Bake-hardenable cold rolled steel sheet and method of producing same

A process for producing a ferritic, cold-rolled steel sheet having excellent formability comprising the steps of:

• obtaining a slab or sheet of a steel having a composition consisting essentially of (in weight percent):
• ##EQU3## balance Fe and unavoidable impurities;
• hot rolling said steel to a first thickness;
• coiling the hot rolled steel when said hot rolled steel is at a temperature not higher than about 1450.degree. F. (788.degree. C.);
• after said hot rolled steel has cooled, cold rolling said steel to a thickness less than about 50% of said first thickness;
• batch annealing said steel in a two-phase batch anneal, a first annealing phase of which comprises:
• heating said cold-rolled steel to a first temperature in a range of greater than about an A.sub.1 temperature of the steel and lower than about an A.sub.3 temperature of the steel;
• holding said steel at said first temperature for at least about 30 minutes;
• and
• then cooling said steel at a cooling rate less than or equal to about 270.degree. F./hour (150.degree. C./hour), to a subcritical temperature below said A.sub.1 temperature and above 900.degree. F. (482.degree. C.);
• and wherein
• a second annealing phase comprises maintaining said steel at said subcritical temperature for at least about 30 minutes, and then cooling said steel at a cooling rate less than or equal to about 270.degree. F./hour (150.degree. C./hour), to a temperature lower than about 752.degree. F. (400.degree. C.).