304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 304 steel single crystal were investigated in H2SO4-NaCl solution with reference to faceting dissolution and the crystallographic plane of the fracture surface in the two potential zones: I (near the corrosion potential) and II (active-passive transition region). The kinds of facet change in the order of {100}→{100}+{111}→{111} in 1N-H2SO4+0.5M-NaCl solution, and change in the order of {110}→{110}+{100}→{100}+{110}+{111} in 5N-H2SO4+0.5M-NaCl solution with an increase in potential from the corrosion potential to the active-passive transition potential. At the potential of zone I in 5N-H2SO4+0.5M-NaCl solution, cracks are found mainly to initiate at the traces of {110} with large normal stress (σ) and shear stress (τ), and to propagate along {110} in the crystal. On the other hand, at the potential of zone I in 1N-H2SO4+0.5M-NaCl solution, cracks mainly nucleate at the traces of {110} with large σ and τ, and propagate along {100} in the crystal. At the potential of zone II in both solutions, {111} faceting dissolution occurs over all specimen surfaces, and cracks are rarely found. Since the crystallographic plane {hkl} of the fracture surface in zone I corresponds to the slowest dissolution plane {hkl} under the above condition, there is an important relationship between SCC and {hkl} faceting dissolution.