Effects of rare earth Ce on TiN inclusion modifications in 20CrMnTi steel under deoxygenation conditions of Si–Ca–Ba alloy

20CrMnTi steel is widely used in the gear manufacturing field of engineering machinery. The addition of Ti element to steel can effectively improve its low-temperature impact toughness and enhance its mechanical properties. However, during the smelting process of 20CrMnTi, large-sized TiN inclusions are inevitably formed in the steel, which affects its service performance improvement. This paper focuses on the directional modification behaviors of TiN inclusions in 20CrMnTi gear steel by rare earth Ce under deoxygenation conditions of Si–Ca–Ba alloy. The results show that under the deoxygenation conditions of Si–Ca–Ba alone, there are composite inclusions in 20CrMnTi steel with CaAl12O19 as the core and TiN wrapped around the periphery, all of which have sizes greater than 2 μm. This type of inclusion is square or diamond shaped, and the addition of Si–Ca–Ba deoxygenation alone has poor TiN modification effect on gear steel 20CrMnTi. Adding Ce element can effectively improve the nucleation core of inclusions. The CeAlO3–TiN and (CaAl12O19–Ba–Ce)–TiN composite inclusions are formed, and the TiN inclusions are modified in terms of morphology and size. The average size of inclusions decreases from 4.1 to 3.0 μm, which prevented the excessive growth of pure TiN inclusions to some extent.