凝固速率对M2高速工具钢铸态组织的影响

Effect of solidification rate on as-cast microstructure of M2 high speed steel

采用OM、SEM等手段分析了采用水冷铜模和铸铁模铸造获得的不同冷速M2高速钢的铸锭,研究了冷却速度对其铸态组织的影响。结果表明,随着冷却速度的增加,铸态组织明显细化,原始结晶的奥氏体晶粒尺寸明显减小,晶粒均匀性明显增加;莱氏体网的均匀性增加,莱氏体共晶碳化物的厚度变薄,莱氏体团尺寸减小;M_2C共晶碳化物由片层状转变为尺寸较小的棒状,棒状碳化物的界面没有片状平直光滑,更易形成缩颈或断开,棒状碳化物的长度和厚度更小;与片状共晶碳化物相比,棒状M_2C共晶碳化物在高温加热时更容易发生分解和分断球化,其主要原因是具有弯曲表面和较多缩颈的M_2C碳化物具有更大的热力学和动力学驱动力。

The effect of solidification rate on as-cast microstructure of M2 high speed steel ingot obtained by water-cooling copper mould and cast iron mould was investigated by OM and SEM.The results indicate that with the increase of solidification rate,the as-cast microstructure of the steel is refined,the primary grain size and ledeburite carbides are distributed more homogeneously; the eutectic carbide thickness becomes more thin,the eutectic cell size becomes more fine; the morphology of M_2C eutectic carbides transforms from the plate-like to the rod-like shape.The interface of rod-like eutectic carbides is rougher,the length and thickness of rod-like carbides are finer.Compared to plate-like carbides,the rod-like carbides are more easy to decomposition and spheroidized at high temperature heating,which is favorable for carbide refinement.The reason is the rod-like eutectic carbides have larger driving force of thermodynamics and kinetics,which determined by the curved surface and necking down of rod-like eutectic carbides.