Growth behavior of surface oxide layer on SUS316L stainless steel at the early stage of exposure to 288C water

Soma, Yasutaka   ; Kato, Chiaki   ; Yamamoto, Masahiro 

Surface oxide layer on SUS316L stainless steels exposed to 288C pure water with 2ppm dissolved oxygen (DO) for 1100h were analyzed using Focused Ion Beam and Scanning Transmission Electron Microscope equipped with EDS to understand the early stage of surface oxide layer formation. At 1h exposure, double oxide layer which is composed of compact inner oxide layer and outer oxide layer with Fe-rich and Ni-rich oxide particles was formed. At the outermost region of the SUS316L substrate, Ni and Cr were enriched. At 100h exposure, growth of the inner oxide layer was suppressed and the Ni and Cr enriched region at the alloy substrate was preserved underneath the Ni-rich outer oxide particles. At 1h exposure, most of the outer oxide particles were composed of Fe-rich ones, at 10h exposure, another Ni-rich outer oxide particles were nucleated and grew faster than Fe-rich ones. Consequently, a part of pre-formed Fe-rich outer oxide particles were covered with Ni-rich ones.