Microstructural and fracture analysis of aged cast duplex steel
The effect of increased carbon content and heat treatment parameters on the microstructure and selected properties of ferritic-austenitic duplex cast steel is discussed. Test results show that the cast steel microstructure after the solution heat treatment changes substantially with increasing carbo...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
2008
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| Cite this: | Microstructural and fracture analysis of aged cast duplex steel / D. Dyja, Z. Stradomski, A. Pirek // Проблемы прочности. — 2008. — № 1. — С. 133-136. — Бібліогр.: 9 назв. — англ. |
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| citation_txt | Microstructural and fracture analysis of aged cast duplex steel / D. Dyja, Z. Stradomski, A. Pirek // Проблемы прочности. — 2008. — № 1. — С. 133-136. — Бібліогр.: 9 назв. — англ. |
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| description | The effect of increased carbon content and heat treatment parameters on the microstructure and selected properties of ferritic-austenitic duplex cast steel is discussed. Test results show that the cast steel microstructure after the solution heat treatment changes substantially with increasing carbon content. Ageing after the solution heat treatment results in approx. 20% increase in hardness and a few-times decrease in impact strength. Fractographic examinations show thatfracture surfaces of specimens of steel with low carbon content are typically of transcrystalline ductile micromechanism. An increase in carbon content is accompanied by a decline in ductility areas, whilefracture of specimens is of mixed nature: ductile and brittle. After ageing, only cases of mixed fracture were observed.
Исследовано влияние повышенного содержания углерода и параметров термообработки на микроструктуру и некоторые свойства ферритоаустенитной литой двухфазной стали. Из экспериментальных результатов следует, что микроструктура литой стали после термической обработки на твердый раствор существенно изменяется при повышении содержания углерода. Процесс старения стали после термической обработки на твердый раствор приводит к примерно 20%- ному повышению твердости и снижению ударной прочности в несколько раз. Фрактографические исследования показывают, что для поверхностей разрушения образцов из стали с низким содержанием углерода характерным является транскристаллитный вязкий микромеханизм разрушения. Повышение содержания углерода сопровождается уменьшением удельной доли зон пластического разрушения и проявлением смешанного (хрупкого и вязкого) разрушения образцов. После старения стали наблюдался лишь смешанный характер разрушения.
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UDC 539. 4
M ic r o s tr u c tu r a l a n d F r a c tu r e A n a ly s is o f A g e d C a s t D u p le x S te e l
D . D y ja ,1a Z . S trad om sk i,1b and A . P irek 1,c
1 Czestochowa University o f Technology, Institute o f Materials Engineering, Czestochowa, Poland
a dyjad@mim.pcz.czest.pl, b zbigniew@mim.pcz.czest.pl, c pireka@mim.pcz.czest.pl
The effect o f increased carbon content and heat treatment parameters on the microstructure and
selected properties offerritic-austenitic duplex cast steel is discussed. Test results show that the cast
steel microstructure after the solution heat treatment changes substantially with increasing carbon
content. Ageing after the solution heat treatment results in approx. 20% increase in hardness and a
few-times decrease in impact strength. Fractographic examinations show that fracture surfaces o f
specimens o f steel with low carbon content are typically o f transcrystalline ductile micromechanism.
An increase in carbon content is accompanied by a decline in ductility areas, while fracture o f
specimens is o f mixed nature: ductile and brittle. After ageing, only cases o f mixed fracture were
observed.
K eyw o rd s : duplex cast steel, heat treatment, brittle fracture, carbides, im pact energy.
In trod uction . C hem ical com position o f cast alloyed duplex steels is selected, in
order to ensure the required properties v ia appropriate amount o f ferrite and austenite in
the microstructure. H ow ever, depending on the chem ical com position, conditions o f
thermal treatment and manufacturing technology intermetallic phases (о , %, л , R) and
carbides can cause increase o f brittleness and reduction o f corrosion resistance [1, 2]. A s
observed in literature and show n in numerous advertising materials o f casting com panies
this is prom oted by the trend to increase the carbon content above the value m ost often
presented in standards (C max = 0.03% ). H igher carbon content facilitates the handling o f
m etallurgical process (in particular, in casting shops w hich do not have secondary
m etallurgy) and has a favourable effect on erosion resistance o f duplex cast steels [3, 4].
H ow ever, an increased carbon content creates qualitative problem s related both to the
solidification course and processes during cooling o f the casing in the solid state, what has
been described in detail in [5, 6].
D espite technological d ifficulties related to casting propensity for cracking, the
optim um com bination o f m echanical properties w ith erosion wear resistance m akes that
the demand for this material perm anently increases, especia lly for the com ponents
operating in environm ent o f liquid solutions heavily polluted w ith solid particles [7].
Erosion-corrosion influence o f such environm ent is the reason o f costly breakdowns and
dow n tim es caused by premature wear o f com ponents. This applies, in particular, to
com ponents o f dewatering sets including m ainly pump im pellers, sleeves or elem ents o f
pipelines [8]. This problem is resolved, among others, by the use o f h igh-alloy F e-C r-N i
cast steels containing addition o f 3-4% o f copper, w hich increases resistance to acid
action and ensures obtaining o f precipitation hardening by £-Cu phase as a result o f ageing
at 480oC [9]. The aim o f this study w as determ ination o f the effect o f increased carbon
content on selected m echanical and plastic properties o f the solution heat-treated and aged
duplex cast steel.
M a ter ia ls and M ethodology . The chem ical com position (in m ass %) o f the
ferritic-austenitic duplex cast steels used for the present work is listed in Table 1. The cast
steel w as solution heat-treated in water after tw o-hour soaking at 1080oC and then aged at
480oC for 4 hours. Specim ens for optical m etallography (OM ) were chem ically etched in
a 30 g potassium ferricyanide + 30 g potassium hydroxide + 60 m l distilled water.
Hardness w as m easured b y the B rinell m ethod under a load o f 1838 N w ith a steel ball o f
© D. D Y JA , Z. STR A D O M SK I, A. P IR EK , 2008
ISSN 0556-171X. Проблемы прочности, 2008, № 1 133
mailto:dyjad@mim.pcz.czest.pl
mailto:zbigniew@mim.pcz.czest.pl
mailto:pireka@mim.pcz.czest.pl
D. Dyja, Z. Stradomski, and A. Pirek
a diameter o f 2 .5 mm. Charpy im pact energy w as m easured on Charpy V specim ens at
ambient temperature on a hamm er o f an initial energy o f 300 J. Fractography o f the
broken specim ens w as performed in a JEOL JSM 5400 scanning electron m icroscope.
T a b l e 1
Chemical Composition of Examined Cast Steels
Heat No. C Cr Ni Cu Mo Mn N Si S P
1 0.028 24.20 8.82 0.02 2.30 0.4б 0.0б8 0.85 0.010 0.011
2 0.040 24.70 б.74 3.11 2.22 0.88 0.140 0.88 0.012 0.017
З 0.055 24.40 б.71 3.08 2.40 0.14 0.085 0.81 0.020 0.020
4 0.0б0 24.70 б.91 3.00 2.90 0.14 0.078 0.73 0.018 0.019
5 0.090 24.00 8.02 2.б0 2.25 0.24 0.080 1.05 0.010 0.01б
б 0.120 25.00 б.95 2.85 2.5б 0.19 0.075 0.90 0.030 0.020
R esu lts. Exam ples o f the steel microstructure after the solution heat treatment from
1080°C/2 h/water are presented in Fig. 1. Cast steels from heat 1 -3 , containing C max =
0.055% feature a tw o-phase ferritic-austenitic microstructure w ith austenite grains
distributed in the ferritic matrix (Fig. 1a).
Fig. 1. Microstructure of the cast steel: (a) heat 1; (b) heat 4; (c) heat 6, after 1080°C/2 h/water.
A carbide eutectic (Fig. 1b and 1c), non-dissolved during the heat treatment, is
observed in the microstructure o f solution heat-treated cast steel w ith increased carbon
content (heat 4 -6 ); its volum e fraction increases from Ve = 0.03% (0.06% C for heat 4)
to Ve = 2.00% (0.12% C for heat 6) w ith carbon content increasing. Effects o f ageing at
480°C in the microstructure changes are not v isib le v ia optical m icroscopy. How ever, as a
result o f isothermal holding at this temperature, a spinodal decom position o f ferrite occurs
(w ith creation o f a phase, enriched in iron, and chromium-rich a phase) as w ell as
precipitation in the ferrite o f copper-rich £-Cu phase.
R esults o f m easurem ents o f the steel hardness and im pact energy after ageing
specified in Table 2 show a sm all, about 20%, increase in hardness as compared to the
solution heat-treated material w ith sim ultaneous clear decline in im pact energy. General
increase in the steel hardness after ageing is affected m ainly b y the increase in ferrite
m icrohardness related to spinodal decom position into a and a ' phase as w ell as to
precipitation o f copper-rich £-Cu phase. N otew orthy is very unfavourable influence o f
increased carbon content on cast steel im pact energy. A s show n in Table 2, the im pact
energy o f cast steel containing 0.028% carbon (heat 1) after solution heat treatment has to
160 J and falls to 10 J for cast steel containing 0.12% carbon (heat 6). The ageing at
480°C, causing a slight increase in hardness, results in a clear few -tim es decrease in the
im pact energy as com pared to solution heat-treated cast steel.
134 ISSN Ü556-171X. Проблемыг прочности, 2ÜÜ8, N 1
Microstructural and Fracture Analysis o f Aged Cast Duplex Steel
T a b l e 2
Results of Hardness, Microhardness, and Impact Energy of Investigated Steels
Process Heat 1 Heat 2 Heat 3
HB KV h v 0 HVy HB K V h v 0 HVy HB KV h v 0 HVy
Solutioning 2І5 І60 ЗЗ5 205 245 І48 З5З 216 242 142 350 214
Ageing 259 58 420 2І0 279 55 4З4 232 285 50 437 233
Heat 4 Heat 5 Heat 6
HB KV HV0 HVy HB K V h v 0 HVy HB K V h v 0 HVy
Solutioning 25І ІІ8 З48 2З0 258 З8 351 228 266 10 355 240
Ageing 298 28 4З9 260 З07 І9 445 239 313 6 450 248
Note. Values o f HVà and HVy correspond ferrite and austenite microhardnesses, respectively.
To explain microstructural origins o f changes in m echanical properties, selected
fracture surfaces o f broken im pact test specim ens were subjected to fractographic analysis
using SEM. The exam ples o f fracture surfaces observed are presented in Figs. 2 and 3.
Fig. 2. SEM microphotographs o f the steel: (a) heat 1; (b) heat 6; after 1080°C/2 h/water.
Fig. 3. SEM microphotograph o f the investigated steel after the ageing (heat 1).
For the steels w ith low carbon content after the solution heat treatment characteristic
ductile fracture is observed (Fig. 2a) and sulphide inclusions, m ost often o f spheroidal
shape, have been revealed on fracture surfaces. A n increase in carbon content in the cast
steel is accom panied by a decline in ductility areas, specim en fractures are o f m ixed
ductile and brittle nature (Fig. 2b). M orphology o f specim en fracture is subject o f
significant change after ageing. Two m echanism s o f cracking are observed on the
ISSN Ü556-171X. Проблемыг прочности, 2ÜÜ8, N І 135
D. Dyja, Z. Stradomski, and A. Pirek
surfaces: transcrystalline cleavage and ductile, the former one prevailing. A typical
exam ple o f m ixed fracture is presented in Fig. 3. N um erous faults and changes o f cracking
surfaces and on ly a few traces o f ductile cracking exist in elem entary interfaces.
C onclusions
1. The cast steel structure after the solution heat treatment changes substantially w ith
increasing carbon content. The steels containing C max = 0.055% feature a ferritic-
austenitic structure. In the microstructure o f solution heat-treated steel w ith increased
carbon content a carbide eutectic, non-dissolved during the heat treatment, is observed.
Isothermal holding at 480oC results in spinodal decom position o f ferrite w ith creation o f
a and a phases as w ell as precipitation in the ferrite o f £-Cu phases.
2. D uplex cast steel allow s obtaining very h igh im pact energy after the solution heat
treatment, reaching 160 J, how ever sm all fraction o f eutectic carbides in the cast steel
containing 0.06% C reduces the im pact strength to about 118 J. Once the carbide eutectic
creates a netw ork (in the steel containing 0.12% C) the im pact strength does not exceed
10 J.
3. A geing after the solution heat treatment results in approx. 20% increase in
hardness related to precipitation processes in the ferrite, sim ultaneous w ith a few -tim es
decrease in im pact energy.
4. Fractographic exam inations have show n that fractures o f specim ens o f cast steel
w ith low carbon content are typical ductile transcrystalline m icrom echanism . The size o f
ductile fracture ‘d im ples’ depends clearly on the size o f their initiators, w hich are pretty
large inclusions o f third-type sulphides and m uch sm aller precipitates o f carbides or
carbonitrides. A n increase in carbon content in the cast steel is accom panied by a decline
in ductility areas and fracture surfaces o f specim ens are o f m ixed nature, ductile and
brittle.
1. R. A. Perren, T. A. Suter, C. Solenthaler, et al., “Corrosion resistance o f super duplex stainless
steels in chloride ion containing environments: investigations by means o f a new
microelectrochemical method. II. Influence o f precipitates,” Corros. Sci., 43, 727-745 (2001).
2. C. J. Park, V. R. Shankar, and H. S. Kwon, “Effect o f sigma phase on the initiation and
propagation of pitting corrosion o f duplex stainless steel,” Corrosion, 61, No. 1, 76-83
(2005).
3. J. Tissier, D. Balloy, J. Dairon, et al., “Décarborution sous vide: une solution â la portée des
PME de fonderie,” Fonderie: Fondeur d ’Aujourd’hui, No. 246, 28-39 (2005).
4. W. Hubner and E. Leitel, “Peculiarities o f erosion-corrosion processes,” Tribology Int., 29,
No. 3, 199-206 (1996).
5. Z. Stradomski, S. Stachura, and D. Dyja, “Technological problems in elaboration o f massive
casting from duplex cast steel,” in: Stainless Steel World Conference&Expo, Maastricht,
Netherlands (2005), pp. 363-368.
6. Z. Stradomski and D. Dyja, “Influence o f carbon content on the segregation processes in
duplex cast steel,” Arch. Foundry Eng., 7, Issue 1, 139-142 (2007).
7. J. Peultier, F. Barrau, and J. P. Audouard, “Corrosion resistance o f duplex and superduplex
stainless steels for air pollution control process systems,” Stainless Steel World, 17, 45-55
(2005).
8. K. A. Bakken, “Cost effective materials selections - what is true?,” in: Stainless Steel World
Conference&Expo, Maastricht, Netherlands (2005), pp. 18-23.
9. D. Dyja and Z. Stradomski, “Quench ageing behavior o f duplex cast steel with nano-scale
e-Cu particles,” J. Achiev. Mater. Manufact. Eng., 20, Issue 1-2, 435-438 (2007).
Received 28. 06. 2007
136 ISSN 0556-171X. n poôëeu u npouuocmu, 2008, № 1
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| id | nasplib_isofts_kiev_ua-123456789-48431 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 0556-171X |
| language | English |
| last_indexed | 2025-12-02T11:47:34Z |
| publishDate | 2008 |
| publisher | Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| record_format | dspace |
| spelling | Dyja, D. Stradomski, Z. Pirek, A. 2013-08-19T14:26:41Z 2013-08-19T14:26:41Z 2008 Microstructural and fracture analysis of aged cast duplex steel / D. Dyja, Z. Stradomski, A. Pirek // Проблемы прочности. — 2008. — № 1. — С. 133-136. — Бібліогр.: 9 назв. — англ. 0556-171X https://nasplib.isofts.kiev.ua/handle/123456789/48431 539.4 The effect of increased carbon content and heat treatment parameters on the microstructure and selected properties of ferritic-austenitic duplex cast steel is discussed. Test results show that the cast steel microstructure after the solution heat treatment changes substantially with increasing carbon content. Ageing after the solution heat treatment results in approx. 20% increase in hardness and a few-times decrease in impact strength. Fractographic examinations show thatfracture surfaces of specimens of steel with low carbon content are typically of transcrystalline ductile micromechanism. An increase in carbon content is accompanied by a decline in ductility areas, whilefracture of specimens is of mixed nature: ductile and brittle. After ageing, only cases of mixed fracture were observed. Исследовано влияние повышенного содержания углерода и параметров термообработки на микроструктуру и некоторые свойства ферритоаустенитной литой двухфазной стали. Из экспериментальных результатов следует, что микроструктура литой стали после термической обработки на твердый раствор существенно изменяется при повышении содержания углерода. Процесс старения стали после термической обработки на твердый раствор приводит к примерно 20%- ному повышению твердости и снижению ударной прочности в несколько раз. Фрактографические исследования показывают, что для поверхностей разрушения образцов из стали с низким содержанием углерода характерным является транскристаллитный вязкий микромеханизм разрушения. Повышение содержания углерода сопровождается уменьшением удельной доли зон пластического разрушения и проявлением смешанного (хрупкого и вязкого) разрушения образцов. После старения стали наблюдался лишь смешанный характер разрушения. en Інститут проблем міцності ім. Г.С. Писаренко НАН України Проблемы прочности Научно-технический раздел Microstructural and fracture analysis of aged cast duplex steel Анализ микроструктуры и разрушения состаренной литой двухфазной стали Article published earlier |
| spellingShingle | Microstructural and fracture analysis of aged cast duplex steel Dyja, D. Stradomski, Z. Pirek, A. Научно-технический раздел |
| title | Microstructural and fracture analysis of aged cast duplex steel |
| title_alt | Анализ микроструктуры и разрушения состаренной литой двухфазной стали |
| title_full | Microstructural and fracture analysis of aged cast duplex steel |
| title_fullStr | Microstructural and fracture analysis of aged cast duplex steel |
| title_full_unstemmed | Microstructural and fracture analysis of aged cast duplex steel |
| title_short | Microstructural and fracture analysis of aged cast duplex steel |
| title_sort | microstructural and fracture analysis of aged cast duplex steel |
| topic | Научно-технический раздел |
| topic_facet | Научно-технический раздел |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/48431 |
| work_keys_str_mv | AT dyjad microstructuralandfractureanalysisofagedcastduplexsteel AT stradomskiz microstructuralandfractureanalysisofagedcastduplexsteel AT pireka microstructuralandfractureanalysisofagedcastduplexsteel AT dyjad analizmikrostrukturyirazrušeniâsostarennoilitoidvuhfaznoistali AT stradomskiz analizmikrostrukturyirazrušeniâsostarennoilitoidvuhfaznoistali AT pireka analizmikrostrukturyirazrušeniâsostarennoilitoidvuhfaznoistali |