Volume 7 Preprint 37
Comparison of Oxidation of Ferritic-Martensitic Steel EP-823 and Armco-Fe in Pb Melt Saturated by Oxygen
O. Yeliseyeva and V. Tsisar
Keywords: Steel, Armco-Fe, Pb melt, Oxidation
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Volume 7 Paper 37
FerriticMartensitic Steel EP-823 and Armco-Fe in Pb
Melt Saturated by Oxygen
O. Yeliseyeva, V. Tsisar
Physico-Mechanical Institute of National Academy of Sciences of
Ukraine, 5, Naukova St., Lviv 79601, Ukraine.
The kinetic peculiarities of scale formation on the surface of ferriticmartensitic steel EP-823 and Armco-Fe in the Pb melt saturated by
oxygen (CO[Pb] = 6
10-3 wt %) at 650ºС were elucidated. It was
determined that the corrosion rate measured as decreasing of
thickness of specimens is similar for Armco-Fe and steel EP-823,
however the scale formed on the steel is thicker then that one on the
Armco-Fe. Scale on the steel surface has multiplayer morphology,
consists of magnetite, totally penetrated by Pb and includes also the
complex compounds n PbO
m Fe2O 3 – plumboferrites. The scale
formed on the surface of Armco-Fe consists of thin outer magnetite
layer followed by the thick inner wüstite one. Contrary to the steel the
scale formed on the Armco-Fe is compact and contains neither Pb nor
plumboferrites. The possible mechanisms of scales formation were
Keywords: Steel, Armco-Fe, Pb melt, Oxidation.
This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science
and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at
http://www.umist.ac.uk/corrosion/jcse in due course. Until such time as it has been fully publish ed it
should not normally be referenced in published work. © UMIST 2004.
Compatibility of structural materials and heavy liquid metals (Pb, PbBi) proposed as candidate heat-transfers for fast reactors and
accelerator driven systems is one of main problems of state-of-the-art
reactor materials knowledge . The physical-chemical interaction
between lead melt and stainless steel depends on the concentration of
oxygen impurity in the liquid metal. When oxygen concentration in
lead melt is low (CO[Pb] 10-7 wt%) the liquid medium is an aggressive
dissolvent of main steel’s components (Ni, Cr, Fe) and vice versa when
concentration of oxygen is high (10 -7 CO[Pb] 10-3 wt%) lead melt
becomes strong oxidizing medium [2, 3]. Operation experience of the
Pb-Bi eutectic as a heat-transfer in nuclear reactors of submarines
testifies that the high corrosion aggressiveness of lead melt can be
sufficiently suppressed by in-situ inhibition of liquid metal by oxygen
impurity under restricted concentration diapason (CO[Pb] 10 -7106 wt %) . It allows to form on the steels surface the Me3O 4 protective
oxide layer (Me: Fe, Cr) which inhibits the dissolution of steel’s
components into the melt . The intensive experimental works are
under performing in the leading research institutions of Russia,
European Union, USA and Japan [1-13]. In spite of the heightened
interest to the problem of compatibility of structural materials with the
melts of heavy metals (Pb, Pb-Bi) the obtained results remain very
scarce and therefore the nature of interaction in the complex system
Fe[Cr,Ni,Si]/Pb[O] under various temperature - oxygen concentration
conditions has not been elucidated yet. This paper is dedicated to the
revealing of the peculiarities of oxidation of ferritic-martensitic steel
EP-823 and model material – Armco-Fe in stagnant lead melt
saturated by oxygen at 650
2. Experimental Conditions
The specimens (1051 mm) of steel ЕP-823 (wt. %: 0,17С; 2,04Si;
0,74Mn; 13,46Cr; 1,60Mo; 0,19W; 0,2V; 0,2Nb; 0,28Ni; 0,094N2) and
Armco-Fe were made of sheets. After thermal treatment (EP-823:
vacuum annealing at 1050
C for 15 min vacuum tempering at 750
for 30 min; Armco-Fe: vacuum annealing at 700
C for 30 min)
specimens were placed in the alumina crucibles then filled by lead at
C. The corrosion tests were carried out at 650
C. The liquid lead
was saturated by oxygen since Pb-oxides were observed on the free
surface of the melt. Accordingly to lgCO[Pb]max=3,2-5000/T  the
oxygen concentration in melt was 6
10-3 wt %. After exposures
samples were extracted from the melt quickly to save the hightemperature state of scale. The cross-sections were examined by
optical (OM) to measure the thickness of scale and non-oxidized
matrix. In order to estimate the direction of scale growing the initial
interface between solid metal and liquid metal (X=0) was marked on
the scheme obtained owing to microscope measuring (Fig. 1).
Figure 1. Scheme of determination of initial interface (X=0)
solid metal / Pb melt on the cross sections.
Scanning electron microscopy (SEM), electron probe microanalysis
(EPMA) and X-ray diffraction analysis (XRD) using Cu-K radiation
(0.052Ө step) were used to determine the element and phase
composition of scale. Microhardness was measured under the loads 20
and 50 g.
Fig. 2 shows the oxidation kinetics of Armco-Fe and steel EP-823 at
650°Сin Pb melt saturated by oxygen. Under herein conditions of test,
the scale formed on the surface of steel EP-823 is thicker then that
one formed on the Armco-Fe while the decreasing of thickness of
specimens is similar. The scales on the both materials grow in two
directions with regard to the initial interface X=0: towards the melt
and solid metal. The scale formed on the Armco-Fe has two equal
outer and inner parts. Contrary to the Armco-Fe the outer part of the
steel’s scale is thicker then the inner one and this difference is being
increased with time.
Figure 2. Oxidation kinetics of Armco-Fe and steel EP-823 in Pb melt
saturated by oxygen at 650°С.
The scale formed on the surface of Armco-Fe is sufficiently compact,
though the inner half of scale is porous (Fig. 3 a). In BE imaging the
white contrast of Fe-matrix is changed by the grey color of scale upper
part of which is taupe-colored. The microhardness of scale is averaged
4,5 GPa that corresponds to the hardness of wüstite and/or magnetite
(4÷5.5 GPa). In spite of the general uniform growing of scale into the
matrix the wüstite / matrix interface looks like fjord (has jagged form)
(Fig. 3 b). Similarly to the pores the white islands of non-oxidized Fe
are situated only in the inner half of scale growing towards the matrix
(Fig. 3 b). In turn, the ellipse-shape oxide precipitates both big and
small are observed in the matrix (Fig. 3 c). Such interosculation of
phases, as well as the jagged form of the interface, provides the good
scale’s adhesion and mass exchange of reagents and, as a result,
ensures the intensive growth of scale (~ 0,8 µm/h). It should be
noticed that Pb does not penetrate into the scale, although it contains
the pores. It testifies once more that scale is impervious to liquid
Figure 3. Scale microstructure ( a, b) and elements distribution in the
vicinity of interface “scale - matrix” (c) of Armco-Fe specimen after
exposure to Pb melt saturated by oxygen at 650
Сfor 100 h.
Х= 0 – initial interface “solid metal / melt”.
Accordingly to XRD analysis the upper part of scale consists of
magnetite (Fe3O4) (Fig. 4 а). The peaks of Pb are present in the XRD
pattern because of residuals of solidified Pb on the scale surface. The
scale was mechanically detached from the specimen surface to study
the phase composition of inner part of scale by XRD. The inner part of
scale consists of wüstite (FeO) (Fig. 4 b). Thus, the XRD result of inner
and outer parts of scale correlates with the atomic contrast of scale
(Fig. 3 a), which testifies that the ratio of wüstite and magnetite layers
is 10:1. Haematite that is formed on pure iron under air oxidation is
not detected in the composition of scale formed in liquid Pb. It could
be seen from the image contrast that precipitates of magnetite are
situated in the bulk of wüstite close to the wüstite / magnetite
Figure 4. XRD patterns of outer (a) and inner (b) surface of scale
formed on the Armco-Fe specimen in the Pb melt saturated by oxygen
Сfor 500 h (CuK).
Contrary to the Armco-Fe the scale formed on the steel surface is
totally penetrated by Pb (Fig. 5 a). The porous belts parallel to the
interface are observed in the scale, especially in inner part at the
scale / matrix interface. It was revealed by EPMA that scale consists of
the repetitive layers: Fe-enriched oxide layers alternates with layer
enriched by Cr, Si and Pb (Fig. 5 b, c). The redistribution of Cr is
observed in the steel matrix only near the scale / matrix interface
(Fig. 5 c). It should be noticed that Pb is observed in the scale but does
not penetrate into the bulk of steel. Microhardness value of scale is
1 ÷ 3,5 GPa that does not correspond to the hardness of magnetite
(~ 5 GPa) while the microhardness of steel matrix is not changed with
time and averages 2,8 GPa. In spite of the fact that the scale is thick,
multilayered and contained free Pb, it is holistic and adheres well to
the steel surface.
Accordingly to the XRD analysis the scale consists of magnetite mainly
(Fig. 6). The peaks of free Pb and its oxides and complex compounds
m Fe2O 3 - plumboferrites are observed also in the XRD pattern.
Figure 5. Microstructure (a) and elements distribution in the scale (b)
and near “scale / matrix” interface (c) of steel EP-823 specimen after
exposure to Pb melt saturated by oxygen at 650
Сfor 50 h.
The thickness of the specimens of both investigated materials are
decreased substantially as a result of intensive oxidation. The
corrosion rates are almost the same: 3.0 and 3.82 mm / year for
Armco-Fe and steel EP-823 correspondingly.
Distinction in kind of oxidation of specimen’s edges of Armco-Fe and
steel EP-823 was observed (Fig. 7). The specimen’s edges of Armco-Fe
are covered completely by scale, whereas the edges on the steel
specimens are uncovered. Such configuration of the scale on the
specimen’s edges can be as evidence that the formation of scales on
the Armco-Fe and steel EP-823 in liquid Pb saturated by oxygen
Figure 6. XRD pattern of scale formed on the steel EP-823 specimen in
the Pb melt saturated by oxygen at 650
Сfor 500 h.
M – magnetite, PF – plumboferrite (CuK).
Figure 7. Cross section of edges of Armco-Fe (a) and steel EP-823 (b)
specimens exposured to oxygen-saturated Pb melt at 650
C for 100 h.
When thermodynamic activity of oxygen in the liquid Pb aO → 1 the
clusters [Pb-O] appear in the melt . These clusters on a par with
the solute [O]-atoms can deposit on the surface of oxidized metal (FeArmco or steel). The following chemical reaction between growing
oxide and adsorbed components depends on the activity of Fe-cations
(a Fe) at the oxide / melt interface. If a Fe is high enough the next
reactions take place mainly:
Fe--+[PbO]→FexO y+Pb and Fe--+[O]→FexOy
Thus, magnetite (or wüstite-magnetite) scale grows during oxidation.
The lack of Fe-cations (a Fe→0) provokes reaction between [Pb-O]clusters and Fe-oxides:
FexOy + [Pb-O]→FexPbyO z
Thus the plumboferrite layer appears.
Plumboferrites were detected in the composition of the scale formed
on the steel EP-823. Contrary to the steel the scale formed on the
Armco-Fe does not contain plumboferrites and is impervious to the
liquid metal. The similar result was observed after exposure of pure Fe
to oxygen-saturated Pb-Bi eutectic (CO[Pb-Bi] =1.2
10-3 mass %) at 550
for 500 h . As it can be seen from the micrograph presented in 
the scale (~ 70 µm) is free from Pb and Bi and possesses by good
adhesion to matrix. Authors do not give a composition of the scale,
though it is reasonably to suppose that the scale consists of
Symmetrical growing of scale with regard to the initial interface X=0,
arrangement of pores and non-oxidized incorporations of iron in the
inner part of scale mainly allow to suppose that structural defects are
of primary importance in the diffusion processes of scale growing. The
role of structure defects becomes more evident under taking into
account the next considerations: the bulk diffusion of oxygen is
impossible because of low oxygen solubility in the iron lattice; both
magnetite and wüstite are p -type oxides where Fe-cations diffuse
Flow of Fe-cations towards the melt causes the growth of scale over
the initial interface X=0. Here well-known cation mechanism of scale
growth like in gas medium is realized. As a result, the opposite flow of
Fe -vacancies towards the matrix is initiated. It should be emphasized
that besides of cation flow for scale growth the additional flow of Featoms towards the melt is necessary in order to support the
equilibrium state between the liquid metal and surface of oxidizing
metal. That means that opposite flow of cation vacancy towards the
matrix becomes stronger as well in comparison with oxidation in gas
medium. The non-equilibrium vacancies deposit at the structural
defects (grain boundaries, sub-boundaries etc.) and coalesce. In such
manner the network of micro-pores allowing the non-regular oxygen
diffusion into the matrix is formed. Formation of pores under the
oxide / matrix interface causes the dissociation of outer oxide and
diffusion of oxygen along micro-channels. In this way the scale grows
towards the melt and matrix simultaneously. Owing to high activity of
iron ( aFe) the [Pb-O]-clusters are being reduced permanently on the
scale surface. As a result the scale does not contain Pb.
Therefore, in spite of the thermodynamics the kinetic factor is primary
of significance. Permanent moving of cations prevents the formation of
plumboferrites (Fe xPbyOz ) and the scale impervious for liquid metal
grows on the surface of Armco iron (Fig. 2).
With respect to steel EP-823 it was reported [9-11, 13] that under
lower temperatures and oxygen concentrations in the melt the scale
formed on the steel surface consists of outer – Fe 3O4 and inner
(Fe, Cr)3O 4 oxide layers and inner oxidation zone where Cr and / or Si
are oxidized selectively. Moreover it should be noticed that outer and
inner oxides look like mirror image of each other that testifies about
their interdependent growing .
Under herein test conditions the scale formed on the EP-823 consists
of repetitive layers. It seems this layer has the sub-layers enriched by
Fe alternating with areas enriched by Cr, Si and Pb (Fig. 5) and reminds
the double oxide layer reported in [9-11, 13]. Therefore, it is
reasonably to suppose that behavior of steel EP-823 in Pb melt look
like cyclic corrosion in gaseous medium. During each cycle the thin
double oxide layer grows accordingly to the cation-vacancy
mechanism described above for Armco-Fe. Due to active alloying
elements (Si, Cr), high temperature and oxygen activity in the melt
(T = 650ºC, a O = 1) The protective double oxide layer could be formed
very quickly. Formation of inner spinel (Fe, Cr)3O 4 enriched by Si
hampers effectively the iron diffusion towards the melt ( aFe=0). Thus
the clusters [Pb-O] absorbed on the oxidizing steel’s surface become
more active and can react with outer magnetite as well as with inner
spinel according to state diagram . Because of transformation of
spinel layer into plumboferrite the moving of Fe-cations towards the
melt renewals and the process of inner spinel and outer magnetite
formation repeats. In turn, the increasing of Fe activity in the scale
leads to the dissociation of plumboferrite and appearance of free Pb in
Future investigation should be carried out in order to specify the
mechanism of interaction. Especially the questions: why the scale on
the steel’s surface keeps integrity at high temperature in spite of free
Pb in its structure and why the scale does not cover the edges of steel
specimen (Fig. 7) should be answered.
Very intensive oxidation of cladding candidate material for fast
reactors - ferritic-martensitic steel EP-823 in Pb melt saturated by
oxygen underline once more the necessity of keeping of the oxygen
content in the melt in the narrow concentration range (CO[Pb] 10710 -6 wt %) to suppress on the one hand the steel’s components
dissolution and from the other hand to prevent their intensive
oxidation and loop contamination by PbO oxides [4, 13].
The kinetic peculiarities of scale formation on the surface of ferriticmartensitic steel EP-823 and Armco-Fe in the Pb melt saturated by
oxygen (CO[Pb] = 6
10-3 wt %) at 650ºСwere elucidated.
The corrosion of Armco-Fe and steel EP-823 as a function of
decreasing of specimens thickness is almost similar, while the scale
formed on steel is thicker in comparison with that on the ArmcoFe;
The phase composition and morphology of scales formed on the
investigated materials differ entirely. The spongy scale consisting of
magnetite and plumboferrites, totally penetrated by Pb is formed
on the steel surface. Contrary to the steel the scale formed on the
Armco-Fe is compact, consists of magnetite and wüstite and
contains neither Pb nor plumboferrites. Pb does not penetrate into
the matrix of investigated materials and was observed only in the
scale formed on the steel;
The cation-vacancy model of scale growing on the Armco-Fe and
steel EP-823 in Pb[O] melt taking into account the participation of
defects (cation vacancies) in diffusion processes, dissociation of Feoxides at the “scale/matrix” interface, existence of the [Pb-O]
clusters in the Pb melt and its adsorption on the oxidizing surface
of solid metal is discussed.
1. ‘Power reactors and sub-critical blanket systems with lead and
lead-bismuth as coolant and/or target material’, IAEA-TECDOC1348, 224 p., 2003.
2. ‘Corrosion resistance of structure materials in lead coolant with
reference to reactor installation BREST.OD.300’, A. Roussanov,
V. Troyanov, G. Jachmenev, A. Demishonkov, IAEA-TECDOC-1348,
pp. 122-124, 2000.
3. ‘Issues of the technology of heavy liquid-metals heats transfers
(lead-bismuth, lead)’, B.F. Gromov, Y.I. Orlov, P.N. Martynov,
V.A. Gulevsky, Proceedings of Heavy Liquid Metal Coolants in
Nuclear Technology-HLMC’98, Obninsk-1999, Russia, 2, pp. 92107, 1999. (in Russian)
4. ‘Oxide protection of materials in melts of lead and bismuth’
Shmatko and А.Е. Rusanov, Materials Science, 36, 5, pp. 689 –
5. ‘Behaviour of materials for accelerator driven systems in stagnant
molten lead’, G. Benamati, P. Buttol, V. Imbeni, C. Martini,
G. Palombarini, Journal of Nuclear Materials, 279, 2-3, pp. 308316, 2000.
6. ‘Influence of temperature on the oxidation/corrosion process of
F82Hmod. martensitic steel in lead–bismuth’, D.G. Briceño, L.S.
Crespo, F.J. Martín Muñoz, F.H. Arroyo, Journal of Nuclear
Materials, 303, 2-3, pp. 137-146, 2002.
7. ‘Results of steel corrosion tests in Flowing liquid Pb/Bi at 420–600 C
after 2000 h’, G. Muller, A. Heinzel, J. Konys et. al, Journal of
Nuclear Materials, 301, 1, pp. 40-46, 2002.
8. ‘Corrosion studies in liquid Pb-Bi alloy at JAERI: R D program and
first experimental results’, Y. Kurata, M. Futakawa, K. Kikuchi et
al., Journal of Nuclear Materials, 301, 1, pp. 28-34, 2002.
9. ‘Corrosion behavior of steels in flowing lead-bismuth’, F. Barbier,
A. Rusanov, Journal of Nuclear Materials, 296, 1-3, pp. 231-236,
10. ‘Compatibility tests of steels in flowing liquid lead-bismuth’,
F. Barbier, G. Benamati, C. Fazio, A. Rusanov, Journal of Nuclear
Materials, 295, 2-3, pp. 149-156, 2001.
11. ‘Temperature effect on the corrosion mechanism of austenitic and
martensitic steels in lead-bismuth’, G. Benamati, C. Fazio,
H. Piankova, A. Rusanov, Journal of Nuclear Materials, 301, 1, pp.
12. ‘Corrosion behaviors of US steels in flowing lead–bismuth eutectic
(LBE)’, J. Zhang, N. Li, Y. Chen, A.E. Rusanov, Journal of Nuclear
Materials, 336, 1, pp. 1-10, 2005.
13. ‘Changes in phase composition of an oxide film on EP-823 steel in
contact with stagnant lead melt’, O.I. Eliseeva, V.P. Tsisar,
V. M. Fedirko, Ya. S. Matychak, Materials Science, 40, 2, pp. 260269, 2004.
14. ‘Structure, atomic dynamics, thermodynamics and impurity state of
melts of lead and bismuth’, V. A. Blohin et al., Review, IPPE-0290,
76p., 2000. (in Russian)
15. ‘Kinetic model of stainless steels oxidation in Pb melts’,
O. Yeliseyeva, G. Benamati, V. Tsisar, CD-ROM of Eurocorr 2005,
16. ‘State diagrams of systems of refractory oxides’, Issue 5, part 4,
1988, 348 p. (in Russian)