Abstract: The spalling causes of working roll of tandem cold rolling mill housing F2 during rolling process were analyzed by ZEISS-AXIO microscope, Keyence VE9800 scanning electron microscope and Edax energy spectrometer. The results show that the spalling of the working roll is caused by the internal defects of the roll body. The macro-morphology of the spalling appearance is obviously different from the spalling appearance caused by the roll body surface cracks. The crack growth is formed at trajectory of concentric circle, which is center on the internal defect, and then the remaining parts are separated to form a spalling appearance when the cracks are extended to a certain position. The spalling occur from the inside in a concentric circle mode, and the crack source at the center of the roll often accompanied by metallurgical inclusion defects. The presence of inclusions will cut off the continuity of the roll materials and decrease its mechanical properties. Meanwhile, the local stress concentration in the roll will provide favorable conditions for the initiation and propagate of cracks. In order to avoid this problem, the purity of molten steel should be further improved, therefore, the probability of inclusion formation can be reduced.

Key words: forged steel, cold rolling mill work roll, spalling, inclusions