Effect of Adding Cerium on Microstructure and Morphology of Ce-Based Inclusions Formed in Low-Carbon Steel

Z Adabavazeh,Y H Su,W S Hwang

doi:10.1038/srep46503

Abstract

Intra-granular Acicular Ferrite (IAF), as one of the most well-known desirable microstructure of ferrite with a chaotic crystallographic orientation, can not only refine the microstructure and retard the propagation of cleavage crack but also provide excellent combination of strength and toughness in steel. The effect of adding cerium on microstructure and controlling proper cerium-based inclusions in order to improve properties in low-carbon commercial steel (SS400) were investigated. The type of inclusions can be controlled by changing S/O ratio and Ce content. Without Ce modification, MnS is a dominate inclusion. After adding Ce, the stable inclusion phases change from AlCeO3 to Ce2O2S. The optimum amount of cerium, 0.0235 wt.%, lead in proper grain refinement and formation of cerium oxide, oxy-sulfide and sulfide inclusions. Having a high amount of cerium results in increasing the number of inclusions significantly as a result it cannot be effective enough and the inclusions will act like barriers for others. It is found that the inclusions with a size of about 4∼7 μm can serve as heterogeneous nucleation sites for AF formation. Thermodynamic calculations have been applied to predict the inclusion formation in this molten steel as well, which show a good agreement with experimental one.

Highlights

Lots of studies have indicated that the inclusions, such as Ti, Al, and Zr oxides, Ti, Nb, and V carbonitrides, would contribute to the Intra-granular Acicular Ferrite (IAF) nucleation, and the optimal heterogeneous nucleus was Ti2O35–9
At high temperatures are so low that REM elements can combine readily with oxygen and sulfur when added to liquid steel[11,12]
It is reported that Ce2O3 with a low misfit value with ferrite can act as the nucleation sites for IAF under fast cooling rate

Summary

Introduction

Lots of studies have indicated that the inclusions, such as Ti, Al, and Zr oxides, Ti, Nb, and V carbonitrides, would contribute to the IAF nucleation, and the optimal heterogeneous nucleus was Ti2O35–9. The adding sulfur improves the machinability of steel, anisotropy in mechanical and fatigue properties would occur due to the presence of deformable MnS inclusions. In order to modify MnS inclusions, different methods are used by adding of Ca, REM (Rare-Earth-Metals) or Zr in the melt. Anmark et al.[10] reviewed and summarized the effect of different non-metallic inclusions on the machinability of various steels. The value of the αcoefficients can be different based on the contents of carbon and alloying elements He concluded that the effect of the oxides and sulfides of REM and Zr on improving of machinability will be higher than the effect of MnS inclusions, which can be explained by the significantly lower magnitude of the difference between the values of αMnS and αsteel for the stainless and high alloyed steels

Methods

Results

Conclusion