Dynamic Recrystallization Kinetics of 690 Alloy During Hot Compression of Double-Cone Samples
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JMEPEG (2017) 26:1433–1443 DOI: 10.1007/s11665-017-2551-8
Dynamic Recrystallization Kinetics of 690 Alloy During Hot Compression of Double-Cone Samples Jue Wang and Shun-Chao Zhai (Submitted July 31, 2016; in revised form December 7, 2016; published online February 15, 2017) Hot compression tests of double-cone samples were conducted for 690 alloy to study the kinetic behavior of the complete dynamic recrystallization (DRX) process under low deformation temperatures from 960 to 1080 °C. The microstructure of 82 points in the vertical section of every deformed sample was quantitatively analyzed to determine the DRX fraction. Corresponding strain of these points was calculated by finite element simulations. Kinetic curves of the specimens with different preheating temperatures were then constructed. The features of various boundaries with different misorientation angles were investigated by electron backscatter diffraction technology and transmission electron microscope. The results showed that the strain is continuously and symmetrically distributed along the centerline of the vertical section. Large strain of 1.84 was obtained when the compression amount is 12 mm for double-cone samples. All the fitted kinetic curves display an ‘‘S’’ type, which possess a low growth rate of DRX at the beginning and the end of compression. The critical strain of recrystallization decreases with the increase in preheating temperature, while the completion strain remains around 1.5 for all the samples. The initial and maximum growth rates of DRX fraction have the opposite trend with the change in temperature, which is considered to be attributed to the behaviors of different misorientation boundaries. Keywords
double-cone samples, dynamic recrystallization, kinetics, superalloys, thermomechanical processing
1. Introduction Dynamic recrystallization (DRX) process is commonly employed in the hot working of wrought superalloys for grain refinement and ductility improvement. The effect of this processing optimization relies on the development of DRX (Ref 1-4). For instance, a complete recrystallization process exists in the hot extrusion of seamless tube or hot die forging of turbine disk and blade for its high strain and temperature (Ref 5, 6). In contrast, multi-pass partial recrystallization and subsequent meta-DRX are present in strip rolling and ingot cogging by radial forging (Ref 7), which requires the design of deformation amount, temperature and holding time between two heats to obtain the appropriate workability. In scientific and engineering research, dynamic recrystallization kinetics, which is always represented by DRX volume fraction (XDRX), is mainly decided by the function of deformation temperature (T), strain rate (_e), true strain (e) and initial grain size (D0) as follows. XDRX ¼ f ðe; e_ ; T ; D0 Þ
ðEq 1Þ
The variable-controlling method has been widely used to establish the relationship between DRX fraction and process parameters, which is always achieved by the thermal simulation Jue Wang, Jiangsu Key Laboratory of
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