Production method for high-toughness ultra-thick steel plate at position half of plate thickness

The invention discloses a production method for a high-toughness ultra-thick steel plate at a position half of a plate thickness. According to the production method, the steel plate is subjected to II-type controlled rolling, the rolling is carried out in a low-speed heavy-reduction-rate rolling manner, a two-stage initial rolling temperature is 860-880 DEG C, and a single-pass reduction rate of at least one pass of the first three passes is more than 10%. According to the production method disclosed by the invention, with the adoption of the low-speed heavy-reduction-rate rolling manner and a normalization heat treatment manner, the steel plate is effectively prevented from directly entering water to generate a thick martensite layer on a surface, and tempering treatment is avoided, thus the problems of non-uniform overall performance, difficulty to ensure the performances of the position which is 1/2 of the plate thickness, and high tempering treatment cost of the ultra-thick steel plate are effectively sol