Nickel-chromium and nickel-chromium-iron alloys containing at least one of the following: alkali metal, alkaline earth metal, rare earth metal, thorium, zirconium or titanium, are annealed in the finished state in air once or repeatedly for at least one minute at 1000-1350 DEG C and after each heating are pickled in mineral acid until all scale has been removed and preferably for a further 5 to 15 minutes. Preferably the alloy is annealed from two to five times on each occasion for 2-24 hours. The annealing temperature maybe 50 DEG C above the subsequent operating temperature of the alloy. Particular compositions exemplified are: .(a).(b) .Cr 19.65.Ni 74.2 .Si 0.96.Cr 16.55 .Mn 0.85.Fe 8.5 .Cu 0.10.Ti 0.3 .C 0.03.Si 0.25 .Ce 0.21.Mn 0.2 .Ca 0.08. .Ni balance.