Precoated sheets for manufacturing press-hardened coated steel parts

A precoated, cold-rolled and annealed sheet with a thickness between 0.5 and 2.6 mm for the fabrication of press hardened parts, comprising:

• a steel substrate for heat treatment with a carbon content C0 between 0.07% and 0.5%, expressed by weight;
• a metal pre-coating on at least the two principal faces of the steel substrate, the metal pre-coating being aluminum, an aluminum alloy, zinc or a zinc alloy, or is composed of a layer of aluminum or an aluminum-based alloy topped by a layer of zinc or a zinc alloy;
• a composition of the steel substrate contains, expressed in percent by weight:
• 0.07%≤C≤0.5%;
• 0.5%≤Mn≤3%;
• 0.02%≤Si≤0.5%;
• 0.01%≤Cr≤1%;
• Ti≤0.2%;
• Al≤0.25%;
• S≤0.05%;
• P≤0.1%;
• 0.0005%≤B≤0.010%;
• and
• a remainder of the composition being iron and the unavoidable impurities resulting from processing;
• the steel substrate including a decarburized area on the surface of each of the two principal faces, the depth p50% of the decarburized area being between 6 and 30 micrometers, p50% being the depth at which the carbon content is equal to 50% of the content C0,
• the sheet not including a layer of iron oxide between the substrate and the metal pre-coating, and
• the steel substrate having an oxygen content O0 and having, underneath an interface between the pre-coating and the substrate, at a depth located between 0 and 5 micrometers starting from the interface, an average oxygen content Om, whereby Om/O0 is greater than 15.