| 摘要 |
A cold-rolled steel sheet having an ultrafine grain structure and a manufacturing method thereof are provided to manufacture a high-tension cold-rolled steel sheet with superior elongation flange stably without modifying the existing manufacturing facility. A manufacturing method of a cold-rolled steel sheet having an ultrafine grain structure comprises a step of heating a steel material over 1200�C and hot- and cold-rolling it, a step of performing recrystallization annealing, a step of cooling to 600�C or below at the speed more than 5�C/s, and a step of cooling to 500�C~350�C in 30~400 seconds. The steel material contains one or two selected from Mo: 1.0 wt% or less and Cr: 1.0 wt% or less, and one or two selected from Ca, REM, and B, the total content 0.005 wt% or less. |
