Hastelloy N (N10003) Hastelloy
Hastelloy N alloy is a nickel-based high-temperature alloy material used in molten salt reactors. It has excellent corrosion resistance, resistance to neutron radiation and good high-temperature mechanical properties.
However, the reactor outlet temperature reached 750°C, exceeding the allowable temperature of Hastelloy N alloy of 704°C, which means that the alloy cannot operate stably in a 750°C molten salt environment for a long time. Therefore, there is an urgent need to optimize Hastelloy N alloy to meet the requirements of higher temperature molten salt reactors.
Since the Mn element has the advantages of stabilizing austenite and improving oxidation resistance in high-temperature alloys, this article takes Hastelloy N alloy as the research target. By designing and preparing Hastelloy N alloys with different Mn contents, and using optical microscope (OM) and scanning The influence of Mn content on the microstructure, mechanical properties and oxidation properties of HastelloyN alloy was studied using experimental analysis methods such as electron microscope (SEM+EDS+EBSD), universal tensile machine, X-ray diffractometer (XRD) and electron probe (EPMA). . The following research results were obtained:
(1) The addition of Mn element can promote the refinement of Hastelly N alloy grains, increase the number of separated carbides, and the carbides gradually condense into blocks and long chains, and gather at the grain boundaries.
(2) When stretched at room temperature, the tensile strength of 0.5Mn alloy is poor. When the Mn content exceeds 1wt%, the tensile strength is improved. Dimples and step-like textures appear on the fracture surface. The cracking method is composed of cleavage cracking and resistant cracking. The mix cracks. When stretched at high temperature of 850°C, Mn has no obvious effect on the tensile strength of the alloy. Lubricant crystal planes appear on the fracture surface, and the cracking method is intergranular brittle cracking.
(3) As the Mn content increases, the antioxidant properties of the alloy are improved. At 700°C, the 1wt% Mn content alloy has the best oxidation resistance, and the oxidation rate is 25.9% lower than that of the 0Mn alloy. At 850°C, the 0.75wt% Mn content alloy has the best oxidation resistance, and the oxidation rate is 52.1% lower than that of the 0Mn alloy.
(4) The oxide film has a layered structure. After oxidation at 700℃/200h, the oxide film of all alloys is divided into two layers. The outer layer is NiO, Fe2O3 and other oxides, and the inner layer is Cr2O3, MoOz and NiMn2O4 and other oxides. The surface of the alloy There is no obvious drop, and the NiO layer is intact and dense. As the Mn content increases, the oxide layer of the alloy gradually becomes thinner. After oxidation at 850℃/100h, the oxide film of an alloy with a Mn content of 0~0.2wt% is divided into three layers. The outer layer is mainly NiO, the middle layer is NiO, NiMn2O4 and other composite oxides, and the inner layer is Cr2O3, MoO2 and other oxides. Material; For alloys with a Mn content of 0~0.2wt%, the oxide film is divided into two layers, the outer layer is NiO and a small amount of NiFeO4, NiMn2O4, and the inner layer is Cr2O3, MoO2 and other oxides. As the Mn content increases, the internal oxidation phenomenon of the alloy gradually weakens.
(5) The addition of Mn can promote the formation of a NiMn2O4 spinel protective layer between NiO and the matrix, effectively preventing the intrusion of the outside world and the outward diffusion of alloying elements, and improving the anti-oxidation performance of the alloy.
Hastelloy N has excellent resistance to thermal fluoride salt oxidation at 704-871°C, and has excellent antioxidant capacity in the air. It has good resistance to aging and embrittlement, and has good processing properties.
Usage: Molten fluoride salt container
