THE CARBURIZATION RESISTANCE OF FECRALLOY (FECRALY) STEELS
The corrosion behaviour of two commercial Fecralloy (R)- (16% Cr, 5% Al, 0.4% Y) steels, with and without a 0.4 w-% Ti addition, has been investigated in a carburizing environment (a-c = 0.8), with a low oxygen potential (p0-2 < 10**-25 bar), at 825 degrees and 1000 degrees C. The steels were exposed in two conditions, as-fabricated and pre-oxidized for 24 h in air at 1100 degrees C. Both steels exhibited superior carburization resistance to alloys such as Alloy 800H and HP 40Nb. In accordance with the predictions of the metal - carbon - oxygen stability diagrams the corrosion behaviour of the Fecralloy steels was determined by the competing processes of Al-2O-3 scale formation and the ingress of carbon leading to the precipitation of either Cr-rich carbides or TiC. Carburization of the FeCrAlY steel was inhibited at 1000 degrees C by the formation of an essentially Al-2O-3 scale but at 825 degrees C the slower kinetics of scale growth could not stop the precipitation by M-23C-6 carbides within a near surface region. This was prevented, however, by pre-oxidation. The small carbon uptakes on both the as-fabricated and pre-oxidized FeCrAlY-Ti steel, at both temperatures, were associated primarily with the formation of TiC, while M-23C-6 also formed on the as-fabricated steel at 825 degrees C. The oxide scale on the FeCrAlY-Ti steel was less protective due to the incorporation of Ti, which reacted with carbon to provide a pathway for carbon ingress.
Bibliographic Reference: CONGRES EUROPEEN DE CORROSION, NICE (FRANCE), NOV 19-21, 1985 WRITE TO CEC LUXEMBOURG, DG XIII/A2, POB 1907 MENTIONING PAPER E 32265 ORA
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Record Number: 1989123119400 / Last updated on: 1987-01-01
Available languages: en