Experimental study on the residual stress of the power spinning rod bushing with main technological parameters

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ScienceDirect Materials Today: Proceedings 20 (2020) 283–294

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ANM 2018

Experimental study on the residual stress of the power spinning rod bushing with main technological parameters Yue Wang1 Xin Zhang2* Beijing Key Laboratory of Powertrain for New Energy Vehicle, School of Mechanical, Electronic and Control Engineering, Beijing Jiao tong University, Beijing, 100044, PR China

Abstract In the course of plastic forming, the residual stress of the power spinning connecting rod bushing will be produced. The residual stress will influence the dimensional precision and leads to bushing fatigue failure. In view of the residual stress size and distribution and the elimination of residual stress. In this paper, a single factor test was carried out for the research object with the power spinning rod bushing of tin bronze (QSn7-0.2). This paper puts forward the X-ray diffraction method combine with electrolytic polishing method to measure different levels of residual stress and carry on the analysis to the experimental result. The influences of the main parameters (thinning ratio, the first wheel of reduction, feed rate, heat treatment temperature and holding time) on the residual stress were obtained. The results show that: after the power spinning, the surface of the connecting rod bushing is the residual compressive stress, the inner layer is the residual tensile stress, the residual stress at both ends of the bushing is greater than the residual stress in the middle part of the work. In a certain range, the surface residual stress of the connecting rod liner increases with the increase of the thinning ratio, and decreases with the increase of the feed ratio then increases, and decreases with the increase of the first wheel thinning. In a certain range of temperature, the connecting rod bushing after the strong spinning is treated by heat treatment, the surface residual stress will decrease with the increase of temperature, and the longer the holding time, the more obvious the effect of removing residual stress. © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of 11th International Conference on Advanced Nano Materials. Keywords: Connecting rod bushing; Power spinning; Residual stress; X-ray diffraction

* Corresponding author. E-mail address: [email protected] 2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of 11th International Conference on Advanced Nano Materials.

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1. Introduction During the working process of diesel engine, the connecting rod bushing is affected by high temperature and high pressure, and the working environment is poor. Therefore, the connecting rod bushing needs higher dimensional accuracy and mechanical properties. Power spinning technology can enhance the material utilization rate, density and mechanical properties of connecting rod bushing [2,3,4]. However, due to the inhomogeneous plastic deformation in the forming process, the residual stress is generated [5,6]. About microscopic explanation, the residual stress is produced by the anisotropy of the slip in the grain, the thermal expansion coefficient of the grain, the elastic coefficient and the different orientation between the grains. Residual stress is the elastic force that balances the material internally when it is not subjected to external action. Residual stress causes deformation and dimensional accuracy change of workpiece during processing and using. The natural releasing of residual stress in the working process of workpieces will cause the mechanical properties such as fatigue strength, corrosion cracking and so on are reduced and the workpiece are invalidated [7]. Therefore, the production of residual stress, numerical distribution and elimination methods are the key issues in the technological field. Residual stress measurement technology is divided into destructive measurement technology and nondestructive measurement technology. Destructive measurement technology includes slitting, layer removal method and holedrilling and so on. Nondestructive measurement technology includes magnetic strain method, ultrasonic method, neutron diffraction method, X-ray diffraction method and so on. In 1929, the X-ay diffraction method was the first proposed by the former Soviet Union scholars. In recent years, domestic and foreign scholars have studied deeply the residual stress of X-ray diffraction method. In order to prove the accuracy of the X-ray diffraction method, comparing with the hole-drilling method and the finite element method, the results are consistent [8,9]. X-ray diffraction is widely used in scientific research and industrial production because of its nondestructive advantages and high accuracy. It can be used for residual stress detection of key parts of car body. [9] It can test the change of residual stress before and after shot peening gear [10]. It can be applied to welding residual stress measurement of B subway frame [11]. It can be used for spinning residual stress detection of thin-walled cylinder parts and other aspects [12]. By testing the distribution of residual stress, the processing technology is optimized and optimized. X-ray stress measurement can also be used to detect residual stress of different layers in combination with delamination method [13] Willems et al. obtained the radial stress gradient of steel wire by X-ray diffraction combined with chemical etching process [14]. Experimental investigations on residual stress gradient of axle by X-ray diffraction and delamination method in Central South University [15]. Research shows that the heat treatment process can reduce or eliminate residual stress. Researchers have used heat treatment to change the thermal expansion coefficient and elastic modulus of the pyrocarbon coating on artificial heart valve silicon to relieve residual stress in the coating [16]. The residual stress produced during welding is reduced by 70% by heat treatment [17]. Sany Heavy Industry Co. has carried on the experiment research to reduce the concrete pump truck conveyor pipe residual stress, increased the stress relief annealing process to improve the specimen elongation phenomenon [18]. The residual stress of 27SiMn cold-drawn steel pipe was tested by Xuzhou Industrial Hydraulic Co. Ltd. After stress relief annealing, the residual compressive stress decreased by about 80% [19]. After cold rolling of dual phase high strength steel DP780, the residual stress was measured by X-ray diffraction and delamination method. The residual stress can be significantly reduced after annealing [20]. The essence of the X-ray method is to measure the atomic spacing of crystals and calculate the residual stress through elastic theory. After X-ray diffraction of crystal lattice, the plane spacing of crystal lattice can be calculated by Bragg equation. Finally, the stress value of workpiece can be obtained by using the plane spacing. The Bragg equation is about the X ray diffraction conditions of crystals. 2d sin θ = n λ , n =1,2… (1) d is the distance between crystal planes, θ is the angle between the incident X-ray and the corresponding crystal plane, λ is the wavelength of X-ray, n is the diffraction series. Diffraction occurs when the optical path difference between the two adjacent crystal planes is n times the wavelength of the X-ray, so that the diffraction intensity of the X-ray will be reinforcing. The penetration depth of X ray is about 10-35um. The X ray diffraction method does not

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change the stress state and material of the material surface under the condition of measuring the surface residual stress. In this paper, the residual stress gradient of spinning workpiece is measured by combination X-ray diffraction and electrolytic polishing method. The influence of main process parameters on the residual stress is analyzed and explored. Finally, the residual stress is eliminated by heat treatment. 2. Experimental details 2.1. Test equipment and testing objects （ 1 ） X ray diffraction residual stress analyzer is produced by Proto Corporation of Canada, Equipment parameters: Mn target, K β filter is Cr, （311）Diffraction crystal plane, Diffraction angle is 152°. Depth of measurement is 10 μ m . The measurement software is XRDWin 2.0. Shown in Fig. 1. （2）SXD100/3-CNC Powerful CNC spinning machine has parameters of 100KN longitudinal thrust, 3 *80KN radial thrust, 40KN tail top force and 45KW total power. Shown in Fig. 2.

Fig.1 X-ray diffraction residual stress analyzer

Fig.2 Power spinning machine

（3）BPG-9200BH high temperature blast drying box can intelligently control the heating rate and holding time, which can be used for stress relief annealing of spinning workpiece. （4）The surface of the spinning workpiece is marked with a line per 120 degrees. Each line is divided into 10 parts according to the height L of each spinning workpiece. Marking the spinning parts with the index head is shown in Fig. 3. There are 12 test pieces the height is 81mm, the inner diameter is Φ50.3mm, and the outer diameter is Φ 64.06mm.

(a) Index head

(b) Marked spinning workpiece Fig.3 Marked points

2.2. Selection of main process parameters 2.2.1. Process parameters of powerful spinning： （1）Thinning rate ψt: Thinning rate is one of the main technological parameters of the powerful spinning machine. When the thinning rate is too large, the flange instability will cause wrinkles and peeling during spinning. The small thinning rate will cause uneven deformation of the workpiece, resulting in delamination of the workpiece wall thickness or inadequate deformation of the inner surface of the workpiece and cracks. According to the experience of work and experiments, the thinning rates were 25%, 35% and 45%.

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（2）The feed ratio f: The feed ratio is the ratio of the feeding speed of the spinning wheel to the spindle speed of the spinning machine, f = v / n . The spindle speed of the powerful spinning machine is 600 r/min. According to the work and test experience, the feeding speed of the spinning wheel is set to 120, 360 and 600 mm/min respectively. So the feed ratio is 0.2, 0.6 and 1mm/r. （3）First wheel thinning: t is the total reduction amount, t= (D-d) /2. d is the spinning blank diameter, D is the outer diameter of the spinning workpiece, and the unit is mm. The test set a certain amount of thinning under the first wheel of pressure, and the remaining two wheels evenly shared the remaining amount of thinning. The three rotating wheels bear the weight reduction of the spinning parts respectively, so that the number of passes becomes more and the efficiency is improved; the force of each rotating wheel is reduced, the life of the rotating wheel is prolonged; and the dimension precision and surface quality of the workpiece are improved. Considering the practical experience, the first wheel reduction is 0.4t, 0.5t and 0.6t. 2.2.2. Heat treatment parameters （1）Annealing temperature: According to the phase diagram of Cu-Sn binary alloy as shown in Fig. 4 and Table 1, it is known that the annealing temperature of QSn7-0.2 should be 200-300℃, and the experimental parameters should be 200℃, 240℃ and 280℃. Table. 1 QSn7-0.2 chemical composition (mass fraction, %) element

Sn

Al

Zn

Ni

Fe

measured value

6-8

<0.002

<0.05

<0.1

<0.010

Pb <0.010

P 0.18

Fig.4 Phase diagram of tin bronze alloy

（ 2 ） Holding time: Holding time can make the residual stress between the crystal and the crystal more effectively release. The holding time of the test setup is 1hour and 2hours. 2.3. Test scheme Based on single factor test method, the influence of thinning rate, feed ratio, first wheel thinning, annealing temperature and holding time on residual stress was studied. The design of the test plan is shown in Table 2.

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Table. 2 Design table of single factor test annealing temperature(℃)

holding

240

1

0.5

200

1

0.6

0.5

280

1

35

0.6

0.5

240

2

11

35

0.6

0.5

200

2

12

35

0.6

0.5

280

2

Thinning

Feed ratio

Thinning of

rate (%)

(mm/r)

first wheel (t)

1

25

0.6

0.5

2

35

0.6

0.5

3

45

0.6

0.5

4

35

0.2

0.5

5

35

1

0.5

6

35

0.6

0.4

7

35

0.6

0.6

8

35

0.6

9

35

10

number

time (h)

（Note: t is the total thinning, t = (D-d)/2, D is the outer diameter of spinning blank, d is the outer diameter of spinning workpiece, unit mm.） 3. Results and discussion 3.1. Study on the effect of spinning parameters on residual stress of workpiece According to table 2, workpieces from No. 1 to No. 7 are selected, and No. 2 workpiece is not heat-treated temporarily. The residual stress was measured at the bottom, the middle and the head of the spinning part. The height of each spinning part was measured by vernier and recorded as L. Starting from the bottom of the workpiece as marking starting point, the section 0.2L, 0.5L, 0.8L away from the bottom of each workpiece is selected to correspond to the bottom, middle and head of the workpiece. The residual stress values of three sections of spinning workpiece are measured and analyzed. It is found that the tangential residual stress is very small and can be neglected. The axial residual stress is measured in Table 3. The three points equally divided into section i are called Ai1, Ai2 and Ai3 respectively. Table. 3 Measurements of residual stress before heat treatment No.

0.2 L Section stress /MPa

0.5L Section stress /MPa

0.8L Section stress /MPa

A11

A12

A13

A21

A22

A23

A31

A32

A33

1

-161

-150

-151

-108

-116

-106

-181

-176

-177

2

-165

-158

-157

-131

-126

-124

-196

-199

-193

3

-170

178

-177

-119

-142

-147

-230

-216

-238

4

-227

-216

-232

-150

137

-148

-268

-251

-249

5

-275

-271

-258

-155

-178

-195

-301

-287

-306

6

-196

-173

-171

-125

-141

-142

-228

-197

-244

7

-115

-127

-156

-78

-70

-68

-161

-142

-156

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The stress values at three points in each section of each workpiece are averaged, (A11 + A12 + A13) / 3 = F0.2L; (A21 + A22 + A23) / 3 = F0.5L; (A31 + A32 + A33) / 3 = F0.8L, as shown in Table 4. Tab.4 Measurements of average residual stress of workpiece before heat treatment No.

F0.2 L/MPa

F0.5 L/MPa

F0.8 L/MPa

1

-154

-110

-178

2

-160

-127

-196

3

-175

-136

-228

4

-225

-145

-256

5

-268

-176

-298

6

-180

-136

-223

7

-136

-72

-153

3.1.1. Influence of thinning rate on residual stress

Fig.5 distribution of residual stress at different thinning rates

According to table 4, the influence of thinning rate on the residual stress of workpiece is obtained by comparing and analyzing the residual stress values of test serial No. 1, 2 and 3. As shown in Fig. 5, the surface of the workpiece is compressive stress. Under the action of the rotating wheel force, the metal of the spinning layer is in the condition of the extrusion of the rotating wheel and the resistance of the workpiece, and the cold plastic flow occurs. As a result, the machined surface is stretched, while the inner metal is elastically deformed, which limits the surface extension. The elastic deformation of inner layer material tends to recover after the removal of the rotating wheel force. But it is restrained by the growth part of plastic deformation of surface layer material, resulting in compressive stress on the surface layer. The residual stress at the head and bottom of the workpiece are greater than in the middle. This is due to less material and uneven flow at the beginning of spinning, more uniform flow in the middle of spinning, material accumulation or bulging at the back of spinning, resulting in greater residual stresses at the head. The circumferential residual stress of the spinning workpiece is uniform, and stresses values are similar. The value of residual stress of workpiece increases with the increase of thinning rate, which indicates that the larger the thinning rate, the greater the metal material flow of workpiece, the accumulation and uplift will occur, resulting in uneven deformation of material and the greater the residual stress. The workpiece with less thinning rate has small material flow and is not easy to produce material accumulation. The spinning process is stable and the plastic deformation is uniform, so the residual stress is small.

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3.1.2. Analysis of influence of feed ratio on residual stress

Fig.6 Distribution of residual stress at different feed ratios

According to the data in Table 4, the influence of feed ratio on the residual stress of workpiece can be obtained by comparing and analyzing the residual stress values of No. 4, 2 and 5. As shown in Fig. 6, the residual stress decreases with the increase of feed ratio and then increases. When the feed ratio increases, the radial force of the spinning wheel increases, the inner diameter of the spinning workpiece and the film adherence of the mandrel will be better, the metal flow is stable, so the surface residual stress value will be reduced. When it increases to a certain value, the feed rate of the rotating wheel is too fast, which leads to the increase of the metal flow rate, exceeding the optimum flow rate of material fluidity, resulting in the flow of materials can’t move forward in time, resulting in the accumulation of excessive residual stress. 3.1.3. Analysis of the influence of first wheel thinning on residual stress

Fig.7 Residual stress distribution of different first wheel thinning

According to table 4, the influence of the first wheel thinning on the residual stress of the workpiece can be obtained by comparing and analyzing the residual stress values of No. 6, 2 and 7. As shown in Fig. 7, the residual

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stress decreases with the increase of the first wheel reduction. This is due to the increase of the first wheel thinning, after the offset of the two rotating wheels on the workpiece to respin, the latter two wheels thinning will reduce, will make the workpiece metal flow smoothly, the radial rotating pressure of the rotating wheel will be reduced, so that the workpiece surface residual stress will be reduced. If the excessive increase of the first wheel thinning, the first wheel will be subject to a large spinning radial force, resulting in damage to the first wheel, eventually leading to uneven force on the spinning process, resulting in damage to other rotating wheels and failure of workpiece processing. 3.2. Heat treatment to eliminate residual stress Based on Table 2, single factor tests were carried out on workpieces No. 2 and No. 8-12, and the effects of annealing temperature and holding time on residual stress were obtained. 3.2.1. Surface residual stress measurement of workpiece after heat treatment Table. 5 Measurements of residual stress after heat treatment F 0.2L/MPa

F0.5L /MPa

F 0.8L /MPa

No.

A11

A12

A13

A21

A22

A23

A31

A32

A33

2

-10

-12

-14

-9

-9

-9

-10

-17

-15

8

-30

-17

-49

-25

-27

-26

-30

-34

-50

9

0

-2

-4

-1

-1

-1

-3

-5

-1

10

-2

-4

-3

-1

0

-2

-3

-1

-2

11

-25

-36

-19

-27

-25

-20

-36

-30

-39

12

-2

0

-4

-1

-1

-1

0

-2

-4

Table. 6 Average residual stress after heat treatment No.

F 0.2 L/MPa

F0.5L/MPa

F0.8L/MPa

2

-12

-9

-14

8

-32

-26

-38

9

-2

-1

-3

10

-3

-1

-2

11

-30

-24

-35

12

-2

-1

-2

According to table 2, No.2 and No.8-12 are selected for stress relief annealing. The sections 0.2L, 0.5L and 0.8L from the bottom. Table 5 is the measurement value of axial residual stress of three sections of spinning workpiece after heat treatment. Table 6 is the average axial residual stress of three selected sections.

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(a) Holding time 1h

291

(b) Holding time 2h

Fig.8 Distribution of residual stress at different heat treatment temperatures

Fig. 8a shows that the surface residual stress decreases with the increase of temperature, approaching zero at 280 ℃ and about 40MP at 200℃, indicating that the residual stress of the spinning workpiece decreases significantly after heat treatment. As shown in Figure 8b, the residual stresses of 240℃ and 280℃ are basically eliminated under 2 hours of heat preservation, but there is little difference between the residual stresses of 200℃ for 2 hours and that of 1 hour of heat preservation, so it is a better process parameter to keep 240℃ for 2 hours and 280℃ for 1 hour. 3.2.2. Electrolytic polishing method to measure different levels of residual stress In order to further analyze the effect of heat treatment, the residual stress in the workpiece was detected, and the workpiece was electrolytically polished to remove layers of 0.5mm and 1.1mm. Then the three points on the workpiece cross section are measured, and the average value is measured, as shown in Table 7. Table. 7 Measurement of residual stress after heat treatment Layer 0.5mm/MPa

Layer 1.1mm/MPa

No.

F0.2 L

F0.5 L

F0.8 L

F0.2 L

F0.5 L

F0.8 L

2

120

110

130

35

25

40

8

160

130

140

50

30

55

9

100

75

115

22

18

25

10

80

70

90

24

13

28

11

120

90

110

40

20

43

12

60

55

75

10

5

12

(a) Holding time 1h

(b) Holding time 2h Fig.9 The residual stress distribution of the 0.5mm layer

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Fig. 9 the residual stress distribution of the workpiece at 1 hours and 2 hours at the time of 0.5mm removal. The inner part of the spinning workpiece is tensile stress, which is due to the elastic deformation of the inner layer material tends to recover after the removal of the rotating wheel force, but is restrained by the plastic deformation growth part of the surface layer material, so the inner part of the workpiece presents tensile stress. It can be seen from Fig. 9a diagram that the residual stress in the workpiece decreases with the increase of temperature, and there is still a large residual stress in the workpiece when holding for 1 hour. It can be seen in the Fig. 9b that the residual stress can be well removed at 280 ℃ for 2 hours. Under the condition of high temperature annealing and long holding time, the workpiece will be heated uniformly and the residual stress of the workpiece will be fully released after spinning.

(a) Holding time 1h

(b) Holding time 2h

Fig.10 The residual stress distribution of the 1.1mm layer

Fig. 10 is the residual stress distribution of the workpiece removed from 1.1mm at 1 hours and 2 hours respectively. As can be seen from Fig. 10, the residual stress values are not greater than 50 MPa, and it is inferred that the residual stress layer is basically 1 mm. The residual stress in the 1.1mm layer is less than that in the 0.5mm layer, and the value of the residual stress is very small. This is due to the small metal fluidity in the innermost layer and the small radial force and shear stress of the rotating wheel. 4. Conclusion （1）After spinning, the residual stress on the surface of the connecting rod bushing is compressive stress, while the inner layer is tensile stress. The residual stress values of the head and bottom are greater than the middle. （2）The single factor test was carried out on the residual stress of the connecting rod bushing by the main technological parameters of the strong spinning: within a certain range, the surface residual stress of the connecting rod bushing increases with the increase of the thinning rate, the surface residual stress decreases first and then increases with the increase of the feed rate, and the surface residual stress decreases with the increase of the first round thinning amount.

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（3）The effect of heat treatment on eliminating residual stress is obvious. In a certain temperature range, the surface residual stress decreases with the increase of temperature. The longer the holding time is, the more obvious the effect of eliminating residual stress is. After heat treatment, the residual stress in the inner layer decreases with the increase of temperature, and the longer the holding time, the better the elimination effect. Acknowledgements This work was supported by the National Natural Science Foundation of China (NO. 51676011). References [1] Yamagata H. The science and technology of materials in automotive engines. Science & Technology of Materials in Automotive Engines, 2005:261–264. [2] Zhang Tao. Spinning forming technology. Chemical Industry Press, 2009. [3] Miao H, Zuo D, Zhang M, et al. Research on metal flow of internal thread of high strength steel during cold extrusion for aircraft landing gear. China Mechanical Engineering, 2010, 21(14):1714-1718. [4] Ma Fei,Yang He Zhan Mei. Effects of material properties on power spinning process of parts with transverse inner rib. Transactions of Nonferrous Metals Society of China, 2010, 20(8):1476-1481. [5] Tsivoulas D, Fonseca J Q D, Tuffs M, et al. Effects of flow forming parameters on the development of residual stresses in Cr–Mo–V steel tubes. Materials Science & Engineering A, 2015, 624(12):193-202. [6] Miao H, Zuo D, Wang M, et al. Numerical Calculation and Experimental Research on Residual Stresses in Precipitation-hardening Layer of NAK80 Steel for Shot Peening. Chinese Journal of Mechanical Engineering, 2011, 24(3):439-445. [7] Liu S, Li Y, Chen P, et al. Residual stresses and mechanical properties of Si3N4/SiC multilayered composites with different SiC layers. Boletin De La Sociedad Espanola De Ceramica Y Vidrio, 2017. [8] Roberts S G, Lawrence C W, Bisrat Y, et al. Determination of Surface Residual Stresses in Brittle Materials by Hertzian Indentation: Theory and Experiment. Journal of the American Ceramic Society, 1999, 82(7):1809-1816. [9] Guo Guoqing, Huang Nan, Chen Hui, et al. Detection of Residual Stress in Aluminum Alloy Carbody of High-Speed Train Using X-ray Diffraction Technology. Journal of Southwest Jiaotong University,2012,47(4):618-622. [10] Pariente I F, Guagliano M. Contact fatigue damage analysis of shot peened gears by means of X-ray measurements. Engineering Failure Analysis, 2009, 16(3):964-971. [11] Zhang Shixin, Deng Xiaojun, Wang Mingyan, et al. Measurement of the welding residual stress of the B-type metro bogie frame by X-ray diffraction method. Welding Machine, 2014, 44(5):252-255. [12] Zhang Tan, Li Xinhe Luo Yazhou, et al. Influence of process parameters on surface residual stress for thin-wall cylindrical part in the reduction spinning. Forging and Stamping Technology, 2017, 42(1):47-53. [13] Liu Chuanming, Yang Jianhong, Lei Jianzhong, et al. Analysis on Stress Distribution for Steel Balls Made of GCr15 Under Different Treatment States. Bearing, 2015, (6):24-26. [14] Zhang Wenchao, Chen Wenlin. Research on residual stress of cold drawn steel wire. Materials Research and Application, 2010, 4(1):19-22. [15] Li Yihua. Research on axle stress evolution during forging and residual stress during heat treating. Central south university, 2013 [16] Yang Huan, Zhang Jianhui. Analysis of Residual Stress of Silicon-alloyed Pyrocarbon Coatings for Artificial Heart Valves. Surface Technology, 2014, 43(1):7-10. [17] Zhou Jinzhi, Zhong Bin. The residual stress of austenitic stainless steel was eliminated by heat treatment. Journal of Hubei University of Technology, 2007, 22(4):88-90.

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