The effect of pre-melting refining slag containing different contents of Ce2O3 on the absorption and modification of Al2O3 inclusion in an Al-killed steel was investigated through the slag/steel reaction experiment at 1600 oC.It was found that the replacement of 10 wt.% Al2O3 with Ce2O3 for 50 wt.%CaO-33 wt.%Al2O3-7 wt.%MgO-10 wt.%SiO2 refining slag promoted the slag absorption ability of alumina inclusion,which made the total oxygen content determined by infrared absorption method decrease from 100 to 25 ppm in 15 min.The Mg-Al-Ce-O type inclusion was also detected in the as-solidified samples by scanning electron microscopy(SEM).Thermodynamic analysis indicated that the Ce2O3.Al2O3 type inclusions would be formed with the cerium content in the range of 6.9 ppb to 3.6 ppm when the content of aluminum was 0.01 wt.%.
A new approach to applying the electric current pulse(ECP) with parallel electrodes to the promotion of the transition from columnar crystal to equiaxed crystal and the improvement of macrosegregation was introduced.The ECP was applied to different stages of the solidification.The results showed that the application of the ECP in both the initial stage(the thickness of solidified shell reached 2 mm approximately) and the late stage(the thickness of solidified shell reached 14 mm approximately) of solidification can promote the columnar to equiaxed transition(CET).The analysis showed that during solidification,a large number of nuclei around the upper surface fell off due to ECP,which subsequently showered on the melt and impinged the growth front of the columnar crystal.Therefore,the CET occurred.In addition,this method was also employed to influence the solidification process of bearing steel,and the results showed that the structure was changed from columnar crystal to equiaxed crystal,indicating that ECP can enhance the homogeneity of structure and composition of bearing steel.
LI Jie MA Jian-hong SONG Chang-jiang LI Zhi-jun GAO Yu-lai ZHAI Qi-jie
The experiments on adding Ce,Mn and S to molten iron have been carried out by means of the electric furnace,and the concentration of oxygen,the evolution of inclusions and microstructures of samples are analyzed,indicating that the concentration of dissolved oxygen decreases greatly after adding Ce. The calculated thermodynamics results at 1273 K performed on Factsage show that Ce2O2S and CeAlO3 are formed with the increase of Ce content for w(Ce)>0.0002 and w(S)<0.0001,while three cerium sulphides (CeS,Ce3S4 and Ce2S3,in sequence),MnS and Ce2O2S are formed with the increase of S content and the decrease of Ce content for w(Ce)>0.0002 and w(S)>0.0001. These results are consistent with the SEM observations. Finally,some possible reasons are given to explain the formation of intragranular ferrite in the pure iron.
