ISSN (1897-3310)
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Volume 10
Issue
Special1/2010
of
81-86
FOUNDRY ENGINEERING
Published quarterly as the organ of the Foundry Commission of the Polish Academy of Sciences
14/1
On the possibility of replacing high
manganese cast steel military vehicle track
pads with ADI
a)
M. Kaczorowski a) , P. Skoczylasa), A. Krzyńska b)
Institute of Mechanics and Design, b) Institute of Materials Processing, Faculty of Production Engineering, Warsaw
University of Technology, ul. Narbutta 85, 02-524 Warszawa, POLAND
Received 05.03.2010; accepted in revised form 23.03.2010
Summary
The theoretical considerations of possibility replacing of high manganese cast steel used for military vehicle track pads with ADI are
presented. Except these considerations, comparative investigations including tensile strength tests hardness measurements and impact
resistance were included. Moreover, the structure investigation was carried out using either conventional light metallography and scanning
(SEM). The last one was applied for fractography investigations, the aim of which was to discover the mode of fracture. The discussion of
experimental results leads to conclusion that ADI, known as high friction resistant, looks to be concurrent material with respect to high
manganese cast steel used now for tang track pads.
Key words: High manganese cast steel, ADI, Mechanical properties, Structure
1. Introduction
Before we reach the essence of this paper let me say something
about its origin. As probably many know I was one of the first in
Poland who stared with ADI which was “born” in the end of
1980. Working many years at the division of Casting in Warsaw
University of Technology I was looking for the structure –
mechanical properties relationships in different category of ADI.
Four years ago, i.e. in 2005 I started to work at the Division of
Mechanics and Armor Technology at the Institute of Mechanics
and Design. It was obvious me to switch my interests to the
materials used for armor application. At the end of 2009 I was
invited to the seminar organized in Institute of Casting in Krakow
devoted the promotion of ADI. I was really proud this invitation.
Considering past and today collaboration in subject of ADI, I
have decided to attend at this meeting. The result of it was the
question: why not to start with ADI as a material for parts used
in military equipment? Because of today’s interests and good
collaboration with plants producing for army, and knowing the
most outstanding property of ADI which is hardness and wear
resistance I took decision to begun with military vehicle track
pads which now are produced from high manganese Hadfield type
steel or cast steel. The first step was to receive the original
material from Stalowa Wola factory where the track pads are used
in many different products.
2. Characterization of the material
Because of comparative character of this paper, at the
beginning we had to collect information about original materials
used now in track pad manufacturing. So first the specimens for
mechanical testing and metallography investigations were cut
from track pads used now in MTLB, 2S1 and BWP (fig.1).
Fig.1. The armored transporter MTLB, 2S1
According to information given by producer the material used
for track pads is high manganese cast steel denoted as a L120G13
ARCHIVES OF FOUNDRY ENGINEERING Volume 10, Special Issue 1/2010, 81-86
81
[PN-88/H-83160]. This steel is well known as one of the most
popular wear resistant material. It is used either as wrought or cast
material and was invented by Sir Robert Hadfield in 1882. The
steel contain about 1,2%C and 12%Mn [1]. Hadfield steel is
unique in that it combined high toughness and ductility with high
work hardening ability, and, usually good wear resistance. These
specific properties are caused by martensitic transformation
proceeding under load (shearing). Hadfield’s austenitic
manganese steel is still used extensively with minor modification
in chemical composition and heat treatment parameters mainly for
manufacturing of parts where wear resistance is crucial condition.
The information’s concerning this material in polish text book
is rather poor. The chemical composition taken from [2] is given
in table 1. This steel is usually used in heat treatment state
involving austenitizing from the 1050 – 1100oC
Table 1. The chemical composition of L120G13 cast steel [2]
Element concentration [weight %]
Mn
Cr
Ni
Si
P
12 - 14 ≤ 1.0 ≤ 1.0 0.3 – 1.0 ≤ 0.1
C
1 - 1.4
S
≤ 0.03
1)
The symbol HYS in table 2 denote High Yield Strength grade
manganese steel.
More information is given in book [3] but because it is very old
elaboration the authors decided to look closer into more new
ASM Hand Book [4]. According to [5], chemical composition of
high manganese austenitic cast steel can substantially vary
depends on the properties needed (table 2).
Rm [MPa]
a.
1000
Re [MPa]
900
Table 2. Composition of some high manganese cast steels [3]
Grade
Standard
Chromium
1%Mo
2%Mo
HYS1)
Element concentration [weight %]
Mn
Cr
Mo
Other
12-14
12-14 1.5-2.5
12-15
0.8- 1.2
12-15
1.8-2.2
2.0 - 4.0%Ni,
0.4-0.7 12-15
1.8-2.2
0.5-1.0%V
C
1 -1.4
1-1.4
0.8-1.3
1.0-1.5
The mechanical properties of different grades cast steels given
in table 2 were showed below (fig.2)
Let’s characterize the mechanical properties of some ADI
grades taking into account that the material should posse’s not
high hardness but also ductility and impact resistance. In table 3
three ADI grades were shows.
First of all it is easy to see that mechanical properties of ADI
grades found in ASTM 897 are a little higher than those in EN
Standards. Moreover, the ADI grades given by EN Standard have
no information about impact resistance evaluated with notch - off
specimens. Although it would not be the truth we assume that KC
values for EN grade of ADI are close to those given by ASTM. It
follows from table 3 that only these three grades of ADI can be
considered as materials concurrent to high manganese austenitic
cast steel.
b.
50
45
800
Tensile elongation [%]
Rm& Re [MPa]
40
700
600
500
400
300
200
35
30
25
20
15
10
100
5
0
Standard
Cr
1%Mo
2%Mo
HYS
0
Standard
Steel grade
c.
Cr
1%Mo
2%Mo
HYS
Steel grade
160
Impact Izod Energy [J]
140
120
100
80
60
40
20
0
Standard
Cr
1%Mo
Steel grade
82
2%Mo
HYS
Fig.2. Typical mechanical properties different grades high manganese
cast steel: a – tensile and yield strength, b – tensile elongation and c –
Izod impact energy (According to [5])
ARCHIVES OF FOUNDRY ENGINEERING Volume 10, Special Issue 1/2010, 81-86
Table 3. Mechanical properties some grades of ADI [6, 7]
Grade
EN-GJS-800-8
ASTM 897 Grade 1
EN-GJS-1000-5
ASTM 897 Grade 2
EN-GJS-1200-2
ASTM 897 Grade 3
Rm
MPa
800
850
1000
1050
1200
1200
Mechanical properties
Rp, 0.2 A5
HB
MPa [%]
500
8
260 – 320
550
10 269 – 321
700
5
300 – 360
700
7
302 – 363
850
2
340 – 440
850
4
341 – 444
experiment with those for austempered ductile iron, the results of
earlier ADI studies were recalled.
KC
[J]
100
80
60
4. Results
4.1. Mechanical properties
The results of mechanical testing are given in table 4. Neglecting
for the moment the analysis of the values given in table 4 it is
very easy to see that the results are highly dispersed, especially if
elongation and impact resistance is considered.
Table 4. The mechanical properties of L120G13
Rp,0.2
Rm
A5
3.1. Material for testing
MPa
MPa
[%]
To characterize the properties of the material used for track
pad manufacturing the authors decided to perform experiments
enabling to get the basic information on its mechanical properties.
The specimens for experimental testing were taken from one of
two the track pads received from Stalowa Wola Plant. The
locations of the place from where the specimens were cut are
shown in fig.3.
435
679
12,4
413
732
4,5
447
706
20,1
432
706
3. Experiment
1)
Hardness
HB
174,1±3.2
HRB
89,1±0.5
KC
KCV
[J]
]J/cm2]
71,42
1,77
67,59
1,68
42,28
1,061)
69,50
1.73
Specimen rejected
4.2. The microstructure
Fig.3. The track pad used for the experimental studies
The material was subjected to mechanical testing including
tensile and compression loading. Moreover impact test and
structure observation were performed. The last one included
conventional metallography and SEM investigations.
3.2. Experimental procedure
The tensile test experiment was performed on fivefold
specimens using Instron 1115 machine. To evaluate the average
values of Rm, Rp, 0.2 and A5 three specimens were used. Except
tensile strength, compression and impact test were carried out.
The specimens for microstructure investigations were first
grinded and then polished with automatic Tenupol equipment.
The microstructure was studied with Olympus IX-70 light
microscope using different magnification and observations mode.
For fractography observations scanning electron microscopy
(SEM) was applied. The SEM observations were done with Leo
1530 electron microscope. To compare the results of this
The results of metallography observations are showed in fig.4.
In first photo (fig.4a) the typical as cast microstructure is clear
visible. Except grain boundaries specific contrast suggesting
heterogeneity of chemical composition across the grains can be
discovered.
The second micrograph (fig.4b) illustrates the microstructure
close to the free surface of the specimen. In here characteristic
needle-like microstructure appears. The needles are distributed at
specific angles each to other (fig.4c) The specific microstructure
at free surface of the specimen was caused by shearing stresses
which as all know are responsible for austenite → martensite
transformation in Hadfield type austenitic steel. Careful
inspection of the photo in fig.4c allows discovering very small
equiaxed particles of carbides (fig.4c) very often distributed along
needles of martensite [5].
4.3. Fractography
The aim of scanning electron microscope observations was to
investigate the character of fracture surface of the specimens
broken in tensile test experiment. The examples of fracture
surfaces L120G13 specimens were shown in fig.5 and 6. The first
(fig.5) shows the fracture surface of the specimen with the lowest
(4%), while the next (fig.6) the specimen having 20% elongation.
In both cases the SEM micrographs show quite ductile mode of
fracture [8]. However, except areas representing high ductility
intergranular fracture mode was identified.
Moreover in fig.5b an example void with brittle precipitates
which were identified from time to time was shown. On the other
hand the feature of broken surfaces in the specimen of high
ductility was characteristic intersecting lines visible on the almost
flat surfaces (fig.6b).
ARCHIVES OF FOUNDRY ENGINEERING Volume 10, Special Issue 1/2010, 81-86
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a.
b.
c.
Fig. 4. The microstructure of L120G13 cast steel: a – central part
of the specimen, b – at the free surface and , c – martensite
needles observed at higher magnification
a.
b.
Fig.5. The morphology of the fracture surface in L120G13 austenitic steel with elongation 4%: a – mixed (intergranular and ductile)
mode of fracture, b – small particles located inside the shrinkage voids
5. Discussion and conclusions
In this part of the paper the authors would like to compare the
result of the experiment on L120G13 given above with the
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mechanical properties of ADI (table 3) and microstructure
investigation obtained in earlier studies [10]. It looks to us , that
from point of view replacing of L120G13 austenitic cast steel
with ADI, “low strength” ADI than “high strength” would be
better choice. This is why in table 3 only the “low strength” grade
ARCHIVES OF FOUNDRY ENGINEERING Volume 10, Special Issue 1/2010, 81-86
of ADI were given. The examples of microstructure of these ADI
grades are show below (fig.7).
As can be seen from the pictures the microstructure consists of
ferrite lath in substantial amount of austenite providing high
a.
ductility. The broken surfaces of this ADI grades show many deep
dimples reflecting ductile mode of fracture (fig.8)
b.
Fig.6. The morphology of the fracture surface in L120G13 austenitic steel with elongation 20%: a – mixed (intergranular and
ductile) mode of fracture, b – highly ductile type of fracture
b.
a.
Fig.7. The microstructure of ADI: a – EN – GJS - 1000 - 5 grade and b – EN – GJS – 800 - 8 grade [10]
Fig.8. The fracture surface of high ductile ADI [10]
So let us turn again to comparison of L120G13 austenitic cast
steel with EN-GJS-800-8 grade ADI. ADI has the ultimate yield
strength and tensile strength substantially higher than cast
L120G13 cast steel. The ADI hardness (260 – 320HB) is much
higher than L120G13 cast steel (175HB). It is well known that
mechanism assuring high wear resistance of L120G13 cast steel is
caused by martensitic transformation caused by shearing. In case
of ADI the wear resistance depends on its hardness which as was
said is much higher than cast steel. So probably it would be more
correct compare the hardness of ADI with the hardness of
martensite at the surface. On the other hand, in case of hardness
measurement, the material has to be partially strengthened and we
can suspect that the values given in table 4 reflect the real
hardness although it might be different from that during service.
As follows from our experiment the impact resistance of
L120G13 cast steel is in average 70J (table 4) while EN-GJS-8008 grade ADI reach the value 100J (table 3). Although both
ARCHIVES OF FOUNDRY ENGINEERING Volume 10, Special Issue 1/2010, 81-86
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materials differ in microstructure the mode of fracture is similar.
Both cast steel and ADI show ductile type of fracture surface
characterized with quite deep dimples [ASM].
There are some technological properties which should be
taken into account. These are melting temperature, castability and
shrinkage susceptibility. The casting temperature of ADI is much
lower than cast steel. Castability of ductile iron from which ADI
is produced is much better than cast steel [10]. Finally the
susceptibility of cast steel to shrinkage is very high in case of cast
steel. This force the foundryman for design special high volume
risers what substantially decrease the yield. If the feeding is not
assured the shrinkage may lead to discontinuities and voids, one o
many found in casting being subject of these studies was shown in
fig.5b. Shrinkage is not the real problem in case of ductile iron,
where even riser-less sound casting can be obtained when rigid
moulds were used. In case of ductile iron the expansion
accompanying graphite precipitation compensate the shrinkage
caused by solidification of liquid iron.
One think more should be compared – this is heat treatment.
Both materials are heat treated. The L120G13 cast steel is used in
supersaturated state. It means that after casting it subjected to
austenitizing followed by rapid cooling. ADI is hat treated to.
First the castings are subjected to austenitization and then
isothermally quenched at given temperature. The authors did not
calculate the cost of each heat treatment but it looks to us that
these are not substantially different.
Taking into account the considerations given above lead the
authors to the final conclusion that ADI can be considered as a
good substitute for L120G13 austenitic cast steel used now for
track pad. The reasons pushing us to such conclusion are:
1. Comparable or complementary mechanical properties assuring
good behavior in service.
86
2. Lower manufacturing costs following from lower melting
temperature and much higher yield.
3. More silent work during service.
4. Lower casting rejected because of much better castability, and
lower shrinkage susceptibility.
References
[1] Metals Handbook: vol. 1. Tenth Edition: Properties and
Selection: Iron, Steels and High Performance Alloys, Metals
Park, Ohio, 1990
[2] PN-72?H-83160, GOST 2176-77
[3] G. Kniaginin: Staliwo, Metalurgia i Odlewnictwo, Wyd.
“Śląsk”, Katowice, 1977.
[4] Metals Handbook vol. 19, Ninth Edition: Casting, Metals
Park, Ohio, 1988
[5] Metals Handbook, vol. 9, Tenth Edition: Metallography and
Microstructures, Metals Park, Ohio, 1990
[6] PN – EN 1564
[7] ASTM A A897
[8] Metals Handbook vol. 12, Ninth Edition: Fractography,
Metals Park, Ohio, 1987
[9] Kaczorowski M., Krzyńska A.: The study of mechanical
properties and structure of austempered ductile iron (ADI)
Proc. 4-th International Conference on Advances in
Production Engineering, APE’07, Warsaw, June 2007,
pp.171-180.
[10] Krzyńska A., Kaczorowski M.: The studies of nodular
graphite cast iron early stages austemperingy, Archives of
Foundry Engineering, 2008, vol.8, Issue 4, p. 87.
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