Effect of the Microstructure On the Interface of Laser Welded AISI 304

CO₂ laser beam welding with a continuous wave is a high energy density and low heat input process. The result of this is a small heat-affected zone (HAZ), which cools very rapidly with very little distortion. Welding is a necessary process during fabricating fuel rods and fuel assemblies with Zircaloy-4 cladding, and electron beam welding is one of the commonly- used method [1]. Zhou et al. [2] found that after Zircaloy-4 plates were welded to form butt joints by electron beam welding, the corrosion resistance of welding seams was poor.

In this work, the joining of zirconium alloys was attempted by laser beam welding. A 2 kW CO₂ laser is used and the joints are obtained from similar materials, which are plates of Zircaloy-4 (2 mm thick). A series of zirconium alloys were welded and investigated in a tow-fold approach: (1) process optimisation: the laser processing parameters are optimized to obtain welds with minimum defects, and (2) material characterisation: weld microstructures were evaluated. The microstructure and the phases present in the resolidified zone of the laser -welded specimens were analyzed by optical and scanning electron microscopy, X-ray diffraction, spectrometry Auger and also by the realization of micro hardness diagrams. Additionally, an attempt was made to study the corrosion behaviour of Zircaloy-4 in wrought and welded forms in nitric acid medium. The detailed results of microstructure, microhardness, corrosion rate, morphology of attack and nature of surface film formed are presented will be presented and discussed in the 9^th International Conference on Trends in Welding Research.

References:

[1] Mc. Donald S.G., Zirconium in the Nuclear Industry: Fifth International Conference ASTM STP 754, 1982, 412.

[2] Zhou B.X., Li Q., Miao Z., Nucl. Power Eng., 24 3, 2003, 236.

Keywords: CO₂ laser welded, Zirconium alloy, stainless steel, microstructure.