the silicon content is greater than 0 070 dross is formed in the case of hot dipped coatings and lanthanum and cerium in an amount not exceeding 0 05 favor wettability of the surface with respect to the zinc bath the zinc based precoat may also contain inevitable impurities such as for example cadmium tin or copper when the precoat is formed by a hot dip process iron and manganese may thus be especially present as impurities advantageously the base steel on which the precoat is deposited has the following composition by weight a carbon content of between 0 15 and 0 5 and preferably between 0 15 and 0 25 by weight this element plays a major role in the hardenability and in the mechanical strength obtained after the cooling that follows the austenization and alloying treatment below a content of 0 15 by weight the hardenability is however too low and the strength properties are insufficient in contrast above a content of 0 5 by weight risk of forming defects is greater during hardening particularly in the case of the thickest parts a carbon content of between 0 15 and 0 25 makes it possible to obtain a strength of between approximately 1250 and 1650 mpa manganese apart from its deoxidizing role also has a major effect on the hardenability in particular when its weight content is at least 0 5 and preferably 0 8 however too large an amount 3 by weight or preferably 1 5 results in the risk of excessive segregation the silicon content of the steel must be between 0 1 and 0 5 by weight and preferably between 0 1 and 0.