Crack-containing hot-stamped steel part with a thin coating with excellent spot-weldability and excellent painting adhesion

A method for producing a hot-stamped coated steel part, comprising the successive steps of:

• providing a steel blank having an average thickness eB from 0.6 mm to 3.5 mm, the steel blank comprising, on at least one face, an aluminum or aluminum alloy pre-coating, the pre-coating having an average thickness comprised between 8.0 μm and 19.90 μm;
• heating the steel blank in a furnace to a heating temperature Theat comprised between 850° C. and 970° C. and holding the steel blank at the heating temperature Theat in order to get a fully austenitic structure in the steel of the blank;
• transferring the heated blank to a die, then closing the die;
• hot-stamping the blank in the die, such that a flat portion of the blank having a thickness eBflat from 0.6 mm to 3.5 mm is not subjected to a deformation, and at least one portion of the blank is deformed through hot-stamping, to thereby obtain a hot-stamped blank comprising an undeformed portion and at least one deformed portion;
• cooling the hot-stamped blank to a temperature less than 400° C. to obtain a hot-stamped coated steel part;
• wherein a temperature Tclose of the blank when the die is closed is comprised between 740° C. and 800° C., and a time tM spent by the blank above a melting temperature Tmelt of the pre-coating upon heating, holding, transfer and hot-stamping, is comprised between a minimum time tMmin and a maximum time tMmax, wherein:
• t
• Mmin
• =
• 5.9
• *
• e
• Bflat
• +
• 2.6
• (
• T
• heat
• -
• Tmelt
• 1000
• )
• 2
• ⁢
• and
• ⁢
• t
• Mmax
• =
• 4.96
• *
• 0.444
• *
• e
• Bflat
• +
• 2.71
• *
• arctan
• ⁡
• (
• 9.52
• *
• (
• e
• Bflat
• -
• 1.71
• )
• )
• (
• T
• heat
• -
• Tmelt
• 1000
• )
• 5
• in which tMmin and tMmax are expressed in seconds, Theat designates the heating temperature of the blank in ° C., Tmelt designates the melting temperature of the pre-coating in ° C. and eBflat designates the thickness of the portion of the blank not subjected to a deformation, in mm.