The invention relates essentially to a composite part comprising at least one sheet of steel coated with at least one polymeric film formed beforehand by extrusion of a polymeric blend comprising at least the following components: a polymer formed of a dispersion of elastomer nodules in a polypropylene matrix, the proportion of elastomer in the matrix being less than 20% by weight of the combination formed by the matrix and the elastomer, a first antioxidant from the family of the phenolic antioxidants for a content by weight of greater than or equal to 0.2%, a second antioxidant from the family of the hydroperoxide-decomposing antioxidants for a content by weight of greater than or equal to 0.1%, reinforcing fillers for a content by weight of less than 10%. The invention relates in addition to a process for the manufacture of this composite part and to the application of this composite part in the motor vehicle and transportation fields.