基于镁处理的硫系易切削钢组织与硫化物协同控制基础研究

The machinability and the mechanical properties of the sulfur free-cutting steel are closely related to its rolling structure and the shape and the distribution of sulfide. In this project, based on the thermodynamic analysis, magnesium treatment is induced to the system sulfur free-cutting steel and three items would be studied systematically by means of simulation experiments. One is the evolution of the composition, the quantity, the granularity and its distribution of the nonmetallic inclusions during the steelmaking process. The other is the movement behavior of the inclusions during steel solidification and its effect on the solidification structure and the distribution of the sulfide. The third is the effect of the inclusions on the growth of austenite and the rolling structure and the shape of sulfide. Finally, the synergic control mechanism of inclusion containing magnesium would be established between the structure and the sulfide. The results are of great scientific importance in the improvement of controlling theory of comprehensive properties of sulfur free-cutting steel, and are of great practical importance in the process design and the technological development of magnesium treatment for sulfur free-cutting steel.

硫系易切削钢的切削性能和力学性能决定于钢的组织和硫化物的形态与分布。本项目把镁处理引入到硫系易切削钢中，在热力学分析的基础上，通过模拟实验，系统研究冶炼过程夹杂物成分、数量、粒度及其分布的演变行为，凝固过程夹杂物的运动行为及对凝固组织和硫化物析出的影响，热加工过程夹杂物对奥氏体长大、轧制组织转变和硫化物形态转变的影响，最终建立镁系夹杂物对硫系易切削钢组织和硫化物的协同控制机制。研究结果对于完善硫系易切削钢综合性能控制理论具有重要的科学意义、对于硫系易切削钢镁处理工艺设计与技术开发具有重要的应用价值。

本项目把镁处理引入到硫系易切削钢中，通过热力学分析，获得了Fe-C-Mn-Si(Al)-Mg-O-S钢液体系内非金属夹杂物的热力学稳定存在区域及其转变条件；在此基础上，通过高温模拟试验，获得了硫系易切削钢冶炼过程非金属夹杂物成分、数量、粒度及其分布的演变行为，并通过高温动态观察及界面性质测定，解析了非金属夹杂物特征演变的原因及影响机制；进而开展了含镁硫系易切削钢半工业化制备试验研究，获得了凝固过程非金属夹杂物的冶金行为及其对凝固组织、轧制组织与性能的影响规律，最后提出了适用于硫系易切削钢的镁处理工艺。研究结果有利于拓展镁系非金属夹杂物的功能化应用空间，对于促进硫系易切削钢机械性能与切削性能协同控制技术的开发具有重要应用价值。