高铬铸铁半固态挤压件组织差异性分析

采用过流冷却体式流变挤压成形工艺制备高铬铸铁半固态挤压件,对挤压件内部组织差异进行了分析。结果表明,由于凹模中熔体内部存在温度梯度,从而使制备的高铬铸铁半固态挤压件顶部、中部、底部组织存在明显的差异。顶部组织中部分先共晶枝晶状奥氏体或较粗大的杆状M7C3碳化物经过流冷却体时得以保留,受凸模激冷没有发生长大和相变。中部和底部的组织中枝晶状奥氏体或杆状M7C3碳化物经过流冷却体时发生蔷薇化、球化或折断、破碎、磨圆,因在凹模中凝固时间较长,先共晶相和剩余液相发生相变并有长大现象。比较而言,中部组织中先共晶相的转变产物或先共晶相较底部凝固时间更长,长大更明显。

Analysis on Microstructure Difference in Semi-solid Extrusion Part of High Chromium Cast Iron

Microstructure Difference in semi-solid extrusion parts of high chromium cast iron was analyzed by inclined cooling plate rheology extrusion forming process.The results show that the top,middle and bottom structures in the parts have obvious difference because of temperature gradient of melt in female die.Some dendrite proeutectic austenites or coarse rod shape proeutectic M7C3 carbides in the top structure are preserved as passing inclined cooling plate,they don’t grow up and phase transformations don’t occur during sharp cooling with male die.Dendrite proeutectic austenites or rod shape proeutectic M7C3 carbides in the middle and bottom structure become rose and spheroidization or were broke,crushed and round,which have grow up and phase transformations occur because of relatively long solidification time of alloy melt in male die.Comparatively speaking,the growth of proeutectic phases or their transformation product in the middle structure is more obvious than that in the bottom structure.