effect of sintering time and cooling rate on sinterhardenable materials

ABSTRACT
EFFECT OF SINTERING TIME AND COOLING RATE
ON SINTERHARDENABLE MATERIALS
Ingalill Nyberg, Mary Schmidt <strong>and</strong> Peter Thorne, North American Höganäs Inc.
Jason Gabler, Thomas J. Jesberger <strong>and</strong> Stephen Feldbauer, ABBOTT Furnace Co.
Sinter hardening is a cost-<strong>effect</strong>ive process that combines <strong>sintering</strong> <strong>and</strong> heat treatment in one step. It is
known that the <strong>cooling</strong> <strong>rate</strong> following <strong>sintering</strong> greatly affects material microstructures, which determine
the final properties <strong>of</strong> sinter-hardened materials.
This study investigated the properties <strong>of</strong> three sinter-hardenable materials (Cr/Mo pre-alloy, Cu/Mo
diffusion bonded <strong>and</strong> Ni/Mo pre-alloy) at three <strong>sintering</strong> <strong>time</strong>s <strong>and</strong> three <strong>cooling</strong> <strong>rate</strong>s. The objective was
to underst<strong>and</strong> how these <strong>sintering</strong> conditions influence the development <strong>of</strong> martensite in the
microstructure <strong>and</strong> thereby control the hardness <strong>and</strong> mechanical properties <strong>of</strong> materials. This was
accomplished through examining the percentage <strong>of</strong> martensite <strong>and</strong> microstructural homogeneity.
INTRODUCTION
Sinter hardening combines <strong>sintering</strong> <strong>and</strong> heat treatment in a single step to confer high strength <strong>and</strong> wear
resistance while minimizing the number <strong>of</strong> processing steps. The microstructure <strong>of</strong> sinter hardened steels
is primarily martensitic. Both <strong>sintering</strong> <strong>time</strong> <strong>and</strong> <strong>cooling</strong> <strong>rate</strong> affect the material’s microstructure. To
better underst<strong>and</strong> how <strong>sintering</strong> conditions affect material microstructure <strong>and</strong> hence mechanical
properties, the percentage <strong>of</strong> martensite <strong>and</strong> the microstructural homogeneity were evaluated for three
sinter hardenable materials at each <strong>of</strong> three different <strong>sintering</strong> <strong>time</strong>s <strong>and</strong> three different <strong>cooling</strong> <strong>rate</strong>s.
Changing the type <strong>and</strong> amount <strong>of</strong> alloying elements, the <strong>time</strong> at <strong>sintering</strong> temperature <strong>and</strong> the post<strong>sintering</strong>
<strong>cooling</strong> <strong>rate</strong>, will affect the amount <strong>of</strong> martensite <strong>and</strong> bainite in the microstructure.
EXPERIMENTAL PROCEDURE
Materials
Three sinter hardenable materials were analyzed for this investigation. Astaloy CrL <strong>and</strong> Astaloy A are
pre-alloyed materials while D. DH is a diffusion-alloyed material. D. DH is based on a fully pre-alloyed
powder with 1.5% Mo to which 2%Cu has been diffusion alloyed. The chemical composition <strong>of</strong> the base
1

powders used is reported in Table I. The chemical compositions <strong>of</strong> the studied mixes are reported in Table
II.
Table I. Chemical composition <strong>of</strong> the investigated base powders.
Grade Ni* Mo Cr Cu Mn
(%) (%) (%) (%) (%)
Astaloy CrL - 0.2 1.5 - -
D. DH - 1.5 - 2.0 -
Astaloy A
*Pre-alloyed
1.9 0.55 - - 0.2
Table II. Chemical composition <strong>of</strong> investigated mixes.
Mix MPIF Designation Grade Cu Graphite Lubricant Total metallic
alloying
elements
(wt %) (wt%) (wt%) (%)
1 - Astaloy CrL 1 0.75 0.60 2.7
2 FLC-4908 D. DH - 0.75 0.60 3.5
3 FL-4608 + 2%Cu Astaloy A 2 0.85 0.60 4.65
Graphite Asbury 1651 (C 96 – 97% C) <strong>and</strong> Acu Powder copper -165 mesh were admixed with the base
powder. Kenolube was used as lubricant.
Each mix was pressed to green density 7.0g/cm³ in a manual TONI laboratory press. The test bars used
were transverse rupture strength test bars (MPIF-41), tensile strength test bars (MPIF-10) <strong>and</strong> impact
energy test bars (MPIF-40). The compaction pressures required to reach 7.0g/cm³ are reported in table III.
It is important to note that the compaction pressure required to reach the desired density varied
considerably with the base material selected.
Table III: Compaction pressure required to reach 7.0g/cm³.
Mix tsi MPa
1 44.7 617
2 41.1 567
3 46.5 641
The reason for the lower compressibility <strong>of</strong> mix 3 based on Astaloy A is the higher amount <strong>of</strong> pre-alloyed
metallic elements, 4.65% in total. Mix 2 has a good compressibility since it is based on a powder where
the molybdenum is pre-alloyed <strong>and</strong> the copper is diffusion alloyed to the powder, 3.5% <strong>of</strong> metallic
alloying elements in total. Mix 1, which is also a fully pre-alloyed powder, has a rather good
compressibility due to the low level <strong>of</strong> metallic alloying elements, only 2.7% in total.
Processing conditions
Each material was sintered at 2050°F (1121°C) in a 90% N2 / 10% H2 atmosphere without carbon control.
Sintering <strong>time</strong> <strong>and</strong> <strong>cooling</strong> <strong>rate</strong> were varied. Sintering <strong>time</strong>s were 10, 25 <strong>and</strong> 40 minutes. The <strong>sintering</strong>
was carried out in a laboratory furnace from ABOTT equipped with VARICOOL convection <strong>cooling</strong>
system to vary the <strong>cooling</strong> <strong>rate</strong>s <strong>of</strong> fan speeds from 5, 10 to 15 Hz. Temperature pr<strong>of</strong>iles were obtained
for each condition in order to verify the <strong>sintering</strong> <strong>time</strong>s <strong>and</strong> <strong>cooling</strong> <strong>rate</strong>s.
After <strong>sintering</strong>, all materials were tempered for 60 minutes in air at 400°F (204°C) in order to stress
relieve the martensite.
2

Testing
After the final tempering operation, density, dimensional change, tensile <strong>and</strong> yield strength, elongation,
transverse rupture strength, impact energy, hardness, <strong>and</strong> microstructure were evaluated for all bars
cooled at 5 <strong>and</strong> 10Hz. The bars cooled at 15 Hz were only evaluated for hardness <strong>and</strong> metallography. The
sintered carbon level was determined for all materials. Oxygen <strong>and</strong> nitrogen were also determined for
material 1.
Metallography
Impact energy bars were prepared for metallographic analysis. Photomicrographs were taken <strong>of</strong> the
structures after etching in a 50/50 mix <strong>of</strong> 1%Nital <strong>and</strong> Picral for mixes 1 <strong>and</strong> 2 <strong>and</strong> in 1%Nital for mix 3.
The amount <strong>of</strong> martensite <strong>and</strong> bainite was determined by line analysis.
RESULTS AND DISCUSSION
Density <strong>and</strong> dimensional change
Compaction pressure <strong>and</strong> sintered densities after 10, 25 <strong>and</strong> 40 minutes <strong>sintering</strong> are reported in table IV.
Table IV. Compaction pressure <strong>and</strong> sintered density obtained after 10, 25 <strong>and</strong> 40 minutes <strong>sintering</strong>.
Mix Pressure to reach
7.0g/cm³
tsi (MPa)
10 min. <strong>sintering</strong>
(g/cm³)
3
25 min. <strong>sintering</strong>
(g/cm³)
40 min. <strong>sintering</strong>
(g/cm³)
1 44.7 (617) 6.97 6.97 6.98
2 41.1 (567) 6.98 6.99 6.99
3 46.5 (641) 6.95 6.95 6.96
Dimensional change measured from die size to tempered TRS-bar is reported in figure 1.
(%)
0,450
0,400
0,350
0,300
0,250
0,200
0,150
0,100
0,050
0,000
DC after <strong>sintering</strong> at 10, 25 <strong>and</strong> 40 minutes
SD 6.97 - 6.98g/cm³ SD 6.98 - 6.99g/cm³ SD 6.95 - 6.96g/cm³
10 25 40 10 25 40 10 25 40
Mix 1 Mix 2
Mix 3
Figure 1. Dimensional change (die to tempered) at different <strong>sintering</strong> <strong>time</strong>s <strong>and</strong> <strong>cooling</strong> <strong>rate</strong>s.
The data in Figure 1 show that the dimensional change decreases slightly when the <strong>sintering</strong> <strong>time</strong> is
increased <strong>and</strong> the <strong>cooling</strong> <strong>rate</strong> is kept constant, this is especially pronounced for mix 1. The differences in
5 Hz
10
Hz

microstructure <strong>and</strong> dimensional change are not significant enough to be reflected in measured sintered
density.
Another observation is that mix 1, with the lowest amount <strong>of</strong> copper, shows the least swelling. Thereafter
come mixes 2 <strong>and</strong> 3, which both contain 2% copper, however mix 3 has a higher total amount <strong>of</strong> alloying
elements. The higher level <strong>of</strong> swelling for mix 3 also explains the lower sintered density <strong>of</strong> that material.
Mix 2 shows a rather high density even though it showed more growth during <strong>sintering</strong> compared to mix
1. Part <strong>of</strong> the explanation for this can be found in the microstructure. Mix 2 had more bainite than mix 1
in the microstructure, <strong>and</strong> bainite has higher density than martensite. All <strong>of</strong> the tested mixes grow during
<strong>sintering</strong> since they are alloyed with copper, which promotes growth.
Hardness <strong>and</strong> Mechanical properties
Hardness measured after <strong>sintering</strong> for 10, 25 <strong>and</strong> 40 minutes <strong>and</strong> <strong>cooling</strong> at 5, 10 <strong>and</strong> 15 Hz is reported in
Figure 2. Hardness was measured as Rockwell C. Mix 1 showed a very good response to increased
<strong>cooling</strong> <strong>rate</strong> both at 10 <strong>and</strong> 25 minutes <strong>sintering</strong> <strong>time</strong>. Hardness above 30 HRC was achieved for all
<strong>sintering</strong> <strong>time</strong>s when <strong>cooling</strong> at 10 <strong>and</strong> 15 Hz. The reason for the slight drop in hardness when <strong>sintering</strong>
for 40 minutes is probably due to the higher degree <strong>of</strong> decarburization after 40 minutes compared to 25
minutes <strong>sintering</strong> <strong>time</strong>. In order to reach hardness values above 30HRC with mix 2, either 15Hz <strong>cooling</strong>
<strong>rate</strong> or 40 minutes <strong>sintering</strong> <strong>time</strong> is needed. Mix 3, with the highest amount <strong>of</strong> metallic alloying elements,
shows good hardness values; however the increase due to increased <strong>cooling</strong> <strong>rate</strong> is not as pronounced as
for mixes 1 <strong>and</strong> 2. Bars sintered for 40 minutes showed an increased surface decarburization due to the
lack <strong>of</strong> carbon control <strong>of</strong> the <strong>sintering</strong> atmosphere.
HRC
40
35
30
25
20
15
HRC after <strong>sintering</strong> at 10, 25 <strong>and</strong> 40 minutes
10 25 40 10 25 40 10 25 40
Mix 1 Mix 2 Mix 3
Figure 2. Hardness HRC at different <strong>cooling</strong> <strong>rate</strong>s <strong>and</strong> <strong>sintering</strong> <strong>time</strong>s.
4
5 Hz
10 Hz
15 Hz

Mix 1 shows very good results for the 0.2% <strong>of</strong>fset yield strength even at longer <strong>sintering</strong> <strong>time</strong>s, whereas
the yield <strong>of</strong> mixes 2 <strong>and</strong> 3 dropped at longer <strong>sintering</strong> <strong>time</strong>s. The good yield strength in combination with
the good hardness makes mix 1 an interesting material for sinter hardening.
(ksi)
130
120
110
100
90
80
70
YS after <strong>sintering</strong> at 10, 25 <strong>and</strong> 40 minutes
10 25 40 10 25 40 10 25 40
Mix 1 Mix 2 Mix 3
Figure 3. Yield strength at different <strong>cooling</strong> <strong>rate</strong>s <strong>and</strong> <strong>sintering</strong> <strong>time</strong>s.
(ksi)
150
140
130
120
110
100
TS after <strong>sintering</strong> at 10, 25 <strong>and</strong> 40 minutes
10 25 40 10 25 40 10 25 40
Mix 1 Mix 2 Mix 3
Figure 4. Tensile strength at different <strong>sintering</strong> <strong>time</strong>s <strong>and</strong> <strong>cooling</strong> <strong>rate</strong>s.
5
5 Hz
10 Hz
5 Hz
10 Hz
In figure 4, where the ultimate tensile strength is shown, it can be seen that for <strong>sintering</strong> <strong>time</strong>s 10 <strong>and</strong> 25
minutes an increased <strong>cooling</strong> <strong>rate</strong> results in higher strength. However, at 40 minutes <strong>sintering</strong> <strong>time</strong> the
strength decreases or remains almost equal at the higher <strong>cooling</strong> <strong>rate</strong> for mixes 1 <strong>and</strong> 3. Two probable
reasons for this behavior are that the copper has had longer <strong>time</strong> to diffuse <strong>and</strong> the copper concentration
has evened out <strong>and</strong>, as a result, the strengthening <strong>effect</strong> <strong>of</strong> locally higher copper concentration has
decreased. The second possible reason is that the long <strong>sintering</strong> <strong>time</strong> has enabled a grain growth <strong>of</strong> the
austenitic grains, which during the rapid <strong>cooling</strong> results in a coarser <strong>and</strong> more brittle martensite. Mix 2
shows the highest results for tensile strength for both 25 <strong>and</strong> 40 minutes <strong>sintering</strong> <strong>time</strong> when cooled at
10Hz.

Table V: Mechanical properties after different <strong>sintering</strong> conditions.
Mix Cooling Sintering C TS YS A IE TRS
<strong>rate</strong> <strong>time</strong> as-sint
Hz minutes Wt% ksi (MPa) ksi (MPa) % Ft-lb (J) ksi (MPa)
1 5 10 0.63 118 (811) 94 (646) 0.6 10 (14) 206 (1419)
1 5 25 0.66 129 (887) 114 (789) 0.4 11 (15) 224 (1545)
1 5 40 0.64 139 (961) 121 (832) 0.5 14 (19) 220 (1514)
1 10 10 0.63 124 (855) 118 (815) 0.3 11 (15) 211 (1457)
1 10 25 0.65 133 (918) 119 (817) 0.4 12 (16) 216 (1488)
1 10 40 0.64 138 (951) 119 (819) 0.4 15 (20) 220 (1514)
2 5 10 0.61 124 (854) 91 (625) 0.9 14 (19) 201 (1386)
2 5 25 0.66 133 (919) 99 (682) 0.9 15 (20) 229 (1576)
2 5 40 0.66 141 (975) 97 (670) 1.0 16 (21) 227 (1562)
2 10 10 0.65 131 (901) 103 (707) 0.8 14 (19) 243 (1672)
2 10 25 0.65 147 (1015) 95 (652) 0.8 16 (21) 244 (1673)
2 10 40 0.67 147 (1016) 93 (639) 0.9 16 (21) 246 (1700)
3 5 10 0.71 128 (880) 99 (682) 0.6 15 (20) 218 (1505)
3 5 25 0.71 136 (940) 90 (621) 0.8 17 (23) 233 (1609)
3 5 40 0.69 145 (1003) 84 (580) 0.8 15 (20) 234 (1616)
3 10 10 0.70 135 (933) 105 (723) 0.6 14 (19) 228 (1572)
3 10 25 0.70 142 (979) 88 (610) 0.8 15 (20) 239 (1645)
3 10 40 0.69 136 (940) 89 (614) 0.7 16 (22) 240 (1654)
In table V, where mechanical data are shown it can be seen that there is no significant difference in
impact energy between 5 <strong>and</strong> 10Hz <strong>cooling</strong> <strong>rate</strong>.
Regarding transverse rupture strength cooled at 10 Hz, it can be noted that mix 2 based on the diffusionalloyed
powder showed the highest values even though mix 3 has a considerably higher level <strong>of</strong> metallic
alloying elements. This can be explained by the microstructure, which will be discussed later in this
paper.
Metallography
A general comment regarding the 10 minutes <strong>sintering</strong> is that the <strong>sintering</strong> necks were not as well
developed as for 25 <strong>and</strong> 40 minutes <strong>sintering</strong> <strong>time</strong>. Figures 5a-c show the difference in <strong>sintering</strong> necks
between 10, 25 <strong>and</strong> 40 minutes <strong>sintering</strong> <strong>time</strong>.
Figure 5a: Mix 1, 10 min at 10 Hz Figure 5b: Mix 1, 25 min at 10Hz Figure 5c: Mix 1, 40 min at 10Hz
6

Tables VI - VIII show the phase analysis for the microstructures <strong>of</strong> materials 1, 2 <strong>and</strong> 3.
Table VI: Phase analysis for material 1.
Sintering <strong>time</strong> Cooling <strong>rate</strong> C as-sint M B
(minutes) (Hz) (%) (%) (%)
10 5 0.63 35 Bal.
10 10 0.63 65 Bal.
10 15 0.66 90 Bal.
25 5 0.66 45 Bal.
25 10 0.65 75 Bal.
25 15 0.65 90 Bal.
40 5 0.64 60 Bal.
40 10 0.64 80 Bal.
40 15 0.63 90 Bal.
The copper content was high in the grain boundaries <strong>of</strong> the bars sintered for 10 minutes. The reason for
the increased amount <strong>of</strong> martensite with increased <strong>sintering</strong> <strong>time</strong> is due to the longer diffusion <strong>time</strong>.
Figure 6a: Mix 1, 10 min at 15Hz Figure 6b: Mix 1, 25 min at 10Hz Figure 6c: Mix 1, 25 min at 15Hz
Figure 6a shows the microstructure <strong>of</strong> mix 1 sintered for 10 minutes <strong>and</strong> cooled at 10Hz. The structure
contains 90% martensite <strong>and</strong> the hardness was 36HRC. The darker border around the larger pores <strong>and</strong> in
the grain boundaries indicates that the copper concentration is high there due to the short <strong>sintering</strong> <strong>time</strong>.
Figure 6b shows the microstructure <strong>of</strong> mix 1 sintered for 25 minutes <strong>and</strong> cooled at 10 Hz, which resulted
in 75% martensite <strong>and</strong> hardness 35HRC. Figure 6c shows the same mix also sintered for 25 minutes but
cooled at 15Hz. Here the microstructure was 90% martensite <strong>and</strong> the hardness had increased slightly to
37HRC.
7

Table VII: Phase analysis for material 2.
Sintering <strong>time</strong> Cooling <strong>rate</strong> C as-sint M B
(minutes) (Hz) (%) (%) (%)
10 5 0.61 35 Bal.
10 10 0.65 35 *Bal.
10 15 0.68 60 Bal.
25 5 0.66 35 Bal.
25 10 0.65 60 Bal.
25 15 0.67 75 Bal.
40 5 0.66 45 Bal.
40 10 0.67 65 Bal.
40 15 0.67 80 Bal.
*Finer bainite compared to 10 minutes <strong>sintering</strong> <strong>time</strong> cooled at 5 Hz.
Figure 7a: Mix 2, 25 min at 15Hz Figure 7b: Mix 2, 40 min at 10Hz Figure 7c: Mix 2, 40 min at 15Hz
Figure 7a shows mix 2 sintered for 25 minutes <strong>and</strong> cooled at 15Hz. The structure contains 75%
martensite. The hardness was 36HRC. Figures 7b-c show the difference between 10 <strong>and</strong> 15 Hz <strong>cooling</strong>
<strong>rate</strong> when <strong>sintering</strong> for 40 minutes. After 10Hz <strong>cooling</strong> <strong>rate</strong>, the obtained structure contained 65%
martensite <strong>and</strong> the hardness was 34HRC. After 15Hz the martensite content had increased to 80% but the
hardness remained at 34 HRC. The reason for this is the decarburization <strong>of</strong> the surface during the 40
minute <strong>sintering</strong>.
Table VIII: Phase analysis for material 3.
Sintering <strong>time</strong> Cooling <strong>rate</strong> C as-sint M B
(minutes) (Hz) (%) (%) (%)
10 5 0.71 85 Bal.
10 10 0.70 90 Bal.
10 15 0.71 95 Bal.
25 5 0.71 90 Bal.
25 10 0.70 95 Bal.
25 15 0.70 96 Bal.
40 5 0.69 90 Bal.
40 10 0.69 98 Bal.
40 15 0.70 99 Bal.
8

Figure 8a: Mix 3, 25 min at 10Hz Figure 8b: Mix 3, 25 min at 15Hz Figure 8c: Mix 3, 40 min at 15Hz
Figures 8a-b show the microstructure <strong>of</strong> mix 3 sintered for 25 minutes <strong>and</strong> cooled at 10 or 15Hz
respectively. In figure 8a the structure contains 95% martensite <strong>and</strong> the hardness was 35HRC. In figure 8b
the structure contains 96% martensite <strong>and</strong> the measured hardness was 38HRC. Figure 8c shows a
structure with 98% martensite <strong>and</strong> hardness <strong>of</strong> almost 40HRC, which was achieved after <strong>sintering</strong> for 40
minutes <strong>and</strong> <strong>cooling</strong> at a <strong>rate</strong> <strong>of</strong> 15Hz.
Cooling <strong>rate</strong>s
An interesting question that arises is what <strong>cooling</strong> <strong>rate</strong> settings <strong>of</strong> 5, 10 <strong>and</strong> 15 Hz correspond to in °F/sec
(or °C/s). This question can be answered by comparing the actual phase amount analysis presented above
in tables VI – VIII with available phase amount diagrams derived from CCT diagrams <strong>and</strong> analysis <strong>of</strong>
samples cooled at different <strong>rate</strong>s using a dilatometer. In figure 9 such a phase diagram for Astaloy A +
2% Cu + 0.7% C is shown. At setting 5Hz <strong>and</strong> 25 minutes <strong>sintering</strong> <strong>time</strong> the microstructure contained
90% martensite. By comparing that value to the diagram it can be concluded that the 5Hz setting
corresponds to 1 - 1.5°C/s (1.8 - 2.7°F/s). At setting 10Hz, the amount <strong>of</strong> martensite was 95%, which
indicates a <strong>cooling</strong> <strong>rate</strong> <strong>of</strong> 2 - 2.5°C/s (3.6 - 4.5°F/s). At the setting 15Hz the amount <strong>of</strong> martensite was
96%, which indicates that the <strong>cooling</strong> <strong>rate</strong> was only somewhat faster than the setting 10Hz, ~3°C/s
(5.4°F/s). However, as shown before in figure 2, there was an increase in hardness at setting 15Hz.
Phases %
100
80
60
40
20
0
Astaloy A + 2%Cu + 0.7%C
Phase amount vs <strong>cooling</strong> <strong>rate</strong>
0,1 1 10 dT/dt (°C/s)
B 5Hz 10Hz 15Hz
M
Figure 9. Effect <strong>of</strong> <strong>cooling</strong> <strong>rate</strong> on microstructure <strong>of</strong> Astaloy A + 2% Cu + 0.7% C.
By studying figure 11, which shows the <strong>cooling</strong> <strong>rate</strong> for a 10 Hz <strong>sintering</strong>, it can be seen that the <strong>cooling</strong>
<strong>rate</strong> is different for different parts <strong>of</strong> the <strong>cooling</strong> cycle even though the fan speed was set to 10 Hz all the
<strong>time</strong>. Comparing the <strong>cooling</strong> <strong>rate</strong> diagram in figure 11 to the CCT-diagram in figure 10, which shows the
bainite noses <strong>and</strong> the start <strong>of</strong> martensite formation. Bainite can be formed due to the lower <strong>cooling</strong> <strong>rate</strong>
between 300 – 200°C.
9

10
°C
1200
1000
800
600
400
200
0
Cooling at 10Hz
45,00 47,00 49,00 51,00 53,00 55,00 57,00
<strong>time</strong> (minutes)
Figure 10. CCT-diagram for Astaloy A + 2%Cu + C Figure 11. Cooling <strong>rate</strong> at 10Hz setting.
CONCLUSIONS
• The hardness increase is primarily dependent on the microstructure, which is controlled
by the <strong>cooling</strong> <strong>rate</strong>.
• Longer <strong>sintering</strong> <strong>time</strong> increases the hardenability.
• Sintering <strong>time</strong> had the largest impact on strength. However, longer <strong>sintering</strong> <strong>time</strong> also
resulted in increased surface decarburization <strong>and</strong> thereby lower hardness.
• The <strong>effect</strong> <strong>of</strong> the process parameters is dependent on the material <strong>and</strong> alloying system.
• Mix 1 (Astaloy CrL + 1% Cu + 0.75%C) with only 2.7% <strong>of</strong> metallic alloying elements
showed hardness values equal to mix 3 (Astaloy A + 2% Cu + 0.85% C) with a total <strong>of</strong>
4.65% <strong>of</strong> metallic alloying elements. This proves the good hardenability <strong>effect</strong>s <strong>of</strong>
chromium. Usage <strong>of</strong> a mix with lower total alloying content should be beneficial both
regarding cost <strong>and</strong> environmentally.
• Mix 1 (Astaloy CrL + 1% Cu + 0.75%C) with only 2.7% <strong>of</strong> metallic alloying elements
showed the highest yield strength, which is an interesting combination with good
hardenability.
REFERENCES
[1]Höganäs H<strong>and</strong>book for sintered components, 1999, Vol. 6
[2] J. McLell<strong>and</strong>, O. Mårs, <strong>and</strong> T. Jesberger. “Sintering Furnace Cycle Influence on Sinter
Hardened Part Parameters” Presented at PM 2 Tec 2001 in New Orleans on May 16, 2001.
[3] U. Engström. Advances in Powder metallurgy & Particulate Materials, 2000, p 5-147 to 5-157