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/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
2MnO
4 (100-300 nm). During the reaction between enamel and pretreated steel for firing process, TiS is presumed to worsen adhesion, while Cr
2MnO
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
2SO
4 at 70-80°C and Ni-deposition for about 5 min with 13-18 g/L NiSO
4·7H
2O 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/m
2 as pickling loss weight in order to keep over 80% adhesion in Ti-IF steel.
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