To estimation of contact-fatigue durability of thermo-chemically strengthened gears

Introduction. The specification of the strength characteristics of the diffusion layer of carburized (C) and nitro-carburized (NC) involute gears is described. Regulated by GOST 21354-87, the dependence of the surface endurance limit of steel parts on hardness in the region of finite (up to 10-12 million cycles) life is overstated. The work objective is to determine the maximum allowable load level of the involute gearing under the conditions of alternative failure forms and the area of correct application of GOST 21354-87 recommendations. Materials and Methods. In the case-hardened parts, both deep and surface processes of contact fracture occur simultaneously. However, these processes have essentially different mechanisms of contact-fatigue durability with fundamentally different mechanisms of the contact-fatigue life. The high-end fracture mode is determined by a variety of factors, the key ones being the level of intensity and the properties of the near-surface layers of the material. The loading capacity of the diffusion layer is investigated on the basis of the experimental data by the strength assessment procedure of a structurally inhomogeneous material. Here, Pisarenko-Lebedev generalized criterion of limiting state is used. Research Results. Consideration of the effect of the plastic properties of the material and its variation within the diffusion layer has allowed significantly increase the forecasting validity of the loading capacity level of the carburized and nitro-carburized gears for contact strength. The occurrence of the threshold value of the working surface hardness of the wheels teeth is confirmed at the level of 60-61 Rockwell units. This level increase leads to the decrease in contact-fatigue life. The plasticity parameter impact on the capability level and the variation of this parameter value for different types of the thermo-chemical treatment (TCT) is assessed. In the finite life area, deep contact fractures are leading. And the limits of contact fatigue life upon surface pitting readings should be oriented to the allowed normal deep contact stress. Discussion and Conclusions . The obtained results are in qualitative agreement with the experimental data, but they exceed them a little in some cases. Studies on the plasticity parameter value and its variation depending on the chemical composition of the steel and the TCT type are needed. But already at this stage, the results obtained can be used in the design of heavy-loaded case-hardened gears to determine the surface hardness and the diffusion layer thickness. The application domain includes the tractor track gear transmissions, oil-producing beam engines, mining and handling facilities.

убчатая передача, контактная прочность, химико-термическая обработка, конкурирующие виды отказов, упрочненный слой, твердость, критерии прочности, gear, contact strength, thermo-chemical treatment, competing failure modes, hardened layer, hardness, strength criteria

1. GOST 21354-87. Peredachi zubchatye, tsilindricheskie, evol'ventnye. Raschet na prochnost'. Gosudarstvennyy komitet po standartam. [GOST 21354-87. Cylindrical evolvent gears of external engagement. Strength calculation.] Moscow: Standartinform, 1988, 125 p. (in Russian).

2. British standard. Implementation of ISO 6336-1:1996. Calculation of load capacity of spur and helical gears. Technical Committee MCE/5, Gears. London: BSI, 92 p.

3. Zinchenko, V.M. Inzheneriya poverkhnosti zubchatykh koles metodami khimiko-termicheskoy obrabotki. [Gear surface engineering by thermal-chemical treatment methods.] Moscow: Bauman University Publ. House, 2002, 303 p. (in Russian).

4. Yoshida, A., et al. Effect of case dept of fatigue strength. Bulletin of JSME, 1986, no. 247, pp. 228–234.

5. Konovalov, L.V., Petrova, I.M. Osobennosti tsiklicheskoy prochnosti konstruktsionnykh staley v oblasti dlitel'noy dolgovechnosti. [Features of cyclic strength of structural steels in long life area.] Vestnik Mashinostroeniya, 1998, no. 9, pp. 3– 11 (in Russian).

6. Kalashnikov, A.S., Morgunov, Y.A., Kalashnikov, P.A. Sovremennye metody obrabotki zubchatykh koles. [Modern methods of processing gears.] Moscow: Spektr, 2012, 238 p. (in Russian).

7. Korotkin, V.I., Onishkov, N.P., Goltsev, A.V. K otsenke glubinnoy kontaktnoy vynoslivosti evol'ventnykh zubchatykh peredach s poverkhnostno uprochnennymi zub'yami. [To assessment of deep contact resistance of involute gears with surface- hardened teeth.] Vestnik Mashinostroeniya, 2008, no. 5, pp. 9–14 (in Russian).

8. Onishkov, N.P., Korotkin, V.I., Guznov, K.V. Ob uchete faktora tverdosti v kontaktnykh raschetakh detaley mashin. [On considering hardness factor in contact analysis of machine parts.] Vestnik NTU “KPI”, 2008, no. 28, pp. 76–84 (in Russian).

9. Fujita, K., Yoshida, A. Vliyanie glubiny tsementovannogo sloya i otnositel'nogo radiusa krivizny na dolgovechnost' pri kontaktnoy ustalosti tsemento-vannogo rolika iz khromomolibdenovoy stali. [Effect of carburized layer depth and relative curvature on life time under contact fatigue of carburized roller from chrome- molybdenum steel.] Journal of Engineering for Industry, 1981, no. 2, pp. 115–124 (in Russian).

10. Korotkin, V.I., Onishkov, N.P., Kharitonov, Y.D. Zubchatye peredachi Novikova. Dostizheniya i razvitie. [Novikov gearing. Achievements and development.] Moscow: Mashinostroenie -1, 2007, 384 p. (in Russian).

11. Shapochkin, V.I., et al. Soprotivlenie kontaktnoy ustalosti tyazhelonagruzhennykh zubchatykh koles iz stali 20KhN3A, uprochnyaemykh KhTO. [Fatigue strength of heavy-loaded gears of 20ХН3А steel hardened by TCT.] Metal Science and Heat Treatment, 1987, no. 5, pp. 12–15 (in Russian).

12. Zubarev, N.I., Igdalov, M.P. Optimizatsiya kachestvennykh parametrov zatsepleniya zubchatoy peredachi. [Optimization of qualitative parameters of gearing.]/ Tractors and Agricultural Machinery, 1989, no. 2, pp. 41–69 (in Russian).

13. Pisarenko, G.S., Lebedev, A.A. Deformirovanie i prochnost' materialov pri slozhnom napryazhennom sostoyanii. [Deformation and Strength of Materials in Complex Stress State.] Kiev: Naukova dumka, 1976, 415 p. (in Russian).

14. Kasyanov, V.V., et al. Obespechenie na stadii proizvodstva zadannoy dolgovechnosti grupp rolikovykh podshipnikov v zavisimosti ot tverdosti ikh detaley. [Support of the specified life for roller bearing groups depending on their parts hardness at the stage of production.] Vestnik Mashinostroeniya, 2000, no. 8, pp. 15– 18 (in Russian).

15. Onishkov, N.P. Mestnoe napryazhennoe sostoyanie i otsenka glubinnoy kontaktnoy prochnosti poverkhnostnouprochnennykh zubchatykh peredach Novikova : dis. … kand. tekhn. nauk. [Local stress state and estimation of the deep contact strength of surface-hardened Novikov gearing: Cand.Sci. (Eng.) diss.] Kharkov, 1991, 164 p. (in Russian).

16. Stal' ShKh-15. [ShKh-15 steel.] Tsentral'nyy metallicheskiy portal RF. [RF Central metal portal.] Available at: metallicheckiyportal.ru/marki_metallov/stk/SHX15 (accessed: 14.08.17) (in Russian).

17. Sakhonko, I.M. Kontaktnaya vynoslivost' zakalennoy stali v zavisimosti ot geometricheskikh parametrov soprikasayushchikhsya tel. [Back-to-back endurance of hardened steel depending on geometrics of contacting bodies.] Kontaktnaya prochnost' mashinostroitel'nykh materialov. [Contact strength of engineering materials.] Moscow: Nauka, 1964, pp. 52–59 (in Russian).

18. Geller, Y.A. Instrumental'nye stali. [Instrument steels.] Moscow: Mashinostroenie, 1983, 525 p. (in Russian).

19. Kotov, O.K. Poverkhnostnoe uprochnenie detaley mashin khimiko-termicheskimi metodami. [Surface hardening of machine parts by thermal-chemical methods.] Moscow: Mashinostroenie, 1969. — 344 с.

20. Ponomarev, S.D., et al. Raschety na prochnost' v mashinostroenii. Tom I. [Stress calculations in engineering.] Moscow: Mashgiz, 1956, 884 p. (in Russian).

21. Orlov, A.V., Chermenskiy, O.N., Nesterov, V.M. Ispytaniya konstruktsionnykh materialov na kontaktnuyu ustalost'. [Contact fatigue test of structural materials.] Moscow: Mashinostroenie, 1980, 110 p. (in Russian).