Advanced High Strength Multiphase Steels through a Combined Alloy-Microstructural Design

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In the next few years, the Federal government will implement the most comprehensive overhaul of the U. S. vehicle fleet?s emission and fuel economy standards to date. One of most attractive approaches to improved fuel economy is vehicle?s weight reduction for which near-term and cost-effective solutions can be found through the use of Advanced High Strength Steels (AHSS). Thus, the research objective of this award is to design and fabricate low-alloy, low-cost multiphase steels with a composite microstructure consisting of an ultrafine-grained (UFG) ferrite matrix with dispersions of bainite and stabilized austenite. Such microstructure should assure high strength for weight reduction, high ductility to allow easy formability, and high fracture toughness. These goals will be achieved through the synergistic combination of alloy and microstructural design via both computational and experimental approaches including design of alloy compositions and heat treatment schedules for optimal volume fractions of the constitutive phases, and refinement of the grain size to submicron to nano range using thermomechanical processing techniques including severe strain path changes and severe simple shear deformation with the help of a novel microstructure based modeling for process optimization. If successful, the results of this research will provide an opportunity for revolutionizing the field, by moving away from current expensive or low ductility and poor formability HSSs, to AHSSs possessing high strength-high ductility-good formability-low cost combination; and by the creation of an entirely new family of ?nano-steels?, which will have significant impact on future advanced transportation vehicles, power generation equipment, and weapons systems. Ultimately, the methodologies for alloying and microstructural design developed in this work will significantly contribute to the overall effort to increase the competitiveness of U.S. manufacturing. Graduate and undergraduate students including several minority students will benefit through new course developments, classroom instruction and direct involvement in the research. K-12 students and high school teachers will be engaged in the computational/experimental research activities to increase the awareness of science and engineering among them and provide them firsthand research experience.