The invention relates to a process for manufacturing a part having very high mechanical properties from a hot-rolled or cold-rolled steel strip, comprising precoating said strip with aluminum or an aluminum alloy, cold deformation of the coated strip, possible cutting of the excess sheet with a view to the final geometry of the part, heating of the part so as to form an intermetallic compound from the steel/precoat interface and to austenitize the steel, transfer of the part to a tool and cooling of the part in the tool at a rate such that the steel has, after being cooled, a martensitic or bainitic structure or a martensite-bainite structure. The precoating is carried out by electroplating, by chemical or physical vapor deposition or by co-rolling.