Post-processing is one of the main ways to improve mechanical and microstructural
characteristics of stainless steel 316L fabricated by the laser-based powder bed fusion (LPBF)
process. In this study, optimized LPBF parameters were used to manufacture SS316L bars. For
the post-processing, two main heat treatment strategies have been used, quenching and
tempering, with various heating and dwelling conditions. While micro-CT scanning was used
to identify the porosity inside the as-built specimen, the microstructures of both as-built and
heat-treated specimens were additionally investigated by optical microscopy and scanning
electron microscopy (SEM). The tensile test's wrought specimens were obtained at various
strain rates of 0.1, 0.01, and 0.001 s-1. A two-dimensional (2D) digital image correlation (DIC)
technique and fractography analysis were used to understand the tensile behavior further. The
results show that the as-built specimen density level was in the range of 99.993-99.997%, with
only extremely small pockets of pores present. The microstructure results show that
temperature distribution is the most important factor in the formation of columnar grains (CG).
The columnar-shaped grains formed from the edge of the melt pool (MP) in the direction of
the laser motion path. The resulting dimensions and form of the cellular structures are
presented. The crystal orientation of the specimens was also studied with electron backscatter
diffraction (EBSD). The result shows that the fraction of directional grains is relatively small
due to a scan rotation and the scanning strategies adopted during the LPBF process. With
heating at 1050°C with a dwell time of 40 minutes, followed by quenching in cold water,
smaller grain sizes were obtained, meaning longer grain boundaries and major impediments to
dislocation motion, leading to better mechanical properties and fracture characteristics over
wrought specimens. The results of EBSD and SEM were also correlated with the 2D DIC test
results.
Metadata
Item Type:
Article (Published)
Refereed:
Yes
Additional Information:
Article number: 102058
Uncontrolled Keywords:
Laser based powder bed fusion; Stainless steel 316L;Strain rate; Quenching; Heat treatment