Burring structural member

A burring structural member of high strength steel comprising:

• a burring hole;
• a burring wall part provided around the burring hole and having a vertical wall part and a bent wall part connected to the vertical wall part;
• and
• a sheet-shaped part provided around the burring wall part and connected to the bent wall part,
• wherein a thickness T of the sheet-shaped part is 2.0 mm or more,
• an indicator relating to toughness and cracking at an inside bend of the bent wall part Charpy impact value vE(0) of the sheet-shaped part at 0° C. is 50 J/cm2 or more,
• a BCI value calculated by the following formula (1) based on the Charpy impact value vE(0) and a maximum length Lc of a crack at an inside bend of the bent wall part is 2.5 or more, and
• a curvature radius R of the inside bend of the bent wall part is larger than R1 calculated by the following formula (2):
• BCI
• =
• vE
• ⁢
• (
• 0
• )
• /
• Lc
• (
• 1
• )
• R
• ⁢
• 1
• =
• 2
• ⁢
• 5
• /
• BCI
• -
• 1.5
• (
• 2
• )
• where, the unit of vE(0) is J/cm2, the unit of Lc is μm, and
• the unit of R1 is mm, and
• wherein R/BCI defines a curve and identifies pass values and fail values of R1 calculated in the formula (2), and
• the curvature radius R is selected based on the pass values identified by the curve.