Effect of a novel gradient temperature rolling process on deformation, microstructure and mechanical properties of ultra-heavy plate

To improve the mechanical properties of heavy or ultra-heavy plate, continuous casting slabs have to be thick enough to ensure that the required total rolling reduction ratio can be achieved. A novel called gradient temperature rolling (GTR) process, in which the slab is maintained at 800 °C at its surface and 1100 °C at its core, is suggested to improve the quality of ultra-heavy plate which is limited by a reduction ratio. The phenomenon is studied by means of both modeling and experimentation. Finite element modeling (FEM) of ultra-heavy plate rolling was established with MSC Marc software. The temperature field, strain, and stress of the rolling piece were calculated. Under a temperature gradient of about 300 °C, the effect of GTR on the strain distribution, austenite recrystallization, the microstructure in the direction of thickness, and the mechanical properties of an ultra-heavy plate were investigated in the laboratory. The results indicate that the strain and accumulative deformation in the central area of the rolling piece increases significantly. Due to the gradient temperature, the austenite grains are small, complying with ASTM grades 6.1-7.5 and fine and uniform ferrite is formed in the core area of the plate, which is better than that achieved by traditional uniform temperature rolling (UTR). The plate rolled under gradient temperature conditions had excellent mechanical properties, which increased the impact energy by 98.2% and 174.9% in the rolling and cross directions, respectively, and the enlarge area reduction in thickness direction (Z-direction) by 24% compared with UTR processing.