The effect of severe plastic deformation and annealing conditions on mechanical properties and restoration phenomena in an ultrafine-grains Fe-28.5%Ni steel

ABSTRACT

The effect of annealing condition on the microstructure evolution, together with mechanical properties of Fe-28.5Ni steel processed by one and six cycles of accumulative roll bonding (ARB), was explored. The evolution of microstructure was studied by means of Electron Backscattered Diffraction method. The ARB-processed specimens were annealed for 30 minutes between 500°C and 600°C, and the effect of these annealing processes was elaborated. Results showed a significantly reduced martensite phase during ARB process cycles. Moreover, a refined and stabilised ultrafine structure was obtained in 6-cycle ARB-processed specimen. Results also show that by annealing the 1-cycle specimen at 550°C, no significant microstructural change and mechanical properties variation are identified. As such, no significant microstructural change and mechanical properties variation were notified for annealing of 6-cycle ARB-processed specimen at 500°C. However, annealing at 600°C in both conditions led to a complete recrystallisation of the deformed structure. Annealing at 550°C in 6-cycle ARB-processed specimen showed partial recrystallisation as well as an abnormal grain growth characteristic. The abnormal grain growth was seen by annealing of 1-cycle ARB-processed specimen at 600°C. The changing features of dislocations were discussed in these specimens in terms of changing the dynamics of low- and high-angle grain boundaries. Tensile test results also showed a significant increase in the yield/ultimate tensile strengths with the application of ARB cycles. Although ARB process led to a rapid reduction of total elongation, full restoration during high-temperature annealing returned this value back to the initial, non-deformed, condition.

KEYWORDS:

• Ultrafine grains
• accumulative roll bonding (ARB)
• annealing
• recrystallisation
• total elongation
• microstructure

Acknowledgements

The EBSD analysis of the present study was conducted during Dr Hamidreza Jafarian’s stay in Prof. Tsuji lab in the Dept. of Materials Science & Engineering at Kyoto University, which was supported by the JASSO follow-up fellowship. Therefore, the authors are grateful for all the help provided in this regard. Also, the authors are grateful of Dr Alireza Eivani’s constructive discussion during the preparation of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

S. H. Mousavi Anijdan http://orcid.org/0000-0003-4453-2116

H. R. Jafarian http://orcid.org/0000-0002-8405-3913