Microstructure And Properties Research Of Nickel-base Alloy For Nuclear Power

Nuclear power has an advantage over other sources of power.in the nuclear power technology Our country has been the international top level,however,the domestic high temperature alloy used in the evaporator preparation technology does not meet the safety requirements of nuclear power,which hinder China autonomously development of nuclear power.Inconel 625 alloy is an ideal material for the key components of evaporator,and widely used in nuclear power,petrochemical and Marine engineering.The ultra-low iron Inconel 625 alloy studied in this paper reduce the iron content based on the composition of ASTM B443 N06625.In this paper,the heat treatment process was studied,the performance and structure were characterized,the service environment was simulated and the safety reliability was tested.Determines the low iron Inconel 625 alloy heat treatment process by oxalic acid electrolytic corrosion combined with grain size and hardness of alloy:the microstructure of forging alloy after 1140?C×4h solid solution treatment,second phase into the Ni-base fully,and the hardness is 172.0 HV10,the average grain size is 38.7?m,corrosion weight loss rate is 4.97kg·?m²·h?^-1;Subsequently,1000?C stabilized treatment of 6h,small?Nb,Ti?C precipitation at the grain boundary and the crystal internal,and the hardness is 186.1HV10,the corrosion weight loss rate is 4.89kg·?m²·h?^-1 after exposed at 750?C.In this process,the ultra-low iron Inconel 625 alloy can obtain good corrosion resistance,mechanical properties and appropriate grain size.In the high-temperature oxidation experiment of ultra-low iron Inconel 625 alloy at 900 and 1000?C,showing excellent corrosion resistance and oxidation resistance:Cr₂O₃ and NiCr₂O₄ oxide film were rapidly generated on the surface of the alloy to inhibit the internal proceeding of oxidation.At 345?C/15.5MPa subcritical primary circuit water corrosion oxidation experiment,NiCr₂O₄ oxide film grows slowly,due to the sedimentation of iron elements in the environment,samples weight gain,the average weight gain rate in the 1500h period is 7.475×10^-2?g/?cm²·h?.In 750?C rupture,Its strength exhibits far superior performance to ASTM B443 N06625 technical requirements,R 178MPa,R 120MPa.During the continuous stretching process,the?phase is broken or bent into a bow,showing a certain plasticity.Because the matrix tear apart from the boundary phase precipitates leading the intergranular loose,and gradually develop into the pore or crack,eventually lead to fracture.The elongation rate?A_t?each of the samples are more than20%,and the fracture was covered by oxide,fracture along the crystal boundary.Research and analysis microstructure and properties of low iron Inconel 625 alloy at750?C long-term aging,by scanning electron microscope?SEM?,X-ray diffraction?XRD?,impact testing machine and automatic HV hardness tester,etc.In the process of long-term aging at 750?C,solid solution low iron Inconel 625 alloy forms the thin film boundary carbide in 10h,and the gamma phase is precipitated;In the case of 60h,there was a change in the?'??degeneration.When the aging time was 1000h,the?-Ni₃Nb was scattered throughout the whole grain,and the structure was stable after 2000h.In the aging process,the grain boundary carbide is mostly rich chromium M₂₃C₆ type and M₆C type with molybdenum.The stabilized alloy after aging 20h,the grain boundary was precipitated in the grain boundary.There was?'??degradation transition in 200h,and the whole grain was scattered throughout the whole grain in the case of 3000h.The structure tends to be stable after 4000h.The discontinuous grain boundary carbides were coarsely coarsened,and were mainly composed of?Nb,Ti?C and molybdenum M₆C,with M₂₃C₆ type.The stabilized alloy has higher stability than the solid solution alloy.The stabilization treatment delays the precipitation and transformation of?',?phase,growth and transformation of carbide in the long-term aging.The stability of the structure determines the stability of the alloy mechanical properties,meaning that the hardness and the plasticity change of solid solution alloy with the aging time is more rapid than that of the.The corrosion resistance of alloy was characterized by ASTM G28A acid etch.After aging,the grain falls off cause weightlessness in acid etch process due to the boundary carbide precipitated leading formation of elements dilution zone,boundary phase and staggered?phase dissolved in the sample,and Corrosion weightlessness of stabilization alloy with the aging time is slower than that of the solid solution alloy.