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Abstract
Two kinds of experimental ferritic/martensitic steels (HT-9) with different Si contents were designed for the fourth-generation advanced nuclear reactor cladding material. The effects of Si content and tempering temperature on microstructural evolution and mechanical properties of these HT-9 steel were studied. The microstructure of experimental steels after quenching and tempering were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM); the mechanical properties were investigated by means of tensile test, Charpy impact test, and hardness test. The microscopic mechanism of how the microstructural evolution influences mechanical properties was also discussed. Both XRD and TEM results showed that no residual austenite was detected after heat treatment. The results of mechanical tests showed that the yield strength, tensile strength, and plasticity of the experimental steels with 0.42% (% in mass) Si are higher than that with 0.19% Si, whereas hardness and toughness did not change much; when tempered at 760 °C, the strength and hardness of the experimental steels decreased slightly compared with those tempered at 710 °C, whereas plasticity and toughness increased. Further analysis showed that after quenching at 1050 °C for 1 h and tempering at 760 °C for 1.5 h, the comprehensive mechanical properties of the 0.42% Si experimental steel are the best compared with other experimental steels.
Highlights
Advanced 9%–12%Cr ferritic/martensitic (F/M) steels including HT-9 (12Cr-1MoVW) have been considered as one of the most promising candidate reactor fuel cladding and structural materials in Generation IV advanced nuclear reactors, owing to their superior thermomechanical properties, irradiation resistance and corrosion resistance at elevated temperatures [1,2,3,4,5,6,7,8,9,10]
There are still some serious challenges for the usage of HT-9 in future reactors: neutron irradiation leads to an increase in the ductile–brittle transition temperature (DBTT) and will further affect its fracture resistance considerably; insufficient creep strength and fracture toughness at high temperature [11]
From the recent research on the heat treatment effects, the results show that the tempering temperature is the most important factor affecting the yield strength and elongation of HT-9 steel [21]
Summary
Advanced 9%–12%Cr ferritic/martensitic (F/M) steels including HT-9 (12Cr-1MoVW) have been considered as one of the most promising candidate reactor fuel cladding and structural materials in Generation IV advanced nuclear reactors, owing to their superior thermomechanical properties, irradiation resistance (void swelling and embrittlement) and corrosion resistance at elevated temperatures [1,2,3,4,5,6,7,8,9,10]. Materials 2020, 13, 972 and dislocations strengthening, and the essence of steel strengthening mechanism is to provide better resistance to the slip of dislocations. All these methods mainly depend on the chemical composition and the heat treatment of the steels. The heat treatment processes of HT-9 and other ferritic/martensitic steels have been studied by many researchers [12,13,14,15,16,17,18,19,20]. From the recent research on the heat treatment effects, the results show that the tempering temperature is the most important factor affecting the yield strength and elongation of HT-9 steel [21]. As a result, adjusting the tempering temperature is an effective method to optimize the mechanical properties of HT-9 steel
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