Materials Science and Engineering A 435–436 (2006) 258–265
Corrosion performance of heat resistant alloys in
Na
2
SO
4
–V
2
O
5
molten salts
J.G. Gonzalez-Rodriguez
a,∗
, S. Haro
b
, A. Martinez-Villafa˜ ne
c
,
V.M. Salinas-Bravo
d
, J. Porcayo-Calderon
d
a
Universidad Autonoma del Estado de Morelos, FCQI-CIICAP, Av. Universidad 1001,
Col. Chamilpa, 62210-Cuernavaca, Mor., Mexico
b
Universidad Aut´ onoma de Zacatecas, Zacatecas, Mexico
c
CIMAV, Miguel de Cervantes 120, Complejo Ind. Chih., Chihuahua, Mexico
d
Instituto de Investigaciones El´ ectricas, Cuernavaca, Mor., Mexico
Received 5 January 2006; received in revised form 26 June 2006; accepted 26 June 2006
Abstract
The corrosion resistant of three heat resistant alloys in molten vanadium pentoxide (V
2
O
5
), sodium sulfate (Na
2
SO
4
) and 80(mol%)
V
2
O
5
–20Na
2
SO
4
has been evaluated using the weight loss technique. Materials included Fe–25Cr–35Ni–0.45C, Fe–35Cr–45Ni with 0.12 and 0.45C
alloys. Temperatures included 600, 700 and 800
◦
C for V
2
O
5
and the 80V
2
O
5
–20Na
2
SO
4
mixture, and 800, 900 and 1000
◦
C for Na
2
SO
4
. The tests
were supplemented by detailed electronic microscopy and microanalysis studies. In all cases, the least resistant alloy was the Fe-25Cr–35Ni–0.45C
one whereas the most resistant was the Fe–35Cr–45Ni–0.12C one. The results are discussed in terms of the acidic dissolution of the external
protective Cr
2
O
3
, Al
2
O
3
and SiO
2
layers, by the salts and internal sulfidation.
© 2006 Published by Elsevier B.V.
Keywords: Hot corrosion; Heat resistant alloys; Acidic fluxing
1. Introduction
Hot corrosion is a major failure mode for high temperature
components of many engineering systems such as aircraft and
land-bases gas turbines, fuel oil and coal operated high tempera-
ture power generating devices, coal gasifiers, molten carbonates
fuel cells, etc. This accelerated attack results from condensa-
tion of films containing molten salts such as sulfates, chlorides,
vanadates, carbonates, etc. Particularly, vanadium (V), sodium
(Na), and sulfur (S) are the common impurities of low grade
petroleum fuel used in oil-fired power stations. During com-
bustion, vanadium is oxidized to form different oxides, among
which vanadium pentoxide (V
2
O
5
) is the most common and
forms several compounds of low melting temperature while sul-
fur is involved with sodium and make sodium sulfates [1]. These
compounds make low eutectic salts deposits on the materials
known as “oil ash”.
∗
Corresponding author. Tel.: +52 77739 7084; fax: +52 777 329 7084.
E-mail address: ggonzalez@uaem.mx (J.G. Gonzalez-Rodriguez).
A significant number of Nickel (Ni)–base alloys have been
developed to meet the many demands and applications involv-
ing high temperature corrosive environments such as vanadium
pentoxide (V
2
O
5
), sodium sulfate (Na
2
SO
4
), lithium carbon-
ate (LiCO
3
), potassium carbonate (K
2
CO
3
), sodium chloride
(NaCl), sulfur dioxide (SO
2
), magnesium chloride (MgCl), etc.
By adding adequate amounts of chromium (Cr), aluminum (Al)
or silicon (Ni) to form a protective scale of chromia (Cr
2
O
3
),
alumina (Al
2
O
3
), or silica (SiO
2
), these alloys can be highly
resistant to vanadium (V), sulfur (S)and oxygen (O) attack at
elevated temperatures. Fe–Cr–Ni alloys also meet these require-
ments and some of them are exposed to multioxidant species
containing appreciable partial pressure of sulfur and low partial
pressure of oxygen, or environments where sulfur- or vanadium-
containing molten salts are present.
It is well known, however, that in S-containing environments,
where sulfidation problems are potentially dangerous, for nickel
(Ni) contents higher than 40 wt.% the alloys are more susceptible
to this kind of attack, and decreasing the Ni contents, normally
reduces this risk. The sulfidation behavior of various alloy sys-
tems (e.g. Cr–steels, Fe–Cr alloys, and austenitic stainless steels)
0921-5093/$ – see front matter © 2006 Published by Elsevier B.V.
doi:10.1016/j.msea.2006.06.138