This research aims at clarifying'the mechanical-property distribution in cold roll-formed steel square tubes having, large thickness. It was found that both corners and flat portions are significantly hardened and consequently that increase in strength, decrease both in elongation and impact energy are significant over the entire section in comparison with hot-rolled steel. However, these deficiencies were completely recovered by heat treatment of 850°C-normalizing. The transition value of .width-to-thickness ratio from local buckling to brittle fracture was roughly estimated to be 25 for the roll-formed columns. However, the heat treatment of normalizing is considered to effectively reduce the transition value to 17.
