New approaches in understanding the effects of hydrogen trapping and the fishscaling resistance of enameled steels

Abstract

One of the primary defects in steel enameling is fishscaling, which is caused by excess hydrogen accumulating at the enamel/steel interface. The common solution to prevention of fishscaling is to trap hydrogen by bubbles in an enamel coating or precipitates in the steel. However, no approach for evaluating the effects between bubbles and precipitates has yet been developed. In this study, new approaches, which apply thermal desorption analysis and permeation test directly on two enameled ultralow‑carbon steels, were developed to reveal the relationship between hydrogen trapping and fishscaling. Resistance to fishscaling can be assessed with the new permeation test, named GC-permeation. The trapping capability of bubbles near the interface can be evaluated by thermal desorption analysis of enameled steel. From extensive microstructural characterizations, it is concluded that the critical trapping sites for hydrogen are provided by bubbles near the enamel/steel interface. Moreover, in ultralow‑carbon steel, the amount of excess carbon in steel is helpful in preventing fishscaling by the formation of bubbles. Hence, the trapping capabilities of precipitates such as TiN and TiC were actually minor factors in the two studied steels.