Mechanism and control measures of tail surface cracks near corners of peritectic steel slab castings
The tail strand casting of the slab is an unsteady-state working condition with a relatively higher surface crack occurrence,which significantly impacts molten steel yield during a sequence casting.The microstructure morphology near the surface cracks of the tail strand of a peritectic steel slab was analyzed,and the characteristics,formation mechanism and control methods of the corner transverse cracks were explored.The results show that the room temperature structure of the tail strand surface is ferrite and pearlite with obvious dendrite morphology.Under the tail strand casting process,the corners of the slab after exiting the mold have experienced a process of strong cooling → the corner temperature enters the ferrite temperature zone temperature reheating → the corner structure is austenitized.Near the lowest temperature in this process,the corner of the tail strand is in the third brittle zone,causing fixed-side surface cracking under subsequent bending deformation.The key to the occurrence of such transverse cracks at the corners of the slab is that the corners of the slab are cooled too hard after exiting the mold.The control measures should consider reducing the cooling intensity of the corners of the slab after exiting the mold and shortening the casting time of the tail strand;Additionally,attention should be paid to the coverage of cooling water at the corners of the slab.After replacing the section,the position of the nozzle should be adjusted on time,and attention should be given to ensuring the alignment accuracy of the equipment to reduce the bending strain of the slab.
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