Superior strength and ductility of 316L stainless steel with heterogeneous lamella structure
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Strength and ductility are two of the most important mechanical properties for a metal, but often trade off with each other. Here, we report a 316L stainless steel with superior combinations of strength and ductility that can be controlled by fine-tuning its heterogeneous lamella structure (HLS). The HLS was produced by 85% cold rolling, which produced lamellar coarse grains sandwiched between mixtures of nano-grains and nano-twins. The HLS was fine-tuned by annealing at 750 °C for 5–25 min, which resulted in varying volume fractions of nano-grains, nano-twins, lamellar coarse grains, and recrystallized grains. During tensile testing, large amount of geometrically necessary dislocations were generated near the heterostructure interfaces to coordinate the deformation between soft domains and hard domains, which results in high back stress to achieve superior combination of strength and ductility. An optimal high yield strength of ~ 1 GPa with an elongation-to-failure of ~ 20% was obtained for an optimized HLS sample. Furthermore, the processing technique employed here is conducive to large-scale industrial production at low cost.
The authors acknowledge the financial support of National Key R&D Program of China (2017YFA0204403), National Natural Science Foundation of China (Grant Nos. 51301092 and 51741106 (Yusheng Li), No. 51601094 (Yang Cao)), the Jiangsu Key Laboratory of Advanced Micro & Nano Materials and Technology, and the Pangu Foundation. Yuntian Zhu acknowledges the support of the US Army Research Office (W911 NF-17-1-0350). EBSD and TEM were performed in the Materials Characterization and Research Center of the Nanjing University of Science and Technology.
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Conflicts of interest
The authors declare that they have no conflict of interest.