Role of stress-assisted martensite in the design of strong   ultrafine-grained duplex steels
  This work explains the occurrence of transformation-induced plasticity via stress-assisted martensite, when designing ultrafine-grained duplex steels. It is found that, when the austenite is reduced to a fine scale of about 300 nm, the initial deformation-induced microstructure can be dominated by parallel lamellae of epsilon martensite or mechanical twinning, which cannot efficiently provide nucleation sites for strain-induced martensite. Hence, alpha martensite nucleation occurs independently by a stress-assisted process that enhances transformation-induced plasticity in ultrafine-grained austenite. This metallurgical principle was validated experimentally by using a combination of transmission Kikuchi diffraction mapping, transmission electron microscopy, and atom probe microscopy, and demonstrated theoretically by the thermodynamics model of stress-assisted martensite. 
Hung-Wei Yen, Steve Woei Ooi, Mehdi Eizadjou, Andrew Breen, Ching-Yuan   Huang, H. K. D. H. Bhadeshia, and Simon P. Ringer
cond-mat.mtrl-sci