HIGH TEMPERATURE CORROSION OF SELECTED HIGH ALLOY STEELS IN CARBURIZING - SULPHIDIZING - OXIDIZING ATMOSPHERES RELATING TO COAL CONVERSION PROCESSES
Specimens have been exposed in purpose-designed corrosion furnaces to mixed carburizing - sulphidizing - oxidizing atmospheres (H-2 - 7 % CO + x%H-2S) at 800 degrees C at 1,35 atmospheres (giving values of P-O-2 = 10 -21- atm., P-S-2 = 10**-9, 10**-8, 10**-7 atm. and a approximately equal to 0,4) for durations of up to 500 h. The specimens are high Ni-Cr steels of c-25 Cr and 20 Ni or 33 Ni content and include commercial (AISI 314 & INCOLOY 800H, HP 40A1) and simpler model alloys (Fe-25Cr-20Ni and Fe-25Cr-33Ni). Specimen analysis was done using discontinuous gravimetry with surface and cross-sectional metallography performed on 100h specimens using optical and electron - optical techniques as well as X-ray diffraction. The specimens generally suffered sulphidation attack: the scale appears to form as two layers: an outward-growing and an inward growing sulphide, beneath which is a zone of carburization. The 20Ni alloys class showed the worst behaviour, whilst HP 40 A1 was the most protective. For HP 40 A1 a thin A1 enriched scale was noted and is probably an oxide scale that prevents penetration by sulphur and carbon. The nature of attack also varied e.g. Incoloy 800H had deep intergranular penetrations. The rate of attack also rose sharply with increasing PS-2 value and was explained with the formation of Cr, then Fe and finally Ni sulphides occurring at successively higher PS-2 values.
Bibliographic Reference: 10TH INTERNATIONAL SYMPOSIUM ON THE REACTIVITY OF SOLIDS, DIJON (FRANCE), AUG. 27-31, 1984 WRITE TO CEC LUXEMBOURG, DG XIII/A2, POB 1907 MENTIOING PAPER E 31540 ORA
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Record Number: 1989122071200 / Last updated on: 1987-01-01
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