| 摘要 |
PURPOSE:To enhance the elongation, drawability and corrosion resistance of an ultra low carbon steel by lowering the C content to not more than 0.02%, and to increase the tensile strength to 40-60kg/mm.<2> by offsetting a deterioration in strength due to the lowered C content with an increase in Mn content and grain refining due to controlled rolling. CONSTITUTION:The steel contains C; 0.001-0.02%, Si<0.50%, Mn; 2-4% and sol. Al<0.10% or further contains one or more out of Cu<0.50%, Mi<1.5%, Cr<1.0%, Mo<0.5%, Nb<0.10% and V<0.10%. Since controlled hot rolling of the billet makes the austenite grains fine before transofrmation, primary hot rolling at a reduction ratio more than 50% is carried out at a low temp. right above Ac3 point in the austenite zone and secondary hot rollng at a reduction ratio more than 70% is continuously carried out at a temp. of Ac1 point -Ac3 point to form fine ferrite grains from the sustenite, thereby increasing the tensile strength to 40-60kg/mm.<2>. |
