Residual Stress States in Microstructurally Graded PBF–LB/M Austenitic Steel Components

Abstract

Laser-based powder bed fusion of metals (PBF–LB/M) represents a manufacturing technique enabling the production of application-adapted components. The process is influenced by multiple factors that interact during fabrication. Eventually, these lead to complex cooling conditions, resulting in microstructures strongly affecting the mechanical properties. Understanding the process-microstructure-property relationships is therefore crucial. The present study investigates microstructurally graded components made of austenitic steel 316L. Focus is on microstructural differences and residual stress evolution. Components are manufactured by utilizing a dual-laser system, consisting of a 400 W Gaussian and a 1 kW top-hat laser. Strengthening is strongly promoted by sub-structures, i.e. specific dislocation arrangements, decorated with chromium and molybdenum segregations. As a result, PBF–LB/M processed 316L demonstrates superior quasi-static properties compared to conventionally manufactured 316L. Differing cooling rates prevailing in areas processed either with the 400 W or the 1 kW laser significantly influence the substructure size, eventually resulting in distinctive strength and hardness. The incremental hole drilling method, considering local crystallographic orientation for data evaluation, was used to analyze changes in the residual stress distribution at different specimen-handling stages and lateral residual stress depth distributions. Results obtained pinpoint a pronounced in-depth gradient and a rather homogeneous lateral residual stress depth distribution.