Effect of Rare Earth Ce on Sulfide Characteristics and Microstructure in Non-Quenched and Tempered Steel
LIU Jie1, XU Le1(), SHI Chao2, YANG Shaopeng1,3, HE Xiaofei1, WANG Maoqiu1, SHI Jie1
1.Institute of Special Steels, Central Iron and Steel Research Institute, Beijing 100081, China 2.Inner Monglia North Heavy Industries Group Corp. Ltd. , Baotou 014033, China 3.The Technology Center of Ma'anshan Iron and Steel Co. Ltd. , Ma'anshan 243000, China
Cite this article:
LIU Jie, XU Le, SHI Chao, YANG Shaopeng, HE Xiaofei, WANG Maoqiu, SHI Jie. Effect of Rare Earth Ce on Sulfide Characteristics and Microstructure in Non-Quenched and Tempered Steel. Acta Metall Sin, 2022, 58(3): 365-374.
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.
Fig.2 EDS mappings of composite inclusions in steel
Fig.3 OM images of microstructures of inclusions
Fig.4 Distributions of inclusions in steel
Fig.5 Numbers and sizes of inclusions in steel
Fig.6 Aspect ratios of inclusions in steel
Fig.7 Inclusion accumulation diagram in test steel containing 0.027%Ce (R3)
Fig.8 OM images of microstructures of the test steels
Fig.9 Ferrite contents of the test steels
Fig.10 Uniaxial balance property diagram of R1 steel
Fig.11 The generation process diagram of cerium-based composite inclusions
Steel
Ac1 / oC
Ac3 / oC
R0
715
803
R1
705
780
R2
675
795
R3
710
785
Table 2 Phase transition points of the test steel
Fig.12 Element distributions at grain boundary and phase interface
Fig.13 Element distribution of Ce and S at grain boundary and phase interface
Fig.14 Intra-granular ferrite (IGF) around the composite inclusion
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