Preliminary investigation on the solidification AISI S2 Tool Steel modified by Silicon Carbide additions
A.H. Seidou1, E. Saggionetto1, O. Dedry1, J.T. Tchuindjang1, A. Mertens1
1 Metallic Materials Science (MMS), Aerospace and Mechanical Engineering Dpt., University of Liège.
Email: AHB.Seidou@uliege.be
Laser Powder Bed Fusion (LPBF) is a flexible Additive Manufacturing technique (AM) that allows not only the fabrication of near-net shape components but also the development of new metallic alloys by mixing two or more powders together. However, the ultra-fast cooling and heating rates typical of the process lead to out-of-equilibrium conditions and to the formation of new metastable phases that are difficult to predict. In order to overcome the lack of knowledge about the new solidification mode, techniques which imply near-equilibrium conditions such as Differential Thermal Analysis (DTA) can also be used for preliminary evaluation of new alloys and powders mixtures.
In this work, DTA has thus been used to evaluate the microstructure obtained by mixing AISI S2 tool steel and silicon carbide (SiC) in different amounts. The mixture was heated up to 1550°C (5°C/min) achieving the melting of S2 powder and the dissolution of SiC prior to cooling down to room temperature (20°C/min). The microstructure obtained after solidification was investigated through light microscopy and scanning electron microscopy combined with EDS/EBSD analyses. Depending on the initial amount of SiC, pearlite, ferrite, eutectic carbides, precipitates and several types of graphite have been observed within the microstructure. By combining the observed microstructure with the exothermic peaks of the DTA cooling curve, it was possible to determine the solidification sequence and to gain insights on the modification effects of SiC on S2 under near-equilibrium conditions. These outcomes will be used as reference for the development of this new alloy by LPBF.