Evolution of carbides and microstructure in spray-formed high-vanadium high speed steel

High-vanadium high-speed steel (modified M2: W6Mo5Cr4V4) was manufactured using spray forming. The carbide and microstructure evolution mechanisms during various heat treatment processes were explored. According to the experimental results, spray forming resulted in a fine microstructure of high-speed steel, and there were no large eutectic carbides, which distinguished it from the casting process. The types of carbides in the cast steel are MC, M 2 C and M 6 C, while the types of carbides in the spray-formed steel are MC and M 2 C. With the increase of normalizing temperature, the carbides in the spray-formed steel gradually dissolved and spheroidized with sizes of less than 2 μm. The carbides M 2 C in the spray-formed steel are transformed into MC and M 6 C during quenching and tempering, which further promotes the dissolution of carbides into finer carbides. The microstructure in different directions of spray-formed samples after forging exhibited a high degree of consistency. The spray-formed sample indicated higher hardness values than the cast ones under various heat treatment conditions. This improvement in hardness was attributed to both grain boundary strengthening and the fine, uniform distribution of carbides.