Improvement of toughness at the mid-thickness of thick rolled steel plate (more than 50 mm) and manufacturing procedure for getting uniform properties over the whole thickness position were studied.
High shape factor rolling (large roll diameter and large reduction per pass) at non-recrystallization region brought about excellent toughness at the mid-thickness. We studied by simulation experiment and rigid plastic finite element method (FEM) analysis, and showed that high shape factor rolling increased rolling effect and resulted in fine ferrite grain size at the mid-thickness.
Excessive high shape factor rolling made recrystallization of austenite grain, and toughness deteriorated. Consequently, choice of appropriate rolling temperature and rolling pass schedule is important.
The thick steel plates with 50 kgf/mm2 grade high tensile strength made by applying high shape factor rolling technology have excellent toughness at base plate over the whole thickness position and at welded joints, and can be used for arctic service.
