Effects of processing parameters on the microstructural characteristics of high strength automobile beam steels produced by CSP

The effects of controlled rolling and controlled cooling parameters on the microstructure and mechanieal properties of high strength automobile beam steels produced by CSP technology were investigated. According to the theory of flexible technology, the processing of automobile beam steels with different strength grades by EAF-CSP technology was developed in Zhujiang Steel, China. The differences of microstructure and strength were analyzed by using scanning electron microscopy and transmission electron microscopy. It is shown that the final microstructure is mainly of polygonal ferrite and some pearlite, and the average ferrite grain size is about 3.7~5.6 μm. With decreasing coiling temperature, the cementite lamella of hot strips is fractured and transformed into discrete cementite particles, which is distributed throughout the ferrite matrix. It is also noticed that some granular bainite appears in the microstructure.