Eliminate the contradiction between temperature and toughness by grain-boundary delamination in heterogeneous ultrafine-grained lamellar steels

Heterostructured ferritic steels with bimodal-grained lamellar (BG-L) and ultrafine-grained lamellar (UFG-L) microstructure were prepared through a warm deformation process. The BG-L steel exhibits enhanced mechanical properties compared to conventional quenched and tempered (QT) steel. While the UFG-L steel demonstrates an outstanding combination of strength, ductility, and toughness. Furthermore, the UFG-L steels exhibit no ductile-to-brittle transition (DBT) from room temperature (RT) to liquid nitrogen temperature (LNT) and the Charpy impact energy remains as high as 314 J at LNT. The enhanced toughness at LNT can be attributed to the crack-arrester mechanism caused by grain-boundary delamination.