Cold rolled and annealed steel sheet and method of manufacturing the same

A cold-rolled and heat-treated steel sheet, made of a steel having a composition comprising by weight percent:

• C:
• 0.03-0.25%,
• Mn:
• 3.5-8%,
• Si:
• 0.5-2.0%,
• Al:
• 0.03-2.0%,
• Ti≤0.080%,
• Nb≤0.080%,
• V≤0.2%,
• V+Ti+Nb>0.01%,
• S≤0.010%,
• P≤0.020%
• N≤0.008%,
• and optionally including at least one of the following elements, in weight percentage:
• Mo:
• 0.1-0.5%,
• Cr:
• 0.01-1%,
• B:
• 0.0005-0.004%,
• a remainder of the composition being iron and unavoidable impurities resulting from processing,
• the cold-rolled and heat-treated steel sheet having a microstructure consisting of, in surface area fraction:
• between 10% and 30% of retained austenite, the retained austenite being present as austenite films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of the Martensite Austenite islands having a size above 0.5 μm,
• at most 1% of fresh martensite,
• at most 50% of tempered martensite, and
• recovered martensite containing precipitates of at least one element chosen from the group consisting of:
• niobium, titanium and vanadium.