Hideya Anzai

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 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 γ-ray Irradiation on Crack Growth of Sensitized Type 304 Stainless Steel in 288°C Water

Abstract Propagation of intergranular stress corrosion cracking (IGSCC) in sensitized type 304 (UNS S30400) stainless steel (SS) in 288°C water was enhanced by γ-ray irradiation with a flux of 2.3 ...

Optimized Conditions for Tensile Residual Stress Reducing Weld Using Water-Shower Cooling

To reduce tensile residual stress in a welded region, we developed a new cooling method that applies a water shower behind the welding torch. When this method is applied to the welding of austenitic stainless-steel, the welding and cooling conditions mainly determine how much the residual stress can be reduced. To optimize these conditions, we first used FEM to determine the effects of preheating temperature, heat input quantity, and water-shower area on the residual stress, and found that, to decrease tensile residual stress, preheating temperature should be high, heat input low, and the water-shower large. To confirm the effectiveness of these optimized conditions, residual stresses under optimized or non-optimized conditions were experimentally measured. It was found that the residual stresses were tensile under the non-optimized conditions, but compressive under the optimized ones. These measurements agree well with the FEM analysis. It can therefore be concluded that the optimized conditions are valid and appropriate for reducing residual stress in an austenitic stainless-steel weld.Copyright

Intergranular stress corrosion cracking susceptibility of sensitized type 304 steel in 561 K pure water under γ-ray irradiation

Intergranular stress corrosion cracking (IGSCC) of sensitized type 304 stainless steel has been investigated in 561 K water under γ-ray irradiation at a flux of 2.6 × 103C kg−1h−1 by slow-strain-rate tensile tests. The IGSCC susceptibility was enhanced by γ-ray irradiation in water containing 8 ppm dissolved oxygen (DO). The DO dependence of the IGSCC susceptibility was observed in the water under γ-irradiation. Although slight IGSCC susceptibility was observed even in deaerated water (less than 1 ppb DO) under γ-ray irradiation, the susceptibility was completely suppressed by injection of hydrogen into the water. The enhancement of IGSCC susceptibility seems to be related to the formation of H2O2 in high temperature water by radiolysis under γ-ray irradiation and the H2O2 formation rate is markedly decreased by hydrogen injection.

Evaluation of hydrogen-assisted cracking behavior of low-alloy steel in the range 95 °C to 350 °C

In this report, hydrogen-assisted cracking (HAC) behavior of low-alloy steel was evaluated using a constant elongation rate tensile test, and the temperature and crack tip strain rate effects were observed. It was found that temperature dependence of the threshold condition (Cσmc) of HAC above about 100 °C followed the relation Cσmc = Kexp(−41,300/Rr) whereK is a constant andT is absolute temperature. The relationship between HAC growth rate and crack tip strain rate was established as almost linear, irrespective of temperature and hydrogen concentration at the crack tip. Hydrogen heat release tests were also performed. From these tests, formation and growth of microcracks which are trap sites of hydrogen were thought to be the mechanism of HAC in the steel. From this mechanism, HAC behavior of the low-alloy steel could be qualitatively explained.