THE SULFIDATION PROPERTIES OF TITANIUM-BEARING MANGANESE-BEARING AND NIOBIUM-BEARING FE-25CR ALLOYS IN H2-H2S MIXTURES AT 800-DEGREES-C

An investigation of high-temperature sulphidation properties of 4 wt% Ti-, 9 wt% Mn- and 8 wt% Nb-bearing Fe-25Cr alloys has been carried ou t in H-2-H2S mixtures of sulphur partial pressure in the range of 10(- 3) < pS2 < 1 Pa at 800-degrees-C. On the whole, the sulphidation kinet ics of all alloys obeyed the parabolic law after the initial period of reaction. In some cases, fluctuations in the weight gain-time curves arose due to cracking of sulphide scales. Compared with the weight gai n of Fe-25Cr alloy, the additions of alloying elements improved the su lphidation resistance. The effect of 8 wt% Nb was relatively major. bu t the effects of 4 wt% Ti and 9 wt% Mn were minimal. The addition of t hese elements did not change the surface morphologies or improve the s tructure of sulphide scales. Combining the sulphidation kinetics and t he analysis of sulphide scale structure, the sulphidation mechanisms o f these Fe-25Cr-base alloys have been proposed and the effects of tita nium, manganese and niobium have been discussed.