A novel recrystallization annealing method to cooperatively control the grain size and 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 delta phase content cooperatively. In this study, a novel heat treatment method is proposed, which includes an aging treatment to make many delta phase precipitates come out and a subsequent three-stage recrystallization annealing treatment (TSRT). TSRT consists of a high-temperature (990-1010 degrees C) annealing, a continuous cooling annealing (CRT) and a low-temperature annealing (930-980 degrees 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 degrees C and 950 degrees C. Eventually, two feasible annealing processes are obtained. One is "1000 degrees Cx3 min+1000 degrees C-5 min-980 degrees C+980 degrees Cx20 min". Through this annealing process, the deformed mixed grain microstructure can be uniformly refined to an average grain size of 7.02 mu m, and the delta phase is distributed in spherical shape with a content of 3.28 vol%. The other is "1000 degrees Cx3 min+1000 degrees C-5 min-980 degrees C+950 degrees Cx30 min". Using this process, a grain microstructure with an average size of 4.92 mu m can be obtained and the delta 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.