Abstract
Electron beam (EB) welding has a low tolerance to inter-part gapping distortion and can generate complicated stresses, which pose challenges to weld quality and integrity. This study investigates welding distortion and stresses in an EB welded plate made from SA508 Grade 4N low-alloy steel. A thermal-metallurgical-mechanical model was developed to predict the temperature, micro-constituents, hardness, distortion and stresses in the EB weldment; the predictions are in good agreement with experimental results. Different restraint conditions on the weld plane were modelled to examine their effects on distortion and stresses. If welding is performed with no restraint, inter-part gapping develops ahead of the beam position that could exceed the tolerance for a sound weld. In contrast, tack welds at the plate ends significantly reduce this gapping, but induce additional tensile stress at the stop-end tack weld. This stress is particularly high as the beam approaches the tack weld. Increasing the extent of the tack weld reduces the tensile stress, while increasing number of distantly distributed narrow tack welds does not help. A full through-length restraint eliminates the opening gap and minimises the development of tensile stresses ahead of the beam that could potentially break the restraint. The applied restraint on the weld plane has little effect on the final residual stress field, since this field mostly develops during cooling after the EB weld is complete. The weld-induced martensitic transformation suppressed tension or promoted compression in the EB weld and heat affected zone (HAZ). A steep gradient of residual stress exists, with high tensile stress concentrated in a narrow region immediately outside the HAZ.
Highlights
Electron beam (EB) welding is an advanced joining technique having many advantages over traditional arc welding processes, and it has been increasingly used in energy, automotive, electronics, aerospace and other key industries [1,2]
This technique can generate power densities up to 1012 W/m2 [1], thereby enabling high-speed joining of thicksection components using a single autogenous weld pass. This unique feature means that EB welding can substantially improve productivity and reduce distortion of thicksection weldments, such as those found in nuclear power plants [2,3,4]
Since both the predicted evolution (Fig. 4) and distribution (Fig. 5a, b) of temperature agree well with experimental results, it can be concluded that the idealised heat source and the thermal solution of the weld model are sufficiently accurate for analyses of solid state phase transformation (SSPT), stress and distortion which are mainly determined by material behaviour in solid state, and such a verification of thermal model accuracy has been recommended by R6 structural integrity assessment procedure [55,56]
Summary
Electron beam (EB) welding is an advanced joining technique having many advantages over traditional arc welding processes, and it has been increasingly used in energy, automotive, electronics, aerospace and other key industries [1,2] This technique can generate power densities up to 1012 W/m2 [1], thereby enabling high-speed joining of thicksection components (with thickness up to 250 mm for steel [1]) using a single autogenous weld pass. EB welding still faces a number of challenges regarding the requirements of specific applications Primary circuit components such as the reactor pressure vessel are both safety-critical and high-value items in nuclear power plants. They are usually made of low-alloy steels, such as SA508 Grade 3 and Grade
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