Investigation of Fatigue Damage of Tempered Martensitic Steel during High Cycle Fatigue and Very High Cycle Fatigue Loading Using In Situ Monitoring by Scanning Electron Microscope and High‐Resolution Thermography

• Published in: Steel research international 2021-12, Vol.92 (12), p.n/a
• Main Authors: Giertler, Alexander, Krupp, Ulrich
• Format: Article
• Language: English
• Subjects: Alloying; Carbon steels; Chromium steels; Damage assessment; Electron microscopes; Fatigue cracks; Fatigue failure; Fatigue strength; Fatigue tests; Field tests; fine granular areas; Heat treatment; High cycle fatigue; in situ scanning electron microscope fatigue monitoring; Martensitic stainless steels; Metal fatigue; Size effects; Surface cracks; tempered martensitic steels; Test equipment; Thermography; Ultrasonic testing; very high cycle fatigue
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.202100268

Herein, the fatigue damage mechanisms of a low‐alloyed 0.5 wt% carbon steel (50CrMo4) are examined in the high cycle fatigue and very high cycle fatigue regime, taking into account different strength conditions. For this purpose, the heat treatment of the material is conducted using two different batches at two different tempering temperatures, which lead to hardnesses of 37HRC and 57HRC, respectively. The fatigue tests are conducted accounting for different test frequencies of f = 95 Hz and f = 20 kHz, as well as size effects. It is found that the fatigue behavior of the tempered steel 50CrMo4 can be subdivided into type I (surface cracks) and type II (internal cracks) VHCF damage behavior depending on the material strength condition. With the aid of in situ test equipment, the influence of microstructural banding on the local fatigue strength is demonstrated by high‐resolution thermography. By implementing an ultrasonic testing machine in a high‐resolution scanning electron microscope, the development of a fine granular area (FGA) at an artificial defect in vacuum atmosphere is demonstrated. Fatigue tests with different test frequencies are conducted to investigate the fatigue behavior of low‐alloyed 0.5 wt% carbon steel (50CrMo4) considering different strength conditions. High‐resolution thermography is used to demonstrate the influence of microstructural banding on the local fatigue behavior. The development of a fine granular area at an artificial defect in vacuum atmosphere is demonstrated.