Effect of heat treatment on the recrystallisation of thin-walled stainless steel 316L fabricated by laser beam powder bed fusion

Abstract

• 1050 °C has minimal effect on thin-walled laser beam powder bed fused SS316L with limited recrystallisation observed. • At 1150 °C, partial recrystallisation occurred with unevenly distributed normal, equiaxed, and abnormally large grains. • Sluggish recrystallisation at 1150 °C due to oxide pinning, limiting grain boundary mobility and preventing full recrystallisation. • 1200 °C sufficient to overcome oxide particle pinning, enabling near 100% recrystallisation across all thicknesses. Additive Manufacturing (AM), particularly laser beam powder bed fusion (LB-PBF), enables fabrication of complex thin-wall geometries, yet post-processing studies on such structures are limited. This work investigates heat-treatment annealing of thin-walled stainless steel 316L (SS316L) built via LB-PBF. A novel build geometry with wall thicknesses from 0.2–1.8 mm was used to examine microstructures before and after heat-treatment (HT) at 1050 °C and 1150 °C. In the as-built state, thinner walls showed grains oriented in <001> toward the wall centre, while thicker walls exhibited a <101> orientation due to a central band of preferential grain growth, typical of larger LB-PBF SS316L parts. Annealing at 1150 °C produced partial recrystallisation in all samples, reaching 86 % in the thickest walls, whereas 1050 °C annealing had little effect. Analysis of geometrically necessary dislocation density, low-angle boundaries (LAB), and high-angle boundaries (HAB) showed no correlation with recrystallisation behaviour. The primary factor limiting recrystallisation was Mn- and Si-based oxide distributions, which impeded grain boundary migration. This caused a stop-and-go growth mechanism, leading to abnormal grain growth in some cases. Findings highlight that chemical segregation, rather than dislocation structure, controls recrystallisation in thin-walled LB-PBF SS316L.

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