The Stress Corrosion Behavior Of Alloy690TT And316L Stainless Steel In The Environment Of Simulating Nuclear Power

In order to optimize the energy structure in China, as well as in facing with theproblem of energy shortage and environmental pollution, nuclear power developmentbecomes the important planning in the following decades. At present, the main issue whichthe nuclear power plant faced most is the failure of heat pipe steam generator and primarymain. And the main failure modes of the heat pipe steam generator happened to be stresscorrosion at pipe scratch which makes the corrosion cracking mechanism of the pipe isworth exploring; in our study is the316L stainless steel.Based on the simulation results of the scratch and stress corrosion cracking withdifferent parameters of steam generator heat transfer pipe690TT alloy under nuclearpower service environment and the corrosion cracking behavior of primary main316Lstainless steel stress, we try to find out to security service safe scratch parameters and tosummed up the316L stainless steel stress corrosion cracking mechanism. Hightemperature immersion test was carried out after surface scratch with different parametersof the690TT alloy, the morphology of sample surface and cross-section were characterizedby SEM and the composition of the corrosion products were also tested by EDX spectrumanalysis. Moreover, the safe scratches were selected according to the microcracks initiationsensitivity to the stress. The results show that all scratched samples present stress corrosioncracking, most of the crack located in the plastic deformation accumulation areas andaffected zone of the scratch embankment, meanwhile seldom show up in the scratchesvalley area。The majority of crack length does not exceed30μm，only three kind of scratchsprouted the cracks longer than50μm.The surface oxide film interface morphology of316L stainless steel U-bend samplewas characterized after stress corrosion cracking test, the main crack was examined bySEM, moreover the U-bend samples were analysis by EBSD in order to discuss the stresscorrosion cracking behavior of316L stainless steel. The results show that, the crack initiation and expansion mainly on a major crack through tortuous path, the slender cracktip shows no significant bifurcation; the crack expands along the wide-angle random grainboundary accompanied with a small amount of cracking at the twin boundary; samplescrack sectional also embodies crystal sugar like pattern and accompanied transgranularquasi-cleavage fracture; the Ni, Cr content in the corrosions products was higher than thatin the matrix; crack growth occurs primarily in the intermediate layer; the content of Crwas lower and the content of Fe was higher, and no obvious changes in the distribution ofNi in the cracking oxide layer in compared with that in the matrix.