U.S. patent application number 11/253298 was filed with the patent office on 2006-04-27 for impact of copper and carbon on mechanical properties of iron-carbon-copper alloys for powder metal forging applications.
Invention is credited to Edmond Ilia, Mike O'Neill, Kevin Tutton.
Application Number | 20060086204 11/253298 |
Document ID | / |
Family ID | 36204973 |
Filed Date | 2006-04-27 |
United States Patent
Application |
20060086204 |
Kind Code |
A1 |
Ilia; Edmond ; et
al. |
April 27, 2006 |
Impact of copper and carbon on mechanical properties of
iron-carbon-copper alloys for powder metal forging applications
Abstract
There was perceived a lack of information regarding higher
strength materials for sinter-forging automotive applications.
Work, therefore, was undertaken to develop new higher strength
materials for sinter-forging automotive applications and to fill
this lack of information. Accordingly, a connecting rod that
comprises an iron-based powder metal mixture was developed. The
mixture comprises between 3.01% and 3.03% by weight of copper,
between 0.57% and 0.64% by weight of carbon, between 0.32% and
0.33% by weight of manganese, and about 0.13% by weight of
sulfur.
Inventors: |
Ilia; Edmond; (Ridgway,
PA) ; Tutton; Kevin; (Ridgway, PA) ; O'Neill;
Mike; (St. Mary's, PA) |
Correspondence
Address: |
MCDONALD HOPKINS CO., LPA
2100 BANK ONE CENTER
600 SUPERIOR AVENUE, E.
CLEVELAND
OH
44114-2653
US
|
Family ID: |
36204973 |
Appl. No.: |
11/253298 |
Filed: |
October 18, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60619782 |
Oct 18, 2004 |
|
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Current U.S.
Class: |
75/246 |
Current CPC
Class: |
B22F 2999/00 20130101;
B22F 2998/00 20130101; B22F 2999/00 20130101; C22C 38/16 20130101;
B22F 2998/00 20130101; B22F 3/1007 20130101; B22F 2201/02 20130101;
B22F 3/10 20130101; B22F 1/0003 20130101; B22F 2998/10 20130101;
C22C 33/0264 20130101; B22F 3/17 20130101; B22F 5/10 20130101; B22F
3/1007 20130101; B22F 3/02 20130101; B22F 2201/013 20130101; C22C
38/04 20130101; B22F 2999/00 20130101; B22F 2998/10 20130101; C22C
38/60 20130101; F16C 7/023 20130101 |
Class at
Publication: |
075/246 |
International
Class: |
C22C 38/60 20060101
C22C038/60 |
Claims
1. A connecting rod comprising: an iron-based powder metal mixture,
wherein said mixture comprises: between 3.01% and 3.03% by weight
of copper; between 0.57% and 0.64% by weight of carbon; between
0.32% and 0.33% by weight of manganese; and about 0.13% by weight
of sulfur.
2. The connecting rod of claim 1, wherein said mixture consists of:
between 3.01% to 3.03% by weight of copper; between 0.57% to 0.64%
by weight of carbon; between 0.32% to 0.33% by weight of manganese;
and 0.13% by weight of sulfur.
3. The connecting rod of claim 1, wherein said mixture consists of
about 3.01% by weight of copper.
4. The connecting rod of claim 3, wherein said mixture consists of
about 0.64% by weight of carbon.
5. The connecting rod of claim 4, wherein said mixture consists of
about 0.33% manganese.
6. The connecting rod of claim 5, wherein said mixture consists of
about 0.13% by weight of sulfur.
7. The connecting rod of claim 1, wherein said mixture consists of
about 3.03% by weight of copper.
8. The connecting rod of claim 7, wherein said mixture consists of
about 0.57% by weight of carbon.
9. The connecting rod of claim 8, wherein said mixture consists of
about 0.32% manganese.
10. The connecting rod of claim 9, wherein said mixture consists of
about 0.13% by weight of sulfur.
11. The connecting rod of claim 1, wherein said mixture is used in
sintered-forging to create said connecting rod.
12. The connecting rod of claim 1, further comprising: a crank end;
a shank connected to said crank end; and a pin end connected to
said shank and opposite from said crank end.
13. A sintered-forged connecting rod comprising: an iron-based
powder metal mixture essentially consisting of: between 3.01% and
3.03% by weight of copper; between 0.57% and 0.64% by weight of
carbon; between 0.32% and 0.33% by weight of manganese; and 0.13%
by weight of sulfur.
14. The connecting rod of claim 13, wherein said mixture consists
of: 3.03% by weight of copper; 0.57% by weight of carbon; 0.32% by
weight of manganese; and 0.13% by weight sulfur.
15. The connecting rod of claim 13, wherein said mixture consists
of: 3.01% by weight of copper; 0.64% by weight of carbon; 0.33% by
weight of manganese; and 0.13% by weight sulfur.
16. An iron-based powder metal mixture capable of being
sintered-forged into a connecting rod, said mixture consisting of:
between 3.01% and 3.03% by weight of copper; between 0.57% and
0.64% by weight of carbon; between 0.32% and 0.33% by weight of
manganese; and 0.13% by weight of sulfur.
17. The mixture of claim 16, wherein said mixture consists of:
3.03% by weight of copper; 0.57% by weight of carbon; 0.32% by
weight of manganese; and 0.13% by weight sulfur.
18. The mixture of claim 16, wherein said mixture consists of:
3.01% by weight of copper; 0.64% by weight of carbon; 0.33% by
weight of manganese; and 0.13% by weight sulfur.
19. The mixture of claim 16, wherein said mixture is capable of
being sintered-forged into a connecting rod.
20. The mixture of claim 19, wherein said connecting further
comprises: a crank end; a shank connected to said crank end; and a
pin end connected to said shank and opposite from said crank end
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Patent Application No. 60/619,782 filed on Oct. 18, 2004, which is
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention is generally related to the impact of
copper and carbon on mechanical properties of metal forgings, and
more particularly to the impact of copper and carbon on mechanical
properties of iron-carbon-copper alloys for powder metal
sinter-forging applications.
BACKGROUND OF THE INVENTION
[0003] One of the main requirements for a satisfactory function of
a connecting rod is the fatigue strength, which mainly depends on
design, material, microstructure, and surface condition. Currently,
there are two main processing technologies available to manufacture
connecting rods: drop forging and sinter forging. The cost
effectiveness of each one of these technologies is another main
consideration in high volume production of automotive components.
Better performance and lower cost of the as-finished product are
the main reasons why the use of sinter-forged connecting rods has
significantly increased in the last twenty years.
[0004] The most widely used material for sinter-forged connecting
rods is P/F-I I C50 (FC-0205 admixed with MnS to enhance the
machinability). MPIF Standard 35 covers mechanical properties for
P/F-IOCXX (no MnS added) and P/F-11CXX (MnS added), with 2% copper
(1.80%-2.20%) and with as-forged product carbon content ranging
from 0.40% to 0.60%. Carbon and copper are the main strengthening
elements in the material used to manufacture sinter-forged
connecting rods.
[0005] Additionally, graphite as an additive to a base ferrous
powder is well known to effectively improves strength and hardness.
Carbon, as an interstitial diffusing element, rapidly dissolves in
iron during sintering, thus strengthening and hardening the iron
matrix. Copper is also well known for its ability to strengthen and
harden the ferrite and to hinder the growth of new grains during
recrystallization after forging (resulting in microstructures with
a finer grain), thus increasing the strength. For example, moderate
amounts of copper (approximately 0.2%)-are used in wrought steels
to provide resistance to atmospheric corrosion. At about 1% copper,
the yield strength is increased by about 70 MPa to 140 MPa (10 Ksi
to 20 Ksi), regardless of the effects of other alloying elements.
However, higher copper contents are not used in wrought materials
due to extensive segregation in the molten state (up to 4%).
[0006] A lot of work has been done to characterize several
materials with copper contents ranging from 2% to 10% at densities
ranging from 5.8 g/cc to 7.2 g/cc, but not much has been done to
evaluate the impact of copper and carbon content on mechanical
properties at fully dense conditions, even though copper and carbon
are widely used elements in the powder metal forging industry. One
of the few works studying different copper contents, other than the
2% Cu used in P/F-1OC50 and P/F-11C50, is by Tsumuki et al. Low
fatigue limits of 186 MPa (27 Ksi) for as-forged specimens and of
234 MPa (34 Ksi) for smooth machined specimens for a ferrous powder
with 0.50% C, 3.0% Cu, and 0.30% S were reported.
[0007] The effect of different graphite contents admixed in the
base ferrous powder used to manufacture connecting rods has been
explored in the 1980's and in the 1990's. R. A. Chernenkoff et al.
did not see any significant impact on fatigue strength for carbon
contents varying from 0.28% to 0.69% in a copper steel (2% Cu), but
the tensile strength increased up to 1,000 MPa (145 Ksi) for 0.69%
C and the elongation decreased. An estimated axial fatigue limit of
292 MPa (42.3 Ksi) was obtained from tests on specimens at a stress
ratio r=-1.
[0008] Sanderow et al. reported UTS values of 830 MPa (120.3 Ksi),
YS values of 558 MPa (80.8 Ksi), an elongation of 14%, and an axial
fatigue limit of 297 MPa (43 Ksi) obtained from as-forged specimens
manufactured with P/F-11C40, in the normalized condition, with a
carbon content of 0.4%-0.5%.
[0009] Marra et al. reported UTS values of 950 MPa (138 Ksi), YS
values of 605 MPa (88 Ksi), and elongations of 7.5% obtained from
as-forged specimens having 0.78% C on the surface and 0.66% C in
the core, 2.0% Cu, and 0.35% MnS.
[0010] Bhambri et al. reported UTS values of 925 MPa (134 Ksi), YS
values of 815 MPa (118 Ksi), and a low axial fatigue limit of 28
Ksi (193 MPa) obtained from as-forged specimens manufactured with a
ferrous powder containing 0.5% C, 2.0% Cu, and 0.35% MnS.
[0011] W. B. James et al. studied the impact of carbon content,
heat treating, and forging mode on mechanical properties for
iron-copper-carbon alloys. Improvements in tensile and fatigue
strength were obtained by increasing the amount of carbon from
0.39% to 0.85%. Fatigue limits as high as 525 MPa (76 Ksi) were
obtained from rotating bending tests on smooth specimens.
[0012] The findings of these reports, however, were found to be
contradictory and incomplete. Considering the results obtained on
powder metal components, the need to better understand the effect
of copper and carbon on the strength of iron-copper-carbon systems
is necessary. At this point, therefore, work was undertaken to
develop new higher strength materials for sinter-forging automotive
applications and to fill this lack of information. It was thought
that by increasing the copper content from the current level of 2%
to 3% or even 4%, some improvements in mechanical properties would
obtained, due to the hardening and strengthening effect of copper.
One such previous study led to the development of HS150.TM., which
is 3.06% by weight copper, 0.5% by weight carbon, 0.31% by weight
manganese, and 0.12% by weight sulfur.
SUMMARY OF THE INVENTION
[0013] Accordingly, the present invention provides a connecting
rod. The connecting rod comprises an iron-based powder metal
mixture. The mixture comprises between 3.01% and 3.03% by weight of
copper, between 0.57% and 0.64% by weight of carbon, between 0.32%
and 0.33% by weight of manganese, and about 0.13% by weight of
sulfur.
[0014] In another embodiment, the present invention provides a
sintered-forged connecting rod comprises an iron-based powder metal
mixture essentially consisting of between 3.01% and 3.03% by weight
of copper, between 0.57% and 0.64% by weight of carbon, between
0.32% and 0.33% by weight of manganese, and 0.13% by weight of
sulfur.
[0015] In yet another embodiment of the present invention, an
iron-based powder metal mixture capable of being sintered-forged
into a connecting rod consists of between 3.01% and 3.03% by weight
of copper, between 0.57% and 0.64% by weight of carbon, between
0.32% and 0.33% by weight of manganese, and 0.13% by weight of
sulfur.
[0016] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention.
DESCRIPTION OF THE DRAWINGS
[0017] Objects and advantages together with the operation of the
invention may be better understood by reference to the following
detailed description taken in connection with the following
illustrations, wherein:
[0018] FIG. 1. depicts a connecting rod and a mini cylindrical
tensile specimen using material of an embodiment of the present
invention;
[0019] FIG. 2 summarizes graphically the results of a static test
comparing tensile strength of embodiments of the present invention
and known materials;
[0020] FIG. 3 summarizes graphically the results of a static test
comparing other static properties of embodiments of the present
invention and known materials;
[0021] FIG. 4 summarizes graphically main effect of both copper and
as-forged carbon contents on static mechanical properties of an
embodiment of the present invention and known materials;
[0022] FIG. 5 summarizes graphically copper-carbon interaction on
UTS and YS;
[0023] FIG. 6 summarizes graphically UTS and YS correlation with
as-forged carbon content with approximately 3% copper;
[0024] FIG. 7 is a staircase chart for 2Cu5C and 3Cu5C;
[0025] FIG. 8 is a 3D view of surface texture of 2Cu5C and
3Cu5C;
[0026] FIG. 9 summarizes graphically results of machinability
testing-drilling of bolt holes of an embodiment of the present
invention and known materials; and
[0027] FIG. 10 is a summary of staircase test results, r=-2, for an
embodiment of the present invention and known materials.
DETAILED DESCRIPTION
[0028] While the present invention is described with reference to
the preferred embodiment, it should be clear that the present
invention should not be limited to this embodiment. Therefore, the
description of the preferred embodiment herein is illustrative of
the present invention and should not limit the scope of the
invention as claimed.
[0029] The effect of copper contents (from 2% to 4%) on iron-based
powder metal sintered-forged materials was studied. This study also
included the previously developed HS150.TM. in its results. The
conclusion was that mechanical properties peak at the level of
approximately 3% copper under processing conditions considered.
Graphite contents of approximately 0.58%, 0.68%, and 0.78% were
admixed, along with approximately 2.0% and 3.0% copper, and
approximately 0.32% manganese sulfide (MnS), into an atomized
ferrous base powder. Static and dynamic tests were carried out on
specimens machined out of fully dense (hot forged) components and
pucks. Correlations regarding the impact of these two variables
(copper and carbon content) on several mechanical properties were
evaluated. Two new materials for forging applications were
developed: HS160.TM. and HS170.TM.. A side-by-side comparison of
powder metal sinter-forged connecting rods manufactured with these
materials, along with HS150.TM., and drop-forged connecting rods of
the same design was carried out and fatigue test results were
reported.
[0030] Five different mixes, using an atomized ferrous base powder,
were prepared as shown in Table 1. Copper and graphite contents
were the only variables considered; the rest of the admixed
ingredients were virtually the same for all of the five mixes
(approximately 0.32% MnS and lubricant). TABLE-US-00001 TABLE I 3.0
3Cu5C 3Cu6C 3Cu7C 2.0 2Cu5C 2Cu6C Cu/Graphite 0.58 0.68 0.78
[0031] As shown in Table I, two levels (2% and 3%) were used for
copper and three levels (0.58%, 0.68%, and 0.78%) were used for
graphite. Pucks (100 mm in diameter and 25 mm thick) were
manufactured from all of the considered mixes on the same
production line. The pucks were compacted at a green density of
6.90 g/cm.sup.3 and sintered for 30 minutes at 1150.degree. C.
(2100.degree. F.) in an atmosphere consisting of 90% nitrogen and
10% hydrogen. Subsequently, the pucks were hot forged (re-pressed)
to a fully dense condition and cooled in still air. The density of
the forged pucks was approximately 7.80 g/cm.sup.3. Connecting rods
of the same design were manufactured under the same conditions
using all of the five mixes. These connecting rods comprise a crank
end, a shank connected to the crank end, and a pin end connected to
the shank and opposite from the crank end.
[0032] A summary of the chemical analysis results of the as-forged
components (average of 5 measurements) is represented in Table II.
As shown, the copper and carbon contents were very close to the
target, while the content of the rest of the admixed elements was
almost the same in all of the groups. TABLE-US-00002 TABLE II Cu C
Mn S 2Cu5C 1.98 0.49 0.33 0.12 2Cu6C 2.02 0.56 0.34 0.12 3Cu5C 3.06
0.50 0.31 0.12 3Cu6C 3.03 0.57 0.32 0.13 3Cu7C 3.01- 0.64 0.33
0.13
[0033] Specimens were machined out of components and pucks and both
specimens and components were submitted to a battery of tests
consisting of tensile and compressive testing, shear strength
testing, fatigue testing, machinability testing and crackability
testing.
[0034] Typical pearlitic-ferritic microstructures were obtained
from all of the groups. The microstructure with finer grain is
obtained in the case of the 3% copper material, due to the higher
copper content. Pearlitic grain size measurements were carried out
at Climax Research Services, MI, using the comparison method in
accordance with ASTM Standard El 12-96. As expected, the pearlitic
grain size decreases with increasing copper content from 2% to 3%.
No changes were obtained in grain size for copper contents higher
than 3%.
[0035] Core hardness values are reported in Table III. As shown,
the hardness increases with increasing copper and carbon contents.
In mixes with approximately 0.5% as-forged carbon, the hardness
increases up to 31 HRC when copper is increased from 2% to 3%, and
stabilizes thereafter, even when the copper content is increased up
to 4%. The maximum core hardness is obtained in the case of the
material with higher copper and carbon levels (3Cu7C), which is
HS170.TM.. TABLE-US-00003 TABLE III 2Cu5C 3Cu5C 2Cu6C 3Cu6C 3Cu7C
Hardness (HRC) 24 31 26.5 32 34.7
[0036] At this point, there was a strong indication that mechanical
properties should reach their maximum at or near the level of 3%
copper. To confirm this assumption, mini cylindrical tensile
specimens (3 mm in diameter and 45 mm in length), as shown in FIG.
1, were machined from the bolt boss area of the powder metal forged
connecting rods and were submitted to tensile strength tests.
Fifteen specimens per material were tested and the average results
for the first step obtained are summarized in Table IV. As shown in
Table IV, there are two distinct trends in both ultimate tensile
strength (UTS) and yield strength (YS) in function of copper
levels: one significantly increasing trend (from 2% to 3%) and a
constant-slightly decreasing trend (from 3% to 4%). In other words,
by increasing the copper content up to approximately 3%, both UTS
and YS increase, and stay almost constant (or slightly decrease) by
further increasing the copper content up to 4%, in a mix with 0.58%
graphite (approximately 0.50% as-forged carbon). Slight decreases
in elongation at higher copper levels were reported as well, due to
the hardening effect of copper. It was concluded that the copper
effect on improving yield strength was higher than on improving
tensile strength. TABLE-US-00004 TABLE IV 2Cu5C 2Cu6C 3Cu5C 3Cu6C
3Cu7C Tensile Strength (MPa) 860 945 1000 1060 1120 Yield Strength
(MPa) 560 605 710 724 770 Elongation (%) 15 12 13 11 9 Compressive
Yield 540 635 695 705 775 Strength (MPa) Shear Strength (MPa) 540
625 680 725 785
[0037] The charts shown in FIGS. 2 and 3 summarize graphically the
results of the static tests. Further, a summary of the correlation
coefficients for copper contents varying from 2% to 3% and for
as-forged carbon contents varying from 0.49% to 0.57% is give in
Table V below. TABLE-US-00005 TABLE V Constant Coeff. Cu Coeff. C
Coeff. Cu * C UTS MPa = -425 345 2,045.22 -415.469 YS MPa = -272
258.5 1,116.15 -236.644 CY MPa = -1,215 545 2,988.59 -815.723 SS
MPa = -835 390 2,240.49 -513.102 Elongation (%) = 56 -10 -75.317
16.2299
[0038] The main effect of both copper and as-forged carbon contents
on static mechanical properties is illustrated in the charts shown
in FIG. 4. The effect of 1% copper increase on UTS and YS is
stronger than the effect of 0.07% carbon increase, as illustrated
by the slope of the lines in FIG. 4. Charts illustrating the
interactions of copper and carbon on UTS and on YS are shown in
FIG. 5.
[0039] As shown, the lines representing UTS values at two different
levels of carbon are almost parallel, which indicates that there is
little meaningful interaction between copper and carbon. As a
matter of fact, by increasing the copper content by 1%, UTS
improves by 140 MPa and by 115 MPa respectively for the two levels
of as-forged carbon considered: 0.50% and 0.57% (the lower the
carbon content, the higher the change in UTS due to copper content
increase). This statement is not true in the case of YS: as shown
in FIG. 5, the lines representing YS values at two different levels
of carbon are not parallel, which indicates that there is
interaction between copper and carbon. Quantitatively, by
increasing the copper content by 1% (from 2% to 3%) in the mix with
0.50% as-forged carbon, UTS improved by approximately 16% (140
MPa), while YS improved by approximately 27% (150 MPa).
[0040] Considering the fact that the matrix for the DOE was not
complete (two levels for copper and two and three levels for carbon
in the case of mixes with 2% and 3% copper respectively), separate
correlations for the impact of carbon on mechanical properties were
carried out in the case of mixes with approximately 3% copper only.
Such correlations are illustrated in FIG. 6. As shown, very good
linear correlations were obtained (R.sup.2 of 0.996 for UTS and
0.934 for YS). An improvement of approximately 6% in UTS (60 MPa)
was obtained by increasing the as-forged carbon content by 0.07% in
a mix with approximately 3% copper, thus totaling 12% improvement
for a 0.14% increase in the as-forged amount of carbon. An
improvement of approximately 8.5% in YS (60 MPa) was obtained by
increasing the as-forged carbon content by 0.14% in the same mix
with approximately 3% copper. If copper had a larger effect on YS
(27% improvement for 1% copper increase) than on UTS (16%
improvement for 1% copper increase), carbon had a larger effect on
UTS (12% improvement for 0.14% carbon increase) than on YS (8.5%
improvement for 0.14% carbon increase).
[0041] Hourglass shaped axial fatigue test specimens were machined
from forged pucks. The gauge sections of specimens were polished in
the loading direction using fine emery paper. Axial, constant
amplitude, fully reversed (stress ratio r=-1) fatigue tests were
run at the University of Waterloo, Canada. The fatigue tests were
run at room temperature using an MTS servohydraulic closed loop
controlled testing machine. Fatigue testing on unpeened specimens
was conducted only for two of the materials considered: 2Cu5C and
3Cu5C(HS150.TM.), in order to study the differences between 2% and
3% copper. The staircase test method was used to evaluate fatigue
limits for both materials. Run out was considered the result of the
test for specimens surviving 10.sup.7 cycles. FIG. 7 represents a
comparison of the staircase fatigue test results for specimens
manufactured with 2Cu5C and 3Cu5C.
[0042] Thirty specimens were tested in the case of the 2Cu5C
material and twenty-seven in the case of the 3Cu5C material. A
summary of the fatigue limit calculations is presented in Table VI.
Both fatigue limits @ 50% and 90% probability of survival are
reported. As shown, by increasing the amount of copper by only 1%
(from 2% to 3%), a significant improvement of approximately 36% in
fatigue strength was obtained when considering the fatigue limit @
50% probability of survival in mixes with approximately 0.50%
as-forged carbon. On the other hand, no further improvement was
obtained when copper was increased from 3% to 4%. Thus, confirming
the results obtained from static testing on the specimens.
TABLE-US-00006 TABLE VI 2Cu5C 3Cu5C Fatigue Limit - 50% survival
MPa 294.3 400.2 Fatigue Limit - 90% survival MPa 279.3 386.8
[0043] Endurance ratios calculated using both UTS and YS and the
fatigue limit @ 50% probability of survival is summarized in Table
VII. As shown, the endurance ratio calculated using UTS is not a
constant number; it increases with increasing copper content from
2% to 3% and stabilizes afterwards, even though copper contents are
increased up to 4%. This can be explained with the fact that the
fatigue limit increase was not proportional with the tensile
strength increase, but more likely to the yield strength increase.
The endurance ratios calculated using YS are almost constant in
function of different copper contents (up to 4% copper, with 0.50%
as-forged carbon). TABLE-US-00007 TABLE VII 2Cu5C 3Cu5C 4Cu5C
UTS/FL @ 50% 0.34 0.40 0.41 YS/FL @ 50% 0.53 0.56 0.57
[0044] In order to complete the characterization of these
materials, their split-crackability and machinability were
evaluated. Powder metal connecting rods are forged in one piece and
a "fracture splitting" process separates the rod and the cap. The
irregular mating fracture surfaces provide an intimate interlock
between rod and cap, thus virtually eliminating both rotation and
lateral movement of the cap relative to the rod. Cap shift
(rotation) can lead to accelerated wear of bearing surfaces and, in
extreme cases, to bearing seizure. Lateral movement can result, at
high engine revolutions, in high shear stresses on the bolts. The
roughness of the fracture surface is very critical to provide with
a very good cap-rod alignment. A smooth surface can result in cap
misalignment during the assembly process.
[0045] The 3D surface roughness of the fracture surface after the
splitting process was measured at Michigan Metrology, MI, in the
case of the 2Cu5C and 3Cu5C materials, to compare 2% copper with 3%
copper. R.sub.e, R.sub.Z, and Surface Area Index (SAI) were
considered. SAI represents the ratio between the actual measured
fracture surface to a perfectly flat and smooth surface. The
results of the measurements are represented in Table VIII while 3D
views of the surface texture for two of the considered materials
(2Cu5C and 3Cu5C) are shown in FIG. 8. TABLE-US-00008 TABLE VIII Ra
(nm) Rz (nm) SAI 2Cu5C 27,750 207,157 1.62 3Cu5C 25,536 197,749
1.57
[0046] As shown, slight differences were observed in the case of
the two materials. The 2Cu5C connecting rods had a slightly rougher
surface than the 3Cu5C connecting rods. The difference in SAI is
close to 3%.
[0047] Results of some machining trials on connecting rods
manufactured with 2Cu5C, 2Cu6C, 3Cu5C, and 3Cu6C are summarized in
FIG. 9. This chart illustrates the relative thrust force during the
drilling operation to create the boltholes. The tests were run on
connecting rod machining lines at Metaldyne in Ramos Arizpe,
Mexico, from where fully machined connecting rods are being
supplied. Standard production drill bits and cutting parameters
normally used for the material 2Cu6C were used for all of the four
materials. The thrust force is expressed in measuring equipment
units and hardness values are included in the chart as well for
comparison. The lowest thrust force was needed in the case of 2Cu5C
and the highest, as expected, in the case of 3Cu6C. As shown, the
difference in thrust force is less than 4%. Several thousands of
connecting rods manufactured with 2Cu5C, 2Cu6C, HS150.TM., and
HS160.TM. were submitted to all of the machining operations
required in production. Only slight differences in tool wear were
observed among the groups.
[0048] After previously developing HS150.TM. and now developing
HS160.TM. and HS170.TM. it was very important to verify their
performance against connecting rods manufactured using the drop
forging technology. 1.9 L drop forged connecting rods manufactured
with C70 were submitted to a battery of different fatigue tests
side by side with 1.9 L, powder forged connecting rods of the same
design (used for the same engine). This is very important, because
of the well-known impact of design on fatigue strength.
[0049] Powder forged connecting rods were manufactured using
HS150.TM., HS160.TM. and HS 170.TM. materials, with the chemical
composition shown in Table IX. Axial, constant amplitude, fully
reversed (stress ratio r=-1) and offset loading (stress ratio r=-2)
fatigue tests were run at room temperature using a
servohydraulic-closed loop controlled testing machine. Run out was
considered the result of the test for connecting rods surviving
10.sup.7 cycles. Twenty piece staircase tests were completed for
the three of the four groups of connecting rods at both stress
ratios (this test did not use the HS170.TM. material). The chart
shown in FIG. 10 illustrates the fatigue test results for
connecting rods tested at a stress ratio r=-2. As shown the
drop-forged connecting rods test within a larger range than their
sintered-forged counterparts. As a matter of fact, the drop-forged
connecting rods test within 70 MPa, while the sintered-forged
connecting rods test within 40 MPa, for HS150.TM. and HS160.TM.
materials (not enough data is available at this point to evaluate
HS170.TM.). Another conclusion is that the sinter-forged connecting
rods test at higher stress levels than their drop-forged
counterparts. TABLE-US-00009 TABLE IX Cu C Mn S HS150 .TM. 3.06
0.50 0.31 0.12 HS160 .TM. 3.03 0.57 0.33 0.13 HS170 .TM. 3.01 0.64
0.33 0.13
[0050] A summary of the fatigue limits @ 90% probability of
survival for the stress ratio r=-2, is presented in Table X. The
scatter in the case of connecting rods manufactured with C70 is
from six to four times higher than the scatter of powder metal
forged connecting rods. As shown, the fatigue limits @ 90%
probability of survival are 24.38% and 28.27% respectively higher
in the case of connecting rods manufactured with HS150.TM. and
HS160.TM. when compared to connecting rods manufactured with C70
(r=-2). Similar results were obtained from fatigue testing at a
stress ratio r=-1. TABLE-US-00010 TABLE X HS160 .TM. HS150 .TM. C70
Fatigue Limit @90% (MPa) 363 352 283 Scatter (MPa) 8 13 48
[0051] A summary of the fatigue limits @ 90% probability of
survival for the stress ratio r=-1, is presented in Table XI. As
shown, the fatigue limits @ 90% probability of survival are 30.16%
and 32.94% respectively higher in the case of connecting rods
manufactured with HS150.TM. and HS160.TM. when compared to
connecting rods manufactured with C70 (r=-1). The scatter in the
case of connecting rods manufactured with C70 is again from six to
four times higher than the scatter of powder metal forged
connecting rods. This fact clearly shows the consistency of powder
metal forged connecting rods. Fatigue testing on connecting rods
manufactured with HS170 is not complete. However, the first few
results at r=-2 looks very promising, showing a further improvement
in fatigue strength. TABLE-US-00011 TABLE XI HS160 .TM. HS150 .TM.
C70 Fatigue Limit @90% (MPa) 335 328 252 Scatter (MPa) 10 13 58
[0052] The results obtained from fatigue testing were interpreted
using the Dang Ven criterion. Mechanical properties of materials
are represented as lines with the following equation: =a.+-.b*h,
where a and b are the criterion parameters resulting from fatigue
testing. To obtain a and b, at least two staircase tests at two
different stress ratios (fully reserved, r=-1, and mainly in
compression, for example r=-2) are necessary. This line divides the
-.sub.h- plane into two distinct areas: a safe area below and a
failure area above the line representing the material. From finite
element analysis the most critical point in the component is
determined and through an algorithm of calculations, that point is
transported into the -.sub.h- plane. The further this point is
located below the line representing the mechanical properties of
the material, the higher the safety factor is. As a result, the
larger the area below these lines representing the mechanical
properties of the material, the stronger the material, creating
possibilities for either weight reductions or enduring higher loads
in service. The lines for HS150.TM. and HS160.TM. materials have
larger safe areas than the line representing C70 connecting
rods.
[0053] All of the sinter-forged tested connecting rods that did not
survive 10.sup.7 cycles failed at or near the minimum cross section
of the I-beam. The drop-forged connecting rods, on the other hand,
failed randomly along the I-beam. Surface as well as sub-surface
cracks initiation sites were observed in the case of powder metal
forged connecting rods. Most of the failures in the cost of the
drop forged connected rods started along the trim line at different
defects, such as folds, cavities, micro-cracks, or small oxide
flaws. The random failure location along the I-beam and the defects
found along the trim line, explain the larger scatter observed
during fatigue testing. Thus, making the sinter-forged connecting
rod a more reliable product than the drop-forged connecting
rod.
[0054] Higher strength materials for powder forged connecting rods
were developed. Significant improvements in strength were obtained
almost without any impact at all in cost, machinability, and
crackability. The results of this can be shown in Table XII.
TABLE-US-00012 TABLE XII C70 HS150 .TM. HS160 .TM. HS170 .TM. UTS
(MPa) 990 1000 1060 1120 YS (MPa) 580 710 724 770 El. (%) 14 13 11
9 CYS (MPa) 610 695 705 775 SS (MPa) 655 680 725 785
[0055] Modification of the invention will occur to those skilled in
the art and to those who make or use the invention. It is
understood that the embodiments shown in the drawings and described
above are merely for illustrative purposes and not intended to
limit the scope of the invention, which is defined by the following
claims as interpreted according to the principles of patent law,
including the Doctrine of Equivalents.
* * * * *