A study of the heat-affected zone (HAZ) of an Inconel 718 sheet welded with electron-beam welding (EBW)

Abstract

In this paper the heat-affected zones (HAZs) of the Inconel 718 sheets welded with electron-beam welding (EBW) were studied by using hardness measurement, metallographic etch and electrochemically potentiostatic etch methods. Before EBW, the Inconel 718 sheets were pretreated in three different conditions: as-received, solution- and precipitation-treatments. The results show that there is an obvious difference in the dimension of the widths of HAZs evaluated by the methods. The width, ca. 1.5mm, of the HAZ in solution-pretreated weld can be estimated based on the variation of its hardness distribution curve. But the HAZs in as-received and precipitation-pretreated welds were difficult to detect from their hardness distribution curves. After metallographic etching, the HAZs in the welds were very hard to observe with optical microscope, but those with a width within 100μm in solution- and precipitation-pretreated welds, except in as-received weld, can be observed with scanning electron microscope (SEM). The HAZ with a width ca. 300μm of each weld can be revealed by using anodically potentiostatic etching in 3.5wt.% NaCl solution due to different corrosion rates among the HAZ, fusion zone and base metal in the weld. The above-mentioned behavior of HAZs evaluated by different methods was discussed in detail in this work.