Effects of the microstructure and surface hardness of 316 L stainless steel printed by laser powder bed fusion interacting with a methane gas burner

The manufacturing of high-temperature environment parts (combustion chambers, turbojet or rocket injectors) with the Laser Power Bed Fusion (LPBF) process is very promising due to the freedom on geometries it provides. In order to gain a better understanding on a realistic flame–wall interactions, 316 L steel plates from LPBF and cast /forged processes were subjected to a reacting flow using robust cross-disciplinary methodology. The physical phenomena (thermal, physico-chemical and mechanical) involved in structural parts (full-scale) subjected to combustion-based burnt gases is studied via the use of a laboratory-scale combustion test rig. The generation of a methane-air flow enables to conduct a comparative analysis to understand the influence of a well-controlled thermal stress (1200°C, 1 h) on the material properties (hardness, residual stresses), depending on the manufacturing process and microstructure evolution during the thermal exposure. Results highlights that the interaction between the flame burnt gases and the material does not affect the microstructure and mechanical behaviour for cast whereas localized recrystallization in the range of 0–10 μm near the exposed surface and residual stress state modifications are revealed for LPBF. This is the first study on flame–LPBF alloy interactions.