Hot workability of nickel-containing alloys after reheating using sulfur-containing fuel

Abstract

The effects of fuel sulfur on the hot workability of several nickel-containing alloys have been explored in static exposures and in hot rolling trials following reheating in S-bearing. combustion atmospheres. Using thermochemical calculations, it is shown that the locus of oxidation and sulfidation potentials of such gases over practical air-fuel ratios can be made to coincide for a variety of hydrocarbon fuels, and propane doped with H₂S has been used as a fuel to simulate environments resulting from firing distillate and residual oils. Nickel-base alloys containing chromium are not affected by the presence of sulfur species, and workability is independent of reheating conditions at fuel sulfur levels of up to 2 wt pct. Stainless steels may form solid subscale sulfides under air deficient heating, but there is no effect under lean firing conditions; billet workability is not influenced by sulfur. Nickel and nickel-copper alloys form liquid sulfides during air deficient heating, and very poor workability results. Sulfur is also picked up from the gas, and other properties may be affected. The thermochemical predictions for the occurrence of these liquid sulfides agree well with observations. An attempt has been made to identify safe reheating conditions (temperature and air-fuel ratio) for sensitive alloys on the basis of equilibrium combustion gas computations.