THE INFLUENCE OF ALLOY COMPOSITION UPON THE CORROSION BEHAVIOUR OF 25CR-35NI-FE ALLOYS EXPOSED TO MIXED GASEOUS OXIDIZING - SULPHIDIZING - CARBURIZING ATMOSPHERES
1. Gravimetric and microstructural examinations have clearly demonstrated that raising the pS-2 from 10**-9 bar to 10**-8 bar results in very significant increases in the rates of corrosive attack, due largely to a change from oxidation-governed reactions to those involving the formation of massive sulphide scales. 2. Although Al was beneficial in the higher sulphidizing environment, the HP40Al showing reduced corrosion kinetics, corrosive attack was still relatively severe. 3. The presence of Mn was detrimental in the lower sulphidizing environment since it promoted both the formation of a more defective MnCr-2O-4 spinel and internal Mn-containing sulphides. The Mn-free "model" alloy was the most corrosion resistant material in this environment. 4. Although Si containing oxides were formed internally in the sulphidizing environments, they conferred no obvious long-term protection. 5. Carburization of these alloys occurred only when surface oxides were not formed, i.e. in the atmosphere with pS-2 = 10**-8 bar. The presence of indigenous carbides in the cast HP40 alloys promoted localized oxidation and sulphidation attack in the pS-2 = 10**-9 bar atmosphere.
Bibliographic Reference: INTERNATIONAL CONFERENCE "HIGH TEMPERATURE ALLOYS + THEIR EXPLOITABLE POTENTIAL", PETTEN (THE NETHERLANDS), SEPT. 2, 1985 WRITE TO CEC LUXEMBOURG, DG XIII/A2, POB 1907 MENTIONING PAPER E 32328 ORA
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Record Number: 1989124020600 / Last updated on: 1987-01-01
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