| SA508 Gr.3 Cl.1 steel is an excellent candidate used as nuclear reactor pressure vessel(RPV)that is belong to the non-replaceable component and determines the operating life of nuclear power plant.In this thesis,the microstructure,mechanical properties,fatigue properties and He+ irradiation behavior of domestic SA508 Gr.3 Cl.1 steel were studied and analyzed according to some national testing standards.The microstructure of as-received SA508 Gr.3 Cl.1 steel was observed,analyzed and characterized by using optical microscope,SEM and TEM.The mechanical properties of SA508 Gr.3 Cl.1 steel were tested and evaluated by hardness test,impact test and tensile test.The fatigue life limit,fracture toughness and crack propagation rate of SA508 Gr.3 Cl.1 steel were tested,and the fatigue fractures were also observed and analyzed.The SA508 Gr.3 Cl.l steel was irradiated with 400keV He+ ions with fluence of 1.0×1017 He+/cm2 and 1.0×1016 He+/cm2 at room temperature and 400,respectively.The microstructure of cross-sectional samples prepared along with the direction of ion incident was observed and analyzed by using TEM.The metallographic phase of SA508 Gr.3 Cl.1 steel was upper bainite.There were acicular carbides in the steel matrix.The coarse,moy level 1,ss D ball oxides(almost alumina)distributed in the steel matrix.The grain grade was 8.0.There were a large number of parallel and entangled dislocations distributing in the steel matrix,and the precipitates were mainly Al6(Fe,Mn)particles with the base-centered orthorhombic lattice.The brinell hardness of SA508 Gr.3 Cl.l steel was 200 HBW10/3000/15,and Vickers micro hardness was 222 HV100/5.The results of impact test of the samples which their axis were parallel to the forging direction were more discrete than the results of impact test of the samples which their axis were perpendicular to the forging direction.However,the results of impact test met the ASME specification requirements.The yield strength and tensile strength decreased with temperature increase.The elongation remained at 20.2%?29.1%,but the percentage reduction of area increased after 300?,and the tensile fracture surfaces dominated by dimples.Stretching increased the microhardness of the steel matrix,but its value decreased with the increasing temperature.The increase of microhardness came from the multiplication of dislocation,rather than phase transformation.The phase transformation from austenite to martensite did not happen when stretching.The tensile properties of the SA508 Gr.3 Cl.1 steel met the requirements of the components in the large advanced PWR such as AP1000.The fatigue tests showed that the fatigue limit of S-N curve of the SA508 Gr.3 Cl.l was 268.64 MPa.The test conditions were R=-1 and room temperature.There was only one main crack source on the sample surface at all fatigue test conditions.The average value of the Jic was 331.2 kJ/m2,and Kic was 269.07 MPa(?).The crack propagation rate was increased with the ?K increase.As at the same ?K,the larger the stress ration was,the faster the crack propagation rate would be.The density of irradiation-induced defects(such as dislocations and bubbles)in the SA508 Gr.3 Cl.l steel was increased with the increasing fluence of He+ ions.Some He bubbles with tiny size could be observed at the steel matrix after He+ irradiation with a fluence of 1.0×1017 He+/cm2 at room temperature.The size of helium bubbles was still small even after annealing for 3h at 500?. |
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