PSI - Issue 83

Niccolò Vilotta et al. / Procedia Structural Integrity 83 (2026) 246–255

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1. Introduction Additive manufacturing has significantly expanded the design and manufacturing possibilities for stainless-steel components, especially when complex geometries and reduced material waste are required [1,2]. Among the available technologies, Direct Metal Laser Sintering (DMLS) is particularly attractive for AISI 316L stainless steel because it allows the production of near-net-shape parts with good mechanical performance [3–8]. However, when additively manufactured components are joined by welding, the resulting thermal cycles may alter the local microstructural and mechanical response, generating spatial property gradients across the welded region [9–11]. In this context, the mechanical characterization of welded DMLS-manufactured AISI 316L cannot be limited to a global tensile assessment only, since the weld metal (WM), heat-affected zone (HAZ), and base material (BM) may exhibit different local properties [9–11,15]. A combined analysis is therefore needed, capable of linking the global response of the specimen to the local behaviour of the different metallurgical regions [9–11]. More generally, this type of local-to global mechanical interpretation is also relevant for structural-integrity, full-field, and fatigue-oriented assessment of welded joints and structures [22–24]. The present work investigates DMLS-manufactured AISI 316L dog-bone specimens in both non-welded and welded configurations through static tensile testing, Vickers microhardness mapping, thermographic monitoring, and post fracture observations [9–11,16–19]. In addition, local true stress-true strain curves are reconstructed from hardness measurements by means of the Lopez and Fatemi method and the Kamaya model [13,14]. The aim is to provide a consistent interpretation of the global tensile behaviour and of the local mechanical gradients induced by welding, with particular attention to the differences among BM, HAZ, and WM. 2. Materials and methods DMLS-manufactured AISI 316L dog-bone specimens were investigated in both non-welded and welded configurations with over fill removed. The specimen geometries and the adopted welded-joint layouts are reported in Figure 1. In particular, the welded specimens were characterized by a perimetric X-groove weld. Both specimen types were sectioned to extract the gauge-length region of interest, which was then prepared for metallographic inspection and microhardness mapping by progressively polishing the investigated surfaces.

Figure 1: AM AISI 316L base material and welded specimen with a perimetric X-groove seam with overfill removed.

For the welded specimen, to clearly identify the three key metallurgical regions (e.g. base material, heat-affected zone and weld metal), micro-etching was performed after surface preparation. Specimens were dipped in a glyceregia solution for a few minutes, until the different areas were visible, and rinsed with ethanol (C 2 H 6 O). Non- destructive hardness tests were carried out using a Vickers indenter with a load of 300 gf (≈ 3 N) and a dwell time of 15 s. The spatial distribution of hardness from BM through HAZ to WM on the prepared faces was captured by indentations along measurement lines spanning the welded region. Hardness evaluation provides a local measure of resistance to plastic deformation and is therefore directly related to the mechanisms governing yielding and strain hardening. In welded joints, where mechanical properties vary over short characteristic lengths, hardness mapping represents an effective and minimally invasive approach to infer spatial strength gradients across the three different regions [9–11,15]. In this work, Vickers hardness (HV) values were first converted into Brinell hardness (HB) values using the relation [20]: HB = 0.9801 HV 0.9941 (1) The local yield strength and ultimate tensile strength were then estimated through the following empirical correlations for steels [13]: