Ultrastrong Dual-phase Heterostructure Low C.rbon Steel Reinforced by Ultra Nano Lamellae

Description

Strong materials are desired for advanced technologies in i transportation, energy, aerospace, medical and civil industries. So far, one of the most effective approaches to process ultra-strong materials is grain refinement by severe plastic deformation (SPD). SPD methods are capable of processing bulk nanostructured materials with superior strength, but their scaling up for industrial production is still challenging. Recently, we have produced a new type of heterostructured nano-lamellar material at low cost using readily available industrial facilities [1]. The key to effective and low-cost processing of nano-lamellar material lies in two novel concepts– (1) tuning strain incompatibility in heterostructured materials, and (2) segregating solute atoms to lamellar boundaries to stabilize the nano-lamellae. Using these two concepts, we have successfully processed an ultrastrong low-carbon nanosteel by a simple warm rolling process. The work presents a viable industrial method for processing bulk nanostructured materials, but also raises some fundamental issues that need to be addressed: (1) How does the strain incompatibility in heterostructured materials was accommodated by the local deformation mechanisms? (2) To what extent, the local stress state and the local strain have accelerated the grain refinement process? (3) What are the major effects of segregation on grain refinement and structure stabilization? Here we propose to address the above issues using a low-carbon steel with a nominal composition (weight %) of 0.19 C-1.01 Mn-1.46 Si as the model material. A designated processing route involving pre-heat-treatment and warm rolling will be carried out to produce the nanosteel. Systematic microstructural characterization will be performed to reveal the detailed microstructural evolution and grain refinement processes under the warm rolling condition. State-of-art in-situ microstructural characterization methods will be conducted to analyze the relationship between deformation mechanisms and the local strain. Ex-situ atom probe tomography will be used to investigate the segregation effects induced by warm rolling with increasing strain. This project is expected to lead to an in-depth understanding of heterostructured materials, including the deformation mechanisms, grain refinement process and the character of strain incompatibility. Furthermore, it will offer a scientific knowledge for establishing effective grain refinement methods for other heterostructured materials, thus to expand the industrial applications of heterostructured materials.