The new research results of Dongda can improve the strength and plasticity of steel at the same time

On January 13, the internationally renowned journal Science published the latest research results on the plasticization mechanism and microstructure innovation design of ultra-high strength steel materials led by Wang Guodong, academician of the Chinese Academy of Engineering, executive deputy director of the Academic Committee of the State Key Laboratory of Rolling Technology and Continuous Rolling Automation of Northeastern University, and Yuan Guo, director of the State Key Laboratory of Rolling Technology and Continuous Rolling Automation of Northeastern University.

The simultaneous improvement of strength and plasticity is a major theoretical problem in the field of steel materials for a long time, and it is also a bottleneck from basic research to technological innovation and application practice, especially when the strength reaches the level of 2000 megapascals (MPa), the plasticity has a cliff-like decline, and the uniform elongation is generally less than 10%, the fundamental reason is that the initial high-density dislocation of traditional martensite (a structural name of ferrous metal materials) is difficult to continue to proliferate, and the microscopic plastic deformation of the geometrically oriented structure arranged in disorder is extremely uneven. Local stress/strain concentration is easily generated.

Aiming at the problem of low plasticity of 2000 MPa martensitic ultra-high strength steel, this study of Wang Guodong and Yuan Guo Research Group innovatively proposed a new synergistic plasticization mechanism of “martensitic topological structure design + metastable phase regulation”, and successfully prepared a series of low-cost C-Mn series new ultra-high strength steels, which broke the dependence of ultra-high strength steel on complex preparation processes and expensive alloy components, and also broke through the performance boundary of tensile strength-uniform elongation of existing 2000 MPa martensitic high strength steels.

Organizational structure design of new ultra-high strength steel.Photo courtesy of Northeastern University

Comparison of tensile properties of new ultra-high strength steels with other ultra-high strength steels.Photo courtesy of Northeastern University

The research team proposed a simple and efficient preparation process route to construct a new topological double-ordered arrangement of martensite and multi-scale metastable austenite nanoscale multi-level organizational structure. The structure of this organization induces various enhanced plasticization mechanisms such as slats interface, dislocation slip, interface plasticity and phase change induced plasticity during the deformation process, which promotes the material to have a sustained high work hardening ability, greatly improves its strength and plasticity, and achieves the ultimate performance of yield strength of 1600~1900 MPa, tensile strength of 2000~2400 MPa and uniform elongation of 18%~25%. The research work was supported by the National Natural Science Foundation of China, the Basic Operating Fund of Central Universities and the China Postdoctoral Science Foundation. (Source: China Science News, Wang Fenghui, Chen Bin)

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