Causes of longitudinal crack in hypo-peritectic steel slab and modification of submerged entry nozzle
The problem of high occurrence rate for surface longitudinal crack of hypo-peritectic steel slab casting by continous casting machine in a factory was studied,and the influence of submerged entry nozzle(SEN)with double side holes on crack formation was analyzed.On this basis,the structure of the SEN was optimized and a new-type SEN was developed.Through simulation research and production test,the differences in the structure of double side hole SEN and the new-type SEN,as well as their impact on the molten steel flow field and temperature field in the mold,were compared.The results show that the distribution of molten steel flow field and temperature field in the mold is unreasonable when using double side hole SEN,resulting in uneven thickness of liquid slag inside the mold,especially the thin thickness of liquid slag between the SEN and the mold wall,which induces a large number of sur-face longitudinal crack.The longitudinal cracks are concentrated in the 400 mm range of the slab wide surface cen-ter,with the length of 50-1 200 mm and the depth of 2-12 mm.The new-type SEN is more conducive to the flow of molten steel between the nozzle and the mold wall than the double side hole SEN,and is conducive to increasing the flow capacity of molten steel at the inlet and outlet of the SEN.The flow field of molten steel in the mold is symmet-rical,the temperature field distribution is uniform,the thickness of liquid slag is uniformly increased,and the longi-tudinal cracks on the surface of hypo-peritectic steel slab are significantly improved,the incidence of surface longitu-dinal cracks has decreased from 10.9％to 1.5％.
hypo-peritectic steelsurface longitudinal cracksubmerged entry nozzlethickness of liquid slagtem-perature field
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