Michinori Takano

Direct Observations of Stress Corrosion Crack Tips of Type 304 Stainless Steel in a Boiling 42% MgCl2 Solution

Abstract Using a high voltage electron microscope, direct observations of stress corrosion crack tips in Type 304 sheet specimens of 0.1 mm thickness were carried out to clarify the propagation mechanism for stress corrosion cracking. The propagation behavior of stress corrosion cracks in these sheet specimens were shown to be the same as those in a normal ‘bulk’ material. It has been found that transgranular stress corrosion cracks propagate along the slip planes, forming a small scale of plastic zone resulting from a stress concentration due to the crack. At the stress corrosion crack tips, the slip planes containing moving dislocations were preferentially attacked to form a crack, but there was no evidence of martensite transformation or tunneling corrosion. Direct observations of crack tips revealed that the crack proceeded along {111} slip planes, while fracture planes were {100} or {110} rather than {111} planes by the etch pit method. Appearance of these low indexed planes in the etch pit method wa...

HVEM Observations of Crack Tip Produced in Type 304 Stainless Steel by SCC and HE

Abstract Using a high voltage electron microscope (HVEM), observations of stress corrosion crack tips of a sheet specimen of Type 304 stainless steel in 2.5 mol/l H2SO4 + 0.5 mol/l NaCl at room tem...

The mechanism of stress-corrosion cracking in the brass-ammonia system

Abstract The effect of corrosive environments, compositions of alloying elements and degree of pre-strain on the stress-corrosion cracking of the brass-ammonia system, has been investigated and the mechanism of intergranular cracking and of the transition from intergranular to transgranular cracking have been discussed. Intergranular cracking arises from the formation of thick and large cuprous oxide grains over slip steps and the resulting locking of the movement of dislocations. The transition from intergranular to transgranular cracking depends on the mechanical properties of the surface film produced in a corrosive environment. The mechanism of the stress-corrosion cracking has been explained on the basis of the film theory.

Relationship between stress—corrosion cracking and strain rate in alpha brass

Stress—corrosion cracking of Cu—30%Zn alloy under the constant strain rate in the range of 6·6 × 10−6 s−1 to 1·1 × 10−2 s−1 was investigated in Mattssons solution (pH 7·2) (for inter-granular cracking) and in 1 M/L NH4OH + 0·25 M/L CuCl2 aqueous solution (pH 11·0) (for transgranular cracking). Within strain rates of 6·6 × 10−6 s−1 for intergranular cracking and of 1·1 × 10−5 s−1 for transgranular cracking, the rate-controlling step of stress—corrosion cracking corresponds to the slip step formation. Exceeding the above strain rates the s c c is controlled by the corrosion, where the rate-controlling mechanism requires the activation energy of about 18·7 Kcal/mol. When the strain rate exceeds 1·1 × 10−3 s−1, intergranular s c c never occurs at room temperature. Width of crack tip increases with increase of strain rate for intergranular cracking, while decreases for transgranular cracking.

The effects of crosshead speed and temperature on the stress corrosion cracking of Cu-30% Zn alloy in ammoniacal solution

Abstract Stress corrosion cracking (s.c.c. of Cu-30% Zn alloy in Mattssons solution (0.05 mol/l CuSO 4 + 0.5 mol/l (NH 4 ) 2 SO 4 , pH 7.2) was investigated as a function of temperature (298 K–323 K) and crosshead speed (10 −5 mm/min to 1 mm/min). Crack propagation behaviour in a crosshead speed of 10 −4 mm/min at 298 K was also studied. All tests were carried out using a slow strain rate technique. Cracks occurred intergranularly under all experimental conditions used. At high crosshead speeds (5 × 10 −3 mm/min to 1 mm/min) the susceptibility to s.c.c. increased with increasing temperature. At slow crosshead speeds, however, an inverse effect of temperature on the susceptibility was revealed. Constant crack velocities were obtained in both specimens with or without surface coating, and the velocity in the coated specimen was lower than that in the uncoated specimen by one order of magnitude. Scanning electron microscopic examination revealed that ahead of intergranular cracks small corrosion pits were formed along grain boundaries. Based on the above experimental results, the mechanism of intergranular s.c.c. of Cu-30%Zn alloy was discussed by considering the growth rate of microcrack formed along grain boundary and the corrosion rate (or repassivation rate) of the microcrack.

Stress Corrosion Cracking of Type 304 Stainless Steel under Residual Stress

Abstract A new stress corrosion test method sensitive to residual stress has been developed. In this method, disk type specimens (25 mm ϕ × 3 mm), which were pressed at different loads by a Brinell hardness testing machine, were used. Stress corrosion testing of Type 304 stainless steel in boiling MgCl2 at 416K revealed that cracks occurred radially for a circumferential residual stress and circumferentially for a radial residual stress. Near the edge of sensitized specimens with residual stress, slight intergranular cracking occurred after 783 hours in pure water containing 8 ppm dissolved oxygen at 561K, although intergranular cracking of the specimen without residual stress in this water occurred easily under slow strain rate testing conditions. Since small specimens can be used in this method, a number of specimens can be tested at once in small space and the reliability of the results obtained is high.

Transgranular Stress Corrosion Cracking of Mild Steel in 0.5N H2SO4 + 0.005N KI Solution – Stress Corrosion Behavior Under Constant Crosshead Speed Test

Abstract Investigation of stress corrosion cracking (SCC) of mild steel in 0.5N H2SO4 + 0.005N KI was carried out using a constant crosshead speed method at room temperature. Smooth specimens teste...

Transgranular Stress Corrosion Cracking of Mild Steel in 0.5N H2SO4 + 0.005N Kl Solution – XPS Observation of the Surface Film

Abstract The surface film formed on strained mild steel in 0.5N H2SO4 containing 0.005N Kl was examined by XPS in connection with the SCC susceptibility which is highest around 0.06 V relative to the corrosion potential. The film was found to consist mainly of FeOOH containing small amounts of sulfur and iodide. The iodide content alone varied with the polarization potential and had a critical potential coinciding with that for the SCC susceptibility, which is explained by the instability of the surface film at the potential.