SEMISOLID PROCESSING OF TOOL STEEL

Semi-solid processing (SSP) of alloys has been used commercially since the early eighties for the manufacture of components in the automobil e and aerospace industries. The thrust of the early development has be en in aluminium and copper alloys. The nature of the process makes it an ideal candidate for the manufacture of components in alloys which a re either difficult or virtually impossible to forge by conventional m eans. Alloys such as tool steels, stellites and superalloys, offer the possibility of lucrative niche for commercial exploitation. The work described in this paper is the result of three years of development in the semi-solid processing of high melting point alloys. The developme nt of the appropriate microstructures for thixoforming M2 tool steel ( both through Spray Formed and Recrystallisation and Partial Melting (R AP) routes) is examined and discussed. The thixoforming of M2 tool ste el in non-metallic dies is described in some detail, together with the way process parameters appear to affect the structure and properties of the final product. The resulting microstructures are closely examin ed and presented with values of mechanical properties in the as forged and heat treated conditions.