Corrosion Fatigue Behavior of 316LN Stainless Steel Hollow Specimen in High-Temperature Pressurized Water
TAN Jibo, WANG Xiang, WU Xinqiang(), HAN En-Hou
CAS Key Laboratory of Nuclear Materials and Safety Assessment, Liaoning Key Laboratory for Safety and Assessment Technique of Nuclear Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Cite this article:
TAN Jibo, WANG Xiang, WU Xinqiang, HAN En-Hou. Corrosion Fatigue Behavior of 316LN Stainless Steel Hollow Specimen in High-Temperature Pressurized Water. Acta Metall Sin, 2021, 57(3): 309-316.
Environmentally assisted fatigue is an important factor in the design, safety review, and life management of key components used in nuclear power plants. Piping systems, valves, and small-bore pipes are sensitive to fatigue damage in nuclear power plants. In this work, a kind of hollow specimen for fatigue testing was designed. High-temperature pressurized water flows through the inside of the specimen, and the outside of the specimen is exposed to air. The corrosion fatigue behavior of 316LN stainless steel was investigated in high-temperature pressurized water using the hollow specimens. The experimental results show that the fatigue strength of 316LN stainless steel was reduced in a high-temperature pressurized water environment, and its fatigue life decreased with decreasing strain rate. The fatigue lives obtained by hollow and standard round bar specimens were comparable, which indicate that it is reasonable and feasible to use the hollow specimen to study the environmentally assisted fatigue performance of nuclear-grade structural materials in a high-temperature pressurized water environment. At low strain rate conditions, the fatigue crack initiation region is a typical fan-shaped pattern with quasi-cleavage cracking characteristics. The fatigue crack growth region is characterized by fatigue striation, and the environmental effects are highly significant in the stage of fatigue crack initiation. The fatigue damage mechanism of 316LN stainless steel in a high-temperature pressurized water environment is also discussed.
Fig.1 Schematic of shape and size of 316LN stainless steel hollow specimen (unit: mm)
Fig.2 Schematic of high-temperature pressurized circulating water corrosion fatigue device (DO—dissolved oxygen, Con—conductivity)
Fig.3 Installation of 316LN stainless steel hollow specimen
Parameter
Value
Unit
Strain amplitude
0.4%-0.9%
Strain ratio
0.2
Strain rate
(0.4-0.004) × 10-2
s-1
Temperature
320
oC
Pressure
12
MPa
DO
<5 × 10-9 (by weight)
Li
2.2 × 10-6 (by weight)
B
1200 × 10-6 (by weight)
pH
6.5-7.0
Flow rate
10 (0.142)
L·h-1 (m·s-1)
Table 1 Corrosion fatigue test parameters
Fig.4 OM image of microstructure of 316LN stainless steel
Fig.5 Corrosion fatigue data of 316LN stainless steel hollow specimen and standard round bar specimen[13] in high-temperature pressurized water
Fig.6 The effect of strain rate on fatigue life of 316LN stainless steel hollow specimen
Fig.7 Relationships between peak load and number of cycles for 316LN stainless steel fatigue tested in high-temperature pressurized water
Fig.8 Macromorphologies of fatigue fractures of 316LN stainless steel hollow specimens at different strain rates
Fig.9 Morphologies of fatigue crack initiation sites of 316LN stainless steel hollow specimens at different strain rates (a, c, e), and corresponding enlarged views of marked positions (b, d, f )
Fig.10 Fatigue striation characteristics at different fracture locations (distance from crack initiation site) of 316LN stainless steel hollow specimens at different strain rates of 0.4 × 10-2 s-1 (a, d, g), 0.04 × 10-2 s-1 (b, e, h), and 0.004 × 10-2 s-1 (c, f, i) (The line in the figure dencotes the fatigue crack propagation direction, and the number is the average fatigue striation spacing in the line length area, unit: μm/cyc)
Fig.11 Morphology of secondary cracks (a) and oxides (b) on inner surface of 316LN stainless steel hollow specimen
Fig.12 The fatigue crack growth rate (da/dN) at different distances to crack initiation sites for 316LN stainless steel in high-temperature pressurized water
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