Tunnel Formation in Iron-Nickel-Chromium Alloys

Abstract

Abstract Oxide films were stripped from a series of stressed Fe-Ni-Cr alloys exposed to boiling 42 percent MgCl2. Evidence of dissolution tunnels was found in Types 304 and 310 stainless steels and Incoloy 800. No tunnels were observed in Incoloy 825 or Inconel 600. The frequency of observed tunnels was proportional generally to the susceptibility of these alloys to stress corrosion cracking in MgCl2. The mechanism for formation of the tunnels appears to be related to the interaction between dislocations and prior irregularities in initial dissolution trenches resulting from rapid dissolution at emergent slip steps. Evidence from this work suggests that the tunnels are a special case of local slip step activated dissolution. Tunneling itself appears not to be an integral part of the mechanism of stress corrosion cracking but can occur as an associated or parallel process.