High Cycle Fatigue Tests of Low Carbon 316 Stainless Steels under 20 MeV Proton Irradiation and Thermal Pulse

Effects of In-Situ Proton-Irradiation and Thermal-Pulse on the High-Cycle Fatigue Properties of Low Carbon 316 Stainless Steels

“…As a matter of fact, the work hardening exponent n [8] estimated fiom the line 1 shown in Fig.1 is as high as n=l (see [6] [4] in which the work hardening exponent n is as low as about 0.2 and fatigue induced precipitates can be observed as black dots in TEM observation [5]. Shortening of Nf for the higher (Ph-PO)IPO range and elongation of Nf for the lower (Ph-Po)IPo range are observed for 3 16F in [5] in which the work hardening exponent n is about 0.33 and the fatigue induced precipitation is intermediate between 316(ST-1) and 3 16SI.…”

“…RESULTS Figure 1 shows the (Ph-Po)IPo vs. Nf data observed for the NL-tests at 300 K here or at 333 K [6], the TPtests at 333 K with AT below 10 K [6] and the TPtests at 300 K with AT=70-130 K, where TP with AT below 10 K brings about elongation of Nf but TP with increased AT of 70-130K gives rise to shortening of Nf. Figure 2 is a redrawing of Fig.8 in [6], where the (Ph-Po)Po vs. Nf data observed for the pulse-PI-tests at 333 K are compared with the results for the TPtests at 333 K with AT below 10 K. As mentioned in the section 1, the in situ radiation damage at 333 K causes shortening of Nfi especially in the low (PhPo)/Po range. show good agreement with those observed for the NL-tests at 300 K or 333 K. The outline of the effects of in situ radiation damage on Nf at 403 K is very similar to that of in situ radiation damage on Nf at 333 K.…”

“…The preliminary work on the Ti-modified AISI 316L stainless steel (see [4] and 316(ST-1) below) indicates that the effect of radiation damage on the fatigue life Nf in the %-controlled tests at 333 K, here elongation in Nf, is much larger under irradiation than after irradiation, where is the total strain amplitude. The firther study on the various modified-3161 stainless steels [5,6] shows that the fatigue hardening mainly governs Nf of the solution treated specimens and in situ radiation damage or thermal pulse modities the fatigue hardening process. That is, the elongation in Nf observed for 316(ST-1) is mainly due to enhancement of the fatigue induced precipitation under irradiation.…”

“…61 indicate that Nf shows elongation for the thermal-pulse (AT) tests (the TP-tests) with AT below 10 K (see Fig.1) and shortening under in situ radiation damage (see Fig.2), where the effect of in situ radiation damage is found after the subtraction of the results of the TP-tests from the results of the pulse 20 MeV-proton irradiation tests (the pulse-PI-tests). To pursue the b h e r insight into the fatigue process in 316S1, we carried out the TP-tests at 300 K with the increased AT of about 100 K and the continuous 20 MeV-proton irradiation tests (the PI-tests) at 403 K, because the effects of in situ radiation damage or thermal pulse on the fatigue hardening at 403 K have been compiled in [6] and the specimen temperature attained during thermal-pulses is about 400 K. Further for the no-loading tests (the NL-tests) without thermal-pulse nor proton irradiation, the fatigue properties at 300 K are practically the same to those at 333 K which have also been compiled in 161.…”

“…The fatigue tests were carried out using the flexural vibrations of a U-shaped reed specimen, where the middle of the U-shape forms a composite reed with thickness of 0.12 mm and a gage length of 16 mm and two open ends of the U-shape are thick for clamping. Excitation of the flexural vibrations was made electromagnetically and the fatigue tests were conducted in the atmosphere of 102 Pa He to suppress a heat-up of a specimen (see [4,6] for details). Period P of the resonant flexural vibrations of a specimen in the elastic range will be referred to as Po below, where l/Po here is about 200 Hz.…”