Study on Microstructure and Properties of 700 MPa Grade Hot Rolled Steel with High Hole Expansion Ratio
Taking the Nb-Ti microalloyed testing steel with low carbon as the object of study,the 700 MPa grade hot rolled steel with high hole expansion ratio was developed by studying the effect of different cooling rates during rolling on the microstructure and properties of high hole expansion steel and then the cracking conditions concerning the hot rolled steel after hole-expanding test were studied and analyzed.The analytical results showed that when the finishing rolling temperature was 870 ℃,the coiling temperature was 500 ℃,and the cooling rate was 30 ℃/s,the microstructure of the steel was composed with ferrite and bainite,among of which the tensile strength was 719 MPa and the expanding hole percentage was 81％as the volume fraction of ferrite was about 60％,indicating that this steel had the best comprehensive performance,which met the requirements asked by users.At the same time,the hole expansion test showed that reducing the hardness difference between the two phases was an effective means to reduce the cracking propagation when the cracks occurred in the test steel and propagated in the form of micropored aggregating system.
high hole expansion steelcooling speedmicrostructure and propertiescracks
万方数据
维普
