Influence of processing parameters and particle size on the properties of hot work and high speed tool steels by Spark Plasma Sintering

Spark Plasma Sintering (SPS) is a newly developed rapid technique for powder sintering. In this study, consolidation by SPS of high speed steel (AISI M2) and hot work tool steel (AISI H13) commercial powders is investigated. The influence of sintering temperature (900 to 1150 C) and time (0 to 30 min) as well as the particle size and distribution is evaluated with respect to final density, hardness and fracture toughness. Properties have been compared with those of samples produced by Hot Isostatic Pressing (HIP). Density increases with increasing temperature up to 1050 and 1100 C for H13 and M2, respectively, a minor influence of time being observed for times longer than 5 min. Near fully dense samples (>99.5%) are obtained after sintering at 1100 C for 5 min only under uniaxial pressure of 60 MPa. Fine powders with a narrow size distribution or, alternatively, powders with a wider particle distribution and sufficiently high fraction of small particles show higher propension towards the achievement of full dense samples. The maximum densification rate occurs at lower temperature for H13 than M2, being negatively affected by the ferrite–austenite transformation during heating and the corresponding resistivity variation. Hardness and fracture toughness are found to increase with increasing density. Comparatively good values are obtained with respect to samples produced by Hot Isostatic Pressing confirming the possibility to produce tools by SPS.