Process for the production of a strip of hot rolled steel of very high strength, usable for shaping and particularly for stamping

A process for the production of a hot rolled steel strip, wherein the steel has the following weight composition

• carbon:
• 0.12-0.25%,
• manganese:
• 1-2%,
• aluminum:
• 0.03-2.5%,
• silicon:
• 0.03-2%,
• chromium:
• 0.04-2%,
• phosphorus:
• 0.02-0.09%,
• sulfur optionally up to 0.01%,
• titanium up to 0.15%,
• niobium up to 0.15%,
• vanadium up to 0.15%, balance iron and residual impurities,
• wherein said steel is subjected to:
• rolling at a temperature below 880° C.,
• a first cooling over a time less than 10 seconds,
• a second cooling with a cooling speed V ref1 between 20° C./sec. and 150° C./sec. as a function of the thickness of the rolled steel strip, the temperature at the end of said second cooling being below the Ar3 transformation point for austenite to ferrite, the temperature at the end of the second cooling being between 700° C. and 750° C.,
• a third cooling between 3° C./sec. and 20° C./sec. to a temperature between 700° C. and 640° C.,
• a fourth cooling between 20° C./sec. and 150° C./sec. as a function of the thickness of said rolled steel strip, the temperature at the end of said fourth cooling being between 350° C. and 550° C.