Adhesion of Enamel Layer after Repeated Firings in Ti-Stabilized IF Steel Sheet for Porcelain Enamel Use and Its Mechanism

Abstract

Adhesion of enamel layer in Ti-stabilized Interstitial-Free steel (Ti-IF) for porcelain enamel was studied through pickling loss weight, smuts on a pretreated Ti-IF steel, chemical compositions of steel and the repeated number of firing to form enamel, comparing with high oxygen steel for porcelain enamel. When pickling loss weight in Ti-IF steel is below 30g/m 2 , the adhesion of enamel layer can be over 80% even after firing is repeated four times High oxygen steel, in contrast, has over 80 % adhesion of enamel layer, regardless of the repetition of firing, and its adhesion is not related to pickling loss weight. TEM observation reveals that the smut on pretreated Ti-IF steel is mainly round-shaped TiS (100-300 nm) and the one on pretreated high oxygen steel is mainly Cr 2 MnO 4 (100-300 nm). During the reaction between enamel and pretreated steel for firing process, TiS is presumed to worsen adhesion, while Cr 2 MnO 4 is not related to adhesion. Therefore, reducing TiS (lowering pickling loss weight) is an effective measure to keep satisfactory adhesion in Ti-IF steel at repeated firings. Under conventional pretreatment conditions (ex. pickling for about 5 min with 12-15 % H 2 SO 4 at 70-80°C and Ni-deposition for about 5 min with 13-18 g/L NiSO 4 .7H 2 O at 70-80°C), Cu should be higher than about 0.04 % and P shouid be lower than about 0.013 % to be below 30g/m 2 as pickling loss weight in order to keep over 80 % adhesion in Ti-IF steel.