On the basis of alloy 800 H and alloy AC-66, materials introduced in the 1960s and the late 1980s, respectively, two new alloys, Cronifer III-TM (alloy III-TM) and Nicrofer 45-TM (alloy 45-TM), were developed to resist high sulfur and carbon-bearing environments. Carburization behaviour was examined in the temperature range 750–1100°C for more than 1000 h in CH4/H2 (ac = 0.8). The silicon-containing alloys Cronifer III-TM and Nicrofer 45-TM showed a mass gain similar to or even lower than that of the nickel-base alloy 625. Data on sulfidation resistance up to 650°C obtained in 10% SO2/N2 indicated a mass loss of less than 5gm−2 after 1000h for all alloys tested (800 H, AC-66, 625, III-TM, 45-TM). At 750°C alloy 800 H suffered breakaway corrosion and alloy 625 severe spallation. Alloys AC-66, III-TM and 45-TM showed superior corrosion resistance. Tests performed in a simulated coal gasification environment (1% H2S, 4% CO, 3% H20, balance H2) showed negligible mass gain for the alloys at 550°C. Results at 6...