Gradient temperature rolling induced homogenization of through-thickness mechanical properties and improved surface corrosion resistance in a heavy steel plate

Through-thickness heterogeneity in heavy steel plates is mainly caused by insufficient interior deformation during thermomechanical processing, leading to microstructural coarsening and poor low-temperature toughness. In this study, uniform temperature rolling (UTR) and gradient temperature rolling (GTR) were compared using specimens from the surface, quarter-thickness, and mid-thickness regions. Mechanical testing, EBSD, fractography, corrosion testing, and finite-element simulation were used to reveal the effects of rolling strategy on deformation behavior, microstructure, crystallographic characteristics, and overall properties. GTR produced markedly more homogeneous through-thickness properties than UTR, with the greatest improvement observed in impact toughness. The impact toughness increased from 142.1, 91.7, and 162.8 J under UTR to 209.2, 228.5, and 238.4 J under GTR at the surface, quarter-thickness (1/4), and mid-thickness (1/2), respectively, representing increases of 47.2%, 149.2%, and 46.4%. GTR also refined martensitic laths and prior austenite grains throughout the thickness, especially in the interior regions, and maintained a higher geometrically necessary dislocation density. Simulation results showed that the preset temperature gradient promoted deformation penetration into the plate interior. The improved toughness was associated with refined microstructure and enhanced resistance to slip transfer and crack propagation. In addition, GTR slightly improved surface corrosion resistance. These results demonstrate that GTR is an effective approach to suppress through-thickness heterogeneity in heavy steel plates and to improve both toughness level and toughness uniformity.