K. WIŒNIEWSKA et al.: CORROSION OF THE REFRACTORY ZIRCONIA METERING NOZZLE ...
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CORROSION OF THE REFRACTORY ZIRCONIA METERING
NOZZLE DUE TO MOLTEN STEEL AND SLAG
KOROZIJA OGNJEODPORNE CIRKONSKE DOZIRNE [OBE
S STALJENIM JEKLOM IN @LINDRO
Klaudia Wiœniewska, Dominika Madej, Jacek Szczerba
AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Department of Ceramics and Refractories,
Al. A. Mickiewicza 30, 30-059 Kraków, Poland
kwis@agh.edu.pl
Prejem rokopisa – received: 2014-08-08; sprejem za objavo – accepted for publication: 2015-03-03
doi:10.17222/mit.2014.188
This paper presents a study on the phase composition and microstructure changes of a sintered Mg-stabilized zirconia metering
nozzle exposed to the corrosive effect of the molten steel and slag in a tundish for continuous casting for 30 h. A macroscopic
observation of the corroded material showed cracks and two zones that were distinguished with respect to colour. An X-ray
diffraction analysis showed that the dark layer was richer in stabilized ZrO2 than the light layer. After the corrosion test, the
nozzle had higher contents of MgO, SiO2, CaO, Al2O3 and Fe2O3 than the reference sample as evidenced by an X-ray
fluorescence analysis. Moreover, during the corrosion process, liquid steel and slag infiltrated the zirconia material, which was
confirmed with a SEM investigation. Along the hot face of the metering nozzle, the grains of zirconium oxide recrystallized
with a high-temperature structure of ZrO2 and dissolved MgO and CaO derived from the slag, stabilizing this phase.
Keywords: partially stabilized ZrO2, metering nozzle, corrosive effect of molten steel, refractories
^lanek predstavlja {tudijo fazne sestave in mikrostrukturnih sprememb sintrane, z Mg stabilizirane cirkonske dozirne {obe,
izpostavljene korozijskim vplivom staljenega jekla in `lindre po 30 urnem delovanju v vmesni ponovci pri postopku
kontinuirnega litja. Makroskopsko opazovanje korodiranega materiala je pokazalo razpoke in dve podro~ji, ki sta se razlikovali
po barvi. Rentgenska difrakcijska analiza je pokazala, da je bilo temnej{e podro~je bogatej{e s stabiliziranim ZrO2, kot pa
svetlej{e podro~je. Rentgenska fluorescen~na analiza je pokazala, da ima {oba po korozijskem preizkusu, v primerjavi z
referen~nim vzorcem, vi{jo vsebnost MgO, SiO2, CaO, Al2O3 in Fe2O3. Poleg tega sta, med procesom korozije, teko~e jeklo in
`lindra prodirala v cirkonijev material, kar je bilo potrjeno s SEM preiskavo. Vzdol` vro~ega ~ela dozirne {obe so zrna
cirkonijevega oksida rekristalizirala v visoko temperaturno strukturo ZrO2, raztopila MgO in CaO, ki izvirata iz `lindre in
stabilizirala to fazo.
Klju~ne besede: delno stabiliziran ZrO2, dozirna {oba, korozijski vpliv staljenega jekla, ognjevarna gradiva
1 INTRODUCTION
Partially stabilized ZrO2 (PSZ) materials are widely
used as refractories owing to their high refractoriness,
high corrosion resistance and good thermal-shock resis-
tance. In the metal industry, the most popular are Mg-
and Ca-stabilized zirconia and Y-stabilized zirconia,
applied in the production of thermal-barrier coatings. It
is commonly known that during the corrosion process of
PSZ due to molten steel and slag, a cubic or tetragonal
phase is destabilized and transformed into monoclinic
zirconia, related to the microcrack formation1. The
destabilization process is associated with the reaction of
SiO2 from slag with CaO and MgO from the zirconia
material2,3. Zirconium oxide is used for metering nozzles
in the continuous casting of steel2,4,5. A metering nozzle
is mounted to the bottom of a tundish and used to control
the flow of molten steel. The working temperature of a
metering nozzle is up to 1600 °C.
The main factors causing the damage of the metering
nozzle are the erosion of the liquid flowing steel, the
infiltration of the molten steel and slag into the refrac-
tory material, the slag composition and the rapid tem-
perature changes2. The chemical composition of the slag
is based on the MgO-CaO-SiO2-Al2O3 system, but the
proportion between the components depends on the type
of the produced steel.
In this paper the phase composition and microstruc-
ture changes of a sintered Mg-stabilized zirconia meter-
ing nozzle, exposed to the corrosive effect of the molten
low-carbon steel and slag in a tundish for continuous
casting for 30 h were studied.
2 EXPERIMENTAL METHOD
The procedure of this experiment included the
following steps: preparing a sintered Mg-stabilized
zirconia metering nozzle under industrial conditions, a
corrosion test in a tundish for continuous steel casting
and a post-experiment study of the zirconia metering
nozzle.
The metering nozzle was exposed to a corrosive envi-
ronment for 30 h. The factors influencing the corrosion
of the nozzle were the molten steel and slag. After the
corrosion test, the corroded nozzle (designated as CN)
Materiali in tehnologije / Materials and technology 50 (2016) 1, 29–32 29
UDK 666.76:620.193 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(1)29(2016)
was studied and compared with the reference sample
(designated as RS), which was a zirconia metering
nozzle before serving. For the XRF, XRD and SEM/EDS
investigations, the samples were taken from the middle
of the heights of the metering nozzles.
The X-ray fluorescence (XRF) method was used to
determine the contents of oxides such as MgO, SiO2,
CaO, Al2O3 and Fe2O3. An Axios mAX wavelength dis-
persive X-ray fluorescence spectrometer from PANaly-
tical was used for this study. The crystalline phases were
identified with X-ray diffraction using Cu-K radiation
on a FPM Seifert XRD7 diffractometer with the Bragg-
Brentano geometry, while the quantitative composition
was determined with the Rietveld method. The dark zone
(designated as CN-D) and the light zone (designated as
CN-L) of the corroded nozzle were examined separately.
The microstructure was observed using a scanning elec-
tron microscope (SEM) coupled with an energy-disper-
sive X-ray system (EDS). The ultra-high-definition
NOVA NANO SEM 200 was used for this purpose.
3 RESULTS
During a macroscopic observation of the corroded
material, cracks and two zones were distinguished with
respect to colour. The dark zone was strongly corroded
due to molten steel and slag (the hot-zone refractory
material) while the light zone remain unchanged. Figure
1 shows a photograph of the metering nozzle exposed to
the corrosive effect of the molten steel.
The XRF analysis confirmed that the main compo-
nent of the nozzle was zirconium oxide; the content of
ZrO2 was about 90 % in both CN and RS samples. More-
over, the XRF study revealed content changes in the
oxides such as MgO, SiO2, CaO, Al2O3 and Fe2O3. After
the corrosion test, sample CN had higher contents of
these oxides, which is illustrated in Figure 2.
The XRD analysis with the Rietveld quantitative-
phase analysis showed that the dark layer (CN-D) was
richer in the stabilized ZrO2 than the light layer (CN-L)
or the RS sample. In the CN-D sample, the content of the
stabilized zirconium oxide was 11.5 %, while in the
K. WIŒNIEWSKA et al.: CORROSION OF THE REFRACTORY ZIRCONIA METERING NOZZLE ...
30 Materiali in tehnologije / Materials and technology 50 (2016) 1, 29–32
Figure 4: Microstructure of test sample RS
Slika 4: Mikrostruktura preizkusnega vzorca RS
Figure 1: Refractory zirconia metering nozzle exposed to the corro-
sive effect of the molten steel and slag
Slika 1: Ognjevarna cirkonska dozirna {oba, izpostavljena korozijske-
mu vplivu staljenega jekla in `lindre
Figure 2: Contents of the secondary oxides in test samples RS and CN
(XRF analysis)
Slika 2: Vsebnost sekundarnih oksidov v preizkusnih vzorcih RS in
CN (XRF-analiza)
Figure 3: XRD patterns of test samples RS, CN-L and CN-D
Slika 3: Rentgenogrami preizkusnih vzorcev RS, CN-L in CN-D
CN-L sample, it was 1 % and in the RS sample, it was
3.3 %. The XRD results are shown in Figure 3.
Figures 4 to 6 show the microstructures of test sam-
ples RS, CN-L and CN-D, respectively. The microstruc-
ture of the CN-L sample is similar to the reference
sample. The grains of zirconium oxide are surrounded by
a silicate phase. The microstructure of sample CN-D
shows micro-fracturing along the hot-face of the nozzle.
The crystallites of zirconium oxide are bigger than in
samples CD-L and RS.
4 DISCUSSION
In the reference sample, the main crystalline phases
were monoclinic ZrO2 and Mg-stabilized zirconium
oxide, which were confirmed with the XRD analysis.
The SEM/EDS investigation showed that the secondary
phase was forsterite (Mg2SiO4). However, the content of
forsterite was too low to be detected on the XRD pattern.
After the operation, there were two zones in the nozzle, a
corroded and an uncorroded zone. The XRD analysis
with the Rietveld method confirmed that test samples
CN-L and RS were not significantly different in their
phase composition. The biggest changes in the phase
composition were found in the corroded zone (CN-D),
where the content of stabilized zirconia was the highest.
The obtained results are not in agreement with the
earlier results presented in2,3,5. The stabilization process
of zirconium oxide can be explained with the dissolution
of MgO and CaO derived from the slag in zirconia at a
high temperature. The XRF and SEM/EDS investigations
confirmed that, at the temperature of the corrosion test,
the molten slag and steel penetrated the zirconia nozzle.
As can be seen in Figure 6, the microstructure of
CN-D was changed. The fine grains of ZrO2 recry-
stallized at the corrosion-test temperature, which was
observed as an increase in their dimension. The high-
temperature phase of zirconium oxide was stabilized due
to MgO and CaO, which dissolved in ZrO2. The
micro-fractures along the hot face of the metering nozzle
and the macroscopic cracks present in the corroded
nozzle could be attributed to the rapid temperature
changes during the corrosion test.
K. WIŒNIEWSKA et al.: CORROSION OF THE REFRACTORY ZIRCONIA METERING NOZZLE ...
Materiali in tehnologije / Materials and technology 50 (2016) 1, 29–32 31
Figure 6: Microstructure of test sample CN-D obtained with the EDS analysis; Spot 1 – zirconium oxide, Spot 2 – slag, Spot 3 – iron
Slika 6: Mikrostruktura preizkusnih vzorcev CN-D z EDS-analizo; to~ka 1 – cirkonov oksid, to~ka 2 – `lindra, to~ka 3 – `elezo
Figure 5: Microstructure of test sample CN-L obtained with the EDS analysis; Spot 1 – zirconium oxide, Spot 2 – forsterite
Slika 5: Mikrostruktura preizkusnega vzorca CN-L z EDS-analizo; to~ka 1 – cirkonov oksid, to~ka 2 – forsterit
5 CONCLUSION
The results of the corrosion of a refractory zirconia
metering nozzle tested under industrial conditions are re-
ported. During the service in a continuous-casting
tundish, the molten steel and slag infiltrated the zirconia
nozzle. A rapid change in the temperature had a signifi-
cant influence on the formation of cracks and micro-
fractures.
Along the hot face of the zirconia nozzle, the grains
of ZrO2 recrystallized with a high-temperature structure.
The oxides present in the slag dissolved in zirconia and
stabilized the ZrO2 phase.
Acknowledgments
This work was supported by grant no. INNOTECH-
K2/IN2/16/181920/NCBR/13 of the National Centre for
Research and Development.
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K. WIŒNIEWSKA et al.: CORROSION OF THE REFRACTORY ZIRCONIA METERING NOZZLE ...
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