The invention provides a self-adhesive composition in powder form for the coating of metallic substrates, composed of homopolyamide (A) selected from PA11 and PA12, copolyamide (B), calcium carbonate and, optionally, at least one component selected from a pigment or dye, an anti-crater agent or spreading agent, a reductant, an antioxidant, a reinforcing filler, a UV stabilizer, a fluidizing agent and a corrosion inhibitor, said composition being devoid of silane-type adhesion promoter or of an adhesion promoter containing an epoxy, alcohol and/or carboxylic acid function, or derivatives thereof, and having a dry-state modulus and/or a wet-state modulus of greater than or equal to 2200 MPa [Standard NF EN ISO 527]. The invention also relates to a composite material comprising a metallic substrate directly coated with a coating film resulting from the melting of said composition, the adhesion of the coating film to the metallic substrate being greater than 3 after 2000 hours of salt fog before and after drying, in accordance with Standard NFT 58-112.