Joji Ohta

Effects of Cold Work, Sensitization Treatment, and the Combination on Corrosion Behavior of Stainless Steels in Nitric Acid

Abstract Corrosion behavior of two stainless steels (SS) was investigated in nitric acid (HNO3) for the effect of cold work (CW), sensitization heat treatment (Sens.), and a combination (CW + Sens.). The corrosion rate of the solution-treated type 304 SS (UNS S30400) with extra-low carbon (type 304ELC SS [UNS S30403]) increased with time and reached constant values after 1,000 h of immersion. However, constant corrosion rates were obtained for 25% Cr-20% Ni-Nb (type 310Nb SS [UNS S31040]) from the initial stage of immersion. CW mitigated corrosion of the solution-treated SS. The effect of CW was different on the two types of SS, with the sensitization heat-treated type 304ELC SS showing higher corrosion rates and type 310Nb SS lower corrosion rates by CW. Corrosion resistance of type 310Nb SS was superior to type 304ELC SS after all treatments. Chromium concentration of the sensitization-treated type 304ELC SS was lower in the grain-boundary region than of the solution-treated one, although no chromium ca...

Corrosion Behavior of High-Purity Fe-Cr-Ni Alloys in the Transpassive Condition

Abstract The corrosion behavior of high-purity (99.99%) Fe-Cr-Ni alloys was investigated in 13 kmol/m3 [0.36 kmol/ft3] nitric acid (HNO3) with and without ceric (Ce4+) ions to clarify the effect of...

Effect of various impurities on the transpassive corrosion of high-purity Fe-18%Cr-14%Ni alloys

Abstract Effects of C, P, S, and N on the transpassive corrosion of high-purity (HP) Fe-18%Cr-14%Ni alloys were studied in 13 kmol/m3 (13 N) nitric acid (HNO3) and 13 kmol/m3 HNO3 containing Ce4+ i...

Effect of Silicon and Manganese Additions on the Transpassive Corrosion of High-Purity Fe-18% Cr-14% Ni Alloys

Abstract Effects of Si and Mn on the transpassive corrosion of high-purity Fe-18% Cr-14% Ni alloys were studied in 13 kmol/m3 (0.36 kmol/ft3) nitric acid (HNO3) and 13 kmol/m3 HNO3 containing Ce4+ ...

Synergistic effect of impurities on the corrosion behavior of Fe-18%Cr-14%Ni alloys in concentrated nitric acid

Abstract Synergistic effect of Si, Mn, C, P, and S on the transpassive corrosion of high-purity (HP) Fe-18%Cr-14%Ni (HP18%Cr-14%Ni) alloys was studied in boiling 13 kmol/m3 nitric acid (HNO3). The specimens were fabricated by a cold crucible method in a high-vacuum chamber to reduce contamination. The addition of Si < 1% and Mn < 2% had no effect on the corrosion rate of HP18%Cr-14%Ni alloys, and the addition of Si < 1% also had no effect on the corrosion rate of HP18%Cr-14%Ni-1%Mn alloys, although 1% Si induced intergranular corrosion in both alloys. Thus, HP18%Cr-14%Ni-1%Mn-0.5%Si alloys were selected to evaluate the effect of minor impurities such as C, P, and S. The addition of 100 ppm P, or co-addition of 100 ppm C, 100 ppm P, and 100 ppm S, induced intergranular corrosion of the same degree in solution-annealed HP18%Cr-14%Ni-1%Mn-0.5%Si alloys. This result suggested a synergistic effect of Si and P to induce intergranular corrosion, since a single addition of 0.5% Si or 100 ppm P did not induce inte...

Evaluation of lattice distortion near c-ZrO2/α-Al2O3 interface by plasmon loss

Plasmon energies near a cubic-ZrO2 (c-ZrO2)/α-Al2O3 interface were studied by electron energy loss spectroscopy using a field-emission transmission electron microscope. The plasmon energies measured by scanning an electron probe of 1 nm in diameter across the interface showed that, approaching the interface, the plasmon energy of c-ZrO2 increases from 23.9 to 24.3 eV and that of α-Al2O3 decreases from 24.3 to 23.4 eV. Energy dispersive x-ray spectroscopy revealed that fluctuation of the chemical composition across the interface is small (⩽5%) and causes only a slight change in the plasmon energies (⩽0.16 eV). We conclude that the large energy changes (up to 0.9 eV) are mainly caused by lattice distortion. Using the Drude model, it was found that, 3 nm from the interface, the unit cell volume of c-ZrO2 decreases by 3% and that of α-Al2O3 increases by 6% compared with the volumes at 50 nm. The presence of lattice distortion near the interface was also confirmed by the convergent-beam electron diffraction me...

Mechanical properties of 20% cold-worked 316 stainless steel irradiated at low dose rate.

To assess the effects of long-term, low-dose-rate neutron exposure on mechanical strength and ductility, tensile properties were measured on irradiated 20% cold-worked Type 316 stainless steel. Samples were prepared from reactor core components retrieved from the EBR-II reactor following final shutdown. Sample locations were chosen to cover a dose range of 1-47 dpa at temperatures from 371-385 C and dose rates from 0.8-2.8 x 10{sup -7} dpa/s. These dose rates are about one order of magnitude lower than those of typical EBR-II in-core experiments. Irradiation caused hardening, with the yield strength (YS) following approximately the same trend as the ultimate tensile strength (UTS). At higher dose, the difference between the UTS and YS decreases, suggesting the work-hardening capability of the material is decreasing with increasing dose. Both the uniform elongation and total elongation decrease up to the largest dose. Unlike the strength data, the ductility reduction showed no signs of saturated at 20 dpa. While the material retained respectable ductility at 20 dpa, the uniform and total elongation decreased to <1 and <3%, respectively, at 47 dpa. Fracture in the 30 dpa specimen is mainly ductile but with local regions of mixed-mode failure, consisting of dimples and microvoids. The fracture surface of the higher-exposure 47 dpa specimen displays significantly more brittle features. The fracture consists of mainly small facets and slip bands that suggest channel fracture.The hardening in these low-dose-rate components differs from that measured in test samples irradiated in EBR-II at higher-dose-rate. The material irradiated at higher dose rate loses work hardening capacity faster than the lower dose rate material, although this effect could be due to compositional differences.

Radiation-Induced Segregation in 316 and 304 Stainless Steels Irradiated at Low Dose Rate

As part of the shutdown of the EBR-II reactor, structural materials were retrieved to analyze the effects of long-term irradiation on mechanical properties and microstructure. In this work, the effect of low dose rate irradiation (10 −7 to 10 −8 dpa/s) on grain boundary composition in 316 and 304 stainless steels was analyzed. Samples were taken from surveillance specimens and subassemblies irradiated in the reflector region of EBR-II at temperatures from 371-390°C to maximum doses of 30 dpa. The effects of dose, dose rate, and bulk composition on radiation- induced segregation are analyzed. In 316 stainless steel, changes in grain boundary chromium and nickel concentrations occur faster than changes in iron and molybdenum concentrations. In 304 stainless steel, decreasing the dose rate increases the amount of grain boundary segregation. For a dose of 20 dpa, chromium depletion and nickel enrichment are greater in 304 stainless steel than in 316 stainless steel, the difference most likely due to dose rate. In both 304 and 316 stainless steels, the presence of a grain boundary precipitate significantly changes the composition of the adjacent grain boundary.