A flux for use in a dry process for the flux treatment of the material to be coated with molten metal contains at least one chloride selected from the group consisting of zinc chloride, stannous chloride, an alkali metal chloride and an alkaline earth metal chloride and at least one aliphatic nitrogen derivative with alkyl group having 1 to 18 carbons. The treatment of steel with this flux enables the formation of a coating having a good finish from, among others, a molten alloy of zinc and aluminum, which may further contain other elements, or molten aluminum, by a single dipping operation in an atmospheric environment which has hitherto been difficult. A process for manufacturing steel coated with molten metal, including its treatment with the flux, is also disclosed.