Journal of Failure Analysis and Prevention

, Volume 9, Issue 4, pp 335–341 | Cite as

Failure Investigation on the Cracked Diesel Engine Ring Gears

  • Xiao-lei Xu
  • Zhi-wei Yu
Case History---Peer-Reviewed


Many of the teeth on two ring gears used in a truck fractured in service. The fractographic investigation and metallurgical analysis of the fractured teeth showed that the cracks initiated at the root on the side of the loaded face. The fractured teeth surfaces reveal similar macrofractographic and microfractographic features typical of cleavage and quasi-cleavage and reflective of a low toughness in the material. The microstructure of the core of failed ring gears showed a coarse grain size and a continuous network of Widmannstätten ferrite. The defective microstructure was retained in the hardened layer of the groove, the root fillet, and half tooth height regions, decreasing the strength and the impact toughness of the ring gears and promoting the brittle fracture. Unsuitable forging and normalizing processes are responsible for the defective microstructure.


Ring gear Cleavage fracture Network of grain boundary Widmannstätten ferrite 


  1. 1.
    Properties and metals. In: Metals Handbook, 8th edn., vol. 1. American Society for Metals, Metal Park, OH (1961)Google Scholar
  2. 2.
    Failure analysis and prevention. In: Metals Handbook, vol. 11. ASM International, Materials Park, OH (1986)Google Scholar
  3. 3.
    Brooks, C.R., Choudlhury, A.: Failure Analysis of Engineering Materials. McGraw-Hill (2002)Google Scholar
  4. 4.
    Clegg, R.E.: Failure of planetary pinions in earth moving equipment-a failure analysis approach. Eng. Fail. Anal. 7, 35–41 (2000)CrossRefGoogle Scholar
  5. 5.
    Determination of hardening after induction or flame hardening steel. China Standard, GB5617-85 (2000)Google Scholar
  6. 6.
    Metals-methods of estimating the average grain size. China Standard, GB6394-2002 (2003)Google Scholar
  7. 7.
    Van der Voort, G.F.: Embrittlement of steels. In: Metal Handbook, 10 edn., vol. 1: Properties and Selection: Iron, Steel, and High-Performance Alloys. ASM International, Metal Park, OH (1990)Google Scholar
  8. 8.
    Liu, Y.: Heat Treatment of Steel. Metallurgical Industry Press (1981) (in Chinese)Google Scholar

Copyright information

© ASM International 2009

Authors and Affiliations

  1. 1.Electromechanics and Material Engineering CollegeDalian Maritime UniversityDalianPeople’s Republic of China

Personalised recommendations