Abstract: Toughness, strength, ductility and fatigue properties can be improved with a finer grain microstructure. However in other to get fine microstructure, it becomes necessary to have additional mechanical or thermal process like severe rolling, inter-critical annealing and others. Also they require more cost but we should minimize it for commercial productions. When we produce plate steel products, it becomes more difficult because their large thickness require hard reduction in rolling and longer time in heat treatment. POSCO recently has developed the plate steels with grain refined surface layers. The grain refined surface layers can improve mechanical properties even in thick plates. During rolling process, the difference of temperatures between surface and center of plate is controlled and only surface layer is inter-critical annealed without an additional beat treatment. The microstructure and its properties would be discussed in detail.
Authors: Il-cheol Yi, Jae-Young Cho, and Sang-Ho Han
Keywords: Plate steel; surface layer; grain refinement