镁对20MnCr5齿轮钢中夹杂物的改质研究

Study on modification of inclusions by Mg in 20MnCr5 gear steel

20MnCr5齿轮钢通常有较好的疲劳性能及切削性能,而钢中夹杂物是影响这些性能的重要因素。为了研究镁对20MnCr5齿轮钢中夹杂物的改质行为和规律,开展了相应的工业实验,采用金相显微镜、扫描电镜以及非水溶液电解腐蚀技术对铸坯和轧材进行了分析。结果表明:镁处理后,钢液更加洁净,夹杂物数量变少,尺寸也变小;以Al_(2)O_(3)为核心外围包裹着MnS的复合夹杂,转变为以MgO·Al_(2)O_(3)为核心外围包裹着MnS的复合夹杂物,且复合夹杂物的占比从4.2%提高到8.3%。对轧材进行分析,发现镁的加入使20MnCr5轧材中长条状的硫化物更加短小弥散,硫化物的细系评级从2.5级显著降低到1.5级;由于复合夹杂物内部硬质MgO·Al_(2)O_(3)核心抑制了轧制过程中夹杂物的变形,使夹杂物保持球形或椭球形。

20 MnCr5 gear steel usually needs good fatigue and cutting properties, while inclusions in the steel are important factors affecting these properties. To study the modification behavior and regularity of Mg on inclusions in 20 MnCr5 gear steel, the corresponding industrial experiments were carried out. The industrial billets and rolled products were analyzed by metallographic microscopy, scanning electron microscopy and non-aqueous solution electrolytic corrosion technology. The results show that, after Mg treatment, the molten steel becomes cleaner, the number and size of inclusions decrease. The composite inclusions with Al_(2)O_(3) as the core and MnS as the periphery change into which with MgO·Al_(2)O_(3) as the core and MnS as the periphery, and the proportion of composite inclusions increases from 4.2% to 8.3%. It is found that the addition of Mg makes the long strip sulfide in 20 MnCr5 rolling stock more fine and dispersed, and the fine series rating of the sulfide was significantly reduced from 2.5 to 1.5. Due to the fact that the hard MgO·Al_(2)O_(3) core inside the composite inclusions suppresses the deformation of the inclusions during the rolling process, the inclusions remain spherical or ellipsoidal morphology.