2004 Volume 44 Issue 10 Pages 1767-1773
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 30 g/m2, 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 Cr2MnO4 (100-300 nm). During the reaction between enamel and pretreated steel for firing process, TiS is presumed to worsen adhesion, while Cr2MnO4 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% H2SO4 at 70-80°C and Ni-deposition for about 5 min with 13-18 g/L NiSO4·7H2O at 70-80°C), Cu should be higher than about 0.04% and P should be lower than about 0.013% to be below 30 g/m2 as pickling loss weight in order to keep over 80% adhesion in Ti-IF steel.