High Strength and High Ductility Martensitic Steels
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Nontechnical AbstractThe "martensite" phase of steel is very strong, but is notorious for poor deformability. There is scattered evidence that shows certain forms of martensite may be ductile, but the mechanisms of enhanced ductility are unclear. Ductile martensite could satisfy a long term industry and government need for high-strength high-ductility steel for automobiles and other transportation vehicles, and a host of nuclear, aerospace and petrochemical applications. This project has the potential to significantly advance the design and discovery of high strength and ductile martensitic steels. In this project, a modified 9% Chromium-1% Molybdenum steel is selected as the test material because it has broad applications in the petrochemical and nuclear industries. The Principal Investigators'' (PI''s) recent studies show ductile martensite may exist in this steel. The PIs have long lasting history of collaboration and their expertise on processing and microscopy/nano-mechanics is nicely complementary. Graduate students will visit the Center for Integrated Nanotechnologies (CINT) at Los Alamos National Laboratory to access their advanced microscopy facilities. The knowledge derived from this project will be incorporated into curricula at Texas A&M University and Purdue University. The PIs will endeavor to recruit minority graduate students through the Pathway to Doctoral Program at Texas A&M University, and from surrounding minority institutions.Technical AbstractThe objective of this project is to understand, at a fundamental level, the impact of alloy chemistry, microstructure, and thermo-mechanical treatment (TMT) on the properties of ductile martensitic steel. The long term goal is to accomplish high strength and high tensile ductility in ferritic/martensitic (F/M) steel. To achieve this goal, the PIs will accomplish the following tasks: (1) tailor the carbon concentration in martensite and control the volume fraction of retained austenite by using the quench-partitioning (Q-P) approach; (2) combine TMT (including hot rolling and equal channel angular extrusion) with the Q-P method to achieve grain refinement and control the morphology of the martensite; (3) investigate the influence of retained austenite films on the deformation mechanisms in T91 steel. Micropillar compression experiments will be used to investigate the shearing response along the austenite/martensite interface to understand its role on ductility of F/M steel. In addition, they will use in situ nanoindentation in a transmission electron microscope and in situ neutron scattering (at a DoE National Laboratory through a user project) to study the influence of austenite/martensite interfaces on absorption of dislocations in martensite during deformation. A successful project will enable design of ductile martensitic steels with mechanical properties that far exceed those of advanced structural steels available today.