On-line quenching method for medium-thickness plates

The embodiment of the invention discloses an on-line quenching method for medium-thickness plates. The on-line quenching method comprises the following steps of carrying out dephosphorization, blooming and finish rolling on continuous casting plate blanks to obtain finish rolling plates; wherein the finish rolling plates comprise the first medium-thickness plates with the thickness being smaller than or equal to 50 mm and the length being 8-30 m and second medium-thickness plates with the thickness being 50-90 mm and the length being 8-20 m; and enabling the finish rolling plates to be subjected to two-section type cooling, and obtaining quenched plates, wherein in the two-section type cooling, the first medium-thickness plates adopt straight-through type cooling, the second medium-thickness plates adopt swing type cooling, the two-section type cooling comprises first-section cooling which is achieved under an ADCOS-PM inclined jet flow cooling device and second-stage cooling which is achieved under an ACC la