Background of the invention The connecting rod manufacturing process involves pressure molding metal particles in a closed mold under significant pressure to produce a green compact form of the rod. Next, the green compact is heated in a furnace sufficiently to form a sintered preform in which metal particles are bonded. Next, the sintered preform is hot forged to final rod shape which increases the rod's density and strength.

The automobile industry continues to challenge connecting rod manufacturers to increase the fatigue strength of these articles. As a result, higher performance materials are needed for forged connecting rods. The goal is to engineer a powder metal blend to manufacture connecting rods with the following characteristics: high strength; good machinability ; reasonable cost, good weight and dimensional control.

Our research included materials considerations; metallurgical and microstructure evaluation ; dimensional change measurements ; tensile strength ; fatigue strength and machinability tests.

Brief Summary of the Invention The forged articles or connecting rods of this invention are made from ferrous based powder prealloyed with manganese and sulfur. The prealloyed powder then is admixed with copper at higher than normal

copper contents. Materials considered were as follows. In a first approach, t thought that increasing Cu content from 2% to 3% or even 4% would improve the strength of connecting rods for the following reasons: Cu strengthens the ferrite, Cu hardens the ferrite, and Cu hinders grain growth after forging. In a second approach I thought that using prealloyed MnS base powder, instead of admixed MnS base powder, would improve the strength of connecting rods for the following reasons: smaller inclusion (MnS) size, uniform inclusion (MnS) distribution, and higher Mn content.

As a result, I used a commercially available prealloyed manganese, sulfur, ferrous based powder for producing the forged article. The prealloyed powder then is mixed with copper and carbon to produce a mix comprising by weight percent: Component Weight Percent copper (Cu) < 2.0 to 5.0 carbon (C) 0.2 to 1.0 prealloyed MnS powder balance The resulting forged connecting rods had an improvement in tensile strength and an improvement in fatigue strength.

Brief Description of the Drawings Fig. 1 is a perspective view of a forged connecting rod.

Detailed Description of the Invention The methods for preparing the prealloyed powder may vary widely. Typically, the powder is prepared by atomization of a molten metal stream of iron, manganese and sulfur. The resulting particles usually have an irregular spherical shape. To facilitate. compaction, the

atomized particles can be collected after solidification and subjected to annealing at 1700°F for about 1-1/2 hours, followed by grinding to break up particle cakes, and then passed through an 80 mesh sieve.

The prealloyed ferrous powder then is mixed with copper and graphite at room temperature. The copper powder generally has a purity of 99%. The copper powder and carbon (graphite flake powder), however, are commercial grade materials. The copper powder is mixed in a range of 2.0 to 5. 0% by weight of the mixture. The graphite powder is added to yield a final carbon content in the product ranging from 0.2 to 1.0 weight percent.

Fig. 1 illustrates forged connecting rod 10. Rod 10 has an elongated configuration extending along longitudinal axis A-A. Rod 10 includes midportion 12 ; small end portion 14; and large end portion 16.

Bore 18 is formed through small end portion 14 adapted to receive a wrist or piston pin (not shown) as is well known in the engine art.

Aperture 20 is formed through large diameter end 16 and is adapted to receive a journal of a crankshaft (not shown) as is well known in the engine art. Large end portion 16 has a side thrust face 22. Rod 10 includes large end portion 16 having a pair of oppositely facing edges or end surfaces 24. In the particular design of the connecting rod shown in Fig. 1, side thrust face 22 is in a raised plane with respect to the remaining side surface 26. Side thrust face 22 also includes a pair of radially outwardly extending portions 28,30 located to either side of aperture 20. Portions 28,30 extend radially outward from aperture 20 and terminate at end of edges 24.

Fig. 1 also shows a pair of slits or creases 32,34 formed in the side thrust face including extensions 28,30. Each crease 32,34 is arranged to one side of aperture 20 and they are substantially aligned across aperture 20. Creases 32,34 extend inwardly from surfaces 28,

30 to a considerable depth as is evident by examination of leftward end 24 and the cylindrical surface which forms the bore 20.

The manufacturing processes for making the connecting rod may vary widely. For example, a green compact is made in the form of the rod by molding powder metal particles in a closed mold under great pressure, typically about 80,000 psi. This pressure molding causes the particles to mechanically interlock and form a stable, relatively weak part but strong enough for handling. Next, the green compact is heated in a furnace at temperatures higher than 2000 degrees F. for a period of time sufficient to cause the metal particles to bond. After sintering, the preform has the same configuration as the green compact but is much stronger.

The preform then is hot forged to achieve the shape and increase density and strength as required for a connecting rod. Typically, it is hot forged in a press at a pressure of about 60,000 psi and at a temperature of about 1800 degrees F.

Preferably, the mixture of this invention comprises: Component Weight Percent Cu 2. 5 to 4. 5 C 0.2 to 0.7 prealloyed MnS powder balance More preferably, the mixture is: Component Weight Percent Cu 3.0 to 4.0 C 0. 4 to 0. 7

prealloyed MnS powder balance The mixed powder of this invention may be used to forge articles other than connecting rods. Other automotive uses include piston rings and valve seats for internal combustion engines. Other parts include clutch races, differential gears and similar parts.

The following Examples further illustrates the composition of this invention.

Example t (Prior Art) The following shows average tensile results for standard production powders with varying amounts of copper. Results for a standard manganese sulfur admixture (rather than the prealloyed powder of this invention) also are shown. The average is based on 6 runs.

TENSILE RESULTS Commercial Grade Standard Production Powder Prealloyed Mn S Powder 2% Cu 3% Cu 4% Cu 2% Cu (psi) (psi) (psi) (psi) Avg. 124,534 144,788 145,046 120,268 StDev 3,641 2,771 3,805 1, 755

Example II (Prior Art) The following shows fatigue results for standard production powders with varying amounts of copper. Results for a standard prealloyed manganese sulfur powder also are shown.

FATIGUE RESULTS Standard production powder Commercial Grade Prealloyed Mn S Powder 2% Cu 3% Cu 4% Cu 2% Cu (ksi) (ksi) (ksi) (ksi) Endurance Limit @ 50% 45.21 52.63 52.64 50.77 Scatter 1.07 2.18 2.10 1.88 Standard deviation (s) 0.28 0.49 0.49 0.43 Example III Tensile Results for the prealloyed Mn S ferrous powder of this invention with 3% Cu show an improvement of approximately 5% in tensile strength compared to standard production.

Example IV Fatigue results for the prealloyed Mn S ferrous based powders of this invention with 3% Cu show an improvement of 19% in fatigue strength compared to standard production.

In addition to these embodiments, persons skilled in the art can see that numerous modifications and changes may be made to the above invention without departing from the intended spirit and scope thereof.