Quantitative Analysis of Inclusion Engineering on the Fatigue Property Improvement of Bearing Steel

Abstract

The fatigue property is significantly affected by the inner inclusions in steel. Due to the inhomogeneity of inclusion distribution in the micro-scale, it is not straightforward to quantify the effect of inclusions on fatigue behavior. Various investigations have been performed to correlate the inclusion characteristics, such as inclusion fraction, size, and composition, with fatigue life. However, these studies are generally based on vast types of steels and even for a similar steel grade, the alloy concept and microstructure information can still be of non-negligible difference. For a quantitative analysis of the fatigue life improvement with respect to the inclusion engineering, a systematic and carefully designed study is still needed to explore the engineering dimensions of inclusions. Therefore, in this study, three types of bearing steels with inclusions of the same types, but different sizes and amounts, were produced with 50 kg hot state experiments. The following forging and heat treatment procedures were kept consistent to ensure that the only controlled variable is inclusion. The fatigue properties were compared and the inclusions that triggered the fatigue cracks were analyzed to deduce the critical sizes of inclusions in terms of fatigue failure. The results show that the critical sizes of different inclusion types vary in bearing steels. The critical size of the spinel is 8.5 μm and the critical size of the calcium aluminate is 13.5 μm under the fatigue stress of 1200 MPa. In addition, with the increase of the cleanliness of bearing steels, the improvement of fatigue properties will reach saturation. Under this condition, further increasing of the cleanliness of the bearing steel will not contribute to the improvement of fatigue property for the investigated alloy and process design.

In-depth analysis of the fatigue mechanism induced by inclusions for high-strength bearing steels

“…Gu et al [31][32] further improved the accuracy of the RVE model by considering residual stress around inclusions. These studies continually improved the microstructure model reconstruction methods of material characteristics in three dimensions (3D) [33] and with finer resolution [34] and the accuracy of fatigue life prediction. However, experiments and simulations lacked focus on the actual interface condition between inclusions and the steel matrix.…”

Microstructure-based fatigue modelling with residual stresses: Prediction of the fatigue life for various inclusion sizes

“…2). A small fraction of the fatigue crack initiation was found in the streel matrix 51 , which indicates a different fatigue mechanism 52 . The present study focuses on the fatigue initiation triggered by inclusions, which is the majority of the crack initiation mechanism In the next sections of this paper, only the effect of calcium aluminate inclusion was discussed due to the lack of data of spinel and titanium nitride inclusions.…”

Ultrahigh cycle fatigue fracture mechanism of high-quality bearing steel obtained through different deoxidation methods

“…The inclusions in Aldeoxidized bearing steels mainly include TiN, MnS, and oxides, the most common of which are spinel ((Mg)-Al-O), calcium aluminate (Ca-Al-O), and silicate (Si-(Al)-O) [2][3]. Calcium aluminate and spinel are deemed the most harmful oxides to the fatigue life (N f ) of bearing steel [4][5]. Gu et al [6] compared the fatigue properties of three types of bearing steels and found that the critical size of spinel inclusions is smaller than that of calcium aluminate.…”