20MnCr5齿轮钢连铸坯中硫化物三维形貌的解析

20MnCr5齿轮钢具有良好的疲劳和易切削性能匹配,钢中硫化物形态与分布是影响材料性能的重要因素。为了探究20MnCr5齿轮钢连铸坯中硫化物的三维形貌及分布规律,采用金相显微镜、扫描电镜以及三维腐刻技术对连铸坯进行了分析。结果表明:20MnCr5连铸坯中硫化物主要类型为MnS、MnS+Al₂O₃复合夹杂物,铸坯中硫化物尺寸由边部激冷层到中心等轴晶区呈先增大后减小的趋势。激冷层中硫化物三维形态主要为椭球状和长条状,各占一半左右;在柱状晶区末端椭球状减小到不足10%,长条状和不规则状占比分别为55%和35%,并开始出现少量八面体状;中心等轴晶区硫化物不规则状占比增大到60%,长条状占比减小到约30%,八面体状约占10%,椭球状占比减小到不足5%。在连铸坯不同区域主要的硫化物三维形态不同,激冷层为椭球状和长条状,柱状晶区为长条状,等轴晶区为不规则状。

Analysis of three-dimensional morphology of sulfides in continuous casting billet of 20MnCr5 gear steel

20MnCr5 gear steel has good matching performance between fatigue and easy-to-cut properties. The morphology and distribution of sulfides in the steel are important factors affecting the properties of materials. In order to explore the three-dimensional morphology and distribution law of sulfides in the continuous casting slab of 20MnCr5 gear steel, the continuous casting billet was analyzed by metallographic microscope, scanning electron microscope and three-dimensional etching technology. The results showed that the main type of sulfides in 20MnCr5 continuous casting billet was the composite inclusion of MnS and MnS+Al₂O₃. The size of sulfides in the billet increased at first and then decreased from the edge chilled layer to the central equiaxed crystal zone. The three-dimensional morphology of sulfides in the chilled layer was mainly ellipsoid and strip-like, which accounted for about half of each. At the end of the columnar crystal region, the proportion of ellipsoid sulfides was reduced to less than 10%, and the proportion of long strip and irregular sulfides was 55% and 35%, respectively. Meanwhile, a small amount of octahedron began to appear. The proportion of irregular sulfides in the central equiaxed crystal region increased to 60%, while the proportion of long strip sulfides decreased to about 30%. The proportion of octahedral sulfide accounted for about 10%, and the proportion of ellipsoid decreased to less than 5%. The three-dimensional morphology of the main sulfides was different in different regions of the continuous casting billet: it was ellipsoidal and long strip in the chilled layer, long strip in the columnar crystal zone, and irregular in the equiaxed crystal zone.