Ti-Mg复合脱氧和硫含量对钢中夹杂物特征及MnS析出行为的影响

采用扫描电镜/能谱仪表征了管线钢中夹杂物的形貌、尺寸、成分及数量,考察了不同Ti/Mg比的钢中夹杂物特征、硫含量及脱氧产物数量对MnS析出行为的影响,并进行了热力学计算.结果表明：Ti-Mg脱氧钢中夹杂物以MgO-Al₂O₃-Ti₂O₃、MgO-Ti₂O₃或MgO为核心,表面包裹或局部析出MnS,粒径小于1.3μm,数量为300~450 mm^-2,形貌为圆形、多边形和方形;夹杂物中Ti/Mg原子数比为0.05~0.2时,夹杂物细小且近圆形;随硫含量减少,凝固过程中MnS析出倾向减小,MnS在夹杂物表面由包裹析出向局部析出转变,提高氧化物夹杂数量,有利于细小MnS的包裹或局部异质形核;Ti-Mg复合脱氧产物细小、弥散,可作为MnS异质形核核心,可同时降低MnS及氧化物的危害.

Effects of Ti-Mg complex deoxidation and sulfur content on the characteristics of inclusions and the precipitation behavior of MnS

The morphology, size, composition, and number of inclusions in pipeline steel were characterized by scanning electron microscopy and energy dispersive spectroscopy. The characteristics of the inclusions with different Ti/Mg ratios as well as the influence of sulfur content and the number of deoxidation products on the precipitation behavior of MnS were investigated, and the corresponding thermodynamic calculations were carried out. It is found that the core of the inclusions is mainly composed of MgO-Al₂O₃-Ti₂O₃, MgO-Ti₂O₃ or MgO, and then MnS wraps or locally precipitates on them. The inclusions have the average size smaller than 1.3 txm and the number of 300 to 450 mm-2; moreover, their morphology is diverse such as round, polygonal and square. When the Ti/Mg atomic ratio is 0.05 to 0.2, the inclusions are round and small. With the decrease of sulfur content, MnS less tends to precipitate during solidification, its ways of precipitation on the inclusion surface will change from wrapped to local precipitated. A great number of oxides is conducive to the heterogeneous nucleation of more finely MnS on the surface of complex oxides. The Ti-Mg complex deoxidation products are small and dispersed, can become the heterogeneous nucleation core of MnS, and may reduce the harm of MnS and oxides at the same time.