The microstructure and mechanical properties of fine-grained Inconel 718 ring forging were investigated in this paper. The results indicated that the fine-grained ring forgings can be obtained by forging the fine-grained Inconel 718 bars. The grain size can be as fine as ASTM 10 and the precipitated δ phase are spherical. Heat treated at 980°C/1h/water cooling + 620°C /12h/air cooling, the ring forgings possessed very good mechanical properties. The impact toughness can be over 100J. In the fatigue test with the stress ratio -1, when the theoretical stress concentration factor is 1 and 2.7, the maximum stress for 10 7 fatigue cycles is over 620 MPa and 260 MPa, respectively. IntroductionInconel 718 alloy has been used world-wide in aerospace, aircraft, oil, and chemical industries, and also nuclear power plants because of its high strength, excellent ductility, good formability and weldability etc [1][2][3]. To meet the demands of different service conditions, the die forging process has been investigated intensively in the past few years. Besides two conventional forging processes, including forging driven by hydraulic presses or hammers, and some advanced forging processes, such as hot die forging, insulation die forging and isothermal forging, have been developed to manufacture fine grains forgings. The products of these processes have been applied significantly in new power units [4][5][6].
Continuous improvements of properties for individual parts are indispensable for perpetual development of aircraft engines. Concerning turbine disc, numerical simulation of forging process is one of the most attractive tools to reduce the cost and time and to improve the properties and the reliability at the same time. In this paper, the hot deformation behavior of IN 718 superalloy has been characterized in the temperature range 900-1020 o C and strain rate range 0.001-0.1 s -1 using isothermal constant strain rate compression tests on process annealed material, with a view to obtain a correlation between grain size and the process parameters. Through a comparison study of two forging methods, temperature-field and strain-field finite element analysis modeling were established, and load-time curves were obtained for a turbine disc under routine and hot die forging process conditions. Results of numerical simulation show that compared to routine forging, hot die forging gives a decrease in total forging force, the temperature-field and strain-field of the turbine disc is more uniform. The effect of cold die on the microstructure is decreased notably under hot die forging condition.
In order to meet the growing demand on markets both domestic and international, the manufacturing technologies of superalloys keep improving in China. This paper reviews the progresses and trends on melting, cogging, and forging technologies for China's C&W superalloys in the recent 20 years.
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