微镁处理对铸态低碳钢中夹杂物和组织的影响

Effect of Trace Magnesium Treatment on Inclusion and Microstructure of Cast Low Carbon Steel

在实验室条件下,对低碳钢进行微镁处理,以SEM-EDS和金相显微镜为表征手段,通过与空白样的对比,研究钢中夹杂物、组织的演变过程。结果表明:微镁处理使得夹杂物从Al_2O_3转变为Mg-Al-O复合夹杂物,并且其尺寸明显细化,密度显著增加。组织分析表明:Mg-Al复合夹杂物能够诱导晶内针状铁素体形核,并且在这些夹杂物附近的铁基体中存在贫锰区。理论分析认为这促进了晶内针状铁素体的形核,结晶核心起源于复合夹杂物中镁铝尖晶石的镁空位。

Trace magnesium treatment was carried out for low carbon steel under laboratory conditions.The features of inclusion and microstructure of the material were studied through Scanning Electron microscope,Energy Dispersive Spectrometer（SEM-EDS）and optical microscope,and compared with nontreated sample.It is found that magnesium treatment leads to the inclusion evolution from Al2O3 to Mg-Al-O complex.Moreover,for Mg-treated sample,the average size of the inclusion is reduced,and the corresponding number of inclusion per unit volume is greatly increased.After etching,the typical microstructure of intragranular acicular ferrites is observed in Mg-treated sample,which is due to the nucleation effect induced by Mg-Al-O complex inclusions.Line scanning analysis of EDS hints that Mn-depletion zone（MDZ） exists in steel matrix,where is adjacent to the complex inclusion.Based on theoretical analysis,this phenomenon can be explained by the absorption of Mn due to the magnesium vacancy in MgAl2O4,and this MDZ promotes the nucleation of intragranular acicular ferrite.