金属学报  2020, Vol. 56 Issue (5): 704-714    DOI: 10.11900/0412.1961.2019.00288
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Solidification Structure Refinement in TWIP Steel by Ce Inoculation
LI Gen, LAN Peng(), ZHANG Jiaquan
School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China
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Abstract

Twinning-induced plasticity (TWIP) steel represents a novel grade of advanced high strength and ductility with significant potential for automotive industry. However, high alloying in TWIP steel leads to the inhomogeneous solute distribution and anisotropic local deformation. It is well known that the refinement of solidification structure is an effective solution to the above defects. Much attention has been paid to heterogeneous nucleation by Ce particles, acting as nucleating sites in liquid steel. The present work focuses on how Ce content and casting parameters affect the refinement of solidification structure in Fe-22Mn-0.65C TWIP steel, aiming to provide an effective technology in high alloy steel production. The reaction products of Ce inoculation were predicted by thermodynamics software FactSage 7.0 and their effectiveness of heterogeneous nucleation was estimated by lattice misfit model. The solidification structure refinement by Ce inoculation under different conditions was experimentally studied by OM, SEM, EBSD and EPMA. The results show that, with increasing Ce content the reaction products transferred from Ce2O3 to Ce2O3+a small amount of Ce2O2S, and both kinds of particles can act as heterogeneous nucleation cores theoretically. For as-cast solidification structure, the ratio of equiaxed grain area increased from 25% to 72%, average equiaxed grain size decreased from 480 μm to 130 μm and the segregation ratio of Mn decreased from 1.61 to 1.41. Meanwhile, the tendency of particle agglomeration was weakened by lowering inoculation temperature, resulting in the improvement structure refinement. In this work, the recommended inoculation parameters are concluded as (0.02%~0.04%)Ce with superheat of 20 ℃.

Key wordsCe    TWIP steel    inoculation    solidification structure refinement    micro-segregation

 ZTFLH: TF771.1

Corresponding author: LAN Peng     E-mail: lanpeng@ustb.edu.cn