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为了研究钢锭点状偏析区微观组织特点,对CrMo钢锻坯中的斑点偏析区域进行了分析研究。研究表明,钢坯中的元素偏析区沿锻造方向拉伸且尺寸较小,可判断原铸锭中的偏析为3个维度方向尺寸相近的点状偏析。偏析区中铬、钼元素质量分数相对较高,在冷却后点状偏聚区形成贝氏体组织,与基体的铁素体、珠光体组织呈交错分布的特征,且夹杂物在偏析区富集比较明显,局部偏析区还存在气孔。钢中的点状偏析的出现主要原因是钢液凝固前沿过冷度降低,在成分过冷条件下,高熔点铬、钼组元在枝晶表面局部富集,随温度的下降,钢液中Mn S夹杂物同时受枝晶表面的物理吸附作用聚集,同时增加了枝晶区域液相的黏度,导致气体溢出困难,在凝固后局部形成气孔。通过提高钢液凝固速度,降低钢液在固液两相区的停留时间,将有效缓解钢锭中斑点偏析的形成。
In order to study the microstructure characteristics of the point segregation zone of the ingot, the spot segregation area in the CrMo steel forging was analyzed. The results show that the element segregation zone in the billet is stretched along the forging direction and has a small size. The segregation in the original ingot can be judged as a point-like segregation of similar dimensions in three dimensions. In the segregation zone, the mass fraction of chromium and molybdenum is relatively high, and the bainite microstructure forms in the point segregation zone after cooling, and the ferrite and pearlite structure of the matrix is in a staggered distribution, and the inclusion is rich in the segregation zone Set more obvious, partial segregation zone there are stomata. The main reason for the occurrence of point segregation in steel is that the undercooling of the molten steel decreases. Under the condition of supercooling, the high-melting chromium and molybdenum components locally enrich on the dendritic surface. With the decrease of temperature, MnS inclusions are aggregated by the physical adsorption of the dendrite surface at the same time and the viscosity of the liquid phase in the dendritic zone is increased at the same time, resulting in gas spilling difficulties and local formation of stomata after solidification. By increasing the solidification rate of molten steel and reducing the residence time of the molten steel in the solid-liquid two-phase zone, the formation of speckle segregation in the ingot can be effectively alleviated.