Study On Mechanical Behavior And Microstructure Evolution Of Ferritic/martensitic Steel P92

In Generation-IV Nuclear Reactor,the structure materials will be subjected to higher dose of radiation and higher temperature than in the current reactors.Therefore,better radiation resistance and high temperature mechanical properties are required for the structure materials used for Generation-IV reactor.Under high radiation and temperature,the ferritic/martensitic steel is of better resistance to stress corrosion cracking than the traditional stainless steel.And this kind of alloy is satisfactory to high heat conductivity and low thermal expansivity,which are the general properties for structure materials.Such advanced characteristics of ferritic/martensitic steel prove its feasibility for cladding and other structure materials in Generation-IV reactor such as Super Critical Water Reactor and Sodium-cooled Fast Reactor.Structure materials are the main wrapper for reactor fuel and fission products,and the development of advanced structure materials is crucial for future application of fusion reactor.The safety of reactor will be strongly improved by advanced materials with great strength,creep resistance,corrosion resistance and neutron radiation resistance.So it's important to investigate the mechanical properties and microstructure evolution on ferritic/martensitic steel.The present research consists of two parts.The first one is study on the mechanical properties of P92 steel by tensile experiment.And the other one is focused on the microstructure evolution of P92 steel after different heat treatment.Tensile tests are conducted under various temperatures and strain rates.The results show that the yield strength and ultimate tensile strength retain the trend of slow decrease,while the elongation is low at the strain rate of2?10^-44 s^-1 in the temperature range of 300-350?.Serrations observed at2?10^-44 s^-1 at 306-350?indicate both decreasing critical strain with increasing temperature?normal serration?and with decreasing temperature?inverse serration?.While tests at 319?in the strain rates of 5?10^-55 s^-1-1?10^-33 s^-1 also show two kinds of serrations.The normal behavior of critical strain refers its decrease with decrease of strain rates and the inverse one represents its increase with decreasing strain rates.Based on activation energy of 134 kJ/mol for normal serration and pipe diffusion mechanism,normal serration is explained by interaction of substitutional atoms with dislocations.While the inverse serration is assumed to be caused by sheering of precipitates by moving dislocations.Microstructure analysis on P92 with different heat treatments presents kinds of precipitates,such as MX,M₂X,M₃X,M₂₃C₆,?-FeCr.And M₂₃C₆is dissolved under normalized and then is precipitated under tempered condition.MX phase is of great stability during heat treatment.M₂X and M₃X precipitates are dissolved during tempering.To sum up,the final conclusion of the microstructure evolution is listed as M₃X?M₂X?M₂₃C₆,Fe-rich M₂C?Cr-rich M₂C,Fe-rich M₃X?Fe,Cr-rich M₃C.