通过稀土Ce微合金化手段，采用SEM、EDS和ASPEX等手段对不同Ce含量的非调质钢中的夹杂物形貌、数量和尺寸以及实验用钢的显微组织进行了表征，结合Thermo-Calc热力学软件对含Ce硫化物夹杂的形成过程进行了分析，并通过三维原子探针(3DAP)对晶界和相界面处的元素分布进行表征。结果表明，Ce在1800℃与S结合形成Ce₃S₄夹杂，1480℃转变为Ce₂S₃夹杂，1480℃以下形成Ce₂S₃为内核，Ti₄C₂S₂和MnS包覆生长的复合夹杂物；添加Ce元素的实验用钢中90%以上的夹杂物的长径比小于2.5；Ce含量为0.019% (质量分数)时，实验用钢的组织最细，平均晶粒尺寸为4.17 μm。3DAP的结果证明了Ce在晶界和相界处存在明显偏聚，阻碍了C扩散，抑制晶粒长大，另外，高温区形成的细小弥散含Ce夹杂物提供了形核质点，2者共同作用细化了非调质钢的组织。

A rare-earth Ce microalloyed non-quenching and tempering steel was designed. The morphology, quantity, and size of inclusions in non-quenched and tempered steel with different Ce contents were characterized by SEM, EDS, and ASPEX, as well as the metallography of the test steels. The formation process of Ce sulfide inclusion was analyzed by Thermo-Calc thermodynamic software, and the element distribution at grain boundary and phase interface was characterized by 3DAP. The results showed that Ce combined with S to form Ce₃S₄ inclusion which then transformed into Ce₂S₃ inclusion, and finally formed the composite inclusion with Ce₂S₃ as the core and Ti₄C₂S₂ and MnS as the cladding growth. The aspect ratio of more than 90% inclusions in the steel test with Ce element is less than 2.5; the microstructure of the steel was the smallest with an average grain size of 4.17 μm when the Ce content was 0.019% (mass fraction). The results of 3DAP prove that Ce segregates at the grain boundary and phase boundary, which hinder the diffusion of C and inhibit the growth of grain. In addition, the finely dispersed Ce inclusions as nucleation particles also refine the microstructure of the non-quenched and tempered steel.