Unique strengthening effect in additively manufactured bimetallic Mild Steel and Stainless Steel

We fabricated a unique bimetallic cylinder by Directed Energy Deposition 3D printing. The inner part of the cylinder was built using Mild Steel, while Stainless Steel was used as the perimeter. The tensile properties and microstructures were compared with those of cylinders made from a single material. The bimetallic structure showed an ultimate tensile strength of 757 MPa, which was similar to 150-300 MPa higher than that of cylinders using single Mild Steel or Stainless Steel. The strengthening was attributed to a fully martensite microstructure in the Mild Steel-side, and the martensitic formation was caused by the diffusion of Cr and Ni. Although the bimetallic structure caused a reduction in ductility owing to the formation of twins and debonding of the interface, the moderate elongation to failure of 12.1 % was maintained.