METHOD AND APPARATUS FOR MANUFACTURING STEEL SHEET WITH ULTRA HIGH STRENGTH

摘要

PURPOSE: A device and a method for manufacturing an ultra high strength steel plate are provided to reduce the internal stress of a hot rolled steel plate by maintaining the hot rolled steel plate being rolled into a coil at constant temperature. CONSTITUTION: A method for manufacturing an ultra high strength steel plate comprises the steps of: hot rolling a slab at a temperature higher than the Ar3 temperature, slowly cooling the hot rolled steel plate in order to create ferrite in the steel plate, rapidly cooling the steel plate immediately below the temperature of the martensite transition(Ms) in order to create martensite in the steel plate, maintaining the cooled steel plate at a temperature of 400°C-300°C, and rolling the steel plate into a coil.