Hydrogen pressure build-up in blowholes at pickling of interstitial free steel

During continuous casting of Interstitial Free steel occasionally argon bub bles are entrapped in the solidifying shell. Some of these bubbles can be f ound in the final cold rolled sheet as elongated blisters, so-called blowho les. During processing, the steel is exposed to atomic hydrogen at the pick ling process. Exposure to atomic hydrogen can lead to accumulation of molec ular hydrogen in the blowholes, making them more apparent. This process is examined in this paper. The hydrogen diffusion behaviour is studied by a pe rmeation technique, accumulation is modelled and the deformation process is studied by loading a blowhole with hydrogen electrochemically, The results and implications for pickling lines are discussed.