SUS 310S鋼単結晶のH<SUB>2</SUB>SO<SUB>4</SUB>-NaCl溶液中における応力腐食割れ

Abstract

The characteristics of stress corrosion cracking (SCC) of type 310 S steel single crystal were investigated in H2SO4-NaCl solution with reference to faceting dissolution and a crystallographic plane of the fracture surface in the two potential zones: I (near the corrosion potential) and II (active-passive transition region). Kinds of facets change in the order of {100}→{100}+{111}→{111} in 2.5 kmol/m3-H2SO4+0.2 kmol/m3-NaCl and 2.5 kmol/m3-H2SO4+0.5 kmol/m3-NaCl solutions, and change in the order of {100}→{110}→{111} in 2.5 kmol/m3-H2SO4+0.8 kmol/m3-NaCl solution with an increase in potential from the corrosion potential to the active-passive transition potential. There are many cracks on the {100} specimen surface at the potential of {100} faceting dissolution, and are many cracks on the {110} specimen surface at the potential of {110} faceting dissolution compared with other crystallographic planes. Cracking occurs as the result of a competition process between the dissolution rate on the surface (Ih) and the crack growth rate (\Dot{C}), and the upper critical potential corresponds to a potential to give a relation, Ih\simeq\Dot{C}. At the potentials of zone I in every solution, a crystallographic plane {hkl} of the fracture surface corresponds to the slowest dissolution plane {hkl} under every given condition. On the other hand, at the potentials of zone II {111} faceting dissolution occurs over all specimen surfaces. These results imply an important relationship between SCC and {hkl} faceting dissolution.