连铸结晶器“自适应保护渣”理论及应用

Theory and application of“smart mold powders”for continuous casting of steel

连续铸钢工艺的成功与保护渣的正确使用密不可分,但保护渣在结晶器内发生的氟化物挥发、卷渣、控热与润滑的矛盾又制约了绿色和高效连铸的发展.重庆大学通过对保护渣在结晶器内进行物理化学研究,发现保护渣中以铝为代表的网络形成中间体元素具有适应结晶器工况环境的功效.这些功效包括:(1)抑制保护渣与水之间离子交换程度,起到固氟和固钠的作用;(2)形成异类网络结构,使熔渣产生明显的剪切稀化行为,实现保护渣不同位置黏度大小控制;(3)在低碱度条件下表现出独特的热扩散效应,促使玻璃渣膜变成晶体渣膜.在此基础上,提出连铸结晶器“自适应保护渣”设计理论,利用这一理论开发出环境友好、非牛顿流体及热扩散效应保护渣.工业应用结果表明这类保护渣无需降氟就可达到环境友好、降低超低碳钢冷轧板封锁率及提升304D高氮不锈钢板坯表面质量的效果.

The success of the continuous casting process is inseparable from the correct use of mold powders.However,fluoride volatilization and the contradiction between slag entrapment,heat transfer,and lubrication that occurs in the mold restrict the development of green and efficient continuous casting.Through the physical and chemical research of mold powders,Chongqing University found that the intermediate elements of network formation represented by aluminum in the mold powders have remarkable effects of adapting to the working environment of the mold.These effects include:(1)These elements inhibit the degree of ion exchange between the slag and the water and fix fluorine and sodium.(2)They also form a heterogeneous network structure such that the slag produces shear and thinning behaviors and realizes slag viscosity control in different positions.(3)Under the condition of low basicity,aluminum shows a unique thermal diffusion effect,which promotes the transformation of glass slag film to a crystal slag film.On this basis,the design theory of“Smart Mold Powders”for continuous casting,which is referred to as the“SMP”theory,is proposed.This theory was used to develop environmentally friendly non-Newtonian fluids and thermal diffusion effects to mold powders.Industrial application results show that this type of mold powders can achieve environmental friendliness without fluoride reduction,minimize the rejecting ratio of cold-rolled plates,and improve the surface quality of slabs for high-nitrogen stainless steel.