Continuous cooling transformation of Nb-V-microalloyed high-strength hull steel

A thermo-simulating machine and a dilatometer were used to test the continuous cooling transformation (CCT) diagrams of a kind of Nb-V-microalloyed high-strength hull steel, including the dynamic (with deformation at three temperatures) and the static (without deformation) CCT diagrams, Experimental results show that the dynamic CCT diagrams shift to the left and upper compared with the static ones. With increasing cooling rate the onset temperature of γ/α transformation is gradually lowered, the starting temperature of bainitic transformation B_s increases to a plateau and then decreases, and the ferrite grains are dramatically refined. When the finish rolling temperature reduces from 900℃ to 800℃, the onset temperature of γ/α transformation and the upper critical cooling rate for bainite slightly increase while B_s decreases about 10℃, and the ferrite grains are refined.