喷射成形M3型高速钢碳化物组织特征与加热过程演化

采用常规铸造和喷射成形工艺分别制备了M3型高速钢铸坯和沉积坯.利用扫描电子显微镜、X射线能谱和X射线衍射等分析方法对冷却速度对合金的显微组织的影响,加热温度对M3高速钢中M2C共晶碳化物分解行为的影响,以及热加工变形后铸态和沉积态组织的变化进行了研究.结果表明:铸态合金含有粗大的一次枝晶和M2C共晶碳化物,而喷射成形沉积坯主要为等轴晶且碳化物细小均匀;冷却速度的提高极大地抑制了碳化物的析出和晶粒长大;加热温度的提高有利于M2C共晶碳化物分解,过高的温度使得分解后的M6C长大,不利于合金性能的提高;沉积坯经恰当的预热处理和热变形可以获得理想的变形组织.

Microstructural characterization of carbides in spray-formed M3 high speed steel and its evolution during heating process

As-cast and as-spray formed billets of M3 high speed steel were produced through traditional casting and spray forming,respectively.The effect of cooling rate on the microstructures of the cast and spray-formed steels,the relation of heating temperature to the decomposition of M2C eutectic carbide,and the microstructural evolution of the cast and spray-formed steels after hot working were studied using scanning electron microscopy(SEM),energy dispersive X-ray analysis(EDXA),and X-ray diffraction analysis(XRD).The as-cast structure contains coarse primary dendrites and M2C eutectic carbide,but the spray-formed one consists of equiaxed grains and fine carbides.High cooling rate can suppress the carbide precipitation and grain growth.Elevated temperatures are favorable to the decomposition of M2C eutectic carbide,but an exorbitant temperature results in the growth of M6C carbide,which will cause the properties of the steel to deteriorate.A desired deformation microstructure of the spray-formed steel can be obtained by appropriate preheating and hot deformation.