A novel recrystallization annealing method to cooperatively control the grain size and δ phase content for initial aged GH4169 superalloy forging

For initial aged GH4169 superalloy forging, it is important and difficult to find a suitable heat treatment method which can refine the deformed mixed grain and control δ phase content cooperatively. In this study, a novel heat treatment method is proposed, which includes an aging treatment to make many δ phase precipitates come out and a subsequent three-stage recrystallization annealing treatment (TSRT). TSRT consists of a high-temperature (990–1010 °C) annealing, a continuous cooling annealing (CRT) and a low-temperature annealing (930–980 °C). TSRT retains the advantages of CRT which is also proposed by authors' team. Moreover, the highlight of TSRT is that an ideal microstructure can be obtained by adjusting the parameters of low-temperature stage. Compared with CRT, TSRT is easier to control the microstructure. The results show that it is beneficial to obtain an ideal microstructure when the temperature of low-temperature stage is 980 °C and 950 °C. Eventually, two feasible annealing processes are obtained. One is “1000 °C×3 min+1000°C-5 min-980 °C+980 °C×20 min”. Through this annealing process, the deformed mixed grain microstructure can be uniformly refined to an average grain size of 7.02 μm, and the δ phase is distributed in spherical shape with a content of 3.28 vol%. The other is “1000 °C×3 min+1000°C-5 min-980 °C+950 °C×30 min”. Using this process, a grain microstructure with an average size of 4.92 μm can be obtained and the δ phase is distributed in rod-like and spherical shape with a content of 5.69 vol%. Besides, the formation mechanism of recrystallized mixed grains is revealed.