The morphologies and sizes of TiN inclusions in gear steel 20CrMnTi have a significant impact on its service performance. This paper selects rare earth Ce to modify TiN inclusions in 20CrMnTi. The inclusions are analyzed by SEM (scanning electron microscope), EBSD (electron back-scattered diffraction), EDS (energy disperse spectroscopy), and OTS statistical software, and Thermo-Calc software is used to calculate the inclusion formations. The inclusions of MgAlO₄-Ce and CeAlO₃ can be formed when rare earth Ce is added into 20CrMnTi, which becomes TiN nucleation core after precipitation. Without the addition of rare earth Ce, square TiN inclusions ranging from 2 to 5 μm account for 60% of the total inclusions in 20CrMnTi. After adding rare earth Ce, the TiN inclusions in 20CrMnTiCe account for 36.7% of the total inclusions. Due to the new phase formations of MgAlO₄-TiN and CeAlO₃-TiN with sizes less than 2 μm, the titanium-containing inclusions are refined. Fatigue tests are conducted on the steels before and after the addition of Ce. The average fatigue lives of 20CrMnTi do not reach 10⁷ times, and the deviations between the maximum and minimum fatigue lives are great. Large-sized TiN are the main inclusions that affect the fatigue performance of 20CrMnTi. The average fatigue lives of 20CrMnTiCe exceed 10⁷ times, and the deviations of the fatigue lives are smaller than those of 20CrMnTi.

The occurrence form and size distribution of TiN and sulfide inclusions in 20CrMnTi gear steel directly affect the mechanical and service properties of the steel. Mastering efficient modification methods for TiN and sulfide inclusions in steel is of great significance. In this article, the differential behaviors of rare earth La and Ce on TiN and sulfide inclusions modification of 20CrMnTi gear steel are studied. The results show that the addition of rare earths La and Ce can modify the large TiN and sulfide inclusions into smaller composite inclusions. When rare earth La element (Abbreviated as RE La) is added to steel, the TiN and sulfide inclusions in steel are modified to small size LaAlO ₃ -TiN, LaAlO ₃ -MnS-TiN composite inclusions. When rare earth Ce element (abbreviated as RE Ce) is added to steel, the TiN and sulfide inclusions in steel are modified to small size CeAlO ₃ -TiN and CeAlO ₃ -MnS-TiN composite inclusions. The effect of RE Ce on TiN modification is better than that of RE La. When RE Ce is added, the average size of TiN inclusion in steel is 2.77 μm, and when La is added, the average size of TiN inclusion in steel is 3.24 μm. The modification effect of RE La on sulfide inclusion in steel is better than that of RE Ce. When La is added, the average size of sulfide inclusions in steel is 1.72 μm. When Ce is added alone, the average size of sulfide inclusions in steel is 2.08 μm.

The precise control of non-metallic inclusions is crucial for high-end GCr15 bearing steel. This study investigates cerium (Ce)-induced inclusion modification mechanisms. Smelting experiments with 0 to 0.017 wt% Ce additions, high-temperature in situ observations, thermodynamics, and first-principles calculations were used to evaluate inclusion evolution and aggregation behaviors. Without Ce, coarse Al₂O₃ and MnS phases dominate. As Ce increases to 0.017 wt%, inclusions evolve sequentially into CeAlO₃, Ce₂O₃, and ultimately, finely dispersed Ce₂O₂S and CeS. Thermodynamics indicate CeAlO₃ nucleates preferentially, acting as heterogeneous nucleation sites for MnS. In situ observations and interparticle force calculations reveal an aggregation tendency order of Al₂O₃ > CeAlO₃ > Ce₂O₃ > Ce₂O₂S. Furthermore, first-principles simulations confirm that Ce₂O₂S possesses the lowest formation energy and optimal stability, wherein Ce effectively modifies coarse inclusions into fine, well-dispersed spherical particles. Coupled with its intrinsic deoxidizing and desulfurizing effects, Ce addition synergistically modifies coarse inclusions into fine, well-dispersed spherical particles. These findings elucidate the rare-earth modification micro-mechanisms, providing a theoretical foundation for manufacturing high-quality bearing steel.

This article uses experimental and thermodynamic calculations to study the directional modification behavior of TiN and sulfides in 20CrMnTi steel before and after the addition of rare earth La element. The morphologies (SEM) and elemental distributions (EDS) of TiN and sulfide inclusions in steel are characterized using scanning electron microscopy, and the sizes of the inclusions are statistically analyzed. With the addition of rare earth La, the average sizes of TiN and sulfide inclusions in steel decrease, and the proportions of TiN and sulfide inclusions in all inclusions of the steel decrease. The results show that the addition of La element can promote the formation of LaAlO ₃ in steel, which can be used as the nucleation core of TiN and MnS inclusions in steel, and then form LaAlO ₃ -TiN and LaAlO ₃ -MnS-TiN composite inclusions, which are smaller in size and more uniform in distribution than TiN and sulfide in steel before La element is added. When La is added alone, the average size of TiN inclusion in steel is 2.2 μm. After the deoxidation of Al-La alloy, the average size of TiN inclusion in the steel is 1.9 μm. After Al-La composite deoxidation, the TiN containing inclusions in the steel will be transformed into smaller LaAlO ₃ -TiN composite inclusions. When adding La alone, the average size of sulfide inclusions in the steel is 2.1 μm. When Al-La composite deoxygenation is used, the average size of sulfide inclusions in steel is 1.1 μm, indicating that the Al-La composite deoxygenation has a better improvement effect on sulfide inclusions in steel than the improvement effect of adding La alone.

The size and distribution of TiN inclusions in 20CrMnTi gear steel directly affect its service performance. A reasonable method for controlling the size of TiN inclusions is a prerequisite for obtaining high-quality 20CrMnTi gear steel. This study focuses on the modification behaviour of TiN inclusions in 20CrMnTi gear steel under the conditions of Si-Ca-Ba single deoxidation and Si-Ca-Ba-Ce composite deoxidation, and their effects on the fatigue performances of the steels. The results show that after Si-Ca-Ba-Ce composite deoxidation, in addition to TiN inclusions, TiN containing composite inclusions such as Al₂O₃-TiN and CaAl₁₂O₁₉-TiN are also generated in the steel. When the ratio of Si-Ca-Ba to Ce in the Si-Ca-Ba-Ce composite deoxidiser is 5:1, the effective modification rate of TiN reaches 48.6%, which is better than 44.8% at 7:1 and 45% at 2.4:1, and the average size of the inclusions in the steel is 2.5 μm, which is better than 2.8 at and 3 μm at 2.4:1. At this point, the effect of the TiN inclusion modification in the steel is good, and the fatigue performance of the 20CrMnTi gear steel has been improved.

Ti microalloying can effectively improve the comprehensive properties of 20CrMnTi gear steel, but it also readily leads to the formation of large-sized TiN inclusions with sharp angular edges, which act as preferential initiation sites for fatigue cracks. Rare earth Ce is capable of modifying these coarse TiN inclusions in a targeted manner, and the addition strategy of Ce directly determines the final modification performance. This work systematically compares the inclusion modification effects between the conventional Ce-Fe alloy addition process and the synchronous co-addition process of Al, Ce and Ti. The results show that in the Ce-free steel, most TiN inclusions are large, angular particles with an average size of 4.27 μm. After Ce introduction, the original coarse complex inclusions Al₂O₃-TiN and MnS-TiN are transformed into fine composite inclusions, and are composed of Ce-Al-O-rich or Ce-O-S-rich core phases and TiN. Combined with EDS analysis, thermodynamic calculations and reported crystallographic investigations, the core regions match the characteristic signatures of CeAlO₃ and Ce₂O₂S. Therefore, these phases are tentatively assigned as the two aforementioned inclusions. The synchronous co-addition of Al, Ce and Ti delivers superior modification performance, which can refine the average size of TiN to 2.43 μm. Thermodynamically, CeAlO₃ and Ce₂O₂S possess lower formation Gibbs free energy than Al₂O₃, demonstrating that their formation is thermodynamically favorable after Ce addition. These rare earth phases can act as heterogeneous nucleation cores for subsequent TiN precipitation, thereby achieving the refinement and modification of large-sized TiN inclusions.