Strength and ductility are mutually exclusive if they are manifested as consequence of the coupling between strengthening and toughening mechanisms. One notable example is dislocation strengthening in metals, which invariably leads to reduced ductility. However, this trend is averted in metastable austenitic steels. A one-step thermal mechanical treatment (TMT), i.e. hot rolling, can effectively enhance the yielding strength of the metastable austenitic steel from 322 +/- 18 MPa to 675 +/- 15 MPa, while retaining both the formability and hardenability. It is noted that no boundaries are introduced in the optimized TMT process and all strengthening effect originates from dislocations with inherited thermal stability. The success of this method relies on the decoupled strengthening and toughening mechanisms in metastable austenitic steels, in which yield strength is controlled by initial dislocation density while ductility is retained by the capability to nucleate new dislocations to carry plastic deformation. Especially, the simplicity in processing enables scaling and industrial applications to meet the challenging requirements of emissions reduction. On the other hand, the complexity in the underlying mechanism of dislocation strengthening in this case may shed light on a different route of material strengthening by stimulating dislocation activities, rather than impeding motion of dislocations.
H. Wang acknowledges the financial support from National Natural Science Foundation of China (Nos 11322219 and 11321202), the Fundamental Research Funds for the Central Universities of China (2014XZZX003-19). J. Liu acknowledges the support from the financial support from National Natural Science Foundation of China (Nos 11202183 and 11572281), the National High Technology Research and Development Program (863) of China under Grant No. 2011AA11A101, the State Key Laboratory for Strength and Vibration of Mechanical Structures Program of Xi'an Jiaotong University (SV2014-KF-13).
[Liu, Jiabin] Xi An Jiao Tong Univ, State Key Lab Strength & Vibrat Mech Struct, Xian 710049, Peoples R China; [Liu, Jiabin; Fang, Xiaoyang; Chen, Chenxu; Meng, Liang] Zhejiang Univ, Coll Mat Sci & Engn, Hangzhou 310027, Zhejiang, Peoples R China; [Jin, Yongbin; Feng, Qiong; Wang, Hongtao; Yang, Wei] Zhejiang Univ, Inst Appl Mech, Hangzhou 310027, Zhejiang, Peoples R China; [Liu, Xiaowei; Lu, Jian] City Univ Hong Kong, Dept Mech & Biomed Engn, Hong Kong, Hong Kong, Peoples R China; [Chen, Yuzeng; Suo, Tao] Northwestern Polytech Univ, Xian 710072, Peoples R China; [Zhao, Feng] Ctr High Pressure Sci & Technol Adv Res, Shanghai 201203, Peoples R China; [Huang, Tianlin] Coll Mat Sci & Engn, Chongqing 400044, Peoples R China; [Wang, Xi] Beijing Jiaotong Univ, Sch Mech Elect & Control Engn, Beijing 100044, Peoples R China; [Fang, Youtong] Zhejiang Univ, Coll Elect Engn, Hangzhou 310027, Zhejiang, Peoples R China; [Wei, Yujie] Chinese Acad Sci, Inst Mech, LNM, Beijing 100190, Peoples R China