Ferritic stainless steel and processing therefor

Claim 1

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° F. to provide said steel with a creep life to one percent elongation at 1600° 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##