Abstract: Through microstructure observation and mechanical properties test, the effect of U-shaped laminar cooling process on improve the uneven microstructure and properties of the head, tail and middle of the cold rolled SPCC steel strip produced by the conventional laminar cooling process was studied. The results show that when using the conventional laminar cooling process, the ferrite grain size and carbide morphology of the head, tail and middle of the hot rolled steel strip after coiling are different due to the difference of temperature drop rates, and then inherites to the microstructure after cold rolling and annealing, resulting in the uneven properties of the final product. When using the U-shaped laminar cooling method, the coiling temperature of the head and tail of the steel strip increases, which reduces the microstructure difference, and then the microstructure and properties uniformity of the head, tail and middle part of the steel strip after cold rolling and annealing are significantly improved.

Key words: U-shaped cooling, continuous annealing, microstructure