Calorimetric study and microstructure analysis of the order-disorder phase transformation in silicon steel built by SLM

Innovative Additive Manufacturing (AM) technologies like Selective Laser Melting (SLM) could prove to be efficient for the processing of brittle silicon steel (Fe-Si) with high silicon content. This research elucidates the effects of heat-treatment on the microstructure of SLM-built high silicon steel, with particular emphasis on the formation of ordered phases, which are known to cause undesired material embrittlement. Silicon steel with 6.9 wt % Si is produced by SLM and investigated performing Differential Scanning Calorimetry (DSC), microstructure analysis and hardness measurements. As-built Fe-Si parts are found to consist primarily of disordered A2 phase as the high cooling rates typical of SLM suppress the ordering phase transformations. It is shown how heat treatments can be applied to modify the state of ordering and morphology of the rapidly solidified microstructure. By shedding light on the phase-ordering mechanisms and the effect of heat treatments on microstructure of high-Si steel built by SLM, the present study paves the way towards the optimisation of the mechanical and magnetic properties of this alloy.