CHROMIUM CONTAINING MATERIALS FOR HIGH PERFORMANCE COMPONENTS
Patrick King
Hoeganaes Corporation
Cinnaminson, NJ 08077
Bob Schave and John Sweet
FMS Corporation
Minneapolis, MN 55420
Presented at PM2Tec2004
Chicago, IL June 13-17, 2004
ABSTRACT
Recently developed silicon-bearing alloys were engineered to replace malleable and ductile cast irons,
and have shown excellent property combinations at high sintering temperatures. A modification to these
alloys merges the power of silicon and chromium in one system, and allows for extraordinary
performance. The presence of chromium improves both static and dynamic properties with the added
benefit of being close to die-size after sintering. The current work details extensive laboratory data that
show the effects of compaction pressure on this modified alloy processed at high sintering temperatures.
Also presented is a field experience on a heat-treated production component that combined the high
performance alloy system with warm compaction technology. Static and dynamic properties are
presented for samples sintered in both laboratory and production scale furnaces.
INTRODUCTION
With high performance components demanding superior mechanical properties, powder manufacturers
have accelerated the drive to develop advanced materials systems. Hoeganaes recently introduced a line
of products containing silicon, which were designed to replace malleable and ductile cast irons [1,2]. The
use of silicon helps to increase hardenability and enhance sintering at a modest cost [3]. When processed
at high sintering temperatures, these alloy systems provide extraordinary property combinations. These
properties, achieved using single press / single sinter (SP/SS) processing, were previously only possible in
ferrous P/M by using costly double press / double sinter (DP/DS) processing.
Chromium has long been known to enhance the hardenability of steels, and is widely used throughout the
wrought industry. Due to its high affinity for oxygen, however, oxide reduction during powder
processing and sintering is difficult and adversely affects mechanical properties [4,5]. As a result, the use
of chromium as a hardenability aid in P/M steels has been limited. A modified version of Ancorloy
MDC counteracts the common problems associated with chromium by providing reduced oxygen
contents through proprietary fabrication techniques. This high performance alloy binder-treated product
has a nominal chemistry of 1.0 wt.% Cr, 3.0 wt.% Ni, 0.85 wt.% Mo, and 0.6 wt.% Si. This alloy has the
additional benefit of being much closer to die-size after sintering than its chromium-free predecessors.

Ancorloy and ANCORDENSE are registered trademarks of Hoeganaes Corporation.
This manuscript documents the effects of compaction pressure on the alloy system with high temperature
sintering. Transverse rupture, tensile, impact, axial fatigue, and rotating bending fatigue data are
presented. Also demonstrated is a field experience on a production component using warm compaction
technology. The component was subjected to gas carburization and high temperature vacuum sintering at
densities of approximately 7.30 g/cm3. Property data from laboratory samples processed in the
production furnace alongside the components are also summarized.
EXPERIMENTAL PROCEDURE
A binder-treated premix of Ancorloy MDC-modified was prepared along with FLN2-4405 and FLN44405, which served as reference compositions [6]. Nominal chemistries of these mixes are shown in
Table I. All three of the mixes shown had identical graphite additions of 0.6 wt.%. ANCORDENSE®,
which is a proprietary system that allows for density increases up to 0.20 g/cm3 through warm compaction
technology, was used to make mixes of MDC-modified with both 0.4 and 0.6 wt.% graphite. The
intention of the lower graphite level was to provide higher densities and a more suitable system for
carburization. Asbury Grade 3203 HSC was used as the graphite supply, while Inco 123 was used as the
nickel source.
Table I. Nominal chemistries of the premixes used in this study.
Fe
Mo
Cr
Si
Ni
Gr
(wt.%)
(wt.%) (wt.%) (wt.%)
(wt.%)
(wt.%)
MDC-modified
Bal.
0.85
1.0
0.6
3.0
0.6
FLN2-4405
Bal.
0.85
2.0
0.6
FLN4-4405
Bal.
0.85
4.0
0.6
ID
Lube
(wt.%)
0.75
0.75
0.75
Transverse rupture, tensile, and impact specimens were compacted at 550, 690, and 830 MPa (40, 50, and
60 tsi, respectively) at room temperature. These samples were sintered in an Abbott belt furnace at
1260°C (2300°F) in 90N2-10H2 (by volume) with a dew point of approximately -40°C (-40°F) for 30
minutes. Average cooling rates over the ranges of 850 to 315°C (1560 to 600°F) and 650 to 315°C (1200
to 600°F) were 40°C/min (1.2°F/sec). Following sintering, all samples were stress-relieved at 205°C
(400°F) for 1 hour in air. Percent dimensional change, rupture strength, sintered density, and apparent
hardness values were measured from the transverse rupture samples using standard MPIF procedures.
Tensile testing was performed with standard dog-bone specimens using a crosshead speed of 0.065
cm/min (0.025 in/min). The machine is equipped with a 25 mm (1 in) extensometer, which was left on
until failure. Impact testing was conducted at room temperature on unnotched Charpy samples.
Rotating bending fatigue data were acquired for MDC-modified with a speed of 8,000 rpm at a nominal
density of 7.20 g/cm3. Specimens were machined from blanks sintered at 1260°C (2300°F) under 25N275H2 and stress-relieved at 205°C (400°F) for 1 hour in air. The median fatigue endurance limit (50%
FEL) was calculated by using the “staircase” method [7] until there were both failures and runouts at a
minimum of two stress levels. Thirty samples were tested with a prescribed limit of 107 cycles. Axial
fatigue data were acquired on MDC-modified samples at a density of 7.10 g/cm3 sintered at 1260°C
(2300°F) under 90N2-10H2 and stress-relieved at 205°C (400°F) for 1 hour in air. This testing was
conducted in load control, R-ratio (σmin/σmax) of -1, at a frequency of 40 Hz.
Warm compaction was conducted on ANCORDENSE samples of MDC-modified with graphite contents
of both 0.4 and 0.6 wt.%. Transverse rupture, tensile, and impact samples were pressed using a preheated
die temperature of 145°C (290°F) and powder preheated to 135°C (270°C) at pressures of 415, 550, and
690 MPa (30, 40, and 50 tsi). Large cylindrical blanks were pressed with the 0.4% graphite composition
to a green density of 7.25 g/cm3.
The samples were vacuum sintered at 1260°C (2300°F) for 35 minutes using an Abbott production
furnace at FMS Corporation. The 0.4% graphite samples and blanks were also gas carburized in an
atmosphere of 25N2-75H2 with 157 cm3/s (20 CFH) of CH4 to a case depth of approximately 0.008 cm
(0.003 in). The 0.6% graphite samples were sintered under the same conditions, but were not subjected to
the carburizing step. All samples were stress-relieved after sintering at 205°C (400°F) for 1 hour in air.
Production components of a 19-tooth sprocket were machined from the processed blanks, and subjected
to testing. Details of the component geometry and testing are located in the viability section.
RESULTS AND DISCUSSION
Mechanical Properties
A compressibility plot of the three materials studied is shown in Figure 1 (a). The presence of chromium
and silicon reduce the green density slightly in MDC-modified compared to the FLN2-4405 and FLN44405 standards. Densities after sintering at 1260°C (2300°F) in 90N2-10H2 are shown in Figure 1 (b).
The large amount of nickel in FLN4-4405 causes shrinkage during sintering, and leads to higher densities.
Since the MDC-modified composition is close to die-size after sintering, the sintered densities in this
alloy are very close to the initial green densities.
A plot of dimensional change from die-size as a function of compaction pressure is shown in Figure 2 for
samples sintered at 1260°C (2300°F) in an atmosphere of 90N2-10H2. It is evident that the high nickel
contents of FLN2-4405 and FLN4-4405 lend them to stray farther from die-size than MDC-modified.
Shown in Figure 3 (a), (b), and (c) are the effects of temperature on apparent hardness, yield strength, and
tensile strength, respectively. The most striking feature in these graphs is that MDC-modified has
superior hardness and strength compared to both reference materials at all compaction pressures. At a
compaction pressure of 690 MPa (50 tsi), this alloy has an apparent hardness of 40 HRC; yield strength of
900 MPa (130,000 psi); and a tensile strength of 1300 MPa (190,000 psi). These phenomenal hardness
and strength values are possible due to the low oxygen content of the alloy.
Oxygen and other sintered chemistries are shown in Table II. Due to advanced processing, MDCmodified can be effectively sintered without worry of high oxygen levels degrading properties. Though
the oxygen level is slightly higher than those of FLN2-4405 and FLN4-4405, 200 ppm is far lower than
most conventional chromium-bearing P/M steels, which typically have as-sintered oxygen levels of 1000
to 1500 ppm.
The excellent strength and hardness data are supported by ductility and toughness characteristics that are
similar to FLN2-4405 and FLN4-4405. Transverse rupture strength, elongation, impact, and apparent
hardness properties that correlate with those shown in Figures 2 and 3 are summarized in Table III. These
properties are even more impressive considering the differences in densities between MDC-modified and
the reference materials that result from dimensional characteristics.
Figure 1. Plots of (a) green densities and (b) densities after sintering at 1260°C (2300°F) in 90N2-10H2.
Samples were stress-relieved for 1 hour in air at 205°C (400°F) after sintering.
Figure 2. Dimensional change, sintered at 1260°C (2300°F) in 90N2-10H2. Samples were stress-relieved
for 1 hour in air at 205°C (400°F) after sintering.
Figure 3. Plots of (a) apparent hardness, (b) yield strength, and (c) tensile strength sintered at 1260°C
(2300°F) in 90N2-10H2. Stress-relieved for 1 hour in air at 205°C (400°F).
Table II. Sintered chemistries for samples pressed at 690 MPa (50 tsi), and sintered at 1260°C
(2300°F) in 90N2-10H2. Stress-relieved for 1 hour in air at 205°C (400°F) after sintering.
Mix ID
C
S
O2
N2
(wt.%) (wt.%) (wt.%) (wt.%)
MDC-modified
0.52
0.004
0.02
0.03
FLN4-4405
0.56
0.004
0.01
0.02
FLN2-4405
0.56
0.004
0.01
0.02
Table III. Mechanical properties for samples sintered at 1260°C (2300°F) in 90N2-10H2.
Stress-relieved for 1 hour in air at 205°C (400°F) after sintering. The data
coincide with those shown in Figures 2 and 3. All mixes have 0.6 wt.% graphite.
DC
TRS
Pressure
Mix ID
SD
Elg
Imp
Hard
(MPa /
(MPa / tsi)
(g/cm3) (%)
(%)
(J /
(A / C)
103 psi)
ft.lbf)
MDC-modified
7.06
-0.09 2345 / 340
2.2
27 / 20
69 / 37
550 / 40
FLN4-4405
7.17
-0.39 1930 / 280
2.3
19 / 14
61 / 21
FLN2-4405
7.10
-0.19 1310 / 190
2.4
15 / 11
54 / --MDC-modified
7.18
-0.02 2620 / 380
2.3
31 / 23
70 / 39
690 / 50
FLN4-4405
7.29
-0.30 2000 / 290
2.2
24 / 18
64 / 27
FLN2-4405
7.22
-0.13 1585 / 230
2.4
22 / 16
58 / --MDC-modified
7.24
0.03
2760 / 400
2.4
38 / 28
71 / 41
830 / 60
FLN4-4405
7.36
-0.24 2170 / 315
2.7
34 / 25
65 / 29
FLN2-4405
7.29
-0.10 1620 / 235
2.8
28 / 21
59 / ---
Metallography
To fully understand the effect of chromium and silicon on the mechanical properties demonstrated above,
it is necessary to evaluate the microstructure of this alloy. Figure 4 shows a micrograph of MDCmodified pressed at 690 MPa (50 tsi) after sintering at 1260°C (2300°F) in 90N2-10H2. The
microstructure correlates well with the excellent strength and hardness properties observed at this
temperature. Martensite is the primary microconstituent, with regions of upper and lower bainite
dispersed throughout. The lighter regions indicate higher alloyed areas due to the presence of nickel.
1260°C / 2300°F
100 µm
Figure 4. Microstructures of MDC-modified with 0.6 wt.% graphite, pressed at 690 MPa (50 tsi),
sintered in 90N2-10H2. Stress-relieved for 1 hour in air at 205°C (400°F).
Fatigue
High performance applications for P/M materials generally rely on strong fatigue capability. Rotating
bending fatigue (RBF) data were acquired for MDC-modified after sintering at 1260°C (2300°F). Shown
in Table IV are RBF data at a sintered density of 7.20 g/cm3. The data are compared to those of
Ancorloy MDC [8], a member of the silicon-containing family described in the background section, as
well as those of several standard P/M materials that were sintered at the same temperature [9-11].
The fatigue data indicate the enhancement provided by the chromium versus an alloy that has more nickel
(MDC). At a lower total alloying level, the chromium-containing alloy has equivalent fatigue resistance.
The new alloy has significantly higher fatigue resistance than standard grades such as FLN2-4405, FC0205, and diffusion-alloyed FD-0405 in the as-sintered condition. The ratios of the median fatigue limits
to the ultimate tensile strengths correlate well with historic data. In general, the rotating bending fatigueto-strength ratio (σfat/σuts) for P/M alloys in this density range is 0.25-0.35 [12].
Axial fatigue results for MDC-modified are shown in Figure 5 and are compared to those of Ancorloys
MDC and MDB [13]. The composition of Ancorloy MDB is Fe-2.0Ni-0.85Mo-0.7Si. All data were
generated at nominal densities of 7.10 g/cm3 after sintering at 1260°C (2300°F) under 90N2-10H2 and
stress-relieving at 205°C (400°F) for 1 hour in air. These data also indicate the improvement in fatigue
performance due to the presence of the chromium. The new alloy has a significantly higher axial fatigue
limit compared to both MDC and the slightly lesser alloyed MDB.
Table IV. Rotating bending fatigue properties for MDC-modified compared to standard materials
sintered at 1260°C (2300°F). Stress-relieved at 205°C (400°F) for 1 hour in air. All alloys have
sintered carbon contents of 0.50-0.55 wt.% and nominal sintered densities of 7.20 g/cm3.
ID
Chemistry
50% Fatigue
UTS
Fatigue
(wt.%)
Endurance Limit
(MPa /
Ratio
(MPa / 103 psi)
103 psi)
(σfat/σuts)
MDC-modified
Fe-3.0Ni-1.0Cr-0.85Mo-0.6Si
360 / 52
1345 / 195
0.27
Ancorloy MDC [8]
Fe-4.4Ni-0.85Mo-0.7Si
360 / 52
1275 / 185
0.28
FLN2-4405 [9]
Fe-2.0Ni-0.85Mo
225 / 33
650 / 95
0.35
FC-0205 [10]
Fe-2.0Cu
250 / 36
600 / 85
0.41
FD-0405 [11]
Fe-4.0Ni-1.5Cu-0.55Mo
215 / 32
815 / 120
0.27
Figure 5. Axial fatigue properties of MDC-modified with 0.6 wt.% graphite at a density of 7.10 g/cm3
compared to those of Ancorloys MDC and MDB. Samples were sintered at 1260°C (2300°F) in 90N210H2, and stress-relieved for 1 hour in air at 205°C (400°F) [13].
Use of MDC-modified in a Production Furnace
To demonstrate the use of MDC-modified in a production setting, tensile, impact, and transverse rupture
samples were compacted using ANCORDENSE, a proprietary warm compaction technology. Warm
compaction allowed for green densities close to 7.3 g/cm3 at a pressure of 690 MPa (50 tsi), a greater than
0.10 g/cm3 increase over conventional processing shown in the preceding pages. Essentially the same
green density was achieved at 550 MPa (40 tsi) with the ANCORDENSE as was achieved at 690 MPa (50
tsi) with the conventional binder in the work summarized in the previous sections.
Two mix compositions of MDC-modified, with 0.4 and 0.6 wt.% graphite, were evaluated. The samples
were then vacuum sintered at 1260°C (2300°F) for approximately 35 minutes. Gas carburizing was
performed to a case depth of approximately 0.008 cm (0.0030 in) on the 0.4% graphite samples. Samples
containing 0.6% graphite were vacuum sintered at the same temperature, but not subjected to
carburization. After processing, samples were stress-relieved for 1 hour at 205°C (400°F) in air. Property
results for both graphite contents are shown in Table V.
As can be expected, combining high densities with elevated sintering temperatures is extremely effective.
Even at the lower graphite content, the strength and hardness values are extremely high, but still maintain
a good balance of ductility and toughness. Figure 6 shows photomicrographs of the case and core regions
for the 0.4% graphite samples. While the microstructure is entirely martensitic due to the excellent sinter
hardenability of this alloy, there is a defined case layer. The case consists mostly of plate martensite,
indicating higher carbon areas, while the core is mostly lath martensite, which is indicative of lower
carbon areas [14]. The case had a carbon level of approximately 0.8%. Figure 7 shows a plot of the types
of martensite that are typically found at various carbon levels in steels.
The vacuum sintered properties of the 0.6% graphite samples (no carburizing) also show significant
strength, as expected. Using the heat-treated 0.4% graphite composition provides a strong case with a
tough core, while the higher carbon content provides a stronger case and slightly lower core toughness.
A prototype component was machined from a carburized and vacuum sintered blank of the 0.4 wt.%
graphite mix that was pressed to 7.25 g/cm3. The component is a 19-tooth sprocket that has a pitch
diameter of 5.77 cm (2.27 in) for an ATV silent chain application. The internal involute spline has 26
teeth, and a pitch diameter of 2.74 (1.08 in). It is a two-level part, with a flange height of 2.29 cm (0.90
in), and an overall height of 3.10 cm (1.22 in). At the time of publication, testing was in progress.
Though the strength is slightly lower in the 0.4% graphite samples, the presence of the hard case most
likely would be the better processing route for this component. Fatigue properties in high performance
component typically rely on surface quality, as the majority of cracks initiate in pores at or near the
surface [15-16]. The sacrifice of a small amount of core strength would likely be counterbalanced by a
significant improvement in the fatigue performance of the component.
Table V. Properties for MDC-modified with 0.4 and 0.6 wt.% graphite, sintered in a production vacuum
furnace for 35 minutes at 1260°C (2300°F). Pressed using preheated die temperature of 145°C (290°F)
and powder temperature of 135°C (270°F). Stress-relieved for 1 hour in air at 205°C (400°F).
SD
YS
UTS
Elong
Imp
Hard
Graph
Pressure
GD
3
3
(MPa /
(MPa /
(%)
(J /
(HRC)
(wt.%) (MPa / tsi) (g/cm ) (g/cm )
103 psi)
103 psi)
ft.lbf)
415 / 30
6.97
7.11
760 / 110
965 / 140
1.2
24 / 18
41
0.4*
550 / 40
7.17
7.27
965 / 140
1100 / 160
1.4
27 / 20
45
690 / 50
7.27
7.35
1100 / 160 1450 / 210
1.8
31 / 23
47
415 / 30
6.95
7.03
1000 / 145 1240 / 180
1.5
16 / 12
41
0.6
550 / 40
7.15
7.21
1035 / 150 1380 / 200
1.9
22 / 16
45
690 / 50
7.25
7.30
1170 / 170 1520 / 220
2.1
26 / 19
47
* Samples with 0.4% graphite were case carburized prior to vacuum sintering
Case
Core
40 µm
40 µm
Figure 6. Photomicrographs of the case and core regions of heat-treated MDC-modified with 0.4%
graphite. Stress-relieved at 205°C (400°F) for 1 hour in air. Case microstructure is plate martensite while
core microstructure is lath martensite.
Figure 7. Diagram depicting the effect of carbon content on the type of martensite formed in steels [14].
CONCLUSIONS
Results were presented on MDC-modified, a high performance alloy with a nominal chemistry of 1.0
wt.% Cr, 3.0% Ni, 0.85 wt.% Mo, and 0.6 wt.% Si. Advanced fabrication techniques provide low oxygen
contents, allowing this alloy to avoid the oxide reduction difficulties that often plague chromiumcontaining P/M alloys. This material provides exceptional SP/SS static and dynamic properties, making it
ideal for high performance applications.
Results were also presented on samples of MDC-modified with 0.4% graphite compacted with warm
compaction technology and vacuum sintered in a production furnace. The samples were gas carburized to
a case depth of 0.008 cm (0.0030 in) and subsequently vacuum sintered in a production furnace. The case
had a carbon level of 0.8%, and was predominantly plate martensite. The core consisted of lath
martensite. Processing under these conditions allowed for SP/SS densities above 7.30 g/cm3 after
sintering at 1260°C (2300°F). The high densities and carburizing provided phenomenal properties with
yield strengths of 1100 MPa (160,000 psi), tensile strengths of 1450 MPa (210,000 psi), and apparent
hardness values of 47 HRC.
ACKNOWLEDGMENTS
The authors would like to extend their gratitude to Kevin Lewis for specimen pressing and testing,
William Bentcliff for his assistance with RBF testing, Jerry Golin for his acquisition of metallographic
images, Tom Murphy for assistance with metallographic interpretation, Ken Cradler of Cincinnati, Inc.
for use of their press, and Dr. Nikhilesh Chawla’s research group at Arizona State University for
acquisition of axial fatigue data.
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