Thermal Fracture Of Oxidation Layer And Oxidation-induced Embrittlement In T91 Steel

Ferritic/martensitic steel,T91,is one of the candidate structural materials for LeadCooled Fast Reactor and Accelerator Driven Sub-critical system.Lead-bismuth eutectic creates a severely corrosive environment for T91 at high temperatures,and is accompanied by the effect of Liquid Metal Embrittlement.Although the oxide layer can effectively isolate the direct contact between the liquid metal and the structural material,and slow down the corrosion,the oxide layer may weaken the mechanical properties of the structural material,such as the toughness.So far,there are relatively few studies on the influence of the corrosion oxide layer on the mechanical properties of T91 steel.This thesis numerically and experimentally study the influence of temperature on the corrosion oxide layer itself,and the effect of oxide layer on the overall toughness(elongation at break)of structural materials.The main research contents of this work includes:(1)Considering the large difference in thermal expansion coefficient between heterogeneous phases,thermal variation generates stress in heterogeneous structures. Based on a brief introduction to the microstructure of corrosion oxidation layer on T91 Steel,the thermal stress among the oxide layer and the substrate is analyzed by finite element method,and the cracking behavior of the oxide layer is analyzed using peridynamic thermomechanical model.(2)The tensile behavior of T91 steel and 316 L steel after exposed in cyclic high- temperature environment are studied.Through tensile test,Scanning Electron Microscope,Energy Dispersive Spectrometer and nanoindentation test,the tensile properties,fracture morphology characteristics,element distribution,elastic modulus and hardness of the sample are analyzed.The experimental results show that the corrosion oxide layer reduces the elongation at break of T91 steel and 316L steel,while the yield strength and ultimate strength of the material have little effect.The research results show that the microstructure and thickness of the oxide layer(mainly the inner oxide layer)affect the overall toughness of the material,and the oxide layer can promote the initiation of cracks.This work provides a new understanding to the embrittlement of T91 in LBE,and may guide the establishment of failure criteria for structural materials in lead-bismuth corrosive environments.