between J96(HRC40) and J89(HRC 55).

The hot hardness (in vickers HV 10) comparisons for J89, J91, and J96 (for the alloys summarized in table 2) are summarized in table 3. Although J91 contained no coarse primary carbides in its microstructure, it was found that J91 still had a significantly higher hot hardness than J96.

TABLE 3 comparison of thermal hardness between alloys J89, J91, and J96.

Samples for compressive yield strength testing

The J89 and J91 samples used for the compression test are given in table 4.

TABLE 4

Alloy (I)	C	Si	Mn	Cr	Mo	Fe	W	Ni
									J89	2.51	0.56	0.48	36.47	4.15	6.7	15.44	33.69
J91	1.33	0.24	0.1	30.29	4.81	8.69	14.15	40.39

A comparison of the compressive yield strengths of J89, J91, and J96 is shown in table 5. It is clear that J91 has a compressive yield strength for the temperature range applied between alloys J89 and J96.

TABLE 5 compressive yield Strength (KSI) comparison between alloys J89, J91, and J96

Sample for linear thermal expansion coefficient measurement

Smelt J89(4E18D) and smelt J91(7G10XA) were used to make thermal expansion coefficient measurements. The compositions for the two involved smelt were summarized in table 6.

TABLE 6 compositions of J89 and J91 heats for coefficient of thermal expansion testing

Alloy/smelt No.	C	Si	Mn	Cr	Mo	W	Fe	Ni
									J89/4E18D	2.40	0.39	0.26	34.92	4.38	14.90	5.93	36.64
J91/7G10XA	1.21	0.16	0.02	30.54	4.88	14.20	4.47	41.32

The results of the thermal expansion coefficient measurements for alloys J89 and J91 and the above-described smelt are summarized in table 7.

TABLE 7 thermal expansion coefficient (. times.10) for alloys J89 and J91^-6mm/mm℃)

Alloy/smelt No.	25-200℃	25-300℃	25-400℃	25-500°	25-600℃
						J89/4E18D	10.32	11.07	11.55	11.95	12.38
J91/7G10XA	10.95	11.63	12.15	12.52	13.01

In practice, the coefficient of thermal expansion of J91 is only slightly greater than J89. Such a low coefficient of thermal expansion is advantageous for heavy duty engine valve seat insert applications.

Wear resistance

The wear resistance of alloy J91 under engine wear conditions is expected to be similar to J89. A comparison of wear resistance as a function of test temperature for J91, J3, J130, and J160 comparative Pyromet 31V valve materials is shown in fig. 3 and table 8, respectively.

Clearly showing that: j91 showed the least total material wear among the four pairs of materials evaluated over the exhaust gas temperature range. In the lower test temperature range (ambient to 250 ℃), J91 shows wear resistance similar to alloys J30 and J160 when paired with Pyromet 31V valve material (paired).

Table 8 summary of Plint wear test results.

It should be understood that the alloys of the present invention can be combined in various embodiments, only a few of which are described above. The present invention may be embodied in other forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims (18)

1. A nickel-based alloy comprising, in weight percent: 0.95-1.5 carbon; 25-35 chromium; 12-18 tungsten; 5.0-8.5 iron; 1 to 8 parts of molybdenum; up to 0.50 manganese; up to 1.0 silicon; up to 0.5 cobalt; 30-45 of nickel and incidental impurities;

wherein the alloy has an as-cast microstructure comprising a wear resistant matrix of spherical eutectic domains free of coarse primary carbides.

2. The alloy of claim 1, wherein the alloy comprises 28.5 to 30.5 weight percent chromium.

3. The alloy of claim 1, wherein the alloy comprises at least 14.0 wt.% tungsten.

4. The alloy of claim 1, wherein the alloy comprises up to 7.0 wt.% iron.

5. The alloy of claim 1, wherein the alloy comprises 4.35 to 4.95 weight percent molybdenum.

6. The alloy of claim 1, wherein the alloy comprises up to 1.3 wt.% carbon.

7. The alloy of claim 1, wherein the alloy comprises up to 32.0 wt.% chromium.

8. The alloy of claim 1, wherein the alloy comprises up to 16.0 wt.% tungsten.

9. The alloy of claim 1, wherein the alloy comprises 40-42 wt% nickel.

10. The alloy of claim 1 wherein the relative concentrations of Cr, Ni and W are such that a three-phase eutectic composition is formed at a temperature of 800 ℃.

11. The alloy of claim 1, wherein the alloy consists essentially of: 0.95-1.3 carbon; 28.5 to 31.5 chromium; 14.5-15.5 tungsten; 5.25-8.25 iron; 4.35-4.95 molybdenum; 0.25-0.5 manganese; 0.15-0.6 of silicon; up to 0.5 vanadium, up to 0.5 cobalt, up to 0.03 sulfur, up to 0.03 phosphorus, and 38-42 nickel and incidental impurities, in weight percent.

12. The alloy of claim 1, wherein the alloy is a casting.

13. The alloy of claim 11, wherein the alloy is a casting.

14. The alloy of claim 1, wherein the alloy is a valve seat insert for an internal combustion engine.

15. A valve seat insert for use in an internal combustion engine, said valve seat insert being made of an alloy comprising substantially: 0.95-1.5 carbon; 25-35 chromium; 12-18 tungsten; 5.0-8.5 iron; 1 to 8 parts of molybdenum; up to 0.5 manganese; up to 1.0 silicon; up to 0.5 cobalt; and the balance of nickel and incidental impurities, in weight percent;

wherein the alloy has an as-cast microstructure comprising a wear resistant matrix of spherical eutectic domains free of coarse primary carbides.

16. The valve seat insert of claim 15, wherein the valve seat insert is a casting.

17. The valve seat insert of claim 15, wherein the alloy consists essentially of: 0.95-1.3 carbon; 28.5 to 31.5 chromium; 14.5-15.5 tungsten; 5.25-8.25 iron; 4.35-4.95 molybdenum; 0.25-0.5 manganese; 0.15-0.6 of silicon; vanadium and cobalt in a total amount of no more than 0.5, sulfur in a total amount of no more than 0.03, phosphorus in a total amount of no more than 0.03, and the balance nickel and incidental impurities.

18. The valve seat insert of claim 15, having a rockwell C hardness of 48-52.