Corrosion resistance of stainless steels during thermal cycling in alkali nitrate molten salts. Page: 3 of 39
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Printed August 2001
CORROSION RESISTANCE OF STAINLESS STEELS DURING
THERMAL CYCLING IN ALKALI NITRATE MOLTEN SALTS
R. W. Bradshaw
Materials Chemistry Department
S. H. Goods
Materials Mechanics Department
Sandia National Laboratories/CA
The corrosion behavior of three austenitic stainless steels was evaluated during thermal cycling
in molten salt mixtures consisting of NaNO3 and KNO3. Corrosion tests were conducted with
Types 316, 316L and 304 stainless steels for more than 4000 hours and 500 thermal cycles at a
maximum temperature of 565 C. Corrosion rates were determined by chemically descaling
coupons. Metal losses ranged from 5 to 16 microns and thermal cycling resulted in moderately
higher corrosion rates compared to isothermal conditions. Type 316 SS was somewhat more
corrosion resistant than Type 304 SS in these tests. The effect of carbon content on corrosion
resistance was small, as 316L SS corroded only slightly slower than 316 SS. The corrosion rates
increased as the dissolved chloride content of the molten salt mixtures increased. Chloride
concentrations approximating 1 wt.%, coupled with thermal cycling, resulted in linear weight
loss kinetics, rather than parabolic kinetics, which described corrosion rates for all other
conditions. Optical microscopy and electron microprobe analysis revealed that the corrosion
products consisted of iron-chromium spinel, magnetite, and sodium ferrite, organized as separate
layers. Microanalysis of the elemental composition of the corrosion products further
demonstrated that the chromium content of the iron-chromium spinel layer was relatively high
for conditions in which parabolic kinetics were observed. However, linear kinetics were
observed when the spinel layer contained relatively little chromium.
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Bradshaw, Robert W. & Goods, Steven Howard. Corrosion resistance of stainless steels during thermal cycling in alkali nitrate molten salts., report, September 1, 2001; United States. (digital.library.unt.edu/ark:/67531/metadc833412/m1/3/: accessed January 16, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.