Research On Deformation Behavior And Change Rule Of Microstructure And Properties For Haynes 230 Nickel-based Alloy

The development of key technologies for 700?advanced ultra-supercritical coal-fired power generation is one of China's important measures to achieve the goal of?carbon peak and carbon neutrality?.The nickel-based alloy seamless tube used as the core component of coal-fired power generation system is the"aorta"of the"heart"of power equipment,and the quality stability of the tubes under high temperature and high pressure environment directly affects the reliable operation of the unit.The manufacturing process of nickel-based alloy seamless tubes is relatively complex,involving a series of processes such as smelting,hot forging,hot extrusion,cold rolling(or hot rolling),and heat treatment.There were significant difference in microstructure before and after these manufacturing processes,which will resulting in great changes in the service performance of seamless tubes.Therefore,it is of great engineering value and academic significance to reveal the change rule of microstructure and mechanical properties of nickel-based alloy seamless tubes during the deformation processing,and to achieve high-quality manufacturing and reliable service of seamless tubes for advanced power generation equipment.Aiming at the service environment of heat transfer tubes for superheaters and reheaters of 700?advanced ultra supercritical thermal power units,this paper takes the manufacturing process of Haynes 230 nickel-based alloy seamless tubes as the main line,and adopts characterization methods such as metallographic microscope(OM),scanning electron microscope(SEM),electron backscatter diffraction(EBSD),X-ray diffractometer(XRD),based on the advanced Gleeble thermal simulation technology,analyzed the microstructure evolution law of nickel-based alloy during thermal deformation,and determined the optimal range of thermal deformation parameters.The influence of heat treatment process on the cold-rolled structure and mechanical properties of nickel-based alloy seamless was studied,and the best heat treatment process of nickel-based alloy seamless tube was obtained.The typical specifications seamless tube was selected for solid solution treatment according to this process,and its microstructure and properties were evaluated.The evolution law of microstructure and mechanical properties of the alloy with aging time at service temperature was studied,which provides a scientific basis for optimizing its processing technology and controlling its microstructure and mechanical properties.The main conclusions are as follows:1.The effects of deformation resistance and microstructure of Haynes 230 nickel-based alloy with thermal deformation parameters were obtained by isothermal thermal compression test.An improved constitutive model of coupled strain of Haynes 230 nickel-based alloy is constructed,and the deformation resistance of the alloy in the process of thermal compression is predicted.The results show that the correlation coefficient between the predicted value and the experimental value is 97.94%,and the average relative error is 6.9976%,indicating that the improved model has more accurate prediction ability.The hot deformation mechanism diagram of Haynes 230 nickel-based alloy based on dynamic material model(DMM)was established,and the optimum hot working parameters of Haynes 230 nickel-based alloy are obtained:strain rate is 0.06?0.16 s^-1 and temperature is 1100?1150?.2.The change rule of tensile properties of Haynes 230 nickel-based alloy with strain rate and temperature were obtained by thermal tensile test.Through the fracture and axial microstructure analysis of hot tensile samples,it is proved that the change rule of fracture morphology is consistent with the variation curve of tensile properties.By comprehensively analyzing the tensile property curve,fracture morphology and fracture axial microstructure,it is determined that the best hot working process of Haynes 230 nickel-based alloy is 1150?1200?when the strain rate is 0.01 s^-1 and 1150?1225?when the strain rate is 0.1?5 s^-1.Through calculation and analysis,the activation energy of thermal tensile deformation is greater than that of thermal compression,which shows that under the same deformation conditions,it is more difficult for thermal tensile deformation and dynamic recrystallization,and the complete recrystallization temperature of thermal tensile is about 50?higher than that of thermal compression.3.The effect of different cold rolling deformations and heat treatment processes on the carbide content,average grain size,and room temperature mechanical properties of Haynes230 nickel-based alloy were studied,and the Beck relationship between average grain size and thermodynamic temperature and the Hall-Petch relationship between average grain size and yield strength and hardness were obtained.Considering the grain size,uniformity and mechanical properties of the alloy,the optimal heat treatment parameters of Haynes 230nickel-based alloy seamless tube are 1225?1250?/1 h,water cooling.According to this heat treatment process,the alloy seamless tube with a typical specification of?89×12 mm was solid solution treated.The microstructure and properties test results show that in addition to the austenite matrix structure,Haynes 230 nickel-based alloy mainly contains M₆C carbides and a small amount of M₂₃C₆ carbides.The area percentage of the former is about 2%and the average grain size is about 6.4.Haynes 230 nickel-based alloy seamless tube has good tensile properties at 25?900?,high temperature endurance at 700?,hardness,impact energy absorption and intergranular corrosion resistance,meeting the service requirements of 700?advanced ultra supercritical unit.4.The results of long-term aging test show that two kinds of carbides M₆C and M₂₃C₆precipitate in the alloy matrix,and the content of the former is much greater than that of the latter.In the long-term aging process,M₂₃C₆ changed to M₆C carbide type,and the content of M₆C carbide increased continuously,and finally occupied the dominant position of precipitation strengthening.Haynes 230 nickel-based alloy precipitated after 1000 h aging heat treatment?(P)The tensile strength and hardness at room temperature reach the peak,and then the mechanical properties remain basically stable due to the precipitation of stable M₆C carbides.The mechanical properties at room temperature are still high until aging for 10034 h,indicating that the alloy can maintain the stability of microstructure and mechanical properties under the condition of long-term service at 700?.