Electron Beam Welding of API 5L X65 Steel

The microstructure and mechanical properties were investigated in a 17.48-mm-thick electron beam-welded (EBW) API 5L X65 steel sheet. Electron beam welding has the advantage of joining thick steel parts in a single pass with a high energy conversion efficiency, low heat input and low warpage. The base metal has elongated bands of ferrite interspersed with pearlite colonies aligned along the rolling direction. After welding, a narrow and fine-grained heat affected zone (HAZ) consists of degenerate pearlite and martensite-austenite (M-A) islands. The microstructure of the fusion zone is coarser than the HAZ and more complex, consisting of lower bainite, Widmanstatten ferrite, acicular ferrite, grain boundary ferrite, and small islands of the M-A constituent. These microstructure changes are minimized when EBW is used and do not significantly affect the mechanical properties of the weld. Results of Charpy V-notch tests for weld beads parallel and perpendicular to the rolling direction met the requirements of the API 5L standard. EBW has proven to be a viable alternative for welding thick plates of advanced steels applied in pipeline construction and assembly.