Grain Refinement Caused by Larger Particles in Laser 3D Printing of AISI 304L Stainless Steel

Additively manufactured (AM) stainless steel has attracted a lot of attention for its competitive performance advantages over parts prepared by traditional methods. However, the influence of the powder characteristic of AISI 304L stainless steel on the laser 3D printing (3DP) process has yet to be clarified. In this research, the effect of the particle size of atomized AISI 304L stainless steel powder on 3DP of a powder-fed laser was studied, the grain morphology of different printed samples was analyzed by electron backscatter diffraction (EBSD) technology, and the mechanical properties were investigated via quasi-static tensile experiments. It was found that the use of small particles made the columnar crystal area mix with fine equiaxed grains in single-pass laser melting deposition, resulting in an obvious grain refinement effect. However, in multi-pass deposition, samples deposited with small particles exhibited more significant grain coarsening and anisotropy effects than those of larger particles, resulting in a significant reduction in plasticity. This can be attributed to the grain merging and growth mechanism caused by the thermal shock effect of multi-pass laser deposition, which is controlled by the grain configuration formed in the early-pass deposition. The results show that the use of powder particles greater than 50 μm is of great significance for improving the quality of AISI 304L stainless steel 3DP products.