Effect Of Heat Treatment On Microstructure And Mechanical Properties Of Low Activation Ferrite/ Martensitic Steels Used For The Fusion Reactor

In recent years, more and more attention is paid to the energy problem. ITER plan is one of the biggest international cooperation in the world so far. Its aim is to achieve the controlled thermonuclear fusion for the first time. The structure material used in the fusion reactor is one of the bottle nets to restrict the achievement of nuclear fusion. Due to the unique advantages, RAFM has been chosen as the preferred structure material used in ITER (international thermonuclear experimental reactor) and DEMO. We modified the microstructure and mechanical properties of RAFM through heat treatment; meanwhile, we compared the changes of the microstructure and mechanical properties among different samples using different heat treatment process.Through chemical analysis, we know the components(wt%) of the steel are that: C0.10, Cr8.89, W1.53, Mn0.388, V0.213, Ta<0.1, P0.007, S0.0053, 0.0008.The efforts of heat treatment are big on the microstructure and mechanical properties of RAFM. According to the assessment method of static toughness, we have chosen the heat treatment process which gets the best static toughness on the promise of good ductility, that is 1000℃/30min/air cooling+740℃/90min/ air cooling.Through observing the fracture surface of tensile specimen, we know that the fracture of RAFM is a kind of plastic fracture, named microporous aggregate fracture. The fracture appearance is changed by the tempering temperature. When the tempering temperature is up to 650℃, the size of dimples in the fiber zone is fine, and the dimples in the shear lip region is deeper than before. From these changes, we can understand that the second phase particles have become fine and uniform when tempering temperature is up to 650℃, and at the same time, the plasticity of the steels is better than before.To the samples of RAFM which have the special heat treatment of 1000℃/30min/air cooling+740℃/90min/ air cooling, we did some tensile experiments in different temperatures, and the Charpy impact test in different temperatures. Also we observed the microstructure by TEM. We know that: (1) the structure of the steel is tempered martensite with BCC lattice, and there are a lot of dislocations in the martensite grains. (2) the tensile properties in the room temperature are that: Rp0.2=485MPa, Rm=650MPa, A%=27%, Z%=25%; the tensile properties in 600℃are that: Rp0.2=310.9MPa, Rm=323.5MPa, A%=25%, Z%=87.1%. From these data, we know that RAFM also has good toughness in high temperature. (3) we know from the Charpy impact test that the DBTT of RAFM is about -80℃. The impact absorbed energy in the room temperature is up to 180J. That is to say, RAFM has excellent impact toughness and low DBTT.