Steel plate for plastic mold for rolling continuous casting slab with thickness of 400mm and production method of steel plate

The invention provides a steel plate for a plastic mold for rolling a continuous casting slab with the thickness of 400mm and a production method of the steel plate, belonging to the technical field of mold steel. The steel plate comprises the following chemical components in percentage by weight: 0.3-0.5% of C, 0.2-0.5% of Si, 1.0-1.6% of Mn, at most 0.008% of P, at most 0.006% of S, 0.02-0.05% of Al, 1.3-2.5% of Cr, 0.1-0.6% of Mo and the balance of Fe and unavoidable impurities. The steel plate for the plastic mold, which has HB (Brinell Hardness) of 290-330 and has favorable ultrasonic flow detection performance, can be produced successfully and stably through converter melting, LF (Low Frequency) furnace refining, RH (Relative Humidity) vacuum treatment, continuous casting of a 400-mm thick large-section casting machine, casting blank stack cooling, hot charging and hot feeding, large-deflection controlled rolling, steel plate stack cooling, normalizing and tempering heat treatment and obtainment of fine sorbite and troostite structures.