# Microstructure of Additively Manufactured SUS316L Stainless Steel with SrO Heterogeneous Nucleation Site Particles

## TL;DR

Adding SrO particles refines the microstructure of 3D-printed stainless steel using different additive manufacturing machines.

## Contribution

Demonstrates SrO's effectiveness in grain refinement across different DED systems for AMed SUS316L stainless steel.

## Key findings

- SrO particles refine grains in ALPION Series machine under unidirectional scanning.
- SrO suppresses defects and texture in LAMDA 200 machine samples.
- Differences in melt pool size and cooling affect microstructure refinement.

## Abstract

It is known that the addition of SrO heterogeneous nucleation site particles can refine the microstructure of SUS316L stainless steel additively manufactured (AMed) by powder bed fusion (PBF). In this study, this idea was confirmed by directed energy deposition (DED). However, there are several types of DED machines, and the energy system and the material supply system of these machines are different depending on each machine. In this study, the grain refinement behavior and the formability of AMed SUS316L stainless steel with the addition of SrO heterogeneous nucleation site particles are evaluated using a single-beam type LAMDA 200 machine and a multi-beam type ALPION Series machine. The size of the melt pool made by the ALPION Series machine is smaller than that of the LAMDA 200 machine, which results in a shorter residence time in the liquid state of the melt pool for the ALPION Series machine. The grains formed in the inoculated sample manufactured by the ALPION Series machine under the unidirectional scanning strategy are found to be refined compared to those in the uninoculated sample. On the other hand, it is found that the formation of defects and the crystallographic texture observed in the samples manufactured by the LAMDA 200 machine is suppressed by the addition of SrO heterogeneous nucleation site particles. These differences between the ALPION Series and LAMDA 200 machines would come from the differences in the melting state, including temperature, cooling conditions, and re-heating.