HIGH STRENGTH COLD ROLLED STEEL SHEET HAVING EXCELLENT BURRING PROPERTY AND MANUFACTRING METHOD FOR THE SAME

摘要

The present invention relates to a high strength cold rolled steel sheet having excellent burring properties and a manufacturing method thereof. According to one aspect of the present invention, the high strength cold rolled steel sheet comprises 15-60% of ferrite, 10-35% of martensite, and 5-20% of the remaining austenite with respect to an area fraction. An area ratio of the ferrite phase having the length less than or equal to 5 μm of the entire ferrite phase (Area of ferrite phase having the length less than or equal to 5 μm/Area of the entire ferrite phase x 100) can be greater than or equal to 70%.