采用喷射成形工艺制备直径250 mm大截面M3型高速钢，利用电火花直读光谱仪、金属原位分析仪、XRD、OM、SEM等手段，研究样坯特殊偏析形貌位置处合金元素分布和微观组织特征。结果表明，腐蚀后样坯低倍组织中存在2种偏析形貌：锭型偏析与环状偏析。锭型偏析区域内富集C及溶质元素；环状偏析区域主要富集C及Mo元素，较锭型偏析程度轻。由样坯边部至心部，碳化物形貌由条状向块状、鱼骨状转变；宏观偏析区域内碳化物偏析严重。基于实验结果，讨论了喷射成形工艺糊状区的组织变化及锭型偏析和环状偏析的形成，认为沉积阶段缓慢的冷却速率是出现上述结果的根本原因。因此，在利用喷射成形工艺制备大截面材料时，不应简单考虑为一种快速凝固技术。

Spray forming of various steels and iron-based alloys has been investigated since the 1960s. The microstructure and properties of spray-formed steels are superior to those of cast material, typically resembling those of equivalent powder metallurgy steels. While the wight of the deposits produced in pilot-scale plants is typically less than 100 kg, in some cases, industrial plants are capable of producing preforms that weigh up to several tons. However, in actual industrial production processes, segregation can easily appear in the product structure, especially in large-scale high-speed steel. In this work, M3 high-speed steels with a 250 mm diameter after forging were prepared through spray forming to study their cross-section segregation morphology. An arc-spark direct reading spectrometer, an original position analyzer for metals, OM, SEM, and EDS were used to analyze the distribution of alloy elements and microstructure characteristics of the different parts of a cross-section area. The results show two segregation morphologies in the cross-section of spray-formed M3 high-speed steel: ingot segregation and ring segregation. Carbon and alloy elements are enriched in the ingot segregation, whereas carbon and molybdenum are mainly enriched in the ring segregation, where the degree of segregation is less than that of the ingot segregation. From edge to center, the morphology of carbide changes from plate to massive. In the ring segregation area, there were two morphologies of carbide: one is M₆C-wrapped MC composite carbide of the network distribution and the other M₆C and MC both nucleating at the carbide/matrix interface of the composite carbide. In the ingot segregation area, carbides were mainly distributed independently of massive M₆C and MC, with severe carbide segregation in the macrostructure. On the basis of the above experimental results, the solidification and microstructural evolution of spray forming were discussed, and the slow cooling rate in the deposition stage was the fundamental reason for the above experimental results. It is believed that spray forming loses rapid solidification characteristics in the deposition stage when preparing large-scale products.