Effects of Controlled Rolling and Cooling Technology on Microstructure and Performance of 900 MPa Grade Hot-rolled Strip Steel

Through measurement of dynamic CCT curve and experiment of controlled rolling and cooling in laboratory for 900 MPa grade hot-rolled strip steel,phase transformation during continuous cooling process and relationship of microstructure,precipitate and mechanical properties at various coiling temperatures were investigated. CCT measurement show that with the increase of cooling rate,the volume fraction of polygonal ferrite decreases and the fraction of bainite increases,when cooling rate exceeds 15 ℃/s,the microstructure fully consists of bainite. With the increase of coiling temperature,the volume fraction of acicular ferrite decreases and that of polygonal ferrite increases; when coiling temperature reaches 600 ℃,microstructure is composed of ferrite and reduced pearlite,and precipitates are finely dispersed,and the resulting hot-rolled strip steel with 1 000 MPa of tensile strength and 17% of elongation can be achieved.