Abstract：Cold bending cracking was always the key to restrict the application of high strength structural thick plate, and there were many influencing factors. The reasons for cold bending cracking of Q690D thick plate were deeply analyzed. The metallographic structure analysis showed that a layer of banded structure (about 100μm, which was composed of coarse bainite and fine grain ferrite) on the surface of thick plate was the main reason to cause cold bending cracking of steel plate. In addition, the content of oxygen, nitrogen and hydrogen in the tested steel was detected by chemical method. It was found that the content of oxygen exceeded the standard. The scanning electron microscope (SEM) observation and energy spectrum analysis indicated that many magnesium oxide and aluminum oxide inclusions existed in steel. The grade was Level 1.0 of Class D and Class DS. Therefore, it was proposed to enhance the content of silicon in the tested steel to effectively inhibit the banded structure caused due to the segregation of manganese. Meanwhile, the oxide inclusions in steel could be also reduced.
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