Study On Facial Longitudinal Crack Of Slabs At Shaogang

Longitudinal facial crack is the one of the important surface defects of continuously cast slab. It will seriously influence the slab quality and even cause mold breakout during casting. In the past few years, the longitudinal facial crack ratio of Q235 steel slabs produced at Guangdong Shaogang reached to as high as 20%. That caused big economical loses.Grain size and inclusion composition on the ruptured surface of cracked slabs were studied in this paper. Through observation and analyses of it was found as follo wings:●cavities and deep oscillation marks coexist with longitudinal cracks;●serious sulfur segregation;●inclusions containing Na,Si,Ca,Zr,Al were found in the cracks.By studying on the influence factors on the chemical composition of molten steel and casting process to surface longitudinal crack of slab, the measure such as increasing carbon content of molten steel, decreasing surphur content of molten steel, decreasing mould water flow, adjusting insertion depth of submerged nozzle, optimizing mould powder was applied, which improved the surface crack of slab to varying degrees.On the other way, some measures such as ruduce sulfur content, reduce the water flow in mold, the occurrence and growth of the longitudinal crack would be effectively controlled.Based on the above observations and analyses, some technical measures and suggestions were brought up to Shaogang to reduce the occurrence rate of the longitudinal facial cracking of slab.