THE EFFECT OF SURFACE-ENRICHED ELEMENTS IN KILLED-STEEL ON TINPLATE CORROSION RESISTANCE

摘要

Surface enrichment in elements during annealing of killed-steel sheet for tinplate has been investigated using a Grimm-type glow discharge spectrometer and an electron-probe micro-analyser.It is found that enriched elements. Si, Al, Mn and Cr during annealing at 680 °C are not removed completely by immersing the steel sheet in acidic solution for several seconds before electrotinplating and that they affect tinplate corrosion resistance.The alloy-tin couple current (ATC value) increases with the increase in silicon content in steel, while it is hardly influenced by aluminium content. Manganese tends to enrich at the surface of steel as the silicon content in steel increases.Enrichment in manganese and chromium occurs, as their oxides, at grain boundaries near the surface and they increase the iron solution value (ISV) and the thiocyanate value of tinplate.With these experimental results, steel composition and annealing conditions suitable for tinplate of high corrosion resistance are discussed.