Microstructural and physical investigation on the effect of process parameters on stainless steel 316L prepared by Selective Laser Melting

Abstract

Additive manufacturing by Selective Laser Melting were used to investigate influence of process parameters on microstructural and physical properties. The thesis is in collaboration with Promet AS, which has delivered the specimens for examination.

SLM is a technology to fabricate products in a layer by layer manner – if used for series production, high quality is essential. The basis for this dissertation is reveal what effect the selected set of process parameters have on material quality. Material in topic is stainless steel 316L and varying parameters is: laser power, laser energy density, hatch distance and scan velocity. Experimental work performed is microscopic analysis using optical light microscope, SEM, EBSD, EDS and TEM. Mechanical it is conducted hardness and compression tests, in addition to surface porosity measurements.

Microscopy analysis revealed a solidification process of columnar growth often seen in welds. Within these large columnar crystal grains, a finer sub-grain structure was visible. These sub-grains mainly consisted of cells and dendrite-like columns and are characterised as an intragranular cellular structure. Results obtained is an increased laser energy density, in collaboration with small hatch distance, gave low surface porosity and high hardness. Hardness reached a maximum of 188HV. Surface porosity a minimum of 0.141%, both at 80J/mm3 and 80m. Large laser power allows a higher scan velocity, beneficial for increased production rate. The material possesses isotropic properties under compressive stress. SLM SS316L obtained high elongation and yield strength values.