含锰钢真空处理过程锰元素的迁移行为及控制应用基础研究

Manganese can significantly increase the strength and hardness of steel, increase the hardenability of steel, and improve the hot working properties of steel; thus, there is also a saying of "no manganese and no steel". The carbon steel with the addition of more than 0.7% of manganese is called "manganese steel", and most of the special steel contains relatively high manganese to obtain corresponding properties. Because of the good performance and reasonable cost of manganese steel, the medium or high manganese steel with both high strength and high plasticity, has become an important development direction for the new generation of automotive steel. At present, the TWIP and TRIP steel with 7%-10% and 18%-25% manganese content mostly stay in the laboratory stage in China, and there still are many technical bottlenecks in batch casting production. Effectively improving the recovery rate of manganese in the smelting process and precise control of manganese content in all processes is one of the bottlenecks. Production of high quality steel requires vacuum degassing process, but it causes the volatilization of manganese, and the reaction between the volatile phase and refractory materials, dust particles leads to the life of refractory materials decrease and the emissions index variation. It is the difficulty of vacuum degassing process for manganese steel production. Based on above situation, this application is intended to take the transfer behavior of manganese in gas, slag phase and liquid steel in manganese steel with vacuum condition as the starting point for research, to solve the contradiction between efficient degassing in liquid steel and stable control of manganese, to provide the basis for the development of a new generation of medium or high manganese steel which contains high strength and high plasticity.

锰元素可以显著提高钢的强度和硬度、增加钢的淬透性、改善钢的热加工性能，也有“无锰不成钢”的说法。碳钢中加入超过0.7%的锰称为“锰钢”，绝大多数特钢中含有较高锰以使钢材获得相应性能。由于锰对钢的优良作用和良好性价比，兼具高强/高塑性的中/高锰钢成为新一代汽车用钢的重要发展方向。目前，我国锰含量7%-10%的TRIP钢、锰含量18%-25%的TWIP钢大都停留在实验室阶段，批量连铸生产仍有许多技术瓶颈；有效提高冶炼过程锰的回收率和精准控制工序间锰含量是技术瓶颈之一；高品质钢需经真空脱气，但真空过程造成锰元素不同程度的挥发，且挥发相与耐材、粉尘颗粒间反应导致耐材寿命下降和排放物指标变差，这也是含锰钢真空处理的难点。基于此，本申请拟以真空条件下含锰钢中锰元素在气相/渣相/钢液间的迁移行为为研究切入点，解决钢液高效脱气和稳定控锰间的矛盾，为新一代高强/高塑性中锰、高锰钢的开发提供依据。

锰作为钢中最常见的合金元素，可显著改善钢的机械性能。兼具高强塑积和能量吸收性的4~12%锰含量的中锰钢和15~33%锰含量的高锰TRIP/TWIP钢，已成为下一代汽车用钢的主要发展方向。冶炼过程锰的稳定化和高收得率控制决定着含锰钢冶炼的成本和质量，然而锰元素在高温真空下大量挥发损失，导致成分控制难度加大，影响最终产品性能，且锰挥发相还会使耐材使用寿命下降。本研究以锰元素为研究对象，系统的开展了真空精炼过程中锰元素在含锰钢液/气相/耐材间的迁移行为及控制应用基础研究。通过热态实验揭示了锰挥发的影响规律，得到了锰挥发速率的一阶动力学方程及相应的动力学参数，进一步探明了锰元素在钢液/气相间迁移机理。锰含量升高，真空压力增大，气相传质阻力进一步增大。温度升高，锰挥发过程由钢液边界层传质控制；研究了钢液脱氮的限度及脱气率与锰挥发速率的关系，明晰了真空脱氮和锰挥发的相互作用机制。提出了真空下钢液有效脱氮和稳定控锰的协同处理模式：对于锰含量为5%钢液，在370 Pa下有渣熔炼约40 min，可有效减少锰的挥发，并同时稳定脱氮；建立了锰挥发相与MgO耐材作用机理模型：锰蒸气可将MgO颗粒解离成细小的块状，破坏耐材的内部结构。锰氧化物和液态锰可与MgO耐材的反应生成MgO·MnO固溶体，造成耐材损毁，侵蚀程度相对较大；在有效控锰的基础上，系统研究了不同锰含量钢中夹杂物的三维特征差异和分布规律，认为含锰类夹杂物主要为MnS类。在顶渣和感应搅拌下含锰类夹杂物转变为小于5 μm的斑状和多点状MnS-MnO类，基于此得出了含锰类夹杂物的转变机理和去除行为。本项目的研究对含锰钢液真空精炼过程中锰成分控制和质量控制及中/高锰钢关键冶炼技术研发具有重要指导意义。