Abstract: Three types of nodules, which were found in carbon sleeves of continous annealing units of silicon steel of Maanshan Iron and Steel Co.  Ltd., were studied in this paper, and the forming reasons were also analyzed combined with the actual production situation. The results showed that surface corrosion of carbon sleeves by Hydrogen formed pits, which would provide adhesion positions for nodulation, and the formed nodules were mainly compounded with residual oil and iron, furnace dust and iron scale. By reducing the mass fraction of hydrogen to 5 %-10 % in the protective atmosphere of annealing furnace, and monitoring the electric conductivity of the cleaning section, and standardizing the production system and other measures, the nodulation occurrence of carbon sleeves was effectively reduced. 

Key words: silicon steel, nodulation of carbon sleeve, continous annealing