Einf luss des Emaillierungsprozesses auf die Wasserstoffpermeation

摘要

For both cold rolled and hot rolled steel used for the manufacturing of enamelled parts, fishscale resistance is needed whenever both sides of the steel are coated by vitreous enamel. The high susceptibility of steel towards hydrogen, combined with the fact that enamelling takes place at about 830°C (1526°F), requires different strategies to provide the steel with ample hydrogen trapping capacity. Otherwise, hydrogen desorp-tion during and after cooling down, leads to fishscale formation. In the enamelling process, it is generally accepted that the cause of fishscaling is due to insufficient trapping of hydrogen after its introduction to the steel during the firing process. Hence, steel manufacturers mostly use a hydrogen permeation test at room temperature to assess the susceptibility of their steel coils to this defect. However, there is a processing difference between the steel sheet product state, on which the susceptibility is assessed, and the fishscale appearance occurring after enamelling, which is after further forming, welding and firing. The changes brought to the steel's microstructure by all manufacturing process steps might be responsible for this decrease in hydrogen trapping ability. The present study gives an overview of the impact of the main processing steps of forming and firing on the hydrogen permeation of the major steel grades used for enamelling-especially on Ti-IF grades, known by enamellers to be more sensitive. A second objective is to characterize the hydrogen trapping of susceptible and non-susceptible steels, by using Thermal Desorption Analysis (TDA) after charging with hydrogen and deuterium, either electrochemically at room temperature or via a gaseous phase at high temperature.