Rokuro Nishimura

The effect of chloride ions on stress corrosion cracking of type 304 and type 316 austenitic stainless steels in sulfuric acid solution

Abstract Stress corrosion cracking of type 304 and type 316 austenitic stainless steels has been investigated as a function of chloride ion concentration in 0.82 kmol m −3 pure sulfuric acid solution at 353 K under a constant stress of 392 MPa by using a constant load method. At a concentration of up to approximately 2 × 10 −2 kmol m −3 type 316 has no SCC susceptibility as well as the result in the pure sulfuric acid solution, while type 304 has SCC susceptibility the same as that in the pure sulfuric acid solution except for a narrow concentration range of around 1 × 10 −3 kmol m −3 , at which concentration type 304 has no or little SCC susceptibility. The behavior of type 304 at the narrow concentration range means that chloride ions serve as inhibitor for SCC. At higher concentrations of more than 2 × 10 −2 kmol m −3 the SCC susceptibility of both steels increases with increasing chloride concentration, which implies that chloride ions act as promotor for SCC. In addition, the logarithm relationship between time to failure and steady state elongation rate is found to become a good straight line with a slope of unity independent of the material and chloride concentration. The steady state elongation rate becomes a parameter for the prediction time to failure even in the mixed solution of sulfuric acid and the chloride ions. The present results obtained are qualitatively explained in terms of adsorption of chloride ions at crack tips through a SCC process.

Anodic oxidation and kinetics of titanium in 1 M chloride solutions

Abstract The anodic behaviour of titanium was investigated in 1 M chloride solutions of pH ranging from 0.0 to 12.0 by using electrochemical techniques combined with chemical analysis. No active region appears in solutions of pH above 2.0. In the passive region, the amount of titanium dissolved into the solution during 1 h oxidation decreases with increasing pH, and no dissolution occurs at pH 10.5. The thickness of passive films estimated from the electric charge accumulated on the surface increases linearly with the potential. The kinetic analysis between the anodic current and the film charge indicates that the growth of the passive film obeys the inverse logarithmic rate law, and the kinetic parameters are calculated.

Intensity-following ellipsometry of passive films on iron

Abstract Structures of passive films on iron formed by a two-step passivation method in acidic and neutral phosphate solutions were investigated by means of intensity-following ellipsometry combined with a cathodic reduction technique. The passive films thus formed were generally composed of a barrier layer and a deposit layer each with different optical constants. In pH below 5.5 the barrier layer was divided into two, and below pH 2 the outer deposit layer was dissolved away. The total thickness of the film at a constant overpotential increased with the solution pH, but the thickness of the barrier layer was nearly constant irrespective of the pH.

The effect of potential on stress corrosion cracking of type 316 and type 310 austenitic stainless steels

Abstract The stress corrosion cracking (SCC) of type 316 and type 310 austenitic stainless steels has been investigated as a function of applied potential and solution temperature in 0.82 kmol m −3 HCl solution under a constant stress condition. The results of type 316 show that the cracking behavior is different at a potential below and above −90 mV(SHE) in the vicinity of the corrosion potential, −60 mV(SHE). Type 310 exhibits no failure at potentials in the cathodic region. The double logarithmic relation between steady state elongation rate and time to failure becomes a linear function irrespective of potential, solution temperature and the materials, although the slope depends upon the potential region (cathodic and anodic) and solution temperature. This implies that the steady state elongation rate becomes a useful parameter for the prediction time to failure as compared to the potential. On the basis of the results obtained, it is suggested that the cracking of type 316 is caused by hydrogen embrittlement (HE) in the cathodic potential region, while in the anodic potential region that of type 316 and type 310 takes place by SCC subjected to anodic dissolution.

The effects of passive films formed on iron, nickel and austenitic stainless steels (SUS 304 and SUS 316) on pitting corrosion

Abstract The breakdown of passive films formed on Fe, Ni and austenitic stainless steels (SUS304 and SUS316) was investigated at a constant potential more noble than their critical pitting potentials in a 0.5 kmol/m3 NaCl solution to elucidate the effects of the passive films on pitting corrosion. The results obtained were discussed in terms of film thickness, ion selectivity, film composition and the nature of bound water. Furthermore a mechanism of their film breakdown was proposed along with a modified penetration model.