Ferritic stainless steel and processing therefor

A process for producing a creep resistant ferritic stainless steel, which comprises the steps of:

• preparing a steel melt containing, by weight, up to 0.1% carbon, up to 0.05% nitrogen, from 11 to 20% chromium, up to 5% aluminum, up to 5% molybdenum, up to 1.5% manganese, up to 1.5% silicon, up to 0.5% nickel, up to 0.5% copper, up to 0.6% titanium, and niobium and tantalum in accordance with the following:
• (a) 0.63 to 1.15% effective niobium, in the absence of tantalum
• (b) effective niobium and tantalum in accordance with the equation ##EQU11## when both niobium and tantalum are present;
• casting said steel;
• working said steel;
• and annealing said steel at a temperature of at least 1900.degree. F. to provide said steel with a creep life to one percent elongation at 1600.degree. F. under a load of 1200 pounds per square inch, of at least 160 hours;
• said effective niobium and tantalum being computed in accordance with the following:
• ##EQU12## If A is positive or zero:
• Then Effective Nb content=weight % Nb
• Effective Ta content=weight % Ta
• If A is negative:
• Then When Ta is absent
• Effective Nb content= ##EQU13## When Nb and Ta are present together ##EQU14## Then if B is positive or zero:
• Effective Nb content=B
• Effective Ta content=weight % Ta
• If B is negative:
• Effective Nb content=0
• Effective Ta content= ##EQU15##