Type 304 stainless steel (304SS) used in a nuclear power plant could suffer a disastrous damage called irradiation assisted stress corrosion crack (IASCC). It has been recognized that the radiation induced segregation (RIS) exerts an important effect on IASCC [1]. Wu et al. also did some work on SCC resistance of sensitized 304SS in high-temperature water [2, 3]. Both U-bend and slow strain rate stress corrosion tests were performed, complemented by the electrochemical polarization curve measurement and extensive oxide film analysis by Auger electron spectroscopy (AES). Besides, a considerable effort has already been made to study the relation of electrochemical corrosion potential (ECP) to IASCC under various conditions [4–6]. Lately, some modified measurements have been tried to study the IASCC phenomenon. These methods included electrochemical noise measurement [7], in-situ electrochemical impedance measurement [8], and acoustic emission response measurement [9]. On the other hand, some studies were conducted with ion irradiation. Microstructure and micro-chemical changes of type 304 stainless steel irradiated by protons were quantified and compared with literature results for irradiated specimens [10]. Lee et al. observed effects of helium on radiation-induced defect microstructure in austenitic stainless steel with 360 keV He+ and 3500 keV Fe+ ions beams at 200 ◦C [11]. Distinct swelling was noted by atomic force microscopy observation in austenitic stainless steel SUS316 specimens irradiated by He+ ions [12]. In this work 304SS was irradiated by 460 keV Fe+ ion beam with dose up to 1 × 1021 ions/m2 or by 500 keV He+ ion beam with dose up to 1 × 1021 ions/m2. The micro-hardness and XPS measurement were taken on for the irradiated specimens and the annealed specimen. The material used in the work was commercial 304SS plate with a thickness of 2 mm. The chemical compositions (mass%) of the material was 18.33% Cr, 8.49% Ni, 1.08% Mn, 0.54% Si, 0.066% C, 0.009% S, 0.024% P, and Fe balanced. Specimens of 10 × 10 mm2 square were cut by electrodischarge machine, and were mechanically polished with 1500 grit SiC paper. All specimens were enveloped in a quartz tube (1.33 Pa vacuum degree), annealed at 1050 ◦C for 30 min, and quenched by water. All treated specimens were electrochemically polished for further irradiation or for other measurement. One group of specimens was irradiated using 460 keV Fe+ ions at a rate of 1.5–2.5 × 1016 ions/m2/s (1 × 10−3 dpa/s) and the irradiation dose was up to 1 × 1021 ions/m2. Another group of specimens was irradiated using 500 keV He+ ions at a rate of 1 × 1018 ions/m2/s (5 × 10−3 dpa/s) and the irradiation dose was also up to 1 × 1021 ions/m2. Three groups of specimens such as annealed or irradiated by Fe+ or He+ ions respectively were included in following measurement. The hardness measurement was taken on by the Fischerscope H100VP mechanical probe. The beginning load value was 0.4 mN and max load value was 20 mN. When the load was up to 20 mN, it was removed after remaining 5 s. 10 curves were obtained at different micro-area of the same surface for every specimen. These curves were averaged to become an effective curve. The XPS measurement instrument was MICROLAB MK II using Mg-Kα as light source with the power of 300 W. All specimens were cleaned twice in acetone liquid with supersonic vibration. Then dried specimen was clipped in a support tray with the irradiated surface against the light source. Measurement started by scanning from 0 to 1000 eV with 1 eV step span. Further narrower range scanning was taken on with 0.5 eV step span. The press depth of annealed specimen was the deepest among the three specimens under the same loading and unloading condition in Fig. 1a. While the load started from the beginning value to 7.5 mN the press depth of No.3 specimen was deeper than that of No. 2 specimen. The depth was almost the same for both irradiated specimens during the load between 7.5 and 12.5 mN. The depth of No. 2 specimen was deeper than that of No. 3 specimen while the load increased continuously from 12.5 to 20 mN, remained 5 s at 20 mN, and then unloaded. The same tendency appeared in Fig. 1b. The hardness value of No. 1 specimen was always the lowest whereas the hardness value of No. 2 specimen was the highest between the beginning load value and 7.5 mN and the hardness value of No. 3 specimen was the highest with loading from 7.5 to 20 mN and thereafter. The max hardness value was 18 000 and 14 000 for No. 2 and No. 3 specimen respectively. The micro-hardness measurement result showed that the effect of hardness improvement was larger and
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Jul 5, 2006
T Fukuda + 2
Open Access