高速重轨钢中基于钛处理的MnS改性控制机理研究

Large-sized MnS inclusions are detrimental to the plasticity, fatigue and welding performance of high-speed heavy rails. This project would study the modification mechanism of MnS inclusions by titanium oxide and titanium sulfide, respectively. Based on thermodynamic analysis, a prediction model of inclusion composition in Fe-C-Mn-Si-Ti-Mg-S-O-N system is created by theoretical calculation and experimental test. Then the evolution of inclusion behaviors based on titanium treatment is established by comprehensively investigating the transient behavior of inclusions in titanium treatment process and the morphology, structure and statistical characteristics of the inclusions in two dimensional and three dimensional states. Furthermore, the static and dynamic behaviors of the inclusions during the solidification process and the effect of inclusions behavior on as - cast microstructures are investigated deeply. On the basis of th laboratory experiment, the industrial test of modified MnS are performed in order to determine the appropriate conditions, ways and methods of titanium treatment. According to evaluating the effect of different titanium treatment, the best manner of the morphology and dimension control for the MnS inclusions are put forward and thus achieve the small dispersion of MnS inclusion in high-speed heavy rail steel finally.

大尺寸MnS夹杂对高速重轨钢塑性、疲劳性能、焊接性能产生不利影响。本项目通过钛的氧化物和钛的硫化物两种控制思路进行钛处理改性MnS的效果研究。本项目从热力学分析入手，通过实验室理论计算及实验研究，建立基于钛处理的Fe-C-Mn-Si-Ti-Mg-S-O-N体系夹杂物成分预测模型。对钛处理过程夹杂物瞬态行为展开系统研究，全面考察二维和三维状态下夹杂物的形貌与结构及其统计特征，建立基于钛处理的高速重轨钢夹杂物行为演变机制。凝固过程中，重点考察夹杂物的静态和动态行为以及夹杂物对铸态组织的影响，建立基于钛处理的高速重轨钢凝固过程夹杂物冶金行为机制。在此基础上，开展钛处理改性MnS的工业效果研究，确定不同钛处理过程的条件、途径、方式，并对其效果做出评价，从而提出重轨钢MnS夹杂物形态与尺寸控制的最佳方案，实现高速重轨钢中MnS夹杂的细小弥散化。

高速重轨钢中大尺寸 MnS 夹杂物容易造成材料裂纹、点腐蚀、热撕裂、探伤不合等问题， 对其塑性、疲劳性能、焊接性能等危害较大。本课题采用实验室冶炼的方式，结合ASPEX夹杂物自动分析技术、无水有机溶液电解技术等多重分析手段，结合理论分析，对Ti、Mg、Ce处理重轨钢中的MnS形貌控制展开了系统研究。课题明确了加入Ti、Mg、Ce后钢液中夹杂物的成分、数量密度、尺寸和长宽比等的演变规律，并分析了冷却方式对MnS夹杂析出的影响，阐明了Ti、Mg和Ce改性MnS的机理。后通过热模拟实验模拟了加入Ti、Mg、Ce后MnS在轧制过程中的变形情况。探究了精炼渣碱度和Al2O3含量对夹杂物去除的影响，分析了夹杂物在钢渣界面的去除机理。本课题为重轨钢实际生产中的硫化物和氧化物控制提供了理论支撑。