FACTORS INFLUENCING THE PERFORMANCE OF A CR-NI-FE ALLOY EXPOSED TO SULFIDISING OXIDISING CARBURISING ENVIRONMENTS AT 800 degrees C
Studies concerned with the corrosive degradation of engineering alloys exposed to multi reactant gaseous environments containing sulphur, oxygen and carbon-bearing species have intensified during the past decade. In particular, the attack experienced by materials exposed in coal conversion plants has become one of the major areas of concern. These process atmospheres are generally characterised by low oxygen activities and high sulphur and carbon activities and sulphidation can therefore pose significant problems in the design and operation of such plant. This paper presents the results of studies carried out on a laboratory cast austenitic 25 Cr-35 Ni-Fe "model" alloy exposed to a range of H-2-Co-H-2O gas mixtures containing H-2S additions such that the oxygen and carbon activities remain constant (pO-2 = 10-21 bar, a-c = 0.3) whilst the sulphur activity is varied systematically within the range, pS-2 = 10-9 to 10- 7- bar at 800 deg. C. Tests have also been carried out in an equivalent sulphur free atmosphere for reference purposes. The influence of surface condition upon corrosion behaviour has received some attention by comparing the results obtained on ground samples with those obtained on work free electropolished specimens. The kinetics and mechanisms by which this alloy corrodes have been established for exposure periods ranging from 5 min to 5000 h. These studies provide a clear understanding of the factors which can lead to catastrophic sulphidation attack in these types of environment and they also establish the critical dependence of long-term corrosion resistance upon the sulphur activity of the atmosphere.
Bibliographic Reference: WERKSTOFFE UND KORROSION, VOL. 38 (1987), PP. 473-485
Record Number: 1989126023301 / Last updated on: 1989-01-01
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