Mixed sulfidation/carburization attack on several heat-resistant alloys at 900 C
A sulfidation/carburization study of seven commercial heat-resistant alloys was carried out at 900 C in a H{sub 2}-25 vol.%CH{sub 4}-14.8N{sub 2}-4CO-0.6CO{sub 2}-0.6H{sub 2}S atmosphere. The equilibrium partial pressures for oxygen (O{sub 2}) and sulfur (S{sub 2}) were 1.1 x 10{sup {minus}22} and 4.1 x 10{sup {minus}8} atm, respectively, and the carbon activity for this system was unity. The time of exposure was 500 hr. Relatively thick, mixed sulfide scales were formed on all of the alloys tested. In addition, internal carburization occurred in all of the alloys. Using metal loss (i.e., the reduction in sample thickness) plus internal attack (internal sulfidation plus internal carburization) as a performance criterion, an alloy with a nominal composition of Ni-29 wt.%Co-28Cr-2.75Si performed the best, showing 0.71 mm of attack. An alloy with a nominal composition of Fe-20 wt.%Ni-25Cr performed the worst, being totally consumed by the test (>3.18 mm of attack). Alloys containing relatively high amounts of silicon (> 2.5%) showed a dramatic increase in their sulfidation resistance compared to the other alloys containing lower silicon contents. The amount of iron present within a given material played a dominant role in the carburization attack that occurred, with as expected, high-iron alloys showing significant internal carburization because of a high solubility and diffusivity of carbon in the matrix. The importance of the various alloying elements with respect to sulfidation and carburization resistance is discussed.
- Research Organization:
- Haynes International, Kokomo, IN (US)
- OSTI ID:
- 20050526
- Journal Information:
- Oxidation of Metals, Vol. 53, Issue 5-6; Other Information: PBD: Jun 2000; ISSN 0030-770X
- Country of Publication:
- United States
- Language:
- English
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