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The precipitation processes in the Manaurite XM superalloy during 1000 hours
of ageing
Article in International Journal of Microstructure and Materials Properties · January 2008
DOI: 10.1504/IJMMP.2008.022039
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West Pomeranian University of Technology, Szczecin
West Pomeranian University of Technology, Szczecin
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Int. J.Microstructure and Materials Properties , Vol. x, No. x, 2007
The precipitation processes of Manaurite XM
superalloy after 1000 hours of aging
Walenty Jasiński and Paweł Zawada
Institute of Materials Engineering
Szczecin University of Technology
Al. Piastów 17, 70-310 Szczecin, Poland
E-mail: walenty.jasinski@ps.pl
E-mail: pawel.zawada@ps.pl
Abstract: This paper presents the results of investigations of mechanical
property and microstructures in state of delivery and after 1000 h of aging of
superalloy samples Manaurite XM taken from catalytic centrifugal cast pipe.
The aging material of catalytic pipes in the temperature range 750 ÷ 900 oC
causes precipitation of intermetallic phases in alloyed austenite matrix.
These changes affect mechanical proprieties of material of pipes.
Keywords: reforming, Fe-Ni-Cr alloys, microstructure, G-phase
Reference to this paper should be made as follows: Jasiński W. and Zawada
P. (2007) ‘The precipitation processes of Manaurite XM superalloy after
1000 hours of aging’ , Int. J. Microstucture and Materials Properties, Vol.
3, No 3, pp. 000-000
Biographical notes: Walenty Jasiński is currently an Assistant Professors
at the Institute of Materials Engineering from Szczecin University of
Technology, Poland. He received his MS and PhD degrees from Szczecin
University of Technology. His interests are CVD of titanium hard coating,
superalloy on Fe-base and non-destructive testing. To date, he has published
26 scientific articles and had presentations at 22 conferences.
Paweł Zawada received his MS degree from Szczecin University of
Technology, Poland. Since 2002 he has worked as Assistant in Institute of
Materials Engineering of the same university. His research interests is in
superalloy on Fe-base. He has coauthored 9 refereed journals and 4
conference papers.
1. Introduction
Catalytic pipes are used in chemical and petrochemical industry to obtain
hydrogen. In service conditions in the temperatures range 550 ÷ 900 oC, at the
inside pressure up to 4 MPa, the material of the pipes undergoes creeping which
can result in destruction of the pipe (Jasiński and Ustasiak, 1999; Ray et al., 2003,
Chen et al. 2004, Guan et al. 2005)
The tubes applied in steam reforming, of a total length of 12 meters, were
assembled together by welding of segments. The segments of tubes were made by
centrifugal casting of austenitic chromium-nickel cast steels stabilized with
additions of niobium and titanium. These cast steels are to be numbered among
third generation and as superalloys can work above 816 C, tm. 1500 F
(Mikułowski, 1997). As a result of aging structural changes take place, leading to
essential changes of mechanical proprieties of the material the pipe is made of.
Copyright © 200x Inderscience Enterprises Ltd.
1
W. Jasiński and P. Zawada
Microstructure of the superalloys Manaurite XM in delivery states contains alloys
austenite as well as carbides M23C6 and MC. During aging in adjoining areas to
grain boundary dispersion secondary phase precipitation appears.
2. Experimental details
The tests were carried out on new pipe  136 x 14,5 mm made by centrifugal casting
from the superalloy Manaurite XM (25.19 % Cr, 33.02 % Ni as well as additions 0.84 %
Nb and 0.1 % Ti). The Brinell hardness measurements were conducted on HPO 250
hardness tester Heckert VEB Werkstoffprüfmaschinen in accordance with rules of EN
ISO 6506-4:2005 on samples taken from the centre thicknesses of the wall of pipe.
Temperatures of aging 750, 825 and 900 oC were established in connection with real
terms of operation. The aging was carried out in atmosphere of air in laboratory furnace
SNOL 1 f-m AB Utenos Elektrotechnika stabilizing the temperature in range ± 1C. After
aging the samples was cooling with furnace. The impact resistance measurements of
Charpy'ego methods in accordance with rules of EN 10045-1: 1990 were conducted at the
temperature of 20 C on the samples low-cut along axis of the pipe with notch "U" cut
along ray of pipe. Metallographic and fractography examinations were performed on
cross sections perpendicular to tube axis using the light microscope Nikon EPIPHOT 200
as well as scanning Jeol JSM-6100 the equipped in system EDS LINK ISIS 300. After
mechanical polishing the specimens were etched with Murakami reagent dyeing  phase
and chromium carbide brown. Carbides of MC type under Murakami reagent obtained
brighter tint.
3. Experimental results
Metallographical investigations of the specimen in delivery states (centrifugal cast)
showed dendritic columnar austenite grains located almost perpendiculary to the tube
walls. The structure consists of austenitic matrix with a network of eutectic carbides
precipitated initially during the solidification process and distributed at the dendrite and
grain boundarie (Fig.1a) with fine-grained eutectic (Fig. 1b).
Figure 1
a)
Microstructure of superalloy Manaurite XM – as delivery, Murakami etched
b)
X-ray analysis Manaurite XM in as cast state showed that the eutectic carbides are
niobium-titanium and chromium-iron carbide.
The precipitation processes of Manaurite XM superalloy after 1000 hours of
aging
Figure 2
The diffractogram of superalloys Manaurite XM- as delivery
The results obtained by means of X-Ray analysis were confirmed with EDX
microanalysis. The points data obtained from EDX analysis made on superalloys
Manaurite XM in as delivery state, are given in Fig. 3. The results of local analysis shows
that in point 1 NbC carbides is present, whereas in point 2 chromium carbide is revealed.
The analysis in point 3 means the analysis of the matrix (austenite).
Figure 3
Points of local analysis as delivery, x2000
Element
Cr
Ni
Nb
Ti
Mn
Si
Fe
Content [% weight]
1
2
3
4,97
86,27
25,88
1,44
1,72
34,24
88,71
0,21
0,05
2,21
0,29
1,16
1,39
0,45
0,12
1,46
base
base
base
After aging samples for 100 h the secondary precipitate was observed in areas
adjoining to eutectic. The largest intensity of precipitation was observed in a sample
aging at 900 ºC and the smallest in a sample aging at 750 ºC (Jasiński et al., 2004). After
1000 h aging the fine secondary precipitate in areas adjoining to eutectic was observed in
a sample aging at 750 ºC – Fig 4a. Sample aging at 825 ºC shows the precipitation in all
the grains of austenite – Fig. 4b and 6. Coagulation precipitate in large agglomerates was
noticed in sample aging at 900 ºC – Fig. 4c.
X-ray diffraction shows the presence of (Nb,Ti)C, (Cr,Fe)23C6, Ni3(Nb,Ti) and
Ni16(Nb,Ti)6Si7 phase in the aging structure of Manaurite XM – Fig. 5.
The results obtained by means of X-Ray analysis were confirmed with EDX
microanalysis. The data points obtained from EDX analysis made on superalloys
Manaurite XM after aging for 1000 h, are given in Fig 6.
The analysis of the elements’ distribution in the eutectic indicates increased
amounts of nickel, niobium and silicon in point 3 and 2 – Fig. 6. The element contents in
point 2 fulfil Ni16(Nb,Ti)6Si7 phase.
W. Jasiński and P. Zawada
Figure 4
Microstructure of superalloys Manaurite XM after 1000 h aging in
temperature: a) 750ºC , b) 825ºC ,c) 900ºC; Murakami etched
a)
b)
c)
The precipitation processes of Manaurite XM superalloy after 1000 hours of
aging
Figure 5
The diffractogram of superalloys Manaurite XM after 1000 h aging
Figure 6
Points of local analysis after 1000 h aging at 825ºC, x5000
Element
1
2
3
4
Cr
84,00
2,75
16,44
25,01
Ni
4,05
48,40
44,28
33,14
Nb
0,86
31,66
22,34
-
Ti
-
1,10
3,24
-
Mn
0,75
0,32
0,48
1,30
Si
0,32
9,93
2,16
1,78
Fe
base
base
base
base
The similar concentration elements in G phase was determined in the cast
20Cr32Ni1Nb after service around 760 ºC for about 4 years (Chen et al. 2004). A high
content of nickel and niobium in point 3, accompanied by a low content of chromium,
indicate the intermediate state in transformation of NbC into G phase Ni16(Nb,Ti)6Si7.
Similar phase transformations were affirmed in earlier investigations of pipes made
from second generation superalloy IN 519 (Jasiński, 2002, 2003).
The hardness measurements were carried out after 1, 10, 100 and 1000 h of aging.
The Brinell hardness in state of delivery was 171 HB and increases after 1 hour of aging
achieving the maximum after 100 h of aging. The hardness drops after 1000 h as a result
of coagulation secondary precipitations - Fig. 7.
The results of impact test investigations showed significant changes in relation to
state of delivery. The impact test were made at 20 C and 825 C. The impact resistance
in state of delivery KCU2 was 15 [J/cm2] in temperature 20 C and 30 [J/cm2] in
temperature test 825 C. After 1000 h of aging the impact resistance decreased to 9
[J/cm2] for samples aging at 750 C and to 6 [J cm2] for samples aging at 825 and 900 C
(Fig 8). The investigations of fracture surface were made on samples from the impact test
carried out at room temperature. The fracture surface samples aging by 1000 h did not
have plastic deformation but they had developed surface (Fig. 9 b,c,d). There are a lot of
small, but configurated tear ridges and dimles and few facetes showing the development
of fracture along cleavage planes (Fig. 9a).
W. Jasiński and P. Zawada
Hardness HB
Figure 7
The hardness changes of Manaurite XM cast steel versus time of aging
240
230
220
210
200
190
180
170
1
10
750
Figure 8
825
100
900
Time [h]
1000
The impact resistance of Manaurite XM after aging
KCU2 [J/cm2]
35
30
25
20
15
10
5
1
10
750/20
750/825
825/20
825/825
100
900/20
900/825
Time [h]
1000
Figure 9
The fracture of the notched bar test piece: a) as delivery, b) after aging
750ºC/1000h, c) after aging 825ºC/1000h, d) after aging 900ºC/1000h, x1000, SEM
The precipitation processes of Manaurite XM superalloy after 1000 hours of
aging
4. Discussion of results
The aging of the samples of centrifugally cast catalytic pipe made from superalloy
Manaurite XM leads to appearing dispersion secondary precipitation in the vicinity of
eutectic. It is the result of attempts to reach a state of equilibrium which after
solidification is metastable.
The formation of secondary intermetalic phases causes a growth of hardness of
material after aging 1 h in every analyzed temperature. With prolongation the time of
aging to 10 and 100 h the quantity of dispersion of the secondary precipitation increases,
which causes the growth of hardness, achieving the maximum after 100 h of aging. The
effect of continuing the precipitations processes can also be seen in a considerable
lowering the impact resistance in relation to state of delivery.
After 1000 h aging in all the three investigated temperatures the G phase Ni16(Nb,Ti)6Si7 in structure was observed. This phase appears as a result of
transformation of carbide NbC first into Ni 3Nb, and then into G phase. Superalloys
containing G phase show good performance during long-term service, and there are
indications of greater time to rupture when G phase is present (Ibaňez et al. 1993)
Similar changes were observed in catalytic pipes of the second generation (Jasiński,
2002, 2003: Jasiński et al. 2003).
5. Conclusion
In the as-cast Manaurite XM superalloy Nb-rich MC and Cr-rich M23C6 are widely
observed.
The conducted tests suggest that 1000 hour-long aging of superalloy Manaurite XM
at temperatures approximate to operation conditions leads to changes of mechanical
proprieties as a result of changes in the kind, quantity and morphology of the precipitated
intermetallic phases.
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