Extending the boundaries of mechanical properties of Ti-Nb low-carbon steel via combination of ultrafast cooling and deformation during austenite-to-ferrite transformation

• Published in: Metals and materials international Vol. 23; no. 1; pp. 175 - 183
• Main Authors: Deng, Xiangtao, Fu, Tianliang, Wang, Zhaodong, Liu, Guohuai, Wang, Guodong, Misra, R. D. K.
• Format: Journal Article
• Language: English
• Published: Seoul The Korean Institute of Metals and Materials 2017; Springer Nature B.V; 대한금속·재료학회
• Subjects: Austenite; Boundaries; Carbon content; Cement constituents; Cemented carbides; Cementite; Characterization and Evaluation of Materials; Chemistry and Materials Science; Cooling; Crystal structure; Deformation; Ductility; Engineering Thermodynamics; Ferrite; Heat and Mass Transfer; Hot rolling; Iron constituents; Lamellar structure; Low carbon steel; Low carbon steels; Machines; Magnetic Materials; Magnetism; Manufacturing; Materials Science; Mechanical properties; Metallic Materials; Microscopy; Microstructure; Nanostructure; Niobium; Pearlite; Precipitates; Precipitation; Precipitation hardening; Processes; Solid Mechanics; Transformations; Yield strength; Yield stress; 재료공학; deformation; precipitation behavior; ultra-fast cooling; Ti-Nb bearing steel; mechanical properties
• DOI: 10.1007/s12540-017-6241-8
• ISSN: 1598-9623

We underscore here a novel approach to extend the boundaries of mechanical properties of Ti-Nb low-carbon steel via combination of ultrafast cooling and deformation during austenite-to-ferrite transformation. The proposed approach yields a refined microstructure and high density nano-sized precipitates, with consequent increase in strength. Steels subjected to ultra-fast cooling during austenite-to-ferrite transformation led to 145 MPa increase in yield strength, while the small deformation after ultra-fast cooling process led to increase in strength of 275 MPa. The ultra-fast cooling refined the ferrite and pearlite constituents and enabled uniform dispersion, while the deformation after ultra-fast cooling promoted precipitation and broke the lamellar pearlite to spherical cementite and long thin strips of Fe x C. The contribution of nano-sized precipitates to yield strength was estimated to be ~247.9 MPa and ~358.3 MPa for ultrafast cooling and deformation plus ultrafast cooling processes. The nano precipitates carbides were identified to be (Ti, Nb)C and had a NaCl-type crystal structure, and obeyed the Baker-Nutting orientation relationship with the ferrite matrix.