GB1577185A - Sintered powdered metal wear-resistant composition - Google Patents

Description

(54) SINTERED POWDERED METAL WEAR-RESISTANT COMPOSITION (71) We, STANADYNE, INC., a Corporation organized and existing under the laws of the State of Delaware, United States of America, of 92 Deerfield Road, Windsor, Connecticut, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a powdered metal wear-resistant composition which has the characteristics of heat-treated hardenable iron and finds application in critical wear components of vehicle engines such as tappet bodies, rocker followers, and distributor drive gears.

An aim of the present invention is to provide a wear-resistant composition formed of powdered metal which can be applied in sensitive wear applications where heattreated hardenable iron has hitherto been the standard material.

With this aim in view, the invention is directed to a sintered powdered metal heattreated wear resistant composition for use in vehicle engines and other machines where similar conditions exist having a matrix formed from iron powder, carbon in the range of 0.50-1.0% by weight, and a ferroalloy powder acting as a nucleus for diffusion of the alloying metal into the surrounding iron particles, the alloying metal in the composition being in the range of 1-10% by weight and being selected from the following group of metals: chromium, titanium, boron, vanadium, columbium, molybdenum, tantalum and tungsten; the iron, carbon and ferroalloy having been briquetted at a pressure of 40-60 tons/sq.in. and sintered, in solid phase, at a temperature of 2000-2100 F in a reducing atmosphere.

The invention is illustrated diagramatically in the accompanying photomicrographs taken at 500 times magnification and showing the structure of heat-treated hardenable iron and a heat-treated sintered powdered metal wear-resistant composition in accordance with the present invention.

Heat-treated hardenable iron is used in a number of critical wear components in vehicle engines - for example, in tappet bodies, camshafts, rocker followers, and distributor drive gears. These applications involve high contact stress, sliding type loading, and marginal lubrication. Such severe conditions require a material to possess a high resistance to scufling (welding or adhesive wear), a controlled normal wear (abrasion and plastic deformation), and a realistic endurance limit (pitting and metal fatigue).

In addition, the part in question must be compatible with its mating component under all service conditions.

Hardenable iron has three major constituents, namely, massive, hard carbides; flakes of soft, amorphous graphite; and a matrix like hardened steel. These three constituents must be controlled within narrow limits during casting and heat treatment.

This places certain restrictions on the chemical analysis, melting, moulding and heattreatment of the casting. Controlled processing produces an equilibrium between the carbide and graphite, which are dispersed at random throughout the steel matrix, as shown in the lower photomicrograph. The density and orientation of the carbide/ graphite are in turn related to the volume, size and orientation of the original austenite dendrites formed during solidification. The density of the carbides is maintained at a specific minimum level for wear resistance, and a high level of acicular type carbide is required. The residual graphite is present as flakes. These flakes are discontinuities in the matrix, and they fracture during service, leaving small cavities which entrap lubricant. The matrix is hardened and tempered to produce a high compressive strength and hardness. This produces the strong, tough matrix which holds the carbide and graphite.

The present invention provides a sintered powdered metal wear-resistant composition which replaces the above-described heattreated hardenable iron. The powdered metal contains the three basic elements found in hardenable iron; hard particles, interconnected porosity and a hardened and tempered steel matrix. The wear-resistant material may be present as a layer on the contact surface, for example 1/32-1/8 inch in thickness, backed with a low alloy iron, or it may be used to make the entire part.

The composition is formed from a mixture of iron powder, carbon in the range of 0.501.0% by weight and a ferroalloy powder.

The carbon may be added as graphite, or it may be added in other ways. The alloying metal in the composition is in the range of 1-10% by weight and is selected from the following group of metals: chromium, titanium, boron, vanadium, columbium, molybdenum, tantalum and tungsten. The mixture is briquetted at a pressure of 40-60 tons/sq.in. and sintered, in solid phase, at a temperature of 2000-2100 F in a reducing atmosphere. The resultant product has a density at the wear surface of 6.8-7.0 gm/cc. The sintering step in the process may be for a period of 15-60 minutes, with 30 minutes being a preferred time period.

The reducing atmosphere may be endothermic (40% hydrogen, 40% nitrogen and 20% carbon monoxide) or disassociated ammonia (75% hydrogen, 25% nitrogen).

Although the reducing atmosphere may vary, it is preferred to include the combination of hydrogen and carbon monoxide in the range of 55-80%. These percentage quantities of gases are by volume.

The sintered product is heat-treated at about 1600 F for a period of 1-1/2 hours in an endothermic atmosphere to which has been added natural gas and ammonia. The dew point of the gas is controlled so as to eliminate any loss of carbon. Following the heat treatment, the product is quenched in oil having a temperature in the range of 185-215"F with subsequent tempering at 400"F for one hour.

The ferroalloy used may be a commercial product having a +50-325 mesh size (United States Standard Mesh) and containing low carbon and low silicon. The alloy content of the ferroalloy may vary as follows, the percentage given being in weight: Chromium 65-75 % Titanium 37-47% Vanadium 49-49% Boron 14-24% Columbium 60-70% Tungsten 78-88% Molybdenum 60-64% Tantalum 48-52% Preferably the iron powder has a high compressibility with a mesh size of +80. Although the alloy content of the composition may be in the range of 1 to 10%, 2W% has been found to be a preferred amount.

The ferroalloy particles function as a nucleus for the diffusion of the alloy into the surrounding particles of iron and carbon. This results in a gradient of intermetallic phases around each ferroalloy nucleus being formed during the sintering process.

The ferroalloy nuclei are dispersed throughout the powder blend. They are hard and macroscopic in size, ranging up to 0.010 inch in diameter. These hard particles are keyed into the structure like the islands of carbides in hardenable iron as shown in the drawing and act as bridges to carry the imposed load. The powdered metal has interconnected porosity, and these voids act as reservoirs for the lubricants similar to the graphite in hardenable iron, thereby supplying oil on demand similar to a self-lubricating bearing. The matrix is a high-carbon ferrous powder with sufficient hardenability to develop a semi-marensitic matrix when heat treated in a carbonitriding atmosphere at l600F, quenched in oil, and tempered at 400 F.

The photomicrographs illustrate the similarity between the interconnected porosity and the soft graphite flakes of hardenable iron. The hardened steel matrix is present in both the powdered metal composition and the hardenable iron material. In like manner, the hard ferrochrome nucleus functions as, and appears similar to, the hard carbide particles in hardenable iron.

The resultant structure has a high resistance to scuffing, it compares with hardenable iron for wear and endurance, and shows a high degree of compatibility with mating components. The mating components can be carburized, hardened or induction hardened steel, as well as heat-treated hardenable iron.

It is important in the sintering process that the liquid phase be not reached. By maintaining a solid phase during the sintering operation, it is possible to have substantially less carbon content in the composition and also to have a sintering process which operates over a shorter period of time at substantially lower temperatures. This of course provides for a process which can function at much less cost than one which requires a liquid phase sinter. Processes of the latter kind are described, for example, in the following United States Patents: (a) U.S. Patent No. 3,850,583. Because of the extreme high titanium content (70% by weight) in the ferroalloy of this Patent, the composition goes into liquid phase during sintering at a temperature of approximately 2100"F.

(b) U.S. Patent No. 3,782,930. This des cribes a mixture of cast iron, graphite, carbon and ferrotitanium in which the titanium is present as titanium carbide. Because of an extremely high carbon content (1-4.5% by weight), the composition goes into liquid phase during sintering.

(c) U.S. Patent No. 3,937,630. Here also there is a liquid phase sinter and an extremely high carbon content, i.e. 1.5-6% by weight.

(d) U.S. Patent No. 3,950,165. This provides for liquid phase sintering at a temperature of 2552 F for five hours which is excessive both in temperature and duration and therefore basically an uneconomical process.

The following specific examples of wearresistant compositions in accordance with the invention have been satisfactorily tested for the specific use set forth above: EXAMPLE I A mixture of iron powder having a mesh size of +80 (United States Standard Mesh), 0.9% carbon by weight, and a ferrochromium alloy in an amount to provide 2.5% chromium by weight was briquetted at a pressure of between 40-60 ton/sq.in. and sintered in a disassociated ammonia atmosphere for 30 minutes at a temperature of 2050 F. The composition was used to form a heat-treated tappet body which compared favourably with hardenable iron in regard to the wear characteristics and other properties described above.

EXAMPLE 2 A mixture of iron powder having a mesh size of +80, 0.9% carbon by weight, and a ferrovanadium alloy in an amount to provide 2.5% vanadium by weight was briquetted at a pressure of between 40-60 tons/sq.in.

and sintered in an endothermic atmosphere for 15 minutes at a temperature of 2050 F.

The composition was used to form a heattreated tappet body which compared favourably with hardenable iron in regard to the wear characteristics and other properties described above.

EXAMPLE 3 A mixture of iron powder having a mesh size of +80, 0.9% carbon by weight, and a ferrotitanium alloy in an amount to provide 2.5% titanium by weight was briquitted at a pressure of between 40-60 tons/sq.in.

and sintered in an endothermic atmosphere for 30 minutes at a temperature of 2050"F.

The composition was used to form a heattreated tappet body which compared favourably with hardenable iron in regard to the wear characteristics and other properties described above.

EXAMPLE 4 A mixture of iron powder with a mesh size of + 80, 0.9% carbon by weight, and a ferroboron alloy in an amount to provide 2.5% boron by weight was briquetted at a pressure of between 40-60 ton/sq.in.

and sintered in an endothermic atmosphere for 30 minutes at a temperature of 2050 F.

The composition was used to form a heattreated tappet body which compared favourably with hardenable iron in regard to the wear characteristics and other properties described above.

Although the invention has been described above in connection with vehicle engine components, it has wider application. More specifically, the composition has use where similar wear conditions exist, such as in pump and transmission components.

WHAT WE CLAIM IS: 1. A sintered powdered metal heattreated wear resistant composition for use in vehicle engines and other machines where similar wear conditions exist formed from a mixture of iron powder, carbon in the range of 0.50-1.0% by weight, and a ferroalloy powder acting as a nucleus for diffusion of the alloying metal into the surrounding iron particles, the alloying metal in the composition being in the range of 1-10% by weight and being selected from the following group of metals: chromium, titanium, boron, vanadium, columbium, molybdenum, tantalum and tungsten; the iron, carbon and ferroalloy having been briquetted at a pressure of 40-60 ton/sq.in. and sintered, in solid phase, at a temperature of 2000-2100"F in a reducing atmosphere.

2. A composition according to claim 1, in which the alloying metal is substantially 2.5% by weight of the composition.

3. A composition according to claim 1 or claim 2, in which the composition is one which has been sintered for a period of 15 60 minutes.

4. A composition according to any one of claims 1-3, in which the reducing atmosphere includes the combination of carbon monoxide and hydrogen in the range of 55-80% by volume.

5. A composition according to any preceding claim, in which the reducing atmosphere is endothermic.

6. A composition according to any preceding claim, in which the reducing atmosphere includes approximately 75% hydrogen by volume.

7. A composition according to claim 1 as described in any one of the preceding Examples.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. cribes a mixture of cast iron, graphite, carbon and ferrotitanium in which the titanium is present as titanium carbide. Because of an extremely high carbon content (1-4.5% by weight), the composition goes into liquid phase during sintering. (c) U.S. Patent No. 3,937,630. Here also there is a liquid phase sinter and an extremely high carbon content, i.e. 1.5-6% by weight. (d) U.S. Patent No. 3,950,165. This provides for liquid phase sintering at a temperature of 2552 F for five hours which is excessive both in temperature and duration and therefore basically an uneconomical process. The following specific examples of wearresistant compositions in accordance with the invention have been satisfactorily tested for the specific use set forth above: EXAMPLE I A mixture of iron powder having a mesh size of +80 (United States Standard Mesh), 0.9% carbon by weight, and a ferrochromium alloy in an amount to provide 2.5% chromium by weight was briquetted at a pressure of between 40-60 ton/sq.in. and sintered in a disassociated ammonia atmosphere for 30 minutes at a temperature of 2050 F. The composition was used to form a heat-treated tappet body which compared favourably with hardenable iron in regard to the wear characteristics and other properties described above. EXAMPLE 2 A mixture of iron powder having a mesh size of +80, 0.9% carbon by weight, and a ferrovanadium alloy in an amount to provide 2.5% vanadium by weight was briquetted at a pressure of between 40-60 tons/sq.in. and sintered in an endothermic atmosphere for 15 minutes at a temperature of 2050 F. The composition was used to form a heattreated tappet body which compared favourably with hardenable iron in regard to the wear characteristics and other properties described above. EXAMPLE 3 A mixture of iron powder having a mesh size of +80, 0.9% carbon by weight, and a ferrotitanium alloy in an amount to provide 2.5% titanium by weight was briquitted at a pressure of between 40-60 tons/sq.in. and sintered in an endothermic atmosphere for 30 minutes at a temperature of 2050"F. The composition was used to form a heattreated tappet body which compared favourably with hardenable iron in regard to the wear characteristics and other properties described above. EXAMPLE 4 A mixture of iron powder with a mesh size of + 80, 0.9% carbon by weight, and a ferroboron alloy in an amount to provide 2.5% boron by weight was briquetted at a pressure of between 40-60 ton/sq.in. and sintered in an endothermic atmosphere for 30 minutes at a temperature of 2050 F. The composition was used to form a heattreated tappet body which compared favourably with hardenable iron in regard to the wear characteristics and other properties described above. Although the invention has been described above in connection with vehicle engine components, it has wider application. More specifically, the composition has use where similar wear conditions exist, such as in pump and transmission components. WHAT WE CLAIM IS:

1. A sintered powdered metal heattreated wear resistant composition for use in vehicle engines and other machines where similar wear conditions exist formed from a mixture of iron powder, carbon in the range of 0.50-1.0% by weight, and a ferroalloy powder acting as a nucleus for diffusion of the alloying metal into the surrounding iron particles, the alloying metal in the composition being in the range of 1-10% by weight and being selected from the following group of metals: chromium, titanium, boron, vanadium, columbium, molybdenum, tantalum and tungsten; the iron, carbon and ferroalloy having been briquetted at a pressure of 40-60 ton/sq.in. and sintered, in solid phase, at a temperature of 2000-2100"F in a reducing atmosphere.

2. A composition according to claim 1, in which the alloying metal is substantially 2.5% by weight of the composition.

3. A composition according to claim 1 or claim 2, in which the composition is one which has been sintered for a period of 15 60 minutes.

4. A composition according to any one of claims 1-3, in which the reducing atmosphere includes the combination of carbon monoxide and hydrogen in the range of 55-80% by volume.

5. A composition according to any preceding claim, in which the reducing atmosphere is endothermic.

6. A composition according to any preceding claim, in which the reducing atmosphere includes approximately 75% hydrogen by volume.

7. A composition according to claim 1 as described in any one of the preceding Examples.

8. An engine tappet body, rocker fol

lower or distributor drive gear formed partially or entirely of a composition as claimed in any preceding claim.

9. A pump component or a transmission component formed partially or entirely of a composition as claimed in any one of claims 1 to 7.