Investigation of the tensile failure mechanism of 316L steel produced by selective laser melting after different heat treatments

The selective laser melting (SLM) method is an advanced manufacturing technique used to create parts with complex geometries. The tensile failure mechanisms of 316L steel samples produced using traditional processes (ASTM A276/A276M-17 Condition A) and the SLM technique are investigated and compared. The evaluation included the steel in its initial state and after heat treatment (cooled from 899°C in water or 427°C in air), with a focus on assessing mechanical properties through standard tests and microstructural analysis. Heat treatment to relieve stress only slightly altered the mechanical properties after holding at 427°C. In contrast, cooling from 899°C resulted in a 40% decrease in strength and a 20% increase in plasticity. Additionally, SLM samples produced horizontally exhibited a strength that was 2–5% higher than those manufactured vertically; however, the vertical samples showed greater ductility, likely due to differences in porosity. In traditionally produced samples plastic fracture primarily occurred at the fracture site, revealing a combination of slow and rapid crack development and evidence of the TWIP (Twinning-Induced Plasticity) effect. For laser-melted samples, distinct frac­ture zones were observed at 427°C, where strain hardening resulted from a combination of dislocation slip and the TWIP effect. Fractures following cooling from 899°C demonstrated signs of plastic fracture with an elongated structure and voids.