Journal of Materials Research and Technology Journal of Materials Research and Technology
J Mater Res Technol 2017;6:339-47 DOI: 10.1016/j.jmrt.2017.05.001
Original Article
Stored energy in ultrafine-grained 316L stainless steel processed by high-pressure torsion
Moustafa El-Tahawya,b, Yi Huangc, Taekyung Umd, Heeman Choed, János L. Lábára,e, Terence G. Langdonc, Jenő Gubiczaa,,
a Department of Materials Physics, Eötvös Loránd University, Budapest, Hungary
b Department of Physics, Faculty of Science, Tanta University, Tanta, Egypt
c Materials Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton, United Kingdom
d School of Materials Science & Engineering, Kookmin University, Seoul, Republic of Korea
e Institute for Technical Physics and Materials Science, Centre for Energy Research, Hungarian Academy of Sciences, Budapest, Hungary
Received 10 April 2017, Accepted 06 May 2017
Abstract

The energy stored in severely deformed ultrafine-grained (UFG) 316L stainless steel was investigated by differential scanning calorimetry (DSC). A sample was processed by high-pressure torsion (HPT) for N=10 turns. In the DSC thermogram, two peaks were observed. The first peak was exothermic and related to the annihilation of vacancies and dislocations. During this recovery, the phase composition and the average grain size were practically unchanged. The energy stored in dislocations was calculated and compared with the heat released in the exothermic DSC peak. The difference was related to the annihilation of vacancy-like defects with a concentration of ∼5.2×10−4. The second DSC peak was endothermic which was caused by a reversion of α′-martensite into γ-austenite, however in this temperature range dislocation annihilation and a moderate grain growth also occurred. The specific energy of the reverse martensitic phase transformation was determined as about −11.7J/g.

Keywords
High-pressure torsion, Stored energy, Stainless steel, Phase transformation, Thermal stability
J Mater Res Technol 2017;6:339-47 DOI: 10.1016/j.jmrt.2017.05.001