Effect of Tramp Elements in Steel on the Adherence of Porcelain Enamel

The effect of tramp elements in steel on the adherence of porcelain enamel has been studied using commercial products and specimens prepared from vacuum melting. Firstly, it was found that the steel sheet scarcely containing tramp elements showed very poor adherence. In order to obtain excellent adherence, it is effective for steel sheet to contain the appropriate quantities of Cu and S. Mn and Ni contents have no effect on the adherence, and the increase of P content gives negative effect on the adherence. It is considered that the adequate contents of Cu and S to obtain excellent adherence are more than about 0.03% and 0.01%, respectively.The presence of adequate contents of Cu and S is effective for uniform smut formation on steel surface in pickling, which roughens uniformly the steel surface in pickling, and causes fine Ni deposition in subsequent Ni flash. It is considered that these two effects due to uniform smut formation provide serrated enamel-steel interface in subsequent enamel firing, and finally give excellent adherence.