Influences of cooling rate on microstructure of 600 MPa grade steel after coiling

In order to study the impact of cooling rate on microstructure and mechanical properties in the low carbon bainitic steel of 600 MPa grade,and explore the ways and methods of obtaining the best performance,this paper investigated the microstructure of the 600 MPa grade steel is investigated by OM and TEM observations.After the steel is curled,the effect of cooling rate in the air on the microstructures in the coil plate head,the plate and the plate tail are researched. The results show that for 600 MPa grade steel,the microstructure is mainly composed by acicular ferrite,lath ferrite,granular bainite,lath bainite,and M/A. The higher cooling rate in the coil head and tail leads to more acicular ferrite,while more lath ferrite and granular bainite are obtained due to lower cooling rate in the middle section of the coil. Thus the strength of the coil head and tail is higher than that in the middle.