Effects of space charge on weld geometry and cooling rate during electron beam welding of stainless steel

Abstract

Although heat input rate is universally accepted as a scale-up criterion for weld-geometry, especially for arc/laser welding, its position in electron beam welding (EBW) needs a relook. Our experiments reveal that heat input per unit length cannot always be taken as a parameter indeed to determine weld-geometry accurately. The electron-repulsion-induced space charge effect (SCE), especially during EBW carried out under vacuum, has been attributed for such phenomenon. The change in depth of penetration, bead width, volume of material melted, cooling rate and grain boundary character distribution (GBCD) have been studied as the function of input process parameters. Moreover, a finite element analysis has been carried out to account for this SCE in terms of effective beam spread. Here, some preferences and ranges of these parameters are suggested to suppress SCE, and thereby, obtaining the higher depth of penetration and low bead-width. These desired weld-geometries are observed with high welding speed, and beam current to accelerating voltage ratio (I/V) lying in a range of (0.9, 2.0).