| As the goal of improving nuclear steam temperature and enhancing the power generation efficiency has been proposed in recent years, the traditional heat pipe for nuclear power can no longer served in harsher environment. Therefore, it was urgent to develop a material with excellent high temperature oxidation and creep performance for nuclear power plate. Two kinds of novel austenitic heat resistant steel were prepared through theoretical analysis and previous research. The composition of the alloys can be be simply described as B07(Fe-30Ni-18Cr-0.4Nb-3Al-2Mo) and B08(Fe-35Ni-20Cr-0.4Nb-3Al-2Mo), respectively. However, the high temperature oxidation and creep behavior of these two kinds of alloys have not been thoroughly understood. In this paper, high temperature oxidation and high temperature creep behavior have been studied for the alloys. The main results were summarized as follows:The static oxidation behavior of the alloys in air at 700 °C, 800 °C and 900 °C were studied by using mass gain experiments respectively. Results showed that the oxidation kinetics curves of both alloys followed a parabolic law, at 900 °C, the weight gain of B07 alloy was 0.123 mg·cm-2 in 100 h, while B08 alloy was 0.054mg·cm-2, compared with traditional alloy 800 H, the high temperature oxidation resistance of the novel alloy has improved significantly. Combined with oxide film surface morphology, XRD and cross-sectional analysis, the surface oxide film of B07 alloy and B08 alloy were found to be mainly(Fe0.6Cr0.4)2O3 at 700 °C, Inside the oxide film of B07 alloy, there was a Al-rich oxide while the presence of which inside B08 alloy was not obvious. At 800 °C and 900 °C, the surface oxide films of both alloys were Al2O3 and(Al0.9Cr0.1)2O3, and there was also a more obvious Al-rich oxide inside. Compared with the thickness of the oxide film at the same temperature,it was found the oxide film of B08 alloy was thinner than B07 alloy, which meant B08 alloy had better high temperature oxidation resistance. Results showed that adding appropriate amount of Al can improve the high temperature oxidationresistance and more contents of Ni elements were conducive to the formation of Al2O3 oxide.The high temperature creep property experiments showed that the creep curve of B07 alloy had typical three-phase steady creep rupture mode while B08 alloy only had initial creep stage and steady creep stage. Besides, the steady-state creep rate of B08 alloy was larger than B07 alloy under the same conditions. Using a power law equation to describe the creep date obtained in the study, the stress exponent of B07 and B08 alloy was 6.98 and 16.35, repectively, furthermore, the creep activation energy of B07 alloy was 720 k J/mol while B08 alloy’s activation energy was 838 k J/mol, therefore, the second phase particles strengthening was the creep deformation mechanism for the alloys.The calculation of the high temperature rupture strength for B07 and B08 alloy was 143 MPa and 232 MPa, repectively, which had higher creep rupture strength than alloy 800 H. Analysing the microstructural after different creep tests on these alloys, Nb C and σ phase precipitated in the grains of B07 alloy, while the M23C6 precipitated both in the grains and on the boundaries. the Nb C and M23C6 effectively impeded dislocation motion and strengthened the alloy, while the poor creep elongation and rupture life for B07 alloy may be related to the excessive σphase formation. Moreover, a large number of M23C6 particles dispersed in B08 alloy can improve the creep life. Results showed that adding appropriate amount of Nb can improve high temperature creep property and more Ni can postpone the formation ofσ phase effectively.Based on the above experimental results, it was found the high temperature oxidation resistance and creep properties of B07 and B08 alloy excelled than alloy800 H, and higher content of Ni in the alloy was propitious to improve the high temperature oxidation and creep properties. |
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