Oxide metallurgy technology plays an important role in inclusion control and is also applied to improve the weldability of high strength steel. Based on the requirements of the weldability in high strength steel, the influencing factors of weld heat affected zone (HAZ) as well as the development and application status of oxide metallurgy technology are summarized in this review. Moreover, the advantages and difficulties in the application of rare earth (RE) oxide metallurgy technology are analyzed, combined with the performance mechanism of RE and its formation characteristics of fine and high melting point RE inclusions with distribution dispersed in liquid steel. With the weldability diversities of different high strength steels, the research status of weldability of high strength steel with high carbon equivalent and the effects of RE on the microstructure and properties of HAZ are discussed, and some suggestions about further research in the future are proposed.

The effect of Ce on inclusion evolution in the Al-killed high-strength steel is investigated through experimental observations and thermodynamic calculations. The microstructures are analysed by scanning electron microscope (SEM), optical microscope (OM) and electron backscattered diffraction (EBSD) analysis. Mechanical properties tests are carried out to study the effect of Ce on the tensile and impact properties. The results show that after Ce treatment, the typical inclusions are modified from Al₂O₃ inclusions and Al₂O₃+MnS complex inclusions to Ce-O-S inclusions, and the inclusions are refined. The area fraction, size and length/width ratio of martensite-austenite (M-A) constituents decrease with the addition of Ce. In the Ce-containing steel, the grains are finer, and the proportion of high angle grain boundaries and low-Σ coincidence site lattice boundaries is higher. Ce can improve the plasticity and impact toughness of the steel while maintaining high strength.

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.

Through the application of experimental analysis and mechanical characterisation, the influence of boron on the microstructure, strength and impact toughness of Al-killed high-strength low-alloy steel was examined. The results showed that with increasing boron content, the area fraction and average size of martensite–austenite constituents increased by 11.8% and 2.04 μm, respectively. Owing to the strengthening and combining effects of boron, the proportion of low angle grain boundaries in the boron-containing steel increased from 67.94% to 79.41% in comparison to the boron-free steel. After adding 0.0014% boron, the tensile and yield strength increased by 14.65% and 3.66%, respectively, due to the increasing content of martensite–austenite constituents. The long strip and large-sized martensite–austenite constituents of the steel matrix with 0.003% boron easily became the source of cracks and facilitated crack propagation, resulting in a decrease in strength. The toughness tested at −20 °C of the steel was severely worsened after adding boron, and the impact absorbed energy decreased from 105 to 7.4 J. This was because boron increased the martensite–austenite constituents, low angle grain boundaries and random boundaries, which favoured crack generation and propagation during the impact process, resulting in a sharp deterioration of toughness.