Additive manufacturing of carbon-martensitic hardening ledeburitic cold work tool steels using Fused Filament Fabrication and subsequent Supersolidus Liquid-Phase Sintering

Abstract

In this work, the microstructure property relationship of D2 (X153CrMoV12; 1.2379) ledeburitic cold work steel processed by filament extrusion is investigated. Contrary to the conventional process, which involves a multi-step process of printing, debinding, and solid-state sintering, the specimens in this study were densified using Supersolidus Liquid-Phase Sintering (SLPS). SLPS occurs after thermal debinding in the interval between the solidus and liquidus temperatures. Optimized liquid-phase volume fraction was evaluated by means of thermodynamic calculations using the CALPHAD method and their experimental validation. The microstructure formation process during debinding, solid state, and SLPS sintering was investigated by X-ray diffraction and electron microscopy. Tomography studies confirm a relative density of 99.92% by volume during SLPS sintering at 1280 °C and provide a deep insight into local densification behavior during SLPS processing. In addition, surface roughness, as determined by confocal laser scanning microscopy, could be reduced. The reduction in porosity and surface roughness can be attributed to the presence of a liquid phase during SLPS. Using adapted heat treatment parameters determined by hardness-tempering curves, higher hardness values were achieved for SLPS-post-compacted specimens compared to conventionally processed specimens and the same material in the cast and heat-treated reference state.