DEVELOPMENT OF A DUAL-PHASE
PRECIPITATION-HARDENING PM STAINLESS STEEL
Chris Schade & Tom Murphy
Hoeganaes Corporation
Cinnaminson, NJ 08077
Alan Lawley & Roger Doherty
Drexel University
Philadelphia, PA 19104
ABSTRACT
Stainless steels can now be fabricated by the pressing and sintering of water atomized
powder. PM grades embrace: ferritic, austenitic, martensitic, duplex (ferritic +
austenitic), dual-phase (ferritic + martensitic), and precipitation hardening (martensitic).
Development of dual-phase PM stainless steels reflects the growing need for higher
strength, coupled with ductility and toughness. In the present study, a new low-cost PM
stainless steel has been developed which combines the advantages of a dual-phase (ferrite
+ martensite) microstructure with precipitation hardening. Unlike other precipitation
hardening alloys, ductility and impact toughness increase significantly upon aging,
notwithstanding attendant increases in hardness and strength. The mechanical properties
of the new alloy are evaluated in terms of composition and microstructure.
INTRODUCTION
In the competition between wrought and PM stainless steels, PM materials are at an
extreme disadvantage due to the deleterious effect of porosity on mechanical properties
such as tensile strength, ductility and impact toughness. Furthermore, the use of
increased alloy levels in PM stainless steels is both costly and counter-productive due to
the negative effect on compressibility. The addition of graphite, which is used for
increasing mechanical properties in ferrous PM, is detrimental to the corrosion resistance
of stainless PM steels and reduces ductility. In order to achieve improved mechanical
properties and enhance corrosion resistance in PM stainless steels, it is necessary to
explore non-traditional strengthening mechanisms.
It has been shown that utilizing a dual phase microstructure can lead to increased strength
in a PM stainless steel. 1-3 The microstructure is a combination of ferrite and martensite
(Figure 1). The ferrite allows for a higher sintered density, improving ductility and
toughness, while the martensite imparts strength and hardness. The levels of martensite
and ferrite can be balanced by adjusting the content of the austenite stabilizers (nickel and
copper) and the ferrite stabilizers (chromium, silicon and molybdenum). One of the most
common dual phase PM stainless steels, SS-409LNi (Table I), is commonly used for
exhaust flanges. The ferritic microstructure of SS-409L is altered by admixing nickel
which promotes the formation of high temperature austenite during sintering, and which
transforms to martensite during cooling.
(a)
(b)
Figure 1. Representative microstructures: (a) press + sinter PM dual-phase stainless steel; sintered density
7.20 g/cm3 (b) press + sinter PM 17-4 PH; sintered density 6.70 g/cm3.
Precipitation hardening stainless steels are not defined by their microstructure, but rather
by the strengthening mechanism. These grades can have austenitic, semiaustenitic or
martensitic microstructures and can be hardened by aging at moderately elevated
temperatures, 480 oC to 620 oC (900 oF to 1150 oF). The strengthening effect is due to
the formation of intermetallic precipitates from elements such as copper or aluminum.
Aluminum’s high affinity for nitrogen and oxygen in PM stainless steels necessitates
strict atmosphere control during sintering and, for this reason, copper is the most
commonly used element for precipitation hardening. These alloys generally have high
strength and high apparent hardness while exhibiting superior corrosion resistance
compared with martensitic stainless steels. This improved corrosion resistance is derived
from the fact that the carbon levels are low and the martensite is formed from additions of
nickel and copper. The low carbon martensite that is formed is weaker but more ductile
than the martensite formed in alloys such as SS-410-90HT (carbon bearing), but the
strength of these alloys is developed by aging.
Table I: Composition of Stainless Steel PM Alloys (w/o).
Alloy
C
P
Si
Cr
Ni
Cu
Mn
Mo
Cb
17-4PH
409LNi
DP2
SS-410-90HT
0.018
0.013
0.015
0.200
0.025
0.01
0.014
0.012
0.85
1.00
0.84
0.81
17.1
11.3
11.6
12.0
4.00
1.30
1.03
0.14
3.55
0.04
0.29
0.01
0.15
0.12
0.10
0.11
0.03
0.05
0.22
0.05
0.25
0.56
-----
One of the most common precipitation hardening stainless steel grades in both the
wrought and PM industries is 17-4 PH (Table I). This grade has a martensitic
microstructure and its strength and hardness can be improved by aging treatments.4-7 The
general corrosion response of this alloy is superior to that of standard martensitic
stainless steels due to the higher chromium level.
There are many applications in which stainless steels with only moderate corrosion
resistance (compared with 17-4 PH) but excellent mechanical properties are required. A
widely used alloy is SS-410-90-HT. This is a PM 410L stainless steel in which graphite is
added to the atomized powder and the alloy is sintered in a nitrogen-rich atmosphere.
When carbon and nitrogen are added to 410L stainless steel, the microstructure becomes
martensitic, thereby increasing both strength and hardness. This grade of stainless steel is
used in applications where high strength and hardness are required. The disadvantage of
using carbon and nitrogen is that they degrade corrosion resistance and also reduce
impact strength and ductility. Many PM fabricators select this alloy because there are
few alternative compositions.
ALLOY DEVELOPMENT
The purpose of this work was to develop an alternative composition that makes use of the
two strengthening mechanisms. The combination of a dual phase microstructure and
precipitation hardening should allow for the development of a low cost, high strength
alloy with moderate corrosion resistance. The development of this dual phase
precipitation hardening (DPPH) alloy can improve PM’s competitive advantage over
wrought materials.
Previous work by the authors focused on developing a dual phase microstructure in a
nominal 12 w/o chromium-containing stainless steel.3 This was accomplished by
balancing the ferrite stabilizers (chromium, silicon and molybdenum) and austenite
stabilizers (carbon, nitrogen, nickel and copper) such that the microstructure consisted of
ferrite and martensite (DP2 in Table I). The copper in this alloy was intended only to
stabilize the austenite and was at too low a level for any significant precipitation.
Therefore a new set of alloys was made with copper ranging from 1 w/o to 4 w/o.
Table II: Composition of Experimental DPPH Alloys (w/o)
Alloy
Alloy A
Alloy B
Alloy C
Alloy D
Alloy E
Alloy F
Alloy G
Alloy H
C
0.011
0.015
0.013
0.014
0.017
0.016
0.015
0.016
P
0.007
0.005
0.012
0.007
0.010
0.008
0.011
0.012
Si
0.65
0.82
0.83
0.83
0.78
0.73
0.92
0.80
Cr
11.81
11.71
12.11
12.65
12.13
12.77
11.82
12.17
Ni
1.05
1.22
1.06
0.97
1.05
1.08
1.06
1.07
Cu
0.04
0.35
0.99
2.13
2.55
3.06
3.48
3.95
Mn
0.10
0.12
0.07
0.05
0.06
0.15
0.08
0.06
Mo
0.35
0.31
0.38
0.33
0.35
0.35
0.36
0.34
ALLOY PREPARATION AND TESTING
The powders used in this study were produced by water atomization with a typical
particle size distribution 100 w/o <150 µm (–100 mesh) and 38 to 48 w/o <45 µm (-325
mesh). All the alloying elements were prealloyed into the melt prior to atomization,
unless otherwise noted. The powders were of the same base composition with only the
copper content intentionally varied. Table II list the chemistry of the individual heats
along with a letter designation indicating a change in copper content.
The powders were mixed with 0.75 w/o Acrawax C lubricant. Samples for transverse
rupture (TR) and tensile testing were compacted uniaxially at 690 MPa (50 tsi). All the
test pieces were sintered in a high temperature Abbott continuous-belt furnace at 1260 °C
(2300 °F) for 45 min in a hydrogen atmosphere with a dewpoint of –40 oC (-40 °F),
unless otherwise noted.
Prior to mechanical testing, green and sintered density, dimensional change (DC), and
apparent hardness, were determined on the tensile and TR samples. Five tensile
specimens and five TR specimens were tested for each composition. The densities of the
green and sintered steels were determined in accordance with MPIF Standard 42. Tensile
testing followed MPIF Standard 10 and impact energy specimens were tested in
accordance with MPIF Standard 40. Apparent hardness measurements were conducted
on tensile, TR and impact specimens, following MPIF Standard 43.
Rotating bending fatigue (RBF) specimens were machined from test blanks pressed at
690 MPa (50 tsi) and sintered at 1260 oC (2300 oF). The dimensions of the test blanks
were 12.7 mm x 12.7 mm x 100 mm. RBF tests were performed using rotational speeds
in the range of 7,000-8000 rpm at R equal –1 using four fatigue machines simultaneously.
Thirty specimens were tested for each alloy composition, utilizing the staircase method to
determine the 50% survival limit and the 90% survival limit for 107 cycles (MPIF
Standard 56).
Metallographic specimens of the test materials were examined by optical microscopy in
the polished and etched (glyceregia) conditions. Etched specimens were used for
microindentation hardness testing, per MPIF Standard 51.
Salt spray testing on TR bars was performed in accordance with ASTM Standard B 11703. Five TR bars per alloy (prepared as previously described) were tested. The percent
area of the bars covered by red rust was recorded as a function of time. The level of
corrosion was documented photographically.
RESULTS AND DISCUSSION
Development of Dual Phase Microstructure
The compositon of the DPPH alloys was based on the dual phase chemistry previously
developed. This was a nominal 12 w/o Cr-1 w/o Ni-.35 w/o Mo alloy. For this study the
copper was varied up to 4 w/o. Since copper is an austenite stabilizer, it promotes the
formation of martensite in the sintered microstructure. For this reason metallography was
performed to confirm the level of ferrite and marteniste in the final microstructure. This
was to determine at what level of copper a dual phase microstructure still existed.
Quantitative metallography was performed to measure the actual ferrite content of the
PM alloys.
50
7.4
Ferrite Content (v/o)
3
Sintered Density (g/cm )
40
30
20
7.2
7
6.8
10
6.6
0
0
1
2
3
4
5
0
1
2
3
Copper Content (w/o)
Copper Content (w/o)
(a)
(b)
4
5
Figure 2. Sintered properties of DPPH as a function of copper content: (a) v/o ferrite, and (b) sintered
density.
Figure 2(a) shows the ferrite level as a function of the copper content. At low copper
levels ferrite percentages exceed 40 v/o and at high copper levels the microstructure is
predominately martensitic. There is a range of copper levels between 2 w/o and 4 w/o
over which the ferrite level is relatively stable at 30 v/o. In Figure 2(b) the sintered
densities of the alloys are shown. Since higher copper levels lead to poor
compressibility, the sintered density decreases as the copper level increases, with a
dramatic drop-off in density at 4 w/o Cu. For these reasons the study focused on DPPH
P/M compositions with copper concentrations < 3 w/o.
Most of the studies of dual phase steels have been on wrought low alloy steels. In these
studies the properties of the dual phase steel have been related to the microstructure in
terms of the levels of martensite and ferrite. The tensile strength and other properties
have been shown to vary linearly with the volume fraction of the phases by the law of
mixtures.8-9 Intuitively, the tensile strength and hardness increase with the level of
martensite, while the ductility and impact toughness vary proportionally with the level of
ferrite. In order to optimize the PM alloy, the materials were sintered to a density of 6.60
g/cm3 at temperatures ranging from 1120 °C to 1260 °C (2050 °F to 2300 °F). In this
temperature range the alloy is in the two-phase austenite and ferrite region. Upon cooling
the austenite transforms to martensite. By varying the sintering temperature the levels of
each phase change. In general, higher sintering temperatures and low copper levels favor
the formation of ferrite. Figure 3 shows the mechanical properties as a function of v/o
ferrite and the copper level.
5
621
4
3
Yield Strength (psi x10 )
90
690
Elongation (%)
3 w/o Cu
2 w/o Cu
1 w/o Cu
0.35 w/o Cu
Yield Strength (MPa)
100
80
552
70
483
60
414
1
345
0
50
0
10
20
30
40
3 w/o Cu
2 w/o Cu
1 w/o Cu
0.35 w/o Cu
3
2
50
0
10
Ferrite (v/o)
20
(a)
40
50
(b)
500
Martensite Microindentation Hardness (HV25)
95
3 w/o Cu
2 w/o Cu
1 w/o Cu
0.35 w/o Cu
90
Apparent Hardness (HRB)
30
Ferrite (v/o)
85
80
75
70
3 w/o Cu
2 w/o Cu
1 w/o Cu
0.35 w/o Cu
450
400
350
300
250
65
0
10
20
30
Ferrite (v/o)
(c)
40
50
0
10
20
30
40
Ferrite (v/o)
(d)
Figure 3: Mechanical properties of DPPH PM stainless steel versus v/o ferrite Sintered density = 6.60
gm/cm3.
Similar to the low alloy dual phase wrought steels, as the v/o of ferrite increases the
tensile strength and apparent hardness decrease while the ductility (measured by the
elongation) increases. For a given v/o ferrite, increasing the copper concentration
increases the strength and apparent hardness. This is due to the solution strengthening
effect of the copper in the matrix. The microindentation hardness measurements in
Figure 3(d) support this conclusion with the higher copper contents having the higher
50
microindentation hardness. Table III gives a summary of the mechanical properties of the
DPPH alloys.
Table III: Mechanical Properties of DPPH PM Stainless Steels (As Sintered and Aged Conditions).
Impact
AISI
Alloy A Sintered
Alloy A Aged
Alloy B Sintered
Alloy B Aged
Alloy C Sintered
Alloy C Aged
Alloy D Sintered
Alloy D Aged
Alloy E Sintered
Alloy E Aged
Alloy F Sintered
Alloy F Aged
ft.lbs.f
73
76
49
54
56
56
61
69
36
40
30
36
(J)
98
102
66
72
75
75
82
92
48
54
40
48
Apparent
UTS
Hardness
(HRA)
(103 psi) (MPa)
52
95
654
53
95
654
53
95
654
53
96
660
51
89
612
53
100
688
52
105
722
57
121
832
58
117
805
62
142
977
54
113
777
60
137
943
0.20% Offset
Yield
3
(10 psi) (MPa)
69
475
70
482
70
482
73
502
69
475
79
544
81
557
100
688
95
654
117
805
87
599
116
798
Elongation
(%)
4.3
6.6
4.2
6.6
4.6
7.1
3.2
5.1
2.2
4.6
2.8
3.7
Development of Precipitation Hardening Component
Strengthening, as a result of precipitation hardening, takes place in three steps:10
(1) Solution treatment, in which the alloy is heated to a relatively high temperature,
allows any precipitates or alloying elements to form a supersaturated solid
solution. Typical solution treatment temperatures are in the range of 982 oC to
1066 oC (1800 oF to 1950 oF).
(2) Quenching, in which the solution treated alloy is cooled to create a supersaturated
solid solution. The cooling can be achieved using air, water or oil. In general, the
faster the cooling rate the finer the grain size which can lead to improved
mechanical properties. Regardless of the method of cooling, the cooling rate must
be sufficiently rapid to create a supersaturated solid solution.
(3) Precipitation or age hardening, in which the quenched alloy is heated to an
intermediate temperature or held at room temperature for a period of time.
During aging, the supersaturated solid solution decomposes and the alloying
elements form small precipitate clusters. The precipitates hinder the movement of
dislocations and consequently the metal resists deformation and becomes harder
and stronger.
In the DPPH PM alloys copper is the element involved in precipitation formation.
Similar to 17-4 PH, the DPPH alloys can be aged after sintering to enhance their strength
and hardness. Figure 4 shows an aging profile (by temperature) for a range of copper
levels in the DPPH PM stainless alloys. Both the yield strength and apparent hardness
behave as expected for an alloy in which precipitation hardening is occurring. As the
alloy is heated, precipitates are formed impeding the movement of dislocations causing
an increase in strength and apparent hardness. Above 800 oF ( 427 oC) the alloy starts to
increase in strength and hardness, reaching a maximum in both properties at
approximately 538 oC (1000 oF). Above this temperature the precipitates start to coarsen
and the hardness and strength decrease.
The change in ductility of the DPPH alloys is more complicated. There occurs a ductility
trough in the 2 and 3 w/o copper alloys at 482 oC (900 oF), while the ductility of the 1
w/o copper is relatively constant at this temperature. For a given set of processing
conditions, as the copper level is increased there will be an increase in the level of
martensite in the dual phase alloy. Since both carbon and nitrogen are ferrite stabilizers,
they segregate to the martensite. At low aging temperatures the carbon and nitrogen form
carbides and nitrides in the matrix, strengthening the alloys.
o
Aging Temperature ( C)
0
133
266
o
400
533
0
90
621
Aging Temperature ( C)
266
400
533
5
1 w/o Cu
2 w/o Cu
3 w/o Cu
598
4
85
80
552
529
Elongation (%)
575
Yield Strength (MPa)
3
Yield Strength (psi x10 )
1 w/o Cu
2 w/o Cu
3 w/o Cu
133
3
2
75
1
506
70
0
200
400
600
800
1000
483
1200
0
0
o
200
400
600
800
o
Aging Temperature ( F)
Aging Temperature ( F)
(a)
(b)
o
Aging Temperature ( C)
0
133
266
400
533
60
1 w/o Cu
2 w/o Cu
3 w/o Cu
Apparent Hardness (HRA)
55
50
45
40
35
0
200
400
600
800
1000
1200
o
Aging Temperature ( F)
(c)
Figure 4: Aging profile of DPPH PM stainless steel as a function of copper concentration.
1000
1200
However, as the aging temperatures are increased, the elements diffuse to grain
boundaries and embrittlement occurs. This is the reason for the decrease in elongation at
482 oC (900 oF). This effect is more pronounced as the martensite level of the alloy
increases (1 w/o Cu versus 3 w/o Cu).
Normally the ductility of an alloy decreases as the strength and apparent hardness
increase. The DPPH alloys are remarkable in that, as the strength and hardness increase,
the ductility also increases. At 538 oC (1000 oF), when all the DPPH alloys reach their
maximum strength and apparent hardness, the elongation of the alloys increases and in
fact exceeds the as sintered levels. The higher the v/o ferrite in the dual phase
microstructure, the larger the increase in ductility.
Comparison of Dual Phase Precipitation Hardening Alloy with 17-4 PH
PM applications mandating strength and hardness with moderate corrosion resistance
have experienced limited options.
o
Aging Temperature ( C)
0
133
266
o
Aging Temperature ( C)
400
533
0
110
759
100
690
133
266
400
533
6
621
80
552
17-4 PH
70
483
Elongation (%)
DPPH w/o Cu
90
Yield Strength (MPa)
3
Yield Strength (psi x10 )
5
4
DPPH 2 w/o Cu
3
17-4 PH
414
2
345
1200
1
60
50
0
200
400
600
800
1000
0
200
400
600
o
Aging Temperature ( F)
o
o
266
1200
(b)
Aging Temperature ( C)
Aging Temperature ( C)
133
1000
o
(a)
0
800
Aging Temperature ( F)
400
0
533
133
266
400
533
50
62
45
60
58
DPPH 2 w/o Copper
56
54
DPPH 2 w/o Cu
50
35
30
40
25
30
20
52
17-4 PH
15
20
17-4 PH
10
50
0
200
400
600
800
1000
1200
0
200
o
Aging Temperature ( F)
(c)
Figure 5: Mechanical properties of DPPH (2 w/o Cu) compared with 17-4 PH.
400
600
800
o
Aging Temperature ( F)
(d)
1000
1200
Impact Energy (Joules)
40
Impact Energy (ft.lbs.f)
Apparent Hardness (HRA)
60
Adding carbon (in the form of graphite) to some of the ferritic grades such as SS-410L
and SS-430L can provide a martensitic microstructure with strength and hardness but the
alloys are extremely brittle and exhibit poor corrosion resistance due to the formation of
chromium carbides. 17-4 PH, a significantly more costly alloy, offers high strength and
hardness with excellent corrosion resistance but with limited ductility.
Fıgure 5 shows a mechanical property comparison of 17-4 PH and the 2 w/o Cu DPPH
alloy. Despite being a leaner alloy in terms of chromium, nickel and copper contents, the
strength, apparent hardness and ductility of the DPPH alloy are all superior to the
corresponding properties of 17-4 PH. Under identical processing conditions (pressing
and sintering) the DPPH alloys, because of their leaner chemistry, achieve a higher
sintered density. This is one reason for the superior mechanical properties.
The other factor contributing to the superior strength of the DPPH alloys may be the role
that phase boundaries play in impeding dislocation motion.12 Not only do dual phase
steels contain boundaries between grains of the same phase but also boundaries between
different phases. These boundaries act as barriers to dislocation motion and and result in
higher work hardnening than in a conventional single phase alloy. These barriers become
more effective as the hardness of the two phases differs. The unique feature of this alloy
is not only it’s excellent strength but the fact that, as the strength increases the ductility
also increases. At aging temperatures exceeding 482 oC (900 oF), work hardening occurs
because of the formation of copper precipiates in both the martensite and the ferrite, but
there is also a tempering of the martensite in the dual phase structure. The net effect is an
increase in both tensile strength and in ducility.
(a)
(b)
(c)
Figure 6. Representative appearance of salt spray specimens: (a.) SS-410L-90HT, (b.) 2 w/o Cu DPPH, (c.)
17-4 PH. Magnification 75% of actual size.
To evaluate the corrosion resistance of the 2 w/o Cu DPPH alloy, it was compared with
17-4 PH and SS-410-90HT, both high strength and high hardness alloys. These three
alloys were compacted at 690 MPa (50 tsi) and sintered at 1260 oC (2300 oF) in 100 v/o
hydrogen. Salt spray testing, performed according to ASTM Standard B 117-03, was
conducted for 240 h. The results can be seen in Figure 6; this test is intended as a general
guideline as to the performance of the alloys. As expected, due to the high carbon content
SS-410-90HT performed poorly. The 2w/o Cu DPPH alloy exhibited moderate corrosion
resistance and the highly alloyed 17-4 PH performed the best. Since the mechanism for
corrosion varies by application, specific testing must be undertaken to ensure satisfactory
performance of the alloy under a given set of conditions.
Fatigue tests were performed on PM 17-4 PH and two of the new PM DPPH grades (Alloy D and
Alloy F). The results of these tests, in terms of the 90% survival limit, are compared with other
PM stainless steel fatigue data by Shah et al. 13 in Figure 10. The latter study compared the
fatigue strength of various stainless steels as a function of tensile strength.
The 17-4 PH (6.98 g/cm3) exhibited fatigue strength comparable with that of SS-410L90-HT. The excellent fatigue response of the two PM DPPH alloys appears to be related
to their high tensile strength. In general, fatigue crack propagation rates in PM steels are
high and the fatigue limit is dictated by crack initiation rather than crack propagation.
Thus, resistance to crack initiation increases as the tensile strength increases. Both the
DPPH alloys (D and F) have high tensile strengths, and therefore, high fatigue endurance
limits. It appears that the addition of copper, along with the addition of nickel and
molybdenum, leads to harder martensite, which, in this case has a positive effect on
fatigue strength.
Tensile Strength (MPa)
0
100
200
300
400
500
600
50
800
DPPH
Alloy D
420
900
345
Dual Phase
DPPH
ALLOY F
295
40
409LNi
35
409LNi-HC
410HT
DUPLEX
245
17-4PH
409LE
30
195
430L
25
434L
20
430N2
145
434N
410L
15
95
10
Fatique Endurance Limit MPa)
45
Fatigue Endurance Limit (psi x103)
700
45
5
0
40
50
60
70
80
90
100
110
120
130
-5
140
Tensile Strength (psi x103)
Figure 7. Fatigue endurance limit (90% Survival) as a function of tensile strength for various PM stainless steels.
CONCLUSIONS
•
A lean precipitation hardening grade of stainless steel which utilizes a dual phase
microstructure and copper for precipitation hardening has been developed for
applications that require high strength and toughness, but with moderate corrosion
resistance.
•
The DPPH alloys exhibit a unique combination of high strength, high toughness
and high fatigue resistance. This is attributed to their microstructure, which is
dual-phase, and precipitation hardened.
•
The DPPH alloys exhibit an improvement in ductility with an increase in strength
and hardness.
•
The mechanical properties of the DPPH alloys exceed those of 17-4 PH.
•
The salt spray corrosion resistance of the DPPH alloys falls between that of SS410L-90HT and 17-4 PH.
•
The DPPH alloys are cost effective when high strength, coupled with moderate
corrosion resistance, are mandated.
REFERENCES
1. S.O. Shah, J.R. McMillen, P.K. Samal and L.F. Pease, “Mechanical Properties of
High Temperature Sintered P/M 409LE and 409LNi Stainless Steels Utilized in the
Manufacturing of Exhaust Flanges and Oxygen Sensor Bosses,” 2003, SAE Paper
No. 2003-01-0451. SAE International, Warrendale, PA.
2. P.K. Samal, and J.B. Terrell, “Mechanical Properties Improvement of P/M 400 Series
Stainless Steel via Nickel Addition,” Advances in Powder Metallurgy and Particulate
Materials, compiled by C.L. Rose and M.H. Thibodeau, Metal Powder Industries
Federation, Princeton, NJ, 1999, vol. 3, part 9, pp. 15-28.
3. A. Lawley, E. Wagner, and C.T. Schade, “Development of a High-Strength-DualPhase P/M Stainless Steel,” Advances in Powder Metallurgy and Particulate
Materials – 2005, compiled by C. Ruas and T. Tomlin, Metal Powder Industries
Federation, Princeton, NJ, 2005, part 7 pp.78-89.
4. K.A. Green, “PIM 17-4PH Actuator Arm for Aerospace Applications,” Advances in
Powder Metallurgy and Particulate Materials, ibid reference no. 2, vol. 5, pp. 119130.
5. M.K. Bulger and A.R. Erickson, “Corrosion Resistance of MIM Stainless Steels,”
Advances in Powder Metallurgy and Particulate Materials, compiled by A. Neupaver
and C. Lall, Metal Powder Industries Federation, Princeton, NJ, 1994, vol. 4 pp. 197215.
6. J.H. Reinshagen, and J.C. Witsberger, “Properties of Precipitation Hardening
Stainless Steel Processed by Conventional Powder Metallurgy Techniques,” ibid.
reference no. 5, vol. 7, pp. 313-323.
7. A. Lawley, R.Doherty, P. Stears and C.T. Schade, “Precipitation Hardening Stainless
Steels,” Advances in Powder Metallurgy and Particulate Materials – 2006, compiled
by W. R. Gasbarre and J.W. von Arx, Metal Powder Industries Federation, Princeton,
NJ, 2006, part 7 pp.141-153.
8. A.K.Jena and C. Chaturvedi, “ On the Effect of the Volume Fraction of Martensite on
the Tensile Strength of Dual-phase Steel,” Materials Science and Engineering, No.
100, 1988, pp.1-6.
9. A. Bag, K.K, Ray and E.S. Dwarakadasa, “Influence of Martensite Content and
Morphology on Tensile and Impact Properties of High-Martensite Dual Phase
Steels,” Metallurgical and Materials Transactions A, 1999 vol. 30A, pp. 1193 –1202.
10. L.H. Van Vlack, Elements of Materials Science and Engineering, Sixth Edition,1989,
Addison Wesley Publishing Company, Reading, MA, pp.304-309.
11. K.J. Irvine, D.J. Crowe, M.A. Cantab and F.B. Pickering, “The Physical Metallurgy
of 12% Chromium Steels, Journal Iron and Steel Institute, August 1990, pp. 386- 405.
12. E. Werner and H.P. Stuwe “Phase Boundaries as Obstacles to Dislocation Motion,”
Materials Science and Engineering, 1984-1985, vol. 68 pp. 175-182.
13. S.O. Shah, J.R. McMillen, P.K. Samal and L.F. Pease, “Mechanical Properties of
High Temperature Sintered P/M 409LE and 409LNi Stainless Steels Utilized in the
Manufacturing of Exhaust Flanges and Oxygen Sensor Bosses,” 2003 SAE Paper No.
2003-01-0451, SAE International, Warrendale, PA.