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.

Automated summary

This study investigates the microstructure and mechanical properties of a 17.48-mm-thick electron beam-welded API 5L X65 steel sheet. The advantages of electron beam welding, such as high energy conversion efficiency, low heat input, and low warpage, make it a viable alternative for welding thick plates in pipeline construction. The microstructure changes in the heat affected zone and fusion zone are minimized with electron beam welding and do not significantly affect the weld's mechanical properties. Charpy V-notch tests confirmed that the weld beads met the requirements of the API 5L standard.