A surface treated steel materials coated with manganese having a film of MmOOH (manganic hydroxide) formed thereon, which show excellent corrosion resistance, workability and weldability. The surface treated steel materials may be further coated with zinc as a base coating underlying the manganese coating or further coated with a coating of at least one selected from the group consisting of P, B, Si, Cu, Mn, Cr, Ni, Co, Fe, Zn, Al, Ca, Mg, Ti, Pb, Sn, inorganic carbon and their compounds and still further coated with an organic coating. The film of MmOOH (manganic hydroxide) is formed by a treatment in an aqueous solution containing Cr.sup.6+.