Download ABSTRACT Sinter-hardening is a process in which the martensitic

Reprinted by permission from Advances in Powder Metallurgy & Particulate Materials—2012.
Copyright © 2012 Metal Powder Industries Federation. All rights reserved.
Effect of Ni addition route on static and dynamic
properties of Fe-2Cu-1.8Ni-0.5Mo-0.65C and Fe-2Cu-1.8Ni0.5Mo-0.85C PM steels
François Chagnon
Rio Tinto Metal Powders
ABSTRACT
Sinter-hardening is a process in which the martensitic transformation occurs during the cooling phase of
the sintering cycle. The amount of martensite produced is a function of the alloy and mix composition,
the sintering temperature and the post-sintering cooling rate. The latter is controlled by the cooling
efficiency of the furnace as well as the size and section thickness of the parts. Raising the sintering
temperature promotes diffusion and hence, a better distribution of alloying elements, particularly when Ni
and Cu are admixed. Also, nickel favours retention of austenite, which could affect the fatigue
performance of PM steels. Although, the presence of retained austenite, up to about 25% in a fully
martensitic structure, is beneficial to fatigue strength, it is detrimental to the static properties.
The objective of this work is to study the effect of sintering temperature, carbon concentration and
alloying route of nickel on static and fatigue properties of Fe-2Cu-1.8Ni-0.5Mo and 0.65C or 0.85C PM
steels.
INTRODUCTION
Powder metallurgy offers a great flexibility to achieve different microstructures depending on how the
alloying elements are introduced before sintering. Indeed, while the pre-alloying route achieves a
homogeneous distribution of the elements, it is possible to create heterogeneities in the microstructure
with the admixing route. As an example, admixing nickel to steel powders produces complex
microstructures with Ni-rich areas. Also, for a similar chemical composition, steel powder blends with
admixed nickel show better compressibility than that obtained with pre-alloyed nickel because of Ni
solution hardening effect on ferrite1. Therefore, for a given compacting pressure, the former will achieve
a higher green density. On the other hand, parts made with pre-alloyed nickel can be sinter-hardened. A
good example of such materials is the MPIF Standard 35 FLC-4608HT2. In previous studies3-4, it was
1
shown that the presence of bainite has a detrimental effect on fatigue strength of sinter-hardened
materials, while the presence of retained austenite up to 25% in martensitic materials was very beneficial
to fatigue resistance but detrimental to static properties. Consequently, the presence of Ni-rich phases in
materials with admixed nickel that promotes the formation of retained austenite in localized areas would
have a beneficial effect on fatigue strength. However, the presence of a large quantity of bainite will
result in the opposite effect. Therefore, a study has been carried out with the objective to evaluate the
effect of microstructure on the static and dynamic properties of Fe-1.8Ni-0.5Mo-0.65C and Fe1.8Ni0.5Mo-0.85C materials produced with either 1.8% admixed or pre-alloyed nickel.
EXPERIMENTAL PROCEDURE
ATOMET 4001 and ATOMET 4601 were used as base steel powders for this study. The physical and
chemical properties of the lots used in this study are given in Table 1. ATOMET 4001 (powder A) is a
0.5% Mo pre-alloyed powder while ATOMET 4601 (powder B) is a 0.55% Mo and 1.8% Ni pre-alloyed
powder. Nickel powder, 1.8% Inco 123, was admixed to powder A to achieve comparable nickel
concentrations. Mixes were prepared with 2% copper (Acupowder 165), 0.7 or 0.9% graphite (Timrex
F25) and 0.5% EBS wax (Lonza Acrawax C). Table 2 summarizes the mix compositions.
Table 1. Chemical and physical properties of ATOMET 4001 and ATOMET 4601.
Powder grade
Powder
Ni,
%
Mo,
%
Mn,
%
C, %
O, %
+100
mesh, %
-100/+325
mesh, %
ATOMET 4001
ATOMET 4601
A
B
0.07
1.80
0.50
0.52
0.14
0.19
0.002
0.003
0.09
0.10
15.4
11.2
67.5
65.4
-325
mesh,
%
17.1
23.4
Apparent
density,
g/cm³
2.88
2.87
Flow,
s/50g
25
25
Table 2. Mix compositions.
Base powder
Powder A
Powder A
Powder B
Powder B
Designation
FLNC-4008
FLC-4608
Graphite, %
0.7
0.9
0.7
0.9
Copper,
%
2.0
2.0
2.0
2.0
Nickel, %
Lubricant, %
1.8
1.8
0
0
0.5
0.5
0.5
0.5
Transverse rupture strength (TRS) and dog bone specimens were pressed at 7.00 g/cm³ from each mix and
sintered at either 1120 or 1205°C for 30 minutes in a 90%N2/10%H2 atmosphere. The post-sintering
cooling rate in the range of 650 to 400°C was 1.3°C/s for both sintering temperatures. All the specimens
were tempered at 180°C for 60 minutes.
Tensile strength, yield strength and elongation were determined for each test condition. The plane
bending fatigue strength was also evaluated for the various conditions at a load ratio of R=0.1. The
fatigue limit at 50% survival value was determined by the staircase method with a runout limit of 2.5
millions cycles. The values were reported in terms of maximum stress.
Microstructural characterization was performed by optical microscopy and the proportions of martensite
and bainite/pearlite were evaluated by image analysis. The amount of retained austenite was measured by
X-ray diffraction analysis carried out on polished cross sections of TRS specimens, mounted in Bakelite.
The X-ray scan was carried out using the Cu K radiation,  of 1.540562Å, at a rate of 3 degrees per
minute. The X-ray diffraction pattern of Bakelite was identified in order to eliminate its impact on the
calculation of the retained austenite.
2
RESULTS
Table 3 summarizes the results of the study. The carbon concentrations after sintering specimens pressed
with both powder grades containing 0.7% graphite were similar, 0.65-0.67%, as well as for the 0.9%
graphite addition, 0.84-0.87%. It is worth noting that the test matrix used in this study is an L4 Taguchi
array allowing the evaluation of the interaction of the carbon concentration with the way the nickel is
introduced, admixed or pre-alloyed.
Table 3. Sintered properties of the different materials sintered at 1120 and 1205°C.
Grade
FLNC-4008
Compacting pressure, tsi at 7.0 g/cm³
517
FLC-4608
527
612
617
Graphite, %
0.7
0.7
0.9
0.9
0.7
0.7
0.9
0.9
Sintered carbon, %
0.67
0.65
0.86
0.84
0.66
0.66
0.87
0.86
Sintering temperature, °C
1120
1205
1120
1205
1120
1205
1120
1205
Dimensional change, % vs die size
0.46
0.32
0.39
0.24
0.50
0.40
0.27
0.19
18
21
21
27
30
34
38
40
Transverse rupture strength, MPa
1383
1541
1299
1394
1560
1531
1320
1184
Tensile strength, MPa
744
869
726
815
914
937
774
772
Yield strength, MPa
549
637
570
601
772
850
716
744
Elongation, %
Bending fatigue strength, MPa (max.
stress; 50% surv.)
Martensite, %
1.0
1.0
0.6
0.7
0.5
0.4
0.2
0.2
415
433
410
421
399
428
443
478
Apparent hardness, HRC
31
50
51
59
73
81
69
74
Retained austenite, %
6
5
11
12
9
9
22
23
Pearlite/Bainite, %
63
45
38
29
18
10
9
3
It is worth noting that the mixes with admixed nickel, FLNC-4008, require lower compacting pressures,
90 to 95 MPa , to reach 7.0 g/cm³ compared to FLC-4608 mixes. Also, raising the graphite concentration
from 0.7 to 0.9% increases the pressure required to reach 7.0 g/cm³ by 5 to 10 MPa. Figure 1 illustrates
the mean effect of nickel alloying route and sintered carbon concentration on dimensional change of
specimens pressed with the four mixes. The interaction analysis between the alloying route and the
sintered carbon concentration for both sintering temperatures is also illustrated.
As expected, raising the sintering temperature favours lower growth values with an average difference of
-0.12%. Sintered carbon has the largest influence on dimensional change with a mean effect of -0.15% at
either 1120 or 1205°C, when its concentration increases from 0.66 to 0.86%. On the other hand, the
alloying method has a minor effect on dimensional change but there is significant interaction between the
alloying route and the sintered carbon concentration. Indeed, at 1120°C, the decrease in growth value is
-0.23% when the sintered carbon increases from 0.66 to 0.86% with the FLC-4608 materials and only
-0.07% for the FLNC-4008 materials. These differences remain similar when the sintering temperature is
raised to 1205°C, -0.21% for the FLC-4608 materials and –0.08% for the FLNC-4008 materials.
Figure 2 illustrates the mean effect of nickel alloying route and sintered carbon concentration on apparent
hardness of specimens after tempering 60 minutes at 180°C for both sintering temperatures. The
interaction analysis between the alloying route and the sintered carbon concentration for both sintering
temperatures is also illustrated. On average, higher apparent hardness values are observed at 1205°C, 31
HRC vs 27 HRC at 1120°C. This result can be related not only to better diffusion of the elements but
also by the increased grain size at 1205°C, which is known to promote hardenability5-6. This will be
discussed in the following section. As expected, when nickel is pre-alloyed, significantly higher apparent
hardness values are observed compared to the admixing method, with a mean effect of about +15 HRC
1120°C and +13 HRC at 1205°C. The interaction between the carbon concentration and nickel alloying
route is not significant.
3
Dimensional Change, % vs die size
0.7
1120°C
1205°C
0.6
alloyed
0.5
0.4
alloyed
admix.
admix.
0.3
0.2
0.1
P.All.
Adm.
0.66%C
0.86%C
0.66%C
0.86%C
Figure 1. Mean effect of Ni alloying route and carbon concentration on dimensional change of specimens
sintered at either 1120 or 1205°C and tempered 60 minutes at 180°C.
60
Apparent Hardness, HRC
1120°C
1205°C
50
40
alloyed
alloyed
30
admix.
20
admix.
10
P.All.
Adm.
0.66%C
0.86%C
0.66%C
0.86%C
Figure 2. Mean effect of Ni alloying route and carbon concentration on apparent hardness of specimens
sintered at either 1120 or 1205°C and tempered 60 minutes at 180°C.
Figure 3 shows typical microstructures after Nital etching the specimens made from FLNC-4008 and
FLC-4608 materials sintered at either 1120 or 1205°C for a sintered carbon concentration of 0.66%.
When nickel is admixed, a heterogeneous structure consisting of a mixture of pearlite and bainite with
martensite and a few Ni-rich phase areas is observed at 1120°C. Raising the sintering temperature to
1205°C favours the formation of martensite to the detriment of bainite/pearlite because of the better
homogenisation of nickel. When nickel is pre-alloyed, the microstructure is a mixture of martensite (plate
and lath) and bainite. It is worth noting that sintering at 1205°C seems to favour the formation of lath
4
martensite. Some retained austenite can be found within the martensite needles. Also illustrated in
Figure 3, the coarse grain size of the specimen sintered at 1205°C. This can explain the slightly higher
apparent hardness observed for the different materials when sintered at this temperature, as previously
discussed.
50 µm
50 µm
FLNC-4008; 1120°C
FLNC-4008; 1205°C
50 µm
50 µm
FLC-4608; 1120°C
FLC-4608; 1205°C
Figure 3. Microstructure of Fe-1.8Ni-0.5Mo-0.66C materials produced with either admixed or pre-alloyed Ni
sintered at either 1120 or 1205°C (Nital etching; 500X).
Figure 4 shows typical microstructures after Nital etching FLNC-4008 and FLC-4608 specimens sintered
at either 1120 or 1205°C for a sintered carbon concentration of 0.86%. The FLNC-4008 materials show a
heterogeneous structure composed of martensite, bainite/pearlite and Ni-rich phases with the presence of
retained austenite in areas where some martensite in transformation is also observed, particularly evident
at 1205°C due to a better homogenisation of nickel. For the FLC-4608 materials, the microstructure is
almost fully martensitic with retained austenite and some areas of bainite. Again, coarser grains are
observed in the specimens sintered at 1205°C compared to those sintered at 1120°C. In addition to the
better homogenisation of the alloying elements, when the sintering is carried out at 1205°C, this increase
in grain size has probably contributed to the higher apparent hardness observed at this temperature.
5
50 µm
50 µm
FLNC-4008; 1120°C
FLNC-4008; 1205°C
50 µm
50 µm
FLC-4608; 1120°C
FLC-4608; 1205°C
Figure 4. Microstructure of Fe-1.8Ni-0.5Mo-0.86C materials produced with either admixed or pre-alloyed Ni
sintered at either 1120 or 1205°C (Nital etching; 500X).
Figure 5 illustrates the mean effect of nickel alloying route and sintered carbon concentration on the
proportions of the different phases in specimens sintered at either 1120 or 1205°C and tempered 60
minutes at 180°C. It is worth noting that on average, raising the sintering temperature from 1120 to
1205°C favours the production of martensite to the detriment of bainite and pearlite but does not
influence the amount of retained austenite in the specimens. The amount of bainite and pearlite is mainly
affected by the alloying route. Indeed, at 1120°C, it increases from 13% for the pre-alloyed Ni materials
to 50% for the admixed Ni materials and from 7 to 37% at 1205°C. Raising the carbon concentration also
reduces the amount of bainite and pearlite, more importantly for the admixed Ni materials. Finally, the
amount of bainite and pearlite decreases as the sintering temperature increases for all the materials
studied, indicating a better hardenability due to either better alloy homogenization or larger grain size.
Sintered carbon has the most important effect on retained austenite, when the concentration increases
from 0.66 to 0.86%, with a mean increase from 7.5 to 16.5% at 1120°C and from 7.0 to 17.5% at 1205°C.
FLC-4608 materials also show larger concentrations of retained austenite than FLNC-4008 materials at
both temperatures, 15.5 vs 8.5% at 1120°C and 16.0 vs 8.5% at 1205°C. There is an interaction between
the alloying route and the carbon concentration. Indeed, the increase in retained austenite when the
carbon concentration is raised from 0.66 to 0.86% is significantly larger for FLC-4608 materials than
FLNC-4008 materials, increasing 11-12% vs only 5-7%.
6
As expected, the alloying route has the largest effect on the concentration of martensite in the sintered
specimens. On average, the quantity of martensite increases from 41% for the FLNC-4008 materials to
71% for the FLC-4608 ones at 1120°C and from 54 to 77% at 1205°C. It is also worth noting the
significant interaction between the carbon concentration and the alloying route. Indeed, the amount of
martensite significantly increases with the carbon concentration for the FLNC-4008 materials, while it
slightly decreases for the FLC-4608 ones. For the latter, this can be related to the increased proportion of
retained austenite while for the former, to a decrease of the bainite/pearlite concentration.
30
90
80
1120°C
1205°C
1120°C
1205°C
25
alloyed
Retained Austenite, %
Pearlite/Bainite, %
70
admix.
60
50
admix.
40
30
20
alloyed
15
10
admix.
20
alloyed
10
5
admix.
alloyed
0
0
P.All.
Adm.
0.66%C
0.86%C
0.66%C
P.All.
0.86%C
Adm.
0.66%C
0.86%C
0.66%C
0.86%C
100
1120°C
1205°C
alloyed
80
Martensite, %
alloyed
admix.
60
40
admix.
20
P.All.
Adm.
0.66%C
0.86%C
0.66%C
0.86%C
Figure 5. Mean effect of Ni alloying route and carbon concentration on the proportion of pearlite/bainite,
retained austenite and martensite in specimens sintered at either 1120 or 1205°C.
Figure 6 illustrates the mean effect of Ni alloying route and sintered carbon concentration on tensile
strength (UTS), yield strength (YS), elongation and transverse rupture strength of specimens pressed with
the four mixes sintered at either 1120 or 1205°C and tempered 60 minutes at 180°C.
The carbon concentration has the largest effect on UTS with a mean decrease of 83 MPa and 110 MPa at
1120 and 1205°C, respectively, when the carbon concentration is raised from 0.66 to 0.86%. It is also
worth noting a significant effect of the alloying route of nickel at 1120°C. Indeed, the mean UTS
decreases from 841 MPa for the FLC-4608 materials to 738 MPa for FLNC-4008 materials at 1120°C, a
reduction of 103 MPa while it decreases only from 855 to 841 MPa (-14 MPa) at 1205°C. This is
probably related to a better homogenisation of nickel at high sintering temperature for the FLNC-4008
materials. There is also a significant interaction between the carbon concentration and nickel alloying
route. At 1120°C, when the carbon concentration increases from 0.66 to 0.86%, UTS decreases from 917
MPa to 772 MPa (-145 MPa) for the FLC-4608 materials and from only 745 to 724 MPa (-21 MPa) for
the FLNC-4008 materials. At 1205°C, UTS decreases from 938 to 772 MPa (-66 MPa) for the FLC-4608
7
materials and from 869 to 814 MPa (-55 MPa) for the FLNC-4008 Ni materials. It is worth noting that
for both carbon concentrations, the sintering temperature does not have a large impact on UTS of the
FLC-4608 materials. However, sintering at 1205°C results in significantly higher UTS values for both
carbon concentrations for the FLNC-4008 due to better diffusion of nickel at 1205 compared to 1120°C.
Contrary to UTS, the alloying route has the most important effect on YS with only a minor interaction
between the alloying method and carbon concentrations. Sintering at 1205°C shows, on average, higher
YS values than sintering at 1120°C, 708 vs 651 MPa. The highest values at both sintering temperatures
are reached with the FLC-4608 materials, 178 to 185 MPa better than that of the FLNC-4008 materials.
On average, raising the carbon concentration from 0.66 to 0.86% decreases the YS values by 18 MPa at
1120°C and by 71 MPa at 1205°C.
For all the materials, the elongation values are equal to or less than 1%. FLC-4608 materials show lower
elongation values than FLNC-4008 materials at both sintering temperatures, -0.5 to -0.7% on average.
Raising the carbon concentration from 0.66 to 0.86% results in a small decrease of elongation, -0.3 to
-0.4%, at both temperatures. It is worth noting that the sintering temperature does not significantly affect
elongation values for the various materials.
Carbon concentration has the major effect on TRS, while sintering temperature has only a minor effect.
Indeed, when the carbon concentration is increased from 0.66 to 0.86%, the TRS decreases, on average,
by 159 MPa, from 1469 to 1310 MPa at 1120°C and by 248 MPa, from 1538 to 1290 MPa at 1205°C. A
significant interaction exists between the Ni alloying route and the carbon concentration. At 1120°C,
raising the carbon concentration from 0.66 to 0.86% reduces TRS of the FLC-4608 materials from 1559
to 1317 MPa (-242 MPa) and from 1379 to 1297 MPa (-82 MPa) for the FLNC-4008materials. At
1205°C, the TRS decreases from 1531 to 1184 MPa (-347 MPa) for the FLC-4608 materials but only
from 1541 to 1394 MPa (-147 MPa) for the FLNC-4008 materials.
Figure 7 illustrates the mean effect of Ni alloying route and sintered carbon concentration on plane
bending fatigue resistance of specimens pressed with the four materials sintered at either 1120 or 1205°C
and tempered 60 minutes at 180°C. The interaction analysis between the alloying route and the sintered
carbon concentration for both sintering temperatures is also illustrated.
On average, sintering at 1205°C improves fatigue strength of the various materials by 23 MPa or about
5% compared to 1120°C. The highest fatigue strength is reached with FLC-4608 materials containing
0.86% C. It is worth noting the strong interaction between the carbon concentration and the Ni alloying
route. Raising the carbon concentration for the FLC-4608 materials from 0.66 to 0.86% increases fatigue
strength by 44 MPa, from 399 to 443 MPa, at 1120°C and by 50 MPa, from 428 to 478 MPa, at 1205°C.
On the other hand, for the FLNC-4008 materials, raising the carbon concentration from 0.66 to 0.86% has
no significant effect on fatigue strength at both sintering temperatures with an average value of 413 MPa
at 1120°C and 427 MPa at 1205°C. As illustrated in Figure 8, the occurrence of bainite has a significant
detrimental effect on fatigue strength of FLC-4608 materials. This was also observed by Vachon and al.7.
On the other hand, the amount of bainite and pearlite does not seem to affect fatigue strength of the
FLNC-4008 materials, which seems to be affected only by the sintering temperature. Because of the
heterogeneities introduced by the admixed nickel, the highest concentrations of martensite are observed at
the particle periphery i.e where the former Ni particles were located and are increasing with the sintering
temperature. These areas are also preferential sites, where fatigue cracks can be initiated. Therefore, a
larger concentration of martensite in these areas can prevent crack initiation and this probably explains
the higher fatigue resistance observed with the FLNC-4008 materials containing larger concentrations of
bainite/pearlite than FLC-4608 materials.
8
900
1120°C
1205°C
1000
1120°C
1205°C
850
Yield Strength, MPa
Tensile Strength, MPa
alloyed
800
alloyed
alloyed
900
admix.
800
alloyed
750
700
650
admix.
600
admix.
admix.
700
550
500
P.All.
Adm.
0.66%C
0.86%C
0.66%C
0.86%C
P.All.
Adm.
0.66%C
0.86%C
0.66%C
0.86%C
1120°C
1205°C
1.2
Elongation, %
admix.
1.0
0.8
admix.
0.6
alloyed
0.4
alloyed
0.2
Transverse Rupture Strength, MPa
1800
1.4
1120°C
1205°C
1600
alloyed
admix.
1400
admix.
1200
alloyed
1000
0.0
P.All.
Adm.
0.66%C
0.86%C
0.66%C
0.86%C
P.All.
Adm.
0.66%C
0.86%C
0.66%C
0.86%C
Figure 6. Mean effect of Ni alloying route and carbon concentration on tensile properties and transverse
rupture strength of specimens sintered at either 1120 or 1205°C and tempered 60 minutes at
180°C.
Retained austenite present in the FLC-4608 materials improves fatigue resistance with the highest values
observed at 1205°C. This can be explained by the increased proportion of martensite relative to bainite,
when the sintering temperature increases.
For FLNC-4008 materials, fatigue strength slightly decreases with the amount of retained austenite and
increases with the sintering temperature. However, the amount of retained austenite is below 15%, for
these materials. In their review on fatigue properties, Saritas and al.8 stated that the soft Ni-rich areas and
the retained austenite decreases the fatigue crack propagation rate, which results in better fatigue strength.
A similar observation was made by Engdahl and al.9 for Fe-2Ni-0.5Mo-0.5C made from either diffusion
bonded or pre-alloyed PM steels. However, no comment was made regarding the fractions of martensite,
bainite and retained austenite in these materials.
Results from the present study show that the fatigue strength of FLNC-4008 materials with 1.8% admixed
Ni containing between 30 and 65% bainite/pearlite have similar fatigue strength as those of FLC-4608
materials with 1.85 pre-alloyed Ni containing 10 to 15% bainite. However, for a structure with less than
5% bainite and 23% retained austenite, the FLC-4608 materials showed better fatigue strength than the
admixed materials. Bergman and al.10 reported that a microstructure characterized by a strong martensitic
network with islands of upper bainite in a FLDN4C2-4908 PM steel gives a higher fatigue limit than a
FD-0408 PM steel showing large islands of pearlite surrounded by a thin martensitic network. Engström
and al.11 reported similar results with however the highest fatigue resistance reached for a martensitic prealloyed material free of bainite. The latter is in line with the results of this study since the fatigue strength
9
of FLNC-4008 increases with the sintering temperature which promotes martensite formation but the
highest values are nevertheless reached with a fully martensitic FLC-4608 material.
550
Bending Fatigue Strength
(Maximum Stress), MPa
1120°C
1205°C
500
alloyed
alloyed
450
admix.
admix.
400
350
P.All.
Adm.
0.66%C
0.86%C
0.66%C
0.86%C
Figure 7. Mean effect of Ni alloying route and carbon concentration on bending fatigue strength of
specimens sintered at either 1120 or 1200°C and tempered 60 minutes at 180°C (maximum stress
at R=0.1; 50% survival).
500
500
1205°C 1120°C
1205°C 1120°C
Pre-alloyed; 0.66%C
Pre-alloyed; 0.86%C
Admixed; 0.66%C
Admixed; 0.86%C
Pre-alloyed; 0.66%C
Pre-alloyed; 0.86%C
Admixed; 0.66%C
Admixed; 0.86%C
480
Bending Fatigue Strength
(Maximum Stress), MPa
Bending Fatigue Strength
(Maximum Stress), MPa
480
460
440
1205°C
420
1120°C
400
460
440
420
400
380
380
0
10
20
30
40
50
60
70
0
5
10
15
20
25
Retained austenite, %
Pearlite+Bainite, %
Figure 8. Effect of proportion of pearlite/bainite and retained austenite on bending fatigue strength
(maximum stress at R=0.1; 50% survival).
CONCLUSIONS
Within the limits of this study, for Fe-2Cu-1.8Ni-0.5Mo materials containing either 0.66C or 0.86%C,
and where nickel is introduced by either pre-alloying or admixing routes, the following conclusions can
be drawn:
1. FLC-4608 materials showed better hardenability at both sintering temperatures due to a more
homogeneous microstructure with a high martensite concentration compared to those with admixed
Ni.
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2. Raising the sintering temperature from 1120 to 1205°C did not affect TRS and UTS of FLC-4608
materials while a significant improvement was observed with the FLNC-4008 materials due to a better
homogenization of the admixed elements at high sintering temperature.
3. Raising the sintering temperature from 1120 to 1205°C increased YS of the various materials with the
highest values reached with FLC-4608 materials.
4. All the materials showed elongation values below 1% with slightly better values for the FLNC-4008
materials. Raising the sintering temperature from 1120 to 1205°C did not improve elongation.
5. For both sintering temperatures, raising the carbon concentration from 0.66 to 0.86% lowered static
properties of the different materials.
6. Fatigue strength of FLC-4608 materials was very sensitive to the presence of bainite in the
microstructure. The best fatigue strength, 464 MPa, was reached with the FLC-4608 material with
0.86%C sintered at 1205°C with a minimum quantity of bainite and 23% retained austenite in a
martensitic microstructure. The lowest fatigue strength, 387 MPa, was observed with the FLC-4608
material with 0.66%C material sintered at 1120°C showing 18% bainite.
7. FLNC-4008 materials showed fatigue strength values within 398 and 420 MPa, with the best
performances reached at 1205°C without significant effect of the carbon concentration and the amount
of bainite/pearlite.
REFERENCES
1. S.H. Avner, “Introduction to Physical Metallurgy”, McGraw-Hill Book Company, NY, 1974, p.
355-358.
2.
Materials Standards for PM Structural Parts, 2009 Edition, Metal Powder Industries Federation,
Princeton, p. 22-23.
3.
F. Chagnon; “Effect of Sintering Temperature on Static And Dynamic Properties of Sinter Hardened Materials”,
paper presented at the POWDERMET 2009 Conference in Las Vegas.
4.
F. Chagnon; “Optimization of sinter-hardened material properties ”, paper presented at the POWDERMET
2010 Conference in San Francisco.
5.
D. Herring; “Grain Size and Its Influence on Materials Properties”; Industrialheating.com.
6.
W.F. Smith; “Structure and Properties of Engineering Alloys”; McGraw-Hill, New-York, 1981, pp 122-124.
7. G. Vachon, R. Angers, T. Vo Van and T. Baazi; “Effect of Processing on the Fatigue Properties of a
Sinter-Hardenable PM Steel”; Advances in Powder Metallurgy & Particulate Materials, MPIF,
Princeton, 2006, part 10, pp 65-80.
8. S. Saritas, W.B. James and A. Lawley; “Fatigue Properties of Sintered Steels: a Critical review”;
EPMA, Shrewsbury, 2001, vol. 1, pp 272-285.
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Proceeding of the World Conference on Powder Metallurgy, The Institute of Metals, London, 1990,
Vol. 2, pp 144-154.
10. O. Bergman and A. Bergmark; “Influence of Microstructure on the Fatigue Performance of PM
Steels”, Advance in Powder Metallurgy & particulate Materials, MPIF, Princeton, 2003, Part 7, pp
270-278
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11. U. Engström; “Fatigue Strength of High Performance PM Materials”; Proceedings of the 2003
International Conference on Automotive Fatigue Design & Applications, MPIF, Princeton, 2003, pp
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