MICROSTRUCTURAL AND HARDNESS CHARACTERIZATION OF STAINLESS STEEL 316L/ MILD STEEL ER70-S SANDWICH STRUCTURES FABRICATED BY WIRE-BASED DIRECTED ENERGY DEPOSITION

Abstract

Multi-material additive manufacturing is gaining attention for its ability to combine the strengths of different materials into a single part. In this study, a sandwich structure made of 316L stainless steel and ER70-S mild steel was created using a Meltio M600 laser-based wire Directed Energy Deposition (W-DED) system. Both single-material samples and the multi-layer sandwich structure were produced using the same processing settings. Optical microscopy was used to study the shape and interface of the deposited layers. Further microstructural analysis was done with scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD). The ER70-S area showed a ferritic microstructure with lamellar pearlite, while the 316L area consisted mostly of austenitic grains. EDS analysis showed a gradual change in element concentrations across the interface, particularly the movement of chromium and nickel from stainless steel into mild steel. Microhardness tests (HV0.1) revealed a sharp hardness increase in the interface, suggesting microstructural transformation and element mixing. These results show that wire-based DED can form stable bonds between stainless steel and mild steel in multi-material parts.