Study On Stress Corrosion Behaviors Of 316LN Stainless Steel In Simulated Primary Water Chemistry

316LN stainless steel has been widely used in nuclear power plant as structure material.In the very harsh environment of high temperature,high pressure,corrosion and irradiation in nuclear reactor,stress corrosion cracking is the main cause of equipment failure,which poses a grave threat to the safe,stable and economical operation of the reactor.The slow strain rate tensile test(SSRT)is a fast,sensitive and strict method of testing the stress corrosion sensitivity of nuclear materials in high temperature and high pressure environment.In this paper,the effect of strain rate,zinc injection and irradiation on the stress corrosion resistance of 316LN stainless steel in a simulated primary water chemistry is studied by slow strain rate tensile test,the fracture morphology,composition and structure of oxide film were analyzed by means of various testing methods,and the effects of these factors on the behavior of stress corrosion cracking(SCC)were discussed.The detail studies and results of this dissertation include four parts as follows:1.316LN stainless steel exhibits stress corrosion sensitivity in simulated primary water chemistry whether the tensile rate is O.OOlmm/min or 0.0005mm/min.Zn injection can reduce the thickness of the oxide film on the 316LN surface after SSRT,improve the mechanical properties of the material,reduce the sensitivity of SCC.At the tensile rate of 0.001mm/min,the SCC sensitivity of 316LN with the addition of 50ppb Zn is the lowest.When the tensile rate is 0.0005mm/min,this value is 75ppb.2.Prefilming treatment can increase the content of Cr-rich oxide and Zn-rich oxide in the oxide film,inhibit the initiation and expansion of cracks,thus improving the mechanical properties of 316LN and reducing the sensitivity of SCC.This effect becomes more obvious when prefilming time increase from 300h to 600h.The temperature significantly affects the SCC sensitivity of 316LN stainless steel.As the corrosion temperature increases from 250? to 330?,the Cr-free unstable oxide layer became thinner,so the later the crack initiate and the more slowly the cracks grow,therefore the mechanical properties of 316LN are improved,and the sensitivity of SCC is reduced,3.The dislocation and He bubble caused by He~+ irradiation significantly affected the mechanical properties and SCC sensitivity of 316LN stainless steel by means of thickening the Cr-depleted oxide film.With the increase of irradiation dose,the strength of the samples increased,the elongation decreased,and the sensitivity of SCC increased.4.The strength of 316LN stainless steel increased after irradiation by He~+,Fe~+and Kr~+ at the same dose,but the elongation decreased.With the increase of the mass of the incident ions,the radiation damage of the surface is more serious so the oxide film on the 316LN surface becomes thicker after SSRT due to Cr depletion caused by irradiation,the strength increases,the elongation decreases,and the sensitivity of SCC is increased.