See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/249922136 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 CITATIONS READS 3 1,807 2 authors: Walenty Jasiński Paweł Zawada West Pomeranian University of Technology, Szczecin West Pomeranian University of Technology, Szczecin 8 PUBLICATIONS 47 CITATIONS 3 PUBLICATIONS 3 CITATIONS SEE PROFILE All content following this page was uploaded by Walenty Jasiński on 18 January 2016. The user has requested enhancement of the downloaded file. SEE PROFILE 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 ± 1C. 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. Reference Ibaňez R., Almeida Soares G., Almeida L., May I. (1993) ‘ Effects of Si Content on the Microstructure of Modified-HP Austenitic Steels’ Materials Characterization, Vol. 30, pp. 243-249 Mikułowski B.( 1997) ‘Stopy żaroodporne i żarowytrzymałe – Nadstopy’, Wydawnictwo AGH, Kraków, Poland Jasiński W., Ustasiak M.(1999) ‘Zmiana właściwości materiału rur katalitycznych reformera ‘, Inżynieria Materiałowa – Vol. 113 No. 6, pp. 620-623 Rodriguez J., Haro S., Velasco A., Colas R. (2000) ‘A metallographic study of aging in a cast heat-resisting alloy’, Materials Characterization, Vol. 45, pp. 25-32 Jasiński W. (2002) ‘Właściwości materiału rur katalitycznych reformera’ – Proceedings of the V International Conference Surface Treatments, 18 20 september 2002, Kule k/Częstochowy, Poland pp. 482-485 Jasiński W.( 2002), ‘The Changes of the Reforming Catalytic Tubes Material Structures’, ISSN 1392-1320 Materials Science (Medżiagotyra), Vol. 4, No. 8, pp. 399-402 W. Jasiński and P. 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