Normalizing thermal treatment process for low-temperature toughness steel plate being 120-200mm in thickness

The invention discloses a normalizing thermal treatment process for a low-temperature toughness steel plate being 120-200mm in thickness. The process comprises the following steps: controlling the temperatures of the first and second sections to be 20-40 DEG C below Ac3 temperature, the third section to be 10-20 DEG C below the Ac3 temperature, the fourth section to be 0-10 DEG C above the Ac3 temperature and the fifth and sixth sections to be 20-30 DEG C above the Ac3 temperature, and gradually raising the temperature inside a thermal treatment furnace; when each steel plate is fed or to be discharged, stopping a walking beam for holding the temperature and controlling the standing time being 20-50 minutes; and controlling the walking beam speed at 0.24-0.37m/min and maintaining a distance being over 3m between the two steel plate fed, wherein the insulating temperature of the steel plates is Ac3+5+/-5 DEG C, the insulating time is 0.5-0.7Hmin, and H is the thickness of the steel plate based on mm. The steel plates are uniformly heated by controlling the temperatures in sections in the thermal treatment furnace and the steel plate standing time so as to obtain a matrix structure which is uniform in organization and fine in grain, so that the standard request on the low temperature impact toughness steel plate is satisfied.