During the production of Q355B,there was a batch of steel plate with unqualified elongation,the unqualified steel plate specifications are concentrated in 25～35 mm.After sampling and analyzing the steel plates with unqualified elongation,it was found that MnS inclusions gathered at the 1/3 position of the plate thickness,and layered fractures appeared at the end after stretching,intermediate cracks appeared on the inner arc side of the casting billet with a thickness of 70～100 mm.Using the finite difference method to numerically simulate the continuous casting process,it is found that cracks occurred in sections 7～9 of the continuous casting segment.After on-site investigation,it was found that there were abnormal conditions in sections 7 and 9 of the segment.After maintenance,the elongation of Q355B is improved,and there are no cases of batch steel plate with unqualified elongation.
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