Stuay On Stress Corrosion Cracking Sensibility Of316LN After Solution Treatment And Calculation Of Structral Character Of Austenite Stainless Steel

The nuclear primary pipe is one of the key components of nuclear island,thermalaging and stress corrosion cracking are urged to be solved as the more and more widelydevelopment of nuclear power.Our study has shown that the redistribution and segregationof interstitial atom during thermal aging are the main reason of degradation and increasingSCC susceptibility.Rapid cooling can make homogeneous distribution of interstitialatom,thus increase the SCC resistance.However,after thermal aging treatment,theproperties for samples of different cooling rates are unclear.This article calculated thestructure property of bulk model and surface model for austenite.The microstructure andSCC susceptibility of thermal aged austenite steel after different rate cooling has also beenstudied.C,N atoms prefer to exist in the octahedral interstices,these atom may form polarcovalent bond with atom Fe.The substitute atom Cr,Mo may form antibond with Fe,whichhas lower stability.Ni and Fe tend to united by covalent bond,which has higherstability.The different bond character results in different impact on the dislocation.Duringthermal aging process,C,N atoms may diffuse through the octahedral-octahedral way.Thediffuse barrier of C is2.620eV,while that of N is3.911eV.The surface energy of (111),(110) for austenite structure is2.688J/m2and3.056J/m2,respectively.While C or N atom is added to the surface structure,surface energy mayrise,N atom has more obvious effect to the surface energy.The hybridization of electron atC(N)-2p and Fe-3d orbitals can form polar covalent bonding.The XRD results shown that,the lattice parameter of samples after higher rate coolingis bigger,and the density of dislocation is also higher.Thermal aging process can reduce thelattice parameter and dislocation density, and make the microhardness and electricalresistivity become bigger.Microhardness and electrical resistivity of samples after higherrate cooling is bigger than samples after lower rate cooling.The hardness of grainboundary is bigger than that of inter grain.The SCC susceptibility of samples after higher rate cooling and5000h thermal aging process is lower.Cracking mode for the edge of SSRT fracture surface is predominantlycleavage,and there is dimples at the core.The ductile character is more obvious for thesamples after lower rate cooling.We verified the slip-dissolve-slip mode to SCC throughthe analysis of side surface cracks.During the SCC process,the oxides accumulated at thecracks,incuneation stress induced by these products may accelerated the process of SCC.