|
(11) | EP 0 462 380 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
|
|
|
|
|||||||||||||||||||||||||||
| (54) | Method of producing high-strength cold-rolled steel sheet suitable for working |
| (57) A method of producing a high-strength cold-rolled steel sheet suitable for working
uses which utilizes a steel material having the following composition: not more than
0.02 wt% of C, not more than 1.0 wt% of Si, not more than 2.0 wt% of Mn, and not less
than 0.01 wt% but not more than 0.10 wt% of Ti, the Ti, C and N contents being determined
to meet the condition of Ti > (48/12) C wt% + (48/14) N wt%, the steel also consisting
essentially of not less than 0.0010 wt% but not more than 0.0100 wt% of Nb, not less
than 0.0002 wt% but not more than 0.0020 wt% of B, not less than 0.03 wt% but not
more than 0.20 wt% of P, not more than 0.03 wt% of S, not less than 0.010 wt% but
not more than 0.100 wt% of Aℓ, not more than 0.008 wt% of N, not more than 0.0045
wt% of O, and the balance substantially Fe and incidental inclusions. The steel material
is cast and hot-rolled and then subjected to a cold rolling conducted at a sheet temperature
not higher than 300°C under such a condition that the sum of the rolling reductions
of passes which meet the following condition between said sheet temperature (T °C)
and the strain rate ε̇ (S⁻¹) is 50 % or greater: The steel sheet is then continuously annealed or galvannealed. |