关键词: 镁处理, 凝固组织, 夹杂物, 针状铁素体, 异质形核

Abstract: Increasing the proportion of equiaxed grains and refining the microstructure are of great significance to improve the mechanical properties of steel. In this study, AISI4130 steel was treated with magnesium. SEM, macrostructure observation and microstructure analysis were used to analyze the internal mechanism of the influence of Mg on inclusions control, solidification structure and microstructure of steel. The results show that the proportion of equiaxed grains increases and the average grain size decreases after Mgtreatment. When the Mg mass fraction is between 0.002 %–0.006 %, the proportion of equiaxed crystal increases with the increase of magnesium content.After Mg-treatment, the Al₂O₃, MnS had changed to Al-O-Mg-Mn-S,When the content of Mg is high, the MgS-MnS becomes the most important inclusion in the steel. In the Mg-treatment steel, the density of inclusions of 1-2 μm increased significantly, and the proportion of inclusions of more than 5 μm decreased. The steel after Mg-treatment has acicular ferrite at Mg-O inclusions grow core. The microstructure of AISI4130 ingots with Mg mass fraction of 0.009 % and 0.023 % is staggered fine acicular ferrite, and its impact toughness are significantly improved, and the average impact energy is about three times that of non-Mg-treatment.

Key words: Mg-treatment, solidification structure, inclusion, acicular ferrite, heterogeneous nucleation