Heat treatment method of high-toughness, large-thickness and large-piece-weight 690MPa-grade steel plate

The invention discloses a heat treatment method for a high-toughness, large-thickness and large-piece-weight 690 MPa-grade steel plate, and belongs to the technical field of metallurgy. The heat treatment method comprises a heat treatment procedure and a cooling procedure. A secondary quenching and tempering process is adopted in the heat treatment procedure; in the first quenching process, the quenching temperature ranges from 920 DEG C to 930 DEG C, and the heat preservation coefficient ranges from 2.3 min/mm to 2.6 min/mm; in the second quenching process, the quenching temperature ranges from 900 DEG C to 910 DEG C, and the heat preservation coefficient ranges from 2.3 min/mm to 2.6 min/mm; in the tempering process, the tempering temperature ranges from 620 DEG C to 640 DEG C, and the heat preservation time ranges from 3.0 min/mm to 4.0 min/mm. The toughness of the 690 MPa large-thickness and large-piece-weight steel plate is improved, the obtained steel plate is good in mechanical property, and the-40 DEG