An Experimental Study on the Impact of Deoxidation Methods on the Fatigue Properties of Bearing Steels

et al. 2019

Applied Sciences

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In high-strength martensitic steels, the inclusions significantly affect the material performance especially in terms of fatigue properties. In this study, a numerical procedure to investigate the effect of the inclusions types and shapes on the residual stresses during the cooling process of the martensitic steels is applied systematically based on the scanning electronic microscopy (SEM) and energy dispersive spectrometer (EDS) results of different types of inclusions. The results show that the maximum residual stress around the interface between Mg-Al-O inclusion and the matrix is the largest, followed by TiN, Al-Ca-O-S, and MnS when the inclusions are assumed as perfect spheres for simplicity. However, these results are proved to be 28.0 to 48.0% inaccurate compared to the results considering actual shapes of inclusions. Furthermore, the convex shape of inclusion will lead to stress concentration in the matrix while the concave shape of inclusion will lead to stress concentration in the inclusion. The residual stress increases with the increase of inclusion edge angle. The increase rate is the largest for TiN inclusions on the concave angle, which leads to extreme stress concentration inside TiN inclusion.

Section: Introductionmentioning

confidence: 99%

Numerical Study of the Effect of Inclusions on the Residual Stress Distribution in High-Strength Martensitic Steels During Cooling

Lian

et al. 2019

Applied Sciences

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“…In this Si-deoxidization steel, the Si content in the complex inclusion was more than Al content. However, in Al-deoxidization steel, the Al content in the complex inclusion was more than Si content [8]. This inclusion with more Si content had less effect on the fatigue life of bearing steel.…”

Section: The Change Of Oxides During Rh Processmentioning

confidence: 89%

“…There was no deoxidizer added in the RH process. The T.O content after LF refining in the Si-deoxidization bearing steel was about 20-30 ppm, which was much higher than 15 ppm after LF refining in the Al-deoxidization bearing steel [8]. However, after deoxidization in the RH process and continuous casting, the T.O content in billets can be 8-10 ppm.…”

Section: Introductionmentioning

confidence: 85%

“…Types of inclusions are mainly calcium aluminate (Ca-Al-O), spinal (Al-Mg-O), silicate (Si-Al-O), and a few TiN, in which calcium aluminate, spinal, and TiN are considered as the most hazardous to the fatigue life of bearing steel [7]. Recently, in order to control the type and morphology of inclusions-reducing the content of calcium aluminate and spinal-a kind of production method of bearing steel by using Si instead of Al as deoxidizer was put forward [8]. The production process is BOF → LF → RH (Ruhrstahl-Hereaeus) → CC.…”

Section: Introductionmentioning

confidence: 99%

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The Research of Low-Oxygen Control and Oxygen Behavior during RH Process in Silicon-Deoxidization Bearing Steel

Xiao

Wang

2019

Metals

The variation of total oxygen (T.O) content, characterization of inclusions, slag composition, and off-gas behavior during the smelting process of silicon-deoxidization bearing steel were investigated with industrial experiments. The change of content of combined oxygen during RH (Ruhrstahl–Hereaeus vacuum degassing furnace) process was calculated and compared with T.O content change. It is found that the decrease of oxygen content is mainly caused by the removal of dissolved oxygen rather than the removal of oxides during RH process. Carbon was found to be a strong deoxidizer (stronger than aluminum) in high vacuum degree. Top slag is an oxygen source of the deoxidization process, leading to the re-oxidization of liquid steel, even though the FeO content is low in top slag. During the RH process, the change of oxygen mainly exists in three processes: 1) Deoxidization reaction in vacuum chamber, 2) oxygen mass transfer process between liquid steel out from a vacuum chamber and in ladle, and 3) oxygen mass transfer between ladle slag and liquid steel. It depends mainly on the mass transfer of the oxygen in the liquid steel.

“…Based on this new progress, it is reasonable to doubt whether the fatigue property still improves with the increase of cleanliness. In the previous research by Gu et al [26], the fatigue properties of two high carbon bearing steels deoxidized with different deoxidizing agents with non-negligible differences of cleanliness have been compared. The results show that the fatigue properties are still close regardless of the difference in cleanliness.…”

Section: Introductionmentioning

confidence: 99%

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

Wang

et al. 2019

Metals

Self Cite

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.