Science of Sintering, 45 (2013) 21-29
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doi: 10.2298/SOS1301021I
UDK 669.018;622.785
Research on the Influence of Manganese Content of Physical
and Chemical Characteristics Iron-Based Sintered Products
C. Ionici1, D. Dobrota1*
1
Faculty of Engineering, Constantin Brancusi University of Targu Jiu, Calea Eroilor
Street, 210141, Targu Jiu, Romania
Abstract:
In this paper are presented results obtained from the elaboration of different types of
sintered steels alloyed with manganese content of manganese featuring up to 5% (Fe-0Mn,
1Mn Fe, Fe-2Mn, Fe-3Mn, Fe-4Mn, Fe-5Mn). The main physico-chemical characteristics
determined for sintered steels alloyed with manganese in the paper refer to the apparent
density and fluidity mixtures, but also the dimensional changes, respectively the mass
variation in sintering. Also in this paper it is presented the microstructure of sintered steels
Fe-Mn, with contents of 1÷5% Mn.
Keywords: Sintered steels alloyed with Mn, Chemical composition, Physico-chemical
characteristics, Microstructure.
1. Introduction
As a result of the analysis of the initial stage of the research related to obtaining
sintered steels with a low level of manganese alloy and especially the advantages and
disadvantages of making prealloyed manganese powders [1,3], in this work we used
manganese as the alloying element in ferrous sintered products and we chose to introduce it as
a mixture of unalloyed dust core and ferromanganese powder. The way in which it is alloyed
with manganese significantly determines the conditions of its difusion within the iron crystal
lattice, thus influencing the structure and, implicitly, the properties of the sintered pieces.
The possibility of improving compressability of the mixture of iron powder and
ferromanganese powder as compared to that of the prealloyed manganese powder is based on
a decrease of deformability of the particles of the latter because of the significant hardening
effect of manganese over the ferrite [4,5].
Specialized texts fail to mention the existence of any study concerning the possibility
of getting prealloyed powders of the Fe-Mn-C type with a manganese level beyond 4% [6,8].
2. Materials and Methods
The experimental research we presented in this work aimed mainly at determining the
influence of the manganese and carbon levels over the physical and chemical characteristics
of iron-based sintered products and at emphasizing the possibility of using manganese as the
alloying element in sintered steels. As a means of introducing manganese into the structure of
the steel we chose to mix the iron powder with the ferromanganese powder. In order to blend
_____________________________
*)
Corresponding author: ddan@utgjiu.ro
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C. Ionici et al. /Science of Sintering, 45 (2013) 21-29
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the carbon concentration into the mixture we chose a brand of manganese having a low
carbon level (< 0,1% C).
The materials we used for the experiments were:
• DP 200 iron powder resulting from water atomization, manufactured by Ductil Iron Powder
Buzău, România;
• P40 refined ferromanganese powder (code DB023/B) manufactured by HidroNitro Espanola
S.A., Monzon, Spania;
• type PM5 graphite (>97%C, grain size < 5µm) manufactured by Asbury, USA. The physical
and chemical characteristics of these powders are presented in Table 1.
Tab. I Experimentally determined characteristics of iron powders DP 200 and ferromanganese
Chemical composition, %
Type of
powder
C
Mn
Si
S
P
Fe
H2 losses
DP 200
0.002
0.143 0.021 0.011 0.007
rest
0,17
P 40
0.758
80.89
0.66
0.002 0.002
rest
Feromanganese
Granulometric composition, % gr.
Apparent Fluidity
density
sec/50
>
160 125 100 80 <63
g/cm
g
160µm
125
100
80 µm 63 µm µm
µm
µm
DP 200
3.8
10.4
19
27.8
9.2
29.8
2.94
27.1
P 40
43.2
10.6
21
5.2
6.4
13.6
2.10
34.2
Feromanganese
Taking into consideration the favorable effect of cold hardening the powder has over
the sinterability of powder mixtures [9,10], we ground the fine ferromanganese powder (< 40
µm) with the granulometric composition in Table I (delivery state) in a grinder.
In order to prevent the ferromanganese from oxidizing during the grinding process,
we introduced argon in the grinding barrels. After a relatively brief grinding time (10 min.)
we noticed the fact that the ferromanganese powder becomes pyrophoric, as a result of its
specific surface increasing because of the reduced dimension of its particles and the high
compatibility between the manganese and the oxygen, a phenomenon which was emphasized
for both manganese and ferromanganese powders [11,12].
Fig. 1. Shape of the P40 (Fe20 - Mn80) ferromanganese powder particles after having been
ground for 20 min.
C. Ionici et al./Science of Sintering, 45 (2013) 21-29
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Elaborating and handling potentially pyrophoric powders involve taking appropriate
actions in order to prevent their self-ignition. These actions consist of using grinding
lubricants which create protective layers or post-grinding chemical passivation (controlled
superficial oxidation). In our research, in order to avoid pyrophoricity resulting from grinding
ferromanganese powders and to obtain a fine powder, with a minimal oxygen level, we used
zinc stearate of 3% concentration as a grinding lubricant.
We thus avoided the need to apply any further passivation resulting from controlled
superficial oxidation [13]. Due to the addition of the zinc stearate, we were able to handle the
powder we obtained after 20 min of grinding without any particular issues. The average size
of its particles was below 40 µm, and they consisted of aggregations of very fine particles
(Fig. 1).
We pressed the pills in an uniaxial, bilateral way by applying a static force (the
accuracy of measuring the pressure force was ± 5daN), in a matrix made of hardened steel,
with a cavity aperture of 11.28 mm, corresponding to a 1 cm2 section. The pressing pressure
was between 100 MPa and 800 MPa. We used 7 tests (pills).
We used formula (1) to determine the concentration of the manganese powder mixed
with the iron powder used for elaborating the weakly sintered manganese-alloyed material
(1÷5)% Mn, based on the material balance sheet:
[EP] = [%Mn ] ⋅ 100, [% powder with bearing element]
[%Mn ]Fe−Mn
(1)
where:
[EP] is the concntration of the powder with the bearing element (Fe-Mn) within the
[Fe+(Fe-Mn)] mixture,
[%Mn] – the nominal concentration of the main alloying element (Mn) within the
sintered material,
[%Mn]FeMn – the concentration of the main alloying element (Mn) within the powder
in which the iron is the bearing element (Fe-Mn).
For the comparative studies regarding the was to emphasize the influence of
manganese on the sinterability of iron powders and on the properties of the resulting steels,
there have been various variants of mixtures, consisting of DP 200 iron powder and P40
(Fe20-Mn80) ferromanganese powder, with a nominal manganese level of 0,1, 2, 3, 4 and
5 %.
We used a Turbula space homogenizer in order to mechanically homogenize
pulverous components. The enclosure had a 60 rot/min rotative speed. We allowed 15
minutes for the metallic pulverous components [Fe + (Fe-Mn)] to homogenize, after which we
added 0.6 % zinc stearate as a lubricant and allowed another 20 minutes for the mixture to
continue. The total amount of mixtureed powders was 200 g, which filled 1/3 of the volume
of the homogenizer enclosure. We must mention the fact that, when obtaining the Fe + (FeMn)ground powder mixturees in order to make the test tubes, we took into account the amount
of zinc stearate we introduced during the grilling process, by appropriately decreasing the
amount of zinc stearate we normally add.
The tubes sinterizing was made at a 1150 °C, and 1250 °C, respectively. We used a
Pruffer sinterising oven, with a fireproof bell mouth, with automated temperature adjustment
at soaking durations of 60 and 120 minutes. We used hydrogen of minimum 99.999 % purity
level, with its dew point at 40 °C as a lubricant. The test tubes chilling speed was
approximately 30 °C/min. In order to prevent the test tubes from decarbonizing during the
sinterizing process because of their interaction with the protective atmosphere, we covered
them with a „trap” mixture of alumina and 1 % graphite.
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3. Results and discussion
The aim of the study regarding the sinterability of Fe-Mn-C materials was the
influence of the manganese level in the mixture of iron powder and ferromanganese powder.
The chemical composition, apparent density and ability to flow of the pulverous mixtures are
shown in Tab. II.
In order to study the reaction of powder mixtures to the pressing process we increased
the variation curves for density and tightness of the pressed pills according to the compacting
pressure. In Tab. III we stated the values of the experimental results on the basis of which we
incresed the compressibility curves, and the influence of the compacting pressure on the
density of the compacted pills resulting from powder mixtures Fe+(Fe-Mn) in Fig. 2.
Tab. II Chemical composition, apparent density and fluidity of powder mixtures of iron and
ferro-manganese (0.6 % zinc stearate).
Chemical composition of the mixture, %
Type of
Apparent
Fluidity
mixture
density, g/cm
s/50 g
Mn
C
Fe
Fe-0Mn
0
0.002
99.998
3.09
26.4
Fe-1Mn
1
0.017
98.983
3.07
28.2
Fe-2Mn
2
0.027
97.973
2.96
29.3
Fe-3Mn
3
0.036
96.964
2.89
30.1
Fe-4Mn
4
0.046
95.954
2.82
30.6
Fe-5Mn
5
0.055
94.945
2.74
31.0
Tab. III Raw Density, g/cm3,
pressure of compaction.
Type of
mixture
100
200
Fe-0Mn
4.76
5.72
Fe-1Mn
4.82
5.67
Fe-2Mn
4.83
5.60
Fe-3Mn
4.75
5.46
Fe-4Mn
4.78
5.52
Fe-5Mn
4.61
5.50
of pressed pellets of mixtures of powders studied in the
Compaction pressure, MPa
300
400
500
600
6.19
6.60
6.85
7.03
6.16
6.56
6.82
7.01
6.09
6.47
6.75
6.98
6.04
6.47
6.75
6.95
6.03
6.44
6.72
6.93
6.00
6.38
6.68
6.87
700
7.16
7.15
7.09
7.02
6.98
6.95
800
7.23
7.22
7.16
7.06
7.01
6.95
Fig. 2. Influence of the compacting pressure on the density of the compacted pills resulting
from powder mixtures Fe+(Fe-Mn)
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Tab. IV Influence of the sinterizing parameters with hydrogen with – 40 °C dew point on the
size variation mass variation and sinterizing density of the Fe-Mn alloys (600 MPa
compacting pressure).
Sinterizing conditions
Type of
Raw
Sinterizing
Sinterizing
Postalloy
density
mass
radial
size
sinterizing
Temperature Duration
g/cm
variation
variation
density.
°C
min.
%
%
g/cm
1150
60
7.03
-0.59
-0.20
7.05
Fe-0Mn
120
7.03
-0.59
-0.25
7.06
(control
1250
60
7.03
-0.60
-0.28
7.12
sample)
120
7.03
-0.61
-0.34
7.14
1150
60
7.01
-0.67
-0.14
7.02
120
7.01
-0.69
-0.18
7.04
Fe-1Mn
1250
60
7.01
-0.70
-0.24
7.07
120
7.01
-0.74
-0.30
7.08
1150
60
6.98
-0.75
+0.04
6.97
120
6.98
-0.76
-0.04
6.98
Fe-2Mn
1250
60
6.98
-0.87
-0.08
6.99
120
6.98
-0.89
-0.18
7.00
1150
60
6.95
-0.95
+0.26
6.88
120
6.95
-1.02
+0.20
6.87
Fe-3Mn
1250
60
6.95
-1.19
+0.18
6.90
120
6.95
-1.28
+0.14
6.92
1150
60
6.93
-1.26
+0.40
6.78
120
6.93
-1.34
+0.34
6.79
Fe-4Mn
1250
60
6.93
-1.58
+0.30
6.84
120
6.93
-1.60
+0.26
6.84
1150
60
6.87
-1.62
+0.72
6.67
120
6.87
-1.68
+0.64
6.69
Fe-5Mn
1250
60
6.87
-1.92
+0.56
6.72
120
6.87
-2.02
+0.50
6.73
The fact that the radial dimension of the pressed pills along with the manganese
concentration of the powder mixture is due to a lower level of deformability of the
ferromanganese powder and implicitly of the Fe + (Fe-Mn) powder mixtures.
The experimental research also aimed at the influence of the manganese concentratio
(0 ÷ 5%) on the sinterability of the pressed pills resulting from iron powders, at different
temperatures and at different sinterizing durations. As we well know from classic metallurgy,
low manganese alloyed steels are construction improvement materials. Due to this aspect we
also studied the influence of adding 0 ÷ 1.25 % graphite on the sinterability of the 2 %
manganese alloy. We established the sinterability of the alloys we studied by studying the
density variation and by determining the size contraction during the sinterizing process.
The value of the radial size contraction of the 600 MPa pressed test tubes. sinterized
in hydrogen. at temperatures ranging between 1150 °C and 1250 °C. for 60 and 120 minutes.
is presented in Tab. IV.
After analyzing the information in Tab. IV we can notice the fact that the increase in
the manganese level coincides with a significant change in the values of radial size variations
of the alloys we studied during the sinterizing process.
Thus. while there is barely any significant influence in the case of a manganese level
of up to 1%. this influence significantly increases in case of manganese levels of up to 3 ÷ 5.
The radial size variation of the sintered tests is also sensibly influenced by the increase in
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temperature and sinterizing time.
The size changes of the tests during the sinterizing process are directly influenced by
their mass variations. resulting from the manganese evaporation and devaporation processes.
by the reduction of the iron oxides and the elimination of the pressing lubricant.
The effects of manganese over the microstructure of the sintered steels we studied.
resulting from Fe+(Fe-Mn) powder mixtures are emphasized by some typical examples in
Fig. 3 and Fig. 4. We must mention the fact that, although these alloys contain no carbon,
there is a certain amount of it (0.01 ÷ 0.06 % C) in their structure because of its presence in
the ferromanganese and in the iron powder.
Fig. 3. Microstructure of the Fe-4Mn sintered steel. (Compacting pressure 600 MPa, sintering
1150 0 C, 60 minutes, hydrogen, dew point - 40 0C). Attack: 3 % Nital.
The more the manganese concentration within the alloy increases, the larger the
pearlite concentration becomes, and the finer its structure becomes. In the case of alloys
consisting of 4 – 5 % manganese, besides large areas of alloyed pearlite and ferrite, there also
appear some acicular bainite elements (Fig. 4). The determination of the microhardness values
of the structural constituents of the alloys we studied confirmed the fact that the presence of
the manganese favors the formation of bainite structures even at lower chilling speeds.
Microhardness levels of bainite elements range between 300 and 400 HV0.02.
As seen in Fig. 4. the increase of 100 °C determines. besides a more obvious pore
nodulizing. the increase in the manganese difusion layer within the iron particles. Even in the
case of those alloys which were sintered at 1250 °C, the structure of the material remains
heterogenous. Within the large iron particles. in the ferrite areas microhardness levels range
between 145 and 166 HV0.02, while in the pearlite areas on the outside of these particles, these
values range between 218 and 243 HV0.02.
C. Ionici et al./Science of Sintering, 45 (2013) 21-29
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Steel
type
Sintering temperature, ° C
In order to make a more detailed structural analysis we present in Fig. 5 the structure
of the 2 % manganese steel, consisting of ferrite and and of small uniform areas presumably
consisting of an α solid solution. Fig. 4. Microstructure of some Fe-Mn sintered steels, with
manganese contents of 1÷5 %. at 1150 ºC and 1259 ºC, (Compacting pressure 600 MPa
sinterizing 60 minutes Hydrogen, dew point – 40 ºC). Attack: 3 % Nital.
Fig. 5. SEM microstructure of the
Fe-Mn sintered steel. (Compacting
pressure 600 MPa, sintering 1250 ºC,
60 minutes, hydrogen, dew point 40 ºC). Attack: 3 % Nital.
C. Ionici et al. /Science of Sintering, 45 (2013) 21-29
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4. Conclusions
-
-
-
-
-
-
The increase of the manganese level determines a decrease in apparent density and in
the ability to flow (fluidity) of powder mixtures. This effect is due to the increase,
within the mixture, of the ferromanganese powder of fine druse and large specific
area, and it is well known that fine powders (< 63 µm) have a lower apparent density
and ability to flow.
Adding manganese (ferromanganese) to the iron powder determines a decrease in
density of raw compacted pills. The negative influence of the ferromanganese being
present in the iron powder must be accounted for by the low deformability of the
ferromanganese powder, its high hardness level and the large specific area of the
mechanically ground powder.
The decrease in the tightness of the pressed pill coincides with an increase in the
amount of ferromanganese we added to the mixture, and this decrease is more
significant than that of the density of the pressed pills and results from the decrease in
both raw density and theoretical density of the mixture as a result of the fact that the
manganese density (7.44 g/cm3) is smaller than the iron density (7.875 g/cm3). The
decrease in tightness is significant when subjected to compacting pressures of up to
500 MPa. At a 800 MPa compacting pressure the 1% increase in the manganese level
determines a decrease in the tightness of the pressed pill by approximately 0.9 %.
The increase in radial size and mass losses during the sinterizing process, along with
the increase in the manganese level lead to a decrease in density of the sintered tests
as compared to the raw ones. Thus, in the caase of a 5 % manganese alloy sintered at
1150 °C for 60 min. The density is decreased by up to 3 %. The variation of the
density values for the sintered tests is similar to that of the density values of the
pressed pills, in the sense that their decrease coincides with an increase in the nominal
manganese concentration within the alloy.
By using an electronic scanning microscope to examine the microstructure of the
steels we studied we noticed he rpesence of certain white areas, of micrometrical
dimensions, standing out of the basic matrix, therefore harder, which we assumed to
be martensitic areas, respectively α solid solution of iron-manganese cubic martensite.
Dimensions standing out of the basic matrix therefore harder which we assumed to be
martensitic areas respectively α solid solution of iron-manganese cubic martensite.
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Садржај: У овом раду представљени су резултати синтеровања различитих врста
челичних легура са различитим садржајем мангана до 5% (Fe-0Mn, 1Mn Fe, Fe-2Mn,
Fe-3Mn, Fe-4Mn, Fe-5Mn). Основна физичко-хемијска својства синтерованих легура
челика са додатком мангана упућују на привидну густину и флуидност мешавина али и
промене у димензијама, нарочито промене масе током процеса синтеровања.
Представљене су, такође, микроструктуре синтерованог Fe-Mn, са 1÷5% Mn.
Кључне речи: синтеровани челик са додатком Mn, хемијски састав, физичко-хемијска
својства, микроструктура.