Investigation of crystal growth mechanism during selective laser melting and mechanical property characterization of 316L stainless steel parts

Abstract

A fundamental investigation of the development of grain structure of 316L stainless steel fabricated by selective laser melting (SLM) was conducted. Finite element analysis (FEA) was carried out in order to reveal the growth mechanism of grains under rapid solidification conditions. From this analysis, the crystal growth patterns were determined as a function of the temperature gradient along grain development orientation. A detailed discussion of preferred crystal orientation of dendrites was performed by geometrical analysis in conjunction with experimental findings. In addition, the dendrite spacings were measured, and the variation in spacings as a function of scan speed was studied. It was found that, the rapid solidification induced by high-speed laser scanning brought about sub-micron grains within the final solidified microstructure and a high volume energy density ω could cause the increase of primary dendrite spacing. Furthermore, the result also indicated that both grain size and densification level dependent on ω could affect the mechanical properties significantly. As the ω was settled at the optimal value of 125.00J/mm3, a high Vicker hardness of 281.6HV0.1, a large tensile strength of 590MPa and an attendant elongation rate of 21.1% were obtained.