Porcelain enamel frit for sheet iron ground coat

A fluorine or fluorine compound free porcelain enamel frit for sheet iron ground coat, consisting of, in parts by weight,

• 100 parts of a main component consisting of 30-73 parts of SiO.sub.2 or a mixture of SiO.sub.2 and at least one of TiO.sub.2, ZrO.sub.2 and SnO.sub.2, 8-45 parts of B.sub.2 O.sub.3, and 8-41 parts of Na.sub.2 O or a mixture of Na.sub.2 O and at least one of Li.sub.2 O and K.sub.2 O (provided that, when the total amount of the mixture of Na.sub.2 O and at least one of Li.sub.2 O and K.sub.2 O is assumed to be 100% by weight, the amount of Na.sub.2 O is at least 45% by weight, that of Li.sub.2 O is not more than 25% by weight and that of K.sub.2 O is not more than 50% by weight), and
• - 42parts of an auxiliary component consisting of not more than 12 parts of Al.sub.2 O.sub.3, 1-22 parts of at least one of CaO, BaO, ZnO, MgO and SrO (provided that the amount of each oxide is not more than 12 parts), from more than 0 part to 7 parts of MoO.sub.3 or a mixture of MoO.sub.3 and at least one of V.sub.2 O.sub.5, P.sub.2 O.sub.5 and Sb.sub.2 O.sub.3, and 0.5-10 parts of at least one of CoO, NiO, CuO, MnO.sub.2 and Fe.sub.2 O.sub.3.