Sometimes, stratification problems may occur in right-angle square steel tube billets, resulting in non-conformity in flaw detection. To prevent this defect, we can take the following three measures:
(I) Optimize slow cooling time
Optimize the slow cooling process of right-angle square steel tube slabs, mainly for stacking temperature and stacking duration. After the hot straightening of rolled steel plates with a thickness of no more than 80mm, the residence time on the cooling bed shall not exceed 5 minutes. For steel plates with a thickness greater than 80mm, the time can be appropriately extended to 10 minutes to ensure that the temperature of the steel plates is controlled above 500℃ before stacking. The slow cooling time for steel plates with a thickness of no more than 50mm is 12h; the slow cooling time for steel plates with a thickness greater than 50mm is 24h. It is strictly forbidden to remove the stack and finish in advance.
(II) Optimize controlled cooling
The appearance of bainite in right-angle square steel tube slabs is generally caused by too fast a cooling rate. When the cooling rate is reduced to 3-5℃/s, the bainite structure no longer appears in the segregation zone in the center of the steel plate, and a conventional pearlite structure is formed. After controlled cooling optimization, the structural stress of the segregation zone in the core of the slab is significantly reduced, and the microcracks caused by the structural stress are greatly improved.
(III) Centralized furnace loading system
In actual production, the length and width of the rolled steel plates vary greatly, and there is uneven stacking when the steel plates are slowly cooled, resulting in unqualified flaw detection inspections at the edges of the ultra-wide plates or unqualified flaw detection inspections at the heads of the ultra-long plates. By establishing a centralized furnace loading system, contracts with similar lengths and widths of rolled steel plates are arranged for centralized furnace loading to ensure the neatness of subsequent steel plate stacking. If necessary, the asbestos cloth is used to wrap the periphery of the rectangular square steel tube slab to enhance the thermal insulation effect.
Post time: Oct-21-2024