THE KEY METALLURGICAL FEATURES OF SELECTIVE LASER MELTING OF STAINLESS STEEL POWDER FOR BUILDING METALLIC PART

316L stainless steel parts are manufactured via selective laser melting. The investigation into the main characteristics and metallurgical mechanisms of selective laser melting process are highlighted in this work. The morphologies, microstructures and elemental compositions of as received scan tracks and samples are detected through optical microscope, SEM and energy dispersive X-ray spectroscopy respectively. The morphology of melted track exhibits scaly figures from top view, which is similar to welding process. The central zone of melted track shows a cellular microstructure while the edge zone of molten pool represents a columnar structure, which is caused by the heat transfer process. The surface morphology of SLM part in low magnification can show multi-lined feature, and the surface morphology in high magnification can reflect the solidification and crystallization process. Moreover, a little amount of oxide and splash with balling effect can also be found on the SLM part surface. The microstructure of SLM part is extremely fine coupled with multiple crystal directions. The very fine crystal structure is caused by the extraordinarily rapid cooling and the multiple crystal directions are due to the variable heat transfer direction. The element distribution is homogeneous and no elemental aggregations can be found. The metallurgical mechanisms for the above characteristics are also addressed.