Residual Stress Evolution and Its Mechanism During the Manufacture of Superalloy Disk Forgings
BI Zhongnan1,2(),QIN Hailong1,2,DONG Zhiguo3,WANG Xiangping3,WANG Ming3,LIU Yongquan3,DU Jinhui1,2,ZHANG Ji1,2
1. Beijing Key Laboratory of Advanced High Temperature Materials, Central Iron and Steel Research Institute, Beijing 100081, China 2. CISRI-GAONA Co. , Ltd. , Beijing 100081, China 3. AECC Shenyang Engine Research Institute, Shenyang 110005, China
Cite this article:
BI Zhongnan,QIN Hailong,DONG Zhiguo,WANG Xiangping,WANG Ming,LIU Yongquan,DU Jinhui,ZHANG Ji. Residual Stress Evolution and Its Mechanism During the Manufacture of Superalloy Disk Forgings. Acta Metall Sin, 2019, 55(9): 1160-1174.
Significant interior residual stresses, which were generated during the manufacture process, could affect the machining dimension precision and structural stability during the subsequent machining process and service operation in the superalloys component, such as turbine disk. In this paper, the neutron diffraction method and contour method are described for measuring the distribution of interior residual stresses. The distribution, evolution of interior residual stress, and its mechanism are analyzed during quenching, ageing heat treatment and machining process in superalloys disk forging. The residual stresses are mainly generated by the temperature gradient formed during rapid cooling after solution heat treatment. After quenching, the residual stresses in hoop direction and radial direction of disc forging are significant, and its distribution along the profile is characterized by "internal tension and external pressure". The magnitudes of the residual stresses are equivalent to the yield strength of as-quenched alloys at room temperature. Quenching-induced residual stresses are partially relieved during the ageing process due to plastic strain and creep-controlled dislocation rearrangement. The precipitation behavior of γ″ or γ′ phase during heat treatment has a significant interaction with the distribution and magnitude of residual stress. During the machining process, part of the residual stresses contributing to the equilibrium of the internal forces are removed along with the material. Additional moment caused by re-balance of residual stresses results in the serious consequences of distortion in the remaining body.
Fund: Supported by National Natural Science Foundation of China(U1708253);National Key Research and Deve-lopment Program of China(2017YFB0702901);Shenzhen Municipal Science and Technology Inovation Council(JCYJ20160608161000821)
Fig.1 Measurement penetration vs spatial resolution for various residual stress measurement methods
Fig.2 Schematic of the stress-free sample (a) and set-up of neutron diffraction (εθ, εr and εz indicate hoop, radial and axial strains, respectively) (b, c)
Fig.3 Neutron diffraction spectra of GH4169 alloy stress-free sample and disk sample with residual stress
Fig.4 Schematics of contour method for residual stress testing of turbine disk(a) cutting process(b) surface contour of disk sample(c) hoop residual stress
Fig.5 Numerical temperature history at different positions of a turbine disk forging during oil quenching
Fig.6 Simulated temperature field and residual stress field during oil quenching of a turbine disk forging at 0 s(a1~d1), 100 s (a2~d2), 1000 s (a3~d3) and 2000 s (a4~d4)(a1~a4) temperature field (b1~b4) hoop stress (c1~c4) radial stress (d1~d4) axial stress
Alloy
Mass fraction of element / %
Precipitation
σs
MPa
C
Cr
Nb
Ti
Al
Mo
W
Co
Fe
Ni
m / %
t / s
GH4169[28]
0.03
18.0
5.4
0.9
0.5
2.9
-
-
18.0
Bal.
16
548
367
GH4738[29]
0.03
19.5
-
3.1
1.3
4.3
-
13.5
-
Bal.
21
20
658
GH4720Li[30]
0.02
16.0
-
5.0
2.5
2.8
1.2
15.0
-
Bal.
42
2
990
Table 1 Chemical composition and precipitation behavior and room temperature yield strength of typical disk used superalloys[28,29,30]
Fig.7 Alloy shrinkage strains during cooling of typical turbine disk used superalloys measured using dilatometry at different cooling rates
Fig.8 Hoop residual stress distributions of disk forgings measured by neutron diffraction(a) positions for neutron diffraction experiments (b) GH4720Li (c) GH4738 (d) GH4169
Fig.9 3D residual stress distributions in GH4169 disks quenched with different media(a) water quench (b) oil quench (c) air cooling (d) center forced air coolings
Fig.10 An apparatus to control heat-transfer coefficients (HTCs) at center hole of workpiece[31]
Fig.11 Stress relaxation vs time in the center of the disk during the ageing treatment[32]
Fig.12 Effective residual stress and yield strength of as-quenched disk versus temperature
Fig.13 Alloy shrinkage strains at different ageing temperatures measured using dilatometry[38]
Fig.14 Evolution of lattice parameter and volume shrinkage of GH4169 alloy during ageing process[38](a) evolution of {200}γ peak and {004}γ″ peak with ageing time(b) evolution of {200}γ and {004}γ″ interplanar spacing(c) shrinkage strains during thermal ageing at 720 ℃ measured by neutron diffraction and dilatometry during stress-free ageing
Fig.15 TEM bright-field images with [001]γ of stress free sample (a, b), disk samples with residual stress (c, d) aged for 0.5 h (a, c) and 8 h (b, d)[32]
Fig.16 Schematics of machining process for GH4169 alloy disk forging(a, b) dimensions of disk before and after machining, respectively (unit: mm) (c) schematic of the disks after machining d, e) residual stress measuring locations of disk before and after machining, respectively (unit: mm)
Fig.17 Three-directional residual stress neutron diffraction results of the forging disk before and after machining along Line 1 (a~c), Line 2 (d~f) and Line 3 (g~i) in Fig.16 of disk A and A-M(a, d, g) hoop stress (b, e, h) radial stress (c, f, i) axial stress
Fig.18 Residual stress caused axial deformation(a) after machining with free state and principle sketch (b) symmetry machining allowance (Δσtop and Δσbottom indicate residual stress difference near the upper surface and lower surface at wheel core, respectively) (c) asymmetry machining allowance
Residual stress
Δσtop / MPa
Δσbottom / MPa
Hoop
76
117
Radial
111
155
Axial
7
31
Table 2 Residual stress evolution in the edge of disk before and after machining
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