亚包晶微合金钢表面裂纹缺陷形成及调控机制

本项目的目标是探索连铸过程中防止亚包晶微合金钢表面裂纹缺陷形成的成分和温度控制策略，以解决这类钢一直困扰的铸坯表面纵裂纹和奥氏体晶界微裂纹难题。核心思想是利用表面粗糙度表征包晶转变的收缩程度，以探索纵裂纹和沿奥氏体晶界裂纹形成机制。为此，项目利用高温共聚焦显微镜模拟连铸从钢液到铸坯的整个凝固过程，借助OM（光学显微镜）、SEM（扫描电镜）、TEM（透射电镜）等观察和分析手段，研究结晶器内冷却条件下钢中溶质含量对包晶相变收缩和原始奥氏体晶粒尺寸的影响规律；揭示包晶转变时初始奥氏体晶粒尺寸与高温铁素体枝晶界面和尺寸的对应关系；完善铸坯高温组织（奥氏体晶粒均匀度和微合金元素析出行为）与沿奥氏体晶界裂纹发生率的关系，并寻求获得高塑性铸态组织的冷却工艺。在此基础上，建立起亚包晶微合金钢成分和温度与包晶转变收缩程度以及铸坯表层具有高塑性组织的定量关系。

The purpose of this project is to solve the problem of longitudinal cracks and austenite grain boundary cracks of hypo-peritectic microalloyed steel by investigating the composition and temperature control strategy for preventing the formation of surface cracks defects in the process of continuous casting. The core idea is to explore the formation mechanism of longitudinal cracks and austenite grain boundary cracks by using the surface roughness to characterize the shrinkage degree of peritectic transformation. Therefore, the whole solidification process of continuous casting from molten steel to strand will be simulated by high temperature confocal microscopy. The observation and analysis methods will be carried out by OM (optical microscope), SEM (scanning electron microscope), and TEM (transmission electron microscope). The influence of solute content on the shrinkage of peritectic transformation and prior austenite grain size under the cooling condition of the mold will be studied. The relationship between the initial austenite grain size and the ferrite dendrites’ interface and size at high temperature will be revealed. The relationship between the high temperature microstructure (austenite grain uniformity and the precipitation behavior of micro alloying element) and the cracks occurrence along the austenite grain boundary will be improved, and the cooling technology of the high plasticity casting structure can be obtained. On basis of these, the quantitative relationship among the composition and temperature control strategy of hypo-peritectic microalloyed steel and the shrinkage degree of peritectic transformation, and the high plastic structure of strand will be established.