Abstract: In order to control the blister defects on the slab of boron-bearing low-carbon steels in Meishan steel, gas chromatograph, Heraeus hydrogen gauge, SEM and method of electrochemistry were used to analyze the cause and effect factors of blister defects on the slab. High temperature plasticity of slabs with and without Mg treatment were tested with Gleeble-3500 thermal simulation test machine. Then improvement measures were proposed in accordance with Meishan Steel. The results showed that big Al2O3 inclusions were found in the blisters, the mass fraction of CH4 and H2 were 45.86 % and 51.79 % respectively inside the blisters, and positive segregation of B in the center of slab was the important effect factors of blister defects. Mg treatment was used to improve the quality of the slab, resulting in that the center segregation reduced to 1.8 and the number of inclusions larger than 50 μm reduced to 0.63%. Coolant addition in converter and addition of ladle slag modifier were also optimized. In sunny days, the coolant addition was all iron ore; and in rainy days, less than 31 kg/t pellets and complemental iron ore were added to converter as coolant. The addition of ladle slag modifier was less than 1.5 kg/t and complemented by lime. After process optimization, the frequency of blister defects in month average reduced from 5 to 0.78 in Meishan Steel.

Key words: blister defect, boron-bearing low-carbon steel, hydrogen, Mg treatment