Induction hardening of small gear wheels made of steel 50CrMo4

Transcription

1 Induction hardening of small gear wheels made of steel 50CrMo4 J Barglik, A Smalcerz, A Smagór To cite this version: J Barglik, A Smalcerz, A Smagór. Induction hardening of small gear wheels made of steel 50CrMo4. 8th International Conference on Electromagnetic Processing of Materials, Oct 2015, Cannes, France. EPM2015. <hal > HAL Id: hal Submitted on 22 Jun 2016 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 Induction hardening of small gear wheels made of steel 50CrMo4 J. Barglik 1, A. Smalcerz 1, A. Smagór 1 1 Department of Industrial Informatics, Silesian University of Technology, Katowice, Poland Corresponding author: jerzy.barglik@polsl.pl Abstract Analysis of coupled physical fields in the process of induction hardening of gear wheels is described. Modeling of the process is not easy because of complicated geometry of the system and also due to non-linear dependences of material properties on temperature. The computations are provided for gear wheels with diameter of 41 mm made from steel 50 CrMo4. The Flux 3D software is applied for computations of coupled electromagnetic and temperature fields in a direct coupled formulation. The single owned procedure is used for hardness calculation. Some examples concerning different temperature evolution and process parameters are calculated and compared with measurements. Quite reasonable accordance between computations and measurements is achieved. Key words: surface hardening; induction heating; electromagnetic field; coupled problem Introduction For induction hardening of gear wheels, a complete hardening is carried out in thin surface layer only. The transition zone and internal zones of gear wheels are characterized by incomplete hardening, tempering, remaining or the material soft respectively [1].In general, the process of induction hardening consists of two consecutive stages: induction heating and quenching. A break between heating and cooling should be as short as possible. As usual, the domain of a tooth consists of four zones A, B, C and D with different hardness and microstructure (Fig. 1). The exemplary time evolution of the temperature in particular zones is presented in Fig. 2. Fig. 1: Zones of the tooth with different hardness andmicrostructure requirements: A contour zone, B transition zone, C root of the tooth, D base zone. Fig. 2: Time evolution of induction hardening for surface (A), transition (B) and internal parts (C, D): A c3 austenization temperature, A c1 lower critical temperature, M s martensite temperature, T h hardening temperature. For the surface induction hardening of gear wheels the stage of heating is often divided into two steps differing by frequencies used. Of course, the process could be as well realized at a single frequency or simultaneous dual frequency using a single coil [2]. There are possible other patterns of heating including, for instance, three-step induction heating. For a classical dual frequency heat treatment, first a longer heating is performed at the medium frequency within a time period t = t MF. After a short technological break ( t = t b1 ), high frequency induction heating is applied. Its time t HF is distinctly shorter than t MF. Then, after another short break ( t = t b2 ), the gear wheel is cooled by spraying or by merging into a container with a suitable quenchant. The time of cooling t c is chosen based upon the Continuous Cooling Transformation (CCT) diagram of the investigated steel. The value of the hardness and obtained microstructure depend on the starting temperature of cooling and its velocity. For zone A, for example, cooling lines begin at a temperature bigger than A c3 and terminate at the temperature smaller than the martensitic temperature M s. If the speed of cooling is high enough, the zone A is characterized by a complete hardening with the martensitic microstructure. For the zone B the cooling lines begin from temperatures Tlocated between the lower critical temperature a A c1 and the austenization

3 temperature A c3 (A c3 T A c1 ). It results in an incomplete hardening with lower hardness and microstructure containing not only martensite but also bainite, ferrite and pearlite. For the zone C the cooling lines begin from temperatures slightly lower than the A c1 temperature. The material in this zone is composed from the tempered martensite and its hardness is lower than in the zone B. And finally, for the zone D the cooling lines begin from the temperature distinctly smaller than the lower critical temperature A c1. The material remains soft and the initial microstructure and hardness do not change. However, induction hardening is characterized by a high value of the heating rate h, which could achieve C/s. In order to secure the uniform austenite microstructure before quenching for such a fast heating it is necessary to heat the gear wheel till a modified austenization temperature A c3m being bigger than the conventional austenization temperature A c3. The real value of A c3m should be determined by measurements [3]. o ( ), C c 3 m c 3 h. (1) A A T v T In practice, in order to secure the uniform austenite microstructure within the whole zone A, the hardening temperature T h should be at least 50 Chigherthanthe modifiedaustenization temperature A c3m [3]. Description of the problem The analyzed problem is the induction spin hardening of a small gear wheel made of steel 50 CrMo4. Its chemical composition is as follows: % C, max 0.4% Si, % Mn, % Cr, % Mo, max % P, max % S. Other parameters and dimensions of the gear wheel are: diameter d = 41mm, width b = 13.8 mm, number of teeth n = 41, and the pressure angle = Two different arrangements of the inductor-sprayer system are analyzed: - Dual frequency heating by MF inductor (Fig. 3) and HF inductor (Fig.4) and water spraying. - Single frequency heating by a MF inductor (Fig.3) and water spraying, Fig. 3: MF inductor for single frequency heating: 1 coil, 2 sprayer, 3 bus-bars. Fig. 4: HF inductor: 1 coil, 2 bus-bars, 3 flux concentrator. Due to the symmetry of the arrangement, it is sufficient to analyze just one half of the tooth (Fig. 5). A view of the gear wheel is shown in Fig.6. Fig. 5: Geometry of the gear wheel made of steel 50 CrMo4. Fig. 6: View of wheel gear. The 3D computation of the task is realized by the finite element method, using the code FLUX3D [3 6] supplemented with several own procedures [7-9]. The mathematical model and a way of meshing are depicted in Figs The radial boundaries are characterized by the conditions of periodicity. The number of the nodes for the electromagnetic computations was over 90000, for thermal computations about Radiation is neglected [10]. The computation time of one example takes approximately 8 hours.

4 Fig. 7: Mathematical model. Fig. 8: Meshing. Three cases of dual frequency and one case of single frequency induction hardening with expected different temperature patterns are considered. For the case I the MF induction heating is realized by current 1275 A, frequency 10 khz, in time 10 s. After the technological break of length 0.5 s for removal of the MF inductor, the average temperature in zone A is equal to 290 C. The temperature distribution before HF heating (t MF + t b1 = 10.5 s) is shown in Fig. 9. Then the second step of heating is provided by current 1300 A, frequency 200 khz, in time 1 s. After 0.1 s of technological break the average temperature in zone A is equal to 870 C. The temperature distribution directly before cooling (t hf + t b2 = 1.1s) is shown in Fig. 10. Fig. 9: Case I: Temperature distribution before HF heating. I MF = 1275 A, f = 10 khz, t MF = 10 s, t b1 = 0.5 s. Fig. 10: Case I. Temperature distribution before cooling. I HF = 1300 A, f = 200 khz, t HF = 1 s, t b2 = 0.1 s. For the case II, the MF heating is realized by the current 1750 A of frequency 10 khz acting for 10 s. After 0.5 s of the break, the average temperature in zone A is equal to 485 C. The temperature distribution before HF heating (t MF + t b1 = 10.5 s) is shown in Fig. 11. Then the second heating step is provided by current of 1200 A of frequency 200 khz. After 0.1 s of technological break the average temperature in zone A is equal to 880 C. The temperature distribution before cooling (t hf + t b2 = 1.1 s) is shown in Fig. 12. For the case III the MF induction heating is realized by current 2080 A of the same frequency 10 khz in the same time 10 s. After 0.5 s break the average temperature in zone A is 665 C. The second step of the HF induction heating is performed by the current of 1200 A of frequency 200 khz in time 1 s. After 0.1 s of technological break the average temperature in zone A equals to 915 C. Fig. 11: Case II. Temperature distribution before HF heating: I MF = 1750 A, f = 10 khz, t MF = 10 s, t b1 = 0.5 s. Fig. 12: Case II. Temperature distribution before cooling: I HF = 1200 A, f = 200 khz, t HF = 1 s, t b2 = 0.1 s. The temperature distribution before cooling (t hf + t b2 = 1.1 s) is shown in Fig. 13. In the case IV, induction heating is

5 carried out by the current of 2660 A of frequency 36 khz in time 6 s. The average temperature in zone A is equal to 925 C. The temperature distribution before cooling is shown in Fig. 14. Fig. 13: Case III. Temperature distribution before cooling: I MF = 2080 A, f = 10 khz, t MF = 10 s, t b1 = 0.5 s. I HF = 1200 A, f = 200 khz, t HF = 1 s, t b2 = 0.1 s. Fig. 14: Case IV: Temperature distribution before cooling:i MF = 2660 A, f = 36 khz, t MF = 6 s, t b = 0.1 s The hardness distribution for the case IV in selected points of the wheel body is presented in Fig. 15. Points Calculated hardness Measured hardness Fig. 15:Hardness distribution in points 1 4 located along the teeth body The hardness distribution is measured after the full process of the heat treatment consisting of induction hardening and low temperature tempering (t t = 2h, T t = 160 C). There is a reason that for all points 1 4 the calculated hardness is bigger than the measured one. More detailed description of computations, measurements and discussion of their results will be provided during the conference. Conclusion The paper presents the numerical analysis of single and dual frequently spin induction hardening of gear wheels made of steel 50 CrMo4. Electromagnetic and temperature field were analyzed as directly coupled. Dependences of material properties on temperature are taken into consideration. The modified austenization temperature depending on the speed of heating is determined by measurements. The Flux 3D software is applied for computations of coupled electromagnetic and temperature fields and the single owned procedures for the hardness determination. Quite reasonable accordance between computations and measurements is noticed. Acknowledgment Financial support from National Centre for Research and Development (project PBS2/A5/41/2014) is gratefully acknowledged. References [1] V. I. Rudnev, G. Totten (2014), ASM International. Materials Park [2] V.I. Rudnev (2009), Heat Treating Progress, 10, 9 11 [3] S. Lupi, M. Forzan, A. Alifierov (2015), Springer International Publishing [4] H. Stiele, F. Marquis (2007), Int. Symp. on Heating by Electromagnetic Sources, Padua (Italy) [5] J. Barglik, A. Smalcerz, D. Dołęga, R. Przyłucki (2011), 12 th Conf. EPE, 1-4 [6] I. Dolezel, J. Barglik, C. Sajdak, M. Skopek, B. Ulrych (2003), Compel 22, [7] M. Spezzapria, F. Dughiero, M. Forzan, A. Candeo (2012), Journal of Iron and Steel Research, [8] J. Kolańska-Płuska, J. Barglik, B. Baron Z. Piątek (2011), Przeglad Elektrotechniczny 11, [9] J. Barglik, A. Smalcerz, R. Przyłucki, I. Doležel (2014), Journal of Comp. and Applied Math. 270, [10] J. Barglik, M. Czerwiński, M. Hering, M. Wesołowski (2008), IOS Press,