Fabrication process of coated stamped parts

A manufacturing process of a hot stamped coated part comprising the following successive steps, in this order:

• providing a hot rolled or cold rolled steel sheet comprising a steel substrate and an aluminium-silicon alloy precoating, said precoating containing more than 50% of free aluminium and having a thickness selected to enable alloying with said steel substrate, then
• cutting said steel sheet to obtain a precoated steel blank, then
• heating said blank under a non protective atmosphere up to a temperature Ti, near the melting temperature of said precoating, then
• heating said blank from said temperature Ti, up to an austenitization temperature Tm of said steel substrate, under a non-protective atmosphere at a heating rate V between 30° C./s and 90° C./s, V being the heating rate between said temperature Ti, and said temperature Tm, in order to obtain a coated heated blank, with a surface of precoating having a percentage of a liquid phase between 10 and 60%, wherein the temperature Ti, is between Te−10° C. and Te, where Te is the eutectic or solidus temperature of the precoating, wherein Te is about 577° C., then
• soaking said coated heated blank at said temperature Tm for a time tm between 20 s and 90 s, to bring the percentage of the liquid phase of the surface of precoating to lower than 30% at the end of the soaking, then
• hot stamping said blank in order to obtain a hot stamped coated part, then cooling said stamped part at a cooling rate in order to form a microstructure in said steel substrate comprising at least one constituent chosen among martensite or bainite.