SUMMARY OF THE SUMMARY/POSTER PRESENTATION SESSIONS – Chaired by Gary Was and Anna Hojná

Part I of the summary/poster presentation session consisted of seven short poster introductions on Monday before the coffee break.

Wei Wang (USTB, China), “Characterization of microstructures of 316 stainless steel/Inconel 182 dissimilar welds and its corrosion properties in high temperature water”: Wang summarized a poster that focused on an in-depth characterization of dissimilar metal welds required for evaluating and extending the lifetime of operating PWRs. Results included the following: (i) the microstructure, local misorientation and SKPFM depended on fusion boundary type; (ii) there were typically two fusion boundaries alternately distributed; (iii) the different types of fusion boundaries had different corrosion resistance, in which the thickness of the oxide layer and size of oxide particles were related to the boundary type.

Xinyuan Cao (USTB, China), “Investigation on microstructure and mechanical properties of thermal-aged stainless steel weld overlay cladding”: Xinyuan Cao presented his work on the use of the small punch test (SPT) to evaluate the thermal aging embrittlement of E308L stainless steel used as RPV cladding. He found that thermal aging up to 1000 h led to microstructure evolution by spinodal decomposition and G-phase precipitation in the ferrite phase. The small punch energy decreased with thermal aging time and plasticity reduction was primarily associated with spinodal decomposition. Hardening of the ferrite and high stress concentration on d/g phase boundaries resulted in increased brittle cleavage fracture and phase boundary separation after thermal aging.

Yung-Lin Chen (National Tsing-Hua University, Taiwan), “Stress corrosion cracking of welded type 316L stainless steels in simulated BWR environments”: Yung-Lin used slow strain rate testing in oxygenated pure water to assess the mechanism of SCC in sensitized 316L SS and dissimilar metal welds (DMWs) of 316L and Alloy 52. Chen found that fracture of the PWHT sample exhibited TGSCC initiation from two sites on the edge. The morphology of the SA 316L SS sample and the as-received DMW sample consisted of large dimples typical of ductile fracture. The post weld heat treatment of 550°C/48 h that was intended to minimize or eliminate residual stress of DMW samples in fact, led to a smaller elongation and a reduced yield stress.

Katsuhiko Fuji (INSS, Japan), “APT measurement of stainless steel welds after long time aging and irradiation – Mo effect on microstructure”: Dr. Fuji examined the microstructure of welds in 304 and 316 SS after long aging time and irradiation to determine if there was an effect of Mo. Cr decomposition and G phase formation were observed in the ferrite phase of both 304 and 316 SS. So it was determined that there was no significant effect of Mo.

Koji Fukuya, presented by Katsuhiko Fuji (INSS, Japan), “APT analysis of solute clustering in neutron-irradiated stainless steels”: Katsuhiko Fuji presented his recent observations on samples from a flux thimble tube irradiated in an LWR to 11 and 74 dpa. APT analysis confirmed that the clusters were mainly enriched in Ni and Si. The size, density and composition were similar in 11 and 74 dpa specimens, suggesting that the cluster evolution tended to saturate above 11 dpa, while Ni-Si-Mn clusters were formed at higher doses.

Mi Wang (University of Michigan, USA), “IGSCC behavior of nickel-based alloys in light water reactor environments”: Dr. Wang described work to evaluate the behavior of potential replacement alloys for LWR core internals using proton irradiation to assess the IASCC susceptibility of Ni-base Alloys 625Plus and 725. Results showed that Alloy 725 was less susceptible to IASCC than Alloy 625Plus in both BWR (NWC) and PWR environments. Also, while a correlation can be found between IASCC behavior and microstructure changes, no specific microstructure feature was identified as the cause of the difference.

Farzin Arjmand (SJTU, China), “Solution resistivity, ohmic drop and oxygen reduction rate at high temperature pressurized water”: Mr. Arjmand’s work compared the solution resistivity with conductivity values calculated by a pH and conductivity software and analyzed the discrepancy using the rate of oxygen reduction reaction on Pt and Alloy 690 working electrodes. They found that the conductivity values calculated by the software are in better agreement with the impedence based resistivity values than the values determined by the potentiostatic technique.

Totally six posters were presented in the second part of the summary/poster presentation session.

Wenjun Kuang (University of Michigan, USA), “The effect of cold rolling on grain boundary structure and stress corrosion cracking susceptibility of twins in Alloy 690”: Kuang showed results of a SCC initiation study in simulated primary water environment. The study was performed using the SSRT technique with non-cold-rolled/cold-rolled and non-aged/long-time aged at 475˚C specimens of Alloy 690. Results indicated that cold-work and aging stimulated transformations in twin grain boundary structures and thus influenced the SCC susceptibility.

Long Xin (USTB, China), “Fretting wear behavior and mechanism of Alloy 690TT in high temperature water”: Xin presented a comparison of fretting experiments in air and high-temperature water. Dynamic recrystallization of under surface region was observed in both environments resulting from development of nanostructure twins boundaries and carbides dissolution. However, the oxidation process was found different in the different environments as showed by means of SEM and EDS.

Junjie Chen (Shanghai University, China), “Water chemistry effects on the oxidation and stress corrosion cracking of 316L SS in simulated PWR primary water”: Chen showed results of several techniques applied to characterize the material behavior and the cracking process in PWR water of various hydrogen contents. Electrochemical impedance spectrocopy, TEM/EDS of oxide films and SEM/EBSD were applied to understand the effect of water chemistry and resulting transgranular fracture.

Jiamei Wang (SJTU, China), “Stress corrosion cracking behaviour of cold worked 304 stainless steel”: Wang showed results of an experimental study on effects of dissolved oxygen (DO), chloride and cold-work on the SCC susceptibility. The study was performed by means of SSRT tests with bend specimens. Fracture sections and oxide films were analyzed by Optical Microscope, SEM and EDS, obvious intergranular and transgranular crack morphologies were found. The data showed systematically how the various environments decreased apparent stress vs. elongation curses, where DO environment with addition of chloride had the strongest damage impact.

Qian Xiao (Shanghai University, China), “The effects of environmental factors on corrosion and fracture behaviors of A508III low alloy steel”: Xiao presented experimental data to discuss the effect of hydrogen absorption which can occur at plant start-up or outage conditions. Results of corrosion rate measurements and tensile tests on hydrogen charged/non-charged specimens in aerated solutions at a temperature range from 20 to 100°C. In the tests, the remaining hydrogen after a short time can induce fish-eye-like white spots nucleation and growth, but hydrogen gradually spread out and the mechanical properties and fracture characteristics turned to be similar to those of non-charged specimens.

Xiaouyuan Lou (GE-GRC, USA), “SCC memory effect on pressure vessel steel after chloride transient in high temperature water” (no poster): Lou discussed a delayed behavior during the beginning and end of chloride transients. In both circumstances, incubation times were observed. The objective of this study was providing technical data for quantifying the incubation time and crack growth rate during a chloride transient in BWR environment. The effects of K and transient chloride level was discussed in the talk.