Microstructural and Mechanical Heterogeneity of Electron Beam Welded Thick Pure Titanium/Q235B Steel Bimetallic Plate Joint

Electron beam welding experiments of 13 mm thick titanium/steel bimetallic plates were carried out. Microstructures and mechanical properties of the welded joints were investigated via optical microscopy, scanning electron microscopy, microhardness, and tensile strength tests. Chemical compositions, microstructures, and mechanical properties of the weld along the vertical direction were inhomogeneous for the liquid metal flow during the electron beam welding process. In the steel layer, the tensile strength of the weld was higher than that of the base metal since a small amount of Ti atoms were mixed in this layer. In the titanium layer, many Fe atoms flowed into this layer during welding, and interfacial Ti-Fe intermetallic compounds were produced. Microcracks were observed, and the tensile strength of the weld decreased significantly. A vanadium insertion was embedded in the transition region of titanium and steel layers to avoid microcrack occurrence. The formation of Ti-Fe intermetallic was restricted, and the tensile strength of this layer was increased by 83 MPa. This unique electron beam welding process with a novel structure provides help for the broad application of titanium/steel bimetallic plates.