Abstract: The continuous cooling transformation (CCT) curve of cargo oil tank (COT) steel was obtained by using dilatometric method combined with metallographic analysis-hardness measurement， and the austenites before and after the compress deformation were analyzed， which were tested on MMS-300 thermal mechanical simulation under different cooling rates. The results showed that the dynamic CCT curve compared to static CCT curve obviously moves to the left and up direction， and the starting temperature of austenite increases. With increasing the cooling rate， the microstructures gradually change from polygonal ferrite， pearlite and a little bainite to a small amount of acicular ferrite and granular bainite， finally transform into bainite and martensite.

Key words: cargo oil tank (COT) steel, thermal simulation, continuous cooling transformation (CCT) curve, metallographic analysis-hardness measurement, microstructure