PSI - Issue 74

Jaromír Brůža et al. / Procedia Structural Integrity 74 (2025) 1–8

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Jaromír Brůža / Structural Integrity Procedia 00 (2025 ) 000–000

1. Introduction Numerous metallic materials are extensively studied with the outstanding expansion of additive manufacturing (AM). AISI 316L stainless steel was one of the first materials studied due to its good weldability, mechanical properties, corrosion resistance, wide use, and relatively affordable printing costs. Laser-powder bed fusion (L-PBF) is one of the most frequently adopted AM technologies, not only in academia but also in various industrial sectors. L-PBF 316L steel typically exhibits an outstanding combination of considerably higher strength than its conventionally produced solution annealed counterparts (doubled yield stress is typical) while maintaining a good ductility (Liu et al., 2018), (Wang et al., 2018). The increase in mechanical properties is attributed to a complex hierarchical microstructure formed due to the extremely rapid cooling of locally melted powder and repeated thermal distortions during L-PBF printing. This microstructure is inherently nonequilibrium, but it provides several strengthening mechanisms, including the grain size comparable to wrought materials, unique submicron cellular microstructure with a very high dislocation density and nano-inclusions (Liu et al., 2018), (Wang et al., 2018), (Godec et al. 2020), (Voisin et al., 2021), (Wang et al., 2025). Recently, Fouchereau et al. (2024) reported a row of findings on differences in corrosion resistance and their relationship to microstructure characteristics of L-PBF 316L steels manufactured from powders of two different suppliers. The authors documented several noticeable differences in their hierarchical microstructure; however, there was no clear explanation for the origin of these microstructural discrepancies. Roirand et al. (2024) very recently fabricated L-PBF 316L steel from two batches of powders from one producer under the same processing conditions and revealed two very different microstructural states of the mate rial. The authors analyzed various factors to explain such microstructural differences and concluded that no generally accepted hypothesis exists for the observed considerable grain refinement. The present study represents a continuing effort to clarify the above microstructure discrepancies. For this purpose, L-PBF 316L steels manufactured from three different powders were fabricated to demonstrate the impact of small variations in chemistry on the solidification behavior of processed materials, which considerably alter their final microstructure and hardness. 2. Materials and Methods 2.1. Materials Three types of austenitic stainless steel AISI 316L provided by three different suppliers were used in the present study: (i) Linde, formerly known as Praxair Inc., (ii) EOS GmbH, and (iii) SLM Solutions. All three powders have predominantly spherical particles with low levels of satellites or agglomerates. The p article size distribution was 10 65 µm, 15-60 µm, and 5-45 µm for Praxair, EOS, and SLM powders, respectively. Their chemical composition is listed in Table 1 together with the standard 316L steel specification. It is essential to mention that even though all three materials are considered AISI 316L based on their chemical composition being within the bounds of the standard ASTM A240, as seen in Table 1, the difference between the powders' chemical composition is not negligible. For example, the EOS material has increased content not only of austenite stabilizing elements – mainly nickel and nitrogen, but also chro mium. On the other hand, a very low content of strong austenite stabilizers, namely carbon and nitrogen, is characteristic of the Praxair powder.

Table 1: Chemical composition of the AISI 316L powders used in this work and the standard 316L steel specification

Element [wt%]

C

Cr

Cu 0.2

Mn

Mo 2.5 2.7

N

Ni

S

Si

Fe

Praxair

0.003 0.014

17.1 18.3 16.6

1.11

0.01

12.1 14.0 10.9

0.004 0.007

0.42 0.47 0.54

Bal. Bal. Bal. Bal.

EOS SLM

0.14

1.2

0.1

0.01

… …

0.87

2.05

0.04 ≤ 0.1

…

ASTM A240

≤ 0.03

16-18.5

≤ 2

2-3

10-14

≤ 0.015

≤ 0.75