Dynamic continuous cooling transformation curve of Q690D high strength steel

The thermal simulation test of Q690D high strength steel with different cooling rates was carried out on the thermal simulation testing machine, and the dynamic continuous cooling transformation curve was drawn. The microstructure of the steel was observed by microscope, and the Vickers hardness was tested by Vickers hardness tester. The results show that when the cooling rate was less than 0.1 ℃/s, the microstructure of Q690D high strength steel was basically pearlite, ferrite and a small amount of bainite. When the cooling rate was 0.5 ℃/s, the pearlite disappeared and the microstructure was all bainite. When the cooling rate was 3 ℃/s, martensite appeared in the microstructure. When the cooling rate increased to 8 ℃/s, the bainite almost disappeared, and the matrix structure was basically martensite. When the cooling rate was greater than 10 ℃/s, the microstructure was all martensite, and the critical transformation cooling rate of martensite was 10 ℃/s.