Abstract: The cold rolling strip breakage fault of highefficiency nonoriented silicon steel made in Ansteel was analyzed, of which the hot rolled coil was annealed in a ring furnace before cold rolling. Many inclusions were found on the subsurface of hotrolled steel plate by metallographic observation of steel plate section. And by SEM observation, it was showed that the inclusions were AlN. The main reason of the cold rolling strip breakage was the nitrogen in protection atmosphere permeated into steel during annealing of hot rolled coil, which was then generated into AlN combining with the aluminum in steel, causing the abnormal increase of inclusions and broking the continuity of steel. The nitrogen content in steel had a gradient along the direction of the plate thickness, and the nitrogen content in the edge of steel plate was evidently higher than that in the core, which had a strong corresponding relationship with the oxide scale distribution on the surface of the steel plate, and it is indicated that the oxide scale played a catalytic role in nitrogen infiltration during the annealing process. Meanwhile, the infiltrated nitrogen escaped from the weld and form bubbles, which affected the welding quality seriously.

Key words: high efficiency nonoriented silicon steel, strip breakage, annealing, nitridation