In-situ Observation of Engulfment and Pushing of Small Particl in Molten Metal by Advancing Melt/Solid Interface

用激光共聚焦显微镜原位研究了钢的熔固界面推进对夹杂物颗粒的吞噬或推动作用。当界面推进速度超过某一粒子的临界值时，钢熔体中固体氧化铝团簇粒子或液态硅酸盐/铝酸盐球状粒子被界面吞没，界面向颗粒方向呈凸状延伸形成凸起。在较低的速度或较小的半径下，两类粒子都受到不形成碰撞的界面的推动。通过对熔体从颗粒到界面的热传递进行二维有限元分析，可以合理地再现凸起的形状。由中间粒子引起的热量传递减少被认为是吞噬的原因。我们也展示了这个。根据对枝晶间凝固速率的估计和经验，较小的氧化铝夹杂物在凝固过程中不会被枝晶固体包裹。然而，凝固过程中枝晶间液体中氧和硫浓度的梯度增强了枝晶间液体的吞噬作用。这些元素在液-钢/氧化铝界面上具有表面活性，并在枝晶间氧化铝夹杂物上引入很强的毛细力。观察了低碳钢中δ -铁素体/ γ -奥氏体的相变。测量了一个高能δ / δ晶界和两个非相干δ / γ晶界三相点的二面角。从观测到的二面角的平均值，可以得到γ / δ非相干的自由能。讨论了低硫含量钢的二面角边界和非相干自由能d/g边界。在。同一时间。用本构过冷理论和不稳定性理论对γ相的枝晶生长进行了观察和分析。这表明观测结果与理论吻合良好。少

Engulfment or pushing of inclusion particle by advancing melt/solid interface of steel has been investigated in-situ with a confocal scanning laser microscope. When the velocity of advancing interface exceeds a critical value for a particle, solid alumina cluster particle or liquidsilicate/aluminate globular particle in steel melt is found engulfed by the interface which extends in a convex way to form a bump toward the particle. At lower velocities or for smaller radii, the particles in both classes are pushed by the interface which does not form the bump. The shape of the bump is reasonably reproduced by a two-dimensional FEM analysis of heat transfer from the melt across the particle to the interface. Reduced heat transfer caused by the intervening particle is considered responsible for the engulfment.We also show that. the smaller alumina inclusions are not entrapped in the dendritic solid during solidification, based on estimates of the interdendritic solidification rates and empi … More rical data on the engulfment of alumina inclusions by solidifying steel. Engulfment by the interdendritic liquid however is enhanced by the gradients of the concentrations of oxygen and sulfur in the interdendritic liquid during solidification. These elements are surface active on the liquid-steel/alumina interface and m turn introduce very strong capillary forces on the interdendritic alumina inclusions.Phase transformation of delta-ferrite/gamma-austenite in low carbon steels was observed. Dihedral angles at triple points of one high energy delta/delta grain boundary and two incoherent delta/gamma interphase boundaries were measured. From the average value of observed dihedral angles, free energy of gamma/delta incoherent. boundary for a steel with low sulfur content on the dihedral angle and free energy of incoherent, d/g boundary were discussed. At. the same time. the dendritic growth of gamma-phase was observed and analyzed by the constitutional supercooling and instability theories. which show good agreement between the observations and theories. Less