International Journal of Corrosion
Volume 2015, Article ID 386865, 9 pages
http://dx.doi.org/10.1155/2015/386865
Effects of Strain Energy and Grain Size on Corrosion Resistance of Ultrafine Grained Fe-20%Cr Steels with Extremely low C and N Fabricated by ECAP
1Graduate School of Science and Engineering, Doshisha University, 1-3 Tatara Miyakodani, Kyotanabe, Kyoto 610-0394, Japan
2Department of Mechanical Engineering, Doshisha University, 1-3 Tatara Miyakodani, Kyotanabe, Kyoto 610-0394, Japan
Received 26 August 2014; Revised 9 November 2014; Accepted 21 December 2014
Academic Editor: Raman Singh
Copyright © 2015 Muhammad Rifai et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Effect of strain energy and grain size on corrosion resistance of ultrafine grained (UFG) Fe-20%Cr steels with extremely low C and N fabricated by equal channel angular pressing (ECAP) was investigated. UFG structures of initial grain size of 144 nm exhibited the typical three-stage softening comprising recovery, recrystallization, and grain growth. Potentiodynamic polarization measurements were carried out with a conventional three-electrode cell to evaluate pitting potential. Pitting potential in 1000 molm−3 NaCl solution was nobler in UFG state, but pitting potential started to decrease monotonously at lower temperature compared to hardness. The degradation of corrosion resistance in the early stage of annealing is attributed to stability change of passivation by recovery of dislocation structures inside grains and in nonequilibrium grain boundaries. We therefore conclude that nobler potentials of UFG states were realized by not only grain size reduction but also defective deformation-induced UFG.