Method for making a cold rolled steel strip for deep-drawing

Process for manufacturing a cold-rolled steel strip for deep drawing, said strip having a thickness of between 0.3 mm and 1 mm, said process comprising the steps of:

• subjecting a steel slab to hot rolling in the austenitic region, to obtain a hot-rolled strip, said slab comprising:
• a carbon content C:
• 0.02 wt %<C.<0.08 wt %,
• a manganese content Mn:
• 0.1 wt %<Mn<0.4 wt %,
• a sulfur content S:
• S<0.015 wt %,
• a silicon content Si:
• Si<0.1 wt %,
• a phosphor content P:
• P<0.08 wt %,
• an aluminium content Al:
• Al<0.05 wt %,
• a niobium content Nb:
• Nb<0.02 wt %,
• a titanium content Ti:
• Ti<0.03 wt %,
• winding said hot-rolled strip at a temperature T:
• 680° C.<T<750° C.,
• subjecting said hot-rolled strip to cold rolling with a reduction ratio of between 65% and 80%, to obtain a cold-rolled steel strip,
• heating said cold-rolled steel strip at a heating rate Vh between 150° C./s and 1000° C./s up to an annealing temperature Ta between 650° C. and 750° C.,
• maintaining said strip at said annealing temperature for a time ta between 1 and 20 seconds,
• cooling said strip at a cooling rate Vc between 1000° C./s and 500° C./s down to an overageing temperature Toa between 150° C. and 250° C., and
• winding up said strip to form reels, wherein said reels are introduced at a temperature of between 130° C. and 230° C. in a tunnel furnace under a protective atmosphere to prevent oxidation of said reels, and keeping said reels in said tunnel furnace until they have cooled to a temperature below 100° C.