钢中夹杂物尺寸演变过程的界面特征与调控机制研究

With the rapid development of steelmaking technology, the study of non-metallic inclusions is urgent need for breaking through the conventional thoughtway. Full consideration to the needs of inclusions in different steel grades, first we should look for some other new methods for inclusion removal from liquid steels as possible, moreover we should think carefully how to exert the most potential of small inclusions being the helpful phase in steels. With references of the pertinent research results, this present project puts forward using the theory of interface free energy to study aggregation process of inclusions. After some factors of size evolution of inclusions are obtained, they can be used to achieve the aim control of inclusion size. The main research contents are follows. (1) physical simulation of size evolution of inclusions in water system; (2) quantitative characterization of inclusions by Mg or Ca treatment; (3) thermodynamic analysis and study of interface characterization between inclusion and liquid steel; (4) thermal simulation and verification of inclusion control. This study is to found the narrow composition region and inclusion type in favor of inclusion size decreasing in the different deoxidation systems, also it can be used to reveal the interface parameters and reaction mechanism during the aggregation process of inclusion in liquid steel, which can give us more directions for the study of inclusion harmless. The research results not only perfect the presently known wetting databases between molten steel and slag, but also give full play to the modification technology of inclusion in liquid steel.

随着炼钢技术的进步，非金属夹杂物研究迫切需要突破传统思维的束缚，既要深入挖掘有利于夹杂物去除的新手段，同时也要创新性地开发微小夹杂物“无害化残留”技术，充分发挥其在钢中的弥散增强作用，以适应钢种对夹杂物的特殊要求。本课题借鉴国内外研究成果，系统将界面自由能理论引入夹杂物聚合长大过程研究，深入剖析夹杂物尺寸演变的影响要素，从而实现钢中夹杂物的灵活控制。主要研究内容包括，夹杂物尺寸演变行为的物理模拟，镁、钙处理模式下夹杂物的定量表征，夹杂物—钢液界面特征研究与热力学解析，夹杂物尺寸控制结果的热态模拟与验证。本研究旨在确定典型脱氧模式下有利于颗粒尺寸控制的合理夹杂物类型和窄成分区间，揭示液态钢中主导夹杂物宏观聚合过程的界面参数和反应机制，从而为夹杂物无害化控制指明方向。研究成果既可以完善现有的高温钢液—炉渣/夹杂物基础润湿数据库，又能为充分发挥钢液夹杂物变性技术提供理论指导。

夹杂物问题是制约钢产品质量的重要因素。为了充分发挥钢中微小夹杂物的有益作用，本课题借鉴国内外研究成果，提出钢液镁处理新思想，并系统研究了钢中夹杂物的动态演变规律和细化机理，深入剖析了液态钢液中夹杂物尺寸演变的影响因素，为实现钢中夹杂物尺寸控制提供了理论基础。研究结果表明：采用邻苯二甲酸二辛酯、苯乙醚、硅油等模拟钢中液态夹杂物是可行的，模拟夹杂物的碰撞聚并行为受其自身黏度、液滴与水界面张力的影响较为显著；数值模拟计算结果表明：随着界面张力增大，模拟液滴聚并速度加快。增加液滴的动力黏度会减缓聚并和阻碍液聚并过程。热态试验显示，铝脱氧钢中主要是簇群状氧化铝夹杂物，夹杂物聚合倾向显著；镁处理后，夹杂物转变为弥散分布的尖晶石或氧化镁，夹杂物尺寸明显减小，数量密度显著增加，为第二相粒子非均相形核提供了热力学条件。测量了不同钢液组成与夹杂物基板间的高温接触角，结果表明：氧化镁和镁铝尖晶石与钢液的接触角较小，润湿性明显高于氧化铝，这是含镁夹杂物在钢中不易聚合最直接的原因。基于碰撞聚合理论，结合接触角和界面张力测定结果，本文首次建立了钢液中夹杂物聚并能力与接触角、界面张力间的定量关系；最后，研究采热态模拟实验验证了上述数学物理模拟结论与理论计算结果具有较好的一致性。半工业化试验显示，镁处理能细化低碳微合金钢组织，降低奥氏体晶粒尺寸，促进针状铁素体形成。在含钛包晶钢中，镁处理形成的细小氧化物质点可为TiN外延生长提供有利条件，促进TiN弥散分布，降低了晶界脆性，提高了铸坯高温热塑性，第三脆性区的断面收缩率最小值接近临界值60%。某企业采用镁处理后，含钛包晶钢连铸坯角部裂纹发生率由3.79%降至0.01%，基本消除了裂纹缺陷。