[en] It is almost impossible to measure the contents of ppts in stainless steel weldments by metallography because those are very fine and their ununiform distribution. In this report, electro-chemical method which make it possible to quantitatively analyze the contents of ppts in stainless steel weldments. Furthermore the XRD test results for the extracted ppts were listed. It was confirmed that the possibility of adaption of the ASTM standard electrolytic extraction method for Ni-base supperalloy to quantitative analysis of ppts in austenite stainless steel. It was concluded that the extracted ppts were Nb(C, N) from the XRD test results

[en] The effects of temperature and microstructure on the fatigue crack growth behaviors of type 347 stainless steels for nuclear piping are studied. It was observed that the Fatigue Crack Growth Rate(FCGR) of type 347 increased as the test temperature was increased. However, its temperature sensitivity was reduced when the ΔK was large. The FCGRs at 25 .deg. C and 345 .deg. C were lower than those presented in the ASME code. Though the effect of microstructure on macro-crack growth rate was not significant during stage II, the differences between threshold values for the specimen with a high precipitate density and the one with a low precipitate density were observed at 25 .deg. C, even though the precipitate's effect was diminished above 167 .deg. C. The FCGRs of type 347 at various temperatures were lower than those presented in the ASME code. The FCGRs were higher than isothermal FCGR when the thermo-mechanical stress was imposed on type 347

[en] The microstructures of three type 347 stainless steel weldments for pressurizer surge line, which were welded with each different filler metals, were analysed after J-R fracture resistance tests to investigate the relationship between J-R characteristics and the microstructures of weldments of the pressurizer surge line piping. It was observed the carbon contents was relatively high in the weldment of low J-R fracture resistance and δ-ferrite phase fraction was relatively low in an weldment of high J-R fracture resistance

[en] Materials used in nuclear power plants are low alloy steel, stainless steel, and superalloy steel. Understanding the characteristics of these materials is important in the development of nuclear power plant related technology. Nb-stabilized Type 347 stainless steel is used for the coolant pressurizer surge line of Korea Standard Nuclear Power Plant (KSNPP). Surge line of PWR nuclear reactor are damaged by thermal fatigue due to thermal gradient during heat-up and cool-down, mechanical fatigue due to mechanical stress, and corrosion fatigue due to nuclear reactor water environment. Fatigue is an important factor which limits the life of structure. Fatigue crack growth rate curves in nuclear reactor environment are needed to evaluate the integrity of nuclear reactor structure but that result is not sufficient. In this study, fatigue crack growth rates at nuclear reactor environment are produced to evaluate integrity of nuclear power plant section 5

[en] Fatigue damage could be significant for some locations, especially the welds and bends where stress concentration is typically high. As a possible solution, a large radius hot-bending method has been suggested to eliminate some weld joints and all tight bends. However, for the hot-bending process which involves a high temperature thermal cycle, there is a concern about changes in mechanical properties including low cycle fatigue behaviors. In APR1400, Type 347 SS have been used as surge line pipes. Therefore, to verify the applicability of hot-bending on 347 SS surge line pipes, an environmental fatigue test program was initiated. In this paper, the preliminary results of the on-going test program are introduced. Also, the low cycle fatigue behaviors of 347 SS are compared with those of other grade of stainless steels. The effects of hot bending on the low cycle fatigue behavior of 347 SS were quantitatively evaluated. The fatigue life was compared with the estimated values per NUREG 6909 rev. 1. There are no distinct differences between NUREG 6909 and LCF tests. According to fractography and cross section analysis in progress, basically, the reduction of LCF life of 347 SS in PWR water was caused by operation of HIC mechanism. The cyclic stress responses shows that there is no secondary hardening in 330 .deg.C air and PWR water

[en] Creep properties of a recent 347H austenitic stainless steel plate at 1073 K (800°C) and 1123 K (850 °C) were examined, and microstructural evolution under temperature and creep was characterized using TEM. Creep minimum rate vs. stress plot at 1123 K (850 °C) showed two different slope regions, suggesting a change in the creep-rate controlling mechanism at lower stresses. Detailed TEM characterization showed that in high-stress (or short-term) creep tests, NbC precipitates interacted with dislocations and indicated to slow down the dislocation-controlled creep by orienting towards slip directions. In low-stress (long-term) creep tests, formation of ferrite on NbC was observed and no sigma phase was detected. In long-term low stress creep tests, NbC precipitates gave way to formation of Widmanstatten Cr₂N and Z-phase precipitates, and the rate-controlling mechanism may change to grain boundary sliding. (author)

[en] The effect of hot bending on the Low cycle fatigue (LCF) behavior of 347 SS was evaluated in Room temperature (RT) air and simulated Pressurized water reactor (PWR) water environments. The LCF life of 347 SS in PWR water was shorter than that in RT air for the as-received and hot-bent conditions. The LCF life of hot-bent 347 SS was relatively longer than that of the as-received condition in both RT air and PWR water. Microstructure analysis indicated development of dislocation structure near niobium carbide particles and increase in dislocation density for the hot-bent 347 SS. Such microstructure acted as barriers to dislocation movement during the LCF test, resulting in minimal hardening for the hot-bent 347 SS in RT air

[en] In this study, we evaluated the thermal aging effect of ER347 welds by performing tensile and fracture toughness tests for welding blocks made by GTAW and the build-up welding method. The strength of the aged welds increased by approximately 10% compared to that of the as-welded status, and the variation in strength slowed after 5,000 hours. However, the fracture toughness of welds decreased gradually in inverse proportion over time. The test results suggest that fracture toughness, as well as strength, should be considered to accurately evaluate the thermal aging effect. Furthermore, the fracture toughness of ER347 welds was determined to be higher than that of cast stainless steel, E308 and ER316 welds. This may be occurring due to the δ-ferrite contents and Nb component. A follow-up study will be conducted on this issue.

[en] This paper covers the results obtained from experimental investigations into the stress/strain behaviour of niobium stabilised stainless steel piping material with the German notation X 6 CrNiNb 18 10, which is similar to AISI 347. From specimens tested in uniaxial experiments it could be proved that, independent of the size of the increment in strain and the cyclic strain range, a limited amount of applied, incremental, prior deformation reduced the overall capability to undergo deformation only by the amount of the accumulated, prior deformation. A clear relationship was observed between the level of prior deformation and the change in hardness. (authors)

[en] An exact evaluation of the characteristics of fatigue crack growth rate (FCGR) is very important for the life assessment of the cracked components in nuclear power plant piping system. Surge line is one of the components exposed to severe thermal and mechanical fatigue loads caused by the difference of temperatures and the cyclic internal pressure, respectively. There are no standard methods for the case of cyclic thermomechanical FCGR test. In some papers, authors have used their own method to measure the FCGR. In this study an efficient testing system has been developed to measure the FCGR under cyclic thermal and mechanical loads. Using the developed equipment, the FCGR tests were performed for the specimens of STS 347 weld and base material