To evaluate the rate of thermal embrittlement of type 316 low-carbon stainless steel weld metal at BWR operating temperature, aging test at 310°C, 335°C, and 400°C was carried out. Hardness of each ferrite and austenite phase of s pecimens was measured selectively by microhardness tester. Hardness of ferrite was increased apparently with all three aging temperatures, whereas hardness of austenite was not changed. Changes in the microstructure of ferrite ag ed at 310°C for 11,000h and 18,000h were analyzed ...
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Evaluation of aging embrittlement of low-carbon austenitic stainless steelweld metal near the BWR operating temperature

The crevice former which does not release anion impurities (e.g. Cl-) for SCC (Stress Corrosion Cracking) initiation experiment in simulated boiling water reactor water environment has been ev aluated. The creviced bent beam tests of sensitized stainless steel with using the crevice condition as an experimental parameter were carried out. Even SCC occurred at the part of specimen su rface which tested with only the spacer (no crevice former), it has been difficult to obtain the reproducible result. SCC ini...
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Evaluation of crevice former for SCC initiation experiment in simulated BWR water environment

The method for determining the repassivation potential for corrosion crevice of stainless steel is defined by JIS, but that of Alloy600 is not defined yet. In this paper, the method for determining the repassivation potential was considered based on the experiments with Alloy600 of nuclear constituent material by reference to JIS and intended to contribute to the establishment of it. In preparation for measuring the repassivation potential, the pitting potential dependence of Cl- concentration is measu...
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Study on the electrochemical method for determining the repassivation potential for corrosion crevice of Alloy600.

The purpose of this study is to investigate the following items focused on the microstructure near the fusion boundary of dissimilar weld joint with Ni-based weld metal and low alloy steel; (1) Microstructural characteristics near the fusion boundary, (2) Dominant factor that makes crack retardation near the fusion boundary. Main conclusions can be summarized as follows; (1) From the results of CBB tests, it has been understood that the low alloy s teel has no SCC susceptibility and that there is a differ...
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SCC propagation and cessation behavior near the fusion boundary of dissimilar weld jointwith Ni-based weld metal and low alloy steel

SCC behavior near the fusion boundary of dissimilar weld joint with Ni-based weld metal and low alloy steel in high temperature water has been investigated with special attention on relation t o the characteristics of microstructure. From the results of CBB test (1.0 ppm-Na2SO4 and 8 ppm dissolved oxygen), it has been obvious that the LAS has no SCC susceptibility. On the other hand, Alloy182 in the weld samples have SCC susceptibility. Most of crack tips have located at the fusion boundary, and the penetr...
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Characteristics of microstructure and SCC behavior near the fusion boundaryof Ni-base weld metal and low alloy steel

Crevice corrosion has been concerned in the Fukushima Daiichi Nuclear Power Station, since seawater was injected to make up water level as part of the emergency action. To evaluate structural integrity, it is important to inves tigate whether crevice corrosion occurred. The purpose of this study is to investigate conditions of crevice corrosion initiation and repassivation of SUS304L. SUS304L specimens with acrylic crevice were held at constant electr ochemical potentials in 1000ppm Cl- solution. It was in...
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Evaluation of crevice corrosion initiation condition and repassivation condition of SUS304L

Austenitic stainless steel welds typically have duplex microstructure with a few to over 10 ％ of 8-ferrite in austenite to prevent hot cracking during solidification. Therefore, austenitic stainless steel welds are also susceptible to thermal aging embrittlement similar with cast duplex stainless steels (CDSSs). Although microstructural morphologies of 8-ferrite in austenitic stainless steel welds is different from that of CDSSs, the effect of that on an thermal aging embrittlement behavior is not fully kno...
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Effect of thermal aging on impact behavior of austenitic stainless steel welds

Austenitic stainless steels are widely used as structural materials in many industries. However, stainless steels are susceptible to crevice corrosion in the solution including chloride ions. In this paper, at first, the most inhibitive anion against corrosion was investigated by anodic polarization measurement of type 316L stainless steel in the solution containing Cl- with candidate inhibitive anions (WO42-, MoO42-, VO3-). MoO42- was adopted as the most inhibitive anion in this study. Next, the effec...
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Effect on critical potentials for crevice corrosion initiation and repassivation of stainless steel by addition of inhibitive anion

Flow Acceleration Corrosion (FAC) is one of the mechanisms of pipe wall thinning in power plants. The wall thinning caused by FAC is usually found between 90 ℃ and 230 ℃ with a peak at about 150 ℃. However, FAC has been reported at temperatures below this range. This study evaluated the effect of DO and Cr content on wall thinning rate at 50 ℃. Raman spectroscopy was performed to identify the constituent species of the oxide film. FAC rate was seen to decrease by increasing Cr content. In terms of DO, wall ...
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Combined Effect of Cr content and Dissolved Oxygen Concentration on Wall Thinning Rate by Low Temperature FAC

Stress corrosion cracking (SCC) behavior of low-carbon stainless steel welds in high temperature water has been discussed with special attention on relation to the characteristics of microstructure. To investigate the effect of .-ferrite on SCC behavior, simulated heat-affected zone (partially melted zone) microstructure, where .-ferrite islands were widely distributed on grain boundary, was made by induction heating up to just below melting point. From the results of constant strain SCC test in high ...
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Effect of .-ferrite on stress corrosion cracking behavior of low-carbon stainless steel weld in high temperature water