Effect of Hierarchical Microstructures of Lath Martensite on the Transitional Behavior of Fatigue Crack Growth Rate

• Published in: Metals and materials international Vol. 24; no. 5; pp. 970 - 980
• Main Authors: Yang, Ming, Zhong, Yi, Liang, Yi-long
• Format: Journal Article
• Language: English
• Published: Seoul The Korean Institute of Metals and Materials 01.09.2018; Springer Nature B.V; 대한금속·재료학회
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Crack propagation; Engineering Thermodynamics; Fatigue failure; Fracture mechanics; Grain size; Heat and Mass Transfer; Heat treating; Machines; Magnetic Materials; Magnetism; Manufacturing; Martensite; Materials Science; Metallic Materials; Microstructure; Processes; Solid Mechanics; Stress intensity factors; 재료공학; Fatigue; Transitional behavior; Lath martensite; Microstructure; Crack growth
• ISSN: 1598-9623; 2005-4149
• DOI: 10.1007/s12540-018-0117-4

In this study, the fatigue-crack growth (FCG) behavior of 20CrMTiH steel with different substructure sizes was investigated. The results showed that coarsen microstructures exhibit excellent growth resistance. Moreover, two transitional behaviors were observed in the FCG curves of all specimens. The first transition point occurs in the near-threshold regime, whereas the second transition point occurs in the Paris regime. A comparison of substructure size to cyclic plastic size showed that the block size is almost equal to cyclic plastic size at ∆K T1 , indicating that block size is an effective grain size to control the first transitional behavior of fatigue-crack propagation, whereas the second transitional behavior is related to the packet width or grain size. According to the fracture morphology, the fracture mechanism above and below the transition point responsible for the above phenomenon were distinguished. In addition, two prediction models based on microstructure size were established for lath martensite to evaluate the threshold and stress intensity factor range at the transition point.