Cold Metal Fusion of AISI M2 Steel: Process Development, Microstructure and Suitability for Complex Parts

Additive manufacturing (AM) of high-speed steel (HSS) is of great interest for the manufacture of optimized forming and cutting tools. This study aims to systematically develop the sinter-based Cold Metal Fusion process for M2 steel and enable manufacture of complex shaped part designs. Green parts were printed with surface roughness, R a , of 21 μm and density of 5.40 g/cm 3 . A sintering temperature of 1248 °C yielded a sintered density of >99% theoretical density and significantly decreased surface roughness to 8-10 μm. The microstructure consisted of martensite, and of grain boundary and finer intragranular MC and M 6 C carbides. As-sintered Vickers hardness was 576 10 HV5 and increased to 933 27 HV5 upon oil quenching. Compression tests after air quenching revealed superior compressive strength of >3360 MPa compared to the as-sintered and oil cooled HSS. The fracture mode changed from ductile transgranular fracture for the as-sintered material to brittle intergranular upon oil cooling. As-sintered tensile specimens showed low strength of 681±43 MPa and brittle intergranular fracture as opposed to the as-sintered compression specimens. Finally, the manufacturing capability for an injection molding tool insert was proven, as no defects were identified. This novel process will allow for the manufacture of complex high-performance parts with improved durability and efficiency.