| 摘要 |
<p>PURPOSE: A steel sheet having excellent surface quality and stretch flange ability is provided to properly control a component system and coiling temperature, to use bainite as a casting bed, and to control the island phase martensite fraction to 10% or less, thereby improving stretch flange ability and yield strength. CONSTITUTION: A steel sheet having excellent surface quality and stretch flange ability includes carbon of 0.02 to 0.1wt%, silicon of 0.1 to 2.5wt%, manganese of 0.1 to 2.3wt%, aluminum of 0.02 to 0.1%, chrome 0.01 to 1.5wt%, stannum of 0.06 to 0.2wt%, niobium of 0.01 to 0.08wt%, titanium of 0.5*48/14*[N]wt% to 0.1wt%, phosohorus of 0.05% or less, sulfur of 0.015wt% or less, nitrogen of 0.015wt% or less, the rest of iron, inevitable impurities, and the like. A micro-structure includes bainite of 30 to 95wt%, island phase martensite of 10wt% or less, and the rest of ferrite. The steel sheet further includes one or two kinds of stibium of 0.005 to 0.05 wt% and nickel of 0.01 to 1 wt%.</p> |
