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.

通过温变形工艺制备了具有双峰晶粒层状（BG-L）与超细晶粒层状（UFG-L）微观结构的异质结构铁素体钢。相较于常规调质（QT）钢，BG-L钢的力学性能得到显著提升；而UFG-L钢则展现出强度、塑性与韧性的优异协同组合。进一步研究表明，UFG-L钢在室温（RT）至液氮温度（LNT）区间内未出现韧脆转变（DBT），且在液氮温度下的夏比冲击功仍高达314 J。该钢在液氮温度下韧性增强的原因可归因于晶界分层引发的裂纹止裂机制。