永磁搅拌作用下含硫非调质钢中MnS的调控机制研究

Controlling the size and distribution of MnS precipitation behavior along interdendritic is crucial to the production of sulfur-containing non-quenched and tempered steel due to that MnS inclusions are the key factors affecting the internal quality of billet and the mechanical properties of final products. Our research aims at establish a method of obtaining fine-spindle and dispersively distributed MnS inclusions in sulfur-containing non-quenched and tempered steel during solidification process with physical field. Then, different ingot samples will be prepared by a novel movable permanent magnet stirring (PMS) system under different values of magnetic flux density, rotational speed and stirring period, and a three-dimensional magnetic-temperature-flow-solute field unsteady coupled mathematical model will be established. The evolution of MnS under PMS will be investigated and its relationships with the secondary dendrite arm spacing, microsegregation and mechanical properties will be studied. Besides, the PMS-affected nucleation, growth and movement of MnS will be illuminated by analyzing the quantitative distribution characteristics of the heat and mass transfer and flow behavior of molten steel. Moreover, a model about the relation between the PMS parameters and the size and quantity of MnS will be build. The significance of findings obtained from experimental and simulation are of importance for further control of MnS and industrial application of this innovative technology.

含硫非调质钢凝固过程中MnS夹杂物沿着枝晶间析出的形态与分布控制，是影响铸坯内部质量和成品力学性能的关键。本项目旨在通过外场手段，在凝固阶段对含硫非调质钢中的MnS进行调控，使其呈细小纺锤状、弥散分布。创新采用旋转永磁体搅拌器（简称永磁搅拌），开展不同参数（磁感应强度、磁体转速、搅拌时间）下铸锭中MnS形态与分布的实验研究以及电磁-传热-流动-溶质的多物理场数值模拟计算；探究永磁搅拌下含硫非调质钢中MnS的演变规律及其与二次枝晶间距、微观偏析和力学性能之间的内在关系；揭示钢液搅拌下的传热、传质、流动对MnS的形核、长大与迁移过程的作用机制；构建永磁搅拌参数/MnS尺寸和数量之间的相关性模型；为含硫非调质钢中MnS的精细化控制和节能高效永磁搅拌的工业化应用提供理论依据与技术支持。

含硫非调质钢在凝固过程中易产生硫、锰元素偏析，在凝固末期形成MnS夹杂大量析出，在源头上即凝固阶段调控MnS的尺寸和分布是关键。本项目开展永磁搅拌不同参数下（搅拌时间、磁体转速、磁感应强度）下，典型含硫非调质钢49MnVS3凝固过程中MnS析出行为的实验研究；结合多物理场数值仿真，建立了永磁搅拌下钢液磁场强度-电磁力-流动速度的多物理场耦合模型，计算了永磁搅拌不同参数下钢液所受电磁力和流动速度变化；实验研究与数值计算相结合，揭示了永磁搅拌参数、钢液所受电磁力、流动速度以及MnS尺寸之间的相互关系。得出如下结果：（1）49MnVS3钢中MnS在1419℃时开始析出，凝固阶段有84%的MnS析出；在全过程施加永磁搅拌，MnS的细化效果更稳定。（2）实验研究表明，永磁搅拌磁体转速从0增加到150rpm，或者中心磁感应强度从0增加到1800Gs，49MnVS3钢中细小MnS数量明显增加，MnS分布更加均匀弥散。（3）提高永磁搅拌的磁体转速或者中心磁感应强度，49MnVS3钢中MnS析出相细化，为Ti-V-Nb粒子析出提供更多的形核位点，诱导钢中晶内铁素体形成，钢种强韧性得到改善。（4）数值模拟计算表明，随着永磁搅拌磁体转速或者中心磁感应强度的增加，钢液所受的电磁力和切向流动速度显著增强。（5）永磁搅拌磁体转速为150rpm，中心磁感应强度为1450-1800Gs，此时钢液的最大切向流动速度为0.26-0.38m/s，铸锭中产生了大量平均长度小于5μm的MnS，且呈细小均匀弥散分布。本研究为典型含硫非调质钢凝固过程中MnS的精细化控制提供了新的思路，为节能高效永磁搅拌在连铸过程的应用提供了理论依据与技术支持。