Multiple Fatigue Failure Behaviors and Long-Life Prediction Approach of Carburized Cr-Ni Steel with Variable Stress Ratio.

Hailong Deng,Tatsuo Sakai,Wei Li,Hongqiao Zhao

doi:10.3390/ma10091084

Hailong Deng, Tatsuo Sakai + Show 2 more

Open Access

https://doi.org/10.3390/ma10091084

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Abstract

Axial loading tests with stress ratios R of −1, 0 and 0.3 were performed to examine the fatigue failure behavior of a carburized Cr-Ni steel in the long-life regime from 104 to 108 cycles. Results show that this steel represents continuously descending S-N characteristics with interior inclusion-induced failure under R = −1, whereas it shows duplex S-N characteristics with surface defect-induced failure and interior inclusion-induced failure under R = 0 and 0.3. The increasing tension eliminates the effect of compressive residual stress and promotes crack initiation from the surface or interior defects in the carburized layer. The FGA (fine granular area) formation greatly depends on the number of loading cycles, but can be inhibited by decreasing the compressive stress. Based on the evaluation of the stress intensity factor at the crack tip, the surface and interior failures in the short life regime can be characterized by the crack growth process, while the interior failure with the FGA in the long life regime can be characterized by the crack initiation process. In view of the good agreement between predicted and experimental results, the proposed approach can be well utilized to predict fatigue lives associated with interior inclusion-FGA-fisheye induced failure, interior inclusion-fisheye induced failure, and surface defect induced failure.

Highlights

In order to satisfy the demand for mechanical parts or components with high safety and reliability in long-term service, fatigue properties of materials in the long-life regime beyond 107 cycles have been drawing increasing attention because of their peculiarities [1,2]
Based on the results further reveals that the long life is mainly consumed in the crack initiation stage inside the FGA
The main conclusions obtained in this study are summarized as follows: (1)

Summary

Introduction

In order to satisfy the demand for mechanical parts or components with high safety and reliability in long-term service, fatigue properties of materials in the long-life regime beyond 107 cycles have been drawing increasing attention because of their peculiarities [1,2]. For high strength steels [3], titanium alloys [4], cast irons [5], etc., one of the most typical failure features in the long-life regime beyond. The effects of some factors such as load type [6,7], environment [8], defect size [6,9], and surface condition [10] on fatigue properties of materials in the long-life regime beyond 107 cycles have been investigated, the understanding of the failure mechanisms and the relevant life prediction approaches still need to be further studied. Studies show that sometimes it cannot improve the fatigue strength or life of alloy steel since the probability of interior failure increases [11,12]. The interior failure of steel is often related to metallurgical defects such as inclusions, and a propagating crack

Results

Discussion

Conclusion