| 摘要 |
The invention relates to the production of a cold-rolled steel sheet with a strength of more than 1000 MPa, a uniform elongation of more than 12% and a V-pliability of more than 90°, the composition of which comprises the following with the amounts expressed by weight: 0.15% ≤ C < 0.25%, 1.8% ≤ Mn ≤ 3.0%, 1.2% ≤ Si ≤ 2%, 0% < Al ≤ 0.10%, 0% ≤ Cr ≤ 0.50%, 0% ≤ Cu ≤ 1%, 0% ≤ Ni ≤ 1%, 0% ≤ S - 0.005%, 0% ≤ P < 0.020%, Nb ≤ 0.015%, Ti ≤ 0.020%, V ≤ 0.015%, Co ≤ 1%, N ≤ 0.008%, B ≤ 0.001%, with the understanding that Mn+Ni+Cu ≤ 3%, the rest of the composition consisting of iron and inevitable impurities resulting from the production method. By area, the microstructure consists of between 5 and 20% of polygonal ferrite, between 10 and 15% of residual austenite, and between 5 and 15% of martensite, the remainder consisting of laths of bainite comprising carbides between said laths, such that the number N of inter-lath carbides larger than 0.1 micrometres in size per unit area is 50,000 mm-2 or less. |
