2002 年 42 巻 11 号 p. 1225-1233
During casting of interstitial free steel, argon bubbles are caught in the solidification front of the steel slab. During downstream processing, these bubbles develop into sub-surface defects called blowholes or pencil pipe defects. Atomic hydrogen can enter the steel in the pickling line and accumulate in the defects, causing an increase of the internal pressure. In the presented study, blowholes are charged with hydrogen both electrochemically and by exposing the blowholes to pickling acid. The pressure and composition of the gas inside the blowholes are determined by opening the blowholes under ultra high vacuum conditions. It is shown that the accumulated pressure is capable of deforming the blowholes plastically, enhancing the visibility of the defects in the sheet. Calculations of the threshold pressure for plastic deformation show to be in reasonable agreement with measured pressures inside the blowholes. Industrial pickling conditions are discussed as well. It is concluded that hydrogen does not influence the blowholes significantly for the considered industrial conditions. Most likely the blowholes become visible in sheet steel at recrystallisation annealing. The final shape of the blowholes is determined by the temper rolling process.
