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 rare earth elements Ce and La on the evolution behavior of inclusions in HRB400E steel was studied through experimental observations and thermodynamic calculations. Neutral salt spray corrosion experiments were also conducted to investigate the effect of Ce–La on the corrosion resistance of steel. The results showed that the typical inclusions in steel without rare earth were MnS and MnO–SiO2. A small amount of Mn–Si–O–S inclusions was also observed. After adding rare earth, the typical inclusions were transformed into isolated (Ce,La)2O2S, (Ce,La)2O3 + MnS, and (Ce,La)2O2S + MnS complex inclusions. The thermodynamic calculations indicated that the rare earth elements in molten steel preferentially reacted with MnO–SiO2 inclusions and dissolved oxygen and sulfur to form (Ce,La)2O3 and (Ce,La)2O2S. Small amounts of [S] and [Mn] adhered to the surface of the nucleated rare earth inclusions to form complex inclusions. After Ce–La treatment, the corrosion rate of the steel decreased from 3.491 to 1.992 mm year−1, and the corrosion resistance was improved. The change in corrosion behavior is due to the modification of the inclusions into rare earth inclusions with good compatibility with the steel matrix.

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 Al 2 O 3 inclusions and Al 2 O 3 +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.

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