Influence of surface residual stresses on gigacycle fatigue response of high chromium cold work tool steel
✍ Scribed by C. R. Sohar; A. Betzwar-Kotas; C. Gierl; B. Weiss; H. Danninger
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 456 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0933-5137
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✦ Synopsis
Abstract
The effect of surface compressive residual stresses (RS) induced by surface grinding and polishing on the gigacycle fatigue behavior of medium‐carbon high‐chromium alloy cold work tool steel was evaluated. Two test series were performed: Specimens of series I revealed high compressive RS of about ‐800 MPa at the surface, resulting from grinding with fine emery paper, which treatment had definitely a beneficial influence on the fatigue endurance strength. The existence of surface RS was also revealed to be responsible for the location of the fatigue crack initiation. High compressive RS favored internal crack origins. In this case crack nucleation sites were primary carbide clusters in the interior of the specimen, forming so‐called fish‐eyes at the fracture surface. In contrast, specimens of test series II had only very low RS, which enabled crack initiation near/at the surface at primary carbides/clusters. Furthermore, it has been shown that the high initial RS are prone to partial relaxation through cyclic loading for which the mechanisms are currently unknown. In this case near‐surface induced failure was obtained. It was possible to confirm the experimentally obtained data by the use of the concept of local fatigue strength as function of effective RS. The relaxation of high initial RS was experimentally confirmed through RS measurements at runout specimens (10^10^ cycles without failure).