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Effect of relief-hole diameter on microstructure evolution of 20CrMnTiH steel during hot upsetting
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Procedia Manufacturing 00 (2018) 000–000 Available online atatwww.sciencedirect.com Available online www.sciencedirect.com Procedia Manufacturing 00 (2018) 000–000
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ScienceDirect ScienceDirect Procedia Manufacturing 15 (2018) 388–395 Procedia Manufacturing 00 (2017) 000–000
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17th International Conference on Metal Forming, Metal Forming 2018, 16-19 September 2018, 17th International Conference on MetalToyohashi, Forming, Metal Japan Forming 2018, 16-19 September 2018, Toyohashi, Japan
Effect of relief-hole diameter on microstructure evolution
Effect of relief-hole diameter onConference microstructure evolution Manufacturing Engineering Society International MESIC 2017, 28-30 June of 20CrMnTiH steel during hot 2017, upsetting 2017, Vigo (Pontevedra), Spain of 20CrMnTiH steel during hot upsetting Wei Fenga,b, *, Ling Maoa,b, Mengjuan Zhoua,b Costing models for optimization in Industry 4.0: Trade-off Wei capacity Feng *, Ling Mao , Mengjuan Zhou School of Materials Science and Engineering, Wuhan University of Technology，Wuhan 430070，China between used capacity andUniversity efficiency School of Materials Science and Engineering, Wuhan of Technology ，Wuhan 430070 ，China Hubei Key Laboratory of Advanced Technology of operational Automotive Parts, Wuhan 430070, China a,b,
a,b
a,b
a a
b b
Hubei Key Laboratory of Advanced Technology of Automotive Parts, Wuhan 430070, China
A. Santanaa, P. Afonsoa,*, A. Zaninb, R. Wernkeb
Abstract Abstract a University of Minho, 4800-058 Guimarães, Portugal b Three-dimensional thermo-mechanical coupling numerical simulation of 20CrMnTiH Unochapecó, 89809-000 Chapecó, SC, Brazil cylindrical parts with temperature of 950Three-dimensional thermo-mechanical coupling numerical degree simulation of 20CrMnTiH parts with temperature of 9501150 ˚C, relief-hole diameter of 0-20mm and deformation of 50% was carried cylindrical out by using DEFORM-3D finite element 1150 ˚C, relief-hole of 0-20mm and deformation degree of 50% was carried out by using element (FE) software. Effectsdiameter of the relief-hole diameters on the microstructure evolution of the material were DEFORM-3D revealed duringfinite hot upsetting. (FE)results software. Effects relief-hole diameters on the microstructure evolution the material during hot upsetting. The show that of thethe dynamic recrystallization (DRX) volume fraction firstofincreases and were then revealed decreases, the average grain The results show that the with dynamic recrystallization volume fraction Finally, first increases and then decreases, the average Abstract size gradually increases the increasing of the(DRX) relief-hole diameter. good agreements were found betweengrain the size gradually hot increases with the increasing of the relief-hole corresponding upsetting experiments and numerical simulationdiameter. results. Finally, good agreements were found between the corresponding hot upsetting experiments and production numerical simulation results. Under the concept of "Industry 4.0", processes will be pushed to be increasingly interconnected, © 2018 The Authors. Published by Elsevier B.V. necessarily, much more efficient. In this context, capacity optimization information based on a real time basis and, © 2018 2018 The The Authors. Published by Elsevier B.V. © Authors. Published by Elsevier B.V.maximization, Peer-review responsibility ofof thecapacity scientific committeeof ofthe the 17thInternational International Conference onMetal Metal Forming. and value. goes beyondunder the traditional aim contributing also for organization’s profitability Peer-review under responsibility of the scientific committee 17th Conference on Forming. Peer-review under responsibility of the scientific of the 17th International Conference on Metal Forming. instead of Indeed, lean management and continuouscommittee improvement approaches suggest capacity optimization Keywords: 20CrMnTiH - hole; Microstructure evolution; Thermo - mechanical coupling analysis maximization. The steel; studyHot ofupsetting; capacityRelief optimization and costing models is an important research topic that deserves Keywords: 20CrMnTiH steel; Hot upsetting; Relief - hole; Microstructure evolution; Thermo - mechanical coupling analysis contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been 1. Introduction developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization’s 1. Introduction value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity 20CrMnTiH steel is low-carbon steel widely used as a gear material in China. During precision forming of the gear optimization might hide operational inefficiency. is low-carbon widely as a gearaccuracy materialof in the China. During forming of the gear the20CrMnTiH forging loadsteel is very high, whichsteel affects the used dimensional forged gear.precision The deformation resistance © 2017 The Authors. Published by Elsevier B.V. the load and is very accuracy of thedivided-flow forged gear. The deformation resistance can forging be reduced the high, fillingwhich of theaffects cavitythe candimensional be improved when using method during the forging Peer-review underand responsibility of of thethe scientific committee of the Manufacturing Engineering Society International Conference can be reduced the the filling cavity can isbewidely improved when using divided-flow method during thedesigned forging process. In recent years, divided flow method used in the precision forging of gear. Cheng et al. 2017. process. recent years, divided flow method isthe widely usedload in the precision forging of gear. Cheng et al. a dividedInflow hole in thethe pre-forging to introduce forging during precision forging of spur gears anddesigned studied a divided flow hole in the pre-forging to introduce the forging load during precision forging of spur gears and studied Keywords: Cost Models; ABC; TDABC; Capacity Management; Idle Capacity; Operational Efficiency
1. Introduction
* Corresponding author. Tel.: +86-27-87168391; fax: +86-27-87168391. * E-mail Corresponding Tel.: +86-27-87168391; fax: +86-27-87168391. address:author. [email protected] The cost of idle capacity is a fundamental information for companies and their management of extreme importance E-mail address: [email protected]
in modern©production systems. In general, it isB.V. defined as unused capacity or production potential and can be measured 2351-9789 2018 The Authors. Published by Elsevier 2351-9789 2018 Authors. Published Elsevier B.V.hours of the Peer-review underThe responsibility of theby scientific committee 17th International on Metal Forming. in several©ways: tons of production, available manufacturing, etc.Conference The management of the idle capacity Peer-review under responsibility thefax: scientific committee * Paulo Afonso. Tel.: +351 253 510of 761; +351 253 604 741 of the 17th International Conference on Metal Forming. E-mail address: [email protected]
2351-9789 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. 2351-9789 © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 17th International Conference on Metal Forming. 10.1016/j.promfg.2018.07.234
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the influence of new process on the metal flow and load requirements by FE simulation and experiments [1]. Ming et al. analyzed the effects of different relief-hole diameters on the forging load and the filling effect of gear to optimize die design and forming process parameters [2]. Feng et al. used rigid-plastic finite element method to simulate the open-die forging process of arc bevel gear and obtained the influence of relief-hole diameters on forming resistance and optimum volume of blank [3]. However, these studies mainly focus on the influence of diameters on forging load and cavity filling performance. Some phenomena of microstructure evolution will occur during hot forming process [4-6]. In order to ensure that the part has good microstructure and mechanical properties, it is very important to study the change of microstructure in the process of hot deformation. Therefore, it is necessary to analyze the effects of the relief-hole diameters on the microstructure evolution. 2. Hot upsetting experiment of 20CrMnTiH 2.1. Experimental procedure The material used in this study is the commercial 20CrMnTiH rolling bar, and its chemical composition (wt. %) is 0.18C, 0.29Si, 1.09Mn, 0.015P, 0.017S, 1.18Cr, 0.076Cu and 0.062Ti. The specimens of different relief-hole diameter were machined, as shown in Table 1. The hot compression experiments were carried out on 160T hydraulic press under different temperature of 950, 1050 and 1150 ˚C and different relief-hole diameter of 0, 5, 10, 15 and 20 mm. Table 1. Specimen dimension. Group indication 1 2 3 4 5
External diameter D (mm) Relief-hole diameter d (mm)
Height h (mm)
30 30 30 30 30
36 30 24 18 12
0 5 10 15 20
The specimens with different relief-hole diameter first were heated to deformation temperature and held for 30 min using resistance-heated furnace, then the mould was preheated to 250 ℃ and a part of the specimens were compressed to the reduction in height of 50%. Subsequently, the partial undeformed specimens and the deformed specimens were rapidly quenched into water to maintain the microstructure, respectively. All the specimens were sectioned along the longitudinal compression axis, polished and etched to reveal the austenite grain boundaries. Fig.1 displays the longitudinal section and the characteristic points of the specimen and the point P2 in the center area is used to observe the microstructure by the metallographic microscope.
Fig. 1. (a) Longitudinal section of specimen and (b) characteristic points of microstructure observation.
The initial average grain sizes of the undeformed specimens under different deformation conditions are shown in Table 2. It can be seen from Table 2, the initial average grain sizes of the specimens both increase with the increasing temperature at the same relief-hole diameter and with the increasing relief-hole diameter at the same temperature.
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Table 2. Initial average grain size at different conditions (µm). Relief-hole diameter (mm)
Deformation temperature (˚C) 950
1050
1150
0
8.96
26.73
39.56
5 10
10.50 11.69
36.55 40.89
45.60 49.58
15 20
12.87 13.34
43.85 46.16
52.15 54.36
2.2. Results and discussion Figs. 2, 3 and 4 display the microstructures at the center area of the deformed specimens at the temperatures of 950, 1050 and 1150 ˚C and at the relief-hole diameters of 0, 5, 10, 15 and 20 mm, respectively. It can be observed from Fig. 2(a)-(c) that some new fine equiaxed grains have been formed in the deformed specimens due to DRX when the relief-hole diameters are 0, 5, 10 mm, respectively. The grains are elongated at the relief-hole diameters of 15 and 20 mm from Fig. 2(d) and (e). When the deformation temperature increases, the degree of DRX is much higher and a lot fine grains appear when the relief-hole diameters is 0, 5 10 and 15 mm at the temperature of 1050 and 1150 ˚C from Fig. 3(a)-(d) and Fig. 4(a)-(d). The grains are elongated and the necklace structure is formed at the grain boundary of the elongated grain as seen from Fig. 3(e) and Fig. 4(e). It can be also seen from Figs. 2, 3 and 4 that the average grains size of dynamic recrystallization increased gradually with the increasing deformation temperature at the same relief-hole diameter. The average grain size measured by metallographic analysis software under the temperatures of 1050 ˚C and the relief-hole diameters of 0, 5, 10, 15 and 20 mm is 6.05, 7.1, 8.92, 9.46 and 13.7 µm, respectively.
Fig. 2. Microstructure for 20CrMnTiH at T = 950 ˚C under differentrelief-hole diameters: (a) 0; (b) 5; (c) 10; (d) 15; (e)20 mm.
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Fig. 3. Microstructure for 20CrMnTiH at T = 1050 ˚C under differentrelief-hole diameters: (a) 0; (b) 5; (c) 10; (d) 15; (e) 20 mm.
Fig. 4. Microstructure for 20CrMnTiH at T = 1150 ˚C under differentrelief-hole diameters: (a) 0; (b) 5; (c) 10; (d) 15; (e) 20 mm.
3. Microstructure simulation Based on the constitutive equations and mathematical model for dynamic recrystallization established by Feng et al. [7], a three-dimensional FE model of 20CrMnTiH cylindrical parts was created by integrating the thermomechanical coupled method with microstructure evolution finite element method to simulate the hot compression process for 20CrMnTiH. The speed of the punch was 16mm/s. The friction between the dies and the deformed blank was assumed to be of shear type and the friction factor was set as 0.25.
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3.1. Influence of relief-hole diameter on temperature field Fig. 5 shows the distributions of temperature field under different temperatures and different relief-hole diameters. It can be seen that the peak temperature locates the center of the specimens and their values gradually decrease with the increasing relief-hole diameter at the same forging temperature.
Fig. 5. Distributions of temperature field under different initial forging temperatures and different relief-hole diameters.
3.2. Influence of relief-hole diameter on dynamic recrystallization volume fraction. Fig. 6 shows the distributions of dynamic recrystallization volume fraction of the deformed specimen at the temperatures of 950, 1050 and 1150 ˚C under the different relief-hole diameters by the established FE simulation models. It can be seen that the dynamic recrystallization phenomena occurred mainly the center of the deformed specimen and the degree of the dynamic recrystallization decreased gradually with the increasing relief-hole diameter at the same temperature. Also the degree of the dynamic recrystallization for the deformed specimen increased gradually with the increasing temperature at the same relief-hole diameter. According to DEFORM-3D software, it is considered that the full dynamic recrystallization occurs in regions where dynamic recrystallization volume fraction is greater than 85%. So, the dynamic recrystallization volume fraction with
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different relief-hole diameters at the temperatures of 950, 1050 and 1150 ˚C can be estimated by statistical calculation according to Fig. 6, as shown in Fig. 7. It can be seen from Fig. 7 that the DRX volume fraction first increases then decreases at the temperature of 1050 and 1150 ˚C and decreases gradually at a temperature of 950 ˚C with the increasing relief-hole diameter. This may be due to the fact that the temperature of the deformed blank decreases with the increase of the relief-hole diameter, which has adverse effect on dynamic recrystallization.
Fig. 6. Distributions of DRX volume fraction under different forging temperatures and different relief-hole diameters
Fig. 7. DRX volume fraction under different conditions.
3.3. Influence of relief-hole diameter on average grain size. Fig. 8 illustrates the average grain size of the deformed specimen at the temperatures of 950, 1050 and 1150 ˚C under different relief-hole diameter by the established FE simulation models. It can be seen that the average grain size
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is smaller in the center of the deformed specimen and the number of the fine grain decreases with the increasing reliefhole diameter at the same temperature.
Fig. 8. Average grain size under different temperatures and different relief-hole diameters.
Fig. 9 shows the average grain size with relief-hole diameter at the temperatures of 950, 1050 and 1150 ˚C. It can be seen that the average grain size increases with the increasing relief-hole diameter. It can also been observed that the increasing trend is gentle first and then steeply rising at the temperature of 1050 and 1150 ˚C.
Fig. 9. Average grain size under different conditions.
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Table 3 illustrates the comparison of the average grain size at the temperature of 1050 ˚C between the experimental and simulated results. It can be seen from Table 3, the simulation results are in good agreement with the experimental results. The maximum and minimum relative error between experimental and simulation results are 16.0% and 1.13% respectively, which verify that the established finite element model can successfully predict the microstructure evolution of 20CrMnTiH steel during hot compression. Table 3. Comparison of average grain size between experimental and simulated results. Relief-hole diameter(mm)
Experimental value(µm)
Simulated value(µm)
Relative error (%)
0 5 10 15
6.05 7.10 8.92 9.46
5.08 7.18 8.18 9.69
16.0 1.13 8.29 2.43
20
13.7
14.9
8.70
4. Conclusion
Based on the FE model and metallographic analysis, the effect laws of relief-hole diameter on the microstructure evolution of 20CrMnTiH steel during hot compression process were studied. The main conclusions are as follows: (1) The peak temperature locates the center of the specimens and their values gradually decrease with the increasing relief-hole diameter at the same forging temperature. (2) The dynamic recrystallization volume fraction first increases then decreases with the increasing relief-hole diameter at the same temperature. (3) The average grain size becomes larger with the increasing relief-hole diameter at the same temperature, and the increasing trend is gentle first and then steeply rising at the temperature of 1050 and 1150 ˚C. Acknowledgements The authors would like to thank the National Natural Science Foundation of China (51475344) and Innovative Research Team Development Program of Ministry of Education of China (IRT13087) for the support given to this research. References [1] C. Cheng, Y.T. Zhang, L. Zhang, Precision forging of spur gear by performing divided flow hole and final forging, Journal of Plasticity Engineering, 4 (2015) 21–25. [2] M. Deng, R.H. Wang, L.Z. Liu, Optimization design of spur gear mold structure for closed-extruding fine blanking, Forging and Stamping Technology, 40 (2015) 114–118. [3] W.J. Feng, Y.Y. Ren, T. Yang, Research on divided flow of spiral bevel gear open-die forging, Forging and Stamping Technology, 6 (2010) 89–91. [4] J. Zhou, Y.Y. Qiu, Y.X. Wang, Numerical simulation on dynamic recrystallization in supporting pedestal forging of 42GrMo based on thermal-mechanical coupling, Hot Working Technology, 15 (2010) 106–108. [5] S. Mehdi, Y. Jun, Material data for the kinetics of microstructure evolution of Cr–Mo–V steel in hot forming, Journal of Materials Processing Technology, 212 (2012) 417–426. [6] R.X. Chai, W.B. Su, C. Guo, Constitutive relationship and microstructure for 20CrMnTiH steel during warm deformation, Materials Science & Engineering: A, 556 (2012) 473–478. [7] W. Feng, F.J. Xu, Microstructure evolution and dynamic recrystallization model of 20CrMnTiH steel during hot compression, Journal of Plasticity Engineering, 21 (2014) 78–84.
ScienceDirect ScienceDirect
Procedia Manufacturing 00 (2018) 000–000 Available online atatwww.sciencedirect.com Available online www.sciencedirect.com Procedia Manufacturing 00 (2018) 000–000
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
ScienceDirect ScienceDirect Procedia Manufacturing 15 (2018) 388–395 Procedia Manufacturing 00 (2017) 000–000
www.elsevier.com/locate/procedia
17th International Conference on Metal Forming, Metal Forming 2018, 16-19 September 2018, 17th International Conference on MetalToyohashi, Forming, Metal Japan Forming 2018, 16-19 September 2018, Toyohashi, Japan
Effect of relief-hole diameter on microstructure evolution
Effect of relief-hole diameter onConference microstructure evolution Manufacturing Engineering Society International MESIC 2017, 28-30 June of 20CrMnTiH steel during hot 2017, upsetting 2017, Vigo (Pontevedra), Spain of 20CrMnTiH steel during hot upsetting Wei Fenga,b, *, Ling Maoa,b, Mengjuan Zhoua,b Costing models for optimization in Industry 4.0: Trade-off Wei capacity Feng *, Ling Mao , Mengjuan Zhou School of Materials Science and Engineering, Wuhan University of Technology，Wuhan 430070，China between used capacity andUniversity efficiency School of Materials Science and Engineering, Wuhan of Technology ，Wuhan 430070 ，China Hubei Key Laboratory of Advanced Technology of operational Automotive Parts, Wuhan 430070, China a,b,
a,b
a,b
a a
b b
Hubei Key Laboratory of Advanced Technology of Automotive Parts, Wuhan 430070, China
A. Santanaa, P. Afonsoa,*, A. Zaninb, R. Wernkeb
Abstract Abstract a University of Minho, 4800-058 Guimarães, Portugal b Three-dimensional thermo-mechanical coupling numerical simulation of 20CrMnTiH Unochapecó, 89809-000 Chapecó, SC, Brazil cylindrical parts with temperature of 950Three-dimensional thermo-mechanical coupling numerical degree simulation of 20CrMnTiH parts with temperature of 9501150 ˚C, relief-hole diameter of 0-20mm and deformation of 50% was carried cylindrical out by using DEFORM-3D finite element 1150 ˚C, relief-hole of 0-20mm and deformation degree of 50% was carried out by using element (FE) software. Effectsdiameter of the relief-hole diameters on the microstructure evolution of the material were DEFORM-3D revealed duringfinite hot upsetting. (FE)results software. Effects relief-hole diameters on the microstructure evolution the material during hot upsetting. The show that of thethe dynamic recrystallization (DRX) volume fraction firstofincreases and were then revealed decreases, the average grain The results show that the with dynamic recrystallization volume fraction Finally, first increases and then decreases, the average Abstract size gradually increases the increasing of the(DRX) relief-hole diameter. good agreements were found betweengrain the size gradually hot increases with the increasing of the relief-hole corresponding upsetting experiments and numerical simulationdiameter. results. Finally, good agreements were found between the corresponding hot upsetting experiments and production numerical simulation results. Under the concept of "Industry 4.0", processes will be pushed to be increasingly interconnected, © 2018 The Authors. Published by Elsevier B.V. necessarily, much more efficient. In this context, capacity optimization information based on a real time basis and, © 2018 2018 The The Authors. Published by Elsevier B.V. © Authors. Published by Elsevier B.V.maximization, Peer-review responsibility ofof thecapacity scientific committeeof ofthe the 17thInternational International Conference onMetal Metal Forming. and value. goes beyondunder the traditional aim contributing also for organization’s profitability Peer-review under responsibility of the scientific committee 17th Conference on Forming. Peer-review under responsibility of the scientific of the 17th International Conference on Metal Forming. instead of Indeed, lean management and continuouscommittee improvement approaches suggest capacity optimization Keywords: 20CrMnTiH - hole; Microstructure evolution; Thermo - mechanical coupling analysis maximization. The steel; studyHot ofupsetting; capacityRelief optimization and costing models is an important research topic that deserves Keywords: 20CrMnTiH steel; Hot upsetting; Relief - hole; Microstructure evolution; Thermo - mechanical coupling analysis contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been 1. Introduction developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization’s 1. Introduction value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity 20CrMnTiH steel is low-carbon steel widely used as a gear material in China. During precision forming of the gear optimization might hide operational inefficiency. is low-carbon widely as a gearaccuracy materialof in the China. During forming of the gear the20CrMnTiH forging loadsteel is very high, whichsteel affects the used dimensional forged gear.precision The deformation resistance © 2017 The Authors. Published by Elsevier B.V. the load and is very accuracy of thedivided-flow forged gear. The deformation resistance can forging be reduced the high, fillingwhich of theaffects cavitythe candimensional be improved when using method during the forging Peer-review underand responsibility of of thethe scientific committee of the Manufacturing Engineering Society International Conference can be reduced the the filling cavity can isbewidely improved when using divided-flow method during thedesigned forging process. In recent years, divided flow method used in the precision forging of gear. Cheng et al. 2017. process. recent years, divided flow method isthe widely usedload in the precision forging of gear. Cheng et al. a dividedInflow hole in thethe pre-forging to introduce forging during precision forging of spur gears anddesigned studied a divided flow hole in the pre-forging to introduce the forging load during precision forging of spur gears and studied Keywords: Cost Models; ABC; TDABC; Capacity Management; Idle Capacity; Operational Efficiency
1. Introduction
* Corresponding author. Tel.: +86-27-87168391; fax: +86-27-87168391. * E-mail Corresponding Tel.: +86-27-87168391; fax: +86-27-87168391. address:author. [email protected] The cost of idle capacity is a fundamental information for companies and their management of extreme importance E-mail address: [email protected]
in modern©production systems. In general, it isB.V. defined as unused capacity or production potential and can be measured 2351-9789 2018 The Authors. Published by Elsevier 2351-9789 2018 Authors. Published Elsevier B.V.hours of the Peer-review underThe responsibility of theby scientific committee 17th International on Metal Forming. in several©ways: tons of production, available manufacturing, etc.Conference The management of the idle capacity Peer-review under responsibility thefax: scientific committee * Paulo Afonso. Tel.: +351 253 510of 761; +351 253 604 741 of the 17th International Conference on Metal Forming. E-mail address: [email protected]
2351-9789 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. 2351-9789 © 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 17th International Conference on Metal Forming. 10.1016/j.promfg.2018.07.234
2
Wei Feng et al. / Procedia Manufacturing 15 (2018) 388–395 Author name / Procedia Manufacturing 00 (2018) 000–000
389
the influence of new process on the metal flow and load requirements by FE simulation and experiments [1]. Ming et al. analyzed the effects of different relief-hole diameters on the forging load and the filling effect of gear to optimize die design and forming process parameters [2]. Feng et al. used rigid-plastic finite element method to simulate the open-die forging process of arc bevel gear and obtained the influence of relief-hole diameters on forming resistance and optimum volume of blank [3]. However, these studies mainly focus on the influence of diameters on forging load and cavity filling performance. Some phenomena of microstructure evolution will occur during hot forming process [4-6]. In order to ensure that the part has good microstructure and mechanical properties, it is very important to study the change of microstructure in the process of hot deformation. Therefore, it is necessary to analyze the effects of the relief-hole diameters on the microstructure evolution. 2. Hot upsetting experiment of 20CrMnTiH 2.1. Experimental procedure The material used in this study is the commercial 20CrMnTiH rolling bar, and its chemical composition (wt. %) is 0.18C, 0.29Si, 1.09Mn, 0.015P, 0.017S, 1.18Cr, 0.076Cu and 0.062Ti. The specimens of different relief-hole diameter were machined, as shown in Table 1. The hot compression experiments were carried out on 160T hydraulic press under different temperature of 950, 1050 and 1150 ˚C and different relief-hole diameter of 0, 5, 10, 15 and 20 mm. Table 1. Specimen dimension. Group indication 1 2 3 4 5
External diameter D (mm) Relief-hole diameter d (mm)
Height h (mm)
30 30 30 30 30
36 30 24 18 12
0 5 10 15 20
The specimens with different relief-hole diameter first were heated to deformation temperature and held for 30 min using resistance-heated furnace, then the mould was preheated to 250 ℃ and a part of the specimens were compressed to the reduction in height of 50%. Subsequently, the partial undeformed specimens and the deformed specimens were rapidly quenched into water to maintain the microstructure, respectively. All the specimens were sectioned along the longitudinal compression axis, polished and etched to reveal the austenite grain boundaries. Fig.1 displays the longitudinal section and the characteristic points of the specimen and the point P2 in the center area is used to observe the microstructure by the metallographic microscope.
Fig. 1. (a) Longitudinal section of specimen and (b) characteristic points of microstructure observation.
The initial average grain sizes of the undeformed specimens under different deformation conditions are shown in Table 2. It can be seen from Table 2, the initial average grain sizes of the specimens both increase with the increasing temperature at the same relief-hole diameter and with the increasing relief-hole diameter at the same temperature.
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390
3
Table 2. Initial average grain size at different conditions (µm). Relief-hole diameter (mm)
Deformation temperature (˚C) 950
1050
1150
0
8.96
26.73
39.56
5 10
10.50 11.69
36.55 40.89
45.60 49.58
15 20
12.87 13.34
43.85 46.16
52.15 54.36
2.2. Results and discussion Figs. 2, 3 and 4 display the microstructures at the center area of the deformed specimens at the temperatures of 950, 1050 and 1150 ˚C and at the relief-hole diameters of 0, 5, 10, 15 and 20 mm, respectively. It can be observed from Fig. 2(a)-(c) that some new fine equiaxed grains have been formed in the deformed specimens due to DRX when the relief-hole diameters are 0, 5, 10 mm, respectively. The grains are elongated at the relief-hole diameters of 15 and 20 mm from Fig. 2(d) and (e). When the deformation temperature increases, the degree of DRX is much higher and a lot fine grains appear when the relief-hole diameters is 0, 5 10 and 15 mm at the temperature of 1050 and 1150 ˚C from Fig. 3(a)-(d) and Fig. 4(a)-(d). The grains are elongated and the necklace structure is formed at the grain boundary of the elongated grain as seen from Fig. 3(e) and Fig. 4(e). It can be also seen from Figs. 2, 3 and 4 that the average grains size of dynamic recrystallization increased gradually with the increasing deformation temperature at the same relief-hole diameter. The average grain size measured by metallographic analysis software under the temperatures of 1050 ˚C and the relief-hole diameters of 0, 5, 10, 15 and 20 mm is 6.05, 7.1, 8.92, 9.46 and 13.7 µm, respectively.
Fig. 2. Microstructure for 20CrMnTiH at T = 950 ˚C under differentrelief-hole diameters: (a) 0; (b) 5; (c) 10; (d) 15; (e)20 mm.
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Fig. 3. Microstructure for 20CrMnTiH at T = 1050 ˚C under differentrelief-hole diameters: (a) 0; (b) 5; (c) 10; (d) 15; (e) 20 mm.
Fig. 4. Microstructure for 20CrMnTiH at T = 1150 ˚C under differentrelief-hole diameters: (a) 0; (b) 5; (c) 10; (d) 15; (e) 20 mm.
3. Microstructure simulation Based on the constitutive equations and mathematical model for dynamic recrystallization established by Feng et al. [7], a three-dimensional FE model of 20CrMnTiH cylindrical parts was created by integrating the thermomechanical coupled method with microstructure evolution finite element method to simulate the hot compression process for 20CrMnTiH. The speed of the punch was 16mm/s. The friction between the dies and the deformed blank was assumed to be of shear type and the friction factor was set as 0.25.
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3.1. Influence of relief-hole diameter on temperature field Fig. 5 shows the distributions of temperature field under different temperatures and different relief-hole diameters. It can be seen that the peak temperature locates the center of the specimens and their values gradually decrease with the increasing relief-hole diameter at the same forging temperature.
Fig. 5. Distributions of temperature field under different initial forging temperatures and different relief-hole diameters.
3.2. Influence of relief-hole diameter on dynamic recrystallization volume fraction. Fig. 6 shows the distributions of dynamic recrystallization volume fraction of the deformed specimen at the temperatures of 950, 1050 and 1150 ˚C under the different relief-hole diameters by the established FE simulation models. It can be seen that the dynamic recrystallization phenomena occurred mainly the center of the deformed specimen and the degree of the dynamic recrystallization decreased gradually with the increasing relief-hole diameter at the same temperature. Also the degree of the dynamic recrystallization for the deformed specimen increased gradually with the increasing temperature at the same relief-hole diameter. According to DEFORM-3D software, it is considered that the full dynamic recrystallization occurs in regions where dynamic recrystallization volume fraction is greater than 85%. So, the dynamic recrystallization volume fraction with
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different relief-hole diameters at the temperatures of 950, 1050 and 1150 ˚C can be estimated by statistical calculation according to Fig. 6, as shown in Fig. 7. It can be seen from Fig. 7 that the DRX volume fraction first increases then decreases at the temperature of 1050 and 1150 ˚C and decreases gradually at a temperature of 950 ˚C with the increasing relief-hole diameter. This may be due to the fact that the temperature of the deformed blank decreases with the increase of the relief-hole diameter, which has adverse effect on dynamic recrystallization.
Fig. 6. Distributions of DRX volume fraction under different forging temperatures and different relief-hole diameters
Fig. 7. DRX volume fraction under different conditions.
3.3. Influence of relief-hole diameter on average grain size. Fig. 8 illustrates the average grain size of the deformed specimen at the temperatures of 950, 1050 and 1150 ˚C under different relief-hole diameter by the established FE simulation models. It can be seen that the average grain size
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is smaller in the center of the deformed specimen and the number of the fine grain decreases with the increasing reliefhole diameter at the same temperature.
Fig. 8. Average grain size under different temperatures and different relief-hole diameters.
Fig. 9 shows the average grain size with relief-hole diameter at the temperatures of 950, 1050 and 1150 ˚C. It can be seen that the average grain size increases with the increasing relief-hole diameter. It can also been observed that the increasing trend is gentle first and then steeply rising at the temperature of 1050 and 1150 ˚C.
Fig. 9. Average grain size under different conditions.
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Table 3 illustrates the comparison of the average grain size at the temperature of 1050 ˚C between the experimental and simulated results. It can be seen from Table 3, the simulation results are in good agreement with the experimental results. The maximum and minimum relative error between experimental and simulation results are 16.0% and 1.13% respectively, which verify that the established finite element model can successfully predict the microstructure evolution of 20CrMnTiH steel during hot compression. Table 3. Comparison of average grain size between experimental and simulated results. Relief-hole diameter(mm)
Experimental value(µm)
Simulated value(µm)
Relative error (%)
0 5 10 15
6.05 7.10 8.92 9.46
5.08 7.18 8.18 9.69
16.0 1.13 8.29 2.43
20
13.7
14.9
8.70
4. Conclusion
Based on the FE model and metallographic analysis, the effect laws of relief-hole diameter on the microstructure evolution of 20CrMnTiH steel during hot compression process were studied. The main conclusions are as follows: (1) The peak temperature locates the center of the specimens and their values gradually decrease with the increasing relief-hole diameter at the same forging temperature. (2) The dynamic recrystallization volume fraction first increases then decreases with the increasing relief-hole diameter at the same temperature. (3) The average grain size becomes larger with the increasing relief-hole diameter at the same temperature, and the increasing trend is gentle first and then steeply rising at the temperature of 1050 and 1150 ˚C. Acknowledgements The authors would like to thank the National Natural Science Foundation of China (51475344) and Innovative Research Team Development Program of Ministry of Education of China (IRT13087) for the support given to this research. References [1] C. Cheng, Y.T. Zhang, L. Zhang, Precision forging of spur gear by performing divided flow hole and final forging, Journal of Plasticity Engineering, 4 (2015) 21–25. [2] M. Deng, R.H. Wang, L.Z. Liu, Optimization design of spur gear mold structure for closed-extruding fine blanking, Forging and Stamping Technology, 40 (2015) 114–118. [3] W.J. Feng, Y.Y. Ren, T. Yang, Research on divided flow of spiral bevel gear open-die forging, Forging and Stamping Technology, 6 (2010) 89–91. [4] J. Zhou, Y.Y. Qiu, Y.X. Wang, Numerical simulation on dynamic recrystallization in supporting pedestal forging of 42GrMo based on thermal-mechanical coupling, Hot Working Technology, 15 (2010) 106–108. [5] S. Mehdi, Y. Jun, Material data for the kinetics of microstructure evolution of Cr–Mo–V steel in hot forming, Journal of Materials Processing Technology, 212 (2012) 417–426. [6] R.X. Chai, W.B. Su, C. Guo, Constitutive relationship and microstructure for 20CrMnTiH steel during warm deformation, Materials Science & Engineering: A, 556 (2012) 473–478. [7] W. Feng, F.J. Xu, Microstructure evolution and dynamic recrystallization model of 20CrMnTiH steel during hot compression, Journal of Plasticity Engineering, 21 (2014) 78–84.