| 摘要 |
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.
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