Cause Analysis And Control Measures Of Slab Defects In Jiuquan Steel

By field investigation, measurement and statistics of No.4 continuous slab caster production in Jiuquan Steel steelmaking plant, the influence of billet components, continuous casting process parameters and equipment conditions on the slab surface longitudinal cracks, triangular zone cracks and inter-columnar cracks was analyzed. By using the methods of slab sulfur print, macroscopic examination, scanning electron and energy spectrum analysis, the forming mechanism and reasons for three slab cracks were studied. Furthermore, the corresponding control measures were provided.The results showed that: each of the three slab cracks has its own major cause, but all of the cracks are the combined results of equipments, technologies and operations. The concrete factors are the following: sulfur content in steel, opened angle of roll gap, withdrawal speed, over-heating temperature of liquid steel, level fluctuation in tundish and mould, and secondary cooling zone's cooling strength.So in manufacturing process, in order to reduce the sulfur content, measures which including lowering the tapping temperature and improving Mn content are adopted, and the Mn/S ratio is increased consequently. The tundish capacity should be enlarged to 20t and the liquid height upped to 750mm. Holding withdrawal speed and casting temperature, controlling the liquid steel component and cooling strength strictly, strengthening detection of roll gap and radian, all the above control measures are effective methods to avoid and reduce the formation of the three slab cracks.