Ti micro-alloyed high strength hot rolled steel was developed in Valin Lianyuan Steel in the CSP line. The cleanliness of liquid steel was good enough for thin slab casting after LF refining. The mould powder was adjusted for stabilizing the heat flux of thin slab continuous casting mould. Homogeneous microstructure consisting of ferrite and pearlite was obtained in the hot rolled steel plates by the improving of rolling process. The nano-scale precipitates of Ti(C, N) and Nb(C, N) is the main strengthening mechanism. The yield strength of developed hot rolled plate is higher than 660 MPa and the tension strength is 760 MPa. The ductile-brittle transition temperature is below -60 degree Celsius. The developed Ti alloyed steel with designed composition fulfils the requirements of 600 MPa grade steel for engineering machinery.

Hot rolled Ti microalloyed steel with polygonal ferrite and granular bainite microstructure and 640 MPa yield strength has been developed in BOF-CSP process. By chemical phase analysis, XRD, EDS and high resolution TEM, the particle size distribution, morphology, composition, crystal structure of precipitates were identified. Results revealed the steel containing Ti exhibits fine and uniformly distributed Fe3C-type carbides, the amount of M3C particles less than 18 nm in size was 0.2565 mass %. The high strength of steel is attributed to the precipitation strengthening effect of Fe3C, the yield strength increment from precipitation strengthening of Fe3C calculated according to the formula by Olson and Ashby-Orowan attained 234.4 MPa.