Abstract: A process for manufacturing a cold-rolled steel sheet with a strength of at least 1200 MPa and an elongation at break greater than 10%. A steel is provided having a microstructure comprising 65 to 90% bainite. A semifinished product is cast from the steel and heated to a temperature greater than 1150° C. The semifinished product is hot rolled to obtain a hot-rolled sheet; the coiled and pickled. Cold-rolling occurs with a reduction ratio of between 30 and 80% so as to obtain a cold-rolled sheet; and then reheating occurs at a rate Vc between 5 and 15° C./s up to a temperature T1 between Ac3 and Ac3+20° C. and held at said temperature T1 for a time t1 between 50 and 150 s. The sheet is cooled at a rate VR1 greater than 40° C./s but below 100° C./s down to a temperature T2 between (Ms?30° C. and Ms+30° C.). The sheet is maintained at temperature T2 for a time t2 between 150 and 350 s, and then cooled at a rate VR2 of less than 30° C./s down to an ambient temperature.

Abstract: The present invention provides a cold-rolled and annealed steel sheet with a strength greater than 1200 MPa, the composition of which includes, the contents being expressed by weight: 0.10%?C?0.255, 1%?Mn?3%, A?0.010%, Si?2.990%, S?0.015%, P?0.1% s, N?0.008%, it being understood that 1%?Si+Al?3%, it being understood that Cr+3Mo?0.3%, Ti in an amount such that Ti/N?4 and Ti?0.040%. A balance of the composition includes iron and inevitable impurities resulting from the smelting. The microstructure of the steel includes 15 to 90% bainite, the remainder includes martensite and residual austenite.

Abstract: The present invention provides a cold-rolled and annealed steel sheet with a strength greater than 1200 MPa, the composition of which includes, the contents being expressed by weight: 0.10%?C?0.25%, 1%?Mn?3%, A?0.010%, Si?2.990%, S?0.015%, P?0.1%, N?0.008%, it being understood that 1%?Si+Al?3%, it being understood that Cr+3Mo?0.3%, Ti in an amount such that Ti/N?4 and Ti?0.040%. A balance of the composition includes iron and inevitable impurities resulting from the smelting. The microstructure of the steel includes 15 to 90% bainite, the remainder includes martensite and residual austenite.

Abstract: A process for manufacturing a cold-rolled steel sheet with a strength of at least 1200 MPa and an elongation at break greater than 10%. A steel is provided having a microstructure comprising 65 to 90% bainite. A semifinished product is cast from the steel and heated to a temperature greater than 1150° C. The semifinished product is hot rolled to obtain a hot-rolled sheet; the coiled and pickled. Cold-rolling occurs with a reduction ratio of between 30 and 80% so as to obtain a cold-rolled sheet; and then reheating occurs at a rate Vc between 5 and 15° C./s up to a temperature T1 between Ac3 and Ac3+20° C. and held at said temperature T1 for a time t1 between 50 and 150 s. The sheet is cooled at a rate VR1 greater than 40° C./s but below 100° C./s down to a temperature T2 between (Ms?30° C. and Ms+30° C.). The sheet is maintained at temperature T2 for a time t2 between 150 and 350 s, and then cooled at a rate VR2 of less than 30° C./s down to an ambient temperature.

Abstract: The present invention provides a cold-rolled and annealed steel sheet with a strength greater than 1200 MPa, the composition of which includes, the contents being expressed by weight: 0.10%?C?0.25%, 1%?Mn?3%, A?0.010%, Si?2.990%, S?0.015%, P?0.1%, N?0.008%, it being understood that 1%?Si+Al?3%, it being understood that Cr+3Mo?0.3%, Ti in an amount such that Ti/N?4 and Ti?0.040%. A balance of the composition includes iron and inevitable impurities resulting from the smelting. The microstructure of the steel includes 15 to 90% bainite, the remainder includes martensite and residual austenite.

Abstract: The invention relates to a cold-rolled and annealed steel sheet with a strength greater than 1200 MPa, the composition of which comprises, the contents being expressed by weight: 0.10%?C?0.25%, 1%?Mn?3%, Al?0.010%, Si?2.990%, S?0.015%, P?0.1%, N?0.008%, it being understood that 1%?Si+Al?3%, the composition optionally comprising: 0.05%?V?0.15%, B?0.005%, Mo?0.25%, Cr?1.65%, it being understood that Cr+3Mo?0.3%, Ti in an amount such that Ti/N?4 and Ti?0.040%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting, the microstructure of the steel comprising 15 to 90% bainite, the remainder consisting of martensite and residual austenite.