Effect of post-heat treatment on residual stress and tensile strength of hybrid additive and subtractive manufacturing

This paper presents a comprehensive study of the tensile performance, heat treatment, fracture, decrease of residual stress, second-phase particle and microstructures of a 316L stainless steel fabricated by directed laser deposition (DLD) and thermal milling (starting milling temperature at 250 +/- 50 degrees C), a typical hybrid additive and subtractive manufacturing process. Experiments of different post-heat treatment temperatures and tensile tests at room temperature were performed. The residual stress was eliminated with heat treatment at 400 degrees C for 2 h, and the average residual stress decreased 53.7% while the yield strength and ultimate strength decreased slightly. The fracture surfaces of different heat treatment temperatures were observed. The typical ductile fracture microstructures of dimples were seen in almost all specimens whenever the heat treatment temperature was low or high. The evolution of dimples from formation to destruction by heat treatment was analyzed. The different morphology and composition of the second-phase particles of different heat treatment temperatures were compared. The yield strength of 427.5 MPa, the ultimate strength of 599.27 MPa, and the elongation of 36.48% showed the new hybrid manufacturing technology could be used for further fabrication of components.