Abstract
The fundamental researches and the mill trials have been carried out in order to determine the suitable manufacturing conditions for Ti-containing bainitic 70 and 80 kgf/mm2 class steel sheets with excellent bending and stretch-flanging formability.
The results obtained are as follows:
(1) Addition of Ti to low C-2.0Mn steel enhances acicularity, and the higher the acicularity, the better is the tensile strength-notch elongation balance without decrease of tensile strength-elongation balance.
(2) The tensile strength-notch elongation balance of 0.03C-Ti bearing steel is better than that of 0.08C-Ti bearing steel.
(3) The excellent stretch flanging formability of 70 kgf/mm2 class hot rolled steel sheets is obtained in 0.03C-0.5Si-2.0Mn-0.3Cr-0.08Ti steel coiled at about 600°C.
(4) The excellent bending formability of 80 kgf/mm2 class hot rolled steel sheets is obtained in 0.08C-0.5Si-2.0Mn-0.3Cr-0.15Ti steel coiled at about 550°C.
