Jiro Kuniya

Effect of Cold Work on the Stress Corrosion Cracking of Nonsensitized AISI 304 Stainless Steel in High-Temperature Oxygenated Water

Abstract The effect of cold work on the stress corrosion cracking (SCC) of solution-annealed (nonsensitized) AISI 304 stainless steel (SS) in 288 C oxygenated pure water was studied utilizing crevi...

Mechanochemical model to predict stress corrosion crack growth of stainless steel in high temperature water

Abstract This paper presents a predictive methodology for SCC crack growth using a mechanochemical model based on a slip formation/dissolution mechanism. The mechanochemical model consists of the combined kinetics of the plastic deformation process as a mechanical factor and the slip dissolution–repassivation process as an environmental factor at a crack tip. The predictive equation of SCC crack growth rate for type 304 SS in water at 288°C is formulated as a function of stress intensity factor, material conditions (degree of sensitization, K ISCC , strain hardening coefficient) and water chemistry (water conductivity, corrosion potential). The theoretical predictions according to the mechanochemical model are quantitatively in good agreement with many experimental observations of the effect on SCC crack growth for type 304 SS in 288°C water.

Effect of MnS Inclusions on Stress Corrosion Cracking in Low-Alloy Steels

Abstract Effect of MnS inclusions on the stress corrosion cracking (SCC) of low-alloy steel in 288°C oxygenated pure water was studied using slow strain rate tensile (SSRT) test. MnS inclusions dissolve and can act as starting points of SCC. At high amounts of dissolved oxygen (about 8 ppm), pitting corrosion and MnS inclusions act as starting points of SCC, while at low amounts of dissolved oxygen (about 0.2 ppm), MnS inclusions dominate the SCC initiation. The probability of MnS inclusions existing on the specimen side surface is an important factor for SCC initiation susceptibility of the material. The number of SCC starting points in intermediate sulfur content material (about 0.015 wt%S) is larger than that in low-sulfur content material (about 0.004 wt%S). The existence of MnS inclusions also affects the SCC propagation, particularly at low, dissolved oxygen (about 0.2 ppm).

The effect of solute content on grain boundary segregation in electron-irradiated Fe-Cr-Mn alloys

Solute distribution and microstructural development in the vicinity of grain boundaries in ferritic Fe-10Cr-xMn-3Al (x = 5, 10 or 15) alloys were studied during electron irradiation to 10 dpa at 723 K. In addition, X-ray diffraction analysis was performed for determination of the volume size factor of solutes. The oversized solute atoms, manganese and aluminum, were depleted at grain boundaries, whereas the concentration of the oversized chromium rose sharply at the boundary. The amount of segregation of the solutes decreased with increasing atomic volume depending on manganese content. Segregation of aluminum, which had the greater volume size factor relative to that of manganese, was higher than that of manganese. The amount of radiation-induced segregation of manganese and aluminum at the grain boundary is consistent with arguments based on the atomic size effect, but the enrichment of chromium at the grain boundary is not and seems to related primarily to the formation of chromium-rich precipitates at the boundary.

Phase Transition in YBa2Cu3O7-x through Hydrogen Ion Implantation

Phase transition in YBa2Cu3O7-x through hydrogen ion implantation was investigated by means of X-ray diffraction. It was found that the orthorhombic-to-tetragonal phase transition was induced by the implantations in the ion fluences of 7.6×1016 H+/cm2 and above. At the 2.3×1017 H+/cm2 implantation, the extra phases Y2BaCuO5 and CuO were also formed. These phenomena suggested that the implanted hydrogen atoms deoxidized the YBa2Cu3O7-x to produce H2O which reacted with YBa2Cu3O7-x.

Enhanced Critical Magnetization Currents due to Electron Irradiation in High-Tc Oxide Superconductors

Three kinds of high-Tc oxide superconductors were successively irradiated with 3 MeV electrons up to 1.0×1018 e/cm2 at about 370 K, and magnetization measurements were performed at 77 K in fields up to 10 kG. The critical current density in the field, estimated from the magnetization curves, was enhanced by the electron irradiation to 5.0×1017 e/cm2 in the melt-processed YBa2Cu3O7-x and Tl2Ba2Ca2Cu3Ox compounds. In the Bi1.4Pb0.6Sr2Ca2Cu3Ox compound, the critical current density was expected to be increased by electron irradiation to a dose much less than 5.0×1017 e/cm2.

The effect of hydrogen peroxide on the stress corrosion cracking of 304 stainless steel in high temperature water

Abstract The effect of hydrogen peroxide on stress corrosion crack growth rate of sensitized 304 stainless steel in high temperature water was investigated using a specially designed testing cell which minimizes the decomposition of hydrogen peroxide. Hydrogen peroxide accelerated crack growth irrespective of dissolved oxygen content level within the test range (20–400 ppb dissolved oxygen). The effect of oxygen and hydrogen peroxide could be characterized using an effective oxygen content [O 2 ] eff , defined below, [ O 2 ] eff =[ O 2 ]+ 1 2 [ H 2 O 2 ] . Results were interpreted based on existing cracking mechanisms.

Effects of surface finishing on stress corrosion cracking of austenitic stainless steels in high temperature water

The intergranular stress corrosion cracking (IGSCC) susceptibility of surface finished type 304 and 304L stainless steels has been studied using a constant load tensile specimen in 288 °C water containing 26 ppm dissolved oxygen. The study was to define conditions to prevent IGSCC in piping used in a boiling water reactor (BWR). The results are as follows:1)IGSCC susceptibility of type 304 stainless steel increased markedly by surface finishing, such as grinding, when in a sensitized condition; increasing surface roughness shortened the time to failure.2)Type 304 stainless steel specimens, which are solution heat treated, do not show IGSCC susceptibility even if they are ground.3)Type 304L stainless steels do not show IGSCC susceptibility even if they are ground and sensitized at 621 °C for 2 h.

Damage structure obtained by cross-sectional observation in silicon carbide irradiated with helium ions

Abstract The microstructural change due to He-ion irradiation has been studied by cross-sectional transmission electron microscope observation in hot-pressed SiC irradiated to 1 × 10 20 ions / m 2 at 300 and 1023 K. Dot and loop-shaped defect clusters are formed between 0.74 and 1.20 μm in depth from the ion-bombarded surface, and the damage peak depth is 1.15μm in the 1023 K irradiation. He bubbles, which are formed between 0.94 and 1.16 μm in depth, are aligned on the c -planes and along radiation-induced dislocations. In the 300 K irradiation, the amorphous zone is formed slightly behind the damage peak depth.

Enhancement of Critical Magnetization Current by the Electron Irradiation in Ba2YCu3O7 Superconductor

A single-phased Ba2YCu3O7-y pellet was sequentially irradiated with 3 MeV electrons up to 2.25×1022 m-2 at about 370 K, and the magnetization measurements were carried out at 77 K in fields up to a corresponding magnetic flux density of 1.0 T. The critical current density estimated from the magnetization mesurement was enhanced by the electron irradiation; the enhancement was larger in higher magnetic fields. The current density at 1.0 T of 7.4 MAm-2 was increased to 11.3 MAm-2 by the electron irradiation to 1.75×1022 m-2, and then decreased upon further irradiation.