Achieving 2.2 GPa Ultra-High Strength in Low-Alloy Steel Using a Direct Quenching and Partitioning Process

Gang Niu; Donghao Jin; Yong Wang; Haoxiu Chen; Na Gong; Huibin Wu

doi:10.3390/ma16247533

Achieving 2.2 GPa Ultra-High Strength in Low-Alloy Steel Using a Direct Quenching and Partitioning Process

Materials (Basel). 2023 Dec 6;16(24):7533. doi: 10.3390/ma16247533.

Authors

Gang Niu¹, Donghao Jin¹, Yong Wang², Haoxiu Chen³, Na Gong⁴, Huibin Wu¹

Affiliations

¹ Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing, Beijing 100083, China.
² School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.
³ Department of Materials Science and Engineering, University of Toronto, Toronto, ON M5S 3E4, Canada.
⁴ Institute of Materials Research and Engineering (IMRE), A⁎STAR (Agency for Science, Technology, and Research), 2 Fusionopolis Way, Singapore 138634, Singapore.

Abstract

Advanced high-strength steels (AHSS) have a wide range of applications in equipment safety and lightweight design, and enhancing the strength of AHSS to the ultra-high level of 2 GPa is currently a key focus. In this study, a new process of thermo-mechanical control process followed by direct quenching and partitioning (TMCP-DQP) was developed based on Fe-0.4C-1Mn-0.6Si (wt.%) low-alloy steel, and the effects of microstructure evolution on mechanical properties under TMCP-DQP process and conventional hot rolled quenched and tempered process (HR-QT) were comparatively studied. The results show that the TMCP-DQP process not only shortened the processing steps but also achieved outstanding comprehensive mechanical properties. The TMCP-DQP steel exhibited a tensile strength of 2.23 GPa, accompanied by 11.9% elongation and a Brinell hardness of 624 HBW, with an impact toughness of 28.5 J at -20 °C. In contrast, the HR-QT steel exhibited tensile strengths ranging from 2.16 GPa to 1.7 GPa and elongations between 5.2% and 12.2%. The microstructure of TMCP-DQP steel primarily consisted of lath martensite, containing thin-film retained austenite (RA), nanoscale rod-shaped carbides, and a minor number of nanoscale twins. The volume fraction of RA reached 7.7%, with an average carbon content of 7.1 at.% measured by three-dimensional atom probe tomography (3DAP). Compared with the HR-QT process, the TMCP-DQP process resulted in a finer microstructure, with a prior austenite grain (PAG) size of 11.91 μm, forming packets and blocks with widths of 5.12 μm and 1.63 μm. The TMCP-DQP process achieved the ultra-high strength of low-alloy steel through the synergistic effects of grain refinement, dislocation strengthening, and precipitation strengthening. The dynamic partitioning stage stabilized the RA through carbon enrichment, while the relaxation stage reduced a small portion of the dislocations generated by thermal deformation, and the self-tempering stage eliminated internal stresses, all guaranteeing considerable ductility and toughness. The TMCP-DQP process may offer a means for industries to streamline their manufacturing processes and provide a technological reference for producing 2.2 GPa grade AHSS.

Keywords: 2.2 GPa ultra-high strength steel; TMCP-DQP process; martensite; mechanical properties; retained austenite.

Abstract

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