Abstract: A cold rolled and heat-treated steel sheet, the steel including, in weight percentage, 0.17%?carbon?0.25%, 2%?manganese?3%, 0.9%?silicon?2%, 0%?aluminum?0.09%, 0.01%?molybdenum?0.2%, 0%?phosphorus?0.02%, 0%?sulfur?0.03%, 0%?nitrogen?0.09%, and optionally one or more of the following elements 0%?chromium?0.3%, 0%?niobium?0.06%, 0%?titanium?0.06%, 0%?vanadium?0.1%, 0%?calcium?0.005%, 0%?boron?0.010%, 0%?Magnesium?0.05%, 0%?Zirconium?0.05%, 0%?Cerium?0.1%, and the balance including iron and unavoidable impurities, the steel sheet having a microstructure of—50% to 80% of Bainite, 10% to 30% of residual austenite, 15% to 50% of Partitioned martensite, 0% to 10% of ferrite and 0% to 5% fresh martensite in area fractions, and a ferrite-enriched layer extending up to 50 microns from both surfaces of the steel sheet, such ferrite-enriched layer having a mean ferrite content from 55% to 80% in area fraction.

Abstract: A cold rolled and heat-treated steel sheet, the steel including, in weight percentage, 0.17%?carbon?0.25%, 2%?manganese?3%, 0.9%?silicon?2%, 0%?aluminum?0.09%, 0.01%?molybdenum?0.2%, 0%?phosphorus?0.02%, 0%?sulfur?0.03%, 0%?nitrogen?0.09%, and optionally one or more of the following elements 0%?chromium?0.3%, 0%?niobium?0.06%, 0%?titanium?0.06%, 0%?vanadium?0.1%, 0%?calcium?0.005%, 0%?boron?0.010%, 0%?Magnesium?0.05%, 0%?Zirconium?0.05%, 0%?Cerium?0.1%, and the balance including iron and unavoidable impurities, the steel sheet having a microstructure of—50% to 80% of Bainite, 10% to 30% of residual austenite, 15% to 50% of Partitioned martensite, 0% to 10% of ferrite and 0% to 5% fresh martensite in area fractions, and a ferrite-enriched layer extending up to 50 microns from both surfaces of the steel sheet, such ferrite-enriched layer having a mean ferrite content from 55% to 80% in area fraction.